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Composites Science and Technology
Journal Prestige (SJR): 1.702
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  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0266-3538
Published by Elsevier Homepage  [3159 journals]
  • A new method to prepare composite powders customized for high temperature
           laser sintering
    • Abstract: Publication date: 20 October 2018Source: Composites Science and Technology, Volume 167Author(s): Bahareh Yazdani, Binling Chen, Luiza Benedetti, Richard Davies, Oana Ghita, Yanqiu Zhu Composites have the potential to enhance the mechanical properties of components fabricated by additive manufacturing; however, the bottleneck is the limited number of polymeric composite powders available for this manufacturing process. This paper describes a generically new method to create composite powders that are suitable for High Temperature Laser Sintering (HT-LS). C-coated Inorganic Fullerene-like WS2 (IF-WS2) nanoparticles and graphene nanoplatelets (GNPs) have been chosen to demonstrate their incorporation into a high performance polymer matrix: Poly Ether Ether Ketone (PEEK). The morphological and physical property investigations have confirmed that the resulting composite powders exhibit the desired particle morphology, size, distribution and flowability for HT-LS applications. Further preliminary sintering results have demonstrated that they are comparable to the currently available commercial grade of PEEK powder HT-LS applications in terms of powder packing properties and flow ability. The new strategy reported here brings in great potential for the additive layer manufacturing of high performance polymeric composite components with improved mechanical and added functionalities by choosing the proper matrix and filler combination.
       
  • Micro-mechanical damage model accounting for composite material
           
    • Abstract: Publication date: Available online 13 August 2018Source: Composites Science and TechnologyAuthor(s): Ghazi A.F. Abu-Farsakh, Haitham M. Al-Jarrah A new micromechanical damage model for predicting the effect of matrix-cracking on the mechanical behavior of the composite material is proposed. The model is based on the volumetric change that occurred due to the presence of cracks in a composite lamina due to uniaxial off-axis loading. It determines the volumetric crack-density (VCD) by combining the macro-mechanical and micro-mechanical principles. A representative volume-element is proposed that determines the material mechanical properties (E1, E2, G12 and ν12) in terms of crack-density, fiber and matrix properties and initial volume-fraction of fibers. The rule-of-mixture in combination with Halpin-Tsai model is used to determine the mechanical properties of a cracked composite lamina. It has been shown that, matrix-cracking is the main cause for composite-material nonlinearity. Moreover, the model has been shown to give a reliable and reasonable predictions of the VCD and the tangential damage-factor (TDF) for various fiber/matrix systems using the corresponding available data from literature. An alternative secant damage-factor is being proposed, which has a linear relationship with the VCD. In order to validate the model, two composite materials; Boron/Epoxy (Narmco-5505) and Graphite/Epoxy (4617/Modmor-II), have been considered using laminates at different fiber-orientation angles. The maximum volume-crack-density (MVCD) and maximum secant damage-factor (MSDF) are obtained using equations that depend on the fiber-orientation angle and the initial material mechanical properties.
       
  • The potential impact of DGEBA/amine reaction kinetics on interphase
           formation in glass fiber composites
    • Abstract: Publication date: Available online 11 August 2018Source: Composites Science and TechnologyAuthor(s): Gale A. Holmes A distinctive region known as the fiber-matrix (F-M) interface/interphase (I/I) is formed between the matrix and fiber during composite manufacture. This region is assumed to be created in thermoset matrices by chemistry perturbations induced during the cure reaction. These perturbations occur at the un-sized or sized fiber surface, with the sized surface typically engineered to promote adhesion between matrix and fiber. Given the importance of this region to composite performance, potential chemistry perturbations that may arise are discussed, focusing on epoxy/amine reaction kinetics. These perturbations are linked to morphology changes that arise during fiber fracture. It is hoped that these ideas will facilitate a more complete understanding of the F-M I/I region and promote strategies for developing tougher composites.
       
  • Enhanced fracture toughness in architected interpenetrating phase
           composites by 3D printing
    • Abstract: Publication date: Available online 11 August 2018Source: Composites Science and TechnologyAuthor(s): Tiantian Li, Yanyu Chen, Lifeng Wang Interpenetrating phase composite (IPC), also known as co-continuous composite, is one type of material that exhibits an unusual combination of high stiffness, strength, energy absorption, and damage tolerance. Here we experimentally demonstrate that IPCs fabricated by 3D printing technique with rationally designed architectures can exhibit a fracture toughness 16 times higher than that of conventionally structured composites. The toughening mechanisms arise from the crack-bridging, process zone formation and crack-deflection, which are intrinsically controlled by the rationally designed interpenetrating architectures. We further show that the prominently enhanced fracture toughness in the architected IPCs can be tuned by tailoring the stiffness contrasts between the two compositions. The findings presented here not only quantify the fracture behavior of complex architected IPCs but also demonstrate the potential to achieve tailorable mechanical properties through the integrative rational design and the state-of-the-art advanced manufacturing technique.
       
  • Largely enhanced mechanical property of segregated carbon
           nanotube/poly(vinylidene fluoride) composites with high electromagnetic
           interference shielding performance
    • Abstract: Publication date: Available online 11 August 2018Source: Composites Science and TechnologyAuthor(s): Wan-Cheng Yu, Tao Wang, Guo-Qiang Zhang, Zhi-Guo Wang, Hua-Mo Yin, Ding-Xiang Yan, Jia-Zhuang Xu, Zhong-Ming Li Conductive polymer composites (CPCs) with segregated structure exhibit outstanding electromagnetic interference (EMI) shielding performance at low filler loadings. However, the mechanical performance is compromised due to poor interfacial adhesion resulting from the selective distribution of conductive fillers. Herein, a simple and effective approach, i.e. solid-phase extrusion (SPE), was proposed to fabricate segregated carbon nanotube (CNT)/poly(vinylidene fluoride) composites with high mechanical performance. Morphology examination revealed that both the matrix and segregated conductive network were highly oriented along the extrusion direction under the forceful flow field of SPE. The resultant SPE composites showed an excellent electrical conductivity of 74.5 S/m and a high EMI shielding effectiveness of 36.8 dB with only 4 wt% CNTs. More notably, simultaneous enhancement of the strength and fracture toughness was achieved. Compared to the counterparts with conventional segregated structure, tensile strength and elongation at break of SPE composites were significantly increased by ∼100% and ∼900%, reaching 120–140 MPa and 60%, respectively. This work demonstrates a valuable approach to prepare high-performance CPCs for EMI shielding applications.Graphical abstractImage 1
       
  • Retraction notice to " A transparent pressure-sensitive adhesive with high
           electrical conductivity based on water-soluble nano core-shell hollow
           composite" [CSTE 160 (2018) 119–126]
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Lipei Yue, Xiaoyong Zhang, Weidong Li, Yongping Bai, Yudong Huang
       
  • Ultra-strong, tough and high wear resistance high-density polyethylene for
           structural engineering application: A facile strategy towards using the
           combination of extensional dynamic oscillatory shear flow and
           ultra-high-molecular-weight polyethylene
    • Abstract: Publication date: Available online 9 August 2018Source: Composites Science and TechnologyAuthor(s): Tong Liu, An Huang, Li-Hong Geng, Xing-Han Lian, Binyi Chen, Benjamin S. Hsiao, Tai-Rong Kuang, Xiang-Fang Peng General purpose plastic materials with high strength and toughness are in great demand for structural engineering applications in recent years. Inspired by the relationship of excellent integration of mechanical performance and hierarchically ordered shish-kebab structure of polymeric materials, a facile and efficient strategy based on the combined effect of strong extensional dynamic oscillatory shear flow and ultra-high-molecular-weight polyethylene (UHMWPE) was developed to fabricate ultra-strong, super-tough and high wear resistance integrated high-density polyethylene (HDPE)-based materials. As a result, the maximum value of tensile strength, modulus and toughness were respectively 3.8, 5.9 and 6.8 times higher than that of neat HDPE, even superior to that of most common engineering plastics. Meanwhile, the wear rate of resultant HDPE-based materials could be reduced from 18.6 to 4.2 mg/MC. Overall, the HDPE-based material with extraordinary integrated strong, tough and high wear resistance properties would have a great potential for the replacement of engineering plastics and application in aerospace, military, tissue engineering, etc.
       
  • Simultaneous enhancement of toughness, strength and superhydrophilicity of
           solvent-free microcrystalline cellulose fluids/poly(lactic acid) fibers
           fabricated via electrospinning approach
    • Abstract: Publication date: 20 October 2018Source: Composites Science and Technology, Volume 167Author(s): Xianze Yin, Yun Li, Puxin Weng, Qiao Yu, Lu Han, Jing Xu, Yinshan Zhou, Yeqiang Tan, Luoxin Wang, Hua Wang In this paper, solvent-free microcrystalline cellulose fluids (MCCFs) with liquid-like behavior were synthesized for the first time through surface grafted polyethylene glycol-substituted tertiary amines into microcrystalline cellulose (MCC) followed by fabricating MCCFs based polylactic acid (PLA) fabric (PLA/MCCFs) via electrospinning method. Owing to low viscosity of MCCFs at room temperature, the addition of MCCFs not only hardly affected the viscosity of electrospinning solution, but also improved the thermal stability of as-prepared PLA fibers. Interestingly, it was amazingly found that surface micropore morphology of PLA fabric diminished, and even disappeared with the content of MCCFs increasing during solvent evaporation process, which may be ascribed to the rapid migration of MCCFs into micropore before solidification. More importantly, the tensile strengths of PLA/MCCFs fabric with 10 wt% content of MCCFs achieved as high as 13.68 MPa, which was 3.18 times as much as that of 4.3 MPa for pure PLA fabric meanwhile the elongation at break of PLA/MCCFs fabrics increased from 13.19% for pure PLA fabric to 48.84% for PLA/MCCFs fabric with 15 wt% content of MCCFs. Beyond above mentioned, the water contact angle for pure PLA fabric was 127° (hydrophobicity), whereas other samples were close to 0° with addition of MCCFs, displaying the super-hydrophilicity. It was possibly inferred that MCCFs quickly migrated towards to the surface of fibers rather than staying inside of the fibers during the electrospinning process, leading to positive effect on the hydrophilicity of the PLA fibers. Finally, it is anticipated that this strategy for fabricating PLA fiber using this novel MCCFs as filler will pave the way for developing high performance PLA composites with desirable properties in the future.
       
  • Characteristics and fabrication of piezoelectric GFRP using smart resin
           prepreg for detecting impact signals
    • Abstract: Publication date: Available online 7 August 2018Source: Composites Science and TechnologyAuthor(s): Mun Young Hwang, Lae-Hyong Kang To develop a composite that also functions as an impact sensor, a piezoelectric glass fiber-reinforced polymer (GFRP) was fabricated using a mixture of Pb(Ni1/3Nb2/3)O3-Pb(Zr, Ti)O3 (PNN-PZT) piezoelectric powder and epoxy as a smart resin. Prepreg sheets were prepared by impregnating glass fiber with the smart resin and the specimen was fabricated by autoclave molding. To utilize the composite as a sensor for detecting impacts, electrodes were added to the two sides of the composite, and the specimen was poled briefly at room temperature to activate its piezoelectric properties. A calibrated and instrumented impact test was conducted to demonstrate impact response and measure the sensitivity; a signal processing device was developed that matched the high impedance of the piezoelectric GFRP. The sensitivity of the piezoelectric GFRP sensor was measured by comparing the impact force signals from an impact hammer with the corresponding output voltage from the sensor. The threshold for detection of impacts was below 15 N. The tests confirmed that the piezoelectric GFRP itself could be utilized as an impact sensor.
       
  • Modelling race-tracking variability of resin rich zones on 90° composite
           2.2 twill fibre curved plate
    • Abstract: Publication date: Available online 6 August 2018Source: Composites Science and TechnologyAuthor(s): Spiridon Koutsonas Resin rich zone along component edges is a common phenomenon during composites liquid infusion with the resin transfer moulding process. The challenge in the present work is to be able to predict the realistic race-track flow behaviour along a 90° edge in order to manufacture high-quality composites materials for aerospace or other applications. To that end, there is a lack of an advanced simulation tool capable to predict the manufacture of multi-layer textile composites. The issue of 2D, 3D racetrack prediction on this paper was investigated along a 90° edge for a composite textile. A novel numerical approach for a three-dimensional Finite Element Control/Volume modelling was developed in order to predict race-tracking permeability for any composite structure. The model was experimentally verified for a 2/2 twill carbon fibre geometry. All experiments and simulations used 1 bar pressure and 300 mPa s viscosity.
       
  • Fabrication of polyketone-grafted multi-walled carbon nanotubes using
           Grignard reagent and their composites with polyketone
    • Abstract: Publication date: Available online 4 August 2018Source: Composites Science and TechnologyAuthor(s): Jeong Ung Nam, Eun Yeob Choi, Hye Jin Park, C.K. Kim A Grignard reagent containing pyrene, 1-pyrenylmethylmagnesium bromide (PMgBr), was explored as a novel reactive compatibilizer for producing aliphatic polyketone (PK) composites with multi-walled carbon nanotube (MWCNT) that had improved interfacial adhesion and mechanical strength. 1-Bromomethylpyrene (PBr) was adsorbed on MWCNTs and reacted with Mg to produce PMgBr on MWCNTs (MWCNT-PMgBr). PK-grafted MWCNT (PK-g-MWCNT) was prepared by reacting MWCNT-PMgBr with PK, and its composite with PK was fabricated by melt extrusion. The formation of PK-g-MWCNT was examined by spectroscopy, electron microscopy, and thermal analysis. The PK interfacial adhesion energies with MWCNTs were quantified, and the mechanical strengths of their composites examined. PK-g-MWCNT had the highest interfacial adhesion energy with PK among the MWCNTs. The PK/PK-g-MWCNT composite showed better MWCNT dispersion in PK and interfacial adhesion between MWCNT and PK than the PK/pristine MWCNT composite. Consequently, the PK/PK-g-MWCNT composite exhibited higher mechanical strength than the PK/pristine MWCNT composite when the composite contained the same amount of MWCNTs.
       
  • Enhanced mechanical and thermal performances of epoxy resin by oriented
           solvent-free graphene/carbon nanotube/Fe3O4 composite nanofluid
    • Abstract: Publication date: Available online 3 August 2018Source: Composites Science and TechnologyAuthor(s): Dongdong Yao, Ningkun Peng, Yaping Zheng In this work, we report a simple strategy for improving the mechanical and thermal performances of epoxy resin using a novel magnetic composite nanofluid as filler. The magnetic nanofluid, composed of multicomponent core of graphene oxide (GO)/carbon nanotube (MWCNTs)/Fe3O4 (GMF) and shell of polyether, is fabricated via a combination of ultrasonic assisted chemical coprecipitation process and post-modification. Subsequently, epoxy/GMF composite is prepared under magnetic field, in which the GMF nanoparticles are well dispersed in the epoxy resin matrix without obviously agglomeration and exhibit a directional arrangement along magnetic field. i.e., the GO sheets are induced to align parallel to the magnetic field direction, and the MWCNTs are uniformly dispersed on graphene sheets with the orientation along magnetic field, Fe3O4 nanoparticles are further encapsulated on GO/MWCNTs composites to form GMF core. The orientation degree of GMF is enhanced with an increase in the magnetic field strength. The results indicate that the Tg of composite material increases by 17 °C with increasing of GMF content. Moreover, the impact and bending performances of epoxy resin are apparently enhanced by 136.5% and 30.9% with the 1.5 wt% of oriented GMF nanofluid at 0.6 T. In addition, the epoxy/GMF composite exhibits an anisotropy in the thermal conductivity.Graphical abstractImage 1
       
  • Structure of the in situ produced polyethylene based composites modified
           with multi-walled carbon nanotubes: In situ synchrotron X-ray diffraction
           and differential scanning calorimetry study
    • Abstract: Publication date: Available online 1 August 2018Source: Composites Science and TechnologyAuthor(s): Mariya A. Kazakova, Alexander G. Selyutin, Nina V. Semikolenova, Arcady V. Ishchenko, Sergey I. Moseenkov, Mikhail A. Matsko, Vladimir A. Zakharov, Vladimir L. Kuznetsov Polyethylene based composites modified with multi-walled carbon nanotubes (MWCNTs) were produced via in situ polymerization of ethylene with the Ti-Ziegler–Natta catalyst preliminarily immobilized on MWCNTs. The composite structure was characterized with transmission and scanning electron microscopy, differential scanning calorimetry (DSC) and in situ synchrotron X-ray Diffraction (in situ XRD). For the first time the Ti-containing catalyst species of the size 2–3 nm were observed on the MWСNTs surface stabilized in the polymer matrix. A comparative study of the melting-crystallization cycles of neat polyethylene (PE) and MWCNT-PE composites with in situ XRD and DSC provide information on the nucleation of PE crystals. For the first time, the in situ XRD technique was used for estimation of the coherent scattering region of PE blocks during the melting-crystallization cycles. These experiments and molecular dynamic modeling showed that MWCNTs act as the template for the PE chain orientation and as the nucleating agent for PE crystallization. However, the nucleation of PE crystals in composites occurs on the nanotube surface and also within the space between nanotubes. Thus, the relative volume of PE nucleated on nanotubes depends on their content in the composite and can be significant only for the composites with high nanotube loading.
       
  • Effect of SWCNTs and graphene on the fatigue behavior of antisymmetric
           GFRP laminate
    • Abstract: Publication date: Available online 1 August 2018Source: Composites Science and TechnologyAuthor(s): Mostefa Bourchak, Abdullah Algarni, Adnan Khan, Usama Khashaba In this relatively unique study, the impact of adding nanoparticles (NPs) on the fatigue properties of antisymmetric glass fiber reinforced polymer (GFRP) laminate has been investigated. Antisymmetric GFRP laminates (+45/02/902/02/-45) were prepared and reinforced once with 0.1 wt.% of single walled carbon nanotubes (SWCNTs) and then with 0.1 wt.% of Graphene nanoplatelets (GNPs). The NPs reinforced GFRP laminates are termed here GFNRP nanocomposites. Ultrasonication method was used to disperse the NPs using carefully chosen process parameters. Fatigue tests were analyzed based on S-N curves, stiffness degradation and hysteresis loops. The results showed that the use of 0.1 wt.% of SWCNTs led to an increase in the fatigue strength coefficient (FSC) and the fatigue strength exponent (FSE) of GFNRP nanocomposite specimens by 51% and 24%, respectively, while the use of similar wt.% of GNPs enhanced the FSC and FSE by 33% and 25%, respectively. Consequently, fatigue life of GFNRP nanocomposites are surprisingly enhanced by about three and twelve times when GNPs and SWCNTs are used, respectively. The findings would give designers much more confidence in using antisymmetric composite laminates in specific elastic tailoring structures.
       
  • Combination of 1D Ni(OH)2 nanobelts and 2D graphene sheets to fabricate 3D
           composite hydrogel electrodes with ultrahigh capacitance and superior rate
           capability
    • Abstract: Publication date: Available online 1 August 2018Source: Composites Science and TechnologyAuthor(s): Chengen He, Shengqiang Qiu, Haiyan Peng, Qing Zhang, Xiaoyan Han, Yingkui Yang, Dean Shi, Xiaolin Xie Metal compound/graphene composites have been dominantly fabricated by in-situ intercalation of metal-containing precursors into graphene or graphene oxide (GO) followed by chemical and/or thermal treatment. This process usually leads to the formation of 0D oxide nanoparticles/2D graphene composites with the limited improvements in the supercapacitor performance. Herein a facile two-step method was reported to fabricate 3D porous Ni(OH)2/graphene composite hydrogels (NiGH) by incorporating the pre-synthesized 1D Ni(OH)2 nanobelts into a GO suspension followed by the hydrothermal process. The resulted hydrogels show large specific surface area (370.6 m2/g) and can be directly used as the self-supported electrodes. The NiGH electrode exhibits the specific capacitance up to 1738.3 F/g at 10 mV/s and 1701.5 F/g at 1 A/g, retains 1385.0 F/g at 100 mV/s and 1152.0 F/g at 8 A/g, respectively. The capacitance and rate performance of NiGH are far superior to those of Ni(OH)2 (841.2 F/g at 10 mV/s; 592.5 F/g at 1.0 A/g), graphene hydrogel (207.5 F/g at 10 mV/s), and the control Ni(OH)2 nanoparticle/graphene composite powder (NiGP: 1045.8 F/g at 10 mV/s; 950.8 F/g at 1.0 A/g) prepared by the one-pot hydrothermal processing of Ni salt and GO. Meanwhile, the NiGH electrode also shows lower resistance and higher cycling stability (retaining 100.8% of initial capacitance over 5000 cycles at 5 A/g) as compared to Ni(OH)2, graphene hydrogel, and NiGP due to the efficient combination of pseudo-capacitive 1D Ni(OH)2 nanobelts and conductive 2D graphene sheets to create 3D architectures. Such a facile two-step protocol enables the superiority of ultrathin oxide nanobelts to fabricate 3D graphene-based composite hydrogels for high-performance supercapacitor electrodes.Graphical abstract3D Ni(OH)2 nanobelt/graphene composite hydrogels were fabricated by incorporating the pre-synthesized Ni(OH)2 nanobelts into a suspension of graphene oxide followed by hydrothermal treatment. The resulting self-supported electrodes show much better electrochemical performance compared to the powdery Ni(OH)2 nanoparticle/graphene composites prepared by one-pot hydrothermal processing of Ni salts and graphene oxide.Image 1
       
  • In situ self-sensing of delamination initiation and growth in
           multi-directional laminates using carbon nanotube interleaves
    • Abstract: Publication date: Available online 31 July 2018Source: Composites Science and TechnologyAuthor(s): Lulu Shen, Ling Liu, Wei Wang, Yexin Zhou Self-sensing capability of carbon nanotube buckypapers (BPs), played as in situ sensor on delamination damage in multi-directional laminates, was investigated in this paper. BPs were interleaved into these interfaces of the laminates, where delamination tends to happen firstly under tensile loading. The inserted BPs are porous and conductive, which can benefit infiltration of epoxy resin and give contribution to damage monitoring. Systematic analysis of resistance variation (ΔR/R0%) against strain has demonstrated that BPs are sensitive to the initiation and growth of delamination. When delamination initiates, a sudden rise of the ΔR/R0% or the slope of the ΔR/R0%-strain curves is observed and corresponding delamination initiation stresses are simultaneously obtained. Moreover, effect of thicker laminates on the sensitivity is also examined and the self-sensing ability of BPs has been further proved. Finally, tensile properties of the BPs interleaved laminates slightly change compared with these of base laminates.
       
  • Loading rate dependency of Mode I interlaminar fracture toughness for
           unidirectional composite laminates
    • Abstract: Publication date: Available online 30 July 2018Source: Composites Science and TechnologyAuthor(s): Huifang Liu, Hailiang Nie, Chao Zhang, Yulong Li This study was conducted to investigate the effect of the loading rate on the Mode I interlaminar fracture toughness of unidirectional carbon/epoxy laminates. Double cantilever beam (DCB) test geometry was employed for both quasi-static and dynamic fracture tests. A novel dual electromagnetic Hopkinson bar was employed to load the DCB specimens dynamically and symmetrically with velocities in the range of 10–30 m/s. A hybrid experimental-numerical method was used to determine the interlaminar fracture toughness for both quasi-static and dynamic loading conditions using the virtual crack closure technique (VCCT). The results indicate the presence of a critical loading rate for interlaminar fracture, below which the fracture toughness remains constant and beyond which the fracture toughness increases rapidly. Fractography results suggest that the failure mechanism transitions from a fiber/matrix interface failure under quasi-static loading to a brittle cleavage fracture of the matrix material with microbranching under dynamic loading.
       
  • Accurate evaluation of failure indices of composite layered structures via
           various FE models
    • Abstract: Publication date: Available online 30 July 2018Source: Composites Science and TechnologyAuthor(s): A.G. de Miguel, I. Kaleel, M.H. Nagaraj, A. Pagani, M. Petrolo, E. Carrera The objective of the current work is to perform a failure evaluation of fiber composite structures based on failure indices computed using the Hashin 3D failure criterion. The analysis employs 1D and 3D finite elements. 1D elements use higher-order structural theories from the Carrera Unified Formulation based on Lagrange expansions of the displacement field. The 3D model analysis exploits ABAQUS. Attention is paid to the free-edge effects, the mode of failure initiation - matrix or fiber tension, delamination -, and the loads at which first ply failure occurs. The results underline the paramount importance of out-of-plane stress components for accurate prediction and the computational efficiency of refined 1D models. In fact, 1D models lead from one to twofold reductions of the CPU time if compared to 3D models.
       
  • Preparation of self-healing, recyclable epoxy resins and low-electrical
           resistance composites based on double-disulfide bond exchange
    • Abstract: Publication date: Available online 29 July 2018Source: Composites Science and TechnologyAuthor(s): Fengtao Zhou, Zijian Guo, Wenyan Wang, Xingfeng Lei, Baoliang Zhang, Hepeng Zhang, Qiuyu Zhang Vitrimers have been emerged as a new class of polymers with many attractive properties of material processing such as reshaping, recycling and repairing. Herein, a new type of vitrimers (BDSER) based on thermosetting dynamic epoxy network with double disulfide bonds was synthesized by the reaction of a difunctional epoxy monomer containing disulfide bonds with 4,4′-disulfanediyldianiline (4-AFD). Our results demonstrated that the relaxation time of BDSER at 200 °C was as short as 9 s without any catalyst. The storage modulus of BDSER was up to about 2.2 GPa and its glass transition temperature was higher than 130 °C. Additionally, the thermodynamic and chemical properties of BDSER were no significant loss after 3 cycles of continuous breaking/compression molding. Furthermore, the resistance of CNT/PPy/Vitrimer composites (CPV), synthesized by doped BDSER with the polypyrrole (PPy) decorated multi-walled carbon nanotubes (WMCNTs), was decreased to 109 Ω even the mass ratio was only 1%wt, which could be used a promising candidate as self-repairing materials in the field of antistatic.
       
  • Multi-functional interface sensor with targeted IFSS enhancing, interface
           monitoring and self-healing of GF/EVA thermoplastic composites
    • Abstract: Publication date: Available online 29 July 2018Source: Composites Science and TechnologyAuthor(s): Bin Yang, Fu-Zhen Xuan, Zhenqing Wang, Liming Chen, Hongshuai Lei, Wenyan Liang, Yanxun Xiang, Kang Yang Developing the fiber/matrix interface with combined structural and functional performances is of tremendous importance in ensuring the service safety of fiber reinforced plastic composites (FRPs) and expanding the capabilities of FRPs to perform multiple parallel tasks. Herein, a multi-functional interface sensor that can improve the interfacial shear strength, and simultaneously monitor and heal the interfacial damage between glass fiber yarn and thermoplastic ethylene-vinyl acetate copolymer resin (GF/EVA) is reported. The basic idea is introducing muiti-walled carbon nanotube into GF/EVA interface. By this proposed method, the interfacial shear strength (IFSS) of GF/EVA composites is enhanced by 48.9%. The resistance of the interface sensor is recorded during the pull-out tests, and results show that the relative resistivity change could reflect the interfacial damage information very well. Electric heating of the sensor is adopted to heal the interfacial damage. The applied electrical power is discussed to evaluate the self-healing efficiency of the interfaces at different damage degrees. Successful interfacial self-healing ability is achieved and confirmed using different characterization techniques. Moreover, to verify the feasibility of our method in GF/EVA composite laminates, in-situ monitoring of the laminates under complicated stress and healing of delamination are performed. The results show that the developed sensor could monitor and heal the GF/EVA composite laminates with high sensing/healing ability. The proposed method and the obtained results could help to get a multi-functional sensor to ensure the service safety of composite structures.
       
  • Structural performance and photothermal recovery of carbon fibre
           reinforced shape memory polymer
    • Abstract: Publication date: Available online 29 July 2018Source: Composites Science and TechnologyAuthor(s): H.M.C.M. Herath, J.A. Epaarachchi, M.M. Islam, W. Al-Azzawi, J. Leng, F. Zhang The shape-memory polymers (SMPs) have an interesting capability of keeping a temporary shape and then recovering the original shape when subject to a particular external stimulus. However, due to SMP's relatively low mechanical properties, the use of SMP in wider range of engineering applications is limited. As such SMP's needs to be reinforced before use in engineering applications. This paper presents the mechanical properties, thermomechanical characteristics, photothermal behaviour and light activation of 0/90 woven carbon fibre reinforced shape memory epoxy composite (SMPC) made out of prepreg material. Prepreg is widely used manufacturing technique for large-scale engineering applications. The experimental results have demonstrated that the structural performance of the SMP has increased significantly due to carbon fibre reinforcement as anticipated. According to ASTM standard D 3039/D 3039M-00, the mode of tensile failure was identified as “XMV”, where the failure is explosive type. The dynamic mechanical analysis has revealed that the shape fixity and recovery ratios of the SMPC are 100% and 86% respectively. Under constrained strain, the stress has been recovered up to 5.24 MPa. The SMPC was exposed to five different power densities of 808 nm and the resultant activation has been systematically investigated. Interestingly, the SMPC has been heated over its glass transition temperature, once it exposes to a power density of 1.0 W/cm2. Furthermore, the applicability of carbon fibre reinforced SMPC for a deployable solar panel array, intended for remote and localized activation is demonstrated. The SMPC will be a potential candidate for space engineering applications, because of its enhanced mechanical properties and ability of photothermal activation.
       
  • Damage detection and self-healing of carbon fiber polypropylene
           (CFPP)/carbon nanotube (CNT) nano-composite via addressable conducting
           network
    • Abstract: Publication date: 20 October 2018Source: Composites Science and Technology, Volume 167Author(s): Sung-Jun Joo, Myeong-Hyeon Yu, Won Seock Kim, Hak-Sung Kim In this work, damage sensing and self-healing of carbon fiber polypropylene (CFPP)/carbon nanotube (CNT) nano-composite were performed based on addressable conducting network (ACN). To increase damage sensing resolution of CFPP/CNT nano-composite, through-thickness electrical conductivity was improved by adjusting press condition and spraying carbon nanotubes (CNT) between prepregs. From the results, electrical resistivity in thickness direction was reduced to 19.44 Ω·mm under 1.0 MPa and 1.0 wt% of CNT condition. Also, self-healing efficiency was examined with respect to the temperature and time via resistive heating of CFPP/CNT nano-composite. As a result, the optimized fabrication and self-healing condition exhibited high resolution of damage sensing with outstanding self-healing efficiency (96.83%) under fourth cycle of repeated three-point bending test.
       
  • Al2O3/graphene reinforced bio-inspired interlocking polyurethane
           composites with superior mechanical and thermal properties for solid
           propulsion fuel
    • Abstract: Publication date: 20 October 2018Source: Composites Science and Technology, Volume 167Author(s): Xiao Zhang, Jian Zheng, Haoming Fang, Yafei Zhang, Shulin Bai, Guansong He Nature always provides intelligent strategy for developing advanced materials with superior properties. In this study, by cloning the reinforcing mechanisms in nacre, a nacre-inspired Al2O3/graphene/polyurethane (PU) composite with hybrid hierarchical structure, was successfully fabricated. The structural interlocking interface, together with its excellent force bearing property, leads to exceptional mechanical performance. Compared with pure PU, the bio-inspired, Al2O3/graphene reinforced PU composite demonstrates a unique improvement in Young's modulus (211%), tensile strength (41%), and compressive modulus (145%). Moreover, the thermal conductivity of Al2O3/graphene/PU composite reaches to 0.502 W m−1 K−1, enhanced by 141% compared with pure matrix, showing very high enhancement efficiency, which is attributed to the multilevel aligned structure and multi-contact conductive pathway inside the composite. This design strategy offers a promising approach to handling high mechanical and thermal performance of solid propulsion fuel by synthesizing bio-inspired architecture.
       
  • Tribo-performance enhancement of PAEK composites using
           nano/micro-particles of metal chalcogenides
    • Abstract: Publication date: 20 October 2018Source: Composites Science and Technology, Volume 167Author(s): Jitendra Narayan Panda, Jayashree Bijwe, Raj K. Pandey While designing the ambitious advanced composites based on PAEK (50 wt%), glass fibers (30 wt %) and natural graphite (10 wt %), it was proposed to include one more solid lubricant (10 wt %) from the category of metal chalcogenides. Particles of MoS2 and WS2 in micron and nano-sizes were selected for inclusion in combination with natural graphite. The themes for investigations were; which one is the better performer amongst MoS2 and WS2, and nano-particles can impart beneficial effect or not; and the last how efficient would be these tribo-composites in terms of friction, wear resistance and PVlimit values. The composites were characterized in detail for physical, mechanical, thermal and tribological performance. The WS2 proved more beneficial till moderate PV conditions but not for severe conditions as compared to MoS2. The composites proved excellent tribo-materials in terms of low friction (∼0.04), wear rate (2.2 × 10−16 MPa m/s) and PVsafe values (84 MPa m/s). The chemistry of the counterface surface was studied using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (RS) while the morphology of the worn pins surface and counterface surface was observed using a combination of 3D profilometer and scanning electron microscopy.
       
  • Thermal conductivity and tortuosity of porous composites considering
           percolation of porous network: From spherical to polyhedral pores
    • Abstract: Publication date: Available online 27 July 2018Source: Composites Science and TechnologyAuthor(s): Wenxiang Xu, Mingkun Jia, Zheng Gong Understanding the effect of percolation behavior of complex geometrical pores on the tortuosity and thermal conductivity of porous composites is very crucial to the design and optimization of porous composites. In this work, we adopt the continuum percolation theory to accurately determine the nonlinear thermal conductivity and tortuosity of porous composites composed of homogeneous solid matrix and three-dimensional pores of geometrical morphologies from the isotropic sphere to anisotropic polyhedra. Through extensive Monte Carlo simulations and the finite-size scaling analysis, the percolation threshold of spherical and polyhedral pores is obtained. Two continuum percolation-based models are respectively presented to derive the tortuosity and thermal conductivity of porous composites over the whole porosities range, including near the percolation threshold. Comparison with extensive experimental, numerical and theoretical results confirms that the present models are capable of accurately determining the percolation threshold and tortuosity of complex geometrical porous networks and the effective thermal conductivity of porous composites as conductor-superconductor and insulator-conductor media. Furthermore, we use the proposed models to probe the influences of pore shape and porosity on the tortuosity and thermal conductivity of porous composites. The results elucidate the intrinsic interplay of component, structure, and thermal conductivity of porous composites, which can provide sound guidance for porous composite design and evaluation.
       
  • Effect of composite bone plates on callus generation and healing of
           fractured tibia with different screw configurations
    • Abstract: Publication date: Available online 27 July 2018Source: Composites Science and TechnologyAuthor(s): Ali Mehboob, Seung-Hwan Chang In this paper, finite element analysis of a fractured tibia with a glass/polypropylene composite implant is introduced. A rejection coefficient algorithm (for callus development) that is sensitive to interfragmentary movement is programmed, calibrated (using experimental in vivo statistics), and successfully implemented on a 3D fractured tibia model. A biphasic mechano-regulation algorithm is implemented to verify healing status under five different screw configurations (C1–C5) using glass/polypropylene composite bone plates and the development of tissue phenotypes in calluses is estimated. A 300% increase in circumferential callus volume is obtained when using the composite bone plate. Furthermore, the C5 configuration of the composite bone plate results in a maximum interfragmentary movement of 4.33% on day one with faster and stronger healing through 95% of bone growth during the final day of healing.
       
  • Thermo-magneto-mechanical long-term creep behavior of three-phase
           nano-composite cylinder
    • Abstract: Publication date: Available online 25 July 2018Source: Composites Science and TechnologyAuthor(s): Ahmad Reza Ghasemi, Komeil Hosseinpour This article investigates the history of long-term radial and circumferential creep strains and radial displacement for a three-phase nano-composite exposed to an internal pressure and placed uniform temperature and magnetic field. Three-phase nano-composite made of single-walled carbon. The results in this paper were achieved by presuming a non-linear viscoelasticity, based on Shapery's integral model, classical laminate theory, Prandtl-Reuss's relation and Mendelson's approximation method. The distribution of the radial creep strain, circumferential creep strain and radial displacement in two states of with and without magnetic field and three temperature conditions for two lay-ups [0/45/0/45] and [0/90/0/90] described for 10 years. It has been found that the values of creep strain and radial displacement in magnetic field are lower than without a magnetic field, for two lay-ups.
       
  • Multi-scale toughening of epoxy composites via electric field alignment of
           carbon nanofibres and short carbon fibres
    • Abstract: Publication date: Available online 25 July 2018Source: Composites Science and TechnologyAuthor(s): Anil R. Ravindran, Raj B. Ladani, Shuying Wu, Anthony J. Kinloch, Chun H. Wang, Adrian P. Mouritz The present paper demonstrates that multi-scale fillers such as carbon nanofibres (CNFs) and short carbon fibres (SCFs) can significantly improve the mode I fracture toughness of epoxy composites by various toughening mechanisms. A comparative assessment on the toughening performance promoted by CNFs and SCFs is presented along with the effects of aligning the filler normal to the crack growth using an applied alternating current (AC) electric field. For SCF concentrations of up to 1.5 wt%, with a concentration of CNFs of 1.0 wt%, the multi-scale, hybrid reinforcements additively toughen the epoxy polymer, with the measured fracture toughness being up to about fourteen times the value of the unmodified epoxy polymer. When subjected to an external AC electric field, these two reinforcements rapidly align along the direction of the electrical field in epoxy resin, with the CNFs concentrating between the ends of, and depositing on, the SCFs. For the same concentrations of SCFs and CNFs, the electric field induced alignment of the CNFs and the SCFs further increased the fracture toughness of the multi-scale toughened or hybrid epoxy polymer by up to twenty times that of the unmodified epoxy polymer. The intrinsic and extrinsic toughening mechanisms spanning the nano-to-millimeter length scale have been identified, based upon which an analytical model has been proposed.Graphical abstractImage 1
       
  • Novel phase separated multi-phase materials combining high viscoelastic
           loss and high stiffness
    • Abstract: Publication date: Available online 24 July 2018Source: Composites Science and TechnologyAuthor(s): A.P. Unwin, P.J. Hine, I.M. Ward, M. Fujita, E. Tanaka, A.A. Gusev In a previous study we showed that a unique combination of high stiffness and high viscoelastic loss could be achieved by filling a polystyrene matrix with rigid inorganic spheres coated with a thin (∼200 nm) layer of a viscoelastic material. The sandwiching of this ‘lossy’ layer between the two rigid components was found to give a significant amplification of the tanδ loss peak associated with this material, without significantly compromising the sample stiffness. This was an experimental validation of the effect originally proposed by Gusev using finite element numerical studies. Following on from this, in the current study we have developed this concept further and shown that a similar amplification of viscoelastic loss can be achieved by incorporating rigid, but uncoated, particles into a phase separated matrix blend of polystyrene (PS) and a polystyrene/polyisoprene/polystyrene triblock co-polymer (SIS). The inspiration for this choice of the PS/SIS blend as the matrix came from some previous work where we studied, and modelled, the viscoelastic properties of these materials. In this work we show that in the filled PS/SIS blends, the loss amplification effect can been seen for different PS/SIS ratios, for different SIS polymers with different glass transition temperatures and also for glass fibres as well as for spherical particles. The key to seeing this effect is the fact that the SIS rubber phase was found to form a thin coating on the surface of the embedded particles during processing, effectively producing a surface coating layer on the particles (as well as phase separating within the PS matrix). As with our previous studies, it is shown that the experimentally measured effects are closely predicted by numerical micromechanical modelling based on the measured bulk properties of the three discrete components.
       
  • Reaching maximum inter-laminar properties in GFRP / nanoscale sculptured
           aluminium ply laminates
    • Abstract: Publication date: Available online 24 July 2018Source: Composites Science and TechnologyAuthor(s): Björn Bosbach, Melike Baytekin-Gerngross, Emil Heyden, Mark-Daniel Gerngross, Jürgen Carstensen, Rainer Adelung, Bodo Fiedler The aim of the present work is to reach maximum inter-laminar properties in fibre metal laminates (FML) consisting of glass fibre reinforced polymer (GFRP) and aluminium (Al) plies. The Al plies are AA5019 and AA5754 alloys and pre-treated by nanoscale sculpturing before the FMLs are manufactured by resin transfer moulding. The nanoscale sculpturing of the Al plies leads to the formation of cubical hook-like structures on the surface giving rise to a three-dimensional mechanically interlocking surface. The inter-laminar properties of the FML are investigated by double-notch shear as well as double cantilever beam (Mode I) and end notched flexure (Mode II) testing methods and compared to untreated Al plies and conventional GRFP laminates as reference. As result the nanoscale sculptured Al plies show drastically increased inter-laminar mechanical properties due to highly improved inter-ply bonding between metal surface and resin. For all FMLs with nanoscale sculptured Al plies the delamination appears in the transition zone between glass fibres and matrix due to the lower adhesion of the glass fibre/matrix interface compared to the nanoscale sculptured Al ply/matrix interface. This proves that the maximum necessary inter-laminar properties are achieved.
       
  • Thinner and better: (Ultra-)low grammage bacterial cellulose
           nanopaper-reinforced polylactide composite laminates
    • Abstract: Publication date: Available online 24 July 2018Source: Composites Science and TechnologyAuthor(s): Martin Hervy, Frederic Bock, Koon-Yang Lee One of the rate-limiting steps in the large-scale production of cellulose nanopaper-reinforced polymer composites is the time consuming dewatering step to produce the reinforcing cellulose nanopapers. In this work, we present a method to reduce the dewatering time of bacterial cellulose (BC)-in-water suspension by reducing the grammage of BC nanopaper to be produced. The influence of BC nanopaper grammage on the tensile properties of BC nanopaper-reinforced polylactide (PLLA) composites is also investigated in this work. BC nanopaper with grammages of 5, 10, 25 and 50 g m−2 were produced and it was found that reducing the grammage of BC nanopaper from 50 g m−2 to 5 g m−2 led to a three-fold reduction in the dewatering time of BC-in-water suspension. The porosity of the BC nanopapers, however, increased with decreasing BC nanopaper grammage. While the tensile properties of BC nanopapers were found to decrease with decreasing BC nanopaper grammage, no significant difference in the reinforcing ability of BC nanopaper with different grammages for PLLA was observed. PLLA composite laminates reinforced with BC nanopaper at different grammages possessed a tensile modulus of 10.5–11.8 GPa and tensile strength of 95–111 MPa, respectively, at a vf,fibres  = 39–53 vol.-%, independent of the grammage and tensile properties of the reinforcing BC nanopaper(s).
       
  • Advanced carbon fiber composite out-of-autoclave laminate manufacture via
           nanostructured out-of-oven conductive curing
    • Abstract: Publication date: Available online 26 February 2018Source: Composites Science and TechnologyAuthor(s): Jeonyoon Lee, Xinchen Ni, Frederick Daso, Xianghui Xiao, Dale King, Jose Sánchez Gómez, Tamara Blanco Varela, Seth S. Kessler, Brian L. Wardle Next-generation composite manufacturing processes are needed to overcome several limitations of conventional manufacturing processes (e.g., high energy consumption). Here we explore, via experiments and modeling, the characteristics of the newly developed out-of-oven (OoO) curing technique that cures a composite laminate via resistive heating of a carbon nanotube film. When compared to oven curing of an aerospace-grade out-of-autoclave (OoA) carbon fiber prepreg advanced composite laminate, the OoO curing reduces energy consumption by over two orders of magnitude (14 vs. 0.1 MJ). Thermophysical and mechanical tests including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), short beam shear (SBS), and ex-situ and in-situ double-edge notch tension (DENT) indicate that the physical and mechanical properties of OoO-cured laminates are equivalent to those of oven-cured (baseline) laminates. In addition to energy savings, the OoO curing process has the potential to reduce part-to-part variations through improved spatiotemporal temperature control.
       
  • Mechanical behavior of carbon nanotube yarns with stochastic
           microstructure obtained by stretching buckypaper
    • Abstract: Publication date: Available online 16 February 2018Source: Composites Science and TechnologyAuthor(s): A. Sengab, R.C. Picu The development of yarns composed primarily from carbon nanotubes (CNTs) has been pursued recently with the intent of transferring to the yarn the exceptional mechanical and transport properties of individual nanotubes. In this work we study the process of yarn formation by dry stretching buckypaper, and the mechanical behavior of the resulting yarns, function of the CNT length and of the state of the CNT assembly before stretching. The analysis is performed using a coarse grained, bead-spring representation for individual CNTs. It begins with a random buckypaper structure composed from CNTs of diameter 13.5 Å. This structure is stretched to form a yarn. This occurs once the stretch ratio becomes larger than a threshold which depends on the CNT length. At the threshold, adhesion stabilizes a highly aligned packing of CNT bundles. Packing defects and pores, reminiscent of the initial structure of the buckypaper, are incorporated in the yarn. The yarn is further tested in uniaxial tension. The defects have little effect on the mechanical behavior of the resulting yarns. However, the behavior depends sensitively on the degree of packing of the CNTs in the sub-bundles forming the yarn. Therefore, the initial structure of the buckypaper has little effect on the performance of the yarn. Increasing the CNT length increases the yarn flow stress and this is associated with the residual tortuosity of the CNTs in the yarn. Decreasing the temperature or increasing the strain rate lead to a small increase of the flow stress. These results have implications for yarn design, which are discussed in the article.
       
  • How can we make carbon nanotube yarn stronger'
    • Abstract: Publication date: Available online 15 February 2018Source: Composites Science and TechnologyAuthor(s): Yeonsu Jung, Young Shik Cho, Jae Won Lee, Jun Young Oh, Chong Rae Park There has been remarkable progress with regard to the fabrication of yarns based on high-performance carbon nanotubes (CNTs). However, the theoretically predicted tensile strength of CNTs has yet to be realized in practical CNT yarns or CNT-reinforced composites. Having considered that there are few systematic guidelines for preparing high-strength CNT yarns, we attempted to revisit the-state-of-the-art progress in the theories and yarn formation processes of CNT yarns and then draw possible correlations between the intrinsic and extrinsic structural parameters of elementary CNTs, yarn formation processes and the tensile strength of the resulting CNT yarns. On the basis of these considerations and discussions of advanced technologies and theoretical approaches, possible routes to improve the strength of CNT yarns further are suggested.
       
  • Simulating the effects of carbon nanotube continuity and interfacial
           bonding on composite strength and stiffness
    • Abstract: Publication date: Available online 14 February 2018Source: Composites Science and TechnologyAuthor(s): Benjamin D. Jensen, Gregory M. Odegard, Jae-Woo Kim, Godfrey Sauti, Emilie J. Siochi, Kristopher E. Wise Molecular dynamics simulations of carbon nanotube (CNT) composites, in which the CNTs are continuous across the periodic boundary, overestimate the experimentally measured mechanical properties of CNT composites along the fiber direction. Since the CNTs in these composites are much shorter than the composite dimensions, load must be transferred either directly between CNTs or through the matrix, a mechanism that is absent in simulations of effectively continuous CNTs. In this study, the elastic and fracture properties of high volume fraction discontinuous carbon nanotube/amorphous carbon composite systems were compared to those of otherwise equivalent continuous CNT composites using ReaxFF reactive molecular dynamics simulations. The simulation results quantify the dependence of composite mechanical properties on the number of nanotube-matrix interfacial covalent bonds. Furthermore, the mechanical impact of interfacial bonding was decomposed to reveal its effect on the properties of the CNTs, the interfacial layer of matrix, and the bulk matrix. For the composites with continuous reinforcement, it was found that any degree of interfacial bonding has a negative impact on axial tensile strength and stiffness. This is due to disruption of the structure of the CNTs and interfacial matrix layer by the interfacial bonds. For the discontinuous composites, the modulus was maximized between 4% and 7% interfacial bonding and the strength continued to increase up to the highest levels of interfacial bonding studied. Areas of low stress and voids were observed in the simulated discontinuous composites at the ends of the tubes, from which fracture was observed to initiate. Experimental carbon nanotube yarn composites were fabricated and tested. The experimental results illustrate the knockdown factors that reduce composite mechanical properties relative to those of the tubes themselves.
       
  • Mechanical enhancement effect of the interlayer hybrid CNT film/carbon
           fiber/epoxy composite
    • Abstract: Publication date: Available online 10 February 2018Source: Composites Science and TechnologyAuthor(s): Tianshu Li, Min Li, Yizhuo Gu, Shaokai Wang, Qingwen Li, Zuoguang Zhang Floating catalyst chemical vapor deposition carbon nanotube (CNT) film was intercalated into carbon fiber (CF) prepregs to fabricate hybrid composites. The effect of CNT film thickness was studied by using a 25 μm thick film and an ultrathin 2 μm film respectively. The results showed that the ultrathin CNT film interlayer had dramatically improved the compression strength of hybrid composite by 34% compared with CF/epoxy control composite owing to the altered failure modes. The damping ratio of ultrathin CNT film hybridized composite was substantially increased by two orders of magnitude, due to the energy dissipation of numerous nanoscale interconnections and interfaces. Moreover, the interlaminar properties and water resistance of the hybrid composites were all improved. Since a small amount of CNT film can significantly enhance the mechanical properties of CF/epoxy composite, this type of hybrid composite has potential application in multifunctional lightweight structures.
       
  • Nitrile butadiene rubber composites reinforced with reduced graphene oxide
           and carbon nanotubes show superior mechanical, electrical and icephobic
           properties
    • Abstract: Publication date: Available online 2 February 2018Source: Composites Science and TechnologyAuthor(s): L. Valentini, S. Bittolo Bon, M. Hernández, M.A. Lopez-Manchado, N.M. Pugno In this article, we examine the effects of two different nanostructured carbons when they are incorporated in a rubber matrix in terms of mechanical and electrical properties as well as the icephobic behaviour of the nanocomposites when swollen. Nitrile butadiene rubber composites reinforced with thermally reduced graphene oxide or multiwalled carbon nanotubes or both of them were prepared and characterized. At a particular hybrid filler loading, tensile and electrical tests showed a significant improvement of the composite. From the swelling studies, after the immersion, the nanocomposites experienced a reduction of the cross-link density that promotes weakening of ice adhesion, being this effect more evident for those samples prepared with hybrid fillers. In view of the composite formulations, that utilize commercially available elastomers and fillers, these findings would be applicable to the automotive and aviation sectors, where the demand for multifunctional rubbers is increasing.
       
  • Computer-aided design of three terminal (3T-) zig-zag SWCNT junctions and
           nanotube architectures
    • Abstract: Publication date: Available online 31 January 2018Source: Composites Science and TechnologyAuthor(s): Sushan Nakarmi, Vinu U. Unnikrishnan, Vikas Varshney, Ajit K. Roy Construction of topologically accurate models of nanotube junctions is essential for the determination of its thermal, mechanical and electronic properties. Most of the earlier nanotube junction models have been based on molecular dynamics (MD) simulations and heuristic methods which are either computationally expensive or impossible to model large 3D structures. CAD based approach that uses triangular meshes with remeshing strategies and have desired mesh optimization capability are found to be ideal to generate 3T-nanotube junctions with generic predefined orientation of nanotubes and accurate topological features. These 3T-junctions can be considered as building blocks and can be replicated in multiple directions to build complex nanotube architectures, which are shown via two examples for generating 2D and 3D microstructures by replication, translation, and rotation of a fused 3T-junction.
       
  • Quantized prediction of coefficients of thermal expansion of 3-D
           CNT-Graphene junctioned carbon nanostructures
    • Abstract: Publication date: Available online 10 January 2018Source: Composites Science and TechnologyAuthor(s): Sangwook Sihn, Ajit K. Roy, Barry L. Farmer A computational finite element analysis based on a structural molecular mechanics approach was conducted to predict effective coefficients of thermal expansion (CTE) of a novel three-dimensional carbon nanostructure, pillared graphene structure (PGS), which is constituted with several graphene sheets and single-walled carbon nanotubes. Four sets of representative unitcell models were developed atomistically having different geometric parameters of pillar length and inter-pillar distance in the PGS. Periodic boundary conditions were applied to periodic unitcell geometries to yield consistent results. Parametric study shows that both pillar length and inter-pillar distance significantly affect the effective in-plane and through-thickness CTEs. The PGS with smaller inter-pillar distance and larger pillar length yields higher in-plane CTEs, while that with larger inter-pillar distance and smaller pillar length yields higher through-thickness CTE. The calculation yields negative through-thickness CTE at low temperatures (T
       
  • Correlation between mechanical properties and microscopic structures of an
           optimized silica fraction in silicone rubber
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Dong Liu, Lixian Song, Hongtao Song, Jie Chen, Qiang Tian, Liang Chen, Liangwei Sun, Ai Lu, Chaoqiang Huang, Guangai Sun The mechanical properties and the hierarchical filler structures were characterized on a series silica-filled silicone rubber with a filler fraction (ΦSi) varied from 0.05 phr to 80 phr (parts per hundred rubber). Uniaxial elongation measurement suggests that there is a percolation threshold between 10 and 30 phr. Moreover, an optimum ΦSi range from 40 phr to 50 phr is found, in which the best mechanical performances of reinforcement are shown. The microscopic structures were crosschecked by small-angle neutron scattering (SANS) and scanning electron microscopy (SEM). The effects of the ΦSi and the fabrication process on the morphology of samples are unveiled. The correlation length among aggregates extracted from SANS data monotonically decrease from 237.0 nm to 136.5 nm with increasing the ΦSi from 30 phr to 80 phr. The average radius of gyration of aggregates 〈Rg,agg〉 fitted with the Beaucage model monotonically decrease from 49.2 nm to 37.5 nm with increasing ΦSi from 10 phr to 80 phr. Providing a 10 nm thickness bound rubber as bridge, samples with optimum ΦSi yield a morphology that the radii of aggregates and the gap filled with polymer matrix in between are equivalent as both around 60 nm.
       
  • Low shrinkage, mechanically strong polyimide hybrid aerogels containing
           hollow mesoporous silica nanospheres
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Myoeum Kim, Kyoungbok Eo, Hyun Jun Lim, Yong Ku Kwon Low shrinkage, mechanically-strong polyimide hybrid aerogels were synthesized using a supercritical carbon dioxide (scCO2) drying process. Polyimide hybrid aerogels of biphenyl tetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA) containing surface-modified hollow mesoporous silica (AHMS) nanoparticles were prepared by chemical imidization and scCO2 drying. To avoid the high volume shrinkage of wet gels that occurs mainly during the drying process, AHMS nanoparticles were introduced to the network structure of the PI aerogels as a crosslinker. All aerogels exhibited a highly-interconnected, network-like structure of polyimide nanofibers with an average fiber diameter of approximately 27.6 nm and 92.8% porosity. These hybrid aerogels exhibited an excellent compression modulus, thermal stability, and high surface area, as well as low density, low shrinkage, and low thermal conductivity.
       
  • Mechanical interlock effect between polypropylene/carbon fiber composite
           generated by interfacial branched fibers
    • Abstract: Publication date: Available online 21 July 2018Source: Composites Science and TechnologyAuthor(s): Kailin Zhang, Yijun Li, Xuewei He, Min Nie, Qi Wang Weak interface is a limiting factor to prepare polymer composite with excellent properties. Here, we report an interfacial interlocking strategy to improve interfacial strength of polypropylene (PP)/carbon fiber (CF) by manipulating interfacial diffusion and aggregation of amide-based self-assembling nucleating agent (WBG) and studied the effect of CF surface nature on the interfacial structures. The experimental results showed that when the interfacial energy between CF and WBG became low, it was favorable that the preferential localization of WBG toward the CF surfaces from polymer matrix, leading to the laterally growth of WBG fibers and the formation of interlocking interface. Single fiber fragmentation testing proved that there was a critical size of the laterally grown WBG fibers for the interfacial improvement. Only when the size exceeded 100 μm, the interfacial interlocking was strong enough to enhance the interfacial interaction, as evidenced by the substantial increases of 97% in interfacial shear strength compared to conventional PP/CF composite.
       
  • Extraordinary improvement of ablation resistance of carbon/phenolic
           composites reinforced with low loading of graphene oxide
    • Abstract: Publication date: Available online 20 July 2018Source: Composites Science and TechnologyAuthor(s): Yuanyuan Ma, Yu Yang, Chunxiang Lu, Xiaodong Wen, Xingchen Liu, Kuan Lu, Shijie Wu, Qianxiu Liu The effectiveness of graphene oxide (GO) on improving the ablation resistance of composite is investigated by incorporating a low concentration of GO (0.1wt%) into the carbon/phenolic (CF/PR). The X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy analyses reveal that the superiority of GO-filled composite over the neat in terms of thermal resistance is associated with the promoted char yield of PR and graphitization of fibers by the addition of GO. Molecular dynamics simulations identify the GO inside the matrix, even a small concentration, as a nuclei agent for the graphitized crystal growth of carbonized PR. And the GO at the fiber-matrix interface can bond to the fibers at extreme ablation temperatures, which promotes the formation of the Stone-Thrower-Wales defect (xy plane) and sp2 hybridization (z direction) at the graphene-fiber interface, and further increases the graphitization degree of fibers.
       
  • Exploring polyethylene/polypropylene nonwoven fabrics derived from
           two-dimensionally co-extruded composites: Effects of delamination,
           consolidation, drawing and nanoparticle incorporation on mechanics, pore
           size and permeability
    • Abstract: Publication date: Available online 20 July 2018Source: Composites Science and TechnologyAuthor(s): Keon-Soo Jang Co-extruded fiber-like composites after delamination facilitate the synchronous production of dual component fibers. In this study, high-density polyethylene (HDPE)/polypropylene (PP)/polystyrene (PS) and low-density polyethylene (LDPE)/PP/PS composites (fiber precursor) were melt-processed by using multilayer coextrusion. Each composite was uniaxially drawn to enhance mechanical robustness of HDPE, LDPE and PP fiber-like domains. Following the drawing process, the sacrificial PS layer was removed, and a combination of hydroentanglement, needle-punching, and compression molding was utilized to formulate dual-component HDPE/PP and LDPE/PP nonwoven mats. Drawing of the coextruded fiber precursor enhanced the tensile strength of the HDPE/PP nonwoven mat from 5.5 to 56 MPa up to a draw ratio of 11. To decrease the pore size, in the dual-component nonwoven mat, nanoscale poly (methyl methacrylate) (PMMA) colloids were infused into the large pores comprising the void spaces within the nonwoven fabric, thereby effectively reducing the pore size from 10.7 to 0.8 μm. By using the dual-component fiber system, pore size can be reduced by post-processing at a temperature between the melting points of the two different fiber components. Due to that, the efficacy of these nonwoven mats as a physical separator in battery applications was assessed via thermal shutdown analysis.
       
  • Facile fabrication of POSS-Modified MoS2/PMMA nanocomposites with enhanced
           thermal, mechanical and optical limiting properties
    • Abstract: Publication date: Available online 19 July 2018Source: Composites Science and TechnologyAuthor(s): Qiaobo Liao, Qi Zhang, Xuelin Wang, Xinle Li, Guoqing Deng, Zhen Meng, Kai Xi, Peng Zhan A facile strategy was applied to transfer chemically exfoliated molybdenum disulphide (MoS2) nanosheets from aqueous medium to organic solvents. The MoS2 nanosheets were then modified by trisilanol-phenyl-POSS (T7POSS) which was confirmed by Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and Powder X-Ray Diffraction (PXRD). The modified MoS2 nanosheets were then incorporated into poly (methyl methacrylate) (PMMA) via a simple solution blending method. The Scanning Electron Microscope (SEM) and Transmission electron microscope (TEM) were employed to demonstrate the well-dispersion of nanosheets in polymeric matrix. Compared to neat PMMA, the decomposition temperatures (Td) and the half weight decomposition temperatures (Thalf) of POSS-MoS2/PMMA nanocomposites at nanosheets concentration of 0.2 wt% were dramatically increased by 35.2 °C and 35.3 °C, respectively. Meanwhile, according to the measurements of Dynamic Mechanical Analysis (DMA), the storage modulus at 30 °C is significantly improved by 5.2 times and the glass transition temperature (Tg) is also enhanced by 6.2 °C. Remarkably, POSS-MoS2/PMMA nanocomposites possess low optical limiting differential transmittance Tc (0.5%), low nonlinear optical absorption onset threshold FON (0.02 J cm−2), low optical limiting threshold FOL (0.4 J cm−2) and high nonlinear coefficient β (297 cm GW−1), highlighting their vast potential in the development of solid-state optical limiting materials.
       
  • Hierarchically crosslinked ionic nanocomposite hydrogels with ultrahigh
           mechanical properties for underwater bioinspired capturing device
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Feibo Li, Gongzheng Zhang, Yanhong Xia, Zhaoshuo Wang, Haoyang Jiang, Xianqi Feng, Yaqian Zhang, Mingjie Liu, Huanjun Li Various applications of nanocomposite hydrogels with a single crosslinked network have been largely limited by their poor comprehensive mechanical properties, despite their prominence in certain mechanical properties. Here, we introduce ferric ions into titania-based nanocomposite hydrogels to fabricate robust ionic nanocomposite hydrogels (INC gels) with hierarchically crosslinked networks. The introduction of ion crosslinkers into nanocomposite hydrogels dramatically improves their comprehensive mechanical properties. The mechanical attributes can be changed over wide ranges by adjusting hydrogel components and the optimal INC gel exhibits the super high strength of 13.0 MPa, elastic modulus of 26.8 MPa, and toughness of 34.3 MJ m−3. In addition, The INC gels show a good mechanical and volume stability in saline solutions due to the unique crosslinked network. The reversible phase separation in gels can be used for the achievement of the shape memory effect without significantly destroying the mechanical properties and enable the mussel shell-like hydrogel to imitate the self-protection behaviour of the mussel to grab the bead underwater. Therefore, these hydrogels will hold a great potential in underwater mechanical catching hands.
       
  • Smart cord-rubber composites with integrated sensing capabilities by
           localised carbon nanotubes using a simple swelling and infusion method
    • Abstract: Publication date: Available online 18 July 2018Source: Composites Science and TechnologyAuthor(s): Yinping Tao, Yi Liu, Han Zhang, Christopher A. Stevens, Emiliano Bilotti, Ton Peijs, James J.C. Busfield Smart self-sensing composites with integrated damage detection capabilities are of particular interests in various applications ranging from aerospace and automotive structural components, to wearable electronics and healthcare devices. Here, we demonstrate a feasible strategy to introduce and localise conductive nanofillers into existing elastomeric coatings of reinforcing cords for interfacial damage detection in cord-rubber composites. A simple swelling and infusion method was developed to incorporate carbon nanotubes (CNTs) into the elastomeric adhesive coating of glass cords. Conductive CNT-infused glass cords with good self-sensing functions were achieved without affecting the bonding provided by the coating with rubber matrix. The effectiveness of using these smart cords as interfacial strain and damage sensors in cord-rubber composites was demonstrated under static and cyclic loading. It showed the possibility to identify both reversible deformation and irreversible interfacial damage. The simplicity of the proposed swelling and infusion methodology provides great potential for large-scale industrial production or modification of CNT functionalised elastomeric products such as cord-rubber composites.
       
  • Structural factor of nanoparticles in the stress-induced crystallization
           of poly(ethylene terephthalate)
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Dae Eon Jung, Wan Gyu Hahm, Takeshi Kikutani, Byoung Chul Kim The crystallization behavior of poly(ethylene terephthalate) (PET) nanocomposites with clay and trisilanol isobutyl-polyhedral oligomeric silsesquioxane (TPOSS) in the high-speed spinning process was investigated in terms of take-up speed and content of nanoparticles. The spherical TPOSS promoted the crystallization of PET. On the other hand, the plate-like clay with the aspect ratio of 250 suppressed it. At the take-up speed of 3.5 km/min, the crystallinity of the PET nanocomposite containing 1 wt% of clay was 23%, much lower than 48% of neat PET and 57% of the PET nanocomposite containing 2 wt% of TPOSS. The 2D-WAXS analysis revealed that the anisotropic clay nanoparticles aligned parallel to the fiber axis even in the fiber prepared from the free-fall spinning process. Increasing the take-up speed of spinning further increased the degree of orientation of the particle. Because of the suppressed crystallization of PET by the highly oriented clay nanoparticles, the fiber of the PET/clay nanocomposite did not give any characteristic 2D-SAXS pattern over the take-up speed range examined, indicating the absence of tilted lamellar stacks. In the fibers of neat PET and PET/TPOSS nanocomposites, however, an X-shaped 4-point pattern was obtained at low take-up speeds, which was converted to the scattering pattern of an equatorial streak with the inverse triangular scatterings in the meridional direction at high take-up speeds. The transition of the 2D-SAXS pattern shape took place at the take-up speed of 4.5 km/min for neat PET which was shifted to the lower speeds of 4 and 3.5 km/min by adding 1 and 2 wt% of TPOSS, respectively.
       
  • High temperature rheological behavior and sintering kinetics of CF/PEEK
           composites during selective laser sintering
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Mengxue Yan, Xiaoyong Tian, Gang Peng, Dichen Li, Xiaoyu Zhang As a kind of high performance polymer with excellent mechanical strength, high temperature property and chemical resistance, the polyether-ether-ketone (PEEK) and its composites are the promising candidates that can satisfy the demands for high stiff and lightweight in aerospace industry. So it is very attractive to fabricate PEEK and its composites parts with additive manufacturing technology, especially the selective laser sintering (SLS), due to its advantage on the fabrication of the parts with complex geometries. However, the strengths of the PEEK and its composites prepared by SLS are obviously lower than their injection molded parts and the laser sintering kinetics of the PEEK composites is seldom studied. In this paper, to fabricate the carbon fibers (CF) reinforced PEEK composites with high strength by SLS, the sintering kinetics of CF/PEEK composites was thoroughly studied based on the high temperature rheological behavior. A novel effective melting zone was defined by combining the simulated temperature distribution with the viscosity-temperature relationship and used to predict the process planning. Finally, the calculation results were validated by employing the simulation parameters in experiments and the tensile strength of CF/PEEK composites reached 109 ± 1 MPa with an elasticity modulus of 7365 ± 468 MPa, which is 85% higher than injection molded pure PEEK. Therefore, methods in this work could be considered as a complement to the numerical analysis of SLS process and the reinforced CF/PEEK composites may be used in aerospace industry for the structure optimization and lightweight design with complex geometries.
       
  • Effects of inter-ply angles on the failure mechanisms in bioinspired
           helicoidal laminates
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): J.L. Liu, H.P. Lee, V.B.C. Tan Following encouraging findings on the potential of helicoidal laminates under transverse loads to significantly outperform cross-ply laminates, a more extensive study was undertaken to include thicker helicoidal laminates with the greater range of variation in inter-ply angles. Previous research has shown that thin helicoidal laminates outperform cross-ply laminates when the inter-ply angle is less than 10°. It was reported that the small inter-ply angles in helicoidal laminates make them more resistant to delamination. Consequently, less delamination occurs and they are deeper inside the laminates. This delays catastrophic failure, which occurs when transverse cracks propagating from the surface of the laminates merges with the delamination. The current study shows that thick helicoidal laminates with small inter-ply angles promote a different damage mechanism not apparent in thin laminates. Hence reducing inter-ply angles does not always lead to higher transverse load bearing capability. Observations from CT scan images of thick helicoidal laminates suggest that higher delamination resistance offered by small inter-ply angles is offset by the ease with which cracks between fibers propagates transversely when the angle is too small. Hence, helicoidal laminates comprising 73 plies of unidirectional carbon fiber reinforced laminas with 2.5° inter-ply angle could not achieve the peak loads of 73-ply laminates with 10° inter-ply angle. The optimal inter-ply angle to achieve high peak load appears to be between 5° to 10°. This study shows that the peak transverse load for helicoidal laminates can be up to 73% higher than that of cross-ply laminates when they are optimized.
       
  • Thermal conductivity of polypropylene/aluminum oxide nanocomposites
           prepared based on reactor granule technology
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Bulbul Maira, Kengo Takeuchi, Patchanee Chammingkwan, Minoru Terano, Toshiaki Taniike A reactor granule technology (RGT) is a new method for the in-situ fabrication of polyolefin-based nanocomposites. It involves the impregnation and confinement of inorganic molecular precursors in the porosity of polyolefin reactor granule, and subsequent conversion of the precursors into highly dispersed inorganic nanoparticles during melt processing. In this contribution, the RGT was applied to develop thermally conductive polypropylene (PP)/aluminum oxide (Al2O3) nanocomposites with the aid of two strategies. By melt-blending highly filled reactor granule with unfilled reactor granule, filler-rich and polymer-rich domains were created at around 10 μm scale, in which the filler-rich domains offered a thermally conductive pathway. The other strategy was based on tailoring the interfacial interaction between PP and Al2O3: An aluminum alkoxide precursor and a silane coupling agent were co-impregnated and converted into organically modified Al2O3 nanoparticles. Both of the strategies successfully improved the thermal conductivity of the nanocomposites at a fixed Al2O3 loading. The highest enhancement was achieved based on the interfacial modification using (2-phenylethyl)trimethoxysilane, where the thermal conductivity reached 0.74 W/m K at 20 wt% compared to 0.21 W/m K for pristine PP.
       
  • Using variable interfacial adhesion characteristics within a composite to
           improve flexural strength and decrease fiber volume
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Filip Stojcevski, James D. Randall, Luke C. Henderson This paper investigates the impact of using amine functionalised fibers in composite “hybrid” laminates to improve interfacial shear strength (IFSS) and reduce laminate weight. A comparison of single fiber fragmentation testing (SFFT) and short beam shear testing (SBS) showed that 103.6% improvements of IFSS at a single fiber level only translate to a 23.3% improvement in SBS testing. However, localised use of both functionalised and non-functionalised T300 fibers in a “hybrid interface” laminate improved IFSS by 56.7%. Hence this study shows that careful placement of fibers and localised manipulation of the interface characteristics can be used to great effect when designing a composite material. Ultimately, the use of a hybrid interface approach was able to provide a weight reduction of 11.27% while not sacrificing flexural strength compared to the baseline T300 fibers.
       
  • Optimal synergy between micro and nano scale: Hierarchical all carbon
           composite fibers for enhanced stiffness, interfacial shear strength and
           Raman strain sensing
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Kyriaki Tsirka, Lazaros Tzounis, Apostolos Avgeropoulos, Marco Liebscher, Viktor Mechtcherine, Alkiviadis S. Paipetis Multifunctional hierarchical reinforcements are fabricated by growing multi walled carbon nanotubes (CNTs) onto carbon fibers (CFs) via chemical vapor deposition. In contrast to typical hybrid multi scale reinforced composites, the biomimetic approach of hierarchical interconnection between CFs and CNTs is followed in order to provide the dimensional confinement required for the effective synergy between the nanophase i.e. the CNTs and the micron phase i.e. the CFs. Compared to the reference CF: (i) ASTM single fiber tensile tests reveal up to 50% increase in tensile modulus together with the expected decrease in tensile strength, (ii) Single Fiber Fragmentation Tests (SFFT) reveal up to 134% enhancement for Interfacial Shear Strength (IFSS), (iii) the frequency of the Raman 2D graphitic vibrational mode with strain shows a strain sensitivity enhancement up to 87.4% and (iv) fractographic investigation shows bridging of the CNTs only for specific growth conditions, which correspond to the optimal IFSS. Furthermore, a direct correlation between the Raman strain sensitivity with the young moduli of the CF and the hierarchical CF-CNT is found, proving the efficient stress transfer from the nano to micron scale in a “composite” fiber. Overall, an optimal synergy between the reinforcing graphitic phases is achieved, attaining for the first time an equivalent stiffness for the CNT reinforcement close to theoretically obtained values. Thus, biomimetic hierarchical reinforcements provide the roadmap for the full exploitation of the unique properties of the nanophase in advanced structural composites.
       
  • Design of super-tough co-continuous PLA/NR/SiO2 TPVs with balanced
           stiffness-toughness based on reinforced rubber and interfacial
           compatibilization
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Yutong Liu, Liming Cao, Daosheng Yuan, Yukun Chen Elastomer has been proved to be a prominent toughener for polylactide (PLA), however, the remarkable increase in toughness always accompanies a sharp decrease in tensile strength. In this work, based on rubber reinforcement theory and interfacial compatibilization technique, co-continuous PLA/natural rubber (NR)/silica (SiO2) thermoplastic vulcanizates (TPVs) with balanced stiffness and toughness were designed. By employing thermodynamic and kinetic factors, SiO2 was restricted to distribute in rubber phase or at the interface due to the strong physical entanglements between NR and SiO2, which played a significant role in reinforcing rubber and interfacial compatibilization. As a result, impact strength of the TPVs was greatly improved without decrease in tensile strength. With 12.5 phr SiO2, impact strength increased to 85.1 kJ/m2 (without fracture), which was 8 times of blank sample and 30 times than that of neat PLA, respectively. In addition, the influence of reinforced rubber, superior interfacial adhesion on fracture toughness and deformation mechanism were investigated semi-quantitatively under digital Izod impact tests.Graphical abstractImage 1
       
  • EMI shielding properties of laminated graphene and PbTiO3 reinforced
           poly(3,4-ethylenedioxythiophene) nanocomposites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Jasvir Dalal, Sushma Lather, Anjli Gupta, Sajjan Dahiya, A.S. Maan, Kuldeep Singh, S.K. Dhawan, Anil Ohlan In this paper, PEDOT/reduced graphene oxide (RGO)/PbTiO3 nanocomposites have been synthesized using facile insitu chemical oxidative polymerization method. The synthesis method leads to the formation of core-shell structured nanocomposites containing PbTiO3 as primary filler and RGO as secondary filler in PEDOT matrix. The core-shell morphology of the composites has been confirmed using transmission electron microscope with average particle size 20–30 nm observed for PbTiO3. The incorporation of RGO and PbTiO3 in the PEDOT matrix has been confirmed by X-ray diffraction. A systematic study on electromagnetic shielding properties and the effect of PbTiO3 concentration on different properties has been carried out. The ferro-electric PbTiO3 with RGO induced dielectric loss in the composites, whereas, PEDOT establish a conducting network over RGO layer and PbTiO3 nanoparticles that improve electromagnetic shielding properties by increasing the dielectric loss. As a result, an enhanced electromagnetic shielding effectiveness value of 51.94 dB (>99.999% attenuation) has been achieved in 12.4–18 GHz frequency range. The nanocomposites were further characterized using Fourier transmission infrared spectroscopy and thermal gravimetric analysis.
       
  • A high resolution method for characterisation of fibre misalignment angles
           in composites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): D. Wilhelmsson, L.E. Asp In this paper a novel method to characterise fibre waviness in composites is presented and assessed. The proposed method referred to as the “high resolution misalignment analysis” (HRMA) method and is suitable for measurements with high spatial resolution. The HRMA method measures misalignment angles tracing individual fibres in detailed micrographs. Here, the method is evaluated using software-generated images with known statistics to mimic real micrographs. Results reveal that the HRMA method provides very accurate measurements on composites with high fibre waviness, outperforming existing methods, whereas it performs on par with existing methods for materials featuring medium fibre waviness. The HRMA method is capable of characterising a 2 cm2 micrograph with a spatial resolution of 55 μm in approximately 1 min on a standard laptop computer. The HRMA code and software-generated images are supplied as supplementary material to this paper.
       
  • Effect of elastic modulus mismatch of epoxy/titanium dioxide coated silver
           nanowire composites on the performance of thermal conductivity
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Yunliang Jiang, Maoyuan Li, Chao Chen, Zhigang Xue, Xiaolin Xie, Xingping Zhou, Yiu-Wing Mai The effect of elastic modulus mismatch of epoxy/silver nanowires (epoxy/AgNWs) composites on thermal conductivity was critically evaluated by synthesizing a stiff titanium dioxide (TiO2) coating on the surface of AgNWs (designated as AgNWs@TiO2) with different length/diameter aspect ratio. Compared to epoxy/AgNWs composites, AgNWs@TiO2 could be more uniformly dispersed in epoxy matrix. However, the TiO2 intermediate layer with a higher elastic modulus increased the modulus mismatch with epoxy, exacerbating the interfacial phonon scattering, and the thermal conductivity of the epoxy/AgNWs@TiO2 composites was decreased. Moreover, the epoxy/AgNWs@TiO2 composites possessed enhanced volume electrical resistivity and reduced dielectric properties relative to the epoxy/AgNWs composites. These observed results on thermal conductivity, electrical insulation, dielectric loss and dielectric constant due to TiO2-coated AgNWs are more prominently displayed at higher nanowire loading (4 vol%) and aspect ratio (1000).
       
  • High performance glass fiber reinforced polypropylene realized by reactive
           extrusion technology
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Guojun Luo, Gang liu, Yunlei Chen, Wenbin Liang, Guogang Liu, Yanhua Niu, Guangxian Li High performance polypropylene/glass fiber (PP/GF) composites were prepared by introducing different percentage of maleic anhydride-g-polypropylene (MPP) and epoxy resin (EP) in the matrix. The coupling effect of MPP and EP on the mechanical properties of the hybrid composites were highlighted and the complicated reinforcing mechanism were discussed in detail. Even though the addition of MPP could apparently improve the performance of composites, as the EP coupled especially at higher MPP and EP content, both the tensile and impact strength get further enhancement. For the sample with 10 wt% MPP and 10 wt% EP (10MPP/10EP), the tensile and impact strength show significant enhancement by 136% and 171%, respectively, compared to the control PP/GF composite. It is demonstrated that the good compatibility among each constituent as well as the reaction between EP and MPP, which could efficiently facilitate the network formation, contribute to the high performance of the composites. The finer EP particles caused by the enhanced compatibility as nucleating agent could promote the crystallization, but the crystallinity of the composites does not change so much. A schematic mechanism of the interfacial structure on both molecular and microscopic levels is depicted, where the reaction between MPP and EP are considered as a dominated factor to influence the above-mentioned network formation. This local network structure causes the composites as an integrate showing excellent mechanical performance.
       
  • Multi-dimensional strain sensor based on carbon nanotube film with aligned
           conductive networks
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Lifeng Ma, Wei Yang, Yansong Wang, Hao Chen, Yanfen Xing, Jincheng Wang Carbon nanotubes (CNTs) show a tremendous promise on strain sensor applications, but the stretchable ability of CNT devices is low due to their poor ductility. Herein, novel aligned conductive networks of CNT film were designed and introduced onto polydimethylsiloxane (PDMS) substrate, which realized highly stretchable multi-dimensional strain sensitivity up to a strain of 260% and an excellent cyclical durability. The gauge factor (GF) along the CNT aligned direction, i. e. A direction, can reach 461 up to a strain of 260% while the resistance of the perpendicular direction (B direction) keeps almost the same with initial value, showing a multi-dimensional strain detection capability. The high GF along A direction of the CNT film is caused by the slippage, damage and rupture of CNT bundles with strain increasing, while the CNT entanglement between the adjacent CNTs stabilizes the resistance along B direction. This study rationalizes the aligned CNT network concept to realize the multi-dimensional strain sensors, which have a great potential to be applied in complex strain detection in practical applications.Graphical abstractImage 1
       
  • Microwave-assisted hydrosilylation of polypropylene and its application to
           in-situ grafted polypropylene/SiO2 nanocomposites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Patchanee Chammingkwan, Masahito Toyonaga, Toru Wada, Minoru Terano, Toshiaki Taniike Grafting end-functionalized polypropylene (PP) to the surfaces of nanoparticles is a promising approach in boosting physical properties of PP-based nanocomposites. In this study, a practical pathway is presented for the fabrication of PP-grafted nanocomposites: Reactive silicon alkoxy groups were introduced through microwave-assisted hydrosilylation of terminal unsaturation of vis-breaking PP. Thus obtained hydrosilylated PP was added as a reactive additive in melt compounding of PP with SiO2 nanoparticles to implement in-situ grafting. Significant improvements were attained in the dispersion of SiO2 nanoparticles, the crystallization rate and the tensile strength.
       
  • Multi-functional composite aerogels enabled by chemical integration of
           graphene oxide and waterborne polyurethane via a facile and green method
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Furong Sun, Jiyu Yang, Huan Zhang, Longfei Yi, Kaijun Luo, Lijuan Zhao, Jinrong Wu Practical thermal-insulating applications require aerogels to possess multi-functionality in addition to a low thermal conductivity. However, it is still a challenge to fabricate multi-functional aerogels. Here we use an environmentally friendly method to obtain multi-functional hybrid aerogels by chemical integration of waterborne polyurethane (WPU) and graphene oxide (GO). In the hybrid aerogels, covalent networks are formed in WPU itself and between WPU molecules and GO sheets through the deblocking and condensation reactions, while physical networks are formed by stacking between GO sheets and phase separation in WPU. The existence of both physical and chemical networks imparts high mechanical property and excellent shape-memory capability to the hybrid aerogels. The interfaces between different networks play a role of phonon-scattering, thus enabling a low thermal conductivity for the hybrid aerogels. Moreover, rough structures on the surface endow the hybrid aerogels with high hydrophobicity. The multi-functionality properties presented in this paper provide a potential usage of aerogels with a wide range of thermal-insulating characteristics which can improve the energy efficiency effectively.
       
  • Polypropylene-based ternary nanocomposites for recyclable high-voltage
           direct-current cable insulation
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Yao Zhou, Bin Dang, Haoming Wang, Jiping Liu, Qi Li, Jun Hu, Jinliang He Polymeric high-voltage direct-current (HVDC) cables are the core equipment in energy internet, which enable the long-distance large-capacity electric power transmission, large-scale utilization of renewable electric power and flexible interconnection of large power grids. Performance of the HVDC cables are determined by the properties of their insulation material. However, the traditional polymeric HVDC cable insulation material, crosslinking polyethylene (XLPE) is limited to relatively low working temperature which restricts the power capacity of HVDC cables. XLPE with thermosetting characteristics also presents a major barrier to material recycling and environmental pollution reduction. Here we report the ternary nanocomposites of polypropylene (PP), thermoplastic polyolefin (TPO) and MgO nanoparticles as an efficient way to recyclable HVDC cable insulation material that simultaneously possess excellent thermal, mechanical and electrical properties, especially at high temperatures. At an optimal composition, the ternary nanocomposites integrate the complementary properties of the multi-components to raise the mechanical flexibility at room temperature and greatly improve the electrical properties at high temperatures (including suppressed space charge accumulation and increased breakdown strength and volume resistivity) while retaining high melting temperature comparable to PP of about 160 °C. This work may pave a way for synergistic optimization of the overall properties of insulation materials and enabling the successful development of recyclable insulation material for large-capacity HVDC cable application.
       
  • Core-shell flame retardant/graphene oxide hybrid: a self-assembly
           strategy towards reducing fire hazard and improving toughness of
           polylactic acid
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Jian Jing, Yan Zhang, Zheng-Ping Fang, De-Yi Wang Biobased flame retardant/graphene oxide hybrid (GOH) as a multifunctional flame retardant for polylactic acid (PLA) was synthesized through organic-solvent-free self-assembly. The electrostatic interactions deposited the polyethylenimine (PEI) and biobased polyelectrolyte (BPE) coating on the surface of ammonium polyphosphate (APP) in water, which gave the negatively charged core-shell flame retardant. Then, GOH was obtained via aqueous self-assembling between the positively charged graphene oxide (pGO) obtained by grafting pristine GO with PEI and the core-shell flame retardant. Subsequently, GOH was employed as multifunctional flame retardant to PLA, aiming to enhance both flame retardancy and toughness. Based on the investigation via LOI, UL94 test and the cone calorimetry, it clearly showed that GOH endowed PLA significantly enhanced flame retardancy. The flame retardancy of GOH in PLA was performed in both of the gas-phase and condensed-phase mechanisms according to the analysis of the volatile gases and the residues. As for the mechanical properties of PLA/GOH composites, an over 6 folds increment in elongation at break (52.4%) and 86.7% increase in notched impact strength (5.6 kJ/m2) were achieved for PLA/10%GOH, compared with that of the neat PLA. It meant the introduction of GOH remarkably improved toughness of PLA.
       
  • Size effects in layered composites – Defect tolerance and strength
           optimization
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Junjie Liu, Wenqing Zhu, Zhongliang Yu, Xiaoding Wei Mixture of hard and soft phases in a smart way makes strong and tough materials – this approach, inspired by natural composites, has been widely adopted by scientists and engineers. Behind it exist many interesting fundamental mechanics. In this study, we solve analytically the stress intensity factor for a crack propagating from the hard to the soft phase in a layered composite starting with the postulation on the crack profile inspired by the shear-lag model. Our analysis shows that when a crack extends from the hard phase into the soft one, the stress intensity factor amplifies first at the hard-soft interface and then declines quickly to zero as it progresses toward the next hard phase. This crack arresting mechanism works until a secondary crack initiates in the next hard layer and then merges with the main crack. The efficiency of the defect tolerance, measured by the effective strength of the layered composite, is found to exhibit strong size effects. Overall, the smaller the dimensions of two phases are, the more efficiently of the layered composites tolerate defects. Furthermore, if the dimension of one phase is given, there always exists a critical dimension of the other phase that optimizes the efficiency (or the composite strength). A relationship between the defect tolerance efficiency with the nanostructures which is analogous to the famous “Hall-Petch” and “inverse Hall-Petch” relationships for polycrystalline metals is found. The analysis in this work can be used to guide the micro-to nano-structure design for synthesizing innovative defect-tolerant composites.
       
  • Continuous carbon fiber/crosslinkable poly(ether ether ketone) laminated
           composites with outstanding mechanical properties, robust solvent
           resistance and excellent thermal stability
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Yunhe Zhang, Wei Tao, Yu Zhang, Lin Tang, Junwei Gu, Zhenhua Jiang Continuous carbon fiber (CCF) reinforced polymeric composites have attracted significant attention in the aeronautic and automobile industries. In this study, novel CCF/poly(ether ether ketone) (PEEK) composites with robust solvent resistance, excellent thermal stability and outstanding mechanical properties were successfully fabricated via a facile solution impregnation process, mainly ascribed to the introduction of the crosslinkable phenylethynyl pendant to PEEK (PEP-PEEK) with excellent solubility. After the crosslinking reaction, PEP-PEEK presented robust solvent resistance, good thermal stability, and high mechanical properties. The longitudinal tensile strength of the CCF/PEP-PEEK composites significantly improved to 1610 MPa, which was 19 times stronger than the longitudinal tensile strength of PEP-PEEK. In the meantime, the CCF/PEP-PEEK composites also had a higher long-term operating temperature, excellent thermal stability and high heat distortion temperature. This study was performed as part of a larger effort to provide a simple and feasible method for the preparation of high quality continuous fiber reinforced poly(ether ether ketone) composites.
       
  • Investigation of ultraviolet radiation effects on thermomechanical
           properties and shape memory behaviour of styrene-based shape memory
           polymers and its composite
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Wessam Al Azzawi, J.A. Epaarachchi, Jinsong Leng In recent years, shape memory polymers (SMP) have been researched extensively for space applications, such as deployable solar panels and antenna reflectors. Space applications cause SMP components to be severely exposed to ultraviolet (UV) light which may results in material degradation which may causes catastrophic failures and costs substantial amount of public money. This paper investigates the effect of UV light exposure on thermomechanical properties and shape memory effect (SME) of the Styrene-based SMP and its Glass fibre shape memory polymer composites (SMPC). Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), have been used to investigate the thermomechanical properties, SMEs and thermal stability before and after the UV exposure. Further, Fourier transform infrared spectroscopy (FTIR) was performed to analyse the after effect of UV exposure on the polymer's chemical structure. Results have revealed that UV exposure had different impacts on the SMP samples. UV exposure have degraded the mechanical properties, lowered the glass transition temperature (Tg), considerably reduced shape recovery rate, and programming and recovery stresses in all samples. However, the exposure had no considerable effect on the fixity ratio and relaxation modulus of the neat SMP sample, and it slightly increased the fixity ratio of the SMPC samples.
       
  • The effect of dual-scale carbon fibre network on sensitivity and
           stretchability of wearable sensors
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Fan Zhang, Shuying Wu, Shuhua Peng, Chun H. Wang Sensitivity and stretchability are two key characteristics of wearable sensors and tactile sensors for soft robotics. Here, we present a new technique to increase the sensitivity of wearable sensors by creating a conductive network of dual-scale carbon fibres, i.e., carbon nanofibres (CNFs) and short carbon fibres (SCFs), in a polydimethylsiloxane (PDMS) matrix. To quantify the effects of this dual-scale carbon fibre network on the stretchability, sensitivity, and stability under repeated loading, comprehensive experiments were conducted to characterise the electrical conductivity, mechanical properties, and piezoresistivity of the resultant PDMS composites with varying concentrations of carbon fibres. The Prony series model of viscoelasticity was adapted to model the strain-rate dependent behaviour of the new sensors. The results reveal that this dual-scale network is able to significantly lower the percolation threshold below that of either of the single-scale composites containing only SCFs or CNFs, indicating a strong synergistic effect. Furthermore, the dual-scale carbon network exhibits higher piezoresistive sensitivity than the CNF-reinforced composite while retaining similar stretchability, thus offering a new technique for creating highly sensitive wearable sensors and tactile sensors for soft robotics.
       
  • Facile method to functionalize graphene oxide nanoribbons and its
           application to Poly(p-phenylene benzobisoxazole) composite
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Mingqiang Wang, Chunyan Wang, Yuanjun Song, Chunhua Zhang, Lu Shao, Zaixing Jiang, Yudong Huang Graphene oxide nanoribbons (GONRs), as a new member of carbon family, attracted extensive attention in industry and science field. It has considered to be as a promising nanomaterial for applications in the field of materials science, energy storage and optics science due to its extraordinary mechanical, electrical and thermal properties. Hence, in this study, we carried out a facile and efficient strategy for preparing poly (phenylene benzobisoxazole) (PBO)/GONRs(PGR) composite fibers via one-pot in situ polycondensation method for enhancement in mechanical and thermal properties. The GONRs sheets in this work were obtained by unwrapping multi-walled carbon nanotubes (MWCNTs) side walls, and then directly reacted with PBO monomer 4,6-diaminoresorcinol(DAR) and covalently grafted on PBO molecular chains. The structure and morphology of GONRs and modified GONRs were well demonstrated by the FT-IR, XPS and TEM analysis for confirming the formation of chemical bond between GONRs and PBO molecular chains. The mechanical and thermal properties of PGR composite fibers were also investigated. It was found that the performance of composite fibers about 32.1% improvement in tensile modulus, 24.2% in tensile strength and 10.5% thermal stability, respectively.
       
  • Experimental and numerical investigation of the needling process for
           quartz fibers
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Junbo Xie, Xiaoming Chen, Yifan Zhang, Guodong Fang, Li Chen This paper investigates the deformation and damage of quartz preforms during the needling process. Effect of needling position and fabric thickness on the resistance force of the needle are experimentally researched. A numerical methodology based on the concept of virtual fibers is proposed to establish the geometry models of 2D broken twill and nonwoven fabrics. Then the needling process of the fabric plies is simulated by finite element method using an explicit dynamics algorithm. Deflection, stretch and breakage of the fibers are analyzed. The simulated fiber architectures of the needling positions are fairly close to the practical observations. Resistance force of the needling process can be predicted with satisfactory accuracy. The aim of the proposed approach is to generate the virtual fiber structure of needled preforms and obtain the effect of needling process on the fiber damage. This approach would be helpful for designing low-damage preforms and improve the mechanical properties of needled composites.
       
  • Improved organic-inorganic/graphene hybrid composite as encapsulant for
           white LEDs: Role of graphene, titanium (IV) isopropoxide and
           diphenylsilanediol
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): P. Madhusudhana Reddy, Chi-Jung Chang, Chun-Feng Lai, Min-Ju Su, Mei-Hui Tsai We report a graphene embedded organic-inorganic hybrid (O-I hybrid) composites that can be utilized as robust encapsulants for white light emitting diodes (WLEDs). The effect of graphene and monomers on the thermal resistance, refractive index (RI), transparency, thermal conductivity, and thermal aging stability of the encapsulant were studied. This study has explicitly unveiled that the embedded graphene played a multifunctional role in producing a high-performance encapsulant. Compared with graphene free O-I hybrid encapsulant, RI, thermal conductivity and heat dissipation ability of the graphene embedded encapsulants were significantly improved. After continuous operation for 10 days, the color rendering index (Ra) of WLED with graphene embedded encapsulants changed from 89.5 to 89.2 (driving current 100 mA), while the correlated color temperature (CCT) altered from 4535 to 4546. Its luminous efficiency changed from 82.9 to 81.2 lm/W. The WLEDs with graphene embedded O-I hybrid encapsulant exhibited long-term stability. This work has paved the way for rational design and assembly of graphene embedded composites as robust materials for various requirements of WLED applications.Graphical abstractImage 1
       
  • Chemical vapor deposition-based grafting of CNTs onto basalt fabric and
           their reinforcement in epoxy-based composites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Garima Mittal, Kyong Y. Rhee Basalt fiber (BF) is considered to be a green industrial material, exhibiting outstanding environmental stability along with superior mechanical properties compared to E-type glass fiber. It is also less expensive than carbon fiber, making make it perfect for the mass-production of basalt fiber-reinforced polymer (BFRPs) composites. BFRPs are reinforced with nanomaterials to further enhance their performance. However, nanomaterials have the tendency to agglomerate because of their high surface energy, which hinders their efficient dispersion into the matrix. Hence, in this study, we grafted CNTs onto basalt fabric using chemical vapor deposition (CVD). Furthermore, CNT-grafted basalt fabric (BF-CNT) was sandwiched with epoxy via a hand lay-up technique. XRD, HR-RAMAN, FE-SEM, and thermogravimetric analysis (TGA) were performed to characterize BF-CNT. The properties of the fabricated BF-CNT/epoxy composites were also analyzed and compared with CNT-reinforced BF/epoxy composites. Based on our results, we found that the BF-CNT/epoxy composite shows improved properties.
       
  • Low-velocity impact behaviour of a shear thickening fluid (STF) and
           STF-filled sandwich composite panels
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Kunkun Fu, Hongjian Wang, Li Chang, Matthew Foley, Klaus Friedrich, Lin Ye Sandwich composite panels (SCPs) with carbon fibre reinforced plastic (CFRP) facings are usually vulnerable to low-velocity transverse impact loading. In this study, a method is presented to improve the impact resistance and energy absorption capacity of CFRP-faced SCPs by filling them with a concentrated styrene/acrylate particle based shear thickening fluid (STF). First, for the STF alone, aspects of mechanical performance, namely rheological and low-velocity impact behaviours, were systematically examined. It was found that the critical shear stress of the STF was lower than that of silica particle based STF with a similar particle size and volume fraction, indicating that shear thickening was more easily achieved in the styrene/acrylate particle based STF. In addition, the STF exhibited much higher energy absorption capacity than an aluminium foam. Finally, low-velocity transverse impact experiments were performed on STF-filled SCPs with two core thicknesses, 7.2 mm and 12.7 mm. It was shown that the absorbed energy of the SCPs with a thin core increased by up to 99.3%, while the impact damage of SCPs with a thick core could be effectively suppressed on the back surface of the SCPs. The impact mechanism of the STF-filled SCPs is also discussed. This study provides a new method for the design of impact-resistant SCPs.
       
  • Experimental determination of Through-Thickness Compression (TTC)
           enhancement factor for Mode II fracture energy
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Xiaodong Xu, Michael R. Wisnom, Xiaoyang Sun, Tamas Rev, Stephen R. Hallett Mode II fracture energy, GIIC, is a critical parameter for determining the propagation of delamination in composite laminates. Its value can be affected by Through-Thickness Compression (TTC) stress acting on the crack tip and here this effect has been studied using IM7/8552 carbon/epoxy laminates with cut central plies. External TTC loads were applied through bi-axial testing. Unidirectional (UD) cut-ply specimens were used to determine the TTC enhancement factor, ηG, for GIIC. A similar enhancement effect was also found in Quasi-isotropic (QI) specimens with 2 extra cut central 0° plies inserted into the layup. The TTC enhancement factor was implemented in a Finite Element Analysis (FEA) framework using cohesive interface elements, showing that the determined ηG can be successfully used to model the effect of TTC on delamination.
       
  • Revisiting the thickness reduction approach for near-foldable capacitive
           touch sensors based on a single layer of Ag nanowire-polymer composite
           structure
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Kwang-Seok Kim, Sun Ok Kim, Chul Jong Han, Dae Up Kim, Jin Soo Kim, Yeon-Tae Yu, Cheul-Ro Lee, Jong-Woong Kim Although a percolated network of silver nanowires (AgNWs) is considered the most promising flexible transparent electrode because of its high conductivity, high transmittance, excellent flexibility, and facile patternability, it has encountered a serious delay in its application to most optoelectronic devices. Here, we analyzed the reasons and tried to resolve the current issues to achieve near-foldable transparent touch sensors by employing an inverted layer processing method. A hydroxylated polydimethylsiloxane (PDMS) was used as a preliminary substrate for deposition and patterning of AgNWs, and then the nanowires were completely transferred to the newest version of colorless polyimide (cPI) by hydrophobic recovery of the PDMS surface. For the first time, we designed an automatic apparatus for testing the foldability of the fabricated composite film by a spacer inserting method. The testing of various AgNWs/cPI films with this method revealed that the thickness reduction approach could be an efficient and powerful tool to attain near-foldable electrodes if the AgNWs are solidly adhered to the substrate. Based on these findings, we could successfully demonstrate a near-foldable touch sensor, which is capable of sensing human touches even in the folded state.
       
  • Inter-fibre failure of through-thickness reinforced laminates in combined
           transverse compression and shear load
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Hao Cui, António R. Melro, Mehdi Yasaee Extensive studies have been reported on the improvement of through-thickness reinforcement to inter-laminar performance of composite laminates; current understanding on the in-plane performance is relatively limited, although it is also concerned in industrial application. The influence of through-thickness reinforcement (Z-pinning) on the inter-fibre failure in compression of unidirectional laminates was investigated. Both unpinned and Z-pinned laminates were tested at four different off-axis angles, representing different combinations of transverse compression and in-plane shear stress. It was found that the stiffness of Z-pinned laminates decreased significantly in all off-axis angles. The failure strain and strength were reduced in shear dominated failure modes, while improved in the compression dominated failure modes by the presence of the Z-pins. A further investigation on the angle of failure plane was carried out and a comparison with analytical failure models is presented.
       
  • Electric-field-induced out-of-plane alignment of clay in
           poly(dimethylsiloxane) with enhanced anisotropic thermal conductivity and
           mechanical properties
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Zuqi Liu, Panrui Peng, Zhihong Liu, Wei Fang, Qingzhong Zhou, Xueqing Liu, Jiyan Liu An Alternating current (AC) electrical field was applied to induce the movement of the clay nanoparticles in polydimethylsiloxane (PDMS) to fabricate flexible membranes embedded with thickness-direction aligned nanoparticles. The influence of the electric field strength and frequency on the movement of the particles in the PDMS monomer was investigated using an optical microscope. The morphology of the aligned clay/PDMS membranes frozen with thermal curing was analyzed with scanning electron microscopy (SEM) and confocal Raman spectroscopy. Benefiting from the anisotropic structure of aligned particle chains, the aligned clay/PDMS membranes show enhanced mechanical properties, thermal conductivity, and the light transmittance in the thickness direction compared to nonaligned membranes. This enhancement effect decreases as the particle concentration exceeds 5 wt %. The reason is that at higher clay concentrations, alignment of the particle is frustrated and particle chains become tilted and irregular owing to an increment in the viscosity of the system.
       
  • Fabrication of a piezoelectric polyvinylidene fluoride/carbonyl iron
           (PVDF/CI) magnetic composite film towards the magnetic field and
           deformation bi-sensor
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Min Sang, Sheng Wang, Mei Liu, Linfeng Bai, Wanquan Jiang, Shouhu Xuan, Xinglong Gong In this paper, a versatile polyvinylidene fluoride/carbonyl iron (PVDF/CI) composite film was prepared by doping magnetic carbonyl iron (CI) particles into piezoelectric polyvinylidene fluoride (PVDF) matrix. Without influencing the piezoelectric structure of PVDF, CI particles enhanced the Young's modulus and maximum tensile strength of composite films. Due to the magnetic driven characteristic, PVDF/CI composite films exhibited distinct magnetic-mechanic-electric coupling properties. The piezoelectric charge signals could be generated by applying the bending deformation or magnetic field. Taking PVDF/CI-10% (CI content was 10 wt%) film as an example, the piezoelectric charges under 2, 4, 6, 8, and 10 mm bending displacement were 3.0, 9.6, 14.9, 18.6, and 24.6 pC respectively. Moreover, when the magnetic field varied from 0 to 600 mT, the generated magneto-electric charges of PVDF/CI-10% film increased from 0 to 676 pC. The quantitative relationship between magnetic field and magneto-electric charges was obtained by the polynomial fitting method and the correlation coefficient was up to 0.97. Owing to the ideal piezoelectricity, excellent stability, light weight and desirable flexibility, PVDF/CI composite films showed promising applications in deformation sensor and magnetic field sensor.
       
  • Exchangeable interfacial crosslinks towards mechanically robust
           elastomer/carbon nanotubes vitrimers
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Min Qiu, Siwu Wu, Zhenghai Tang, Baochun Guo Covalent bonds mediated interfaces are generally favorable for transferring interfacial stress and hence rationalizing the mechanical properties of the filled elastomeric composites. Aiming at reprocessable yet robust elastomeric composites, in this contribution, exchangeable interfacial crosslinks are introduced into the interfaces between epoxidized natural rubber (ENR) and multi-walled carbon nanotubes (MWCNTs). This is accomplished by functionalizing MWCNTs with carboxyl groups through diazo-coupling reaction and then incorporating the modified MWCNTs into diacid-cured ENR. Accordingly, covalent β-hydroxy ester bonds result in the interfaces between ENR and MWCNTs. The formation of covalent interfaces enables much uniform dispersion of MWCNTs and stronger interfacial adhesion. Comparing to the ENR filled with pristine MWCNTs, the modified composites exhibit much improved mechanical performance. Importantly, the exchangeable nature of interfacial β-hydroxy ester bonds has promoted effect on the reprocessibility of epoxy-MWCNTs vitrimers. Overall, we envision this interfacial strategy can provide an alternative avenue towards reprocessable yet robust elastomeric composites.
       
  • Uniformly dispersed polymeric nanofiber composites by electrospinning:
           Poly(vinyl alcohol) nanofibers/polydimethylsiloxane composites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Kentaro Watanabe, Tomoki Maeda, Atsushi Hotta A method for the fabrication of homogeneous and well-dispersed polymeric nanofiber composites was investigated. Nanofiber fillers can be used to produce polymeric nanocomposites by mixing the fillers to base polymers, eventually enhancing the mechanical property of the matrix polymers. To produce such composites, nanofibers were usually sandwiched by molten matrix polymers at high temperature before molding. The traditional so-called sandwich method, however, was found to produce rather biased and inhomogeneous composites due largely to the solid entanglement of the nanofibers. In this work, unwoven polymer nanofibers were synthesized through electrospinning by controlling the electrostatic repulsion of the nanofibers. We modified the electrospinning apparatus for the direct synthesis of homogenous composites: nanofibers were electrospun and directly ejected from the electrospinning syringe to the matrix polymer solution (not in a solid state), where a regular metal electrode plate was replaced by an optimized metal container containing the base polymer solution. It was found that this new fabrication method could realize homogeneous mixing of the nanofibers that were eventually uniformly dispersed in the polymer solution. Poly(vinyl alcohol) (PVA) was used for nanofibers and polydimethylsiloxane (PDMS) was used for polymer matrix. The field emission scanning electron microscopy (FE-SEM) revealed the homogeneous and well-dispersed PVA nanofibers in the resulting PDMS composites. The composites also presented higher mechanical properties as compared with the composites fabricated by the traditional sandwich method.
       
  • Nanodiamond decorated graphene oxide and the reinforcement to epoxy
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Weixin Hou, Ya Gao, John Wang, Daniel John Blackwood, Serena Teo Positively charged nanodiamond (ND) is used to decorate negatively charged graphene oxide (GO) to form a GO-ND hybrid nanomaterial by electrostatic force. Structural studies results showed that after the decoration, the aggregation of GO sheets is extensively hindered in both at the powder and dispersion states, with a clear reduction in the layer numbers in the latter. The mechanical properties of epoxy/GO, epoxy/ND and epoxy/GO-ND were investigated and compared. The results showed that the GO increased the ductility of epoxy, while the ND increased the rigidity. The best mechanical performance was found for the epoxy/GO-ND nanocomposites, at a GO:ND ratio of 1:5. The reinforcement mechanism of the nanophases was further illustrated by the fracture surface of SEM/optical images and TGA analysis. In addition, the anti-corrosion property of the thus developed epoxy nanocomposite coatings was revealed by electrochemical impedance spectroscopy (EIS), and the results demonstrated that the epoxy/GO-ND coatings exhibited better anti-corrosion property.
       
  • The effect of polymer particle size on three-dimensional percolation in
           core-shell networks of PMMA/MWCNTs nanocomposites: Properties and
           mathematical percolation model
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Seung Han Ryu, Hong-Baek Cho, Seil Kim, Young-Tae Kwon, Jimin Lee, Kee-Ryung Park, Yong-Ho Choa Segregated highly conductive percolation networks in nanocomposites consisting of a polymethyl methacrylate (PMMA) core and multi-walled carbon nanotube (MWCNT)-shell were investigated experimentally as a means of exploring the relationship between the micro-dimensional size of spherical polymer particles and the number of coated MWCNT layers by a new theoretical approach of filler monolayer model. The measured electrical conductivity of the core-shell structured complex utilizing 20 μm PMMA spheres showed that percolation was achieved at a very low filler content of 0.0099 wt% MWCNTs, whereas 0.149 wt% MWCNT was required to achieve percolation when 5 μm PMMA spheres were utilized. The size of PMMA cores was attributed to the percolation threshold, and conductivity was enhanced by increased layers of MWCNT coating. The percolation behaviors based on the theoretical model and experimental data were elucidated. Furthermore, an advanced theoretical model for prediction of number of MWCNT monolayers was provided.
       
  • Covalent functionalization of carbon nanotubes with hydroxyl-terminated
           polydimethylsiloxane to enhance filler dispersion, interfacial adhesion
           and performance of poly(methylphenylsiloxane) composites
    • Abstract: Publication date: 8 September 2018Source: Composites Science and Technology, Volume 165Author(s): Lu Bai, Zhongxiao Li, Shizhen Zhao, Junping Zheng Surface modification of carbon nanotubes (CNTs) were performed by grafting of hydroxyl-terminated polydimethylsiloxane (HPDMS) covalently. The results of dissolution experiments revealed that long-time stable dispersions of HPDMS-functionalized CNTs (CNTs-HPDMS) were achieved in a range of solvents including ethanol, ethyl acetate, dimethylbenzene and cyclohexane, even after being placed for 3 months. Subsequently, CNTs-HPDMS were incorporated into poly(methylphenylsiloxane) (PMPS) matrix to prepare composites. Scanning electron microscopy analysis showed that CNTs-HPDMS had homogeneous dispersion and strong interfacial adhesion in PMPS, which led to much better mechanical properties of composites compared to those filled with untreated CNTs. Furthermore, the incorporation of CNTs-HPDMS significantly enhanced the thermal stability of PMPS composites both under nitrogen and air. The improved barrier effect of CNTs-HPDMS resulted from the better filler dispersion was considered to play a crucial role, which on the one hand suppressed the depolymerization of PMPS under nitrogen and on the other hand inhibited the oxygen diffusion in matrix under air. Besides, the hydroxyl groups of HPDMS could react with PMPS to form additional crosslinking during heating, and thus delayed the degradation of PMPS to some extent.
       
  • Constructing continuous networks by branched alumina for enhanced thermal
           conductivity of polymer composites
    • Abstract: Publication date: Available online 12 July 2018Source: Composites Science and TechnologyAuthor(s): Yuge Ouyang, Guolin Hou, Liuyang Bai, Baoqiang Li, Fangli Yuan Efficient heat dissipation performance of thermal management materials has become one of the most critical challenges in the development of modern microelectronic devices. However, traditional polymer composites display limited enhancement of thermal conductivity even when highly loaded with thermally conductive fillers due to the lack of efficient heat conductive channels. In this study, branched alumina (b-Al2O3) is first used as the filler to improve thermal conductivity of phenolic resin (PR) and the preparation of the Al2O3 with branched structures is simple and high efficient. It is found that PR composites with b-Al2O3 present excellent thermal conductivity (up to 1.481 W m−1 K−1), which is equivalent to a dramatic enhancement of 7 times compared to neat matrix. The increased thermal conductivity should be attributed to that the branched structures of embedded b-Al2O3 particles tend to overlap each other and form continuous networks, which can act as efficient heat transfer pathways in PR matrix. Furthermore, PR composites with b-Al2O3 own improved thermal stability and decreased coefficient of thermal expansion (CTE) of 23 × 10−6 K−1 compared to neat PR (71 × 10−6 K−1). Meanwhile, composites with decreased dielectric loss tangent are achieved because of the incorporation of b-Al2O3, which is extraordinary and hopeful result for thermal management materials. This strategy provides an insight for the development of high-performance composites with potential to be used in electronic packages fields.
       
  • Improving thermal conductivity of polymer composites by reducing
           interfacial thermal resistance between boron nitride nanotubes
    • Abstract: Publication date: Available online 11 July 2018Source: Composites Science and TechnologyAuthor(s): Chenjie Fu, Qiang Li, Jibao Lu, Srikanth Mateti, Qiran Cai, Xiaoliang Zeng, Guoping Du, Rong Sun, Ying Chen, Jianbin Xu, Ching-Ping Wong Developing polymer composites with high thermal conductivity is a must to improve the thermal-management ability for modern electronic applications, in which power densities rapidly increase. Boron nitride nanotubes are one of the most promising fillers due to their high thermal conductivity and electrical insulator, but the overall thermal conductivity of the obtained polymer composites is limited by high interfacial thermal resistances. Here, we present an approach to reduce the interfacial thermal resistance between adjacent boron nitride nanotubes through low-melting effect of nanoscale silver particles. A sharp increase in thermal conductivity (20.9 Wm−1K−1) is observed in cellulose nanofibers (CNFs)/boron nitride nanotubes (BNNTs) composites, which is approximately 14.3 times larger than that of conventional polymers. The underlying mechanism is understood through Foygel model, and demonstrated that the interfacial thermal resistances play key role in the thermal conductivity. This strategy can become a quotable method for design and prepared of highly thermal conductivity materials in the future.
       
  • Dually self-reinforced Poly(ε-caprolactone) composites based on
           unidirectionally arranged fibers
    • Abstract: Publication date: Available online 9 July 2018Source: Composites Science and TechnologyAuthor(s): Lei Han, Bijia Wang, Yamin Dai, Yunchong Zhang, Hong Xu, Xiaofeng Sui, Linping Zhang, Yi Zhong, Zhiping Mao Dually self-reinforced Poly(ε-caprolactone) (PCL) composites were prepared to broaden its load-bearing applications as tissue engineering scaffolds. The composites were prepared from bi-component PCL yarns composed of self-nucleated PCL drawn fibers and PCL matrix by a combined process of yarns winding and hot pressing. Differential Scanning Calorimetry (DSC) results showed that incorporating of self-nucleating agents can improve the melting points of the fibers, creating a process temperature window for hot pressing. The orientation parameters of the fibers were accurately measured by Confocal Raman microscopy (CRM) and the results showed that the orientation parameter of the fibers could be up to 0.9 after drawn. Tensile tests showed that the self-nucleated drawn fibers had stronger mechanical properties than the control fibers with the same draw ratios. The hot pressing parameters (temperature and pressure) were also optimized during hot-pressing. The Young's modulus and break strength of the dually self-reinforced composites in longitudinal direction could be up to 118% and 400% higher than that of pristine PCL although their elongation at break decreased. Decline of mechanical properties of the composites in transverse direction was not observed, indicating good adhesion between the fibers and the matrix, which was confirmed by scanning electron microscope analysis.
       
  • Study on the interfacial properties of the dual-activity silicone
           resin/carbon fibers composites
    • Abstract: Publication date: Available online 7 July 2018Source: Composites Science and TechnologyAuthor(s): Tong Zhang, Jian Yang, Bo Jiang, Yudong Huang Dual-activity silicone resins (DASR) with double bonds and epoxy groups were prepared via the hydrolysis and condensation of γ-glycidoxypropyltrimethoxysilane (γ-GPS) and γ-methacryloxypropyltrimethoxysilane (γ-MPS). The hydrolysis and condensation degree was monitored during the preparation process of DASR. The epoxy groups of DASR were directly reacted with amine groups on the fiber surface attempting to improve the interfacial properties of carbon fiber (CF) composites. The CF/DASR composites represented a 36.91% and 20.85% enhancement in interfacial shear strength (IFSS), compared to those of MASR composites reinforced with untreated CFs and amine modified CF. In addition, the tensile strength of CF/DASR remained stable after the UV irradiation. Thus, these attractive results demonstrate that the designed dual-activity silicone resin/carbon fiber composites provide a promising approach for preparing high-performance carbon fibers composites.
       
  • Synergistic interfacial reinforcement of carbon fiber/polyamide 6
           composites using carbon-nanotube-modified silane coating on
           ZnO-nanorod-grown carbon fiber
    • Abstract: Publication date: Available online 7 July 2018Source: Composites Science and TechnologyAuthor(s): Byeong-Joo Kim, Sang-Hyup Cha, Kyungil Kong, Wooseok Ji, Hyung Wook Park, Young-Bin Park We report an experimental study on improvement of mechanical properties of a multiscale hybrid composite consisting of in-situ polymerized polyamide-6 and zinc oxide nanorod(ZnO NR)-grown woven carbon fiber (WCF) coated with carbon nanotube(CNT)-modified silane. The ZnO growth process and silane coating process were performed on the fiber surface, and then the composite was fabricated by ultra-fast (
       
  • Special issue on carbon nanotube composites
    • Abstract: Publication date: Available online 5 July 2018Source: Composites Science and TechnologyAuthor(s): Gregory M. Odegard, Richard Liang, Kristopher E. Wise
       
  • Towards quasi isotropic laminates with engineered fracture behaviour for
           industrial applications
    • Abstract: Publication date: Available online 4 July 2018Source: Composites Science and TechnologyAuthor(s): Gianmaria Bullegas, Jacob Benoliel, Pier Luigi Fenelli, Silvestre T. Pinho, Soraia Pimenta Carefully placed patterns of micro-cuts have been inserted in the microstructure of Cross-Ply (CP) and Quasi-Isotropic (QI) thin-ply CFRP laminates to engineer their translaminar fracture behaviour with the purpose of increasing their damage resistance under different loading conditions. A novel Finite Fracture Mechanics model has been developed to predict the translaminar crack propagation behaviour and to guide the microstructure design. This technique led to a 68% increase in the laminate notched strength, and a 460% increase in the laminate translaminar work of fracture during Compact Tension tests for CP laminates. It also allowed to achieve a 27% increase in the laminate notched strength, and a 189% increase in the translaminar work of fracture during Compact Tension tests for QI laminates. Furthermore, an increase of 43% in the total energy dissipated, and of 40% in maximum deflection at complete failure was achieved during quasi-static indentation tests on QI laminates. Given the significant improvements in the mechanical performance under different loading conditions, and the industrial relevance of QI laminates and the increasing industrial interest in thin-ply laminates, these results demonstrate that microstructure design can be used effectively to improve the damage tolerance of CFRP structures in industrially-relevant applications.
       
  • Multistable cantilever shells:Analytical prediction, numerical simulation
           and experimental validation
    • Abstract: Publication date: Available online 27 June 2018Source: Composites Science and TechnologyAuthor(s): Matteo Brunetti, Lukasz Kloda, Francesco Romeo, Jerzy Warminski The numerical and experimental validation of multistable behavior of cantilever shells is addressed. The design of the laminated composite shells is driven by a recently proposed semi-analytical shell model, whose predictions are verified and critically examined by means of finite element simulations and stability tests on two manufactured demonstrators. In addition, the influence of the main design parameters on the shells stability scenario is discussed. Despite its simplicity, the reduced model allows to depict a fairly faithful picture of the stability scenario; therefore, it proves to be a useful tool in the early design stages of morphing shell structures.
       
  • Surface modification of PBO fibers by direct fluorination and
           corresponding chemical reaction mechanism
    • Abstract: Publication date: Available online 21 June 2018Source: Composites Science and TechnologyAuthor(s): Longbo Luo, Dawei Hong, Lingjie Zhang, Zheng Cheng, Xiangyang Liu Due to their excellent mechanical properties and heat resistance, Poly(p-phenylene benzobisoxazole) (PBO) fibers are applied as one of most potential reinforcement in resin matrix composite. However, the poor adhesion with resin limits their application in advanced composite materials. In this study, PBO fibers were first modified by direct fluorination to improve the interface adhesion between fibers and resin. X-ray photoelectron spectroscopy (XPS), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to characterize the change of chemical structure and surface topography of fluorinated fibers. The results show that polar groups of C-F and -COOH are produced and surface roughness is enhanced, which increases the interface bonding strength of PBO fibers/epoxy by 48%. The fluorination reaction mechanism of PBO fibers is investigated on the basis of chemical structure change. It's suggested that oxazole ring reacts with fluorine gas preferentially over benzene ring, and addition reaction dominates when fluorine reacts with benzene ring.
       
  • Molecular engineering of interphases in polymer/carbon nanotube composites
           to reach the limits of mechanical performance
    • Abstract: Publication date: Available online 11 April 2018Source: Composites Science and TechnologyAuthor(s): Chandrani Pramanik, Dhriti Nepal, Michael Nathanson, Jacob R. Gissinger, Amanda Garley, Rajiv J. Berry, Amir Davijani, Satish Kumar, Hendrik Heinz After more than 50 years of development, carbon fiber composites exhibit an order of magnitude higher specific strength as compared to structural metals such as steel. However, the strength of the current state-of-the-art carbon fiber composites remains less than 10% of their theoretical value. Recent studies show that the polymer-carbon nanotube (CNT) interphase, i.e., the region of carbon components in contact with multiple organic components in its vicinity, plays a major role. Engineering the polymer-CNT interphase at the molecular level is a promising pathway to improve the mechanical properties of nano-composite materials on the way to fully realize the potential of mechanical properties of carbon nanotubes. Examples for using pristine and flattened CNTs, combinations of polymers, and surface grafting, as well as analogies to biological systems to prepare strong polymer/CNT composites are reviewed. In support of these developments, molecular simulations have revealed the binding mechanisms of polymers to CNTs and relationships to mechanical properties such as modulus, tensile strength, and interfacial shear strength in the interphase. Recent computational models enable increasingly quantitative predictions, and examples that explain the influence of the type of polymers, polymer crystallinity, carbon nanotubes, and nanotube surface modification on the interphase properties are discussed. The developments in molecular engineering of interphases by experiment and simulations advance rational composite design.
       
  • Microstructure evolution and self-assembling of CNT networks during
           mechanical stretching and mechanical properties of highly aligned CNT
           composites
    • Abstract: Publication date: Available online 4 April 2018Source: Composites Science and TechnologyAuthor(s): Claire Jolowsky, Rebekah Sweat, Jin Gyu Park, Ayou Hao, Richard Liang Using a floating catalyst synthesis process, carbon nanotubes (CNTs) can be produced to form randomly oriented networks. However, to realize their potential high structural performance, the nanotubes must be aligned and closely packed to eliminate molecular and microscale defects, which would be similar to carbon fiber microstructures. This paper describes a mechanical stretching technique using bismaleimide (BMI) resin to transform the randomly oriented networks into aligned networks. The BMI resin acts as a lubricant to decrease the friction between the nanotube bundles within the network during the stretching process. The unique flattening and self-assembling behaviors and the resultant graphitic crystal packing of CNTs were observed. The nanotubes' degree of alignment, measured by Raman and X-ray scattering drastically increased at approximately 40% stretch strain, plateaued at a 60% stretch strain, and achieved a maximum of 0.92 degree of alignment with noticeable graphitic crystal packing at 80% stretch strain. Both TEM and SEM observations indicate that as the stretch strain increased, the CNTs started to align along the stretched direction and self-assembled into large bundles. Additionally, high-resolution TEM analysis indicated that the CNTs exhibited flattening and polygonization self-assembling to form graphitic crystal packing. Tensile testing on the stretched CNT/BMI composite samples revealed an increase in Young's modulus, with a maximum of 252 GPa at 80% stretch strain, while an ultimate tensile strength of 1.58 GPa was reached at 70% stretch strain. The high degree of alignment and polygonization packing resulted in a better load transfer among CNTs, and thus a higher mechanical performance in the resultant CNT composites. Furthermore, this stretching process is scalable and has the potential to realize greater performance for applications using CNTs.
       
  • Machine learning electron density in sulfur crosslinked carbon nanotubes
    • Abstract: Publication date: Available online 29 March 2018Source: Composites Science and TechnologyAuthor(s): John M. Alred, Ksenia V. Bets, Yu Xie, Boris I. Yakobson Mechanical strengthening of composite materials that include carbon nanotubes (CNT) requires strong inter-bonding to achieve significant CNT-CNT or CNT-matrix load transfer. The same principle is applicable to the improvement of CNT bundles and calls for covalent crosslinks between individual tubes. In this work, sulfur crosslinks are studied using a combination of density functional theory (DFT) and classical molecular dynamics (MD). Atomic chains of at least two sulfur atoms or more are shown to be stable between both zigzag and armchair CNTs. All types of crosslinked CNTs exhibit significantly improved load transfer. Moreover, sulfur crosslinks show evidence of a cooperative self-healing mechanism allowing for links to rebond once broken leading to sustained load transfer under shear loading. Additionally, a general approach for utilizing machine learning for assessing the ground state electron density is developed and applied to these sulfur crosslinked CNTs.
       
  • Multiscale modeling of photomechanical behavior of photo-responsive
           nanocomposite with carbon nanotubes
    • Abstract: Publication date: Available online 27 March 2018Source: Composites Science and TechnologyAuthor(s): Junghwan Moon, Hyunseong Shin, Kyungmin Baek, Joonmyung Choi, Maenghyo Cho We propose a scale-bridging methodology to link the microscopic photoreaction of an azobenzene-containing liquid crystalline polymer (LCP) and the macroscopic interfacial and elastic properties of carbon nanotube (CNT)-reinforced photo-responsive nanocomposites. The photo-isomerization of the azobenzene moieties is described by implementing a photo-switching potential that represents the light-excited energy transition path. The relevant time evolution of the molecular shape and the concurrent changes in the interfacial morphology are observed using molecular dynamics (MD) simulations. Finally, the effective elastic properties of the photo-responsive polymer (PRP) nanocomposite with respect to the isomerization ratio are numerically derived using the micromechanics-based homogenization method. It is verified that the size of the CNT and the photo-deformation of the azobenzene molecules influence the intermolecular interactions and the nematic phase of the LCP at the interfacial region. The continuum-scale finite element (FE) model, which reflects the microscopic information, clearly predicts the reinforcing effect of the CNT filler on the elastic properties of the composite and their variation under photo-actuation. We expect our results to shed light on designing the photomechanical energy conversion efficiency of nano-sized soft actuators composed of CNT-reinforced composites.
       
  • Mesoscopic modeling of the uniaxial compression and recovery of vertically
           aligned carbon nanotube forests
    • Abstract: Publication date: Available online 14 March 2018Source: Composites Science and TechnologyAuthor(s): Bernard K. Wittmaack, Alexey N. Volkov, Leonid V. Zhigilei Vertically aligned carbon nanotube (VACNT) arrays or “forests” represent a promising class of mechanically strong and resilient lightweight materials, capable of supporting large reversible deformation and absorbing mechanical energy. The mechanical response of VACNT forests to uniaxial compression is defined by various factors, including the material microstructure, its density, height, rate of deformation, and the nature of interaction between carbon nanotubes (CNTs) and the compressing indenter. In this paper, we use a coarse-grained mesoscopic model to simulate the uniaxial compression of VACNT samples with different densities and microstructures (bundle size distribution and degree of nanotube alignment) to obtain a clear microscopic picture of the structural changes in networks of interconnected CNT bundles undergoing mechanical deformation. The key factors responsible for the coordinated buckling of CNTs, reversible and irreversible modes of deformation in VACNT arrays undergoing uniaxial compression, as well as hysteresis behavior in VACNT arrays subjected to five loading–unloading cycles are investigated in the simulations. The simulation results reveal the important role of the collective buckling of CNTs across bundle cross-sections as well as a complex deformation behavior of VACNT arrays defined by an interplay of different modes of bundle deformation. The loading rate and the CNT attachment to the indenter are found to have a strong effect on the deformation mechanisms and the overall mechanical behavior of VACNT forests. A good agreement with experimental data from in situ mechanical tests is observed for the general trends and magnitudes of loss coefficients predicted in the simulations. The forest morphology can strongly alter the mechanical behavior of VACNT arrays with nominally the same general characteristics, such as CNT radius, length, and material density, thus suggesting the opportunity for substantial enhancement of the mechanical properties through the microstructure modification.
       
  • Grafting carbon nanotubes onto carbon fibres doubles their effective
           strength and the toughness of the composite
    • Abstract: Publication date: Available online 14 March 2018Source: Composites Science and TechnologyAuthor(s): Luca Lavagna, Daniele Massella, Maria F. Pantano, Federico Bosia, Nicola M. Pugno, Matteo Pavese Bioinspiration can lead to exceptional mechanical properties in a number of biological materials as a result of their internal structure. In particular, the hierarchical arrangement of nano-to macro-components can bring to complex energy dissipation mechanisms and unprecedented resistance to crack growth. In this work, we propose to exploit this approach, combining in a multiscale composite structure carbon nanotubes with conventional carbon fibre reinforcements in a polyvinyl butyral matrix. We show that grafting the nanotubes onto the carbon microfibres improves their interface properties with the matrix considerably, effectively doubling their apparent strength. At the same time, the addition of nanotubes to microfibre reinforcements helps to improve the composite toughness, reaching more than twice the value for the conventional, non-hierarchically reinforced composite. Numerical simulations and fracture mechanics considerations are also provided to interpret the results.
       
  • Multiscale modeling of carbon fiber/carbon nanotube/epoxy hybrid
           composites: Comparison of epoxy matrices
    • Abstract: Publication date: Available online 9 March 2018Source: Composites Science and TechnologyAuthor(s): M.S. Radue, G.M. Odegard This study addresses the multiscale modeling of hybrid composites composed of carbon fibers (CFs), carbon nanotubes (CNTs), and three different epoxy systems (di-, tri-, and tetra-functional resin epoxies). Molecular dynamics (MD) simulations are performed to predict the molecular-level interfacial and mechanical behavior of CNT embedded in epoxy. Micromechanics calculations are implemented to translate the molecular phenomena observed to predict the mechanical properties of CNT/epoxy composites with randomly oriented CNTs and CF/CNT/epoxy systems with aligned CFs and randomly oriented CNTs. The model is validated with experimental Young's modulus values for CNT/epoxy available in the literature. The results demonstrate that the tri- and tetra-functional resin epoxies demonstrate comparably high moduli over the di-functional resin for CNT concentrations up to 5 wt%. For higher CNT loadings, the tri-functional resin epoxy is predicted to outperform the other resins with respect to stiffness due to its strong interaction with CNTs and high bulk stiffness.
       
  • Strong process-structure interaction in stoveable poly(urethane-urea)
           aligned carbon nanotube nanocomposites
    • Abstract: Publication date: Available online 3 March 2018Source: Composites Science and TechnologyAuthor(s): Jeffrey L. Gair, Robert H. Lambeth, Daniel P. Cole, Dale L. Lidston, Itai Y. Stein, Estelle Kalfon-Cohen, Alex J. Hsieh, Hugh A. Bruck, Mark L. Bundy, Brian L. Wardle The exceptional static and dynamic physical properties of poly(urethane-urea) (PUU) elastomers make them prime candidates for impulsive loading structural applications, such as blast protection coatings. Since the theoretical physical properties of carbon nanotubes (CNTs) are among the best for any currently known material, a number of previous studies explored the use of CNTs as nanoscale fillers to enhance the properties of PUU nanocomposites. However, due to the challenges inherent in dispersing CNTs in a PUU matrix and the resulting random orientation of the CNTs, these previous works observed marginal improvements in physical properties, and were unable to establish clear structure-property relations. Here, we report the synthesis of aligned-CNT (A-CNT) reinforced PUU polymer nanocomposites (A-PNCs) by infusing A-CNT forests with a stoveable PUU, and establish process-structure-property relations that quantify the contribution of CNT confinement on the PUU mechanical response. This stoveable process was achieved using blocked isocyanate which prevented polymerization until the blocks were removed with heat. PUUs of two distinct compositions were explored: one with 40 wt% hard-segment content (PUU211) and the other with 66 wt% hard-segment content (PUU541). Thermogravimetric analysis indicates that A-CNTs enhance the thermal stability of the hard-segment phase in PUU A-PNCs at 340 °C by up to 45% over the baseline PUUs. Atomic force microscopy reveals that the elongated nanophase hard-segment formations along the CNT axis observed only in the nanocomposites were of similar characteristic size to the average inter-A-CNT spacing (∼70 nm), indicating a strong influence of A-CNTs on the size and orientation of hard-segment nanophases, as corroborated via small angle X-ray scattering. Nanoindentation testing reveals that PUU A-PNCs possess significant elastic anisotropy, and exhibit enhanced longitudinal effective indentation moduli of ∼460 MPa (>3 × that of the PUU211 baseline) and ∼1350 MPa (∼1.5 × that of the PUU541 baseline) for PUU211 and PUU541 nanocomposites, respectively. This difference in magnitude of CNT reinforcement efficacy indicates that CNT confinement leads to significant hard-segment re-organization in the PUU211 A-PNCs, whereas the interconnected network of hard-segments in the PUU541 is affected by CNT templating to a lesser extent. Dynamic nanoindentation testing results are consistent with these interpretations, where longitudinally-loaded PUU211 A-PNCs are found to exhibit a>3 × enhancement in storage modulus at 1 Hz of ∼730 MPa, whereas the longitudinally-loaded PUU541 A-PNCs exhibit a slightly enhanced storage modulus enhancement at 1 Hz of 2190 MPa (∼1.5 × that of the PUU541 baseline). Reinforcement of PUUs with A-CNTs is a promising way to tune the physical properties of the PNCs; higher A-CNT packing densities, where the inter-CNT spacing could approach the nanophase characteristic diameter, could further enhance the PUU performance in ballistic protection applications.
       
 
 
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