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Composite Structures
Journal Prestige (SJR): 1.905
Citation Impact (citeScore): 5
Number of Followers: 316  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0263-8223 - ISSN (Online) 0263-8223
Published by Elsevier Homepage  [3206 journals]
  • Corrigendum to “Numerical buckling analysis of graded CNT-reinforced
           composite sandwich shell structure under thermal loading” [Compos.
           Struct. 216 (2019) 406–414]
    • Abstract: Publication date: 15 May 2020Source: Composite Structures, Volume 240Author(s): Kulmani Mehar, Subrata Kumar Panda, Yuvarajan Devarajan, Gautam Choubey
       
  • Non-destructive testing of carbon-fiber-reinforced plastics with a
           PCB-based T-R probe
    • Abstract: Publication date: 15 May 2020Source: Composite Structures, Volume 240Author(s): Dehui Wu, Fang Cheng, Fan Yang, Wei He
       
  • Evaluation of infrared thermography methods for analysing the damage
           behaviour of adhesively bonded repair solutions
    • Abstract: Publication date: 15 May 2020Source: Composite Structures, Volume 240Author(s): U. Martens, K.-U. Schröder
       
  • Review of recent developments and induced damage assessment in the
           modelling of the machining of long fibre reinforced polymer composites
    • Abstract: Publication date: 15 May 2020Source: Composite Structures, Volume 240Author(s): F. Cepero-Mejías, J.L. Curiel-Sosa, A. Blázquez, T.T. Yu, K. Kerrigan, V.A. Phadnis
       
  • Strain measurement and stress analysis in the vicinity of a fiber Bragg
           grating sensor embedded in a composite material
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): A.Y. Fedorov, N.A. Kosheleva, V.P. Matveenko, G.S. Serovaev
       
  • Three dimensional mechanical behaviors of in-plane functionally graded
           plates
    • Abstract: Publication date: Available online 26 February 2020Source: Composite StructuresAuthor(s): Pengchong Zhang, Chengzhi Qi, Hongyuan Fang, Wei He
       
  • Local and global response of sandwich beams made of GFRP facings and PET
           foam core in three point bending test
    • Abstract: Publication date: Available online 25 February 2020Source: Composite StructuresAuthor(s): Łukasz Pyrzowski, Bartosz Sobczyk
       
  • Mechanical behavior of thick composite tubes under four-point bending
    • Abstract: Publication date: Available online 25 February 2020Source: Composite StructuresAuthor(s): Saeid Khadem Moshir, Suong V. Hoa, Farjad Shadmehri, Daniel Rosca, Ashraf Ahmed
       
  • A delamination failure criterion considering the effects of
           through-thickness compression on the interlaminar shear failure of
           composite laminates
    • Abstract: Publication date: Available online 25 February 2020Source: Composite StructuresAuthor(s): X.M. Chen, X.S. Sun, P.H. Chen, Y.N. Chai
       
  • Shear strengthening of RC beams with FRP grid-reinforced ECC matrix
    • Abstract: Publication date: Available online 25 February 2020Source: Composite StructuresAuthor(s): Xu Yang, Wan-Yang Gao, Jian-Guo Dai, Zhou-Dao Lu
       
  • A hybrid joining insert for sandwich panels with pyramidal lattice truss
           cores
    • Abstract: Publication date: Available online 24 February 2020Source: Composite StructuresAuthor(s): Ge Qi, Yun-Long Chen, Philip Richert, Li Ma, Kai-Uwe Schröder
       
  • FEM analysis of the elastic behavior of composites and nanocomposites with
           arbitrarily oriented reinforcements
    • Abstract: Publication date: Available online 24 February 2020Source: Composite StructuresAuthor(s): A. Greco
       
  • Probabilistic homogenization of hyper-elastic particulate composites with
           random interface
    • Abstract: Publication date: Available online 24 February 2020Source: Composite StructuresAuthor(s): D. Sokołowski, M. Kamiński
       
  • Data-driven ultimate conditions prediction and stress-strain model for
           FRP-confined concrete
    • Abstract: Publication date: Available online 24 February 2020Source: Composite StructuresAuthor(s): Kejie Jiang, Qiang Han, Yulei Bai, Xiuli Du
       
  • Flexural behavior of timber beams strengthened with pultruded glass fiber
           reinforced polymer profiles
    • Abstract: Publication date: Available online 24 February 2020Source: Composite StructuresAuthor(s): Mohammad Shekarchi, Asghar Vatani Oskouei, Gary M. Raftery
       
  • Experimental and theoretical investigation on shear behaviour of
           small-scale timber beams strengthened with Fiber-Reinforced Polymer
           composites
    • Abstract: Publication date: 15 May 2020Source: Composite Structures, Volume 240Author(s): Zhibin Ling, Weiqing Liu, Jingsong ShaoAbstractThis paper presents an experimental program conducted on small-scale timber beams strengthened with Fiber-Reinforced Polymer (FRP) shear reinforcement at shear spans to evaluate the strengthening efficiency of FRP shear reinforcement. The experimental variables involve FPR type, different layers, and attaching configurations. Tests results indicate that the Carbon-FRP (CFRP) shear reinforcement generally shows higher strengthening efficiency than Glass-FRP (GFRP) shear reinforcement. In particular, the shear capacity of the timber beams strengthened with longitudinally attached unidirectional CFRP can be improved by 32.9% for one-layer and 68.6% for two layers, respectively. Transversally attached unidirectional FRP reinforcement at the shear spans of timber beams contributes insignificant increase of shear capacity. The bidirectionally weaving GFRP provides the strengthened timber beams with a limited increase of shear capacity compared to the bidirectionally attaching unidirectional GFRP. Finally, an analytical solution is driven for predicting the shear capacity of the FRP strengthened timber beams. It is shown that the calculated values are in good agreement with the experimental results indicating the theoretical derivations can be used to predict the shear capacity of the timber beams strengthened with FRP shear reinforcement effectively.
       
  • Experimental evaluation of the seismic performance of retrofitted masonry
           walls
    • Abstract: Publication date: 15 May 2020Source: Composite Structures, Volume 240Author(s): Bahador Bagheri, Jung-Han Lee, Han-Gil Kim, Sang-Hoon OhAbstractUnreinforced masonry (URM) buildings are known as seismically vulnerable systems and require retrofitting. In this study, the in-plane seismic behavior of URM walls with and without an opening before and after retrofitting using different developed methods was investigated. Retrofitting methods involving a combination of metal laths, steel plates, connecting steel plates (CSPs) and polymer coating material were considered. Twelve masonry walls, including three non-retrofitted (as reference specimens) and nine retrofitted walls, were tested by subjecting the specimens to cyclic loads. The experimental study was carried out on full-scale specimens, which were tested simultaneously under the conditions of gravity and in-plane cyclic loads. The performance evaluation of each specimen was performed in terms of the lateral strength and deformation, hysteretic response, and energy dissipation. The double side retrofitting/upgrading approach substantially enhanced the lateral strength, displacement, and energy dissipation capacity of the test specimens. Furthermore, it was found that the specimens involving the combination of the polymer coating with the steel plates and CSPs could be an alternative method in terms of high energy dissipation capacity owing to the ultimate strength and displacement enhancement.
       
  • Novel finite element for near real-time design decisions in multi-fastener
           composite bolted joints under various loading rates
    • Abstract: Publication date: 15 May 2020Source: Composite Structures, Volume 240Author(s): P.A. Sharos, C.T. McCarthyAbstractIn this paper, a highly efficient and novel user defined finite-element capable of modelling composite bolted joints at various loading rates was developed and validated against experimental data. The element was shown to be capable of producing high-fidelity simulations of joint behaviour up to and including catastrophic failure, with CPU times being orders of magnitude less than that required for full 3-D simulations, but with no loss in fidelity. Hence, this element makes possible for near real-time design decisions to be made for preliminary design and design for manufacture in multi-fastener composite bolted joints subjected to various loading rates. Using this element, this study finds that the load distribution in dynamically loaded multi-fastener joints is temporal and dependent on loading rate. The relative proportion of load carried by fasteners is found to vary due to the propagation of elastic stress waves in the joint. The magnitude of load imbalance between fasteners, an important design consideration to prevent premature joint failure, was observed to increase by up to 85% due to these dynamic loading effects.
       
  • The multi-physic cell-based smoothed finite element method for dynamic
           characterization of magneto-electro-elastic structures under thermal
           conditions
    • Abstract: Publication date: 15 May 2020Source: Composite Structures, Volume 240Author(s): Liming Zhou, Ming Li, Yan Cai, Hongwei Zhao, Erfei ZhaoAbstractThis study was aimed to computationally investigate the thermal load combining the mechanical load effect on dynamic characteristics of intelligent composite structures. For this purpose, the cell-based smoothed finite element method (CS-FEM) was applied to the multi-physic coupling problem, and the coupled multi-physic CS-FEM (CPCS-FEM) integrating the magneto-electro-thermo-elastic (METE) coupling effect was put forward. Compared with standard FEM, this method with higher accuracy, lower mesh restriction and much less calculation for stochastic issues was more capable in handling severe mesh distortion and deformation. The convergence, accuracy and efficiency of CPCS-FEM were validated with three numerical cases. With CPCS-FEM integrating the modified Newmark scheme, the thermal effects on generalized displacement (x- and z-direction displacement components, electric and magnetic potentials) of magneto-electro-elastic sensors were explored. This study presents an effective approach to model the complicated multi-physic problem, and the simulation findings contribute to the design of intelligent structures in service under thermal conditions.
       
  • Non-linear bending compliance of thin ply composite beams by local
           compression flange buckling
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): F. Schadt, M. Rueppel, C. Brauner, Y. Courvoisier, K. Masania, C. DransfeldAbstractPassive spanwise bending shape-adaption has the potential to increase the efficiency and manoeuvrability of vehicles with wing-like structures. By utilisation of compression flange buckling, the in-plane stiffness can be tuned to design beams with contrasting pre-buckling and post-buckling bending stiffness. The investigated concept is experimentally validated using a thin-ply laminated composite four-point bending beam, which is designed to experience compression flange buckling in the span with constant moment. The bending stiffness was reduced by more than 41% after the onset of buckling which shows the effectiveness of compression flange buckling for non-linear bending compliance.
       
  • The flexural performance of structural concrete beams reinforced with
           carbon textile fabrics
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Lior Nahum, Alva Peled, Erez GalAbstractThe flexural behavior of carbon textile-reinforced concrete (TRC) beams was studied and compared with that of conventional steel-reinforced concrete (SRC) beams. Four types of TRC beams were examined of different fabric layers (2 and 4) and different shear reinforcements (steel cage rebars and U-shaped fabrics). The mode of failure and the flexural behavior were significantly influenced by the shear reinforcement configuration, such that greater flexural load-bearing capacity with no delamination was observed in the U-shaped fabric TRC beams, whereas the steel cage rebar TRC beams exhibited severe delamination with lower flexural load-bearing capacity. This difference was due to the mechanical anchoring of the U-shaped fabric to the matrix, which was not the case for the steel cage rebar TRC beams. A mathematical model for calculating the flexural tolerability of TRC beams at failure was developed, showing an excellent correlation with the experimental results.
       
  • Comparison and experimental verification of simplified one-dimensional
           linear elastic models of multilayer sandwich beams
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): Paweł SzeptyńskiAbstractThree analytical one-dimensional linear elastic models of composite laminated beams are considered – composite Bernoulli-Euler beam (BE), composite Timoshenko beam (T) and multilayer sandwich beam model (MS). They are compared with results obtained via finite element method for a two-dimensional model in plane stress state. Overall system stiffness is verified with experimental data obtained for two statical configurations – three-point bending and four-point bending. The first configuration concerned 8 types of three-panel cross-laminated timber (CLT) beams accounting for various materials and thickness of timber panels as well as various materials and thickness of adhesive layer, while the second one concerned 5 types of two-panel aluminium laminated beams accounting for different thickness of adhesive layer. Simplified multilayer sandwich model is found to be in good accordance with FEA results and with experimental data, while simple BE and T models are shown to provide erroneous estimates.
       
  • Analysis of bond behavior of injected anchors in masonry elements by means
           of Finite Element Modeling
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): Francesca Ceroni, Hossein Darban, Raimondo LucianoLucianoAbstractInjected anchors made of steel bars embedded in masonry elements by means of cement-based grout represented in the past a wide solution for avoiding out-of-plane mechanisms. Corrosion phenomena in steel bars reduced the effectiveness of such type of intervention over time. Innovative materials, as the Fiber Reinforced Plastic ones, can represent a suitable alternative to increase durability and performance of injected anchors. Since the effectiveness of injected anchors is strictly related to bond behaviour along both the bar-grout and the grout-masonry interface, a detailed analysis by means of a Finite Element model was developed for different types of bars embedded in masonry elements. The numerical model was firstly calibrated on some experimental results of pull-out tests available in literature and, then, is used for investigating the effects of several parameters on both local and global behaviour. Load-displacement curves and local distributions of shear stresses are examined in detail. The numerical analyses evidenced that the maximum tensile force in the anchor mainly depends on the shear strength of the bar-grout and the grout-masonry interface and on the embedded length, but for very long embedded length, it can be limited by the tensile failure in the anchor or in the masonry.
       
  • Piezoresistivity of carbon nanotubes (CNT) reinforced cementitious
           composites under integrated cyclic compression and impact load
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): Wenkui Dong, Wengui Li, Luming Shen, Zhihui Sun, Daichao ShengAbstractThe cyclic compression and four series of fixed magnitude impact loads with an increment of 50 times were conducted alternatively on the carbon nanotubes (CNTs) reinforced cementitious composites, to evaluate the piezoresistive sensitivity and repeatability of composites after exposed to different drop impact energies. The results show that the impacts procedure suddenly increased in electrical resistivity due to the emerged micro-cracks and pores, and higher impact energy led to faster resistivity increase. On the other hand, when the impact is repeatedly applied, a high impact resistance of the cementitious composites could be observed, which was attributed to the dense microstructures. Furthermore, instead of instable and uneven output of electrical resistivity during cyclical compression, more stable and uniform fractional changes of resistivity were achieved after exposed to impact load. However, severe nonlinearity with swift resistivity reduction of composites under low loads was observed at the beginning and the end of cyclic compression after subjected to many impacts with impact energy of 18.72×10-4 J/cm3. The related outcomes of conductive cementitious composites subjected to cyclic compression and impact will provide a method for stable electrical signal output and promote the applications of cement-based sensors for structural health monitoring under various loading conditions.
       
  • Numerical prediction of the ultimate condition of circular concrete
           columns confined with a fiber reinforced polymer jacket
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): Chiara Ceccato, J.G. Teng, Gianluca CusatisAbstractCircular concrete columns confined with a fiber reinforced polymer (FRP) jacket fail because of the rupture of the FRP jacket due to hoop tension at an average hoop strain considerably lower than the FRP tensile strain at failure obtained from tensile tests of flat coupons. This well-established phenomenon, referred to as premature rupture, is governed by the interaction between a heterogeneous material (i.e., concrete) and a brittle material (i.e., FRP) and has been difficult to explain. The present study adopts a meso-scale model, the so-called Lattice Discrete Particle Model (LDPM), for the simulation of concrete, in conjunction with the Spectral Stiffness Microplane Model (SSMM) for simulating the fracturing behavior of the FRP jacket. The numerical predictions, experimentally validated, demonstrate clearly that due to the heterogeneity of concrete, the circumferential strain is highly non-uniform around the circumference of the column right from the beginning of the loading process rather than uniform as conventionally assumed or expected. This strain non-uniformity is the main reason for the premature rupture of the FRP jacket. In addition, stress concentrations at the finishing end of the FRP jacket are also shown to have a significant effect on the premature rupture of the FRP jacket.
       
  • Thermo-stamping co-curing process for CFRP/Steel hybrid sheets and its
           interface strength improvement
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): Cong Guo, Ji He, Youhuang Su, Shuhui LiAbstractThe co-curing interface between CFRP and metal has a significant influence on the comprehensive mechanical properties of the composite structure. In this paper, a series of single lap specimens were fabricated by a thermo-stamping process with fast curing prepreg and dual phase steel DP980. The thermo-stamping co-curing experiments were conducted under different forming conditions based on a grit-blasted metal surface to study the effect of process parameters on the interface strength. In addition, two types of interface strength improvement methods were tested: cutting mechanical grooves on the metal surface and smearing different carbon nanotube or graphene coatings on the metal and prepreg surfaces. The interface strength improvement mechanism was further explained by microscopic characterization. Finally, a finite element model combining cohesive element damage and three-dimensional Hashin failure was established to predict the failure mode of the co-curing joint. The results show that the initial pressure, heating curve and laying up methods have a certain degree of influence on the interface strength, and the best interface enhancement effect could be obtained by coating a carbon nanotube/epoxy resin and a curing agent on the metal and prepreg surfaces, respectively.
       
  • Composites Airframe Panel Design for Post-buckling- An Experimental
           Investigation
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): S. Nadeem Masood, S.R. Viswamurthy, Kotresh M GaddikeriAbstractThree series of airframe composite panels with T-stiffener, I-stiffener and J-stiffener are designed and optimized to have the same local skin buckling load and weight. All the panels are designed to undergo local skin buckling between Design Limit Load (DLL) and Design Ultimate Load (DUL), approximately at 120% of DLL to utilize the reserve strength in structures. Additionally, identical panels are designed and fabricated from each series to study the effect of various extrinsic parameters such as disbond, delamination, impact damage and repeated loading to identify the best performing series for post-buckling design. All the panels are tested under compression to demonstrate no onset of damage before DUL. The influence of defects such as disbond, delamination and impact damage on the post-buckling behavior is also demonstrated. One pristine panel of each series is repeatedly loaded 1000 times beyond buckling to determine the onset of damage if any. The panels with I-stiffener and J-stiffener found to be the potential design choices for post-buckling design philosophy due to the high margin between skin buckling and collapse load even in the presence of damage. The results from this study would help in moving closer to the post-buckled composite design philosophy for airframe structure.
       
  • Auxeticity of Monoclinic Tetrachiral Honeycombs
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): X. Lu, V.B.C. Tan, T.E. TayAbstractChiral honeycombs of different types have been found to display auxetic behavior (a negative Poisson’s ratio). This paper investigates the constitutive relations and the auxetic properties of tetrachiral honeycombs. It is found that coupling between shearing and stretching exists in tetrachiral honeycombs and this causes some ambiguity when calculating the Poisson’s ratio. An “effective Poisson’s ratio” is proposed, as opposed to the traditional definition of Poisson’s ratio. This proposed parameter correctly describes the auxeticity of tetrachiral and other honeycombs. An analytical expression for this “effective Poisson’s ratio” is derived, which describes the relationship between the geometric dimensions and auxeticity of the tetrachiral honeycombs.
       
  • Compression and shear buckling performance of finite length plates with
           bending-twisting coupling
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): H.S. Jason Lee, Christopher B. YorkAbstractThis article investigates the compression and shear buckling performance of finite length Bending-Twisting coupled laminated plates with simply supported edges. New contour maps are developed, representing non-dimensional buckling factors, which are superimposed on the lamination parameter design spaces for laminates with standard ply orientations. Changes in buckling mode for finite length plates complicate the contour maps, which are shown to be continuous only within discrete regions of the lamination parameter design space and are strongly influenced by plate aspect ratio. The contour maps also serve to demonstrate the degrading effect of Bending-Twisting coupling on compression buckling performance as well as providing new insights into shear buckling performance improvements, including optima that are non-intuitive. The adoption of two recently developed laminate databases, to which common design rules are now applied, including ply percentages and ply contiguity constraints, ensure that the conclusions drawn are based on practical rather than hypothetical designs.
       
  • Propagation of transient elastic waves in multilayered composite structure
           subjected to dynamic anti-plane loading with thermal effects
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): Xiang Zhou, Guoshuang ShuiAbstractThis paper investigates the transient responses of multilayered composite structure under the action of dynamical anti-plane concentrated forces with thermal effects. To obtain the transient solutions, the boundary value problem is presented by using Fourier-Laplace transform; the Cagniard’s method is adopted in inversing the solution to be expressed in time domain; and the theory of limit is employed to derive the corresponding static solution. Numerical results show that the closer the receiver's vertical position is to the surface, the slower the transient response approaches the static value in the near field of the transient waves. A sharp fluctuation appears after a short time in the intermediate and far field; and the transient response finally approaches the static value in the end. Variation of the temperature does not affect the waveform and non-dimensional arriving time of the transient shear waves. However, the higher the variation of environmental temperature, the smaller the amplitude of the transient responses.
       
  • Flexural Behavior of RC Beams Strengthened with BFRP Bars-Reinforced ECC
           Matrix
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): Wei Hou, Zhi-Qiang Li, Wan-Yang Gao, Pan-deng Zheng, Zi-Xiong GuoAbstractThis paper has proposed a new strengthening system made of basalt fiber-reinforced polymer (BFRP) bars-reinforced engineered cementitious composite (ECC) matrix (hereinafter referred to as “BFREM” for brevity) for repairing of RC beams. Six specimens including a control beam and five beams strengthened with the BFREM layers were prepared and tested. The test variables included the reinforcement ratio of BFRP bars (0.94% or 1.41%) and the installation method (prefabricated or cast-in-place) used for the BFREM layer as well as the presence of the end anchorage system (with steel bolts). The test results showed that two failure modes of the strengthened beams were the tensile rupture of BFRP bars and the concrete cover separation with the strengthening layer attached. The cast-in-place method incorporating the end anchorage system was capable of inhibiting the debonding failure of the BFREM layer, thereby making better utilization of the strengthening materials. Moreover, the proposed strengthening system was efficient in enhancing the ultimate loads of the strengthened beams, which were 34%-48% higher than that of the control beam. A theoretical analysis was then conducted to predict the flexural strengths of the tested beams, and its reliability was verified by comparing the test results and the theoretical predictions.
       
  • Thermomechanical Effects During Impact Testing of WC/Co Composite Material
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): Eligiusz Postek, Tomasz SadowskiAbstractWC/Co metal-matrix ceramic composites (MMCs) are used for manufacturing cutting and drilling tools, surgical tools, mill inserts, jet engines, and other high-responsibility structures. The combination of a phase of hard wolfram carbide (WC) grains with a metallic ductile interface of cobalt (Co) yields a complex microstructure with significantly different mechanical properties of the phases.The aim of this study is to investigate the thermomechanical behavior of the MMC polycrystalline material with ductile binders under impact conditions. An adiabatic and coupled thermomechanical analysis of the WC/Co composite under impact loading is performed using FEM. The heat conduction is considered in the analysis in order to capture heat transfer in the polycrystalline structure, i.e. between the grains and the grain boundaries (GBs). The Johnson-Cook yield function is used in the constitutive model of the ductile Co interface, while the WC phase is linear elastic. The motivation comes from the observation that the heat conductivity effect is often omitted, even in recent papers [75]. Significant differences between temperatures and plastic strains in the adiabatic and coupled solutions are observed, which leads to the main conclusion that the adiabatic solution should not be used for assessing the impact response of the composite material.
       
  • Energy harvesting and vibration reduction by sandwiching piezoelectric
           
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): W. Chen, Z.Y. Xiang, J.L. Mo, Z.Y. Fan, H.H. Qian, J.Y. WangAbstractIn this study a method for simultaneous energy harvesting via friction-induced vibration and vibration reduction is proposed and implemented by sandwiching a piezoelectric patch between two layers of elastic damping components. A test bench that provides good repeatability and generates friction-induced vibration is developed. The experimental results show that the elastic damping components significantly suppress friction-induced vibration. The fluctuating voltage signals indicated the feasibility of the proposed approach for energy harvesting via friction-induced vibration. Several parallel grooves are fabricated on the surface of the elastic damping components to investigate the influence of damping components with different structures on the vibration reduction and energy recovery performance. The results show that the grooved damping components provide a greater reduction in the vibration level of the system than the smooth damping components, but the voltage signals are also weaker. Numerical analysis are performed in ABAQUS 6.14. The unstable mode shape shows that the elastic damping components and piezoelectric patch produce relatively large deformation, demonstrating the feasibility of the proposed energy harvesting approach. The results obtained from the implicit dynamic analysis are identical to the experimental results. Therefore, the implicit dynamic analysis is used to provide some reasonable explanations for the experimental phenomena.
       
  • Experimental static and dynamic response of RC beams damaged and
           strengthened with NSM GFRP rod
    • Abstract: Publication date: Available online 22 February 2020Source: Composite StructuresAuthor(s): R. Capozucca, E. Magagnini, M.V. VecchiettiAbstractInserting FRP rods into grooves using the NSM technique has been demonstrated to be a suitable method for repairing reinforced concrete (RC) beams. There is limited experience with the use of GFRP in the strengthening of RC elements due to low Young’s modulus of glass fibers. The aim of the paper is to analyse the static and dynamic behaviour of RC beams damaged and strengthened by glass fiber reinforced polymer (GFRP) rods utilizing the near surface method (NSM). Undamaged and damaged three RC beams have been experimentally tested under bending loading with and without strengthening by GFRP rods. For a beam, damage has been represented firstly by notches on concrete cover. The beam has been successively strengthened by epoxy resin and NSM GFRP rod and then subjected to bending tests. Vibration tests have been adopted as nondestructive method of control during the experiments to assess the response of RC beams at different damage steps of concrete or due to decrease of bond of GFRP rod. Vibration tests foresaw two boundary conditions, respectively, free-free and hinged ends. Experimental static and vibration results are below shown; discussion and comments on the strengthening bond of NSM GFRP rod have been developed.
       
  • Analysis of process-induced deformations and residual stresses in curved
           composite parts considering transverse shear stress and thickness
           stretching
    • Abstract: Publication date: Available online 21 February 2020Source: Composite StructuresAuthor(s): E. Zappino, N. Zobeiry, M. Petrolo, R. Vaziri, E. Carrera, A. PoursartipAbstractA computationally efficient modeling approach for the accurate evaluation of process-induced deformations and residual stresses in composite parts is presented. A family of refined one-dimensional kinematic models, developed in the framework of the Carrera Unified Formulation, has been used to predict the accurate through-thickness deformation of layered structures during the manufacturing process. The composite material curing phase has been simulated exploiting the capabilities of the software RAVEN. A cure hardening instantaneously linear elastic model has been used. A benchmar based on an L-shaped component has been selected to compare the results obtained using different computational approaches. A closed-form solution, the present refined one-dimensional models and classical solid models, have been considered. The effects of the modeling approach on the prediction of the spring-in angle and on the residual stress field have been evaluated and discussed. The results demonstrate that the use of refined kinematic models can lead to a high-fidelity description of the problem and a quasi-3D accuracy while reducing the computational cost with respect to classical FEM approaches. The through-thickness effects have been predicted with a high level of accuracy and the use of layer-wise models has led to an accurate description of the stress field, including the transverse shear stresses.
       
  • Experimental and numerical investigation of the mixed mode delamination of
           monolithic laminates exhibiting severe fiber bridging
    • Abstract: Publication date: Available online 21 February 2020Source: Composite StructuresAuthor(s): Daniel Höwer, Kumar C. Jois, Bertram Stier, Brett A. Bednarcyk, Evan J. Pineda, Stefanie Reese, Jaan-Willem SimonAbstractA recently developed cohesive zone traction-separation formulation for mode I facesheet to core disbonding, which includes the effects of fiber bridging in a novel way, is extended to account for mode II and mixed mode delamination. The pure mode I and mode II behavior of the model is calibrated based on traction separation curves which are extracted from Double Cantilever Beam (DCB) and End Notched Flexure (ENF) experiments utilizing the J integral. An existing mixed mode framework, which requires no further parameters, is used to predict the load displacement curves of Mixed ode Bending (MMB) tests. Very close agreement between numerical predictions and experimental results is observed for all demonstrated mixed mode ratios.
       
  • A merit parameter to determine the stacking order of heterogeneous
           diphasic soft armor systems
    • Abstract: Publication date: Available online 20 February 2020Source: Composite StructuresAuthor(s): Zherui Guo, Weinong ChenAbstractThe effects of stacking order on the ballistic performance may be detrimental if the order is improperly chosen. When the frontal material is constrained transversely by the rear material, it results in sub-optimal performance compared to the alternate configuration where both layers can freely deform. In this study, we examine the possibility of using the Cunniff velocity as a merit parameter in determining the optimal stacking order of heterogeneous diphasic soft armor systems by reviewing the results from previous studies. Experiments were performed on heterogeneous systems comprising ballistic-grade polyurea, Twaron® fabric, and Dyneema® UD laminate plies. Results show that the two constituent materials should be ordered such that the material with a higher Cunniff velocity is placed at the rear to minimize interference. The use of the merit parameter is then analyzed via existing models to examine the effects of changing various parameters. We further discuss the idea of “ballistically-thin” materials in relation to the concept of membrane strain energy dissipation efficiency of a soft armor target.
       
  • Characterization of Dynamic Compressive Strength and Impact Release Energy
           of Al/PTFE Energetic Materials Reinforced by Aluminum Honeycomb Skeleton
    • Abstract: Publication date: Available online 20 February 2020Source: Composite StructuresAuthor(s): Enling Tang, Zhenhui He, Chuang Chen, Yafei HanAbstractThe insufficient dynamic compressive strength of the Al/PTFE energetic material with traditional ingredients has seriously restricted its application in the field of national defence. However, the improvement of strength must be at the expense of activity. In view of the contradiction, this paper pioneered the use of aluminum honeycomb skeleton reinforcement method to achieve both strength and activity. On the basis of traditional ingredients Al/PTFE (mass percentage of 26.5%/73.5%), three types of energetic materials were prepared by cold pressing sintering process by adding different aluminum honeycomb skeletons with arm lengths of 1 mm, 1.5 mm and 2 mm, respectively. The dynamic compressive strengths of the specimen are obtained by using self-built Split Hopkinson Pressure Bar (SHPB) loading system and high-speed camera acquisition system. Meanwhile, the impact reaction release energies are also evaluated experimentally by using the one-stage light gas gun loading system combined with the transient optical fiber pyrometer measurement system, the overpressure measurement system and the infrared thermal imager measurement system. In terms of dynamic compressive strength and impact reaction release energy, the performances of three types of Aluminum honeycomb reinforced energetic material are compared with those of traditional ingredients energetic material. The experimental results show that compared with the strength (25.17 MPa) of traditional ingredients Al/PTFE energetic material, the strengths of three kinds of energetic materials reinforced by aluminum honeycomb framework with arm lengths of 1 mm, 1.5 mm and 2 mm are 1.5, 3.1 and 2.2 times that of the traditional ingredients Al/PTFE, respectively; Especially, at the impact velocity of 510 m/s, the release energy of three kinds of Al/PTFE energetic materials reinforced by aluminum honeycomb framework with arm length of 1 mm, 1.5 mm and 2 mm are 2.52 kJ/g, 1.94 kJ/g and 2.40 kJ/g, respectively. However, the release energy of traditional ingredients Al/PTFE energetic material is only 1.85 kJ/g. Compared with the traditional ingredients Al/PTFE , the compressive strengths and release energies of three kinds of energetic materials reinforced by different arm lengths of Aluminum honeycomb are significantly improved under the same impact conditions.
       
  • Flexural behaviour of FRP reinforced concrete beams strengthened with NSM
           CFRP strips
    • Abstract: Publication date: Available online 20 February 2020Source: Composite StructuresAuthor(s): Cristina Barris, Pau Sala, Javier Gómez, Lluís TorresAbstractThis paper presents the results on an experimental programme studying the flexural behaviour of internally reinforced Glass-Fibre Reinforced Polymer (GFRP) Reinforced Concrete (RC) beams strengthened with Carbon-FRP strips using the Near-Surface Mounted (NSM) technique. Their theoretical load-carrying capacity is assessed by a cracked sectional analysis. It is seen that NSM CFRP results an effective technique to enhance the flexural capacity of RC beams internally reinforced with GFRP bars, despite the high degrees of deformability of GFRP RC. Additionally, an a analytical study to evaluate the influence of different parameters on the flexural capacity of NSM CFRP strengthened concrete beams internally reinforced with either steel or GFRP bars is performed. In general, increasing the reinforcement ratio and mechanical properties, either internal or NSM, increases the flexural capacity. However, the change in the parameters may affect in a different way the ratios of increase and cause different modes of failure.
       
  • Supersonic flutter study of porous 2D curved panels reinforced with
           graphene platelets using an accurate shear deformable finite element
           procedure
    • Abstract: Publication date: Available online 20 February 2020Source: Composite StructuresAuthor(s): S. Aditya, M. Haboussi, S. Shubhendu, M. Ganapathi, O. PolitAbstractThe flutter behaviour of two-dimensional porous curved panels reinforced by graphene platelets exposed to supersonic flow on one side of the panels is investigated using the trigonometric shear deformation theory that satisfies stress free condition on the upper/lower surface of the panels. This structural model exhibits the thickness stretch effect thereby changing the transverse displacement. The effort to model the fluid-structure interaction is reduced by implementing the first-order approximation of piston theory aerodynamics to describe the flow. The solutions are found by introducing finite element methodology using a curved beam model. The critical flutter boundaries were predicted through the complex eigenvalue solution approach for the governing equations formulated adopting the Lagrangian formulation. Detailed numerical experimentation is made to show the effectiveness of the structural models, the influence of depth and length of curved panel, and panel edge conditions on the flutter boundaries of panels. Also, the material parameters such as porosity level, graphene platelet weight content, through-thickness distributions of nano-fillers and pores, size of nano-fillers are assessed on the flutter characteristics of 2D panels.
       
  • Delamination in GLARE Laminates under Low Velocity Impact
    • Abstract: Publication date: Available online 19 February 2020Source: Composite StructuresAuthor(s): Sasanka Kakati, D ChakrabortyAbstractPresent paper deals with the finite element (FE) analysis for determination of impact induced delamination in GLARE laminates. Despite the fact that GLARE possesses better impact properties compared to those for both aluminium and glass/epoxy composites, the low interface strengths may lead to failure in the form of delamination and debonding under low velocity impacts (LVIs). In the present work, LVI responses of GLARE 5 and GLARE 4-3/2 are studied to compare the contact force-time history, plate deflection and delamination at the interfaces using a transient dynamic FE code developed incorporating Newmark-β method and Hertzian contact law. Results show that under LVI, GLARE 4-3/2 is more susceptible to delamination at the interfaces compared to GLARE 5-2/1. The effects of outer aluminium layer thickness and laminate configuration on the interfacial delamination in GLARE under LVI are also studied.
       
  • Lamb wave propagation in anisotropic multilayered piezoelectric laminates
           made of PVDF-θ° with initial stresses
    • Abstract: Publication date: Available online 19 February 2020Source: Composite StructuresAuthor(s): Cherif Othmani, He ZhangAbstractIn this paper, the influence of an initial stresses on the Lamb waves propagation in an anisotropic multilayered piezoelectric laminates is investigated. Formulations are given for only open circuit surface; while the Legendre polynomial method is employed for calculate the wave propagating characteristics. To validate our numerical strategy, this polynomial approach was applied to simulate lamina composite structures. Relatively good results were obtained compared to reliable data available from the literature ones, with relatively significant computation effort. Convergence of the present method is discussed. Influence of initial stresses and fiber orientation angle on the behaviors of Lamb waves is analyzed. Results confirm that the behavior of Lamb modes depends not only on the initial stress but also on fiber orientation. Next, the dispersion curves of fundamental Lamb modes in sandwich plates with 0°/θ°/0 configuration are calculated. Finally, the optimal angles in PVDF-θ° with initial stresses for which the Lamb modes exist are also analyzed. These results for the composite structures may render as a useful reference for the design of ultrasonic transducers in industry for non-destructive testing especially that encounters initial stresses.
       
  • Deformation of laminated and sandwich cylindrical shell with covered or
           embedded piezoelectric layers under compression and electrical loading
    • Abstract: Publication date: Available online 19 February 2020Source: Composite StructuresAuthor(s): Jun Liu, Wenbin Ye, Quansheng Zang, Gao LinAbstractA three-dimensional (3D) theory of elasticity is presented for the solution of the generalized displacements and stresses in the composite laminated and sandwich cylindrical shell structures with covered or embedded piezoelectric layers based on the scaled boundary finite element method (SBFEM). The SBFEM is a weak-form differential technique, which can lead to accurate results performing discretization only on the middle plane of shell structures so that the considered model can be treated as a two-dimensional (2D) discretizated problem. A new type 2D high order spectral element shape function is introduced both for approximations of geometry model and basis variables in the scaled boundary coordinate system. Employing the weighted residual principle in conjunction with Green’s theorem to the normalized static equilibrium equations of each layer leads to the SBFEM governing equation with respect to the radial generalized displacement fields. Then a system of a first-order ordinary differential equation is obtained by introducing a dual variable and analytically solved by using the precise integration technique (PIT). As a result, the major advantage of the proposed formulations for solving the bending problem of the composite laminated and sandwich cylindrical piezoelectric shell is no need to discretize the 3D model with a great deal of degrees of freedom while ensures the computational accuracy. Two test examples are carried out to demonstrate the adaptability and reliability of the present method and illustrate very good agreements and rapid convergence with the solutions based on the finite element approach only using a small number of elements. Numerical examples about the sandwich cylindrical piezoelectric shell are presented to investigate the parametric effects of the thickness ratio as well as the stacking sequence on the variation of generalized displacements and stresses. The results show that both the thickness ratio and stacking sequence have significant influence on the bending behaviors of the sandwich cylindrical piezoelectric shells.
       
  • An effective microscale approach for determining the aniostropy of polymer
           composites reinforced with randomly distributed short fibers
    • Abstract: Publication date: Available online 19 February 2020Source: Composite StructuresAuthor(s): Heng Cai, Junjie Ye, Yiwei Wang, Mohammed Saafi, Bo Huang, Dongmin Yang, Jianqiao YeAbstractIn this paper, an effective microscopic modeling scheme is presented to analyze mechanical properties of composites with random short fibers. To this end, the displacement-load tests of the standard samples, which are acquired by cutting a short fiber-reinforced composite plate of 650mm×650mm×2.5mm, are firstly executed under the quasi-static tensile loads. To identify the geometric sizes of the short fibers and their distributions at microscopic scale, the advanced micro-computed tomography (micro-CT) is employed by testing a small sample of 1cm×2.5mm×2.5mm. On this basis, a simplified microscopic model is reconstructed by the 3D parametric finite-volume direct averaging micromechanics (FVDAM) theory according to the statistic results of the micro-CT images. The proposed method is further validated by comparing the effective modulus obtained from tensile tests. The scanning electron microscopy (SEM) is also used to visualize the fracture morphology of the fibers. It is found that brittle fracture occurs in the short-fibers paralleled to the external loading.
       
  • Design and optimization of composite sub-stiffened panels
    • Abstract: Publication date: Available online 19 February 2020Source: Composite StructuresAuthor(s): Yaoyao Ye, Weidong Zhu, Junxia Jiang, Qiang Xu, Yinglin KeAbstractThis study concerns the buckling and post-buckling performance of composite stiffened panel with sub-stiffening structure subject to compression. The buckling response of the composite stiffened panel is first predicted and verified by experimental data available in the literature. Then sub-stiffeners are introduced into the composite stiffened panel. The distribution and stacking sequence of sub-stiffeners are optimized to improve the critical buckling load without adding weight. Further, to investigate the underlying mechanism of sub-stiffeners involved panels deformation and failure during compressive post-buckling process, different skin-stiffener interfacial parameters are considered. Results show that the introduction of sub-stiffeners to composite T-stiffened panel causes a significant improvement of buckling load (+122.66%) and induces reestablishment of the stress concentrated zone which leads to different local failure forms with different interfacial properties. In addition, the collapse load of sub-stiffened panel becomes more sensitive to interfacial parameters of skin-stiffener interface due to the presence of sub-stiffeners.
       
  • Process Variables of I-fiber Stitching in Mode I Failure
    • Abstract: Publication date: Available online 17 February 2020Source: Composite StructuresAuthor(s): Woo-Jin An, Gyu-Yeong Park, Jin-Ho ChoiAbstractLaminated composites have excellent mechanical properties in the in-plane direction but poor mechanical properties in the thickness direction. To overcome this problem, several z-directional reinforcement methods such as z-pinning, stitching, and tufting for composites have been developed. However, most of these methods require complicated equipment and processes. They also pose limitations on applicable materials depending on the reinforcement process employed. The I-fiber stitching method is applicable to both prepreg and dry preforms. In addition, because this method involves a process of inserting discontinuous fibers in one direction a high-stiffness fiber such as a carbon fiber can be applied.In this study, to find the optimal process variables of I-fiber stitching in the Mode Ⅰ failure, the failure loads of double cantilever beam (DCB) and in-plane tensile specimens were experimentally investigated based on the stitching pattern, bundle size, and head length of the I-fiber. The Mode I DCB test revealed that the failure loads of DCB specimens with I-fiber heads were greater than those of DCB specimens without I-fiber heads, and the smaller the bundle sizes of the I-fibers, the greater the failure loads of the DCB specimens.
       
  • Influence of Geometrical Parameters on the Strength of Hybrid
           CFRP-Aluminium Tubular Adhesive Joints
    • Abstract: Publication date: Available online 17 February 2020Source: Composite StructuresAuthor(s): Nicolas P. Lavalette, Otto K. Bergsma, Dimitrios Zarouchas, Rinze BenedictusAbstractTubular adhesive joints, used in truss structures to join pultruded carbon fibre-reinforced polymer members to aluminium nodes, are modelled with varying dimensions. The numerical model uses a Cohesive Zone Modelling formulation with a trapezoidal traction-separation law for the adhesive layer, and experimental tests are carried to validate it. The results showed that the joint strength increases significantly with the bonding area, with a limit on the overlap length above which it stops increasing. This upper limit is affected by the thickness and tapering angle of the adherends, due to their influence on the shear stress distribution along the overlap. On the other hand, the adhesive thickness has only a marginal influence on the joint strength.
       
  • High strain rate characterisation of intralaminar fracture toughness of
           GFRPs for longitudinal tension and compression failure
    • Abstract: Publication date: Available online 17 February 2020Source: Composite StructuresAuthor(s): Giuseppe Catalanotti, P. Kuhn, J. Xavier, H. KoerberAbstractThe elastic parameters, strengths, and intralaminar fracture toughness are determined for an E-Glass polymer composite material system, statically and at high strain rate, adapting methodologies previously developed by the authors for different carbon composites. Dynamic experiments are conducted using tension and compression Split-Hopkinson Bars (SHBs). A unique set of experimental parameters is obtained, and reported together with the experimental set-up, in order to ensure reproducibility. While in-plane elastic and strength properties were obtained by testing one specimen geometry, intralaminar fracture properties required the testing of different sized notched specimens with scaled geometries. This allowed the use of the size-effect method for the determination of the dynamic R-curve. When comparing these results with those previously obtained for a carbon/epoxy material system, it is observed that the dynamic fracture toughness exhibits a much more significant increase in both tension and compression. The obtained results permit the identification of the softening law at different strain rates, allowing its use in any analytical or numerical strength predictive method.
       
  • Spatial modelling of 3D woven variable thickness composite plate at the
           mesoscopic scale
    • Abstract: Publication date: Available online 22 January 2020Source: Composite StructuresAuthor(s): Yu Zhou, Weidong Wen, Haitao CuiAbstractThe geometric details of variable thickness 3D woven composite plate, which features varying weft yarn cross section shapes and sizes at each layer and resulting diverse warp yarn path orientations, are quite different from the structure in constant thickness plate. A geometric model to handle these variances is presented in this paper which no doubt can also be used in constant thickness plate. Based on the idealized assumptions that the cross section shape of weft yarn is lenticular and warp yarn is rectangular, the inner structure details of variable thickness plate are illustrated in the efficient geometric model with weaving parameters and some measurements as input data. Two 3D woven sample materials are produced to confirm the accuracy of the proposed geometric model. Even though the idealizations in geometric model lead to some over predictions, the model still captures the majority of details in corresponding real sample architectures.
       
  • A general property-structure relationship from crack stability analysis on
           hybrid staggered composites with elasto-plastic matrices
    • Abstract: Publication date: Available online 17 February 2020Source: Composite StructuresAuthor(s): Zhongliang Yu, Junjie Liu, Xiaoding WeiAbstractIn the present study, fracture analysis is carried out on the representative unit cell of staggered composites consisting of hybrid reinforcements and elasto-plastic matrices. The deformation and failure of hybrid composites are examined through energy-based fracture theory. Analytical formulae for characteristic overlap length, failure strain, and toughness of the unit cell that are related to the properties and geometries of constituents emerge from rigorous derivations. The influences of the matrix plasticity and tablet dissimilarity on the crack stability, the characteristic overlap length, the final failure strain, and toughness are also elucidated. Our study shows that if designed appropriately, the matrix plasticity can effectively improve the material ductility and toughness through crack stabilization. On the other hand, although hybrid reinforcements could effectively tune the ductility, they may cause a loss of material toughness in some cases. More importantly, our model provides guidance to the promising design space where the well-known ductility-strength trade-off dilemma for traditional engineering materials could be resolved.
       
  • Prediction of Residual Mechanical Properties in Flexure-After-Impact of
           Woven Composite Beams through Electrical Resistance Measurement
    • Abstract: Publication date: Available online 17 February 2020Source: Composite StructuresAuthor(s): Xiaoying Cheng, Yi Gong, Yisheng Liu, Zhenyu Wu, Xudong HuAbstractLow-velocity impact and flexure-after-impact (FAI) tests were performed on 2D plain woven fabric (PWF) and 3D orthogonal woven fabric (OWF) reinforced carbon fibers/epoxy composite beams while the electrical resistance measurement was applied during impact and FAI tests via four-probe technique to study the relations between resistance variation (RV) and residual mechanical properties. The impact tests (from 3J to 9J) showed that OWF specimens have better suppression of delamination than PWF, which was also evaluated through thermography and cross-sectional imaging method. Then FAI tests were implemented on impacted specimens while acoustic emission signals were captured. The residual flexural strength and modulus from the FAI tests were normalized by the values of intact specimens and compared with the RV from impact tests. The relations between electrical and mechanical properties revealed that the rise of resistance after the impact is an effective sign that indicates the reduction in the residual flexural strength and modulus of the composite beam. Moreover, the relation between RV and residual modulus is more effective than that with residual strength.
       
  • Development of composite double-hat energy absorber device subjected to
           traverser loads
    • Abstract: Publication date: Available online 15 February 2020Source: Composite StructuresAuthor(s): F. Alkhatib, E. Mahdi, A. DeanAbstractThis paper introduces a new carbon fiber reinforced plastic (CFRP) structural system in the field of crashworthiness. CFRP hat-shaped and angle-shaped stiffeners were used to develop a double-hat collapsible energy absorption system. Three different design alternatives were investigated. The first alternative is an open-cell design (OC) consisting of two flipped hat stiffeners with four right angles on the edges. The second alternative is a one-in-cell double-hat design (1C), consisting of OC design with additional one inside small hat stiffeners edged with angles. The third alternative is a two-in-cell double-hat design (2C), consisting of OC design with additional two inside small hat stiffeners edged with angles. Three modes of failure were observed, classified as local buckling (mode I), top wall bending (mode II), and brittle collapse that resulted from Euler buckling (mode III). The crashworthiness characteristics were evaluated for the three designs. The 2C double-hat design showed the highest peak load and specific energy absorption (SEA). Accordingly, the core of the 2C design was filled with foam to increase the energy absorption capability and enhance the structure’s stability. Results showed that the SEA of the 2C+ foam design was increased by more than 50% compared to the coreless 2C double-hat design.
       
  • A three-dimensional hierarchic finite element-based computational
           framework for the analysis of composite laminates
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Z. Ullah, Ł. Kaczmarczyk, C.J. PearceAbstractA three-dimensional hierarchic finite element-based computational framework is developed for the investigation of inter-laminar stresses and displacements in composite laminates of finite width. As compared to the standard finite elements, hierarchic finite elements allow to change the order of approximation both locally and globally without modifying the underlying finite element mesh leading to very accurate results for relatively coarse meshes. In this paper, both symmetric cross-ply and angle-ply laminates subjected to uniaxial tension are considered as test cases. Tetrahedral elements are used for the discretisation of laminates and uniform or global p-refinement is used to increase the order of approximation. Each ply within laminates is modelled as a linear-elastic, homogenous and orthotropic material. With increasing the order of approximation, the developed computational framework is able to capture the complex profiles of inter-laminar stresses and displacements very accurately. Results are compared with reference results from the literature and found in a very good agreement. The computational model is implemented in our in-house finite element software library Mesh-Oriented Finite Element Method (MoFEM). The computational framework has additional flexibly of high-performance computing and makes use of the state-of-the-art computational libraries including Portable, Extensible Toolkit for Scientific Computation (PETSc) and the Mesh-Oriented datABase (MOAB).
       
  • Stress redistribution around fiber breaks in unidirectional steel fiber
           composites considering the nonlinear material behavior
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Baris Sabuncuoglu, Caglar Mutlu, F. Suat Kadioglu, Yentl SwolfsAbstractThe use of steel fibers as reinforcement in polymer composites is recently increasing thanks to their ductility, high stiffness and wide range of diameters. Unlike carbon and glass fibers, steel fibers often end up with a non-circular cross-section due to their manufacturing technology. This may influence the stress redistribution around fiber breaks, which is important in longitudinal tensile failure of unidirectional composites. A parametric study was performed by using 3D finite element models with randomly distributed and oriented hexagonal fibers. Rather than the fiber shape, the distance between fibers was shown to have an influence on stress concentrations in terms of both average and peak stress concentrations. The plastic behavior of steel fibers resulted in smaller stress concentrations and faster stress recovery whereas the opposite was observed for the plastic behavior of epoxy. For different strain levels, results were shown to depend on the relative stiffness of steel and epoxy in the plastic region.
       
  • Quasi-static bending and transverse crushing behaviors for hat-shaped
           composite tubes made of CFRP, GFRP and their hybrid structures
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Dongdong Chen, Guangyong Sun, Xihong Jin, Qing LiAbstractThis study aims to characterize the crushing responses of hat-shaped composite tube under quasi-static three-point bending (TPB) and transverse compression (TC) conditions. The specimens were fabricated with different stacking configurations considering the effect of ply number, ply angle (containing [±45°] layers) and interply hybrid structure (sandwich-like) with carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) through thermo-forming process. Mechanical parameters were also tested with non-hybrid laminates consisted of net carbon and net glass fibers. The crushing performance was evaluated by comparing load-displacement curves and the images taken in course of the testing processes. Cross-sections of the specimens were also inspected visually to identify the failure mechanisms after the tests. The comparative study on the energy absorption and cost efficiency was conducted for all the samples. It was found that failure modes varied with ply angle under the TPB tests but kept the same under the TC tests. Increasing wall thickness seemed to be an effective way to improve energy absorption under both TPB and TC loading. Addition of [±45°] layers exhibited considerable advantages on the TPB performance except the TC scenario. The hybrid structures comprised of both carbon and glass fiber layers exhibited limited improvement on crashworthiness but excellent cost efficiency. In addition, the initiation and propagation of cracks during tests were clearly visible when stacking glass fiber layers outside, which facilitate proper structural health monitoring.
       
  • Effect of heterogeneity on crushing failure of disordered staggered-square
           honeycombs
    • Abstract: Publication date: Available online 14 February 2020Source: Composite StructuresAuthor(s): Deepak Kumar, Anuradha BanerjeeAbstractUni-axial compressive failure of silica-epoxy based heterogeneous honeycombs is investigated in detail for a range of volume fractions. Introduction of heterogeneity in compression of staggered-square honeycomb is seen to result in damage initiation at multiple locations and subsequent damage growth to be more stable compared to pure epoxy in which damage was observed to be localized until peak load when catastrophic failure of the honeycomb specimen occurs. The increase in stiffness and comparative stability of the response is accompanied with reduction in strength, however, between 0-5% the total work of compressive failure is comparable. From the elastic-plastic analysis it is evident that the non-linearity in the response of pure honeycombs, prior to peak load, is largely due to formation of plastic hinges near corners of cells, whereas in case of heterogeneous honeycomb the non-linearity is mostly due to debonding of hard filler particles and matrix cracking leading to damage growth in cell walls.
       
  • Mechanical properties of SiCp/SiC composite lattice core sandwich panels
           fabricated by 3D printing combined with precursor impregnation and
           pyrolysis
    • Abstract: Publication date: Available online 13 February 2020Source: Composite StructuresAuthor(s): Kun Zhang, Tao Zeng, Guodong Xu, Su Cheng, Siwen YuAbstractSilicon carbide particle/silicon carbide (SiCp/SiC) composite lattice core sandwich panels were fabricated by selective laser sintering (SLS) combined with precursor impregnation and pyrolysis (PIP) process. The compression properties of the SiCp/SiC composite lattice core sandwich panels with three different configurations under room temperature and high temperature were investigated. The room temperature experiment results were compared with the analytical predictions. Experiment results indicated that the compression strength and modulus decreased 34.30% and 44.82% as the temperature increased from 1400℃ to 1800℃. Moreover, the failure mechanisms of the SiCp/SiC composites were analyzed.
       
  • Explicit neural network model for predicting FRP-concrete interfacial bond
           strength based on a large database
    • Abstract: Publication date: Available online 12 February 2020Source: Composite StructuresAuthor(s): Yingwu Zhou, Songbin Zheng, Zhenyu Huang, Lili Sui, Yang ChenAbstractThis study builds a large database from an extensive survey of existing single-lap shear tests on fiber-reinforced polymer (FRP)-concrete interfacial bonds, comprising 969 test results. Twenty shear-bond strength models published over the past 20 years have been collected and analyzed. These models take into account the effects of the concrete compressive strength, concrete width, FRP elastic modulus, FRP thickness, FRP width and FRP bond length on the ultimate bond strength of the FRP-concrete interface. This paper evaluates the predictive accuracy of the 20 collected models and finds that these models have limited accuracy. To accurately predict the bond strength of the FRP-concrete interface, this paper employs the back propagation neural networks (BPNN) method to train and test the database and builds an artificial neural networks (ANN) model that consists of weighted values, biases and transfer functions. The ANN model test conducts 84 training iterations and selects the optimal combination of input nodes. The accuracy of the developed ANN model is higher (i.e., lower predictive error) than that of the existing bond strength models in the literature. Furthermore, this paper develops an explicit user-friendly formula based on the trained ANN model. The proposed formula estimates and validates the 969 bond strength results, and the predictions using the explicit equation fit the test data very well with small error. As such, the formula can be easily applied during practical designs instead of the implicit processes in the ANN model.
       
  • A structured method to generate conformal FE mesh for realistic textile
           composite micro-geometry
    • Abstract: Publication date: Available online 11 February 2020Source: Composite StructuresAuthor(s): Agniprobho Mazumder, Youqi Wang, Chian-Fong YenAbstractA procedure is developed to generate a conformal finite element mesh of a textile composite unit cell with a complex micro-geometry with the aim of improving the accuracy of micro-mechanics analysis. A realistic micro-geometry of a textile composite unit cell is initially generated by using a fiber level dynamic relaxation approach. Yarn surfaces are then discretized into triangle elements. An algorithm is established to remove inter-yarn interferences and gaps induced by numerical errors. The unit cell is first divided into a uniform cuboid element mesh, which is later modified and converted to a conformal finite element (FE) mesh through of a process of node shifting and element splitting. In the conformal mesh, the element boundary perfectly matches the yarn-to-yarn interface. Compatibility between elements is ensured. The quality of each element is examined. The mesh can be input to commercial FEM softwares for composite stress analysis.
       
  • Study on the flexural strengthening effect of RC beams reinforced by FRP
           grid with PCM shotcrete
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): Rui Guo, Wenhao Hu, Mengqi Li, Shinichi HinoAbstractRecently a new repair and retrofit method of reinforced concrete (RC) members that uses fibre-reinforced-polymer (FRP) grid with polymer-cement-mortar (PCM) shotcrete has been proposed. Four RC beams externally strengthened with CFRP grid-PCM at the bottom and one non-reinforced RC beam were tested to reveal their flexural behaviour and strengthening effect. The number of FRP layers and reinforcement amount per unit length of the CFRP grid were selected as the two main parameters in the test programme. The test results indicated that the flexural strengthening effect of the CFRP grid-PCM was sufficient; moreover, two-layer reinforcements were effective as one-layer ones under similar unit-reinforcement values. Furthermore, a new analytical model was proposed to evaluate the flexural capacities of RC beams strengthened with CFRP grid, and the predicted values were well matched to the test results and collected data.
       
  • Optimization of hybrid natural laminated composite beams for a minimum
           weight and cost design
    • Abstract: Publication date: Available online 23 January 2020Source: Composite StructuresAuthor(s): M. Megahed, Rasha M. Abo-bakr, S.A. MohamedAbstractIn recent years, the use of bio-fibers to replace synthetic fibers in composites has gained popularity due to increasing environmental concerns and requirements for developing sustainable materials for engineering applications. The objective of this study is to minimize the weight and cost of a symmetric laminated composite beam with a specified lower bound constraint on its natural frequency. The optimal design of hybrid composite beams with different boundary conditions was considered. The optimization problem accounts for fiber type, fiber volume fractions, thickness, and fiber orientation angles of different layers as design variables. The optimum design of the hybrid carbon/flax/epoxy laminated beam for different values of frequency lower limits was computed and compared with those of the hybrid carbon/glass/epoxy, neat glass/epoxy, and neat flax/epoxy laminated beams. Results showed that hybridization between the carbon fiber and flax fiber results in the best designs with the advantages of a lightweight, low cost and higher fundamental frequencies.
       
  • Modal analysis of a Variable Stiffness Composite Laminated plate with
           diverse boundary conditions: Experiments and modelling
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Ana Margarida Antunes, Pedro Ribeiro, José Dias Rodrigues, Hamed AkhavanAbstractThe modes of vibration of a Variable Stiffness Composite Laminate were obtained by experimental modal analysis and compared with the ones resulting from theoretical/mathematical models. Three types of boundary condition were considered: CFFF, CFCF and FFFF, where C stands for clamped and F for free edges. Frequency response functions were experimentally obtained and employed to identify natural frequencies, modal damping ratios and mode shapes of vibration, using methods known as CMIF - Peak picking and circle-fit. The identified natural frequencies and mode shapes of vibration were compared with the ones resulting from models based on Classical Plate Theory and on First-order Shear Deformation Theory. Although two massive, stiff, steel blocks were bolted with the plate in-between in order to approach a clamped boundary, the modal properties are still significantly influenced by the flexibility of the resulting fixture. After introducing springs along the boundaries in the mathematical model, to better represent a “real clamped” boundary, quite good agreement between theoretical and experimental results was obtained. The experimental results here presented can be used to validate theoretical models of Variable Stiffness Composite Laminated plates.
       
  • Variational analysis of cracking in general composite laminates subject to
           triaxial and bending loads
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): M. Hajikazemi, L.N. McCartney, H. Ahmadi, W. Van PaepegemAbstractA robust variational approach is first developed for predicting stress/displacement fields and effective thermo-elastic constants in a laminate with arbitrary lay-up, containing uniformly spaced ply cracks, subject to general triaxial and bending loads when the effects of thermal residual stresses are also considered. The methodology extends some previously developed variational approaches so that general non-symmetric lay-ups (not only cross-ply) under through-thickness loading conditions can be analyzed. Secondly, an approximate methodology is introduced which enables the approach to predict all effective thermo-elastic constants of laminates having non-uniformly spaced ply cracks, including new types of constant required to account for out-of-plane loading. Thirdly, some novel inter-relationships among effective thermo-elastic constants of cracked and uncracked general laminates are obtained showing that just three macroscopic parameters define the dependence of all relevant laminate constants (thirty five) on the state of cracking. The results are compared with those obtained from finite element methods, experiments and other high accuracy models.
       
  • Modelling of a GFRP adhesive connection by an imperfect soft interface
           model with initial damage
    • Abstract: Publication date: Available online 10 February 2020Source: Composite StructuresAuthor(s): A. Maurel-Pantel, M. Lamberti, M.L. Raffa, C. Suarez, F. Ascione, F. LebonAbstractIn this paper a methodology to model a GFRP adhesive connections by using an imperfect soft interface model is presented. The model based on Kachanov’s theory considered a cracked thin adhesive. Within this framework, the mechanical properties and the initial damage (diffuse initial cracks) of the adhesive layer has been experimentally evaluated. With a modified Arcan system, static tests were performed on adhesively bonded assemblies in tensile and shear solicitation mode considering three different adhesive thicknesses. The experimental results highlighted how the thickness of adhesive influences the mechanical strength and stiffness of the bonded connection. CT-scans were performed to measure the porosity rate in the adhesive layer. Furthermore, the excellent comparison of numerical and experimental data of an adhesive GFRP bonded connections allow us to consider the imperfect soft interface model proposed as highly competitive to evaluate complex structure performance in civil engineering context. A parametric analysis has been proposed to provide a formula able to describe the full response of the structure at varying adhesive property.
       
  • Large amplitude vibration of functionally graded graphene nanocomposite
           annular plates in thermal environments
    • Abstract: Publication date: Available online 8 February 2020Source: Composite StructuresAuthor(s): Helong Wu, Jun Zhu, Sritawat Kitipornchai, Quan Wang, Liao-Liang Ke, Jie YangAbstractThis paper investigates the large amplitude vibration of functionally graded nanocomposite multilayer annular plates reinforced with graphene platelets (GPLs) in thermal environments. It is assumed that the GPL concentration varies from layer to layer across the plate thickness but remains constant in each individual GPL-reinforced composite (GPLRC) layer, whose elastic modulus is estimated by the modified Halpin-Tsai micromechanics model. Within the framework of first-order shear deformation theory and von Kármán geometric nonlinearity, the governing equations are derived by using the Hamilton’s principle and then solve by the differential quadrature method together with an iterative scheme. Numerical results are presented to show the influences of GPL geometry, distribution pattern and concentration, plate geometry, boundary conditions, as well as temperature rise on the nonlinear vibration behaviour of functionally graded GPLRC annular plates. It is found that dispersing more GPLs within the outer layers substantially decreases the nonlinear frequency ratio, while the effect of GPL geometry is insignificant.
       
  • On frequency response of porous functionally graded
           magneto-electro-elastic circular and annular plates with different
           electro-magnetic conditions using HSDT
    • Abstract: Publication date: Available online 8 February 2020Source: Composite StructuresAuthor(s): M VinyasAbstractIn this article, the vibrational behaviour of porous functionally graded magneto-electro-elastic (P-FGMEE) circular and annular plates is explored through finite element procedures. The influence of different electro-magnetic boundary conditions on the coupled natural frequencies of P-FGMEE plates are evaluated for the first time. The governing equations are arrived through Hamilton’s principle under the framework of higher order shear deformation theory (HSDT) in polar coordinates. The magneto-electro-elastic (MEE) material properties are assumed to vary along the thickness based on power-law model. The proposed model is verified for its correctness with previously published literature and also with numerical software. In addition, the effects of various prominent parameters such as gradient index, porosity volume, functionally graded pattern, diameter ratio, coupling fields etc., on the frequency response of P-FGMEE circular and annular pates are also discussed. The results of this article can be effectively incorporated for the accurate design and development of functionally graded smart structures with porosities.
       
  • A double porosity material for low frequency sound absorption
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Honggang Zhao, Yang Wang, Dianlong Yu, Haibin Yang, Jie Zhong, Fei Wu, Jihong WenAbstractThis work designs a double porosity material (DPM) composed of two types of pores, i.e., the micro-pore from the porous layer and the meso-pore made by the labyrinthine channel. The both loss mechanisms of two different pores are combined to explore the low frequency sound absorption. All theoretical, numerical and experimental results show that the DPM possesses much lower frequency sound absorption than that of homogenous porous material (HPM) under the same thickness. Both the pressure and particle velocity distributions reveal that the sound absorption peaks are induced by the resonances of the labyrinthine channel and the hybrid resonance between the porous layer and labyrinthine channel respectively. Moreover, unconventional features such as negative bulk modulus and slow sound speed are observed around the resonant frequencies of the DPM. Finally, the absorption tailoring of the DPM with different strategies is investigated.
       
  • Closed-form approximate solution for linear buckling of Mindlin plates
           with SRSR-boundary conditions
    • Abstract: Publication date: Available online 8 February 2020Source: Composite StructuresAuthor(s): M. Beerhorst, S. Thirusala Suresh BabuAbstractThe present work deals with the buckling analysis of rectangular Mindlin plates consisting of laminated composites with symmetrical, balanced lay-up or isotropic materials. Along the longitudinal edges the plate is rotationally restrained by springs. The transversal edges are simply supported. In agreement with common notation, the boundary conditions are abbreviated as follows: simply supported (S), rotationally restrained (R), and fully clamped (C). As loading situation axial compression is considered. Aiming at high computational efficiency the problem is solved by the Rayleigh-Ritz-method. Since well suited shape functions for deflection and rotations with very few variables are used, closed-form approximate solutions for the buckling load can be obtained. For verification exact transcendental solutions and/or high fidelity finite element analyses are employed. Additionally, results are compared to those of existing closed-form approximate solutions.Apart from the special case of simply supported longitudinal edges where all methods yield exact or nearly exact results, the present method shows clear advantages: 1. Due to the type of shape functions it is able deal with unsymmetrical boundary conditions. 2. For the case of both longitudinal edges fully clamped where all closed-form approximate solutions show the greatest deviations the present method is significantly more accurate.
       
  • An accurate higher order plate theory for vibrations of cross-laminated
           timber panels
    • Abstract: Publication date: Available online 8 February 2020Source: Composite StructuresAuthor(s): Thomas Furtmüller, Christoph AdamAbstractIn this contribution, bending vibrations of cross-laminated timber (CLT) panels are addressed. The focus is on the low to mid audio frequency range in view of the sound radiation properties of CLT. To this end, a plate theory recently proposed by the authors is adapted by introducing a deformation ansatz for the transverse displacement and neglecting insignificant terms, yielding a theory with six degrees of freedom. From the governing equations of motion, dispersion relations for the propagation of bending wave are derived, which also allow to compute the natural frequencies and mode shapes of bounded plates. The weak formulation of the equations of motion is presented. The accuracy of the proposed theory is validated for a simply supported rectangular CLT panel for which an analytical solution is available. The results are compared with first order shear deformation theory, revealing the limitations of this simplified theory in the present context. Finally, finite element solutions for the rectangular plate with non-classical boundary conditions are presented, as well as incorporating a floating floor construction, underlining the importance of numerical solutions for the practical application of this plate theory.
       
  • Post-Impact Flexural Behavior of Carbon-Aramid/Epoxy Hybrid Composites
    • Abstract: Publication date: Available online 6 February 2020Source: Composite StructuresAuthor(s): A. Wagih, T.A. Sebaey, A. Yudhanto, G. LubineauAbstractHybrid polymeric composites are currently used in aerospace structures due to their specific strength and stiffness as well as larger design space. This paper presents an experimental study on residual flexural strength of impacted Carbon-aramid/Epoxy hybrid composite laminates. Specimens are designed in a sandwich form in which plies of aramid/epoxy represent the core and carbon/epoxy plies play the role of face sheets. This design is expected to take advantage of the high energy absorption capabilities of aramid/epoxy composites. We pre-damage such composites by performing low-velocity impact at different energy levels. Three-point bending tests then are used to measure the residual flexural strength for the impacted specimens. The damage sequence during three-point bending is monitored using a camera and, later on, with computed tomography. The results show that, unlike the all-carbon/epoxy laminates, the carbon fiber plies in the lower part of the laminate (non-impacted face) are not fractured after either the impact test or the three-point bending test. The damage is locally concentrated at the impacted face and the upper part of the aramid plies core. As a result, the strength losses are smaller, as compared to available results in the literature for carbon/epoxy composites, glass/epoxy and carbon fibers with aluminium core laminates.
       
  • Studies on the mechanical and absorption properties of achatina fulica
           snail and eggshells reinforced composite materials
    • Abstract: Publication date: Available online 5 February 2020Source: Composite StructuresAuthor(s): O.J. Gbadeyan, S. Adali, G. Bright, B. Sithole, A. OmojoolaAbstractThe present study focuses on the mechanical and absorption properties of composites reinforced by achatina fulica snail (S-shell) and eggshell particles (E-shell). Epoxy composites of snail and eggshell particles were prepared separately with the filler content ranging from 5 to 20% by weight. Hybrid composites of both fillers were also prepared and assessed. Specimens of the composites and hybrid composites with different percentage weights of the reinforcing materials were fabricated using the resin casting method. Mechanical properties such as tensile strength, Young’s modulus, impact strength, hardness and water absorption properties of the specimens were evaluated experimentally. It was observed that the addition of nano-size shell particles improves the mechanical properties of neat epoxy irrespective of the percentage weight of the reinforcement. The mechanical and water absorption properties of composites and hybrid composites varied depending on the amount of the reinforcement. Significantly, hybrid reinforcement by S-shell and E-shell particles offered superior properties in most cases. High percentage weight of calcium carbonate in these naturally sourced fillers and the synergistic effect of the S-shell and E-shells particle fillers can be attributed to high strength, stiffness, and decrease in water uptake of the composites.
       
  • Effect Of Core Density On The Low-Velocity impact Response Of Foam-Based
           Sandwich Composites
    • Abstract: Publication date: Available online 5 February 2020Source: Composite StructuresAuthor(s): D. Feng, F. AymerichAbstractThe paper presents the results of an investigation into the effect of core density on the low-velocity impact response of foam-based sandwich composites. Drop-weight tests were conducted on sandwich panels with carbon/epoxy facesheets and a 10 mm thick PVC foam core. Three foam core densities (65, 100 and 160 kg/m3) and two facesheet layups ([0/903/0], [03/±45]S) were examined in the study. The analyses show that the influence of core density on the damage resistance of the panels is strongly correlated to the layup of the skin. While the damage developing in [0/903/0] panels is not affected by core density, the damage area in [03/±45]S panels reduces with increasing core density. The different influence of core properties on the damage response of [0/903/0] and [03/±45]S sandwich panels may be attributed to the different bending stiffness of the facesheets, with a response to impact dominated by global bending in panels with thin [0/903/0] skins as opposed to one mainly governed by local shear rigidity in panels with thicker [03/±45]S skins. FE analyses were finally carried out to assess the capability of a model developed by the authors to capture the role of foam density in the impact damage response of the panels.
       
  • Nonlinear Vibration Behavior of Functionally Graded Porous Cylindrical
           Panels
    • Abstract: Publication date: Available online 5 February 2020Source: Composite StructuresAuthor(s): M.M. Keleshteri, J. JelovicaAbstractThe paper presents large amplitude free vibration response of functionally graded porous (FGP) cylindrical panels considering different shell theories and boundary conditions. Nonlinear governing equations are obtained based on two shell theories, first order shear deformation theory (FSDT) and higher order shear deformation theory (HSDT). The von Karman geometrical nonlinearity along with the Hamilton principle is utilized. Mechanical properties of the open-cell foam are assumed to vary continuously through the thickness. This graded porosity offers a smooth stress distribution along the thickness of the panel. Generalized differential quadrature method (GDQM) is utilized to discretize the nonlinear dynamic governing equations along with three different boundary conditions. To solve the set of equations that include highly nonlinear parameters, the harmonic balance method along with the direct iterative approach is used. The results present the influence of geometrical parameters, vibration amplitude, porosity distribution, shell theories and boundary conditions on the nonlinear frequencies. It is found that both porosity distribution and porosity coefficient have a remarkable effect on the nonlinear natural frequencies of FGP cylindrical panel. To enhance the dynamic response of the cylindrical panel, porosity should be avoided near the panels’ surfaces.
       
  • A Novel Three-Dimensional Structure Model of Biomimetic Staggered
           Composites
    • Abstract: Publication date: Available online 5 February 2020Source: Composite StructuresAuthor(s): Rui Hao, DongXu Li, Wang LiuAbstractThe staggered structure is considered to be one of the key factors for the excellent mechanical properties of bone. In order to solve the problem of non-uniform stress distribution in the hard component of the original biomimetic staggered composites, a novel three-dimensional structure model with pores is proposed in this paper. By generalizing the shear lag theory model of the original staggered structure to the new model, the constitutive relation of the porous structure is established. On this basis, the stress distribution with respect to the aspect ratio of the hard prisms is studied. Finally, the two composite models are simulated by finite element method. The results show that stress in the novel structure tends to be uniformly distributed under external force. So it has higher stiffness and strength to mass ratio, and maintains stronger toughness. It is illustrated that pores in staggered structure can help to fully exploit the mechanical potential of each phase in the composites, providing an explanation for the existing of large number of voids in bone. This study may have an important inspiration for designing lightweight load-bearing composites with high efficiency of vibration isolation and cushioning.
       
  • Full-range behavior of fiber reinforced cementitious matrix
           (FRCM)-concrete joints using a trilinear bond-slip relationship
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Xingxing Zou, Lesley H. Sneed, Tommaso D'AntinoAbstractInterfacial debonding of fiber reinforced cementitious matrix (FRCM)-concrete joints can be considered as a mainly mode-II fracture process, a problem that can be solved by accounting for one-dimensional interfacial shear stress-slip relationships. This paper presents an analytical approach to predict the load response of FRCM-concrete joints by adopting a trilinear bond-slip relationship consisting of a linear-elastic branch, a softening branch, and a friction branch. The applied load-global slip response of FRCM-concrete joints with (relatively) long bonded length includes five stages: elastic, elastic-softening, elastic-softening-debonding, softening-debonding, and debonding stages. Closed-form solutions of the interfacial slip, shear stress, and axial stress (or strain) distribution along the bonded length are provided. The response of FRCM-concrete joints with (relatively) short bonded length is examined. The effective bond length and a critical length for the existence of the snap-back phenomenon are derived. Experimental results reported in the literature are used to calibrate the parameters needed for the analytical approach. The analytical results are then compared with experimental results and with numerical results determined using a finite difference method (FDM). Finally, the capability of determining the parameters in the trilinear bond-slip relationship using a neural network (NN) with the experimental load response as the input is investigated.
       
  • Modeling and design of a class of hybrid bistable symmetric laminates with
           cantilever boundary configuration
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Aghna Mukherjee, Michael Ian Friswell, Shaikh Faruque Ali, A. ArockiarajanAbstractMultistable laminates have been widely analyzed in the recent past for their potential in morphing applications. However, all the analytical models developed up until now have taken into account only the free-free boundary condition. In this work two objectives are met: (a) an analytical model is developed, which extends the previously available models in literature to account for the cantilever boundary condition for a special class of hybrid bistable symmetric laminates (HBSL); (b) the previously proposed HBSL is modified by replacing the aluminum layers with bi-direction glass-epoxy prepregs in the layup. It is observed that the modified layup has a curvature similar to the previously proposed HBSL while maintaining bistability. The analytical model developed here successfully captures the equilibrium shapes and the snap-through behavior for this special class of laminates which is validated against the results obtained using ABAQUS® and experiments. The developed model is then subsequently used to study the design space and bistability characteristics of the HBSL and the proposed modified layup (m-HBSL) in the cantilever boundary condition.
       
  • Chemical prestressing of high-performance concrete reinforced with CFRP
           tendons
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Mateusz Wyrzykowski, Giovanni Terrasi, Pietro LuraAbstractChemical prestress (self-prestress) is a process, in which expansion of concrete with special additives can be used to generate tension in the reinforcement and prestress in the concrete. Until now, the prestress levels that could be reached with this technique were usually lower than with traditional (external) prestressing. With the new family of expansive high-performance concretes (HPC) developed by us, very high levels of residual expansion can be achieved without compromising the durability and still reaching very good mechanical properties of the concrete. In this paper, we combine the expansive HPC with tendons made of ultra-high modulus (>400 GPa) carbon fiber reinforced polymers (CFRP). Through the expansion of the concrete and its bond with the sand-coated tendons, we could introduce tensile stresses of more than 600 MPa in the tendons (for 1% reinforcement ratio), corresponding to more than 4 MPa compressive stress (prestress) in the concrete. 4-point bending tests show that the chemical prestress increased the cracking moment of slender concrete beams more than three times compared to the reference concrete. Our long-term tests of the strains of the tendons show that the losses of prestress due to shrinkage and compressive creep are very low.
       
  • On the energy release rate extraction and mixed mode behavior of fatigue
           cohesive model
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Tao Chongcong, Zhang Chao, Ji Hongli, Wu Yipeng, Qiu JinhaoAbstractThis paper presents a comprehensive study on the energy release rate (ERR) extractions and mixed mode behavior of fatigue cohesive model. The development of the non-linear cohesive zone ahead of a crack tip is influenced by multiple factors, where the extractions of ERRs and mode ratios are crucial for accurate fatigue analysis in Paris law-based models. Investigations into the effects of different parameters e.g. interfacial strengths, shapes of the cohesive laws and element sizes on the extracted ERRs are studied. In addition, two novel mixed mode bending models i.e. multi-stage mode ratio (MSMR) and continuously various mode ratio (CVMR) models are proposed for mixed-mode behavior study. All results are compared to the theoretical fracture mechanics analysis and to each other. It is found that if the interfacial strength becomes too low, an excessively long cohesive zone can form, where the mode ratio could significantly deviate from the true value and negatively impact the accuracy. The shape of cohesive laws is also found to influence the ERRs and mode ratios to some extent but are not the dominating factor.
       
  • The quasi-static axial compressive properties and energy absorption
           behavior of ex-situ ordered aluminum cellular structure filled tubes
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Han Wang, Mingming Su, Hai HaoAbstractIn this study, the ex-situ ordered aluminum cellular structure filled tubes with different filler types, filling ratios and filling positions were fabricated by inserting the ordered aluminum cellular structure fillers into the aluminum tubes directly. The ordered aluminum cellular structure fillers were prepared by the selective laser sintering and the infiltration casting. The compressive properties and energy absorption behavior of ex-situ ordered aluminum cellular structure filled tubes were assessed by quasi-static axial compression tests. The effects of the ordered cellular structure types, filling ratios and filling positions on compressive properties and energy absorption behavior of ex-situ ordered aluminum cellular structure filled tubes were investigated. The results show that both the uniform and graded ordered aluminum cellular structures as filler materials can significantly improve the compressive properties and energy absorption behavior. Meanwhile, the compressive properties and energy absorption behavior of ex-situ ordered aluminum cellular structure filled tubes can be tailored by changing the filling ratios and positions. It is noticed that the ex-situ ordered aluminum cellular structure vertically filled the middle part of the thin-walled tubes exhibit superior compressive properties and energy absorption behavior compared with the ex-situ ordered aluminum cellular structure horizontally filled the bottom of the thin-walled tubes.
       
  • The compressive response of octet lattice structures with carbon fiber
           composite hollow struts
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Xiao Liu, Vahidreza Alizadeh, Christopher J. HansenAbstractOctet lattice structures were designed with carbon fiber reinforced polymer (CFRP) composite hollow cylindrical struts to improve the specific compressive strength and stiffness of these lightweight structures. A joint connector was designed and manufactured from balanced [0/90] CFRP laminates to assemble the designed octet lattice structures. The compressive modulus and strength of CFRP hollow strut-based lattice structures were measured under quasi-static compression. Two competing failure mechanisms were observed. The fiber fracture of hollow struts dominated the failure of lattice structures with a relative density (ρ-) of 2.17%. In contrast, lattice structures with lower relative densities (ρ-= 1.33% and 0.85%) failed by Euler buckling of the hollow struts. To gain further insight of the compressive behavior of the lattice structures, an analytical model and a series of finite element (FE) models were developed. The predictions showed good agreement with experimental observations of both the compressive properties and failure behaviors. The results demonstrate that CFRP hollow tube-based octet lattice structures exhibited significantly higher relative strength and stiffness than CFRP solid strut-based counterparts. These superior properties of CFRP hollow strut-based octet lattice structure show a strong potential in high performance lightweight load-bearing application.
       
  • Analytical buckling solution of magneto-electro-thermo-elastic cylindrical
           shells under multi-physics fields
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Yiwen Ni, Shengbo Zhu, Jiabin Sun, Zhenzhen Tong, Zhenhuan Zhou, Xinsheng XuAbstractA new analytical buckling solution of a cylindrical shell made of two-phase magneto-electro-thermo-elastic (METE) composites under multi-physical fields is obtained by a Hamiltonian-based approach. Two types of technologically important distribution model are considered: continuous fibers and laminates. Based on the Reissner’s shell theory, the exact solution expanded into symplectic series is rigorously obtained from governing equations under the Hamiltonian description which has four possible forms of explicit expressions. Accurate critical buckling loads and analytical buckling mode shapes for various boundary conditions are obtained. A comprehensive comparison is presented to verify the proposed solution and very good agreement is reported. Effects of geometrical parameters, boundary conditions, cases of eigenfunctions, volume fractions and external magneto-electro-thermal loadings on buckling behaviors of the shell are investigated also.
       
  • Design-oriented approach to determine FRC constitutive law parameters
           considering the size effect
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Eduardo Galeote, Ana Blanco, Albert de la FuenteAbstractTensile strength constitutive laws for fibre reinforced concrete (FRC) are commonly defined through the parameters of flexural tests conducted on standard prismatic specimens. However, there are no specific criteria to determine such parameters using small specimens that could simplify the testing procedure and provide more representative results of slender structural FRC elements. In this line, the influence of size effect becomes an issue particularly relevant during the characterisation stage given that the residual strength decreases while increasing the size of the element. The objective of this document is to propose a methodology to obtain the parameters of the constitutive law using small specimens. For this, FRC residual strength was determined through three-point bending tests on prismatic notched beams of 40x40x160, 100x100x400 and 150x150x600 mm. An analytical model based on sectional analyses aimed at reproducing the flexural strength of FRC was used to assess the results of the alternative methodology to determine the parameters for the constitutive law. The results show that an approach based on the rotation instead of the crack opening as the reference parameter to estimate the stresses for the constitutive law leads to results less influenced by the size effect when designing small elements.
       
  • Computational optimization for porosity-dependent isogeometric analysis of
           functionally graded sandwich nanoplates
    • Abstract: Publication date: Available online 3 February 2020Source: Composite StructuresAuthor(s): P. Phung-Van, A.J.M. Ferreira, Chien H. ThaiAbstractA simply and effectively computational optimization for porosity-dependent isogeometric analysis of functionally graded (FG) sandwich nanoplates is proposed for the first time. Porosity-dependent material properties are defined via the modified power law function. The distribution of ceramic volume fraction is approximated by using the multi-patch B-spline basis functions through the thickness direction. This approach ensures smoothly and continuously vary material properties across each layer, and automatically satisfies the C0-continuity at each layer interfaces. To consider length scale effects, the Eringen’s nonlocal elasticity theory is used to model porous FG sandwich nanoplates. Based on a combination of NURBS formulations and four variables refined plate theory, governing equations of the nanoplates are derived and employed to obtain natural frequencies of the porous FG sandwich nanoplates. The present approximation is easy to satisfy the requirement of at least third order derivatives of basis functions in approximate formulations of nanoplates. To save computational costs, an adaptive hybrid evolutionary firefly algorithm is used. Continuous design variables including the thickness of each layer and the ceramic volume fraction at control points are considered for constraint optimization problems. New results are performed and considered as benchmark results for further studies on the porous FG sandwich nanoplates.
       
  • Ultrasonic Guided Wave Scattering due to Delamination in Curved Composite
           Structures
    • Abstract: Publication date: Available online 3 February 2020Source: Composite StructuresAuthor(s): Rajendra Kumar Munian, D Roy Mahapatra, S GopalakrishnanAbstractWave propagation in a curved composite structure having delamination is simulated using time domain spectral finite element (TSFE) method that enables fast computation with higher-order field interpolation. Curved structures are very common in aerospace, marine and other composite structural components and understanding ways to detect delamination in these curved structures with the help of ultrasonic guided wave simulation is essential. Guided wave interaction with curved region progressively causes mode converted waves, which are present in both reflected as well as transmitted wave packets. The details are poorly understood. The additional wave packets due to interaction cause difficulty in identification of damaged induced responses. Mode conversion and reflection from the curved section reduce the useful signal strength to interrogate any delamination in the curved region. Guided wave interaction with the curved section in an L-shaped structure and a structure with T-joint are studied using TSFE simulation. Simulation results are validated using analytical solutions. Mode conversion and transmission in T-joint is studied using numerical simulation with experimental validation. Signal loss due to mode conversion and reflections at different frequencies is investigated in terms of geometric and wave parameters, which promises to identify the appropriate frequencies and choice of wave mode for monitoring.
       
  • Response of foam concrete-filled aluminum honeycombs subject to
           quasi-static and dynamic compression
    • Abstract: Publication date: Available online 3 February 2020Source: Composite StructuresAuthor(s): Hongyuan Zhou, Xuejian Zhang, Xiaojuan Wang, Yonghui Wang, Tianfei ZhaoAbstractTo prevent premature failure, aluminum honeycombs of the same areal density with and without foam concrete filling subjected to quasi-static and dynamic compression are experimentally tested. The influence of major governing factors including cell size of honeycomb, density of foam concrete, and loading rate on the performance in terms of compressive strength and energy absorption capacity are systematically examined. It is found that without foam concrete filling, the out-of-plane strength and energy absorption capacity of honeycomb of the same areal density increase with decreasing cell size, under both quasi-static and dynamic crushing. With foam concrete filler, the load bearing and energy absorption capacity of the honeycombs increase by 33%-207% compared to those of the corresponding foam concrete and honeycomb added up separately, and increase with increasing foam concrete density and decreasing honeycomb cell size, regardless of being compressed quasi-statically or dynamically.
       
  • Serviceability and ultimate behaviour of GFRP reinforced lightweight
           concrete slabs: experimental test versus code prediction
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): Agnieszka Wiater, Tomasz SiwowskiAbstractThe advantages of GFRP reinforcement and lightweight concrete (LWC) in relation to bridge deck slabs encourage the extension of knowledge regarding the possibilities of combining these two materials and to use the synergy of benefits that can be achieved in the construction and/or rehabilitation of bridges. This paper presents the research aimed to evaluate the static performance of LWC slabs reinforced with GFRP bars for flexure without shear reinforcement. The serviceability and ultimate behaviour were evaluated for the LWC/GFRP slabs in comparison with those made of normal-weight concrete (NWC). Comparison of measured and ACI code predicted behaviour of LWC and NWC slabs is also presented. Generally, the serviceability and ultimate behaviour of LWC slabs under static load was less favourable than their NWC counterparts. Research revealed the considerable differences between the NWC and LWC slabs behaviour as well as between test results and ACI code predictions.
       
  • Strengthening bonding strength in NiTi SMA fiber-reinforced polymer
           composites through acid immersion and Nanosilica coating
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): Yongchao Zhang, Changwen MiAbstractExtensive applications of shape-memory alloy fiber-reinforced polymer composites are limited by the weak bonding conditions between alloy fibers and their surrounding matrix. In this work, we aim to investigate an effective means for elevating the interfacial bonding between nickel-titanium shape-memory alloy fibers and epoxy matrix by the combination of nitric acid immersion and nanosilica particles coating. Three experimental tests were carefully designed and conducted for verifying and validating the proposal. They include the uniaxial tensile test of chemically etched fibers, the pull-out test against a single fiber embedded inside a cylindrical epoxy matrix, and the three-point flexural test on fiber-reinforced polymer composites. Extensive parametric tests were performed in order to both qualify and quantify the effects of chemical etching, nanoparticle coating, and their combination. Experimental tests were followed a comprehensive analysis on both the mechanical behavior and the microscopic and macroscopic morphology of the specimens. Experimental results suggest the possibility of effectively elevating the interfacial bonding strength between nickel-titanium shape-memory alloy and epoxy matrix by the appropriate coupling of acid immersion and nanoparticle coating. Microscopical optimization mechanisms were also proposed and validated in terms of both intergranular and transgranular cracking along fiber/matrix interface subjected to shear loading.
       
  • Experimental and numerical investigations on concrete filled carbon FRP
           tube (CFRP-CFFT) columns manufactured with ultra-high-performance fibre
           reinforced concrete
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): C. Fang, M.S. Mohamed Ali, A.H. SheikhAbstractThis study aims to investigate the structural responses of five concrete filled carbon FRP tube (CFRP-CFFT) columns manufactured with ultra-high-performance fibre reinforced concrete (UHPFRC) under concentric or eccentric loading protocols with eccentricities ranging from 0.067D (depth) to 0.57D (depth). One CFRP-CFFT UHPFRC beam with the same cross-section configuration used for columns was subjected to four-point flexural bending. Furthermore, finite element (FE) analysis incorporating concrete damage plasticity (CDP) model was also conducted to simulate the behaviours of CFRP-CFFT UHPFRC members; the corresponding load-axial displacement and load-lateral deflection relationships were numerically generated to compare with the experimental results. FE simulations exhibit a high correlation compared to experimental results, which further highlights the applicability of FE modelling in predicting the structural response of the CFRP-CFTT UHPFRC members. A load-moment (P-M) interaction envelope was generated from the FE modelling to facilitate the development of a design guideline of CFRP-CFFT UHPFRC columns subjected to axial load with a varying eccentricity.
       
  • Study on Bearing Strength and Failure Mode of a Carbon-Epoxy Composite
           Laminate for Designing Bolted Joint Structures
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): Donghyun Yoon, Sangdeok Kim, Jaehoon Kim, Youngdae DohAbstractA composite single-lap bolted joint was experimentally studied and its bearing behavior was predicted numerically. Prior to performing the experiment, an appropriate e/D ratio of the composite material was determined via double-lap bolted joint tests. Using the obtained e/D ratio, specimens were manufactured, and single-lap composite bolted joint tests were subsequently performed. Various joint tests were conducted with the number of bolt holes, pre-torque, and thickness as experimental variables. The preferred bearing failure mode was observed with the designed e/D ratio and bearing strength increased with increasing tightening torque. The bearing strength was significantly affected by the projected bearing area and exhibited a linearly proportional relation with the joint bearing area. The fracture mechanism was observed using optical microscopy, indicating fiber buckling, breakage, and delamination induced from the initial damage. An energy-based progressive failure analysis (PFA) was implemented to predict the composite bolted joints strengths. The adopted PFA accurately predicted the strength of the bolted joint in range of 12%.
       
  • Radar-absorbing nickel-coated fabric composite for wing-shaped structure
           in the X-band
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): Won-Ho Choi, Byeong-Su Kwak, Yeong-Hoon Noh, Jong-Gwan Yook, Jin-Hwe Kweon, Young-Woo NamAbstractThis study presents a thin radar-absorbing nickel-coated fabric composite through an electroless plating technique for wing-shaped structure to reduce the radar cross section (RCS) in terms of a practical application. The newly proposed absorber with high permittivity of NCF can accomplish high absorption performance on a curved surface at the target frequency. The NCF was fabricated using an electroless plating process, which is suitable for mass production. Utilizing the concept of the change in surface resistance depending on skin depth, the NCF absorption mechanism was discussed. From the interlaminar shear strength (ILSS) test, it was confirmed that the interfacial adhesion properties between the fiber and polymer matrix caused no serious degradation to the mechanical properties and structural integrity. The total thickness of the designed NCF RAS with optimization process for the X-band target is 2.02 mm, which is a very thin thickness compared with previous reported RAS. To demonstrate absorption and RCS reduction on a curved surface, a planar and wingbox with leading edge of NCF RAS were fabricated and measured. Although the planar NCF RAS showed a slightly smaller absorption bandwidth than previous RASs, the proposed absorber demonstrated excellent performance in RCS reduction despite its thin thickness.
       
 
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