Journal Cover Composites Part B : Engineering
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   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1359-8368
   Published by Elsevier Homepage  [3177 journals]
  • Recycled and devulcanized rubber modified epoxy-based composites
           reinforced with nano-magnetic iron oxide, Fe3O4
    • Authors: A.B. Irez; E. Bayraktar; I. Miskioglu
      Pages: 1 - 13
      Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): A.B. Irez, E. Bayraktar, I. Miskioglu
      Rubber modified epoxy based composites were designed by low cost production methods. Basically, clean and recycled materials were used to provide a solution for manufacturing of lightweight, cost efficient composites in industrial applications such as automotive and aeronautical engineering. In the present study four different compositions have been developed and characterized for their potential usage as structural materials. The matrix was prepared by treatment of epoxy with 10% recycled rubber. Nano-magnetic iron oxide, Fe3O4, was added to the matrix as reinforcement elements in different percentages. Nickel and aluminium were also add as auxiliary additional elements. Measurements of magnetic permeability and dielectrically properties have been carried out for electronic devise applications basically in aeronautical engineering. Dynamic Scanning Calorimeter (DSC) and Dynamic Mechanical Analysis (DMA) were carried out to determine thermo-mechanical properties. Static tests have been carried out by 3-point bending (3PB) tests for mechanical characterization. Furthermore, creep and wear behaviour of these compositions were evaluated by means of nanoindentation tests to analyze time dependent behaviour of these composites. Macro scratch tests were made in very high cycle test conditions for their measurements in long time resistance. Microstructural and fracture surface analyses have been carried out on the scanning electron microscopy (SEM). All of the experiments; scanning electron microscopy, nanoindentation, static (3PB), test results expose a combined effect of toughening mechanisms high strength and ductile, lightweight and low-cost composites based on the rubber modified epoxy composites reinforced with nano magnetic iron oxide and auxiliary fine nickel and nano aluminium powders.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.047
      Issue No: Vol. 148 (2018)
       
  • Experimental characterization of in-plane behaviour of old masonry walls
           strengthened through the addition of CFRP reinforced render
    • Authors: João Guerreiro; Jorge Proença; João Gomes Ferreira; António Gago
      Pages: 14 - 26
      Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): João Guerreiro, Jorge Proença, João Gomes Ferreira, António Gago
      This article presents the results of an extensive experimental programme investigating the structural performance for in-plane loads of old masonry walls strengthened using a specific technique that consisted of applying a CFRP mesh embedded within a shotcreted render. In this article the expression old masonry refers to rubble stone masonry with lime-based mortar but it is believed that the strengthening technique can also be applied to other types of old masonry (e.g. solid or almost solid clay or concrete brick masonry). The reinforcing composite material, called CFRP reinforced render (CFRP-RR), is characterized by the use of a CFRP mesh and the shotcreted pre-mixed mortar, lime-based, specific for the rehabilitation of old masonry load bearing walls. This material is applied to one or both faces of the masonry walls, thus improving both the in-plane and out-of-plane behaviour for horizontal loads (the latter benefits are described in Ref. [1]). The experimental programme consisted of the in-plane testing of full-scale physical models of walls, herewith called specimens. These were subjected to reversed cyclic horizontal loads (simulating earthquake loads) with constant vertical loads (simulating gravity loads). The comparison between the experimental results of the non-reinforced with the reinforced (strengthened) specimens allowed the quantification of the inherent benefits in terms of structural performance under earthquake actions.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.045
      Issue No: Vol. 148 (2018)
       
  • Experimental and numerical analysis of dynamic compressive response of
           Nomex honeycombs
    • Authors: Yuwu Zhang; Tao Liu; Walid Tizani
      Pages: 27 - 39
      Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Yuwu Zhang, Tao Liu, Walid Tizani
      Lightweight phenolic resin-impregnated aramid paper honeycombs, commercially known as Nomex® honeycombs, are promising cores for sandwich structures in aerospace applications due to their high ratios of stiffness and strength to density. The out-of-plane compressive properties of the Nomex honeycombs have been widely investigated under quasi-static and low strain rates (up to 300 s−1). There is a need to understand the behaviour of this structure under higher strain rate compression. This will widen the applicability of these structures to more areas such as debris impact and other impacts which induce high strain rates. This paper reports the out-of-plane compressive responses of Nomex honeycombs subject to quasi-static loading and high strain rate dynamic loading up to 1500 s−1. The work involves experimental measurements and numerical modelling and validation. The compressive responses of the honeycombs were measured using a sensitive magnesium alloy Kolsky bar setup with front and back face impacts. The failure modes of the Nomex honeycombs were identified to be different under quasi-static and dynamic compressions. Under quasi-static compression, the honeycombs failed with local phenolic resin fracture after the elastic buckling of the honeycomb walls. For the dynamic compression, the honeycombs failed with the stubbing of cell walls at the ends of specimens. A finite element (FE) numerical model was devised and validated with the experimental data. The FE model considered the strain rate effect of phenolic resin material. The model predictions were in good agreement with the experimental measurements and facilitated interpreting the out-of-plane compressive response of the Nomex honeycombs. It was shown that there was a linear compressive strength enhancement up to 30% from quasi-static to strain rate of 1500 s−1. The strength enhancement was governed by two mechanisms: the strain rate effect of the phenolic resin and inertial stabilization of the honeycomb unit cell walls, where 61%–74% of the enhancement was contributed by the inertial stabilization of the unit cell walls. In addition, it was shown that the impact method and initial imperfections had negligible effect on the compressive response of the Nomex honeycombs.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.025
      Issue No: Vol. 148 (2018)
       
  • Experimental design of the bearing performances of flax fiber reinforced
           epoxy composites by a failure map
    • Authors: V. Fiore; L. Calabrese; T. Scalici; P. Bruzzaniti; A. Valenza
      Pages: 40 - 48
      Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): V. Fiore, L. Calabrese, T. Scalici, P. Bruzzaniti, A. Valenza
      This paper represents the first effort aimed to the investigation of the pin/hole contact stress and failure mechanisms of epoxy composites reinforced with woven flax fabrics, underwent to tensile bearing tests. In particular, the maximum loads and failure modes are evaluated at varying the laminate geometrical configuration. In order to optimize the use of polymer composites reinforced with flax fibers in structural applications, an experimental failure map, identifying main failure modes of mechanically fastened joints, is obtained as function of hole diameter, distance of the hole from the free edge of the laminate and laminate width. Moreover, a theoretical approach based on the observation that a particular fracture mechanism occurs when its threshold fracture load is lower than the loads of the other competitive ones, is proposed. Main goal of this paper is to give a simple experimental methodology to support the joining design of natural composite laminates reinforced with woven flax fabrics.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.044
      Issue No: Vol. 148 (2018)
       
  • Two-step hierarchical micromechanics model of partially saturated porous
           composites doped with ellipsoidal particles with interface effects
    • Authors: Enrique García-Macías; Rafael Castro-Triguero; Filippo Ubertini
      Pages: 49 - 60
      Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Enrique García-Macías, Rafael Castro-Triguero, Filippo Ubertini
      Recent advances in the manufacture of micro- and nano-composites have made it possible to produce new multifunctional materials. However, the development of theoretical models that assist their design still remains an open research issue. This paper presents a two-step hierarchical micromechanics approach for the mechanical homogenization of particle-reinforced porous composites, including particle/matrix interfacial bonding and porosity saturation effects. Firstly, the particle-reinforced matrix is homogenized by means of a double-inclusion approach. The interfacial bonding effect is accounted for by both compliant and hard interphases surrounding the particles. Secondly, another homogenization step is conducted by considering the particle-reinforced composite as a homogeneous matrix and voids as embedded inclusions. Pores saturation is also taken into account by means of homogeneous equivalent pores. Comparative analyses against experimental data are presented to demonstrate the effectiveness of the present approach, followed by detailed parametric analyses to illustrate the influence of the major micromechanical variables, including interphase thickness and stiffness, filler aspect ratio, porosity and saturation degree.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.037
      Issue No: Vol. 148 (2018)
       
  • Interfacial properties and permeability of three patterned glass
           fiber/epoxy composites by VARTM
    • Authors: Jong-Hyun Kim; Dong-Jun Kwon; Pyeong-Su Shin; Yeong-Min Beak; Ha-Seung Park; K. Lawrence DeVries; Joung-Man Park
      Pages: 61 - 67
      Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Jong-Hyun Kim, Dong-Jun Kwon, Pyeong-Su Shin, Yeong-Min Beak, Ha-Seung Park, K. Lawrence DeVries, Joung-Man Park
      The interfacial properties for three different glass fiber (GF) mats were evaluated by examining permeability through combining the results of wettability and interlaminar shear strength (ILSS) testing. Three types of GF mats were studied: (1) unidirectional (UD), (2) bidirectional (BD, 0/90°), and (3) randomly-chopped (RC). Single fiber tensile tests were used to compare the fibers in the 3 mats, forty single fibers were extracted from each mat. FE-SEM was used to study damages on the GF in each of the mat types. Fibers from the UD mat exhibited the best mechanical properties and less damage was observed with the FE-SEM. Vacuum assisted resin transfer molding (VARTM) was used to manufacture glass fiber reinforced composite (GFRC) specimens, with the three different mat types. The permeability of the different GF mats was measured, during manufacture of the GFRC, and related to the spreading of the epoxy resins in the GF mats. Short beam tests were performed as a measure of interfacial properties and related to the observed permeability and spreading. GFRC manufactured with UD GF mat exhibited the best interfacial and mechanical properties and displayed the least physical damage while GFRC manufactured with BD GF mat had the poorest interfacial and mechanical properties while exhibiting the most visible damage. The UD GF mat also displayed the smallest change in contact angle and the best permeability. The longitudinal fiber pattern in the UD GF mat apparently promotes capillary effects leading to an increase in wetting rate. This study demonstrates that GF mat pattern affect the interfacial and mechanical properties as well as matt permeability and resin spreading.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.041
      Issue No: Vol. 148 (2018)
       
  • Study on mechanical and ballistic performances of boron carbide reinforced
           Al 6061 aluminum alloy produced by powder metallurgy
    • Authors: Halil Karakoç; Şener Karabulut; Ramazan Çıtak
      Pages: 68 - 80
      Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Halil Karakoç, Şener Karabulut, Ramazan Çıtak
      In this study, the density, hardness, impact toughness, transverse rupture strength, tensile strength and ballistic resistance of Al 6061 alloy reinforced with boron carbide (B4C) powders were studied to elucidate the influence of the ceramic content and production process on the physical and ballistic properties of the resulting composites. Powder-metallurgy and hot-extrusion techniques were used to manufacture the Al 6061-based metal matrix composites reinforced with 5 wt%, 10 wt%, 15 wt% and 20 wt% B4C. The hot-rolling process was performed on a group of specimens to examine the effect on the mechanical and ballistic behaviors. The results revealed that a uniform particle distribution was achieved in a matrix structure and higher relative density values were measured in all specimens. The hardness, transverse rupture strength and tensile strength were improved and impact toughness was decreased with increasing volume fraction of B4C particle reinforcement for both hot-extruded and hot-rolled specimens. The highest flexural strength was measured in hot-extruded specimens and the maximum tensile strength was obtained in hot-rolled composites. The deformation tests showed that transgranular cracking occurred on B4C particles and particles were retained in the matrix. The hot-extruded, hot-rolled and laminated with two hot-rolled specimens were subjected to a ballistic test with a 7.62 mm × 51 mm M80 projectile for Type III and the ballistic resistance investigated by analyzing the hole surface in the armor. The hot-rolled and hot-extruded specimens were perforated in ballistic tests and exhibited ductile behavior with the petal failure mechanism. The two-layer hot-rolled specimens successfully absorbed the impact energy of the bullet with the lowest depth of penetration and smooth bulging.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.043
      Issue No: Vol. 148 (2018)
       
  • Cryogenic machining of carbon fiber reinforced plastic (CFRP) composites
           and the effects of cryogenic treatment on tensile properties: A
           comparative study
    • Authors: Sezer Morkavuk; Uğur Köklü; Mehmet Bağcı; Lokman Gemi
      Pages: 1 - 11
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Sezer Morkavuk, Uğur Köklü, Mehmet Bağcı, Lokman Gemi
      Carbon fiber reinforced plastics (CFRPs) are prone to damage locally during machining due to the applied cutting forced and generated heat. Cryogenic machining can reduce the heat generated damages of CFRPs by utilizing cryogenic liquids instead of conventional cutting fluids. The goal of this study is to investigate milling performance of CFRPs in cryogenic medium. For this, a new cryogenic machining approach was adopted to slot milling of CFRPs by submerging the workpiece within a cryogenic liquid. The CFRPs were fabricated via vacuum assisted resin transfer method by using woven carbon fiber fabric as a reinforcement and epoxy as a matrix. Machining performance was evaluated based on the resulting cutting force, delamination factor, surface roughness, and surface damage. Moreover, the influences of cryogenic coolant on the tensile properties, fracture surface microstructure, and machined surface of the CFRP laminates were analyzed with scanning electron microscopy (SEM). SEM analysis revealed that combination of different damage modes such as debonding, micro matrix crack, fiber pull out, and bundle pull out, delamination, and fiber breakage were observed. The results showed that cryogenic machining approach provided less damage formation on the machined surface, reduced delamination factor and surface roughness but increased resulting cutting force during machining of the CFRPs. On the other hand, there was a slight improvement (about 3%) of the tensile properties for the CFRPs exposed to cryogenic coolant due to matrix hardening and increasing in the fiber strength and shear strength.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.024
      Issue No: Vol. 147 (2018)
       
  • Morphological, rheological and electrical properties of composites filled
           with carbon nanotubes functionalized with 1-pyrenebutyric acid
    • Authors: L. Guadagno; M. Raimondo; L. Vertuccio; C. Naddeo; G. Barra; P. Longo; P. Lamberti; G. Spinelli; M.R. Nobile
      Pages: 12 - 21
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): L. Guadagno, M. Raimondo, L. Vertuccio, C. Naddeo, G. Barra, P. Longo, P. Lamberti, G. Spinelli, M.R. Nobile
      Non-covalent functionalization of Multi Wall Carbon Nanotubes (MWCNTs) could provide a solution for preserving their electronic structure facilitating the nanocomposite process preparation. Functionalization of MWCNTs by π-stacking interaction between nanofiller and a pyrene derivative has been explored. The rheological properties of filled epoxy resins highlight very interesting benefits from this kind of functionalization. Besides its peculiar capability for preventing agglomeration in the nanofiller dispersion step, it also efficiently contributes to a decrease in the viscosity of the nanocomposites; hence contrasting one of the most relevant drawback related to the manufacturing processes of the nanocomposites at MWCNTs loading rates beyond the Electrical Percolation Threshold (EPT). Because no damage of MWCNTs occurs, sp2 hybridization of carbon atoms is preserved together with the π-electron delocalization typical of polynuclear aromatic rings. Consequently, no deterioration in the electrical properties are detected; the measured EPT values are typical of nanocomposites containing embedded unfunctionalized MWCNTs (lower than 0.28 wt%), whereas for the electrical conductivity beyond the EPT, an enhancement is observed.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.036
      Issue No: Vol. 147 (2018)
       
  • Damage characterization of stiffened glass-epoxy laminates under tensile
           loading with acoustic emission monitoring
    • Authors: V. Arumugam; K. Saravanakumar; C. Santulli
      Pages: 22 - 32
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): V. Arumugam, K. Saravanakumar, C. Santulli
      The design of composite components in the aerospace industry often includes structural discontinuities, such as cutouts, for functional requirements like ventilation, tunnel passage, maintenance and repair. The presence of cutout holes leads to complicated stress concentrations with a substantial reduction in structural stability and strength of the resulting composites. It is known that reinforcing with additional material at the cutout zones can extend the damage tolerance of a structure, therefore maintaining structural integrity and load carrying capacity. This study focuses on the experimental investigation of the tensile behavior and failure characteristics of stiffened glass/epoxy composite laminates, with cutouts, under acoustic emission monitoring. The progressive failure mechanisms of laminates with cutouts and the potential benefits of additionally dropped reinforcements are evaluated under tensile loading. The additional reinforcements were provided in either a step-like or as a simultaneous drop-off sequence between adjacent continuous plies. Results showed that adding ply drop reinforcements at the location of the cutout hole improves the stiffness, strength, and also prolongs the life of the composite laminates. It is also observed that step-like ply drop arrangements performed more effectively than simultaneously dropped configurations. The location and extent of damage identified by microscopic images correlated well with the acoustic emission results.

      PubDate: 2018-04-15T23:38:48Z
      DOI: 10.1016/j.compositesb.2018.04.031
      Issue No: Vol. 147 (2018)
       
  • Effect of sonication on the mechanical response of graphene
           nanoplatelets/glass fabric/epoxy laminated nanocomposites
    • Authors: G.V. Seretis; I.D. Theodorakopoulos; D.E. Manolakos; C.G. Provatidis
      Pages: 33 - 41
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): G.V. Seretis, I.D. Theodorakopoulos, D.E. Manolakos, C.G. Provatidis
      This study focuses on the effect of sonication process time on the morphological characteristics of the graphene nanoplatelets (GNPs) and the mechanical performance of the produced GNPs/glass fabric/epoxy nanocomposites. Specifically, three different times, 20, 40 and 60 min, were tested. The rest of the sonication process parameters were kept constant, i.e. 100 W and 28 kHz. Both a scanning electron microscope (SEM) and an atomic force microscope (AFM) were used for the morphological investigation of the GNPs. Based on the microstructural investigations, the effect of the sonication time on the mechanical performance was explained and discussed.

      PubDate: 2018-04-15T23:38:48Z
      DOI: 10.1016/j.compositesb.2018.04.034
      Issue No: Vol. 147 (2018)
       
  • Smart coatings of epoxy based CNTs designed to meet practical expectations
           in aeronautics
    • Authors: L. Vertuccio; L. Guadagno; G. Spinelli; P. Lamberti; M. Zarrelli; S. Russo; G. Iannuzzo
      Pages: 42 - 46
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): L. Vertuccio, L. Guadagno, G. Spinelli, P. Lamberti, M. Zarrelli, S. Russo, G. Iannuzzo
      A smart coating exhibiting self-diagnostic capability is designed to meet industrial requirements in aeronautics. The coating made of epoxy-based carbon nanotubes (CNTs) has been applied on industrial Carbon Fiber Reinforced Plastics (CFRPs) currently employed in aeronautics. The correlations between mechanical strain and electrical properties of coated CFRPs highlights the feasibility in manufacturing CFRPs having integrated high sensitivity in providing an effective real-time structural health monitoring. The reliability of the developed CFRPs, in the normal operational temperature range of aircrafts, opens new perspectives in the field of self-responsive structures in aeronautics. Self-responsive panels can simultaneously act as sensor and structural element.

      PubDate: 2018-04-15T23:38:48Z
      DOI: 10.1016/j.compositesb.2018.04.027
      Issue No: Vol. 147 (2018)
       
  • Effect of consolidation pressure on the impact behavior of UHMWPE
           composites
    • Authors: Torsten R. Lässig; Michael May; Ulrich Heisserer; Werner Riedel; Frank Bagusat; Harm van der Werff; Stefan J. Hiermaier
      Pages: 47 - 55
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Torsten R. Lässig, Michael May, Ulrich Heisserer, Werner Riedel, Frank Bagusat, Harm van der Werff, Stefan J. Hiermaier
      For the first time, the influence of the manufacturing process on the dynamic performance of ultra-high molecular weight polyethylene (UHMWPE, Dyneema® HB26) composites is investigated. The material is significantly influenced by the hot-pressing parameters temperature and pressure. The ballistic resistance and shock wave behavior was characterized for the UHMWPE composite consolidated with three different pressures. In the case of UHMWPE composites, higher consolidation pressures result in a better ballistic performance. The shock wave behavior converges to high-density polyethylene (HDPE). Based on these observations, an analytical approach is proposed describing the equation of state as a function of consolidation pressure.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.030
      Issue No: Vol. 147 (2018)
       
  • Experimental investigation of pre-damaged thin-walled channel section
           column subjected to compression
    • Authors: A. Gliszczynski; T. Kubiak; L. Borkowski
      Pages: 56 - 68
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): A. Gliszczynski, T. Kubiak, L. Borkowski
      Experimental investigations of channel-section profiles subjected to compression after low-velocity impacts (20 J) leading to global failure are presented. The columns under discussion were made of an eight-layer GFRP laminate with quasi-isotropic, quasi-orthotropic and angle ply arrangements of layers. The profiles were impacted in mid-width of the web or mid-width of the flange in various locations along the profile length. An influence of the impact position and the layer arrangement on buckling and failure phenomena, post-buckling behaviour for impacted and non-impacted columns was thoroughly examined and described. It was found that the local degradation introduced by low-velocity impacts did not affect the global behaviour of the analysed structures to a considerable extent. Moreover, it was noted that the failure mechanism was initiated in the impact location in none of the cases analysed. Additionally, it was stated that a number of fracture points did not have any significant impact on the capacity reduction.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.022
      Issue No: Vol. 147 (2018)
       
  • Experimental investigation of the mechanical robustness of a commercial
           module and membrane-printed functional layers for flexible organic solar
           cells
    • Authors: Zhengyu Fan; Michele De Bastiani; Michele Garbugli; Carol Monticelli; Alessandra Zanelli; Mario Caironi
      Pages: 69 - 75
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Zhengyu Fan, Michele De Bastiani, Michele Garbugli, Carol Monticelli, Alessandra Zanelli, Mario Caironi
      A coupled mechanical and electrical characterization method to monitor the correlation of organic photovoltaic (OPV) electrode resistance and cell performance upon tensile strain and to verify the cause of deterioration and the effect of OPV performance under tensile stress has been developed. Both a commercial OPV module and ethylene tetrafluoroethylene (ETFE) membrane-printed OPV electrode layers have been tested by applying the method. The encapsulation layer strength has been found to be the mechanical bottleneck of the tested commercial OPV module. The decrease in the transparent electrode conductance has been found to be responsible for cell degradation upon tensile strain, with the threshold tensile strain at approximately 2%. A test results comparison between ETFE- and polyethylene terephthalate (PET)-printed OPV layers demonstrated that ETFE-printed electrodes are less brittle and sensitive to tensile strain owing to the network pattern response of ETFE-printed electrodes. In addition, the adoption of Ag/poly(3,4-ethylenedioxythiophene) (PEDOT) layering can improve the tensile strain threshold to almost double to maintaining 80% of the initial normalized layer conductance through the advantage of its “bridging effect”. Collectively, our results provide valuable information and illustrate a promising future for architectural membrane printed OPV.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.007
      Issue No: Vol. 147 (2018)
       
  • A comparative study of mechanical, thermal and electrical properties of
           graphene-, graphene oxide- and reduced graphene oxide-doped
           microfibrillated cellulose nanocomposites
    • Authors: Josphat Phiri; Leena-Sisko Johansson; Patrick Gane; Thad Maloney
      Pages: 104 - 113
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Josphat Phiri, Leena-Sisko Johansson, Patrick Gane, Thad Maloney
      Micro-nanofibrillated cellulose (MFC/NFC) and graphene-based composites are interesting materials due to their complementary functional properties, opening up potential in a variety of applications. Graphene, graphene oxide (GO) and reduced graphene oxide (RGO) were used in this comparative study as reinforcement functional fillers for the fabrication of multifunctional MFC nanocomposites using a simple aqueous dispersion based mixing method. The MFC composites showed different properties depending on the type of filler used. Graphene was seen to agglomerate and was poorly dispersed in the MFC matrix, whilst GO and RGO were homogeneously dispersed due to the presence of functional groups that promoted a strong interfacial molecular interaction between the filler and the MFC matrix. At 0.6 wt% filler loading, the tensile strength for MFC/GO and MFC/RGO increased by 17 % and 22 %, respectively, whilst the Young's modulus increased from 18 GPa to 21 GPa and 25 GPa, respectively. Compared to the neat MFC, addition of 5 wt% of graphene enhanced the thermal stability by 5 % and whilst with the addition of GO and RGO stability increased by 2 and 3 %, respectively. Graphene/MFC and RGO/MFC showed a high electrical conductivity of 1.7 S m-1 and 0.5 S m-1, respectively while the GO reinforced composites were insulators.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.018
      Issue No: Vol. 147 (2018)
       
  • Determination of adhesion strength of pre-bond contaminated
           composite-to-metal bonded joints by centrifuge tests
    • Authors: M. Hoffmann; K. Tserpes; E. Moutsompegka; M. Schlag; K. Brune
      Pages: 114 - 121
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): M. Hoffmann, K. Tserpes, E. Moutsompegka, M. Schlag, K. Brune
      In the present work, the effect of pre-bond contamination scenarios related to production and repair processes on the adhesion strength of composite-to-metal joints is investigated by means of the novel centrifuge testing technology. The composite substrates have been subjected to contamination with release agent, moisture, fingerprint, thermal degradation and de-icing fluid before being bonded on the metallic stamp. Different contamination levels have been considered for each scenario. The standard deviation of adhesion strength values differs for each sample category and in some cases, is relatively high. The experimental results show a considerable decrease of adhesion strength for all contamination scenarios. The evaluation of the adhesion strength values is assisted by the characterization of the failure modes. In most cases, the transition between the failure modes explains the variation of adhesion strength. By taking into advantage the simplicity of the experimental process, numerous tests have been conducted within a very short time. Based on the practicality of the experimental process and the validity of the findings, it can be concluded that the centrifuge testing technology can be potentially used as a reliable testing method for the characterization of bonded joints.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.014
      Issue No: Vol. 147 (2018)
       
  • Effect of the exposition temperature on the behaviour of partially
           pyrolysed hybrid basalt fibre composites
    • Authors: Zdeněk Chlup; Martin Černý; Adam Strachota; Hynek Hadraba; Petr Kácha; Martina Halasová
      Pages: 122 - 127
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Zdeněk Chlup, Martin Černý, Adam Strachota, Hynek Hadraba, Petr Kácha, Martina Halasová
      Composites utilising long fibres as reinforcement are the most effective from the point of view of the toughening effect. A brittle matrix reinforced by brittle fibres was investigated in this work. Polysiloxane resin was used as matrix precursor in the studied composite, while continuous basalt fibres served as reinforcement. An optimised pyrolysis process conducted at 650 °C under nitrogen atmosphere turned the polymeric precursor into the so-called hybrid matrix consisting of nano-domains of pyrolytic SiOC glass and of non-transformed polysiloxane polymer. The pyrolysis temperature of 650 °C was found to be optimal, resulting in the fracture toughness attacking the level of 20 MPa m1/2 and the strength reaching the value of 1 GPa. The main aim of this paper is to investigate microstructural changes occurring during long-term (1000 h = 41.7 days) exposition to an oxidative air atmosphere at temperatures from 250 °C to 600 °C and to describe the effect on the mechanical properties of the studied hybrid-matrix composite. The increasing exposition temperature leads to a significant embrittlement of the composite, while the elastic properties (modulus) remain unchanged. Chemical or microstructural changes in the basalt fibres were not detected after the long-term exposition to the tested high temperatures. Nevertheless, fibre embrittlement can be estimated from the tests. Both matrix and fibre-matrix interface were found to suffer from the applied exposition. Distinct changes in chemical composition as well as in microstructure were observed for the matrix. Hence, the observed embrittlement of the composite can be ascribed partly to the changes in the hybrid matrix and the fibre-matrix interface, and partially to fibre embrittlement.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.021
      Issue No: Vol. 147 (2018)
       
  • Depth determination of defects in CFRP-structures using lock-in
           thermography
    • Authors: Sarah Ekanayake; Sumit Gurram; Robert H. Schmitt
      Pages: 128 - 134
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Sarah Ekanayake, Sumit Gurram, Robert H. Schmitt
      Due to the increasing application of CFRP in mass application, an economic repair process gains importance. As the typical repair process starts with the defect detection, the accuracy of the measurement system is a limiting factor of the repair process. Lock-in thermography is a promising approach for non-destructive defect detection. Since the phase images contain a superposition of depth information, the determination of the defects' depth is a challenge. Based on the complex wave field, this paper introduces a method to determine the thermal properties and the defects' depth in CFRP structures using lock-in thermography.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.032
      Issue No: Vol. 147 (2018)
       
  • Design of curved composite panels for optimal dynamic response using
           lamination parameters
    • Authors: Gokhan Serhat; Ipek Basdogan
      Pages: 135 - 146
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Gokhan Serhat, Ipek Basdogan
      In this paper, dynamic response of composite panels is investigated using lamination parameters as design variables. Finite element analyses are performed to observe the individual and combined effects of different panel aspect ratios, curvatures and boundary conditions on the dynamic responses. Fundamental frequency contours for curved panels are obtained in lamination parameters domain and optimal points yielding maximum values are found. Subsequently, forced dynamic analyses are carried out to calculate equivalent radiated power (ERP) for the panels under harmonic pressure excitation. ERP contours at the maximum fundamental frequency are presented. Optimal lamination parameters providing minimum ERP are determined for different excitation frequencies and their effective frequency bands are shown. The relationship between the designs optimized for maximum fundamental frequency and minimum ERP responses is investigated to study the effectiveness of the frequency maximization technique. The results demonstrate the potential of using lamination parameters technique in the design of curved composite panels for optimal dynamic response and provide valuable insight on the effect of various design parameters.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.033
      Issue No: Vol. 147 (2018)
       
  • A heat treatable TiB2/Al-3.5Cu-1.5Mg-1Si composite fabricated by selective
           laser melting: Microstructure, heat treatment and mechanical properties
    • Authors: P. Wang; C. Gammer; F. Brenne; T. Niendorf; J. Eckert; S. Scudino
      Pages: 162 - 168
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): P. Wang, C. Gammer, F. Brenne, T. Niendorf, J. Eckert, S. Scudino
      A heat treatable TiB2/Al-3.5Cu-1.5Mg-1Si composite was successfully fabricated by selective laser melting (SLM). The results show that the Q phase forms in the matrix of the as-fabricated TiB2/Al-3.5Cu-1.5Mg-1Si composite. After T6 heat treatment, the Q phase disappears and the AlxMny, Mg2Si and Al2Cu(Mg) phases are formed. The same results can be observed before and after heat treatment in the unreinforced Al-Cu-Mg-Si alloy. EBSD and TEM analyses indicate that the addition of the TiB2 particles results in a remarkable grain refinement, leading to enhanced strength of the TiB2/Al-Cu-Mg-Si composite in comparison to the unreinforced Al-Cu-Mg-Si alloy in both the as-fabricated and heat-treated conditions. Both grain refinement and Orowan strengthening contribute to the high strength of the heat treated TiB2/Al-Cu-Mg-Si composite.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.026
      Issue No: Vol. 147 (2018)
       
  • Free vibration of FG-CNT reinforced composite skew cylindrical shells
           using the Chebyshev-Ritz formulation
    • Authors: Yaser Kiani; Rossana Dimitri; Francesco Tornabene
      Pages: 169 - 177
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Yaser Kiani, Rossana Dimitri, Francesco Tornabene
      In the present research, the free vibration characteristics of a skew cylindrical panel made of functionally graded carbon nanotube reinforced composites (FG-CNTRCs) is investigated. A dual distribution of CNTs is considered across the panel thickness, namely a uniform and a nonuniform distribution. A refined rule of mixtures approach is applied to estimate the mechanical properties of the composite body, by means of the introduction of some efficiency parameters. A first order shear deformation shell theory (FSDT) is also combined with the Donnell's kinematic assumptions to determine the basic governing equations of the problem for thin-to-moderately thick shells. The governing equations are here referred to an oblique coordinate system, in order to handle any kind of boundary conditions. With the aid of the Ritz method, a system of homogeneous equations governs the eigenvalue problem, whose shape functions are built on Chebyshev polynomials. This system allows to compute the natural frequencies of the shell. A comparative evaluation of the formulation is performed to demonstrate its accuracy and efficiency. Further parametric studies are aimed at exploring the sensitivity of the response to some reinforcement parameters, as the volume fraction or the distribution of CNTs within the matrix.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.028
      Issue No: Vol. 147 (2018)
       
  • On the design of shear-strengthened RC members through the use of textile
           reinforced mortar overlays
    • Authors: Zoi C. Tetta; Thanasis C. Triantafillou; Dionysios A. Bournas
      Pages: 178 - 196
      Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Zoi C. Tetta, Thanasis C. Triantafillou, Dionysios A. Bournas
      Textile reinforced mortar (TRM) is a promising alternative to the FRP retrofitting solution for shear strengthening of reinforced concrete (RC) beams, based on the experimental results presented so far in the literature. Thus, the development of reliable and accurate design models for shear strengthening of concrete members with TRM is required for enabling their wider use in real applications. The available experimental data in the literature are limited and in most cases, a detailed description of the failure modes observed in the TRM jackets and information related to the characteristics of the textile material and the mortar strength are missing, complicating the development of design guidelines. In this paper, a design model to calculate the contribution of the TRM jacket to the total shear resistance was developed using all the well reported available data that were grouped based on the observed failure modes. Specifically, local damage of the jacket including slippage of the fibres through the mortar constitutes a recurring failure mode in concrete beams strengthened in shear with TRM jackets, apart from debonding of the jacket from the concrete substrate including peeling-off of the concrete cover or fracture of TRM jacketing that are also observed in case of fibre reinforced polymer (FRP) jacketing. The key parameters affecting each failure mode were defined and design formulations to calculate the contribution of the TRM jacket to the total shear resistance of RC beams for each failure mode were suggested, whereas a criterion indicating when each failure mode is possible to be observed was also set for using the proper formulation for each TRM system.

      PubDate: 2018-04-30T14:58:19Z
      DOI: 10.1016/j.compositesb.2018.04.008
      Issue No: Vol. 147 (2018)
       
  • Thermo-mechanical performances of polypropylene biocomposites based on
           untreated, treated and compatibilized spent coffee grounds
    • Abstract: Publication date: 15 September 2018
      Source:Composites Part B: Engineering, Volume 149
      Author(s): Hamid Essabir, Marya Raji, Sana Ait Laaziz, Denis Rodrique, Rachid Bouhfid, Abou el kacem Qaiss
      In this work, biocomposites were produced by compounding polypropylene (PP) with spent coffee grounds (SCG) obtained after soluble coffee preparation. The samples were prepared by extrusion compounding and injection molding using different SCG contents (0, 5, 10, 15 and 20wt.) in order to investigate the effect of particle loading on the thermal, rheological and mechanical properties. Then, the effect of bleaching treatments and the use of compatibilizers (silane and styrene-ethylene-butene-styrene-graft-maleic anhydride) on the biocomposites properties at 15 wt% was examined. The results showed that good SCG dispersion and distribution into PP was achieved and that bleaching led to better interfacial interaction, which was further increased by using a coupling agent. As a result, the tensile and torsion properties were increased.

      PubDate: 2018-05-17T16:03:54Z
       
  • Experimental study on CFRP-strengthened steel beams
    • Abstract: Publication date: 15 September 2018
      Source:Composites Part B: Engineering, Volume 149
      Author(s): Tomasz W. Siwowski, Paulina Siwowska
      Recently, as a viable alternative to strengthening or repairing steel bridges with welded or bolted plates, bonded CFRP plates have been used. The main goal of the presented study is to compare the flexural behaviour of steel beams strengthened with the CFRP plates. The research has evaluated two strengthening schemes: adhesive-bonded passive plates and adhesive-bonded prestressed or active plates. The ductility and yield/ultimate carrying capacity of steel beams as well as the effectiveness of strengthening have been established in each case. The failure modes of the strengthened beams comprised the CFRP plate debonding or plate rupture, depending on the strengthening system (passive or active) and some system parameters, as the CFRP modulus of elasticity, end plate anchoring and plate prestressing level. The influence of these parameters on the strengthening effectiveness has been also discussed.

      PubDate: 2018-05-17T16:03:54Z
       
  • Single and repeated impact behaviors of bio-sandwich structures consisting
           of thermoplastic face sheets and different balsa core thicknesses
    • Abstract: Publication date: 15 September 2018
      Source:Composites Part B: Engineering, Volume 149
      Author(s): Okan Ozdemir, Nahit Oztoprak, Halis Kandas
      This paper aims to investigate the single and repeated impact behaviors of bio-sandwich structures consisting of E-glass fiber – reinforced thermoplastic face sheets and balsa cores. Low velocity impact tests were performed using a drop-weight impact machine under a hemispherical impactor. Preliminary single low velocity impact loadings were applied to the bio-sandwich composites with different core thicknesses (namely 15 and 25 mm) so as to obtain the energy limits which were ranged from fully elastic level (10 J) to perforation energy level (80 J). Impact behaviors and damage mechanisms which occurred at both face sheets and internal parts of the balsa core were elucidated through the energy profile diagrams and force – deformation (F-D) curves under low velocity single impact loadings. Besides, low velocity repeated impact tests of the bio-sandwich structures were performed with the same impact energy levels. Repetitive impact behaviors were also investigated with F-D curves at some specific repeated impact numbers. Impact failures which occurred in the upside and bottom of composite structures were detected with digital camera. According to the experimental findings, it was concluded that the total number of impact loads under impact energy level of 10 J until perforation were 38 for the sandwich structures with 15 mm balsa core thickness while it was 98 for the sandwich structures with 25 mm balsa core thickness. Based upon the test results, the number of impacts for perforation (N r ) under smaller impact energies without testing was easily predicted with the derived equation in the form of E i = a N r b , where E i represents the impact energy while a and b are the constants.

      PubDate: 2018-05-17T16:03:54Z
       
  • Hybrid bio-composites reinforced with sisal-glass fibres and Portland
           cement particles: A statistical approach
    • Abstract: Publication date: 15 September 2018
      Source:Composites Part B: Engineering, Volume 149
      Author(s): Sergio Luiz Moni Ribeiro Filho, Pablo Resende Oliveira, Luciano Machado Gomes Vieira, Tulio Hallak Panzera, Rodrigo Teixeira Santos Freire, Fabrizio Scarpa
      The hybrid configuration of bio-reinforced composites has established a new extended boundary for the development of pro-ecological technologies due to light weight, moderate specific strength, low cost, environmental benefits, and potential applications of natural components. This work investigates the physical and mechanical properties of hybrid composites made of sisal/glass fibres and Portland cement inclusions. A full factorial design was generated to identify the effects of the stacking sequence and cement particles on the flexural strength, flexural stiffness, apparent density, apparent porosity and water absorption of the composites. The significant contributions of these main factors and their interactions were determined via Design of Experiments (DoE) and Analysis of Variance (ANOVA). The fracture features and damage mechanisms of hybrid composite were also reported. The inclusion of cement microparticles led to an increased apparent porosity, as well as enhanced water absorption, flexural stiffness and flexural strength of the hybrid composites. The mechanical properties were strongly dependent on the fibre stacking sequence, which accounts for approximately 98% of the effects observed. Moreover, the stacking sequence affected the damage mechanism of the bio-composites. Finally, the replacement of glass fibres by unidirectional sisal reinforcements may potentially improve the specific properties in structural applications with an environmental sustainable footprint.

      PubDate: 2018-05-17T16:03:54Z
       
  • Concurrent seismic and energy retrofitting of RC and masonry building
           envelopes using inorganic textile-based composites combined with
           insulation materials: A new concept
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Dionysios A. Bournas
      This paper explores innovative techniques by combining inorganic textile-based composites with thermal insulation for the simultaneous seismic and energy retrofitting of the existing old buildings. A brief state-of-the-art review on energy and seismic retrofitting materials and techniques is initially made, followed by the introduction of a novel concept for the simultaneous seismic and energy retrofitting of the Reinforced Concrete (RC) and masonry building envelopes, combining Textile Reinforced Mortar (TRM) jacketing and thermal insulation materials or systems. The hybrid structural-plus-energy retrofitting solutions examined are based on inorganic materials providing both cost effectiveness and fire resistance for the building envelope. The overall effectiveness of the combined energy and seismic retrofitting is demonstrated via a case study on a five stories old-type RC building. Moreover by proposing a common approach based on the expected annual loss (of consumed energy or expected seismic loss), it is possible to evaluate the financial feasibility and benefits of the proposed combined retrofitting approach. It was shown that the proposed concept is economically efficient as the payback period of the intervention (return of the retrofitting investment) can be significantly reduced for seismic zones when energy is applied concurrently with seismic retrofitting by exploiting advanced construction materials, thanks to large savings related to the labour costs.

      PubDate: 2018-05-17T16:03:54Z
       
  • Prediction of mechanical properties of knitted fabrics under tensile and
           shear loading: Mesoscale analysis using representative unit cells and its
           validation
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): T.D. Dinh, O. Weeger, S. Kaijima, S.-K. Yeung
      This article presents a numerical framework to predict the mechanical behavior of knitted fabrics from their discrete structure at the fabric yarn level, i.e., the mesostructure, utilizing the hierarchical multiscale method. Due to the regular distribution of yarn loops in a knitted structure, the homogenization theory for periodic materials can be employed. Thus, instead of considering the whole fabric sample under loading, a significantly less computationally demanding analysis can be done on a repeated unit cell (RUC). This RUC is created based on simple structural parameters of knitted yarn loops and its fabric yarns are assumed to behave transversely isotropic. Nonlinear finite element analyses are performed to determine the stress fields in the RUC under tensile and shear loading. During this analysis, contact friction among yarns is considered as well as the periodic boundary conditions are employed. The macroscopic stresses then can be derived from the stress fields in the RUC by means of the numerical homogenization scheme. The physical fidelity of the proposed framework is shown by the good agreement between the predicted mechanical properties of knitted fabrics and corresponding experimental data.

      PubDate: 2018-05-17T16:03:54Z
       
  • Impact damage resistance of 3D printed continuous fibre reinforced
           thermoplastic composites using fused deposition modelling
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): M.A. Caminero, J.M. Chacón, I. García-Moreno, G.P. Rodríguez
      Fused deposition modelling (FDM) is a promising additive manufacturing technology and an alternative of conventional processes for the fabrication of fibre reinforced composites due to its ability to build functional parts having complex geometries. Continuous fibre reinforced thermoplastic composites (CFRTPCs) are becoming more significant in industrial applications due to their inherit advantages such as excellent mechanical performance, recycling and potential lightweight structures [1,2]. However, a major concern affecting the efficient use of 3D printed composites is the effect of impact damage on the structural integrity, compared to conventional pre-preg composites. The aim of this study is to evaluate the effect of build orientation, layer thickness and fibre volume content on the impact performance of 3D printed continuous carbon, glass, and Kevlar® fibre reinforced nylon composites, manufactured by FDM technique. Charpy impact tests are carried out to determine impact strength. SEM images of fractured surfaces are examined to assess failure mechanics of the different configurations. It is observed that the effect of layer thickness of nylon samples on the impact performance was different for flat and on-edge samples. Impact strength increases as layer thickness increases in flat samples but, conversely, it decreases in on-edge samples, depicting a more brittle fracture. In addition, the results show that impact strength increases as fibre volume content increases in most cases. Glass fibre reinforced samples exhibits the highest impact strength and carbon fibre reinforced samples the lowest one and similar to nylon performance. Furthermore, on-edge reinforced samples exhibit higher values of impact strength than flat reinforced samples. Finally, the results obtained demonstrate that impact strength exhibited by 3D printed composites are significantly higher than the usual 3D printed thermoplastics and, in some cases, even better than common pre-preg materials.

      PubDate: 2018-05-17T16:03:54Z
       
  • Probabilistic modelling of tool unbalance during cutting of
           hard-heterogeneous materials: A case study in Ceramic Matrix Composites
           (CMCs)
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): O. Gavalda Diaz, D.A. Axinte, D. Novovic
      Compared to other materials, CMCs display a unique high hardness and heterogeneous nature which are critically reflected during the drilling process where asymmetrical high forces are suffered by the tool, resulting in an unbalance of the drill bit. Hence, this study proposes a mechanistic approach where the hard nature resulting in high radial forces is analytically studied and coupled with a probabilistic model where the heterogeneous nature of CMCs is taken into consideration. This theoretical study results in an in-depth understanding of the loading unbalance occurring on different tool sizes during drilling of CMCs which can lead to a premature tool breakage. The nature of this unique force that is assumed in the theoretical approach to influence the cutting of hard-heterogeneous materials is experimentally validated by drilling a homogeneous and a heterogeneous hard ceramics, i.e. a monolithic SiC and a SiC/SiC CMC. Moreover, the model developed together the with drilling experiments with different tool diameters result in an understanding of why small tool diameters suffer a premature tool breakage when drilling difficult-to-machine CMCs.

      PubDate: 2018-05-17T16:03:54Z
       
  • Epoxy coupling agent for PLA and PHB copolymer-based cotton fabric
           bio-composites
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Daniele Battegazzore, Alberto Frache, Tobias Abt, Maria Lluisa Maspoch
      Epoxy coupling agent was deposited on cotton fabric used for the manufacture of film stacked composites based on poly(lactic acid) (PLA) or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB copolymer) matrices. The additive confined on the fabric surface allowed it to be reactive in the heating stage of the composite production right at the interface between fibres and matrix. The resulting composites were tensile tested comparing the data with the neat matrices and the composites with untreated fabric. A discussion to explain the mechanical results taking in consideration the density, porosity and crystallinity as well as exploiting some micro-mechanical models is presented. The ability of the additive to increase the adhesion between cotton and both matrices is verified and is essential to lighten the structures and to reach application requirements.

      PubDate: 2018-05-17T16:03:54Z
       
  • Flexural behaviour of RC members strengthened with FRCM: State-of-the-art
           and predictive formulas
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Francesco Bencardino, Christian Carloni, Antonio Condello, Francesco Focacci, Annalisa Napoli, Roberto Realfonzo
      Fabric-reinforced cementitious matrix (FRCM) composites are a promising and cost-effective technology for strengthening applications of reinforced concrete (RC) structures. The experimental and theoretical research on FRCM composites is still quite limited if compared with the amount of work carried out on fiber-reinforced polymer (FRP) systems. In addition, the knowledge gained on FRCMs so far has never been collected and reviewed in a systematic framework. This paper contributes to filling this gap by collecting and reviewing the main experimental research available in the literature on flexural strengthening of RC members with FRCM composites. A large database focused on the flexural behavior of strengthened RC beams is compiled. The experimental evidence is critically examined. Comparison within groups of tests of the database is made in terms of flexural capacity and failure modes. Key aspects of the design of the FRCM reinforcement are also analyzed and open issues for possible future research areas are pointed out. For Steel-FRCM systems, a predictive formula for the strain corresponding to the debonding of the external reinforcement is proposed.

      PubDate: 2018-05-17T16:03:54Z
       
  • Oberst and aging tests of damped CFRP materials: New fitting procedure and
           experimental results
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Alessandro Fasana, Alessandro Ferraris, Andrea Giancarlo Airale, Davide Berti Polato, Massimiliana Carello
      Materials play a fundamental role in defining the vibrational and acoustic characteristics of structures and their importance is even increasing because of the continuing demand for lightweight products. Carbon Fibre Reinforced Plastics (CRFP) components are becoming more and more popular because of their excellent mechanical properties but are unfortunately almost unable to dissipate energy. This is one of the reasons why their usage is limited to structural components and does not directly affect acoustic and vibrational response, which are among the factors responsible for harshness and comfort. In vehicles, for example, large panels of CFRP are as noisy as metallic panels so that this kind of lightweight structures is only used when a limited mass is of paramount importance, e.g. in racing cars. The chance of incorporating a damping material in the stacking sequence of CF layers that define a composite seems to be a viable solution to ameliorate the vibrational behaviour of composite materials. This configuration permits to cure the damping layers together with the resins, in order to obtain both free and constrained layer solutions. In this paper, the Oberst beam method has been chosen to determine the elastic modulus and loss factor of such materials, as a function of both frequency and temperature. Three nominally identical samples for each configuration have been tested in a temperature controlled environment, according to the Oberst beam test method. The effects of aging have been simulated by an accelerated standard procedure, with cyclically varying temperature and humidity for a total of 792 h (3 cycles x 264 h). The analysis of experimental data has been performed in the frequency domain by a least square fitting procedure, aimed at outperforming the simple half-power point method. An open source version of the fitting technique has also been implemented and can be obtained from the authors under the CC-by license.

      PubDate: 2018-05-17T16:03:54Z
       
  • Analysis of the mechanical properties and effective diffusion coefficient
           under static creep loading of low-density foams based on
           polyethylene/clays nanocomposites
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Ester Laguna-Gutierrez, Javier Escudero, Miguel Angel Rodriguez-Perez
      In several applications, cellular materials are required to be subjected to static loads that could affect their properties due to the plastic deformation and the gas diffusion from the cells. In this work, the gas diffusion behavior under static creep loading has been determined in low-density cellular materials based on polyethylene and different contents of clays and coupling agent. To understand the role played by these components in the barrier properties, an analysis of the properties of both solid and foamed formulations has been performed including: thermal properties, clays morphology, density and cellular structure. Tensile and compression mechanical properties have also been analyzed. When adding clays the polymer crystallinity increases and the polymer degradation window is broadened. The addition of clays does not have a significant effect on the density and structure of the foamed materials. Both tensile and compression properties improved by the addition of clays. Mechanical properties in compression are also influenced by the coupling agent content. Regarding the effective diffusion coefficients, lower reductions than those expected by the addition of clays are obtained. This result could be explained considering a poor adhesion between the clays and the polymer. It has also been found that the highest reductions in diffusivity are obtained when increasing the coupling agent content.

      PubDate: 2018-05-17T16:03:54Z
       
  • Temperature-dependent response of quasi-unidirectional E-glass fabric
           reinforced polypropylene composites under off-axis tensile loading
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Zhanyu Zhai, Bingyan Jiang, Dietmar Drummer
      The temperature-dependent off-axis tensile behavior of quasi-unidirectional E-glass fabric reinforced polypropylene composites has been investigated both experimentally and constitutively in this paper. The nonlinearity in composites under off-axis loading is shown to be a combination of damage and plasticity regardless of temperature. A nonlinear constitutive model is established to predict the temperature-dependent nonlinear stress-strain curves of composites, in which the accumulation of plastic strain and evolution of damage in composites are described by the plasticity and damage theories, respectively. A full suite of temperature-dependent plastic and damage parameters in the model are determined through cyclic loading-unloading tests.

      PubDate: 2018-05-17T16:03:54Z
       
  • Instabilities and pattern formations in 3D-printed deformable fiber
           composites
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Jian Li, Viacheslav Slesarenko, Pavel I. Galich, Stephan Rudykh
      We investigate elastic instabilities and pattern formations in 3D-printed deformable fiber composites. We experimentally realize the instability induced patterns in the deformable 3D systems of periodically distributed fibers embedded in soft matrix. We observe that the fiber composites exhibit significant softening upon achieving the critical strain at which the stiff fibers cooperatively buckle into wavy patterns. For periodically distributed fiber composites with square in-plane periodicity, we observe the transition of the instability induced patterns from small wavelength wavy pattern to long wave mode with an increase in fiber volume fraction. Both experimental results and rigorous Bloch-Floquet numerical analysis show that the critical wavenumber and critical strain decrease with an increase in fiber volume fraction. For composites with rectangular in-plane periodicity of fibers, we observe that the cooperative buckling mode develops in the direction, where the fibers are close to each other; and an increase in the periodicity aspect ratio leads to a decrease in critical wavenumber and critical strain. In addition, we present our theoretical, numerical, and experimental results for single fiber in soft matrix system. For the single fiber system, we observe that the critical wavelength has a linear dependence on fiber diameter. An explicit formula is derived to estimate the dependence of critical wavelength on shear modulus contrast, and further verified by experimental data and numerical simulations.
      Graphical abstract image

      PubDate: 2018-05-17T16:03:54Z
       
  • Nonlinear free and forced vibration analyses of axially functionally
           graded Euler-Bernoulli beams with non-uniform cross-section
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Sümeyye Sınır, Mehmet Çevik, B.Gültekin Sınır
      Nonlinear free and forced vibrations of axially functionally graded Euler-Bernoulli beams with non-uniform cross-section are investigated. The beam has immovable, namely clamped-clamped and pinned-pinned boundary conditions, which leads to midplane stretching in the course of vibrations. Nonlinearities occur in the system due to this stretching. Damping and forcing terms are included after nondimensionalization. The equations are solved approximately using perturbation method and mode shapes by differential quadrature method. In the linear order natural frequencies and mode shapes are computed. In the nonlinear order, some corrections arise to the linear problem; the effect of these nonlinear correction terms on natural frequency is examined and frequency –response curves are drawn to show the unstable regions. In order to confirm the validity, our results are compared with others available in literature.

      PubDate: 2018-05-17T16:03:54Z
       
  • GO/glucose/PEDOT:PSS ternary nanocomposites for flexible supercapacitors
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Antonella Giuri, Silvia Colella, Andrea Listorti, Aurora Rizzo, Claudio Mele, Carola Esposito Corcione
      Poly (3,4 ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS), among the most used conductive polymers, shows properties easily modulating by adding fillers as Graphene Oxide (GO). Recently, PEDOT-based polymers have been used with encouraging results as electrodes for flexible supercapacitors. We have already developed a green ternary nanocomposite based on PEDOT:PSS doped with GO and glucose (GGO-PEDOT) with a specific capacitance of 16 F/g, indicating how this nanocomposite is potentially suitable to be used as an electrode material for a supercapacitor. In this work, a free-standing nanocomposite film was realized by drop casting the solution in a proper silicone mould, followed by peeling and thermal annealing. Specific analyses, such as thermogravimetric, colorimetric and contact angle measurements, have been performed aiming at assessing the stability of the thermal and of the surface properties, even in severe moisture and UV aging conditions. Finally, The capacitive performance of PEDOT:PSS and of GGO-PEDOT was investigated by means of cyclic voltammetry (CV), in the pristine conditions and under UV aging. The deposited GGO-PEDOT film showed a good conductive behaviour and stability under UV treatment of 4 h.

      PubDate: 2018-05-17T16:03:54Z
       
  • Local anisotropy analysis based on the Mori-Tanaka model for multiphase
           composites with fiber length and orientation distributions
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Doojin Lee
      A local anisotropy takes place in filler reinforced polymer composites due to the high aspect ratio of inclusions, which influences the mechanical or thermo-mechanical performances of the final products such as dimensional stability, flowability, toughness, and strength. It is of importance to investigate the local anisotropy and the relationship between the anisotropy and the mechanical strength of composites. Here, we visually represent the microstructural anisotropy of the multiphase polymer composites composed of talcs and glass fibers based on the Mori-Tanaka approach. The internal structures of the composites are observed by using an X-ray micro-tomographic scanning method to characterize fiber length and orientation distributions. The fiber length distributions are fitted to the Weibull distribution statistical function. It is confirmed that the fiber orientation distributions should also be taken into account to predict the accurate theoretical elastic moduli and local anisotropy of the composites. The effective elastic moduli of the composites with the fiber length and orientation distributions are estimated based on the Mori-Tanaka model.

      PubDate: 2018-05-17T16:03:54Z
       
  • Experimental performance of FRCM retrofit on out-of-plane behaviour of
           clay brick walls
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Claudio D'Ambra, Gian Piero Lignola, Andrea Prota, Elio Sacco, Francesco Fabbrocino
      In this paper the capacity of an innovative composite basalt grid with inorganic matrix (FRCM) has been evaluated both in terms of repairing pre-damaged and strengthening clay brick walls under out-of-plane loads. Experimental tests have been performed on full scale clay brick walls subjected to out-of-plane loads. A wall, damaged after a test, has been repaired by means of basalt FRCM. A similar wall has been tested directly, without pre-damage, after strengthening by means of FRCM. This allowed to remark the effect of retrofitting pre-damaged and new walls. To simulate a non-uniform out-of-plane behaviour of the wall, two adjacent edges of the wall have been constrained and the other two were left free while a pointwise normal force has been applied at the free opposite corner of the wall. The purpose of this work was to assess the potentiality of FRCM to recover the capacity of a wall after significant damage and to increase the global response of strengthened wall not previously damaged. The experimental results demonstrated that the externally bonded strengthening was able to prevent a brittle failure and it was not affected by debonding; ultimate load of the retrofitted wall almost doubled with respect to the unreinforced configuration, despite complex stress state, and that the failure was governed by shear sliding at higher displacement levels.

      PubDate: 2018-05-17T16:03:54Z
       
  • Optimization of filament winding parameters for the design of a composite
           pipe
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): Chiara Colombo, Laura Vergani
      In the oil&gas field, common steel pipelines experience well-known problems of corrosion and maintenance. The design with composite materials could avoid these problems and provide lightness to the overall structures. Standards and regulations guide the designer through the qualification steps, but they are constantly under review based on the increasing knowledge of the long term mechanical behaviour of these materials. The aim of this work is to provide the designer with an analytical tool for the optimal design of a composite plain pipe, i.e. minimizing the wall thickness. The paper presents considerations useful in the design stage for the selection of the optimal fiber, matrix, volume fraction V f , and winding angle θ. The study simulates tests with inner pressure and axial loads, in accordance with the main applicable standards. Based on the analytical estimations, we found a locus of optimal technological parameters with volume fraction 40% < V f < 60% and winding angle ±44.5°<θ<±52.5°. From these considerations, we can suggest a customization in the pipe production, based on the estimated axial loads in exercise.

      PubDate: 2018-05-17T16:03:54Z
       
  • Effect of the drum height on the bearing capacity of composite multi-drum
           column under static load
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): A. Buzov, J. Radnić, N. Grgić, G. Baloević
      The results of a experimental study on the effect of the drum height on the bearing capacity of composite multi-drum column under axial compression force and lateral horizontal force were presented. Small scale columns with two, four, six and twelve drums were tested. It was concluded that an increased number of drums reduces bearing capacity, flexural and shear stiffness, and increases horizontal and vertical deformability of columns. The reason is the simultaneous increase of the joints number, which are the weakest point in column. The column loaded by axial force only had a brittle failure, and by combined axial force and lateral force more ductile failure.

      PubDate: 2018-05-17T16:03:54Z
       
  • Evolution of single carbon and glass fibrous tow cross-sections in dry and
           lubricated states during compaction perpendicular to the fibers
    • Abstract: Publication date: 1 September 2018
      Source:Composites Part B: Engineering, Volume 148
      Author(s): A. Sakkalatty Dharmalingam, J. Hemmer, A.-S. Lectez, C. Binetruy, S. Comas-Cardona
      Fibrous fabrics are used in a variety of applications, among them, for structural composites. Most fabrics are efficiently manufactured from tows or yarns. During textile manufacturing or during fiber reinforced composites manufacturing, the fabrics and tows undergo several movements and deformations. Although there have been several attempts by different authors to model micro structural mechanical behavior of fabrics, they often suffer from unknown geometric dimensions at various loads or unknown materials' mechanical parameters. This paper presents a method for measuring and comparing tows (or yarns) geometrical evolution during compaction perpendicular to the fibers. The tows are compacted and dimensions are continuously measured using confocal chromatograph. Fabrics and tows of the study are composed of glass or carbon fibers, in dry or lubricated states. Volume, compacity evolutions and Poisson's ratio are extracted for a wide range of compaction levels. Tables of material characteristics and experimental data are also provided for a further use or analysis.

      PubDate: 2018-05-17T16:03:54Z
       
  • Influence of grain boundary interface on ionic conduction of (Zn1-x,Cox)O
    • Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Shalima Shawuti, Musa Mutlu Can, Mehmet Ali Gülgün, Satoru Kaneko, Tamio Endo
      We investigated the effect of Co atoms, doped into ZnO lattice, on ionic conductivity in the internal grains or through the grain boundaries. Influence of Co amount on the conductivity was associated with enhanced activation energies of the ionic conductivity through the grain boundaries. The change in activation energy implies that the mechanism of ionic conduction through the boundaries can be modified by the Co amount in the lattice. Three conductance mechanisms were identified by the Cole-Cole plots in order to understand the relaxation mechanism and activation energies of ionic transportations. Newly formed activation energy, 395 meV, by increasing Co amount up to 10 mol% was attributed to the ionic conductivity through the enhanced (or increased) (Zn,Co)O/ZnO) interface at the grain boundaries. In addition, the activation energy was also enhanced by the electronic stability at high temperatures due to decrease in electronic conductivity in the Co-doped ZnO compared to that in undoped ZnO.

      PubDate: 2018-05-17T16:03:54Z
       
  • The post-breakage response of laminated heat-treated glass under in plane
           and out of plane loading
    • Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Laura Galuppi, Gianni Royer-Carfagni
      Any reliable use of glass for structural purposes cannot neglect that its breakage may be provoked by imponderable events, like impacts at critical spots or thermal shocks. Laminated glass, composed by glass plies sandwiching polymeric interlayer sheets, is used in architectural application thanks to its safe post-glass breakage response. When glass breaks, the interlayer retains the glass shards, and the cracked element maintain a certain residual load-bearing capacity, strongly influenced by the tension stiffening of the polymer due to the adhesion with the glass shards, which depends upon the size of the shards and of the debonded zones. Here, we review the most recent experimental results on the post-glass breakage response of laminated heat-treated glass elements, providing charts for the evaluation of such a stiffening effect. Based on this, simple formulas to analyze and interpret the experimental findings under both in-plane and out-of plane bending are proposed, providing analogies with the bending of bimodulus materials and the load-bearing mechanism of reinforced concrete, respectively.

      PubDate: 2018-05-17T16:03:54Z
       
  • Synergy assessment of hybrid reinforcements in concrete
    • Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Sabrina Vantadori, Andrea Carpinteri, Li-Ping Guo, Camilla Ronchei, Andrea Zanichelli
      The present paper is devoted to the assessment of synergy due to the combined use of metallic and synthetic fibres in concrete matrix. Such an evaluation is performed both at first cracking stage by computing fracture toughness, and at post-peak stage by determining two toughness indexes. The results from experimental three-point bending tests on concrete specimens reinforced with copper-coated steel fibres and polypropylene fibres are employed for such computations. The novelty of this research work is that the Mixed Mode loading effect occurring at crack tip is taken into account when computing fracture toughness. Plain concrete specimens and specimens reinforced with only one type of fibres are experimentally and analytically examined for comparison.

      PubDate: 2018-05-17T16:03:54Z
       
  • Elastic constants of achiral single-wall CNTs: Analytical expressions and
           a focus on size and small scale effects
    • Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Alessandra Genoese, Andrea Genoese, Ginevra Salerno
      The paper presents a study of defect-free achiral single-wall CNTs starting from a simple and effective molecular mechanics model (stick-and-spring), accounting for binary and ternary interactions at the atomic scale. The analytical expressions of the elastic constants related to the membrane behaviour of a Donnell thin shell are derived exploiting proper discrete homogenization tools and the results are compared with those of numerical analyses of the tubes under tensile, radial and torsional loads. By the analysis of the results, size and small scale effects are clearly highlighted and a discussion about their relevance is carried out.

      PubDate: 2018-05-17T16:03:54Z
       
  • Nonlinear compressive failure analysis of biaxially loaded fiber
           reinforced materials
    • Abstract: Publication date: 15 August 2018
      Source:Composites Part B: Engineering, Volume 147
      Author(s): Fabrizio Greco, Lorenzo Leonetti, Carlo Maria Medaglia, Rosa Penna, Andrea Pranno
      The compressive failure behavior of defected periodic fiber-reinforced composites subjected to macroscopic biaxial loadings is here analyzed from both the theoretical and numerical point of view. The coupled effects of local fiber buckling and matrix or fiber/matrix interface microcracks under unilateral self-contact are included in the analysis by adopting an original full finite deformation approach. The obtained uniqueness and stability conditions associated with a continuum rate formulation of the microscopic equilibrium problem, contain unusual nonlinear contributions arising from crack interface self-contact mechanisms whose significance for an accurate evaluation of macroscopic critical loads at the onset of instability and bifurcation is then investigated in an innovative way. To this end by using a nonlinear FE model and analytical developments, the composite failure domains are determined for radial macroscopic loading paths, ranging from biaxial compression to combined axial compression and lateral expansion, and for different microgeometrical parameters. Comparisons with stability and uniqueness domains obtained when simplified crack contact interface approaches are adopted, show the notable role of the above mentioned crack interface contributions for a realistic prediction of the real failure behavior of the composite solid.

      PubDate: 2018-05-17T16:03:54Z
       
 
 
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