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Journal Cover Composite Structures
  [SJR: 2.408]   [H-I: 92]   [261 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0263-8223
   Published by Elsevier Homepage  [3043 journals]
  • Mechanical behavior of ultra-high toughness cementitious composite
           strengthened with Fiber Reinforced Polymer grid
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Yu-Zhou Zheng, Wen-Wei Wang, Khalid M. Mosalam, Zhong-Feng Zhu
      A new strengthening composite system, namely Basalt Fiber Reinforced Polymer (BFRP) grid – Ultra-High Toughness Cementitious Composite (UHTCC) for Reinforced Concrete (RC) structures is explored in this paper. Thirty UHTCC specimens internally strengthened with BFRP grid and six similar reference specimens without strengthening were tested to investigate the tensile mechanical behavior. The reinforcement ratio of the BFRP grid (0.17%, 0.68%, and 1.16%) and the mix proportion of the UHTCC were the two main test parameters. The experimental results highlighted two failure modes: 1) rupture or slip off failure of chopped PolyVinyl Alcohol (PVA) fibers at the critical crack sections in the reference specimens, and 2) partial rupture failure of BFRP grid within the UHTCC in all strengthened specimens. Moreover, the relative slip at the interface between the BFRP grid and the UHTCC substrate was not observed during testing. The tensile force capacity of the strengthened BFRP–UHTCC specimens increased by 42% to 172% compared to the reference specimens depending on the reinforcement ratio of the BFRP grid. On the other hand, the tensile force capacity of BFRP–UHTCC specimens slightly decreased by 1% to 14% with the increase of the water-to-cement material ratio of the UHTCC layer from 24% to 38%. Additionally, a stress–strain relationship and strength models of the strengthened specimens are proposed and verified with the test results to predict the tensile mechanical behavior.

      PubDate: 2017-10-11T07:43:48Z
       
  • 3D-printed multimaterial composites tailored for compliancy and strain
           recovery
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): M.R. Mansouri, H. Montazerian, S. Schmauder, J. Kadkhodapour
      Co-continuous multimaterial composites are novel types of multifunctional structures. This study focuses on numerical and experimental investigation of the mechanical behavior of 3D periodic single-material cellular D-structure and the corresponding co-continuous composite. Different volume fractions of desired geometry were fabricated by multimaterial fused deposition modeling (FDM) technology and compressive mechanical properties of the samples were obtained by mechanical tests. It was observed that embedding a hyperelastic material to the cellular structure dramatically hindered the shearing bands in localized regions to develop, thereby made it feasible for composite material to undergo larger deformations without failure. Furthermore, it was demonstrated that the soft phase in multimaterial composite induces a homogeneous deformation to cellular structure, which enhances the load-bearing capacity and flexibility of the whole composite. In this paper, it was shown that the co-continuous multimaterial composite provides a well-balanced approach between desired flexibility and load-bearing which is referred to as compliancy. A strain recovery between 82 and 93% was also measured when unloading for multimaterial composite. These integrated properties could be valuable to various engineering applications such as synthetic limbs, soft robotics, and wearable structures as shoes and splints.
      Graphical abstract image

      PubDate: 2017-10-11T07:43:48Z
       
  • Effect of bending-twisting coupling on the compression and shear buckling
           strength of infinitely long plates
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Christopher Bronn York, Sergio Frascino Muller de Almeida
      This article describes the development of closed form polynomial equations for compression and shear buckling to assess the effect of Bending-Twisting coupling on infinitely long laminated plates with simply supported edges. The equations are used to generate contour maps, representing non-dimensional buckling factors, which are superimposed on the lamination parameter design spaces for laminates with standard ply orientations. The contour maps are applicable to two recently developed databases containing symmetric and non-symmetric laminates with either Bending-Twisting or Extension-Shearing Bending-Twisting coupling. The contour maps provide new insights into buckling performance improvements that are non-intuitive and facilitate comparison between hypothetical and practical designs. The databases are illustrated through point clouds of lamination parameter coordinates, which demonstrate the effect of applying common design heuristics, including ply angle, ply percentage and ply contiguity constraints.

      PubDate: 2017-10-11T07:43:48Z
       
  • Automatically assembled large-scale tensegrities by truncated regular
           polyhedral and prismatic elementary cells
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Li-Yuan Zhang, Song-Xue Li, Shi-Xin Zhu, Bo-Yang Zhang, Guang-Kui Xu
      As a novel type of reticulated structures, tensegrities have found various applications in science and engineering. In this paper, an ingenious assembly method is developed to construct large-scale tensegrities using truncated regular polyhedral tensegrities and prismatic tensegrities as elementary cells. The truncated polyhedral tensegrities with regular polygons on their surfaces are specified as islands, and the prismatic tensegrities are used as bridges to connect these polygons along different directions. This method allows us to construct many types of large-scale tensegrities satisfying the demands of the size and topology. Based on the node-on-node assembly scheme, Z-based truncated regular octahedral tensegrity and its matching quadruplex prismatic tensegrity are employed to produce representative examples with traditional and untraditional shapes. Their mechanical properties are evaluated from the viewpoints of self-equilibrium, stability, and mechanical responses. Our results help to manufacture demanded large-scale tensegrities with delicate mechanical properties, and may be beneficial to construct composite metamaterials.

      PubDate: 2017-10-11T07:43:48Z
       
  • Modeling for CFRP structures subjected to quasi-static crushing
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Guohua Zhu, Guangyong Sun, Guangyao Li, Aiguo Cheng, Qing Li
      Carbon fiber reinforced plastic (CFRP) composite materials demonstrate significant promise to further improve weight to performance in automotive engineering. Nevertheless, design of CFRP components for crashworthiness criteria remains rather challenging and typically requires laborious trial-and-error processes. This study aims to promote computational design of CFRP structures by establishing effective constitutive model that is implemented in the commercial finite element code Abaqus/Explicit. Two different numerical models (namely, the single layer shell model and the stacked shell model) were developed to simulate experimental crushing tests on the square CFRP tube. The effects of key parameters for these two FE models were analyzed, respectively. The comparisons of numerical results with experimental data indicated that the 9 layers stacked shell model is capable of reproducing experimental results with relatively higher accuracy. Based on the validated modeling approach, crushing behaviors of several CFRP thin-walled structures with different cross sectional geometries and thicknesses were further explored. The failure modes and key indicators in relation to the structural crashworthiness were investigated for identifying a best possible sectional configuration. It is found that the circular tube shows superior specific energy absorption capacity of all different tubal configurations with the same wall thickness, meaning that the tube with circular section is of good potential asa crashworthy CFRP structure.

      PubDate: 2017-10-11T07:43:48Z
       
  • Experimental investigation of substandard RC columns confined with SRG
           jackets under compression
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Georgia E. Thermou, Konstantinos Katakalos, George Manos
      This paper aims to explore the behaviour of substandard reinforced concrete (RC) columns confined with Steel-Reinforced Grout (SRG) jackets under monotonically increasing uniaxial compression. A total of 24 specimens of short RC columns of square cross section were designed to fail due to longitudinal reinforcement buckling. Single-layered SRG jackets were applied to 18 of these specimens, whereas the rest served for control without SRG jackets. Parameters of this investigation were the type and density of the steel fabric as well as the corner radius of the cross section. The employed SRG jacketing managed to increase the strength and strain capacity and postpone the buckling of the longitudinal steel bars to occur at higher compressive strain level. Confinement effectiveness with respect to the lateral confining pressure exerted by the used SRG jacketing is discussed along with the observed mode of failure.

      PubDate: 2017-10-11T07:43:48Z
       
  • Application of Kalman Filter based Neutral Axis tracking for damage
           detection in composites structures
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Rohan Soman, Katarzyna Majewska, Magdalena Mieloszyk, Pawel Malinowski, Wieslaw Ostachowicz
      Structural Health Monitoring (SHM) systems allow early detection of damage which allows maintenance planning and reduces the maintenance cost. The SHM system should be low cost, suitable for continuous monitoring, able to detect small levels of damage, and insensitive to ambient loading, changes in ambient temperature, and measurement noise. Neutral Axis (NA) location is a function of the condition of the structure alone and may be used as a damage sensitive feature. It has been shown that through proper signal processing, NA location is insensitive to measurement noise and ambient temperature changes. This paper aims at validating the use of NA as a damage sensitive feature through experimental study. This paper demonstrates the use of multi-rate Kalman Filter (KF) for accurate estimation of NA under different loading conditions. The methodology was employed on a composite beam instrumented with fiber optic strain sensors. Delamination was introduced in the beam and then progressively increased. The beam was subjected to different loading and temperature conditions for the different damage scenarios. The measured strains were then used for NA tracking. The results show that indeed the NA location may be used as a damage sensitive feature. Some of the loading scenarios were difficult to realise in the laboratory, so these loading scenarios were applied on a validated Finite Element (FE) model of the composite beam. The results indicate that under these dynamic loading scenarios, NA may be used for SHM. Based on the results it can be concluded that KF based NA tracking may be applied to structures for in-service SHM.

      PubDate: 2017-10-11T07:43:48Z
       
  • Shear strengthening of steel plates using small-diameter CFRP strands
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Hamid Kazem, Sami Rizkalla, Akira Kobayashi
      This paper presents the results of a comprehensive research program, including experimental and analytical studies, to examine the use of small-diameter CFRP strands for shear strengthening of steel structures and bridges. The experimental program examined the effectiveness of the proposed strengthening system to increase the shear capacity of steel plates subjected to pure shear stresses using a unique test set up. A nonlinear finite element analysis (FEA), calibrated the experimental results, was used to study parameters which were not included in the experiments. Research findings indicated that the proposed system is effective for shear strengthening of steel structures and eliminated the typical debonding failure commonly observed by CFRP laminates.

      PubDate: 2017-10-11T07:43:48Z
       
  • Large deformation of an auxetic structure in tension: Experiments and
           finite element analysis
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Jianjun Zhang, Guoxing Lu, Zhihua Wang, Dong Ruan, Amer Alomarah, Yvonne Durandet
      The present paper reports on the post-yield behaviors of an auxetic structure, honeycomb with representative re-entrant topology. Specimens were made of stainless steel and polymer, respectively. Quasi-static uniaxial tensile tests were conducted in the two principal directions, followed by simulations using the commercial code – ABAQUS 6.11-2. The deformation, tensile stress-strain curves and Poisson’s ratio were of interest. A good agreement was observed between the numerical simulations and the experimental results. Subsequently, the effect of cell wall thickness and initial cell angle was studied by means of finite element analysis. An analytical equation was also given for the yield stress of such materials under tension.

      PubDate: 2017-10-11T07:43:48Z
       
  • Nacre-inspired design of CFRP composite for improved energy absorption
           properties
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Zhibo Xin, Xiaohui Zhang, Yugang Duan, Wu Xu
      Discontinuous unidirectional fiber-reinforced composites are shown to possibly exhibit pseudo-ductile failure that is lacking in continuous fiber composites. The aim of this paper is to use a discontinuous and interdigitated design strategy which mimicks the nacre structure to improve the specific energy absorption (SEA) of a carbon/expoxy composite tube. Quasi-static axial compressive experiment is combined with a digital image correlation system to analyze the failure process of the specimens. Four kinds of tubular specimens which are based on different ply cut intervals and distributions are fabricated and crushed. The load-crushed displacement curves and the SEA values are obtained showing that circular shaped continuous ply cuts result is the highest fluctuation of the compressive force. Moreover, the tubes with helical and nacre mimicking ply cut structures result in a flatter load-crushed displacement curve. This work demonstrates that in a crush process, unidirectional composites with a well-designed discontinuity at the ply level can improve the SEA over 51% as compared to the unidirectional continuous tubes.

      PubDate: 2017-10-11T07:43:48Z
       
  • Experimental and numerical studies on indentation and perforation
           characteristics of honeycomb sandwich panels
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Guangyong Sun, Dongdong Chen, Xintao Huo, Gang Zheng, Qing Li
      Aluminum sandwich panels with honeycomb core have been widely used as energy absorption structure in lightweight design. This study aimed to characterize the indentation and perforation behaviors of sandwich structures with different geometric configurations. The specimens with four characteristic geometric variables, namely, facesheet thickness, core height, honeycomb core thickness and side length of hexagon cell were tested experimentally. Photographs of cross-sectional view near the loading area and failure modes in the tests were investigated in detail. For the first time, digital image correlation (DIC) technique through an ARAMIS™ real-time optical strain measurement system was adopted for capturing the deformation process of lower skin by acquiring the displacement-time data. Three typical damage modes were identified from the force-displacement curves with different geometric parameters and configurations. It was found that the thickness of facesheet has the most significant effects on both force-displacement curves and energy absorption capacity. Changes in the core parameters have relatively small influences in total energy absorption but sizeable effects on the force-displacement curve and failure modes. A finite element model for predicting damage evolution was also developed and validated through the force-displacement relation and deformation process on the bottom skin. The damage mechanisms of the sandwich panel subject to quasi-static indentation and perforation were analyzed through the numerical models. The present study contributed on understanding how the geometric parameters affect the characteristics of indentation and perforation, thereby providing useful guidelines for its potential applications in impact engineering.

      PubDate: 2017-10-11T07:43:48Z
       
  • Load transfer mechanisms in CFRP ground anchors with multi-strap ends
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Haifeng Fan, Anastasios P. Vassilopoulos, Thomas Keller
      An investigation of the load-transfer mechanism in carbon fiber-reinforced polymer (CFRP) ground anchors with multi-strap ends was conducted based on experimental and numerical studies of one- and two-strap anchors. Differences in the strap geometry, i.e. different curvature distributions and transitions from the rod to the strap cross section, and different strap numbers only influenced the local load transfer from the straps to the grout, but not the global pull-out behavior. At higher loads, frictional load transfer along the straps occurred only in the outer strap; the friction was not sensitive to confinement variations provided by different rock types. The load transfer at the strap division, however, was proportional to the confinement level. An empirical model was derived to predict the load transfer in multi-strap anchors and applied to design a new three-strap anchor with a targeted capacity of 2500 kN.

      PubDate: 2017-10-11T07:43:48Z
       
  • Thermomechanical deflection and stress responses of delaminated shallow
           shell structure using higher-order theories
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Chetan Kumar Hirwani, Subrata Kumar Panda, Trupti Ranjan Mahapatra
      The deflection responses of the damaged doubly curved shallow shell panels under the combined thermomechanical loading are investigated numerically in this article. The debonded layered structures are modeled mathematically using two higher-order displacement kinematic theories and solved via finite element method. The separation between the consecutive layers is included using two sub-laminate approaches in the current model including the intermittent displacement continuity conditions. Further, the weak form of the equilibrium equation for the deflected shell panel structure under the combined action of loading is achieved via two-dimensional nine noded isoparametric Lagrangian elements. The responses are obtained by minimising the total potential energy expression with the help of an original computer code (MATLAB) in association with the currently developed mathematical models. The consistency of the present numerical solutions is demonstrated by conducting the convergence test and the validity of the models checked through the proper comparison test. Lastly, some new examples are solved using the current models to show the consequence of the delamination (size and position) including the other structural parameters (the side to thickness ratio, the length to width ratio, the curvature ratio and the boundary condition) on the deflection responses under the influence of thermomechanical loading.

      PubDate: 2017-10-11T07:43:48Z
       
  • Design, manufacturing, and testing of a variable stiffness composite
           cylinder
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Mohammad Rouhi, Hossein Ghayoor, Jeffrey Fortin-Simpson, Tom T. Zacchia, Suong V. Hoa, Mehdi Hojjati
      Fiber steering is one of the promising capabilities of Automated Fiber Placement (AFP) technology in manufacturing of advanced composite structures with spatially tailored properties. The so-called variable stiffness (VS) composites have considerable scope to outperform their traditionally made constant stiffness (CS) counterparts. However, there are several design and manufacturing challenges to be addressed before practically using them as structural components. In this work we demonstrate the design, manufacturing and testing procedure of a variable stiffness (VS) composite cylinder made by fiber steering. The improved bending-induced buckling performance is the objective of the VS cylinder to be compared with its CS counterpart. The experimental results show that the buckling capacity of the VS cylinder is about 18.5% higher than its CS counterpart.

      PubDate: 2017-10-11T07:43:48Z
       
  • Mathematical simulation of pultrusion processes: A review
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Alexander A. Safonov, Pierpaolo Carlone, Iskander Akhatov
      A review of computational modelling and simulation of pultrusion processes is presented including such aspects as: resin flow and pressure distribution in a forming die; impregnation of reinforcing fibers; heat transfer and resin reaction; pulling force, stresses and strains development; methods for numerical optimization of the process. Development of models provides deeper knowledge concerning the mechanisms behind the process as well as the influence of constituent materials’ properties and manufacturing parameters. Consequently, accelerated development of pultrusion process, allowing for the manufacturing of geometrically complex profiles is promoted.

      PubDate: 2017-10-11T07:43:48Z
       
  • An experimental investigation of the mechanical behavior and damage of
           thick laminated carbon/epoxy composite
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Abderrahmane Djabali, Lotfi Toubal, Redouane Zitoune, Saïd Rechak
      In this study, mechanical behavior and damage of thick laminated carbon/epoxy composite are investigated through static and fatigue three-point bending tests. In order to supply a maximum of information about the mechanical behavior of these materials, which have been little studied in the literature, and to provide an accurate description of the different mechanisms involved during their damage process, three non-destructive evaluation and monitoring techniques were used in this study. The acoustic emission for damage assessment, identification, and their threshold detection, the infrared thermography for fatigue damage evaluation and fatigue limit estimation and the digital image correlation for strain and displacement fields measurements.

      PubDate: 2017-10-11T07:43:48Z
       
  • Modeling of honeycombs with laminated composite cell walls
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Ruoshui Wang, Jyhwen Wang
      Honeycombs are versatile structures. They have been widely employed in industries where the characteristics of high stiffness, high buckling resistance, large shock absorption and light weight are required. To explore the potential of honeycombs in various mechanical applications, this paper proposes a novel honeycomb with composite laminate cell walls in order to provide wider selection of constituent materials, improved specific stiffness and distinct cell wall surfaces. Analytical homogenization model of this special type of honeycombs is established by modeling the locally heterogeneous honeycomb as a homogeneous orthotropic bulk. Both full-detailed and homogenized models are built and tested using finite element analysis, and the results showed that the analytical model has excellent accuracy in property prediction at a relatively small computational cost. Parametric studies are also conducted to investigate the effect of thickness and elastic moduli of the cell wall plies on the structure’s overall mechanical response. Based on the results, suggestions on property optimizations are discussed.

      PubDate: 2017-10-11T07:43:48Z
       
  • Effect of stiffener damage caused by low velocity impact on compressive
           buckling and failure modes of T-stiffened composite panels
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Wei Sun, Zhidong Guan, Tian Ouyang, Riming Tan, Xiaodan Zhong
      Effect of stiffener damage caused by Low Velocity Impact (LVI) on compressive buckling and failure load of the three T-stiffened composite panel was studied by experiment in this paper. Stiffener damages were introduced at four impact energy levels with the impact position located on the panel side over the middle stiffener. The impact experimental results show that the impact energy inducing the initial damage of the stiffened panel is about 34 J. With the increase of impact energy, the damage of the panel is slighter than Barely Visible Impact Damage (BVID), while the stiffener damage and stiffener/panel debonding are serious. The panel dent will not be visible until the stiffener is completely fractured under a higher energy impact. Compression after Impact (CAI) experimental results show that although the initial compression stiffness of the stiffened panel is not affected by the stiffener damage, the compressive stiffness decreases with the increase of compressive load due to the damage propagation of the impacted stiffener and buckling of panel. The failure loads decrease significantly when the damage of stiffener and the stiffener/panel debonding occur as the result of LVI, with a maximum drop of 44% compared to the undamaged specimen.

      PubDate: 2017-10-11T07:43:48Z
       
  • A simple first-order shear deformation shell theory for vibration analysis
           of composite laminated open cylindrical shells with general boundary
           conditions
    • Abstract: Publication date: 15 January 2018
      Source:Composite Structures, Volume 184
      Author(s): Qingshan Wang, Dong Shao, Bin Qin
      This paper presents, for the first time, a simple first-order shear deformation shell theory (S-FSDST) for free and transient vibration analysis of composite laminated open cylindrical shells with general boundary conditions. By partitioning the radial displacement into bending and shear components, the present theory contains only four unknowns and can be regarded as an enhanced classical shell theory with the consideration of the effects of shear deformation and rotary inertia terms. The governing equations and appropriate boundary conditions are derived from Hamilton’s principle. To obtain natural frequencies and transient responses accurately, the method of reverberation ray matrix (MRRM) is employed based on the obtained exact closed-form solutions. The artificial spring technology is adopted to achieve the general boundary conditions. Accordingly, the scattering matrix is redefined in MRRM to make it suitable for different boundary cases. The excellent accuracy, reliability and efficiency of the present theory and approach are verified by examining the free and transient vibrations of composite laminated open cylindrical shells under various combinations of classical and non-classical boundary conditions. Meanwhile, a variety of new parameter studies regarding the influence of the boundary conditions, geometry parameters, lamina number, material properties and loading forms are performed in detail.

      PubDate: 2017-10-11T07:43:48Z
       
  • Multiscale modeling of carbon nanotube reinforced concrete
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Vissarion Papadopoulos, Marios Impraimakis
      The present paper proposes a hierarchical multiscale approach in order to evaluate the nonlinear constitutive behavior of concrete reinforced with carbon nanotubes (CNTs). To this purpose, representative volume elements, consistent to the microstructural topology of the material, are constructed and analyzed using finite elements. As the dimensions of the CNTs and those of a typical mesoscale concrete RVE differ by orders of magnitude, a hierarchical multiscale analysis strategy is implemented to pass information through scales with different RVEs assigned at each scale of separation. Both elastic and inelastic analyses are performed on all scales for various CNT weight fractions, defining a different nonlinear constitutive stress–strain behavior at each scale of separation. It is shown that the proposed computational approach can be used alternatively to corresponding costly experiments in order to accurately evaluate the nonlinear constitutive behavior of such complex materials.

      PubDate: 2017-10-04T11:06:17Z
       
  • Bending of multilayer nanomembranes
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): A.D. Drozdov, J. deClaville Christiansen
      Governing equations are developed for bending of an elastic circular membrane under in-plane tension (prestress) and out-of-plane uniform pressure or concentrated force. These relations are applied to fitting observations on nanomembranes made of CVD-grown and mechanically exfoliated graphene, graphene oxides with various concentrations of defects, molybdenum disulfide, bismuth selenite, and tungsten diselenide. Good agreement is demonstrated between the experimental data and results of simulation. It is shown that the elastic modulus per layer of a multilayer membrane is independent of the number of layers n, whereas the prestress grows exponentially with n. Simple equations are suggested to describe the effect of defects in the crystalline structure of a nanomembrane on its mechanical properties. These equations and validated by comparison of the model predictions with observations of graphene oxide.

      PubDate: 2017-10-04T11:06:17Z
       
  • Optimization of composite structures with continuous spatial variation of
           fiber angle through Shepard interpolation
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Qi Xia, Tielin Shi
      In the present paper, we propose a method for the optimization of composite structures with continuous spatial variation of fiber angle. The key idea is to construct a continuous global function interpolating scattered design points to represent the fiber angle arrangement throughout the design domain. To be more specific, the Shepard interpolation method is employed to construct the interpolation function. The angles at scattered design points are taken as the design variables to be optimized. The Shepard interpolation inherently guarantees spatial continuity of fiber angle. In addition, the design freedom of the proposed method can be readily enlarged by increasing the number of design points or the number of design variables to accommodate complex or rapid local variation of fiber angle. Several examples with in-plane load are investigated. In the simple representative numerical examples, the proposed method shows good performance.

      PubDate: 2017-10-04T11:06:17Z
       
  • Evaluation on material behaviors of pultruded glass fiber reinforced
           polymer (GFRP) laminates
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Haohui Xin, Yuqing Liu, Ayman S. Mosallam, Jun He, Ao Du
      In order to extend the use of pultruded glass fiber reinforced polymer (GFRP) composite materials in civil engineering, a systematic study on pultruded GFRP laminate is important and realistic for the design and construction of GFRP structures in bridge engineering. A practical method to evaluate the fiber volume fractions and the equivalent thickness of each lamina is proposed considering that a typical pultruded FRP profile is not truly laminated structure in rigorous sense. The elastic modulus and ultimate strength of each lamina were predicted based on micromechanics. In terms of the facts that lack of knowledge of the majority of bridge engineers on the behavior of composites, an innovative carpet plots with different fiber volume fraction are adopted to finish the laminate design procedure without much complicated calculation. In addition, a continuum damage model considering lamina shear nonlinearity, lamina damage along thickness direction, innovative damage evaluation methods, loading/unloading strategy and viscous methods to alleviate the convergence difficulties is proposed and implemented via user material subroutine. Three different types of pultruded GFRP laminate were fabricated, and material properties have been tested to validate the numerical and theoretical models. The Finite element simulation results agreed well with tests and could provide reference for the design and construction of GFRP structures.

      PubDate: 2017-10-04T11:06:17Z
       
  • Comprehensive local buckling equations for FRP I-sections in pure bending
           or compression
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Daniel C.T. Cardoso, Janine D. Vieira
      In this work, explicit equations to determine local buckling critical stress of thin-walled fiber reinforced polymer (FRP) profiles in pure bending or compression are proposed. Interaction between flange and web is considered and the expressions allow for different orthotropy ratios and ranges of flange-to-web widths and thicknesses. To obtain the equations, Rayleigh Quotient energy method is adopted for assumed approximate buckled shapes. As quality of selected functions affects the accuracy, different shapes are investigated and the results are compared with those obtained with Generalized Beam Theory (GBT) for typical I-section dimensions and material properties. A comparison is made to the solutions based on discrete plate with simplified support conditions as well as to a recently proposed equation for major-axis bending. Finally, a general form for the local buckling critical coefficient is also presented along with tabulated parameters for prompt assessment of critical stresses, consisting in a simple and reliable alternative for design approach.

      PubDate: 2017-10-04T11:06:17Z
       
  • Low velocity impact performance investigation on square hollow glass
           columns via full-scale experiments and Finite Element analyses
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Chiara Bedon, Roman Kalamar, Martina Eliášová
      Taking advantage of two full-scale experimental tests carried out on square hollow glass columns under low velocity impacts, the paper aims to further assess via Finite Element models the structural performance of such structural systems. In them, the resisting cross-section consists of four adhesively bonded laminated glass panes. Adhesive joints are also used for the connection between glass columns and top/bottom restraints. As a result, careful consideration in the analysis and design of these innovative systems is required, to guarantee appropriate fail-safe design principles for a typically tensile brittle material, as well as to account for possible accidental or exceptional loading conditions. Simplified but computationally efficient FE models are validated in the paper towards the available full-scale test results. Key aspects in the observed overall performances under low velocity impact are then emphasized, with careful consideration for several loading configurations, including variations in the release distance for the impacting mass as well as in the type of impact (hard/soft body). In conclusion, a FE sensitivity analysis is also carried out, giving preliminary evidence of the effects of some main input parameters on the overall performance of the examined systems, including possible localized damage in glass, as well as geometrical and mechanical features in the column restraints.

      PubDate: 2017-10-04T11:06:17Z
       
  • The effect of through-thickness compressive stress on mode II interlaminar
           crack propagation: A computational micromechanics approach
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): L.F. Varandas, A. Arteiro, M.A. Bessa, A.R. Melro, G. Catalanotti
      A micromechanics framework for modelling the mode II interlaminar crack onset and propagation in fibre-reinforced composites is presented with the aim of i) modelling the micro-scale failure mechanisms that underlie interlaminar crack propagation, and ii) determining the effect of the through-thickness pressure on mode II fracture toughness. An algorithm for the generation of the fibre distribution is proposed for the generation of three-dimensional Representative Volume Elements (RVEs). Appropriate constitutive models are used to model the different dissipative effects that occur at crack propagation. Numerical predictions are compared with experiments obtained in previous investigations: it is concluded that the proposed micromechanical model is able to simulate conveniently the interlaminar crack propagation and to take into account the effect of the through-thickness pressure on mode II interlaminar fracture toughness.

      PubDate: 2017-10-04T11:06:17Z
       
  • Dynamic analysis of laminated rotors using a layerwise theory
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Safa Ben Arab, José Dias Rodrigues, Slim Bouaziz, Mohamed Haddar
      This paper deals with the dynamic analysis of rotating laminated shafts. A new multi-layer finite element for rotating laminated shaft based on layerwise and shaft theories is formulated and implemented to dispose of a more realistic description of the displacement field through the laminated shaft thickness. This formulation is developed to take into account the influences of stacking sequence, fiber orientation and shear-normal coupling on rotating composite shafts characteristics: natural frequencies and critical speeds and also to analyse the dynamic behaviour of functionally graded material rotating shafts. Obtained results prove that the developed Layerwise Shaft Theory can be efficiently used for rotating laminated shaft dynamic analysis. Furthermore, Layerwise Shaft Theory results revealed that fiber orientations, stacking sequences and shear-normal coupling have a significant effect on the dynamic behaviour of rotating composite shafts and that constituent material properties and power law index have an important influence on the dynamic behaviour of functionally graded material rotating shafts.

      PubDate: 2017-10-04T11:06:17Z
       
  • Static analysis of thin-walled laminated composite closed-section beams
           with variable stiffness
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): M. Gökhan Günay, Taner Timarci
      Static behavior of thin-walled laminated composite closed cross-section beams having variable stiffness is investigated in this study. The analytical model used accounts for flexural–torsional coupling and warping effects as well as the variable stiffness along the contour of the cross-section of the beam. The variable stiffness is acquired by constructing the laminates with curvilinear fibres having certain specific paths. The orientation of fibres varies by depending on the fibre path along the contour of the cross-section in each layer. Equilibrium equations are derived by use of minimum potential energy principle. Although the formulation given can be applied to any shape of the closed cross-section with straight or curved edges, preliminary numerical results are presented only for box-beams. A displacement based finite element method is developed to solve the analytical model and to predict displacements and rotations under the effect of different types of loading conditions. Numerical results are obtained for different fibre paths and lay-up configurations and compared with the available solutions in the literature also with the results of a finite element analysis software using shell element.

      PubDate: 2017-09-26T01:40:23Z
       
  • Experimental investigation of load carrying mechanisms and failure
           phenomena in the transition zone of locally metal reinforced joining areas
           
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): E. Petersen, D. Stefaniak, C. Hühne
      In modern lightweight structures the use of fasteners is preferred to other joining techniques due to the simple disassembly. Because of the low bearing strength of carbon fibre reinforced plastics often a local increase of the thickness is necessary, what is accompanied by eccentricities. A different approach is the local metal hybridisation, where CFRP layers are substituted locally by metal sheets of the same thickness. The local replacement leads to a transition zone between the hybrid region and the pure CFRP region. The present work deals with an experimental investigation of different transition zone patterns and especially the damage behaviour of CFRP-steel hybrid specimens in static tension and bending tests. Digital image correlation is used to measure the strain state during the testing. It is revealed that a staggered pattern with centre endings leads to a high load carrying capacity and a robust transition zone.

      PubDate: 2017-09-26T01:40:23Z
       
  • Investigating post-buckling of geometrically imperfect metal foam
           nanobeams with symmetric and asymmetric porosity distributions
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Mohammad Reza Barati, Ashraf M. Zenkour
      In this research, analysis of post-buckling behavior of porous metal foam nanobeams is performed based on a nonlocal nonlinear refined shear deformation beam model with geometric nonlinearity and imperfection. In the metal foam nanobeam, porosities are dispersed by uniform, symmetric and asymmetric models. The present nanobeam model satisfies the shear deformation effect needless of any shear correction factor. The post-buckling load-deflection relation is obtained by solving the governing equations having cubic nonlinearity applying Galerkin’s method needless of any iteration process. New results show the importance of porosity coefficient, porosity distribution, geometrical imperfection, nonlocal parameter, foundation parameters and slenderness ratio on nonlinear buckling behavior of porous nanoscale beams. Specially, porosities have a great impact on post-buckling configuration of both ideal and imperfect nanobeams.

      PubDate: 2017-09-26T01:40:23Z
       
  • Three dimensional analysis of functionally graded plates up to yielding,
           using full layer-wise finite element method
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): S. Nikbakht, S. Jedari Salami, M. Shakeri
      In this paper, full layer-wise method is employed to analyze the elastic bending of functionally graded plates up to yielding. The solution procedure is presented in two steps. Firstly, the elastic bending of simply supported FG plates is studied to find the deflection and stress distribution. Until this step, the mechanical properties are assumed to vary through the thickness following the rule of mixture. The numerical results are compared with those obtained from quasi 3D elasticity and various shear deformation theories and there has been an excellent agreement between them. In the next step, the mechanical properties of FG plates are determined by using TTO model as the modified rule of mixture. The volume fraction of material constituents is assumed to vary via a power-law function through the thickness in both steps. Finally, Tresca and Von Mises’ yield criteria are utilized to predict the onset of yielding. The results obtained for four different boundary conditions and demonstrated that boundary conditions has a remarkable influence on the region in which yielding initiates. The effect of power-law index has been depicted on the onset of yielding as well.

      PubDate: 2017-09-26T01:40:23Z
       
  • Multi-scale modeling of triaxial braided composites for FE-based modal
           analysis of hybrid metal-composite gears
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Piervincenzo Giovanni Catera, Francesco Gagliardi, Domenico Mundo, Luigi De Napoli, Anna Matveeva, Laszlo Farkas
      The paper presents a description of a methodology to accurately estimate the natural frequencies of a hybrid metal-composite gear, where the web is made of a polymer matrix reinforced with two-dimensional (2D) triaxial braided fabrics. The proposed approach is based on a multi-scale composite modeling starting from evaluation of homogenized material properties of the gear web at the meso-scale for a subsequent FE-based modal analysis. For this purpose, the mechanical behavior of a single Repetitive Unit Cell (RUC) at the meso-scale is analyzed with a FE procedure which takes into account the interweaving and cross-section geometry of the yarns, volume fraction and local fiber orientation. It is shown that the described modeling strategy allows to predict gear’s natural frequencies that are close to the experimental results. Significant accuracy enhancement is achieved with respect to the model in which the web material is considered as perfectly isotropic.

      PubDate: 2017-09-26T01:40:23Z
       
  • Ductile corrosion-free GFRP-stainless steel reinforced concrete elements
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Maged A. Youssef, Mohamed E. Meshaly, Ahmed A. Elansary
      Corrosion of steel rebars is known to cause deterioration of concrete structures that can lead to catastrophic failures. To mitigate this problem, steel rebars can be replaced with Glass Fiber-Reinforced Polymer (GFRP) rebars. However, the lack of ductility of GFRP-reinforced elements has prevented their use in many structural applications, especially in seismic areas. Stainless Steel (SS) rebars are corrosion resistant and have adequate energy absorption and ductility. However, they are much more expensive than steel rebars. This paper proposes the combined use of SS and GFRP rebars to achieve ductile and corrosion-free elements. The first challenge for such a proposal relates to designing SS-GFRP reinforced concrete frame with adequate lateral performance in terms of initial stiffness, ductility, and strength. Design equations, which are based on a comprehensive parametric study, are developed to allow designing such a frame. A six-storey concrete frame is then designed using the proposed equations and its lateral performance is examined using pushover analysis.

      PubDate: 2017-09-26T01:40:23Z
       
  • Multi-objective robust optimization of multi-directional carbon/glass
           fibre-reinforced hybrid composites with manufacture related uncertainties
           under flexural loading
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Mehdi Kalantari, Chensong Dong, Ian J. Davies
      Multi-objective robust optimization of multi-directional carbon/glass fibre-reinforced epoxy hybrid composites has been presented in this study. Two conflicting objectives, namely minimizing the density and minimizing the cost under the constraint of a specified minimum flexural strength, were considered with the design variables being the fibre type, fibre orientation angle and fibre volume fraction of each lamina. A modified version of the non-dominated sorting genetic algorithm (NSGA-II) was used in order to find the Pareto optimal solutions. Furthermore, robust optimization problems were defined by including manufacturing related uncertainties in the thickness and orientation of each lamina. These uncertain variables were considered as uncertain-but-bounded with the worst case for the minimum flexural strength being determined through an internal anti-optimization solver. The optimization and anti-optimization problems were solved with Pareto optimal and robust solutions being presented for carbon/glass fibre hybrid composites with different levels of minimum flexural strength. The results showed that, in general, consideration of uncertainties in thickness and fibre orientation angle increased the material cost and/or density with this effect being more important for high strength composites.

      PubDate: 2017-09-26T01:40:23Z
       
  • Some modifications of Hashin’s failure criteria for unidirectional
           composite materials
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Jiefei Gu, Puhui Chen
      Failure criteria for unidirectional composite materials based on Hashin’s theory are developed. Although Hashin’s criteria are very popular in composite structural applications due to their simplicity of concept and ease of use, they do not always fit experimental results well. In the present study, the fundamental hypotheses proposed by Hashin are re-examined and re-evaluated. Hashin’s criteria for the tensile fiber mode and tensile matrix mode are modified based on physical considerations. The interaction between the fiber and matrix failure modes is also taken into account. Experimental verification for different kinds of unidirectional composites under various stress states demonstrates that the proposed failure criteria have good improvements over Hashin’s criteria, especially in the tensile fiber and matrix mode region. The present theory is in good agreement with physical reality and has a wide range of applicability.

      PubDate: 2017-09-26T01:40:23Z
       
  • The effect of through-thickness compressive stress on mode II interlaminar
           fracture toughness
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): G. Catalanotti, C. Furtado, T. Scalici, G. Pitarresi, F.P. van der Meer, P.P. Camanho
      The effect of through-thickness compressive stress on mode II interlaminar fracture toughness is investigated experimentally and replicated numerically. The modified Transverse Crack Tensile specimen recently proposed by the authors is used, together with an experimental device designed to apply a constant transverse compressive stress on the surface of the specimen. Experiments are conducted using IM7/8552 specimens for different compressive stresses, ranging from 0 to 100MPa, covering all the practical applications commonly encountered in the aeronautical industry (e.g., tightened filled holes or bolted joints). It is shown that mode II interlaminar fracture toughness increases with the applied compressive through-thickness stress. Finally, experiments are replicated using appropriate numerical models based on cohesive elements that take into account frictional effects. A good agreement between numerical predictions and experiments is found.

      PubDate: 2017-09-26T01:40:23Z
       
  • Fracture toughness and crack resistance curves for fiber compressive
           failure mode in polymer composites under high rate loading
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): P. Kuhn, G. Catalanotti, J. Xavier, P.P. Camanho, H. Koerber
      This work presents an experimental method to measure the compressive crack resistance curve of fiber-reinforced polymer composites when subjected to dynamic loading. The data reduction couples the concepts of energy release rate, size effect law and R-curve. Double-edge notched specimens of four different sizes are used. Both split-Hopkinson pressure bar and quasi-static reference tests are performed. The full crack resistance curves at both investigated strain rate regimes are obtained on the basis of quasi-static fracture analysis theory. The results show that the steady state fracture toughness of the fiber compressive failure mode of the unidirectional carbon-epoxy composite material IM7-8552 is 165.6kJ/m2 and 101.6kJ/m2 under dynamic and quasi-static loading, respectively. Therefore the intralaminar fracture toughness in compression is found to increase with increasing strain rate.

      PubDate: 2017-09-26T01:40:23Z
       
  • Prediction methodology for fatigue crack growth behaviour in Fibre Metal
           Laminates subjected to tension and pin loading
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Wandong Wang, Calvin Rans, Zhinan Zhang, Rinze Benedictus
      Fibre Metal Laminates (FMLs) are a hybrid metal-composite laminate technology known for their superior resistance to fatigue crack growth compared to monolithic metals. This crack growth behaviour has been the subject of many studies, resulting in numerous empirical and analytical models to describe the complex damage growth phenomenon in the material. This study builds upon the analytical Alderliesten crack growth prediction methodology for FMLs, extending it from a tension loaded plate to a case of a combined tension-pin loaded plate. This new loading case is a more representative case to utilise for predicting fatigue crack growth behaviour in mechanically fastened joints. Development of the model extension and validation through experimental testing are detailed within this paper.

      PubDate: 2017-09-26T01:40:23Z
       
  • Impact responses of sandwich panels with fibre metal laminate skins and
           aluminium foam core
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Chengjun Liu, Y.X. Zhang, Jing Li
      Low velocity impact responses of a newly developed sandwich panel with aluminium foam core and fibre metal laminate (FML) skins, comprised of aluminium sheets and plain woven E glass fibres, are investigated in this paper. Drop weight impact tests were conducted and the effect of the thickness of foam core and FML skin on the impact response of the panels was investigated via the experimental study. A finite element model is also developed and validated against the experiments to prove the effectiveness and accuracy for analyzing the impact responses of the sandwich panels under low-velocity impact. The research findings are summarized and concluded finally.

      PubDate: 2017-09-26T01:40:23Z
       
  • Effect of the electric current on the impact fatigue strength of CFRP
           composites
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): A.M. Amaro, P.N.B. Reis, J.B. Santos, M.J. Santos, M.A. Neto
      The present study intends to analyse and quantify the effect of the electric exposure on the impact fatigue strength of carbon/epoxy laminates subject to a DC electric current flowing through-thickness at the impact point. For this purpose several laminates were tested with different stacking sequences: [0]16 and [0i,90i]S, i=2, 3, 4, 5. The samples were submitted to a DC electric current of 1A, corresponding to an electric current density of 0.142(A/mm2). The unidirectional samples were exposed over 2h, 4h and 8h, and the cross-ply ones to 8h. The tests were carried out using a drop weight-testing machine and a 10mm diameter impactor. It was possible to conclude that the exposure to the electric current decreases the impact fatigue life, but the unidirectional laminates show to be much more sensible than the cross-ply ones as consequence of the higher pre-damages induced. Thicker samples are also minus sensible to the effects promoted by the electric current and, consequently, the impact fatigue life is less affected.

      PubDate: 2017-09-26T01:40:23Z
       
  • Nonlinear analysis of functionally graded piezoelectric energy harvesters
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Mahdi Derayatifar, Masuod Tahani, Hamid Moeenfard
      This study deals with nonlinear vibrational analysis of functionally graded piezoelectric energy harvesters (FGPEH) carrying concentrated mass at free end, while taking into account the geometrical nonlinear terms as well as electromechanical couplings. Hamilton’s principle and Rayleigh’s beam theory are utilized to obtain the coupled electromechanical governing equations. The first mode shape of the system is derived analytically which is also validated by comparing it with numerical findings of a three-dimensional finite element simulation performed in COMSOL Multiphysics commercial software. The Galerkin projection method is employed along with a single mode approximation to derive the nonlinear coupled electromechanical governing equations which are then solved analytically using the method of multiple time scales perturbation technique for both cases of free and forced vibrations. Time domain responses of free vibration are compared with those of numerical simulations carried out in MATLAB and excellent agreement is observed. Moreover, the nonlinear frequency responses of the forced vibration are obtained for the case of near resonance excitation. A parametric study is also accomplished to reveal the effects of power low index of the FG material as well as the scaled amplitude of the input displacements of the base on the shape of the frequency response.

      PubDate: 2017-09-26T01:40:23Z
       
  • Large deformation of an arc-Miura structure under quasi-static load
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): X.M. Xiang, G. Lu, D. Ruan, Z. You, M. Zolghadr
      Miura-Ori based foldcores have been regarded asa potential substitute for conventional honeycomb cores due to many advantages, such as open structure and continuous manufacturing process. Arc-Miura foldcore is one of the Miura-derivative cores which does not have curvature limitations. In this research, the arc-Miura specimens were successfully manufactured using a stamping process and tested under a quasi-static out-of-plane compressive load. An explicit finite element analysis (FEA) of arc-Miura models was developed and validated with the experimental results. Furthermore, a parametric study of arc-Miura models subjected to quasi-static out-of-plane compression was performed, through which the relationships between the mechanical properties and the geometric parameters were established. Finally, the mechanical properties of arc-Miura models and corresponding monolithic arches were compared. It was shown that arc-Miura patterns perform better than the corresponding monolithic arches in terms of force and energy absorption.

      PubDate: 2017-09-26T01:40:23Z
       
  • Hybrid micromechanical-phenomenological modelling of anisotropic damage
           and anelasticity induced by micro-cracks in unidirectional composites
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): F. Praud, G. Chatzigeorgiou, Y. Chemisky, F. Meraghni
      In this paper, a new damage modelling approach is presented to describe the mechanical response of unidirectional composites under the small strain assumption. The proposed constitutive equations inherits from the phenomenological theories of Continuum Damage Mechanics (CDM) but brings out a micromechanical description of the damaged Representative Volume Element (RVE) while being formulated in a proper thermodynamical framework. The model is provided with an implicit numerical scheme based on the so-called “return mapping algorithm” as well as the formulation of the tangent operator. The identification and the prediction capabilities of the model are validated using experimental data including off-axis tensile tests. Finally, to provide a better understanding of the model, a multi-axial non-proportional simulation is performed and analysed.

      PubDate: 2017-09-26T01:40:23Z
       
  • GDQ analysis of a beam-plate with delaminations
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): C.C. Hong
      The buckling load and post-buckling deformation of a composite beam-plate having two non-overlapping delaminated regions under axial compression is studied by using the generalized differential quadrature (GDQ) method. Applying the GDQ method to each region and using the continuity conditions in transverse displacements, the slopes, the moments and shear forces for upper and lower parts at tips of delamination, the problem will transform to the generalized eigen problem. Various combinations of delaminated length, depth and locations to obtain the buckling load and post-buckling deformation are investigated.

      PubDate: 2017-09-26T01:40:23Z
       
  • On the relationship between failure mechanism and compression after impact
           (CAI) strength in composites
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): M.R. Abir, T.E. Tay, M. Ridha, H.P. Lee
      This work explores the relationship between different failure mechanisms and compression after impact (CAI) strength through an advanced finite element analysis. A Continuum Damage Mechanics (CDM) approach is used to model intra-laminar failure and Cohesive Zone Modelling (CZM) for inter-laminar failure. The FE progressive failure analysis is performed in two consecutive steps. The first is a low-velocity impact analysis in which the induced damage maps are obtained. In the second step, the boundary conditions are modified and an analysis of CAI is performed. The effect of change in ply layup sequence, sub-laminate scaling and ply blocking are investigated and a link between failure and CAI strength is established. Results suggest that changes in ply layup sequence affect delamination sizes, positions and shapes during impact, which in turn result in either global or sub-laminate buckling failure during compression. A global buckling mode results in higher CAI strength compared to failure by sub-laminate buckling for quasi-isotropic laminates of the same thickness. Ply-blocking increases tendency towards delamination, causing a decrease in CAI strength. Sub-laminate scaling causes a transition in failure mode from out-of-plane buckling to in-plane compressive fiber failure. These results suggest a strong correlation between failure mechanism and CAI strength.

      PubDate: 2017-09-26T01:40:23Z
       
  • Free vibration analysis of thick viscoelastic composite plates on
           visco-Pasternak foundation using higher-order theory
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): H.A. Zamani, M.M. Aghdam, M. Sadighi
      Free vibration of laminated viscoelastic composite plates on Pasternak viscoelastic medium with simply supported edge conditions is investigated. The composite plate consists of linear viscoelastic polymeric matrix reinforced by transversely isotropic elastic fibers. Multi-cell micromechanical approach together with relaxation functions of bulk/shear moduli and Boltzmann superposition principle are adopted to establish time-dependent stiffness coefficients of laminates. The coupled integro-PDEs of motions are derived based on third-order shear deformation theory by Laplace transformation and Hamilton principle. Complex frequencies and closed form solutions for transient response are achieved by weighted residual method, iterative numerical algorithm and Fourier transform. To verify, the results are compared for thick elastic composite plates on Pasternak elastic foundation and thick viscoelastic composite sandwich plates without foundation that represent acceptable accuracy. By parametric study, effects of materials, lamination scheme, geometry and medium on dynamic characteristics are scrutinized.

      PubDate: 2017-09-20T01:24:54Z
       
  • A review on additive manufacturing of polymer-fiber composites
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Pedram Parandoush, Dong Lin
      Additive manufacturing (AM) of polymer-fiber composites has transformed AM into a robust manufacturing paradigm and enabled producing highly customized parts with significantly improved mechanical properties, compared to un-reinforced polymers. Almost all commercially available AM methods could benefit from various fiber reinforcement techniques. Recent developments in 3D printing methods of fiber reinforced polymers, namely, fused deposition modeling (FDM), laminated object manufacturing (LOM), stereolithography (SL), extrusion, and selective laser sintering (SLS) are reviewed in this study to understand the trends and future directions in the respective areas. In addition to extra strength, fibers have also been used in 4D printing to control and manipulate the change of shape or swelling after 3D printing, right out of the printing bed. Although AM of fiber/polymer composites are increasingly developing and under intense attention, there are some issues needed to be addressed including void formation, poor adhesion of fibers and matrix, blockage due to filler inclusion, increased curing time, modelling, simulation, etc. Nonetheless, numerous innovative techniques were spotted amongst recent work trying to overcome these challenges with new material or manufacturing techniques.

      PubDate: 2017-09-20T01:24:54Z
       
  • Cyclic stress-strain model incorporating buckling effect for steel
           reinforcing bars embedded in FRP-confined concrete
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Yu-Lei Bai, Jian-Guo Dai, Togay Ozbakkaloglu
      Buckling of steel reinforcement usually causes a sudden loss of the load-carrying capacity and the ultimate state of conventional reinforced concrete (RC) cylinders. However, reinforcing bars behave differently in fiber-reinforced polymer (FRP)-confined RC cylinders due to the lateral confinement effect of FRP. This paper presents a theoretical study into the buckling behavior of longitudinal steel reinforcing bars embedded in FRP-confined concrete subjected to cyclic axial compression. An empirical monotonic compressive stress-strain model considering the buckling effects proposed previously for laterally supported reinforcing bars is extended to a cyclic model by combining the monotonic envelope and the Menegotto-Pinto model accounting for the cyclic loops. The cyclic stress-strain models for both laterally supported reinforcing bars and FRP-confined plain concrete are then implemented into the OpenSees software platform and validated through comparisons with compressive test results on cyclically loaded FRP-confined plain and RC cylinders. The proposed cyclic stress-strain model for laterally supported reinforcing bars is expected to serve as a fundamental model for predicting the seismic behavior of FRP-strengthened RC cylinders with widely-spaced transverse ties under cyclic axial compression, in which case the local buckling of reinforcing bars usually occurs between two adjacent transverse ties.

      PubDate: 2017-09-20T01:24:54Z
       
  • Small perforations in corrugated sandwich panel significantly enhance low
           frequency sound absorption and transmission loss
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): H. Meng, M.A. Galland, M. Ichchou, O. Bareille, F.X. Xin, T.J. Lu
      Numerical and experimental investigations are performed to evaluate the low frequency sound absorption coefficient (SAC) and sound transmission loss (STL) of corrugated sandwich panels with different perforation configurations, including perforations in one of the face plates, in the corrugated core, and in both the face plate and the corrugated core. Finite element (FE) models are constructed with considerations of acoustic-structure interactions and viscous and thermal energy dissipations inside the perforations. The validity of FE calculations is checked against experimental measurements with the tested samples provided by additive manufacturing. Compared with the classical corrugated sandwich without perforation, the corrugated sandwich with perforated pores in one of its face plate not only exhibits a higher SAC at low frequencies but also a better STL as a consequence of the enlarged SAC. The influences of perforation diameter and perforation ratio on the vibroacoustic performance of the sandwich are also explored. For a corrugated sandwich with uniform perforations, the acoustical resonance frequencies and bandwidth in its SAC and STL curves decrease with increasing pore diameter and decreasing perforation ratio. Non-uniform perforation diameters and perforation ratios result in larger bandwidth and lower acoustical resonance frequencies relative to the case of uniform perforations. The proposed perforated sandwich panels with corrugated cores are attractive ultralightweight structures for multifunctional applications such as simultaneous load-bearing, energy absorption, sound proofing and sound absorption.

      PubDate: 2017-09-14T08:08:21Z
       
  • Acoustic scattering from immersed composite cylindrical shells: Existence
           of zero group velocity circumferential waves
    • Abstract: Publication date: 15 December 2017
      Source:Composite Structures, Volume 182
      Author(s): Said Agounad, El Houcein Aassif, Younes Khandouch, Dominique Décultot, Gérard Maze, Abdelkader Elhanaoui
      Some Lamb waves in a plate and some circumferential waves in a one-layer cylinder are characterized by the resonance frequencies where the group velocity is vanishing while the phase velocity remains finite. This paper investigates on the existence of these special waves which call zero group velocity waves (ZGV waves) in the case of the copper/polymer composite cylindrical shell immersed in water and filled with air. The acoustic scattering of a plane wave from this composite cylindrical shell is analyzed in the reduced frequency range ( 0.1 < k 1 a 1 < 200 ; k 1 is the wave number and a 1 is the outer radius of the composite cylindrical shell). The study of the respective influence of the inner layer thickness (polymer) and the outer layer thickness (copper) shows that the existence of these waves is a function of these thicknesses. Moreover, this study depicts that the dispersion curves of the considered bilayer shell tend towards the dispersion curves of the one-layer cylindrical shell made from the material of the thicker layer of the bi-layer cylindrical shell (polymer or copper). The time-frequency representation of smoothed pseudo Wigner-Ville (SPWV) is used to extract some properties of the circumferential waves propagating in and around the bi-layer cylindrical shell. The obtained results by this representation are in good agreement with those obtained by the theoretical approach.

      PubDate: 2017-09-14T08:08:21Z
       
 
 
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