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Polymer‐matrix composites are widely used in various industries due to their high specific strength and specific stiffness. However, the void formation is inevitable as a by‐product during manufacturing processes, which may have negative effects on its mechanical properties. The purposes of this paper are to quantitatively evaluate the influence of voids on the anisotropic elastic properties of composites and to provide corresponding theoretical prediction models. Firstly, three‐dimensional representative volume elements (RVE) of fiber‐reinforced composite materials with different fiber contents (36.37%, 45.47%, 50.92%) and different void contents (1%, 3%, 5%, 7%) are established. To obtain the elastic properties in different directions, various periodic boundary conditions are applied to the RVE models and corresponding subroutines are developed by ABAQUS‐PYTHON. Secondly, a series of theoretical models are proposed to quickly predict the anisotropic elastic properties of unidirectional fiber/epoxy composites containing random‐sized void defects, which agree well with the finite element simulation results. Especially, the proposed models have concise expressions, which require only a few parameters to be input, and hence they are convenient for engineering application. Both theoretical and numerical results show that void defects have an obvious influence on the transverse modulus, major Poisson's ratio, and the out‐of‐plane shear modulus. When the void volume reaches 7%, all of the properties mentioned above decrease by more than 10% for the FRPs studied. [ABSTRACT FROM AUTHOR]

Multiscale finite element analysis based on the asymptotic homogenization theory was carried out for short fiber reinforced plastics (FRP), and the effects of fiber morphologies on mechanical properties were systematically organized. Cellulose microfibers were used as the reinforcing fibers and polypropylene was used as the matrix. In order to quantify the enhancement effect of intrinsic fibers on the mechanical properties, a new indicator based on strain energy, contribution proportion of fiber (CPf) was proposed. In this paper, as the first demonstration of introducing the CPf, unidirectionally oriented short FRP was focused and elastic properties were analyzed for fundamental fiber morphologies. In terms of the fluctuation rate based on the elastic modulus of the matrix, when the volume content of fiber is 3.0 vol%, the elastic modulus of composites varied by 106%, 105%, 97.6%, and 35.1%, respectively, depending on the fiber orientation, fiber aspect ratio, fiber/matrix interface and fiber‐to‐fiber distance. Based on the CPf, fiber morphologies could be divided into two. The first factors are fiber orientation angle and fiber content, which determine the rate of change in mechanical properties with respect to the CPf. The second factors are fiber aspect ratio, fiber/matrix interface, and fiber‐to‐fiber distance, which affect the mechanical properties according to the rate of change determined by the first factors. The complicated influence of the fiber morphologies on the mechanical properties could be unified by introducing the CPf. These computations show that CPf is effective for systematic analysis and design of fiber morphologies. [ABSTRACT FROM AUTHOR]

This paper presents an analysis on the elastic characteristics of luffa and palm natural fiber composites (NFC) with epoxy and ecopoxy matrixes, taking into account the impact of fiber volume fractions. Furthermore, longitudinal modulus, transverse modulus, shear modulus, and Poisson's ratio were predicted using representative volume elements (RVEs) with chopped random and unidirectional fiber arrangements. However, analytical approaches such as rule of mixture, Chamis, Halpin–Tsai, and Nielsen were considered for validating and comparing the findings of finite element analyses. Hence, it was found that increasing fiber volume fraction increased the elastic properties of palm/epoxy, palm/ecopoxy, and luffa/epoxy NFCs, but decreased that of luffa/ecopoxy NFC. Addition of palm fibers in ecopoxy and epoxy had stronger effect than luffa on enhancing the elastic properties of the final structure. However, greatest elastic characteristics observed through analytical and numerical models were obtained for ecopoxy matrix with 0.5 palm fibers. A strong agreement was observed between the results obtained from analytical approaches and RVE unidirectional model. Chamis model exhibited higher outcomes compared to the considered analytical techniques, while Halpin–Tsai model showed the least values. [ABSTRACT FROM AUTHOR]

Advanced composite polymer matrix and their different manufacturing processes tend to develop pores of varying size and play a major limiting role in residual stress, damage initiation, matrix cracking, strength, and durability. Direct imaging or simulations to understand the pore formation mechanism in the viscous polymer is difficult. Ultimately, the mechanical performance of the solidified matrix needs better prediction. This paper presents a stochastic micromechanical model, including the effect of pores' formation on the polymer matrix's elastic properties. Theoretical homogenization based micromechanical models for polymer composites is reviewed in the first part. Later, a micromechanical model is proposed considering the different stages of pore formation in a polymer matrix. Polymer samples are fabricated for determining the pore distribution parameters and used appropriately in the proposed model to estimate the elastic properties for a given distribution and volume fraction of the pores. A modified Mori‐Tanaka homogenization approach and a differential scheme of inclusion of pores are incorporated in the model. Results obtained from the proposed model are compared with the experimental measurements, and a significant correlation is found. [ABSTRACT FROM AUTHOR]

This article describes in detail the research on the elastic properties of carbon nanotube reinforced composite materials and graphene‐carbon nanotube (G‐C) reinforced composite materials. Several different composite material models were established using finite element software ABAQUS to study the influence of the inclination angle, quantity and volume fraction of carbon nanotubes and graphene on the elastic modulus of reinforced composites. The results show that as the volume fraction of graphene and carbon nanotubes increases, the Young's modulus and shear modulus of the reinforced composite material increase significantly. In addition, the tilt angle and quantity of graphene and carbon nanotubes will also affect the elastic properties of the composite material. The Young's modulus E and the shear modulus G decrease with the increase of the inclination angle, and increase with the increase of the number of graphene and carbon nanotubes. [ABSTRACT FROM AUTHOR]

This article deals with free vibration analysis of thick nanocomposite laminated curved panels with finite length resting on two-parameter elastic foundations, based on the three-dimensional elasticity theory. The main objective of this research paper is to present a 3D elasticity solution for free vibration analysis of thick laminated curved panels with continuously graded carbon nanotube-reinforced sheets. The structure is supported by an elastic foundation with Winkler's (normal) and Pasternak's (shear) coefficients. The volume fractions of oriented, straight single-walled carbon nanotubes are assumed to be a three-parameter power-law distribution which is graded in the radial direction of the panels. An equivalent continuum model based on the Eshelby-Mori-Tanaka approach is employed to estimate the effective constitutive law of the elastic isotropic medium (matrix) with oriented, straight carbon nanotubes. Because of using two-dimensional generalized differential quadrature method, the present approach makes possible vibration analysis of cylindrical panels with two opposite axial edges simply supported and arbitrary boundary conditions including Free, Simply supported and Clamped at the curved edges. The convergence of the method is demonstrated and comparisons are made between the present results and results reported by well-known references and have confirmed accuracy and efficiency of the present approach. This study serves as a benchmark for assessing the validity of numerical methods or two-dimensional theories used to analysis of laminated curved panels. POLYM. COMPOS., 38:E563-E576, 2017. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The present paper deals with the dynamic behavior of rotating nanobeam subjected to follower force using the nonlocal elasticity theory. The nonlocal elasticity theory is used to analyze the mechanical behavior of nanoscale materials. The used method of solution is the Differential Quadrature Method (DQM). It is shown that the frequencies are affected when the size effect is taken into consideration. The effects of the nonlocal small scale parameter and the hub radii on the natural frequencies of the rotating nanobeam with respect to the rotating angular velocity are investigated in the present work. This study could be useful in design of the next generation of nanodevices such as blades of a nanoturbine, nanogears, nanoscale molecular bearings, that make use of the vibration analysis of rotating nanobeam. [ABSTRACT FROM AUTHOR]

Most of the early studies on plates vibration were focused on two-dimensional (2D) theories; these theories reduce the dimensions of problems from three to two by introducing some assumptions in mathematical modeling leading to simpler expressions and derivation of solutions. However, these simplifications inherently bring errors and therefore may lead to unreliable results for relatively thick plates. The main objective of this research paper is to present 3D elasticity solution for free vibration analysis of 2D continuously graded carbon nanotube-reinforced (CGCNTR) annular plates resting on a two-parameter elastic foundation. The volume fractions of oriented, straight single-walled carbon nanotubes (SWCNTs) are assumed to be graded in the thickness and radial directions. Various material profiles along the thickness and radial directions are illustrated using the 2D power-law distribution. An equivalent continuum model based on the Eshelby-Mori-Tanaka approach is employed to estimate the effective constitutive law of the elastic isotropic medium (matrix) with oriented, straight carbon nanotubes (CNTs). A semi-analytical approach composed of 2D differential quadrature method (DQM) and series solution is adopted to solve the equations of motion. The convergence of the method is demonstrated and comparisons are made between the present results and results reported by well-known references and have confirmed accuracy and efficiency of the present approach. The novelty of the present work is to exploit Eshelby-Mori-Tanaka approach to reveal the impacts of the volume fractions of oriented CNTs and different CNTs distributions on the vibrational characteristics of annular plates which are assumed to be graded in one (or more) direction(s). POLYM. COMPOS., 35:1644-1661, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

A two‐scale method combined with micro‐CT is presented for the prediction of 3D printed continuous fiber reinforced thermoplastic composites. The proposed method is verified by tensile experiments. The distribution of voids and fibers is reconstructed and quantified by two micro‐CT scans with different resolutions. Then the two‐scale models are established according to the scanned data. Effective properties of fiber‐rich region are predicted by the micro‐scale analysis of the representative volume element, and then transferred into the meso‐scale analysis. In meso‐scale analysis, the high‐fidelity generalized method of cells is applied to predicted elastic parameters of the printed samples. While maintaining the overall fiber volume fraction, the fiber volume fraction in the fiber‐rich region is very important for the accuracy of prediction. [ABSTRACT FROM AUTHOR]

A new portable resin injection device has been developed to repair barely visible impact damage (BVID) in carbon fiber reinforced polymer (CFRP) laminates. Repair was conducted on damaged 16‐ and 24‐ply laminates at two different ambient pressures, that is, atmospheric pressure and vacuum, using three different adhesive types, that is, neat epoxy, epoxy blended with respective halloysite nanotubes (E1HNT) and carbon nanotubes (NF100). The repair effectiveness was assessed by infrared thermography and in‐plane compression testing. All damaged laminates suffered significant degradation in fracture properties as compared to pristine laminates. According to Taguchi method, the main factor affecting the repair efficiency is the laminate ply number. The findings revealed that the optimal repair parameters corresponds to using neat epoxy or E1HNT in vacuum could restore the elastic properties and using E1HNT adhesive at atmospheric pressure could restore the fracture properties of damaged 16‐ply laminate after repair. Regardless of repair parameters, the repair efficiency for the mechanical properties of 24‐ply laminates revealed minimal restoration to the laminate pristine conditions after repairing the damaged laminates due to the complexity of BVID for allowing the adhesive to infiltrate and filled the crack structures. The choice of repair parameters was discussed based on the effectiveness of restoring elastic and fracture properties. [ABSTRACT FROM AUTHOR]

A mathematical model for semicrystalline polymers is proposed to predict the specific features of thermal and deformation phenomena, which are realized in the processes of phase (crystallization) and relaxation (glassy-type) transitions. To describe deformation phenomena, constitutive equations for evolution of the stress-strain state have been constructed within the framework of the phenomenological theory of continuum mechanics. The equations take into account the influence of phase and relaxation transitions on deformation processes. The polymeric material is approximated as a continuum consisting of two components, one representing the amorphous state of the material and the other the crystalline state of the material. Numerical experiments have indicated that the system of constitutive equations describes the peculiarities of the thermomechanical behavior of semicrystalline polymers in a broad temperature range that includes high elasticity, glass transition, and crystallization intervals. Based on the obtained results, a program for physical thermomechanical experiments has been developed which makes it possible to find the parameters of constitutive equations. In the experiments, two types of polymers exhibiting the characteristic behavior of semicrystalline materials, namely high-pressure polyethylene (HPPE) with a crystalline phase content of 50% and polyamide PA-6, were investigated. POLYM. COMPOS., 36:1055-1062, 2015. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The mechanical properties of biobased composites of poly(β-hydroxybutyrate)-co-poly(β-hydroxyvalerate) biopolymer continuously reinforced with unidirectional Alfa fibers are investigated via tensile testing of oriented composite laminates. Simple mechanical models for the elastic stiffness, strength, and nonlinear hardening of the biobased composites are proposed with an emphasis on techniques that only require the independent properties of the fiber and matrix to facilitate composite design. Rule of mixtures (ROM) approaches are found to effectively predict the elastic properties of the composites but generally overestimate strength. Modified ROM approaches that discount the contribution of the matrix in the fiber loading direction and the contribution of the fiber in the transverse loading direction provide the most accurate strength predictions. Apparent elastic properties for composites with varying fiber orientations are predicted using a modified orthotropic laminate plate method which was found to overestimate composite stiffness in off-axis loading directions. Post-yield nonlinear hardening is modeled using a calibrated continuum yield and plasticity model and demonstrated to provide a close match of the experimental results. [ABSTRACT FROM AUTHOR]

In the present article, the influence of bis-(triethoxysilylpropyl)-tetrasulfide (TESPT) content on the viscoelastic behavior of silica filled Solution Styrene Butadiene Rubber (SSBR) was carefully studied in terms of loss tangent spectrum and bound rubber content. The results showed that both relative tan δ area and tan δmax of filled SSBR with TESPT were detected to present maximum value at 2.5 wt% TESPT(with respect to silica loading). Larger tan δ area and tan δmax meant more chains participating in the glass transition in the present system, which is reflected by the variation of effective filler volume with TESPT content. The interaction between filler and rubber can be improved remarkably when a little amount of TESPT up to 2.5 wt% was incorporated, whereas as the TESPT content exceeds 2.5 wt% the filler-rubber interaction was weakened, which was also proven by TEM images and Payne effect. The bound rubber content of this SSBR system studied presents the same tendency as tan δmax. Once TESPT linked with rubber chains, the condensation reaction between silica and SCA is somewhat hindered because of the difficulty in diffusion of large molecules after SCA is chemically bonded with rubber molecules. The network structure of the filled SSBR was analyzed by applying elasticity model. The consecutive increase of crosslink density compensated the reduction of topological tube-like constrains and thus tensile strength continued to ascend with TESPT content, but sacrificed the ultimate strain. POLYM. COMPOS., 34:1575-1582, 2013. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]