Properties Of Unidirectional Fiber-reinforced Composites Research Articles

A Numerical Model for the Effective Damping Properties of Unidirectional Fiber-Reinforced Composites

A Numerical Model for the Effective Damping Properties of Unidirectional Fiber-Reinforced Composites

Efficient generation of random fiber distribution by combining random sequential expansion and particle swarm optimization algorithms

Representative volume elements (RVEs) with random fiber distribution are widely used in micro-mechanics for determining the properties of unidirectional fiber-reinforced composites from their microstructure. In this paper, the random sequential expansion (RSE) and particle swarm optimization (PSO) algorithms are combined to develop an efficient methodology for generating such RVEs. This methodology can successfully eliminate the biased regions of dense fiber population and unreal matrix-rich corners that usually appear in created RVEs and resolve the complications in selection of the input parameters in the RSE algorithm. Statistical analysis of the generated microstructures and two- and three-dimensional finite element analyses are performed to validate the capability of the proposed algorithms.

A Multiscale Analysis Method for Predicting the Transverse Mechanical Properties of Unidirectional Fibre-reinforced Composites

Mechanical property prediction methods for composites are very important as theoretical tools for engineering structural design. To more accurately capture the transverse mechanical properties of composites, a multiscale analysis method is developed in this paper. The multiscale analysis method includes three scales: (1) At the microscale, a microscopic cohesive model based on atomic potential energy is established for the interface; (2) At the mesoscale, a unit cell model is established for the fibre, matrix and interface; and (3) At the macroscale, the homogenization method, failure criteria and damage degradation models are used for predicting the transverse mechanical properties. Subsequently, the transverse mechanical properties and the damage evolution process are simulated with the multiscale analysis method. A comparison between the simulations and experiments shows that the maximum error of the predicted transverse modulus and transverse strength is −4.45 % and −12.05 %, respectively. Finally, the effects of the interfacial strength on the macroscopic transverse mechanical properties and the damage onset are analysed. The following conclusions are drawn from the simulation results: (1) The interfacial strength has a more significant effect on the transverse strength and ultimate strain than on the transverse modulus; (2) Decreasing the interfacial strength has a greater effect on the transverse modulus, strength and ultimate strain than increasing the interfacial strength; and (3) The interfacial strength can change the damage onset.

Characterization and Uncertainty Analysis of the Interlaminar Inelastic Properties of Unidirectional Fibre-reinforced Composites

The compression failure mode has been achieved through changing the SBS (Short Beam Shear) experiment parameters, and the nonlinear constitutive relationship along thickness direction for the typical specimens loaded in 1-3 principal material plane has been computed iterative by FEMU with the reconstruction strain field and the numerical simulated stress data of FEM model. The uncertainly of the constitutive parameters is induced by the measurement system noise in the DIC technique and the approximation error in the displacements and strains smoothing algorithm. The covariance matrix of the extracted material constitutive parameters has been given explicitly. Three material constitutive parameters were identified from a customized short-shear experiment simultaneously using an estimated optimal reconstruction mesh size as an illustration. Sensitivity of measurement noise and reconstruction parameter on extracted material properties has been investigated. The effects of region of interest (ROI) and DIC image number on uncertainties of extracted material properties have been addressed. It is suggested that there exist an appropriate ROI and the number of images, from which reliable material parameters can be identified, but much more data used in identification process always lead to smaller standard deviation and COV. It is observed that the material constants used to characterize the interlaminar stress-strain behavior show strong robustness to the measurement noise. Another key finding is that the reconstruction parameter in the global finite-element based approximation approach is critical for reliable material properties identification. Its value has to stay close to optimum for guaranteeing reliable identification of material properties.

Statistical analysis of composites reinforced with randomly distributed fibers using a meshless method

This paper adopts a meshless method that combines the moving least-squares approximation and Galerkin weak form to investigate the mechanical properties of unidirectional fiber-reinforced composites under a lateral load. The degree of nonuniformity is adopted to quantify the spatial distribution of randomness during simulation, and then the numerical implementation is developed to generate a representative volume element (RVE) model with random distribution of fibers. A statistical analysis is carried out by using three descriptors, that is, inter-fiber distance, second-order intensity function and radial distribution function. Numerical examples are presented to illustrate the accuracy of the proposed multiscale meshless method, and excellent agreement is achieved in comparison with experiments and the finite element method. Finally, the performance of the proposed numerical technique is evaluated by considering the effects of RVE size, node influence domain, degree of nonuniformity and fiber volume fraction separately.

Elastic properties of unidirectional fiber-reinforced composites using asymptotic homogenization techniques

The objective of this work is to use an asymptotic homogenization numerical model to obtain elastic properties of unidirectional fiber-reinforced composites. Square and perfect hexagonal unit cells are employed, and the influence of the fiber volume fraction over the homogenized elastic properties is studied. The effectiveness of the predictions is assessed by comparisons to experimental properties, and also another micromechanical model based on a representative volume element. The composites E-Glass 21xK43 Gevetex (glass fiber)/LY556/HT907/DY063 (epoxy matrix) and AS4 (carbon fiber)/3501-6 (epoxy matrix) were studied and good agreement between experimental and numerical predictions was found. Discrepancies between experimental and numerical data are explained in terms of simplifications considered in the homogenization model. An adjustment of properties here performed, based on varying fiber volume fractions, showed to be effective to physically represent the studied fiber composites in a micromechanical stress model based on asymptotic homogenization, developed to estimate failure envelopes of such materials.

3D FE analysis of tensile behavior for co-PP/SGF composite by considering interfacial debonding using CZM

A numerical study was performed to investigate the tensile properties of unidirectional fiber-reinforced composites containing co-polypropylene and short glass fiber (SGF) using a three-dimensional representative volume element (RVE) and finite element method (FEM). The initiation and propagation of interfacial crack were simulated based on a bilinear cohesive zone method (CZM). The FE simulation indicated that the transverse tensile strength of composite reinforced by SGF was strongly affected by the interface strength, critical fracture energy owing to interfacial debonding as well as loading direction. By increasing of SGF aspect ratio, the anisotropy of tensile strength was slightly affected; however, the anisotropy of modulus was noticeably elevated. The results of FE analysis indicated the proposed CZM can be used to simulate the crack-induced softening mechanism of reinforced thermoplastic polymers.

Effect of Fiber Geometry and Representative Volume Element on Elastic and Thermal Properties of Unidirectional Fiber-Reinforced Composites

The aim of present work is focused on the evaluation of elastic and thermal properties of unidirectional fiber-reinforced polymer composites with different volume fractions of fiber up to 0.7 using micromechanical approach. Two ways for calculating the material properties, that is, analytical and numerical approaches, were presented. In numerical approach, finite element analysis was used to evaluate the elastic modulus and thermal conductivity of composite from the constituent material properties. The finite element model based on three-dimensional micromechanical representative volume element (RVE) with a square and hexagonal packing geometry was implemented by using finite element code ANSYS. Circular cross section of fiber and square cross section of fiber were considered to develop RVE. The periodic boundary conditions are applied to the RVE to calculate elastic modulus of composite. The steady state heat transfer simulations were performed in thermal analysis to calculate thermal conductivity of composite. In analytical approach, the elastic modulus is calculated by rule of mixture, Halpin-Tsai model, and periodic microstructure. Thermal conductivity is calculated analytically by using rule of mixture, the Chawla model, and the Hashin model. The material properties obtained using finite element techniques were compared with different analytical methods and good agreement was achieved. The results are affected by a number of parameters such as volume fraction of the fibers, geometry of fiber, and RVE.

A numerical study of the influence of microvoids in the transverse mechanical response of unidirectional composites

Abstract The effect of porosity on the transverse mechanical properties of unidirectional fiber-reinforced composites is studied by means of computational micromechanics. The composite behavior is simulated by the finite element analysis of a representative volume element of the composite microstructure in which the random distribution of fibers and the voids are explicitly included. Two types of voids – interfiber voids and matrix voids – were included in the microstructure and the actual damage mechanisms in the composite, namely matrix and interface failure, were accounted for. It was found that porosity (in the range 1–5%) led to a large reduction in the transverse strength and the influence of both types of voids in the onset and propagation of damage throughout the microstructure was studied under transverse tension and compression. Finally, the failure locus of the composite lamina under transverse tension/compression and out-of-plane shear was obtained by means of computational micromechanics and compared with the predictions of Puck’s model and with experimental data available in the literature. The results show that the strength of composites is significantly reduced by the presence of voids.

Evaluation of effective transverse mechanical properties of transversely isotropic viscoelastic composite materials

A new computational approach for calculation of the effective transverse mechanical properties of unidirectional fiber-reinforced composites with linear viscoelastic matrix and elastic fibers is presented. The approach requires the knowledge of stresses outside a cluster representing the structure of composite in question. The effective properties are found from the assumption that the viscoelastic stresses at the distances far away from the cluster are the same as those from a single equivalent inhomogeneity. The approach directly takes into account the interactions between the inhomogeneities. The comparison of the results with several benchmark solutions reveals the advantages of the developed approach.

Inversion of composite material elastic constants from ultrasonic bulk wave phase velocity data using genetic algorithms

In this paper, efforts on the reconstruction of material stiffness properties of unidirectional fiber-reinforced composites from obliquely incident ultrasonic bulk wave data, employing an inverse technique based on genetic algorithms, is described. Computer-generated ultrasonic phase velocity data, as a function of the angle of refraction in both symmetry and nonsymmetry through the thickness planes of unidirectional composites were used as the input to the genetic algorithm. A simple genetic algorithm, with optimal parameters chosen from the literature and numerical analysis (reported here), was implemented for the reconstruction. The inversion using this novel technique was found to be extremely promising in the characterization of the material stiffness properties. Stability to noise in the input phase velocity data set was also investigated. Advantages and disadvantages of the genetic reconstruction technique over conventional methods are also discussed.

Effective thermoelastic and thermal properties of unidirectional fiber-reinforced composites and their sensitivity coefficients

Three-dimensional finite element models are used to assess the accuracy of the thermoelastic and thermal properties of unidirectional fiber-reinforced composites predicted by six different micromechanical models. The six models are: simple mechanics of materials type equations, fiber substructuring model, vanishing fiber diameter model, self-consistent model, Mori-Tanaka model, and method of cells. In addition, the finite element models are used to assess the accuracy of derivatives of the effective properties, with respect to each of the constituent material properties and fiber-volume ratio, computed using the six micromechanical models. The predictions of the micromechanical and finite element models for four advanced composite material systems are compared with experimental data. The results obtained in the present study show that the predictions of the Mori-Tanaka model and the method of cells are closer to those of the finite element models than those of all the other micromechanical models.

Micromechanical Analysis of Fiber-Reinforced Composites with Interfacial Phenomena. 4th Report, Evaluation of Mechanical Properties of Unidirectional Fiber-Reinforced Composites.

In the 3rd report of the sequential papers which dealt with analysis of the composite showing interfacial phenomena, micromechanical analysis was performed on a unidirectional fiber-reinforced composite producing interfacial debonding between a fiber and a matrix, and analytical expressions for energy release rates of a matrix crack and a debonding one were derived. In the present paper, evaluation of mechanical properties of a composite with such an interfacial debonding like a resin-based composite, is carried out based on the theoretical analysis of the 3rd paper. As a result, fracture toughness of such a composite can be evaluated in terms of the critical size of the crack at which the unstable propagation of the matrix crack will be arrested and then the debonding between a matrix and a fiber will occur. The effect of material parameters such as the volume fraction of a fiber, and the length of the debonding, etc., on the toughness can be explained by the interfacial phenomenon. The results obtained are consistent with the common experimantal facts. It should be particularly emphasized that there exists an optimal value of the surface energy of the interface for obtaining a tougher composite.

Amino vinyl esters useful for fiber-reinforced composites. 2. Influence of matrix resin on the properties of unidirectional fiber-reinforced composites

Amino vinyl esters useful for fiber-reinforced composites. 2. Influence of matrix resin on the properties of unidirectional fiber-reinforced composites