Zhi Zhai

Micromechanical Modeling of Viscoplastic Behavior of Laminated Polymer Composites With Thermal Residual Stress Effect

In this paper, a multiscale approach has been developed for investigating the rate-dependent viscoplastic behavior of polymer matrix composites (PMCs) with thermal residual stress effect. The finite-volume direct averaging micromechanics (FVDAM), which effectively predicts nonlinear response of unidirectional fiber reinforced composites, is incorporated with improved Bodner-Partom model to describe the viscoplastic behavior of PMCs. The new micromechanical model is then implemented into the classical laminate theory, enabling efficient and accurate analysis of multidirectional PMCs. The deformation behaviors of several AS4/PEEK PMCs with various fiber configurations are simulated at different strain rates. Thermal residual stress influence on the nonlinear behavior of PMCs is addressed. The research results show that the proposed method can predict the viscoplastic behavior of unidirectional and multidirectional PMCs reasonably. Influence of thermal residual stress on the viscoplastic behavior of PMCs is closely related to fiber orientation. In addition, the thermal residual stress effect cannot be neglected in order to accurately describe the rate-dependent viscoplastic behavior of PMCs.

Micromechanical modeling on the rate-dependent viscoplastic behavior of polymer composites with thermal residual stress effect

The research focuses on the effect of thermal residual stress on the rate-sensitive viscoplastic behavior of polymer matrix composites with various fiber cross-sectional shapes. Micromechanical analysis was then conducted to incorporate the inelastic deformation and thermal residual stress into the micromechanical properties of a repeating cell and obtained the macromechanical response of polymer matrix composites by using homogenization theory. The responses of AS4/Polyetheretherketone (PEEK) with circular, square, and elliptical fibers are predicted by the method above at 10−5, 10−1, and 100/s with respect to 15°, 30°, 45°, 60°, 75°, and 90° off-axis angles. The results show that the viscoplastic difference of the response for various fiber shapes becomes more evident with the increase of strain rate. The effect of thermal residual stress varying with off-axis angle is similar to the sinusoidal curve. Besides, the thermal residual stress provides the largest effect on the response with square fiber and the smallest effect on the response with elliptical fiber, which of the effect decreases with the strain rate increasing.

Working temperature variation effect on the failure envelope of continuous fiber-reinforced composites

In this study, a micromechanical method is presented to study working temperature variation effect on biaxial failure envelopes of continuous fiber-reinforced composites with imperfect interfacial bonding. Generalized viscoplastic potential structure model is used to describe nonlinear response of composites. The interfacial debonding model is incorporated into the micromechanical model for describing the interfacial damage evolution. Theoretical results show good consistency with experimental data. On this basis, a series of numerical examples are performed to investigate working temperature variation and interfacial debonding effect on macroscopic tensile response and biaxial loading failure, respectively. The results indicate that the stress–strain responses and failure strength are closely dependent on working temperature. And biaxial compressive loadings in axial-transverse and transverse–transverse, as well as axial tensile and compressive loadings, do not generate interfacial debonding.

A Study of Failure Strength for Fiber-Reinforced Composite Laminates with Consideration of Interface

Composite laminates can exhibit the nonlinear properties due to the fiber/matrix interface debonding and matrix plastic deformation. In this paper, by incorporating the interface stress-displacement relations between fibers and matrix, as well as the viscoplastic constitutive model for describing plastic behaviors of matrix materials, a micromechanical model is used to investigate the failure strength of the composites with imperfect interface bonding. Meanwhile, the classic laminate theory, which provides the relation between micro- and macroscale responses for composite laminates, is employed. Theory results show good consistency with the experimental data under unidirectional tensile conditions at both 23°C and 650°C. On this basis, the interface debonding influences on the failure strength of the [0/90]s and [0/±45/90]s composite laminates are studied. The numerical results show that all of the unidirectional (UD) laminates with imperfect interface bonding provide a sharp decrease in failure strength in the plane at 23°C. However, the decreasing is restricted in some specific region. In addition, for [0/90]s and [0/±45/90]s composite laminates, the debonding interface influences on the failure envelope can be ignored when the working temperature is increased to 650°C.

Biaxial Yield Surface Investigation of Polymer-Matrix Composites

This article presents a numerical technique for computing the biaxial yield surface of polymer-matrix composites with a given microstructure. Generalized Method of Cells in combination with an Improved Bodner-Partom Viscoplastic model is used to compute the inelastic deformation. The validation of presented model is proved by a fiber Bragg gratings (FBGs) strain test system through uniaxial testing under two different strain rate conditions. On this basis, the manufacturing process thermal residual stress and strain rate effect on the biaxial yield surface of composites are considered. The results show that the effect of thermal residual stress on the biaxial yield response is closely dependent on loading conditions. Moreover, biaxial yield strength tends to increase with the increasing strain rate.

The effects of thermal residual stresses and interfacial properties on the transverse behaviors of fiber composites with different microstructures

Abstract This study presents a new micromechanical model to investigate the effects of thermal residual stresses and interfacial properties on the transverse behaviors of SiC/Ti composites with different microstructures. In this model, the fiber-matrix interface is modeled by the bilinear cohesive zone model. The interface model is introduced into the generalized method of cells, which has the advantage of computational accuracy and efficiency. At the same time, the generalized method of cells is extended to consider thermal residual stresses within the fiber and matrix phases. Thermal residual stresses are found to have a significant influence on the transverse behaviors of the composites. Compared with the perfect interface, the transverse behaviors of the composites with weak interface bonding are much lower. Moreover, with the increase of fiber fraction, the stiffness of the composites increases before debonding occurs while the saturation stress decreases. The predicted results using the circular fiber model and considering thermal residual stresses are more consistent with the experimental values compared with the results using the square or elliptical fiber model. When the stress concentration factor is considered and the interface is weakly bonding, the strength predictions are much better than the results using the perfect bonding.

Strain Rate Dependent Deformation of a Polymer Matrix Composite with Different Microstructures Subjected to Off-Axis Loading

This paper aims to investigate the comprehensive influence of three microstructure parameters (fiber cross-section shape, fiber volume fraction, and fiber off-axis orientation) and strain rate on the macroscopic property of a polymer matrix composite. During the analysis, AS4 fibers are considered as elastic solids, while the surrounding PEEK resin matrix exhibiting rate sensitivities are described using the modified Ramaswamy-Stouffer viscoplastic state variable model. The micromechanical method based on generalized model of cells has been used to analyze the representative volume element of composites. An acceptable agreement is observed between the model predictions and experimental results found in the literature. The research results show that the stress-strain curves are sensitive to the strain rate and the microstructure parameters play an important role in the behavior of polymer matrix.

Fiber Cross-Section Shape Effect on Rate-Dependent Behavior of Polymer Matrix Composites with Fbgs Sensors

The micromechanical investigation of fiber cross-section shape effect on the rate sensitive nonlinear behavior of a glass/epoxy was performed at 10-5/s and 1/s, which considering four shapes, square, cross, circle and ellipse. With the strain of different rate loadings measured by Fibre Bragg gratings (FBGs) sensors, the rate-dependent inelastic constitutive relationship of epoxy is built by using an internal state variables viscoplasticity model. Then, through homogenizing the properties of unit cells, the responses of resin and its composites at 30° and 60° off-axis loadings are predicted by a micromechanical model compared with the experiments data. The effect of fiber cross-section fiber on the 30° and 90° off-axis responses are discussed with respect to the viscoplastic parameters of the resin determined. The results indicate that the micromechanical model accurately calculates the behavior of the PMCs employed. The square fiber causes the largest flow stress and plastic strain in the four cases. And the influences on overall responses for the four fiber shapes are enhanced with raising off-axis angles but weaken with the rate increase. However, the elliptical fiber yields the highest modulus in linear elastic stage. The square fiber is the most effective and the elliptical fiber is the least effective in the nonlinear deformation stage. Besides, the elastic properties are unaffected by loading rates when it is less than 1/s.

A Micromechanical Method for the Analysis of Three-Dimensional Smart Composites

The aim of this paper is to develop a micromechanical method based on a proper representative volume element to investigate the effective coefficients and fully coupled electromagnetoelastic responses for three-dimensional smart composites. Relations between the particulate volume fraction, effective moduli, piezoelectric coefficients, and dielectric coefficients are investigated for the composites. Their effective responses, with account of electric, magnetic, and displacement fields, are analyzed. The numerical results obtained indicate that the overall strains of piezoelectric-piezomagnetic composites strongly depend on variations of the electric and magnetic fields.

Numerical simulation of strain rate effect on the inelastic behavior of metal matrix composites

Abstract The primary goal of this paper is to investigate the combined effects of strain rate and microscopic parameters (fiber off-axis orientation, array pattern and cross-sectional shape) on the mechanical behavior of metal matrix composites (MMCs). To this end, a rate-dependent micromechanical model by the combination of finite-volume theory and Bodner-Partom viscoplastic model is developed to analyze the inelastic response of MMCs. In the simulations, the fibers are modeled as linearly elastic while the metal matrix exhibits viscoplasticity. The macroscopic stress-strain response, local stress and strain fields are obtained simultaneously. An acceptable agreement has been found between the model’s prediction and finite-element results, which demonstrates the good predictive capabilities of the proposed method. It is concluded that the composite response is strongly affected by strain rate, fiber array pattern and cross-sectional shape in the elastic-plastic region but to a lesser extent in the elastic region. Furthermore, the clustering array provides stiffer response than random and square ones; the square fiber predicts stiffer response than circular and elliptical ones. However, increasing the strain rate will weaken the influence of clustering array and square fibers.