A method of plasticity for general aligned spheroidal void or fiber-reinforced composites

Based on the general concept of the secant moduli method, together with a new way of evaluating the average matrix effective stress originally proposed by Qiu and Weng ("A Theory of Plasticity for Porous Materials and Particle-Reinforced Composites," ASME J. Appl. Mech. (1992), 59, 261.), a method for nonlinear effective properties of general aligned fiber or void composites is proposed. The method is capable of predicting composite (especially for porous materials) yielding under a hydrostatic load. Compared to the Tandon and Weng ("A Theory of Particle-Reinforced Plasticity," ASME J. Appl. Mech. (1988), 55, 126.), model the proposed method always gives softer prediction in the uniaxial tension. The proposed method will predict the same nonlinear stress and strain relation as the Ponte Castaneda ("The Effective Mechanical Properties of Nonlinear Isotropic Composite," J. Mech., Phys. Solids (1991), 39, 45.) variational model if the same estimates or bounds for the linear comparison composite are adopted.