The influence of a ductile interphase on the overall elastoplastic behavior of a fiber-reinforced composite

While there exist various homogenization theories for the plasticity of a fiber-reinforced composite, no such theories have been explicitly developed to account for the influence of a ductile interphase. In this paper a simple scheme is developed for such a purpose. The theory evolved out of the work of Qiu and Weng (1992) and Hu (1996), and bears an identical structure to Ponte Castaneda's (1991) variational procedure and Suquet's (1995, 1996) modified secant moduli approach. An exact solution under the plane-strain biaxial loading is also developed to assess the accuracy of the theory. It is found that, with either a soft or a hard interphase and with or without work-hardening, the homogenization theory can produce sufficiently accurate results under this condition. The theory is then used to examine the influence of the interphase volume concentration on the anisotropic behavior of the composite under axial tension, transverse tension, axial shear, and transverse shear, with both a soft and a hard interphase, The results indicate that, while the axial tensile behavior is not sensitive to the interphase concentration, the behaviors under other types of loading are greatly affected by its presence, especially when the interphase is softer than the matrix.