A Three-Dimensional Mesoscale Damage Model for Simulating Combined Shear and Compressive Failure in Unidirectional Fiber-Reinforced Plastics

Fiber-reinforced plastics (FRPs) exhibit significantly lower compressive strength than tensile strength, mainly because of fiber micro-buckling. During compressive failure, fiber micro-buckling leads to the formation of a kink band, in which fractured fibers are reoriented at a constant angle. Previous studies have shown that compressive strength and the fiber collapse direction are affected by initial fiber misalignment and remote shear stress, and that kink-band formation can induce subsequent damage, such as delamination. In this study, a three-dimensional mesoscale constitutive model is developed to represent these compressive failure mechanisms by introducing a coupling term between longitudinal normal stress and shear strain. The formulation is implemented in a numerical framework using a user subroutine in a commercial finite element solver. Numerical examples demonstrate that the proposed model reproduces the dependence of compressive failure behavior on both initial fiber misalignment and remote shear stress. Comparisons with experimental observations indicate the potential of the proposed model to predict compressive strength, while qualitatively capturing the interaction between compressive damage and delamination.