Modeling and simulation for ductile fracture prediction of crystalline polymer based on craze behavior

Ductile fracture of crystalline polymer is caused by accumulation of craze, which is a damage peculiar to polymers. A simulation for fracture prediction based on this mechanism of polymer is recently recognized as one of the most important industrial themes. In this study, a non-coaxial elastoviscoplastic constitutive equation for polymers with craze effects is thermodynamically derived and an evolution equation of craze that can express propagation and growth cessation of craze is newly proposed. Then, the evolution equation of mean normal plastic strain and the criterion for craze initiation with strain rate dependency are developed. Combining the above models a new material model for ductile polymers expressing craze behavior is presented. Moreover, a three-dimensional FE simulation for a polypropylene plate under uni-axial tension is performed by use of a commercial FEM solver in which the present material model is installed through the user subroutine. The validity of this material model is shown by predicting the accurate failure prediction based on craze accumulation and strength of fibril.