Predicting Ductile Fracture in Maritime Crash with a Modified Implementation of BWH Criterion

This paper presents a modified numerical implementation of the BWH (Bressan-Williams-Hill) criterion for predicting ductile fracture in non-linear finite element analysis of steel-plated structures with shell elements. The original BWH criterion is transformed to the equivalent plastic strain-stress triaxiality space and considered as the failure envelope under proportional loading. A linear damage evolution law is used, which expresses the necking indicator as equivalent plastic strain increment weighted with the localized necking envelope under proportional loading. The bending induced suppression of localized necking is considered by tracing the evolution of the necking indicator in all through-thickness integration points separately. The BWH criterion with the proposed modifications is implemented in a user-defined VUMAT subroutine and applied in the simulations of various stretch-bending and stiffened panel penetration tests reported in the literature. It is demonstrated that the proposed implementation of the BWH criterion provides a better estimate of displacement to fracture initiation.