Implicit finite element analysis of ductile fracture of a steel frame under cyclic deformation

Abstract

A ductile fracture model is implemented to an elastoplastic constitutive model of steel material for large-scale finite element analysis of steel frames. The stress modified critical strain model is extended to simulate the structural response after initiation of ductile fracture. The yield stress, Young's modulus, as well as the stress are reduced using the fracture variable. Positive definiteness of the material tangent stiffness matrix is always maintained, and the unbalanced loads are carried over to the succeeding step to analyze the responses in the range of degrading strength using an implicit finite element analysis. It is shown using a notched rod model and a double notched plate that the proposed model can simulate steep stiffness degradation due to strain localization after ductile fracture. Applicability to a large-scale finite element analysis is investigated using a component frame of moment frame subjected to cyclic forced deformation.