COMPARISON OF CONSTRAINT MEASURING PARAMETERS IN FRACTURE THEORIES FOR DUCTILE MATERIALS

摘要

Ductile fracture of metals occurs as a result of nucleation, growth and coalescence of microscopic voids. The main parameters that control void growth are the triaxiality factor, σ_m/σ_v, and the plastic strain. Recently, two-parameter theories (e.g. J-Q) have been proposed to quantify crack front constraints and to predict the effects of constraint on macroscopic fracture toughness values. In this paper we use finite element models of low constraint geometries to study the variation of σ_m/σ_v, plastic strain and Q-value with deformation. Our numerical results show that, for a given material, there exists a unique relationship between σ_m/σ_v and Q that is independent of specimen geometry, dimensions, crack depth and deformation level. It can be concluded that σ_m/σ_v and Q are equivalent constraint parameters.