Micromechanics characterization of constraint and ductile tearing effects in small scale yielding fracture

This study describes a methodology based on a local failure model to predict the strong e€ects of constraint variations on (macroscopic) cleavage fracture toughness. We limit our focus to a stress-controlled, cleavage mechanism for material failure and adopt the Weibull stress (rw) as the local parameter to describe crack-tip conditions. A central feature of the present investigation involves the interpretation of rw as a macroscopic crack driving force and the implications of its use in assessments of brittle fracture behavior. When implemented in a ®nite element code, the computational model predicts the evolution of Weibull stress with crack-tip stress triaxiality and stable crack growth. The small-scale yielding analyses under varying levels of T-stress exhibit the essential features of the micromechanics approach in correlating macroscopic fracture toughness with constraint variations and ductile tearing