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 predic t the strong effects of constraint variations on (macroscopic) cleavage fra cture toughness. We limit our focus to a stress-controlled, cleavage mechan ism for material failure and adopt the Weibull stress (sigma (w)) as the lo cal parameter to describe crack-tip conditions. A central feature of the pr esent investigation involves the interpretation of sigma (w) as a macroscop ic crack driving force and the implications of its use in assessments of br ittle fracture behavior. When implemented in a finite element code, the com putational model predicts the evolution of Weibull stress with crack-tip st ress triaxiality and stable crack growth. The small-scale yielding analyses under varying levels of T-stress exhibit the essential features of the mic romechanics approach in correlating macroscopic fracture toughness with con straint variations and ductile tearing. (C) 2001 Elsevier Science Ltd. All rights reserved.