Fracture Toughness for Ductile Materials Under Low Constraint Conditions

Abstract

The crack tip stress field for low constraint conditions arising from short cracked bars, thin cracked bars, and across the thickness of the bar itself is examined. The reduction of crack tip stresses is correlated with the fracture resistance. The material failure curve that correlates the critical fracture toughness with the mean stress is constructed. It is observed that testing deeply thin geometries would provide similar fracture resistance to that measured on shallow cracked thick geometries. Fracture toughness data obtained from finite elements analysis were consistent with the experimental fracture data. The ductile fracture resistance defined as tearing modulus (TR=∂J/E∂a) reveals that fracture data obtained from different cracked geometries have similar effect on crack tip constraint. This investigation emphasised that fracture toughness is strongly influenced by the level of stress. The finding of this research of low constrained geometries is essential in structural integrity assessment as it quantifies precisely the stress condition and the fracture toughness, inherently avoiding the unnecessary replacement.