Ductile fracture prediction based on J-integral and unified constraint parameters for cracked pipes

Abstract

In actual engineering cracked components, both in-plane and out-of-plane constraints exist simultaneously, thus it is desirable to develop fracture prediction and assessment methodology incorporating both constraints. The constraint parameters Ap based on crack-tip equivalent plastic strain and Ad based on crack-tip opening displacement (CTOD) are two new unified constraint parameters for characterizing both constraints. In this work, by extensive three-dimensional finite element analyses of the parameters Ap and Ad for cracked pipes, the crack driving force (CDF) approaches for predicting ductile fracture based on two-parameter J–Ap and J–Ad have been investigated and developed. The results show that the two approaches can produce similar prediction results for ductile fracture toughness and initiation load of cracked pipes with different crack sizes. Compared with the fracture prediction based on the conventional single parameter J-integral, the application of the two-parameter approaches can reduce conservatism degree for shallower and shorter pipe cracks with low constraint. Because the parameter Ad based on CTOD can be easily measured and determined in finite element analyses. Therefore, it is recommended that the J–Ad approach may be adopted in fracture prediction and assessment of cracked components.