PAPER 29 - The influence of weld strength mismatch on crack tip constraint in single edge notch bend specimens

Abstract

Dodds and Anderson provide a framework to quantify finite size and crack depth effects on fracture toughness when failure occurs at deformation levels where J no longer uniquely describes the state of stresses and strains in the vicinity of the crack tip. Size effects on cleavage fracture are quantified by defining a value termed JSSY: the J to which an infinite body must be loaded to achieve the same stressed volume, and thereby the same likelihood of cleavage fracture, as in a finite body. In weld metal fracture toughness testing, mismatch between weld metal and baseplate strength can alter deformation patterns, which complicates size and crack depth effects on cleavage fracture toughness. However, the virtually limitless number of weld joint geometry / crack depth combinations preclude calculation of JSSY for each individual case. This study addresses the accuracy with which JSSY for a welded single edge notch bend, SE(B), specimen can be approximated by previously published results for homogeneous specimens. The case of a crack located on the weld joint centerline is treated. The combined effects of weld groove type, degree of mismatch, and crack depth to specimen width (a/W) ratio are considered by performing plane strain elastic - plastic finite element analyses of SE(B) specimens containing a variety of common weld groove details. These results demonstrate virtually no effect of ± 20% mismatch on JSSY if the distance from the crack tip to the weld/plate interface (Lmin) exceeds 5 mm. If Lmin falls below 5 mm, there exists a deformation (applied-J) dependent value of Lmin below which reasonably accurate JSSY estimation is possible. At higher levels of overmatch (50% to 100%), it is no longer possible to parameterize departure of JSSY for a weldment from that for a homogeneous SE(B) based on Lmin alone. Weld geometry significantly influences the accuracy with which JSSY for a welded SE(B) can be approximated by JSSY for a homogeneous specimen at these extreme overmatch levels.