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

Abstract

Interim: 1-1-91 to 1-1-92 14. Dodds and Anderson provide a framework to quantify finite size and crack depth effects on fracture toughness when failure occurs at deformation levels where 1 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 lssy: 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 lssy for each individual case. This study addresses the accuracy with which lssy 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 (all¥) ratio are considered by performing plane-strain elastic-plastic finite clement analyses ofSE(B) specimens containing a variety of common weld groove details. These results demonstrate virtually no effect of ± 20% mismatch on lssy if the distance from the crack-tip to the weld/plate interface (Lmin) exceeds 0.2-inches. If Lmin falls below 0.2-inches, there exists a deformation (applied-J) dependent value of Lmin below which reasonably accuratelssy estimation is possible. At higher levels of overmatch (500/0 to 100%), it is no longer possible to parameterize departure of1ssy for a weldment from that for a homogeneous SE(B) based on Lmin alone. Weld geon1etry significantly influences the accuracywith whichlssy for a welded SE(B) can be approximated by lssy for a homogeneous specimen at these extreme overmatch levels. ABSTRACTDodds and Anderson provide a framework to quantify finite size and crack depth effects on fracture toughness when failure occurs at deformation levels wherel 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 derming a value termed lssy: the 1 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 I crack depth combinations preclude calculation of lssy for each individual case. This study addresses the accuracy with which lssy for a welded single edge notch bend, SE(B), specimen can be approximated by prcviously published results ...

Effects of work hardening mismatch on fracture resistance behavior of bi-material interface regions

“…The strength mismatch is commonly defined by the ratio of the yield strengths of weld metal and base metal. This global strength mismatch has effects on the fracture mechanics crack driving force, crack-tip stress field, crack-tip constraint and fracture resistance, and has been widely investigated [2][3][4][5][6][7][8] and considered in the structural integrity assessment [9,10].…”

Fracture toughness of laser welds in ship steel

“…The very narrow nature of the laser weld zone also makes it likely that there will be a profound effect on crack tip stress distributions. Kirk and Dodds [5] present a limited range of computations for 100% overmatched welds which confirm a trend of significant errors in a KJ characterisation.…”

“…The best published review known to the authors is that by Kirk and Dodds [5]. Their study mainly covered a weld to plate strength mismatch of ±20% with the crack at the weld centreline.…”

Modelling the effect of HAZ undermatching on the crack-tip stress distribution in idealized welds

“…This maximum is a consequence of crack-tip blunting, which causes a local reduction in stress triaxiality, promoting a decrease in s yy ; very close to the crack tip [13][14][15].…”