Mismatch Effect on Fracture Driving Force in Mismatched Girth Welded Pipes

Abstract

Elasto-Plastic Fracture Mechanics (EPFM) is a useful tool for analyzing the structural integrity of components. However, EPFM has originally been developed for homogeneous materials and there are some concerns when it is applied to inhomogeneous materials. In the case of welds, the material fracture toughness and the applied fracture mechanics parameter on the structural member (J-integral, CTOD) should be adequately estimated. Furthermore, the mechanic mismatch influences on the local constraint may increase the risk of unstable failure. Hence, to study the effects of weld mismatch and crack locations on fracture behavior, single edge notch under tension (SE(T)) specimens and girth welded pipes under bending containing circumferential cracks were studied by means of finite elements simulations. Different weld widths and locations of cracks over the weld are considered. A study of the opening stresses ahead the crack tip developed in mismatched SE(T) specimens and cracked pipes allows the determination of the most critical combination of weld width and crack location in terms of applied J-integral and crack tip constraint level.

Effect of Mechanical Heterogeneity on Strain and Stress Fields at Crack Tips of SCC in Dissimilar Metal Welded Joints

“…In general, the mechanical property mismatch is defined by the strength mismatch ratio of the yield strength of the weld metal and base metal. Many efforts were made regarding the effect of strength mismatch on the crack-tip stress and strain field [ 5 ] and corresponding crack driving force [ 6 , 7 ], crack-tip constraint [ 8 , 9 ]. In most of these studies, the default weld metal and base metal have the same hardening properties, i.e., the true stress–strain curves of two metals after yielding are parallel.…”