Evaluation of CTOD resistance curves in clamped SE(T) specimens with weld centerline cracks

This work addresses the characterization of the crack tip opening displacement (CTOD or delta) for extending cracks in clamped single edge notched tension, SE(T), fracture specimens based upon fracture toughness tests and numerical analyses of stable crack growth conducted on specimen geometries extracted from pipe girth welds with different material properties. The study covers fracture resistance tests and crack growth analysis of plane strain and 3-D models for clamped SE (T) specimens with a weld centerline crack, in which a computational cell methodology to model Mode I crack extension in ductile materials is utilized to describe the evolution of J and CTOD with increased loading for the extending crack. Laboratory testing of girth welds made of different materials provides the measured crack growth resistance curves from which the key micro-structural parameters utilized in the growth analysis are calibrated. The present investigation shows that CTOD resistance curves based on the double clip-gage (DCG) procedure are consistently higher than the corresponding fracture resistance data based on J -CTOD relationships, thereby potentially yielding nonconservative fracture toughness estimates.