Normalisation of Material Crack Resistance Curves by the T Stress

ABSTRACT: The effect of geometry constraint on ductile fracture is qualitatively known in the literature. Lower constraint will increase the crack resistance curve, and vice versa. The traditional use of fracture mechanics specimens with high geometry constraint often leads to very conservative results when the crack resistance curves are used for failure assessment analyses of low constraint geometries. In this paper crack resistance curves are studied as a function of the T-stress. It is demonstrated that ductile crack resistance curves can be normalised by the T stress. The work is based on J-R curves obtained by FE analyses using different ductile damage models, and experimental verification by testing of three different geometries of an aluminium alloy (7108). This finding implies that the T stress is also controlling the ductile fracture. A materials resistance curve can be separated into a reference material resistance curve, which is transferable, and a geometry factor, which is a function of the T stress. The results indicate that the materials crack resistance curve can be found for all different geometries and loading conditions if the T stress is known. Many solutions for the T-stress for different geometries exist in the literature. The results open for a simple and more accurate method to establish the material resistance curves for different geometries that may lead to more accurate failure assessment analyses and more realistic acceptance criteria for cracks