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Normalisation of Material Crack Resistance Curves by the T Stress

Last modified: 2013-02-10

#### Abstract

The effect of geometry constraint on ductile fracture is qualitatively known inthe literature. Lower constraint will increase the crack resistance curve, and vice versa.The traditional use of fracture mechanics specimens with high geometry constraint oftenleads to very conservative results when the crack resistance curves are used for failureassessment analyses of low constraint geometries. In this paper crack resistance curves arestudied as a function of the T-stress. It is demonstrated that ductile crack resistance curvescan be normalised by the T stress. The work is based on J-R curves obtained by FEanalyses using different ductile damage models, and experimental verification by testing ofthree different geometries of an aluminium alloy (7108). This finding implies that the Tstress is also controlling the ductile fracture. A materials resistance curve can be separatedinto 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 resistancecurve can be found for all different geometries and loading conditions if the T stress isknown. Many solutions for the T-stress for different geometries exist in the literature. Theresults open for a simple and more accurate method to establish the material resistancecurves for different geometries that may lead to more accurate failure assessment analysesand more realistic acceptance criteria for cracks.

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