Stable crack growth of axial surface flaws in pressure vessels

Abstract

Several tests on pressure vessels with axial surface flaws have shown the well known ‘canoe phenomenon’, i.e. the ductile crack extension has been larger in axial direction than in wall thickness direction. Two of the tests performed at the BAM have been analysed by finite element calculations to obtain the variation of the J- integral along the crack front and the stress and strain state in the vicinity of the crack. It was found that the local crack resistance depended significantly on the local stress state. In order to predict ductile crack extension correctly, J R curves have to account for the varying triaxiality of the stress state along the crack front.