Anders Wormsen

Non-linear analysis of shallow cracks in smooth and notched plates Part 1: Analytical evaluation

This is the first paper of two that deal with the non-linear analysis of shallow cracks. Simple formulae are given for estimating the J integral for a power-hardening elastic-plastic solid. The proposed equation for estimating J makes use of the linear elastic and the fully plastic solution to interpolate over the entire range from small- to large-scale yielding. The elastic geometry factor is obtained by means of the stress intensity factor. In the fully plastic formulation, the plastic geometry factors are obtained by considering a pure power-hardening solid, which reduces at one limit to an incompressible linear elastic solid, and at the other to a perfectly plastic solid. The solutions are given for three basic configurations: a double-edge-cracked plate under tension and bending; a notched plate under tension with a crack at the root of the notch; a single-edge-cracked plate under bending. Both force control and displacement control are considered. The accuracy of the formulae is assessed using the finite element calculations in Part 2.

Fatigue Assessment of Threaded Segment Specimens Based on the Weakest Link Theory

In this paper, the weakest link approach has been used to estimate the fatigue life of threaded segment specimens based on fatigue test data of smooth specimens of the same material. The segment specimens are cut outs from an ACME threaded component with a thread geometry typically used in subsea connectors.Fatigue life estimates of the threaded specimens were also made by means of the local stress approach which is often the prescribed method in standards and recommended practices, such as DNV-RP-C203. This method uses the von Mises stress range at the most severe location of the specimen when estimating the fatigue life.The estimated S–N curve based on the weakest link approach shows good correspondence with fatigue test results of the threaded segment specimens. The estimated S–N curve based on the local stress approach is well below the S–N curve for the threaded segment specimen. A factor between two and three on stress is observed. Hence, the inherent level of conservatism related to the local stress approach when assessing the fatigue strength of components with very high stress concentration factors is considered to be high.Copyright