Mixed mode fatigue crack growth at 550°c under plane stress conditions in Jethete M152

Abstract

This paper describes the experimental and theoretical results obtained from mixed mode (I and II) fatigue crack growth tests in Jethete at 550°C. Mixed mode crack tip conditions were achieved using the Compact Mixed Mode (CMM) specimen, using initial crack tip conditions corresponding to K I K II = 1.6 (mixed mode) and K I K II = 0.0 (or pure mode II). Two tests have also been performed under pure mode I conditions using the standard Compact Tension (CT) specimen. The results indicate that the mixed mode crack growth data can be correlated with the pure mode I data using a stress intensity factor range, ΔK ϵ obtained from ΔK I and ΔK II , based upon the angular position, θ, of maximum plastic tangential strain. Hence a Paris law obtained from the pure mode I data can be applied to mixed mode behaviour. The direction of fatigue crack growth is shown to be dependent upon the K I / K II ratio and can be predicted using either the proposed maximum tangential strain criterion or the maximum tangential stress theory.