A MODEL FOR THE EFFECT OF A GASEOUS ENVIRONMENT ON THE LEFM FATIGUE THRESHOLD CONDITION OF STEELS

Abstract

Using a different approach to those methods involving hydrogen‐embrittlement and crack‐closure mechanisms a previously developed model is extended to predict the commonly observed effects of yield strength and a gaseous environment on the long‐crack fatigue crack growth threshold. The model assumes the existence of two intrinsic thresholds namely an upper bound value and a lower bound value related to, respectively, Kmax‐controlled cleavage and δK‐controlled reversed shear mechanisms of crack growth in a critically stressed volume at the crack tip. This new development assumes that nascent hydrogen atoms, liberated from moisture in the environment, assist in reducing dislocation mobility thereby rationalizing experimental observations on low strength materials in moist laboratory air when compared to a dry inert environment. Quantitative predictions of fatigue thresholds in laboratory air and inert environments show good agreement with experimental data for several low and high strength steels. This alternative procedure may be found to be useful in practical design applications when reasonably fast and accurate estimates are required. Copyright © 1992, Wiley Blackwell. All rights reserved