Atmospheric influence on fatigue crack propagation

The present paper addresses the issue of environmentally-assisted fatigue crack propagation. A logical framework is firstly proposed to analyse the intrinsic behaviour of a large variety of steels, Aluminium- and Titanium-based alloys. Then experiments conducted in different gaseous environmental conditions clearly demonstrate the deleterious effect of water vapour. Crack closure measurements are used to uncouple the effect of closure and environment with respect to microstructure. Two distinct mechanisms are considered to account for the observed enhancement, namely adsorption of water vapour and hydrogen-assisted cracking mode. Details of micromechanisms are discussed with respect to constitutive laws.