ON FATIGUE-CRACK PROPAGATION ENHANCEMENT BY A GASEOUS ATMOSPHERE - EXPERIMENTAL AND THEORETICAL ASPECTS

This paper is concerned with environmentally-assisted stage II fatigue crack propagation and specifically the interaction between the fatigue damage mechanisms and the exposure of the material to an active environment like ambient air. A brief state-of-the-art in the understanding of these well-knit connected processes is first presented. On the basis of original experimental results obtained on a high-strength low-alloy steel exposed to an atmosphere of very low water vapour pressure, a new light is shed on the physical description and on the modelling of environmentally-assisted fatigue damage. The salient feature is that physical adsorption of water vapour on freshly cracked surfaces can by itself enhance the damage process at the crack tip and therefore promote the stage II crack propagation in a wide range of alloys.