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 fatigu e damage mechanisms and the exposure of the material to an active envi ronment like ambient air. A brief state-of-the-art in the understandin g of these well-knit connected processes is first presented. On the ba sis of original experimental results obtained on a high-strength low-a lloy 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 tha t physical adsorption of water vapour on freshly cracked surfaces can by itself enhance the damage process at the crack tip and therefore pr omote the stage II crack propagation in a wide range of alloys.