Surface Reactions and Fatigue Crack Growth

Abstract

Recent fracture mechanics and surface chemistry studies of environment assisted crack growth in gaseous environments1–4 have shown that crack growth may be controlled in some systems by the rate of surface reactions and in others by the rate of transport of the aggressive environment to the crack tip. Based on considerations of surface reactions and gas transport, a model for surface reaction and transport controlled fatigue crack growth in single component gaseous environments was proposed and experimentally verified.5–8This model is able to account for the influences of gas pressure and cyclic load frequency on the rate of fatigue crack growth. In practice, however, there is usually more than one gas in a given environment. The various component gases can compete for surface reaction sites and therefore alter the fatigue crack growth response. The effect of this competition needs to be considered. In this paper, the development of the model for surface reaction and transport controlled fatigue crack growth in single component gaseous environments is briefly reviewed. Extension of the same considerations to fatigue crack growth in a binary gas mixture, in which one of the components acts as an inhibitor, is described. Quantitative application of this model to the consideration of oxygen on fatigue crack growth in humid air is discussed.