A new parameter for characterizing corrosion fatigue crack growth

The role of mechanical factors, such as ΔK, R, and K (loading rate), and its significance on corrosion fatigue crack growth acceleration were discussed in terms of crack tip strain rate and/or nucleation rate of fresh metal surface. A new parameter for characterizing corrosion fatigue crack growth was proposed, paying attention to rates of crack tip mechanochemical reactions, i.e., oxide film rupture rate, passivation rate, and solution renewal rate, which are influenced by the crack tip mechanical condition, microstructure of material, and environment. Hence a new parameter da/dt]_air, the time base pure fatigue crack growth rate which was related closely to crack tip deformation rate, was introduced as a measure of actual crack tip strain rate. In various combinations of materials and environments, it was shown that the value ofda/dt]_air determines a crack growth rate in the environment, irrespective of mechanical factors such as ΔK, K_max, R, and k, or frequency.