Effect of Crack-Tip Stresses on Stress Corrosion Cracking Behavior

It is well documented that the applied load for a given material/environment system has a significant effect on the stress corrosion cracking (SCC) behavior in terms of K _ISCC values as well as on the K-da/dt relation. Traditionally, the role of crack-tip stress has not received proper attention but rather the crack-tip strain that is supposedly critical in cracking the passive oxide exposing the fresh metal surface at the crack tip to the environment. This article discusses a different point of view pertinent to crack-tip stress calculations and their role on SCC behavior. We have examined different continuum mechanics solutions with respect to the role of blunting on crack-tip stress. Both solutions where free traction boundary conditions are satisfied on a sharp and blunt crack are analyzed and discussed. It was shown that the stress component perpendicular to the crack plane at the crack tip for the plateau region remains essentially the same due to blunting even with the increase in applied load. Constant crack-tip stress would also result in rather constant crack-tip strain or creep rate, and as such, the crack growth rate remains the same or constant with respect to applied stress. Presented stress analysis is based on available solutions taken from the literature and assumes that a chemical potential at the crack tip is fixed.