Modeling of environmentally assisted fatigue crack growth behavior

摘要

It is well recognized that environment has a significant role on the failure of mechanically loaded structures. In most cases of cyclic loading, fatigue crack growth (FCG) behavior exhibits lower threshold and faster growth rate in air than in vacuum. It is well documented that the effect of loading frequency on FCG behavior can be more pronounced in aggressive environment/material systems. This is seen in the K-max term of the FCG. On the other hand, a weak dependence of FCG behavior with R ratio in inert environment indicates that a crack extension is governed mainly by Delta K. Existing experimental data indicate that the actual crack extension per cycle is associated with the rising part of the load cycle than the unloading part. In this paper, the synergetic role of environment and mechanical loading on crack growth behavior is considered to see their roles on FCG. In this article, we attempt to model how crack extension interplays between a crack-tip opening and crack-tip blunting angle associated with the applied load and environment, respectively. To support such a model for discussion, we have selected limited FCG data taken from literature corresponding to different environments ranging from vacuum to air and NaCl solution for a number of alloys and with different specimens geometries. We are also not discussing innate mechanisms for each alloy, due to space concerns.