Extension of the Unified Approach to fatigue crack growth to environmental interactions

Environmental effects on fatigue crack growth were examined using the Unified Approach developed by the authors. According to this approach, Kmax and ΔK are two intrinsic parameters simultaneously required for quantifying fatigue crack growth data. The two parameters led to two intrinsic thresholds that must be simultaneously exceeded for a fatigue crack to grow. Environmental interactions being time and stress-dependent processes affect fatigue crack growth through Kmax parameter. Based on an extensive analysis of literature data, we have classified environmental effects into four basic types. In addition, we have defined a true reference state for an inert fatigue behavior. Classification procedures and methods of estimating the magnitude of environmental effects using the Unified Approach for fatigue crack growth were discussed taking examples from the literature.