Load interaction effects during fatigue crack growth under variable amplitude loading - a literature review. Part II: qualitative interpretation

The current understanding of the underlying reasons behind the load interac tion effects in fatigue crack growth under variable amplitude loading is pr esented. Mechanistic arguments proposed to control the load interaction phe nomena are reviewed and evaluated based on their capability to qualitativel y explain empirical trends in variable amplitude fatigue crack growth summa rized in Part I [Fatigue Fract. Engng Mater. Struct. 1998, 21(8), 987-1006] of the present paper. Mechanisms linked to plastic straining at the crack tip enable an interpretation of the majority of the experimental results. S ome observations, however, which cannot be understood in terms of plasticit y-induced crack closure, or which are even in contradiction with the crack closure approach, indicate a possible role of other factors. A general conc lusion is that conditions under which various phenomena can affect variable amplitude fatigue crack growth and interactions between them are insuffici ently recognized.