Growth behavior of mixed mode fatigue crack

Abstract

Multiaxial fatigue studies are performed in two parts: i.e., multiaxial fatigue assessments of metals for fatigue life estimation, and growth behavior of mixed mode fatigue crack. Multiaxial fatigue researches which have been suggested after 1980 were classified and some problems in those studies were evaluated critically. Multiaxial fatigue assessments are categorized in five viewpoints, i.e., empirical formulas and modifications of Coffin-Manson equation, application of stress or strain invariants, use of space averages of stress or strain, critical plane approaches, and use of energy which is accumulated on the materials. During these periods major progresses in multiaxial fatigue analysis are the consideration of anisotropy of materials and the suggestion of energy method using Mohr``s circles. Besides, existing equations or parameters were modified to consider the mean stress, loading path, etc. And also there have been some trials for the generalization of the existing theories. The practical applications of crack growth studies based on constant amplitude mode I loading are somewhat limited, since it is not common that the mode I crack growth occurs independently under the influence of mode II(sliding mode) or mode III(tearing mode). For these cases, criteria, rules, and laws have to be worked out and verified by experiments. However, it is very difficult to evaluate the mixed mode fatigue crack due to the crack surface interference, crack closure, crack branching, etc. This work, defining the branched crack as effective slant crack with the length of the distance between two crack tips, explains the influences of the crack surface interference by introducing the concepts of adhesion wear and scrutinizes some related researches on mixed mode crack growth behavior. And also, an effective stress intensity factor is developed under the consideration of crack closure and crack surface interference and verified with the experimental results of mode I test an...