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The literature on the subject of the mechanism of fatigue crack growth is reviewed. Historically two different mechanisms have been proposed. One is based upon the concept of damage accumulation, the other on a plastic sliding-off process at the tip of the advancing crack. The experimental evidence supports the latter mechanism as the basic process of crack growth. Damage due to static modes of separation can also be important, however, particularly in low-toughness materials. In addition, localized soft zones such as persistent slip bands can be construed as a type of damage if they form at a crack tip and facilitate crack advance.
A method for the quantitative analysis of fatigue crack growth based on a sliding-off process which is related to the crack tip opening displacement is described. The method includes consideration of R-effects, the threshold and cyclic fracture toughness. The method is potentially of use in both the elastic and plastic ranges.
fatigue, fatigue crack growth, fatigue threshold, crack-opening displacement, mean stress effects in fatigue, fatigue damage
Professor, University of Connecticut, Storrs, Conn.