Analysis of fatigue crack closure during simulated threshold testing

Load shedding procedures during fatigue crack growth threshold testing can, under some conditions, induce significant changes in fatigue crack closure levels, which can in turn artificially influence the apparent threshold le vel. In this paper, mechanics analyses of growing fatigue cracks that accou nt for plasticity-induced closure: are used to study load shed effects on c rack opening levels during simulated threshold testing. Both finite element and FASTRAN Strip yield models sie employed, and the two approaches are co mpared. The current ASTM standard test method for determining thresholds is evaluated. analyses:explore the effects of initial stress,initial stress i ntensity factor, specimen size, material flow strength, and load shed rates or, crack closure.