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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 level. In this paper, mechanics analyses of growing fatigue cracks that account for plasticity-induced closure are used to study load shed effects on crack opening levels during simulated threshold testing. Both finite element and FASTRAN strip yield models are employed, and the two approaches are compared. The current ASTM standard test method for determining thresholds is evaluated. Analyses explore the effects of initial stress, initial stress intensity factor, specimen size, material flow strength, and load shed rates on crack closure.
fatigue crack growth, fatigue crack closure, threshold testing, finite element model, FASTRAN, strip yield model, load shedding
Manager, Southwest Research Institute, San Antonio, TX