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Overloads separated by below-threshold minor cycles are applied to ASTM A588 steel specimens. Fatigue crack propagation data were recorded and acoustic emission (AE) signals were monitored throughout each test. Estimates of crack growth based on a linear summation are less than experimentally observed rates, even when below-threshold cycles are conservatively assumed damaging. Acoustic emission data provide additional evidence that below-threshold cycles within a variable amplitude load history contribute to fatigue damage. The intensity of the AE signals increases with the number of minor cycles between overloads, even though all minor cycles are below the threshold stress intensity.
acceleration, acoustic emission (AE), crack growth, fatigue damage, lifetime prediction, load interaction, overload, retardation, threshold
Senior engineer, Research and Development, Digital Logging, Inc., Tulsa, OK
Associate professor, Oklahoma State University, Stillwater, OK