A computer-controlled narrowband ultrasonic pulser/receiver system was used to determine changes in the coefficient of attenuation and the acoustic velocity in pearlitic steel specimens during reverse bending fatigue. The specimens were interrogated through their length, in a direction normal to the loading and crack formation planes, using longitudinal wave bursts at 5 MHz. The ultrasonic data are compared with microscopic observations of microcracks in the fatigue-damaged zone and the fractured surfaces. The pattern in which attenuation evolves with respect to fatigue life is found to be sensitive to the onset of microcracks but appears to be unaffected by the magnitude of fatigue load, number of cracks causing failure, prior low-load fatigue history, or the hardness of the specimen. The change in velocity is found to be more pronounced during the early stages of fatigue than during the more advanced stages. It appears to be insensitive to microcracks but sensitive to stress accumulation and dislocation pileup.
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