NONDESTRUCTIVE EVALUATION OF METAL FATIGUE.
Final scientific rept.,
SOUTHWEST RESEARCH INST SAN ANTONIO TEX DEPT OF INSTRUMENTATION RESEARCH
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Attention is called to the significance of localized defects in the development of fatigue damage in metals of engineering interest. In this regard, recent studies, conducted both in air and in vacuo using nondestructive evaluation techniques, have established the influence of surface and near-surface inclusions on crack initiation in AISI 4340 steel. Accompanying metallurgical investigations indicate that bonding at the inclusion-metal matrix interface is crucial to crack initiation and is followed in order of importance by inclusion size and inclusion depth below the specimen surface. The relationship to and the significance of ultrasonic and magnetic perturbation nondestructive evaluation results in terms of fatigue crack development are discussed. An earlier analytical treatment of the growth of surface fatigue microcracks is extended to describe the configuration of the propagating crack, and an approximate analysis has been initiated to ascertain the extent of plastic yielding expected in the neighborhood of a hemispherical cavity. A historical review of the nondestructive evaluation technique development and crack propagation analysis efforts, which were previously conducted under this contract, is also presented. Author
- Metallurgy and Metallography
- Test Facilities, Equipment and Methods