Nondestructive Evaluation of Metal Fatigue.
Scientific rept. 1972-1973,
SOUTHWEST RESEARCH INST SAN ANTONIO TEX DEPT OF INSTRUMENTATION RESEARCH
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The complementary role of nondestructive evaluation NDE methods in the application of fracture mechanics approaches for preventing catastrophic failures in engineering structures and extending the useful life of critical components is discussed. Observations via metallurgical investigations of the early stages of macrocrack propagation at inclusions in AISI 4340 steel are described. A model is proposed which is consistent with the early phases of crack front propagation observed and the dormant period in surface crack-extension heretofore observed in steels by others. Precycle magnetic signatures from inclusions are analyzed and the results presented show a functional relationship between signal amplitude and life to crack initiation. Experiments in the local removal of fatigue cracks show that significant extensions in fatigue life are possible through such rework and that subsequent crack initiation occurs at a location different from that corresponding to prior crack removal. Magnetic signatures from a fatigue crack at several intervals during propagation are presented. Modified author abstract
- Metallurgy and Metallography