10. Ultrasonics, Surface Waves
The scattered radiation of elastic waves from fatigue cracks in metals is interpreted for their detection and characterizations. The studies concentrated on predicting the remaining fatigue life for single fatigue cracks above the "threshold" value for macrocrack propagation. Acoustic surface waves were used to interrogate the crack during cyclic fatigue. The inversion of the scattering data provided crack depth and crack length as a function of fatigue. Auxiliary experiments were conducted to study effects of crack closure. Since the closure load depends strongly upon crack depth, especially in the near-threshold regime, improved life prediction is the expected result.
Tittmann, Bernard R. and Buck, Otto, "Fatigue Lifetime Prediction with the Aid of SAW NDE" (1980). Proceedings of the DARPA/AFML Review of Progress in Quantitative NDE, July 1978–September 1979. 64.