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A surface acoustic wave (SAW) technique has been observed to be effective in the detection of initiation and measurement of growth behavior of surface microcracks during fatigue cycling. The experimental procedure involving excitation of Rayleigh waves on the surface of a specimen under investigation is described in detail in conjunction with automated data acquisition of the reflected echo from a small surface crack. The effectiveness of a split spectrum processing algorithm to separate specular reflections of isolated cracks from non-specular reflections of microstructural features is also described. A simplified model for predicting the relationship between crack size and the amplitude of the reflected echo from a crack is included along with a description of the technique for measuring opening behavior of individual cracks in-situ during fatigue cycling. Examples of effective utilization of the SAW technique in contemporary investigations of small fatigue crack growth behavior are presented. Finally, the advantages and limitations of the technique are discussed.
surface acoustic waves, crack initiation, small crack growth, crack opening stress, closure, crack opening displacement, fatigue, nondestructive evaluation, residual stress, laser interferometric technique, nonlinear signal processing, split spectrum processing
Assistant professor, University of Nebraska-Lincoln, Lincoln, NE
Associate professor, Stanford University, Stanford, CA