Remaining fatigue life prediction in the initiation regime using SAW NDE

Harmonic generation of surface acoustic waves (SAW) is shown to be a useful tool for the detection of the initiation of surface cracks during fatigue of high strength aluminum alloys. A model that relates the length and density of microcracks to the amplitude of a SAW harmonic signal is described, and an associated coefficient of generation efficiency for the second harmonic amplitude is derived. A correlation between experimentally measured harmonic amplitude and remaining fatigue life is then demonstrated, which allows the mean remaining fatigue lifetime to be estimated to within 5% over the last 50% of the fatigue life for an Al 7075 alloy if the cyclic stress amplitude, but not the duration of fatigue, is known.