Location and Length Measurement of Invisible Fatigue Crack in Metal Components Using Wave Mixing Methods

For the invisible fatigue crack embedded in metal components, wave mixing methods are applied for the fatigue crack location and length measurement. When two incident waves meet within a component, a nonlinear interaction occurs and a third wave is generated, which is related to the damage degree of the meeting position of the two incident waves. When the delay time of incident waves changed in collinear wave mixing experiments, different meeting positions along the length direction of components were detected. The relationship between the sideband amplitude at difference or sum frequencies and delay time is obtained, and the delay time corresponding to the maximum amplitude is applied to locate the fatigue crack along the length direction. Then, adjusting the placing locations of transducers in the noncollinear wave mixing experiment, the meeting position of incident waves is controlled at the fatigue crack decided by the collinear wave mixing experiment. Next, changing the separation distance of two transmitters, the detection positions would be along the vertical direction of the components. The mixing nonlinear parameters of different detection positions are calculated, and the length of the fatigue crack can be measured in a vertical direction based on the distribution of the mixing nonlinear parameter.