Modulation scheme of nonlinear waves for effective crack detection

Abstract

This study presents nonlinear ultrasonic wave modulations that can be effectively used for crack detection in thin structural components. Fatigue cracks occur when structure is exposed to repeated load although the load causes the smaller stress than the yield stress. The existence of cracks deteriorates the integrity of structures and reduces the safety. To detect these cracks, several kinds of nonlinear ultrasonic wave modulation techniques have been proposed for many years. However, the fundamental reason of the nonlinearity has not been well explained theoretically yet. Mostly, the phenomenon has been investigated experimentally. In order to find the reasons of the observed modulation, numerical studies are performed considering a variety of sizes of crack widths and depths using a commercial FEA program.