Nonlinear nonclassical acoustic method for detecting the location of cracks

Abstract

In this study, a new nonlinear acoustic method that makes full use of the sensitivity of higher harmonics caused by internal microcracks is proposed to locate multiple cracks in a one-dimensional bar. The tested bar was coupled with an acoustic emitter, the frequency used by the transducer is the eigenfrequency of the bar, and the boundary of the emitter can be treated as free. A mass load was added to the other end of the bar to provide an asymmetrical boundary condition. The receiver was scanned along the propagation direction of acoustic wave. The relationships between the amplitude, the phase of the harmonics, and the positions of the cracks can be used to locate multiple cracks in the bar. The higher harmonic frequencies induced due to crack nonlinearity are different from the eigenfrequencies of the bar. This creates an amplitude difference in the vibration on each side of the cracks and can be used to locate multiple cracks in a one-dimensional bar. Numerical calculations were carried out to verify the method and possible approaches to improve the accuracy of this method are discussed.