Nonlinear Acoustic Methods for Crack Vision

A crack is acoustically highly nonlinear object. It produces different nonlinear acoustic responses such as higher harmonics generation or nonlinear modulation of an ultrasound wave passing through or reflected from a crack by low frequency vibrations of a tested object. These effects are used for development of the methods of nonlinear acoustic nondestructive testing. Simple nonlinear techniques can be used for detection of damaged objects. However, they cannot give information on crack location. Advanced methods allow one to measure crack position. In this paper we describe the modulation acoustic methods of crack location in a testing sample.