Full-field imaging of nonclassical acoustic nonlinearity

The feasibility of full field shearographic detection of nonclassical acoustic nonlinearity is investigated. Traditional frequency analysis of the sinusoidally excited sample, as used in scanning techniques, turns out to be not practical due to the inherent optical detection nonlinearity of the shearography system itself. An alternative method, based on determining the asymmetry between shearographic images stroboscopically obtained for positive and negative displacements, is proposed. This approach allows us to easily and rapidly detect the tension-compression asymmetry which typically arises where nonbounded contact interface defects are present.