Measuring acoustic nonlinearity parameter using collinear wave mixing

This study introduces a new acoustic nonlinearity parameter beta(T). It is shown that beta(T) is associated with the interaction between a longitudinal wave and a shear wave in isotropic elastic solids with quadratic nonlinearity. Experimental measurements are conducted to demonstrate that the collinear wave mixing technique is capable of measuring beta(T) nondestructively. Further, it is shown that beta(T) is well-correlated with the plastic deformation in Al-6061 alloys. These results indicate that collinear wave mixing is a promising method for nondestructive assessment of plastic deformation, and possibly, fatigue damage in metallic materials. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739746]