Experimental evaluation of non-collinear shear wave mixing to characterize interface nonlinearity

In the search for techniques to distinguish between merely good and excellent bond conditions, linear reflection based methods are simple to apply, but their sensitivity decreases rapidly with increasing bond quality. As an alternative, this research reports on the experimental validation of analytical and computational models of interface properties using non-collinear shear wave mixing. The interface between two solids in dry contact under varying contact pressures serves as a model for diffusion bonds with different degrees of imperfection. Both nonlinear shear–shear wave mixing and linear reflection and transmission measurements are considered. The results show that under increasing load, the nonlinear interface interaction coefficients decrease more slowly in comparison to analogous linear coefficients, demonstrating the higher sensitivity of nonlinear coefficients to subtle interface imperfections in high quality bonds. This comparison is achieved by integrating approximate phenomenological models with the experimentally measured data. Overall, these findings demonstrate the utility of non-collinear shear wave mixing for localized nonlinear interface measurements, and highlight advantages over linear methods for interface characterization.