Impact damage detection in composites using a guided wave mixing technique.

Combined harmonics at sum- or difference-frequencies can be generated by the cross-interactions of guided wave mixing in tested samples with material nonlinearity. However, it is also observed that there are multiple combined harmonic modes generated at various mixing frequencies during the guided wave mixing process. It is still difficult to select certain combined harmonic modes to identify damage because the acoustic nonlinear response is much more complicated than the damage itself. Considering that multiple mixing frequency components can be generated during guided wave mixing, this paper investigates the feasibility of detecting impact damage in composite laminates through the combination of a guided wave mixing technique and a mixing frequency peak counting approach. Experimental observation of the combined harmonics at the mixing frequency generated by guided wave mixing clearly identifies the existence of material nonlinearity in the specimen. The present results show a monotonic increase in the correlation of the value of the mixing frequency spectral peak count with respect to the impact energy induced in the specimens. The developed technique provides an alternative for practical application of guided wave mixing for nondestructive testing in a quantizable manner. [ABSTRACT FROM AUTHOR]