A nonlinear ultrasonic approach to evaluate adhesive bond cure conditions

We have investigated several linear and nonlinear ultrasonic methods to study different cure conditions of adhesive bonds in an aluminum/adhesive/aluminum system. In this paper, we report on some theoretical aspects and experimental results obtained using a normal incidence harmonic generation setup in which the sample is embedded in water. In our approach, ultrasonic tone burst signals at increasing power levels and over a wide frequency range are coupled into a sample in order to analyze its nonlinear resonance behavior. Using a local strain analysis in the linear approximation, we will discuss excitation-power dependent changes observed particularly in the higher harmonic frequency transfer spectrum.