Determination of epoxy film parameters in a three-layer metal/adhesive/metal structure

The aim of this work is to propose a method to determine the elastic parameters and the thickness of a thin epoxy film located inside a 3-layer aluminum/epoxy/aluminum structure, based on ultrasonic measurements. This study is conducted at low frequencies, to allow the vibration of the whole structure. First, the direct problem is addressed. The sensitivity of the vibration modes to the parameters of interest is studied to select the most sensitive one for a given parameter to be determined. Second, the identification of the parameters with the selected modes is obtained by a minimization of the characteristic equation. This process is applied to experimental data: the longitudinal and shear wave velocities and the thickness of the epoxy film are obtained within a 3% error range.