Theoretical and experimental investigation of the interaction forces in thin bonded interfaces by nonlinear ultrasonic transmission

Nonlinear stress-strain relations of adhesive bonds cause a nonlinear modulation of ultrasonic waves in reflection as well as in transmission provided sufficiently high strain amplitudes can be obtained. The amplitudes and phases of these waves contain information about the transfering interaction forces. Thin bonded interfaces can be approximately described only by binding forces without taking into account directly the material properties of the adhesive layer. In this case, the local interaction forces, which may contain damping and hysteretic effects, can be probed by the measured amplitudes and phases of the ultrasonic waves transmitted through the interface. The input and output wave parameters are calibrated interferometriacally to yield absolute interaction force values. This paper presents calibrated measurements on samples consisting of two aluminum plates joined together by a thin epoxy layer.