Measurement of Adhesion Strength of Bonds Using Nonlinear Acoustics
It is well known that the nonlinear elastic behavior of solids modulates transmitting ultrasonic wave , Higher harmonics of the fundamental frequency are generated, especially second harmonics describing the deviation from the linear elastic behavior of the solid. Some effects were also observed in ultrasonic velocity  and transmission of ultrasound  due to the nonlinear elastic behavior of interfaces. In general, reduced bonding of joined materials causes a strong nonlinear elastic behavior . We exploit this for the observation of the modulation of the ultrasonic wave at interfaces [5,6]. There exist several models based on a macroscopic description of the interface restoring forces using for example the extended Hooke’s Law  or nonlinear spring relations [3,8].