Experimental Characterization of Impact Fatigue Damage in an Adhesive Bonding Using the Second Harmonics

An adhesive bonding is widely used in various industrial applications. In this paper, an application of non-destructive evaluation (NDE) technique based on the second harmonics for experimental characterization of impact fatigue damage in an adhesive bonding is presented. Adhesively bonded specimens made from AZ31 magnesium–aluminum alloy were firstly subjected to impact fatigue loading; the ultrasonic harmonics generated due to impact fatigue damage within the adhesive layer were thereafter measured. The acoustic nonlinearity parameter (ANP) based on the fundamental and second harmonics was thus obtained. The experimental results show that the normalized ANP, which is an indicator of material properties, increases with the impact fatigue life. Further discussion based on a theoretical model with different interfacial compression and tension stiffness was also conducted. The experimental results consist well with the theoretical ones. The results in this paper demonstrate that the nonlinear ultrasonic method based on the second harmonic generation technique can be used to characterize the impact fatigue damage in an adhesive bonding.