Ultrasonic nonlinear resonant characteristics at adhesion interfaces of bonded two-layer plate

The electricity-mechanics-acoustics analogy model was employed to derive the analytical resonant equation of adhesive bonded two-layer plates.We theoretically studied the effect of the adhesive parameters on the nonlinear resonant behavior,such as linear stiffness,high order stiffness and the excitation strength and so on.In the ultrasonic experiments of two-layer aluminum plates,the measured resonance frequencies of the imperfect adhesive bonds were found larger than those of perfect bonds and the more stronger third-order harmonic was generated;while the second-order harmonics related to the second-order stiffness had little correlation to the nonlinear resonance frequencies.The ultrasonic experimental results basically agreed with the theoretical analysis,and demonstrated that the nonlinear resonance would be more significant in imperfect adhesive bonds with bigger linear stiffness,particularly for early degradation and weak bonding of the bonded plate;the third-order stiffness made more contribution to the nonlinear resonant frequencies.