Longitudinal wave propagation in adhesive structure under different forms of interfaces

The description of the wave propagation in the multilayer adhesive structure under different forms of interfaces is very complex. For this issue, the reflection and transmission coefficient expressions of longitudinal and transverse waves with the dimensionless parameter of ωτ in the trilaminar plate-like adhesive structure are derived when the adhesive layer is assumed to be viscoelastic material with a relaxed time of τ. Aluminum-epoxy resin-polystyrene adhesive structure is taken as an example to analyze the impact of changes in the angle of incidence on acoustic wave reflection and transmission characteristics. Numerical results show that regardless of the value of ωτ, interface form can not be identified in the case of normal incidence or grazing incidence of longitudinal wave. In a particular products of frequency-thickness, if the angle of incidence is appropriate, the methods of reflection and transmission coefficients of longitudinal wave or transverse wave reflection coefficient can be adopted to detect the perfect, sliding and weak bonding interfaces. The results provide a theoretical basis for the experiment of the adhesive structure by means of ultrasonic testing.