Ultrasonic wave propagation in thick, layered composites containing degraded interfaces

Abstract

The ultrasonic wave propagation of thick, layered composites containing degraded bonds is investigated. A theoretical one-dimensional model of three attenuative viscoelastic layers containing two imperfect interfaces is introduced. Elastic material properties and measured 'values of ultrasonic phase velocity and attenuation are used to represent E-glass and vinyl ester resin fiber-reinforced plastic (FRP) laminate, syntactic foam, and resin putty materials in the model. The ultrasonic phase velocity in all three materials is shown to be essentially constant in the range of 1.0 to 5.0 megahertz (MHz). The attenuation in all three materials is constant or slightly increasing in the range 1.0 to 3.0 MHz. Numerical simulation of the model via the mass- spring-dashpot lattice model reveals the importance of the input signal shape, wave speed, and layer thickness on obtaining non-overlapping, distinct return signals in pulse-echo ultrasonic nondestructive evaluation. The effect of the interface contact quality on the reflection and transmission coefficients of degraded interfaces is observed in both the simulated and theoretical results.