Linear and nonlinear ultrasonic characterization of single-layered structures

The linear and nonlinear properties of a solid and single layered material can be described by the second- and third-order elastic constants measured from the bulk wave velocities and dispersive properties of special guided wave modes. A new technique was developed to measure the acoustoelastic effects in 6061-T6 aluminum and perspex. The calculated third-order elastic constants were in good agreement with previously published results. Theoretical and experimental results for measuring higher-order nonlinearities were presented. By reducing or eliminating the strong first-order shear wave birefringence effect the much weaker higher-order nonlinearities for 6061-T6 aluminum could be measured. The acoustoelastic effects for a prestressed adhesive layer were calculated using the finite deformation theory. Newly developed equations relating the stress-dependent bulk wave velocities and the second- and third-order elastic constants for the adhesive layer are presented. An ultrasonic technique used to measure the bulk wave velocities from the reflected spectrum of a single layer was further developed to measure the stress-dependent bulk wave velocities of a prestressed adhesive layer. Results are presented for the stress-dependent longitudinal and shear wave velocities as a function of the normal stress component in the adhesive layer. The frequency-dependent transmission coefficients were calculated and measured for the Lamb and interface waves in an adhesive joint. A double transmission technique was developed in order to measure both types of guided wave modes in the adhesive joint. The acoustical coupling efficiency for the Lamb waves in an adhesive joint were evaluated by comparing the measured Lamb waves in the adhesive joint to numerical calculations made for a single adherend plate. The Lamb waves are very complicated to analyze and evaluate and are mostly sensitive to the properties of the adherend plates and less sensitive to the adhesive layer and interface. On the other hand, the interface waves are much easier to analyze and evaluate and are more sensitive to the properties of the adhesive layer.