Numerical analysis of the effect of longitudinal tensile stress on the time-reversal focusing of Lamb waves in plates

The evaluation of the strain state is a usual practice to health monitoring mechanical structures. In a previous work, the time-reversal signal processing was theoretically and experimentally evaluated to measure the strain in plates. In this work, the theoretical analysis is extended to include acoustoelastic effects and border conditions. The influence of high longitudinal tensile stress on the time-reversal process in plates is analyzed by means of finite element simulations using commercial software. The load effect is introduced in simulations by using the effective elastic constants as the material stiffness matrix according to the acoustoelastic theory. As an example to evaluate the simulations, a 3mm thick aluminum plate has been modeled subjected to longitudinal tensile loads from zero up to 120 MPa. A single emitter-receiver setup is used. The spectral content and the Lamb modes able to propagate are selected by the excitation signal, imposed as an out-of-plane displacement. Two scenarios are analyzed, an infinite plate and finite long plate considering reflections at the borders. Results show the ability of the commercial software to simulate the time reversal process in strained media using acoustoelastic constants. In the finite-length plate scenario, where end reflections occur, the time-reversal focus sensitivity to stress changes is much greater.