Sensitivity of Higher Order Acoustoelastic Lamb Wave in Stressed Plates

Residual stress can occur during various metal working processes including rolling, forging and welding. Such stress can impact the performance of the material, including generating cracking and corrosion. To better control residual stresses, the initial distribution of stresses in materials must be known. Ultrasonic methods can be used as a good tool for non-destructive residual stress characterization and this can be achieved at modest cost. One approach is to employ Lamb waves the acoustoelastic effect for thin plate materials. This paper reports a study in which a numerical model is used to investigate Lamb wave dispersion curves for plates under load. The numerical result shows that the sensitivity of different modes varies and that the S-1 mode is the most sensitivity to the effects of load, as compared with S-0, A(0) and A(1) modes. If a local load of 100 MPa is applied the change in velocity for the S-1 mode can be as large to 40 m/s, which is about 6 times more than the effect on traditional bulk waves. This makes the S-1 mode potentially a good option for residual stress characterization in thin plates industry application.