Thermal stress estimation of a constrained metallic plate using symmetric and antisymmetric Lamb wave group velocities

This paper presents a technique for estimating thermal-induced stress in constrained metallic plates using the group velocity of Lamb waves, the accuracy of which is crucial for assessing the structural integrity and serviceability of metallic structures. However, without the ability to gauge the current stress levels, obtaining such measurements is technically challenging. To overcome this, we propose a thermal stress estimation technique that uses changes in the group velocities of the fundamental symmetric (S₀) and antisymmetric (A₀) Lamb wave modes caused by thermal and stress variations. First, this study introduces a theoretical-based zero-crossing algorithm to measure the group velocities of S₀ and A₀ Lamb wave modes. Next, leveraging the acoustoelastic coefficients corresponding to the S₀ and A₀ modes, which are determined before the plate’s installation, this study generates the lines depicting the changes in group velocity induced by temperature variations (C_T) for both the S₀ and A₀ modes. These C_T lines are derived from the lines illustrating changes in group velocity due to thermal stress variations (C_TS), which are obtained after plate installation. Ultimately, the generated C_T lines can be used to estimate thermal stress throughout the entirety of the plate’s operational life span by isolating the distinct stress variation effects from the C_TS lines. The numerical validation results show favorable accuracy in thermal stress estimation in a constrained plate subjected to temperature variation using both S₀ and A₀ Lamb wave modes, with average errors of 0.63 % and 0.91 %, respectively.