Towards an Inverse Characterization of Third Order Elastic Constants Using Guided Waves

The acoustoelastic effect describes the change in propagation velocities of elastic waves due to mechanical prestress and is based on geometric and material nonlinearity. Models describing the effect heavily depend on the knowledge of the third order elastic constants (TOEC). Established acquisition methods of these constants rely on the measurement of bulk speeds of sound and analytic calculations. In this contribution, we propose an alternative method by making use of the dispersive character of guided waves in plates. Uniaxial tensile stress is applied to homogeneous metallic plates. The changes in wavenumber are calculated from laser vibrometer aided measurements. These changes depend on a trigonometric function of the direction of wave propagation and increase linearly with the prestress amplitude. Using this prior knowledge, we perform an inverse characterization of the TOEC by iteratively fitting a numerical model of the prestressed waveguide to constants of the trigonometric relation. The proposed method is verified using simulated reference data.