Measurement of dynamic stress using linear and nonlinear acoustoelastic effects due to colinear wave mixing

This paper investigates a new method to evaluate dynamic stress in plate or shell-like components due to propagation of elastic waves. The proposed method is based on collinear mixing of the stress wave with a high frequency (probe) wave, which is excited in the ultrasonic frequency range. The wave interactions generate linear and nonlinear responses such as the changes of the group velocity of the probe wave and generation of higher-order harmonics, respectively. A three-dimensional finite element (FE) model is developed to investigate and link these changes to the magnitude of the dynamic stress excited by the elastic waves. In the current work two S₀ Lamb wave modes at relatively low and high frequences were utilised to demonstrate the proposed method, which can be extended to the measurement of dynamic stress generated by different elastic wave modes or vibrations. The numerical results have been validated by an experimental study confirming that the nonlinear effects are much more sensitive to the induced dynamic stress rather than the corresponding linear changes of the wave velocities. In addition, two parametric studies are conducted using the experimentally verified FE model. These studies are focused on the effects associated with the stress variation in the mixed region and the wavelength ratio of the probe wave to the pump waves on the dynamic stress evaluation with the proposed method.