Monitoring prestress in plates by sideband peak count-index (SPC-I) and nonlinear higher harmonics techniques

Propagating guided waves in a homogeneous, isotropic, prestressed, hyperelastic plate show nonlinear characteristics that depend on the state of initial prestress. These nonlinear phenomena include higher harmonic generation, occurring when Lamb wave modes of different frequencies (ωa and ωb) are allowed to mix within the material generating secondary waves at frequencies 2ωa, 2ωb and ωa ± ωb. Further, if prescribed internal-resonance conditions are satisfied, the amplitude of secondary waves increases in space, providing a response quantity which is dependent on prestress and easy to be observed. Using the finite element method, in this paper we investigatthe time and space evolution of higher harmonics arising in one-way wave mixing. The influence of prestress on the response is elucidated, observing the nonlinear parameter β. It is further shown that the nonlinear ultrasonic technique called Sideband Peak Count-Index (SPC-I) can provide an effective monitoring tool for prestress.