Nonlinear Lamb wave mixing for assessing localized deformation during creep

Nonlinear ultrasonic is known to be a promising technique to characterize the microstructural degradation in engineering materials. This work demonstrates the use of nonlinear Lamb wave mixing technique to assess the localized deformation in modified 9Cr1Mo steel during creep. Two Lamb wave modes of different frequencies (ω1 & ω2) are allowed to mix within the material under certain resonant condition to generate third type of harmonic waves of frequencies (ω1±ω2). This new generated wave carries the information of material nonlinearity from the mixing site and independent of the other extraneous nonlinear factors. Amplitude of the generated third wave depends on the third order elastic constants of the material. This study reveals that nonlinear Lamb wave mixing technique could be used to assess the localized deformation much prior to its failure.