Numerical modeling of ultrasonic coda wave interferometry in a multiple scattering medium with a localized nonlinear defect

Nonlinear Coda Wave Interferometry: Sensitivity to wave-induced material property changes analyzed via numerical simulations in 2D

“…This so-called nonlinear coda wave interferometry (NCWI) method was then successfully applied to a mortar sample by Hilloulin et al [9] and subsequently to concrete [10]. In this context, we recently performed a numerical parametric study in [1] using a 2D spectral element method (SEM2D) [23] as a forward modeling tool. In [1], the objective was to reproduce the coda wave signal modifications induced by slight local modifications to the effective elastic properties of a given sample.…”

“…In this context, we recently performed a numerical parametric study in [1] using a 2D spectral element method (SEM2D) [23] as a forward modeling tool. In [1], the objective was to reproduce the coda wave signal modifications induced by slight local modifications to the effective elastic properties of a given sample. These modifications were supposedly produced via nonlinear elastic effects from a pump wave of varying amplitude, like in the experiment by Zhang et al [21] and by considering the same material configuration, i.e.…”

“…These parameters could be useful for the diagnosis or comparison of samples quality, for the evaluation of fatigue. The numerical study [1] thus consisted of a number of linear elastic wave propagation simulations, each extending for a time of hundreds of probe wave periods.…”

“…The present paper makes use of the numerical tools developed in [1] to further investigate the impacts of various EDZ parameters on the CWI observables for a multiply reverberated coda wave. The first part tests the method limitations by parametric studies that consider a broad array of elastic EDZ contrasts with the matrix material, for a wide range of relative EDZ sizes.…”

“…The numerical studies conducted in this paper are based on our previous research (Chen et al, 2017); through use of the spectral element method, parametric sensitivity studies of Nonlinear Coda Wave Interferometry (NCWI) are established here and divided into two parts. In the first part, CWI observables are found to be proportional to the product of the changes in elastic modulus within the Effective Damaged Zone (EDZ) and the EDZ surface area.…”