Nonlinear mixing of ultrasonic coda waves with lower frequency-swept pump waves for a global detection of defects in multiple scattering media

Abstract

An ultrasonic method providing for an efficient global detection of defects in complex media (multiple scattering or reverberating media) is reported herein; this method is based on the nonlinear acoustic mixing of coda waves (stemming from multiple scattering) with lower frequency-swept pump waves. Such a nonlinear mixing step is made possible by the presence of nonlinear scatterers, such as cracks and delamination, yet remains absent when the waves are scattered only by linear scatterers, as is the case in a complex but defect-free medium. A global inspection is achieved thanks to the use of wide-band coda and pump signals, which ensure the excitation of many resonances along with a homogeneous acoustic energy distribution in the medium. We introduce the existing sensitivity tools developed for Coda Wave Interferometry in extracting the pump amplitude-dependent parameters of the coda waves associated with effective nonlinear parameters of the medium. By comparing results at two damage levels, these effective nonlinear parameters are shown to be correlated with crack presence in glass samples. The mechanisms potentially responsible for the observed amplitude dependence on the tested elastic parameters and waveform modification are discussed.

Coda wave interferometry for the measurement of thermally induced ultrasonic velocity variations in CFRP laminates

“…The comparison of several multiply scattered ultrasonic waves and the extraction of differential signal features makes Coda Wave Interferometry (CWI) very sensitive to the detection of small perturbations of the elastic wave propagation within scattering media. Several perturbation types (thermal loading [6][7][8][9][10], mechanical loading [11][12][13], and cracking/degradation [14][15][16]) have already been examined. The sensitivity of CWI has been demonstrated for rocks [17], concrete [6][7][8][9][10][11][12][13][14][15][16], and metals [18].…”

Fatigue crack detection using nonlinear vibro-acoustic cross-modulations based on the Luxemburg-Gorky effect

“…The Luxembourg-Gorky effect based method has been applied for detection of thermal cracks in glass [15,16,22,23], impact damage in composite plates [24] and damage in granular media [25]. …”

Monitoring of autogenous crack healing in cementitious materials by the nonlinear modulation of ultrasonic coda waves, 3D microscopy and X-ray microtomography

“…Many distinct signal shapes may be input as pump and probe waves; however, the use of higherorder modulation side lobes or amplitude-modulated pump waves has shown greater sensitivity to the presence of cracks than other nonlinear modulation techniques [46]. By using nonlinear modulation and diffuse ultrasound to perform coda wave interferometry, we have recently proven that a very high level of precision can be obtained, hence enabling the detection of very small cracks as well as discriminating between different crack volumes [47,48]. Then throughout this paper, we describe the methodology we fol-lowed to increase nonlinear coda wave interferometry so that it can detect small cracks and can be used as a monitoring technique.…”