PhD topic - MSCA Doctoral Networks USES2 - DC07: Nonlinear Coda Wave Interferometry imaging (NCWIi) with active and passive pumps

Context

The development of structures with high added value exposed to severe environmental conditions requires the development and monitoring of innovative materials that are adapted to each situation. 

Research on Non Destructive Evaluation and Structural Health Monitoring has followed this trend. At the same time, nonlinear acoustic methods developed over the last few years make it possible to access additional information, sometimes with more sensitivity and at an earlier stage of degradation than with linear methods. It is our aim to make the recently designed Nonlinear Coda Wave Interferometry (NCWI) method attractive for multiple application domains.

Recent works suggest that localisation of cracks that cannot be detected by more conventional methods (such as closed cracks in very heterogeneous materials) is possible with NCWI. This very sensitive method requires permanently installed sensors. The sensors have been so far mostly attached at the external surface of the material, but the method is in principle particularly well suited to the use of embedded sensors, which are the core of the USES2 project. It is expected that the robustness and imaging resolution of NCWI should benefit from such sensors.  Furthermore to lessen the energy required to operate NCWI, the challenge of using ambient noise is to be tackled. NCWI was first implemented on glass, then on concrete and lately to steel. Other embedding materials, such as composite materials, will be considered in connexion with USES2 members.

Objectives

NCWI tracks early damage in very heterogeneous materials like concrete - see e.g. (Zhang et al, 2012, Hilloulin et al, 2016, 2014) for laboratory studies and (Legland et al, 2017) for an on-site application. The physical idea behind NCWI is to activate, non destructively, the lips of cracks, including closed cracks, with a mechanical pump wave (clapping, sliding) and to detect this activation with coda waves. Very recent works link the new NCWI observables, initially obtained only experimentally, to intrinsic properties of the cracked zones via numerical modelling with the spectral element method (Chen et al., 2017, 2019). Laws connecting dimensions of the cracked area, its actual viscoelastic properties, the sizes of cracks, to NCWI observables were obtained numerically and validated in the laboratory with controlled cracks. Imaging with NCWI is still in its infancy but ongoing laboratory work (Smangin et al., 2020, Chen, 2019) suggests possible solutions for future on-site applications.

The aim of the thesis is to develop and validate a new imaging method, based on NCWI observables, that will locate and characterize closed cracks or micro-cracked areas in heterogeneous environments, that are inaccessible to linear ultrasonic imaging methods. The activation of the crack lips by ambient noise will be addressed. The optimization of the use of embedded sensors (type, number, location) to generate and record the coda wave probe for a given required resolution will also be studied.

Main tasks:
1) Define the characteristics of ambient noise compatible with relevant activation of crack lips through numerical and laboratory experiments
2) Develop an inverse problem with a forward model that uses NCWI observables, in reverberating and non reverberating media. Validate with dedicated numerical and laboratory data using an active pump.
3) Based on 1) and 2), adapt the NCWI imaging technique to passive pump, and design a controlled laboratory experiment that uses simulated ambient noise for the pump for validation.
4) Develop a methodology to optimise experimental set-ups that make use of embedded sensors to improve the resolution.
5) Validate the newly developed semi-passive NCWI imaging method with embedded sensors through a controlled laboratory experiment and on-site case studies recognized as pertinent in 1)

Expected Results

(1) Relevant characteristics of the ambient noise for NCWI
(2) Inverse problem algorithm in reverberating and nonreverberatingmedia
(3) Methodology to optimise experimental set-ups using embedded sources and receivers to improve spatial resolution
(4) Validation both in the laboratory and on-site with active and passive pumps.

References

• Chen G., Pageot D., Abraham O., Zhang Y., Chekroun M., Tournat V, Nonlinear Coda Wave Interferometry: sensitivity to wave-induced material property changes analyzed via numerical simulations in 2D, Ultrasonics, 99, 2019. https://doi.org/10.1016/j.ultras.2019.105968
• Chen G., Pageot D., Legland J.-B., Abraham O., Chekroun M., Tournat V., Numerical modeling of ultrasonic coda wave interferometry in a multiple scattering medium with a localized nonlinear defect, Wave Motion, 72, pp228-243, 2017. http://dx.doi.org/10.1016/j.wavemoti.2017.03.004
• Hilloulin B., Zhang Y., Abraham O.,  Loukili A. , Grondin F. , Durand O., Tournat V.,  Small crack detection in concrete with coda wave nonlinear modulation, International Journal of Nondestructive Testing and Evaluation, 68, pp.98-104, 2014. http://dx.doi.org/10.1016/j.ndteint.2014.08.010
• Hilloulin B., Legland J.-B., Lys E., Abraham O., Loukili A., Grondin F. , Durand D., Tournat V., Monitoring of autogenous crack healing in cementitious materials by the nonlinear modulation of ultrasonic coda waves, 3D microscopy and X-ray microtomography, JCBM, 123, pp143-152, 2016.  http://dx.doi.org/10.1016/j.conbuildmat.2016.06.138
• Legland J.-B., Zhang Y., Abraham O., Durand O., Tournat V., Evaluation of crack status in a meter-size concrete structure using the ultrasonic nonlinear coda wave interferometry, JASA, 142, 2233, 2017. http://dx.doi.org/10.1121/1.5007832
• Smagin N., Trifonov A., Bou Matar O., Aleshin. V., Local damage detection by nonlinear coda wave interferometry combined with time reversal,  Ultrasonics 108 (2020), p. 106226. issn: 0041-624X https://doi.org/10.1016/j.ultras.2020.106226
• Zhang Y., Abraham O., Tournat V., Le Duff A., Lascoup B., Loukili A., Grondin F., Durand O., Study of stress-induced velocity variation in concrete under direct tensile force and monitoring of the damage level by using thermally-compensated Coda Wave Interferometry, Ultrasonics, 52(8), pp1038-1045, 2012. http://dx.doi.org/10.1016/j.ultras.2012.08.011

Keywords

coda wave, non linear acoustics, ambient noise, imagery, ultrasonics