http://ieeexplore.ieee.org/iel5/5/31047/01444179.pdf

Fundamentals of acoustics

The nondestructive assessment of the damage that occurs in components during service plays a key role for condition monitoring and residual life estimation of in-service components/structures. Ultrasound has been widely utilized for this; however most of these conventional methods using ultrasonic characteristics in the linear elastic region are only sensitive to gross defects but much less sensitive to micro-damage. Recently, the nonlinear ultrasonic technique, which uses nonlinear ultrasonic behavior such as higher-harmonic generation, subharmonic generation, nonlinear resonance, or mixed frequency response, has been studied as a positive method for overcoming this limitation. In this paper, overall progress in this technique is reviewed with the brief introduction of basic principle in the application of each nonlinear ultrasonic phenomenon.

Nonlinear ultrasonic techniques for nondestructive assessment of micro damage in material: A review

The influence of fluid mobility on seismic velocity dispersion is directly observed in laboratory measurements from seismic to ultrasonic frequencies. A forceddeformation system is used in conjunction with pulse transmission to obtain elastic properties at seismic strain amplitude (10 −7 ) from 5 Hz to 800 kHz. Varying fluid types and saturations document the influence of pore-fluids. The ratio of rock permeability to fluid viscosity defines mobility, which largely controls pore-fluid motion and pore pressure in a porous medium. High fluid mobility permits pore-pressure equilibrium either between pores or between heterogeneous regions, resulting in a low-frequency domain where Gassmann’s equations are valid. In contrast, low fluid mobility can produce strong dispersion, even within the seismic band. Here, the low-frequency assumption fails. Since most rocks in the general sedimentary section have very low permeability and fluid mobility (shales, siltstones, tight limestones, etc.), most rocks are not in the lowfrequency domain, even at seismic frequencies. Only those rocks with high permeability (porous sands and carbonates) will remain in the low-frequency domain in the seismic or sonic band.

/pdf/fluid-mobility-and-frequency-dependent-seismic-velocity-1ld9hdd9r6.pdf

Fluid mobility and frequency-dependent seismic velocity — Direct measurements

流体力学用語集 非線形音響学(Nonlinear acoustics)

Modelling of nonlinear crack–wave interactions for damage detection based on ultrasound—A review

(Received 14 July 2006; published 7 March 2007)This Letter reports on work performed to locate and interrogate a nonlinear scatterer in a linearly elasticmedium through the use of a time reversal mirror in combination with nonlinear dynamics. Time reversalprovides the means to spatially and temporally localize elastic energy on a scattering feature while thenonlinear dynamics spectrum allows one to determine whether the scatterer is nonlinear (e.g., mechanicaldamage). Here elastic wavesare measured in a solid and processed to extract the nonlinear elastic response.The processed elastic signals are then time reversed, rebroadcast, and found to focus on the nonlinearscatterer, thus deﬁning a time-reversed nonlinear elastic wave spectroscopy process. Additionally, thefocusing process illuminates the complexity of the nonlinear scatterer in both space and time, providing ameans to image and investigate the origins and physical mechanisms of the nonlinear elastic response.

Interaction dynamics of elastic waves with a complex nonlinear scatterer through the use of a time reversal mirror.

Nonlinear elastic wave spectroscopy (NEWS) has been shown to exhibit a high degree of sensitivity to both distributed and isolated nonlinear scatterers in solids. In the case of an isolated nonlinear scatterer such as a crack, by combining the elastic energy localization of the time reversal mirror with NEWS, it is shown here that one can isolate surfacial nonlinear scatterers in solids. The experiments presented here are conducted in a doped glass block applying two different fixed frequency time-reversed signals at each focal point and scanning over a localized nonlinear scatterer (a complex crack). The results show a distinct increase in nonlinear response, via intermodulation distortion, over the damaged area. The techniques described herein provide the means to discriminate between linear and nonlinear scatterers, and thus to ultimately image and characterize damaged regions.

Imaging nonlinear scatterers applying the time reversal mirror

Developed in the late 1980s, Nonlinear Resonant Ultrasound Spectroscopy (NRUS) has been widely employed in the field of material characterization. Most of the studies assume the measured amplitude to be proportional to the strain amplitude which drives nonlinear phenomena. In 1D resonant bar experiments, the configuration for which NRUS was initially developed, this assumption holds. However, it is not true for samples of general shape which exhibit several resonance mode shapes. This paper proposes a methodology based on linear resonant ultrasound spectroscopy, numerical simulations and nonlinear resonant ultrasound spectroscopy to provide quantitative values of nonlinear elastic moduli taking into account the 3D nature of the samples. In the context of license renewal in the field of nuclear energy, this study aims at providing some quantitative information related to the degree of micro-cracking of concrete and cement based materials in the presence of thermal damage. The resonance based method is validated as regard with concrete microstructure evolution during thermal exposure.

https://hal.archives-ouvertes.fr/hal-01044669/document

Quantitative linear and nonlinear resonance inspection techniques and analysis for material characterization: Application to concrete thermal damage

With the recent application of time reversed acoustics and nonlinear elasticity to imaging mechanical damage, the development of time reversal based nondestructive evaluation techniques has begun. Here, diffusion bonded metal disks containing intentionally disbonded regions are analyzed using the time reversed elastic nonlinearity diagnostic. The nonlinear results are compared with linear ultrasonic imaging (C scan). Scanning electron microscopy is shown to illustrate the differences between the features seen by the linear and nonlinear methods.

/pdf/the-time-reversed-elastic-nonlinearity-diagnostic-applied-to-27xnz3euli.pdf

The time reversed elastic nonlinearity diagnostic applied to evaluation of diffusion bonds

Non-linear elastic wave spectroscopy (NEWS) has been shown to exhibit a high degree of sensitivity to both distributed and isolated nonlinear scatterers in solids. In the case of an isolated non-linear scatterer such as a crack, by combining the elastic energy localization of time reversal (TR) with NEWS, it is shown that one can isolate non-linear scatterers in solids. The experiments reviewed here present two distinct methods of combining TR and NEWS for this purpose. The techniques each have there own advantages and disadvantages, with respect to each other and other non-linear methods, which are discussed. 2008 Published by Elsevier Ltd.

Timothy J. Ulrich

Papers

Interaction dynamics of elastic waves with a complex nonlinear scatterer through the use of a time reversal mirror.

Imaging nonlinear scatterers applying the time reversal mirror

Quantitative linear and nonlinear resonance inspection techniques and analysis for material characterization: Application to concrete thermal damage

The time reversed elastic nonlinearity diagnostic applied to evaluation of diffusion bonds

Time reversal and non-linear elastic wave spectroscopy (TR NEWS) techniques