The paper provides a state of the art review of guided wave based structural health monitoring (SHM). First, the fundamental concepts of guided wave propagation and its implementation for SHM is explained. Following sections present the different modeling schemes adopted, developments in the area of transducers for generation, and sensing of wave, signal processing and imaging technique, statistical and machine learning schemes for feature extraction. Next, a section is presented on the recent advancements in nonlinear guided wave for SHM. This is followed by section on Rayleigh and SH waves. Next is a section on real-life implementation of guided wave for industrial problems. The paper, though briefly talks about the early development for completeness,. is primarily focussed on the recent progress made in the last decade. The paper ends by discussing and highlighting the future directions and open areas of research in guided wave based SHM.

https://iopscience.iop.org/article/10.1088/0964-1726/25/5/053001/pdf

Guided wave based structural health monitoring: A review

The level of nonlinearity in the elastic response of materials containing structural damage is far greater than in materials with no structural damage. This is the basis for nonlinear wave diagnostics of damage, methods which are remarkably sensitive to the detection and progression of damage in materials. Nonlinear wave modulation spectroscopy (NWMS) is one exemplary method in this class of dynamic nondestructive evaluation techniques. The method focuses on the application of harmonics and sum and difference frequency to discern damage in materials. It consists of exciting a sample with continuous waves of two separate frequencies simultaneously, and inspecting the harmonics of the two waves, and their sum and difference frequencies (sidebands). Undamaged materials are essentially linear in their response to the two waves, while the same material, when damaged, becomes highly nonlinear, manifested by harmonics and sideband generation. We illustrate the method by experiments on uncracked and crac...

Nonlinear Elastic Wave Spectroscopy (NEWS) Techniques to Discern Material Damage, Part I: Nonlinear Wave Modulation Spectroscopy (NWMS)

Review of progress, QNDE

Dynamic nonlinear elasticity in geomaterials

Finite-amplitude waves in isotropic elastic plates

Novel nonlinear-modulation methods for crack detection are discussed. The approach is based on the so-called cross-modulation effect consisting of the modulation transfer from an intensive, initially slowly amplitude-modulated stronger (pump) excitation to the probe signal. Advantage of this technique is a very flexible choice of the operation frequencies, since their ratio for both carriers and the modulation may be rather arbitrary. This in its turn allows one to effectively use the sample resonances in order to achieve the necessary level of the pump excitation and to ameliorate conditions for detection of the modulation sidelobes for the probe wave. Unlike higher harmonic-generation methods the initial nonlinear distortions of the pump and probe excitations (e.g. due to nonlinearities in the electronics) are not critical for this technique. In the paper we summarise results of recent test experiments that indicated high sensitivity of the new technique.

/pdf/novel-nonlinear-modulation-acoustic-technique-for-crack-19q1rc4h0s.pdf

Novel nonlinear-modulation acoustic technique for crack detection

Rectification (demodulation) of high-frequency shear acoustic bursts is applied to probe the distribution of contact forces in 3D granular media. Symmetry principles allow for rectification of the shear waves only with their conversion into longitudinal mode. The rectification is due to nonlinear dynamic dilatancy, which is found to follow a quadratic or Hertzian power law in the shear wave amplitude. Evidence is given that a significant portion of weak contact forces is localized below ${10}^{\ensuremath{-}2}$ of the mean force---a range previously inaccessible by experiment. Strong anisotropy of nonlinearity for shear waves with different polarization is observed.

/pdf/probing-weak-forces-in-granular-media-through-nonlinear-41mtdir5fb.pdf

Probing weak forces in granular media through nonlinear dynamic dilatancy: clapping contacts and polarization anisotropy.

This paper is a brief overeview of experimental studies of nonlinear acoustic phenomena due to the presence of cracks in solids. The possibilities for using these phenomena in crack diagnostics are discussed. To explain the observed effects, we present the physical models of a single crack and a fractured medium.

Nonlinear acoustic methods of crack diagnostics

An interaction of a CW acoustic wave and a powerful acoustic pulse due to nonlinear properties of a crack-type discontinuity in a solid is considered. Characteristics of nonstationary variations of the reflected wave amplitude and the phase of the transmitted wave, which are induced by the powerful pulse, are determined. The effects should allow one to distinguish cracks from other scatterers and can be used as a base of a new method of crack detection and positioning. Demonstrative signal estimates based on two simplified crack models are presented.

Nonlinear Interaction of Acoustical Waves Due to Cracks and Its Possible Usage for Cracks Detection

A nonlinear effect consisting of transfer of modulation from one amplitude-modulated elastic wave, the "pump" wave, to the second initially monochromatic probe wave has been recently introduced in nonlinear acoustics by analogy with radio waves. For the first time, this effect is applied to probe perturbations of the state of a granular material induced by shocks, "seismic events". The experiments indicate a much stronger variability of the nonlinearity-induced modulation sidelobes in comparison with changes in the components at the fundamental frequencies of the probe and pump waves. Another new feature revealed in the experiments is that the transitional shock-induced variations in the amplitudes of the modulation sidelobes are several times stronger than the relaxed, residual values of the changes. The effects observed suggest interesting possibilities to application in active acoustic/seismic monitoring schemes.

/pdf/luxemburg-gorky-effect-in-a-granular-medium-probing-52e7frkiif.pdf

V. E. Nazarov

Papers

Novel nonlinear-modulation acoustic technique for crack detection

Probing weak forces in granular media through nonlinear dynamic dilatancy: clapping contacts and polarization anisotropy.

Nonlinear acoustic methods of crack diagnostics

Nonlinear Interaction of Acoustical Waves Due to Cracks and Its Possible Usage for Cracks Detection

Luxemburg-Gorky effect in a granular medium: Probing perturbations of the material state via cross-modulation of elastic waves