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

Review of progress, QNDE

This paper presents a comprehensive review of the current state of knowledge of second harmonic generation (SHG) measurements, a subset of nonlinear ultrasonic nondestructive evaluation techniques. These SHG techniques exploit the material nonlinearity of metals in order to measure the acoustic nonlinearity parameter, $$\beta $$
 . In these measurements, a second harmonic wave is generated from a propagating monochromatic elastic wave, due to the anharmonicity of the crystal lattice, as well as the presence of microstructural features such as dislocations and precipitates. This article provides a summary of models that relate the different microstructural contributions to $$\beta $$
 , and provides details of the different SHG measurement and analysis techniques available, focusing on longitudinal and Rayleigh wave methods. The main focus of this paper is a critical review of the literature that utilizes these SHG methods for the nondestructive evaluation of plasticity, fatigue, thermal aging, creep, and radiation damage in metals.

/pdf/review-of-second-harmonic-generation-measurement-techniques-8pdcwltmqt.pdf

Review of Second Harmonic Generation Measurement Techniques for Material State Determination in Metals

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

Review of air-coupled ultrasonic materials characterization.

Nonlinear modulation technique for NDE with air-coupled ultrasound.

Air-coupled ultrasound inspection of various materials.

The area of NDE-applications of air-coupled ultrasound is expanded substantially for a weakly focused acoustic wave incident obliquely on a plate-like sample at an angle of ‘resonance’ transmission. Such a focused slanted transmission mode (FSTM) combines the benefits of plate wave excitation with a high spatial resolution and enables to characterise local elastic properties of a material. It was shown that the in-plain elastic anisotropy could be obtained by measurement of the ‘resonance’ transmission angle of the FSTM-output signal as a function of the azimuth angle. A striking contrast enhancement was demonstrated for the FSTM-C-scan imaging of cracked defects and delaminations. Non-contact FSTM-measurements of local variations of flexural wave velocity were used to detect fine structural changes and damage induced in polymer and composite materials during tensile tests.

New opportunities for NDE with air-coupled ultrasound

Characterization of stiffness degradation caused by fatigue damage in textile composites using circumferential plate acoustic waves

The results of non-contact measurements of local inplane elastic anisotropy in wood by monitoring the flexural plate wave velocity as a function of azimuth angle of propagation are reported. The Focused Slanted Transmission of air-coupled ultrasound is used to generate and detect locally the flexural waves in wood as well as to measure their velocities. The analysis presented shows that for thin plates the flexural wave velocity can be readily used to evaluate the anisotropy of Young's modulus. This conclusion is confirmed by measurements of the plate wave anisotropy factors for veneer laminae and cross-ply laminates of spruce and beech. The technique is sensitive enough to detect the anisotropy variation of earlywood caused by the incorporation of latewood areas in growth rings. A new approach based on dynamic nonlinearity of wood is developed and applied to acoustic imaging of wood structure and detecting of defects in wood. The hysteresis mechanism of the dynamic nonlinearity is shown to dominate in clear wood and to manifest in a primary generation of odd acoustic harmonics. Local maxima of the odd higher harmonic amplitudes in the LR- and LT-planes of softwood are observed in the earlywood area close to latewood/earlywood transition interface that indicates the lower stiffness and strength of wood in those areas. The higher-order even harmonics and subharmonics in the nonlinear vibration spectra of wood are mostly produced by clapping in defect areas. Measurements of local amplitudes of these modes are applied to nonlinear acoustic imaging of cracks, delaminations and knots in wood and wood composites.

K. Pfleiderer

Papers

Nonlinear modulation technique for NDE with air-coupled ultrasound.

Air-coupled ultrasound inspection of various materials.

New opportunities for NDE with air-coupled ultrasound

Characterization of stiffness degradation caused by fatigue damage in textile composites using circumferential plate acoustic waves

Nondestructive characterization of wood by monitoring of local elastic anisotropy and dynamic nonlinearity