Igor Solodov

Nonlinear self-modulation and subharmonic acoustic spectroscopyfor damage detection and location

A self-modulation mode of nonlinear acoustic vibrations of cracked defects has been analyzed and observed experimentally. Spectral patterns of the self-modulation are attributed to the sum-frequency type resonance in a multi-degree-of-freedom system and include a subharmonic spectrum as a particular case. Both the subharmonic and self-modulation modes demonstrate a high localization around the defect and provide opportunities for early detection and recognition of damaged areas.

Nonlinear air-coupled emission: The signature to reveal and image microdamage in solid materials

It is shown that low-frequency elastic vibrations of near-surface planar defects cause high-frequency ultrasonic radiation in surrounding air. The frequency conversion mechanism is concerned with contact nonlinearity of the defect vibrations and provides efficient generation of air-coupled higher-order ultraharmonics, ultrasubharmonics, and combination frequencies. The nonlinear air-coupled ultrasonic emission is applied for location and high-resolution imaging of damage-induced defects in a variety of solid materials.

A local defect resonance to enhance acoustic wave-defect interaction in ultrasonic nondestructive evaluation

It is experimentally shown that, to provide maximum acoustic wave-defect interaction, the concept of a local defect resonance should be applied. The model of a resonant defect is used for the selection of the wave frequency to enhance the excitation of the defect in nonlinear acoustics and ultrasonic thermography. An increase in nonlinear response of the defect at its local resonance exceeds substantially the one at natural frequencies of the specimen. The strong wave-defect interaction is confirmed by resonance induced rise of local temperature of the defect in the frequency band of its local resonance.

Resonant ultrasound spectroscopy of defects: Case study of flat-bottomed holes

Unlike conventional resonant ultrasonic spectroscopy aimed at determining elastic constants and related parameters of solids, resonant ultrasound spectroscopy of defects (RUSOD) addresses an opportunity to detect, visualize, and classify mechanical defects in materials. The approach is based on the resonant ultrasonic wave-defect interaction due to local defect resonance. RUSOD is shown to be defect- and frequency selective imaging technique capable of distinguishing between different defects by variation of ultrasonic frequency.

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

Abstract The results of non-contact measurements of local in-plane 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.

Highly-efficient and noncontact vibro-thermography via local defect resonance

A frequency match between the driving ultrasonic wave and characteristic frequency of a defect provides an efficient energy pumping from the wave directly into the defect (local defect resonance (LDR)). Due to a strong resonance amplification of the local vibrations, the LDR-driven defects exhibit a high-Q thermal response and enable to implement frequency-selective thermosonic imaging with an opportunity to distinguish between different defects by changing the driving frequency. The LDR-thermosonics requires much lower acoustic power to activate defects that makes it possible to avoid high-power ultrasonic instrumentation and even proceed to a remote ultrasonic thermography by using air-coupled ultrasonic excitation.

Nonlinear Acoustic NDE: Inherent Potential of Complete Nonclassical Spectra

The classical approach to nonlinear acoustic nondestructive evaluation (NDE) is based on the higher (ultra-)harmonic or mixed frequency response of an imperfect material. In the nonclassical case, beyond the well-known ultraharmonics and the modulation sidebands nonlinear spectra acquire a number of new spectral components: subharmonics, ultrasubharmonics, and ultrafrequency pairs. These nonclassical nonlinear modes demonstrate a high localization around defects and provide new opportunities for early detection and recognition of damaged areas. The chapter includes theoretical background and extensive experimental results on defect selective nonlinear imaging and NDE using complete multifrequency nonclassical spectra.

Resonance ultrasonic thermography: Highly efficient contact and air-coupled remote modes

A frequency match between the driving ultrasonic wave and characteristic frequency of a defect provides an efficient energy pumping from the wave directly into the defect. The application of the concept of local defect resonance is shown to enhance substantially the efficiency of vibro-thermal conversion in ultrasonic thermography (ULT). Therefore, the resonance modes of ultrasonic thermography require much lower acoustic power to activate defects that makes it possible to avoid high-power ultrasonic instrumentation and proceed to a remote ultrasonic thermography version by using air-coupled ultrasonic excitation.

Nonlinear Acoustic Imaging: Fundamentals, Methodology, and NDE-Applications

Most of current acoustic imaging systems are “linear” systems, i.e. they image a linear sound field of the frequency identical to that of the acoustic wave injected into the medium. As a result, the image obtained normally provides information on some linear elastic parameters or flaws responsible for sound transmission and reflection inside a sample. Imaging of local elastic nonlinear properties has always been a challenging task with possible promising outcome for seismology, medical diagnostics, material characterisation and NDE applications.

Nondestructive Evaluation of Anisotropy in Composite Materials Via Acoustic Birefringence

A linearly polarized ultrasonic shear wave propagating in fiber-reinforced composites produces an elliptical vibration pattern due to birefringence. The acoustic birefringence of shear waves is analyzed and applied for evaluation of in-plane stiffness anisotropy of uni-axial nonfabric, biaxial, and quadra-axial fabric composite materials. The parameters of the elliptical motion are determined by measurements of the amplitude and phase of the transmitted/reflected shear wave as functions of the receiver polarization angle. The strength of birefringence is derived from the measured elliptical pattern and used to quantify the in-plane stiffness asymmetry in glass and carbon fiber-reinforced nonfabric and fabric composites. The technique is shown to be sensitive enough to detect damage induced variation in stiffness anisotropy. The correlation between the asymmetry of shear stiffness and orientation of impact cracking in composites is also discussed.