Phase Velocity Of Acoustic Waves Research Articles

QUANTITATIVE ANALYSIS OF THE DISTRIBUTION OF LOCAL POROSITY IN CARBON FIBER STRUCTURES BY LASER OPTOACOUSTIC METHOD

Currently, an urgent problem is the development of non-destructive diagnostic techniques for quantifying the level of local porosity of composite structures. The paper presents a method for estimating the porosity of a material from the experimentally measured phase velocity of longitudinal acoustic waves propagating in it. Laser excitation of ultrasound was used to create probing pulses. Porosity was calculated using experimentally measured phase velocities of longitudinal acoustic waves propagating in the composite. The proposed method allows one-way access to the object during measurements, which makes it possible to study structures of variable thickness and complex shape. The possibility of obtaining distributions of local porosity values in the studied section of the structure is demonstrated by the example of three carbon fiber stringer panels. The study showed that locality of the porosity value and its change from point to point plays an important role in such constructions, and the maximum local porosity of this area of the panel may differ from the average volumetric porosity by more than two times. The possibility of obtaining a “map” of the distribution of the local porosity of the panel section in the plane of laying the carbon fabric is also demonstrated. This method is quite operational, which allows it to be used within the framework of real production in order to improve the conditions and methods of production.

Pure- and Pseudo-Lateral-Field-Excitation Characteristics of Relaxor Ferroelectric Single Crystal PMN-PT.

The relaxor ferroelectric single crystal (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) has high piezoelectric constants, and thus has a good application prospect in the field of highly sensitive piezoelectric sensors. In this paper, for relaxor ferroelectric single crystal PMN-PT, the bulk acoustic wave characteristics on pure- and pseudo-lateral-field-excitation (pure- and pseudo-LFE) modes are investigated. LFE piezoelectric coupling coefficients and acoustic wave phase velocities for PMN-PT crystals in different cuts and electric field directions are calculated. On this basis, the optimal cuts of pure-LFE and pseudo-LFE modes of relaxor ferroelectric single crystal PMN-PT are obtained, namely, (zxt)45° and (zxtl)90°/90°, respectively. Finally, finite element simulations are carried out to verify the cuts of pure-LFE and pseudo-LFE modes. The simulation results show that the PMN-PT acoustic wave devices in pure-LFE mode have good energy-trapping effects. For PMN-PT acoustic wave devices in pseudo-LFE mode, when the device is in air, no obvious energy-trapping emerges; when the water (as a virtual electrode) is added to the surface of the crystal plate, an obvious resonance peak and the energy-trapping effect appears. Therefore, the PMN-PT pure-LFE device is suitable for gas-phase detections. While the PMN-PT pseudo-LFE device is suitable for liquid-phase detections. The above results verify the correctness of the cuts of the two modes. The research results provide an important basis for the development of highly sensitive LFE piezoelectric sensors based on relaxor ferroelectric single crystal PMN-PT.

Observation of high phase velocity of dust acoustic waves with elongated dust grains in a cryogenic dusty plasma experiment

Self-excited dust acoustic waves (DAWs) with a high phase velocity were observed in the cryogenic dusty plasma experiment, where submillimeter, elongated, and fractal-like water-ice dust grains are formed. The phase velocity of the observed DAWs was obtained by the fast Fourier transform of the sequential images of the DAWs and it ranges from 8 to 15 cm s−1. The length of the dust grains was measured between 100 and 250 μm and the thermal speed of the dust grains was obtained between 1.5 and 2.8 cm s−1. It is shown that the linear theory including the effect of the dust thermal speed can explain the observed fast phase velocity. The possible mechanisms by which the submillimeter dust grains gain such high kinetic energies are discussed.

Measurement of temperature dependent shear modulus using frequency dependent SAWs ToF delay in laser-induced temperature gradient

Phase velocity of surface acoustic waves(SAWs) is frequency dependent when propagate on medium with inhomogeneous elasticity over depth. In this work, frequency dependent Time-of-Flight (ToF) variation of SAWs induced by a local and dynamic heating was applied for measurement of temperature dependent shear modulus. Laser-generated broad-band SAWs propagated through the material with elastic properties and density modified by dynamic inhomogeneous temperature field induced by a millisecond laser heating. Sample with spatial dependent material properties introduces phase velocity dispersion in the SAW propagation. As consequence, ToF of SAW becomes frequency dependent. Frequency dependent ToF variation curves at two time instants respected to laser heating were measured by time–frequency analysis together with a differential technique. Free fitted parameters, temperature dependent shear modulus and surface temperature distribution were evaluated by solving the inverse problem by fitting the experimental ToF variation curves into the theoretical ones by means of the differential evolution method. The inversed temperature dependent parameter of shear modulus of Ti–6Al–4V alloy was in good agreement with literature value.

Influence of top-coat thickness of thermal barrier coating on time–frequency domain and dispersion characteristics of laser-induced surface acoustic wave

Thermal barrier coating is commonly used to insulate the hot end components of aero engine and gas turbine in order to meet extreme high temperature service conditions. The performance of the thermal barrier coating will be significantly impacted by thinning or even spalling during the service process. Given the uniqueness of thermal barrier coating in structure and composition materials, and the fact that laser-induced surface acoustic waves are extremely sensitive to material surface characteristic parameters, laser-induced ultrasonic technology is used to detect the thermal barrier coating in this paper. To characterize the size and defect of thermal barrier coating, the excitation mechanism and propagation law of surface acoustic waves are very crucial. Firstly, the surface acoustic wave propagation law is investigated using spectral analysis and wavelet transform. Then, to study the influence of top-coat thickness on laser-induced surface acoustic wave, the surface acoustic wave velocity dispersion curves of thermal barrier coating with different top-coat thicknesses are extracted using wavelet analysis. The simulative and experimental results indicate that the time–frequency domain and dispersion characteristics of laser-induced surface acoustic wave in multilayered heterostructure are strongly affected by the top-coat thickness. By the establishment of the relationship between phase velocity of laser-induced surface acoustic wave and top-coat thickness, a theoretical basis is provided to characterize the top-coat thickness of multilayered heterostructure.

Лазерно-ультразвуковое исследование распределения локальной пористости в углепластиковых стрингерных панелях

The paper presents a method for quantifying the porosity of carbon fiber structures based on laser excitation of probing ultrasonic pulses. A method for estimating the porosity of a material from the experimentally measured phase velocity of longitudinal acoustic waves propagating in it is proposed. Using the example of control samples and real structures made of carbon fiber, the possibility of obtaining distributions of local porosity values in the studied section of the structure is demonstrated. It is shown that in the studied structures there are regions with a significant variation in the value of local porosity. The proposed method can be used to control the quality of manufactured composite structures, as well as to study the internal changes in structure during operation.

Using Broadband Acoustic Spectroscopy with a Laser Source of Ultrasound to Study the Frequency Dependences of the Phase Velocity of Longitudinal Acoustic Waves in Porous Carbon Fiber Reinforced Plastic Composites

Using Broadband Acoustic Spectroscopy with a Laser Source of Ultrasound to Study the Frequency Dependences of the Phase Velocity of Longitudinal Acoustic Waves in Porous Carbon Fiber Reinforced Plastic Composites

Применение широкополосной лазерно-ультразвуковой спектроскопии для неразрушающего контроля пористости углепластиков с различным объемным содержанием углеродного волокна

In this work, to obtain the frequency dependences of the phase velocity of longitudinal acoustic waves in composite materials, we use the method of broadband laser-ultrasonic spectroscopy, based on laser thermo-optical excitation of broadband acoustic pulses. Unidirectional carbon fiber reinforced plasticsampes with different volume contents of the matrix and fiber were taken as objects of study.For the studied samples, the frequency dependences of the phase velocity were obtained in the spectral range of 0.8 – 10 MHz, and the existence of the phase velocity dispersion in this range was shown. The phase velocity dispersion of longitudinal acoustic waves in the sample was calculated using the phase spectra of the probe ultrasonic pulse and the pulse transmitted through the sample under study. It is also shown that the relative dispersion of the phase velocity characterizes the porosity of the sample, and the higher the porosity, the greater the relative dispersion. Empirical relations obtained for the relationship between porosity and relative dispersion can be used for the operational non-destructive assessment of the porosity of composites. The results obtained can be useful both for quality control of the materials obtained with the aim of modernizing manufacturing technologies and for predicting the behavior of structures and parts of this material under external loads.

Surface Brillouin scattering study of tantalum nitride (TaN) thin films.

Elastic properties of TaN films on (001)Si are investigated by surface Brillouin scattering (SBS). The velocity dispersion is obtained from Brillouin frequency shifts and surface acoustic wave phase velocities derived from measured SBS spectra. The observed Rayleigh surface acoustic and Sezawa waves indicate a soft on hard configuration. The elastic stiffnesses from the best fit of the calculated and measured spectra were C11=288 and C44=80GPa. Using these elastic constants in the surface elastodynamic Green's function yielded theoretical Brillouin spectra in agreement with measured spectra. Employing a least squares fitting procedure to the elastic constants gives uncertainties in C11 and C44 as ±3.7 and ±2.5GPa, respectively.

Determinating the Volume Content of a Polymeric Matrix in CFRP Structures Using a Laser-Ultrasonic Method

An acoustic method for a quantitative assessment of the volume content of a polymeric matrix in CFRPs is proposed and realized experimentally. For this purpose, a laser-ultrasonic method based on the thermo-optical excitation of broadband pulses of longitudinal acoustic waves is used. A formula for calculating the volume content of the polymeric matrix in a CFRP from experimentally measured phase velocities of longitudinal acoustic waves in this material is proposed. Distributions of the volume content of the matrix in a control CFRP specimen and in a CFRP structure made under similar conditions are obtained. It is shown that the laser-ultrasonic method allows one to detect the areas with excess and deficient matrix content in CFRP specimens and areas of CFRP constructions and to quantitatively assess the spread of matrix content. The spread between the maximum and minimum matrix content observed depends on the shape of the investigated area of the structure. This method can be used for the quality control of composite structures before their exploitation.

On the characteristics of shear acoustic waves propagating in an imperfectly bonded functionally graded piezoelectric layer over a piezoelectric cylinder

A theoretical approach is taken into consideration to investigate the propagation behaviour of shear acoustic waves in a piezoelectric cylindrical layered structure composed of a piezoelectric material cylinder imperfectly bonded to a concentric functionally graded piezoelectric material (FGPM) cylindrical layer of finite width. The functional gradient in the FGPM cylindrical layer is considered to vary continuously along the radial direction (function of radial coordinate), and the imperfection of the interface of the cylindrical structure is taken into account which may practically exist due to some mechanical and/or electrical damage. By means of mathematical transformation, the governing electromechanical coupled field differential equations are reduced to Bessel’s equations. An analytical treatment has been employed to determine the dispersion relations of propagating shear acoustic waves for both electrically short and electrically open conditions, which are further validated by reducing the obtained results to the pre-established standard results and classical Love wave equation as a special case of the problem. The effects of functional gradient parameter, radii ratio, wave number, order of Bessel’s function appearing in the dispersion relations and mechanical/electrical imperfection parameters associated with the imperfect bonding of a piezoelectric material cylinder and FGPM layer on the phase velocity of shear acoustic waves have been reported through numerical simulation and graphical demonstration. For the sake of numerical computation, the data of PZT-5H for the FGPM cylindrical layer and AlN for a piezoelectric material cylinder have been considered.

Акустооптические свойства сплавов на основе германия, селена, кремния и теллура

We examined the acoustical, optical and acousto-optical properties amorphous alloys based on germanium, selenium, silicium and tellurium. The phase velocities of longitudinal acoustic waves and the value of acousto-optic figure of merit of the tellurium-based compounds were measured using the infrared sources of light radiation on the wavelength λ = 3.39 μm. We measured the acousto-optic figure of merit of germanium single crystal in case of diffraction on the acoustic modes along [110] and [111].

Features of the Metallization Influence on Phase Velocities of Acoustic Waves in Piezoelectric Plates

The paper presents an analysis of the influence of the load represented by two metal layers on the change in the phase velocity of the dispersion modes of the elastic Lamb and SH-waves in "Me/ZnO/Me" and "Me/AlN/Me" structures depending on the elastic wave frequency and the ratio of the metal layer to the piezoelectric layer thickness. Aluminum (Al), molybdenum (Mo) and platinum (Pt) are considered as the metal layer materials (Me). Only the elastic Lamb wave modes have localized maxima of the sensitivity curve S for all types of structures. Systems with low values of acoustic impedances for layers and plates materials have maximum values of S for metallization with thin layers, and also have minimal differences in the profiles of the components of the displacement vectors of the elastic wave. Systems with the most different values of acoustic impedances of layers and plates materials have maximum values of S when metallized with thick layers, and also have maximum differences in the profiles of the components of the displacement vectors of the elastic wave. PACS: 43.25.Fe; 43.35.Cg; 77.65.-j

Ultrasonic Testing Analysis of Concrete Structure Based on S Transform

Ultrasonic testing analysis is a crucial scientific component during the process and interpretation of the ultrasonic detection signal. Focusing on the ultrasonic testing characteristics, the time-invariant spectral analysis method cannot meet the processing requirements of the detection signal fully. Thus, S transform, the time-varying analysis method, was introduced into the ultrasonic testing data processing of the concrete structure. The acoustic wave phase velocity was derived based on the spectrum analysis, and the S transform time-frequency analysis method was established. Finally, based on the method of concrete experimental data set, studies show that the frequency energy spectrum with S transform can realize flexible and effective identification of defects in the concrete structure. Definitely, this analysis method can significantly improve the resolution and practicality of ultrasonic testing.

Laser-ultrasonic nondestructive evaluation of porosity in particulate reinforced metal-matrix composites

In this work, we propose the laser-ultrasonic method for nondestructive evaluation of porosity in particulate reinforced metal-matrix composites fabricated by stir and in-situ reactive casting techniques. The method is based on the influence of porosity on dispersion of the phase velocity of longitudinal acoustic waves, which is measured by the broadband acoustic spectroscopy with laser excitation of ultrasound (laser-ultrasonic spectroscopy). We studied stir cast hypereutectic aluminum-silicon alloy A336 matrix composites reinforced with the SiC micro particles (3.3–13.5 vol%) and in-situ reactive cast Al/Al3Ti composites reinforced with the Al3Ti intermetallic particles (4–11.5 vol%). In the spectral range of 3–40 MHz, the phase-velocity dispersion in both types of composites was observed: the high-frequency velocity in the range of 20–40 MHz increases with the increase of the reinforcement content independent of porosity, whereas the low-frequency velocity in the range of 3–10 MHz decreases with the increase of porosity independent of the reinforcement content. As a result, the relative dispersion grows up with the increase in the composite porosity independent of the variation in the reinforcement content. The empirical dependence between the porosity in a scanning composite region and the relative phase-velocity dispersion in this region is approximated by the same unified function. For the first time, such unified porosity-phase velocity functional relationship is obtained for particulate reinforced metal-matrix composites completely different in fabrication techniques as well as in chemical composition and elastic properties of reinforcing particles.

On the influence of initial stresses on the phase velocities of acoustic waves in the compressible elastic half-space interacting with the layer of a viscous fluid

On the influence of initial stresses on the phase velocities of acoustic waves in the compressible elastic half-space interacting with the layer of a viscous fluid

Verification of the Kramers-Kronig relations between ultrasonic attenuation and phase velocity in a finite spectral range for CFRP composites

The aim of this work is to verify applicability of the Kramers-Kronig relations between the attenuation coefficient and phase velocity of longitudinal acoustic waves in carbon fiber reinforced plastic (CFRP) composites in a finite megahertz frequency range. To measure these characteristics, the method of broadband acoustic spectroscopy with a laser source of ultrasound is used. We have experimentally shown that absolute attenuation in CFRPs is determined by both absorption in a polymer matrix and scattering on carbon fibers and gas pores of several tenths of microns in size. We have also found that the increasing composite porosity leads to the decrease in the absolute value of the ultrasonic velocity and to the increase in its relative dispersion in the entire studied frequency range of 1–10 MHz. The experimental results have shown that for the studied CFRPs in this range, features of the mechanism causing attenuation and dispersion of longitudinal acoustic waves by propagation in composites do not influence on applicability of the local Kramers-Kronig relations.

Local Kramers–Kronig Relations between the Attenuation Coefficient and Phase Velocity of Longitudinal Ultrasonic Waves in Polymer Composites

The relationship between the experimentally obtained attenuation coefficient and dispersion of the phase velocity of longitudinal ultrasonic waves in polymer composite materials has been analyzed. The laser optoacoustic method has been used to measure the ultrasonic attenuation and velocity in a wide frequency range. Verification of the Kramers–Kronig relations for ultrasound-scattering and absorbing carbon fiber reinforced plastic (CFRP) composites has been performed using the analysis of the relationship between the frequency dependences of the attenuation coefficient and phase velocity of longitudinal acoustic waves in samples. We have shown that the Kramers–Kronig relations between the ultrasonic attenuation and phase velocity are valid within the 1–10 MHz frequency range without regard to a particular mechanism of the decay in the energy of an initial acoustic wave during its propagation in a composite.

Temperature dependent angular dispersions of surface acoustic waves on GaAs

We measure the phase velocities of surface acoustic waves (SAWs) propagating at different crystal orientations on (001)-cut GaAs substrates and their temperature dependance. We design and fabricate sets of interdigital transducers (IDTs) to induce 4 μm SAWs via the inverse piezoelectric (PZE) effect between the PZE [110] direction (set as θ = 0°) and the non-PZE [100] direction (θ = 45°) on GaAs. We also prepare ZnO film sputtered GaAs substrates in order to launch SAWs efficiently by IDTs even in the non-PZE direction. We quantify acoustic velocities between 1.4 and 300 K from the resonant frequencies in the S11 parameter using a network analyzer. We observe parabolic velocity–temperature trends at all θ-values both on GaAs and ZnO/GaAs substrates. Below 200 K, in ZnO/GaAs substrates slower SAW modes appear around the [110] direction, which are unseen at RT.

Effect of electron temperature on small-amplitude electron acoustic solitary waves in non-planar geometry

Effects of electron temperature on the propagation of electron acoustic solitary waves in plasma with stationary ions, cold and superthermal hot electrons is investigated in non-planar geometry employing reductive perturbation method. Modified Korteweg–de Vries equation is derived in the small amplitude approximation limit. The analytical and numerical calculations of the KdV equation reveal that the phase velocity of the electron acoustic waves increases as one goes from planar to non planar geometry. It is shown that the electron temperature ratio changes the width and amplitude of the solitary waves and when electron temperature is not taken into account,our results completely agree with the results of Javidan & Pakzad (2012). It is found that at small values of \(\tau \), solitary wave structures behave differently in cylindrical (\(\text {m} = 1\)), spherical (\(\text {m} = 2\)) and planar geometry (\(\text {m} = 0\)) but looks similar at large values of \(\tau \). These results may be useful to understand the solitary wave characteristics in laboratory and space environments where the plasma have multiple temperature electrons.