Laser Optoacoustic Method Research Articles

Laser Optoacoustic Method for Detecting Violations in the Periodicity of the Structure of Carbon Fiber Reinforced Plastic Composites

Laser Optoacoustic Method for Detecting Violations in the Periodicity of the Structure of Carbon Fiber Reinforced Plastic Composites

Optoacoustic Sensing of Surfactant Crude Oil in Thermal Relaxation and Nonlinear Regimes.

We propose a laser optoacoustic method for the complex characterization of crude oil pollution of the water surface by the thickness of the layer, the speed of sound, the coefficient of optical absorption, and the temperature dependence of the Grüneisen parameter. Using a 532 nm pulsed laser and a 1–100 MHz ultra-wideband ultrasonic antenna, we have demonstrated the capability of accurate (>95%) optoacoustic thickness measurements in the 5 to 500-micron range, covering 88% of slicks observed during 2010 oil spill in the Gulf of Mexico. In the thermal relaxation regime of optoacoustic measurements, the value of optical absorption coefficient (30 mm−1) agreed with the data of independent spectrophotometric measurements, while the sound speed (1430 m/s) agreed with the tabular data. When operating in a nonlinear regime, the effect of local deformation of the surface of the oil film induced by heating laser radiation was revealed. The dose-time parameters of laser radiation ensuring the transition from the thermal relaxation regime of optoacoustic generation to nonlinear one were experimentally investigated. The developed OA method has potential for quantitative characterization of not only the volume, but also the degree and even the type of oil pollution of the water surface.

Analysis of changes in optical properties with time as a way to assess the instability of the structure of diluted aqueous-based ferromagnetic fluids

The work demonstrates the use of the laser optoacoustic method for observing the changes of the light extinction coefficient in unstable ferromagnetic fluids over time. The initial stabilized fluids were further diluted with a carrier liquid to violate the stability of the colloidal system. The form of optoacoustic signals excited in a ferromagnetic fluid carries information about its optical properties, which allows one to measure the light extinction coefficient of this fluid and obtain its distribution over the depth of fluid. The effect of dilution of ferromagnetic fluid on its optical properties was demonstrated. It was shown that the light extinction coefficient decreases by about 20% after 7 days after dilution, and after 30 days, its value decreases by half. The observed decrease in the extinction coefficient over time is a result of structural changes occurring in diluted ferromagnetic fluids. The proposed optoacoustic method can be useful for studying the optical properties of ferromagnetic fluids for developing optical devices based on them and also may be used to evaluate the stability of ferromagnetic fluids obtained by new technologies and fluids with a new type of stabilizer or carrier liquid.

Laser Optoacoustic Method for Quantitative Estimation of Porosity in Cast Dispersion-Strengthened Metal-Matrix Composite Materials

A laser optoacoustic method for quantitative assessment of the volumetric porosity of cast dispersion-strengthened metal-matrix composite materials has been proposed and experimentally implemented. The method is based on a statistical analysis of the distribution of amplitudes of backscattered broadband pulses of longitudinal acoustic waves in the tested materials. Laser excitation and piezoelectric recording of ultrasound is implemented with one-way access to the test object using a special laser-ultrasonic transducer. Silumin-based composites reinforced with silicon carbide microparticles in various volume concentrations (0.033–0.135) and composites obtained by reaction injection moulding based on aluminum reinforced with intermetallic $${\text{A}}{{{\text{l}}}_{3}}{\text{Ti}}$$ (volume concentration 0.04–0.115) have been studied. For both types of composites, the distribution of amplitudes of backscattered ultrasonic signals is approximated by a Gaussian distribution function applicable for a large number of statistically independent quantities. The empirically obtained dependence of the half-width of this distribution on the volumetric porosity of composites of two different types is approximated by the same linear function regardless of the manufacturing technology, as well as of the type, size, and concentration of strengthening particles.

Лазерный оптико-акустический метод количественной оценки пористости литых дисперсно-упрочненных металломатричных композиционных материалов

A laser optoacoustic method for quantitative porosity assessment of cast particulate reinforced metalmatrix composite materials is proposed and experimentally realized. The method is based on statistical analysis of the amplitude distribution of backscattered broadband pulses of longitudinal ultrasonic waves in the studied materials. Laser excitation and piezoelectric detection of ultrasound are realized by one-side access to a tested object using a special laser-ultrasonic transducer. Stir cast siluminmatrix composites reinforced with the SiC micro particles (volume fractions 0.033–0.135) and in-situ reactive cast aluminummatrix composites reinforced with the Al3Ti intermetallic particles (volume fractions 0.04–0.115). For both types of composites, the amplitude distribution of backscattered ultrasonic signals is approximated by the Gaussian distribution function applicable for statistics of large number of statistically independent variables. The derived empirical dependence of the half-width of this distribution on the volume porosity of two different types of composites is approximated by one and the same linear function independently of the fabrication technique, as well as on the type, size, and volume fraction of reinforcing particles.

Application of the Laser Optoacoustic Method for Studying the Spatial Distribution of the Light Extinction Coefficient in Ferromagnetic Fluids

The possibility of using the laser optoacoustic method for studying spatial inhomogeneities of the optical properties of colloidal solutions is demonstrated. The proposed method for obtaining spatial distributions of the light extinction coefficient in the studied medium is based on the dependence of the time profile of the excited optical-acoustic signal on the absorption and light scattering coefficients in this medium. The solutions are ferromagnetic fluids based on water and kerosene with different volume concentrations of magnetite particles. The diagnostics of the optical properties of these ferromagnetic fluids has been carried out with high spatial resolution. It is shown that in a near-surface layer with a thickness of tens or hundreds of microns, the light extinction coefficient increases with the fluid depth. A nonlinear dependence of the light extinction coefficient on the liquid concentration at depths of more than 200 microns is found. The relative change in the light extinction with depth depends on the concentration of magnetite particles and the properties of the carrier liquid, as well as on the type of acoustic boundary.

Laser Optoacoustic Method for Measurement of Light Extinction Coefficient and Investigation of Its Spatial Distribution in Colloidal Media

In the present work, the method which allows investigating the spatial distribution of light extinction coefficient in colloidal media is experimentally realized. The proposed method is based on the dependence of temporal profiles of excited OA-signals on the absorption and extinction coefficients of the studied medium. Water-based and kerosene-based magnetic fluids with volume content of magnetite particles in the range 0.35–3.5 % were studied as an example of the medium with spatially non-uniform optical properties. The capability of the reconstruction of the one-dimensional spatial distribution for the light extinction coefficient in the investigated media is demonstrated. It was shown that the relative change of the extinction coefficient with depth depends on volume concentration of magnetite particles, type of acoustical boundary and properties of carrier liquids. In the case of acoustical rigid boundary of magnetic fluid, an additional induced anisotropy occurs, which leads to increasing of the light extinction coefficient with depth in comparison with acoustical free boundary of fluid.

Laser Optoacoustic Method for Quantitative Porosity Assessment of Carbon Fiber Reinforced Plastic Composites Based on Acoustic Impedance Measurement

Abstract—A method for measuring the acoustic impedance for the assessment of the porosity of carbon fiber reinforced plastic composites using laser thermo-optical excitation of longitudinal acoustic waves is proposed and experimentally realized. The acoustic impedance of the test sample is measured from the magnitude of the antiderivative ultrasonic pulse reflected from the immersion liquid–sample interface. A method for calculating the porosity of carbon fiber plastic composites based on the measured acoustic impedance is presented. Composite samples with three different carbon fiber layers stacking schemes were investigated. It is shown that in the studied composites, the local porosity distribution is nonuniform along the fiber stacking plane. The porosity value, averaged from optoacoustic measurement results, actually coincides with X-ray tomography data within the error limits. The presented method for determining porosity does not require determining the volume and mass of the studied object and can be used for investigation of composite structures with complex shapes.

STUDY OF THE PROPERTIES OF COMPOSITE MATERIALS BASED ON ANTIFRICTION ALLOY B83

The antifriction composite materials (CM) based on a B83 babbit alloy containing silicon carbide (SiC) and modifided shungite (MS) particles have been fabricated by hot pressing. The matrix powder was prepared using a planetary ball mill for processing chips obtained by machining of cast aabbitt. The resulting powder was sieved on a sieve analyzer. Powder mixtures for pressing were prepared by mechanical alloying in a planetary mill for 2 h at a stirring speed of 300 rpm. Composite semi-product was obtained by pressing the obtained powder mixtures on an ОМА mechanical press (P max = 150 kN) at pressure of 320 ± 5 MPa. Semi-products were heated in a muffle furnace in a mold at a temperature up to 300°C, kept at this temperature for 30 min and then pressed. We have shown that CM obtained using methods of powder metallurgy exhibit increased wear resistance at comparable values of the friction coefficient compared to the same properties of a cast alloy. Local elastic moduli of the obtained samples have been determined using the laser optoacoustic method based on the measurements of the phase velocities of thermo-optically excited longitudinal and shear ultrasonic waves. We have shown that B83-based CM containing MS (0.5 wt.%) and SiC (3 wt.%) can be recommended as an alternative to a B83 cast alloy due to the higher wear resistance compared to cast babbit. The friction surface of this composite material reveals the sliding areas and friction relief less distinct compared to the cast alloy.

Optoacoustic gas-analysis for diagnostics of biosystems

A possibility of detecting biogenic gases by the laser optoacoustic gas-analysis method is shown. The construction and specifications of instruments, developed for this purpose, are described. Examples of the analysis of gas samples of various biological objects, like air, expired by patients, suffered from different illnesses, and residual gases in the wood of year rings of conifers are given together with recommendations on applying the received information.

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.

Laser Optoacoustic Measurement of the Volume Concentration of Epoxy Resin in Carbon Fiber Reinforced Plastic Composites

A laser optoacoustic method for determining the volume concentration of a polymer binding and carbon filler in carbon fiber reinforced plastic (CFRP) composites has been proposed and realized. Composite samples fabricated by the vacuum infusion method were studied. The volume concentrations of epoxy resin were measured for a set of CFRP samples. We have shown that there are regions with an excess and a deficiency of the epoxy resin. The method could be used for testing of both reference samples and real composite structures.

Structure and Properties of the B83 Babbit Alloy Based Composite Materials Produced by Extrusion

Extruded bars of hardfacing B83 babbit alloy reinforced by silicon carbide particles with an average size of 40 μm and modified with shungite rock (MSR) were manufactured. Specimens of the powder mixture of babbit alloy and fillers produced by mechanical alloying were cold pressed, heated to the temperature of 310 ± 10 °C, exposed at this temperature for 30 min, and then extruded on a mechanical press at 320 ± 5 MPa. The structure, physical, mechanical, and tribological properties of produced composite material (CM) were studied. A uniform distribution of reinforcing fillers and changes in the morphology of intermetallic SnSb and Cu3Sn phases with size reduced by 1.5–1.8 times were observed in the specimens produced by extrusion. The values of hardness, density, and elastic modulus measured by laser optoacoustic method were not worse than those for the cast B83 babbit alloy. Introduction of SiC and MSR particles into the babbit composition led to its strengthening and wear resistance increase by ~20% as compared with the cast material. The best wear resistance, 1.7 times greater than for the cast alloy, was obtained in SiC+MSR polyreinforced CM. This material was characterized by the least variation of the friction coefficients in the whole range of tribological loading studied and by the most stable process of friction.

Laser optoacoustic method for investigation of some physical parameters of oil and oil products

An operational laser optoacoustic method, which allows simultaneous determination of the light absorption coefficient and the speed of sound in oil and oil products is proposed and experimentally implemented. These values are the most important parameters of oil. The existing traditional methods for measuring these quantities are complex, as they involve the use of quartz converters, optics, etc. The method is based on investigating the front of the optoacoustic signal and measuring the speed of acoustic pulses in the samples. Acoustic pulses are produced by the thermo-optical mechanism of ultrasound excitation when the radiation pulse of a neodymium laser falls at a wavelength of 1.06 μm for ~20 ns on the surface of the medium. The resulting temperature gradient causes additional mechanical stresses. These stresses are the sources of acoustic waves that propagate from the heat-release zone. Since the leading edge of the pulse is formed by a straight wave propagating directly from the border, its profile repeats the spatial distribution of stress sources. For a homogeneous liquid, the theoretically calculated form of the thermo-acoustic compression pulse has a simple form p' ~ exp (–α z ) ( p' is the excess pressure in the depth z of the medium, and α is the absorption coefficient of the laser radiation in the medium). The measured values of the absorption coefficient for various oils were 2–40 cm -1 . Based on the proposed method, the method for determining the temperature coefficient of sound speed and oil tarness was developed

Laser optoacoustic method for quantitative nondestructive evaluation of the subsurface damage depth in ground silicon wafers

This paper is a report on the novel laser optoacoustic method for nondestructive evaluation of the depth of the subsurface damage in ground single-crystal silicon wafers. It is based on different mechanisms of laser excitation of ultrasound by absorption of Q-switched Nd:YAG laser pulses at the fundamental wavelength: the concentration-deformation mechanism in the undamaged single-crystal silicon and the thermoelastic one in the subsurface damaged layer. Due to the uniform heating of the whole damaged layer during the laser pulse action the amplitude of the compression phase of the laser-induced ultrasonic signal is proportional to the damaged depth. The rarefaction phase of this signal arises by absorption of the remaining laser energy in the single-crystal silicon beneath the damaged layer. The empirical relation between the depth of the subsurface damage and the ratio of the amplitudes of compression and rarefaction phases of the laser-induced ultrasonic signal can be fitted by a linear function within the depth variation and the corresponding spread of the signal amplitudes. The proposed method attracts some interest for in situ control of the solid surface condition that is important in different tasks of linear and nonlinear optics.

Quantitative Evaluation of the Effect of Porosity on the Local Young’s Modulus of Isotropic Composites by Using the Laser Optoacoustic Method

An impulse acoustic method with a laser source of ultrasound is proposed and realized experimentally for a quantitative evaluation of the joint effect of porosity (the volume fraction of pores) and the concentration of dispersed filler on the local Young’s modulus of isotropic metal-matrix composite materials. The determination of Young’s modulus is based on the laser thermooptical excitation of ultrasound and measurements of the phase speed of longitudinal and shears acoustic waves in composite specimens. Silumin-matrix composite specimens reinforced with various volume fractions of silicon carbide (SiC) microparticles of the mean size of 14 μm were investigated. It was found that, to provide an effective growth in Young’s modulus by increasing the concentration of SiC, the porosity of a ready specimen should not exceed 2%. The technique developed allows one to carry out a nondestructive local testing of the acoustical and mechanical properties of composites in the actual state, which is necessary for a technological development and improvement of the fabrication process of the materials.

Laser optoacoustic method for measuring local porosity of dispersion strengthened metal-matrix composite materials

The laser optoacoustic method for porosity measurement of isotropic dispersion strengthened metal-matrix composite materials (CM) is proposed and experimentally realized. It is based on a laser thermooptical excitation of ultrasound, measurement of phase velocity of longitudinal acoustic waves in the studied material, and then application of a theoretical model for the dependence of phase velocity on porosity. The results of local porosity measurements (lateral resolution 1–2 mm) for the samples of CM based on AK12M2MgN silumin strengthened with silicon carbide particles with an average diameter 14 μm at different concentration are in agreement with the results of gravimetric measurements of the average sample porosity within the relative error of 10–15%.

Measuring the dependence of the local Young’s modulus on the porosity of isotropic composite materials by a pulsed acoustic method using a laser source of ultrasound

A laser optoacoustic method for analyzing the effect of porosity on the local isotropic Young’s modulus of composite materials was proposed and experimentally implemented. Using as an example samples of a metal matrix composite based on silumin with reinforcing microparticles of silicon carbide, SiC, in various concentrations, it is shown that to provide an effective increase in Young’s modulus with increasing concentration of SiC, the porosity of the final sample should not exceed 2%.

Laser optoacoustic method of local porosity measurement of particles reinforced composites

In the present work we have realized experimentally the laser optoacoustic method for the measurements of local volume fraction of air pores (porosity P) of isotropic composite materials. It is based on measurements of phase velocities of thermooptically excited longitudinal ultrasonic waves in composite samples in the frequency range 0.5÷50 MHz. The local porosity (lateral resolution 1÷2 mm) is determined using the dependence of phase velocity of longitudinal acoustic wave on porosity for porous metals and theoretical calculation of phase velocity in a composite with the two-phase medium model. A number of aluminum alloy (silumin) matrix composite samples reinforced by SiC particles of a different mass concentration with the mean particle size of 14 mm was investigated. The samples were disks with the diameter d = 40 mm and the porosity in the center and in the periphery area of each sample was determined. The increase of mass concentration of the filler SiC leads to the growth of P. The results coincide within relative inaccuracy of 2–3% with the gravimetrical measurements of average <P> value, the porosity in the center of each sample was slightly higher than in the periphery.

Laser optoacoustic method for measuring thermal characteristics of condensed substances under the action of an intense heavy-ion beam

The results of the development of a contactless remote technique for studying thermal characteristics of condensed matter under a pulsed action of an intense heavy-ion beam are presented. This technique is based on measuring the velocity of sound from the time of passage of a probing optoacoustic pulse in a target exposed to an ion beam. To record an acoustic response, we have developed a schlieren system based on the shadow technique for visualizing optical phase nonuniformities. The efficiency of this technique was checked in test experiments on the TWAC-ITEP facility.