Papers by Keyword: Sound Velocity

Abstract: The ranging greater than 3m is not accorded with china engineering construction standardization association standard TECHNOLOGICAL SPECIFICATION FOR INSPECTION OF CONCRETE DEFECTS BY ULTRASONIC METHOD[CECS 21:200 (Transducer spacing is 2~3m). This paper studied large ranging of ultrasonic test mass concrete structure, and analyzed a project instance that was inspected the internal defects of mass concrete structures with various test methods, compared of those results. As detection is shown, first, with the test distance increased to 5.1m, the velocity of sound shows a linear trend of continuous development trend. Second, responds to improve of concrete strength, the velocity of sound increases, but not shows a linear trend. In addition, with the test distance increasing, concrete strength increases, but the velocity is down. A large ranging of ultrasonic test method was developed based on these observations.

Abstract: According to the different thickness of the thin coatings, the echo signal of ultrasonic testing was extracted. The sound velocity in the coating medium was obtained by solving the mathematical model for transfer function and the time delay spectrometry method, and the coating thickness was calculated, the comparison error of the calculated thickness and the actual thickness, combined with the actual thickness of the coating. The results showed that, two kinds of testing methods are able to detect thin coating thickness.

Abstract: Ultrasonic velocity measurements are carried out on four nOm compounds viz., N-(p-n-methoxy and ethoxy benzylidene)-p-n-dodecyl and tetradecyl anilines, 1O.12, 1O.14, 2O.12 and 2O.14. The first three compounds exhibit mono variant nematic phase while the last compound exhibits nematic and smectic-A phases with variable thermal ranges. The temperature dependence of sound velocity, U shows minima at the isotropic-nematic and nematic-smectic-A transitions. In conjunction with the density data of these compounds, the thermo acoustic parameters such as adiabatic compressibility (β_ad), the molar sound velocity (Rao’s number) (R_n), molar compressibility (W), molecular free length (L_f) and available volume (V_a) are estimated. In addition the intermolecular free length (L_f) is estimated in three different ways employing density and ultrasonic velocity data. The results are compared with the data available in literature of other compounds.

Abstract: For the purpose of measuring physical property of a coating by non-destructive testing (NDT), acoustic characteristics of plasma-sprayed coating has been studied with the ultrasonic testing. The analytic equation of ultrasonic propagation in the coating based on spectrum analysis is deduced. A transfer function H(f) is established, which contains information on the acoustic properties of the coating. Not only the ultrasonic propagation velocity in the coating, but reflection coefficient, attenuation coefficient, density of the coating can be acquired. This method overcomes shortcomings that the acoustic parameters cannot be measured due to mutual superposition of multiple reflected waves at the same interface of the coating. Porosities of the coatings were tested by buoyancy method. It is found these parameters mentioned above can characterize physical property of the coating. The relationships between porosity and reflection coefficient, sound velocity, attenuation coefficient were investigated, respectively.The results show that reflection coefficient and attenuation coefficient increases with the increase of porosity of the coating. The sound velocity decreases with the increase of porosity. The method is suitable for the evaluation of the coating quality.

Abstract: The rheological response of magnetorheological fluid (MRF) results from the polarization induced in the suspended particles by application of an external magnetic field. Characteristics of an MRF depend on the volume faction, that is the percentage of magnetic particles in the carrier liquid. We propose a qualitative investigation of these volume fraction effects by measuring properties of ultrasonic wave propagation velocity in MRFs having various volume fractions. The ultrasonic wave propagation velocity changes under the effect of an external magnetic field as a result of arrangement of clusters along the direction of the field in the MRF.

Abstract: We applied a picosecond dynamic grating technique for investigation of thermal diffusivity, sound velocity, thermo-optic and photoelastic coefficients in heavily doped 4H-SiC substrates. Spatial modulation of thermal properties was achieved by intraband carrier absorption at excitation by an IR picosecond laser pulse (1064 nm) and subsequent carrier thermalisation. Decay of dynamic grating at its various periods and sample temperatures was monitored at 532 nm wavelength. The thermal diffusivity DT = 0.94 cm2/s, thermo-optic coefficient dn/dT = 3.610–5 K-1 and effective photoelastic constant = – 0.10 were determined at 300 K. DT value increased at lower temperatures and saturated below 100 K. Temperature dependences of thermo-optic coefficient and thermal expansion were found in good correlation with heat capacity peculiarities.

Abstract: In this paper, we report on the effect of stress on the mechanical relaxation in the quenched Ni55Fe20Al25 Ferromagnetic Shape Memory Alloy (FSMA). The sound velocity and internal friction measurements were carried out using a vibrating reed setup. The results of such measurements on this system with varying stress amplitudes are presented. The present study provides a new insight into the stress amplitude and temperature dependence of the damping process and their bearing on the structural changes in the FSMAs.

Abstract: The pressure dependences of the second-order elastic constants ij C and the velocity of sound in 3C-SiC and 2H-SiC crystals are calculated in the framework of the Keating model with the additional assumption that the central α and the noncentral β force constants are linear functions of external hydrostatic pressure. Grüneisen parameters for the different acoustic modes of 3C-SiC have been also calculated. The third –order elastic constants ijk C for 3C-SiC are determined from the dependences of ij C on the pressure.