Basic investigation on identification of tissue composition based on propagation speeds of longitudinal and shear waves

The elastic modulus of tissue as a useful biomarker of disease detection can be quantitatively evaluated based on shear wave speed (SWS) measurements in shear wave elastography. Although the longitudinal wave speed (LWS) is also expected to be a promising biomarker for disease detection, the elasticity is not always dominant because the LWS is affected by the bulk modulus. In other words, LWS and SWS may reflect different tissue properties. Therefore, in this study, based on the improvement in LWS measurement, the relationship between the composition of a phantom mixed with agar and glycerol and ultrasonically measured LWS and SWS was investigated. The LWS had a good sensitivity in detecting glycerol, while the SWS had a good sensitivity in detecting agar. The calculated Poisson's ratio had a better sensitivity in detecting agar. In conclusion, a simultaneous measurement of LWS and SWS may help identify the tissue composition.

Study of the dependence of the strength characteristics of metals on variations in the modes of manufacturing process using microstructure-sensitive acoustic parameters

The microstructure-sensitive acoustic parameters (MSA parameters) of metal of the object under control are determined using measurements of the propagation time of bulk elastic waves of the ultrasonic range by the echo-pulse method. The structural features of the metal are thus evaluated not only in the surface layer, but also throughout the entire volume. We present the results of practical application of the MSA-parameters to estimation of the deviation of the velocity ratios of longitudinal and shear waves relative to the «basic» state with known strength characteristics. A correlation of the MSA-parameters with variations in the elastic moduli of metals attributed to modification of their microstructure is discussed. The generalized values of the ratios of wave velocities for steels of the same group are used in calculations to characterize the «base» state. It is shown that when calculating the MSA-parameters for a certain kind of construction steel, it is possible to use the averaged ratios of the velocities measured for quasi-isotropic reference samples made of the same type of steel. The generalized baseline ratios of the longitudinal and shear wave velocities are determined for the samples made of carbon steel, low-alloy, and alloyed steels. We present experimental evidence of using MSA-parameters to detect microstructural changes in metal samples and accompanying changes in their strength characteristics that occur during changes in modes and conditions of welding and heat treatment. A comparative analysis of the MSA parameters with the values of the mechanical properties and parameters of the crack resistance of the metal is carried out. It was shown that the accuracy of measuring the MCA parameters provided by modern hardware significantly exceeds changes in them occurred under significant deviations of the strength characteristics. The experimental results obtained clearly indicate that the MSA-parameters can be successfully used to improve the methods of quantitative non-destructive assessment of the features of metal microstructures

Internal Cylinder Identification Based on Different Transmission of Longitudinal and Shear Ultrasonic Waves

We have built a Fizeau fiber interferometer to investigate the internal cylindrical defects in an aluminum plate based on laser ultrasonic techniques. The ultrasound is excited in the plate by a Q-switched Nd:YAG laser. When the ultrasonic waves interact with the internal defects, the transmitted amplitudes of longitudinal and shear waves are different. The experimental results show that the difference in transmission amplitudes can be attributed to the high frequency damping of internal cylinders. When the scanning point is close to the internal defect, the longitudinal waves attenuate significantly in the whole defect area, and their amplitude is always smaller than that of shear waves. By comparing the transmitted amplitudes of longitudinal and shear waves at different scanning points, we can achieve a C scan image of the sample to realize the visual inspection of internal defects. Our system exhibits outstanding performance in detecting internal cylinders, which could be used not only in evaluating structure cracks but also in exploring ultrasonic transmission characteristics.

Mathematical modeling of transfer intensive of edges of spatial cracks on the fronts of longitudinal and shear waves by a ray method

В ближайшей окрестности вершины плоской трещины, а в общем случае, вблизи передней кромки пространственной трещины, деформирование материала носит неупругий характер. В работе предложено лучевое моделирование высокоскоростного деформирования материала в δ-окрестности подвижной передней кромки трещины, используя динамическую упруговязкопластическую модель тела Бингама с условием пластичности Мизеса. Показано, что распространяющаяся передняя кромка трещины продольного сдвига лежит на поверхности сильного разрыва продольной скорости, бегущей со скоростью упругих продольных волн, а передняя кромка трещины отрыва и трещины поперечного сдвига лежит на поверхности сдвиговой волны, бегущей со скоростью волн сдвига. Введены интенсивности передних кромок трещин: скачок скорости сдвига поперек передней кромки трещины продольного сдвига, скачок поперечной скорости на передней кромке трещины отрыва, скачок касательной скорости к передней кромке трещины поперечного сдвига. Построены обыкновенные дифференциальные уравнения переноса интенсивностей передних кромок трещин вдоль лучей как ортогональных траекторий точек переднего фронта. Получены приближенные решения уравнений переноса интенсивностей передних кромок пространственных трещин в напряженный материал и приведены выражения для глубины проникания пространственных трещин. Показано изменение направления сдвига и отрыва в передних кромках соответствующих трещин в зависимости от напряженного состояния перед трещинами. Приведены графики численных расчетов переноса интенсивностей передних кромок трещин и глубины их проникания. In the near neighborhood of the top of the plane crack, and in General, in the space case, near the edge of the spatial crack, the deformations of the material have the inelastic character. In this article proposes the elasticviscoplastic model of the Bingham body with the condition of plasticity of Mises for modeling high velocity deformation material near of the top of crack. Shown that an edge of crack belong a surface of elastic wave: cracks of longitudinal shear belong of longitudinal wave and a crack of untiplane shear and avulsion belong a surface of shear wave. For intensity of the crack suggest a shock velocity on the curve of the edge of crack and made ordinary differential equation for transfer intensity of crack on the front of the wave. Shown that a distant of propagation edge of the crack depend from plastic deformation material on the front of the wave. In the process of propagation crack this direction of shear can change from a stresses in front of the wave. Three-D graphics show change intensity of the crack in a process of propagation from parameters.

Ultrasonic testing of axial stress of high strength bolts for bridges

The axial stress of high strength bolts for bridges affects the service life directly, it is necessary to measure it regularly. Based on the theory of acoustic elasticity and combination of longitudinal and shear waves, a new theoretical analysis method is proposed. The stressed and non-stressed areas of bolt are separated, and the derived formula only use the flight time and difference of acoustoelastic coefficients to get axial stress. Further, the preload experiments with high strength bolts of grade 8.8S and 10.9S is designed, the experimental results show that the proposed method is applicable to the axial stress of the bridge bolts with any specifications, material and different screwing depth used in this paper, the effect of elastic deformation on the flight time is eliminated, and the measuring error is within 5%.

MEASURING OF ELASTIC MODULI BY MEANS OF SUB-SURFACE SOUNDING METHOD

The method of determination of elastic moduli for different materials by means of measuring of longitudinal and shear waves’ velocities is discussed in the paper. The velocities are measured by obtaining the time of flight between a pair of low frequency ultrasonic dry point contact transducers installed on the surface of the studied material sample. Factors defining the accuracy of such measurement are indicated which mainly consist of physical velocity frequency dispersion, fundamental although small differences between static and dynamic elastic moduli measurements, velocity dependence on temperature etc. Comparison between Young’s modulus and Poisson’s ratio, obtained experimentally and from table data, is given for various plastics and steel samples. It shows good agreement of different methods’ data and demonstrates the applicability of the suggested elastic moduli ultrasonic sub-surface measurement method.

Modes of Bars

The perspectives and techniques developed in the previous chapters will now be applied to calculation of wave propagation in solids. Their application to longitudinal and shear waves will be both familiar and simple. Even more satisfying is the success of those same techniques in finding solutions for waves in a system that does not obey the wave equation and exhibit a phase speed that varies with frequency. Measurement of the frequencies of the normal modes of thin bars will be used to determine the bars’ elastic constants to high precision. The relationship between measured modal frequencies and the elastic moduli is particularly simple because the torsional, flexural, and longitudinal modes of bars can be selectively excited and detected. The technique of resonant ultrasound spectroscopy will allow the extraction of moduli from resonance frequencies even for samples with dimensions that are not as conducive as those of thin bars by a process that is significantly more computationally intensive. The flexural rigidity of wires under tension will be analyzed to determine the normal modes of a “stiff string,” and those effects will be discussed in relation to the tuning of pianos

Estimation of Local Elastic Moduli of Carbon-Containing Materials by Laser Ultrasound

The elastic properties of two carbon-containing materials are investigated. Shungite rock is a natural nanocomposite; isotropic pyrolytic graphite is an artificial material. Precision measurement of the local velocities of longitudinal and shear waves propagating in shungite and isotropic pyrographite samples was performed by laser ultrasonic techniques. Young's modulus, the shear modulus and Poisson's ratio are calculated, and the chemical composition of the samples is given.