Impact of contact force on the ultrasonic signal amplitude in carbon steel: A systematic evaluation

Ultrasonic measurements have been used to characterise the solutionising phenomenon in Rene 80, a Ni based superalloy. Starting material was solutionised at 1204°C for 30–120 min on identical samples. The microstructures of these samples were evaluated by ultrasonic immersion technique, X-ray diffraction and scanning electron microscopy. It was observed that the area fractions and, consequently, the γ′ volume fractions were decreased by increasing the solutionising time. A direct correlation was observed between ultrasonic wave velocity and solutionising time at 1204°C. The ultrasonic compression wave velocity followed a descending pattern similar to that of γ′ area fraction with the increase in solutionising time. The observed variation in ultrasonic velocity has been attributed to the effect of the γ′ dissolution on the elastic constants of the material.

To determine whether ultrasonic wave velocities are affected by the occurrence and amount of methane hydrate in the pore spaces of sediments, we measured ultrasonic velocities in artificial methane hydrate-bearing sandy sediments during the formation and dissociation processes of methane hydrate. An artificial core specimen was made based on the properties of a natural core recovered from a site in the Nankai Trough near Japan. A core holder was used that permitted the independent application of both confining and pore pressures to the artificial core using a rubber sleeve and two syringe pumps. Piezoelectric ceramic sensors were positioned at both end faces of the core and used to oscillate and detect the compressional and shear ultrasonic waves. The formation of methane hydrate, by pressurizing water in the pore spaces of the core sample using methane gas, was associated with an increase in both wave velocities. The increase in ultrasonic velocities was particularly marked at saturations of methane hydrate in the pore spaces above 30% and the maximum velocity of the compressional wave exceeded 3,000 m/s. While ultrasonic wave velocities decreased with the dissociation of methane hydrate due to depressurization or heating, they exhibit hysteresis during formation and dissociation. These findings indicate that the velocities depend on the occurrence of methane hydrate in pore spaces as well as the concentration. Introduction Methane hydrate has considerable potential for use as a new energy resource. Marine methane hydrate occurs in a variety forms several hundred meters below the sea floor. The form considered to be the most well suited to exploitation is that contained within the pore spaces of sandy sediments, as it has relatively larger gas permeability compared to other forms. Since shallow sandy sediments are not usually consolidated, the methane hydrate within pores acts to increase the mechanical strength of the sediments which, consequently, affects production methods. It is thought that methods employing ultrasonic wave velocities are effective for studying the occurrence of interstitial methane hydrate in sandy sediments, and also for undertaking resource assessments of methane hydrate. To determine whether ultrasonic wave velocities are affected by both the occurrence and the amount of interstitial methane hydrate, we measured ultrasonic wave velocities in artificial methane hydrate-bearing sandy sediments during the formation and dissociation of methane hydrate. A resonant column method was developed to study the seismic velocities of methane gas hydrate-bearing sand1,2. Velocities of compressional and shear waves, as well as the dynamic modulus were investigated at methane hydrate saturations below 35%; saturation is defined as the volume ratio of methane hydrate to pore space. Although measurements were performed under dry conditions, the properties under water-saturated conditions were theoretically calculated. The compressional and shear wave velocities increased to 2500 m/s and 1500 m/s at methane hydrate saturation of 35%, respectively. In the present study, ultrasonic wave velocities were measured under water-saturated conditions at methane hydrate saturations of less than 75%. The velocities were also measured at the dissociation of methane hydrate due to depressurization and heating.

Study on the service life prediction of freeze–thaw damaged concrete with high permeability and inorganic crystal waterproof agent additions based on ultrasonic velocity

The frequency dependence of the phase velocity and attenuation of ultrasonic waves were measured as a function of time during the polymerization (curing) reaction of epoxy resins. The phase velocity and attenuation were evaluated from the amplitude and phase spectra of ultrasonic signals transmitted through a layer of curing epoxy resin. The measurements were made in the frequency range of 2–20 MHz. From the experimental data follows an important conclusion: The attenuation coefficient increases linearly with frequency at all stages of the curing reaction from the viscous liquid to the solid state. The slope of the attenuation coefficient as a function of frequency is strongly dependent on the time of cure (degree of cure). The linear behavior of attenuation versus frequency suggests that the attenuation effect cannot be explained by classical viscothermal absorption or relaxation theory. This type of behavior (so-called hysteresis behavior) is poorly understood on the molecular level and was found previously for some highly viscous liquids, for solid polymers, and for biological tissue. The phase velocity data were evaluated from the phase spectrum of the transmitted signal. The ultrasonic velocity changes with time according to an S-shaped curve. It is also moderately dependent on the frequency.

In the metallurgical industry, ultrasonic inspection is routinely used for the detection of defects. For the non-destructive inspection of small high strength steel parts, the material can be considered isotropic. However, when the size of the parts under inspection is large, the isotropic material hypothesis does not necessarily hold. The aim of this study is to investigate the effect of the variation in mechanical properties such as grain size, Young’s modulus, Poissons ratio, chemical composition on longitudinal and transversal ultrasonic wave velocities. A 2 cm thick slice cut from a 40-ton bainitic steel ingot that was forged and heat treated was divided into 875 parallelepiped samples of 2x4x7 cm3. A metallurgical study has been performed to identify the phase and measure the grain size. Ultrasonic velocity measurements at 2.25 MHz for longitudinal and transversal waves were performed. The original location of the parallelepiped samples in the large forged ingot, and the measured velocities were used to produce an ultrasonic velocity map. Using a local isotropy assumption as well as the local density of the parallelepiped samples calculated from the chemical composition of the ingot provided by a previously published study, Youngs modulus and Poissons ratio were calculated from the longitudinal and transversal wave velocities. Micro-tensile test was used to validate Youngs modulus obtained by the ultrasonic wave velocity and an excellent agreement was observed.

Evaluation of ductile iron casting material quality using ultrasonic testing

Nondestructive ultrasonic testing is commonly used to assess damage in infrastructure mostly based on elastic wave velocity. This study focuses on understanding the effects of a thin fracture not only on ultrasonic elastic wave velocity but also on attenuation. Experiments are performed to quantitatively assess the effects of a thin fracture within polymethylmethacrylate (PMMA) specimens. Wave velocity and attenuation are measured across the width of these homogeneous specimens using the ultrasonic pulse velocity method. Seventeen specimens are tested for three different conditions (intact, with a hole, and with a fracture) for two different thicknesses. First, specimens made of two PMMA blocks with an intact fused interface are tested; then, specimens with a small hole (created for generating stress concentration) perpendicular to the interface and milled ends are tested; and, finally, specimens with an induced fracture at the fused interface are tested. Four additional specimens, two with fused (but weak) interfaces between blocks and two solid blocks, are tested during fracture growth under uniaxial strain-controlled test conditions. In fact, wave attenuation can cause the first arrival to be undetected and overestimated by up to 10 %. This error in the selection of the first arrival could be misinterpreted as a change in wave velocity when fractures are present in the material. Although wave velocity shows marginal reduction, less than 4 %, when a thin fracture is present, wave energy attenuates by up to 60 %. This work demonstrates quantitatively that wave attenuation measurements from selected frequency bands in the Fourier spectra can be used to identify the presence of thin fractures using ultrasonic testing.

To investigate the influence of temperature, water content, and dry density on ultrasonic wave velocity, a serial of ultrasonic tests were conducted on frozen silty clay by using the supersonic test meter. In the mean time, compressive strength of frozen silty clay was measured under various temperature conditions. Results indicate that the ultrasonic wave velocity rapidly changed in the range of −1°C to −7°C, due to the frozen pore water, and that their relations can be described by the same formula. The ultrasonic wave velocity increased with an increase in dry density and showed a good linear relationship with dry density. Ultrasonic wave velocity increased with an increase in water content until the water content reached the critical water content. In terms of the ultrasonic wave velocities versus unfrozen water content, it was found that they have linear relationships. Based on the ultrasonic tests and strength tests results, it is found that, as the compressive strength increased, ultrasonic wave velocity increased and both of them increased with the temperature. In terms of the ultrasonic wave velocities versus temperature and compressive strength versus temperature, the relationship can be set up between ultrasonic wave velocities and compressive strength. Based on the previous research and experimental data, the relationship between ultrasonic wave velocity and frozen silty clay strength was obtained through analysis. The fitting curves show that good correlations exist between them.

To study the influence of temperature and water content on ultrasonic wave velocity and to establish the relationship between ultrasonic wave velocity and frozen silty clay strength, ultrasonic tests were conducted to frozen silty clay by using RSM-SY5(T) nonmetal supersonic test meter, and the tensile strength and compressive strength of silty clay were measured under various negative temperatures. Test and analysis results indicate that, ultrasonic wave velocity rapidly changes in the temperature range of −1 °C to −5 °C. Ultrasonic wave velocity increased with an increase of water content until the water content reached the critical water content, while decreased with an increase of water content after the water content exceeded the critical water content. This study showed that there was strong positive correlation between the ultrasonic wave velocity and the frozen soil strength. As ultrasonic wave velocity increased, either tensile strength or compressive strength increased. Based on the experimental data, the relationship between ultrasonic wave velocity and frozen silty clay strength was obtained through regression analysis. It was found that the ultrasonic test technique can be used to test frozen soils and lay the foundation for the determination of frozen soil strength.

As a result of civilization, a lot of underground and surface structures have been constructed on or within complex rocks such as melange and lahars. There are many engineering problems related to this group of rocks called block-in-matrix rocks (bimrock). In the literature, the more important parameter controlling the geomechanical characteristics of bimrocks is volumetric block proportion (VBP), and there is much uncertainty related to estimated VBP applying sieve or image analysis. So, in this research, to develop a relation between the VBP and ultrasonic wave velocities and find how the fractal dimension and maximum block size affect the P and S wave velocities, 90 large-scale cubic samples were fabricated and the P and S wave velocities were measured in three perpendicular directions inside the physical samples. The fabricated samples were almost isotropic, and there was a direct relation between ultrasonic wave velocities and VBP. The difference between the evaluated VBP and the real one was in the range of −10 to +15% when the real VBP was equal or less than 60% and up to +25% when the real VBP was equal to 75%. In general, the fractal dimension had an indirect relation with ultrasonic velocities and there was no dominant trend for ultrasonic wave velocity variation versus the maximum block size.

Correlation between ultrasonic shear wave velocity and Poisson’s ratio for isotropic solid materials

naturally cured to different ages, to acquire the ultrasonic wave velocity of the test blocks under different ages and working stresses. On this basis, the authors analyze how the ultrasonic wave velocity changes with the age and working stress, and fit the relationship between working stress of concrete and ultrasonic wave velocity. The results show that the ultrasonic wave velocity grows with the age of concrete, but the growth rate slows down over time; the working stress of the concrete has a good correlation with the ultrasonic wave velocity, and the relationship between working stress and ultrasonic wave velocity is well described by the linear function and quadratic polynomial function.

Ultrasonic wave timing inspection was used to detect the internal decay in standing Iranian beech trees (Fagus orientalis). To evaluate the influence of internal decay on ultrasonic velocity, healthy round sections of freshly cut fallen beech trees were selected. Holes [as heart or internal decay indicator and with different shapes (circular and slot) and locations] were manually created and progressively enlarged in the wood section disks, and ultrasonic wave velocity was measured by using a commercial ultrasonic tester (Sylvatest Duo). The results showed that ultrasonic wave velocity linearly and significantly decreased by increasing hole dimensions, and location of holes had no influence on the extent and trend of velocity decrease. Although slots covered a small volume fraction of disks, they had a greater effect on ultrasonic velocities reduction as compared with circular holes.

Characterizing texture in polycrystalline materials by ultrasonic waves

A new approach to the effect of sample dimensions and measurement techniques on ultrasonic wave velocity