Ultrasonic Velocity Anisotropy Research Articles

Ultrasonic velocity anisotropy of Jurassic shales with different lithofacies

Abstract Given the growing importance of organic-rich shale as unconventional reservoirs, a thorough understanding of the elastic and anisotropic behavior of shales is of great concern. However, for lacustrine shales, the complex lithofacies assemblage with geological deposition makes it challenging. Four lithofacies (argillaceous, mixed, siliceous, and calcareous) are recognized for 40 lacustrine shale samples from Jurassic formation in Sichuan Basin on the basis of their mineral compositions. We perform ultrasonic velocity measurements on 40 pairs of shale plugs at varied confining pressures, attempting to uncover the controls on the anisotropic properties of different lithofacies. The experimental results reveal that the total porosity, clay, and organic matter would positively contribute to velocity anisotropy of Jurassic shales. Combined with microstructure and pressure-dependent velocity analysis, the preferred orientations of platy clay particles and lenticular kerogen, the development of clay pores along clay fabric, and the sub-parallel micro-cracks induced by hydrocarbon expulsion are treated to be the controlling mechanisms. We add the total porosity, clay content, and kerogen volume together, intending to distinguish the elastic and anisotropic properties of four lithofacies. Generally, argillaceous shales, the dominant lithofacies in Jurassic formation, could be characterized by the highest clay and total organic content (TOC), the lowest bedding-normal velocities, and the strongest velocity anisotropy. Finally, with the laboratory data, two rock-physics-driven exponential relationships are proposed to predict the P- and S-wave velocity anisotropy with the bedding-normal velocities.

Experimental investigation of ultrasonic velocity anisotropy in magnetic fluids: Influence of grain–grain interaction

Magnetic field-induced dispersion of ultrasonic velocity in a Mn0.7Zn0.3Fe2O4 fluid (applied magnetic field is perpendicular to the ultrasonic propagation vector) is determined by employing continuous wave method. The magnitude of dispersion initially decreases with increasing field, then increases and reaches a plateau at higher fields. Results indicate that the velocity anisotropy is dominated by grain-grain interactions rather than grain-field interaction. At the critical temper- ature, the grain-grain interaction becomes weak as the transverse component of the particle/cluster moment is larger than the longitudinal one and the system reaches saturation even at low field. These observed variations in the field-induced anisotropy are analysed by incorporating the moment distribution of particles in Tarapov's theory (J. Magn. Magn. Mater. 39, 51 (1983)).

Comparison between elastic modulus and ultrasonic velocity anisotropy with respect to rolling direction in steels

Elastic modulus anisotropy with respect to sheet rolling direction was calculated, using X-ray diffraction determined texture components and their known individual anisotropies, for a deep drawing grade steel in the cold rolled as received and three heat treated conditions. The calculated elastic modulus anisotropy was compared to mechanically measured modulus values, at 0, 45 and 90° to the rolling direction, and ultrasonic velocity anisotropy, measured using an electromagnetic acoustic transducer (EMAT) system. It was found that the EMAT velocity anisotropy matched the measured modulus variation with angle, with differences between the as rolled and heat treated conditions being observed. However the predicted modulus variation did not show much difference between the as rolled and heat treated conditions, despite different textures being measured, resulting in a slight discrepancy with the EMAT velocity and measured modulus values at 90° for one heat treatment condition.

Measurements of the anisotropy of ultrasonic velocity in freshly excised and formalin-fixed myocardial tissue

The objective of this study was to quantify the anisotropy of ultrasonic velocity in freshly excised myocardial tissue and to examine the effects of formalin-fixation. Through-transmission radio-frequency-based measurements were performed on ovine and bovine myocardial specimens from 24 different hearts. A total of 81 specimens were obtained from specific locations within each heart to investigate the possibility of regional differences in anisotropy of velocity in the left ventricular wall and septum. No regional differences were observed for either lamb or cow myocardial specimens. In addition, no specific species-dependent differences were observed between ovine and bovine myocardium. Average values of velocity at room temperature for perpendicular and parallel insonification were 1556.9 +/- 0.6 and 1565.2 +/- 0.7 m/s (mean +/- standard error), respectively, for bovine myocardium (N=45) and 1556.3 +/- 0.6 and 1564.7 +/- 0.7 m/s for ovine myocardium (N=36). Immediately after measurements of freshly excised myocardium, ovine specimens were fixed in formalin for at least one month and then measurements were repeated. Formalin-fixation appears to increase the overall velocity at all angles of insonification and to increase the magnitude of anisotropy of velocity.

Non-destructive evaluation of formability in cold rolled steel sheets using the SH 0-mode plate wave by electromagnetic acoustic transducer

We evaluated the relation between the Lankford value ( r-value) and the velocity of cold rolled steel sheets using the fundamental shear horizontal plate wave (SH 0-mode plate wave) and the fundamental symmetrical Lamb wave ( S 0-mode Lamb wave) as a function of the propagation angle. The SH 0-mode plate wave at the traveling angle of 45° showed the opposite tendency compared with that of other traveling angles or other ultrasonic modes. Using the velocity equations derived by accounting for texture and cubic crystal anisotropy, we found that the velocity at 45° was strongly influenced by the 1 0 0 crystallographic plane compared with that of other ultrasonic conditions. Next, the measurement accuracy for the formability of cold rolled steel sheets using the S 0-mode Lamb wave and the SH 0-mode plate wave was estimated to find that the evaluation accuracy using the SH 0-mode plate wave became poor as compared with the case of the S 0-mode Lamb wave. For this, the effect of the ultrasonic velocity anisotropy to the propagation direction was the main cause, because the anisotropy of the SH 0-mode plate wave was bigger than that of the S 0-mode Lamb wave. Finally, we confirmed that the evaluation precision could be improved by using the SH 0-mode EMAT with a narrow-width sensor coil to transmit and receive the sharp ultrasonic beam.

Anisotropic damage evolution in unidirectional fiber reinforced ceramics

Damage transverse to the loading direction of a unidirectionally reinforced ceramic matrix composite has been observed and characterized by ultrasonic methods and acetate replicas. A laser-ultrasonic technique approach was developed and used to measure the ultrasonic velocity anisotropy, thus the complete elastic stiffness tensor, during uniaxial tensile loading/unloading of calcium aluminosilicate (CAS) composites reinforced by Nicalon™ SiC fibers. Acoustic emission and surface replica observations link degradation of the axial stiffness to the accumulation of matrix cracks normal to the loading (and fiber) direction. The substantial loss of transverse stiffness is proposed to originate from the fiber/matrix interface debonding near matrix cracks. These observations may significantly impact the constitutive models used to design multiaxially loaded ceramic matrix composites.

Effect of collagen on the anisotropy of quasi-longitudinal mode ultrasonic velocity in fibrous soft tissues: A comparison of fixed tendon and fixed myocardium

The widespread use of echocardiography has generated considerable interest in the ultrasonic properties of myocardial collagen. This study was designed to investigate the effect of collagen on the propagation of ultrasound by measuring the anisotropy of ultrasonic velocity through formalin fixed specimens of bovine Achilles tendon. Tendon was chosen for this study because it possesses a high content of collagen and a well-defined unidirectional arrangement of fibers. Ultrasonic velocity data were acquired from nine samples of fixed tendon that were each insonified at multiple angles relative to the fibers in 2 degrees increments for a full 360 degrees. Analysis of the data revealed a substantial angular dependence of velocity qualitatively similar to that reported for formalin fixed specimens of normal human myocardium, but approximately 17 times larger in magnitude. Together with measured values of density, these results were used to compute the elastic stiffness coefficients C11 (corresponding to propagation perpendicular to the fibers) and C33 (corresponding to propagation parallel to the fibers) of fixed tendon, yielding 3.08 and 4.51 GPa, respectively.

Microcrack‐induced versus intrinsic elastic anisotropy in mature HC‐source shales

Recent experimental studies of ultrasonic velocity anisotropy in kerogen‐rich shales indicate that these rocks are characterized by a very strong anisotropic response related to a very fine, bedding‐parallel lamination of organic matter and preferred orientation of clay particles in the rock matrix (Vernik and Nur, 1992). This intrinsic anisotropy is further enhanced in thermally mature shales by bedding‐parallel microcracks caused by the processes of hydrocarbon generation (Vernik, paper in preparation). However, the potential of recognizing mature source‐rocks in situ using downhole sonic, crosshole seismic, or VSP data clearly depends on our ability to discriminate between these two major causes of elastic anisotropy, remove the effect of the intrinsic anisotropy, and estimate crack density and crack porosity from velocity measurements.

A study on the ultrasonic velocity and attenuation in NdFeB magnet within the temperature range of 80-300 K(I) anisotropy of ultrasonic velocity and its variation with the temperature

The ultrasonic velocity V and attenuation A of both longitudinal and shear waves in an anisotropic NdFeB magnet were measured over the temperature range from 80K to 300 K by the pulse echo method. The anisotropy of the ultrasonic wave propagating in a NdFeB magnet was observed. Anomalous changes in both V-T and A-T curves in the temperature range of 110-160 K were found, which might be due to the spin reorientation phase transition of Nd2Fe14B.

Anisotropy of ultrasonic velocity and elastic properties in normal human myocardium.

Measurements of ultrasonic quasilongitudinal velocity were made in the muscle fiber plane of excised human myocardium. Multiple adjacent planes across the left ventricular wall were interrogated to assess the transmural dependence of velocity. For each measurement plane, data were obtained in 2-deg increments through the full 360 deg relative to the myofibers. An approximate 1.3% magnitude of anisotropy was observed with maximum velocity along the muscle fibers and minimum velocity perpendicular to the muscle fibers. The known transmural shift in myofiber orientation was evidenced in the anisotropy of velocity as angular shifts between plots obtained from adjacent transmural planes within the same specimen. Measured values of velocity and density were used to estimate the effective C33 and C11 elastic constants of a thin layer of normal myocardium.

Ultrasonic anisotropy of metal-matrix composites

In recent work, Spies and Salama have attributed the ultrasonic velocity anisotropy observed in A1/SiC metal-matrix composites to the preferential alignment (texture) of crystallites in the aluminum matrix. In this paper it is shown that a simple relation exists between the compressional and shear wave anisotropy for an orthotropic orientation distribution of crystallites. It is shown that the data of Spies and Salama violates this relation and therefore that the ultrasonic anisotropy observed by these authors cannot be explained in terms of texture. It is proposed instead that the observed anisotropy is due to an anisotropic microstructure which may develop in the composites as a result of thermomechanical processing (extrusion), and a theory for this is presented.

Ultrasonic velocity anisotropy in ferrofluids under the influence of a magnetic field

The propagation of ultrasonic waves in a water-base ferrofluid has been investigated by pulse-echo and continuous wave (CW) methods. The CW methods proved to be well suited for studying the velocity changes (Δv/v) due to a magnetic field. The magnitude of Δv/v was about 10 percent for fields as low as 125 gauss. In order to determine the velocity anisotropy, Δv/v was studied as a function of the relative angle (ϑ) between the magnetic field and the propagation vector. The anisotropy in Δv/v did not show a sin22ϑ dependence as the theory predicts. Also the magnitude of Δv/v was larger than the theoretical value by a factor of 103.

Use of ultrasound in assessing the susceptibility of steel to lamellar tearing

Increasingly, developments in welded constructions means that steel plate with high resistance to lamellar tearing has to be used. An experimental programme has been carried out on 17 C/Mn Fe52D steels, to indicate what features of longitudinal wave transmission ultrasonics may be used in assessing susceptibility to lamerllar tearing. A combination of two kinds of evaluation proved promising: the contribution of matrix toughness, measured from the anisotropy of ultrasonic velocity; and the contribution of the amount of inclusions, assessed by ultrasonic attenuation measurements and inclusion counting by ultrasonic reflection. No useful results have been obtained from ultrasonic spectroscopy.