Longitudinal Wave Velocity Changes Research Articles

Preliminary evaluation of the rock mass permeability of a granite site based on sonic logging

It is of great value to reasonably obtain the permeability characteristic value of a site’s bedrock, especially for the deep rock mass space excavation, site layout design, and subsequent effective management of some major engineering sites. Previous studies have found that the permeability of water-bearing media decreases with depth, and the compressional wave velocity can be used to estimate the permeability coefficient. Taking a preselected granite site as an example, we used deep borehole acoustic logging technology to obtain the longitudinal wave velocity data at different depths. The empirical relationship between the longitudinal wave velocity and the permeability coefficient in the granite field was further used to obtain the permeability coefficient at different depths of a borehole in the study area; we then compared these data with in situ borehole water pressure test data and found that the empirical relationship between the longitudinal wave velocity values and the permeability coefficient values at different depths cannot be directly applied. For example, the permeability coefficient increased sharply at –405 m to –425 m, instead of continuing to decrease according to the previous law, the measured value was 1 orders of magnitude larger than the empirical value. Through comprehensive analysis of the borehole acoustic testing of the longitudinal wave velocity changes and the corresponding core data, it can be preliminarily determined that the permeability characteristics of the deep rock mass in this area are obviously influenced by the geological structure.

Influence of Aggregate Gradation on the Longitudinal Wave Velocity Changes in Unloaded Concrete

Diagnosis is an important factor in the assessment of structural and operational condition of a concrete structure. Among diagnostic methods, non-destructive testing methods play a special role. Acoustic emission evaluation based on the identification and location of destructive processes is one of such methods. The 3D location of AE events and moment tensor of fracture analysis are calculated by longitudinal wave velocity. Therefore, determining the velocity of longitudinal wave of concrete and the impact of the material and destructive factors are of essential importance. This paper reports the investigation of the effect of aggregate gradation on the change in wave velocity of unloaded concrete. The investigation was carried out on six 150 x 150 x 600 mm elements. Three elements contained aggregate fraction 8/16 mm and the other three were made with aggregate fraction 2/16 mm. Two acoustic emission sensors were used on the surface of the elements, and the wave was generated by the Hsu – Nielsen source. Longitudinal wave velocities for each group of elements were calculated and statistical test of significance was used for the comparison of two means. The results of the test indicated a substantial effect of the aggregate grain size on the change in longitudinal wave velocity. The average wave velocity in the concrete containing 8/16 mm fraction was 4672 m/s. In the concrete with 2/16 mm fraction, the velocity decreased to 4373 m/s. The velocity of the wave decreases at larger quantities of aggregate. The propagating longitudinal wave encounters more aggregate grains on its way and is reflected, also from air voids, multiple times and so its velocity is noticeably lower in the concrete with the 2/16 fraction. Thus, to be able to accurately locate AE events and analyse moment tensor during concrete structure testing, the aggregate grain size used in the concrete should be taken into account.

Experimental study of hydrogen embrittlement on AISI 304 stainless steels and Rayleigh wave characterization

Many failures due to hydrogen embrittlement or hydrogen damage are widely reported in oil and refinery industry. Despite many ultrasonic testing methods have been developed to assess hydrogen embrittlement, they are applied well to serious hydrogen attack instead of earlier degradation. This paper aims to characterize nascent hydrogen embrittlement of AISI 304 austenitic stainless steels under cathodic hydrogenation using Rayleigh wave. After cathodic hydrogen charging of AISI 304 stainless steel, XRD and metallographic examination show that martensite transformation occurs within the subsurface region of the specimens. Microhardness testing indicates that hydrogen leads to hardening of the material. It is found that Rayleigh wave are better to inspect local degradation than bulk waves. Rayleigh wave velocity of 5MHz and 10MHz decreases significantly with cathodic charging time, while longitudinal wave velocity changes not. Acoustic velocity change is due to elastic modulus reduction resulting from hydrogen-induced phase transformation in the subsurface region.

Material microstructure effects on ultrasonic waves under simple shear and pure shear

In this paper, the longitudinal and transverse wave velocities propagating into aluminum alloy A6061 under simple shear and pure shear were studied experimentally. Compared with the same velocity change tendencies of transverse wave under simple shear and pure shear, longitudinal wave velocity showed different change tendencies under both shear states, regardless of the same shear strain states in two cases. Furthermore, the measured longitudinal wave velocity changes under pure shear state were apparently categorized into two types according to different material surface states, i.e., simply decreasing change tendency at polished surface state, and chaotic change tendencies at unpolished material surface state. Consequently, the finite element analysis was carried out to investigate the deformation-induced microstructure effects on ultrasonic waves under plastic deformation. The analyzed results indicate that the transverse wave velocity changes depend on textures mainly, whereas the longitudinal wave velocity shows a sensitive response to the point defects.

Effects of texture evolutions and point defects on ultrasonic waves under simple shear and pure shear

In this paper, longitudinal and transverse wave velocities propagating into aluminum alloy A6061 under simple shear and pure shear were studied experimentally. Compared with the same velocity change tendencies of transverse wave under simple shear and pure shear, longitudinal wave velocity shows different change tendencies under both shear states, regardless of the same shear strain states in two cases. Finite element analysis was performed and the analyzed results indicate that the transverse wave velocity depends on texture evolutions mainly, whereas the longitudinal wave velocity is sensitively influenced by point defects induced by cross-slips. Consequently, the longitudinal wave velocity showing a sensitive response to the point defects was examined by measuring longitudinal wave velocity changes propagating into Al single crystal subjected to the combination loads of equi-biaxial tension and compression.

Ultrasonic characterization of point defects induced by cross slip under pure shear

Longitudinal wave velocity is used to characterize the point defects in crystalline solids. High purity Al single crystal was selected for both the finite element analysis and experimental work. Since the jog motions of dislocations caused by intersected slides such as cross slips induce point defects, the total amount of cross slips was calculated instead of calculating directly from the point defects. The effect of crystal orientations on total amount of cross slips under pure shear was also investigated via the finite element method. The result suggest that if the initial shear stress direction is located at the inner side of stereographic triangle, only single slip activities occurred at the beginning of plastic deformation and no effects due to point defects were present. However, as the shear stress direction rotates along the slip direction, point defects are induced by cross slips between primary and secondary slip systems due to work-hardening. This phenomenon was then examined by measuring longitudinal wave velocity changes propagating in Al single crystal subjected to the combination loads of equi-biaxial tension and compression (a pure shear state). Good qualitative agreement between the finite element result and measured data suggest that the longitudinal wave velocity can be used as an index to characterize point defects in crystalline materials.

Pure Aluminum Single Crystal Study on Point Defect Dependence of Ultrasonic Longitudinal Wave Velocity

In the authors' previous study, velocity changes of ultrasonic waves under simple and pure shear states were studied both theoretically and experimentally. The research work revealed the quite different longitudinal wave velocity changes between under the simple and pure shear states and also distinguished longitudinal velocity change under the pure shear state, on the other hand transverse wave velocity changes under simple and pure shear states showed almost the same change tendencies similar to the texture development under both shear states. Therefore, to clear the different effects due to plastic deformation on transverse and longitudinal waves velocity changes under simple and pure shear states the microstructural changes of polycrystal solids were investigated via finite element polycrystal model (FEPM). The analyzed results suggested that the transverse wave velocity depends upon texture developments mainly, whereas the longitudinal wave velocity depends heavily upon point defects induced by intersected cross slips among dislocations. The principal object of this paper is experimental verification of point defects dependence of the longitudinal wave velocity using a pure Aluminum single crystal. As a result, no point defects occurring under single slip stage was simulated by FEM analysis for crystal plasticity and experimental evidence of no longitudinal wave velocity changes under same stage was shown. It was confirmed that the longitudinal waves velocity depends under the point defects.

Ultrasonic Velocity Technique for Nondestructive Quantification of Elastic Moduli Degradation during Creep in Silicon Nitride

The ultrasonic velocity technique was used for nondestructive quantification of creep damage during interrupted tensile creep tests at 1400°C in an advanced silicon nitride to investigate the possibilities of this technique for creep damage monitoring in ceramic components. The longitudinal and shear wave velocities, Poisson's ratio, and Young's, shear, and bulk moduli linearly decreased with strain. Precise density change measurements indicated a linear relationship with a coefficient of proportionality of 0.69 between the volume fraction of cavities and tensile strain. Cavitation was identified as the main creep mechanism in the studied silicon nitride and the reason for ultrasonic velocity and elastic moduli degradation. The measurement of just the longitudinal wave velocity changes was found to be sufficient for quantification of cavitation during creep. The capability of the ultrasonic velocity technique for simple, sensitive, and reliable nondestructive monitoring of creep damage during intermittent creep was demonstrated in silicon nitride.

Preferred orientations of open microcracks in granite and their relation with anisotropic elasticity

Abstract In order to study how to deal with open microcracks in rock, anisotropic behaviors of Oshima granite were investigated by carrying out wave velocity tests and uniaxial compression tests, together with observations of microcracks under an optical microscope equipped with a universal stage. Anisotropy in the longitudinal wave velocity VL and secant deformation modulus E10 at 10% strength is caused by pre-existing open microcracks, not by pre-existing healed microcracks. The structural anisotropy formed by open microcracks, which is quantitatively represented by a second-rank tensor (called crack tensor), is in good agreement with the directional changes of E10 and VL. The mechanical, as well as structural, anisotropy shows rhombic symmetry with orthogonal symmetry axes in the directions roughly normal to the rift, grain and hardway planes, which are parallel to the major joint sets in the field. Since longitudinal wave velocity changes drastically depending on the density and orientation of open microcracks in granitic rocks, it is suggested that the crack tensor can be determined from non-destructive wave velocity tests. The elastic modulus tensor theoretically formulated in terms of the second-rank crack tensor can be used, as a first-order approximation at least, to describe the anisotropic elasticity of Oshima granite induced by pre-existing open microcracks. It is of particular importance to point out that the micro-scale structure by open microcracks is geometrically similar to the macro-scale structure by joints and faults (scale independent). This finding strongly suggests that some of the conclusions related to open microcracks are applicable to deal with macro-scale cracks in rock masses.

Texture and Cross Slip Effects on Ultrasonic Wave Velocity Changes Under Simple and Pure Shear States.

Although stress and strain states are same in simple and pure shear states, longitudinal wave velocity changes propagating in the plastically deformed medium under simple and pure shear states are apparently different each other according to authors' theoretical and experimental research works. The objective of this paper is to discuss the effect on ultrasonic wave velocity changes due to texture and cross slip under simple and pure shear states via finite element polycrystal analysis. In small plastic deformation range, in spite of quite different longitudinal wave velocity changes under simple and pure shear states, the texture developments and transverse wave velocity changes under both states are similar each other. That suggests dependence of transverse wave velocity on texture. Next, the multiplicative amounts of intersected slides between primary and secondary slip systems, which relates closely to the amount of cross slip, under simple and pure shear states are examined. The result, i.e., this multiplicative amount under pure shear state is larger than that under simple shear state, means the point defects induced by cross slip are much easier to introduce under pure shear state than under simple shear state and suggests that the point defects induced by cross slip may cause quite different longitudinal wave velocity changes.

119 単純せん断と純粋せん断状態における超音波速度変化に及ぼす集合組織と塑性スピンの影響(材料力学III)(オーガナイズドセッション(a)材料力学・材料強度に関する新展開)

Although stress and strain states are same in simple and pure shear states, longitudinal wave velocity changes propagating in the plastically deformed medium under simple and pure shear states are apparently different each other as the results of authors' theoretical and experimental research works. The objective of this paper is to discuss the effect on ultrasonic wave velocity changes due to texture and cross slip under simple and pure shear states via finite element polycrystal analysis. First the texture developments under both states are studied and the results suggest the dependence of transverse wave velocity changes on texture in the small plastic deformation range. Next, the multiplicative amounts of intersected slids between primary and secondary slip systems, which relates closely to the amount of cross slip under both states are calculated and the results show that the point defects induced by cross slip are much easier to be introduced under pure shear state than that under simple shear state, this suggests that the point defects induced by cross slip may cause quite different longitudinal wave velocity changes.

51123 Surface residual stress analysis of metals and alloys

Abstract : The critically refracted longitudinal wave (CRLW) technique was used to establish how feasible it is to measure stress changes at the surface and interior of a material, in particular naval airframe metals such as Ti-6AI-4V, 6061-T651 Aluminum, and 4340 steel. The CRLW propagation characteristics were found to be potentially practical if use of the 2P wave is implementable to have it as a reference wave. The CRLW technique was effective in detecting stress gradients in bent plates by measuring the acoustoelastic effect on the longitudinal wave velocity. The CRLW technique was applied in the range of 1.0 to 10 MHz and the expected longitudinal wave velocity changes followed the expected trends in the A16061-T651 and 4340 steel plates (0.50 inch thick). The longitudinal wave velocity changes measured in the Ti-6Al-4V plate did not follow the expected trends probably due to its thickness (0.25 inch).