Longitudinal Wave Velocity Research Articles

An experimental study of the penetration resistance of UHMWPE laminates with limited thickness

Ultra-high molecular weight polyethylene (UHMWPE) laminates represent the most weight-efficient industrial fiber-reinforced resin-based composite material for ballistic protection. To comprehensively understand the anti-penetration mechanism and quantify the anti-penetration performance of UHMWPE laminates, theoretical, experimental, and equation-fitting methods are employed to study and test the ballistic response characteristics of UHMWPE laminates. The results reveal that UHMWPE fibers possess a theoretically determined longitudinal wave velocity that exceeds 10 km/s and exhibit an extremely strong stress diffusion capacity. The anti-penetration mechanism and performance of UHMWPE laminates are significantly influenced by the laminate thicknesses, projectile velocities, and temperatures. As the laminate thickness increases, the ballistic limits of UHMWPE laminates increase almost linearly. Large area delamination and back face deformation play a crucial role in the energy dissipation of UHMWPE laminates. With the increase of projectile velocities, there exists an energy limit representing the maximum energy absorption capacity of the UHMWPE laminates that is worthy of reasonable utilization in spacing ballistic-proof armors. Additionally, the ballistic performance of UHMWPE laminates generally decreases with increasing temperatures, and this trend becomes more pronounced after 80 ℃. Based on data-driven analysis, this paper proposes an equation for calculating the ballistic limit of UHMWPE laminates that takes into account the temperatures and projectile shapes, with a prediction error basically within 5 %. The research results can offer valuable guidance for the ballistic-proof design of UHMWPE laminates.

Ultrasonic Characterization of Polymer Based Sille Stone Powder Composite Mortars

The Sille stone mined in the Sille Region of Konya province in Türkiye, is an andesitic rock. This stone is a material used in the construction of traditional and modern buildings. The Sille stone is cut while being used in buildings. The Sille stone powder (SSP) is formed during this cutting process. The SSPs cause environmental pollution. Therefore, this study was carried out to produce durable and eco-friendly new restoration mortars from the SSP that can be used in the restoration of historical buildings. The SSP composites were prepared by contributing SSP into epoxy and polyester resins in varied ratios such as 60‒75 wt.%. The effect of resin types and SSP contribution ratios on the elastic properties of epoxy resin (ER)/SSP and polyester resin (PR)/SSP composites was investigated by the ultrasonic pulse-echo method. Additionally, the morphology of these composites was investigated by scanning electron microscopy (SEM). Experimental results figured out that both longitudinal and shear wave velocity values of the PR/SSP composites were higher than of the ER/SSP composites. Furthermore, a linear increase was observed in the elastic properties of obtained composites with the increasing amounts of SSP.

Оценка геомеханического состояния массива пород в окрестности глубоких выработок рудника «Скалистый» комплексом натурных методов

In recent years, deep levels of exploited deposits have been a priority for the Polar Branch of MMC Norilsk Nickel. In the first half of 2023, KANEX SHAKHTOSTROY LLC has completed exploration workings EW-1 at the –1650 m level and EW-2 at the –1750 m level from the ventilation shaft VS-10 to the skip-cage shaft SCS-1 (2 km below the daytime surface). Comprehensive studies of mining-induced disturbance were carried out at 17 measuring stations in EW-1 and EW-2 sections driven in 2020–2022 (the length of about 1500 m). The rheometric, ultrasonic logging and seismic profiling methods were used as the principal in-situ methods to solve the task. It has been established that the size of the disturbed zone in the vicinity of EW-1 and EW-2 is characterized by longitudinal wave velocities, Vp, in the range of 2–4 km/s, averaging over the entire length of 1m from the contour of the working. The results of the seismic studies indicate moderate disturbance of the rock mass in the horizontal plane of the working's wall. The results of in-situ complex studies are qualitatively comparable with the results of visual inspection of the fixed surface of the working, thus indicating its satisfactory geomechanical condition.

Method for Predicting Transverse Wave Velocity Using a Gated Recurrent Unit Based on Spatiotemporal Attention Mechanism

Abstract Transverse wave velocity plays an important role in seismic exploration and reservoir assessment in the oil and gas industry. Due to the lack of transverse wave velocity data from actual production activities, it is necessary to predict transverse wave velocity based on longitudinal wave velocity and other reservoir parameters. This paper proposes a fusion network based on spatiotemporal attention mechanism and gated recurrent unit (STAGRU) due to the significant correlation between the transverse wave velocity and reservoir parameters in the spatiotemporal domain. In the case of tight sandstone reservoirs in the Junggar Basin, the intersection plot technique is used to select four well logging parameters that are sensitive to transverse wave velocity: longitudinal wave velocity, density, natural gamma, and neutron porosity. The autocorrelation technique is employed to analyze the depth-related correlation of well logging curves. The relationship between the spatiotemporal characteristics of these well logging data and the network attention weights is also examined to validate the rationale behind incorporating the spatiotemporal attention mechanism. Finally, the actual measurement data from multiple wells are utilized to analyze the performance of the training set and test set separately. The results indicate that the predictive accuracy and generalization ability of the proposed STAGRU method are superior to the single-parameter fitting method, multiparameter fitting method, Xu-White model method, GRU network, and 2DCNN-GRU hybrid network. This demonstrates the feasibility of the transverse wave velocity prediction method based on the spatiotemporal attention mechanism in the study of rock physics modeling for tight sandstone reservoirs.

Modification of the optical and elastic properties of TlGaSe2 layered semiconductor produced by the memory effect

A comparative analysis of the temperature behaviors of optical and elastic properties of single crystals under a memory effect experimental condition are presented for the first time. A memory effect condition suggests that the sample is thermally annealed inside the incommensurate (INC) phase for a time interval the corresponding physical parameters is measured experimentally. From ultrasound velocity measurements, carried out before and after the thermal annealing process subjected to the sample, the noticeable changes in the temperature variation of the longitudinal ultrasonic wave velocity associated with the elastic constants of due to the memory effect was detected. Our results reveal that thermal annealing performed at the INC - phase has some influence on the optical absorption of crystals in the visible spectral region. We assumed that thermal annealing within INC - phase is accompanied with the appearance, inside samples, a new quasiperiodic frozen structure formed from the intrinsic defects migrated into the lowest energy diffusion barriers of the INC - modulation wave. Such structural modulation is incommensurate with the underlying lattice of and can lead to changes in the electronic band structure and the optical bandgaps of

Porosity dependence of sound velocities in partially sintered alumina, zirconia, ATZ, and mullite ceramics

AbstractYoung's modulus and sound velocities of partially sintered alumina, zirconia, ATZ, and mullite ceramics with a broad range of porosities determined via the impulse excitation technique (IET) and the ultrasonic wave propagation pulse‐echo technique (UPT) are found to be in good agreement and exhibit sigmoidal curves as a function of the sintering temperature. The porosity dependence of the relative values of Young's modulus and sound velocities is either close to or below (but never above) the prediction based on an exponential relation, and none of them is significantly below the prediction based on a percolation relation or a recently proposed numerical benchmark relation for overlapping monosized spheres. Values are lower when concave pores or irregular anisometric grains are dominating. The correlation of the normalized longitudinal wave velocities and relative transverse wave velocities, with VL/VT ratios ranging from 0.50 to 1.91, is well predicted by models for Poisson's ratios between 0.35 and 0.2.

Khangai Intramantle Plume (Mongolia): 3D Model, Impact on Cenozoic Tectonics and Comparative Analysis

The Khangai plume is located beneath Central and Eastern Mongolia and corresponds to the mantle volume with significantly reduced longitudinal wave (P) velocities. The plume was identified as a result of the analysis of the MITP08 volumetric model of variations in P wave velocities, expressed as deviations of these velocities from the mean values for the corresponding depths in percent. Above the plume, the lithospheric mantle is thinned to ~50 km. Particularly low velocities (up to –6%) were found in the sublithospheric mantle down to a depth of 400 km. The main body of the plume is located under the Khangai Highland and spreads north to the edge of the Siberian Platform. The Khentei branch of the plume is identified southeast of the Khentei Highlands. It is connected to the main body of the plume at depths of 800–1000 km. Branches of the plume and its Khentei branch spread to Transbaikalia. The size of the plume decreases with depth, and its deepest part (1250–1300 km) is located under the southern part of the Khangai Highland. On the Earth’s surface, the main body of the Khangai plume corresponds to a Cenozoic uplift up to 3500–4000 m high in the south of the Khangai Highland. From the southeast, the territory of the Khangai plume and its Khentei branch is limited by the Late Cenozoic troughs stretching along the southeastern border of Mongolia. On other sides, the Khangai uplift is limited by a C-shaped belt of depressions, consisting of the southeastern part of the Baikal rift zone, the Tunka and Tuva basins in the north, the Ubsunur Basin and the Great Lakes Basin in the west and the Valley of Lakes in the south. The depressions are filled with lacustrine and fluvial sediments from the Late Oligocene to the Pliocene. In the Quaternary, the Southern and Central basins of Baikal, formed no later than the Early Paleogene, became part of the Baikal rift, and other depressions were involved in the general uplift of the region. The structural paragenesis of the Khangai uplift and surrounding basins is due to the impact of the Khangai plume. Above the plume with its Khentei and Transbaikalian branches, the Cenozoic basaltic volcanism of the plume type occurred, in some places inheriting Cretaceous volcanic manifestations. Plume structural paragenesis is combined with structural paragenesis, derived from the interaction of plates and lithosphere blocks, which is expressed by active faults, but developed synchronously with plume paragenesis. The kinematics of active faults shows that the western and central parts of the region develop under conditions of transpression, and the northeastern part ‒ under conditions of extension and transtension. The Khangai plume is connected at depth with the Tibetan plume, located under the central and eastern parts of Tibet north of the Lhasa block. The Tibetan plume rises from depths of 1400–1600 km and is accompanied by thinning of the lithosphere and rise of the earth’s surface. The Khangai and Tibetan plumes represent a special category of plumes that rise from the upper part of the lower mantle and this differs from the upper mantle plumes and the African and Pacific superplumes, rising from the core-mantle boundary. A connection between the Khangai and Tibet plumes with branches of superplumes is possible, but their independent origin is also admitted.

Experimental Wave-Based Assessment of Liquefaction Resistance for Different Degrees of Saturation

Abstract This paper presents the results of an experimental program carried out in the laboratory aimed at assessing the liquefaction resistance by correlations between longitudinal wave (P-wave) and shear wave (S-wave) velocities (VP and VS) and cyclic stress ratio from triaxial testing (CSRCTx) for different degrees of saturation (Sr). The liquefaction resistance was assessed using a cyclic triaxial apparatus equipped with Hall-effect transducers and bender elements, combining stress-based (large-strain level) and wave-based (small-strain level) approaches. These tests were carried out in soil specimens at relatively high degrees of saturation, which were estimated during testing by VP measurements interpreted using Biot’s theory. The results revealed that, for the same relative density and confinement stress, the S-wave-based approach did not predict the liquefaction resistance well because of the negligible variation in the stress state and soil stiffness for the assessed Sr values, which were above the air-entry value. In turn, the P-wave-based approach effectively predicted the liquefaction resistance increment of the TP-Lisbon sand for different Sr conditions because of the strong dependency of P-wave propagation on the degree of saturation in granular media. This is a consequence of the most relevant factor conditioning the pore pressure buildup in partially saturated sands, e.g., the compressibility of the occluded air bubbles, which can be detected by VP but not by VS.

Precision Measurement of the Group Velocity of Ultrasound in Samples with Millimeter Thickness

A methodology is proposed for high-precision local measurement of the group velocity of longitudinal waves in solid samples with millimeter thickness. Achievement of the required accuracy involves laser thermo-optical excitation of submicrosecond ultrasonic video pulses and ultrawideband piezoelectric recording of acoustic signals reflected from the test sample. Plane-parallel samples made of duralumin, quartz, and steel with a thickness of 2–6 mm are studied. To achieve the required accuracy in measuring the group velocityof ultrasound, the signal shape is mathematically processed with compensation for diffraction of the ultrasonic beam as it propagates through the sample. The possibility of ensuring the uncertainty in measuring the group velocity of ultrasound in the 1–15 MHz frequency range at a level of 0.1% in samples with millimeterthickness is demonstrated.

Computer information technology-based green excavation of tunnels in complex strata and technical decision of deformation control

Abstract Currently, information processing of tunnel engineering has mainly adopted conventional mathematical statistics-based methods. Moreover, some nonlinear processing methods are implemented to derive more insights, even though the degree of research is not deep enough. In the research, the rock mechanics test is carried out by drilling a method and taking samples in situ according to the construction technology of tunnels in complex geological conditions and implementing computer information-based methods. Also, rock mechanics tests are carried out in the excavation test area of the flat tunnel. Based on the tests using physical properties, such as deformation, tensile, uniaxial compression, triaxial compression, and longitudinal wave velocity, the physical and mechanical characteristics of the surrounding rock in the tunnel area are comprehensively evaluated, and the stability of the tunnel rock mass is assessed to devise convenient conditions for the subsequent research of the complex geological tunnels based on green excavation. The particle density of sandy mudstone, the bulk density, the porosity, and the natural water content are represented by 2.67 ± 0.61 g/cm3, 2.56 ± 1.42 g/cm3, 7.45%, and 2.86%, respectively, in terms of physical characteristics. These indicate that the sandy mudstone structure is relatively loose, with relatively large pores, micro-fractures, and a high degree of natural water content. The representative deformation test curve of the rock block shows that the ratio of deformation modulus to the compressive strength of the rock block is 650 on average, and Poisson’s ratio ranges from 0.21 to 0.38. These show that sandy mudstone has deformation properties after compression. The tensile strength of sandy mudstone, the shear strength, and c are represented by 1.25 ± 0.23 MPa, f = 1.32, and = 2.35 MPa, respectively. The stated test results can provide a scientific basis for selecting engineering design and its construction parameters in similar areas. In addition, the measurement results show that the surrounding rock will gradually increase, and the tunnel space will gradually become shorter with the increase of buried depth when the gravity stress field occurs. The linear elastic displacement of soft rock is smaller than that of elastic–plastic analysis, and the deeper the tunnel is buried, the larger the displacement difference would be. Therefore, establishing a stable and orderly monitoring and detection system could fully understand the intrinsic law between surrounding rock stress release and surrounding rock pressure and obtain accurate monitoring and measured data to evaluate the grading management standard of a tunnel at the ultimate displacement. In a word, this research provides a feasible idea to study the decision process of green excavation and deformation control technology of tunnels in complex strata.

Study on mechanical characteristics and damage model of layered sandstone after high temperature action

Rock engineering, which includes slopes, tunnels, and mines, often encounters stratified rocks. These projects are also frequently exposed to special environments of high temperatures, such as deep underground or fire-related conditions. It is of significant importance to conduct research on the damage characteristics and constitutive models of stratified rocks under high-temperature conditions to accurately reflect the influences of rock structure characteristics, geological conditions, and load effects on the damage and deformation characteristics of rock engineering. Under five temperature conditions (20, 200, 400, 600, 800 ℃), the intact sandstone rock samples and the layered sandstone samples are subjected to high-temperature treatment, followed by triaxial compression tests. Based on existing research on statistical damage constitutive models for rocks, a high-temperature layered rock statistical damage constitutive model is established by introducing the Weibull distribution function and high-temperature, bedding, and load coupling damage variables, under the condition that the microelement strength follows the Drucker-Prager (D-P) criterion. The results indicate that the peak strength, damage threshold, elastic modulus, and longitudinal wave velocity show a "U"-shaped trend with an increasing bedding angle, with an opening upwards. As the temperature increases, the anisotropy of the rock initially increases and then decreases, with obvious ductile characteristics after the temperature reaches 600 ℃. The analysis of damage threshold, stress-strain curve, and macroscopic failure morphology shows that the 60° dipping angle sandstone is prone to undergo compressive-shear failure along the weak plane of bedding, exhibiting low toughness mechanical characteristics. Theoretical curves of the statistical damage constitutive model for high-temperature rock are in good agreement with the Triaxial shear test curve of sandstone, which indicates that the constitutive model can reflect the stress-strain process of layered sandstone after high-temperature action, and verifies the applicability of the model. This model does not include unconventional mechanical parameters and can reflect the ductility, brittleness, and strength characteristics with clear physical meanings. The findings of the study can offer theoretical support for computing and numerically modeling rock mechanics after high-temperature action.

Influence of growth ring number and width on elastic constants of poplar

The objective of this work was to evaluate the effect of growth ring number (specimens including 2, 4, and 6 rings from the bark) and growth ring width on elastic constants in the radial direction of Populus x canadensis, which has not been revealed before. The longitudinal (2.25 MHz) and transverse (1 MHz) ultrasonic waves were propagated to calculate the longitudinal (VRR) and shear (VRL, VLR, VTR, and VRT) wave velocities and used to determine the elasticity modulus (ER), and shear moduli (GRL and GRT). The average growth ring widths of specimens including 2, 4, and 6 rings were 17.0 mm, 17.8 mm, and 18.2 mm, respectively. According to the results, only VRL steadily increased with increased ring number, while other velocities fluctuated. The same fluctuations were observed for moduli except for GLR, which constantly increased with ring number. The influence of ring number on velocity was statistically significant only for VRL and VRT. However, all moduli were significantly affected by ring number. Linear regression statistics revealed that there were significant relations between the ring width and density, VRL, VLR, VRT, GRL, and GRT.

Investigations of Dynamic Mechanical Performance of Rubber Concrete under Freeze-Thaw Cycle Damage

In order to study the effect of the freeze-thaw cycle on the integrity and dynamic mechanical performance of rubber concrete, the wave speed of rubber concrete specimens with 10% rubber volume was measured by a nonmetallic ultrasonic detector. The impact tests were also performed on rubber concrete specimens with different numbers of freeze-thaw cycles (0, 25, 50, 75, 100, and 125) at different impact air pressures (0.3, 0.4, 0.5, and 0.6 MPa) using a 74 mm diameter split Hopkinson pressure bar (SHPB) device, peak stress, ultimate strain dynamic intensity enhancement factor (DIF), and energy absorption effect. The results show that with the increase of freeze-thaw cycles, the wave speed decreases, and the freeze-thaw action will damage the rubber concrete and reduce the longitudinal wave velocity. Under the same freeze-thaw cycles, with the rise of strain rate, the peak stress, limit strain, DIF, and absorbed energy increase, and there is an obvious strain rate effect; under the pressure of 0.6 MPa, the peak stress of 25, 50, 75, 100, and 125 freeze-thaw cycles decreases by 25.1%, 37.1%, 46%, 52.5%, and 54.8%. With the increase of the freeze-thaw cycles, the peak stress of the specimen decreases, and the decrease gradually decreases. After the number of cycles exceeds 100, the stress decrease of the specimen is no longer obvious, the limit strain increases, and the absorbed energy decreases. The freeze-thaw environment significantly reduces the strength and integrity of rubber concrete specimens.

Collective motion in hcp-Fe at Earth’s inner core conditions

Earth's inner core is predominantly composed of solid iron (Fe) and displays intriguing properties such as strong shear softening and an ultrahigh Poisson's ratio. Insofar, physical mechanisms to explain these features coherently remain highly debated. Here, we have studied longitudinal and shear wave velocities of hcp-Fe (hexagonal close-packed iron) at relevant pressure-temperature conditions of the inner core using in situ shock experiments and machine learning molecular dynamics (MLMD) simulations. Our results demonstrate that the shear wave velocity of hcp-Fe along the Hugoniot in the premelting condition, defined as T/Tm (Tm: melting temperature of iron) above 0.96, is significantly reduced by ~30%, while Poisson's ratio jumps to approximately 0.44. MLMD simulations at 230 to 330 GPa indicate that collective motion with fast diffusive atomic migration occurs in premelting hcp-Fe primarily along [100] or [010] crystallographic direction, contributing to its elastic softening and enhanced Poisson's ratio. Our study reveals that hcp-Fe atoms can diffusively migrate to neighboring positions, forming open-loop and close-loop clusters in the inner core conditions. Hcp-Fe with collective motion at the inner core conditions is thus not an ideal solid previously believed. The premelting hcp-Fe with collective motion behaves like an extremely soft solid with an ultralow shear modulus and an ultrahigh Poisson's ratio that are consistent with seismic observations of the region. Our findings indicate that premelting hcp-Fe with fast diffusive motion represents the underlying physical mechanism to help explain the unique seismic and geodynamic features of the inner core.

Study on the deterioration characteristics and mechanism of physical and mechanical properties of natural gypsum rock under freeze–thaw action

The physical and mechanical properties, microstructure degradation characteristics, and damage mechanism of natural gypsum rock under 15, 30, and 45 freeze–thaw cycles were studied by using a self-developed program-controlled freeze–thaw experimental device. The results show that compared with natural gypsum, with the increase in freeze–thaw cycles, the mass of the sample increases first and then decreases, Poisson's ratio increases, the density decreases, and the longitudinal wave velocity, the uniaxial compressive strength, and the elastic modulus decrease. Indexes decrease greatly in the early stage of freeze–thaw and slowdown in the later stage. With the increase in freeze–thaw cycles, the slope of the pre-peak stage of the stress–strain curve decreases, the compaction stage is significantly prolonged, and the brittleness of the post-peak failure process decreases. Failure cracks of the specimens after freeze–thaw cycles are mainly inclined shear failure and axial tensile cracks. The analysis shows that the freeze–thaw damage of gypsum rock is caused by the superposition and mutual promotion of water-rock softening and pore frost heave. The specific performance is the damage of crystal particles and the loose pore structure at the mesoscale. On this basis, the cracks gradually develop and expand, which is consistent with the macroscopic test results of the sample. The research results have reference significance for the construction scheme design and frost damage prevention of gypsum surrounding rock tunnels in cold regions.

Investigation of long-wavelength elastic wave propagation through wet bentonite-filled rock joints

The saturation of the compacted bentonite buffer in the deep geological repository can cause bentonite swelling, intrusion into rock fractures, and erosion. Inevitably, erosion and subsequent bentonite mass loss due to groundwater inflow can aggravate the overall integrity of the engineered barrier system. Therefore, the coupled hydro-mechanical interaction between the buffer and rock during groundwater inflow and bentonite intrusion should be evaluated to guarantee the long-term safety of deep geological disposal. This study investigated the effect of bentonite erosion and intrusion on the elastic wave propagation characteristics in jointed rocks using a quasi-static resonant column test. Jointed rock specimens with different joint conditions (i.e. joint surface saturation and bentonite filling) were prepared using granite rock discs sampled from the Korea Underground Research Tunnel (KURT) and Gyeongju bentonite. The long-wavelength longitudinal and shear wave velocities were measured under different normal stress levels. A Hertzian-type power model was used to fit the wave velocities, and the relationship between the two fitted parameters provided the trend of joint conditions. Numerical simulations using three-dimensional distinct element code (3DEC) were conducted to better understand how the long-wavelength wave propagates through wet bentonite-filled rock joints.

Microseismic Signal Characteristics of the Coal Failure Process under Weak-Energy and Low-Frequency Disturbance

In deep mining, “critical static stress + slight disturbance” is an important inducing form of coal mine rockburst disasters. In previous studies, the critical static stress has been shown to be consistent with the loading direction of a slight disturbance but cannot reflect all types of rockbursts. In addition, the research that uses microseismic (MS) signals to reflect the overall process and critical stages of coal failure and instability under weak-energy and low-frequency disturbance conditions is immature, and more information, such as the critical state, has not been fully revealed. The aims of this paper are to further elucidate the important role of weak-energy and low-frequency disturbances in the occurrence of rockburst disasters. First, briquette samples were prepared from the Tashan Coal Mine, which is severely affected by rockbursts, and their homogeneity was verified using ultrasonic longitudinal wave velocity. Second, the natural frequency of the coal sample specimens was measured using a testing system. Then, based on the self-developed static pressure loading system, dynamic and static combined loading test system and MS signal monitoring device, the MS signal characteristics during the process of coal body failure and instability were comprehensively analysed. Finally, a comparison was made between weak-energy and low-frequency disturbances and impact disturbances. The results are summarized as follows. (1) The longitudinal wave velocity test results reflect that the briquette samples prepared in the experiment have high homogeneity. The smaller the particle size is, the higher the density and moulding pressure, and the denser the sample. (2) The natural frequency of the briquette samples is between 30.79 Hz and 43.34 Hz, and most of them fluctuate at approximately 35 Hz. (3) During the static loading stage, the occurrence of more than three MS signals of larger magnitude in a continuous cluster is an important criterion for the critical failure of the samples. (4) The weak-energy and low-frequency disturbance actually leads to fatigue damage, and the briquette sample experiences three stages: the near-threshold stage, the high-speed expansion stage and the final fracture stage. The smaller the particle size of the coal sample, the denser the specimen, the stronger the amplitude and energy of the single effective MS signal formed during the destruction process, the longer the time duration of crack expansion from the near-threshold stage to the high-speed expansion stage, and the stronger the ability of the coal sample to resist weak-energy and low-frequency disturbances. This study may contribute to a more comprehensive understanding of the destabilization mechanism of coal bodies and MS signal characteristics under weak-energy and low-frequency disturbances and provide a reference for further research and discussion.

Discontinuity Detection System in Marble: Analysis of the Time-Frequency Characteristics of Ultrasonic P-waves

Abstract This study attempted to determine both the presence and the appearance of the surface of a crack artificially created in a marble block without axial loading or compression by FFT analysis of ultrasonic longitudinal sound waves by scanning the surface. In such respect, the study differs from other studies in the literature. The aim of the study was to minimize marble waste by determining the most appropriate slab cut direction based on the orientation of the fracture or discontinuity within the marble block. During location-controlled scanning of the marble surface, mean longitudinal wave velocity, Young modulus, Poisson ratio and longitudinal wave velocity variation data were obtained using a V-Meter Mark IV™ ultrasonic test device. For each location, longitudinal ultrasonic velocity data was taken at 250 kHz sampling rate and 256 data points were created. Data from the computer environment were subsequently reorganized using the MATLAB software and FFT conversions for such velocity data were obtained for each location. Then, the peaks of the FFT transformation components were determined by using the “Findpeaks” function in MATLAB‘s signal processing toolbox. The number of peaks in the 50-60 kHz range was determined for each location. A single difference was determined between the peak numbers at the locations within the cracked and uncracked regions. By examining the FFT graphs, it was determined that such additional peak occurring in the cracked regions appeared as a second frequency component near the dominant frequency values. Points with secondary frequency were recorded as 1, while all other points were recorded as 0 in a new matrix. Such data matrices created for each sample were examined by visualization in the form of surface graphics. Using these graphics, the orientations of discontinuities within the marble block may be determined according to the scanning surface.

Experimental Research into the Cumulative Damage Effect and Strength Anisotropy of Fresh Concrete under Blast Vibration

To evaluate influence of blast vibrations on the long-term mechanical deterioration and damage anisotropy of fresh concrete, blast vibration tests were conducted by preparing concrete test blocks at different curing ages. On this basis, the internal relationships of factors including the curing age during vibrations, vibration blast velocity, and number of blast vibrations with the damage evolution were investigated. The results show that fresh concrete is more susceptible to blasting vibration in the initial setting stage, which changes the bonding performance between cementing materials and aggregates. Then irreversible damage is generated along the main direction of vibration, and cumulative damage occurs with the increasing number of blast vibrations. Fresh concrete was affected most by blasting vibration at an age of 1 day, and the compressive strength at 28 days was reduced by 44.17% under a single vibration event. The damage increased slowly in the concrete at curing ages from 1 to 7 day. Blast vibrations with a velocity of less than 96.2 mm/s had a slight influence on changes in the compressive strength of concrete cured for 28 days. As the blast vibration velocity increased from 96.2 to 180.6 mm/s, the decrease rate of compressive strength in various directions accelerated and the strength decreased by as much as 40.59%. Therefore, it is suggested that the influence of the blast vibration velocity and the number of blast vibrations should be considered in alternating and parallel construction of blasting and concrete pouring work. Furthermore, blast vibration velocity, number of blast vibrations, and maximum attenuation coefficients of longitudinal wave velocities of vibrated concrete test blocks with the same curing age during vibrations differed along three directions, showing anisotropic characteristics. As the velocity and number of blast vibrations increased, the damage anisotropy became more significant. Therefore, the influence of anisotropy of cumulative damage evolution should be considered when establishing the safety criteria for fresh concrete subjected to blast vibrations.

NbSbO4 Kristalinin Yapısal, Elastik ve Piezoelektrik Özelliklerinin İncelenmesi

The structural, elastic, and piezoelectric properties of the NbSbO4 crystal were calculated based on the density functional theory. These properties were calculated using the ABINIT package program under both the generalized gradient approximation and the local density approximation. The elastic stiffness tensor and the elastic compliance tensor for the NbSbO4 crystal were calculated in the ground state. Voigt Bulk Modulus, Reuss Bulk Modulus, Hill Bulk Modulus, Voigt Shear Modulus, Reuss Shear Modulus, Hill Shear Modulus, Young Modulus, Poisson Ratio, Flexibility Coefficient, Debye temperature, Longitudinal sound wave velocity for NbSbO4 crystal using elastic stiffness and elastic compliance tensor, Transverse sound wave velocity and Average speed of sound were calculated. Then, the ground state piezoelectric tensor of the NbSbO4 crystal was calculated. Accordingly, 2D longitudinal surfaces and 3D representation surfaces of the piezoelectric tensor were obtained using MTEX software. The properties obtained with both the generalized gradient approximation and the local density approximation are compared. As a result of the calculations, it was understood that the material was a flexible and formable material in both approximations.