Mechanical Testing System Research Articles

Finite element analysis of the treatment of cervical spondylotic radiculopathy with three dimensional balanced manipulation

To explore the biomechanical characteristics of "three-dimensional balanced manipulation" for the treatment of cervical spondylotic radiculopathy(CSR). A CSR patient was treated with "three-dimensional balanced manipulation", and the mechanical changes during the manipulation were monitored by mechanical testing system. Using spiral CT to scan the neck of the patient to obtain DICOM data. The three-dimensional finite element model of cervical spondylotic radiculopathy was established by using Mimics software, Geographic Studio software. The "three-dimensional balance manipulation" was simulated and loaded, and the mechanical parameters of each part were replaced into the finite element model, and the finite element analysis was carried out by using ANSYS software to study the internal stress changes and displacement deformation of vertebral body and intervertebral disc under the action of "three-dimensional balance manipulation". The established C3-C7 finite element model of the CSR patient consisted of 5 vertebrae, 4 intervertebral discs and 3 ligaments, involving 153 471 nodes and 64 978 units. The stress of C3-C7 vertebral body was mainly located in anterior and root of C5 spinous processes, arch, vertebral arch and the combination of the two after full loading of manipulation, and the maximum stress was 17.781 MPa. The deformation sites were mainly concentrated in articular processes and anterior transverse processes of C3, superior articular processes and transverse processes of C4, articular processes of C5. The stress of C3-C7 intervertebral disc mainly distributed in the anterior part of C3, 4 intervertebral disc and the nucleus pulposus of C4, 5 and C5, 6. The displace mentextended to the middle and posterior part of C3, 4 nucleus pulposus, around the nucleus of C4, 5 and C5, 6 and anterior part of cervical intervertebral disc. The establishment of three-dimensional finite element model of C3-C7 cervical spondylotic radiculopathy can simulate the geometry and material properties of cervical spine, and also accurately reflects the biomechanical characteristics of cervical spine, verifys the internal mechanism of "three-dimensional balanced manipulation" on CSR, proves the safety and effectiveness of treatment, guides more standardized manipulation, and avoids medical accidents.

Study on Strain Characterization and Failure Location of Rock Fracture Process Using Distributed Optical Fiber under Uniaxial Compression

A rock fracture test is a very important method in the study of rock mechanics. Based on the Mechanics Test System (MTS), the dynamic strain response of the failure process of cylindrical granite specimens under uniaxial compression was observed by using distributed optical fiber strain sensors. Two groups of tests were designed and studied for rock sample fracturing. The main comparison and analysis were made between the distributed optical fiber testing technology and the MTS testing system in terms of the circumferential strain response curve and the evolution characteristics of strain with time. The strain characterization of distributed optical fiber in the process of rock fracturing was obtained. The results show that the ring strains measured by the distributed optical fiber sensor and the circumferential strain gauge were consistent, with a minimum ring strain error of 1.27%. The relationship between the strain jump or gradient band of the distributed optical fiber and the crack space on the sample surface is clear, which can reasonably determine the time of crack initiation and propagation, point out the location of the rock failure area, and provide precursory information about rock fracture. The distributed optical fiber strain sensor can realize the linear and continuous measurement of rock mass deformation, which can provide some reference for the study of macro damage evolution and the fracture instability prediction of field engineering rock mass.

Experimental study on the effect of strain rate on rock acoustic emission characteristics

To explore the variation in rock acoustic emission (AE) characteristics with strain rate, uniaxial compression tests at different loading rates and impact loading tests were conducted on granite using a MTS322 rock mechanical test system and split Hopkinson pressure bar (SHPB) system, respectively. The effect of the strain rate on the AE characteristic parameters, rock fracture properties, and destruction evolution were systematically analyzed. The results demonstrated that with increasing strain rate, the cumulative AE count decreases as a power function, and the variation between the cumulative AE count and strain rate can be fitted log-linearly with a slope of 0.48. The peak frequencies of the AE signals are mostly distributed in the zones of 0–100 kHz, 175–250 kHz, and 400–550 kHz. The signal proportion in the 0–100 kHz zone gradually increases with strain rate, while the signal proportions in the 175–250 kHz and 400–550 kHz zone exhibit decreasing trends. A transition of a sudden increase in the RA-value and decrease in the AF-value occurs when the stress reaches a certain level, and the stress level corresponding to this transition will increase with strain rate. Meanwhile, the RA–AF distribution is mostly concentrated on the abscissa in the low strain rate tests, but gradually concentrates on the longitudinal axis as the strain rate increases. This indicates that tensile cracking becomes the dominant fracture mode with increasing strain rate. The b-value decreases with increasing strain rate in the uniaxial compression tests; however, the b-value in the impact loading tests is higher than that in the uniaxial compression tests. Furthermore, to distinguish the signals generated by stress wave propagation from the signals generated by rock fracturing in the impact loading tests, a four-parameter k-means algorithm is used to conduct a clustering analysis. The results indicate that the signals can be classified into four clusters: tensile fracturing signals (cluster A), mixed stress wave and shear fracture signals (cluster B), mixed stress wave and tensile fracture signals (cluster C), and stress wave signals (cluster D).

The effect of phase on microstructure and mechanical performance in TiAlN and TiSiN films

To study the effect of phase on the microstructure and mechanical properties of nitride coatings, three films of TiN, TiAlN, and TiSiN were prepared on the surface of high-speed steel using hollow cathode assisted multi-arc ion plating technique. The XRD lines of the three films were analyzed and calculated by linear analysis. The element and phase of the film were observed and analyzed by x-ray Diffraction (XRD), Transmission Electron Microscope (TEM), energy dispersive x-ray analysis (EDS). The microstructure and film thickness of the coating were characterized by scanning electron microscopy (SEM). The surface roughness of the film was observed by Confocal laser scanning microscope (CLSM). The hardness, friction coefficient, and coating/substrate adhesion of the film were tested by the G200 nanometer hardness tester and CETR UNMT-1 surface micro-nano mechanical test system. We discovered two different reinforcement mechanisms. The high microscopic strain value (1.309 × 10−3) in the TiAlN film was related to the formation of Ti3AlN substitutional solid solution in the film formed a large lattice distortion,however, the coating/substrate adhesion (33.5 N) was lowered. The result of independent nucleation and growth of the Si3N4 phase in the TiSiN film refines the structure of the film, alleviating the increase of microscopic strain. At this time, the coating/substrate adhesion reaches the highest value of 40 N and the film surface roughness reaches the minimum value of 0.451 μm. The results also show that the TiSiN coating can obtain good coating/substrate adhesion without pre-plating.

Permeability Experiment of Fractured Rock with Rough Surfaces under Different Stress Conditions

To investigate the permeability changes and the mechanisms of fractured rock under dynamic and static stresses produced by earthquakes, permeability experiments on fractured rock with rough surfaces under axial dynamic and static stresses were conducted on the MTS815 Rock Mechanics Testing System. Surface asperity was investigated by scanning the specimen surfaces before and after testing. The results show that the roughness of fracture surface has a great influence on the permeability when the axial displacement is not enough to cause the fracture rock to slip. Moreover, the rougher fracture surface leads to severer surface damage as indicated by the more gouge productions. The accumulation of gouge materials on larger roughness fracture surfaces causes a slow drop in permeability. The fracture surfaces experience larger degradations, but it has small weights of gouge materials on fracture surface after testing under axial dynamic stress. The reason is that the gouge material transport and mobilization tend to occur in process of dynamic loading. Therefore, the permeability drops of axial dynamic stress are larger than those of axial static stress.

Multi-scale analysis of the interaction in ultra-long carbon nanotubes and bundles

Ultralow inter-wall interaction is realized in centimeter-long double-walled carbon nanotube (DWCNT) (Zhang, R. et al. Nat. Nanotech. 8, 912-916 (2013)). To further illustrate the mechanism of this special phenomenon, theoretical analysis combining with the experimental test is conducted, where study of the inter-tube interaction in the carbon nanotube bundles (CNTBs) is also included in this paper. In experiment, nanomanipulation difficulties of the ultra-long carbon nanotube (CNT)/CNTB is overcome by establishing a micro/nanoscale mechanical testing system (m/n-MTS), based on which the inter-wall/inter-tube interaction is firstly in-situ measured under optical microscope (OM). In theory, according to the bottom-up approach, a multi-scale model is developed specially, by which results obtained can be directly compared with the experimental data. The pull-out force consists of three parts: the boundary effect, the configuration force and the dynamic friction. The boundary effect can account for more than 70% when the pull-out velocity equals to 1 μm/s. The configuration force is greatly enhanced for the CNTB because of the commensurate configuration in the circumferential direction. The dynamic friction shows linear dependence on the pull-out velocity and relates to the overlapped area, which can be manifested when the pull-out velocity reaches to a dozen μm/s for the ultra-long DWCNT. The dynamic friction coefficient is proved to be 0.29 multiple of critical value based on the experiment data. The pull-out force in the CNTB is found far less than that in the DWCNT due to the greatly reduced contact area. Moreover, it can be deduced that the dynamic friction will show the same order of magnitude as the contribution from the boundary when the pull-out velocity equals to 10 μm/s or the length is 10 mm. This research reveals the underlying mechanism of the interaction, especially for the dynamic friction force exhibited in the ultra-long CNT/CNTB, and can provide help for designing devices with ultralow friction on macroscale.

A novel type of neural networks for feature engineering of geological data: Case studies of coal and gas hydrate-bearing sediments

The nature of the measured data varies among different disciplines of geosciences. In rock engineering, features of data play a leading role in determining the feasible methods of its proper manipulation. The present study focuses on resolving one of the major deficiencies of conventional neural networks (NNs) in dealing with rock engineering data. Herein, since the samples are obtained from hundreds of meters below the surface with the utmost difficulty, the number of samples is always limited. Meanwhile, the experimental analysis of these samples may result in many repetitive values and 0s. However, conventional neural networks are incapable of making robust models in the presence of such data. On the other hand, these networks strongly depend on the initial weights and bias values for making reliable predictions. With this in mind, the current research introduces a novel kind of neural network processing framework for the geological that does not suffer from the limitations of the conventional NNs. The introduced single-data-based feature engineering network extracts all the information wrapped in every single data point without being affected by the other points. This method, being completely different from the conventional NNs, re-arranges all the basic elements of the neuron model into a new structure. Therefore, its mathematical calculations were performed from the very beginning. Moreover, the corresponding programming codes were developed in MATLAB and Python since they could not be found in any common programming software at the time being. This new kind of network was first evaluated through computer-based simulations of rock cracks in the 3DEC environment. After the model’s reliability was confirmed, it was adopted in two case studies for estimating respectively tensile strength and shear strength of real rock samples. These samples were coal core samples from the Southern Qinshui Basin of China, and gas hydrate-bearing sediment (GHBS) samples from the Nankai Trough of Japan. The coal samples used in the experiments underwent nuclear magnetic resonance (NMR) measurements, and Scanning Electron Microscopy (SEM) imaging to investigate their original micro and macro fractures. Once done with these experiments, measurement of the rock mechanical properties, including tensile strength, was performed using a rock mechanical test system. However, the shear strength of GHBS samples was acquired through triaxial and direct shear tests. According to the obtained result, the new network structure outperformed the conventional neural networks in both cases of simulation-based and case study estimations of the tensile and shear strength. Even though the proposed approach of the current study originally aimed at resolving the issue of having a limited dataset, its unique properties would also be applied to larger datasets from other subsurface measurements.

Investigation of the evolution of damage and permeability of coal containing gas based on acoustic emission characteristics

AbstractThe gas permeability of a coal seam was the main factor determining the efficiency of gas extraction from the mines and was closely related to the coal damages. In this paper, a triaxial compression failure test of the raw coal was carried out in the gas seepage state using the MTS 815 rock mechanics testing system. The damage evolution law of the coal containing gas under triaxial compression was studied based on acoustic emission characteristics. The damage evolution parameters were determined using acoustic emission signals, and the relationship between the permeability and damage evolution of the coal containing gas was quantitatively analyzed. The results demonstrated that the acoustic emission signals could reflect the development of the damage and failure inside the coal, and the turning point of the acoustic emission characteristic curve marked different damage development stages. The periodic changes in the permeability of the coal samples were consistent with the damage change law, and some lag existed in permeability changes compared with damage evolution. The permeability of the coal containing gas saw a stepwise exponential growth with the damage development. The piecewise exponential function better reflected the relationship between the gas permeability and damage variables.

New Insights into the Role of Surface Nanobubbles in Bubble-Particle Detachment.

It is well recognized that an improved flotation recovery can be achieved by introducing nanobubbles to common flotation practice due to the increased capture efficiency between bubbles and particles. However, the specific role of nanobubbles in bubble-particle interactions (collision, attachment, and detachment) is not well understood. In the present study, we explore the role of surface nanobubbles in bubble-particle detachment. Surface nanobubbles were introduced via ethanol-water exchange and their presence was confirmed using laser scanning confocal microscopy (LSCM). The effect of surface nanobubbles on bubble-particle detachment behavior was then investigated using an oscillating bubble apparatus. Bubble-particle aggregate stability was evaluated using critical detachment amplitude. Further, bubble-particle detachment forces in the absence and presence of nanobubbles were measured directly using a micro-nano mechanical testing system. Using LSCM, numerous surface nanobubbles were observed on a glass surface after ethanol-water exchange, regardless of wettability. The number and lateral dimensions of generated nanobubbles on the hydrophilic surface were significantly smaller than that on the hydrophobic surface. Surface nanobubbles increased the stability of bubble-particle aggregates. Macroscopic air bubbles coalesce with the nanobubbles on the particle surface, increasing the pinning effect of the three-phase contact line and advancing contact angle. As a result, the capillary force between bubbles and particles increased in the presence of surface nanobubbles.

Short‐term hindlimb immobilization induces rapid loss of bone strength in a mouse model of disuse atrophy

Muscle atrophy and bone loss are known to occur in settings of disuse such as prolonged bedrest, spinal cord injury, or exposure to microgravity with spaceflight. It is also well‐established that crosstalk exists between muscle and bone mediated by myokines such as myostatin and irisin, and that changes in these muscle‐derived factors with exercise, aging, or muscle atrophy may contribute to changes in bone formation and resorption. Muscle loss in many cases often precedes bone loss, and can be more rapid relative to detectable changes in bone mass or density. We investigated short‐term (2 weeks) changes in muscle and bone with disuse atrophy utilizing a single hindlimb immobilization model to identify associated between changes in muscle mass and bone strength. Twelve‐month C57/BL6 mice (8 male, 4 female) were subjected to two weeks of hindlimb (left hindlimb) immobilization, using a casting technique that involved wrapping surgical tape from the pad of the foot to the proximal thigh with a final layer of vetwrap covering the surgical tape. Mice were euthanized following IACUC‐approved procedures, and quadriceps muscles weighed and fiber size measured histologically. Femora were snap frozen in liquid nitrogen and later rehydrated in PBS for 1 hour prior to mechanical testing, after which they were loaded to failure in 3‐point bending (10 mm span length, 10 mm/min) on a Bose ELF mechanical testing system. Results indicate that quadriceps mass and fiber size declined significantly in immobilized (left) hindlimb compared to the non‐immobilized hindlimb, decreasing approximately ~20% and 30%, respectively over the two‐week treatment period. Ultimate force of the femur also declined significantly in the mice over this timeframe, decreasing up to 20% in the male mice. Regression analyses demonstrate that quadriceps mass and fiber size were each significantly correlated with femur ultimate force (P=.01), and that correlation coefficients between muscle mass and fiber size (r=.48) were similar to correlations between muscle mass and femur ultimate force (r=.47) and muscle fiber size and femur ultimate force (r=.47). These findings suggest that even in the setting of short‐term disuse declines in muscle mass and bone strength are tightly coupled, and that therapeutic interventions to mitigate loss of muscle and bone should be considered to reduce fracture risk.

Comparative experimental study on mechanical mechanism of combined arches in large section tunnels

The large section tunnel support is facing tremendous challenges. They are large in span and poor in self-stability of surrounding rocks. Traditional I-steel arches are easily subject to buckling failure. As a result, safety accidents always occur, such as the failure of supporting system and the collapse of tunnels. To solve the problems, a new support technology of confined concrete and corresponding arches are invented. With high strength and rigidity, it can effectively control the deformation of surrounding rocks on large section tunnels. To clarify the bearing capacity and failure mechanism of the new arch, a mechanical testing system for the combined arches in large section tunnels is developed. Comparative tests were carried out on the mechanical mechanism of the combined arches of confined concrete and traditional I-steel. The tests took Longding Tunnel, one of the largest city road tunnels in China, as engineering background. In the test, the following results were found. The in-plane flexural buckling occurred on the vault of the combined I-steel arch first, and then out-plane flexural-torsional buckling occurred on the hance and bottom of the arch. It resulted in the overall loss of its bearing capacity and the entire arch being flattened. In the other hand, the confined concrete combined arch showed no severe deformation; its bearing capacity was 2.63 times that of the I-steel arch; and its average rigidity at the coordinated bearing stage is 2.51 times that of the I-steel arch. It is superior in bearing capacity and stability to the I-steel arch. Based on the experimental research conclusions, the engineering suggestions are put forward for the application of the confined concrete support technology in tunnels and the field application was carried out. The control effect is excellent on surrounding rocks. The results can provide a reference for the future research and design in this field.

Cross-elements to enhance fixation in osteoporotic bone with application to proximal humeral locking plates: a biomechanical study

Proximal humeral fractures occur predominantly in elderly, osteoporotic individuals, especially women, with surgery performed in one-fifth. Proximal humeral locking plates are the gold standard operative treatment; however, complications are frequent, partially because of poor screw purchase in osteoporotic bone. A new method uses threaded posts through which threaded cross-elements orthogonally pass to create a 3-dimensional scaffold for bone engagement. We examined the pullout characteristics of the posts with (1 or 2) or without the cross-elementsand tested 2 types of 3.5-mm cortical locking screws for comparison. Low-density closed-cell polyurethane foam served as a model osteoporotic bone substrate. Following implantation in the substrate, the devices were axially loaded by a mechanical test system. Quantities of interest included failure mode, peak load, displacement to peak load, initial stiffness, and work expended. The post groups outperformed the 3.5-mm screw groups, as expected. Relative to posts with no cross-elements, 1 and 2 cross-elements increased the peak load by 29% and 87% and increased the work to peak load by 126% and 343%, respectively. After reaching peak load, 1 and 2 cross-elements increased the work-resistance to further displacement by 158% and 330%, respectively. Cross-elements significantly increased the ability of the threaded posts to resist axial displacement from a model osteoporotic bone substrate. This suggests that posts, used in conjunction with cross-elements, have the potential to enhance the stability of proximal humeral locking plates in osteoporotic bone.

Load-bearing characteristics of square footing on geogrid-reinforced sand subjected to repeated loading

A series of dynamic model tests that were performed on a geogrid-reinforced square footing are presented. The dynamic (sinusoidal) loading was applied using a mechanical testing and simulation (MTS) electro-hydraulic servo loading system. In all the tests, the amplitude of loading was ±160 kPa; the frequency of loading was 2 Hz. To better ascertain the effect of reinforcement, an unreinforced square footing was first tested. This was followed by a series of tests, each with a single layer of reinforcement. The reinforcement was placed at depths of 0.3B, 0.6B and 0.9B, where B is the width of footing. The optimal depth of reinforcement was found to be 0.6B. The effect of adopting this value versus the other two depths was quantified. The single layer of geogrid had an effective reinforcement depth of 1.7B below the footing base. The increase of the depth between the topmost geogrid layer and the bottom of the footing (within the range of 0.9B) did not change the failure mode of the foundation.

Analysis of triaxial compression deformation and strength characteristics of limestone after high temperature

Understanding the mechanical behavior of rock under conditions of high temperature and pressure is critical when it comes to implementing underground coal gasification, deep disposal of highly radioactive nuclear waste, development and utilization of deep underground space, development and utilization of geothermal resources, etc. To understand the effect of confining pressure on limestone at high temperature, uniaxial and triaxial compression testing was conducted on limestone under high temperature (20–800 °C) using the MTS 815 rock mechanics testing system. Using this system, the change in the strength and deformation parameters of the limestone at varying temperature and confining pressure conditions were studied. The results show that the triaxial compression stress-strain curve of limestone at high temperatures is divided into five stages: compaction stage, elastic stage, plastic deformation stage, post-peak failure stage, and residual stage. In addition, the rock brittleness and ductility decrease as the temperature increases. The peak stress and residual strength of the limestone at high temperatures increase as the confining pressure increases, and the strength of the rock specimens decreases as the temperature increases. The internal friction angle (φ) first increases and then decreases as the temperature increases, but the relationship of the cohesive force (c) to temperature is opposite that of φ, indicating that the shear strength of limestone at high temperatures is determined by both c and φ. The elastic modulus of limestone at high temperatures increases with the increase in confining pressure and decreases as the temperature increases, and the peak strain of limestone at high temperatures increases as the confining pressure and temperature increase. The effect of temperature on the failure of limestone is not obvious, and the failure of rock specimens during uniaxial compression testing was mostly through axial splitting, while the failure of rock specimens under triaxial compression testing was mostly through shear failure. As the confining pressure increases, the fracture type of the rock specimens gradually changes from brittle tensile fracture to shear fracture, and the instability type of the rock specimen changed from the sudden instability type to the progressive failure type. Our research results are especially useful in areas where engineering is performed on rocks under high temperature.

Data mining technology for mechanical engineering computer test system

With the continuous development of information technology, data resources have become increasingly rich, but the knowledge contained in data resources has not been fully explored and utilized. In order to find an effective computer testing technology, the paper introduces the partial differential equation (PDE) into the denoising process of rotor vibration signal through data mining technology, and generalizes the unified model of PDE filtering. Several filtering methods are compared through simulation experiments. The effect is that the flexible rotor is balanced by different dynamic balancing methods, and satisfactory results are obtained. From the simulation results, it can be concluded that the integration method is not suitable to extract the unbalanced signal with strong noise background, but it provides a way to calculate the amplitude and phase of sinusoidal signal without noise; The processing is simple and suitable for the calculation of the dynamic balance test system with fewer sampling points; both the DFT method and the FFT method use the principle of Fourier transform spectrum analysis, but the FFT method calculates the speed much faster than the DFT method. Experiments on the classification of fault data prove that the improved Apriori algorithm is greatly improved compared with the original Apriori algorithm, and the speed of acquiring fault rules is improved.

Permeability Evolution of Fractured Rock Subjected to Cyclic Axial Load Conditions

Permeability experiments on saw-cut fractured rock subjected to cyclic axial load conditions were conducted on the MTS815 rock mechanics testing system. The influence of the frequency and amplitude of cyclic axial forces on axial displacement and permeability evolution of fractured rock was experimentally investigated. Results show that the increasing frequency under the same amplitude of axial load leads to a reduction in axial displacement, but a drop followed by an increase in permeability, while the permeability values oscillated sharply under high amplitude of cyclic loads, which can be attributed to the production of gouge materials. Besides, the increase in axial displacement roughly contributed to the permeability reduction, and excessive amplitude of cyclic load posed limited boost to the permeability enhancement. By comparing with the quasistatic function, we found that it did not completely correspond to the trend of the permeability evolution subjected to cyclic axial forces, and sensitivity coefficients evolving with frequency and amplitude should be considered. A new function of the permeability evolution subjected to the amplitude and frequency of cyclic axial forces was derived and verified by the experimental data. This study suggests that small amplitude and high frequency of dynamic forces have the potential for enhancing the permeability of fracture and triggering the disaster of fractured rock.

Bearing Grounding Mechanical Properties of Engineering Vehicle Retreaded Tire

In this study, a multivariate composite layer model, computer geometry models, contact pair models, finite element analysis (FEA) models, and bearing grounding mechanical property test system were constructed. FEA and experimental study on the bearing grounding mechanical properties of retreaded tires of engineering vehicles were processed. Therefore, features and rules of load grounding pressure, load grounding mark, load grounding area, load grounding coefficient, and load grounding hardness coefficient of retreaded tires under the static grounding working condition were summarized, from which load-bearing grounding mathematical models of 26.5R25 engineering vehicle retreaded tire were constructed. Analysis results show that the grounding pressure at the tread center of grounding pressure and grounding friction, which increased along the tire width and rolling direction at different degrees, were the smallest under the static grounding working condition. The shape of the earthing marks turned from circular to elliptical, and then close to the rectangle with the load increase, and finally into an approximate saddle shape. When the tire pressure was certain, the earthing area increased gradually with the increasing load and the increasing trend was nonlinear. The ground pressure and grounding force on the tire shoulder of the engineering re-treaded tire was the largest, which could be damaged easily.

The Establishment of Segmented Constitutive Relationship of Coal under Triaxial Compression: Take the No. 3 Coal of Xinhe Colliery as an Example

Constitutive relationship of coal under triaxial compression must be determined during solving the theoretical calculation and numerical simulation about coal body failure. This paper carried out the conventional triaxial compression test on No. 3 coal of Xinhe Colliery using the MTS815.03 servo‐controlled rock mechanical test system. The results indicate that the failure process of coal can be divided into 5 stages: densification stage, apparent linear elastic deformation stage, accelerated inelastic deformation stage, fracture and developing stage, and plasticity flow stage. Within the test confining pressure (20 MPa), the peak strain of coal is approximately linearly positively correlated with the confining pressure. The relationship between elastic modulus of coal and confining pressure is quadratic polynomial. The triaxial compressive strength and residual strength of coal are approximately linearly positively correlated with confining pressure. The constitutive relationship model of coal can be simplified as the four segments of straight line model of “elastic–plastic hardening–plastic softening–residual perfectly plastic.” Through fitting calculation of test data, the segmented constitutive equation of coal can be obtained, and the every segment span of strain.

Experimental Study on Lateral Permeability Evolution of Sandstone under Seepage‐Damage Coupling

To analyze the internal pore evolution law of aquifer rock in a coal mining front under the coupling effect of stress and seepage and the influence on the water inrush performance of the working face, research on the working face was conducted to improve the RTR‐1000 high‐temperature and high‐pressure rock triaxial mechanical testing system, using hollow cylindrical and complete sandstone samples and by considering the stress change law in the actual mining process as the reference loading path. At the initial stage of loading, the permeability of sandstone demonstrates a rapid downward trend within a small range of stress change, with a decline rate of 50%. At lower permeabilities, the fluctuation is small; the plastic and failure stages are transient, and the relationship curve between the horizontal permeability and the axial confining pressure of sandstone is divided into compaction, multiple fluctuations, surrender, and failure. In several stages, the sandstone lateral permeability experiment under the coupling effect of stress and seepage demonstrates that the permeability of the aquifer in the coal mining front is significantly reduced after the original rock stress is disturbed by mining, suggesting that the water inrush calculation of the traditional water‐flowing fractured zone and caving zone aquifer rock permeability experiment is inaccurate. Further research can deepen the stress and seepage coupling evolution process under the action of working face water inrush.

Comparative Analysis of Thermomechanical Properties and Thermal Damage Constitutive Models of Three Soft Sedimentary Rocks

In order to study the difference in thermomechanical properties of soft sedimentary rocks of different coal measures, three types of soft sedimentary rocks, sandstone, sandy mudstone, and mudstone, which are common in deep mines, are tested using the RMT‐150B rock mechanics test system and GD‐65/150. Uniaxial compression experiments were conducted on three kinds of soft rock‐cement mixed specimens at 25°C～55°C multistage temperature in an environmental chamber. The difference of important parameters such as stress‐strain curve, peak stress, and elastic modulus was analyzed and compared. The results show that (i) in the test temperature range, the stress‐strain curves of the three types of soft rocks at different temperatures are roughly divided into four stages: compaction, elasticity, yield, and failure. The proportion of deformation in the compaction stage to the total deformation decreases gradually with the increase of temperature. (ii) When the temperature is lower than 40°C, the yield stage is shorter, and the peak stress and elastic modulus of the three types of soft rocks decrease significantly with the increase of temperature. (iii) Above 40°C, the decreasing trend of peak stress and elastic modulus curve decreases, and the yield stage becomes more and more obvious. The decreasing rate of elastic modulus of sandstone is 0.041 GPa/°C; the decreasing rate of peak stress is 0.193 MPa/°C, the decreasing rate of sandy mudstone is 0.022 GPa/°C and 0.124 MPa/°C, and the decreasing rate of mudstone is 0.020 GPa/°C and 0.051 MPa/°C. (iv) The rationality of the established thermal damage constitutive model of sedimentary soft rock was verified.