Characterization Of Mechanical Behavior Research Articles

Injection Temperature Impacts on Reservoir Response during CO2 Storage

SummarySustained injection of industrial-scale volumes of cold CO2 into warmer subsurface rock will result in extensive cooling which can alter rock mass mechanical behavior and fluid migration characteristics. Advanced simulation tools are available to assess and characterize such phenomena; however, the effective use of these tools requires appropriate injection temperatures and rock thermophysical parameters (in addition to geomechanical and hydraulic properties). The primary objective of this study was to demonstrate the sensitivity of injection-induced tensile fracturing and fault reactivation to injection temperature and reservoir thermophysical properties during CO2 injection operations. This was achieved by (1) compiling and reviewing thermophysical parameter data available for formations in the province of Alberta, Canada, and CO2 injection temperature records for CO2 injection projects in western Canada and (2) using a 3D, physics-based, fully integrated hydraulic fracturing and reservoir simulation numerical model to examine the geomechanical response of several potential CO2 reservoirs in the Alberta Basin as a function of injection temperature, thermal conductivity (TC), and coefficient of linear thermal expansion (CLTE) values. The simulation results indicate that reducing the fluid injection temperature from 15°C (assumed in previous work) to 2°C (conservative value selected based on temperature data reviewed in this work) could trigger extensive vertical (20–130 m high, 100–600 m long) tensile fractures with rapid fracture initiation and full vertical growth within short periods (weeks to months) and continued horizontal length increase. When low values for thermophysical properties are used, the results show that thermally-induced tensile fracturing is unlikely, whereas the use of high values results in extensive tensile fracturing in all simulations. A similar conclusion was reached for the thermally-induced reactivation (unclamping) of proximal, critically-stressed faults. Notably, slip is predicted for all simulations where high thermophysical property values are used. This confirms that accurate determination of minimum fluid injection temperature and thermophysical parameters is important for containment risk assessment for commercial-scale CO2 storage projects. Another significant outcome of this work is the observation that most thermophysical parameters in the available data were measured using experimental conditions and/or temperature paths that are not representative of CO2 injection projects. As such, the development and validation of best practice approaches for accurate assessment of these parameters seem necessary.

Numerical Simulation Study on the Mechanics and Pore Characteristics of Tectonically Deformed Coal under Multi-Level and Multi-Cycle Loading and Unloading Conditions

Horizontal well cavern completion and stress release is considered a potential technique for efficient development of coalbed methane in tectonically deformed coal (TDC). Pulsating loading and unloading is a key technique for the controlled expansion of caverns and broader stress release within the reservoir. However, current understanding of the mechanical characteristics and pore network structure evolution of TDC under cyclic loading and unloading conditions is still limited. This paper employs numerical simulation methods to study the mechanical behavior and damage characteristics of TDC under cyclic loading and unloading. After obtaining a set of micromechanical parameters reflecting the behavior of TDC samples under triaxial compression in high-stress states, the effects of different stress gradients and cyclic amplitudes on the stress–strain curve, porosity changes, and crack propagation in TDC samples were analyzed. The study results indicate that under various cyclic loading and unloading conditions, the mechanical response characteristics of TDC samples are broadly similar, primarily divided into compression, slow expansion, and accelerated expansion phases. Under low unloading level conditions, the volume expansion of TDC samples is minimal. Also, at the same unloading level, the strain increment decreases with an increasing number of cycles. Correspondingly, under these conditions, the porosity and microcrack expansion in TDC are less than in high-stress gradient scenarios. Under the same unloading level but different amplitudes, the volume expansion rate at 50% unloading amplitude is higher than at 1 MPa unloading amplitude for TDC, with an increased number of crack expansions. Therefore, under cyclic loading conditions, the sensitivity of crack propagation within TDC samples to amplitude is greater than that to unloading level. Under actual pulsating excitation conditions, a low-amplitude, low-stress gradient pulsation method should be used to maintain the stability of horizontal well caverns, and gradually increase the cyclic amplitude to achieve the efficient extraction of coalbed methane in TDC reservoirs. The findings of this study can serve as an important reference for optimizing process parameters in cyclic pulsating stress release engineering for TDC.

Research on the Influence Mechanism of Moisture Content on Macroscopic Mechanical Response and Microscopic Evolution Characteristic of Limestone

The uniaxial compression experiments and acoustic emission (AE) monitoring are conducted to investigate the macroscopic mechanical behavior and microscopic fracture characteristics of limestone samples with varying moisture contents. The findings revealed that as the moisture content increases from 0 to 6.6%, there is a decrease in peak stress and an increase in peak strain. A clear trend towards greater complexity in fracture characteristics is observed with increasing moisture content. In addition, AE activities demonstrate a heightened frequency, accompanied by an elevation in the corresponding multifractal parameter Δα as the moisture content rises. These variations are attributed to the increase in moisture content, which promotes the proliferation of small-scale microcracks and inhibits their evolution into large-scale microcracks. Consequently, the damage and failure process of the limestone samples transitions from being predominantly controlled by a few large-scale microcracks to being collectively influenced by a multitude of small-scale microcracks as the moisture content increases. In conjunction with the Criterion of Microcrack Density, the correctness of the analysis above is substantiated through mathematical derivation. Further, a quantitative model that links the microcrack system to moisture content is established based on the multifractal parameter Δα. Following this, a characterization model that depicts the macroscopic mechanical properties of limestone affected by moisture content is developed. This model effectively encapsulates the quantitative relationship between moisture content and the macroscopic characteristics of limestone and is validated through fitting experimental data. This research contributes to understanding the macroscopic mechanical response and microscopic fracture characteristics of limestone samples with different moisture contents, providing valuable insights and guidance for ensuring safety during engineering construction processes.

Mechanical behaviour and grain breakage characteristics of Tibetan glacial tills under triaxial compression

Deglaciation due to warming climate has left a great amount of glacial tills in ravine slopes and channels in southern Tibet, which can lead to destructive debris flows and pose great threats to downstream residents and infrastructures. The mechanical properties and grain size characteristics of glacial tills are key factors that influence the initiation and development of these debris flows. In this work, a series of consolidated undrained (CU) triaxial compression tests under different confining pressures were carried out on Zelongnong glacial tills at various relative densities of 9.2%, 49.5%, 69.0% and 88.7%. The grain size distribution change before and after the CU tests was also determined. Results show that the glacial tills at relative densities of 9.2%, 49.5% and 69.0% exhibited a remarkable strain-softening and contractive behaviour during shearing, while those at a relative density of 88.7% presented a dilatant behaviour. As the relative density increased, the shear strength, elastic modulus and shearing friction angle increased, reducing the liquefaction potential. Based on the increasing rate of mechanical resistance with the increasing relative density, a critical value of 69.0% was identified to appreciate the distinct mechanical responses of the specimens. From the grain size distributions before and after CU tests, the content of grains with a diameter larger than 0.85 mm decreased due to the grain breakage while that of grains smaller than 0.3 mm increased. The higher the specimen relative density, the larger the grain breakage ratio owing to the increasing friction resistance. This grain breakage in turn causes a downward shift of the critical state line on the plane of void ratio and mean effective stress.

Narrowing band gap and enhanced optoelectronic properties in methylammonium lead chloride perovskite under pressure

In this study, we explore the impact of hydrostatic pressure on the structural stability, elastic properties, mechanical behavior, thermodynamics, and optoelectronic characteristics of lead halide perovskite, specifically focusing on CH3NH3PbCl3. Through high-level ab initio simulation techniques, we investigate the lattice squeezing effects on this methylammonium lead chloride perovskite. Our findings reveal that applying hydrostatic pressure squeezes lattice parameters, influences the electronic profile, and results in spin-split band edges. The band gaps in compressed perovskites are observed to be narrower, with the potential for pressure-induced closures, offering new electronic features under various thermodynamic conditions. Because of the high-quality crystal and its optimal optical band gap, we successfully construct an efficient UV-photodetector, highlighting its promising applications in optoelectronics. This work contributes to a deeper atomistic understanding of inorganic halide perovskite behavior under external pressure and demonstrates the potential for realizing enhanced electronic functionalities through pressure conditions.

Experimental and modeling study of shear strength of unsaturated fine-grained soils with bi-modal water-retention characteristics

The mechanical behavior and strength characteristics of unsaturated fine-grained soils with dual-porosity are of crucial importance in geotechnical designs. Nanyang fine-grained soils have been selected as typical dual-porosity structure soils to perform experimental tests under a wide range of suction and different initial densities while studying its stress-strain-strength properties constitute the main scope of this study. Axial translation and vapor equilibrium techniques are jointly employed to apply a wide suction range. Our data suggest that soil behavior transits from strain-hardening with shear-induced contraction to strain-softening with shear-induced dilation as suction and density increase. By exploiting a bi-modal soil–water retention curve (SWRC) explicitly separating capillarity and adsorption mechanisms, the shear strength is allowed to be analyzed in the capillary suction stress-shear stress space. The strength envelop exhibits bi-linear characteristics. Building upon these findings, we propose a bi-linear shear strength criterion specifically for dual-porosity fine-grained soils. We utilize the obtained test data to evaluate existing strength criteria based on effective stress and dual stress variables that consider the bi-modal SWRC characteristics. The comparison indicates that the proposed bi-linear shear strength criterion can more reasonably represent the variation of shear strength under a wide range of suction for unsaturated dual-porosity fine-grained soils.

Experimental study on the characterization of mechanical behavior of concrete under hot-arid climatic conditions

Experimental study on the characterization of mechanical behavior of concrete under hot-arid climatic conditions

Dynamic behavior of polyethylene terephthalate (PET) foam under compressive loads: Experimental and numerical study

The behavior of PET foam under quasi-static and dynamic compressive loads is analyzed. An experimental study is performed to evaluate its mechanical behavior and energy absorption characteristics at different strain rates. Also, a numerical model is developed to reproduce the dynamic compression behavior of the PET foam. Differences between the properties obtained in the quasi-static and dynamic tests show that the strength, stiffness and energy absorption efficiency are dependent on strain rate. The evolution of the Poisson ratio with strain and strain ratio is studied. A decrease in the Poisson ratio is observed as the strain rate increases.

Investigating the Mechanical Deterioration Effect of Hard Sandstone Induced by Layer Structure under Uniaxial Compression

The deterioration of the surrounding rock at the tunnel bottom is a damage mechanics issue that occurs under disturbance load. To investigate the anisotropic characteristics of mechanical behavior and the AE response mechanism of layered sandstone, uniaxial compression tests and acoustic emission (AE) monitoring were conducted. The results show that the layer structure causes remarkable anisotropic characteristics in the wave velocities. The strain characteristics and mechanical parameters of layered sandstone exhibit obvious deterioration effects. The local strain and overall strain show a synergistic feature, with the local strain path being more complex and the deformation response being extremely sensitive. The peak stress and elastic modulus both exhibit V-type distribution rules, slowly decreasing first, then rapidly decreasing, and finally increasing rapidly, with the boundary points of the layer angle being 45° and 67.50°. The peak stress and elastic modulus show a nonlinear exponential correlation with the layer angle, and the sandstone belongs to the intermediate anisotropy level. The rupture pattern shows significant anisotropic characteristics, with the failure modes including tension failure, including tension failure I and tension failure Ⅱ, shear failure, and tension–shear composite failure. The fractal dimension shows a negative correlation with the layer deterioration effect. The AE activity exhibits a phased response characteristic to the aging deformation of layer structure. The more obvious the layer deterioration effect is, the longer the AE delay is. The AE intensity of tensile failure sandstone is generally greater than that of oblique shear failure.

Study on the formability of copper foils during multi-step micro deep drawing

In this work, the formability of copper foils was analyzed based on a series of multi-step micro deep drawing (MMDD) tests. The copper foils were annealed at temperatures ranging from 300 to 700 °C for 5 min, followed by tensile tests and electron backscatter diffraction (EBSD) tests for the exploration of mechanical behavior and microstructural characterization of annealed specimens. The results show that the as-received copper foils exhibit poor formability and cannot form micro cups during MMDD. When the annealing temperature attains 500 °C, a homogeneous microstructure was formed inside copper foils, enhancing the formability of materials and improving the surface quality of formed products. Nevertheless, both the elongation and tensile strength decrease dramatically due to the easy occurrence of incoordination deformation in coarse grain bands with further increase in annealing temperature to 700 °C. Consequently, marked wrinkling is generated on the surface of drawn cups and obvious thinning occurs at the nose radius region due to metal flow. In addition, the results show that the E texture component within the copper foils is favorable for MMDD. Overall, an optimal annealing temperature of 500 °C is obtained with improved formability of copper foils and forming quality of drawn cups.

Revealing the microstructure evolution, deformation behavior and tensile properties of AZ31/AM60 dissimilar Mg alloy joints under different welding technologies

In this work, friction stir welding (FSW) and tungsten inert gas welding (TIG) were applied to prepare two kinds of dissimilar AZ31/AM60 Mg joints. The relationship between mechanical properties, deformation behavior, and microstructure characteristics of both joints was investigated. Microstructural characterization demonstrated that a significant grain orientation fluctuation occurred in the weld zone (WZ) of the FSW joint, but this was not obvious for the TIG joint. Compared with the base metals, the grain size of the FSW joint slightly decreased, but the grain of the TIG joint obviously coarsened. Locally strong texture appeared in the WZ of the FSW joint with a symmetrical distribution, while a random texture character occurred in the TIG joint. Furthermore, the WZ of the TIG joint possessed more and larger second phases than the FSW joint. Tensile tests indicated that both joints had equivalent yield strength (∼120 MPa) and ultimate tensile strength (∼255 MPa), but the elongation (9.0 %) of the FSW joint was lower than that of the TIG joint (12.1%). The similar strength originated from the higher Schmid factors (SFs) of basal slip and extension twinning in the WZ side of the FSW joint and the larger grain size and lower dislocation degree in the heat-affected zone of the TIG joint. The decreased elongation in the FSW joint was due to the apparent inhomogeneous deformation caused by significant SFs (basal slip) fluctuation, while the weaker SFs fluctuation and notable twinning behavior in the TIG joint contributed to the relatively higher elongation.

Use of nano-silica to improve the performance of LC3-UHPC: Mechanical behavior and microstructural characteristics

Ultra-high-performance concrete (UHPC) made of limestone calcined clay cement (LC3) exhibits excellent mechanical properties as well as good environmental friendliness. This paper studied the improving effect of nano-SiO2 on the mechanical properties and microstructure of LC3-UHPC. The experimental results show that the addition of nano-SiO2 demonstrates obvious advantages. The mechanical properties of LC3-UHPC are enhanced, and the frictional bond performance between steel fiber and cementitious matrix is also improved. The fiber/matrix bond strength is increased. A constitutive model describing the single fiber pullout behavior is established, and the values of related parameters are suggested. Besides, nano-SiO2 also refined the cementitious microstructure of UHPC and made the matrix denser. Based on the comprehensive analysis of mechanical properties and microstructural characteristics, the optimal content of LC3 and nano-SiO2 were proposed.

Mechanical behavior and fracture characteristics of high-temperature sandstone under true triaxial loading conditions

To understand the stability of deep underground engineering rocks at high temperatures, it is necessary to conduct comprehensive tests on the mechanical properties of the rocks. In this study, a series of true triaxial tests (TTT) were conducted on sandstones using a self-developed true triaxial testing system combined with XRD, FE-SEM and CT analyses. The study systematically examined the microstructural characteristics, physical phase behavior, deformation properties and internal fracture development of the sandstone before and after heat treatment. The results of the study show that sandstone has temperature-dependent true triaxial mechanical properties after heat treatment. The stress-strain characteristic curves of the post-peak portion from room temperature to 800 °C show a significant stress-reducing segment, indicating the presence of brittle behavior. In addition, when the temperature exceeds 1000 °C, the sandstone exhibits brittle-ductile change characteristics, with a peak stress threshold observed at 800 °C. Notably, the peak stresses corresponding to 800 °C increased by 84.5 %, 63.1 %, 47 %, and 49.8 %, respectively, compared with the room temperature intermediate principal stresses(IPS) ranging from 20 MPa to 50 MPa, respectively. Importantly, the linear Mogi-Coulomb criterion remains valid for the peak strength of the high-temperature sandstone, while the internal fracture damage pattern of the specimens shows an inverted "Y" or inverted "W" configuration. The internal fracture network of rock samples above 800 °C is more complex. Intergranular crack is the main form of microcracking. This experimental study on the mechanical properties of sandstone under the combined effects of high temperature and real triaxial stresses provides valuable guidance for the selection of sandstone parameters and safety evaluation of coal underground gasification roofs.

Study on mechanical properties and failure mode of single-fissure sandstone discs under bi-directional linear loading

The tensile failure of discontinuous geological rock masses in underground spaces is an enduring issue in geotechnical engineering. Understanding the mechanical behaviour and failure characteristics of cracked rock under tension is vital for the safe practice of underground projects. In this study, bi-directional linear load tests were conducted on single-fissure sandstone discs under different stress ratios i (axial stress P1: lateral stress P2) = 1:1, 2:1, 3:1, 4:1, and ∞:1, with crack inclination angles α = 0°, 30°, 45°, 60°, and 90°. The specimens’ deformation characteristics, acoustic emission features, and microfracture characteristics were recorded using the digital image correlation (DIC), PIC-2 acoustic emission(AE) system, and the scanning electron microscopic (SEM). The results showed that the strength at α = 0° was not significantly different from that of intact discs. The AE results and test results indicated that the peak load and initiation load decreased when increasing α and i, and the initiation load approached the peak load. In addition, when the stress ratio was small(i ∼ 1:1), the failure mode of the specimens was mainly controlled by the lateral stress P2. As i increased, the constraint of the lateral stress weakened, and the final failure mode of the specimens was primarily determined by the crack inclination angles. Furthermore, fracture trajectories between adjacent load points were shear cracks, fractures along the axial load line were tensile cracks, and the failure between the end of the fissure and the axial load point was a tensile-shear mixed crack with tensile failure as the dominant mode. DIC displacement vector analysis and SEM results confirmed these failure characteristics. The findings provide a reference for underground support structures' design and safety maintenance.

Characterization of Microstructure and Mechanical Behaviour in Activated Tungsten Inert Gas Welded Dissimilar AA Joint of AA 5083 and AA 6061 Alloys

Characterization of Microstructure and Mechanical Behaviour in Activated Tungsten Inert Gas Welded Dissimilar AA Joint of AA 5083 and AA 6061 Alloys

Computational and experimental investigation of a new non equiatomic FCC single-phase Cr15Cu5Fe20Mn25Ni35 high-entropy alloy

The structural, mechanical, and thermal properties of a new non-equiatomic face-centered cubic (FCC) structured high entropy alloy (HEA) were examined computationally using density functional theory (DFT) calculations and validated experimentally. To identify potential single phase HEA candidates, the composition space of the CrCuFeMnNi alloy system, including 1451 alloys, was investigated using the CALculation of PHAse Diagrams (CALPHAD) method and Thermo-Calc software. The CALPHAD approach successfully predicted an FCC single-phase Cr15Cu5Fe20Mn25Ni35 alloy. Elastic constants and thermal properties of the Cr15Cu5Fe20Mn25Ni35 HEA were determined through DFT calculations using a 100-atom supercell. To validate the DFT calculations, HEA samples were prepared by the arc melting technique, and X-ray diffraction (XRD) analysis confirmed a single-phase FCC structure.The DFT calculated elastic constants values satisfied the Born stability conditions for stability of a cubic crystal structure. Pugh's theory indicated that this alloy exhibits ductility and metallic behavior due to its B/G ratio exceeding 1.75 and positive Cauchy pressure. Additionally, Poisson's ratio exceeded 0.26, further confirming its ductile nature. Experimental tests confirmed these findings by measuring bulk modulus, shear modulus, Young's modulus, and Poisson's ratio. The calculated CV values showed good agreement with experimental data at different temperatures. The linear coefficient of thermal expansion increased rapidly at lower temperatures before becoming linear. Both XRD as well as DFT calculations yielded similar lattice constant results for this HEA. These findings provide insights into various properties of the Cr15Cu5Fe20Mn25Ni35 HEA, including its structural stability, mechanical behavior and thermal characteristics.

Mechanical weakening behavior and energy evolution characteristics of shale with different bedding angles after microwave irradiation

Microwave irradiation, as a novel, clean, and efficient rock-breaking technology, can be employed in shale gas exploitation to address the challenges of low fracture efficiency and environmental pollution. Therefore, it is essential to investigate the physico-mechanical properties of shale under microwave irradiation. Firstly, samples with different bedding angles (0°, 30°, 60°, and 90°) were subjected to microwave irradiation at a power of 1 kW and frequency of 2.45 GHz for durations of 0, 20, 40, 60, and 80 s. Additionally, measurements of mass, P-wave velocity, and porosity were taken before and after microwave irradiation, followed by uniaxial compression testing using acoustic emission (AE). The results demonstrated that with increasing microwave irradiation duration, the P-wave velocity and mass of shale gradually decreased, exhibiting anisotropic behavior for the P-wave velocity. The highest degree of weakening (24.75%) was observed for shale at 0°, while the lowest (7.03%) occurred at 90°. Both uniaxial compressive strength and elastic modulus weakened gradually. Notably, USC displayed more significant weakening at 30° and 60°. The energy evolution pattern revealed increasing dissipated energy and decreasing brittleness index, enhancing anisotropy with duration, particularly at 60°. Moreover, AE captured the transition of failure mode from tensile splitting to tensile-shear failure. The results indicated the significant and anisotropic weakening effect of microwave irradiation on shale. The increase in porosity and permeability also provided preliminary evidence for the enhanced permeability ability of shale, resulting in reduced hydraulic fracturing pressures and decreased environmental pollution. Furthermore, the changes of most parameters revealed threshold effect of microwave irradiation duration, which can be classified as weak or strong depending on whether it occurs before or after 40 s. Therefore, attention should be paid to the threshold conditions of microwave irradiation duration to achieve efficient extraction. This research provided initial theoretical support for microwave-assisted shale gas exploitation.

Characterization of mechanical behavior of different types of masonry with a detailed investigation of full-field strain using digital image correlation

This article presents an experimental study on the mechanical characterization of three different types of masonry: burnt clay bricks, fly ash bricks, and autoclaved aerated concrete (AAC) blocks, with a detailed focus on strain distribution and failure mechanism. The specimens were subjected to direct and diagonal compression loading, and the stress–strain curves and failure modes were studied. Digital image correlation (DIC) was used to obtain full-field strain data, allowing for detailed analysis of failure mechanisms, tracking of crack propagation, and examination of other intricate details. The DIC analysis showed that in burnt clay brick and fly ash brick masonry, failure under compression was initiated by the tensile splitting of the brick, while in AAC block masonry, it was initiated by the tensile splitting of the mortar. Additionally, the study identified that the failure modes under diagonal compression were different for each type of masonry, with bed joint sliding being the dominant failure mode in fly ash brick and AAC block masonry. In contrast, the failure mode in burnt clay brick masonry was due to vertical splitting along the loaded diagonal. In the diagonal compression test, the shear strain along both diagonals was negligible, and principal strain directions were observed to be aligned along the two diagonals.

Mechanical Behavior and Wear Characteristics of a Conform Extruded C18150 (Cu-Cr-Zr Alloy) Rod

The demand level of Cu-Cr base alloys is on the top notch from miniature parts to large parts based on their mechanical, metallurgical, chemical, and electrical properties. Due to these, the processing of Cu-Cr-Zr alloys for the betterment of those properties has been a prospect for researchers. Commonly, Cu-Cr alloys are manufactured through the conventional extrusion process at the industrial level. However, conventional extrusion processes have some limitations, specifically regarding grain size refinement and accompanying strength. To avoid such a problem, the conform extrusion process is inculcated for the Cu and Al alloys extrusion. In the present study, C18150 copper rods were extruded from the feed stock rod of 12.5 mm to 10 and 8 mm in diameter through the conform extrusion process; however, no posttreatment and artificial aging have been made to the extrudates. The extrudates of C18150 rods were tested mechanically and microstructurally. Significant mechanical properties improvement has been observed as the diameter decreased to a certain dimension. Same phenomenon is also observed in the microstructural and hardness case. Wear test results also followed the similarity with that of mechanical properties.

Investigation of mechanical behavior, AE and EMR characteristics of rocks under compression-shear loading via variable-angle shear tests

The surrounding rocks of underground engineering are usually subjected to the coupling of compressive and shear stresses. The mechanical characteristics of underground geomaterials subjected submitted to compression-shear loading have received considerable attention recently. The complex response arises from the microstructure redistribution under high in-situ stress and the resulting fracture behaviors at multiaxial stress states. Understanding the compression-shear behavior and failure mechanism of rocks is of essential importance for mechanical characterization and construction safety in deep underground engineering applications. In this study, variable-angle shear tests are conducted for cubic sandstone samples to investigate damage evolution under compression-shear loading, and the acoustic emission (AE) and electromagnetic radiation (EMR) are simultaneously monitored to record crack development. The mechanical behaviors of rock with AE and EMR responses in variable-angle shear tests with shear angle of 30°, 45° and 60° are analyzed. Then, correlation between AE and EMR is evaluated. Damage evolution of the rock specimen is described based on AE and EMR energy. Fractal dimension and b-value of AE and EMR time series are calculated to further reveal the microscopic crack mechanism of rocks. The results suggest that the continuous decline of fractal dimension and b-value of AE and EMR can act as the precursor of rock failure.