Mechanical Testing System Research Articles

Strength degradation characteristics and damage constitutive model of sandstone under freeze-thaw cycles.

Thorough investigation into the laws governing frozen rock damage in high-altitude and cold regions can offer valuable insights for advancing infrastructure construction, ecological environment protection, and sustainable development on the Qinghai-Xizang Plateau. This study combined with the seasonal variation patterns of frozen rocks in the Qinghai-Xizang Plateau, and processed the rock samples using a freeze-thaw interval of -20 °C~20 °C. Uniaxial compression test was conducted based on the MTS816 rock mechanics testing system. The porosity changes of rock samples with different freeze-thaw cycles were analyzed using the MesoMR12-060H-I nuclear magnetic response analysis system. A rock freeze-thaw load coupled damage constitutive model was derived using the Lemaitre equivalent strain theory. Research has shown that during the freezing process, the pore water inside the rock sample is affected by the phase change of water-ice, resulting in frost heave force, which further promotes the expansion of the pore walls and the initiation of new cracks. When melted, pore water migrates towards newly formed micropores, thereby affecting the changes in the pores of rock samples. The increase in porosity at the micro level weakens the mechanical parameters of rocks at the macro level. The segmented freeze-thaw damage constitutive model based on Lemaitre equivalent strain theory can well fit the experimental results involved in this study, as well as the experimental results obtained by other researchers. The compaction stage can partially reflect the changes in sandstone pore structure under freeze-thaw cycles.

Creep deformation characteristics and control technology in deep mine soft rock roadway

In order to control the strong ageing creep and large deformation of deep soft rock roadway effectively, with the 61–71 track on the uphill of the mining area in Suzhou, Anhui as the research background, the triaxial creep test of mudstone was conducted using the TYJ-1500 M rock mechanics testing system. The creep deformation and failure characteristics of mudstone were analyzed. Additionally, the creep deformation characteristics of deep soft rock roadways were obtained through FLAC3D numerical simulation experiment, and the control techniques for deep soft rock roadway was proposed. The results showed that the axial strain and lateral strain of the specimen were mainly instantaneous strain and creep strain under triaxial stress conditions, and the both confining pressure and the axial pressure have a significant impact on the deformation and creep failure strength of the specimen. Under the condition of high ground stress and complex geological structure, the high stress concentration of roadway roof and floor and two bottom angles is the main cause of creep failure of soft rock roadway, and the large degree of surrounding rock fragmentation and unreasonable support mode reduce the bearing capacity of surrounding rock and aggravate the creep failure of roadway. The 'anchor net cable shotcrete + floor and two corners in floor bolt-grouting + deep and shallow hole grouting + secondary reinforcement support' combined support method was proposed and industrially tested, with average deformation of the roof, floor, and two sidewalls being 111.9 and 62.5 mm, respectively, representing 13.2 and 10.3% of the deformation under the original support scheme.

Effect of Lithiation and Delithiation on the Mechanical Properties of Electrodeposited LiCoO2 Cathode

Mechanical degradation of cathode active material, such as cracks result from volume changes and phase transitions, is one of the main causes of capacity fading in lithium-ion batteries. Understanding the active material’s deformation behavior during cycling and the impact of electrochemical charging on mechanical properties is crucial for understanding the mechanical degradation mechanism and extending battery lifetime.Herein, we investigate the mechanical properties of an electroplated LiCoO2 (LCO) cathode with crystallographic texture as a function of state of charge/discharge. Nanoindentation mapping is used to detect the differences in mechanical behavior between grain boundary and grain interior region. To determine the charged LCO crystals’ mechanical properties and avoid the effects from grain boundaries and air-exposure, in-situ nanoindentation experiments are conducted in a custom mechanical testing system within a scanning electron microscope. Considering the anisotropy of LCO, electron backscatter diffraction analysis is utilized to clarify the crystallographic orientation of the electrodeposited LCO cathode. Our result shows a decreasing tendency in elastic modulus and hardness with state of charge, which can be attributed to the expansion of LCO layered structure. The recovery of mechanical properties after discharge indicates that the changes in measured mechanical properties mainly come from Li deintercalation and intercalation rather than intergranular fracture during cycling. By releasing the relationship between mechanical properties and degree of delithiation, our study provides an insight into modeling studies of electro-chemo-mechanics for electrode materials. Figure 1

AN EXPERIMENTAL RIGHT ATRIUM PLATFORM TO ASSESS RECIRCULATION IN HEMODIALYSIS CATHETERS

Hemodialysis (HD) is a treatment supporting decreased kidney function, via a catheter inserted into the heart’s Right Atrium (RA). Recirculation is a source of inefficiency for treatment, where blood is dialyzed again due to poor catheter design. Lab-testing is still relatively unexplored, hence, a mechanical testing system was designed with the intention of providing a consistent and repeatable environment for testing HD catheters. System geometry was composed using a Computer-Aided Design (CAD) model of a heart, with the RA scaled to appropriate dimensions, and a PolyDiMethylSiloxane (PDMS) model produced through 3D printing and negative wax casting. Pulsatile blood flow was mimicked by peristaltic pumps driving a blood analogue (BA). Recirculation was induced by adding dyed BA to the system via the catheter and measured using a colorimeter. The developed platform was initially evaluated using two catheters, demonstrating the capability to accurately replicate atrial hemodynamic conditions. Two step-tipped catheters, A and B, were tested at 350 ml/min, producing recirculation values of 13.11% and 18.58%, respectively. The results exhibit the ability of the system developed to evaluate HD catheter performance, with the potential to explore a wider range of tip geometries relevant to clinical preference. Furthermore, this advancement towards an anatomically accurate lab-based test system could be paired with computational methods to progress the evaluation of such medical devices and enhance their development.

Strength characteristics of different stress spaces of red sandstone under loading and unloading tests

Red sandstone tests were conducted on the rock mechanics test system to clarify the strength and failure characteristics of red sandstone under triaxial loading and different unloading confining pressure rates. Strength change rules of the red sandstone in various stress spaces were analyzed. Results show that a large initial confining pressure indicates a long yield section and large axial strain. A small unloading confining pressure rate indicates a long yield section and large axial strain at failure under the identical initial confining pressure. The confining pressure reduction increases with the unloading confining pressure rate increasing when the red sandstone fails. The stress path of unloading confining pressure weakens the red sandstone cohesion and strengthens its internal friction angle. The general octahedral shear stress formula for judging whether the red sandstone fails under loading and different unloading rates was acquired on the basis of the octahedral shear stress characteristics of the red sandstone. In addition, a 3D empirical criterion for evaluating the red sandstone strength was constructed through the deviator plane function of Eekelen and the strength envelope curve on the meridian plane. A great initial confining pressure indicates serious internal damage of the red sandstone at failure under the identical unloading rate of confining pressure. A low unloading rate of confining pressure indicates internal serious damage of the red sandstone at failure when the initial confining pressure is the same. The analysis of macroscopic failure characteristics revealed that the stress path significantly influences the failure mechanism of the red sandstone. The results are instructive for determining the stability of underground engineering of the red sandstone.

Investigation of Fiber-Matrix Interface Strength via Single-Fiber Pull-Out Test in 3D-Printed Thermoset Composites: A Simplified Methodology.

The emergence of additive manufacturing technologies for fiber-reinforced thermoset composites has greatly bolstered their utilization, particularly within the aerospace industry. However, the ability to precisely measure the interface strength between the fiber and thermoset matrix in additively manufactured composites has been constrained by the cumbersome nature of single-fiber pull-out experiments and the need for costly instrumentation. This study aims to introduce a novel methodology for conducting single-fiber pull-out tests aimed at quantifying interface shear strength in additively manufactured thermoset composites. Our findings substantiate the viability of this approach, showcasing successful fiber embedding within composite test specimens and precise characterization of fiber pull-out strength using a conventional mechanical testing system. The test outcome revealed an average interfacial strength value of 2.4 MPa between carbon fiber and the thermoset epoxy matrix, aligning with similar studies in the existing literature. The outcome of this study offers an affordable and versatile test methodology to revolutionize composite material fabrication for superior mechanical performance.

A thermal stress loading technique for large‐sized hot dry rock mechanical tests

AbstractTesting of large‐sized specimens is becoming increasingly important in deep underground rock mechanics and engineering. In traditional mechanical loading, stresses on large‐sized specimens are achieved by large host frames and hydraulic pumps, which could lead to great investment. Low‐cost testing machines clearly always have great appeal. In this study, a new approach is proposed using thermal expansion stress to load rock specimens, which may be particularly suitable for tests of deep hot dry rock with high temperatures. This is a different technical route from traditional mechanical loading through hydraulic pressure. For the rock mechanics test system of hot dry rock that already has an investment in heating systems, this technology may reduce the cost of the loading subsystem by fully utilizing the temperature changes. This paper presents the basic principle and a typical design of this technical solution. Preliminary feasibility analysis is then conducted based on numerical simulations. Although some technical details still need to be resolved, the feasibility of this loading approach has been preliminarily confirmed.

The impact of high temperature on mechanical properties and behaviors of sandstone

The impact of high temperature environments on the physical and mechanical properties of rocks is a significant factor to consider. The investigation into the impact of elevated temperatures on the physical and mechanical characteristics of rocks holds great importance in the advancement and exploitation of deep-seated mineral reserves, as well as in ensuring the safety and stability of subterranean engineering projects. This study utilizes the state-of-the-art GCTS Mechanical Loading Test System to conduct uniaxial and triaxial compression tests on sandstone after thermal treatment from 25°C to 650°C. In addition, XRD, SEM and nuclear magnetic resonance experiments were carried out on the sandstone after thermal treatment. The aim of the experiments is to provide a quantitative characterization of mechanical properties and behaviors of the rock samples. The results show that the mass, density, and wave velocity of sandstone decrease with increasing temperature, while volume and porosity increase. The mass, volume, and rate of density change of sandstone exhibit a significant increase when subjected to temperatures above 500°C. The uniaxial compressive strength and elastic modulus exhibit an initial increase followed by a subsequent decrease as the temperature rises, with 300°C serving as the critical turning point. The axial peak strain and Poisson’s ratio increase with increasing temperature. The cohesion decreases with increasing temperature, while the internal friction angle increases. Additionally, it is observed that the rate of change for both properties exhibits an increase beyond the temperature threshold of 400°C.

Effects of length-to-diameter ratio and strain rate on strain energy accumulation and dissipation in sandstone

To investigate the influence of the length-to-diameter (L/D) ratio and strain rate on the evolution of strain energy of sandstone under uniaxial compression, experimental tests were conducted using the RMT-150B rock mechanics test system. Specifically, uniaxial compression experiments (UCE), uniaxial loading-unloading experiment(ULUE) and uniaxial cyclic loading-unloading experiments (UCLUE) were performed. The results show that: 1) Based on an investigation of the Kaiser effect in UCLUE, it is postulated that a small degree of loading-unloading has negligible impact on the storage of strain energy in rock masses. The hypothesis regarding the limited influence of loading-unloading on the elastic strain energy storage of rocks is confirmed through a comparative analysis between the elastic strain energy storage in UCLUE and ULUE. 2) By analyzing the ESED and ISED of sandstone under different L/D ratios and strain rates, it is found that it follows the linear energy storage law. The evolution of elastic strain energy is not affected by strain rate. Therefore, the UCLUE at any strain rate can analyze the elastic strain energy of uniaxial compression experiment with the same size at any strain rate, and provide a new method for strain energy analysis at different length-diameter ratios and strain rates. 3) When the stress of sandstone samples of equal size is equal, the smaller the strain rate, the longer the loading experiment of sandstone, the more time the friction development and interconnection of cracks in sandstone are, and the more dissipated strain energy and input strain energy are generated. 4) Smaller L/D ratios are associated with larger ESED and DSED values in sandstone. As the stress intensifies, the ESED and DSED of certain sandstones with larger L/D ratios experience a sharp increase when approaching the failure stress. Under equal stress levels, it is possible for sandstones with larger L/D ratios to exhibit higher ESED and DSED values compared to those with smaller L/D ratios.

Study on the Effect of Cyclic Loading on the Geomechanics of Sandstone Reservoirs in Gas Storage

In the implementation process of carbon capture and storage (CCS), the geomechanical problems arising from the cyclic injection of carbon dioxide into the formation cannot be ignored. To clarify the influence of cyclic loading on the geomechanics properties of reservoir rocks, cyclic loading tests were carried out on rocks in sandstone reservoirs with the RTR‐2000 Rock Mechanics Test System, and the evolution of compressive strength, elastic modulus, and Poisson’s ratio parameters was analyzed, which revealed the law of the geomechanical deterioration and damage evolution of sandstone reservoirs under cyclic loading. The results show that under the same cyclic load, when the number of cycles is increased to a certain degree, the influence on the peak strength is small. As the number of cycles increases, the modulus of elasticity of rock appears to be increasing and then decreasing, whereas a rapid increase in Poisson’s ratio and a slow increase in Poisson’s ratio occur with the increase in the number of cycles. Under the same number of cycles, the peak strength of the core gradually decreased with the increase of the maximum cyclic stress. When the cyclic load was smaller than the yield stress of the core, the effect of cyclic loading on the strength of the core was small, and when the cyclic load was larger than the yield stress, the effect of cyclic loading on the strength increased significantly. With the increase of cyclic load, the modulus of elasticity showed a tendency to increase and then decrease, and Poisson’s ratio had a tendency of decreasing and the overall degree of change was small.

Novel contactless torque sensor based on optical coherence

This work proposes a novel contactless sensor to measure the micro torque of a rotating shaft based on the optical coherence displacement measurement (OCDM) principle. The experimental system features a simple mechanical testing system to measure the torque, a calibration device to establish the measurement baseline, and a polyetheretherketone (PEEK) shaft to improve the theoretical resolution of the system up to 0.003 Nm. The torque measurement results indicate that this sensor achieved a maximum nonlinearity error of 0.0484 %, maximum repeatability error of 0.2771 %, and maximum hysteresis error of 0.2252 %. This high accuracy of our system stems from the use of high-precision optical principles and the novel physical mapping of the torque (i.e., processing scales on the shaft surface to represent the twist angle by designing a laser engraving system) capable of resisting the negative effects of radial vibrations. Additionally, our torque measurement sensor possesses broader applicability by effectively resisting the impacts of temperature variations and electromagnetic interference. These attributes make it excel other torque sensors presented in the literature in recent years.

Energy Evolution Law of Sandstone Material during Post-Peak Cyclic Loading and Unloading under Hydraulic Coupling

The sustainability of rock engineering is an emerging trend in future development, as society increasingly recognizes the importance of environmental conservation and responsible resource utilization. In this context, the field of rock engineering is undergoing a paradigm shift toward more sustainable practices. A significant aspect of this shift is the investigation of energy evolution laws specific to rocks, which assumes paramount importance in ensuring the sustainable utilization of damaged rock roadways. To investigate the impact of confining pressure and pore pressure on the energy evolution characteristics of rock beyond the peak, post-peak cyclic loading and unloading tests were conducted on sandstone specimens under hydraulic coupling conditions using the MTS815 rock mechanical test system. The study encompassed three sets of confining pressures, namely, 10 MPa, 20 MPa, and 30 MPa. Different levels of pore pressure were applied within each confining pressure group. For the 10 MPa confining pressure, the pore pressure values were set at 2 MPa, 4 MPa, 6 MPa, and 8 MPa. Similarly, for the 20 MPa and 30 MPa confining pressures, the corresponding pore pressure values were 2 MPa, 6 MPa, 10 MPa, 14 MPa, 18 MPa, and 22 MPa. The experimental findings indicate that as the confining pressure increases, both the maximum and residual elastic energy densities of the rock gradually increase. The rise in confining pressure impedes the release of elastic energy. Moreover, with increasing confining pressure, the rate of increase in the maximum dissipated energy density diminishes, highlighting the inhibitory effect of confining pressure on energy dissipation and release within the rock. Pore pressure, on the other hand, disrupts the load-bearing structure of the rock and reduces its energy storage capacity. Under a constant confining pressure, for a fixed number of cycles (axial strain), the total input energy density, elastic energy density, and dissipation energy density exhibit a negative correlation with pore pressure. With an increase in the number of cycles (axial strain), the proportion of elastic energy initially rises but subsequently declines, while the proportion of dissipated energy follows the opposite trend. Furthermore, as the confining pressure increases, the peak proportion of elastic energy also tends to increase. This indicates that higher confining pressures promote energy accumulation after rock failure, enhancing the rock’s ability to store elastic energy.

Full-field contact dynamic mechanical properties of tread rubber material under rolling and slippery conditions based on digital image correlation

The dynamic mechanical properties of rolling tire on special road surface were closely related to the vehicle’s handling stability, driving safety and braking effectiveness. The tire tread rubber material was the only contact part of the vehicle with the road surface, so the strain distribution characteristics of tread rubber material within the contact patch of rolling tire on thin water film pavement played a crucial role in the mechanical characteristics of vehicle. In this paper, a non-contact tire tread rubber rolling mechanical test system was developed. The improved digital image correlation (DIC) method was used to obtain the full-field strain distribution of tread rubber blocks. The effects of load and velocity on the strain rate of the marked points, the full-field strain distribution in the region of interest and rolling resistance were investigated under thin water film pavement. The experimental results were compared with dry condition to analyze the effect of water film on the rolling dynamic characteristics. The results showed that the strain rate increased first and then fluctuated under the action of thin water film. With the increase of speed and load, the full-field strain distribution of tread rubber contact patch was gradually occupied by low strain zone. The change rate of rolling resistance firstly increased and then decreased with the increase of rotational speed.

Superior Capsular Reconstruction Combined With Lower Trapezius Tendon Transfer Improves the Biomechanics in Posterosuperior Massive Rotator Cuff Tears

Background: Surgical treatments for chronic posterosuperior massive rotator cuff tear (MRCT) are still controversial. Superior capsular reconstruction (SCR), which provides a static stabilizer to decrease superior humeral head translation, and lower trapezius tendon transfer (LTTT) with centralization of the humeral head, which prevents superior humeral head migration, are potential surgical options. To date, SCR combined with LTTT has not been fully investigated. Hypothesis: Restoration of static stabilizer and dynamic stabilizer together would effectively improve shoulder kinematics in posterosuperior MRCT. Study Design: Controlled laboratory study. Methods: A custom-made shoulder mechanics testing system was used to test 8 fresh-frozen cadaveric shoulders. The testing conditions were as follows: (1) intact; (2) posterosuperior MRCT (supraspinatus and infraspinatus removed); (3) SCR using the fascia lata; (4) LTTT; and (5) SCR combined with LTTT. The total rotational range of motion (ROM), superior translation, anteroposterior translation, and peak subacromial contact pressure were evaluated at 0°, 30°, and 60° of shoulder abduction. Repeated-measures analysis of variance and Tukey post hoc tests were performed. Results: The total rotational ROM, superior translation, anteroposterior translation, and peak subacromial contact pressure increased in posterosuperior MRCTs (all, P < .05). The rotational ROM, superior translation, anteroposterior translation, and peak subacromial contact pressure at 0° and 30° of shoulder abduction decreased in SCR (all, P < .05). However, there was no significant improvement in rotational ROM, superior translation, and peak subacromial contact pressure at 60° of shoulder abduction (P > .05). LTTT resulted in a significant decrease in the superior translation, anteroposterior translation, and peak subacromial contact pressure at 0°, 30°, and 60° of shoulder abduction (P < .05). SCR combined with LTTT restored the total rotational ROM, superior translation, anteroposterior translation, and peak subacromial contact pressure at 0°, 30°, and 60° of shoulder abduction (all, P < .05). Conclusion: In the cadaveric model, SCR combined with LTTT showed improved shoulder kinematics and contact pressures in the posterosuperior MRCT model compared with SCR or LTTT alone. Clinical Relevance: SCR combined with LTTT may be regarded as an alternative surgical procedure for posterosuperior MRCTs.

Deformation Characteristics and Permeability Properties of Cap Rocks in Gas Storage of Depleted Reservoirs under Alternating Load

Gas reservoirs have significant engineering characteristics of injection and extraction. The reservoir cap rock is subjected to cyclic alternating loading and has the potential risk of seal failure. Therefore, it is necessary to study the stress−percolation−damage mechanism of the reservoir cap rock in depleted gas reservoirs. The rock Mechanics Test System (MTS) was used to study the permeability characteristics of a typical mud shale cap layer under different loading and unloading rates, analyze the deformation characteristics and permeability performance evolution law of the rock under the confining pressure alternation, and study the effects of loading and unloading rate, confining pressure and number of cycles on the permeability of the cap rock. The test results show that with the increase in the number of cycles, the hysteresis loop moves in the direction of axial strain increase offset. The overall morphology is presented as an elongated type, and the damage of the specimen is small in the cyclic confining pressure; At the beginning of the cycling period, the permeability decreases with the increase in the confining pressure in the form of a negative exponential. At the later stage of the cycling period, the permeability basically stays unchanged, and is maintained at a low level; At low confining pressure, permeability also decreases in a negative exponential form with the increase in the number of confining pressure cycles; The greater the loading and unloading rate at the beginning of the cycle, the more the permeability decreases; There is a tendency of sealing improvement under cyclic loading in the gas storage of depleted reservoirs with mud shale as the cap layer. The results of the study can provide technical parameters for the evaluation of the cap sealing of gas storage of depleted reservoirs.

Bond Wire Fatigue of Au, Cu, and PCC in Power LED Packages.

Bond wire failure, primarily wire neck breakage, in power LED devices due to thermomechanical fatigue is one of the main reliability issues in power LED devices. Currently, the standard testing methods to evaluate the device's lifetime involve time-consuming thermal cycling or thermal shock tests. While numerical or simulation methods are used as convenient and quick alternatives, obtaining data from material lifetime models with accurate reliability and without experimental fatigue has proven challenging. To address this issue, a mechanical fatigue testing system was developed with the purpose of inducing mechanical stresses in the critical region of the bond wire connection above the ball bond. The aim was to accelerate fatigue cracks at this bottleneck, inducing a similar failure mode as observed during thermal tests. Experimental investigations were conducted on Au, Cu, and Pd-coated Cu bonding wires, each with a diameter of 25 µm, using both low- and high-frequency excitation. The lifetime of the wire bond obtained from these tests ranged from 100 to 1,000,000 cycles. This proposed testing method offers material lifetime data in a significantly shorter timeframe and requires minimal sample preparation. Additionally, finite element simulations were performed to quantify the stresses at the wire neck, facilitating comparisons to conventional testing methods, fatigue test results under various operating conditions, material models, and design evaluations of the fine wire bond reliability in LED and microelectronic packages.

Investigation of crack recognition and spatio-temporal evolution pattern in coal samples damage

Understanding the evolution mechanism of cracks helps to evaluate the behavior and performance of rock masses and provides a theoretical basis for the mechanism of crack propagation and instability. For this purpose, a rock mechanics testing system and an acoustic emission monitoring system were used to conduct acoustic emission positioning experiments on coal samples under uniaxial compression. According to clustering theory, the distribution pattern of microcracks and the dynamic evolution process of multiple cracks were studied. Subsequently, the reasons for the change in the spatio-temporal entropy (H) and fractal dimension (D) of a single crack were revealed. The research results show that microcracks present a statistical equilibrium distribution, the Gaussian distribution model is applicable to cluster crack distribution patterns, and a machine learning method can effectively identify cracks. The fractal dimension reflects the spatial characteristics of three-dimensional elliptical cracks, and low-dimensional cluster cracks are more likely to develop into macroscopic cracks. The change of H is related to the formation process of cracks, and an abnormal H (sudden increase and sudden decrease) could provide precursor information for the instability of coal samples. This research provides a new method to study crack distributions and formations and shows the competitiveness of the method in evaluating the damage state of coal.

Effect of Water Content on the Impact Propensity of White Sandstone

Impact ground pressure is one of the most common dynamic disasters induced by mining activities, and water content is an important factor affecting such dynamic disasters. In this paper, uniaxial compression test, cyclic loading and unloading test, and acoustic emission test were conducted on white sandstone using RMT-150B rock mechanics test system and DS5 acoustic emission test system. The influence law of water content was analyzed on the strength characteristics, energy change characteristics, and impact propensity of white sandstone. The results showed that (1) the internal structure of the sandstone gets softened with the increase of the water content. The cohesive effect within the rock also begins to weaken, which in turn reduces the stiffness of the material and enhances its plasticity. The ability of the rock to resist elastic deformation becomes weaker, resulting in lower compressive strength and elastic modulus when the rock is subjected to external forces, making it more prone to deform and fail. The decrease in compressive strength of the water-saturated rock is 33.3%, and the decrease in its elastic modulus is 28.1% compared to the dry rock. (2) As the water content increases, the cohesion of the rock decreases and the internal structure of the rock fails more easily, which ultimately makes the energy needed for rock destruction lower. As a result, the total energy, elastic energy, and dissipative energy of the rock are reduced. The accumulated AE energy also decreases with the increase of the water content, indicating that rocks with higher water content gather less elastic energy before damage and accumulate less energy when deformation damage occurs. (3) The impact energy index and elastic energy index are negatively correlated with the water content. The impact energy index is reduced by 28.6%, and the elastic energy index is reduced by 20.9% for the saturated rock compared to the dry rock. The elastic energy index and impact energy index both decrease with the increase of rock water content, indicating that the less elastic energy is stored before the destruction of the rock and no excess energy is transformed into energy in rock crushing when the rock breaks, and therefore, the impact propensity of the rock is smaller. The results of the study can provide a theoretical basis for underground construction as well as rock fracture destabilization.

Mechanical damage characteristics and acoustic emission characteristics of a bolt-slurry interface under cyclic pull-out loading

To consider the effects of various mining stresses in an actual project, a comprehensive laboratory pull-out study of the bolting system under different cyclic loads was carried out, a high stiffness MTS815.04 rock mechanics test system and an independently designed indirect pullout test device and an acoustic emission system was used for synchronous monitoring. Damage failure mechanism of bolt-slurry interface under cyclic loading revealed from macroscopic strength and deformation characteristics and microscopic damage in depth. The results are as follows.: (1) Compared with static pull-out loading, the bolting system under cyclic loading will enter the damage failure state earlier. (2) The greater the cyclic loading and unloading rate are, the greater the impact on the bolt-slurry interface, and the easier it is for sudden macroscopic damage to occur. (3) The greater the cyclic load stress amplitude is, the stronger the acoustic emission activity of the bolt-slurry interface, the greater the damage to the bolt-slurry interface, and the easier it is to fail and de-bond. (4) Finally, the acoustic emission energy, energy rate and count can be used to evaluate the damage characteristics of the anchor interface during cyclic drawing, and the analysis results are in good agreement with the macroscopic damage results. The research results can provide a reference for the support design and performance monitoring of full-length anchor bolts under different cyclic loads.

Tensile strength degradations of mineral grain interfaces (MGIs) of granite after thermo-hydro-mechanical (THM) treatment

Granite for hosting the deep geological repository (DGR) is subjected to thermo-hydro-mechanical (THM) treatment for decades of years, while the variations in the tensile strengths of mineral grain interfaces (MGIs) with THM treatment are still unknown. Served as an important parameter in determining the macro mechanical properties of granite, quantifying the tensile strength degradation of MGI with THM treatment is crucial for ensuring the long-term safety of DGR. In this study, the varied tensile strengths of MGIs in the granite after different THM treatments were first directly measured based on a self-developed single-MGI mechanical test system. Three-bending tests were conducted on six-hundred MGIs, which were submitted to various THM treatments with a temperature of 25–175 °C and a pore pressure of 0–15 MPa. The tensile strengths of the interfaces of quartz, feldspar and the interfaces between quartz and feldspar were derived based on the Dugdale–Barenblatt (D–B) model. Results show that the average tensile strength of the interfaces of quartz is 1.06 times larger than that of interfaces between quartz and feldspar, and 1.13 times larger than that of the interfaces of feldspar. Besides, the tensile strength of MGIs seems more susceptible to the pore pressure than to the temperature, and the degradation of tensile strength is the most obvious in the interfaces between quartz and feldspar, followed by the interfaces of feldspar and finally the interfaces of quartz after THM treatments. Based on the characteristics of the tensile strength distributions of different MGIs after THM treatments, the tensile strength degradation models of MGIs related to THM treatments were proposed in meso scale.