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To ensure that the discrete element model of the coal wall accurately reflects the actual cutting process of coal and rock during virtual prototype simulation of mining equipment, this study aims to expedite the development of intelligent mining machinery. Using coal samples from the 4602 working face of Yangcun Coal Mine, operated by Yanzhou Coal Mining Group, we conducted coal rock packing experiments and uniaxial compression tests to obtain the packing angle and compressive strength of the coal samples. Based on the experimental results, we designed Plackett–Burman experiments (PB experiments), steepest ascent experiments, and Box-Behnken experiments to study the influence of particle contact mechanics parameters and bonding mechanics parameters on the packing angle and compressive strength, using the packing angle and compressive strength as response variables. Our objective is to minimize the relative error between the simulated packing angle and the measured packing angle. We solved and optimized the parameter calibration model and conducted simulation calibration experiments based on the optimization results. A comparative analysis with the actual test results revealed that the maximum relative errors between the simulated and measured values for the packing angle and compressive strength were only 2.9% and 5.0%, respectively. Additionally, a discrete element model of a typical working face coal wall was established based on the parameters obtained from this calibration method. A bidirectional coupling model of the cutting process between the coal and rock was created using EDEM-RecurDyn to simulate the rigid-flexible coupling of the coal cutter. An experimental coal wall model was constructed based on similarity theory, and both simulation and physical experiments were conducted. The evaluation metrics for comparison were the time-domain and frequency-domain characteristics of the drum's vibration signals. The maximum relative error for the time-domain signal characteristics between the two experimental setups was only 4.19%, while the maximum relative error for the frequency-domain signal characteristics was 3.75%. This validates the feasibility of the proposed calibration method for the discrete element coal wall model and the accuracy of the calibration results. Furthermore, it demonstrates that the constructed discrete element coal wall accurately represents the actual coal and rock properties. The virtual simulation based on this model effectively replicates the interaction process between mining machinery and coal, providing a safe, efficient, and low-cost technological approach for performance analysis of mining equipment and intelligent control of supporting devices. [ABSTRACT FROM AUTHOR]

To explore the mechanical properties and fracture modes of basalt fiber-reinforced concrete, single-doped and hybrid-doped basalt fiber-reinforced concrete was prepared, and uniaxial failure tests under different basalt fiber-reinforced concrete contents were carried out. At the same time, the smooth kernel function in the traditional SPH method was improved, and the basalt fiber random generation algorithm was embedded in the SPH program to realize the simulation of the progressive failure of basalt fiber-reinforced concrete. The results show that under the circumstance with no basalt fiber, the specimen final failure mode is damage on the upper and lower surface, as well as the side edge, while the interior of the specimen center is basically intact, indicating that there is an obvious stress concentration phenomenon on the upper and lower surface when the specimen is compressed. Under the circumstance with basalt fiber, longitudinal cracks begin to appear inside the specimen. With the increase in the content, the crack location gradually develops from the edge to the middle, and the crack number gradually increases. This indicates that appropriately increasing the fiber content in concrete may improve the stress state of concrete, change the eccentric compression to axial compression, and indirectly increase the compressive strength of concrete. The numerical simulation results are consistent with the test results, verifying the rationality of the numerical simulation algorithm. For the concrete model without the basalt fiber, shear cracks are generated around the model. For the concrete model with basalt fiber, in addition to shear cracks, the tensile cracks generated at the basalt fiber inside the model eventually lead to the splitting failure of the model. The strength of concrete samples with basalt content of 0.1%, 0.2%, and 0.3% is increased by 1.69%, 5.10%, and 4.31%, respectively, compared to the concrete sample without basalt fiber. It can be seen that with the increase in the content of single-doped basalt fiber, the concrete strength is improved to a certain extent, but the improvement degree is not high; For hybrid-doped basalt fiber-reinforced concrete, the strength of concrete samples with basalt content of 0.1%, 0.2%, and 0.3% is increased by 14.51%, 15.02%, and 30.31%, respectively, compared to the concrete sample without basalt fiber. Therefore, compared with the single-doped basalt fiber process, hybrid doping is easier to improve the strength of concrete. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of crack propagation and failure behavior in rocks is fundamental for geotechnical engineering and mining applications. This study employs a coupled damage model based on the Smoothed Particle Hydrodynamics (SPH) method that integrates the Drucker–Prager and Grady–Kipp models. This mixed failure model is then implemented to simulate the crack propagation morphology and failure modes in uniaxial compression tests of flawed rock samples, and validated against multiple experimental observations. The numerical results exhibit good agreement with experimental observations from the literature in terms of the initiation and propagation of tensile and shear fractures, as well as the final failure morphology. Additionally, this work incorporates contact algorithms to simulate the loading plates, thereby better representing the actual experimental conditions encountered in uniaxial compression tests. Furthermore, a comprehensive parametric study is conducted to investigate the influence of key factors, such as pre-flaw geometry, cohesion, friction at the loading plate interface, and discretization parameters, on the simulated fracture processes and mechanical response. The outcomes indicate the proposed coupled damage model within the SPH framework can accurately capture complex fracture patterns and failure mechanisms in uniaxial compression of flawed rocks. This work demonstrates the capability of the SPH-based mixed-mode failure model to provide insights into rock fracture and failure mechanisms. Highlights: A coupled damage model integrating the Drucker–Prager and Grady–Kipp criteria within a smoothed particle hydrodynamics (SPH) framework is applied to simulate both shear and tensile failure modes in rocks firstly. The model is validated against more experimental observations, demonstrating the model's ability to reproduce the crack propagation and characteristic stress–strain behavior. This work presents a comprehensive parametric study investigating the influence of key factors, such as pre-flaw geometry, cohesion, friction at the loading plate interface, and discretization parameters, on the simulated fracture processes and mechanical response. These systematic investigations provide valuable insights into the governing mechanisms and highlight the importance of proper model calibration for accurate predictions. This work incorporates contact algorithms to simulate the loading plates, thereby better representing the actual experimental conditions encountered in uniaxial compression tests. The tensile wing cracks subjected to uniaxial compression, oriented vertically towards the top boundary of the specimen, are successfully captured. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the accuracy of electromagnetic radiation and microseismic signals in determining the anti-scour effect resulting from coal seam water injection. We established a simultaneous acquisition system of electromagnetic and microseismic full waveforms for coal rock damages under load, and an image acquisition system that captured the entire coal damage process was used. Uniaxial compression experiments of coal samples with different moisture contents were conducted, and the influence of water on the physical and mechanical properties of the coal samples and the generation of electromagnetic and microseismic signals were theoretically analyzed. The results showed that water reduced the adhesion and friction coefficient of particles in the coal body, promoted coal and rock fracture development, and weakened the generation of electromagnetic and microseismic signals. A significant positive correlation was found among stress drop, electromagnetic radiation signals, and microseismic signals, and the temporal distribution of the three variables was synchronous. As moisture content increased, the electromagnetic radiation and microseismic signal amplitude of the coal samples decreased, and the average signal of both signals exhibited an exponential downward trend. The relationship between the mean value of the signal and moisture content was obtained. To evaluate the water-injection effect of the coal samples, we also determined the theoretical percentage of the signal amplitude reduction corresponding to the increment in moisture content required by the on-site coal seam water injection and anti-erosion. [ABSTRACT FROM AUTHOR]

This study investigates the influence of expanded perlite (EP) replacement rate and curing methods on the compressive strength of concrete at different ages through the uniaxial compression test. The stress–strain full curve model of concrete considering EP replacement rate is established, and a damage evolution model considering curing conditions, EP replacement rate and load effects is developed based on the damage theory. The results show that: (1) The lack of water in concrete curing will have a huge negative impact on its mechanical properties, and the internal curing effect of pre‐wet EP can effectively alleviate the phenomenon of incomplete hydration. (2) Under dry curing, the addition of EP will reduce the early compressive strength of concrete, while its internal curing effect can improve the compressive strength of concrete in the later stages. (3) The C & C model and the Guozhenhai model are used to construct the segmented model in the rising and falling sections, and the model parameter formula is deduced by the replacement rate. The model can fully describe the stress–strain relationship of expanded perlite concrete (EPC). (4) The damage evolution model of EPC shows an "S" shape growth curve. Dry curing and EP replacement can both reduce the development rate of damage, while the former has a more significant impact. [ABSTRACT FROM AUTHOR]

This study examines the failure process of coal under uniaxial compression using in-situ CT scanning with X-ray computed tomography. By integrating digital core technology and digital volume correlation (DVC), the research analyzes the development and evolution of fractures and calculates displacement and strain fields, offering reliable data for understanding failure mechanisms. Additionally, the study simulates fluid seepage within coal under varying loads, revealing the relationship between structural changes and permeability. The findings show that coal under uniaxial loading experiences both fracture development and compression, influenced by axial forces and the development of adjacent fractures. Minerals within coal play a guiding role in fracture development, shaped by their form and distribution. DVC results demonstrate that coal destruction is a dynamic, evolving process driven by deformation differences across regions and directions. Displacement vectors show coal matrix migration in multiple directions, while strain fields reveal lateral fracture expansion under axial compression. As loading progresses, fracture tortuosity decreases, and throat numbers rise to 6353, leading to increased permeability, notably a 149.35 μm2 increase at the 1.1kN stage. This study deepens the understanding of coal's destructive characteristics and contributes to mining disaster prevention and control, with significant implications for coal engineering and resource development. [ABSTRACT FROM AUTHOR]

In this work, the plastic deformation of micro/nanoscale AlON ceramic pillars with different crystallographic orientations was investigated by in situ compression on scanning electron microscopy (SEM) system. The experimental results demonstrated a "smaller is stronger" size dependence of the yield strength of <100>-, <110>- and <111>-oriented AlON micro/nanopillars with scaling exponents of −0.19, −0.24 and −0.33, respectively. Transmission electron microscopy (TEM) illustrated that the Lomer-Cottrell dislocation reaction dominated the plastic deformation of <111>-oriented pillars. The plastic deformation of <110>-oriented AlON pillars was driven by rotation of the slip region, whereas the stress of <001>-oriented pillars were released through microcracks and plastic deformation. • In situ compression of micro/nanopillars. • Nanomechanical of AlON transparent ceramic. • The size dependent property of different crystallographic orientations AlON pillars. • The plastic deformation phenomenon of AlON micro/nanopillars at room temperature. • The variation of AlON plastic deformation mechanisms with different crystallographic orientations. [ABSTRACT FROM AUTHOR]

Complex underground conditions make it challenging to conduct extensive coring, and it is difficult for laboratories to carry out a large number of rock mechanics experiments due to the limited number of cores. Rock-like specimens are commonly used in the laboratory to replace coal-rock specimens. In this paper, rock-like specimens with different proportions are produced to study the mechanical properties, failure characteristics, and acoustic emission laws of rock-like specimens under uniaxial compression. The results show that when the rock-like specimen does not contain gypsum, the stress of the specimen decreases rapidly after reaching the peak stress, which is similar to the mechanical properties of hard brittle rock. When the rock-like specimen contains gypsum, the stress of the specimen decreases slowly after reaching the compressive limit, and the failure of the specimen is gentle, which is similar to the mechanical properties of soft rock. When the specimen lacks gypsum, the strength of the rock-like specimen is larger, and the strength of the specimen is positively correlated with the proportion of cement. When the specimen contains gypsum, the strength of the rock-like specimen decreases sharply, and the strength of the rock-like specimen is negatively correlated with the proportion of gypsum. The maximum acoustic emission ringing count increases with higher cement content but decreases with increased gypsum content. The cumulative count change of acoustic emissions approximately underwent four stages, aligning well with the four stages of uniaxial compression failure observed in typical rock. The research results have important reference value for the selection of rock-like materials to replace the original rock materials for laboratory research. [ABSTRACT FROM AUTHOR]

AbstractThe mechanical properties and failure characteristics of soil–rock mixtures (SRMs) directly affect the stability of tunnels constructed in SRMs. A new SRM modelling method based on the combined finite–discrete element method (FDEM) was proposed. Using this new SRM modelling method based on the FDEM, the mechanical characteristics and failure behaviour of SRM samples under uniaxial compression, as well as the failure mechanism of SRMs around a tunnel, were further investigated. The study results support the following findings: (1) The modelling of SRM samples can be achieved using a heterogeneous rock modelling method based on the Weibull distribution. By adjusting the relevant parameters, such as the soil–rock boundaries, element sizes and modelling control points, SRM models with different rock contents and morphologies can be obtained. (2) The simulation results of uniaxial compression tests of SRM samples with different element sizes and morphologies validate the reliability and robustness of the new modelling method. In addition, with increasing rock content, VBP (volumetric block proportion), the uniaxial compressive strength and Young’s modulus increase exponentially, but the samples all undergo single shear failure within the soil or along the soil–rock interfaces, and the shear failure angles are all close to the theoretical values. (3) Tunnels in SRMs with different rock contents all exhibit X-shaped conjugate shear failure, but the fracture network propagation depth, the maximum displacement around the tunnel, and the failure degree of the tunnel in the SRM roughly decreases via a power function as the rock content increases. In addition, as the rock content increases, such as when VBP = 40%, large rocks have a significant blocking effect on fracture propagation, resulting in an asymmetric fracture network around the tunnel. (4) The comparisons of uniaxial compression and tunnel excavation simulation results with previous theoretical results, laboratory test results, and numerical simulation results verify the correctness of the new modelling method proposed in this paper. [ABSTRACT FROM AUTHOR]

The energy dissipation and stress-strain characteristics, and characteristic stresses, namely the crack initiation σci , dilatancy σcd , and peak σf stresses, of polypropylene fiber-reinforced recycled concrete under uniaxial compression were studied. According to the research results, the crack initiation and peak stresses of the specimen with single-blend polypropylene coarse fiber (No. 3) and the specimens with mixed-blend coarse and fine polypropylene fibers (No. 4 and No. 5) are higher than those of the specimen with single-blend fine fiber and plain concrete. The analysis of the energy characteristics and failure mechanism of polypropylene fiber-reinforced recycled concrete during loading based on the principle of energy conservation showed that the total strain energy, elastic strain energy, and dissipation energy absorbed per unit volume increase with the blending of polypropylene fiber. The strain energy and elastic strain energy of coarse aggregates with a 5-10 to 10-20 mm coarse aggregate size ratios of 5:5 are higher than those of 4:6 and 6:4. It was found that the continuous blending of polypropylene fiber increases the elastic strain energy, causing the point at which the dissipation energy exceeds the elastic strain energy move further and further back. The position where the dissipation energy exceeds the elastic strain energy can be used to evaluate the blending effect of polypropylene fiber. The further back the position, the better the blending effect. [ABSTRACT FROM AUTHOR]

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Grey cast iron releases energy in the form of stress waves when damaged. To analyse the evolution of the physical and mechanical properties and acoustic emission characteristics of grey cast iron under uniaxial compression, acoustic emission signals were collected at different rates (0.5, 1, and 2 mm/s). Combined with load-time curves, damage modes were identified and classified using the parametric RA-AF correlation analysis method. The results indicate the loading rate effects on the strength, deformation, acoustic emission (AE), and energy evolution of grey cast iron specimens. The acoustic emission counts align with the engineering stress–strain response. To better illustrate the entire failure process of grey cast iron, from its internal microstructure to its macroscopic appearance, X-ray diffraction (XRD) and optical microscopy (OM) were employed for qualitative and quantitative analyses of the material's internal microstructural characteristics. The equivalent crystal model of grey cast iron was constructed using a Particle Flow Software PFC2D 6.00.30 grain-based model (GBM) to simulate uniaxial compression acoustic emission tests. The calibration of fine parameters with indoor test results ensured good agreement with numerical simulation results. Acoustic emission dynamically monitors the compression process, while discrete element particle flow software further analyses the entire damage process from the inside to the outside. It provides a new research method and idea for the study of crack extension in some metal materials such as grey cast iron. [ABSTRACT FROM AUTHOR]

Layered rocks are widely distributed in mining and underground engineering. The evolution processes, such as crack initiation, development and penetration, inevitably occur due to stress changes. This study carried out an experiment and numerical simulation to explore the correspondence between crack distribution and bedding dip, and to reveal the mechanical mechanism of layered rock fracturing. The results show that the layered rock specimens with different bedding dips obtained different stress combinations under the same uniaxial compression conditions. There are a total of five types of stress combinations, including pure compression type, compression shear type, pure shear type, tension shear type, and pure tension type. The Mohr circle is effective in characterizing the relationship between the stress combinations and failure modes. The failure mode of layered rocks in the range of 0° to 150° is presented the variation features of "tensile failure → compression-shear failure → shear failure → tensile shear failure → tensile failure". Furthermore, the combined distributions of dominant and secondary cracks are summarized into the penetrating mode, the exfoliation mode, the feather crack mode, and the associated mode in high-dip of layered marbles. This paper provides research ideas for stability monitoring and crack tracking of layered rock mass engineering. [ABSTRACT FROM AUTHOR]

In order to cope with climate change and achieve the goal of carbon neutrality, the use of carbonization technology to enhance the performance of cement-based materials and achieve the purpose of carbon sequestration has become a very promising research direction. This paper considers the use of CO2NBW as mixing water for cement-based materials, aiming to improve the carbonization efficiency of materials to achieve the goal of carbon neutrality. This time, the effect of CO2NBW on cementitious filling materials under different aggregate fractal dimensions was studied through uniaxial compression tests and acoustic emission technology. The effect of CO2NBW on the mechanical properties and crack evolution of the material was discussed. The results showed that CO2 nanobubbles significantly improved the strength of cemented filling materials under different fractal dimensions, and the uniaxial compressive strength was most significantly improved by 23.04% when the fractal dimension was 2.7824. In addition, the characteristics of acoustic emission ring counts and energy parameters indicate that CO2 nanobubbles help improve the overall pore structure of the sample, affecting the macroscopic strength. However, the addition of CO2 nanobubbles reduces the limit energy storage ratio of elastic strain energy, which indicates that excessive CO2 concentration may affect the hydration reaction of the cementing material. [ABSTRACT FROM AUTHOR]

Layered composite rocks (abbreviated as LCRs) are frequently encountered in rock engineering, and it is difficult to predict whether the stress-induced crack propagates through the layers or is contained within a layer when subjected to external loads. There was limited advanced knowledge of the crack propagation mechanism of flawed LCRs because the previous research mainly focused on the single lithologic layer. This study conducts uniaxial compression tests on weaker and stronger interbedded sandstone with pre-existing flaws. The crack propagation process of two-layer weaker and stronger interbedded sandstone specimens is studied using acoustic emission (abbreviated as AE) and digital image correlation (abbreviated as DIC) techniques, with the focus being on the influences of the flaw position. The results indicate that the crack initiation mode and final failure mode of weaker and stronger interbedded sandstone are dominated by the tensile mechanism. Three crack initiation modes are identified, which are closely related to the flaw position. When the flaw exists inside the weaker layer or the flaw is far away from the interface, the crack initiation mode is the tensile anti-wing crack initiation from the flaw tip. Whatever the flaw positions, the upward-propagating cracks arrest within the stronger layer, but the downward-propagating cracks eventually cross the weaker layer, which is the main mechanism causing failure. This study sheds light on the failure mechanism of LCRs considering the flaw position under uniaxial compression. [ABSTRACT FROM AUTHOR]

To study the damage and acoustic emission (AE) energy evolution of basalt under high temperature, a series of tests under uniaxial stress are carried out on basalt heated at 25 °C, 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. Through the comprehensive analysis of AE parameters such as absolute energy and amplitude, the AE characteristics and damage evolution laws of basalt were explored. The results show that high temperature has a significant effect on the characteristics of rock stress–strain curve. With the increase of temperature, the compaction stage of the curve becomes longer, the plasticity increases, and the peak strength of basalt decreases. The higher the heat treatment temperature, the faster the strength decreases, and the strength decreases by 63.91% at 1000 °C. The AE localization points converge from the dispersed state to the aggregated state. With the increase of temperature, the period of convergent nucleation of the AE localization sites is advanced, high amplitude AE signals shifted from a concentrated distribution near the peak stress to a discrete distribution throughout the entire process. The heat treatment of the rock has an additive effect on the burstiness. 600–800 °C can be used as the threshold temperature of basalt to transform from brittle failure to plastic failure. The high temperature effect is responsible for the transition of the AE cumulative absolute energy at 400–600 °C. The influence of high temperature on damage evolution is discussed. The initial damage increases exponentially after 800 °C. With the increase of temperature, the evolution rate of damage variable becomes faster and gradually changes from linear to nonlinear. [ABSTRACT FROM AUTHOR]

Abstract To ensure that the discrete element model of the coal wall accurately reflects the actual cutting process of coal and rock during virtual prototype simulation of mining equipment, this study aims to expedite the development of intelligent mining machinery. Using coal samples from the 4602 working face of Yangcun Coal Mine, operated by Yanzhou Coal Mining Group, we conducted coal rock packing experiments and uniaxial compression tests to obtain the packing angle and compressive strength of the coal samples. Based on the experimental results, we designed Plackett–Burman experiments (PB experiments), steepest ascent experiments, and Box-Behnken experiments to study the influence of particle contact mechanics parameters and bonding mechanics parameters on the packing angle and compressive strength, using the packing angle and compressive strength as response variables. Our objective is to minimize the relative error between the simulated packing angle and the measured packing angle. We solved and optimized the parameter calibration model and conducted simulation calibration experiments based on the optimization results. A comparative analysis with the actual test results revealed that the maximum relative errors between the simulated and measured values for the packing angle and compressive strength were only 2.9% and 5.0%, respectively. Additionally, a discrete element model of a typical working face coal wall was established based on the parameters obtained from this calibration method. A bidirectional coupling model of the cutting process between the coal and rock was created using EDEM-RecurDyn to simulate the rigid-flexible coupling of the coal cutter. An experimental coal wall model was constructed based on similarity theory, and both simulation and physical experiments were conducted. The evaluation metrics for comparison were the time-domain and frequency-domain characteristics of the drum’s vibration signals. The maximum relative error for the time-domain signal characteristics between the two experimental setups was only 4.19%, while the maximum relative error for the frequency-domain signal characteristics was 3.75%. This validates the feasibility of the proposed calibration method for the discrete element coal wall model and the accuracy of the calibration results. Furthermore, it demonstrates that the constructed discrete element coal wall accurately represents the actual coal and rock properties. The virtual simulation based on this model effectively replicates the interaction process between mining machinery and coal, providing a safe, efficient, and low-cost technological approach for performance analysis of mining equipment and intelligent control of supporting devices.

Granitic veins (GVs) have a significant influence on the mechanical responses of tunnels excavated in granitic strata. Distinguishing the mechanical properties of host granites (HGs), GVs and vein-granite interfaces (VGIs) is critical. For this, this paper analyzed the mechanical behaviors and rupture processes of typical HG, GV, and VGI samples under uniaxial compression condition. For the rocks studied, although the linear axial stress‒strain relation can be identified and the deformation modulus can be determined, the transverse deformation developed nonlinearly with axial stress. As a result, the instantaneous Poisson's ratio increases continuously and may even exceed 0.5, making it extremely difficult to accurately determine the Poisson's ratio. In addition, the studied GV samples were found to be significantly brittle, indicating that large-scale GVs cannot be ignored when assessing rockburst hazards in granitic strata with brittle GVs. In terms of the rupture process, the HG and GV samples were gradually damaged by the formation of small-scale cracks and then ruptured by large cracks formed from small-scale cracks, whereas the VGI samples ruptured along large cracks with significant energy release. By examining the characteristic stress thresholds of these three granites, it is noted that the crack closure stress σcc exceeds both the crack initiation stress σci and the crack damage stress σcd for the HG and VGI samples. The transverse damage to a tested sample appears to be significantly greater than the axial damage, which is essentially related to the rock grain size and grain size distribution.

An in-depth understanding of the mechanical properties and damage and fracture mechanism of selected rocks in a diversion tunnel plays an important role in promoting the efficient construction and safety of rock blasting excavation in a diversion tunnel. To study the mechanical properties and damage evolution characteristics of selected rocks in diversion tunnels under uniaxial loading, the uniaxial compression and uniaxial splitting tests of granite and tuff were carried out. In terms of mechanical properties, the evolution characteristics of complete stress-strain curves, instantaneous modulus-strain curves, and input energy density-strain curves were analyzed. In the aspect of damage characteristics, the macroscopic and mesoscopic failure modes were analyzed and the damage fracture mechanism was revealed. Compression-shear failure mainly occurred in granite and tuff under uniaxial compression, showing the characteristics of elastic-brittle fracture failure. Both granite and tuff showed a failure mode of coexistence of “compression-shear failure zone at the loading ends” and “tension-shear failure zone in the middle” under uniaxial splitting. The compression-shear fracture of granite was relatively smooth, and the matrix and mineral particles produced fine particles due to friction in the process of shear slip. The compression-shear fracture of tuff was relatively rough and the characteristics of shear slip were not prominent enough. The fracture failure of granite and tuff was mainly caused by the common fracture of rock matrix and mineral particles. Based on the Lemaitre equivalent strain principle, the pre-peak-post-peak two-stage damage constitutive model established by Weibull statistical distribution theory can accurately describe the static stress-strain relationships of granite and tuff under uniaxial compression.

Purposes The internally porous and highly thermally stable glazed hollow beads (GHB) can reduce the high temperature damage and deterioration of concrete to a certain extent, and improve the fire resistance of concrete. In order to further clarify the mechanism of GHB in improving the fire resistance of concrete, starting from the meso-scale concrete, we proposed a modeling method for RATIC meso-scale model that can take into account the initial defects and the replacement rate of recycled coarse aggregate (RCA). Methods The effects of RCA replacement rates (0, 50%, 100%), GHB contents (0, 70%, 100%), and porosity (0, 2%, 4%) on the mechanical properties of RATIC after high temperature were explored by utilizing the plastic damage model commonly used at curent stage. Findings The results show that with the increase of fire temperature, the damage distributions of the RATIC specimens under load exhibit a gradually increasing trend, and the damage distribution of the specimens after 500 ℃ is more serious than that before 400 ℃. The addition of GHB alleviates the damage and deterioration inside the concrete to a certain extent, while the addition of RCA exacerbates this phenomenon. In addition, the strength of RATIC specimens gradually decreases with the increase of porosity.

In order to study the size effect law of carbon fiber reinforced polymer (CFRP) constrained coal cylinders, a numerical model of coal circular confined by carbon fiber reinforced polymer (CFRP) sheet is established by a three-dimensional PFC-FLAC coupling method. The validity of the model was verified with experimental data. On this basis, the study of the size effect of 0, 1, 2 and 3 layers of CFRP sheet on different sizes (50 mm, 100 mm, 150 mm) of coal cylinders were studied; the functional relationship of the evolution law of compressive strength under different layer number (L) is obtained; the functional relationship of elastic modulus evolution under different number of layers is obtained; a modified Richart strength analysis model of coal cylinder confined by CFRP sheet is established. The results show that when the number of CFRP sheets is constant, the compressive strength of coal cylinders is constrained by different sizes of CFRP sheets, and the size effect is obvious; the relative peak strength enhancement ratio of coal cylinder constrained by CFRP sheet increases with the increase of the size. The elastic modulus of a coal cylinder with a diameter of 50 mm increases with the number of CFRP layers. The elastic modulus of a coal cylinder with a diameter of 100 mm and 150 mm increases first and then decreases at 0≤L≤3 layers, showing an obvious layer effect law. The accumulation of cracks increases with the increase of the number of CFRP layers.

Abstract With regard to deep mining in metal mines, an investigation into the failure mode of deep fractured rock masses and their corresponding acoustic emission signal characteristics is conducted via uniaxial compression tests. Subsequently, a fractal damage renormalization group mechanical model is developed to explain the behavior of those fractured rock masses. Employing the bonded block model (BBM) numerical simulation method, fracture process in synthetic rock samples is analyzed, thereby validating the efficacy of the mechanical model. The numerical simulations highlight the critical role of fractures expansion in underlying the deterioration of rock mass strength. As the peak load decreases, the fracture fractal dimension increases, leading to a significant 14.2% reduction in compressive strength accompanied by an approximate 8.7% rise in average fracture fractal dimension. A comparative analysis of tetrahedral and voronoi block synthetic rock samples reveals the tetrahedral block samples exhibit a superior ability to depict the fracture behavior of fractured rock masses. Specifically, they offer a more accurate simulation of acoustic emission characteristics and failure modes. Furthermore, variations in the fracture fractal dimension with respect to the hole defect’s position are observed, with the maximum value occurring along the vertical axis of the hole defect. This observation underscores the potential utility of visually monitoring deep rock fracture dynamics as an effective mean for quantitatively evaluating fracture damage and strength degradation in deep rock formations.

Abstract We carried out uniaxial compression tests on brittle red sandstone with different heights. The test results show that the uniaxial compressive strength of rock sample increases first and then tends to be stable with the increase of the size, which is approximately stable between 75 and 81 MPa. Both elastic energy and dissipated energy increase with the increase of rock sample size. In order to further analyze the mechanism behind these phenomena, we combined advanced numerical simulation and theoretical analysis to explain these phenomena, and systematically analyzed the end face effect as one of the key factors affecting the uniaxial compression characteristics of brittle red sandstone for the first time. Small sized rock samples are very sensitive to end effect. The middle of the large sized rock samples is in a uniform compression state, and the effect of end effect is weakend. When there are rigid pads at both ends of the rock sample, there is an obvious elastic vertebral body during the loading process of the rock sample. The bearing capacity of rock samples with rigid pads is greater than that of rock samples without rigid pads, and the energy released during instantaneous failure of rock samples without rigid pads is greater than that of rock samples with rigid pads. The findings of this paper make a valuable contribution to establishing optimal study sample sizes and advancing the utilization of laboratory test mechanics parameters in engineering applications.

Thermal damage and thermal fracture of rocks are two important indicators in geothermal mining projects. This paper investigates the effects of heating and water-cooling on granite specimens at various temperatures. The laboratory uniaxial compression experiments were also conducted. Then, a coupled thermo-mechanical ordinary state-based peridynamic (OSB-PD) model and corresponding numerical scheme were developed to simulate the damage of rocks after the heating and cooling processes, and the change of crack evolution process was predicted. The results demonstrate that elevated heating temperatures exacerbate the thermal damage to the specimens, resulting in a decrease in peak strength and an increase in ductility of granite. The escalating occurrence of thermal-induced cracks significantly affects the crack evolution process during the loading phase. The numerical results accurately reproduce the damage and fracture characteristics of the granite under different final heating temperatures (FHTs), which are consistent with the test results in terms of strength, crack evolution process, and failure mode.

Abstract The sandstone is in a state of dry–wet cycle under the repeated action of rainfall, and its mechanical properties are deteriorated to varying degrees, which causes cracks in the sandstone. Therefore, it is of great significance to study the mechanical properties and fracture propagation of sandstone under the action of dry–wet cycles. Currently, there are limited studies using numerical simulation methods to study the fracture extension of rocks under various dry and wet cycling conditions.Therefore, in this paper, the effects of different amounts of dry and wet cycling on the mechanical properties and fracture behavior of sandstone are investigated through uniaxial compression tests and numerical simulations of fracture extension. The findings indicate that the deformation stage of sandstone remains unchanged by the dry–wet cycle. The uniaxial compressive potency and coefficient of restitution gradually diminish as the quantity of cycles rises, while the Poisson's ratio exhibits the opposite trend, and the impact on the mechanical performance of sandstone wanes with cycle increments, and the correlation coefficient surpasses 0.93, signifying a substantial influence of the dry–wet cycle on sandstone's mechanical performances. The discrepancy between the numerical simulation and experimental results is minimal, with a maximum error of only 3.1%, demonstrating the congruence of the simulation and experimental outcomes.The mesoscopic examination of the simulations indicates that the quantity of fractures in the sandstone specimens rises with the escalation of dry–wet cycles, and the steps of analysis linked to crack inception and fracture propagation are accelerated, and the analysis steps from fracture initiation to penetration are also reduced.

Real-time high-temperature CT scanning and a rock-mechanics test system were employed to investigate the mechanical properties of oil shale at temperatures from 20 to 600 °C. The results reveal that up to 400 °C, the aperture of fractures initially decreases and then increases when loading is perpendicular to the bedding. However, the number and aperture continuously increase when loading is parallel to the bedding. Beyond 400 °C, the number of pores increases and the aperture of the fractures becomes larger with rising temperature. The changes in microstructures significantly impact the mechanical properties. Between 20 and 600 °C, the compressive strength, elastic modulus, and Poisson's ratio initially decrease and then increase under perpendicular and parallel bedding loadings. The compressive strength and elastic modulus reach minimum values at 400 °C. However, for Poisson's ratio, the minimum occurs at 500 °C and 200 °C under perpendicular and parallel bedding loadings, respectively. Simultaneously, while the crack damage stress during perpendicular bedding loading, σcd-per, initially exhibits an upward trend followed by a decline and subsequently increases again with temperature increasing, the initial stress during perpendicular bedding loading, σci-per, parallel bedding loading, σci-par, and damage stress, σcd-par, decrease initially and then increase, reaching minimum values at 400 °C. These research findings provide essential data for reservoir reconstruction and cementing technology in the in situ mining of oil shale. [ABSTRACT FROM AUTHOR]

With regard to deep mining in metal mines, an investigation into the failure mode of deep fractured rock masses and their corresponding acoustic emission signal characteristics is conducted via uniaxial compression tests. Subsequently, a fractal damage renormalization group mechanical model is developed to explain the behavior of those fractured rock masses. Employing the bonded block model (BBM) numerical simulation method, fracture process in synthetic rock samples is analyzed, thereby validating the efficacy of the mechanical model. The numerical simulations highlight the critical role of fractures expansion in underlying the deterioration of rock mass strength. As the peak load decreases, the fracture fractal dimension increases, leading to a significant 14.2% reduction in compressive strength accompanied by an approximate 8.7% rise in average fracture fractal dimension. A comparative analysis of tetrahedral and voronoi block synthetic rock samples reveals the tetrahedral block samples exhibit a superior ability to depict the fracture behavior of fractured rock masses. Specifically, they offer a more accurate simulation of acoustic emission characteristics and failure modes. Furthermore, variations in the fracture fractal dimension with respect to the hole defect's position are observed, with the maximum value occurring along the vertical axis of the hole defect. This observation underscores the potential utility of visually monitoring deep rock fracture dynamics as an effective mean for quantitatively evaluating fracture damage and strength degradation in deep rock formations. [ABSTRACT FROM AUTHOR]

The water–cement ratio significantly affects the mechanical properties of concrete with changes in porosity serving as a key indicator of these properties, which are correlated with the ultrasonic wave velocity and energy evolution. This study conducts uniaxial compression tests on concrete with varying water–cement ratios, analyzing energy evolution and ultrasonic wave velocity variations during the pore compaction stage and comparing damage variables defined by dissipated energy and ultrasonic wave velocity. The results indicate the following findings. (1) Higher water–cement ratios lead to more complete hydration, lower initial porosity, and a less pronounced pore compaction stage, but they deteriorate mechanical properties. (2) In the pore compaction stage, damage variables defined by dissipated energy are more regular than those defined by ultrasonic wave velocity, showing a nearly linear increase with stress (D = 0~0.025); ultrasonic wave variables fluctuate within −0.06 to 0.04 due to diffraction caused by changes in the pore medium. (3) In the pre-peak stress stage, damage variables defined by ultrasonic wave velocity show a distinct threshold. When the stress ratio exceeds about 0.3, the damage variable curve's growth shows clear regularity, significantly reflecting porosity changes. In conclusion, for studying porosity changes during the pore compaction stage, damage variables defined by dissipated energy are more effective. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Flaw length has a significant effect on the cracking behaviour of fractured rock. PFC2D was used to simulate the uniaxial compression of red sandstone samples with secondary flaw lengths L2 of 0 mm, 5 mm, 10 mm, 15 and 20 mm under different primary flaw angles α(α = 0°, 15°, 30°, 45°, 60°, 75°, and 90°). Based on the simulation results, the effects of the secondary flaw length on the mechanical parameters, crack initiation location and crack evolution process of the fractured rock were analysed. Then, a method for judging the initiation location of the first cracks was proposed. Finally, the characteristics of the particle displacement field at preexisting flaw tips during first and secondary crack initiation were analysed. The results of this study are helpful for more deeply understanding the cracking behaviour of fractured rock. [ABSTRACT FROM AUTHOR]

In order to study the change of mechanical properties and failure behavior of self-compacting concrete with different fly ash content, the FISH language in PFC2D and the linear bonding model built in the program were used to establish a single self-compacting concrete with different fly ash content. The discrete element model of the axial compression test was compared with the actual test results to analyze the internal failure form and force chain changes. The research shows that the ultimate strength of FA-SCC with different fly ash content increases first and then decreases, and the failure cracks are all diagonal cracks. The difference lies in the number of vertical cracks in the middle. The established two-dimensional discrete element numerical model type can well simulate the uniaxial compression test of fly ash self-compacting concrete structure, and can well observe the processcess of the generation of micro-cracks in the material, the expansion of cracks and the formation of diagonal penetration cracks when the axial compression failure occurs, which makes up for the indoor test only relying on the naked eye. At the same time, the axial compressive strength and stress-strain curves of the self-compacting concrete output by the model under different fly ash content are highly consistent with the laboratory test results, and the error of the maximum compressive strength measured does not exceed 7.1%, which is the result of fly ash. The discrete element simulation and mesostructure research of grey self-compacting concrete provide reference. [ABSTRACT FROM AUTHOR]

Shotcrete has been widely used in the excavation of caverns and tunnels as a key load-bearing element in the support system. However, the interfacial stresses and bond strengths within the composite structures formed by the interaction of geologic bodies and tectonic formations are not well understood, which can lead to safety accidents and excessive wastage of support materials in engineering. To address this gap, rock-concrete composite specimens were created using six distinct types of surrounding rocks. The strength law of composite specimens was analyzed, and the uniaxial compressive strength prediction model of composite specimens was derived based on Mohr-Coulomb strength yield criterion. The results show that the uniaxial compressive strength of the composite specimen changes with the change of rock type, which is between the strength of rock and concrete. The uniaxial peak strength and elastic modulus of composite specimens are linearly positively correlated with the ratio (Y) of concrete-rock elastic modulus, which is easily affected by concrete properties. However, the peak strain is linearly and negatively correlated with Y, which is greatly influenced by rock. The rock-concrete interface of the composite specimen plays an important role in the failure of the specimen, which changes the stress transfer state of the composite specimen, produces uncoordinated deformation, and finally causes the failure of the specimen. The theoretical and test value error of the derived composite specimen uniaxial compressive strength prediction model are -1.19%~12.20%, and the theoretical calculation model can be used to predict the uniaxial compressive strength of rock-concrete composite specimens. [ABSTRACT FROM AUTHOR]

In the evolving field of geotechnical engineering, the study of bimrocks (block-in-matrix rocks) presents unique challenges and opportunities. Based on laboratory uniaxial compression tests (UCTs) and their corresponding numerical simulations, this study delves into the intricate mechanics of bimrocks to enhance the understanding of these complex materials. Firstly, this study innovatively proposes a “masking” modeling method, which allows for the creation of numerical models of bimrocks with realistic shapes and breakable blocks based on the discrete element method (DEM). Furthermore, two indicators are introduced to characterize the type of cementation, demonstrating their strong correlation with the Volumetric Block Proportion (VBP) and block sizes. The experimental results indicate that the peak strength of bimrocks in UCTs shows a negative linear correlation with the number of block-matrix contacts, and this relationship is independent of the block size. Moreover, when the number of block-matrix contacts exceeds a certain threshold, the strain corresponding to the initial fracture significantly decreases. For similar bimrocks in field, these results have significant implications for predicting their mechanical strength and understanding the micromechanical deformation and failure mechanisms. [ABSTRACT FROM AUTHOR]

This paper investigates the mechanical properties and damage laws of marine shale from the Silurian Longmaxi Formation by conducting uniaxial compression experiments with varying lamination angles with respect to the loading direction. Data are analyzed via computed tomography scanning and fractal theory to reveal a series of mechanical properties, considering stress-strain curve, compressive strength, Young's modulus, and Poisson's ratio. The results indicate three damage modes in shale samples: shear, tensionshear, and tension. The shales are anisotropic as the mechanical properties vary with the lamination orientation and the loading direction. The compressive strength decreases nonlinearly with increasing lamination angle, whereas the Young's modulus and Poisson's ratio correlate almost linearly with the lamination angle. To overcome the defect of visual images when quantitatively evaluating cracks and rock damage to investigate the mechanical properties of shale, we propose block fractal dimension and crack fractal dimensions calculated using post-experimental photographs and computed tomography images. Fractal dimensions are useful tools for identifying variations in uniaxial compressive strength and correlate positively with the sample damage, particularly their damage class. This study highlights the value of applying fractal theory for the quantitative characterization of shale mechanical properties, and reveals that the lamination orientation to the loading direction is a parameter that significantly controls the mechanical properties of shale. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, we assessed the impact of substituting natural fine aggregates with municipal solid waste incineration bottom ash (MSWI-BA) in steel fiber (SF)-reinforced concrete on its compressive properties post high-temperature exposure. The concrete specimens incorporating MSWI-BA as the fine aggregate and SFs for reinforcement underwent uniaxial compression tests after exposure to high temperatures. Through the tests, we investigated the impact of high-temperature exposure on mechanical properties, such as mass loss rate, stress-strain full curve, compressive strength, peak strain, elastic modulus, and so on, over different thermostatic durations. The analysis revealed that with the increasing exposure temperature and durations, the mass loss rate gradually increased; compressive strength initially increased and then decreased; peak strain significantly increased; stress-strain curve flattened, and elasticity modulus monotonically decreased. Different thermostatic durations led to distinct critical temperatures for the compressive strength (700°C for 1.0 and 1.5 h, and 500°C for 2 h). The concrete specimens exhibited an increasing compressive strength below the critical temperature, followed by a rapid decrease upon exceeding it. Based on the strain equivalence hypothesis and Weibull distribution theory, we derived expressions for the total damage variables and a uniaxial compression constitutive model, which accurately reflected the changing macro mechanical properties of concrete under various exposure temperatures and thermostatic durations. The concrete matrix microscopic morphology continuously deteriorated beyond 500°C, resulting in a loss of compressive strength. This degradation in the concrete microstructure serves as the fundamental cause for the decline in its macroscopic mechanical properties. [ABSTRACT FROM AUTHOR]

Tempering, the controlled addition of water to wheat before milling, is an essential step for maximizing flour yield in the milling industry. However, the limited availability of water significantly impacts moisture migration within the kernels, consequently influencing their breakage behavior. This study investigates the effects of tempering time (3, 6, 9, and 12 h) and moisture content (14%, 16% and 18%) on the moisture diffusivity and compressibility characteristics of single wheat kernels from hard red winter (HRW) and hard red spring (HRS) varieties. Uniaxial compression tests revealed a significant influence of tempering time on the viscoelastic properties of the kernels. Tempering moisture content significantly decreased elasticity of HRW kernels from 155. 8 MPa to 89.2 MPa, whereas for HRS the decrease was from 192.2 MPa to 115.0 MPa. Higher tempering moistures decreased the elastic work from 8.8 to 5.4 N. mm while increased the plastic work to 1. 92 N.mm, suggesting improved flour extraction. Compressibility followed first order kinetics, with rate constants ranging from 0.002 to 0.0057 h− 1 for HRS and from 0.0026 to 0.0066 h− 1 for HRW. Kernel diffusivity exhibited variations with tempering moisture for both the kernels, although these differences were not statistically significant. These findings provide insights into the interaction between tempering conditions and kernel properties, for optimizing the tempering processes to enhance flour extraction efficiency. [ABSTRACT FROM AUTHOR]

In order to explore the mechanical properties of undisturbed sea sand concrete with high chlorine concentration and high shell content, taking the chloride ion content and shell content of sea sand as variables, nine groups of sea sand concrete were designed and prepared to carry out concrete cube compressive strength test and uniaxial compressive stress-strain curve test, and compared with ordinary concrete. The results show that with the increase of chloride ion content, the pore structure of concrete becomes finer, the early strength increases, the peak stress of uniaxial compressive stress-strain complete curve increases, the peak strain decreases, and the elastic modulus increases. With the increase of shell content, the slump of concrete decreases significantly, the pore structure of concrete becomes looser, the strength decreases, and the peak stress of uniaxial compressive stress-strain complete curve decreases, the peak strain increases, and the elastic modulus decreases. Finally, based on the existing models, the formula for calculating the model parameters of chloride ion content and shell content is put forward. [ABSTRACT FROM AUTHOR]

Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to investigate the impact of moisture content on energy evolution, three types of rock samples with varying moisture contents were subjected to uniaxial compression tests. The study aimed to analyze the reasons behind the differences in energy during the deformation process of rocks with different moisture contents. The findings indicate that with increasing moisture content, the peak strength and elastic modulus of the samples decrease. However, the ratio of crack initiation strength σci to peak strength σf shows little effect, primarily because the characteristic strength ratio σci/σf is determined by external loads. The growth rate of elastic energy reaches its maximum value in the early stage of yield, while the proportion of elastic energy reaches its peak value in the later stage of yield. In the deformation and failure process of rocks with varying moisture contents, the increment in elastic performance is smallest in the initial compaction stage for saturated rocks, whereas it is the largest in the yield stage for dry rocks. Additionally, a damage evolution equation based on energy dissipation was established and validated. [ABSTRACT FROM AUTHOR]

Uniaxial compression tests were conducted on quartz mica schist in a laboratory to study the brittle failure modes of foliated rocks. By focusing on the crack evolution pattern, the failure mechanisms of foliated rocks were investigated by numerical tests based on particle discrete element theory. Furthermore, the effect of fabric on the mechanical anisotropy of foliated rocks was explored. The results indicated that the failure of foliated rocks subjected to uniaxial compression is heavily controlled by the rock fabric, exhibiting complex modes depending on the loading direction, including axial tensile fracture, oblique shear fracture, conical shear fracture, slip shear failure and splitting failure. Cracks initiated in the compressed rocks are induced from the contact surfaces of granular and flaky minerals and from the tips of flaky minerals. The crack initiation of foliated rocks, attributed to the concentration of tensile stress within the rock, responds to the loading direction in terms of the induced mechanism. When α = 90°, 45° and 0°, crack initiation depends on the differences in the mechanical properties of different minerals, the slipping of flaky minerals, and the kinking of flaky minerals, respectively. The formation of primary fracture planes results from tension crack coalescence + shear crack connection (α = 90°), shear crack or tension‒shear composite crack connection (α = 45°), and tension crack coalescence (α = 0°). As the orientation degree of flaky minerals decreases, the failure mode experiences a gradual decrease in sensitivity to the loading direction, and the curve of strength variation with orientation angle changes from U-shaped to shoulder-shaped or wave-shaped, accompanied by a decreasing anisotropy degree of rock strength. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is important to clarify the uniaxial compressive mechanical properties and fracture mechanism of recycled aggregate concrete (RAC) from a mesoscale perspective for its further application in engineering. In this study, the cohesive zone model (CZM) based on the Benzeggagh–Kenane (B–K) criterion was used to simulate the RAC's complex fracture behavior. Meanwhile, the effects of cohesive element parameters and mechanical properties of mesoscale components on macroscopic mechanical properties and damage modes of RAC were investigated. The results show that the CZM based on the B–K criterion can be used to characterize the whole fracture process of RAC. The RAC's compressive strength has an exponential relationship with the shear strengths of the mortars as well as the ITZs and is quadratically related to the logarithm of cohesive element stiffness. The RAC's damage morphology is more sensitive to the change of element stiffness, Mode II fracture energy and hybrid fracture energy ratio.

In view of the stability problem of coal pillars left over during coal resource mining, (Carbon Fiber Reinforced Polymer) CFRP sheet is applied in coal pillar reinforcement. Uniaxial compression tests of CFRP passively confined coal samples are carried out to explore the mechanical response mechanism of passively confined coal samples under different layers, and the energy dissipation damage constitutive relationship of CFRP passively confined coal samples is established based on the energy dissipation principle. The conclusions are: As CFRP layers increased, the local damage of coal samples before the peak evolved from a 'cliff-like jagged' to a 'capillary jagged', with post-peak instability marked by a shift to more 'cliff-like' characteristics. The tests revealed improvements in peak strength and elastic modulus, with a defined functional relationship between these properties and CFRP layers. The energy storage capacity of passively confined coal samples improved with CFRP layers, requiring less axial deformation to achieve equivalent energy levels. The energy dissipation rate showed an initial decrease followed by an increase, with a minimum inflection point, the elastic energy consumption ratio tends to decrease slowly and then rapidly during post-peak instability. A damage constitutive relationship and evolution equation were developed, highlighting that the CFRP sheet significantly inhibits damage, with diminishing effectiveness beyond two layers. The study concludes that three-layer CFRP sheets provide optimal confinement, offering a novel strategy for the reinforcement of coal pillars and the prevention and control of rock burst, without considering the actual coal pillar dimensions and shape. To sum up, the use of CFRP sheet to strengthen coal pillar has considerable potential research value in strengthening coal pillar and improving the recovery rate of coal resources.