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To study the enhancement effect of carbon nanotubes (CNTs) on the splitting tensile properties of foamed concrete backfill in which cement and fly ash were used as the cementitious materials and natural sand was used as the aggregate, specimens of CNT-modified foamed concrete backfill were prepared. Brazilian splitting tests were used to investigate the splitting tensile strength of the CNT-modified foamed concrete backfill, and the digital speckle correlation method was used to analyze the stress field characteristics and crack expansion law of the specimens during splitting tensile testing. The stress-strain characteristics and energy dissipation laws of the backfill were studied at various static loading rates, and a relationship between the splitting tensile strength, ultimate strain, and loading rate was established. The results showed that at the optimum CNT content of 0.05%, the peak strength and ultimate strain of the modified foamed concrete backfill increased by an average of 67.2% and 21.7%, respectively. Moreover, after modification with CNTs, the foamed concrete backfill was less likely to develop strain concentration areas before reaching peak strength. The triangular stable loadbearing structure formed by the modified foamed concrete backfill after splitting caused the end of the stress-strain curve to exhibit varying degrees of "backlash". For the CNT-modified foamed concrete backfill, the peak strength correlated logarithmically with the loading rate, while the ultimate strain correlated as a power function of the loading rate. At a low loading rate, the CNT-modified foamed concrete backfill dissipated less energy, and the reverse was true for higher rates., Competing Interests: Declarations. Competing interest: We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted., (© 2024. The Author(s).)

This paper investigates the effects of defects on tensile failure of additive manufactured AlSi10Mg alloy focusing particularly on the role of large pancake shaped loss of fusion (LOF) defects lying perpendicular to the build direction (BD). Time-lapse in situ synchrotron radiation X-ray micro-computed tomography during straining reveals how, when tested parallel to the BD, the LOF defects extend laterally with straining connecting to other defects and giving rise to low plasticity and an essentially brittle failure mode. When they are aligned edge-on to the straining direction, failure is characterised by a ductile cup-cone failure with significant elongation of the defects axially and extensive necking prior to failure. The soft fish-scale melt pool boundaries were also found to affect the fracture path. These results highlight the anisotropic effect of loss of fusion defects in controlling tensile ductility and the need to minimize their size and aspect ratio. In cases where these cannot be fully eliminated the component should be fabricated such that the BD is not aligned with the dominant in-service loading direction., (© 2023. Springer Nature Limited.)

The mechanical properties and fracture behavior of concrete are controlled by aggregate characteristics, and the distribution of aggregates is uncertain. Traditional studies on concrete crack propagation mainly conduct deterministic analysis based on the position and size of the aggregates, rarely considering the uncertainty of aggregate distribution. Based on the Peridynamics (PD) theory, random distribution functions are introduced to describe the geometric characteristics and positional parameters of concrete aggregates. Simulating the effect of random distribution of aggregates on concrete crack propagation by presetting random aggregates. For the first time, the Boundary Damage Ratio (BDR) is proposed to quantitatively describe the influence of cement mortar and aggregate on crack propagation, revealing the influence rules of random aggregate parameters on concrete damage provides a new method for studying concrete crack propagation. The research results show that the size and position of aggregates determine the crack propagation path during concrete failure. The BDR can indicate the quality of the concrete grading and the intensity of the aggregate's guiding effect on crack propagation. It was found that the aggregate size and the BDR follow a Weibull distribution; the larger the aggregate size, the smaller the shape parameter., Competing Interests: Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

To study the dynamic mechanical characteristics of coal in the area affected by mining in front of the mining face under different mining methods, an improved split Hopkinson pressure bar (SHPB) was used to apply different static loads to different positions. Then, dynamic mechanical tests were conducted on coal at different positions on the mining face, analyzing the dynamic response under strong dynamic load disturbances, under three different mining layouts. Within the range of static water pressure to the peak support pressure, the dynamic strength of coal gradually increases with increasing distance from the mining face. The dynamic strength is the smallest at the peak support pressure stress, and under strong external disturbances, instability and failure are increasingly likely to occur at the peak stress. Under the same loading rate conditions, the dynamic strength of the peak stress in coal is as follows: Protective coal-seam mining (PCM) > Top-coal caving mining (TCM) > Nonpillar mining (NM)., (© 2024. The Author(s).)

In the process of fully mechanized top-coal caving mining, the top-coal is affected by mining-induced stress, and the stress varies along the strike direction of working face, so the boundary position of its entering the limit equilibrium state changes accordingly. The determination of the boundary along the strike direction of working face can provide scientific guidance for the stability control of support-surrounding rock in fully mechanized top-coal caving face. Using the research methods of theoretical analysis, physical similarity simulation experiment and numerical simulation experiment, the stress state analysis model of the boundary position of the top-coal limit equilibrium zone under macro-scale conditions was established, the stress state characterization method of the boundary of the top-coal limit equilibrium zone along the strike direction of working face was given, and the quantitative characterization of the boundary of the top-coal limit equilibrium zone along the strike direction of working face was realized by combining with the mining-induced stress path, and the distance relationship between the boundary of the top-coal limit equilibrium zone and the langwall face along the strike direction of working face was revealed. The results show that after critical mining in fully mechanized top-coal caving face, the distance between the boundary of top-coal limit equilibrium zone and the langwall face along the strike direction of working face presents a relationship of increasing from top to bottom. The distance between the top-coal upper boundary and the langwall face was 2.85 m and the distance between the top-coal lower boundary and the langwall face was 5.39 m. The boundary of top-coal limit equilibrium zone along the strike direction of working face was verified by the top-coal elastic-plastic zone boundary and the boundary of the peak position of front abutment pressure in different layers of top-coal. The results show that the quantitative characterization of the top-coal limit equilibrium zone boundary along the strike direction of working face was reasonable. In order to improve mine production efficiency, optimization measures were put forward for hard coal seam and soft coal seam respectively., (© 2024. The Author(s).)

The mechanical properties of rocks in cold regions undergo significant changes as a result of decades of freeze‒thaw cycles with seasonal variations, which can lead to a series of geological disasters, such as collapse. This study investigates the evolution of the mechanical characteristics and internal progressive damage characteristics of mixed granite under freeze‒thaw cycling and axial loading. By measuring the mass, wave velocity, and uniaxial compressive strength of rock samples and combining these metrics with acoustic emission (AE) characteristics, the physical and mechanical properties and microfracture development of mixed granite after different numbers of freeze‒thaw cycles were investigated. The results indicate that as the number of freeze‒thaw cycles increases, the longitudinal wave velocity, uniaxial compressive strength, and elastic modulus of the mixed granite decrease nonlinearly, while the peak strain gradually increases. Combined with the stress‒strain curve, the AE characteristics can be divided into four stages. As the number of freeze‒thaw cycles increases, the AE cumulative count decreases, and the AE counts of the four stages are different. The low-frequency-high-amplitude signals first increases and then tends to stabilize, and they only appeared in the third and fourth stages. At the same time, the proportion of the low-frequency ratio gradually increases, and the proportion of the high-frequency ratio decreases. In addition, based on the rise time/amplitude (RA) and average frequency (AF) characteristics and failure modes, it was found that the internal crack types of mixed granite transition from shear cracks to tensile cracks, among which tensile cracks play a crucial role in rock failure., (© 2024. The Author(s).)

A detailed numerical simulation of Colored Self-Compacting Concrete (CSCC) was conducted in this research. Emphasis was placed on an innovative calibration methodology tailored for ten unique CSCC mix designs. Through the incorporation of multi-objective optimization, MATLAB's Genetic Algorithm (GA) was seamlessly integrated with PFC3D, a prominent Discrete Element Modeling (DEM) software package. This integration facilitates the exchange of micro-parameter values, where MATLAB's GA optimizes these parameters, which are then input into PFC3D to simulate the behavior of CSCC mix designs. The calibration process is fully automated through a MATLAB script, complemented by a fish script in PFC, allowing for an efficient and precise calibration mechanism that automatically terminates based on predefined criteria. Central to this approach is the Uniaxial Compressive Strength (UCS) test, which forms the foundation of the calibration process. A distinguishing aspect of this study was the incorporation of pigment effects, reflecting the cohesive behavior of cementitious components, into the micro-parameters influencing the cohesion coefficient within DEM. This innovative approach ensured significant alignment between simulations and observed macro properties, as evidenced by fitness values consistently exceeding 0.94. This investigation not only expanded the understanding of CSCC dynamics but also contributed significantly to the discourse on advanced concrete simulation methodologies, underscoring the importance of multi-objective optimization in such studies., (© 2024. The Author(s).)

Laser beam directed energy deposition (DED-LB) is an attractive additive manufacturing technique to produce versatile and complex 3D structures on demand, apply a cladding, or repair local defects. However, the quality of manufactured parts is difficult to assess by inspection prior to completion, and parts must be extensively inspected post-production to ensure conformance. Consequently, critical defects occurring during the build go undetected. In this work, a new monitoring system combining three infrared cameras along different optical axes capable of monitoring melt pool geometry and vertical displacement throughout deposition is reported. By combining multiple sensor data, an automated algorithm is developed which is capable of identifying the formation of structural features and defects. An intersecting, thin-walled geometry is used to demonstrate the capability of the system to detect process-induced porosity in samples with narrow intersection angles, which is validated using micro-CT observations. The recorded results indicate the root cause of this process-induced porosity at the intersection, and it is shown that advanced toolpath planning can eliminate such defects. The presented methodology demonstrates the value of multi-axis monitoring for identifying both defects and structural features, providing an advancement towards automated detection and alert systems in DED-LB., (© 2024. The Author(s).)

This research delineates the energy dissipation characteristics in coal crushing under impact loads, leveraging the capabilities of Separated Hopkinson Pressure Bar experimental system. A meticulous examination of both burst-prone and non-burst-prone coal samples during destruction processes was undertaken to decipher the dynamic compression mechanical attributes from perspectives of energy and fragmentatio's fractal dimensions. Burst-prone coal showcases a more pronounced escalation in fragmentation work in comparison to non-burst-prone samples, thereby illustrating a perceptible strain-rate dependent effect correlating with enhanced strain rates. Additionally, it was observed that incident, reflected, and transmitted energy trajectories for both sample categories follow an approximately linear ascendancy, albeit exhibiting diverse magnitudes. Burst-prone coal manifests a more rapid and focused energy growth compared to its non-burst-prone counterpart. When subjected to impact loads, a notable trend was discerned where the fragmentation's fractional dimension escalated persistently with both the incident energy and the crushing work, portraying a prominent growth effect. The insights garnered from this study pave the way for distinguishing between impacted and unimpacted coal samples using energy perspectives and fragmentation's fractal dimensions., (© 2023. Springer Nature Limited.)

To comprehensively understand the mechanical response of a rock-coal combination structure containing a weak layer, a series of laboratory static loading and impact loading experiments were conducted. The results showed that under static load, the sliding process of the rock coal structure was relatively slow, and fragments can be observed. Under the action of horizontal impact loading, the whole coal stratum slipped out rapidly, and the process lasted only 0.05 s. Under the horizontal and axial impact loads, the coal stratum remained stable first, and then it slipped out as a whole under the action of static load. Additionally, a sliding instability criterion of a rock coal structure containing a weak layer was established based on theoretical analysis. The key parameter P value was checked through a numerical simulation experiment. It was found that the value was linearly related to the mechanical properties of the weak layer and overburden stress, and the experimental results coincided with the theoretical results. Finally, the relationship between sliding rockburst and strain rockburst was discussed, and these results can provide an important scientific basis for the prevention and control of dynamic disasters in deep mining., (© 2023. The Author(s).)

Natural defects, such as joints, structural surfaces and voids, significantly affect the mechanical properties and fracture modes of rock mass. Hidden fissures are widely distributed in magmatic rock, while their influences on the mechanical properties and the cracking mechanism are still unclear. Laboratory tests were conducted on prefabricating hidden-fissured rock-like specimens, as well as intact specimens and close-fissured specimens as a comparison. The real-time digital image correlation technology and acoustic emission monitoring technology were synchronously adopted to capture both the external and internal cracking process. The results show that the hidden fissures can weaken the uniaxial compression strength, while the deterioration effect of hidden fissures is weaker than closed fissures due to the internal cohesion among fissure internal particles. What's more, the initiation behavior of the α = 90° hidden-fissured specimen is different from that of β = 90° closed-fissured specimen. Finally, the cracking mechanism of hidden-fissured specimens was revealed by analyzing the RA-AF relationship. The failure of the close-fissured specimens is mainly the tensile-shear mixed fracture mode, while the failure of the hidden-fissured specimens is mainly the tensile fracture mode and supplemented by the shear. The experimental results contribute to the understanding of cracking properties in hidden-fissured rock., (© 2023. The Author(s).)

The static and fatigue tensile properties of high-strength polyacrylonitrile (PAN)-based carbon (IMS60) and electronic (E)-class glass (E-glass) hybrid fiber-reinforced epoxy matrix composites (HFRPs) were investigated. The fiber orientations of the HFRP specimens were set to unidirectional with [(0 (IMS60) )/(0 (E-glass) )] S (subscript S means symmetry and [(0 (IMS60) )/(0 (E-glass) )/(0 (E-glass) )/(0 (IMS60) )]), [(0 (E-glass) )/(0 (IMS60) )] S , [(0 (E-glass) )/(0 (IMS60) ) 2 ] S , [(0 (E-glass) )/(0 (IMS60) ) 3 ] S , [(0 (E-glass) )/(0 (IMS60) ) 5 ] S , [(0 (E-glass) ) 2 /(0 (IMS60) )] S , [(0 (E-glass) ) 3 /(0 (IMS60) )] S , and [(0 (E-glass) ) 5 /(0 (IMS60) )] S . Under static loading for the [(0 (IMS60) )/(0 (E-glass) )] S , [(0 (E-glass) )/(0 (IMS60) )] S , [(0 (E-glass) )/(0 (IMS60) ) 2 ] S , [(0 (E-glass) )/(0 (IMS60) ) 3 ] S , and [(0 (E-glass) )/(0 (IMS60) ) 5 ] S HFRP specimens, the stress applied to the specimen was almost linearly proportional to the strain until failure. However, the tensile stress-strain curves of the [(0 (E-glass) ) 2 /(0 (IMS60) )] S , [(0 (E-glass) ) 3 /(0 (IMS60) )] S , and [(0 (E-glass) ) 5 /(0 (IMS60) )] S HFRP specimens had a complicated shape (jagged trace). The Weibull statistical distributions of the tensile strength values were also examined. The Weibull moduli for the [(0 (E-glass) )/(0 (IMS60) )] S , [(0 (E-glass) )/(0 (IMS60) ) 2 ] S , [(0 (E-glass) )/(0 (IMS60) ) 3 ] S , [(0 (E-glass) )/(0 (IMS60) ) 5 ] S , [(0 (E-glass) ) 2 /(0 (IMS60) )] S , [(0 (E-glass) ) 3 /(0 (IMS60) )] S , and [(0 (E-glass) ) 5 /(0 (IMS60) )] S HFRP specimens were higher than those for the mono carbon fiber-reinforced epoxy (CFRP) and glass fiber-reinforced epoxy (GFRP) specimens. Under fatigue loading, the fatigue properties of the HFRP specimens showed CFRP-dominant behaviour at high stress levels and GFRP-dominant behaviour at low stress levels. The fatigue properties of the HFRP specimens increased with increasing volume fraction of CFRP in the following order: ([(0 (E-glass) )/(0 (IMS60) ) 5 ] S  > [(0 (E-glass) )/(0 (IMS60) ) 3 ] S  > [(0 (E-glass) )/(0 (IMS60) ) 2 ] S  > [(0 (IMS60) )/(0 (E-glass) )] S  > [(0 (E-glass) )/(0 (IMS60) )] S  > [(0 (E-glass) ) 2 /(0 (IMS60) )] S  > [(0 (E-glass) ) 3 /(0 (IMS60) )] S  > [(0 (E-glass) ) 5 /(0 (IMS60) )] S )., (© 2022. The Author(s).)

Heat treatment is often required for ultra-high-performance concrete (UHPC) to achieve high strength. To broad its use in construction, the effect of different curing conditions on the properties of UHPC has been developed for many years. The experimental investigation of large scale ultra-high-performance fibre reinforced concrete (UHPFRC) beams is limited. In the present study, UHPFRC specimens and concrete cured at 20 °C were prepared to investigate the properties and flexural behaviour. The standard cubic compressive strength of UHPFRC specimens cannot be achieved at curing temperature of 20 °C. The bearing capacity under flexure was enhanced with the increase of reinforcement ratio. The failure modes of beams changed from ductile to brittle as the reinforcement ratio increased from 1.26 to 9.50%. The flexural behaviour of UHPFRC beams cured at room temperature was in accordance with the UHPFRC beams cured at high temperature in previous studies. In addition, the calculation model of CECS38-2004 underestimated the bending moment capacity of the under-reinforced UHPFRC beams (with reinforcement ratio from 0 to 7.85%) and overestimated the bending moment capacity of the UHPFRC beams with high reinforcement ration of 9.50%., (© 2021. The Author(s).)

The temperature-dependent mechanical behaviors of open-hole composite plates are essential for composite design and structures. Here, tensile experiments of shallow straight-link-shaped 2.5D woven composites (abbr. 2.5DWC) with/without a center hole are first conducted at different temperatures (20 °C, 180 °C and 240 °C). Failure modes are examined by scanning electron microscope (SEM). Thermal property of QY8911-IV resin is investigated by DMA analysis. It is noted for samples without the center hole that with the increase of temperature, the tensile stress-strain curves exhibit a linear response until that a slight nonlinearity at the end stage. The strength retention rates at 180 °C and 240 °C are totally equal. For the open-hole samples, it is interestingly found that the strength retention rates are higher than that of samples without the hole at 180 °C, resulting from the stress concentration accommodation and fiber-dominated failure mode. Even at 240 °C, there is no necking phenomenon for all the failed samples, but more broom-like damage extent is observed in the cross-section. Due to the primary load-bearing warp yarns and hole-edge stress concentration, obvious pull-out warp yarns emerge near the hole edge.

Nanoscale mineralized collagen fibrils may be important determinants of whole-bone mechanical properties and contribute to the risk of age-related fractures. In a cross-sectional study nano- and tissue-level mechanics were compared across trabecular sections from the proximal femora of three groups (n = 10 each): ageing non-fractured donors (Controls); untreated fracture patients (Fx-Untreated); bisphosphonate-treated fracture patients (Fx-BisTreated). Collagen fibril, mineral and tissue mechanics were measured using synchrotron X-Ray diffraction of bone sections under load. Mechanical data were compared across groups, and tissue-level data were regressed against nano. Compared to controls fracture patients exhibited significantly lower critical tissue strain, max strain and normalized strength, with lower peak fibril and mineral strain. Bisphosphonate-treated exhibited the lowest properties. In all three groups, peak mineral strain coincided with maximum tissue strength (i.e. ultimate stress), whilst peak fibril strain occurred afterwards (i.e. higher tissue strain). Tissue strain and strength were positively and strongly correlated with peak fibril and mineral strains. Age-related fractures were associated with lower peak fibril and mineral strain irrespective of treatment. Indicating earlier mineral disengagement and the subsequent onset of fibril sliding is one of the key mechanisms leading to fracture. Treatments for fragility should target collagen-mineral interactions to restore nano-scale strain to that of healthy bone.

Atmospheric warming threatens to accelerate the retreat of the Antarctic Ice Sheet by increasing surface melting and facilitating 'hydrofracturing' 1-7 , where meltwater flows into and enlarges fractures, potentially triggering ice-shelf collapse 3-5,8-10 . The collapse of ice shelves that buttress 11-13 the ice sheet accelerates ice flow and sea-level rise 14-16 . However, we do not know if and how much of the buttressing regions of Antarctica's ice shelves are vulnerable to hydrofracture if inundated with water. Here we provide two lines of evidence suggesting that many buttressing regions are vulnerable. First, we trained a deep convolutional neural network (DCNN) to map the surface expressions of fractures in satellite imagery across all Antarctic ice shelves. Second, we developed a stability diagram of fractures based on linear elastic fracture mechanics to predict where basal and dry surface fractures form under current stress conditions. We find close agreement between the theoretical prediction and the DCNN-mapped fractures, despite limitations associated with detecting fractures in satellite imagery. Finally, we used linear elastic fracture mechanics theory to predict where surface fractures would become unstable if filled with water. Many regions regularly inundated with meltwater today are resilient to hydrofracture-stresses are low enough that all water-filled fractures are stable. Conversely, 60 ± 10 per cent of ice shelves (by area) both buttress upstream ice and are vulnerable to hydrofracture if inundated with water. The DCNN map confirms the presence of fractures in these buttressing regions. Increased surface melting 17 could trigger hydrofracturing if it leads to water inundating the widespread vulnerable regions we identify. These regions are where atmospheric warming may have the largest impact on ice-sheet mass balance.

Nanophase materials can result in harder metals, but more brittle. However it is still reasonable to expected that nanometre-scale composite materials may be better than conventional composites. Researchers have discussed the challenges of making nanocomposites at a conference in Alaska, and concluded that inputs from several fields would be required to make it work. Nanotubes and nanoparticles are simple systems for molecular modellers and computer simulation show deformation that is characteristic of tensile failure of spiralled cardboard tubes and hollow plant cells.

This study investigates the challenge of borehole instability in shale gas development, focusing on the interactions among temperature, fluid flow, and stress. Using a thermal-hydro-mechanical coupling model of borehole elastic stress combined with a true triaxial rock strength criterion and tensile failure criterion, the research systematically examines the effects of different models on borehole stability in shale formations. The findings reveal that while temperature has a relatively minor impact on the stress distribution and failure zones around boreholes, bottom hole pressure plays a critical role in influencing both the extent of unstable regions and the modes of rock failure. Under varying inclination angles, the unstable zones and failure patterns generally remain consistent, with higher stability observed when drilling aligns with the direction of minimum horizontal stress. Moreover, the study highlights the significance of appropriate drilling fluid density in maintaining borehole stability. Specifically, when the bottom hole pressure ranges from 50.66 to 70.66 MPa, the tensile and shear instability areas are minimized within seven days of contact with the drilling fluid. The research underscores the importance of optimizing drilling fluid density, carefully managing bottom hole pressure, and selecting proper borehole trajectories to enhance stability during shale gas drilling. These findings provide both theoretical insights and practical guidance, contributing to the optimization of shale gas drilling engineering practices., Competing Interests: Declarations. Competing interests: The authors declare no competing interests. Informed consent: All individuals involved in this study have provided their consent for the publication of the study findings. Any personal or identifying information that could potentially compromise privacy has been carefully removed or anonymized. Institutional review board statement: All research activities were conducted in accordance with the ethical guidelines and principles outlined by the Committee on Publication Ethics., (© 2025. The Author(s).)

The collapse column may result in failure of the surrounding rock during roadway excavation. It is of considerable importance to elucidate the failure characteristics and develop the corresponding control technologies for the surrounding rock. A discrete fracture mesh (DFN) and a strain-softening constitutive model are employed to simulate the properties of a collapse column. The stress zoning model was developed to characterize the rock surrounding the collapse column. Additionally, the zoned support technology was proposed to stabilize the roadway surrounding the rock. From the center outward, the results indicate that the collapse column can be individually divided into four zones: an internal impact zone of the collapse column, a stress decreasing zone, a stress increasing zone, and an initial stress zone. Upon the visibility of the collapse column, the tensile failure occurs in the roof, leading to a decrease in stress in front of the roadway and an increase in stress on both sides of the collapse column. The collapse amplifies the range of plastic failure by inducing an overlap between the roof stress and the stress elevation zones. The impact zone of the collapse column was reinforced by means of an integrated support system consisting of "pre-grouting, bolt cable mesh, and steel shed". The "bolt cable mesh" provides integrated support beyond the area affected by the collapse column. Following a 20d excavation period, the roof and the two sides were stabilized, with an effectively controlling for the surrounding rock., Competing Interests: Declarations Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

To study the influence of cyclic disturbance stress on the mechanical behavior of coal during mining, a gas containing coal fluid-solid coupling servo seepage experimental system was used to conduct experimental research on the acoustic emission (AE) characteristics of gas containing coal under two stress paths of graded cyclic loading and unloading. The AE characteristics of coal damage and failure processes under different cyclic stress paths were analyzed. The research results indicate that: (1) The overall characteristics of AE signals for both graded cyclic loading and unloading paths are basically the same. With increasing of the amount of graded cyclic loading or unloading, the AE count reaches its maximum value when reaching failure, and the cumulative ringing calculation of AE increases exponentially. (2) The AE signals under the graded cyclic loading or unloading path exhibit obvious zoning characteristics. In the low and medium stress regions, the AE signal basically satisfies the Kaiser effect, while reaching the high stress region before failure, the AE signal exhibits a significant Felicity effect. (3) The concentration coefficient of AE and the intensity coefficient of the Kaiser effect have been newly defined. They are used to quantitatively characterize the extent of the Kaiser effect of AEs under graded cyclic stress. It was found that as the variation of graded cyclic stress increases, the concentration coefficient and Kaiser effect intensity coefficient both show a decreasing trend. (4) Combining the AF and RA values of AE, it was found that the coal failure signals of the two stress paths were basically similar, that is, the overall failure was mainly tensile failure, and the signals of cyclic unloading tensile failure were significantly more than those of cyclic loading. The AE signal characteristics studied in this article are of great significance for predicting coal power disasters., (© 2024. The Author(s).)

Underground grouting is a concealed project, and it is difficult to test the strength of grouting stones in engineering practice. Aiming at the problems of high confined water pressure and strong water-richness of the roadway floor, a pressure filtration test device was developed, and a PFC2D uniaxial compression model was established to study the variation law of stone strength and crack evolution mechanism of grouting materials under different grouting pressures. The results show that with the increase of pressure filtration value, the amount of slurry dehydration increases, the pore water pressure dissipates, the pores between particles are tightly compressed, the contact force between particle skeletons increases, and the strength of stone body increases. Under the condition of the same cement powder ratio (mass ratio of cement to stone powder) or stone powder particle size, the strength of stone body of stone powder-cement grouting material increases with the increase of pressure filtration value. The stress-strain curves of the stone body with different pressure filtration values all experienced three stages: continuous elasticity, fracture expansion and strength failure. Before the peak, the number of cracks increases slowly; after reaching the peak, the micro-cracks extend rapidly and the number increases rapidly, resulting in the final tensile failure of the specimen. This study can provide a basis for the selection of grouting engineering material ratio and grouting pressure parameters., (© 2024. The Author(s).)

The ore pass wall in underground mines is often damaged by the impact and wear caused by unloaded ores. Studying the mechanisms of rock damage and failure under different impact angles can provide technical insights for the design and maintenance of the ore passes. This study employed an inclined impact experimental device along with a drop hammer loading test machine to perform cyclic low-energy impact tests on sandstone samples at five different inclined plane angles. The porosity of the rock samples was measured using a nuclear magnetic resonance (NMR) detection system, which provided data on porosity, T 2 spectrum distribution, and NMR images of the samples after different numbers of impacts at different slope angles. The results indicate that: (1) Under cyclic inclined plane impact loading, an increase in the inclination angle, leads to reduced damage to the rock sample. The rock sample impacted at a 45° inclined plane exhibited the most severe damage. Rock samples with large inclination angles are more prone to experience rupture fractures at the tip of the inclined plane, primarily due to shear-tensile failure. The porosity changes dramatically at initially slope angles, resulting in greater damage. (2) As the number of impacts increases, the porosity of the samples first decreases, then increases, and subsequently decreases again. This progression corresponds to the closure of large pores following the first impact, followed by the expansion of micropores into macropores after 5 impacts, ultimately leading to gradual degradation of the samples until failure. (3) As the number of impacts increases, new cracks form within the rock sample and small cracks expand. Despite an increase in the number of micropores, the macropores still exert a significant influence on the rock samples, with the macropore spectrum area accounting for over 95%., (© 2024. The Author(s).)

The frame beam anchor plate is a new supporting structure reinforcing fill slopes. At present, only a few studies have evaluated its static stability based on the two-dimensional plane assumption. In this paper, the limit analysis method is combined with the three-dimensional spiral failure mechanism to evaluate the factor of safety (Fs) of a slope supported by a frame beam anchor plate. The pseudo-static approach is used to express the seismic effects. When calculating the internal energy dissipations, both the pull-out failure of anchor plates and tensile failure of tie rods are considered. The accuracy of the approach is verified by comparison with calculation results from the finite element method. Parameter analysis summarizes the influence law of each supporting structure design parameter on the Fs. Therefore, this study develops a theoretical basis for evaluating slope stability reinforced by frame beam anchor plates, which can better guide the design of slopes reinforced by this supporting structure., (© 2024. The Author(s).)

Author(s): R.-L. Ballouz [sup.1] , K. J. Walsh [sup.2] , O. S. Barnouin [sup.3] , D. N. DellaGiustina [sup.1] , M. Al Asad [sup.4] , E. R. Jawin [sup.5] , [...], An asteroid's history is determined in large part by its strength against collisions with other objects.sup.1,2 (impact strength). Laboratory experiments on centimetre-scale meteorites.sup.3 have been extrapolated and buttressed with numerical simulations to derive the impact strength at the asteroid scale.sup.4,5. In situ evidence of impacts on boulders on airless planetary bodies has come from Apollo lunar samples.sup.6 and images of the asteroid (25143) Itokawa.sup.7. It has not yet been possible, however, to assess directly the impact strength, and thus the absolute surface age, of the boulders that constitute the building blocks of a rubble-pile asteroid. Here we report an analysis of the size and depth of craters observed on boulders on the asteroid (101955) Bennu. We show that the impact strength of metre-sized boulders is 0.44 to 1.7 megapascals, which is low compared to that of solid terrestrial materials. We infer that Bennu's metre-sized boulders record its history of impact by millimetre- to centimetre-scale objects in near-Earth space. We conclude that this population of near-Earth impactors has a size frequency distribution similar to that of metre-scale bolides and originates from the asteroidal population. Our results indicate that Bennu has been dynamically decoupled from the main asteroid belt for 1.75 [plus or minus] 0.75 million years. Analysis of the size and depth of craters on boulders on the asteroid (101955) Bennu indicates that Bennu has been in near-Earth space for 1.75 [plus or minus] 0.75 million years.

Author(s): Jamie I. Farquharson [sup.1] , Falk Amelung [sup.1] Author Affiliations: (1) Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, USA Main Compelling evidence exists for seismicity [...], The May 2018 rift intrusion and eruption of Kilauea Volcano, Hawai'i, represented one of its most extraordinary eruptive sequences in at least 200 years, yet the trigger mechanism remains elusive.sup.1. The event was preceded by several months of anomalously high precipitation. It has been proposed that rainfall can modulate shallow volcanic activity.sup.2,3, but it remains unknown whether it can have impacts at the greater depths associated with magma transport. Here we show that immediately before and during the eruption, infiltration of rainfall into Kilauea Volcano's subsurface increased pore pressure at depths of 1 to 3 kilometres by 0.1 to 1 kilopascals, to its highest pressure in almost 50 years. We propose that weakening and mechanical failure of the edifice was driven by changes in pore pressure within the rift zone, prompting opportunistic dyke intrusion and ultimately facilitating the eruption. A precipitation-induced eruption trigger is consistent with the lack of precursory summit inflation, showing that this intrusion--unlike others--was not caused by the forceful intrusion of new magma into the rift zone. Moreover, statistical analysis of historic eruption occurrence suggests that rainfall patterns contribute substantially to the timing and frequency of Kilauea's eruptions and intrusions. Thus, volcanic activity can be modulated by extreme rainfall triggering edifice rock failure--a factor that should be considered when assessing volcanic hazards. Notably, the increasingly extreme weather patterns associated with ongoing anthropogenic climate change could increase the potential for rainfall-triggered volcanic phenomena worldwide. Immediately before and during the eruption of Ki[combining macron]lauea Volcano in May 2018, anomalously high rainfall increased the pore pressure in the subsurface to its highest level in 50 years, causing weakening and mechanical failure of the edifice.

The tensile properties of coal under dynamic loading are important mechanical characteristics of coal and are highly important for controlling coal rock stability under impact loading conditions, selecting blasting engineering parameters, and studying the mechanism of rockburst disasters. To investigate the dynamic tensile failure process of coal subjected to impact loading, this study used high-speed photography and digital image correlation technology to capture the dynamic tensile failure of coal under impact loading. The dynamic tensile evolution was quantitatively analyzed from the beginning of coal sample being loaded to failure. The captured images of the coal were processed, and the fractal dimension was used to quantitatively describe the evolution of the coal surface cracks under impact loading. The following conclusions were drawn from the experimental results: (1) An empirical formula was established to describe the dynamic tensile strength characteristics of coal under different loading rates. (2) Under impact loading, the maximum strain of a Brazilian disc coal sample first appeared at the contact end between the sample and the incident rod. (3) Under impact loading, a Brazilian disc coal sample cracked from the center of the sample outward, and the crack subsequently extended toward both ends. The fractal dimension of the crack exhibited a power function relationship with time, and the variation range of the fractal dimension of the crack was 1.05-1.39., (© 2024. The Author(s).)

The lining structures of tunnels are typically constructed using sprayed or cast concrete materials, and their performance and quality during tunnel excavation and blasting are crucial for the stability and safety of tunnels. Therefore, the safe distance between the lining structure and blasting source should be determined to avoid concrete damage caused by blasting vibrations. In this study, taking the subway tunnel of Danshan Station in Qingdao as an example, the JH-2 model is introduced as the constitutive model of the tunnel blasting simulation, and the JH-2 model parameters of the local surrounding rock are obtained by experiments, and finally the numerical simulation and theoretical verification are carried out to study the safety distance of shotcrete under various safety judgment standards. The results indicate that the JH-2 model can effectively simulate the propagation of stress waves under different media conditions, and the closer the strength parameters and pressure constant of the lining structure are to those of the surrounding rock, the safer the concrete-rock bonding interface. During tunnel blasting construction using the ring blasting method, the peak particle velocity (PPV) of the lining structure increases with an increase in the arch angle. Based on the numerical simulation results, we recommend that concrete lining be constructed at a distance of at least 62 m from the blasting source to avoid damage caused by vibrations. The effect of concrete tensile failure caused by longitudinal stress is much smaller than the damage to the bonding interface caused by the PPV and can be neglected., (© 2024. The Author(s).)

In order to study the failure mode and fracture evolution characteristics of red shale in Kaiyang Phosphorus mining area, conventional triaxial compression mechanical tests of red shale with different bedding dip angles were carried out by using DSTD-1000 electro-hydraulic servo rock mechanics experiment system. Based on the laboratory test results, the conventional triaxial particle flow simulation of red shale samples with different bedding dip angles was carried out using discrete element PFC2D. The results show that: (1) the failure mode of red shale is controlled by bedrock when the bedding dip angle is 0° and 60° ~ 90°. When the bedding dip angle is 15° ~ 45°, the rock failure mode is controlled by bedding. The compressive strength of rock is the minimum when the bedding dip angle is 30°and the maximum at 0°, which is about 2 times of the minimum. (2) In the failure process of red shale, the cracks with different bedding dip angles show slow growth stage, accelerated growth stage and stable stage with axial strain. The whole failure process is dominated by tensile cracks, accompanied by a few shear cracks. (3) The type of displacement field varies with the bedding dip angle: tensile failure and shear failure are the main displacement field types at 15° ~ 45°, and mixed failure is often the main mode at 60° ~ 90°and 0°. The research results provide the basis and reference for the safety control of red shale roadway., (© 2024. The Author(s).)

A two-dimensional unsteady seepage model for coal using a finite element program is developed, and the temporal variations of key factors such as water pressure and hydraulic gradient are analyzed in this paper. Additionally, the triaxial rock mechanical experiment and utilized pneumatic fracturing equipment on raw coal samples to investigate both hydraulic and pneumatic fracturing processes are conducted. Through these experiments, the relationship between pressure and crack formation and expansion are examined. The analysis reveals that the pore pressure gradient at the coal inlet reaches its peak during rapid surges in water pressure but diminishes over time. Conversely, the pore pressure gradient at the outlet side exhibits a gradual increase. Hydraulic fracturing is most likely to occur at the water inlet during sudden increases in water pressure. Besides, as the permeability of coal decreases, the duration for seepage stabilization prolongs due to the intensified pore pressure gradient resulting from sudden increases in water pressure. Moreover, an extended period of high hydraulic gradient further increases the risk of hydraulic fracturing. The experimental findings indicate that coal samples initially experience tensile failure influenced by water and air pressure. Subsequently, mode I cracks form under pressure, propagating along the fracture surface and becoming visible. The main types of failure observed in hydraulic and pneumatic fracturing are diametrical tensile failure, and the development of fractures can be categorized into three distinct stages, which contains the initial stage characterized by slight volume changes while water pressure increases, the expansion stage when pressure reaches the failure strength, and the crack closure stage marked by little or even decreasing volume changes during pressure unloading. The acoustic emission signal accurately corresponds to these three stages., (© 2024. The Author(s).)

Author(s): Jianwei Song [1]; Chaoji Chen [1]; Shuze Zhu [2]; Mingwei Zhu [1]; Jiaqi Dai [1]; Upamanyu Ray [2]; Yiju Li [1]; Yudi Kuang [1]; Yongfeng Li [1]; Nelson Quispe [...]

Studying the failure characteristics of the common composite strata structure in western China is essential for evaluating stope stability and predicting coal mine dynamic disasters. To investigate the influence of different stress loading and unloading conditions on the instability characteristics of composite samples, three triaxial loading and unloading test schemes simulating different in-situ mining depths were designed. Complex triaxial tests were conducted on 12 sets of composite samples, and the bearing capacity, acoustic emission (AE) parameters and dynamic multifractal characteristics of the samples under different stress loading or unloading conditions were analyzed. The results indicate that samples tested by stress schemes simulating greater mining depths exhibit less damage, and the failure mode is a tensile-shear mixed failure, but the tensile failure is the main failure mode. The multifractal spectral parameters Δ α of AE time series during the failure of composite samples tested with triaxial loading and unloading schemes simulating different mining depths show a decreasing trend in Δ α values with increasing mining depth, while the change rules of Δ f α values are the opposite. The multifractal parameter changes degree in four-layer rock structure composite samples under different stress conditions are lower than those in three-layer rock structure composite samples, indicating that the microcrack propagation process in the three-layer composite sample is more complex, resulting in higher levels of damage. The dynamic change of multifractal parameters Δ α and Δ f α during different stress loading and unloading stages reflects the influence of axial pressure or confining pressure changes on crack propagation in composite samples. Compared to the initial stress stage, the non-uniformity of AE signals increases in the residual stress stage, and the proportion of large signals becomes more prominent, signifying a complex micro-fracture process in the composite samples., (© 2024. The Author(s).)

In the present study, the effect of mild to high-temperature regimes on the quasi-static and dynamic tensile behaviours of Barakar sandstone from the Jharia coal mine fire region has been experimentally investigated. The experimental work has been performed on Brazilian disk specimens of Barakar sandstone, which are thermally treated up to 800 °C. The quasi-static and dynamic split tensile strength tests were carried out on a servo-controlled universal testing machine and Split Hopkinson Pressure Bar (SHPB), respectively. Microscopic and mineralogical changes were studied through a petrographic investigation. The experimental results suggest the prevalence of both, static and dynamic loading scenarios after 400 °C. Up to 400 °C, the quasi-static and dynamic tensile strengths increased due to the evaporation of water, which suggests a strengthening effect. However, beyond 400 °C, both strengths decreased significantly as newly formed thermal microcracks became prevalent. The dynamic tensile strength exhibits strain rate sensitivity up to 400 °C, although it shows a marginal decline in this sensitivity beyond this temperature threshold. The Dynamic Increase Factor (DIF) remained constant up to 400 °C and slightly increased after 400 °C. Furthermore, the characteristic strain rate at which the dynamic strength becomes twice the quasi-static strength remains consistent until reaching 400 °C but steadily decreases beyond this temperature. This experimental study represents the first attempt to validate the Kimberley model specifically for thermally treated rocks. Interestingly, the presence of water did not have a significant impact on the failure modes up to 400 °C, as the samples exhibited a dominant tensile failure mode, breaking into two halves with fewer fragments. However, as temperature increased, the failure behaviours became more complex due to the combined influence of thermally induced microcracks and the applied impact load. Cracks initially formed at the centre and subsequently, multiple shear cracks emerged and propagated in the loading direction, resulting in a high degree of fragmentation. This study also demonstrates that shear failure is not solely dependent on the loading rate but can also be influenced by temperature, further affecting the failure mode of the sandstone., (© 2024. The Author(s).)

Along the neck of 67P's nucleus (the Hapi region) are two straight cracks, each a few hundred metres long and separated from each other by 750 metres (Fig. 1a, b) [...], The solid, central part of a comet--its nucleus--is subject to destructive processes (1,2), which cause nuclei to split at a rate of about 0.01 per year per comet (3). These destructive events are due to a range of possible thermophysical effects (4); however, the geophysical expressions of these effects are unknown. Separately, over two-thirds of comet nuclei that have been imaged at high resolution show bilobate shapes (5), including the nucleus of comet 67P/Churyumov-Gerasimenko (67P), visited by the Rosetta spacecraft. Analysis of the Rosetta observations suggests that 67P's components were brought together at low speed after their separate formation (6). Here, we study the structure and dynamics of 67P's nucleus. We find that sublimation torques have caused the nucleus to spin up in the past to form the large cracks observed on its neck. However, the chaotic evolution of its spin state has so far forestalled its splitting, although it should eventually reach a rapid enough spin rate to do so. Once this occurs, the separated components will be unable to escape each other; they will orbit each other for a time, ultimately undergoing a low-speed merger that will result in a new bilobate configuration. The components of four other imaged bilobate nuclei have volume ratios that are consistent with a similar reconfiguration cycle, pointing to such cycles as a fundamental process in the evolution of short-period comet nuclei. It has been shown (7,8) that comets were not strong contributors to the so-called late heavy bombardment about 4 billion years ago. The reconfiguration process suggested here would preferentially decimate comet nuclei during migration to the inner solar system, perhaps explaining this lack of a substantial cometary flux.

In order to study the axial tensile properties of polypropylene fiber reinforced concrete, an axial tensile test device for concrete is developed in this paper. The device is composed of three parts: rigid frame, spherical hinge and puller, and specimen fabrication part. The test device can accurately measure the tensile strength and peak tensile strain of concrete, and perfectly solves the eccentricity problem of concrete specimens under tension. It can measure the post peak segment tensile strain, such that the whole process tensile stress-strain curve can be obtained. The axial tensile test of polypropylene fiber concrete was carried out using the above test device, and the results show that the tensile strength of concrete can be clearly improved by adding polypropylene fiber, which makes the tensile failure of concrete show certain plastic characteristics. The test results show that with the increase in fiber content, the tensile strength of concrete increases first and then decreases. The effects of polypropylene fiber content and curing age on the tensile properties of concrete were studied and the optimum polypropylene fiber content was determined. When the fiber content is 0.9 kg/m 3 , the tensile strength of concrete reaches the maximum value. The splitting tensile test of concrete under the same condition was carried out simultaneously. The damage phenomenon and test results of the axial tensile test and splitting tensile test of concrete were compared and analyzed, and the applicability of the new developed device in the concrete axial tensile test was verified., (© 2023. Springer Nature Limited.)

To study the mechanism and performance of rock breakage by an undercutting disc cutter with advanced slotting, a three-dimensional numerical model of rock cutting by a disc cutter with advanced slotting assistance was established based on the discrete element method. The parallel bond constitutive model was selected to describe the micromechanical properties of rock. The correctness of the established numerical model is verified through rock breakage experiments, and the rock cutting process by the disc cutter was analyzed by a combination of the force chain and crack distribution. The influencing factors, such as advanced slotting depth, cutting thickness, rock strength, and cutter rotation speed, on rock cutting performance were investigated. The results show that a compact zone is gradually formed between the rock and disc cutter at the beginning, then a large number of microscopic tensile and shear cracks in the compact zone due to micro failure of rock are formed; the subsequent main rock fragment is mainly caused by tensile failure; advanced slotting can reduce the rock bearing capacity and bending resistance, the rock above the advanced slotting fractured easily due to its lower bending resistance, and the volume compact zone is relatively small. When the advanced slotting depth is equal to 12.5 mm, the propulsive force and specific energy consumption of rock cutting by the disc cutter are reduced by 61.6% and 16.5%, respectively. The propulsive force and specific energy consumption increase as the rock strength increases, but they tend to close when the rock strength is greater than 80 MPa, which indicates that advanced slotting assistance is more suitable for hard rock. The results obtained in this paper can provide the operating parameters determination under different factors to some extent of the undercutting disc cutter in a pre-cut condition, which further improve the rock breaking performance of mechanized cutter., (© 2023. The Author(s).)

A series of creep tests were carried out on sandstone specimens with different pre-peak instantaneous damage characteristics under different confining pressures. The results revealed that the creep stress was the key factor affecting the occurrence of the three stages of creep, and the steady-state creep rate increased exponentially with increasing creep stress. Under the same confining pressure, the larger the instantaneous damage of the rock specimen was, the more quickly creep failure occurred and the lower the creep failure stress was. For the pre-peak damaged rock specimens, the strain threshold for accelerating creep was the same for a given confining pressure. The strain threshold increased with increasing confining pressure. In addition, the long-term strength was determined using the isochronous stress-strain curve and the variation in the creep contribution factor. The results revealed that the long-term strength decreased gradually with increasing pre-peak instantaneous damage under lower confining pressures. However, the instantaneous damage had little effect on the long-term strength under higher confining pressures. Finally, the macro-micro-failure modes of the sandstone were analyzed according to the fracture morphology observed via scanning electron microscopy. It was found that the macroscale creep failure patterns of the sandstone specimens could be divided into a shear-dominated failure mode under high confining pressures and a mixed shear-tensile failure mode under low confining pressures. At the microscale, as the confining pressure increased, the micro-fracture mode of the sandstone changed gradually from a single brittle fracture to a mixed brittle and ductile fracture mode., (© 2023. The Author(s).)

Aiming at the problem of large deformation and difficulty in surrounding rock control of the top coal roadway in thick seam, theoretical analysis, theoretical analysis, numerical simulation, orthogonal matrix analysis and other methods were used to study the roof deformation and support parameter optimization of the top coal roadway in thick seam. Firstly, the structural model and roof mechanical model of the top coal roadway in thick seam were established, and the deformation coefficient T K was defined based on the relationship between curvature radius and bending moment, maximum bending moment and ultimate tensile strength of beam. According to the ratio of deformation rate between T K and beam to determine the roof deformation mode of top coal roadway, the discriminant conditions of roadway roof stability under two deformation conditions are obtained. Due to the characteristics of serious coal-rock fragmentation, large roof deformation, and integration of top coal and side coal. Therefore, the combined support method of "high prestressed long and short anchor cables" is proposed by double arch bearing structure control technology. Finally, based on the orthogonal matrix analysis method of supporting parameters optimization of the top coal roadway in thick seam, the analysis amount of supporting scheme is significantly reduced, the comprehensive evaluation of multi-factor and multi-supporting effect of roadway support is realized, and the optimal supporting scheme is obtained. Compared with the surrounding rock of the roadway without support, the deformation of the roof is reduced by 27.27%, the deformation of the two sides is reduced by 45.24%, and the tensile failure volume is reduced by 54.66%. The top coal roadway in thick seam has been effectively controlled, which provides guarantee for high yield and high efficiency of the mine., (© 2023. The Author(s).)

It has long been assumed that seismogenic faulting is confined to cool, brittle rocks, with a temperature upper limit of ~600°C (ref. 1). This thinking underpins our understanding of volcanic [...]

Author(s): Jonathan M. Ramsey [1, 2]; Frederick M. Chester (corresponding author) [1] Fracture is a fundamental mechanism of material failure. Two basic types of brittle fractures are commonly observed in [...]

Author(s): Hyoung-Joon Jin; David L. Kaplan (corresponding author) Silk spinning by insects and spiders leads to the formation of fibres that exhibit high strength and toughness [1]. The lack of [...]

In underground engineering, disturbance of dynamic load can change layered rock mass stress state and induce accidents. Traditional elastic mechanics can't effectively solve the complex deformation problem. However, Hamiltonian mechanics system can overcome this problem. Dual variables are introduced in symplectic space to solve the deflection equations of single-layered thin plate rock mass. Comparing vibration parameters, it's found the 1st, 5th and 6th order are effective vibration modes. The resonance characteristics of thin plate are obtained with three dynamic loads. It's found the thin plate is most likely to resonate and damage due to the smallest resonance frequency interval and the largest vibration amplitude by impact wave and rectangular wave respectively. Then, the vibration mode of multi-layered rock mass is analyzed through Multiple Reference Impact Testing. The failure of fine sandstone is caused by the resonance of effective vibration modes by hammer excitation. Finally, the failure mechanism of thin plate is obtained by the failure theory and LS-DYNA. It's found the four sides and corners suffer tensile shear failure and shear failure respectively. When tensile failure occurs in central, the main crack and secondary crack propagate along long axis and short axis to form "O-" failure mode., (© 2022. The Author(s).)

Circular saw blades are widely used in stone processing. The circular saw blade cutting hard rock numerical simulation model based on ANSYS/LS-DYNA was established to investigate the complex dynamic problem in rock cutting. The failure mechanism of the rock and the influence of cutting parameters on the cutting force and rock fragments were studied by numerical simulation. The results demonstrated that the failure modes of the rock were mainly tensile failure with some shear failure and compressive failure. The cutting force and the number of fragments increased with the feed speed. With the increasing circular saw blade rotational speed, the cutting force and the number of fragments decreased and tended to stabilize. With the distance between the circular saw blades increasing, the cutting force and rock fragments number increase and then maintain basic stability, and when the distance between double circular saw blades reaches 25 mm, it will form a completed rock plate and the interaction of circular saw blades will decrease. The numerical simulation can accurately simulate rock breakage and force when a circular saw blade cuts rock., (© 2022. The Author(s).)

Safe mud window (SMW) defines the allowable limits of the mud weights that can be used while drilling O&G wells. Controlling the mud weight within the SMW limits would help avoid many serious problems such as wellbore instability issues, loss of circulation, etc. SMW can be defined by the minimum mud weight below which shear failure (breakout) may occur (MW BO ) and the maximum mud weight above which tensile failure (breakdown) may occur (MW BD ). These limits can be determined from the geomechanical analysis of downhole formations. However, such analysis is not always accessible for most drilled wells. Therefore, in this study, a new approach is introduced to develop a new data-driven model to estimate the safe mud weight range in no time and without additional cost. New models were developed using an artificial neural network (ANN) to estimate both MW BO and MW BD directly from the logging data that are usually available for most wells. The ANN-based models were trained using actual data from a Middle Eastern field before being tested by an unseen dataset. The models achieved high accuracy exceeding 92% upon comparing the predicted and observed output values. Additionally, new equations were established based on the optimized ANN models' weights and biases whereby both MW BO and MW BD can be calculated without the need for any complicated codes. Finally, another dataset from the same field was then used to validate the new equations and the results demonstrated the high robustness of the new equations to estimate MW BO and MW BD with a low mean absolute percentage error of 0.60% at maximum. So, unlike the costly conventional approaches, the newly developed equations would facilitate determining the SMW limits in a timely and economically effective way, with high accuracy whenever the logging data are available., (© 2022. The Author(s).)

The ballistic performance of edge-clamped monolithic polyimide aerogel blocks (12 mm thickness) has been studied through a series of impact tests using a helium-filled gas gun connected to a vacuum chamber and a spherical steel projectile (approximately 3 mm diameter) with an impact velocity range of 150-1300 m s -1 . The aerogels had an average bulk density of 0.17 g cm -3 with high porosity of approximately 88%. The ballistic limit velocity of the aerogels was estimated to be in the range of 175-179 m s -1 . Moreover, the aerogels showed a robust ballistic energy absorption performance (e.g., at the impact velocity of 1283 m s -1 at least 18% of the impact energy was absorbed). At low impact velocities, the aerogels failed by ductile hole enlargement followed by a tensile failure. By contrast, at high impact velocities, the aerogels failed through an adiabatic shearing process. Given the substantially robust ballistic performance, the polyimide aerogels have a potential to combat multiple constraints such as cost, weight, and volume restrictions in aeronautical and aerospace applications with high blast resistance and ballistic performance requirements such as in stuffed Whipple shields for orbital debris containment application., (© 2022. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

When subjected to constant static load, after a period of damage accumulation and crack development, the rock will fail under a load lower than its compressive strength. The transform of loading rate may have a certain influence on the mechanical properties of rock. In order to investigate the effect of loading rate on mechanical properties of red sandstone, the propagation form of internal cracks in the subcritical propagation stage in rock under static loading is defined as tensile. Based on Maxwell model, the expression of effective tensile stress for crack extension in rock is deduced, which explains the phenomenon of rock tensile failure. Based on the uniaxial compression test of red sandstone under different loading rates, and the surface deformation field of specimens is analysed with the method of digital image correlation, and the corresponding relationship between the loading rate effect and the change of mechanical properties as well as the energy accumulation and release characteristics is analysed, the phenomenon of rock tensile failure is further verified. This research can be effectively applied to geotechnical engineering disaster warning., (© 2022. The Author(s).)

Instability failure in rock mass engineering is closely related to expansion of joint fissures. In this study, uniaxial compression tests and acoustic emission (AE) measurements were carried out simultaneously on specimens of soft rock-like material with different fracture angles and connectivity values to better understand their influence on the deformation and failure of the material. The stress-strain curve and AE signal of fractured soft rock-like material are similar to those of intact soft rock-like; specifically, they exhibit a compaction, elastic deformation, stable fracture development, and unstable fracture development. The main differences between fractured and intact material occur during post-peak failure stage. Under the combined influence of fracture angle and connectivity, the uniaxial compressive strength of fractured soft rock-like material ([Formula: see text]) is lower than that of the intact soft rock-like material (f cu ), and can be described by the relationship [Formula: see text], where [Formula: see text] is the strength reduction coefficient, fitted as [Formula: see text]. In this equation, x is the fracture angle ([Formula: see text]) and y is the fracture connectivity (%). Under uniaxial compression, the main types of secondary cracks were wing cracks and secondary coplanar cracks. The specimen with a fracture angle of 30° mainly underwent tensile failure under loading, whereas those with fracture angles of 45° and 60°mainly experienced shear failure under high-connectivity conditions (45%)., (© 2022. The Author(s).)

Geo-materials may present varying mechanical properties under different stress paths, especially for tunnel excavation, which is typically characterized by the decreased radial stress and increased axial stress during the complex loading and unloading process. This study carried out a comparative analysis between the loading and unloading model testing, which was then combined with PFC 2D simulation, aiming to reveal the fracture propagation pattern, microscopic stress and force chain distribution of the rock mass surrounding the tunnel. Comparisons of extents and development of tensile strain between loading and unloading testing results were made. The overall stability, the integrity of rock mass, and the failure pattern transition under loading and unloading processes were systematically examined. In addition, for the two unloading cases with different vertical stresses imposed, the failure patterns were both identified as the collapse of the V - shaped extruded sidewall, due to the coupling of the shear failure and the vertical tensile failure in the sidewall wedge., (© 2021. The Author(s).)

Disc coal samples with different water content were tested using the split Hopkinson press bar test system. Their dynamic tensile failure process was monitored via an ultra-high-speed digital image correlation system. The deformation trend and failure characteristics as a function of the water content were analyzed, and the water content effect on dynamic mechanical properties was investigated. The results demonstrated that the dynamic stress-strain curve of the coal samples consisted of four stages. As the water content increased, the coal sample brittleness degraded, while its ductility was enhanced. Quadratic polynomial functions can describe dynamic peak stress, peak strain, and loading pressure. Under different loading pressures, the dynamic peak stress exhibited a concave bending trend as the water content increased. The coal sample's dynamic tensile strength had a strong rate correlation, and the saturated coal sample exhibited the highest rate correlation. Under high-rate loading, the inertia effect and the Stefan effect of water in coal samples hinder the initiation and propagation of coal sample cracks, improving the coal sample's strength. The research results provide a basic theoretical basis for the prevention and control of rock burst in coal mines.

Based on the engineering environment where rocks surrounding wellbores in energy storage areas are influenced by high temperature, cool and hot water, thermal stress etc. in the exploitation of hydrothermally geothermal energy, the experimental study on mechanical properties of ring granite under the static and dynamic loads in the water-heat condition was performed. The experimental results showed that when the ring granite was influenced by the inner diameters, heating temperatures, curing temperatures and heat recovery cycle times, the impact load-strain curves were nonlinear. However, the concave stages, platform stages and cliff-like drop stages appeared in the load-strain curves under the static loads. The radical peak loads decreased exponentially with the growth of the damage factors and the dynamic peak loads were far greater than the static peak loads. By analyzing the damage cracks and broken fragments, it was found that under the static and dynamic radical loads, the cracks generated in the ring specimens were tensile cracks and the failure mode was tensile failure. However, the dynamic failure was more aggressive than the static failure. Then, the apparent deformation modulus was defined to describe the deformation characteristics of ring granite before the radical peak loads. And it is found that the variation law of dynamic apparent deformation modulus is more dispersed than the changes of static apparent deformation modulus. Finally, based on the deformation and failure characteristics of ring granite obtained from the tests, the static and dynamic failure criteria considering whether the cracks along the loading direction were generated in the inner ring wall were deduced and verified by the corresponding tests.