Macroscopic Surface Research Articles

Fracture Process of Rock Containing a Hole Before and After Reinforcement: Experimental Test and Numerical Simulation

A deeper understanding of the fracture evolution of hole-containing rocks is helpful for predicting the fracture of engineering rock mass. Based on this, uniaxial compression tests and two-dimensional numerical tests were conducted on red sandstone containing three different shapes of holes before and after reinforcement. The mechanical properties, stress field evolution, and AE energy and AE events during the sample fracture process were studied. The conclusions are that: (1) The reinforced specimens exhibited a significant increase in Young’s modulus and strength compared to the unreinforced specimens (containing a semicircular arch hole). (2) The sample always cracks from the loaded axial direction of the hole, presenting as tensile cracks. Subsequently, stress concentration at the corners of the hole results in shear cracks. Finally, the cracks gradually expand and merge with the holes; there are obvious macroscopic cracks and fracture surfaces on the sample surface, which proves that the sample has been fractured. (3) The reinforcement of the hole-containing sandstone can effectively inhibit the expansion of cracks in the rock. (4) When the stress on the specimen is less than its peak stress, the accumulation of the AE energy and AE events in the reinforced sample are greater than those in the unreinforced sample. The specimen experiences more intense compression-induced fracturing and has a stronger load-bearing capacity.

Mechanical and Physicochemical Properties of Ti6Al4V Alloy After Plastic Working and 3D Printing Intended for Orthopedics Implants

The aim of this study was to compare the mechanical and physicochemical properties of Ti6Al4V alloy samples produced using 3D printing (Direct Metal Laser Sintering) and bar after plastic working. Both sets of samples were subjected to various surface-processing methods, including sandblasting, heat treatment (hardening for 120 min at 820 ± 10 °C, followed by cooling to room temperature), mechanical polishing, and steam sterilization. This research included macroscopic surface evaluation before and after pitting corrosion resistance tests, metallographic microscopic research, scanning electron microscopy, and energy-dispersive spectroscopy, as well as measurements of hardness, roughness, and surface wettability. The results showed that heat and surface treatment (grinding and mechanical polishing) significantly increased the material’s hardness and corrosion resistance. Furthermore, the steam sterilization process had a positive effect by increasing surface wettability, which is important for biomedical applications, as higher wettability promotes better integration with biological tissues. This is especially relevant in implantology, where surface properties influence osseointegration and overall biocompatibility. In summary, these findings indicate that the selection of manufacturing method and the application of subsequent treatment processes significantly affect the mechanical and physicochemical properties of Ti6Al4V alloy, thereby influencing its performance and suitability for diverse engineering and biomedical applications.

Characteristics of rock strength failure and identification of hazardous areas in the roof of deep mining stope

The roof of deep mining stopes is notoriously unstable and challenging to manage due to high in-situ stress and deteriorating rock conditions. To address this issue, a comprehensive approach was employed, incorporating indoor physical experiments, numerical simulations, and field tests to investigate the stope roof rock composition characteristics and strength failure modes in the Laoyingshan deep coal mine. The study revealed the distribution characteristics of the high in-situ stress field in this mining area and delineated different levels of hazards in the roof. The results indicate that, under identical lithological conditions, the mineral composition of deep rock formations is complex. Changes in some mineral components and properties were observed, leading to increased expansiveness and water absorption in clay minerals such as sodium montmorillonite and kaolinite within the basic roof layer. In simulated tests of surrounding rock strength in deep mining stopes, as stress levels approached 2 MPa, the damage factor increased, showing a trend of localized concentration. Internal damage began to exhibit noticeable spatial evolutionary expansion patterns and gradual nucleation. When stress exceeded 8 MPa, rocks transitioned from macroscopic fracture surfaces to microscopic fragmentation zones, with a sudden decrease in stiffness degradation values, internal instantaneous collapse, and phenomena akin to “rock burst” under high stress disturbance. In-situ stress testing determined that the stress field in the deep mining zone of Laoyingshan is in a thrust fault stress state, with horizontal stress predominance. The maximum stress direction is predominantly southwest-northeast, with stress magnitude reaching 25.49 MPa. By arranging post-mining and pre-mining borehole observation stations and utilizing image grayscale fracture recognition technology in MATLAB, the roof was classified into four danger levels: “extremely broken,” “broken,” “significant fractures,” and “minor fractures.” Main control measures for coupling grouting in deep-shallow zonation rigidity were proposed based on these classifications.

The influence of laser process parameters on the Iron loss of grain-oriented silicon steel

Laser scribing effectively reduces the energy loss of grain-oriented silicon steel in alternating and pulsating magnetic fields. This study focuses on the 27Q120 material, analyzes the macroscopic surface morphology and iron loss variations of grain-oriented silicon steel under the influence of two types of laser spots (circular spots without the application of a diffractive optical element (DOE) and rectangular spots formed by a DOE), laser power (600W to 2400W), and scribing spacing (3.5mm to 7.5mm) as process parameters. The relationship between magnetic domain width, stress, and iron loss was analyzed. The result shows that the iron loss improvement rates (β) achieved with circular and rectangular spot scribing were 16.054% and 17.116%, respectively. Corresponding magnetic domain widths were 0.17754 mm and 0.1636 mm, with hysteresis losses of 0.5114 W/kg and 0.5033 W/kg, respectively. Under the same laser power and scribing spacing, a lower energy density significantly reduced the damage to the surface macroscopic morphology by the laser, leading to improved iron loss. Furthermore, the iron loss of grain-oriented steel is positively correlated with the width of magnetic domains and negatively correlated with compressive stress.

Research on Deterioration Behavior of Magnesium Oxychloride Cement Under High Humidity and High Temperature.

To clarify the deterioration behavior of magnesium oxychloride cement (MOC) under conditions of high humidity and high temperature, we first placed MOC slurry samples in a simulated environment with a relative humidity of 97 ± 1% and a temperature of 38 ± 2 °C; then, we observed the changes in the macroscopic and microscopic morphology, water erosion depth, bulk density, phase composition, and mechanical properties of the samples. The results show that, over time, under the promotion of high temperature, water molecules infiltrate the MOC samples. This results in the appearance of cracks on the macroscopic surface of the MOC samples due to the volume expansion caused by the hydrolysis of P5 (5Mg(OH)2·MgCl2·8H2O) and the hydration of unreacted active MgO in the samples. The microscopic morphology of the samples changes from needle/gel-like, to flake-like, and finally leaf-like. Simultaneously, the major phase composition turns into Mg(OH)2. Since the structure of the samples becomes looser and the content of the main strength phase decreases, the overall compressive strength and flexural strength are both reduced. The compressive strength of the MOC slurry samples (0 day) is 93.2 Mpa, and the flexural strength is 16.4 MPa. However, after 18 days of treatment, water molecules reach the center of the MOC samples, and the MOC samples completely lose their integrity. As a result, their compressive and flexural strengths cannot be obtained.

Effect of Coarse Aggregate Type on the Fracture Toughness of Ordinary Concrete

This research work aims to compare the strength and fracture mechanics properties of plain concretes, obtained from different coarse aggregates. During the study, mechanical parameters including compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture parameters involving critical stress intensity factor (KIcS) and critical crack tip opening displacement (CTODc) were evaluated. The effect of the aggregates used on the brittleness of the concretes was also analyzed. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Crushed aggregates covered were basalt (BA), granite (GT), and limestone (LM), and natural peeble gravel aggregate (GL) were used in the concrete mixtures. Fracture toughness tests were performed on an MTS 810 testing machine. Due to the high strength of the rock material, the rough surface of the aggregate grains, and good bonding in the ITZ area between the aggregate and the paste, the concretes with crushed aggregates exhibited high fracture toughness. Both of the analyzed fracture mechanics parameters, i.e., KIcS and CTODc, increased significantly in the case of concretes which were manufactured with crushed aggregates. They amounted, in comparison to concrete based on gravel aggregate, to levels ranging from 20% for concrete with limestone aggregate to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. On the other hand, the concrete with gravel aggregate showed the lowest fracture toughness because of the smooth surface of the aggregate grains and poor bonding between the aggregate and the cement paste. However, the fracture process in each series of concrete was quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregates. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending.

Comparison of fracture behavior of set concretes based on natural and crushed aggregates

Abstract The studies were carried out to diagnose the effects of coarse aggregate type on the mechanical behavior of plain concretes under incremental loading. During the studies mechanical parameters including compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture parameters involving critical stress intensity factor (K_Ic^S) and critical crack tip opening displacement (CTODc) were evaluated. Crushed aggregates covered: basalt (BA), granite (GT) and limestone (LM) and natural peeble gravel aggregate (GL) were used in the concrete mixtures. The composite made on pebble aggregate acted as a reference concrete, as it were, in the analysis of the test results. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Both of the analyzed fracture mechanics parameters, i.e. 〖 K〗_Ic^S and CTODc increased significantly in the case of concretes which were manufactured based on crushed aggregates. They amounted in comparison to concrete based on gravel aggregate at levels ranging from 20% for concrete with limestone aggregate, to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. Moreover, a clear correlation in the changes in the obtained results between the main strength parameters and fracture mechanics parameters was observed. The fracture process in each series of concrete was: quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregate. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending.

Effect of macro- and micro-morphology on fluid film properties based on plasto-elastohydrodynamic lubrication

Purpose The developed plasto-elastohydrodynamic lubrication (PEHL) model is used to demonstrate the permanent change of macro morphology by critical high local stress at micro asperities in contact, which may further affect the fluid-film characteristics. Design/methodology/approach Geometric morphology is integrated into the PEHL model to elucidate the fluid-film properties governed by both macro- and micromorphologies. Findings Results show the model, accounting for combination of elastic and plastic deformations, realistically reveals fluid film distribution affected by the significant pressure highly concentrated within surface micro roughness interaction. The designed macroscopic textured surface mitigates the fluid film rupture phenomenon and prevents accumulated wear degradation from plastic deformation. Originality/value The PEHL model takes into account both elastic and plastic deformations and realistically reveals the fluid film distribution affected by large pressures that are highly concentrated in surface micro-roughness interactions. The macro-textured surfaces are designed to mitigate fluid film rupture phenomena and prevent cumulative wear caused by plastic deformation. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2024-0170/

Cracking the physical insight of power law models: Bridging the gap between macroscopic kinetics and surface coverages

AbstractWe propose a methodological framework to quantify the relative abundance of key surface intermediates via analysis of the macroscopic intrinsic kinetic characteristics of gas‐phase data. At the core of this approach is the development of analytical expressions, which link reaction orders and activation energies in macroscopic power law models to the fractional coverage of the non‐observable intermediates. Through the design of an advanced parameter estimation methodology, these relationships were further exploited to develop thermodynamically consistent and mechanistic‐based power law models which could capture the evolution of surface occupancy profiles along the reactor length. The developed framework was tested through in‐silico water gas shift reaction case‐studies; the results indicate the robustness of the approach and the mechanistic insight that can be gained from its application. The methodology proposed in this study could thus be of general value to assist in reaction mechanism analysis, identification of key surface intermediates, and reactor optimization.

Fatigue mechanical properties and Kaiser effect characteristics of the saturated weakly cemented sandstone under different loading rate conditions

Weakly cemented sandstone (WCS) is a unique rock type widely distributed on the surface. Environmental factors such as groundwater and stress variations easily influence its fatigue mechanical properties and fracture characteristics. To design and evaluate the long-term stability of surrounding rock support in tunnel excavation and underground resource mining projects, investigating the fatigue mechanical properties and acoustic emission (AE) response characteristics of saturated WCS under different loading rates is of great practical and theoretical significance. This study employed experimental techniques such as X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and natural water absorption tests to investigate the mineral composition, pore size, and connectivity characteristics of WCS. The multi-level cyclic loading-unloading tests (MCLU) combined with the AE system were conducted on dry and saturated WCS specimens at different loading rates. The results reveal that the deformation modulus of these specimens initially increases and then decreases under cyclic loading conditions. Water significantly influences the fatigue strength and deformation resistance of sandstone. As the loading rate increases, the range of RA values broadens, accompanied by a marked increase in the number of AE signals with high RA values. Saturated sandstone specimens are more prone to developing macroscopic shear fracture surfaces. Water has a more substantial effect on the stress distribution ranges corresponding to the response of the Kaiser effect in WCS than loading rates. The capacity of the Kaiser effect to indicate the extent of rock damage is intricately linked to the progression of internal micro-cracks. When internal damage surpasses the critical value of the Kaiser effect memory damage, the accelerated propagation of shear cracks becomes pivotal in the internal damage of the sandstone. It seems that the presence of water within the interior of the rock may facilitate the dissolution of K-feldspar in WCS, which could result in the formation of kaolinite, which will be further transformed into illite. The hydration expansion of illite may further exacerbate the deterioration effect of the mechanical properties of WCS.

Multiscale contact homogenisation: A novel perspective through the method of multiscale virtual power

The interaction between deformable bodies and rigid foundations undergoing finite strains is explored in this work with the Method of Multiscale Virtual Power, unlocking novel insights into contact homogenisation theories. The focus lies in establishing the foundational kinematical links across scales and achieving seamless homogenisation of the traction vector through rigorous duality arguments. Two distinct families of contact homogenisation models are formulated: surface–surface and surface–volume models. These families emerge from the virtual power balance established between the target macroscopic surface and the corresponding microscopic contact surface or volume. They not only represent fundamental kinematical entities at each scale but also enable the replacement of the heterogeneous contact traction distribution with a smooth, homogenised version. Microscale equilibrium problems and homogenisation relations, along with the relevant macro- and microscale quantities, are derived by means of straightforward variational arguments. Furthermore, potential finite size effects are addressed in the homogenised response, enhancing the reliability and applicability of the strategy across diverse scenarios. Promising submodels have been identified within both families, broadening the understanding of multiscale contact phenomena and including existing models as particular cases. The proposed continuum-based variational families of models naturally lead to generic finite element-based frameworks for contact homogenisation of heterogeneous solids, as described in a forthcoming paper.

Magnetic and ultrasonic vibration dual-field assisted ultra-precision diamond cutting of high-entropy alloys

Despite the remarkable achievements in single-energy field-assisted diamond cutting technology, its performance remains unsatisfactory for processing high-entropy alloys (HEAs), targeted for next-generation large-scale industrial applications due to their exceptional properties. The challenge lies in overcoming the limitations of current single-energy field-assisted processing to achieve ultra-precision manufacturing of these advanced materials. This study proposes a multi-energy field-assisted ultra-precision machining technology, the magnetic and ultrasonic vibration dual-field assisted diamond cutting (MUVFDC), to address the current challenges. The phenomenological aspects of the dual-field coupling effect on HEAs are explored and investigated through comprehensive characterization of the workpiece material, ranging from macroscopic surface morphology to microscopic structural features. These analyses are performed based on experimental results from four different processing technologies: non-energy field, magnetic field, ultrasonic vibration field, and dual-field assisted machining. Research results demonstrate that MUVFDC technology effectively combines the advantages of a vibration field, which enhances cutting stability, and a magnetic field, which improves the machinability of materials. Additionally, this coupling technology addresses the challenges associated with single-energy field machining: it mitigates the difficulty of controlling surface scratches caused by tiny hard particles in a vibration field and suppresses the rapid tool wear encountered in a magnetic field. Furthermore, the gradient evolution of the subsurface microstructure reveals that the vibration field suppresses the severe matrix deformation induced by magnetic excitation. Simultaneously, the magnetic field reduces the size inhomogeneity of recrystallized grains caused by intermittent cutting. Overall, MUVFDC technology enhances surface quality, suppresses tool wear, smooths chip morphology, and reduces subsurface damage compared to single-energy field or non-energy-assisted machining. This work breaks through the performance limitations of traditional single-energy field-assisted processing and advances the understanding of the dual-field coupling effects in HEAs machining. It also presents a promising processing technology for the future ultra-precision manufacturing of advanced materials.

Unveiling the Mechanisms of the 1819 M 7.7 Kachchh Earthquake, India: Integrating Physics‐Based Simulation and Strong Ground Motion Estimates

AbstractThis study provided a comprehensive understanding of the source process of the 1819 M 7.7 Kachchh Indian earthquake using physics‐based dynamic rupture modeling and strong ground motion simulations. We successfully simulated the spontaneous dynamic rupture along a curved non‐planar fault using the 3‐D curved‐grid finite‐difference method (CGFDM). The estimated earthquake magnitude is around 7.6, consistent with previous estimations. Our simulations accurately replicated macroscopic rupture patterns and surface deformation, showing agreement with observed data along the Allah Bund fault (ABF) with a maximum displacement ∼5.5 m at the Earth's surface. The maximum modeled coseismic slip on the fault was approximately 7.5 m. Notably, the ABF exhibited characteristics of a weak barrier (leaky barrier) at the bending part, allowing the rupture to propagate further. Despite limitations in surface deformation calculations, the modeled values aligned with the trend of surface fault slip, with a slight deviation in the epicenter toward the east compared to earlier studies. We observed a homogeneous principal stress oriented N25°E, consistent with the present day Indian plate motion. The estimated horizontal peak ground velocities (PGVh) and the maximum value of Intensity X+ aligns well with observations. Furthermore, conducting thorough case studies on significant earthquakes and potential seismic scenarios in stable continental regions is crucial. Such studies play a vital role in validating and improving dynamic rupture models. When combined with statistical methods, this research holds great promise for advancing seismic hazard assessments, earthquake engineering, and strategies for disaster management.

Analysis of interfacial effect and boundary layer for forced convection on the macroscopic hydrophilic-hydrophobic hybrid surface: A large eddy simulation

Hydrophilic-hydrophobic hybrid surfaces are developed to solve the flow and heat transfer performance contradiction. However, hybrid surfaces often have micro- or nano-scale featured sizes and are used in phase change heat transfer because hydrophilic regions contribute to droplet nucleation, and hydrophobic regions contribute to bubble nucleation. In this study, large eddy simulation is used to investigate the forced convection on macroscopic hydrophilic-hydrophobic hybrid surfaces where only the surface local wettability is changed. Three hybrid surfaces with different hydrophilic-hydrophobic ratios and two homogeneous wettability surfaces are designed, and representative flow Reynolds numbers of 4000, 6000, 10 000, and 40 000 are explored to achieve different turbulent styles. The transient parameters of kinematics, vorticity, and boundary layer are analyzed to clarify the mechanism of turbulence change and eddy generation and explain the causes of variations in flow and heat transfer performances. It proves that macroscopic hydrophilic-hydrophobic hybrid surfaces are suitable for forced convection due to the drag reduction on hydrophobic regions, backflows at hydrophilic-hydrophobic interfaces, and eddies at hydrophobic-hydrophilic interfaces, which can enhance the internal disturbance and harmonize the flow and heat transfer performances. The mechanism has a profound significance in broadening the application of hydrophilic-hydrophobic hybrid surfaces and designing the arrangement of hydrophobic regions.

Stimuli-Responsive Ion Transport Regulation in Nanochannels by Adhesion-Induced Functionalization of Macroscopic Outer Surface.

Responsive regulation of ion transport through nanochannels is crucial in the design of smart nanofluidic devices for sequencing, sensing, and water-energy nexus. Functionalization of the inner wall of the nanochannel enhances interaction with ions and fluid but restricts versatile chemical approaches and accurate characterizations of fluidic interfaces. Herein, we reveal a responsive regulating mechanism of ion transport through nanochannels by polydopamine (PDA)-induced functionalization on the macroscopic outer surface of nanochannels. Responsive molecules were codeposited with PDA on the outer surface of nanochannels and formed a valve of nanometer thickness to manually manipulate ion transport by changing its gap spacing, surface charge, and wettability under external stimulus. The response ratio can be up to 100-fold by maximizing the proportion of responsive molecules on the outer surface. Laminating the codepositions of different responsive molecules with PDA on the channel's outer surface produces multiple responses. A nearly universal adhesion of PDA with responsive molecules on the open outer surface induces nanochannels responsive to different external stimuli with variable response ratios and arbitrary combinations. The results challenge the primary role of functionalization on the nanoconfined interface of nanofluidics and open opportunities for developing new-style nanofluidic devices through the functionalization of macroscopic interface.

Improved Ga2O3 films on variously oriented Si substrates with Al2O3 or HfO2 buffer layer via atomic layer deposition

Ga2O3 is an ultrawide-band-gap semiconductor with excellent properties and promising applications in the electronic and optoelectronics. For acting as the substrate for heteroepitaxial Ga2O3 films, Si has the advantages of wafer-level size, cheap price and nice compatibility whereas also perform the disadvantage of large thermal mismatch. In this paper, the apparent flower-like defects are exhibited on the macroscopic surfaces of annealed Ga2O3 films deposited on (100), (110) and (111) oriented Si substrates by atomic layer deposition (ALD) method. The reason is ascribed to the different thermal expansion coefficients between Ga2O3 and Si induced compressive and tensile stresses. The Al2O3 or HfO2 buffer layer intercalated between Ga2O3 films and Si substrates via successive ALD process suppress the flower-like defects effectively while the surface roughnesses are low to be 1.290 nm and 2.393 nm, respectively. XRD spectra demonstrate that buffer layer indeed relieves the stress of Ga2O3 films on Si substrates while the amorphous Al2O3 has better influence than the polycrystalline HfO2. The results are helpful to the improvement of growth quality and device property of Ga2O3.

Establishing the relationship between generalized crystallographic texture and macroscopic yield surfaces using partial input convex neural networks

In this study, we present a methodology to predict the macroscopic yield surface of metals and metallic alloys with general crystallographic textures. In previous work, we have established the use of partially input convex neural networks (pICNN) as macroscopic yield functions of crystal plasticity simulations. However, this work was performed with an over-abundance of data, and on limited crystallographic textures. Here, we extend this study to approach more realistic material states (i.e., complex crystallographic textures), and consider data-availability as a major driver for our approach. We present our modified framework capable of handling generalized material states and demonstrate its effectiveness on samples with multi-modal textures deformed under plane stress conditions. We further describe an adaptive algorithm for the generation of training data as informed by the shape of yield surfaces to reduce the time for both the generation of training data as well as pICNN training. Finally, we will discuss errors in both training and test datasets, limitations, and future extensibility.

Observations on Macroscopic Surface Modification and Oxidation of Tungsten and Tungsten Carbide in Laser Focus in Air

Tungsten and tungsten carbide were damaged in ambient air with varying incident angles (0, 30, 45, and 60 deg) for approximately 5000 shots. The goal of these experiments was to observe the macroscopic surface modification in tungsten and tungsten carbide surfaces in harsh environments. At low pulse numbers (one to eight laser pulses on the same spot), tungsten aerial surface damage was less than tungsten carbide damage; however, at very high pulse numbers (5000), the opposite was true. Surface damage was mostly in the form of craters that were near circular at low impact angles and became more elongated at higher laser pulse impact angles. On the tungsten surface, a cluster of tungsten oxide debris formed. During laser exposure, laser-induced periodic surface structures and grooves were formed, and their geometries varied with laser intensity and laser impact angle. The period of laser-induced surface changes increased as the incident angle increased for both tungsten and tungsten carbide surfaces. More mass was lost in tungsten than tungsten carbide, which agrees with the morphological responses.

Constraining Shear Strength of Fault Damage Zone Using Geodetic Data and Numerical Simulation

AbstractShear strength of damage zone, representing the stress threshold for rupture initiation, is a critical parameter in faulting mechanics. Despite its significance, the damage‐zone's shear strength has not been estimated in natural earthquake ruptures. Here we employed coseismic deformation and strain, kinematic slip model, and finite element modeling to determine the elastic properties and peak shear stress of coseismic damage zones along the 2021 Mw 7.4 Maduo earthquake. Through the analysis of the lowest shear stress resulting in surface ruptures and the highest stress without surface rupture, we constrained the strength within a range of 7–17 MPa. Our result is consistent with strength (5–16 MPa) of sandstone samples from laboratory tests, demonstrating the validity of this estimation. Although factors such as fault maturity and confining pressure influence strength variation, the strength can directly reflect the stress threshold required for macroscopic surface rupture formation in fault damage zones dominated by sandstone.

Experimental Study on Energy Release Mechanism and Crack Propagation Evolution of Sandstone under True Triaxial Loading

The instability of hard and brittle rock often leads to disastrous consequences in underground engineering. Under various surrounding rock pressure conditions, in situ stress induces corresponding deformation and damage to the floor post-mining. Therefore, it is crucial to examine the effects of mining under different confining pressures on rock disturbance, damage characteristics, and their distribution. Consequently, triaxial loading experiments under varying intermediate principal stress conditions were conducted on red sandstone specimens, using an acoustic emission monitoring system to track energy changes during rock damage and failure. This approach aids in studying crack generation, propagation, and fracture damage evolution. The results indicate that rock deformation results in axial compression and dilatancy, aligned with the direction of minimum and intermediate principal stresses. Ductility in rock failure becomes more pronounced with increased stress, primarily manifesting as shear failure. Internal cracks in the specimen lead to stress concentration and marked plastic deformation under compression, yet do not result in macroscopic surface cracks. The fracture angle θ of specimens post-failure generally exceeds 45° and varies with stress changes; at consistent burial depths, the angle of the sandstone failure surface increases with intermediate principal stress. This paper preliminarily establishes the informational linkage between rock failure and energy release, analyzing the rock samples over time and space. This research offers insights for analyzing and mitigating sudden rock instability.