Evolution Of Strength Research Articles

An exploration of potentially reversible controls on millennial-scale variations in the slip rate of seismogenic faults: Linking structural observations with variable earthquake recurrence patterns

Paleoseismic studies show that faults within a fault system may trade off slip over time, with mechanically complementary faults displaying alternating fast- and slow periods. Each of these periods spans multiple seismic cycles, and typically involves ~20-25m of slip. This suggests that the relative strength (or tendency to slip) of individual faults varies, over time and displacement scales larger than those of individual seismic cycles. The mechanisms responsible for these strength variations must: affect rocks in the strongest portion of the fault (the brittle-ductile transition) as this likely controls the overall slip rate of the fault; be reversible (or able to be counteracted) on a cyclical basis; provide a negative feedback that operates to change the fault from its current state; and have a measurable effect on fault strength over a time or length scale that corresponds to the observed fast and slow periods of fault slip. In this paper, we systematically explore 19 potentially weakening and 11 potential strengthening mechanisms and evaluate them in light of these criteria. This analysis reveals a relatively small subset of mechanisms that could account for the observed behavior, leading us to suggest a possible model for fault strength evolution.

Laboratory investigation on static and dynamic properties, durability, and microscopic structure of Nano-SiO2 and polypropylene fiber cemented soil under coupled seawater corrosion and cyclic loading

Cemented soils in coastal harbors are susceptible to adverse factors such as seawater corrosion and cyclic dynamic loading, which may consequently reduce their stability and durability. In recent years, Nano-SiO2(NS) has been widely used to enhance the mechanical properties of cemented soil. However, this enhancement may potentially lead to a reduction in ductility. Conversely, polypropylene fibers (PP) have attracted widespread attention for their potential to enhance the ductility of cemented soils, but their ability to improve the strength of cemented soils is limited. To address these issues, this study focused on utilizing five different nano-dosages combined with four different fiber dosages to enhance cemented soils. These enhanced soils were then subjected to curing periods of 7, 28, and 60 days in seawater environments. The study employed various tests including unconfined compressive strength tests (UCS), uniaxial cyclic loading tests, scanning electron microscopy tests (SEM), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) to investigate the potential impacts of these additives on durability, strength, corrosion resistance, and microstructure evolution. The results of the study indicate that seawater corrosion and cyclic loading contribute to a reduction in the stability of cemented soils. However, the addition of NS and PP effectively enhances the compressive strength and durability of these soils. The optimal combination ratio is achieved when the dosages of NS and PP are 3.6 % and 0.8 %, respectively. In this case, the growth rate of unconfined compressive strength of cemented soils surpasses the sum of each individual dosage, increasing by 137.7 %, 245.6 %, and 235.3 % after 7, 28, and 60 days of curing, respectively. Furthermore, the growth rate of PP on the compressive strength of cemented soils remains largely unaffected by seawater corrosion. The optimal composite dosage of cemented soils effectively mitigates the increase in porosity caused by seawater corrosion. C-S-H enhances the mechanical interlocking between hydration products and PP by encapsulating PP, reducing energy transfer losses in cemented soils, and increasing their dynamic modulus. The volcanic ash reaction and nucleation effect of NS further enhance this effect, and their combined use significantly improves the seawater corrosion resistance of cemented soils.

Microstructure evolution and mechanical properties of Cu–9Ni–6Sn alloy during continuous cold deformation process

A Cu–9Ni–6Sn alloy bar with pronounced axial columnar grains and a diameter of 10.5 mm was fabricated by using directional solidification technology, which was directly cold-drawn into a superfine alloy wire with a diameter of 40 μm without intermediate annealing. The strength and microstructure evolutions of the Cu–9Ni–6Sn alloy during the cold drawing were studied. The results indicate that twinning is more likely to occur in fiber structures ranging from 60 to 120 nm. A dual-fiber structure consisting of <111> and <100> orientations formed after cold-drawing. Unexpectedly, a large number of deformation twins were discovered within the <111> fibrous texture and later transformed into detwinning structures, disrupting the axial fibrous texture. The generation of deformation twinning primarily results from Ni and Sn elements disrupting crystal symmetry and reducing stacking fault energy of the alloy and the formation of <111> texture. The combined effects of detwinning structures and dislocation wall induced work-softening of the alloy, enabling high-strain processing and ultimately yielding nanocrystalline grains, i.e., the Cu–9Ni–6Sn alloy underwent cold drawing with a high train of 11.23 and obtained an average grain size of ∼38 nm, which exhibited a tensile strength of 1453 MPa.

Strength, deformation and crack evolution behaviour of cemented tailings backfill composite structures with different strength ratios

ABSTRACT This work comprehensively investigated cemented tailings backfill composite structures (BCS) mechanics and crack evolution mechanisms. A new crack classification method combining Gaussian Mixture Modeling (GMM) and Moving Average Filtering is proposed for the BCS acoustic emission RA-AF dataset. The findings indicate that the upper CTB did not incur significant damage following BCS destruction, enabling BCS to maintain a certain bearing capacity post-failure. The compressive strength of BCS often approximates that of CTB monomers with a lower cement-tailings ratio (this trend diminishes as the upper CTB’s strength increases), and the loss of bearing capacity in BCS is attributed to the failure of CTB monomers with lower strength. The deformation damage in the upper and lower CTB displays a cooperative characteristic throughout the loading-induced damage process, with the axial and transverse strains in the lower CTB surpassing those in the upper CTB. Analysis results from GMM reveal that the compression failure process of BCS is predominantly characterized by tensile failure, with minimal shear failure. The propagation of cracks in the lower CTB exerts a certain influence on the crack evolution of the upper CTB. The findings offer a novel perspective on discerning the fracture evolution behavior of materials.

Numerical simulations on compression behaviors of the laminated shale based on the digital image technology and the discrete element method

As an unconventional reservoir sedimentary rock, shale contains a series of layers and various microstructures that lead to complex mechanical properties, such as the anisotropy of stiffness and strength. This study is directed towards the anisotropy caused by the microstructures of the shale, employing the 2D particle flow code (PFC2D) to explore stiffness, strength, failure mode, and micro-crack evolution. More realistic microstructures and the calibration of microscopic parameters of the shale are reasonably considered through the computed tomography (CT) images and mineral analysis. The corresponding numerical simulation results are fully compared with the experimental results. In what follows, the sensitivity analysis is conducted on the key microscopic parameters and microstructure characteristics in numerical samples with laminated characteristics. The results show that the influence of microscopic parameters of the parallel bonding model on macroscopic parameters is related to the layering angle and the face type, and the microstructures and initial cracks of numerical samples can considerably affect the macroscopic mechanical behaviors of the laminated samples. Next, the effect of confining pressure on the mechanical properties of layered shale is also discussed based on the numerical results. These findings highlight the potential of this approach for applications in micro-scaled models and calibration of microscopic parameters to probe mechanical behaviors of the laminated rock.

Sulfate resistance of UHPC during dry-wet cycling and energy dissipation under compression

To study the sulfate resistance of ultra-high performance concrete (UHPC) in saline soil area of western China, four kinds of sulfate solution concentrations (0 %, 5 %, 10 %, 15 %) and 18 dry-wet cycle tests for 540 days were carried out on UHPC specimens. The effects of sulfate dry-wet cycles on the evolution of UHPC strength and energy were studied, the characteristic stress points during uniaxial compression of UHPC under sulfate dry-wet cycle were determined, based on the evolution law of each energy (total energy U, dissipated energy Ud , elastic stress Ue) at the characteristic stress points, the energy storage index was established to measure the damage degree of UHPC. The results show that the energy evolution process and damage mechanism of UHPC samples under sulfate-wet and dry cycle erosion are closely related to macro and micro changes. With the development of sulfate dry-wet cycle, the dissipative energy Ud and elastic strain energy Ue of UHPC at the characteristic stress points increased first and then decreased. The development trend of elastic strain energy Ue and dissipative energy Ud is more severe with the increase of sulfate solution concentration. The ratio of elastic strain energy at damage stress to elastic strain energy at peak stress (Ueib/Uei) is taken as the energy storage index Kib to measure the damage degree of UHPC, under 10%Na2SO4 erosion, Kib can be increased by 21.41 % at the highest and decreased by 29.67 % at the lowest compared with the initial value. It shows that the damage process of UHPC is difficult and then easy, and this index can accurately reflect the external force required for the damage of UHPC under sulfate dry-wet cyclic erosion, and provide a reference for the safe and stable operation of UHPC in saline soil area.

Investigating Different Heat Treatment Methods to Enhance the Mechanical Properties of 9254 Steel

This study investigates the impact of varied heat treatment parameters on the mechanical and metallurgical characteristics of 9254 steel. Different cylindrical specimens underwent controlled heat treatments targeting three different phases. The interplay of time and temperature was systematically explored to understand their influence on bending strength, bending deflection, hardness, and microstructural evolution. The results revealed that a partially tempered martensitic structure exhibiting an exceptional ultimate strength of 4308 MPa. Achieving this involved a heat treatment, starting at 900°C for 30 minutes, followed by rapid cooling in an oil bath, quenching at 165°C for 5 minutes, annealing at 180°C for 60 minutes, and gradual air-cooling. This treatment regimen produced a specimen with a desirable combination of mechanical properties, showcasing its potential significance in advanced engineering applications.

Enhanced graphitization and reduced radial heterogeneity of carbon fibers inheriting from irradiated/thermo-chemically stabilized PAN-fibers

The cross-section of carbon fibers (CFs) possessed radial heterostructure, which restricted its mechanical properties. In this paper, heating and γ-irradiation were integrated during PAN fibers stabilization process to improve the radial structure of CFs. The synergy between irradiation and heating during stabilization caused the decrease of ID/IG, increase of crystal size, and reduction of pore fractal dimension in whole CFs. Through Raman spectra along fibers cross-section, a radial heterogeneity was found during the whole carbonization process. The combination of γ-irradiation and heating reduced the ID/IG of core part more significantly compared to the skin part of CFs, which weakened radial heterogeneity of CFs. At the same time, it significantly enhanced the tensile strength of CFs. Subsequently, a hierarchy model with three zones containing outer-surface, sub-surface and core parts was presented to explain the evolution of tensile strength for CFs. The γ-irradiation during stabilization enhanced the structure of each part in CFs by generating more cross-linked structures.

Handgrip Strength and Clinical Evolution of People Living with HIV: A Mini Narrative Review.

HIV infection is a worldwide epidemic. Antiretroviral therapy allows people living with HIV (PLHIV) increased longevity and a better quality of life. Among the various ways of monitoring the clinical evolution of PLHIV, handgrip strength (HGS) is a promising strategy, as this test can be used to assess the health condition quickly and at a low cost. In this sense, the present study aims to describe, through a literature review, the relationship between HGS and the clinical evolution of PLHIV, especially with morbimortality. Initially, it is highlighted that aging, HIV infection, and excess body fat are related to the loss of HGS in PLHIV. Furthermore, PLHIV is more likely to present cardiometabolic diseases that can be aggravated by reduced HGS. Thus, in people without positive HIV serology, low HGS indirectly, through the presence of risk factors or cardiometabolic diseases, or directly increases the chance of mortality. In conclusion, the lack of studies on this topic for PLHIV is highlighted, and more longitudinal studies, including control groups, are needed.

Research on dynamic mechanical properties and damage model of ceramic materials under multi‐axial stress

AbstractDue to their exceptional impact resistance, ceramics are extensively used in various fields. However, unavoidable pores, microcracks, and inherent defects can degrade the performance of ceramic materials. A damage model of SiC ceramics under passive confining pressure was constructed based on the Lemaitre strain equivalence principle and the Weibull distribution function. This paper presented a dynamic damage model for SiC ceramics subjected to passive confinement pressure based on the principles of damage mechanics. Additionally, the split Hopkinson pressure bar device was employed to investigate the compressive strength and damage evolution of SiC ceramics at various shock pressures and confinement degrees. The experimental results indicate that constraints can reduce the damage to ceramics. The metal sleeve increased stiffness when compressing the ceramic material, allowing the specimen to convert from brittle–plastic–brittle. When sufficient constraints can be provided, the peak strain decreases gradually with the increase of the impact air pressure. Experimental data showing good agreement with the proposed model validated and analyzed the established model. Thinner boundary constraints cannot maintain the stability of ceramic structures, thicker boundaries do not significantly improve performance, and thicker boundaries can cause more weak areas. This paper provides guidance for the design of encapsulated ceramic composite armor by quantitatively studying the constraint thickness.

An experimental investigation on the failure behavior of sandstone with filled fissure under triaxial multilevel cyclic loading

AbstractRoadways are common in infrastructure of the underground engineering. The surrounding rocks of these roadways are often allowed to work with flaws and are subjected to cyclic loading with variable magnitude. However, the existing experimental data regarding their behavior are insufficient. This study investigated how confining pressure and the inclination of pre‐existing fissures affect the mechanical properties and failure mechanisms of sandstones from the Lu‐Xi coal roadway in Shandong Province. Utilizing triaxial cyclic experiments along with real‐time acoustic emission (AE) monitoring, the findings were presented with respect to the evolution of strength as well as deformation behaviors, failure modes, and AE event frequency. Finally, the impact of the above two factors on damage mechanisms of preflawed sandstone materials were detailed discussed in terms of the fracture mechanics. This study highlights the importance the buried depth and flaws for the rock engineering and the sensitivity of sandstone's mechanical responses in changes in the lateral restriction and fissure angle.

3D DEM investigation of shear behavior and interaction mechanism of woven geotextile-sand interfaces

This paper presents a numerical study on the investigation of microscopic mechanism governing the interaction of woven geotextile and angular sand employing the 3D discrete element method (DEM). The surface texture and tensile properties of the geotextile were simulated using overlapping spherical particles, and the angular sand was simulated using rigid blocks. The DEM models were fully calibrated based on previous experimental data. The shear and dilation zones of sand near the interface were quantitatively determined based on particle displacement gradients. Analysis of contact forces was conducted to explain the microscopic mechanism behind the macroscopic strength evolution. The influence of geotextile surface roughness on the shear strength of the geotextile-sand interface is also discussed. The results show that the failure mode of the woven geotextile-sand interface is a combination of particle sliding failure along the geotextile surface and shear failure of the sand within the shear zone above the interface. There is a rapid redistribution of contact forces prior to reaching peak shear resistance, and the average normal contact force within the shear zone remains relatively constant after the peak shear stress is achieved. A completely developed shear zone stabilizes soil deformation, typically after achieving the peak shear resistance.

Investigation of effects of aluminum additions on microstructural evolution and mechanical properties of ultra-high strength and vanadium bearing dual-phase steels

The effects of aluminum (Al) additions (0.04, 0.4, and 0.8 wt%) on the microstructural evolution, tensile properties, and sheared-edge ductility of dual phase (DP) steels were investigated. The DP steels were processed with distinct coiling temperatures after finish rolling, cold rolled, and subjected to two continuous galvanizing line (CGL) simulations: standard galvanizing (GI) and supercooling process (SC). Al expanded both the ɑ-ferrite and (ɑ+γ) phase fields at the expense of the γ-austenite region. Continuous cooling transformation (CCT) diagrams showed that Al increased ferrite start temperatures, broadened the ferrite transformation zone, and reduced austenite stability. Austenite growth kinetics during intercritical annealing, quantified using a modified Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, revealed Avrami exponents ranging from 0.72 to 0.81 and apparent activation energies increasing from 422.9 to 496.7 kJ mol−1 with Al additions. Microstructural characterization revealed larger ferrite grain sizes and higher ferrite volume fractions with higher Al levels. Ultimate tensile strength (UTS) was influenced by Al contents, coiling temperatures, and CGL simulation methods. Global ductility (total elongation, TE) was highest for the 0.8Al Steel with a high coiling temperature and GI annealing, while local ductility (hole expansion ratio, HER) was maximized for the 0.04 Al Steel with a low coiling temperature and SC annealing. The majority of the CGL simulated DP steels exhibited good strength-ductility combinations, with the 0.8Al Steels demonstrating superior properties compared to current automotive advanced high-strength steel (AHSS) grades.

Sustainable approach to quality assurance in cement-improved soil: applications of handheld XRF for geotechnical solutions

Traditional methods for evaluating the quality of the Deep Mixing Method (DMM) in Japan, such as the phenolphthalein tracer method, present limitations in ensuring strength improvement. This study explores handheld X-ray fluorescence (XRF) as a sustainable alternative for quality assessment. The elemental composition of cement-treated soil was investigated, focusing on Calcium (Ca), Silicate (Si), and Sulfate (S), which play crucial roles in the formation of hydrated products, aiming to accurately determine their influence on the strength development of the improved soil. A controlled protocol was employed using commercial Kaolin clay and the needle penetration test for strength assessment. Our laboratory experiments, conducted with a cement-based binder (C) dosage of 110 kg/m3 and a water-cement (W/C) ratio of 1, furthered our understanding of the hydration process. Results indicate an apparent increase in Ca amount over time, correlating with improved strength, while the apparent amount of Si decreases, suggesting its integration into hydration products such as C-S–H gel. Strength assessment rose significantly between day 1 and 28, aligning with variations observed in Si, Ca, and S, underlining their role in strength evolution. This research underscores the potential of handheld XRF as a sustainable substitute for conventional methods in field-quality assurance, offering real-time data on the formation of possible hydrated products during the hydration process for improved soil in geotechnical engineering.

A case study on early-age cracking of high-strength concrete construction by coupled thermal-mechanical analysis and field monitoring

The use of high-strength concrete (HSC) in constructing high-rise reinforced concrete buildings and their deep foundations is becoming more popular because of the significant reduction in member size and, thus, self-weight in structural members. However, the higher cement content in HSC may result in increased heat of hydration and autogenous shrinkage, growing concerns about forming early-age cracks in HSC structural members. This case study assessed the early-age cracking of HSC in bored pile construction of high-rise buildings. A nonlinear transient coupled thermal-mechanical response analysis was performed to evaluate the potential of early-age cracking caused by the heat of hydration generated in the HSC using ABAQUS and two subprograms, USDFLD and UEXPAN. A 3-D finite element model was developed considering thermal effects, time-dependent evolution of early-age strength and stiffness of HSC, crack strain development, autogenous shrinkage, and stress-relaxation in the analysis. Field measurements were carried out on a 3-m diameter bored pile constructed using Grade C50/60 HSC (fck,cube = 60 MPa) for a high-rise building project in Hong Kong to evaluate the validity of the numerical model. Optical fiber sensors were used to monitor the temperature changes of the pile for approximately 380 hours after casting. The temporal and spatial temperature distributions measured in the field measurements agree well with the simulations. Large thermal gradients and high tensile stress zones were observed across the horizontal cross-sections of the pile, resulting in the formation of vertical annular cracks. Based on the results of the analysis, the maximum crack widths were predicted and compared with the durability crack width limits.

Conventional triaxial loading and unloading test and PFC numerical simulation of rock with single fracture

Take the metamorphic sandstone as the reference object, by making rock like samples with fractures, the conventional triaxial loading and unloading test and PFC numerical simulation of rock like sample with single fracture were conducted, and the effects of the loading path, inclined angle of fracture, axial stress level during unloading, initial confining pressure during unloading on the compressive strength, peak strain and crack propagation evolution of the samples were considered. The compressive strength of the specimen under triaxial unloading is smaller than that under triaxial loading. The peak strain of the specimen under triaxial unloading is also smaller than that under triaxial loading. The specimen is more prone to brittle failure. When the axial stress level is the same during unloading, with the increase of the initial confining pressure during unloading, the difference of the compressive strength of the specimens with different inclined angles of fracture gradually decreases. Under the condition of uniaxial compression and triaxial compression, the failure of all specimens is tensile failure, and the shear failure is the main one during unloading.

Influence of the multiple element ions contained in seawater and sea sand on the freeze-thaw resistance of cementitious materials

Preparation of concrete with seawater and sea sand can increase the pore solution salinity due to the introduced multiple ions, which can affect the freeze-thaw resistance of concrete by changing the crystallization pressure and freezing temperature. This study aims to investigate the influence of these multiple element ions in seawater and sea sand on the freeze-thaw damage characteristics of cementitious materials. The seawater sea-sand mortar (SSM) samples and reference specimens (Freshwater and river sand-FRM) were first prepared with same mix design. The accelerated freeze-thaw tests were then conducted in an environment chamber under the temperature range of [-20 °C, 7 °C]. The surface spalling, mass loss, and mechanical performance (Compressive strength, stiffness and fracture resistance) evolution during freeze-thaw cycles were characterized to examine the freeze-thaw resistance. The influence mechanism is analyzed through characterization of pore solution and structure, and Discrete Element Method (DEM) simulation. It is indicated that the introduced multi-element ions from seawater and sea sand accelerate the freeze-thaw deterioration of cementitious materials. After 150 freeze-thaw cycles, the mass loss rates of SSM and FRM samples reach above 10 % and 8 %, respectively. And the corresponding reduction rates for dynamic modulus are 51 % and 36 % for the SSM and FRM specimens. The deterioration in compressive strength is slightly higher than the loss of fracture resistance. The mechanism analysis indicated that deteriorated freeze-thaw resistance due to the introduced multi-element ions from seawater and sea sand mainly originated from the degradation of pore structure and the increase in freezing pressure. This study can serve as a solid base for the durability design and application of seawater sea-sand concrete in cold regions.

Enabling multi-stage high-temperature strength evolution prediction of ceramizable composites using a novel multi-field coupled model

Strength varies significantly under high-temperature environment, due to the inherent thermomechanical behavior of the ceramizable material and its coupling with possible chemical reactions. The complexity amplifies for composite materials, considering their multi-phase and multi-scale features, and more importantly, their complicated chemical reactions under high-temperature service conditions. This study proposes an innovative multi-field coupling theory framework for predicting the multi-stage evolution behavior of high-temperature mechanical properties of a ceramizable composite, through incorporating an extended chemical kinetics method, coupled deformation, mass diffusion and heat conduction. The developed model enables direct coupling and simultaneous solving of physical, chemical and thermal variables. It captures well the degradation of mechanical properties for the initial stage and the increase of strength for the later stage, along with the increasing of temperature. The validated model also enables well prediction of time-dependent mechanical properties at high service temperature, with an average error of 8.67% against experimental measured results. The developed method can serve as a general method for the prediction of high-temperature mechanical property of thermal protection composites and structures.

Rheological Bridge Zones: The Initialization of Strain Localization

Strain localization occurs across the crust in both brittle and viscous regimes, but the exact causes remain debated. Natural rock observations suggest that changes in phase properties (such as physical properties, phase distribution, and grain geometry) are more influential in weakening than variations in stress and temperature. Investigating the early stages of strain accumulation in various pressure-temperature conditions leads to a better understanding of these causes. Our study focuses on three weakly deformed rocks showing zones of localization on a millimeter or smaller scale, which we term “bridge zones”. These localized zones appear to mechanically connect weak domains and typically exhibit finer grain sizes within a narrow band. Importantly, these zones occur in less deformed rocks from the margins of shear zones. They result from both in-situ grain size reduction and chemical processes leading to phase mixing or element mobility on a limited spatial scale. Numerical modeling aligns high-stress areas with these zones, supporting their impact on reducing rock strength. We propose a conceptual model linking far-field loading to microscale changes in developing these zones. Characterization of bridge zones aids in elucidating the microstructural processes driving deformation localization, which is fundamental for plate tectonics, metamorphism, seismicity, and other lithospheric processes. This research reveals microscale mechanisms driving weak domain development, improving our knowledge of rheological changes and laying the groundwork for predictive models regarding strength evolution in the lithosphere.

Experimental and numerical study on the damage evolution and acoustic emission multi-parameter responses of single flaw sandstone under uniaxial compression

Cracks are generally the weakest position in engineering rock mass. It is of great practical significance to study the influence of cracks on the fracture process of rock mass and the precursor criterion of failure for disaster prevention and mitigation projects. In this paper, particle flow program (PFC2D) is used to analyze the mechanical strength and damage evolution of fractured rock. The multi-parameter stage characteristics of acoustic emission (AE) and the difference of fracture precursor information of fractured rock mass under uniaxial compression (UC) are explored. The results are as follows: (1) The strength and modulus of elasticity of fractured rock samples are smaller than that of intact rock mass, and increase in quadratic function with the increase of fracture angle, and the strength of B-90 sample is closest to intact rock samples; (2) The PFC analysis shows that the cracks in the defective rock samples all originate from the tip of the prefabricated crack, and the crack initiation angle is basically in the range of 60°∼90°. The loading process mainly produces tensile damage, and the number of tensile cracks are far more than that of shear cracks. Compressive stress and tensile stress increase with the increase of load, but the force chain of failure surface is the smallest after complete failure of rock; (3) The acoustic emission ringing number, RA/AF value, b value and entropy value of sandstone have obvious stage characteristics, the main frequency signal is mainly low frequency signal, and large-scale cracks are mainly produced in the failure process. The sudden increase point of AE ringing times and RA/AF value accumulation curve can be used as critical failure point. The fluctuation of B value and entropy value reflects the instability of fracture development, and “cliff-like” descending point and ascending point can be regarded as the precursor of critical failure of rock; (4) The failure precursor of acoustic emission parameters of sandstone appears in the peak load period of 85 %–98 %. The order of response time of different parameters is: cumulative RA/AF value, cumulative event number, entropy value, B value. The response time of B-45 and B-15 is earlier, while that of B-60 and B-30 is later. The research results are expected to deepen the understanding of the relevant standards of damage evolution and failure precursors of defective rocks in engineering applications.