Tensile Microcracks Research Articles

Investigation on the mechanical behavior, permeability and failure modes of limestone rock under stress-seepage coupling

Limestone rock widely exists in various rock engineering, its mechanical behavior and permeability evolution have a great influence on the safety and stability of related engineering projects. To study the mechanical behavior, permeability and failure modes of limestone rock under stress-seepage coupling, triaxial compression coupled with permeability tests were carried out. Experimental results reveal that the failure of limestone still conforms to the Mohr-Coulomb criterion under stress-seepage coupling, and effective confining pressure σ3eff can indicate the effect of gas pressure PG and confining pressure σ3 on the deformation parameters of limestone samples. Peak stress σP and residual stress σR increase with the enhancement of confining pressure and decrease with the ascent of gas pressure. Permeability evolution of limestone under different gas pressures and confining pressures is generally similar, and the trend of initial permeability kI, peak permeability kP and residual permeability kR decreasing with effective confining pressure σ3eff can be expressed by the exponential function. The increase of confining pressure and decrease of gas pressure will retard the acoustic emission (AE) response and inhibit the propagation of microcracks. More importantly, limestone samples always show composite failure modes dominated by tensile cracks under low confining pressure, while under high confining pressure, the limestone samples show shear failure modes. The difference is limestone samples are composed of tensile microcracks on the microscale under stress-seepage coupling, and the proportion of shear microcracks grows as gas pressure PG and confining pressure σ3 increases. This research can provide a basic reference for relevant engineering applications.

Mechanical behavior of PBX with different HMX crystal size during die pressing: Experimental study and DEM simulation

The effects of crystal size on the mechanical properties and meso-mechanical behavior of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) based polymer bonded explosives (PBX) during die pressing were systematically studied based on experiments and Discrete Element Method (DEM) simulations. The experimental results show that under the same pressure, larger crystal size will show higher relative breakage (Br), and further lead to the increase of density and the decrease of mechanical strength. By using DEM simulations which considered the realistic particle shape and microstructure of component crystals and binder, a comprehensive understanding of meso-mechanical behavior of PBX powder during die pressing has been achieved. Under the same stress, the maximum contact force between particles increases along with the crystal size. Tensile micro-cracks dominated the crystal breakage during the loading process. Energy dissipation results indicate crystal breakage plays a key role in promoting crystal displacement and enhancing the interparticle friction dissipation. Particularly, at small strains, crystal breakage disrupts the strain energy build-up. At large strains, particle breakage is greatly reduced, steady energy dissipation by elastic potential energy build-up and interparticle friction can be observed.

Fracturing of shales with slots under uniaxial compression parallel to bedding layers

Shale samples containing single pre-machined slots were tested under uniaxial compression directed along with bedding layers. Observed fractures were initiated by the slots, however, their further development was controlled by the shale bedding layers. Slots normal to the loading direction also cause fracturing and reduce failure load. The fracturing is initiated by tensile stress generated at the slot surface due to convergence of the initial open slot. Therefore, the presence of initial aperture in pre-existing cracks or fractures is capable of changing the mechanism of fracture generation. Three kinds of macroscopic fractures are observed: tensile fractures along bedding layers, shear fractures along the inclined direction, and buckling fractures at the final failure moment. Three types of microcracks are identified: shear microcracks produced from initial weak micro-planes unrelated to the bedding layers, tensile microcracks produced from the shear microcracks in the form of wing cracks, and shear microcracks induced by high uniaxial compression stress. The growth of wing cracks can be assisted by the bedding layers. The research results will contribute to the understanding of failure mechanisms of rocks containing prominent bedding layers.

THE MECHANISM OF THE KAISER EFFECT IN PHYLLITE UNDER INDIRECT TENSILE LOADING

Determination of in-situ stress serves as an important step in the design and construction of civil and mining projects, among others. Conventional methods of the in-situ stress measurement are time- and cost-intensive. Therefore, the application of low-cost yet rapid methodologies for in-situ stress evaluation has been increasingly regarded by researchers. The Kaiser effect-based acoustic emission method is one of such novel approaches to the in-situ stress evaluation. Not only the point at which the Kaiser effect occurs, but also the mechanism of the Kaiser effect is of paramount importance. In this research, acoustic emission tests were conducted on phyllite rock samples under Brazilian tensile loading to collect a variety of acoustic data, including the amplitude, rise time, count, duration, and energy. Then, the Kaiser effect point was determined using the collected data on acoustic parameters, with its occurrence mechanism investigated. In addition, mathematical transformations were adopted to transform the acoustic signal from the time domain to the frequency domain, where the peak frequency was analyzed. The results of the RA/AF ratio analysis showed that the acoustic emission was sourced from tensile micro-cracks. Moreover, the high level of energy indicated a high intensity of crack formation at the Kaiser effect point. The large number of received hits showed that the count of generated cracks increases abruptly within the range of the Kaiser effect. In addition, the obtained high value of the peak frequency implied that the crack growth rate is high at the Kaiser effect point.

Experimental and numerical simulation study of crack coalescence modes and microcrack propagation law of fissured sandstone under uniaxial compression

Fissured rock mass is the most common construction object in geotechnical engineering and its mechanical properties are closely related to the stability of geotechnical engineering. A laboratory uniaxial compression test and a numerical simulation test were separately carried out on the fissured sandstone samples. Based on parameters, such as crack coalescence modes, the ratio of rise time to amplitude (RA) and the ratio of acoustic emission (AE) counts to duration (AF) of AE signals and spatial distribution of microcracks, failure modes and microcrack propagation laws of fissured sandstone were studied. The results demonstrate that the failure mode of fissured sandstone changes from being dominated by tensile failure into by shear failure with the increase of the dip angle of prefabricated fissures. The results of RA and AF of AE signals illustrate that it is difficult to produce tensile microcracks, but easy to generate shear microcracks in the samples with the rise of the dip angle of prefabricated fissures. In the numerical simulation test, when the dip angle of prefabricated fissures is small (θ ≤ 60°), microcracks initiate near the tip of prefabricated fissures. However, if the dip angle is large (θ ≥ 75°), the initiation location of microcrack is slightly affected by prefabricated fissures. In addition, the method for determining tensile and shear cracks was proposed based on the velocity field of particles. The results show that as the dip angle of prefabricated fissures increases, there are increasingly less tensile macrocracks, but increasingly more shear cracks at failure of the samples, which is basically consistent with conclusions obtained in the laboratory test of rock mechanics.

Effect of surface characteristics of aggregates on the compressive damage of high-strength concrete based on 3D discrete element method

As the main component of concrete, aggregate has an important influence on the performance of concrete. In this study, the influence of coarse aggregate content and surface characteristics on the compressive mechanical properties and the damage evolution process of high-strength concrete were studied by using a 3D discrete element method (DEM). In order to improve the reliability of simulation results of concrete, a more accurate numerical simulation method was proposed. First, clumped-particle modules from the real aggregate geometry obtained by 3D Scanning were generated and then randomly distributed in the concrete model according to the specified aggregate content. Then the Flat-Joint Model (FJM) which can represent the micro-structure characteristics of concrete more reasonably was used to define the contact mechanical characteristics between different components. Based on this, the compressive strength, number of microcracks and damage evolution process of concrete with different aggregate surface texture factor (STF) and volume ratio were analyzed. The simulation results showed that aggregate surface texture and volume ratio were closely related to the compressive strength of concrete, and both have an exponential correlation with the compressive strength. The STF and volume ratio of aggregate have a significant effect on the proportion of tensile microcracks, and the concrete with large aggregates STF has more uniform stress distribution and wider damage range.

Damage and failure mechanism of concentric perforated granite under static pressure after alternating action of high temperature and water at different temperatures

In this study, concentric perforated granite alternately treated with high temperature and water at different temperatures was evaluated based on the engineering environment of surrounding rock in the deep geothermal well energy storage area. The damage and failure mechanism of concentric perforated granite under radial load was studied using a combination of mechanical test, theoretical analysis, and numerical simulation. The results revealed that the inner bore diameter, high treatment temperature, soaking water temperature, and alternating times between cold and heat could weaken the resistance of concentric perforated granite to radial load, but the influence of the deformation pattern on the rock sample was relatively slight. The load–displacement curve during the loading process exhibited the following sections: initial upper concave, short straight line, slowly ascending platform, approximately straight line, short upper convex curve, and post-peak cliff descending sections. Based on the theory of biological population growth, the damage variables of the concentric perforated granite were defined, and the analysis revealed that the internal damage of the rock sample experienced a slow-growth deceleration to a critical state. The numerical simulation results of the shape of the broken rock block and the strain on the side of the rock sample were combined. It was found that two concentration zones of vertical tensile-stress effect were formed inside the rock sample under the action of radial load, which led to the germination of tensile microcracks in the interior of the rock sample and resulted in macroscopic failure. In addition, the tensile microcracks were generated inside the concentric perforated granite. First, they propagated from the inner wall of the rock sample in the loading direction and then, along the outer wall in the vertical loading direction. Then, the microcracks spread and penetrated the outer and inner walls of the rock sample to form the macroscopic fracture surface.

A plastic-damage model for rock-like materials focused on damage mechanisms under high pressure

The purpose of this study is to present a plastic-damage model that can well capture the mechanical behaviors of rock-like materials. To this end, a three-invariant yield function combined with a cap function is employed to concurrently consider the physical mechanisms due to the presence of microcracks and pores as well as their combinations. The major contribution falls into the establishment of three damage mechanisms with clear physical backgrounds, including hydrostatic damage due to pore collapse, shear damage due to shear-induced microcracking, and tensile damage due to tensile microcracking. Particularly, the hydrostatic damage that can accumulate under even purely hydrostatic loading is proposed to account for the material properties degradations due to pore collapse. Results show that pore collapse under high pressure will cause a great loss of material properties. Without consideration of this will cause overestimation of the residual strength and modulus of materials. The validation examples demonstrated that the proposed hydrostatic damage can well accommodate the degradations of material strength and modulus due to pore collapse, which, however, has not been considered in most of the existing material models.

Numerical Simulation of Damage Behaviour of Building Sandstone Exposed to Fire

In this study, numerical simulations of the behaviour of large-size sandstone specimens exposed to wood crib fires were conducted. The developed numerical model, which innovatively considers the reversible quartz expansion behaviour during heating–cooling cycles, can replicate the temperature distributions, cracking behaviours, and strength variations of sandstone samples under various thermal loads (e.g., fires). Results show that the cracking mechanisms during heating and cooling are different, and the spalling is due to their combining effects. During the heating process, tensile stresses are induced mainly inside the sample due to significant expansions of the outer layer. The induced tensile microcracks beneath the surface will be furtherly extended and widened due to the re-distributed local stresses caused by local failures. After the fire, significant tensile stresses appear in the outer part of the sample due to the increased thermal gradients (i.e., volumetric expansions) of the inner part, leading to crack widening on the surface. These widened cracks will coalesce with the heating-induced cracks in the earlier time and boost the fracturing and spalling behaviour until the temperature across the sample reaches an equilibrium state. The findings are essential for understanding the failure mechanism of sandstone during real fire development. The good agreements between lab tests and numerical simulation also reveal the feasibility of using numerical models to predict the fire-induced damage in sandstone elements in architecture.

Bond thickness effect in mixed-mode fracture and its significance to delamination resistance

The fracture behavior of adhesively bonded joints is of interest in a variety of industrial, natural and biological applications. This effort re-examines literature data with an emphasis on thin bonds and their relation to delamination resistance. Brittle, ductile and particulate epoxy adhesives were considered with the bond thickness t varying from 1 to 1000 μm. The results shed new light on some basic morphological and fracture characteristics. The fracture energy is affected by numerous factors including adhesive material, bond thickness and loading mode. Shear fracture generally begins with growth of tensile microcracks ahead of the crack tip and continues with coalescence of these cracks along the interface in a process accompanied by extensive plasticity. With GIIC ≈ GIIIC, mixed-mode fracture can be described by tensile (GI) vs. shearing (GSC) ERR. For thin bonds (t < ≈ 10 μm), GIC ≈ constant, GSC increases virtually linearly with t, and GSC ≈ GIC = G0 when t → 0. These traits result in a closed-form expression for GC given in terms of basic material properties. The thin-bond results provide cost-effective means for predicting interlaminar fracture energy GIC or GIIC and elucidating an interleaf thickness for optimal delamination resistance. A detailed examination of published data reveals that within certain limitations, the mixed-mode fracture envelope is independent of t or material type. This finding may help develop analytical fracture models for practical use.

Growth of cataclastic bands into a fault zone: A multiscalar process by microcrack coalescence in sandstones of Rio do Peixe Basin, NE Brazil

We propose a structural evolutionary model for deformation band (DB) development via microcrack propagation and coalescence process in a normal fault zone affecting arkosic sandstones. Based on structural analysis and reconstruction of the paleostress, we infer that a sub-horizontal minimum principal stress (σ3) in the NNW-SSE direction controlled the multiscalar evolution of microcracks and DBs. Two main sets of coalesced microcracks and DBs are recognized: (1) NE-SW and (2) E-W, in which the coalescence pattern of microcracks is also observed among the DBs at meso-scale. Our results suggest that the DBs develop during three deformation stages: (1) pore collapse followed by initial grain breakage and the formation of NE-SW tensile microcracks favoured by cleavage planes in feldspars. These microcracks coalesce through linking NW-SE shear microcracks to form intermediary microplanes. An intense microcracking crush the grains, enhancing the cataclastic process. The further coalescence of these intermediary microplanes with other intermediary microplanes and/or microcracks might generate through-going microplanes inside the band, causing the formation of E-W DBs; (2) the E-W structures coalesce through NE-SW hard-linking DBs, which corresponds to the DBs clusters, generating NE-SW intermediary planes at meso-scale; (3) the NE-SW intermediary planes coalesce through an E-W hard-linking structure, which results in the DB fault zone.

A study of crack initiation and source mechanism in the Brazilian test based on moment tensor

It has been widely accepted that the Brazilian test can be used to obtain the indirect tensile strength of geo-materials. However, the effects of the contact conditions and the heterogeneity of the rock affect the micro-failure of the disc and the accuracy and feasibility of the Brazilian tensile strength (BTS), which typically leads to deviations from the results of the direct test. This study uses active and passive ultrasonic techniques and a three-dimensional flat-joint model (FJM3D) to quantitatively investigate the effects of these factors on the location and source mechanism with a Brazilian test, both in the laboratory and with numerical tests. During the laboratory tests, eight channels were used to record full waveform data continuously, and a total of 1090 and 928 acoustic emission (AE) events were located successfully under line loads and non-line loads, respectively. Both cases showed that the crack initiation points occurred away from the centre of the disc, indicating that the true tensile strength value may be somewhat underestimated. Three classification methods based on moment tensor inversion were used to quantitatively study the AE source analysis, which revealed that tensile micro-cracks that contain some deviatoric components predominantly occurred in micro-failure events. With the use of the FJM3D, the effects of the contact conditions and the heterogeneity of the rocks were analysed in detail. Four types of numerical tests were performed with different contact conditions and degrees of heterogeneity for comparison, indicating that the heterogeneity of rocks has a remarkable effect on the distribution of horizontal stress. This microcosmic and quantitative perspective can provide new data that can be used to modify the Brazilian test to obtain more accurate tensile strength values.

Comparative Study on Mineral-Scale Microcrack Propagation of Shale under Different Loading Methods

Producing a sufficient volume of multiscale crack networks is key to enhancing recovery of shale gas. The formation of crack network largely depends on initiation and propagation of microcracks. To reveal the influence of different loading methods on the propagation of mineral-scale microcracks, this study used the Voronoi tessellation technique to establish a cohesive zone model of shale mineral distribution and applied six different boundary conditions to represent different loading methods. Crack path characteristics, rupture characteristics, continuous crack propagation and turning, and en echelon intermittent crack propagation under different loading methods were compared and analyzed. The essence of different loading methods affecting the length and complexity of cracks was the spreading range of tensile microcracks. The mechanical properties of minerals led to dissimilarities in continuous crack propagation and turning. The formation and propagation of en echelon intermittent fractures of different scales were mainly impacted by the heterogeneity of minerals and mineral aggregates. The spreading direction and connection form of en echelon intermittent fractures were mainly affected by the loading method. Conclusions arising from mineral-scale simulations contribute to understanding the mechanism of microcrack propagation resulting from different loading methods, and these conclusions have a guiding significance to enhanced shale gas recovery.

Modelling damage mechanisms of concrete under high confinement pressure

Dynamic failures (e.g., crater, crack and spall) can be observed in concrete structures when suffered from possible blast and impact loadings. Understanding the physical mechanisms behind these failures needs a sound material model that thoroughly considers the damage mechanisms of concrete material, especially under the high confinement situation existed near the projectile and explosion. Modelling the damage mechanisms is a challenging problem that is not fully resolved in the commonly-used concrete material models. In this study, three kinds of damage mechanisms of concrete material, i.e., the hydrostatic damage due to pore collapse, shear damage due to shear-induced microcracking and tensile damage due to tensile microcracking are identified and physically modelled respectively using corresponding damage indexes. The interaction of the three damage is also considered by introducing two stress-dependent factors. The damage model is implemented into the Kong-Fang material model recently proposed, in which improvements on the strength surfaces, strain-rate enhancement and erosion criterion are accompanied made based on a few years use of this model. Numerical triaxial compression test and hydrostatic compression to unconfined compression test are conducted using a single element to validate the proposed hydrostatic damage model and the shear damage model. And the competition mechanism between hydrostatic damage and shear damage during the triaxial compression test is discussed. Then the modified Kong-Fang model is used to numerically simulate the reinforced concrete slabs subjected to a contact explosion load and projectile impact load, in which the physical mechanisms of the experimentally observed crater, crack, tunnel and spall failures are revealed.

Experimental Study on Damage and Fracture Characteristics of Beishan Granite Subjected to High-temperature Treatment with DIC and AE Techniques

The effect of high temperatures up to 800 °C on the physical and mechanical characteristics and fracturing behaviour of Beishan granite is experimentally studied with a combination of acoustic emission (AE), digital image correlation (DIC) and optical microscope observations. The experimental results show that the responses of the P-wave velocity, the effective porosity, Young’s modulus, and the uniaxial compressive strength (UCS) of the granite to temperature are different. The critical temperature for the brittle–ductile transition of Beishan granite is between 500 and 600 °C. The counts, cumulative energy, b value, and waveform from AE and the full-field deformation evolution from DIC are combined to investigate the damage evolution and fracture mechanism in heated granite. It is found that a rise in temperature increases the number of AE events but reduces the cumulative energy release. Tensile microcracking mainly occurs in granite exposed to low temperatures, while shear fracturing gradually dominates in granite exposed to higher temperatures. With increasing temperature from 25 to 800 °C, the failure mode of granite specimens changes from being controlled by longitudinal splitting cracks to a single shear fracture and finally to multiple conjugate shear fractures. Microscopic observation of granite thin sections is conducted to further reveal the essential mechanism driving the physical–mechanical response and fracturing behaviour of heated Beishan granite.

Experimental Study on Strain Burst Characteristics of Sandstone Under True Triaxial Loading and Double Faces Unloading in One Direction

In this study, a new strain burst test system was used to conduct two types of strain burst experiments by rapidly unloading single and double faces (in one direction), to simulate the strain burst occurring in surrounding rock of tunnel or double tunnel faces during the opposite tunneling. A high-speed image recording system and an acoustic emission system were used to monitor the failure process of strain burst of red sandstone. The commonalities of these two types of strain burst are as follows: failure stress and percentage of dissipation energy due to crack propagation were approximately equal; the evolution of mean velocity of free face was similar, which suddenly increased first and then decreased, then the gradient increased to the extremum value, and finally decreased to zero. Subregions of the fracture were consistent, and both showed shear, buckling, splitting, and ejection zones. However, the strain burst intensity for unloading double faces was larger than that for unloading single face, as demonstrated by a larger initial ejection velocity, larger volume of burst pit, and lower peak frequency. Furthermore, when double faces were unloaded, the flaky and massive features of fragments obtained due to strain burst were more obvious than the fragments obtained from the unloading of single face. Moreover, from yield to burst, when double faces were unloaded, the sandstone strain burst contained more shear microcracks, whereas the strain burst when unloading single face contained more tensile microcracks.

Discrete Element Modeling on Mechanical Behavior of Heterogeneous Rock Containing X-Shaped Fissure under Uniaxial Compression

Based on the experimental results of an intact rock specimen under uniaxial compression, particle flow code (PFC2D) was adopted to carry out a discrete element modeling (DEM) for the mechanical behavior of heterogeneous rocks containing X-shaped fissures (two intersecting symmetric single fissures) under uniaxial compression. The influences of β (the acute angle between two single fissures) and the direction angle α (the acute angle between the bisector of β and perpendicular to the loading direction) on the strength, deformation, energy, crack propagation, and ultimate failure mode were analyzed in detail. Numerical simulated results showed the following: (1) Due to the X-shaped fissures, not only the peak strength, elastic modulus, crack initiation stress, and damage stress were significantly reduced, and the reduced degree of the peak strength was obviously greater than that of the elastic modulus, but also the brittleness and energy were significantly weakened. (2) The peak strength and elastic modulus generally decreased with the increase of β and increased with the increase of α . Moreover, the change trends of crack initiation stress, damage stress, boundary energy, and total strain energy at the peak stress were consistent with the peak strength. (3) Regardless of the changes of α and β , models all firstly initiated wing cracks at the two tips of the single fissure with a larger inclination angle, and the crack initiation angle decreased with the increase of the inclination angle of the single fissure. (4) The fracture was dominated by tensile microcracks, and no microcracks were generated in a certain range of the X-shaped fissure center. The failure mode was mainly split along the axial direction, and the failure surface started from the tips of the fissure and extended to both ends of models. (5) The uniaxial compressive strength and elastic modulus increased exponentially with the increase of the homogeneity factor. When the homogeneity factor was small, the microcracks were more evenly distributed in the models; when the homogeneity factor was large, the microcracks were mainly concentrated at the tips of the fissure in the models. This study can provide some references for the correct understanding of the mechanical properties of rock masses containing X-shaped fissures.

A systematic analysis method for rock failure mechanism under stress unloading conditions: a case of rock burst

The aim of this study was to develop a systematic method to analyze the rock failure mechanism under stress unloading conditions. In this method, three types of basic tests (Brazilian splitting, direct shear, and three-point bending) were used to extract acoustic emission (AE), dissipative energy, and fracture parameters to analyze the failure mechanism under stress unloading. The key parameters are as follows: the critical slope in rise time/amplitude—average frequency (RA-AF) coordinate system; the dissipation energy (us and ut) of unit shear and tensile cracks; relative roughness (δ) of fracture—variation coefficient of gray value of digital image for fracture. Additionally, the effectiveness of this method was illustrated by a rock burst experiment. The results show that most (92.3%) of the fragments during rock burst were produced by tension, while the energy consumed by shear cracks is ~ 1.03 times of tensile cracks. Moreover, the density of AE events is negatively correlated with the amount of released energy. Furthermore, the tensile microcracks concentrated as a splitting zone after yielding but before burst. However, in the burst stage, the shear microcracks breakthrough to form a shear zone, while the elastic strain energy released was partially transformed into kinetic energy to form the ejection zone. In addition, for the dissipation energy, the energy consumptions by shear, tension, and plastic deformation account for 62.5%, 25.2%, and 12.3%, respectively.

Damage evolution of tuff under cyclic tension–compression loading based on 3D digital image correlation

We have investigated the damage evolution and crack propagation of tuff rocks under axially cyclic tension–compression (T–C) loading with different amplitudes. The field of axial strains in the rock surface was obtained by three-dimensional digital image correlation (3D-DIC) method. The apparent strains were used to analyze the damage evolution along with the nucleation and propagation of microcracks until rock failure. The experimental results demonstrated that a local damage zone (LDZ) was formed when the loading amplitude exceeded a certain value, and the rock sample was prone to tensile failure under T–C cyclic loading. Based on arrangement of the virtual extensometers on the field of axial strains, the axial stress–strain curves, maximum axial strain, secant moduli, and dissipated energy evolution were obtained as a function of cycle number. It was observed that the variations in these mechanical parameters and dissipated energy significantly increased in the T–C cycle test with the increase in the loading amplitude. Particularly, due to obvious accumulation of residual compressive strain during the first cycle, the maximum tension stress increased, secant modulus decreased, and the dissipated energy evidently increased under tension during the second cycle. Furthermore, the mechanical parameters and dissipated energy evolution as a function of cycle number inside and outside the LDZ under 80% amplitude confirmed that the deformation mainly occurred inside the LDZ and the energy mainly dissipated for the nucleation and propagation of tensile microcracks vertical to the loading direction inside the LDZ during rock failure process.

Time-sensitivity mechanism of rock stress memory properties under tensile stress

Abstract In deep underground engineering, understanding of time-related stress memory properties is critical to evaluate the in situ stress conditions of a rock mass. In this study, the time-sensitivity mechanism of the rock stress memory properties under tensile stress was investigated. It was found that the material property (Poisson's ratio) and crack angle were the controlling factors of the Kaiser effect (KE) under tensile stress. In particular, the time-sensitivity of the stress memory properties was closely related to the crack growth path. When the failure of the rock specimen was dominated by tensile microcracks and the crack development direction was deflected by up to 30° in the successive loading process, the stress memory capacity was likely to be time-independent for a sandstone specimen. The distribution of the Felicity ratio in a Brazilian test was more discrete than that in a three-point bending test. It also showed that the changes in the crack path, rather than the time interval between successive loading cycles, led to inaccuracy of the detected KE. This study provides insights into stress memory-related issues under uniaxial or more complex stress conditions and thus facilitates development of methods for testing in situ mechanical behaviors of rocks with acoustic emission (AE) technology.