Understanding the anisotropic fracture behavior and the characteristics of the fracture process zone(FPZ)under size effects in laminated rocks,as well as its role in rock fracturing,is crucial for various engineering ...Understanding the anisotropic fracture behavior and the characteristics of the fracture process zone(FPZ)under size effects in laminated rocks,as well as its role in rock fracturing,is crucial for various engineering applications.In this study,three-point bending tests were conducted on shale specimens with varying bedding angles and sizes.The anisotropic characteristics and size effects of fracture parameters were revealed.A comparative analysis was performed on the evolutions of FPZs computed using size effect theory,digital image correlation(DIC),and linear elastic fracture mechanics.The results divulged that:(i)With increasing bedding angles,there is a noticeable decrease in apparent fracture toughness(KICA),apparent fracture energy(GICA),and nominal strength(σ_(Nu)).When the bedding angle of shale is less than 45°,the crack propagation and fracture parameters are mainly influenced by the matrix.Contrary,shale with bedding angles greater than 60°,the crack propagation and fracture parameters are mainly controlled by the bedding.When the bedding angle is between 45°and 60°,the fracture propagation evolves from permeating the matrix to extending along the bedding;(ii)The fracture parameters exhibit significant size dependent behavior,as KICA and GICA rise with increasing specimen size,butσNu falls with increasing specimen sizes.The fracture parameters align with the theoretical predictions of Bažant size effect law;and(iii)The lengths of DIC-based FPZ,effective FPZ,and inelastic zone follow W-shape variations with bedding angle.The dimensionless sizes of FPZ and inelastic zone decrease with specimen size,indicating a size effect.Furthermore,there is a negative relation between KICA and the dimensionless size of the FPZ,whileσNu is positively correlated to the dimensionless size of the FPZ.This highlights the essential role of the FPZ in the size effect of rock fracture.The bedding angle exerts an influence on the FPZ,subsequently affecting the anisotropic fracture and size-dependent behavior of shale.展开更多
An analytical expression for the prediction of shear-compressive fracture process zone(SCFPZ) is derived by using a proposed local strain energy density criterion, in which the strain energy density is separated into ...An analytical expression for the prediction of shear-compressive fracture process zone(SCFPZ) is derived by using a proposed local strain energy density criterion, in which the strain energy density is separated into the dilatational and distortional strain energy density, only the former is considered to contribute to the brittle fracture of rock in different loading cases. The theoretical prediction by this criterion shows that the SCFPZ is of asymmetric mulberry leaf in shape, which forms a shear-compression fracture kern. Dilatational strain energy density along the boundary of SCFPZ reaches its maximum value. The dimension of SCFPZ is governed by the ratio of K_Ⅱ to (K_Ⅰ.) The analytical results are then compared with those from literatures and the tests conducted on double edge cracked Brazilian disk subjected to diametrical compression. The obtained results are useful to the prediction of crack extension and to nonlinear analysis of shear-compressive fracture of brittle rock.展开更多
Thefracture processof an ascast ZA27 alloy under thetensiletest atthe room temperature wasstudied. Theresultsshow thatthecracksof ZA27 alloy form at(α+ η)eutectic phaseand develop bypropagatingalongthe(α+ η) phas...Thefracture processof an ascast ZA27 alloy under thetensiletest atthe room temperature wasstudied. Theresultsshow thatthecracksof ZA27 alloy form at(α+ η)eutectic phaseand develop bypropagatingalongthe(α+ η) phaseandcuttingthroughthe dendriteαphaseand εphase. Theinfluenceof every phasein ZA27 on thestrength and ductility was ana lyzed.展开更多
On the basis of that rock material usually has a larger fracture process zone,a new fracture criterion which is different from that of linear elastic fracture theory was presented.On this basis,the fracture behavior a...On the basis of that rock material usually has a larger fracture process zone,a new fracture criterion which is different from that of linear elastic fracture theory was presented.On this basis,the fracture behavior and influencing factors under modeⅡor compressive shear loading were investigated.展开更多
This study investigates the fracture characteristics and the fracture process zone(FPZ)of mode I fracture in sandstone,aiming to analyze the propagation behaviors of mode I crack under different freeze-thaw cycles.Sem...This study investigates the fracture characteristics and the fracture process zone(FPZ)of mode I fracture in sandstone,aiming to analyze the propagation behaviors of mode I crack under different freeze-thaw cycles.Semicircular bending tests(SCB)were conducted using different freeze-thaw cycles to evaluate mode I fracture toughness,FPZ dynamics,and macroscopic microscopic features.Digital image correlation(DIC)and scanning electron microscopy(SEM)techniques were employed for detailed analysis.Experimental results reveal that freeze-thaw cycling leads to the widening of both preexisting and newly formed microcracks between internal particles.Under external loading,crack propagation deviates from prefabricated paths,forming serrated crack patterns.The FPZ initiates at the prefabricated crack tip and extends toward the loading end,exhibiting an arcshaped tip shape.The FPZ length increases with loading but decreases after reaching a peak value.With additional freeze-thaw cycles,the maximum FPZ length first increases and then diminishes.展开更多
This paper aims to characterize the evolution of the fracture process and the cracking behavior in fortaferro(FF)and polypropylene(PP)fiber-reinforced concrete under the uniaxial compressive loading using experimental...This paper aims to characterize the evolution of the fracture process and the cracking behavior in fortaferro(FF)and polypropylene(PP)fiber-reinforced concrete under the uniaxial compressive loading using experimental analysis and digital image correlation(DIC)on the surface displacement.For this purpose,6 mix designs,including two FF volume fractions of 0.10%,and 0.20%and three PP volume fractions of 0.20%,0.30%,and 0.40%,in addition to a control mix were evaluated according to compressive strength,modulus of elasticity,toughness index,and stress–strain curves.The influence of fibers on the microstructural texture of specimens was analyzed by scanning electron microscope(SEM)imaging.Results show that FF fiber-reinforced concrete specimens demonstrated increased ductility and strength compared to PP fiber.DIC results revealed that the major crack and fracture appeared at the peak load of the control specimen due to brittleness and sudden gain of large lateral strain,while a gradual increase in micro-crack quantity at 75%of peak load was observed in the fiber specimens,which thenbegan to connect with each other up to the final fracture.The accuracy of the results supports DIC as a reliable alternative for the characterization of the fracture process in fiber-reinforced concrete.展开更多
The development of geological lamination in shale reservoirs influences fracture propagation during hydraulic stimulation,and the fracture generation mechanism as it propagates through the laminated interface is close...The development of geological lamination in shale reservoirs influences fracture propagation during hydraulic stimulation,and the fracture generation mechanism as it propagates through the laminated interface is closely related to fracturing effects.In this paper,the laminated shale was selected to conduct three-point bending experiments using digital image correlation(DIC)and acoustic emission(AE)techniques,which revealed that the propagation path of cross-layer fractures exhibits dislocation features.The cohesive fracture mechanism of cross-layer fractures is investigated from the viewpoint of the fracture process zone(FPZ),which displays the characteristics of intermittence and dislocation during fracture development.A computational criterion for predicting the dislocation of cross-layer fracture at the interface is proposed,which shows that the maximum dislocation range does not exceed 72%of the FPZ length.Considering the mechanical differences between adjacent layers of laminated shale,the cohesive zone model of cross-layer fracture is discussed,from which the constitutive relationship and fracture energy during FPZ development are characterized,and the discontinuous nature of the constitutive relationship is found.This study improves the understanding of the geometry and cohesive fracture mechanism of the cross-layer fracture and provides valuable insights for field fracturing in shale reservoirs.展开更多
The deformation characters and load status of the blank＇s potential fracture zone are analyzed at the moment when blank is approaching to punch comer in drawing process of cone shape part. Based on tension instabilit...The deformation characters and load status of the blank＇s potential fracture zone are analyzed at the moment when blank is approaching to punch comer in drawing process of cone shape part. Based on tension instability theory, the formula for calculating fracture limit load of cone shape part in drawing process is derived. Also, the formula is analyzed and verified by experiment.展开更多
Fracture of the lateral process of the talus(FLPT)is uncommon in clinical practice and can be easily missed or misdiagnosed.In recent years,as researchers from all over the world have further deepened their research o...Fracture of the lateral process of the talus(FLPT)is uncommon in clinical practice and can be easily missed or misdiagnosed.In recent years,as researchers from all over the world have further deepened their research on FLPT,there has been a breakthrough in the classification,and the methods and principles of clinical management have changed accordingly;however,there is still no standardized guideline for the diagnosis and management of FLPT,and there have been few relevant literature review articles related to this kind of fracture in the past at least 5 years.In this article,we review the clinical classification,classification-based therapeutic recommendations,and prognosis of FLPT,with the aim of providing a reference for the clinical diagnosis and management of this infrequent fracture.展开更多
Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important g...Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important geometrical parameters, joint orientation and joint persistence, was studied systematically by carrying out a series of uniaxial compression tests on gypsum specimens with regularly arranged multiple parallel pre-existing joints. According to crack position, mechanism and temporal sequence, seven types of crack initiations and sixteen types of crack coalescences, were identified. It was observed that both tensile cracks and shear cracks can emanate from the pre-existing joints as well as the matrix. Vertical joints were included and coplanar tensile cracks initiation and coalescence were observed accordingly. For specimen with joint inclination angle ,8=75~, it was found that collinear joints can be linked not only by coplanar shear cracks but also by mixed tensile-shear cracks, and that a pair of them can form a small rotation block. Seven failure modes, including axial cleavage, crushing, crushing and rotation of new blocks, stepped failure, stepped failure and rotation of new blocks, shear failure along a single plane and shear failure along multiple planes, were observed. These modes shift gradually in accordance with the combined variation of joint orientation and joint persistence. It is concluded that cracking process and failure modes are more strongly affected by joint orientation than by joint persistence, especially when joint inclination angle is larger than 45~. Finally, variations of macroscopic mechanical behaviors with the two geometrical parameters, such as patterns of the complete axial stress-axial strain curves, peak strength and elastic modulus, are summarized and their mechanisms are successfully explained according to their different cracking process.展开更多
Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering.This investigation developed a brittle fracture model to predict te...Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering.This investigation developed a brittle fracture model to predict tensile mode(mode I)failure loads of cracked rocks.The basic principle of the model is to estimate the reference crack corresponding to the fracture process zone(FPZ)based on the maximum normal strain(MNSN)ahead of the crack tip,and then use the effective crack to calculate the fracture toughness.We emphasize that the non-singular stress/strain terms should be considered in the description of the MNSN.In this way,the FPZ,non-singular terms and the biaxial stress state at the crack tip are simul-taneously considered.The principle of the model is explicit and easy to apply.To verify the proposed model,laboratory experiments were performed on a rock material using six groups of specimens.The model predicted the specimen geometry dependence of the measured fracture toughness well.More-over,the potential of the model in analyzing the size effect of apparent fracture toughness was discussed and validated through experimental data reported in the literature.The model was demonstrated su-perior to some commonly used fracture models and is an excellent tool for the safety assessment of cracked rock structures.展开更多
The electro-magnetic (EM) and acoustic emission (AE) in the fracture process of both dry and wet rock samples including gabbro, granite, sandstone and marble are studied in the experiment in the laboratory under uniax...The electro-magnetic (EM) and acoustic emission (AE) in the fracture process of both dry and wet rock samples including gabbro, granite, sandstone and marble are studied in the experiment in the laboratory under uniaxial pressure. Signals during the test are detected in ultralow frequency band. The experimental results may be outlined as follows: original waveforms of the electro-magnetic radiation (EMR) and AE in the range of 0-20 kHz frequencies are obtained; the EMR's intensity in fracture process is related to some factors as rock type, content of water, fracture intensity of rocks, loading rates and fracture state etc.; the EMR'S rate is proportional to that of AE during fracture statistically. About 70% of maximum values of EMR rate and AE rate are corresponded with each other; furthermore, the EM signals (EMS) are generally more developed and longer duration than AE signals; the principal energy of EMS detected by copper coin antenna as sensor in power spectra are distributed in frequencies lower than 6 kHz and otherwise those detected by EMinduction coil are at about 10 kHz, and in contrast the major energies of AE are in frequencies less than3 kHz; another notable phenomenon is that distinct electro-magnetic signals are detected before AE occurrence. Since EMR and AE signals obtained in the process of rock fracture are better corresponded to eachother, therefore it'S reasonable to propose that the EMR anormalies observed prior to some earthquakes aremainly produced by fractures of rock in source region, as for the EMS occurred before AE may be related topiezoelectric and piezomagnetic effects.展开更多
The understanding of the mechanical behavior of granite containing fissures is of great significance for geothermal energy exploitation and high-level nuclear waste disposal repository.To consider the grain interlocki...The understanding of the mechanical behavior of granite containing fissures is of great significance for geothermal energy exploitation and high-level nuclear waste disposal repository.To consider the grain interlocking and rotational resistance behavior in granite specimens,the grain-based model 3D(GBM3D)was constructed to investigate the fracture behavior of granite specimens containing a single fissure.The numerical result indicates that this GBM3D can be used to investigate the mechanical behavior of granite constituted by different minerals,and it can provide more information to understand the mechanical behavior of specimens under loading process.The inter-granular cracks initiate in the first place,but the initiation of intra-granular cracks mainly concentrates after the peak strength.The tensile cracks between different minerals are more than that between the same minerals,and the intra-granular cracks in muscovite initiate firstly,and the number of them is more than that in other minerals.The wing crack is mainly constituted by the inter-granular cracks,and the shape of it is different in different depths,whereas the anti-wing is similar in different depths.展开更多
Punch shear tests have been widely used to determine rock shear mechanical properties but without a standard sample geometric dimension suggestion.To investigate the impacts of sample geometric dimensions on shear beh...Punch shear tests have been widely used to determine rock shear mechanical properties but without a standard sample geometric dimension suggestion.To investigate the impacts of sample geometric dimensions on shear behaviors in a punch shear test,simulations using Particle Flow Code were carried out.The effects of three geometric dimensions(i.e.,disk diameter,ratio of shear surface diameter to disk diameter,and ratio of disk height to shear surface diameter)were discussed.Variations of shear strength,shear stiffness,and shear dilatancy angles were studied,and the fracture processes and patterns of samples were investigated.Then,normal stress on the shear surface during test was analyzed and a suggested disk geometric dimension was given.Simulation results show that when the ratio of the shear surface diameter to the disk diameter and the ratio of disk height to the shear surface diameter is small enough,the shear strength,shear stiffness,and shear dilatancy angles are extremely sensitive to the three geometric parameters.If the ratio of surface diameter to disk diameter is too large or the ratio of disk height to surface diameter is too small,a part of the sample within the shear surface will fail due to macro tensile cracks,which is characterized by break off.Samples with a greater ratio of disk height to shear surface diameter,namely when the sample is relatively thick,crack from one end to the other while others crack from both ends towards the middle.During test,the actual normal stress on the shear surface is greater than the target value because of the extra compressive stress from the part of sample outside shear surface.展开更多
Low-cycle fatigue behavior of Ni-based superalloy GH586 with laser shock processing（LSP） was investigated. The residual stress of the specimens treated with LSP was assessed by X-ray diffraction method. The microstr...Low-cycle fatigue behavior of Ni-based superalloy GH586 with laser shock processing（LSP） was investigated. The residual stress of the specimens treated with LSP was assessed by X-ray diffraction method. The microstructure and fracture morphology were characterized by using an optical microscope（OM）, a scanning electron microscope（SEM）, and a transmission electron microscope（TEM）. The results indicated that the maximum residual compressive stress was at about 1 mm from the shocking spot center, where the residual compressive stress was slightly lower. High density tangling dislocations, dislocation walls, and dislocation cells in the microstructure of the specimens treated with LSP effectively prevented fatigue cracks propagation. The fatigue life was roughly twice as long as that of the specimens without LSP. The fatigue crack initiation（FCI） in specimens treated with LSP was observed in the lateral section and the subsurface simultaneously. The fatigue striation in the fracture treated with LSP was narrower than that in the untreated specimens. Moreover, dimples with tear ridges were found in the fatigued zones of the LSP treated specimens, which would be caused by severe plastic deformation.展开更多
In the application of high-pressure water jet assisted breaking of deep underground rock engineering,the influence mechanism of rock temperature on the rock fragmentation process under jet action is still unclear.Ther...In the application of high-pressure water jet assisted breaking of deep underground rock engineering,the influence mechanism of rock temperature on the rock fragmentation process under jet action is still unclear.Therefore,the fluid evolution characteristics and rock fracture behavior during jet impingement were studied.The results indicate that the breaking process of high-temperature rock by jet impact can be divided into four stages:initial fluid-solid contact stage,intense thermal exchange stage,perforation and fracturing stage,and crack propagation and penetration stage.With the increase of rock temperature,the jet reflection angles and the time required for complete cooling of the impact surface significantly decrease,while the number of cracks and crack propagation rate significantly increase,and the rock breaking critical time is shortened by up to 34.5%.Based on numerical simulation results,it was found that the center temperature of granite at 400℃ rapidly decreased from 390 to 260℃ within 0.7 s under jet impact.In addition,a critical temperature and critical heat flux prediction model considering the staged breaking of hot rocks was established.These findings provide valuable insights to guide the water jet technology assisted deep ground hot rock excavation project.展开更多
Based on the parallel bar system, combining with the synergetic method, the catastrophe theory and the acoustic emission test, a new motivated statistical damage model for quasi-brittle solid was developed. Taking con...Based on the parallel bar system, combining with the synergetic method, the catastrophe theory and the acoustic emission test, a new motivated statistical damage model for quasi-brittle solid was developed. Taking concrete for instances, the rationality and the flexibility of this model and its parameters-determining method were identified by the comparative analyses between theoretical and experimental curves. The results show that the model can simulate the whole damage and fracture process in the fracture process zone of material when the materials arc exposed to quasi-static uniaxial tensile traction. The influence of the mesoscopic damage mechanism on the macroscopic mechanical properties of quasi-brittle materials is summarized into two aspects, rupture damage and yield damage. The whole damage course is divided into the statistical even damage phase and the local breach phase, corresponding to the two stages described by the catastrophe theory. The two characteristic states, the peak nominal stress state and the critical state are distinguished, and the critical state plays a key role during the whole damage evolution course.展开更多
Reliable prediction of the shale fracturing process is a challenging problem in exploiting deep shale oil and gas resources.Complex fracture networks need to be artificially created to employ deep shale oil and gas re...Reliable prediction of the shale fracturing process is a challenging problem in exploiting deep shale oil and gas resources.Complex fracture networks need to be artificially created to employ deep shale oil and gas reserves.Randomly distributed minerals and heterogeneities in shales significantly affect mechanical properties and fracturing behaviors in oil and gas exploitation.Describing the actual microstructure and associated heterogeneities in shales constitutes a significant challenge.The RFPA3D(rock failure process analysis parallel computing program)-based modeling approach is a promising numerical technique due to its unique capability to simulate the fracturing behavior of rocks.To improve traditional numerical technology and study crack propagation in shale on the microscopic scale,a combination of high-precision internal structure detection technology with the RFPA^(3D) numerical simulation method was developed to construct a real mineral structure-based modeling method.First,an improved digital image processing technique was developed to incorporate actual shale microstructures(focused ion beam scanning electron microscopy was used to capture shale microstructure images that reflect the distri-butions of different minerals)into the numerical model.Second,the effect of mineral inhomogeneity was considered by integrating the mineral statistical model obtained from the mineral nanoindentation experiments into the numerical model.By simulating a shale numerical model in which pyrite particles are wrapped by organic matter,the effects of shale microstructure and applied stress state on microcrack behavior and mechanical properties were investigated and analyzed.In this study,the effect of pyrite particles on fracture propagation was systematically analyzed and summarized for the first time.The results indicate that the distribution of minerals and initial defects dominated the fracture evolution and the failure mode.Cracks are generally initiated and propagated along the boundaries of hard mineral particles such as pyrite or in soft minerals such as organic matter.Locations with collections of hard minerals are more likely to produce complex fractures.This study provides a valuable method for un-derstanding the microfracture behavior of shales.展开更多
Rock fracture mechanisms can be inferred from moment tensors(MT)inverted from microseismic events.However,MT can only be inverted for events whose waveforms are acquired across a network of sensors.This is limiting fo...Rock fracture mechanisms can be inferred from moment tensors(MT)inverted from microseismic events.However,MT can only be inverted for events whose waveforms are acquired across a network of sensors.This is limiting for underground mines where the microseismic stations often lack azimuthal coverage.Thus,there is a need for a method to invert fracture mechanisms using waveforms acquired by a sparse microseismic network.Here,we present a novel,multi-scale framework to classify whether a rock crack contracts or dilates based on a single waveform.The framework consists of a deep learning model that is initially trained on 2400000+manually labelled field-scale seismic and microseismic waveforms acquired across 692 stations.Transfer learning is then applied to fine-tune the model on 300000+MT-labelled labscale acoustic emission waveforms from 39 individual experiments instrumented with different sensor layouts,loading,and rock types in training.The optimal model achieves over 86%F-score on unseen waveforms at both the lab-and field-scale.This model outperforms existing empirical methods in classification of rock fracture mechanisms monitored by a sparse microseismic network.This facilitates rapid assessment of,and early warning against,various rock engineering hazard such as induced earthquakes and rock bursts.展开更多
Earthquakes result from continuous geodynamic processes.A topic of significant interest for the scientific community is to elaborate on the phenomena governing the faulting and fracturing of crustal rocks.Therefore,in...Earthquakes result from continuous geodynamic processes.A topic of significant interest for the scientific community is to elaborate on the phenomena governing the faulting and fracturing of crustal rocks.Therefore,in this study,uniaxial compressive shear failure experiments were conducted on Fangshan marble rock samples with a prefabricated slot to simulate thrust faulting.The center of each marble plate(105 mm × 80 mm × 5 mm) was engraved with a 30-mm long double-sided nonpenetrating slot(depth:2 mm,width:0.5 mm).The deformation and destruction processes of the rock surface were recorded using a high-speed camera.The digital image correlation method was used to calculate the displacement and strain distribution and variation at different loading stages.The accumulative and incremental displacement fields u and v,strain field exand e_(y),and shear strain e_(xy) were analyzed.When the loading level reached its ultimate value,the strain field was concentrated around the prefabricated slot.The concentration reached a maximum at the ends of the prefabricated slot.The magnitude of shear strain reached 0.1.This experiment contributes to our understanding of the dynamic process of active faulting.展开更多
基金funded by the National Natural Science Foundation of China(Grant Nos.12172230,U22A20166)the Department of Science and Technology of Guangdong Province(Grant No.2019ZT08G315).
文摘Understanding the anisotropic fracture behavior and the characteristics of the fracture process zone(FPZ)under size effects in laminated rocks,as well as its role in rock fracturing,is crucial for various engineering applications.In this study,three-point bending tests were conducted on shale specimens with varying bedding angles and sizes.The anisotropic characteristics and size effects of fracture parameters were revealed.A comparative analysis was performed on the evolutions of FPZs computed using size effect theory,digital image correlation(DIC),and linear elastic fracture mechanics.The results divulged that:(i)With increasing bedding angles,there is a noticeable decrease in apparent fracture toughness(KICA),apparent fracture energy(GICA),and nominal strength(σ_(Nu)).When the bedding angle of shale is less than 45°,the crack propagation and fracture parameters are mainly influenced by the matrix.Contrary,shale with bedding angles greater than 60°,the crack propagation and fracture parameters are mainly controlled by the bedding.When the bedding angle is between 45°and 60°,the fracture propagation evolves from permeating the matrix to extending along the bedding;(ii)The fracture parameters exhibit significant size dependent behavior,as KICA and GICA rise with increasing specimen size,butσNu falls with increasing specimen sizes.The fracture parameters align with the theoretical predictions of Bažant size effect law;and(iii)The lengths of DIC-based FPZ,effective FPZ,and inelastic zone follow W-shape variations with bedding angle.The dimensionless sizes of FPZ and inelastic zone decrease with specimen size,indicating a size effect.Furthermore,there is a negative relation between KICA and the dimensionless size of the FPZ,whileσNu is positively correlated to the dimensionless size of the FPZ.This highlights the essential role of the FPZ in the size effect of rock fracture.The bedding angle exerts an influence on the FPZ,subsequently affecting the anisotropic fracture and size-dependent behavior of shale.
基金Project(50274074) supported by the National Natural Science Foundation of China project(04JJ6030) supported by theNatural Science Foundation of Hunan Province
文摘An analytical expression for the prediction of shear-compressive fracture process zone(SCFPZ) is derived by using a proposed local strain energy density criterion, in which the strain energy density is separated into the dilatational and distortional strain energy density, only the former is considered to contribute to the brittle fracture of rock in different loading cases. The theoretical prediction by this criterion shows that the SCFPZ is of asymmetric mulberry leaf in shape, which forms a shear-compression fracture kern. Dilatational strain energy density along the boundary of SCFPZ reaches its maximum value. The dimension of SCFPZ is governed by the ratio of K_Ⅱ to (K_Ⅰ.) The analytical results are then compared with those from literatures and the tests conducted on double edge cracked Brazilian disk subjected to diametrical compression. The obtained results are useful to the prediction of crack extension and to nonlinear analysis of shear-compressive fracture of brittle rock.
文摘Thefracture processof an ascast ZA27 alloy under thetensiletest atthe room temperature wasstudied. Theresultsshow thatthecracksof ZA27 alloy form at(α+ η)eutectic phaseand develop bypropagatingalongthe(α+ η) phaseandcuttingthroughthe dendriteαphaseand εphase. Theinfluenceof every phasein ZA27 on thestrength and ductility was ana lyzed.
文摘On the basis of that rock material usually has a larger fracture process zone,a new fracture criterion which is different from that of linear elastic fracture theory was presented.On this basis,the fracture behavior and influencing factors under modeⅡor compressive shear loading were investigated.
基金supported by the projects(Grant No.:52304118)supported by National Natural Science Foundation of China,the Scientific Research Foundation for High-level Talents of Anhui University of Science and Technology(2023yjrc18)the Open Fund of the State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mine(Grant No.:SKLMRDPC23KF08).
文摘This study investigates the fracture characteristics and the fracture process zone(FPZ)of mode I fracture in sandstone,aiming to analyze the propagation behaviors of mode I crack under different freeze-thaw cycles.Semicircular bending tests(SCB)were conducted using different freeze-thaw cycles to evaluate mode I fracture toughness,FPZ dynamics,and macroscopic microscopic features.Digital image correlation(DIC)and scanning electron microscopy(SEM)techniques were employed for detailed analysis.Experimental results reveal that freeze-thaw cycling leads to the widening of both preexisting and newly formed microcracks between internal particles.Under external loading,crack propagation deviates from prefabricated paths,forming serrated crack patterns.The FPZ initiates at the prefabricated crack tip and extends toward the loading end,exhibiting an arcshaped tip shape.The FPZ length increases with loading but decreases after reaching a peak value.With additional freeze-thaw cycles,the maximum FPZ length first increases and then diminishes.
文摘This paper aims to characterize the evolution of the fracture process and the cracking behavior in fortaferro(FF)and polypropylene(PP)fiber-reinforced concrete under the uniaxial compressive loading using experimental analysis and digital image correlation(DIC)on the surface displacement.For this purpose,6 mix designs,including two FF volume fractions of 0.10%,and 0.20%and three PP volume fractions of 0.20%,0.30%,and 0.40%,in addition to a control mix were evaluated according to compressive strength,modulus of elasticity,toughness index,and stress–strain curves.The influence of fibers on the microstructural texture of specimens was analyzed by scanning electron microscope(SEM)imaging.Results show that FF fiber-reinforced concrete specimens demonstrated increased ductility and strength compared to PP fiber.DIC results revealed that the major crack and fracture appeared at the peak load of the control specimen due to brittleness and sudden gain of large lateral strain,while a gradual increase in micro-crack quantity at 75%of peak load was observed in the fiber specimens,which thenbegan to connect with each other up to the final fracture.The accuracy of the results supports DIC as a reliable alternative for the characterization of the fracture process in fiber-reinforced concrete.
基金financiallysupported by the Excellent Young Fund of Sinopec Petroleum Exploration and Production Research Institute(Grant No.YK2024009)the National Natural Science Foundation of China(Grant Nos.U23B6004 and 51925405).
文摘The development of geological lamination in shale reservoirs influences fracture propagation during hydraulic stimulation,and the fracture generation mechanism as it propagates through the laminated interface is closely related to fracturing effects.In this paper,the laminated shale was selected to conduct three-point bending experiments using digital image correlation(DIC)and acoustic emission(AE)techniques,which revealed that the propagation path of cross-layer fractures exhibits dislocation features.The cohesive fracture mechanism of cross-layer fractures is investigated from the viewpoint of the fracture process zone(FPZ),which displays the characteristics of intermittence and dislocation during fracture development.A computational criterion for predicting the dislocation of cross-layer fracture at the interface is proposed,which shows that the maximum dislocation range does not exceed 72%of the FPZ length.Considering the mechanical differences between adjacent layers of laminated shale,the cohesive zone model of cross-layer fracture is discussed,from which the constitutive relationship and fracture energy during FPZ development are characterized,and the discontinuous nature of the constitutive relationship is found.This study improves the understanding of the geometry and cohesive fracture mechanism of the cross-layer fracture and provides valuable insights for field fracturing in shale reservoirs.
基金This project is supported by Doctoral Education Foundation of Ministry ofEducation of China (No.96021602).
文摘The deformation characters and load status of the blank＇s potential fracture zone are analyzed at the moment when blank is approaching to punch comer in drawing process of cone shape part. Based on tension instability theory, the formula for calculating fracture limit load of cone shape part in drawing process is derived. Also, the formula is analyzed and verified by experiment.
基金Supported by The China Scholarship Council,No.202308420035.
文摘Fracture of the lateral process of the talus(FLPT)is uncommon in clinical practice and can be easily missed or misdiagnosed.In recent years,as researchers from all over the world have further deepened their research on FLPT,there has been a breakthrough in the classification,and the methods and principles of clinical management have changed accordingly;however,there is still no standardized guideline for the diagnosis and management of FLPT,and there have been few relevant literature review articles related to this kind of fracture in the past at least 5 years.In this article,we review the clinical classification,classification-based therapeutic recommendations,and prognosis of FLPT,with the aim of providing a reference for the clinical diagnosis and management of this infrequent fracture.
基金Project(11102224)supported by the National Natural Science Foundation of ChinaProject(2009QL05)supported by the Fundamental Research Funds for the Central Universities of China
文摘Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important geometrical parameters, joint orientation and joint persistence, was studied systematically by carrying out a series of uniaxial compression tests on gypsum specimens with regularly arranged multiple parallel pre-existing joints. According to crack position, mechanism and temporal sequence, seven types of crack initiations and sixteen types of crack coalescences, were identified. It was observed that both tensile cracks and shear cracks can emanate from the pre-existing joints as well as the matrix. Vertical joints were included and coplanar tensile cracks initiation and coalescence were observed accordingly. For specimen with joint inclination angle ,8=75~, it was found that collinear joints can be linked not only by coplanar shear cracks but also by mixed tensile-shear cracks, and that a pair of them can form a small rotation block. Seven failure modes, including axial cleavage, crushing, crushing and rotation of new blocks, stepped failure, stepped failure and rotation of new blocks, shear failure along a single plane and shear failure along multiple planes, were observed. These modes shift gradually in accordance with the combined variation of joint orientation and joint persistence. It is concluded that cracking process and failure modes are more strongly affected by joint orientation than by joint persistence, especially when joint inclination angle is larger than 45~. Finally, variations of macroscopic mechanical behaviors with the two geometrical parameters, such as patterns of the complete axial stress-axial strain curves, peak strength and elastic modulus, are summarized and their mechanisms are successfully explained according to their different cracking process.
基金he authors thank the financial support fromthe Key Program of National Natural Science Foundation of China(GrantNo.52039007)the Youth Science and Technology Innovation Research Team Fund of Sichuan Province(Grant No.2020JDTD0001).
文摘Evaluating the fracture resistance of rocks is essential for predicting and preventing catastrophic failure of cracked structures in rock engineering.This investigation developed a brittle fracture model to predict tensile mode(mode I)failure loads of cracked rocks.The basic principle of the model is to estimate the reference crack corresponding to the fracture process zone(FPZ)based on the maximum normal strain(MNSN)ahead of the crack tip,and then use the effective crack to calculate the fracture toughness.We emphasize that the non-singular stress/strain terms should be considered in the description of the MNSN.In this way,the FPZ,non-singular terms and the biaxial stress state at the crack tip are simul-taneously considered.The principle of the model is explicit and easy to apply.To verify the proposed model,laboratory experiments were performed on a rock material using six groups of specimens.The model predicted the specimen geometry dependence of the measured fracture toughness well.More-over,the potential of the model in analyzing the size effect of apparent fracture toughness was discussed and validated through experimental data reported in the literature.The model was demonstrated su-perior to some commonly used fracture models and is an excellent tool for the safety assessment of cracked rock structures.
文摘The electro-magnetic (EM) and acoustic emission (AE) in the fracture process of both dry and wet rock samples including gabbro, granite, sandstone and marble are studied in the experiment in the laboratory under uniaxial pressure. Signals during the test are detected in ultralow frequency band. The experimental results may be outlined as follows: original waveforms of the electro-magnetic radiation (EMR) and AE in the range of 0-20 kHz frequencies are obtained; the EMR's intensity in fracture process is related to some factors as rock type, content of water, fracture intensity of rocks, loading rates and fracture state etc.; the EMR'S rate is proportional to that of AE during fracture statistically. About 70% of maximum values of EMR rate and AE rate are corresponded with each other; furthermore, the EM signals (EMS) are generally more developed and longer duration than AE signals; the principal energy of EMS detected by copper coin antenna as sensor in power spectra are distributed in frequencies lower than 6 kHz and otherwise those detected by EMinduction coil are at about 10 kHz, and in contrast the major energies of AE are in frequencies less than3 kHz; another notable phenomenon is that distinct electro-magnetic signals are detected before AE occurrence. Since EMR and AE signals obtained in the process of rock fracture are better corresponded to eachother, therefore it'S reasonable to propose that the EMR anormalies observed prior to some earthquakes aremainly produced by fractures of rock in source region, as for the EMS occurred before AE may be related topiezoelectric and piezomagnetic effects.
基金This work was supported by the Project of National Natural Science Foundation of China(Grant No.42107159)Fundamental Research Funds for the Central Universities(Grant No.2021ZDPYJQ002).
文摘The understanding of the mechanical behavior of granite containing fissures is of great significance for geothermal energy exploitation and high-level nuclear waste disposal repository.To consider the grain interlocking and rotational resistance behavior in granite specimens,the grain-based model 3D(GBM3D)was constructed to investigate the fracture behavior of granite specimens containing a single fissure.The numerical result indicates that this GBM3D can be used to investigate the mechanical behavior of granite constituted by different minerals,and it can provide more information to understand the mechanical behavior of specimens under loading process.The inter-granular cracks initiate in the first place,but the initiation of intra-granular cracks mainly concentrates after the peak strength.The tensile cracks between different minerals are more than that between the same minerals,and the intra-granular cracks in muscovite initiate firstly,and the number of them is more than that in other minerals.The wing crack is mainly constituted by the inter-granular cracks,and the shape of it is different in different depths,whereas the anti-wing is similar in different depths.
基金supported by the Fundamental Research Funds for the Central Universities,CHD(Nos.300102210307,300102210308)the National Natural Science Foundation of China(Nos.51708040,41831286,51678063,51978065).
文摘Punch shear tests have been widely used to determine rock shear mechanical properties but without a standard sample geometric dimension suggestion.To investigate the impacts of sample geometric dimensions on shear behaviors in a punch shear test,simulations using Particle Flow Code were carried out.The effects of three geometric dimensions(i.e.,disk diameter,ratio of shear surface diameter to disk diameter,and ratio of disk height to shear surface diameter)were discussed.Variations of shear strength,shear stiffness,and shear dilatancy angles were studied,and the fracture processes and patterns of samples were investigated.Then,normal stress on the shear surface during test was analyzed and a suggested disk geometric dimension was given.Simulation results show that when the ratio of the shear surface diameter to the disk diameter and the ratio of disk height to the shear surface diameter is small enough,the shear strength,shear stiffness,and shear dilatancy angles are extremely sensitive to the three geometric parameters.If the ratio of surface diameter to disk diameter is too large or the ratio of disk height to surface diameter is too small,a part of the sample within the shear surface will fail due to macro tensile cracks,which is characterized by break off.Samples with a greater ratio of disk height to shear surface diameter,namely when the sample is relatively thick,crack from one end to the other while others crack from both ends towards the middle.During test,the actual normal stress on the shear surface is greater than the target value because of the extra compressive stress from the part of sample outside shear surface.
基金Funded by the Key Program Project of National Natural Science Foundation of China(NSFC)(No.51641102)Natural Science Foundation of Jiangsu Province(No.16KJB430035)+1 种基金Qing Lan Project of Jiangsu Province in ChinaNational Key Laboratory of Science and Technology on Power Beam Processes of Beijing Aeronautical Manufacturing Technology Research Institute
文摘Low-cycle fatigue behavior of Ni-based superalloy GH586 with laser shock processing（LSP） was investigated. The residual stress of the specimens treated with LSP was assessed by X-ray diffraction method. The microstructure and fracture morphology were characterized by using an optical microscope（OM）, a scanning electron microscope（SEM）, and a transmission electron microscope（TEM）. The results indicated that the maximum residual compressive stress was at about 1 mm from the shocking spot center, where the residual compressive stress was slightly lower. High density tangling dislocations, dislocation walls, and dislocation cells in the microstructure of the specimens treated with LSP effectively prevented fatigue cracks propagation. The fatigue life was roughly twice as long as that of the specimens without LSP. The fatigue crack initiation（FCI） in specimens treated with LSP was observed in the lateral section and the subsurface simultaneously. The fatigue striation in the fracture treated with LSP was narrower than that in the untreated specimens. Moreover, dimples with tear ridges were found in the fatigued zones of the LSP treated specimens, which would be caused by severe plastic deformation.
基金supported by National Natural Science Foundation of China (No.U23A20597)National Major Science and Technology Project of China (No.2024ZD1003803)+1 种基金Chongqing Science Fund for Distinguished Young Scholars of Chongqing Municipality (No.CSTB2022NSCQ-JQX0028)Natural Science Foundation of Chongqing (No.CSTB2024NSCQ-MSX0503)。
文摘In the application of high-pressure water jet assisted breaking of deep underground rock engineering,the influence mechanism of rock temperature on the rock fragmentation process under jet action is still unclear.Therefore,the fluid evolution characteristics and rock fracture behavior during jet impingement were studied.The results indicate that the breaking process of high-temperature rock by jet impact can be divided into four stages:initial fluid-solid contact stage,intense thermal exchange stage,perforation and fracturing stage,and crack propagation and penetration stage.With the increase of rock temperature,the jet reflection angles and the time required for complete cooling of the impact surface significantly decrease,while the number of cracks and crack propagation rate significantly increase,and the rock breaking critical time is shortened by up to 34.5%.Based on numerical simulation results,it was found that the center temperature of granite at 400℃ rapidly decreased from 390 to 260℃ within 0.7 s under jet impact.In addition,a critical temperature and critical heat flux prediction model considering the staged breaking of hot rocks was established.These findings provide valuable insights to guide the water jet technology assisted deep ground hot rock excavation project.
基金Projects(90510018, 50679006) supported by the National Natural Science Foundation of ChinaProject(NCET-05-0413) support by the Program for New Century Excellent Talents in University
文摘Based on the parallel bar system, combining with the synergetic method, the catastrophe theory and the acoustic emission test, a new motivated statistical damage model for quasi-brittle solid was developed. Taking concrete for instances, the rationality and the flexibility of this model and its parameters-determining method were identified by the comparative analyses between theoretical and experimental curves. The results show that the model can simulate the whole damage and fracture process in the fracture process zone of material when the materials arc exposed to quasi-static uniaxial tensile traction. The influence of the mesoscopic damage mechanism on the macroscopic mechanical properties of quasi-brittle materials is summarized into two aspects, rupture damage and yield damage. The whole damage course is divided into the statistical even damage phase and the local breach phase, corresponding to the two stages described by the catastrophe theory. The two characteristic states, the peak nominal stress state and the critical state are distinguished, and the critical state plays a key role during the whole damage evolution course.
基金supported by the Central Program of Basic Science of the National Natural Science Foundation of China(No.72088101)"The theory and application of resource and environment management in the digital economy era"+1 种基金The National Natural Science Foundation of China(No.41941018)Scientific research and technological development program of RIPED,"major research of basic geologic and synergy research of engineering practice on Gulong shale oil"(No.2021ycq01).
文摘Reliable prediction of the shale fracturing process is a challenging problem in exploiting deep shale oil and gas resources.Complex fracture networks need to be artificially created to employ deep shale oil and gas reserves.Randomly distributed minerals and heterogeneities in shales significantly affect mechanical properties and fracturing behaviors in oil and gas exploitation.Describing the actual microstructure and associated heterogeneities in shales constitutes a significant challenge.The RFPA3D(rock failure process analysis parallel computing program)-based modeling approach is a promising numerical technique due to its unique capability to simulate the fracturing behavior of rocks.To improve traditional numerical technology and study crack propagation in shale on the microscopic scale,a combination of high-precision internal structure detection technology with the RFPA^(3D) numerical simulation method was developed to construct a real mineral structure-based modeling method.First,an improved digital image processing technique was developed to incorporate actual shale microstructures(focused ion beam scanning electron microscopy was used to capture shale microstructure images that reflect the distri-butions of different minerals)into the numerical model.Second,the effect of mineral inhomogeneity was considered by integrating the mineral statistical model obtained from the mineral nanoindentation experiments into the numerical model.By simulating a shale numerical model in which pyrite particles are wrapped by organic matter,the effects of shale microstructure and applied stress state on microcrack behavior and mechanical properties were investigated and analyzed.In this study,the effect of pyrite particles on fracture propagation was systematically analyzed and summarized for the first time.The results indicate that the distribution of minerals and initial defects dominated the fracture evolution and the failure mode.Cracks are generally initiated and propagated along the boundaries of hard mineral particles such as pyrite or in soft minerals such as organic matter.Locations with collections of hard minerals are more likely to produce complex fractures.This study provides a valuable method for un-derstanding the microfracture behavior of shales.
基金supported by Western Research Interdisciplinary Initiative R6259A03.
文摘Rock fracture mechanisms can be inferred from moment tensors(MT)inverted from microseismic events.However,MT can only be inverted for events whose waveforms are acquired across a network of sensors.This is limiting for underground mines where the microseismic stations often lack azimuthal coverage.Thus,there is a need for a method to invert fracture mechanisms using waveforms acquired by a sparse microseismic network.Here,we present a novel,multi-scale framework to classify whether a rock crack contracts or dilates based on a single waveform.The framework consists of a deep learning model that is initially trained on 2400000+manually labelled field-scale seismic and microseismic waveforms acquired across 692 stations.Transfer learning is then applied to fine-tune the model on 300000+MT-labelled labscale acoustic emission waveforms from 39 individual experiments instrumented with different sensor layouts,loading,and rock types in training.The optimal model achieves over 86%F-score on unseen waveforms at both the lab-and field-scale.This model outperforms existing empirical methods in classification of rock fracture mechanisms monitored by a sparse microseismic network.This facilitates rapid assessment of,and early warning against,various rock engineering hazard such as induced earthquakes and rock bursts.
基金This research was supported by the National Key R&D Program of China(Nos.2018YFC1504203 and SQ2017YFSF040025).
文摘Earthquakes result from continuous geodynamic processes.A topic of significant interest for the scientific community is to elaborate on the phenomena governing the faulting and fracturing of crustal rocks.Therefore,in this study,uniaxial compressive shear failure experiments were conducted on Fangshan marble rock samples with a prefabricated slot to simulate thrust faulting.The center of each marble plate(105 mm × 80 mm × 5 mm) was engraved with a 30-mm long double-sided nonpenetrating slot(depth:2 mm,width:0.5 mm).The deformation and destruction processes of the rock surface were recorded using a high-speed camera.The digital image correlation method was used to calculate the displacement and strain distribution and variation at different loading stages.The accumulative and incremental displacement fields u and v,strain field exand e_(y),and shear strain e_(xy) were analyzed.When the loading level reached its ultimate value,the strain field was concentrated around the prefabricated slot.The concentration reached a maximum at the ends of the prefabricated slot.The magnitude of shear strain reached 0.1.This experiment contributes to our understanding of the dynamic process of active faulting.
