The roughness of the fracture surface directly affects the strength,deformation,and permeability of the surrounding rock in deep underground engineering.Understanding the effect of high temperature and thermal cycle o...The roughness of the fracture surface directly affects the strength,deformation,and permeability of the surrounding rock in deep underground engineering.Understanding the effect of high temperature and thermal cycle on the fracture surface roughness plays an important role in estimating the damage degree and stability of deep rock mass.In this paper,the variations of fracture surface roughness of granite after different heating and thermal cycles were investigated using the joint roughness coefficient method(JRC),three-dimensional(3D)roughness parameters,and fractal dimension(D),and the mechanism of damage and deterioration of granite were revealed.The experimental results show an increase in the roughness of the granite fracture surface as temperature and cycle number were incremented.The variations of JRC,height parameter,inclination parameter and area parameter with the temperature conformed to the Boltzmann's functional distribution,while the D decreased linearly as the temperature increased.Besides,the anisotropy index(Ip)of the granite fracture surface increased as the temperature increased,and the larger parameter values of roughness characterization at different temperatures were attained mainly in directions of 20°–40°,60°–100°and 140°–160°.The fracture aperture of granite after fracture followed the Gauss distribution and the average aperture increased with increasing temperature,which increased from 0.665 mm at 25℃to 1.058 mm at 800℃.High temperature caused an uneven thermal expansion,water evaporation,and oxidation of minerals within the granite,which promoted the growth and expansion of microfractures,and reduced interparticle bonding strength.In particular,the damage was exacerbated by the expansion and cracking of the quartz phase transition after T>500℃.Thermal cycles contributed to the accumulation of this damage and further weakened the interparticle bonding forces,resulting in a significant increase in the roughness,anisotropy,and aperture of the fracture surface after five cycles.展开更多
In order to understand the mechanical properties and the fracture surface roughness characteristics of thermally damaged granite under dynamic splitting,dynamic Brazilian splitting tests were conducted on granite samp...In order to understand the mechanical properties and the fracture surface roughness characteristics of thermally damaged granite under dynamic splitting,dynamic Brazilian splitting tests were conducted on granite samples after thermal treatment at 25,200,400,and 600℃.Results show that the dynamic peak splitting strength of thermally damaged granite samples increases with increasing strain rate,showing obvious strain‐rate sensitivity.With increasing temperature,thermally induced cracks in granite transform from intergranular cracks to intragranular cracks,and to a transgranular crack network.Thermally induced damages reduce the dynamic peak splitting strength and the maximum absorbed energy while increasing the peak radial strain.The fracture mode of the thermally damaged granite under dynamic loads is mode Ⅱ splitting failure.By using the axial roughness index Z2 a,the distribution ranges of the wedge‐shaped failure zones and the tensile failure zones in the fracture surfaces under dynamic Brazilian splitting can be effectively identified.The radial roughness index Z_(2)^(r)is sensitive to the strain rate and temperature.It shows a linear correlation with the peak splitting strength and the maximum absorbed energy and a linear negative correlation with the peak radial strain.Z_(2)^(r)can be used to quantitatively estimate the dynamic parameters based on the models proposed.展开更多
Deep geothermal extraction processes expose rock masses to frequent and significant temperature fluctuations. Developing a comprehensive understanding of the shear fracture mechanisms and crack propagation behaviors i...Deep geothermal extraction processes expose rock masses to frequent and significant temperature fluctuations. Developing a comprehensive understanding of the shear fracture mechanisms and crack propagation behaviors in rocks under the influence of cyclic heating is imperative for optimizing geothermal energy extraction. This study encompasses several critical aspects under cyclic heating conditions, including the assessment of stress distribution states, the characterization of two-dimensional fracture paths, the quantitative analysis of three-dimensional damage characteristics on fracture surfaces, and the determination of the fractal dimension of debris generated after the failure of granite. The test results demonstrate that cyclic heating has a pronounced adverse effect on the physical and mechanical properties of granite. Consequently, stress tends to develop and propagate in a direction perpendicular to the two-dimensional fracture path. This leads to an increase in the extent of tensile damage on the fracture surface and accelerates the overall rock failure process. This increases the number of small-sized debris, raises the fractal dimension, and enhances the rock’s rupture degree. In practical enhanced geothermal energy extraction, the real-time monitoring of fracture propagation within the reservoir rock mass is achieved through the analysis of rock debris generated during the staged fracturing process.展开更多
Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted r...Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted regarding various initial normal stresses(1e7 MPa)and numbers of shearing cycles(1 e5).The peak shear stress of fractures decreased with shear cycles due to progressively smooth surface morphologies,while increased with both JRC and initial normal stress and could be verified using the nonlinear Barton-Bandis failure criterion.The joint friction angle of fractures exponentially increased by 62.22%e64.87%with JRC while decreased by 22.1%e24.85%with shearing cycles.After unloading normal stress,the sliding initiation time of fractures increased with both JRC and initial normal stress due to more tortuous fracture morphologies and enhanced shearing resistance capacity.The surface resistance index(SRI)of fractures decreased by 4.35%e32.02%with increasing shearing cycles due to a more significant reduction of sliding initiation shear stress than that for sliding initiation normal stress,but increased by a factor of 0.41e1.64 with JRC.After sliding initiation,the shear displacement of fractures showed an increase in power function.By defining a sliding rate threshold of 5105 m/s,transition from“quasi-static”to“dynamic”sliding of fractures was identified,and the increase of sliding acceleration steepened with JRC while slowed down with shearing cycles.The normal displacement experienced a slight increase before shear sliding due to deformation recovery as the unloading stress was unloaded,and then enhanced shear dilation after sliding initiation due to climbing effects of surface asperities.Dilation was positively related to the shear sliding velocity of fractures.Wear characteristics of the fracture surfaces after shearing failure were evaluated using binary calculation,indicating an increasing shear area ratio by 45.24%e91.02%with normal stress.展开更多
In order to improve the properties of silica sol shell for investment casting process, various contents of cattail fibers were added into the slurry to prepare a fiber-reinforced shell in the present study. The bendin...In order to improve the properties of silica sol shell for investment casting process, various contents of cattail fibers were added into the slurry to prepare a fiber-reinforced shell in the present study. The bending strength of fiber-reinforced shell was investigated and the fracture surfaces of shell specimens were observed using SEM. It is found that the bending strength increases with the increase of fiber content, and the bending strength of a green shell with 1.0 wt.% fiber addition increases by 44% compared to the fiber-free shell. The failure of specimens of the fiber-reinforced green shell results from fiber rupture and debonding between the interface of fibers and adhesive under the bending load. The micro-crack propagation in the matrix is inhibited by the micro-holes for ablation of f ibers in specimens of the f iber-reinforced shell during the stage of being fired. As a result, the bending strength of specimens of the fired shell had no significant drop. Particularly, the bending strength of specimens of the fired shell reinforced with 0.6wt.% fiber reached the maximum value of 4.6 MPa.展开更多
Molecular dynamics simulation of uniaxial tension along [001] has been performed to study the influence of various surface defects on the initiation of plastic deformation and fracture of γ-TiAl single crystals.The r...Molecular dynamics simulation of uniaxial tension along [001] has been performed to study the influence of various surface defects on the initiation of plastic deformation and fracture of γ-TiAl single crystals.The results indicate that brittle fracture occurs in perfect bulk; surfaces and edges will be detrimental to the strength of materials and provide dislocation nucleation site. The defects on surfaces and edges cause further weakening with various effects depending on defect type, size, position and orientation,while the edge dimples are the most influential. For γ-TiAl rods with surface dimples, dislocations nucleate from an edge of the rod when dimples are small, dimple dislocation nucleation occurs only when the dimples are larger than a strain rate dependent critical size. The dislocations nucleated upon [001]tension are super dislocations with Burger vectors 〈011] or 1/2 〈 112] containing four 1/6 〈 112 〉 partials. The effects of surface scratches are orientation and shape sensitive. Scratches parallel to the loading direction have little influence, while sharp ones perpendicular to the loading direction may cause crack and thus should be avoided. This simulation also shows that, any type of surface defect would lower strength,and cause crack in some cases. But some may facilitate dislocation nucleation and improve ductility of TiAl if well controlled.展开更多
In this paper, simulated experiment device of coal and gas outburst was employed to perform the experiment on gas-containing coal extrusion. In the experiment, coal surface cracks were observed with a high-speed camer...In this paper, simulated experiment device of coal and gas outburst was employed to perform the experiment on gas-containing coal extrusion. In the experiment, coal surface cracks were observed with a high-speed camera and then the images were processed by sketch. Based on the above description, the paper studied the fractal dimension values from different positions of coal surface as well as their changing laws with time. The results show that there is a growing parabola trend of crack dimension value in the process of coal extrusion. Accordingly, we drew the conclusion that extruded coal crack evolution is a process of fractal dimension value increase. On the basis of fractal dimension values taken from different parts of coal masses, a fractal dimension of the contour map was drawn. Thus, it is clear that the contour map involves different crack fractal dimension values from different positions. To be specific, where there are complicated force and violent movement in coal mass, there are higher fractal dimension values, i.e., the further the middle of observation surface is from the exit of coal mass, and the lower the fractal dimension value is. In line with fractal geometry and energy theory of coal and gas outburst, this study presents the relation between fractal dimension and energy in the process of extruding. In conclusion, the evolution of crack fractal dimension value can signify that of energy, which has laid a solid foundation for the quantification research on the mechanism of gas-containing coal extrusion.展开更多
The tensile properties and fracture surface of 07MnNiCrMoVDR steel welded joint at low temperature have been studied by universal testing machine and scanning electron microscope. The results show that the tensile pro...The tensile properties and fracture surface of 07MnNiCrMoVDR steel welded joint at low temperature have been studied by universal testing machine and scanning electron microscope. The results show that the tensile properties of 07MnNiCrMoVDR steel welded joint are greatly affected by temperature. Tensile strength and yield strength of 07MnNiCrMoVDR steel welded joint increase, but elongation and reduction of area decrease with temperature decreasing. The macro-fracture of 07 MnNiCrMoVDR steel welded joint exhibits that the shear lip is not significant and micro-fracture makes up of dimpled fracture and tear fracture, and dimple becomes tiny and uniform with temperature decreasing.展开更多
After calculation on the fracture angles under various conditions of specific surface energies with different symmetry operations of rotation, the complicated behavior of dependence of fractal dimension on the structu...After calculation on the fracture angles under various conditions of specific surface energies with different symmetry operations of rotation, the complicated behavior of dependence of fractal dimension on the structure of crystal is shown. It is found that the crack propagates along the weakest crystal plane no matter what the direction of the maximum stress is if the anisotropy is sufficiently strong; and then, the fractal dimension of the fractured surfaces might be determined by the approximate fractal structure already existed in the material. Specificity of the fractal dimension of fractured surfaces would be easy to appear in this case. Reversely, the crack propagates along the direction of the maximum stress no matter what direction of the weakest crystal plane is if the anisotropy is sufficiently weak. Universality of the fractal dimension of fractured surfaces would be possible to appear in this case. In many real materials, universality and specificity of the materials are associated. The fractal dimension measured may more or less be influenced by the structure of materials and it shows its universality through the specificity of materials.展开更多
The surface fracture toughness is an important mechanical parameter for studying the failure behavior of air plasma sprayed(APS)thermal barrier coatings(TBCs).As APS TBCs are typical multilayer porous ceramic material...The surface fracture toughness is an important mechanical parameter for studying the failure behavior of air plasma sprayed(APS)thermal barrier coatings(TBCs).As APS TBCs are typical multilayer porous ceramic materials,the direct applications of the traditional single edge notched beam(SENB)method that ignores those typical structural characters may cause errors.To measure the surface fracture toughness more accurately,the effects of multilayer and porous characters on the fracture toughness of APS TBCs should be considered.In this paper,a modified single edge V-notched beam(MSEVNB)method with typical structural characters is developed.According to the finite element analysis(FEA),the geometry factor of the multilayer structure is recalculated.Owing to the narrower V-notches,a more accurate critical fracture stress is obtained.Based on the Griffith energy balance,the reduction of the crack surface caused by micro-defects is corrected.The MSEVNB method can measure the surface fracture toughness more accurately than the SENB method.展开更多
Supercritical CO_(2) fracturing is an important development trend to reach the goal of"dual carbon"and avoid the problem that hydraulic fracturing is influenced by water resource.In order to clarify the trans...Supercritical CO_(2) fracturing is an important development trend to reach the goal of"dual carbon"and avoid the problem that hydraulic fracturing is influenced by water resource.In order to clarify the transport characteristics of proppant in the fractures induced by supercritical CO_(2) fracturing,this paper reconstructs the fracture surface of rock samples after supercritical CO_(2) fracturing using the laser morphological scanning technology,and establishes a model of proppant carrying and transport of supercritical CO_(2) in tortuous fractures on the basis of CFD-DEM method.In addition,the transport and placement characteristics of proppant in tortuous fractures are analyzed by comparing withflat fractures,and the effects of proppant density,injection rate of proppant carrying liquid,proppant concentration and other key parameters on proppant transport and distribution in fractures are investigated.And the following research results are obtained.First,compared with those inflat fractures,theflow paths of the proppant carrying supercritical CO_(2) liquid in tortuous fractures are tortuous and diverse,and the proppant presents strongerfluctuations and jumps laterally and vertically during its transport.Second,the proppant placement in tortuous fractures morphologically presents a wavy or even clustered non-uniform distribution.Third,low-density proppant has a better pass-ability in tortuous fractures,and the high injection rate can reduce the influence of tortuous fracture structure on proppant blocking.Fourth,if the concentration of injected proppant in the tortuous fracture is too low,good fracturing support effect cannot be achieved,and the optimal value under the simulation conditions in this paper is around 3%.In conclusion,the simulation results are of important theoretical and engineering significance to understanding the mechanism of proppant blocking in the pumping process of proppant carrying liquid for supercritical CO_(2) fracturing and optimizing thefield fracturing design.展开更多
To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture surfaces for determining the fracture toughness parameters of J-integral for plain strain wa...To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed The principle of the fracture-surface topography analysis （FRASTA） was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each other well.展开更多
Three different punches are designed for the hydropiercing experiments and finite element simulations are conducted by finite element program ABAQUS-3D to investigate the influence of punch shape on the fracture surfa...Three different punches are designed for the hydropiercing experiments and finite element simulations are conducted by finite element program ABAQUS-3D to investigate the influence of punch shape on the fracture surface quality of hydropiercing holes. The results show the fracture burrs are not obvious punched by all the three punches. The collapse punched by the round punch is a little larger than the others. The fracture surface quality punched by the round punch is good with larger smooth zone and the interface between smooth zone and tear zone is even with large gradient. The size of the smooth zone is larger and the interface between smooth zone and tear zone is uneven with large gradient punched by the flat punch. The size of the smooth zone is smaller and the size of the tear zone increases from the first fractured to the last fractured punched by the inclined punch.展开更多
Fractal analysis of fracture surfaces in different kinds of refractories including magnesia-carbon and magnesia-chrome refractories was investigated.The fractal dimensions of fracture surfaces for three points bending...Fractal analysis of fracture surfaces in different kinds of refractories including magnesia-carbon and magnesia-chrome refractories was investigated.The fractal dimensions of fracture surfaces for three points bending test were determined by slit island method.The results show that the cold modulus of rupture increases with fractal dimension increasing due to the change in fracture mode depending on the bonding mechanism for a certain refractory material.展开更多
6082-T6 aluminum alloy is a commonly used aluminum alloy material in the field of rail transit because of its good molding properties,high mechanical properties,excellent corrosion resistance and weldability.In the hi...6082-T6 aluminum alloy is a commonly used aluminum alloy material in the field of rail transit because of its good molding properties,high mechanical properties,excellent corrosion resistance and weldability.In the high temperature and humid environment,the temperature change is bound to affect the stress corrosion resistance of the aluminum alloy and their welded joint.However,the influence mechanism of temperature on its stress corrosion resistance has not been explained in the existing research.In this paper,the mechanical properties and stress corrosion behaviors of melt-inert gas welded(MIG)6082-T6 aluminum alloy welded joints were systematically studied under various temperatures condition.Results indicated the temperature scarcely affected stress corrosion cracking susceptibility index(P_(SCC))of base metal,while significantly affected the welded joint and higher temperature caused lower P_(SCC).After slow strain rate tensile test,a corrosion layer was formed,which was a typical brittle-toughness mixed failure,and the degree of brittleness increased with the increasing of temperature.Electrochemical analysis showed that corrosion resistance of the joint slightly decreased due to aluminum alloy accelerated dissolution caused by increasing of temperature.The proposed research will provide a theoretical basis for solving aluminum alloys used in rail transit,ship accessories and other industrial fields.展开更多
The aim of this research was to develop an intrarradicular dental post based on epoxy resin/nano zirconium phosphate composite with potential appli-cation in prosthetic dentistry. Zirconium phosphate (ZrP) nanoparticl...The aim of this research was to develop an intrarradicular dental post based on epoxy resin/nano zirconium phosphate composite with potential appli-cation in prosthetic dentistry. Zirconium phosphate (ZrP) nanoparticle was synthesized by a reaction between phosphoric acid (H3PO4) and zirconium (IV) oxide chloride 8-hydrate (ZrOCl2·8H2O) and applied as filler. Commer-cial epoxy resin and hardener were used as polymer matrix. The composites were prepared at different proportions of epoxy resin/hardener, filler amount, reaction time and temperature. Infrared revealed that degree of conversion decreased with amount of ZrP. Insoluble matter was upper than 97%. Thermogravimetry indicated two steps of degradation. The best values of flexural modulus and flexural strength were achieved for the post desig-nated as 1:0.25:0.25. Laser scanning confocal microscopy suggested that the morphology of the posts fractured surface varied according to epoxy-resin:hardener ratio and the ZrP amount. From atomic force micros-copy, the topographic view exposed the shape and size of ZrP particles. Field emission scanning electron microscopy and energy dispersive spectroscopy indicated good adhesion between epoxy resin matrix-ZrP and that the pres-ence of phosphate rendered brittle the fracture surface.展开更多
The crack propagation rates of T6 peak aging and T7951 secondary aging 7055 aluminium alloys were tested under stress ratios (R) of 0.6, 0.05 and ?1, respectively. The microstructures and fracture surfaces were analyz...The crack propagation rates of T6 peak aging and T7951 secondary aging 7055 aluminium alloys were tested under stress ratios (R) of 0.6, 0.05 and ?1, respectively. The microstructures and fracture surfaces were analyzed by TEM and SEM. The results reveal that the crack propagation rate is affected by the stress ratio and microstructure such as the distribution, dimension and volume fraction of matrix precipitates, grain boundary precipitates and precipitate free zone. For both heat-treated specimens, crack propagation rate increases with the improvement of R when it is a positive value while crack propagation rate at R=?1 is much similar to that at R=0.06. The crack growth rates exhibit no obvious difference in lower stress intensity factor range (ΔK), while the difference starts to be obvious when ΔK exceeds certain value. The fracture analysis testifies a better fracture toughness for 7055-T7951 with a smaller striation space in Paris region.展开更多
The microstructure and mechanical properties of rheocasting AZ91 magnesium alloy were investigated. The semisolid slurry of this alloy was prepared by ultrasonic vibration （USV） process and then shaped by high press...The microstructure and mechanical properties of rheocasting AZ91 magnesium alloy were investigated. The semisolid slurry of this alloy was prepared by ultrasonic vibration （USV） process and then shaped by high pressure diecasting （HPDC）. The results show that fine and spherical a-Mg particles were obtained by USV at the nucleation stage, which was mainly attributed to the cavitation and acoustic streaming induced by the USV. Extending USV treatment time increased the solid volume fraction and average particle size, the shape factors were nearly the same, about 0.7. Excellent semisolid slurry of AZ91 magnesium alloy could be obtained within 6 rain by USV near its liquidus temperature. The rheo-HPDC samples treated by USV for 6 min had the maximum ultimate tensile strength and elongation, which were 248 MPa and 7.4%, respectively. It was also found that the ductile fracture mode prevailed in the rheocasting AZ91 magnesium alloy.展开更多
Fractures in rock strata serve as flow pathways for gas flow.The undulation of fracture channels can influence the guidance of gas flow.In this context,four-point bending experiments on prefabricated fractured rocks a...Fractures in rock strata serve as flow pathways for gas flow.The undulation of fracture channels can influence the guidance of gas flow.In this context,four-point bending experiments on prefabricated fractured rocks at different angles under stable stepped loading stress.The experiment results clarified the evolutionary law that the undulation degree of the rock tensile fracture surface is separated by an initial fracture angle of 45°.The high undulation intervals were less than 45°,whereas the low undulation intervals were more than 45°.Furthermore,the relative undulation degree,undulation frequency,and matching degree of the fracture surface were quantified.The relationship between the change in fracture surface undulation and gas flow guidance was established.Based on this,the stability,tortuosity,and uniformity of the gas flow in the fracture channel were quantitatively characterized.Subsequently,numerical models of the fracture channels were constructed to validate the indices proposed in this study.The results of the study clarified the influence of different initial fracture angles on the undulation changes of fracture surfaces,and established the relationship between these changes and gas flow,which is conducive to understanding the role of internal fracture channels in rocks in guiding the gas flow process.展开更多
The effect of friction coefficient on the deep drawing of aluminum alloy AA6111 at elevated temperatures was analyzed based on the three conditions using the finite element analysis and the experimental approach.Resul...The effect of friction coefficient on the deep drawing of aluminum alloy AA6111 at elevated temperatures was analyzed based on the three conditions using the finite element analysis and the experimental approach.Results indicate that the friction coefficient and lubrication position significantly influence the minimum thickness,the thickness deviation and the failure mode of the formed parts.During the hot forming process,the failure modes are draw mode,stretch mode and equi-biaxial stretch mode induced by different lubrication conditions.In terms of formability,the optimal value of friction coefficient determined in this work is 0.15.At the same time,the good agreement is performed between the experimental and simulated results.Fracture often occurs at the center of cup bottom or near the cup corner in a ductile mode or ductile-brittle mixed mode,respectively.展开更多
基金funding support from the National Natural Science Foundation of China(Grant No.52274082)the Program of Qingjiang Excellent Young Talents,Jiangxi University of Science and Technology(Grant No.JXUSTQJBJ2020003)the Innovation Fund Designated for Graduate Students of Jiangxi Province(Grant No.YC2023-B215).
文摘The roughness of the fracture surface directly affects the strength,deformation,and permeability of the surrounding rock in deep underground engineering.Understanding the effect of high temperature and thermal cycle on the fracture surface roughness plays an important role in estimating the damage degree and stability of deep rock mass.In this paper,the variations of fracture surface roughness of granite after different heating and thermal cycles were investigated using the joint roughness coefficient method(JRC),three-dimensional(3D)roughness parameters,and fractal dimension(D),and the mechanism of damage and deterioration of granite were revealed.The experimental results show an increase in the roughness of the granite fracture surface as temperature and cycle number were incremented.The variations of JRC,height parameter,inclination parameter and area parameter with the temperature conformed to the Boltzmann's functional distribution,while the D decreased linearly as the temperature increased.Besides,the anisotropy index(Ip)of the granite fracture surface increased as the temperature increased,and the larger parameter values of roughness characterization at different temperatures were attained mainly in directions of 20°–40°,60°–100°and 140°–160°.The fracture aperture of granite after fracture followed the Gauss distribution and the average aperture increased with increasing temperature,which increased from 0.665 mm at 25℃to 1.058 mm at 800℃.High temperature caused an uneven thermal expansion,water evaporation,and oxidation of minerals within the granite,which promoted the growth and expansion of microfractures,and reduced interparticle bonding strength.In particular,the damage was exacerbated by the expansion and cracking of the quartz phase transition after T>500℃.Thermal cycles contributed to the accumulation of this damage and further weakened the interparticle bonding forces,resulting in a significant increase in the roughness,anisotropy,and aperture of the fracture surface after five cycles.
基金supported by the National Natural Science Foundation of China(52174071,U1903216,52004052)the National Key R&D Program of China(2022YFC2903903).
文摘In order to understand the mechanical properties and the fracture surface roughness characteristics of thermally damaged granite under dynamic splitting,dynamic Brazilian splitting tests were conducted on granite samples after thermal treatment at 25,200,400,and 600℃.Results show that the dynamic peak splitting strength of thermally damaged granite samples increases with increasing strain rate,showing obvious strain‐rate sensitivity.With increasing temperature,thermally induced cracks in granite transform from intergranular cracks to intragranular cracks,and to a transgranular crack network.Thermally induced damages reduce the dynamic peak splitting strength and the maximum absorbed energy while increasing the peak radial strain.The fracture mode of the thermally damaged granite under dynamic loads is mode Ⅱ splitting failure.By using the axial roughness index Z2 a,the distribution ranges of the wedge‐shaped failure zones and the tensile failure zones in the fracture surfaces under dynamic Brazilian splitting can be effectively identified.The radial roughness index Z_(2)^(r)is sensitive to the strain rate and temperature.It shows a linear correlation with the peak splitting strength and the maximum absorbed energy and a linear negative correlation with the peak radial strain.Z_(2)^(r)can be used to quantitatively estimate the dynamic parameters based on the models proposed.
基金Project(52409132) supported by the National Natural Science Foundation of ChinaProject(ZR2024QE018) supported by the Natural Science Foundation of Shandong Province,China+2 种基金Project(BK20240431) supported by Basic Research Program of Jiangsu,ChinaProject(SNKJ2023A07-R14) supported by the Major Key Technical Research Projects of Shandong Energy Group,ChinaProject(2024M751813) supported by China Postdoctoral Science Foundation。
文摘Deep geothermal extraction processes expose rock masses to frequent and significant temperature fluctuations. Developing a comprehensive understanding of the shear fracture mechanisms and crack propagation behaviors in rocks under the influence of cyclic heating is imperative for optimizing geothermal energy extraction. This study encompasses several critical aspects under cyclic heating conditions, including the assessment of stress distribution states, the characterization of two-dimensional fracture paths, the quantitative analysis of three-dimensional damage characteristics on fracture surfaces, and the determination of the fractal dimension of debris generated after the failure of granite. The test results demonstrate that cyclic heating has a pronounced adverse effect on the physical and mechanical properties of granite. Consequently, stress tends to develop and propagate in a direction perpendicular to the two-dimensional fracture path. This leads to an increase in the extent of tensile damage on the fracture surface and accelerates the overall rock failure process. This increases the number of small-sized debris, raises the fractal dimension, and enhances the rock’s rupture degree. In practical enhanced geothermal energy extraction, the real-time monitoring of fracture propagation within the reservoir rock mass is achieved through the analysis of rock debris generated during the staged fracturing process.
基金support from the National Natural Science Foundation of China(Grant Nos.52174092 and 52104125)the Fundamental Research Funds for the Central Universities,China(Grant No.2022YCPY0202)is gratefully acknowledged.
文摘Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted regarding various initial normal stresses(1e7 MPa)and numbers of shearing cycles(1 e5).The peak shear stress of fractures decreased with shear cycles due to progressively smooth surface morphologies,while increased with both JRC and initial normal stress and could be verified using the nonlinear Barton-Bandis failure criterion.The joint friction angle of fractures exponentially increased by 62.22%e64.87%with JRC while decreased by 22.1%e24.85%with shearing cycles.After unloading normal stress,the sliding initiation time of fractures increased with both JRC and initial normal stress due to more tortuous fracture morphologies and enhanced shearing resistance capacity.The surface resistance index(SRI)of fractures decreased by 4.35%e32.02%with increasing shearing cycles due to a more significant reduction of sliding initiation shear stress than that for sliding initiation normal stress,but increased by a factor of 0.41e1.64 with JRC.After sliding initiation,the shear displacement of fractures showed an increase in power function.By defining a sliding rate threshold of 5105 m/s,transition from“quasi-static”to“dynamic”sliding of fractures was identified,and the increase of sliding acceleration steepened with JRC while slowed down with shearing cycles.The normal displacement experienced a slight increase before shear sliding due to deformation recovery as the unloading stress was unloaded,and then enhanced shear dilation after sliding initiation due to climbing effects of surface asperities.Dilation was positively related to the shear sliding velocity of fractures.Wear characteristics of the fracture surfaces after shearing failure were evaluated using binary calculation,indicating an increasing shear area ratio by 45.24%e91.02%with normal stress.
基金financially supported by the Foundation for Chunhui Program of the Ministry of Education of the People's Republic of China under contract No.Z2011-062
文摘In order to improve the properties of silica sol shell for investment casting process, various contents of cattail fibers were added into the slurry to prepare a fiber-reinforced shell in the present study. The bending strength of fiber-reinforced shell was investigated and the fracture surfaces of shell specimens were observed using SEM. It is found that the bending strength increases with the increase of fiber content, and the bending strength of a green shell with 1.0 wt.% fiber addition increases by 44% compared to the fiber-free shell. The failure of specimens of the fiber-reinforced green shell results from fiber rupture and debonding between the interface of fibers and adhesive under the bending load. The micro-crack propagation in the matrix is inhibited by the micro-holes for ablation of f ibers in specimens of the f iber-reinforced shell during the stage of being fired. As a result, the bending strength of specimens of the fired shell had no significant drop. Particularly, the bending strength of specimens of the fired shell reinforced with 0.6wt.% fiber reached the maximum value of 4.6 MPa.
基金supported by the National Basic Research Program of China (No.2011CB606404)the National Natural Science Foundation of China (No.51171195)the GM Research Project
文摘Molecular dynamics simulation of uniaxial tension along [001] has been performed to study the influence of various surface defects on the initiation of plastic deformation and fracture of γ-TiAl single crystals.The results indicate that brittle fracture occurs in perfect bulk; surfaces and edges will be detrimental to the strength of materials and provide dislocation nucleation site. The defects on surfaces and edges cause further weakening with various effects depending on defect type, size, position and orientation,while the edge dimples are the most influential. For γ-TiAl rods with surface dimples, dislocations nucleate from an edge of the rod when dimples are small, dimple dislocation nucleation occurs only when the dimples are larger than a strain rate dependent critical size. The dislocations nucleated upon [001]tension are super dislocations with Burger vectors 〈011] or 1/2 〈 112] containing four 1/6 〈 112 〉 partials. The effects of surface scratches are orientation and shape sensitive. Scratches parallel to the loading direction have little influence, while sharp ones perpendicular to the loading direction may cause crack and thus should be avoided. This simulation also shows that, any type of surface defect would lower strength,and cause crack in some cases. But some may facilitate dislocation nucleation and improve ductility of TiAl if well controlled.
基金the National Natural Science Foundation of China (Nos. 50904067 and 51104156)the New Century Excellent Talents in University (No. NCET-10-0768) for their support of this project
文摘In this paper, simulated experiment device of coal and gas outburst was employed to perform the experiment on gas-containing coal extrusion. In the experiment, coal surface cracks were observed with a high-speed camera and then the images were processed by sketch. Based on the above description, the paper studied the fractal dimension values from different positions of coal surface as well as their changing laws with time. The results show that there is a growing parabola trend of crack dimension value in the process of coal extrusion. Accordingly, we drew the conclusion that extruded coal crack evolution is a process of fractal dimension value increase. On the basis of fractal dimension values taken from different parts of coal masses, a fractal dimension of the contour map was drawn. Thus, it is clear that the contour map involves different crack fractal dimension values from different positions. To be specific, where there are complicated force and violent movement in coal mass, there are higher fractal dimension values, i.e., the further the middle of observation surface is from the exit of coal mass, and the lower the fractal dimension value is. In line with fractal geometry and energy theory of coal and gas outburst, this study presents the relation between fractal dimension and energy in the process of extruding. In conclusion, the evolution of crack fractal dimension value can signify that of energy, which has laid a solid foundation for the quantification research on the mechanism of gas-containing coal extrusion.
文摘The tensile properties and fracture surface of 07MnNiCrMoVDR steel welded joint at low temperature have been studied by universal testing machine and scanning electron microscope. The results show that the tensile properties of 07MnNiCrMoVDR steel welded joint are greatly affected by temperature. Tensile strength and yield strength of 07MnNiCrMoVDR steel welded joint increase, but elongation and reduction of area decrease with temperature decreasing. The macro-fracture of 07 MnNiCrMoVDR steel welded joint exhibits that the shear lip is not significant and micro-fracture makes up of dimpled fracture and tear fracture, and dimple becomes tiny and uniform with temperature decreasing.
基金National Natural Science Foundation of China!59671093 National Natural Science Foundation of China !19874064
文摘After calculation on the fracture angles under various conditions of specific surface energies with different symmetry operations of rotation, the complicated behavior of dependence of fractal dimension on the structure of crystal is shown. It is found that the crack propagates along the weakest crystal plane no matter what the direction of the maximum stress is if the anisotropy is sufficiently strong; and then, the fractal dimension of the fractured surfaces might be determined by the approximate fractal structure already existed in the material. Specificity of the fractal dimension of fractured surfaces would be easy to appear in this case. Reversely, the crack propagates along the direction of the maximum stress no matter what direction of the weakest crystal plane is if the anisotropy is sufficiently weak. Universality of the fractal dimension of fractured surfaces would be possible to appear in this case. In many real materials, universality and specificity of the materials are associated. The fractal dimension measured may more or less be influenced by the structure of materials and it shows its universality through the specificity of materials.
基金Project supported by the National Natural Science Foundation of China(Nos.12172048 and 12027901)the National Science and Technology Major Project of China(Nos.2019-Ⅶ-0007-0147 and 2017-Ⅵ-0020-0093)。
文摘The surface fracture toughness is an important mechanical parameter for studying the failure behavior of air plasma sprayed(APS)thermal barrier coatings(TBCs).As APS TBCs are typical multilayer porous ceramic materials,the direct applications of the traditional single edge notched beam(SENB)method that ignores those typical structural characters may cause errors.To measure the surface fracture toughness more accurately,the effects of multilayer and porous characters on the fracture toughness of APS TBCs should be considered.In this paper,a modified single edge V-notched beam(MSEVNB)method with typical structural characters is developed.According to the finite element analysis(FEA),the geometry factor of the multilayer structure is recalculated.Owing to the narrower V-notches,a more accurate critical fracture stress is obtained.Based on the Griffith energy balance,the reduction of the crack surface caused by micro-defects is corrected.The MSEVNB method can measure the surface fracture toughness more accurately than the SENB method.
基金The National Natural Science Foundation of China(NSFC)has developed a“comprehensive experimental system for hydro-jet radial horizontal wells”(No.51827804)in the Major Scientific Research Instrument Development ProjectNSFC General Project of“Research on Sand Carrying Mechanism in Supercritical CO_(2)Fractures”(No.51874318)NSFC Outstanding Youth Science Fund Project OF“Oil and Gas Well Fluid Mechanics and Engineering”(No.51922107).
文摘Supercritical CO_(2) fracturing is an important development trend to reach the goal of"dual carbon"and avoid the problem that hydraulic fracturing is influenced by water resource.In order to clarify the transport characteristics of proppant in the fractures induced by supercritical CO_(2) fracturing,this paper reconstructs the fracture surface of rock samples after supercritical CO_(2) fracturing using the laser morphological scanning technology,and establishes a model of proppant carrying and transport of supercritical CO_(2) in tortuous fractures on the basis of CFD-DEM method.In addition,the transport and placement characteristics of proppant in tortuous fractures are analyzed by comparing withflat fractures,and the effects of proppant density,injection rate of proppant carrying liquid,proppant concentration and other key parameters on proppant transport and distribution in fractures are investigated.And the following research results are obtained.First,compared with those inflat fractures,theflow paths of the proppant carrying supercritical CO_(2) liquid in tortuous fractures are tortuous and diverse,and the proppant presents strongerfluctuations and jumps laterally and vertically during its transport.Second,the proppant placement in tortuous fractures morphologically presents a wavy or even clustered non-uniform distribution.Third,low-density proppant has a better pass-ability in tortuous fractures,and the high injection rate can reduce the influence of tortuous fracture structure on proppant blocking.Fourth,if the concentration of injected proppant in the tortuous fracture is too low,good fracturing support effect cannot be achieved,and the optimal value under the simulation conditions in this paper is around 3%.In conclusion,the simulation results are of important theoretical and engineering significance to understanding the mechanism of proppant blocking in the pumping process of proppant carrying liquid for supercritical CO_(2) fracturing and optimizing thefield fracturing design.
文摘To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed The principle of the fracture-surface topography analysis （FRASTA） was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each other well.
基金Sponsored by the High-End CNC Machine Tools and Basic Manufacturing Equipment Technology Major Project(Grant No.2011ZX04001-011)partly supported by Program for Changjiang Scholars and Innovative Research Team in University(Grant No.IRT1229)
文摘Three different punches are designed for the hydropiercing experiments and finite element simulations are conducted by finite element program ABAQUS-3D to investigate the influence of punch shape on the fracture surface quality of hydropiercing holes. The results show the fracture burrs are not obvious punched by all the three punches. The collapse punched by the round punch is a little larger than the others. The fracture surface quality punched by the round punch is good with larger smooth zone and the interface between smooth zone and tear zone is even with large gradient. The size of the smooth zone is larger and the interface between smooth zone and tear zone is uneven with large gradient punched by the flat punch. The size of the smooth zone is smaller and the size of the tear zone increases from the first fractured to the last fractured punched by the inclined punch.
基金the National Basic Research Program of China ( Grant No. 2012CB722702 )the Key Project of Natural Science Foundation of Hubei Province of China under Grant No. 2012FFA103
文摘Fractal analysis of fracture surfaces in different kinds of refractories including magnesia-carbon and magnesia-chrome refractories was investigated.The fractal dimensions of fracture surfaces for three points bending test were determined by slit island method.The results show that the cold modulus of rupture increases with fractal dimension increasing due to the change in fracture mode depending on the bonding mechanism for a certain refractory material.
基金Supported by Beijing Municipal Natural Science Foundation of China(Grant Nos.3202016,52175283)。
文摘6082-T6 aluminum alloy is a commonly used aluminum alloy material in the field of rail transit because of its good molding properties,high mechanical properties,excellent corrosion resistance and weldability.In the high temperature and humid environment,the temperature change is bound to affect the stress corrosion resistance of the aluminum alloy and their welded joint.However,the influence mechanism of temperature on its stress corrosion resistance has not been explained in the existing research.In this paper,the mechanical properties and stress corrosion behaviors of melt-inert gas welded(MIG)6082-T6 aluminum alloy welded joints were systematically studied under various temperatures condition.Results indicated the temperature scarcely affected stress corrosion cracking susceptibility index(P_(SCC))of base metal,while significantly affected the welded joint and higher temperature caused lower P_(SCC).After slow strain rate tensile test,a corrosion layer was formed,which was a typical brittle-toughness mixed failure,and the degree of brittleness increased with the increasing of temperature.Electrochemical analysis showed that corrosion resistance of the joint slightly decreased due to aluminum alloy accelerated dissolution caused by increasing of temperature.The proposed research will provide a theoretical basis for solving aluminum alloys used in rail transit,ship accessories and other industrial fields.
文摘The aim of this research was to develop an intrarradicular dental post based on epoxy resin/nano zirconium phosphate composite with potential appli-cation in prosthetic dentistry. Zirconium phosphate (ZrP) nanoparticle was synthesized by a reaction between phosphoric acid (H3PO4) and zirconium (IV) oxide chloride 8-hydrate (ZrOCl2·8H2O) and applied as filler. Commer-cial epoxy resin and hardener were used as polymer matrix. The composites were prepared at different proportions of epoxy resin/hardener, filler amount, reaction time and temperature. Infrared revealed that degree of conversion decreased with amount of ZrP. Insoluble matter was upper than 97%. Thermogravimetry indicated two steps of degradation. The best values of flexural modulus and flexural strength were achieved for the post desig-nated as 1:0.25:0.25. Laser scanning confocal microscopy suggested that the morphology of the posts fractured surface varied according to epoxy-resin:hardener ratio and the ZrP amount. From atomic force micros-copy, the topographic view exposed the shape and size of ZrP particles. Field emission scanning electron microscopy and energy dispersive spectroscopy indicated good adhesion between epoxy resin matrix-ZrP and that the pres-ence of phosphate rendered brittle the fracture surface.
基金Project(51405309)supported by the National Natural Science Foundation of ChinaProject(2013024012)supported by the Natural Science Foundation of Liaoning Province,China
文摘The crack propagation rates of T6 peak aging and T7951 secondary aging 7055 aluminium alloys were tested under stress ratios (R) of 0.6, 0.05 and ?1, respectively. The microstructures and fracture surfaces were analyzed by TEM and SEM. The results reveal that the crack propagation rate is affected by the stress ratio and microstructure such as the distribution, dimension and volume fraction of matrix precipitates, grain boundary precipitates and precipitate free zone. For both heat-treated specimens, crack propagation rate increases with the improvement of R when it is a positive value while crack propagation rate at R=?1 is much similar to that at R=0.06. The crack growth rates exhibit no obvious difference in lower stress intensity factor range (ΔK), while the difference starts to be obvious when ΔK exceeds certain value. The fracture analysis testifies a better fracture toughness for 7055-T7951 with a smaller striation space in Paris region.
文摘The microstructure and mechanical properties of rheocasting AZ91 magnesium alloy were investigated. The semisolid slurry of this alloy was prepared by ultrasonic vibration （USV） process and then shaped by high pressure diecasting （HPDC）. The results show that fine and spherical a-Mg particles were obtained by USV at the nucleation stage, which was mainly attributed to the cavitation and acoustic streaming induced by the USV. Extending USV treatment time increased the solid volume fraction and average particle size, the shape factors were nearly the same, about 0.7. Excellent semisolid slurry of AZ91 magnesium alloy could be obtained within 6 rain by USV near its liquidus temperature. The rheo-HPDC samples treated by USV for 6 min had the maximum ultimate tensile strength and elongation, which were 248 MPa and 7.4%, respectively. It was also found that the ductile fracture mode prevailed in the rheocasting AZ91 magnesium alloy.
基金supported by the National Natural Science Foundation of China(No.52522405)Henan Provincial Natural Science Foundation(No.252300421323).
文摘Fractures in rock strata serve as flow pathways for gas flow.The undulation of fracture channels can influence the guidance of gas flow.In this context,four-point bending experiments on prefabricated fractured rocks at different angles under stable stepped loading stress.The experiment results clarified the evolutionary law that the undulation degree of the rock tensile fracture surface is separated by an initial fracture angle of 45°.The high undulation intervals were less than 45°,whereas the low undulation intervals were more than 45°.Furthermore,the relative undulation degree,undulation frequency,and matching degree of the fracture surface were quantified.The relationship between the change in fracture surface undulation and gas flow guidance was established.Based on this,the stability,tortuosity,and uniformity of the gas flow in the fracture channel were quantitatively characterized.Subsequently,numerical models of the fracture channels were constructed to validate the indices proposed in this study.The results of the study clarified the influence of different initial fracture angles on the undulation changes of fracture surfaces,and established the relationship between these changes and gas flow,which is conducive to understanding the role of internal fracture channels in rocks in guiding the gas flow process.
基金Project(2009ZX04014-074)supported by the National Science and Technology Major Project of ChinaProject(P2014-15)supported by the State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology,ChinaProject(20120006110017)supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘The effect of friction coefficient on the deep drawing of aluminum alloy AA6111 at elevated temperatures was analyzed based on the three conditions using the finite element analysis and the experimental approach.Results indicate that the friction coefficient and lubrication position significantly influence the minimum thickness,the thickness deviation and the failure mode of the formed parts.During the hot forming process,the failure modes are draw mode,stretch mode and equi-biaxial stretch mode induced by different lubrication conditions.In terms of formability,the optimal value of friction coefficient determined in this work is 0.15.At the same time,the good agreement is performed between the experimental and simulated results.Fracture often occurs at the center of cup bottom or near the cup corner in a ductile mode or ductile-brittle mixed mode,respectively.
