The surfaces of X80 pipeline steel welded joints were processed with a CO2 laser, and the effects of laser heat treatment （LHT） on H2S stress corrosion in the National Association of Corrosion Engineers （NACE） sol...The surfaces of X80 pipeline steel welded joints were processed with a CO2 laser, and the effects of laser heat treatment （LHT） on H2S stress corrosion in the National Association of Corrosion Engineers （NACE） solution were analyzed by a slow strain rate test. The fracture morphologies and chemical components of corrosive products before and after LHT were analyzed by scanning electron microscopy and energy-dispersive spectroscopy, respectively, and the mechanism of LHT on stress corrosion cracking was discussed. Results showed that the fracture for welded joints was brittle in its original state, while it was transformed to a ductile fracture after LHT. The tendencies of hydrogen-induced corrosion were reduced, and the stress corrosion sensitivity index decreased from 35.2% to 25.3%, indicating that the stress corrosion resistance of X80 pipeline steel welded joints has been improved by LHT.展开更多
The fracture morphologies of several advanced high-strength steels （DP590, DP780, DP980, Ml180, and M1300） formed in uniaxial tension and piercing were observed by scanning electron microscope, and then quantitative...The fracture morphologies of several advanced high-strength steels （DP590, DP780, DP980, Ml180, and M1300） formed in uniaxial tension and piercing were observed by scanning electron microscope, and then quantitatively analyzed by image processing technique. The tension-induced fractographs are dominated by obvious uniform or bimodal size dimples, while shearing-induced fractographs have smooth surfaces and few dimples. The fracture zone of higher grade DP steels is smoother. As for M1180 and M1300, the fracture zones consist of very small dimples and smooth brittle surfaces. The dimple size of M1300（ ,- 1.2 tm） is smaller than that of M1180（ 1.6 tm）. Moreover, in the tensile fracture, the quantitative correlation between average dimple diameter （d） and tensile strength （a） can be represented by d = 10,502.32a-121. However, the relation between dimple density and tensile strength is not monotonic due to the appearance of bimodal size dimples with increase of tensile strength. For shearing-induced fracture during piercing, the fitted empirical model between the percentage of burnish zone （f） and tensile strength can be described asf --- 239.9a-＇36.展开更多
The fracture behaviour and morphologies of high-strength boron steel were investigated at different temperatures at a constant strain rate of 0.1 s-1 based on isothermal tensile tests. Fracture mechanisms were also an...The fracture behaviour and morphologies of high-strength boron steel were investigated at different temperatures at a constant strain rate of 0.1 s-1 based on isothermal tensile tests. Fracture mechanisms were also analyzed based on the relationship between microstructure transformation and continuous cooling transformation(CCT) curves. It is found that 1) fractures of the investigated steel at high temperatures are dimple fractures; 2) the deformation of high-strength boron steel at high temperatures accelerates diffusion transformations; thus, to obtain full martensite, a higher cooling rate is needed; and 3) the investigated steel has the best plasticity when the deformation temperature is 750 °C.展开更多
To more accurately describe the coal damage and fracture evolution law during liquid nitrogen(LN_(2))fracturing under true triaxial stress,a thermal-hydraulic-mechanical-damage(THMD)coupling model for LN_(2) fracturin...To more accurately describe the coal damage and fracture evolution law during liquid nitrogen(LN_(2))fracturing under true triaxial stress,a thermal-hydraulic-mechanical-damage(THMD)coupling model for LN_(2) fracturing coal was developed,considering the coal heterogeneity and thermophysical parameters of nitrogen.The accuracy and applicability of model were verified by comparing with LN_(2) injection pre-cooling and fracturing experimental data.The effects of different pre-cooling times and horizontal stress ratios on coal damage evolution,permeability,temperature distribution,and fracture characteristics were analyzed.The results show that the permeability and damage of the coal increase exponentially,while the temperature decreases exponentially during the fracturing process.As the pre-cooling time increases,the damage range of the coal expands,and the fracture propagation becomes more pronounced.The initiation pressure and rupture pressure decrease and tend to stabilize with longer precooling times.As the horizontal stress ratio increases,fractures preferentially extend along the direction of maximum horizontal principal stress,leading to a significant decrease in both initiation and rupture pressures.At a horizontal stress ratio of 3,the initiation pressure drops by 48.07%,and the rupture pressure decreases by 41.36%.The results provide a theoretical basis for optimizing LN_(2) fracturing techniques and improving coal seam modification.展开更多
Heterogeneity in carbonate formations due to discontinuities(e.g.,fractures and cavities)will bring about distinctive acid stimulation effects.However,the differences in fracturing behavior between homogeneous and het...Heterogeneity in carbonate formations due to discontinuities(e.g.,fractures and cavities)will bring about distinctive acid stimulation effects.However,the differences in fracturing behavior between homogeneous and heterogeneous carbonate formations remain unclear,complicating the optimization of acid fracturing strategies.In this paper,full-diameter carbonate rock samples with different degrees of discontinuity development are selected to investigate the fracturing behavior under different fluid types and injection schemes.Advanced techniques,including 3D CT scanning and 3D laser scanning,are employed to analyze fracture morphology and etching characteristics,respectively.Experimental results show that the coupled hydraulic-chemical effects play different roles in fracture induction between fracture-cavity developed and undeveloped carbonate rocks.Acid-fracturing stimulation consistently induces multiple types of complex fractures in fracture-cavity carbonate rocks,whereas it results in a single artificial fracture in less fracture-cavity carbonate rocks.Furthermore,localized etching patterns are prevalent in most fracture-cavity carbonate rocks,whereas homogeneous carbonate rocks exhibit regional or global etching characteristics.In both carbonate rocks,the stimulation effect of guar fluid is inferior to that of gelled acid but comparable to self-generating acid.Further findings are that alternating fracturing with guar and acid fluids in fracture-cavity carbonate rocks can sustain or even increase the injection pressure,facilitating the formation of new or depth-penetrating fractures.This phenomenon,however,is not observed in fracture-cavity undeveloped carbonate rocks.Potential interaction modes between induced fracture and natural fractures/cavities under different injection conditions are also identified.Finally,preferred fracturing schemes applicable to different carbonate formations are recommended based on the area,number and roughness of the induced fractures.展开更多
The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal ...The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal samples for experiments, and clean fracturing fluid samples were prepared using CTAB surfactant. A series of hydraulic fracturing tests were conducted with an in-house developed triaxial hydraulic fracturing simulator and the fracturing process was monitored with an acoustic emission instrument to analyze the influences of fracturing fluid viscosity and horizontal in-situ stress difference on coal fracture propagation. The results show that the number of branched fractures decreased, the fracture pattern became simpler, the fractures width increased obviously, and the distribution of AE event points was concentrated with the increase of the fracturing fluid viscosity or the horizontal in-situ stress difference. The acoustic emission energy decreases with the increase of fracturing fluid viscosity and increases with the increase of horizontal in situ stress difference. The low viscosity clean fracturing fluid has strong elasticity and is easy to be compressed into the tip of fractures, resulting in complex fractures. The high viscosity clean fracturing fluids are the opposite. Our experimental results provide a reference and scientific basis for the design and optimization of field hydraulic fracturing parameters.展开更多
Understanding the mechanical behavior of diagenetic mineral granules and interfaces in granite provides essential experimental references for constructing micromechanical models of granite.The micromechanical behavior...Understanding the mechanical behavior of diagenetic mineral granules and interfaces in granite provides essential experimental references for constructing micromechanical models of granite.The micromechanical behavior of Yanshanian granite is investigated using scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS)and nanoindentation tests.The results demonstrate transitional mechanical properties at mineral interfaces.The elastic modulus and hardness exhibit intermediate values between adjacent mineral phases.The higher plasticity indices at the interfaces suggest higher plastic deformation capacity of hard-phase minerals in these regions.Additionally,fracture toughness measurements of minerals and interfaces were obtained,with interfacial values ranging from 0.90 to 1.63 MPa·m^(0.5).The analysis of mechanical property relationships shows a significant positive linear correlation between rock-scale elastic modulus and fracture toughness.However,this correlation is substantially lower at the mineral scale,demonstrating a scale effect in the relationship of different mechanical properties.展开更多
This study investigates the fatigue crack propagation mechanism of a new high-strength and high-tough Ti-Mo-Cr-V-Nb-Al titanium alloy with three types of microstructures(basketweave structure,lamellar structure,and bi...This study investigates the fatigue crack propagation mechanism of a new high-strength and high-tough Ti-Mo-Cr-V-Nb-Al titanium alloy with three types of microstructures(basketweave structure,lamellar structure,and bimodal structure)through fatigue crack propagation rate tests and fatigue threshold value tests.The resistance of the alloy to fatigue crack propagation was found to be closely correlated with the morphology and distribution ofαparticles,as evidenced by microscopic examination of fracture surfaces and analysis of crack propagation paths.The primaryαparticles demonstrated superior resistance to crack propagation compared to the secondaryαparticles.The basketweave structure showed exceptional resistance to fatigue crack propagation at all stages.The lamellar structure mainly resists long crack propagation during rapid propagation,and its threshold value is the lowest,which makes it easy to produce microcrack propagation.On the contrary,the bimodal structure has the highest threshold value among the three,so its resistance to short crack growth is more excellent,but it has the highest crack growth rate in the higher stress intensity factor range.Theαparticles in the three microstructures also undergo rotational motion relative to the force axis during fatigue crack propagation,thereby adjusting the uneven stress distribution betweenα/βphases through slip behavior and further coordinating deformation.展开更多
Shale oil reservoir is generally characterized by well-developed bedding planes,and multi-cluster fracturing is the most effective technique to achieve stable shale oil production.In this paper,a multi-cluster fractur...Shale oil reservoir is generally characterized by well-developed bedding planes,and multi-cluster fracturing is the most effective technique to achieve stable shale oil production.In this paper,a multi-cluster fracturing model for a horizontal well in shale with high-density bedding planes is established.The fracture morphology,fracture geometry,fracturing area and multiple fracture propagation mechanism are analyzed under simultaneous fracturing,sequential fracturing,and alternative fracturing.Results show that in the case of small cluster spacing and three clusters,the growth of the middle fracture is inhibited and develops along the bedding planes under both simultaneous fracturing and alternative fracturing.For sequential fracturing,the increase in the interval time between each fracturing advances the post fracturing fracture deflecting to the pre-existing fractures through the bedding planes.The reactivation of the bedding planes can promote the extension of the fracturing area.Increasing the injection rate and the number of clusters promotes the activation of bedding planes.However,it is preferable to reduce the number of clusters to obtain more main fractures.Compared with modified alternating fracturing and cyclic alternating fracturing,alternating shut-in fracturing creates more main fractures towards the direction of the maximum in-situ stress.The fracturing efficiency for high-density layered shale is ranked as simultaneous fracturing>alternative fracturing>sequential fracturing.展开更多
The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate t...The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate that after MDF at a temperature of 350℃and strain rates of 0.1 and 0.01 s^(−1)(1-MDFed and 2-MDFed),the superplasticity of the alloy can be significantly improved.The elongations of the MDFed alloys exceed 400%under the strain rate of 6.06×10^(−4)s^(−1)and temperatures of 350,375,and 400℃,and reach the maximum values of 766%(1-MDFed)and 693%(2-MDFed)at 375℃.The grain boundary sliding of the MDFed alloy is sufficient,and the energy barrier of deformation decreases.Theβphase limits the grain growth and promotes dynamic recrystallization,maintaining the stability of the fine-grained structure during superplastic deformation.Several Y-rich phases nucleate in the high-strain region(i.e.,the final fracture region)at high temperatures,accelerating the fracture of the specimen.展开更多
Fracture propagation mechanisms in coalbed methane(CBM) reservoirs are very complex due to the development of the internal cleat system. In this paper, the characteristics of initiation and propagation of hydraulic fr...Fracture propagation mechanisms in coalbed methane(CBM) reservoirs are very complex due to the development of the internal cleat system. In this paper, the characteristics of initiation and propagation of hydraulic fractures in coal specimens at different angles between the face cleat and the maximum horizontal principal stress were investigated with hydraulic fracturing tests. The results indicate that the interactions between the hydraulic fractures and the cleat system have a major effect on fracture networks. "Step-like’’ fractures were formed in most experiments due to the existence of discontinuous butt cleats. The hydraulic fractures were more likely to divert or propagate along the butt cleat with an increase in the angles and a decrease in the horizontal principal stress difference. An increase in the injection rate and a decrease in the fracturing fluid viscosity were more conducive to fracture networks. In addition, the influence on fracture propagation of the residual coal fines in the wellbore was also studied. The existence of coal fines was an obstacle in fracturing, and no effective connection can be formed between fractures. The experimental investigation revealed the fracture propagation mechanisms and can provide guidance for hydraulic fracturing design of CBM reservoirs.展开更多
Crack is found to be a major distress that affects the performance of the epoxy asphalt pavement.An extended finite element method was proposed for investigating the fracture properties of the epoxy asphalt mixture.Fi...Crack is found to be a major distress that affects the performance of the epoxy asphalt pavement.An extended finite element method was proposed for investigating the fracture properties of the epoxy asphalt mixture.Firstly,the single-edge notched beam test was used to analyze the temperature effect and calculate the material parameters.Then,the mechanical responses were studied using numerical analysis.It is concluded that 5℃ can be selected as the critical temperature that affects the fracture properties,and numerical simulations indicate that crack propagation is found to significantly affect the stress state of the epoxy asphalt mixture.The maximum principal stress at the crack surface exhibits different trends at various temperatures.Numerical solution of stress intensity factor can well meet the theoretical solution,especially when the temperature is lower than 5℃.展开更多
Based on previous research results, this paper investigated the influence of fracture morphology on mechanical properties and failure modes of rock mass with two diagonal intersected fractures. This study carried out ...Based on previous research results, this paper investigated the influence of fracture morphology on mechanical properties and failure modes of rock mass with two diagonal intersected fractures. This study carried out a series of triaxial compression tests on rock-like specimens with two crossed fractures under negative temperature, concluded the following conclusions. The strength and failure modes of rock mass are significantly influenced by the dips of two crossed fractures. The strength of rock mass with two frac- tures cannot simply be estimated using the method that was developed for the rock mass with a single fracture. When the intersecting angle is less than 30~, the failure plane initiates at the tip of ＂artificial rup- tures＂ and extends to the upper and lower ends of the specimen. In case of a higher dip and intersecting angle ranging from 30° to 60°, the failure plane propagates along one of these two fractures. The mechan- lca! parameters of rock mass are not only related to the trace length, but also depend on the trace !ength ratio. One could roughly calculate the strength parameters using the approximation proposed in.this paper..For the rock mass with a trace length ratio 〈0.3 （short trace length/long trace length）, the failure mode is dependent on the fracture with a longer trace length. When the trace length becomes significant and the trace length ratio approximates to 1, the failure plane propagates along two fractures, where an X-shaped.failure pattern is presented： For the rock mass with moderate frac!ures and a trace length ratio of approxlmately 1, the failure mode Is.Independent on fractures, which is simllar to .the damage pattern of intact rock. The strength, and elastic .modulus of rock mass decrease with the increase of spacing between fractures, whl!e Polsson＇s ratio is Independent on the spacing. The failure mode can be deter- mined by the area. of triangle created by two fractures. Damage occurs at the smaller triangle area first, and propagates with the two sides of the larger triangle.展开更多
Different contents of Ni(0.3wt.%to 1.2wt.%)were added to the QT400-18L ductile iron to investigate the effect of Ni addition on the impact toughness of cast ductile irons at low temperatures.The impact toughnesses of ...Different contents of Ni(0.3wt.%to 1.2wt.%)were added to the QT400-18L ductile iron to investigate the effect of Ni addition on the impact toughness of cast ductile irons at low temperatures.The impact toughnesses of the samples at room and low temperatures were tested.The microstructures and fractographs were observed.Results show that with the increase of Ni addition there is a general trend of refinement of the ferrite matrix while the nodule density shows no obvious change.When the Ni content is 0.7wt.%,the matrix structure is the refined ferrite with a very small fraction(about 2%)of pearlite near the eutectic cell boundaries.When the Ni content is further increased,the fraction of pearlite increases significantly and reaches more than 5%when 1.2wt.%Ni is added.The impact toughness at room temperature increases as the content of Ni increases from 0.3 wt.%to 0.7 wt.%,but decreases as the Ni content further increases to 1.2wt.%due to the increase of pearlite fraction.The maximum value of the impact work is 18.5 J at room temperature with 0.7wt.%Ni addition.The average value of the impact work is still more than 13 J even at-30℃.In addition,the fracture mechanism changes from ductile manner to brittleness as the testing temperature decreases from 20℃to-60℃.展开更多
To investigate fracture generation and strain variation during SC-CO_(2)(supercritical carbon dioxide)jet fracturing,the model of induced strain is established and the experiments are comprehensively studied.The influ...To investigate fracture generation and strain variation during SC-CO_(2)(supercritical carbon dioxide)jet fracturing,the model of induced strain is established and the experiments are comprehensively studied.The influence factors are comprehensively explored,such as jet pressure,ambient pressure,etc.With the increasing jet pressure,the fracture morphology changes from parallel cracks to oblique cracks.Both the mass loss of specimen and CO_(2) absorption increase significantly,and the growth rate and minimum value of strain also rise exponentially.Under a high ambient pressure of 8.0 MPa,the main fractures mostly propagated from the surface to the bottom surface of the specimen.The maximum strain and the stable duration under higher ambient pressure are 1.5 times and 10 times,respectively,of the case under the ambient pressure of 5.0 MPa.The comparison shows that the optimal jet distance is 5-7 times the nozzle diameter,resulting in massive mass loss,large CO_(2)absorption,and peak strain.Moreover,the nonlinear variation of strain curve during jet pressurization is related to the type of rock and ambient pressure.These studies clearly show the relationship between the fracture morphology and induced strain,which are crucial for SC-CO_(2)fracturing in shale gas reservoirs.展开更多
Fe-Al-Ta eutectic composites were obtained by a modified Bridgman directional solidification technique at different solidification rates.Solidification microstructure transforms from regular eutectic to eutectic colon...Fe-Al-Ta eutectic composites were obtained by a modified Bridgman directional solidification technique at different solidification rates.Solidification microstructure transforms from regular eutectic to eutectic colony with the increase of the solidification rate.The solid/liquid interface of Fe-Al-Ta eutectic evolves from planar interface to cellular interface with the increase of the solidification rate.In addition,threepoint bending method was adopted to study the room-temperature fracture toughness of the as-cast Fe-Al-Ta eutectic alloy and the Fe-Al-Ta eutectic composites.Moreover,the fracture morphologies,the crack propagation path and the strengthening mechanism of Fe-Al-Ta eutectic were discussed.展开更多
Efficient flow simulation and optimization methods of hydraulic fracture morphology in unconventional reservoirs are effective ways to enhance oil/gas recovery.Based on the connection element method(CEM)and distributi...Efficient flow simulation and optimization methods of hydraulic fracture morphology in unconventional reservoirs are effective ways to enhance oil/gas recovery.Based on the connection element method(CEM)and distribution of stimulated reservoir volume,the complex hydraulic fracture morphology was accurately described using heterogeneous node connection system.Then a new fracture connection element method(FCEM)for fluid flow in stimulated unconventional reservoirs with complex hydraulic fracture morphology was proposed.In the proposed FCEM,the arrangement of dense nodes in the stimulated area and sparse nodes in the unstimulated area ensures the calculation accuracy and efficiency.The key parameter,transmissibility,was also modified according to the strong heterogeneity of stimulated reservoirs.The finite difference and semi-analytical tracking were used to accurately solve the pressure and saturation distribution between nodes.The FCEM is validated by comparing with traditional numerical simulation method,and the results show that the bottom hole pressure simulated by the FCEM is consistent with the results from traditional numerical simulation method,and the matching rate is larger than 95%.The proposed FCEM was also used in the optimization of fracturing parameters by coupling the hydraulic fracture propagation method and intelligent optimization algorithm.The integrated intelligent optimization approach for multi-parameters,such as perforation number,perforation location,and displacement in hydraulic fracturing is proposed.The proposed approach was applied in a shale gas reservoir,and the result shows that the optimized perforation location and morphology distribution are related to the distribution of porosity/permeability.When the perforation location and displacement are optimized with the same fracture number,NPV increases by 70.58%,which greatly improves the economic benefits of unconventional reservoirs.This work provides a new way for flow simulation and optimization of hydraulic fracture morphology of multi-fractured horizontal wells in unconventional reservoirs.展开更多
Cu46Zr46A14.8Ti3.2 bulk metallic glass （BMG） was successfully synthesized by copper-mold casting and the mechanical properties at room temperature were measured by compression tests. The structure and thermal charac...Cu46Zr46A14.8Ti3.2 bulk metallic glass （BMG） was successfully synthesized by copper-mold casting and the mechanical properties at room temperature were measured by compression tests. The structure and thermal characteristics were analyzed by XRD and DSC, and the fracture surface morphology was examined by SEM. The glassy alloy with 4 mm in diameter shows an high fracture strength of 1 960 MPa, with an improvement of about 20% compared to the ultimate compression fracture strength of the Cu46Zr46A18 BMG, which suggests that the Ti addition improves the compression fracture strength. The different degrees of the adiabatic heating induce four types of fracture features： a vein-like structure, an elongated and striated vein pattern, melting and smooth regions. The elongated and striated vein patterns as well as the melting region show that enormous strain energy is released, which causes significant adiabatic heating. Furthernaore, many micro-cracks observed in the smooth region are caused by the strong shear force. In addition, the strong shear force leads to many shear bands as well as the melting in the lateral surface.展开更多
The inclusion parameters,fracture surface morphology and void growth characteristics of ten- sile and fracture toughness specimens of 2.25Cr-1Mo steels with and without rare-earth (RE)additions have been investigated ...The inclusion parameters,fracture surface morphology and void growth characteristics of ten- sile and fracture toughness specimens of 2.25Cr-1Mo steels with and without rare-earth (RE)additions have been investigated by quantitative metaltography(QTM),scanning elec- tron microscopy(SEM)and energy dispersive spectroscopy(EDS).There is a substantially higher density of inclusions in the RE-treated steel,which has lower values of fracture proper- ties including critical values of COD and J integral(δ_c and J_(IC)),fracture strain(ε_f) and Charpy V-notch energy(CVN).The fracture surface of the RE-treated steel comprises equiaxed dimples of diameters comparable with its inclusion spacing,whereas for the non-RE-treated steels,a wide range of dimple sizes is found with average diameter much smaller than the corresponding inclusion spacing.The investigation indicates that the lower values of fracture properties for the steel with RE at room temperature may be ascribed to its large content of RE-containing inclusions.展开更多
基金financially supported by the Chief Expert (Engineer) Project of Jiangsu Provincial Association for Science (No. 2012-09)
文摘The surfaces of X80 pipeline steel welded joints were processed with a CO2 laser, and the effects of laser heat treatment （LHT） on H2S stress corrosion in the National Association of Corrosion Engineers （NACE） solution were analyzed by a slow strain rate test. The fracture morphologies and chemical components of corrosive products before and after LHT were analyzed by scanning electron microscopy and energy-dispersive spectroscopy, respectively, and the mechanism of LHT on stress corrosion cracking was discussed. Results showed that the fracture for welded joints was brittle in its original state, while it was transformed to a ductile fracture after LHT. The tendencies of hydrogen-induced corrosion were reduced, and the stress corrosion sensitivity index decreased from 35.2% to 25.3%, indicating that the stress corrosion resistance of X80 pipeline steel welded joints has been improved by LHT.
基金financially supported by the National Natural Science Foundation of China(No.51105246)
文摘The fracture morphologies of several advanced high-strength steels （DP590, DP780, DP980, Ml180, and M1300） formed in uniaxial tension and piercing were observed by scanning electron microscope, and then quantitatively analyzed by image processing technique. The tension-induced fractographs are dominated by obvious uniform or bimodal size dimples, while shearing-induced fractographs have smooth surfaces and few dimples. The fracture zone of higher grade DP steels is smoother. As for M1180 and M1300, the fracture zones consist of very small dimples and smooth brittle surfaces. The dimple size of M1300（ ,- 1.2 tm） is smaller than that of M1180（ 1.6 tm）. Moreover, in the tensile fracture, the quantitative correlation between average dimple diameter （d） and tensile strength （a） can be represented by d = 10,502.32a-121. However, the relation between dimple density and tensile strength is not monotonic due to the appearance of bimodal size dimples with increase of tensile strength. For shearing-induced fracture during piercing, the fitted empirical model between the percentage of burnish zone （f） and tensile strength can be described asf --- 239.9a-＇36.
基金Project(51305317)supported by the National Natural Science Foundation of ChinaProjects(WUT:2013-IV-092,WUT:2014-VII-002)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(IRT13087)supported by Innovative Research Team Development Program of Ministry of Education of China
文摘The fracture behaviour and morphologies of high-strength boron steel were investigated at different temperatures at a constant strain rate of 0.1 s-1 based on isothermal tensile tests. Fracture mechanisms were also analyzed based on the relationship between microstructure transformation and continuous cooling transformation(CCT) curves. It is found that 1) fractures of the investigated steel at high temperatures are dimple fractures; 2) the deformation of high-strength boron steel at high temperatures accelerates diffusion transformations; thus, to obtain full martensite, a higher cooling rate is needed; and 3) the investigated steel has the best plasticity when the deformation temperature is 750 °C.
基金financially supported by the National Natural Science Foundation of China(Nos.51874236 and 52174207)Shaanxi Science and Technology Innovation Team(No.2022TD02)Henan University of Science and Technology PhD Funded Projects(No.B2025-9)。
文摘To more accurately describe the coal damage and fracture evolution law during liquid nitrogen(LN_(2))fracturing under true triaxial stress,a thermal-hydraulic-mechanical-damage(THMD)coupling model for LN_(2) fracturing coal was developed,considering the coal heterogeneity and thermophysical parameters of nitrogen.The accuracy and applicability of model were verified by comparing with LN_(2) injection pre-cooling and fracturing experimental data.The effects of different pre-cooling times and horizontal stress ratios on coal damage evolution,permeability,temperature distribution,and fracture characteristics were analyzed.The results show that the permeability and damage of the coal increase exponentially,while the temperature decreases exponentially during the fracturing process.As the pre-cooling time increases,the damage range of the coal expands,and the fracture propagation becomes more pronounced.The initiation pressure and rupture pressure decrease and tend to stabilize with longer precooling times.As the horizontal stress ratio increases,fractures preferentially extend along the direction of maximum horizontal principal stress,leading to a significant decrease in both initiation and rupture pressures.At a horizontal stress ratio of 3,the initiation pressure drops by 48.07%,and the rupture pressure decreases by 41.36%.The results provide a theoretical basis for optimizing LN_(2) fracturing techniques and improving coal seam modification.
基金supported by the National Natural Science Foundation of China(Grant No.52404020 and Grant No.U1762216).
文摘Heterogeneity in carbonate formations due to discontinuities(e.g.,fractures and cavities)will bring about distinctive acid stimulation effects.However,the differences in fracturing behavior between homogeneous and heterogeneous carbonate formations remain unclear,complicating the optimization of acid fracturing strategies.In this paper,full-diameter carbonate rock samples with different degrees of discontinuity development are selected to investigate the fracturing behavior under different fluid types and injection schemes.Advanced techniques,including 3D CT scanning and 3D laser scanning,are employed to analyze fracture morphology and etching characteristics,respectively.Experimental results show that the coupled hydraulic-chemical effects play different roles in fracture induction between fracture-cavity developed and undeveloped carbonate rocks.Acid-fracturing stimulation consistently induces multiple types of complex fractures in fracture-cavity carbonate rocks,whereas it results in a single artificial fracture in less fracture-cavity carbonate rocks.Furthermore,localized etching patterns are prevalent in most fracture-cavity carbonate rocks,whereas homogeneous carbonate rocks exhibit regional or global etching characteristics.In both carbonate rocks,the stimulation effect of guar fluid is inferior to that of gelled acid but comparable to self-generating acid.Further findings are that alternating fracturing with guar and acid fluids in fracture-cavity carbonate rocks can sustain or even increase the injection pressure,facilitating the formation of new or depth-penetrating fractures.This phenomenon,however,is not observed in fracture-cavity undeveloped carbonate rocks.Potential interaction modes between induced fracture and natural fractures/cavities under different injection conditions are also identified.Finally,preferred fracturing schemes applicable to different carbonate formations are recommended based on the area,number and roughness of the induced fractures.
基金National Natural Science Foundation of China (51974176, 52174194, 51934004)Shandong Provincial Colleges and Universities Youth Innovation and Technology Support Program (2019KJH006)+1 种基金Taishan Scholars Project (TS20190935)Shandong outstanding youth fund (ZR2020JQ22).
文摘The viscosity of fracturing fluid and in-situ stress difference are the two important factors that affect the hydraulic fracturing pressure and propagation morphology. In this study, raw coal was used to prepare coal samples for experiments, and clean fracturing fluid samples were prepared using CTAB surfactant. A series of hydraulic fracturing tests were conducted with an in-house developed triaxial hydraulic fracturing simulator and the fracturing process was monitored with an acoustic emission instrument to analyze the influences of fracturing fluid viscosity and horizontal in-situ stress difference on coal fracture propagation. The results show that the number of branched fractures decreased, the fracture pattern became simpler, the fractures width increased obviously, and the distribution of AE event points was concentrated with the increase of the fracturing fluid viscosity or the horizontal in-situ stress difference. The acoustic emission energy decreases with the increase of fracturing fluid viscosity and increases with the increase of horizontal in situ stress difference. The low viscosity clean fracturing fluid has strong elasticity and is easy to be compressed into the tip of fractures, resulting in complex fractures. The high viscosity clean fracturing fluids are the opposite. Our experimental results provide a reference and scientific basis for the design and optimization of field hydraulic fracturing parameters.
基金funded by the National Natural Science Foundation of China(Nos.52422403 and U22A20166)the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(No.2024ZD1003903)+1 种基金the Department of Science and Technology of Guangdong Province(No.2019ZT08G315)Guangdong Basic and Applied Basic Research Foundation(No.2023A1515012654).
文摘Understanding the mechanical behavior of diagenetic mineral granules and interfaces in granite provides essential experimental references for constructing micromechanical models of granite.The micromechanical behavior of Yanshanian granite is investigated using scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS)and nanoindentation tests.The results demonstrate transitional mechanical properties at mineral interfaces.The elastic modulus and hardness exhibit intermediate values between adjacent mineral phases.The higher plasticity indices at the interfaces suggest higher plastic deformation capacity of hard-phase minerals in these regions.Additionally,fracture toughness measurements of minerals and interfaces were obtained,with interfacial values ranging from 0.90 to 1.63 MPa·m^(0.5).The analysis of mechanical property relationships shows a significant positive linear correlation between rock-scale elastic modulus and fracture toughness.However,this correlation is substantially lower at the mineral scale,demonstrating a scale effect in the relationship of different mechanical properties.
基金financial support from the Equipment Pre-research Project(51312030507).
文摘This study investigates the fatigue crack propagation mechanism of a new high-strength and high-tough Ti-Mo-Cr-V-Nb-Al titanium alloy with three types of microstructures(basketweave structure,lamellar structure,and bimodal structure)through fatigue crack propagation rate tests and fatigue threshold value tests.The resistance of the alloy to fatigue crack propagation was found to be closely correlated with the morphology and distribution ofαparticles,as evidenced by microscopic examination of fracture surfaces and analysis of crack propagation paths.The primaryαparticles demonstrated superior resistance to crack propagation compared to the secondaryαparticles.The basketweave structure showed exceptional resistance to fatigue crack propagation at all stages.The lamellar structure mainly resists long crack propagation during rapid propagation,and its threshold value is the lowest,which makes it easy to produce microcrack propagation.On the contrary,the bimodal structure has the highest threshold value among the three,so its resistance to short crack growth is more excellent,but it has the highest crack growth rate in the higher stress intensity factor range.Theαparticles in the three microstructures also undergo rotational motion relative to the force axis during fatigue crack propagation,thereby adjusting the uneven stress distribution betweenα/βphases through slip behavior and further coordinating deformation.
基金the financial support from Intergovernmental International Science and Technology Innovation Cooperation Key Project(2022YFE0128400)National Natural Science Foundation of China(42307209)+2 种基金Shanghai Pujiang Program(2022PJD076)State Energy Center for Shale Oil Research and Development(33550000-22-ZC0613-0365)Natural Science Foundation of Qinghai Province(No.2024-ZJ-717).
文摘Shale oil reservoir is generally characterized by well-developed bedding planes,and multi-cluster fracturing is the most effective technique to achieve stable shale oil production.In this paper,a multi-cluster fracturing model for a horizontal well in shale with high-density bedding planes is established.The fracture morphology,fracture geometry,fracturing area and multiple fracture propagation mechanism are analyzed under simultaneous fracturing,sequential fracturing,and alternative fracturing.Results show that in the case of small cluster spacing and three clusters,the growth of the middle fracture is inhibited and develops along the bedding planes under both simultaneous fracturing and alternative fracturing.For sequential fracturing,the increase in the interval time between each fracturing advances the post fracturing fracture deflecting to the pre-existing fractures through the bedding planes.The reactivation of the bedding planes can promote the extension of the fracturing area.Increasing the injection rate and the number of clusters promotes the activation of bedding planes.However,it is preferable to reduce the number of clusters to obtain more main fractures.Compared with modified alternating fracturing and cyclic alternating fracturing,alternating shut-in fracturing creates more main fractures towards the direction of the maximum in-situ stress.The fracturing efficiency for high-density layered shale is ranked as simultaneous fracturing>alternative fracturing>sequential fracturing.
基金supported by the National Natural Science Foundation of China(No.52127808)。
文摘The superplasticity of the Mg−8.59Gd−3.85Y−1.14Zn−0.49Zr alloy was investigated before and after multi-directional forging(MDF)and the mechanisms affecting superplastic deformation were analyzed.The results indicate that after MDF at a temperature of 350℃and strain rates of 0.1 and 0.01 s^(−1)(1-MDFed and 2-MDFed),the superplasticity of the alloy can be significantly improved.The elongations of the MDFed alloys exceed 400%under the strain rate of 6.06×10^(−4)s^(−1)and temperatures of 350,375,and 400℃,and reach the maximum values of 766%(1-MDFed)and 693%(2-MDFed)at 375℃.The grain boundary sliding of the MDFed alloy is sufficient,and the energy barrier of deformation decreases.Theβphase limits the grain growth and promotes dynamic recrystallization,maintaining the stability of the fine-grained structure during superplastic deformation.Several Y-rich phases nucleate in the high-strain region(i.e.,the final fracture region)at high temperatures,accelerating the fracture of the specimen.
基金funded by the National Science and Technology Major Project of China (2016ZX05046004-003)Northeast Petroleum University Innovation Foundation for Postgraduate (YJSCX2017-010NEPU and YJSCX2017-009NEPU)
文摘Fracture propagation mechanisms in coalbed methane(CBM) reservoirs are very complex due to the development of the internal cleat system. In this paper, the characteristics of initiation and propagation of hydraulic fractures in coal specimens at different angles between the face cleat and the maximum horizontal principal stress were investigated with hydraulic fracturing tests. The results indicate that the interactions between the hydraulic fractures and the cleat system have a major effect on fracture networks. "Step-like’’ fractures were formed in most experiments due to the existence of discontinuous butt cleats. The hydraulic fractures were more likely to divert or propagate along the butt cleat with an increase in the angles and a decrease in the horizontal principal stress difference. An increase in the injection rate and a decrease in the fracturing fluid viscosity were more conducive to fracture networks. In addition, the influence on fracture propagation of the residual coal fines in the wellbore was also studied. The existence of coal fines was an obstacle in fracturing, and no effective connection can be formed between fractures. The experimental investigation revealed the fracture propagation mechanisms and can provide guidance for hydraulic fracturing design of CBM reservoirs.
基金Project(50578038)supported by the National Natural Science Foundation of China
文摘Crack is found to be a major distress that affects the performance of the epoxy asphalt pavement.An extended finite element method was proposed for investigating the fracture properties of the epoxy asphalt mixture.Firstly,the single-edge notched beam test was used to analyze the temperature effect and calculate the material parameters.Then,the mechanical responses were studied using numerical analysis.It is concluded that 5℃ can be selected as the critical temperature that affects the fracture properties,and numerical simulations indicate that crack propagation is found to significantly affect the stress state of the epoxy asphalt mixture.The maximum principal stress at the crack surface exhibits different trends at various temperatures.Numerical solution of stress intensity factor can well meet the theoretical solution,especially when the temperature is lower than 5℃.
文摘Based on previous research results, this paper investigated the influence of fracture morphology on mechanical properties and failure modes of rock mass with two diagonal intersected fractures. This study carried out a series of triaxial compression tests on rock-like specimens with two crossed fractures under negative temperature, concluded the following conclusions. The strength and failure modes of rock mass are significantly influenced by the dips of two crossed fractures. The strength of rock mass with two frac- tures cannot simply be estimated using the method that was developed for the rock mass with a single fracture. When the intersecting angle is less than 30~, the failure plane initiates at the tip of ＂artificial rup- tures＂ and extends to the upper and lower ends of the specimen. In case of a higher dip and intersecting angle ranging from 30° to 60°, the failure plane propagates along one of these two fractures. The mechan- lca! parameters of rock mass are not only related to the trace length, but also depend on the trace !ength ratio. One could roughly calculate the strength parameters using the approximation proposed in.this paper..For the rock mass with a trace length ratio 〈0.3 （short trace length/long trace length）, the failure mode is dependent on the fracture with a longer trace length. When the trace length becomes significant and the trace length ratio approximates to 1, the failure plane propagates along two fractures, where an X-shaped.failure pattern is presented： For the rock mass with moderate frac!ures and a trace length ratio of approxlmately 1, the failure mode Is.Independent on fractures, which is simllar to .the damage pattern of intact rock. The strength, and elastic .modulus of rock mass decrease with the increase of spacing between fractures, whl!e Polsson＇s ratio is Independent on the spacing. The failure mode can be deter- mined by the area. of triangle created by two fractures. Damage occurs at the smaller triangle area first, and propagates with the two sides of the larger triangle.
基金financially supported by the National Natural Science Foundation of China(No.51274142)the Science&Technology Project of Liaoning Province(No.2009221005)the Science&Technology Project of Shenyang City(Nos.F10-035-2-00 and F11-069-2-00)
文摘Different contents of Ni(0.3wt.%to 1.2wt.%)were added to the QT400-18L ductile iron to investigate the effect of Ni addition on the impact toughness of cast ductile irons at low temperatures.The impact toughnesses of the samples at room and low temperatures were tested.The microstructures and fractographs were observed.Results show that with the increase of Ni addition there is a general trend of refinement of the ferrite matrix while the nodule density shows no obvious change.When the Ni content is 0.7wt.%,the matrix structure is the refined ferrite with a very small fraction(about 2%)of pearlite near the eutectic cell boundaries.When the Ni content is further increased,the fraction of pearlite increases significantly and reaches more than 5%when 1.2wt.%Ni is added.The impact toughness at room temperature increases as the content of Ni increases from 0.3 wt.%to 0.7 wt.%,but decreases as the Ni content further increases to 1.2wt.%due to the increase of pearlite fraction.The maximum value of the impact work is 18.5 J at room temperature with 0.7wt.%Ni addition.The average value of the impact work is still more than 13 J even at-30℃.In addition,the fracture mechanism changes from ductile manner to brittleness as the testing temperature decreases from 20℃to-60℃.
基金the National Natural Science Foundation of China(Grant No.52004236)Sichuan Science and Technology Program(Grant No.2021JDRC0114)+3 种基金the Starting Project of SWPU(Grant No.2019QHZ009)the China Postdoctoral Science Foundation(Grant No.2020M673285)the Open Project Program of Key Laboratory of Groundwater Resources and Environment(Jilin University),Ministry of Education(Grant No.202005009KF)the National Key Basic Research Program of China(Grant No.2014CB239203)for the financial support of this work。
文摘To investigate fracture generation and strain variation during SC-CO_(2)(supercritical carbon dioxide)jet fracturing,the model of induced strain is established and the experiments are comprehensively studied.The influence factors are comprehensively explored,such as jet pressure,ambient pressure,etc.With the increasing jet pressure,the fracture morphology changes from parallel cracks to oblique cracks.Both the mass loss of specimen and CO_(2) absorption increase significantly,and the growth rate and minimum value of strain also rise exponentially.Under a high ambient pressure of 8.0 MPa,the main fractures mostly propagated from the surface to the bottom surface of the specimen.The maximum strain and the stable duration under higher ambient pressure are 1.5 times and 10 times,respectively,of the case under the ambient pressure of 5.0 MPa.The comparison shows that the optimal jet distance is 5-7 times the nozzle diameter,resulting in massive mass loss,large CO_(2)absorption,and peak strain.Moreover,the nonlinear variation of strain curve during jet pressurization is related to the type of rock and ambient pressure.These studies clearly show the relationship between the fracture morphology and induced strain,which are crucial for SC-CO_(2)fracturing in shale gas reservoirs.
基金This work was supported financially by the National Natural Science Foundation of China(No.51201121)the Science and Technology Foundation for Selected Overseas Chinese Scholars of Shaanxi Province(2015)+1 种基金the Key Industry Innovation Chain(group)Project of Shaanxi Province(No.2019ZDLGY 04-04)the Research Project of Shaanxi Engineering Technology Research Center for Wear-resisting Materials(No.2016NMZX03).
文摘Fe-Al-Ta eutectic composites were obtained by a modified Bridgman directional solidification technique at different solidification rates.Solidification microstructure transforms from regular eutectic to eutectic colony with the increase of the solidification rate.The solid/liquid interface of Fe-Al-Ta eutectic evolves from planar interface to cellular interface with the increase of the solidification rate.In addition,threepoint bending method was adopted to study the room-temperature fracture toughness of the as-cast Fe-Al-Ta eutectic alloy and the Fe-Al-Ta eutectic composites.Moreover,the fracture morphologies,the crack propagation path and the strengthening mechanism of Fe-Al-Ta eutectic were discussed.
基金supported the National Natural Science Foundation of China(No.52004033,51922007,and 51874044).
文摘Efficient flow simulation and optimization methods of hydraulic fracture morphology in unconventional reservoirs are effective ways to enhance oil/gas recovery.Based on the connection element method(CEM)and distribution of stimulated reservoir volume,the complex hydraulic fracture morphology was accurately described using heterogeneous node connection system.Then a new fracture connection element method(FCEM)for fluid flow in stimulated unconventional reservoirs with complex hydraulic fracture morphology was proposed.In the proposed FCEM,the arrangement of dense nodes in the stimulated area and sparse nodes in the unstimulated area ensures the calculation accuracy and efficiency.The key parameter,transmissibility,was also modified according to the strong heterogeneity of stimulated reservoirs.The finite difference and semi-analytical tracking were used to accurately solve the pressure and saturation distribution between nodes.The FCEM is validated by comparing with traditional numerical simulation method,and the results show that the bottom hole pressure simulated by the FCEM is consistent with the results from traditional numerical simulation method,and the matching rate is larger than 95%.The proposed FCEM was also used in the optimization of fracturing parameters by coupling the hydraulic fracture propagation method and intelligent optimization algorithm.The integrated intelligent optimization approach for multi-parameters,such as perforation number,perforation location,and displacement in hydraulic fracturing is proposed.The proposed approach was applied in a shale gas reservoir,and the result shows that the optimized perforation location and morphology distribution are related to the distribution of porosity/permeability.When the perforation location and displacement are optimized with the same fracture number,NPV increases by 70.58%,which greatly improves the economic benefits of unconventional reservoirs.This work provides a new way for flow simulation and optimization of hydraulic fracture morphology of multi-fractured horizontal wells in unconventional reservoirs.
基金Project(NCET-10-0360) supported by the Program for New Century Excellent Talents in University,ChinaProject supported by the Fundamental Research Funds for the Central Universities,China
文摘Cu46Zr46A14.8Ti3.2 bulk metallic glass （BMG） was successfully synthesized by copper-mold casting and the mechanical properties at room temperature were measured by compression tests. The structure and thermal characteristics were analyzed by XRD and DSC, and the fracture surface morphology was examined by SEM. The glassy alloy with 4 mm in diameter shows an high fracture strength of 1 960 MPa, with an improvement of about 20% compared to the ultimate compression fracture strength of the Cu46Zr46A18 BMG, which suggests that the Ti addition improves the compression fracture strength. The different degrees of the adiabatic heating induce four types of fracture features： a vein-like structure, an elongated and striated vein pattern, melting and smooth regions. The elongated and striated vein patterns as well as the melting region show that enormous strain energy is released, which causes significant adiabatic heating. Furthernaore, many micro-cracks observed in the smooth region are caused by the strong shear force. In addition, the strong shear force leads to many shear bands as well as the melting in the lateral surface.
文摘The inclusion parameters,fracture surface morphology and void growth characteristics of ten- sile and fracture toughness specimens of 2.25Cr-1Mo steels with and without rare-earth (RE)additions have been investigated by quantitative metaltography(QTM),scanning elec- tron microscopy(SEM)and energy dispersive spectroscopy(EDS).There is a substantially higher density of inclusions in the RE-treated steel,which has lower values of fracture proper- ties including critical values of COD and J integral(δ_c and J_(IC)),fracture strain(ε_f) and Charpy V-notch energy(CVN).The fracture surface of the RE-treated steel comprises equiaxed dimples of diameters comparable with its inclusion spacing,whereas for the non-RE-treated steels,a wide range of dimple sizes is found with average diameter much smaller than the corresponding inclusion spacing.The investigation indicates that the lower values of fracture properties for the steel with RE at room temperature may be ascribed to its large content of RE-containing inclusions.
