Due to the gradually prominent impact of fracture characteristics and serrated yielding in the application of nickel-based superalloys,the hot tensile properties of Inconel 718 superalloy were studied,including fractu...Due to the gradually prominent impact of fracture characteristics and serrated yielding in the application of nickel-based superalloys,the hot tensile properties of Inconel 718 superalloy were studied,including fracture behavior,mechanical properties,and plastic behavior.The experiments adopted three heat treatment regimes and two tensile directions.Results show that various heat treatments make grain sizes different.The larger-sized grains make the vertical surface uneven,which also decrease the number of grain boundaries and carbides,restricting the occurrence of dimples and ultimately reducing the material plasticity.The reduced grain boundaries can decrease dislocations,increase the demand for thermal activation energy,and transform the serration mode of serrated yielding.In addition,various heat treatments also make precipitates different.Carbides can promote the formation of dimples.The needle-shaped δ phase precipitates at grain boundaries and twin boundaries,and slightly inclines towards the rolling direction.Therefore,its pinning effect is outstanding along the transverse direction,which can affect the dimple aggregation and the dislocation movement,ultimately exhibiting anisotropy in fracture characteristics,mechanical properties,and serrated yielding.展开更多
TiAl alloys were produced by investment casting method combined with induction skull melting （ISM） technique. In situ scanning electron microscopy （SEM） was utilized to study the fracture characteristics and crack...TiAl alloys were produced by investment casting method combined with induction skull melting （ISM） technique. In situ scanning electron microscopy （SEM） was utilized to study the fracture characteristics and crack propagation of a notched investment cast TiAl specimens in tension under incremental loading conditions. The whole process of crack initiation, propagation and failure during tensile deformation was observed and characterized. The results show that the fracture mechanism was sensitive to not only the microcracks near the notched area but also lamellar orientation to loading axis. The high tensile stress leads to the new microcracks nucleate along lamellar interfaces of grains with favorable orientation when local stress intensity reaches the toughness threshold of the material. Thus, both plasticity and high tensile stress are required to cause notched TiAl failure.展开更多
The fracture characteristics of austempered spheroidal graphite aluminum cast iron had been investigated. The chemical content of the alloy was C3.2, Al2.2, Ni0.8 and Mg0.05 （in mass percent, %）. Impact test samples...The fracture characteristics of austempered spheroidal graphite aluminum cast iron had been investigated. The chemical content of the alloy was C3.2, Al2.2, Ni0.8 and Mg0.05 （in mass percent, %）. Impact test samples were produced from keel blocks cast in CO2 molding process. The oversized impact samples were austenitized at 850 and 950 ℃ for 2h followed by austempering at 300 and 400 ℃ for 30, 60, 120 and 180min. The austempered samples were machined and tested at room temperature. The impact strength values for those samples austempered at 400 ℃ varied between 90 and 110J. Lower bainitie structures showed impact strength values of 22 to 50J. The fractures of the samples were examined using SEM. The results showed that the upper bainitic fracture revealed a honey Comb-like topography, which confirmed the ductile fracture behavior. The lower bainitic fractures of those samples austempered for short times revealed brittle fracture.展开更多
The present paper concerns the fracture characteristics and ductility of cracked concrete beam externally bonded with carbon fiber-reinforced polymer (CFRP) sheet as well as the integration behaviors between CFRP/conc...The present paper concerns the fracture characteristics and ductility of cracked concrete beam externally bonded with carbon fiber-reinforced polymer (CFRP) sheet as well as the integration behaviors between CFRP/concrete interfacial debonding and concrete cracking.Three-point bending tests were carried out on the CFRP-strengthened cracked concrete beams with varying specimen depth and initial crack length.A straingauge method was developed to monitor the crack initiation and propagation in concrete,and the CFRP/concrete interfacial bonding behaviors,respectively.Clip gauges were used to measure crack mouth opening displacement (CMOD) and the deflection at midspan.Experimental results revealed that CFRP-strengthened specimen shows a higher load capacity under the same deformation level and a better inelastic deformation capacity compared with the unstrengthened one.For there are two manifest peak values in the obtained load versus displacement curve,the ductility of CFRP-strengthened concrete beams were investigated using index expressed as area ratio on the load versus displacement curve.The calculated results indicated that the contribution from CFRP sheet to the ductility improvement of specimen is notable when the deflection at midspan exceeded 10.5 times the first-crack deflection.展开更多
The initial location of the crack and the controlling factor of the fracture in the squeeze casting composites δ-Al2 O3/Al-5.5Zn, δ-Al2 O3/Al-5.5Mg and δ-Al2 O3/Al-cSi were studied by microscopic observation and fi...The initial location of the crack and the controlling factor of the fracture in the squeeze casting composites δ-Al2 O3/Al-5.5Zn, δ-Al2 O3/Al-5.5Mg and δ-Al2 O3/Al-cSi were studied by microscopic observation and finite element analysis(FEA). The in situ failure processes were obseroed bU the scanning electronic microscope mp. The distributions of stress components along the fiber length in matta, and the tnean axial stresses of fiber and matrix were calculated by three-dimensional elasto-plastic FEA.It is found that the failure modes of short fiber reiwtreed metal matrix composites change with the variations of the micro-structurnl characteristics of composites, such as fiber orientation, matrix strength and intedecial bonding, etc.展开更多
Tensile testing results of spray cast Ni3Al-based superalloy indicated that the yield strength and tensile strength increase with the increasing of temperature and reached maximum at around 760℃, then decrease with t...Tensile testing results of spray cast Ni3Al-based superalloy indicated that the yield strength and tensile strength increase with the increasing of temperature and reached maximum at around 760℃, then decrease with the increasing of temperature. After high temperature isostatic pressing (HIP), yield strength decreased and ductility and tensile strength increased. Stereographic projection showed that no matter at room temperature, medium temperature or high temperature, cracks extend along (111).展开更多
The bonding characteristics of (0001)α2||(111)γ interface in two-phase TiAl alloy have beeninvestigated with the recursion method. The results of bond order integral and interaction energybetween atoms are presented...The bonding characteristics of (0001)α2||(111)γ interface in two-phase TiAl alloy have beeninvestigated with the recursion method. The results of bond order integral and interaction energybetween atoms are presented. The effects of B on atoms bonding both in constituent phase andat the α2/γ interface have been studied. The correlation between the mechanical propertiesof the alloy and the bonding at the interface has been discussed. The results suggest that Bsegregation to the interface benefits the ductility. This is supported by the related experiment.展开更多
Micron-scale molybdenum(Mo)wires are vital in numerous technological applications,including micro-electromechanical systems and nanodevices.Understanding their mechanical behavior under cyclic torsion loading is criti...Micron-scale molybdenum(Mo)wires are vital in numerous technological applications,including micro-electromechanical systems and nanodevices.Understanding their mechanical behavior under cyclic torsion loading is critical in designing reliable and durable components.This work investigates the mechanical behavior and fracture characteristics of micron Mo wires under various torsional loading conditions,including monotonic,symmetric,and asymmetric cyclic torsion.The results reveal that the fractures observed in Mo wires exhibit a relatively planar characteristic with noticeable clockwise river-patterned cleavage steps under monotonic torsion,mirroring the direction of the torsional stress applied during the experiment.In terms of symmetric cyclic torsion,it is notable that cyclic softening becomes increasingly pronounced as the increase of strain amplitude.The fractures exhibit distinctive stratification,characterized by the longitudinal cracks propagating radially.When the unloading strain is less than the loaded strain,the extent of the strain hysteresis effect amplifies with an increase in unloading strain.And the observed fracture characteristics are consistent with those under monotonic torsion.Differently,when the loading strain equals the unloading strain,a distinctive fracture pattern emerges in the Mo wire,characterized by a"peak"shape.This research provides valuable insights for optimizing the mechanical reliability of micron wires in microscale and nanoscale applications.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
A new type of nickel-based single-crystal superalloy was subjected to creep performance test,microstructure observation,and composition analysis under the condition of 1100℃/140 MPa.The variation characteristics of t...A new type of nickel-based single-crystal superalloy was subjected to creep performance test,microstructure observation,and composition analysis under the condition of 1100℃/140 MPa.The variation characteristics of the creep rate during the creep fracture process and the microstructure evolution before and after creep were investigated,thereby revealing the creep fracture mechanism of the new nickel-based single-crystal superalloy.The results indicate that the creep life of the alloy is 104.5 h,and the strain can reach 33.58%.The creep rate decreases first,then increases,and finally tends to be stable until fracture.At the initial stage of creep,the creep rate decreases first,then rises and finally decreases again with time.Furthermore,the creep fracture microstructure is composed of dimples and tearing edges without obvious slip planes.Oxides and recrystallized structures exist inside the fracture surface,and the voids inside the fracture are elongated and perpendicular to the stress axis,showing a fracture mechanism of microcrack accumulation.展开更多
This study employs similar simulation testing and discrete element simulation coupling to analyze the failure and deformation processes of a model coal seam's roof.The caving area of the overburden rock is divided...This study employs similar simulation testing and discrete element simulation coupling to analyze the failure and deformation processes of a model coal seam's roof.The caving area of the overburden rock is divided into three zones:the delamination fracture zone,broken fracture zone,and compaction zone.The caving and fracture zones'heights are approximately 110 m above the coal seam,with a maximum subsidence of 11 m.The delamination fracture zone's porosity range is between 0.2 and 0.3,while the remainder of the roof predominantly exhibits a porosity of less than 0.1.In addition,the numerical model's stress analysis revealed that the overburden rock's displacement zone forms an'arch-beam'structure starting from 160 m,with the maximum and minimum stress values decreasing as the distance of advancement increases.In the stress beam interval of the overburden rock,the maximum value changes periodically as the advancement distance increases.Based on a comparative analysis between observable data from on-site work and numerical simulation results,the stress data from the numerical simulation are essentially consistent with the actual results detected on-site,indicating the validity of the numerical simulation results.展开更多
Based on uniaxial compression experimental results on fractured sandstone with grouting and anchorage, we studied the strength and deformation properties, the failure model, crack formation and evolution laws of fract...Based on uniaxial compression experimental results on fractured sandstone with grouting and anchorage, we studied the strength and deformation properties, the failure model, crack formation and evolution laws of fractured sandstone under different conditions of anchorage. The experimental results show that the strength and elastic modulus of fractured sandstone with different fracture angles are significantly lower than those of intact sandstone. Compared with the fractured samples without anchorage,the peak strength, residual strength, peak and ultimate axial strain of fractured sandstone under different anchorage increase by 64.5–320.0%, 62.8–493.0%, and 31.6–181.4%, respectively. The number of bolts and degree of pre-stress has certain effects on the peak strength and failure model of fractured sandstone. The peak strength of fractured sandstone under different anchorage increases to some extent, and the failure model of fractured sandstone also transforms from tensile failure to tensile–shear mixed failure with the number of bolts. The pre-stress can restrain the formation and evolution process of tensile cracks, delay the failure process of fractured sandstone under anchorage and impel the transformation of failure model from brittle failure to plastic failure.展开更多
The reinforcement and stabilization of loess soil are duscussed by using fibers as the reinforcement and cement as the stabilization materials.To study the strength characteristics of loess soil reinforced by modified...The reinforcement and stabilization of loess soil are duscussed by using fibers as the reinforcement and cement as the stabilization materials.To study the strength characteristics of loess soil reinforced by modified polypropylene(MPP) fiber and cement,samples were prepared with six different fiber contents,three different cement contents,three different curing periods and three kinds of fiber length.The samples were tested under submergence and non-submergence conditions for the unconfined compressive strength(UCS),the splitting tensile strength and the compressive resilient modulus.The results indicated that combined reinforcement by PP fiber and cement could significantly improve the early strength of loess to 3.65–5.99 MPa in three days.With an increase in cement content,the specimens exhibited brittle fracture.However,the addition of fibers gradually modified the mode of fracture from brittle to ductile to plastic.The optimal dosage of fiber to reinforce loess was in the range of 0.3%–0.45% and the optimum fiber length was 12 mm,for which the unconfined compressive strength and tensile strength reached their maxima.Based on the analysis of failure properties,cement-reinforced loess specimens were susceptible to brittle damage under pressure,and the effect of modified polypropylene fiber as the connecting "bridge" could help the specimens achieve a satisfactory level of ductility when under pressure.展开更多
Shale gas has currently attracted much attention during oil and gas exploration and development. Fractures in shale have an important influence on the enrichment and preservation of shale gas. This work studied the de...Shale gas has currently attracted much attention during oil and gas exploration and development. Fractures in shale have an important influence on the enrichment and preservation of shale gas. This work studied the developmental period and formation mechanism of tectonic fractures in the Longmaxi Formation shale in the Dingshan area of southeastern Sichuan Basin based on extensive observations of outcrops and cores, rock acoustic emission(Kaiser) experiments, homogenization temperature of fracture fill inclusions, apatite fission track, thermal burial history. The research shows that the fracture types of the Longmaxi Formation include tectonic fractures, diagenetic fractures and horizontal slip fractures. The main types are tectonic high-angle shear and horizontal slip fractures, with small openings, large spacing, low densities, and high degrees of filling. Six dominant directions of the fractures after correction by plane included NWW, nearly SN, NNW, NEE, nearly EW and NW. The analysis of field fracture stage and fracture system of the borehole suggests that the fractures in the Longmaxi Formation could be paired with two sets of plane X-shaped conjugate shear fractures, i.e., profile X-shaped conjugate shear fractures and extension fractures. The combination of qualitative geological analysis and quantitative experimental testing techniques indicates that the tectonic fractures in the Longmaxi Formation have undergone three periods of tectonic movement, namely mid-late Yanshanian movement(82–71.1 Ma), late Yanshanian and middle Himalaya movements(71.1–22.3 Ma), and the late Himalayan movement(22.3–0 Ma). The middle-late period of the Yanshanian movement and end of the Yanshanian movement-middle period of the Himalayan movement were the main fractureforming periods. The fractures were mostly filled with minerals, such as calcite and siliceous. The homogenization temperature of fracture fill inclusions was high, and the paleo-stress value was large; the tectonic movement from the late to present period was mainly a slight transformation and superposition of existing fractures and tectonic systems. Based on the principle of tectonic analysis and theory of geomechanics, we clarified the mechanism of the fractures in the Longmaxi Formation, and established the genetic model of the Longmaxi Formation. The research on the qualitative and quantitative techniques of the fracture-phase study could be effectively used to analyze the causes of the marine shale gas fractures in the Sichuan Basin. The research findings and results provide important references and technical support for further exploration and development of marine shale gas in South China.展开更多
The rock fracture characteristics and principal stress directions are crucial for prevention of geological disasters.In this study,we carried out biaxial compression tests on cubic granite samples of 100 mm in side le...The rock fracture characteristics and principal stress directions are crucial for prevention of geological disasters.In this study,we carried out biaxial compression tests on cubic granite samples of 100 mm in side length with different intermediate principal stress gradients in combination with acoustic emission(AE)technique.Results show that the fracture characteristics of granite samples change from‘sudden and aggregated’to‘continuous and dispersed’with the increase of the intermediate principal stress.The effect of increasing intermediate principal stress on AE amplitude is not significant,but it increases the proportions of high-frequency AE signals and shear cracks,which in turn increases the possibility of unstable rock failure.The difference of stress in different directions causes the anisotropy of rock fracture and thus leads to the obvious anisotropic characteristics of wave velocity variations.The anisotropy of wave velocity variations with stress difference is probable to identify the principal stress directions.The AE characteristics and the anisotropy of wave velocity variations of granite under two-dimensional stress are not only beneficial complements for rock fracture characteristic and principal stress direction identification,but also can provide a new analysis method for stability monitoring in practical rock engineering.展开更多
To clarify the effects of ferrite morphologies and contents on high-cycle fatigue property of pearlite-ferrite dual-phase(DP)steel used for fabrication of commercial vehicle crankshafts,two types of DP steels with dif...To clarify the effects of ferrite morphologies and contents on high-cycle fatigue property of pearlite-ferrite dual-phase(DP)steel used for fabrication of commercial vehicle crankshafts,two types of DP steels with different ferrite grain sizes(S10:13.1μm and S30:21.4μm)and ferrite contents(S10:~9.5 vol.%and S30:~30.4 vol.%)were prepared.Stress amplitude-logarithm of number of high cycles to failure fatigue of the two DP steels was evaluated.Experimental results showed a fatigue strength of 510 and 400 MPa for S10 and S30 steels,respectively,at 10^(7) cycles.Fatigue cracks in S10 steel extended preferentially along the grain boundary,but it was easy for crack propagation to extend within a pearlite colony to form a zigzag crack morphology.Crack roughness was enhanced and high stress was introduced to the crack surface due to this kind of crack propagation behavior,which has positive effects on slowing down crack propagation.However,the crack propagation in S30 steel mainly occurred inside the soft equiaxed coarse ferrite grain.Analysis revealed that little stress was introduced to the crack surface.These results show that it is possible to improve high cycle fatigue strength of pearlite-ferrite DP steel by appropriately manipulating the volume fraction and microstructure morphology of ferrite phase.展开更多
By using thin section identification, cathodoluminescence, major and trace elements and fluid inclusion tests and authigenic illite dating, based on observation of core cracks, combined with the microscopic characteri...By using thin section identification, cathodoluminescence, major and trace elements and fluid inclusion tests and authigenic illite dating, based on observation of core cracks, combined with the microscopic characteristics and imaging logging characteristics of fractures, the stages of the fractures in the Huagang Formation of the central reversal tectonic belt of the Xihu Sag in the East China Sea, and the matching relationship between the fracture development stages and the oil and gas charging stages are clarified. There are diagenetic fractures and tectonic fractures in the reservoirs of the Huagang Formation in the study area. The diagenetic fractures developed during the diagenetic stage of the reservoirs and have less effect on oil and gas migration and transport. The tectonic fractures are divided into three stages based on tectonic movements controlling the fractures and their relationships with hydrocarbon charging: The first stage of fractures was generated in the early stage of the Himalayan Movement–Longjing Movement(12–13 Ma ago), when the tectonic stress caused the sutures and shale strips to twist, deform, and break. Tectonic microfractures generated in this period had short extension, narrow width, and poor effectiveness, and had little effect on oil and gas migration and transport. The second stage of fractures came up during the middle-late period of Himalayan Movement–Longjing Movement(9–12 Ma ago), when tectonic movements caused the development of tectonic fractures in the central reversal tectonic belt, these fractures are of large scale, long extension, and good effectiveness, and matched with the first stage of large scale oil and gas charging(9–12 Ma ago), so they play an important role in oil and gas migration, transportation, and accumulation. The third stage of fractures were created from Himalayan Movement–Okinawa Trough movement to the present day(0–3 Ma ago), the fractures are tectonic ones developing successively;matching with the second stage(0–3 Ma ago) of large-scale oil and gas charging, they created conditions for continuous natural gas migration and transportation. All these prove that the development of reservoir fractures in the Huagang Formation of Xihu Sag can provide seepage space and continuous and effective channels for efficient migration and accumulation of oil and gas.展开更多
Tight reservoirs are typically developed by horizontal wells and multi-stage hydraulic fracturing.The conglomerate reservoir is one type of tight reservoirs,which is different from homogeneous rock,such as tight sands...Tight reservoirs are typically developed by horizontal wells and multi-stage hydraulic fracturing.The conglomerate reservoir is one type of tight reservoirs,which is different from homogeneous rock,such as tight sandstone.This is because that the existence of gravels makes conglomerate have strong hetero-geneity.Thus,it is difficult to grasp the fracture mechanism and the law of fracture propagation of conglomerate,which limits the efficient development of the conglomerate reservoir.In this paper,the fracture characteristics and factors influencing the fracturing of Mahu conglomerate were studied by uniaxial compression,acoustic emission monitoring and X-ray computed tomography(CT)scanning experiments.The results show that the fracture characteristics of conglomerates are influenced by the gravel content and cement.The conglomerate in the study area is mainly divided into carbonate cemented conglomerate and clay cemented conglomerate.The fracture complexity of carbonate cemented conglomerate first increases and then decreases with increasing gravel content.However,for clay cemented conglomerates,the fracture complexity increases over the gravel content.The crack development stress is a significant parameter in the crack assessment of conglomerates.This study is useful to understand the influence of meso-fabric characteristics of conglomerates on their fracturing and crack evolution and guides the design of hydraulic fracturing.展开更多
The microscopic morphology and pore structure characteristics of concrete with composite admixtures(fly ash and mineral powder) after chlorine salt erosion were analyzed via scanning electron microscopy(SEM) and mercu...The microscopic morphology and pore structure characteristics of concrete with composite admixtures(fly ash and mineral powder) after chlorine salt erosion were analyzed via scanning electron microscopy(SEM) and mercury injection porosimetry(MIP), providing the basis for the design and maintenance of concrete shafts in coal mines. The above-mentioned characteristics were compared with the macroscopic characteristic of concrete fractures under uniaxial compression. The results show that the macroscopic fracture characteristics of concrete under uniaxial compression change from longitudinal split fracture and oblique section shear fracture to conjugate cant fracture, and the degree of breakage increases.Interface cracks, cement paste cracks, spherical surface cracks, and aggregate cracks appear in concrete under uniaxial compression. In the early stages of corrosion, the original cracks which are obvious are repaired. When the corrosion becomes more serious, cement paste cracks appear, and the number of harmful holes increases while the number of harmless holes decreases. This study also reveals the relationship between the macroscopic properties and microscopic structure of concrete under chloride salt erosion. Finally, the paper preliminarily discussed the relationship between the macroscopic properties and mesoscopic characteristics of concrete under chlorine salt erosion.展开更多
基金National Natural Science Foundation of China(52175353)Shanxi Province Key Research and Development Program(202102150401002)Shanxi Province Major Science and Technology Special Project(202101110401009)。
文摘Due to the gradually prominent impact of fracture characteristics and serrated yielding in the application of nickel-based superalloys,the hot tensile properties of Inconel 718 superalloy were studied,including fracture behavior,mechanical properties,and plastic behavior.The experiments adopted three heat treatment regimes and two tensile directions.Results show that various heat treatments make grain sizes different.The larger-sized grains make the vertical surface uneven,which also decrease the number of grain boundaries and carbides,restricting the occurrence of dimples and ultimately reducing the material plasticity.The reduced grain boundaries can decrease dislocations,increase the demand for thermal activation energy,and transform the serration mode of serrated yielding.In addition,various heat treatments also make precipitates different.Carbides can promote the formation of dimples.The needle-shaped δ phase precipitates at grain boundaries and twin boundaries,and slightly inclines towards the rolling direction.Therefore,its pinning effect is outstanding along the transverse direction,which can affect the dimple aggregation and the dislocation movement,ultimately exhibiting anisotropy in fracture characteristics,mechanical properties,and serrated yielding.
基金Project(51001040)supported by the National Natural Science Foundation of ChinaProject(200802130014)supported by Specialized Research Fund for the Doctoral Program of Higher Education,China+1 种基金Project(HIT.NSRIF.2010116)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(HITQNJS 2009022)supported by Development Program for Outstanding Young Teachers in Harbin Institute of Technology
文摘TiAl alloys were produced by investment casting method combined with induction skull melting （ISM） technique. In situ scanning electron microscopy （SEM） was utilized to study the fracture characteristics and crack propagation of a notched investment cast TiAl specimens in tension under incremental loading conditions. The whole process of crack initiation, propagation and failure during tensile deformation was observed and characterized. The results show that the fracture mechanism was sensitive to not only the microcracks near the notched area but also lamellar orientation to loading axis. The high tensile stress leads to the new microcracks nucleate along lamellar interfaces of grains with favorable orientation when local stress intensity reaches the toughness threshold of the material. Thus, both plasticity and high tensile stress are required to cause notched TiAl failure.
文摘The fracture characteristics of austempered spheroidal graphite aluminum cast iron had been investigated. The chemical content of the alloy was C3.2, Al2.2, Ni0.8 and Mg0.05 （in mass percent, %）. Impact test samples were produced from keel blocks cast in CO2 molding process. The oversized impact samples were austenitized at 850 and 950 ℃ for 2h followed by austempering at 300 and 400 ℃ for 30, 60, 120 and 180min. The austempered samples were machined and tested at room temperature. The impact strength values for those samples austempered at 400 ℃ varied between 90 and 110J. Lower bainitie structures showed impact strength values of 22 to 50J. The fractures of the samples were examined using SEM. The results showed that the upper bainitic fracture revealed a honey Comb-like topography, which confirmed the ductile fracture behavior. The lower bainitic fractures of those samples austempered for short times revealed brittle fracture.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50578025)the National Key Project of Science and Technology (Grant No. 2006BAJ03A03-09)
文摘The present paper concerns the fracture characteristics and ductility of cracked concrete beam externally bonded with carbon fiber-reinforced polymer (CFRP) sheet as well as the integration behaviors between CFRP/concrete interfacial debonding and concrete cracking.Three-point bending tests were carried out on the CFRP-strengthened cracked concrete beams with varying specimen depth and initial crack length.A straingauge method was developed to monitor the crack initiation and propagation in concrete,and the CFRP/concrete interfacial bonding behaviors,respectively.Clip gauges were used to measure crack mouth opening displacement (CMOD) and the deflection at midspan.Experimental results revealed that CFRP-strengthened specimen shows a higher load capacity under the same deformation level and a better inelastic deformation capacity compared with the unstrengthened one.For there are two manifest peak values in the obtained load versus displacement curve,the ductility of CFRP-strengthened concrete beams were investigated using index expressed as area ratio on the load versus displacement curve.The calculated results indicated that the contribution from CFRP sheet to the ductility improvement of specimen is notable when the deflection at midspan exceeded 10.5 times the first-crack deflection.
文摘The initial location of the crack and the controlling factor of the fracture in the squeeze casting composites δ-Al2 O3/Al-5.5Zn, δ-Al2 O3/Al-5.5Mg and δ-Al2 O3/Al-cSi were studied by microscopic observation and finite element analysis(FEA). The in situ failure processes were obseroed bU the scanning electronic microscope mp. The distributions of stress components along the fiber length in matta, and the tnean axial stresses of fiber and matrix were calculated by three-dimensional elasto-plastic FEA.It is found that the failure modes of short fiber reiwtreed metal matrix composites change with the variations of the micro-structurnl characteristics of composites, such as fiber orientation, matrix strength and intedecial bonding, etc.
文摘Tensile testing results of spray cast Ni3Al-based superalloy indicated that the yield strength and tensile strength increase with the increasing of temperature and reached maximum at around 760℃, then decrease with the increasing of temperature. After high temperature isostatic pressing (HIP), yield strength decreased and ductility and tensile strength increased. Stereographic projection showed that no matter at room temperature, medium temperature or high temperature, cracks extend along (111).
文摘The bonding characteristics of (0001)α2||(111)γ interface in two-phase TiAl alloy have beeninvestigated with the recursion method. The results of bond order integral and interaction energybetween atoms are presented. The effects of B on atoms bonding both in constituent phase andat the α2/γ interface have been studied. The correlation between the mechanical propertiesof the alloy and the bonding at the interface has been discussed. The results suggest that Bsegregation to the interface benefits the ductility. This is supported by the related experiment.
基金financially supported by the National Natural Science Foundation of China(Grant No.12072241).
文摘Micron-scale molybdenum(Mo)wires are vital in numerous technological applications,including micro-electromechanical systems and nanodevices.Understanding their mechanical behavior under cyclic torsion loading is critical in designing reliable and durable components.This work investigates the mechanical behavior and fracture characteristics of micron Mo wires under various torsional loading conditions,including monotonic,symmetric,and asymmetric cyclic torsion.The results reveal that the fractures observed in Mo wires exhibit a relatively planar characteristic with noticeable clockwise river-patterned cleavage steps under monotonic torsion,mirroring the direction of the torsional stress applied during the experiment.In terms of symmetric cyclic torsion,it is notable that cyclic softening becomes increasingly pronounced as the increase of strain amplitude.The fractures exhibit distinctive stratification,characterized by the longitudinal cracks propagating radially.When the unloading strain is less than the loaded strain,the extent of the strain hysteresis effect amplifies with an increase in unloading strain.And the observed fracture characteristics are consistent with those under monotonic torsion.Differently,when the loading strain equals the unloading strain,a distinctive fracture pattern emerges in the Mo wire,characterized by a"peak"shape.This research provides valuable insights for optimizing the mechanical reliability of micron wires in microscale and nanoscale applications.
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China Postdoctoral Science Foundation General Project(2024M760034)Postdoctoral Research Programs of Anhui Province(2024A774)。
文摘A new type of nickel-based single-crystal superalloy was subjected to creep performance test,microstructure observation,and composition analysis under the condition of 1100℃/140 MPa.The variation characteristics of the creep rate during the creep fracture process and the microstructure evolution before and after creep were investigated,thereby revealing the creep fracture mechanism of the new nickel-based single-crystal superalloy.The results indicate that the creep life of the alloy is 104.5 h,and the strain can reach 33.58%.The creep rate decreases first,then increases,and finally tends to be stable until fracture.At the initial stage of creep,the creep rate decreases first,then rises and finally decreases again with time.Furthermore,the creep fracture microstructure is composed of dimples and tearing edges without obvious slip planes.Oxides and recrystallized structures exist inside the fracture surface,and the voids inside the fracture are elongated and perpendicular to the stress axis,showing a fracture mechanism of microcrack accumulation.
基金National Key R&D Program of China(2023YFC3009100,2023YFC3009102)National Natural Science Foundation of China(52304198)Open Fund of the National and Local Joint Engineering Research Center for Safe and Accurate Coal Mining(EC2021016).
文摘This study employs similar simulation testing and discrete element simulation coupling to analyze the failure and deformation processes of a model coal seam's roof.The caving area of the overburden rock is divided into three zones:the delamination fracture zone,broken fracture zone,and compaction zone.The caving and fracture zones'heights are approximately 110 m above the coal seam,with a maximum subsidence of 11 m.The delamination fracture zone's porosity range is between 0.2 and 0.3,while the remainder of the roof predominantly exhibits a porosity of less than 0.1.In addition,the numerical model's stress analysis revealed that the overburden rock's displacement zone forms an'arch-beam'structure starting from 160 m,with the maximum and minimum stress values decreasing as the distance of advancement increases.In the stress beam interval of the overburden rock,the maximum value changes periodically as the advancement distance increases.Based on a comparative analysis between observable data from on-site work and numerical simulation results,the stress data from the numerical simulation are essentially consistent with the actual results detected on-site,indicating the validity of the numerical simulation results.
基金Financial support for this work, provided by the National Natural Science Foundation of China (Nos. 50774082, 50804046 and 51109209)
文摘Based on uniaxial compression experimental results on fractured sandstone with grouting and anchorage, we studied the strength and deformation properties, the failure model, crack formation and evolution laws of fractured sandstone under different conditions of anchorage. The experimental results show that the strength and elastic modulus of fractured sandstone with different fracture angles are significantly lower than those of intact sandstone. Compared with the fractured samples without anchorage,the peak strength, residual strength, peak and ultimate axial strain of fractured sandstone under different anchorage increase by 64.5–320.0%, 62.8–493.0%, and 31.6–181.4%, respectively. The number of bolts and degree of pre-stress has certain effects on the peak strength and failure model of fractured sandstone. The peak strength of fractured sandstone under different anchorage increases to some extent, and the failure model of fractured sandstone also transforms from tensile failure to tensile–shear mixed failure with the number of bolts. The pre-stress can restrain the formation and evolution process of tensile cracks, delay the failure process of fractured sandstone under anchorage and impel the transformation of failure model from brittle failure to plastic failure.
基金Project(050101)supported by Horizontal Research Foundation of PLA Air Force Engineering University,ChinaProject(51478462)supported by the National Natural Science Foundation of China
文摘The reinforcement and stabilization of loess soil are duscussed by using fibers as the reinforcement and cement as the stabilization materials.To study the strength characteristics of loess soil reinforced by modified polypropylene(MPP) fiber and cement,samples were prepared with six different fiber contents,three different cement contents,three different curing periods and three kinds of fiber length.The samples were tested under submergence and non-submergence conditions for the unconfined compressive strength(UCS),the splitting tensile strength and the compressive resilient modulus.The results indicated that combined reinforcement by PP fiber and cement could significantly improve the early strength of loess to 3.65–5.99 MPa in three days.With an increase in cement content,the specimens exhibited brittle fracture.However,the addition of fibers gradually modified the mode of fracture from brittle to ductile to plastic.The optimal dosage of fiber to reinforce loess was in the range of 0.3%–0.45% and the optimum fiber length was 12 mm,for which the unconfined compressive strength and tensile strength reached their maxima.Based on the analysis of failure properties,cement-reinforced loess specimens were susceptible to brittle damage under pressure,and the effect of modified polypropylene fiber as the connecting "bridge" could help the specimens achieve a satisfactory level of ductility when under pressure.
基金financially supported by the Open Fund (grant No. PLC 20180404) of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology
文摘Shale gas has currently attracted much attention during oil and gas exploration and development. Fractures in shale have an important influence on the enrichment and preservation of shale gas. This work studied the developmental period and formation mechanism of tectonic fractures in the Longmaxi Formation shale in the Dingshan area of southeastern Sichuan Basin based on extensive observations of outcrops and cores, rock acoustic emission(Kaiser) experiments, homogenization temperature of fracture fill inclusions, apatite fission track, thermal burial history. The research shows that the fracture types of the Longmaxi Formation include tectonic fractures, diagenetic fractures and horizontal slip fractures. The main types are tectonic high-angle shear and horizontal slip fractures, with small openings, large spacing, low densities, and high degrees of filling. Six dominant directions of the fractures after correction by plane included NWW, nearly SN, NNW, NEE, nearly EW and NW. The analysis of field fracture stage and fracture system of the borehole suggests that the fractures in the Longmaxi Formation could be paired with two sets of plane X-shaped conjugate shear fractures, i.e., profile X-shaped conjugate shear fractures and extension fractures. The combination of qualitative geological analysis and quantitative experimental testing techniques indicates that the tectonic fractures in the Longmaxi Formation have undergone three periods of tectonic movement, namely mid-late Yanshanian movement(82–71.1 Ma), late Yanshanian and middle Himalaya movements(71.1–22.3 Ma), and the late Himalayan movement(22.3–0 Ma). The middle-late period of the Yanshanian movement and end of the Yanshanian movement-middle period of the Himalayan movement were the main fractureforming periods. The fractures were mostly filled with minerals, such as calcite and siliceous. The homogenization temperature of fracture fill inclusions was high, and the paleo-stress value was large; the tectonic movement from the late to present period was mainly a slight transformation and superposition of existing fractures and tectonic systems. Based on the principle of tectonic analysis and theory of geomechanics, we clarified the mechanism of the fractures in the Longmaxi Formation, and established the genetic model of the Longmaxi Formation. The research on the qualitative and quantitative techniques of the fracture-phase study could be effectively used to analyze the causes of the marine shale gas fractures in the Sichuan Basin. The research findings and results provide important references and technical support for further exploration and development of marine shale gas in South China.
基金This work was financially supported by the National Key Research and Development Program of China(Grant No.2021YFC2900500)the International(Regional)Cooperation and Exchange Program of National Natural Science Foundation of China(Grant No.52161135301)the Special Fund for Basic Scientific Research Operations in Universities(Grant No.2282020cxqd055).
文摘The rock fracture characteristics and principal stress directions are crucial for prevention of geological disasters.In this study,we carried out biaxial compression tests on cubic granite samples of 100 mm in side length with different intermediate principal stress gradients in combination with acoustic emission(AE)technique.Results show that the fracture characteristics of granite samples change from‘sudden and aggregated’to‘continuous and dispersed’with the increase of the intermediate principal stress.The effect of increasing intermediate principal stress on AE amplitude is not significant,but it increases the proportions of high-frequency AE signals and shear cracks,which in turn increases the possibility of unstable rock failure.The difference of stress in different directions causes the anisotropy of rock fracture and thus leads to the obvious anisotropic characteristics of wave velocity variations.The anisotropy of wave velocity variations with stress difference is probable to identify the principal stress directions.The AE characteristics and the anisotropy of wave velocity variations of granite under two-dimensional stress are not only beneficial complements for rock fracture characteristic and principal stress direction identification,but also can provide a new analysis method for stability monitoring in practical rock engineering.
基金supported from BAOSTEEL-SJTU Joint Research Center for Future Steelgrateful to the financial support from Startup Fund for Youngman Research at SJTU(SFYR at SJTU).
文摘To clarify the effects of ferrite morphologies and contents on high-cycle fatigue property of pearlite-ferrite dual-phase(DP)steel used for fabrication of commercial vehicle crankshafts,two types of DP steels with different ferrite grain sizes(S10:13.1μm and S30:21.4μm)and ferrite contents(S10:~9.5 vol.%and S30:~30.4 vol.%)were prepared.Stress amplitude-logarithm of number of high cycles to failure fatigue of the two DP steels was evaluated.Experimental results showed a fatigue strength of 510 and 400 MPa for S10 and S30 steels,respectively,at 10^(7) cycles.Fatigue cracks in S10 steel extended preferentially along the grain boundary,but it was easy for crack propagation to extend within a pearlite colony to form a zigzag crack morphology.Crack roughness was enhanced and high stress was introduced to the crack surface due to this kind of crack propagation behavior,which has positive effects on slowing down crack propagation.However,the crack propagation in S30 steel mainly occurred inside the soft equiaxed coarse ferrite grain.Analysis revealed that little stress was introduced to the crack surface.These results show that it is possible to improve high cycle fatigue strength of pearlite-ferrite DP steel by appropriately manipulating the volume fraction and microstructure morphology of ferrite phase.
基金Supported by the China National Science and Technology Major Project(2016ZX05027,2016ZX05027-002-006)
文摘By using thin section identification, cathodoluminescence, major and trace elements and fluid inclusion tests and authigenic illite dating, based on observation of core cracks, combined with the microscopic characteristics and imaging logging characteristics of fractures, the stages of the fractures in the Huagang Formation of the central reversal tectonic belt of the Xihu Sag in the East China Sea, and the matching relationship between the fracture development stages and the oil and gas charging stages are clarified. There are diagenetic fractures and tectonic fractures in the reservoirs of the Huagang Formation in the study area. The diagenetic fractures developed during the diagenetic stage of the reservoirs and have less effect on oil and gas migration and transport. The tectonic fractures are divided into three stages based on tectonic movements controlling the fractures and their relationships with hydrocarbon charging: The first stage of fractures was generated in the early stage of the Himalayan Movement–Longjing Movement(12–13 Ma ago), when the tectonic stress caused the sutures and shale strips to twist, deform, and break. Tectonic microfractures generated in this period had short extension, narrow width, and poor effectiveness, and had little effect on oil and gas migration and transport. The second stage of fractures came up during the middle-late period of Himalayan Movement–Longjing Movement(9–12 Ma ago), when tectonic movements caused the development of tectonic fractures in the central reversal tectonic belt, these fractures are of large scale, long extension, and good effectiveness, and matched with the first stage of large scale oil and gas charging(9–12 Ma ago), so they play an important role in oil and gas migration, transportation, and accumulation. The third stage of fractures were created from Himalayan Movement–Okinawa Trough movement to the present day(0–3 Ma ago), the fractures are tectonic ones developing successively;matching with the second stage(0–3 Ma ago) of large-scale oil and gas charging, they created conditions for continuous natural gas migration and transportation. All these prove that the development of reservoir fractures in the Huagang Formation of Xihu Sag can provide seepage space and continuous and effective channels for efficient migration and accumulation of oil and gas.
基金supported by the Natural Science Youth Project of University Scientific Research Plan in Xinjiang(XJEDU2021Y053)the Talent Introduction Research Project of China University of Petroleum Beijing at Karamay(XQSQ20200056)+1 种基金Development of Conglomerate Reservoir Laboratory in Xinjiang(2019D04008)the Strategic Cooperation Technology Projects of CNPC and CUPB(Grant No.ZLZX2020-01).
文摘Tight reservoirs are typically developed by horizontal wells and multi-stage hydraulic fracturing.The conglomerate reservoir is one type of tight reservoirs,which is different from homogeneous rock,such as tight sandstone.This is because that the existence of gravels makes conglomerate have strong hetero-geneity.Thus,it is difficult to grasp the fracture mechanism and the law of fracture propagation of conglomerate,which limits the efficient development of the conglomerate reservoir.In this paper,the fracture characteristics and factors influencing the fracturing of Mahu conglomerate were studied by uniaxial compression,acoustic emission monitoring and X-ray computed tomography(CT)scanning experiments.The results show that the fracture characteristics of conglomerates are influenced by the gravel content and cement.The conglomerate in the study area is mainly divided into carbonate cemented conglomerate and clay cemented conglomerate.The fracture complexity of carbonate cemented conglomerate first increases and then decreases with increasing gravel content.However,for clay cemented conglomerates,the fracture complexity increases over the gravel content.The crack development stress is a significant parameter in the crack assessment of conglomerates.This study is useful to understand the influence of meso-fabric characteristics of conglomerates on their fracturing and crack evolution and guides the design of hydraulic fracturing.
基金The authors gratefully acknowledge the financial support for this work,provided by the Outstanding Youth Science Foundation of China(No.51322401)the Key Project of Chinese National Programs for Fundamental Research and Development of China(No.2015CB251601)+1 种基金the Science and Technology Project of the Chinese Ministry of Housing and Urban-Rural Construction of China(Nos.2013-K4-22 and 2014-K4-042)the General Program of Chinese National Building Materials Industry Technology Innovation Program of China(Nos.2014-M5-1 and 2014-M5-2)
文摘The microscopic morphology and pore structure characteristics of concrete with composite admixtures(fly ash and mineral powder) after chlorine salt erosion were analyzed via scanning electron microscopy(SEM) and mercury injection porosimetry(MIP), providing the basis for the design and maintenance of concrete shafts in coal mines. The above-mentioned characteristics were compared with the macroscopic characteristic of concrete fractures under uniaxial compression. The results show that the macroscopic fracture characteristics of concrete under uniaxial compression change from longitudinal split fracture and oblique section shear fracture to conjugate cant fracture, and the degree of breakage increases.Interface cracks, cement paste cracks, spherical surface cracks, and aggregate cracks appear in concrete under uniaxial compression. In the early stages of corrosion, the original cracks which are obvious are repaired. When the corrosion becomes more serious, cement paste cracks appear, and the number of harmful holes increases while the number of harmless holes decreases. This study also reveals the relationship between the macroscopic properties and microscopic structure of concrete under chloride salt erosion. Finally, the paper preliminarily discussed the relationship between the macroscopic properties and mesoscopic characteristics of concrete under chlorine salt erosion.
