A series of true triaxial unloading tests are conducted on sandstone specimens with a single structural plane to investigate their mechanical behaviors and failure characteristics under different in situ stress states...A series of true triaxial unloading tests are conducted on sandstone specimens with a single structural plane to investigate their mechanical behaviors and failure characteristics under different in situ stress states.The experimental results indicate that the dip angle of structural plane(θ)and the intermediate principal stress(σ2)have an important influence on the peak strength,cracking mode,and rockburst severity.The peak strength exhibits a first increase and then decrease as a function ofσ2 for a constantθ.However,whenσ2 is constant,the maximum peak strength is obtained atθof 90°,and the minimum peak strength is obtained atθof 30°or 45°.For the case of an inclined structural plane,the crack type at the tips of structural plane transforms from a mix of wing and anti-wing cracks to wing cracks with an increase inσ2,while the crack type around the tips of structural plane is always anti-wing cracks for the vertical structural plane,accompanied by a series of tensile cracks besides.The specimens with structural plane do not undergo slabbing failure regardless ofθ,and always exhibit composite tensile-shear failure whatever theσ2 value is.With an increase inσ2 andθ,the intensity of the rockburst is consistent with the tendency of the peak strength.By analyzing the relationship between the cohesion(c),internal friction angle(φ),andθin sandstone specimens,we incorporateθinto the true triaxial unloading strength criterion,and propose a modified linear Mogi-Coulomb criterion.Moreover,the crack propagation mechanism at the tips of structural plane,and closure degree of the structural plane under true triaxial unloading conditions are also discussed and summarized.This study provides theoretical guidance for stability assessment of surrounding rocks containing geological structures in deep complex stress environments.展开更多
The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique natu...The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique nature of this soil type.In this study,a series of unconfined compression tests were carried out on unsaturated CWG soil in an underground engineering site,and the effects of varying the environmental variables on the main undrained mechanical properties were analyzed.Based on the experimental results,a novel constitutive model was then established using the damage mechanics theory and the undetermined coefficient method.The results demonstrate that the curves of remolded CWG specimens with different moisture contents and dry densities exhibited diverse characteristics,including brittleness,significant softening,and ductility.As a typical indicator,the unconfined compression strength of soil specimens initially increased with an increase in moisture content and then decreased.Meanwhile,an optimal moisture content of approximately 10.5%could be observed,while a critical moisture content value of 13.0%was identified,beyond which the strength of the specimen decreases sharply.Moreover,the deformation and fracture of CWG specimens were predominantly caused by shear failure,and the ultimate failure modes were primarily influenced by moisture content rather than dry density.Furthermore,by comparing several similar models and the experimental data,the proposed model could accurately replicate the undrained mechanical characteristics of unsaturated CWG soil,and quantitatively describe the key mechanical indexes.These findings offer a valuable reference point for understanding the underlying mechanisms,anticipating potential risks,and implementing effective control measures in similar underground engineering projects.展开更多
The reservoir landslide undergoes periodic saturation-drying cycles affected by reservoir fluctuation in hydropower project area,leading to the irreversible impact on the landslide materials.Sliding zone is the sheari...The reservoir landslide undergoes periodic saturation-drying cycles affected by reservoir fluctuation in hydropower project area,leading to the irreversible impact on the landslide materials.Sliding zone is the shearing part in formation of landslide and controls the further development of landslide.The mechanical behavior of sliding zone soil under compression is a crucial factor in the stability analysis in landslides.In this paper,the sliding zone soil from a giant landslide in the biggest hydropower project area,Three Gorges Reservoir Area,is taken as the research case.The particlesize distribution of the sliding zone soil from this landslide is studied and fractal dimension is adopted as representation.Periodic saturation-drying is introduced as the affecting factor on sliding zone soil properties.The triaxial compression test is conducted to reveal the mechanical behavior of the soil,including stress-strain behavior,elastic modulus,failure stress and strength parameters.These behavior of sliding zone soils with different fractal dimensions are studied under the effects of periodic saturation-drying cycles.The normalized stress-strain curves are displayed for further calculation.The data considering saturation-drying cycles are obtained and compared with the experimental results.展开更多
Smart materials,especially shape memory composites and 4D printing materials,are widely used in aerospace.Deflectors are essential equipment in wind tunnel construction.Classical deflectors are made of metal materials...Smart materials,especially shape memory composites and 4D printing materials,are widely used in aerospace.Deflectors are essential equipment in wind tunnel construction.Classical deflectors are made of metal materials and have a relatively high structural weight.The deflector made of smart material has the advantage of being lighter in weight compared to classical structure,and it could change the bending angle of the deflector structure under external excitation.In this study,the corresponding mechanical property test and finite element simulation of the smart material are carried out,and the deflector made of smart material is further studied and analyzed.Maxwell viscoelasticity model for the material is established,and relevant parameters are obtained through stress relaxation test fitting.According to relevant parameters and literature,finite element simulation of intelligent deflector structure is carried out.The pressure loss coefficient,airflow deflection angle,and velocity uniformity are studied.The numerical model of the minimum pressure loss coefficient is established with reference to the relevant data,and the formula for calculating the optimal upwind radius of the deflector is obtained.Combined with the numerical simulation results of the flow deflection angle and velocity uniformity of the flow field,it provides a reference for the selection of the size of the deflector.展开更多
In this work,through performing microstructural characterization,tensile testing and failure analysis,the influence of electrochemical hydrogen charging on the microstructure and mechanical behavior of an as-cast Mg-8...In this work,through performing microstructural characterization,tensile testing and failure analysis,the influence of electrochemical hydrogen charging on the microstructure and mechanical behavior of an as-cast Mg-8wt.%Li alloy was investigated.It revealed that after being hydrogen charged at 50 mA/cm2 for respectively 3 h,6 h and 18 h in 0.1 M NaCl solution,obvious HID occurred and the damage degree was gradually increased with the hydrogen charging time.For the sample being hydrogen charged for 3 h,micro pores with the diameter ranging from 10~30µm were formed and preferentially present inα-Mg phase.Moreover,micro cracks with the length ranging from 10~50µm mainly initiated inα-Mg phase,atα-Mg/β-Li interfaces and the peripheries of pores.With the increase of hydrogen charging time,the numbers of pores and cracks were obviously increased.Tensile results revealed that the hydrogen charging can simultaneously decrease the tensile strength and ductility of the alloy.Compared with the uncharged sample,the tensile yield strength,ultimate tensile strength and the elongation ratio to failure were respectively reduced by 5.7%,7.3%,31.7%for the 3h-charged sample and 24.6%,24.8%,67.0%for the 18h-charged sample.Failure analysis indicated that hydrogen charging can induce the brittle cracking of the alloy and the size of brittle cracking region being composed of quasi-cleavage facets and interfacial cracks on the fracture surfaces was increased with the hydrogen charging time.展开更多
Exploring dynamic mechanical responses and failure behaviors of hot dry rock(HDR)is significant for geothermal exploitation and stability assessment.In this study,via the split Hopkinson pressure bar(SHPB)system,a ser...Exploring dynamic mechanical responses and failure behaviors of hot dry rock(HDR)is significant for geothermal exploitation and stability assessment.In this study,via the split Hopkinson pressure bar(SHPB)system,a series of dynamic compression tests were conducted on granite treated by cyclic thermal shocks at different temperatures.We analyzed the effects of cyclic thermal shock on the thermal-related physical and dynamic mechanical behaviors of granite.Specifically,the P-wave velocity,dynamic strength,and elastic modulus of the tested granite decrease with increasing temperature and cycle number,while porosity and peak strain increase.The degradation law of dynamic mechanical properties could be described by a cubic polynomial.Cyclic thermal shock promotes shear cracks propagation,causing dynamic failure mode of granite to transition from splitting to tensile-shear composite failure,accompanied by surface spalling and debris splashing.Moreover,the thermal shock damage evolution and coupled failure mechanism of tested granite are discussed.The evolution of thermal shock damage with thermal shock cycle numbers shows an obvious S-shaped surface,featured by an exponential correlation with dynamic mechanical parameters.In addition,with increasing thermal shock temperature and cycles,granite mineral species barely change,but the length and width of thermal cracks increase significantly.The non-uniform expansion of minerals,thermal shock-induced cracking,and water-rock interaction are primary factors for deteriorating dynamic mechanical properties of granite under cyclic thermal shock.展开更多
In this study,microstructure and mechanical behavior of Mg/Al composite plates with Ti foil interlayer were systematically studied,with a great emphasis on the effect of different thicknesses of Ti foil interlayer.The...In this study,microstructure and mechanical behavior of Mg/Al composite plates with Ti foil interlayer were systematically studied,with a great emphasis on the effect of different thicknesses of Ti foil interlayer.The results show that compared to 100μm thick Ti foil,10μm thick Ti foil is more prone to fracture and is evenly distributed in fragments at the interface.The introduction of Ti foil can effectively refine the grain size of Mg layers of as-rolled Mg/Al composite plates,10μm thick Ti foil has a better refining effect than 100μm thick Ti foil.Ti foil can effectively increase the yield strength(YS)and ultimate strength(UTS)of as-rolled Mg/Al composite plates,10μm thick Ti foil significantly improves the elongation(El)of Mg/Al composite plate,while 100μm thick Ti foil slightly weakens the El.After annealing at 420℃ for 0.5 h and 4 h,Ti foil can inhibit the formation of intermetallic compounds(IMCs)at the interface of Mg/Al composite plates,which effectively improves the YS,UTS and El of Mg/Al composite plates.In addition,Ti foil can also significantly enhance the interfacial shear strength(SS)of Mg/Al composite plates before and after annealing.展开更多
Compressive mechanical behavior and microstructure evolution of Ti−5.7Al−2.9Nb−1.8Fe−1.6Mo−1.5V−1Zr alloy under extreme conditions were systematically investigated.The results show that strain rate and temperature hav...Compressive mechanical behavior and microstructure evolution of Ti−5.7Al−2.9Nb−1.8Fe−1.6Mo−1.5V−1Zr alloy under extreme conditions were systematically investigated.The results show that strain rate and temperature have a significant influence on the mechanical behavior and microstructure.The alloy exhibits a positive strain rate sensitivity and negative temperature sensitivity under all temperature and strain rate conditions.The hot-rolled alloy is composed of a bimodal structure including an equiaxed primary α_(p) phase and a transformedβphase.After compression deformation,the bimodal deformed structural features highly rely on the temperature and strain rate.At low temperature and room temperature,the volume fraction and size of α_(p) phase decrease with increasing temperature and strain rate.At high temperature,the volume fraction of the α_(p)hase is inversely correlated with temperature.A modified Johnson−Cook constitutive model is established,and the predicted results coincide well with the experimental results.展开更多
Steel lazy-wave riser(SLWR)is one of the key technical components of offshore oil-gas production systems and is widely utilized in deepwater areas.On the basis of the vector form intrinsic finite element(VFIFE)method,...Steel lazy-wave riser(SLWR)is one of the key technical components of offshore oil-gas production systems and is widely utilized in deepwater areas.On the basis of the vector form intrinsic finite element(VFIFE)method,this study develops a reasonable numerical model for the SLWR to investigate the effects of the buoyancy section on its mechanical characteristics.In the SLWR model,the buoyancy section is simulated using an equivalent riser segment with the same outer diameter and unit weight.The riser is considered to be composed of a series of space vector particles connected by elements,and virtual reverse motions are applied to establish the fundamental equations of forces and displacements.The explicit central difference technique is used to solve the governing equations for particle motion within the riser through programming implementation.To provide a detailed explanation of the process by which the SLWR achieves a stable lazy-wave configuration,a numerical model of a 2800-m-long riser is established at a water depth of 1600 m,and the feasibility of this model for riser behavior analysis is validated.The remarkable influences of the position,length,number and spacing of the buoyancy section on the mechanical behavior of the SLWR are observed,which provides a theoretical foundation for the optimal design of the SLWR in deepwaters.展开更多
In order to research the concrete archaized buildings with lintel-column joint,2 specimens were tested under dynamic experiment.The failure characteristics,skeleton curves,mechanical behavior such as the load-displace...In order to research the concrete archaized buildings with lintel-column joint,2 specimens were tested under dynamic experiment.The failure characteristics,skeleton curves,mechanical behavior such as the load-displacement hysteretic loops,load carrying capacity,degradation of strength and stiffness,ductility and energy dissipation of the joints were analyzed.The results indicate that comparies with the lintel-column joints,the loading capacity and energy dissipation of the concrete archaized buildings with dual lintel-column joints are higher,and the hysteretic loops is in plump-shape.However,the displacement ductility coefficient is less than that of lintel-column joints.Both of them of the regularity of rigidity degeneration are basically the same.Generally,the joints have the good energy dissipation capacity.And the concrete archaized buildings with lintel-column joints exhibit excellent seismic behavior.展开更多
Many rock engineering projects show that the growth of tensile cracks is often an important cause of engineering disasters,and the mechanical behavior of rocks is essentially the transmission,storage,dissipation and r...Many rock engineering projects show that the growth of tensile cracks is often an important cause of engineering disasters,and the mechanical behavior of rocks is essentially the transmission,storage,dissipation and release of energy.To investigate the tensile behavior of rock from the perspective of energy,uniaxial tension tests(UTTs)and uniaxial compression tests(UCTs)were carried out on three typical rocks(granite,sandstone and marble).Different unloading points were set before the peak stress to separate elastic energy and dissipated energy.The input energy density ut,elastic energy density ue,and dissipated energy density ud at each unloading point were calculated by integrating stress-strain curves.The results show that there is a strong linear relationship between the three energy parameters and the square of the unloading stress in UCT,but this linear relationship is weaker in UTT.The ue and ud increase linearly with the increase in ut in UCT and UTT.Based on the phenomenon that ue and ud increase linearly with ut,the applicability of W_(et)^(p) index in UTT was proved and the relative energy storage capacity and absolute energy distribution characteristics of three rocks in UCT and UTT were evaluated.The tensile behavior of marble and sandstone in UTT can be divided into two stages vaguely according to the energy distribution,but granite is not the case.In addition,based on dissipated energy,the damage evolution of three types of rocks in UCT and UTT was discussed.This study provides some new insights for understanding the tensile behavior of rock.展开更多
Cold rolling process can regulate the microstructure and mechanical properties of amorphous alloys,but it is still a challenging task to reveal their microscopic mechanism.Here,we designed an in-situ SEM observation d...Cold rolling process can regulate the microstructure and mechanical properties of amorphous alloys,but it is still a challenging task to reveal their microscopic mechanism.Here,we designed an in-situ SEM observation device for the cold rolling process of amorphous alloy,and visually observed the formation and evolution of shear bands during single-pass and multi-pass rolling process of the Zr_(55)Cu_(30)Al_(10)Ni_(5)amorphous alloy sheets.It is found that the evolution process of shear bands in the rolling process of amorphous alloy shows heritability,which is mainly reflected in two aspects:one is that the shear band formation pattern in the single-pass rolling process is more inclined to inherit the previous shear band formation pattern;the other is that the shear deformation is more likely to occur in the pre-existing shear bands in the multi-pass rolling process.This rule can be used to guide the controlled genera-tion of shear bands in amorphous alloys.Moreover,we emphasized the importance of pre-existing shear band orientations and systematically investigated the mechanical behavior of the amorphous alloys with pre-existing shear bands by in-situ SEM observation.It is found that the mechanical properties of the as-rolled amorphous alloys are determined by the competition between the work-softening of the pre-existing shear band itself and the work-hardening caused by the blocking effect of the pre-existing shear bands on the shear deformation.Based on this,we enhance the tensile fracture strength and the tensile ductility of the amorphous alloy by adjusting the orientation of the pre-existing shear bands parallel to the tensile stress axis so that the pre-existing shear bands prevent the linear propagation and destruction of the new shear bands.展开更多
The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures an...The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. In this study, a novel approach for stabilizing the warm and ice-rich frozen soil with sulphoaluminate cement was proposed based on chemical stabilization. The mechanical behaviors of the stabilized soil, such as strength and stress-strain relationship, were investigated through a series of triaxial compression tests conducted at -1.0℃, and the mechanism of strength variations of the stabilized soil was also explained based on scanning electron microscope test. The investigations indicated that the strength of stabilized soil to resist failure has been improved, and the linear Mohr-Coulomb criteria can accurately reflect the shear strength of stabilized soil under various applied confining pressure. The increase in both curing age and cement mixing ratio were favorable to the growth of cohesion and internal friction angle. More importantly, the strength improvement mechanism of the stabilized soil is attributed to the formation of structural skeleton and the generation of cementitious hydration products within itself. Therefore, the investigations conducted in this study provide valuable references for chemical stabilization of warm and ice-rich frozen ground, thereby providing a basis for in-situ ground improvement for reinforcing warm and ice-rich permafrost foundations by soil-cement column installation.展开更多
In this study,microstructure and mechanical behavior of two types of Mg-based bimetal plates with a high formability sleeve were systematically studied,with a great emphasis on the effect of the interface characterist...In this study,microstructure and mechanical behavior of two types of Mg-based bimetal plates with a high formability sleeve were systematically studied,with a great emphasis on the effect of the interface characteristic and the sleeve fraction on the plasticity of composite plates.The rule of mixtures(ROM)for elongation was also addressed.The results show that when there is no or thin diffusion layer with thickness of about 3μm,Mg-based bimetal plates have a good plasticity with elongation of about 19-24%,and the ROM predicted elongations are very close to the experimental ones.In contrast,with a diffusion layer about 95-155μm thick,Mg-based bimetal plates exhibit a poor plasticity with elongation of about 11-17%,and the experimental elongations largely deviate from the ROM predictions.The plasticity of Mg-based bimetal plates increases with increasing sleeve fraction.This study provides new insights on the plastic deformation of Mg-based bimetal composites with a high formability sleeve.展开更多
IN706 superalloy is particularly sensitive to the parameters of hot working process.The flow stress of the IN706 superalloy was investigated during reduction deformation of 30%,45%,and 60%under the isothermal compress...IN706 superalloy is particularly sensitive to the parameters of hot working process.The flow stress of the IN706 superalloy was investigated during reduction deformation of 30%,45%,and 60%under the isothermal compression conditions of temperature at 1143–1393 K and strain rate at 0.01,0.1,0.5,and 1 s^(−1).The exponent-type Zener-Hollomon equation was used to describe the impact of strain and temperature on the thermal deformation.Meanwhile,the strain effect of various material constants,such asα,n,Q,and lnA,was considered in the constitutive equation considering the strain compensation,and the correlation coefficient R and the average absolute relative error were verified.On the basis of constitutive equation construction,the hot processing map of IN706 superalloy was drawn,and the instability region was obtained based on the Murty criterion.Results show that the reasonable thermal working process parameter window is strain rate of 0.1 s^(−1)and temperature of 1313–1353 K.展开更多
Al Si10Mg porous protective structure often produces different damage forms under compressive loading,and these damage modes affect its protective function.In order to well meet the service requirements,there is an ur...Al Si10Mg porous protective structure often produces different damage forms under compressive loading,and these damage modes affect its protective function.In order to well meet the service requirements,there is an urgent need to comprehensively understand the mechanical behavior and response mechanism of AlSi10Mg porous structures under compressive loading.In this paper,Al Si10Mg porous structures with three kinds of volume fractions are designed and optimized to meet the requirements of high-impact,strong-energy absorption,and lightweight characteristics.The mechanical behaviors of AlSi10Mg porous structures,including the stress-strain relationship,structural bearing state,deformation and damage modes,and energy absorption characteristics,were obtained through experimental studies at different loading rates.The damage pattern of the damage section indicates that AlSi10Mg porous structures have both ductile and brittle mechanical properties.Numerical simulation studies show that the AlSi10Mg porous structure undergoes shear damage due to relative misalignment along the diagonal cross-section,and the damage location is almost at 45°to the load direction,which is the most direct cause of its structural damage,revealing the damage mechanism of AlSi10Mg porous structures under the compressive load.The normalized energy absorption model constructed in the paper well interprets the energy absorption state of Al Si10Mg porous structures and gives the sensitive location of the structures,and the results of this paper provide important references for peers in structural design and optimization.展开更多
In practical engineering applications,rock mass are often found to be subjected to a triaxial stress state.Concurrently,defects like joints and fractures have a notable impact on the mechanical behavior of rock mass.S...In practical engineering applications,rock mass are often found to be subjected to a triaxial stress state.Concurrently,defects like joints and fractures have a notable impact on the mechanical behavior of rock mass.Such defects are identified as crucial contributors to the failure and instability of the surrounding rock,subsequently impacting the engineering stability.The study aimed to investigate the impact of fracture geometry and confining pressure on the deformation,failure characteristics,and strength of specimens using sand powder 3D printing technology and conventional triaxial compression tests.The results indicate that the number of fractures present considerably influences the peak strength,axial peak strain and elastic modulus of the specimens.Confining pressure is an important factor affecting the failure pattern of the specimen,under which the specimen is more prone to shear failure,but the initiation,expansion and penetration processes of secondary cracks in different fracture specimens are different.This study confirmed the feasibility of using sand powder 3D printing specimens as soft rock analogs for triaxial compression research.The insights from this research are deemed essential for a deeper understanding of the mechanical behavior of fractured surrounding rocks when under triaxial stress state.展开更多
The phase equilibrium and mechanical behaviors of natural gas hydrate-bearing sediment are essential for gas recovery from hydrate reservoirs.In heating closed systems,the temperature-pressure path of hydrate-bearing ...The phase equilibrium and mechanical behaviors of natural gas hydrate-bearing sediment are essential for gas recovery from hydrate reservoirs.In heating closed systems,the temperature-pressure path of hydrate-bearing sediment deviates from that of pure bulk hydrate,reflecting the porous media effect in phase equilibrium.A generalized phase equilibrium equation was established for hydrate-bearing sediments,which indicates that both capillary and osmotic pressures cause the phase equilibrium curve to shift leftward on the temperature-pressure plane.In contrast to bulk hydrate,hydrate-bearing sediment always contains a certain amount of unhydrated water,which keeps phase equilibrium with the hydrate within the hydrate stability field.With changes in temperature and pressure,a portion of pore hydrate and unhydrated water may transform into each other,affecting the shear strength of hydrate-bearing sediment.A shear strength model is proposed to consider not only hydrate saturation but also the change in temperature and pressure of hydrate-bearing sediment.The model is validated by experimental data with various hydrate saturation,temperature and pressure conditions.The deformation induced by partial dissociation was studied through depressurization tests under constant effective stress.The reduction in gas pressure within the hydrate stability field indeed caused sediment deformation.The dissociation-induced deformation can be reasonably estimated as the difference in volume between hydrate-bearing and hydrate-free sediments from the compression curves.展开更多
Laying the under-sleeper pad(USP)is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload.To explore the impact of application of the USP on the dynamic and static me...Laying the under-sleeper pad(USP)is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload.To explore the impact of application of the USP on the dynamic and static mechanical behavior of the ballast track in the heavy-haul railway system,numerical simulation models of the ballast bed with USP and without USP are presented in this paper by using the discrete element method(DEM)-multi-flexible body dynamic(MFBD)coupling analysis method.The ballast bed support stiffness test and dynamic displacement tests were carried out on the actual operation of a heavy-haul railway line to verify the validity of the models.The results show that using the USP results in a 43.01%reduction in the ballast bed support stiffness and achieves a more uniform distribution of track loads on the sleepers.It effectively reduces the load borne by the sleeper directly under the wheel load,with a 7.89%reduction in the pressure on the sleeper.Furthermore,the laying of the USP changes the lateral resistance sharing ratio of the ballast bed,significantly reducing the stress level of the ballast bed under train loads,with an average stress reduction of 42.19 kPa.It also reduces the plastic displacement of ballast particles and lowers the peak value of rotational angular velocity by about 50%to 70%,which is conducive to slowing down ballast bed settlement deformation and reducing maintenance costs.In summary,laying the USP has a potential value in enhancing the stability and extending the lifespan of the ballast bed in heavy-haul railway systems.展开更多
Developing high-temperature metallic glass thin films(MGTFs)with excellent combination properties is crucial for extending the practical applications of metallic glasses.A high-temperature multicomponent Mo-based MGTF...Developing high-temperature metallic glass thin films(MGTFs)with excellent combination properties is crucial for extending the practical applications of metallic glasses.A high-temperature multicomponent Mo-based MGTF with tunable microstructure prepared by single-target magnetron sputtering was presented in this study.Corresponding mechanical behaviors and thermal stability of MGTFs related to microstructure are systemically explored.By adjusting deposition parameters(pressure and power),the microstructure of as-deposited MGTFs can be altered from the dense homogeneous type to the loose nanoglass type.Such structure evolution can be explained by the competition between the surface diffusion and geometric shadowing effect.MGTFs with dense microstructure possess smaller surface roughness,higher hardness,higher Young's modulus,and better wear resistance.Moreover,they also possess higher thermal stability where the fully amorphous structure and smooth surface can be well maintained after vacuum annealing at 1123 K for 30 min.By contrast,the MGTF with nanoglass microstructure shows inferior mechanical properties and thermal stability due to plentiful loose interface regions,providing abundant free volumes during deformation and acting as favorable crystal nucleation sites during annealing.The correlation between the microstructure and properties of as-deposited MGTFs is clarified with the universal scaling law of glasses.The annealing treatment distinctly increases the hardness and Young's modulus of MGTFs.Meanwhile,after annealing,pop-in behaviors occur in the as-annealed MGTFs with dense microstructure but not in the as-annealed MGTF with nanoglass microstructure during the nanoindentation.These phenomena can be rationalized by the annihilation of free volumes during annealing and the evolution of the dynamical variable,shear transition zone,for the plastic deformation in MGTFs.展开更多
基金supports from the National Natural Science Foundation of China (Grant Nos.52004143 and 52374095)the open fund for the Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mines (Grant No.SKLMRDPC21KF06).
文摘A series of true triaxial unloading tests are conducted on sandstone specimens with a single structural plane to investigate their mechanical behaviors and failure characteristics under different in situ stress states.The experimental results indicate that the dip angle of structural plane(θ)and the intermediate principal stress(σ2)have an important influence on the peak strength,cracking mode,and rockburst severity.The peak strength exhibits a first increase and then decrease as a function ofσ2 for a constantθ.However,whenσ2 is constant,the maximum peak strength is obtained atθof 90°,and the minimum peak strength is obtained atθof 30°or 45°.For the case of an inclined structural plane,the crack type at the tips of structural plane transforms from a mix of wing and anti-wing cracks to wing cracks with an increase inσ2,while the crack type around the tips of structural plane is always anti-wing cracks for the vertical structural plane,accompanied by a series of tensile cracks besides.The specimens with structural plane do not undergo slabbing failure regardless ofθ,and always exhibit composite tensile-shear failure whatever theσ2 value is.With an increase inσ2 andθ,the intensity of the rockburst is consistent with the tendency of the peak strength.By analyzing the relationship between the cohesion(c),internal friction angle(φ),andθin sandstone specimens,we incorporateθinto the true triaxial unloading strength criterion,and propose a modified linear Mogi-Coulomb criterion.Moreover,the crack propagation mechanism at the tips of structural plane,and closure degree of the structural plane under true triaxial unloading conditions are also discussed and summarized.This study provides theoretical guidance for stability assessment of surrounding rocks containing geological structures in deep complex stress environments.
基金Project(42202318)supported by the National Natural Science Foundation of ChinaProject(252300421199)supported by the Natural Science Foundation of Henan Province,ChinaProject(2024JJ6219)supported by the Hunan Provincial Natural Science Foundation of China。
文摘The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique nature of this soil type.In this study,a series of unconfined compression tests were carried out on unsaturated CWG soil in an underground engineering site,and the effects of varying the environmental variables on the main undrained mechanical properties were analyzed.Based on the experimental results,a novel constitutive model was then established using the damage mechanics theory and the undetermined coefficient method.The results demonstrate that the curves of remolded CWG specimens with different moisture contents and dry densities exhibited diverse characteristics,including brittleness,significant softening,and ductility.As a typical indicator,the unconfined compression strength of soil specimens initially increased with an increase in moisture content and then decreased.Meanwhile,an optimal moisture content of approximately 10.5%could be observed,while a critical moisture content value of 13.0%was identified,beyond which the strength of the specimen decreases sharply.Moreover,the deformation and fracture of CWG specimens were predominantly caused by shear failure,and the ultimate failure modes were primarily influenced by moisture content rather than dry density.Furthermore,by comparing several similar models and the experimental data,the proposed model could accurately replicate the undrained mechanical characteristics of unsaturated CWG soil,and quantitatively describe the key mechanical indexes.These findings offer a valuable reference point for understanding the underlying mechanisms,anticipating potential risks,and implementing effective control measures in similar underground engineering projects.
基金financially supported by the National Natural Science Foundation of China(Nos.42107194,42090054,42377182)the Fundamental Research Funds for the Central Universities(No.CUGL190810)the Open Foundation of Engineering Research Center of Rock-Soil Drilling&Excavation and Protection,Ministry of Education(No.201802)。
文摘The reservoir landslide undergoes periodic saturation-drying cycles affected by reservoir fluctuation in hydropower project area,leading to the irreversible impact on the landslide materials.Sliding zone is the shearing part in formation of landslide and controls the further development of landslide.The mechanical behavior of sliding zone soil under compression is a crucial factor in the stability analysis in landslides.In this paper,the sliding zone soil from a giant landslide in the biggest hydropower project area,Three Gorges Reservoir Area,is taken as the research case.The particlesize distribution of the sliding zone soil from this landslide is studied and fractal dimension is adopted as representation.Periodic saturation-drying is introduced as the affecting factor on sliding zone soil properties.The triaxial compression test is conducted to reveal the mechanical behavior of the soil,including stress-strain behavior,elastic modulus,failure stress and strength parameters.These behavior of sliding zone soils with different fractal dimensions are studied under the effects of periodic saturation-drying cycles.The normalized stress-strain curves are displayed for further calculation.The data considering saturation-drying cycles are obtained and compared with the experimental results.
文摘Smart materials,especially shape memory composites and 4D printing materials,are widely used in aerospace.Deflectors are essential equipment in wind tunnel construction.Classical deflectors are made of metal materials and have a relatively high structural weight.The deflector made of smart material has the advantage of being lighter in weight compared to classical structure,and it could change the bending angle of the deflector structure under external excitation.In this study,the corresponding mechanical property test and finite element simulation of the smart material are carried out,and the deflector made of smart material is further studied and analyzed.Maxwell viscoelasticity model for the material is established,and relevant parameters are obtained through stress relaxation test fitting.According to relevant parameters and literature,finite element simulation of intelligent deflector structure is carried out.The pressure loss coefficient,airflow deflection angle,and velocity uniformity are studied.The numerical model of the minimum pressure loss coefficient is established with reference to the relevant data,and the formula for calculating the optimal upwind radius of the deflector is obtained.Combined with the numerical simulation results of the flow deflection angle and velocity uniformity of the flow field,it provides a reference for the selection of the size of the deflector.
基金supported by the National Natural Science Foundation of China Projects under grant[nos.U21A2049,52071220,51871211,51701129 and 51971054]Liaoning Province's project of“Revitalizing Liaoning Talents”(XLYC1907062)+6 种基金the Doctor Startup Fund of Natural Science Foundation Program of Liaoning Province(no.2019-BS-200)the Strategic New Industry Development Special Foundation of Shenzhen(JCYJ20170306141749970)the funds of International Joint Laboratory for Light Alloys,Liaoning BaiQianWan Talents Program,the Domain Foundation of Equipment Advance Research of 13th Five-year Plan(61409220118)National Key Research and Development Program of China under grant[nos.2017YFB0702001 and 2016YFB0301105]the Innovation Fund of Institute of Metal Research(IMR),Chinese Academy of Sciences(CAS),the National Basic Research Program of China(973 Program)project under grant no.2013CB632205the Fundamental Research Fund for the Central Universities under grant[no.N2009006]Bintech-IMR R&D Program[no.GYY-JSBU-2022-009].
文摘In this work,through performing microstructural characterization,tensile testing and failure analysis,the influence of electrochemical hydrogen charging on the microstructure and mechanical behavior of an as-cast Mg-8wt.%Li alloy was investigated.It revealed that after being hydrogen charged at 50 mA/cm2 for respectively 3 h,6 h and 18 h in 0.1 M NaCl solution,obvious HID occurred and the damage degree was gradually increased with the hydrogen charging time.For the sample being hydrogen charged for 3 h,micro pores with the diameter ranging from 10~30µm were formed and preferentially present inα-Mg phase.Moreover,micro cracks with the length ranging from 10~50µm mainly initiated inα-Mg phase,atα-Mg/β-Li interfaces and the peripheries of pores.With the increase of hydrogen charging time,the numbers of pores and cracks were obviously increased.Tensile results revealed that the hydrogen charging can simultaneously decrease the tensile strength and ductility of the alloy.Compared with the uncharged sample,the tensile yield strength,ultimate tensile strength and the elongation ratio to failure were respectively reduced by 5.7%,7.3%,31.7%for the 3h-charged sample and 24.6%,24.8%,67.0%for the 18h-charged sample.Failure analysis indicated that hydrogen charging can induce the brittle cracking of the alloy and the size of brittle cracking region being composed of quasi-cleavage facets and interfacial cracks on the fracture surfaces was increased with the hydrogen charging time.
基金The authors are grateful for the financial support from the National Natural Science Foundation of China(Grant Nos.52225904 and 52039007)the Natural Science Foundation of Sichuan Province(Grant No.2023NSFSC0377)supported by the New Cornerstone Science Foundation through the XPLORER PRIZE.
文摘Exploring dynamic mechanical responses and failure behaviors of hot dry rock(HDR)is significant for geothermal exploitation and stability assessment.In this study,via the split Hopkinson pressure bar(SHPB)system,a series of dynamic compression tests were conducted on granite treated by cyclic thermal shocks at different temperatures.We analyzed the effects of cyclic thermal shock on the thermal-related physical and dynamic mechanical behaviors of granite.Specifically,the P-wave velocity,dynamic strength,and elastic modulus of the tested granite decrease with increasing temperature and cycle number,while porosity and peak strain increase.The degradation law of dynamic mechanical properties could be described by a cubic polynomial.Cyclic thermal shock promotes shear cracks propagation,causing dynamic failure mode of granite to transition from splitting to tensile-shear composite failure,accompanied by surface spalling and debris splashing.Moreover,the thermal shock damage evolution and coupled failure mechanism of tested granite are discussed.The evolution of thermal shock damage with thermal shock cycle numbers shows an obvious S-shaped surface,featured by an exponential correlation with dynamic mechanical parameters.In addition,with increasing thermal shock temperature and cycles,granite mineral species barely change,but the length and width of thermal cracks increase significantly.The non-uniform expansion of minerals,thermal shock-induced cracking,and water-rock interaction are primary factors for deteriorating dynamic mechanical properties of granite under cyclic thermal shock.
基金supported by the National Key Research and Development Program of China(2022YFB3708400)the Guangdong Major Project of Basic and Applied Basic Research(2020B0301030006)+4 种基金the Youth Talent Support Programme of Guangdong Provincial Association for Science and Technology(SKXRC202301)the Guangdong Academy of Science Fund(2020GDASYL-20200101001,2023GDASQNRC-0210,2023GDASQNRC-0321)the Guangdong Science and Technology plan project(2023A0505030002)the GINM’Special Project of Science and Technology Development(2023GINMZX-202301020108)Evaluation Project of Guangdong Provincial Key Laboratory(2023B1212060043).
文摘In this study,microstructure and mechanical behavior of Mg/Al composite plates with Ti foil interlayer were systematically studied,with a great emphasis on the effect of different thicknesses of Ti foil interlayer.The results show that compared to 100μm thick Ti foil,10μm thick Ti foil is more prone to fracture and is evenly distributed in fragments at the interface.The introduction of Ti foil can effectively refine the grain size of Mg layers of as-rolled Mg/Al composite plates,10μm thick Ti foil has a better refining effect than 100μm thick Ti foil.Ti foil can effectively increase the yield strength(YS)and ultimate strength(UTS)of as-rolled Mg/Al composite plates,10μm thick Ti foil significantly improves the elongation(El)of Mg/Al composite plate,while 100μm thick Ti foil slightly weakens the El.After annealing at 420℃ for 0.5 h and 4 h,Ti foil can inhibit the formation of intermetallic compounds(IMCs)at the interface of Mg/Al composite plates,which effectively improves the YS,UTS and El of Mg/Al composite plates.In addition,Ti foil can also significantly enhance the interfacial shear strength(SS)of Mg/Al composite plates before and after annealing.
基金supported by the National Natural Science Foundation of China(Nos.11972202,52075272)the Major Project of Ningbo Science and Technology Innovation,China(Nos.2021Z099,2023Z005)+3 种基金National Key Laboratory of Shock Wave and Detonation Physics,China(No.JCKYS2023212005)State Key Laboratory for Advanced Metals and Materials,China(No.2023-Z04)Zhejiang Provincial Natural Science Foundation,China(No.LMS25E050015)the K.C.Wong Magna Fund from Ningbo University,China.
文摘Compressive mechanical behavior and microstructure evolution of Ti−5.7Al−2.9Nb−1.8Fe−1.6Mo−1.5V−1Zr alloy under extreme conditions were systematically investigated.The results show that strain rate and temperature have a significant influence on the mechanical behavior and microstructure.The alloy exhibits a positive strain rate sensitivity and negative temperature sensitivity under all temperature and strain rate conditions.The hot-rolled alloy is composed of a bimodal structure including an equiaxed primary α_(p) phase and a transformedβphase.After compression deformation,the bimodal deformed structural features highly rely on the temperature and strain rate.At low temperature and room temperature,the volume fraction and size of α_(p) phase decrease with increasing temperature and strain rate.At high temperature,the volume fraction of the α_(p)hase is inversely correlated with temperature.A modified Johnson−Cook constitutive model is established,and the predicted results coincide well with the experimental results.
基金supported by the National Natural Science Foundation of China(Grant Nos.52471275,U23A20663,51809048,51909236)the Natural Science Foundation of Fujian Province(Grant No.2022J01092)+1 种基金the Natural Science Foundation of Zhejiang Province(Grant No.LY23E090004)the Ningbo Natural Science Foundation(Grant No.2021J039).
文摘Steel lazy-wave riser(SLWR)is one of the key technical components of offshore oil-gas production systems and is widely utilized in deepwater areas.On the basis of the vector form intrinsic finite element(VFIFE)method,this study develops a reasonable numerical model for the SLWR to investigate the effects of the buoyancy section on its mechanical characteristics.In the SLWR model,the buoyancy section is simulated using an equivalent riser segment with the same outer diameter and unit weight.The riser is considered to be composed of a series of space vector particles connected by elements,and virtual reverse motions are applied to establish the fundamental equations of forces and displacements.The explicit central difference technique is used to solve the governing equations for particle motion within the riser through programming implementation.To provide a detailed explanation of the process by which the SLWR achieves a stable lazy-wave configuration,a numerical model of a 2800-m-long riser is established at a water depth of 1600 m,and the feasibility of this model for riser behavior analysis is validated.The remarkable influences of the position,length,number and spacing of the buoyancy section on the mechanical behavior of the SLWR are observed,which provides a theoretical foundation for the optimal design of the SLWR in deepwaters.
基金supported by Crosswise Tasks of Enterprise Entrusted(JG-ZH-A-202411-003)High-level Talents Program of Hainan Basic and Applied Basic Research Program of China(520RC543)。
文摘In order to research the concrete archaized buildings with lintel-column joint,2 specimens were tested under dynamic experiment.The failure characteristics,skeleton curves,mechanical behavior such as the load-displacement hysteretic loops,load carrying capacity,degradation of strength and stiffness,ductility and energy dissipation of the joints were analyzed.The results indicate that comparies with the lintel-column joints,the loading capacity and energy dissipation of the concrete archaized buildings with dual lintel-column joints are higher,and the hysteretic loops is in plump-shape.However,the displacement ductility coefficient is less than that of lintel-column joints.Both of them of the regularity of rigidity degeneration are basically the same.Generally,the joints have the good energy dissipation capacity.And the concrete archaized buildings with lintel-column joints exhibit excellent seismic behavior.
基金supported by the National Natural Science Foundation of China(Grant No.52074352)the National Natural Science Foundation of Hunan Province of China(Grant No.2023JJ30680)the Fundamental Research Funds for the Central Universities of Central South University(Grant No.2024ZZTS0423).
文摘Many rock engineering projects show that the growth of tensile cracks is often an important cause of engineering disasters,and the mechanical behavior of rocks is essentially the transmission,storage,dissipation and release of energy.To investigate the tensile behavior of rock from the perspective of energy,uniaxial tension tests(UTTs)and uniaxial compression tests(UCTs)were carried out on three typical rocks(granite,sandstone and marble).Different unloading points were set before the peak stress to separate elastic energy and dissipated energy.The input energy density ut,elastic energy density ue,and dissipated energy density ud at each unloading point were calculated by integrating stress-strain curves.The results show that there is a strong linear relationship between the three energy parameters and the square of the unloading stress in UCT,but this linear relationship is weaker in UTT.The ue and ud increase linearly with the increase in ut in UCT and UTT.Based on the phenomenon that ue and ud increase linearly with ut,the applicability of W_(et)^(p) index in UTT was proved and the relative energy storage capacity and absolute energy distribution characteristics of three rocks in UCT and UTT were evaluated.The tensile behavior of marble and sandstone in UTT can be divided into two stages vaguely according to the energy distribution,but granite is not the case.In addition,based on dissipated energy,the damage evolution of three types of rocks in UCT and UTT was discussed.This study provides some new insights for understanding the tensile behavior of rock.
基金supported by the National Natural Science Foundation of China(No.52074257)the Project supported by the Space Application System of China Manned Space Program(No.YYMT1201-EXP08).
文摘Cold rolling process can regulate the microstructure and mechanical properties of amorphous alloys,but it is still a challenging task to reveal their microscopic mechanism.Here,we designed an in-situ SEM observation device for the cold rolling process of amorphous alloy,and visually observed the formation and evolution of shear bands during single-pass and multi-pass rolling process of the Zr_(55)Cu_(30)Al_(10)Ni_(5)amorphous alloy sheets.It is found that the evolution process of shear bands in the rolling process of amorphous alloy shows heritability,which is mainly reflected in two aspects:one is that the shear band formation pattern in the single-pass rolling process is more inclined to inherit the previous shear band formation pattern;the other is that the shear deformation is more likely to occur in the pre-existing shear bands in the multi-pass rolling process.This rule can be used to guide the controlled genera-tion of shear bands in amorphous alloys.Moreover,we emphasized the importance of pre-existing shear band orientations and systematically investigated the mechanical behavior of the amorphous alloys with pre-existing shear bands by in-situ SEM observation.It is found that the mechanical properties of the as-rolled amorphous alloys are determined by the competition between the work-softening of the pre-existing shear band itself and the work-hardening caused by the blocking effect of the pre-existing shear bands on the shear deformation.Based on this,we enhance the tensile fracture strength and the tensile ductility of the amorphous alloy by adjusting the orientation of the pre-existing shear bands parallel to the tensile stress axis so that the pre-existing shear bands prevent the linear propagation and destruction of the new shear bands.
基金supported by the National Natural Science Foundation of China (No. 41471062, No. 41971085, No. 41971086)。
文摘The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. In this study, a novel approach for stabilizing the warm and ice-rich frozen soil with sulphoaluminate cement was proposed based on chemical stabilization. The mechanical behaviors of the stabilized soil, such as strength and stress-strain relationship, were investigated through a series of triaxial compression tests conducted at -1.0℃, and the mechanism of strength variations of the stabilized soil was also explained based on scanning electron microscope test. The investigations indicated that the strength of stabilized soil to resist failure has been improved, and the linear Mohr-Coulomb criteria can accurately reflect the shear strength of stabilized soil under various applied confining pressure. The increase in both curing age and cement mixing ratio were favorable to the growth of cohesion and internal friction angle. More importantly, the strength improvement mechanism of the stabilized soil is attributed to the formation of structural skeleton and the generation of cementitious hydration products within itself. Therefore, the investigations conducted in this study provide valuable references for chemical stabilization of warm and ice-rich frozen ground, thereby providing a basis for in-situ ground improvement for reinforcing warm and ice-rich permafrost foundations by soil-cement column installation.
基金supported by the National Key Research and Development Program of China (No.2022YFB3708400)the Guangdong Major Project of Basic and Applied Basic Research (No.2020B0301030006)+3 种基金the Guangdong Academy of Science Fund (No.2020GDASYL-20200101001,2021GDASYL-20210102002,2021GDASYL-20210103103)the National Natural Science Foundation of China (Nos.51905111 and 12002092)the Youth Talent Support Programme of Guangdong Provincial Association for Science and Technology (No.SKXRC202301)the Natural Science Foundation of Guangdong Province (Nos.2021A1515011730 and 2019A1515012096).
文摘In this study,microstructure and mechanical behavior of two types of Mg-based bimetal plates with a high formability sleeve were systematically studied,with a great emphasis on the effect of the interface characteristic and the sleeve fraction on the plasticity of composite plates.The rule of mixtures(ROM)for elongation was also addressed.The results show that when there is no or thin diffusion layer with thickness of about 3μm,Mg-based bimetal plates have a good plasticity with elongation of about 19-24%,and the ROM predicted elongations are very close to the experimental ones.In contrast,with a diffusion layer about 95-155μm thick,Mg-based bimetal plates exhibit a poor plasticity with elongation of about 11-17%,and the experimental elongations largely deviate from the ROM predictions.The plasticity of Mg-based bimetal plates increases with increasing sleeve fraction.This study provides new insights on the plastic deformation of Mg-based bimetal composites with a high formability sleeve.
文摘IN706 superalloy is particularly sensitive to the parameters of hot working process.The flow stress of the IN706 superalloy was investigated during reduction deformation of 30%,45%,and 60%under the isothermal compression conditions of temperature at 1143–1393 K and strain rate at 0.01,0.1,0.5,and 1 s^(−1).The exponent-type Zener-Hollomon equation was used to describe the impact of strain and temperature on the thermal deformation.Meanwhile,the strain effect of various material constants,such asα,n,Q,and lnA,was considered in the constitutive equation considering the strain compensation,and the correlation coefficient R and the average absolute relative error were verified.On the basis of constitutive equation construction,the hot processing map of IN706 superalloy was drawn,and the instability region was obtained based on the Murty criterion.Results show that the reasonable thermal working process parameter window is strain rate of 0.1 s^(−1)and temperature of 1313–1353 K.
基金financially supported by the National Natural Science Foundation of China(Nos.12272356,12072326,and 12172337)the State Key Laboratory of Dynamic Measurement Technology,North University of China(No.2022-SYSJJ-03)。
文摘Al Si10Mg porous protective structure often produces different damage forms under compressive loading,and these damage modes affect its protective function.In order to well meet the service requirements,there is an urgent need to comprehensively understand the mechanical behavior and response mechanism of AlSi10Mg porous structures under compressive loading.In this paper,Al Si10Mg porous structures with three kinds of volume fractions are designed and optimized to meet the requirements of high-impact,strong-energy absorption,and lightweight characteristics.The mechanical behaviors of AlSi10Mg porous structures,including the stress-strain relationship,structural bearing state,deformation and damage modes,and energy absorption characteristics,were obtained through experimental studies at different loading rates.The damage pattern of the damage section indicates that AlSi10Mg porous structures have both ductile and brittle mechanical properties.Numerical simulation studies show that the AlSi10Mg porous structure undergoes shear damage due to relative misalignment along the diagonal cross-section,and the damage location is almost at 45°to the load direction,which is the most direct cause of its structural damage,revealing the damage mechanism of AlSi10Mg porous structures under the compressive load.The normalized energy absorption model constructed in the paper well interprets the energy absorption state of Al Si10Mg porous structures and gives the sensitive location of the structures,and the results of this paper provide important references for peers in structural design and optimization.
基金Project(2021YFC2900600)supported by the Young Scientist Project of National Key Research and Development Program of ChinaProject(52074166)supported by the National Natural Science Foundation of China+1 种基金Projects(ZR2021YQ38,ZR2020QE121)supported by the Natural Science Foundation of Shandong Province,ChinaProject(2022KJ101)supported by the Science and Technology Support Plan for Youth Innovation of Colleges and Universities in Shandong Province,China。
文摘In practical engineering applications,rock mass are often found to be subjected to a triaxial stress state.Concurrently,defects like joints and fractures have a notable impact on the mechanical behavior of rock mass.Such defects are identified as crucial contributors to the failure and instability of the surrounding rock,subsequently impacting the engineering stability.The study aimed to investigate the impact of fracture geometry and confining pressure on the deformation,failure characteristics,and strength of specimens using sand powder 3D printing technology and conventional triaxial compression tests.The results indicate that the number of fractures present considerably influences the peak strength,axial peak strain and elastic modulus of the specimens.Confining pressure is an important factor affecting the failure pattern of the specimen,under which the specimen is more prone to shear failure,but the initiation,expansion and penetration processes of secondary cracks in different fracture specimens are different.This study confirmed the feasibility of using sand powder 3D printing specimens as soft rock analogs for triaxial compression research.The insights from this research are deemed essential for a deeper understanding of the mechanical behavior of fractured surrounding rocks when under triaxial stress state.
基金supported by the National Natural Science Foundation of China(Grant Nos.42171135 and 12262009)the“CUG Scholar”Scientific Research Funds at China University of Geosciences(Wuhan)(Project No.2022098).
文摘The phase equilibrium and mechanical behaviors of natural gas hydrate-bearing sediment are essential for gas recovery from hydrate reservoirs.In heating closed systems,the temperature-pressure path of hydrate-bearing sediment deviates from that of pure bulk hydrate,reflecting the porous media effect in phase equilibrium.A generalized phase equilibrium equation was established for hydrate-bearing sediments,which indicates that both capillary and osmotic pressures cause the phase equilibrium curve to shift leftward on the temperature-pressure plane.In contrast to bulk hydrate,hydrate-bearing sediment always contains a certain amount of unhydrated water,which keeps phase equilibrium with the hydrate within the hydrate stability field.With changes in temperature and pressure,a portion of pore hydrate and unhydrated water may transform into each other,affecting the shear strength of hydrate-bearing sediment.A shear strength model is proposed to consider not only hydrate saturation but also the change in temperature and pressure of hydrate-bearing sediment.The model is validated by experimental data with various hydrate saturation,temperature and pressure conditions.The deformation induced by partial dissociation was studied through depressurization tests under constant effective stress.The reduction in gas pressure within the hydrate stability field indeed caused sediment deformation.The dissociation-induced deformation can be reasonably estimated as the difference in volume between hydrate-bearing and hydrate-free sediments from the compression curves.
基金the project supported by the National Natural Science Foundation of China(Grant No.52372425)the Fundamental Research Funds for the Central Universities(Science and technology leading talent team project)(Grant No.2022JBXT010).
文摘Laying the under-sleeper pad(USP)is one of the effective measures commonly used to delay ballast degradation and reduce maintenance workload.To explore the impact of application of the USP on the dynamic and static mechanical behavior of the ballast track in the heavy-haul railway system,numerical simulation models of the ballast bed with USP and without USP are presented in this paper by using the discrete element method(DEM)-multi-flexible body dynamic(MFBD)coupling analysis method.The ballast bed support stiffness test and dynamic displacement tests were carried out on the actual operation of a heavy-haul railway line to verify the validity of the models.The results show that using the USP results in a 43.01%reduction in the ballast bed support stiffness and achieves a more uniform distribution of track loads on the sleepers.It effectively reduces the load borne by the sleeper directly under the wheel load,with a 7.89%reduction in the pressure on the sleeper.Furthermore,the laying of the USP changes the lateral resistance sharing ratio of the ballast bed,significantly reducing the stress level of the ballast bed under train loads,with an average stress reduction of 42.19 kPa.It also reduces the plastic displacement of ballast particles and lowers the peak value of rotational angular velocity by about 50%to 70%,which is conducive to slowing down ballast bed settlement deformation and reducing maintenance costs.In summary,laying the USP has a potential value in enhancing the stability and extending the lifespan of the ballast bed in heavy-haul railway systems.
基金supported by the National Natural Science Foun-dation of China(Nos.51821001 and 52173224).
文摘Developing high-temperature metallic glass thin films(MGTFs)with excellent combination properties is crucial for extending the practical applications of metallic glasses.A high-temperature multicomponent Mo-based MGTF with tunable microstructure prepared by single-target magnetron sputtering was presented in this study.Corresponding mechanical behaviors and thermal stability of MGTFs related to microstructure are systemically explored.By adjusting deposition parameters(pressure and power),the microstructure of as-deposited MGTFs can be altered from the dense homogeneous type to the loose nanoglass type.Such structure evolution can be explained by the competition between the surface diffusion and geometric shadowing effect.MGTFs with dense microstructure possess smaller surface roughness,higher hardness,higher Young's modulus,and better wear resistance.Moreover,they also possess higher thermal stability where the fully amorphous structure and smooth surface can be well maintained after vacuum annealing at 1123 K for 30 min.By contrast,the MGTF with nanoglass microstructure shows inferior mechanical properties and thermal stability due to plentiful loose interface regions,providing abundant free volumes during deformation and acting as favorable crystal nucleation sites during annealing.The correlation between the microstructure and properties of as-deposited MGTFs is clarified with the universal scaling law of glasses.The annealing treatment distinctly increases the hardness and Young's modulus of MGTFs.Meanwhile,after annealing,pop-in behaviors occur in the as-annealed MGTFs with dense microstructure but not in the as-annealed MGTF with nanoglass microstructure during the nanoindentation.These phenomena can be rationalized by the annihilation of free volumes during annealing and the evolution of the dynamical variable,shear transition zone,for the plastic deformation in MGTFs.
