A complex geological environment with faults can be encountered in the process of coal mining.Fault activation can cause instantaneous structure slipping,releasing a significant amount of elastic strain energy during ...A complex geological environment with faults can be encountered in the process of coal mining.Fault activation can cause instantaneous structure slipping,releasing a significant amount of elastic strain energy during underground coal mining.This would trigger strong rockburst disasters.To understand the occurrence of fault-slip induced rockbursts,we developed a physical model test system for fault-slip induced rockbursts in coal mine drifts.The boundary energy storage(BES)loading apparatus and bottom rapid retraction(BRR)apparatus are designed to realize energy compensation and continuous boundary stress transfer of the surrounding rocks for instantaneous fault slip,as well as to provide space for the potential fault slip.Taking the typical fault-slip induced rockburst in the Xinjulong Coal Mine,China,as the background,we conducted a model test using the test system.The deformation and stress in the rock surrounding the drift and the support unit force during fault slip are analyzed.The deformation and failure characteristics and dynamic responses of drifts under fault-slip induced rockbursts are obtained.The test results illustrate the rationality and effectiveness of the test system.Finally,corresponding recommendations and prospects are proposed based on our findings.展开更多
Rock fractures or faults could be reactivated by the thermal stress generated during the decay process of the high-level radioactive waste in deep geological repositories(DGRs).Understanding thermoshearing behavior an...Rock fractures or faults could be reactivated by the thermal stress generated during the decay process of the high-level radioactive waste in deep geological repositories(DGRs).Understanding thermoshearing behavior and its influencing factors are important for the long-term performance assessment of DGRs.We designed multistage mechanical(M)shear tests and thermomechanical(TM)shear tests on three 100 mm-cubic granite specimens,each containing a single inclined sawcut fracture with distinct microroughness of 8-15μm.M test results have shown that the static friction coefficient of the granite fracture decreases in proportion to the increase in the logarithm of the loading rate within the range of 1-15 kPa/s.For the given heating and boundary conditions,thermal loading rate,i.e.,thermal stress increment with heating time,is measured to be around 1 kPa/s in the fractured granite.Thermoshearing can be well predicted by the linear Mohr-Coulomb failure envelope deduced from M shear tests employing a loading rate that is comparable with the thermal loading rate.The granite fractures exhibited two distinct slip patterns during the mechanical shearing,i.e.,stick-slip observed in the smooth fracture and stable sliding in the relatively rough surface.In contrast,the mechanical loading rate(1-15 kPa/s)investigated in this study appears to not influence the slip pattern.Unlike those in M shear tests,thermoshearing in both smooth and relatively rough fractures show stable sliding with a very slow peak velocity of around 0.002μm/s.展开更多
As coal mining depth increases,the combined effects of high stress,mining stress,and fault structures make dynamic impact hazards more frequent.The reproduction of dynamic impact phenomena is basis for studying their ...As coal mining depth increases,the combined effects of high stress,mining stress,and fault structures make dynamic impact hazards more frequent.The reproduction of dynamic impact phenomena is basis for studying their occurrence patterns and control mechanisms.Physical simulation test represents an efficacious methodology.However,there is currently a lack of simulation devices that can effectively simulate two types of dynamic impact phenomena,including high stress and fault slip dynamic impact.To solve aforementioned issues,the physical simulation test system for dynamic impact in deep roadways developed by authors is employed to carry out comparative tests of high stress and fault slip dynamic impact.The phenomena of high stress and fault slip dynamic impact are reproduced successfully.A comparative analysis is conducted on dynamic phenomena,stress evolution,roadway deformation,and support force.The high stress dynamic impact roadway instability mode,which is characterized by the release of high energy accompanied by symmetric damage,and the fault slip dynamic impact roadway instability mode,which is characterized by the propagation of unilateral stress waves accompanied by asymmetric damage,are clarified.On the basis,the differentiated control concepts for different types of dynamic impact in deep roadways are proposed.展开更多
This study investigates the development of novel high-entropy alloys(HEAs)with enhanced mechanical properties through an innovative fabrication method of direct energy deposition(DED).The focus is on the creation of m...This study investigates the development of novel high-entropy alloys(HEAs)with enhanced mechanical properties through an innovative fabrication method of direct energy deposition(DED).The focus is on the creation of metastable core-shell precipitation-strengthened HEAs that exhibit a unique multi-stage terrace-like slip wave toughening mechanism,a novel approach to improving both strength and ductility simultaneously.Mechanical testing reveals that the developed HEAs exhibit superior mechanical proper-ties,including high yield strength,ultimate tensile strength,and exceptional ductility.The improvement in these properties is attributed to the multi-stage terrace-like slip wave toughening mechanism activated by the unique microstructural features.This toughening mechanism involves the sequential activation of slip systems,facilitated by the stress concentration around the core-shell precipitates and the subsequent propagation of slip waves across the material.The terrace-like pattern of these slip waves enhances the material's ability to deform plastically,providing a significant toughening effect while maintaining high strength levels.Furthermore,the study delves into the fundamental interactions between the microstruc-tural elements and the deformation mechanisms.It elucidates how the core-shell precipitates and the matrix cooperate to distribute stress uniformly,delay the onset of necking,and prevent premature failure.This synergistic interaction between the microstructural features and the slip wave toughening mecha-nism is central to the remarkable balance of strength and ductility achieved in the HEAs.The introduction of a multi-stage terrace-like slip wave toughening mechanism offers a new pathway to designing HEAs with an exceptional amalgamation of strength and ductility.展开更多
Tension-compression asymmetry is a critical concern for magnesium(Mg)alloys,particularly in automo-tive crash structures.This study systematically examines the tension-compression asymmetry of a cast Mg-Gd-Y alloy at ...Tension-compression asymmetry is a critical concern for magnesium(Mg)alloys,particularly in automo-tive crash structures.This study systematically examines the tension-compression asymmetry of a cast Mg-Gd-Y alloy at various strain rates.Experimental results indicate symmetric yielding stress under both tension and compression at all strain rates,along with a reduction in the tension-compression asym-metry of ultimate stress and plastic strain as the strain rate increases.This trend arises from an unusual strain rate-dependent tension-compression asymmetry,characterized by strain rate toughening in tension and negligible strain rate effect in compression.The differing behavior is linked to the distinct twinning mechanisms under tension and compression.The suppression of twinning under tension contributes to the positive strain rate dependence of pyramidal slip,whereas the activation of abundant twins during compression means that pyramidal slip is unnecessary to accommodate c-axis strain,leading to the ab-sence of a strain rate effect in compression.Abundant twins nucleate consistently from yielding to 2%strain,but only after basal and prismaticslip have mediated microplasticity,suggesting that these slip systems reduce the nucleation stress for twinning during compression,resulting in a lower activation stress for twinning compared to tension.This study provides new insights into micromechanisms of the tension-compression asymmetry in cast Mg-Gd-Y alloys and offers practical guidance for the application of these materials in critical components that must endure both tension and compression under varying strain rates.展开更多
The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy(RMEA)and its systematic comparison with pure niobium(Nb).Fully-recrystallized specimens ...The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy(RMEA)and its systematic comparison with pure niobium(Nb).Fully-recrystallized specimens were fabricated by cold rolling and subsequent annealing,and uniaxial tensile deformation was applied at room temperature.Slip trace morphologies on the surfaces of the tensile-deformed ma-terials were quantitatively characterized,and the so-calledψand x relationships of the observed slip traces were evaluated by a newly developed method for polycrystalline specimens.Wavy slip traces were observed in most grains in the pure Nb.They consisted of low-indexed slip planes,such as{110},and{112},and high-indexed(or undetermined)slip planes.Some straight slip traces persisting on the low-indexed slip planes were also found in the pure Nb.In contrast,straight slip traces were dominant in the RMEA.The straight slip traces in the RMEA were not parallel to particular slip planes but mostly distributed along the maximum shear stress plane(MSSP),indicating that frequent cross slip in very short intervals occurred.Large deviations of slip planes from the MSSP in a few grains of the RMEA were attributed to the slip transfer from neighboring grains as a characteristic of polycrystalline materi-als.Frequent cross slip in short intervals,attributed to homogeneous slip resistance distribution for screw dislocations in the RMEA originating from the chemical heterogeneity on an atomic scale,was proposed as a novel mechanism responsible for the unique slip behavior and macroscopic deformation behavior.展开更多
The grain-scale tension-compression(T-C)asymmetric slip behavior and geometrically necessary dislocation(GND)density in an aged and twin-free Mg-10Y sheet were statistically studied using slip trace analysis and elect...The grain-scale tension-compression(T-C)asymmetric slip behavior and geometrically necessary dislocation(GND)density in an aged and twin-free Mg-10Y sheet were statistically studied using slip trace analysis and electron backscatter diffraction(EBSD)analysis.A significantly asymmetric slip activity,i.e.,higher tensile slip activity and proportion of non-basal slip,was manifested.Prismatic〈a〉(37.1%)and basal〈a〉(27.6%)slips dominated the tensile deformation,followed by pyramidalⅡ〈c+a〉slip(20.0%).While during compression,basal〈a〉slip(61.9%)was the most active slip mode,and only 6.9% pyramidalⅡ〈c+a〉slip was observed.The critical resolved shear stress(CRSS)ratio was estimated based on~800 sets of the identified slip traces,which suggested that the CRSS_(pyrⅡ)/CRSS_(bas)for compression was~3 times than that of tension.The pyramidalⅡ〈c+a〉slip was more active when the slip plane was under tension than under compression,which was consistent with the calculated asymmetric CRSS_(pyrⅡ)/CRSS_(bas).The activity of multiple slip,cross slip and slip transfer,as well as the GND density were also T-C asymmetric.This work thoughtfully demonstrated the T-C asymmetric slip behavior and plastic heterogeneity in Mg alloys which was believed to be responsible for the macroscopic T-C asymmetry when twinning was absent.The present statistical results are valuable for validating and/or facilitating crystal plasticity simulations.展开更多
This study investigates the influence of initial crystallographic texture on the deformation mechanisms during three-point bending of AZ31 Mg alloy sheets.Three distinct orientations are examined by using the followin...This study investigates the influence of initial crystallographic texture on the deformation mechanisms during three-point bending of AZ31 Mg alloy sheets.Three distinct orientations are examined by using the following bending specimens:(i)the normal direction(ND)sample,where the c-axes are predominantly aligned along the specimen thickness,(ii)the rolling direction(RD)sample,where the c-axes are mostly aligned along the longitudinal direction,and(iii)the 45 sample,where the c-axes are tilted at approximately 45°from both the thickness and longitudinal directions.The bending properties vary significantly depending on the initial texture,thereby affecting the strain accommodation and dominant deformation modes.The ND sample exhibits the lowest bendability due to its unfavorable orientation for{10–12}extension twinning and basal slip,which results in poor strain accommodation and early crack initiation in the outer tensile side.By comparison,the RD sample demonstrates an approximately 22.1%improvement,with extensive{10–12}extension twinning in the outer tensile zone.Meanwhile,the 45 sample exhibits the highest bendability(approximately 75.7%greater than that of the ND sample)due to sustained activation of both basal slip and{10–12}extension twinning,promoting uniform strain distribution and delaying fracture.Detailed electron backscatter diffraction analysis reveals that the 45 sample retains favorable crystallographic orientations for basal slip throughout bending,minimizing strain localization and enhancing the bendability.These findings highlight the importance of tailoring the initial texture in order to optimize the bending properties of Mg alloy sheets,and provide valuable insights for improving the manufacturability of Mg-based structural components.展开更多
When a coin is tossed to a gravity well,it will spiral instead of falling directly to the center.Inspired by this phenomenon,a gravity well-inspired double friction pendulum system(GW-DFPS)is developed to extend the l...When a coin is tossed to a gravity well,it will spiral instead of falling directly to the center.Inspired by this phenomenon,a gravity well-inspired double friction pendulum system(GW-DFPS)is developed to extend the length of sliding trajectories of bridge superstructures during pulse-like near-fault earthquakes.As a result,a greater amount of energy will be dissipated due to the frictional sliding of the isolators.The GW-DFPS consists of a spherical surface and an outer surface described by a 1/x or logarithmic function to build gravity well.Full-scale isolators were fabricated and their response was characterized considering various parameters such as the friction material of slider,surface roughness of sliding surfaces,and applied vertical loads.Additionally,a finite element model of the isolator was created using the experimental test data.Numerical simulations were performed on a case-study bridge structure isolated using both a conventional DFPS system and the proposed GW-DFPS systems.The experimental results reveal that the proposed isolators exhibit stable response under vertical loads varying from 200 kN to 1000 kN with a negative stiffness response when the isolator slides at the outer sliding surface.The numerical simulations of the selected bridge structure demonstrate that the GW-DFPS significantly extends the sliding trajectory lengths of the superstructure during half of the earthquake pulses,resulting in increased energy dissipation during this interval.The kinetic energies of the bridge isolated by GW-DFPS are consistently lower than those of the bridge isolated by the other two kinds of isolators,resulting lower shear forces on the bridge.展开更多
Accurate thrust assessment is crucial for characterizing the performance of micro-thrusters.This paper presents a comprehensive evaluation of the thrust generated by a needle-type indium field emission electric propul...Accurate thrust assessment is crucial for characterizing the performance of micro-thrusters.This paper presents a comprehensive evaluation of the thrust generated by a needle-type indium field emission electric propulsion(In-FEEP)micro-thruster using three methods based on a pendulum:direct thrust measurement,indirect plume momentum transfer and beam current diagnostics.The experimental setup utilized capacitive displacement sensors for force detection and a voice coil motor as a feedback actuator,achieving a resolution better than 0.1μN.Key performance factors such as ionization and plume divergence of ejected charged particles were also examined.The study reveals that the high applied voltage induces significant electrostatic interference,becoming the dominant source of error in direct thrust measurements.Beam current diagnostics and indirect plume momentum measurements were conducted simultaneously,showing strong agreement within a deviation of less than 0.2N across the operational thrust range.The results from all three methods are consistent within the error margins,verifying the reliability of the indirect measurement approach and the theoretical thrust model based on the electrical parameters of In-FEEP.展开更多
This work is intended to further understand the controversial temperature dependencies of various slip modes in Mg alloys,and their effects on the mechanical properties at high temperature(HT).A systematical and stati...This work is intended to further understand the controversial temperature dependencies of various slip modes in Mg alloys,and their effects on the mechanical properties at high temperature(HT).A systematical and statistical investigation on the temperature-dependent macroscopic deformation behavior and the corresponding grain-scale slip activity was performed for both an extruded Mg-10Y(wt.%)sheet and a pure Mg sheet during tension at 25-300℃.The alloy’s strength increased by up to 44 MPa(14.0%)at HT compared to that at 25℃and this was accompanied by decreased pyramidal II(c+a)slip activity;both phenomena were opposite to that for pure Mg.The critical resolved shear stress(CRSS)ratios were estimated based on the~1700 sets of observed slip traces,and a positive temperature-dependent CRSS_(pyr II)/CRSS_(bas)was found in Mg-10Y.Compared to pure Mg,Mg-10Y exhibited pronounced strain hard-ening at HT due to enhanced slip-slip interactions,including multiple slip and cross slip,increased GND accumulation,and Y solute-dislocation interactions.The significant pyramidal II(c+a)slip activity(up to 30%frequency),its thermal hardening and pronounced strain hardening nature are proposed to be the key reasons for the observed anomalous strength increase in Mg-10Y.The grain-scale experimental evidence for(c+a)dislocation activity and its correlation to mechanical properties were revealed in this study and compared to recent atomic-scale simulations.展开更多
This work investigated the effects of grain size(GS)on individual slip mode activities and the corresponding Hall-Petch coefficients in a rolled basal-textured pure Mg sheet under uniaxial tension using statistical sl...This work investigated the effects of grain size(GS)on individual slip mode activities and the corresponding Hall-Petch coefficients in a rolled basal-textured pure Mg sheet under uniaxial tension using statistical slip trace analysis and electron backscatter diffraction.The studied regions covered a total of 1150 grains,in which 136 sets of slip traces were identified and analyzed in detail.The basalslip always dominated the deformation,whose frequencies decreased(from 81.0%to 62.5%)with increasing GS(from 10 to 85μm).The prismaticslip activity increased from 10.8%(10μm)to 27.5%(85μm),while that for pyramidal II<c+a>slip was almost constant.Critical resolved shear stress(CRSS)ratios were estimated based on the identified slip activity statistics,and then the Hall-Petch coefficients(k)of individual slip modes were calculated.The k value for prismaticslip(194 MPa·μm^(1/2))was lower than that for pyramidal II<c+a>slip(309 MPa·μm^(1/2)),which implies that pyramidal II<c+a>slip was more GS sensitive.Twinning activity exhibited a positive correlation with GS,though it remained limited partly due to the unfavorable loading direction.The macroscopic Hall-Petch relationship was divided into two regions,i.e.,the k value(753 MPa·μm^(1/2))for the coarse-grain region(30-85μm)was significantly larger than that(118 MPa·μm^(1/2))of the fine-grain region(10-30μm),which could be attributed to the transition of predominant deformation mechanisms from slip to slip combined twinning with increasing GS.This work provides detailed and quantitative experimental data of the GS effects on individual slip activities of Mg and provides new insights into the Hall-Petch relationship for individual slip modes.展开更多
In this study,the typical Mg-14Gd-0.3Zr alloy was rolled at the high-temperature range of 450–500℃.The rolled Mg alloy plate with thickness of 30 mm exhibits an ultra-high ultimate tensile strength of 428 MPa and el...In this study,the typical Mg-14Gd-0.3Zr alloy was rolled at the high-temperature range of 450–500℃.The rolled Mg alloy plate with thickness of 30 mm exhibits an ultra-high ultimate tensile strength of 428 MPa and elongation of 3.4%,which has rarely been reported,and the strong fiber texture played a critical role in strengthening.The mechanisms underlying the evolution of texture during rolling were systematically investigated.At the early stage of rolling,alloys(450℃and 475℃)exhibited a[10.10]texture due to twinning assisted by Prismaticslipping.At 500℃,the alloy underwent nearly complete dynamic recrystallization(DRX)process.With increasing the rolling reduction,the DRX occurred in the whole temperature range,exhibiting the typical[10.10]–[11.20]double fiber texture.For continuous DRX,Prismaticdislocations accumulate to form grains with 30°[0001]grain boundaries,which exhibit a[10.10]fiber texture.During discontinuous DRX,Prismaticslip induced grain rotation around the[0001]axis,stabilizing either the<10.10>//RD(rolling direction)or<11.20>//RD orientations,leading to the formation of[10.10]–[11.20]double fiber texture.TEM observations confirmed that Prismaticdislocations can accumulate to form sub-grain lamellae,which gradually transform into high-angle grain boundaries by absorbing more Prismaticdislocations.First-principle calculation demonstrated that with increasing Gd content,the unstable stacking fault energy of prismatic slipping significantly decreases,promoting the activation of Prismaticslipping.These findings elucidate the critical role of twinning and Prismaticdislocations in texture evolution and the DRX process during thick plate rolling of the high-Gd content Mg-Gd-Zr alloy.展开更多
Massive fracturing fluid injection in reservoir stimulation can alter the fluid pressure field,potentially inducing the faults to slip in an aseismic or seismic phenomenon.In this work,laboratory friction experiments ...Massive fracturing fluid injection in reservoir stimulation can alter the fluid pressure field,potentially inducing the faults to slip in an aseismic or seismic phenomenon.In this work,laboratory friction experiments were performed on split-cutting granite fracture to investigate the effect of fluid pressure on injection-induced slip behavior.The injection experiments spanned a fluid pressure range of 1-20 MPa,which was up to half of the confining pressure.The laboratory results demonstrated that an increase in confining pressure led to a marginal reduction in the friction coefficient,decreasing from a range of 0.70-0.80 at 10 MPa to 0.71-0.75 at 40 MPa.Friction constitutive parameters in experiments with fluid pressure above 10 MPa exhibited a transition from velocity-strengthening to velocity-weakening behavior,while remaining consistently velocity-strengthening below this threshold.Similarly,measurements of dilatancy and critical slip distance exhibited a similar evolution,first increasing and then becoming approximately constant,independent of fluid pressure.The observed microstructural evolution of the split-cutting fractures during slip testing supported these mechanical responses.Post-shear slip,a decrease in the fracture roughness and asperity distribution of the split-cutting fracture was noted,with the decrease in amplitude being more pronounced at high confining pressure.Research may provide a prospect on slip-on faults with fluid pressure.展开更多
Steel-concrete composite beams,due to their superior mechanical properties,are widely utilized in engineering structures.This study systematically investigates the calculation methods for internal forces and load-bear...Steel-concrete composite beams,due to their superior mechanical properties,are widely utilized in engineering structures.This study systematically investigates the calculation methods for internal forces and load-bearing capacity of composite beams based on elastic theory,with a focus on the transformed section method and its application under varying neutral axis positions.By deriving the geometric characteristics of the transformed section and incorporating a reduction factor accounting for slip effects,a computational model for sectional stress and ultimate load-bearing capacity is established.The results demonstrate that the slip effect significantly influences the flexural load-bearing capacity of composite beams.The proposed reduction factor,which considers the influence of the steel beam’s top flange thickness,offers higher accuracy compared to traditional methods.These findings provide a theoretical foundation for the design and analysis of composite beams,with significant practical engineering value.展开更多
The thermal effect has a significant impact on the activation and slip characteristics of fractures.In this study,four pairs of granite fractures were treated by temperatures T ranging from 25℃to 900℃.The fractures ...The thermal effect has a significant impact on the activation and slip characteristics of fractures.In this study,four pairs of granite fractures were treated by temperatures T ranging from 25℃to 900℃.The fractures were then employed to carry out triaxial unloading-induced shear slip experiments.The step unloading of confining pressure σ_(3) was used as a disturbed stress to activate fractures that were in a near-critical stress state.The slip characteristics,frictional behaviors,as well as damage modes of fractures with different T,were systematically investigated.The results show that at T=25℃ and 300℃,no stick-slip events were observed,and the slipping process of the fractures was characterized by aseismic slip and creep,respectively.For T=600℃ and 900℃,the fractures slipped stably,with occasional interruptions by episodic stick-slip events.Ultimately,they entered the dynamic slip stage after a series of consecutive stick-slip episodes.With increasing T,the number of sheared-off asperities increases due to thermal damage,which in turn leads to an increase in the occurrence of stick-slip events.The slip modes of the fractures transited from friction strengthening to friction weakening.As T increased from 300℃to 900℃,a considerable quantity of generated gouge layer acted as a lubricant for the slipping of fractures.This resulted in a notable increase in the proportion of aseismic slip,which rose from 24%to 54%.As the temperature increased from 25℃to 900℃,the crack length increased exponentially from 2.975 mm to 45.349 mm.For T=600℃ and 900℃,the duration between stick-slip events decreased as stick-slip events occurred more frequently.展开更多
Given the limitations of traditional hot extrusion methods in improving the microstructure and mechanical properties of magnesium(Mg)alloys,this paper attempts to treat AZ31 Mg alloy billet by pre-upsetting continuous...Given the limitations of traditional hot extrusion methods in improving the microstructure and mechanical properties of magnesium(Mg)alloys,this paper attempts to treat AZ31 Mg alloy billet by pre-upsetting continuous variable cross-section direct extrusion(U-CVCDE).The effects of dynamic recrystallization behavior and slip system activity on texture evolution and mechanical properties of CVCDE Mg alloys with different pre-upsetting amounts were systematically analyzed.The results indicate that the introduction of the pre-upsetting process promotes dynamic recrystallization during the CVCDE process.The recrystallization proportion shows a trend of first rising and then decreasing with the increase of the pre-upsetting amount.Among them,the proportion of recrystallization grains in the U2-CVCDE-formed structural parts is as high as 88.3%.The average grain sizes of U1-CVCDE,U2-CVCDE,and U3-CVCDE were 6.01μm,4.90μm,and10.45μm,respectively.In addition,following U-CVCDE,the pyramidal slip of each forming component consistently maintains a high level of activation and opening and dominates,making more grains deflect in the axial extrusion direction of C to varying degrees,which is conducive to the uniform distribution of stress in more grains during plastic deformation.The synergistic effect of dynamic recrystallization behavior and the high activity of the pyramidal slip system significantly weakened the(0001)basal texture strength,and the maximum basal texture strength showed a gradually decreasing trend,among which the base surface texture strength of U3-CVCDE formed parts was only 9.9.The U-CVCDE process is employed to achieve deep modification of Mg alloy,and excellent comprehensive mechanical properties are obtained;among them,the yield and tensile strength of U2-CVCDE are as high as 243.4 MPa and 317.5 MPa,respectively,and the elongation after breaking is up to 21.3%.This study introduces a practical new idea for investigating the extrusion forming technology of high-performance Mg alloys.展开更多
The variable salinity in stored reservoirs connected by a long channel attracts the attention of scientists worldwide,having applications in environmental and geophysical engineering.This study explores the impact of ...The variable salinity in stored reservoirs connected by a long channel attracts the attention of scientists worldwide,having applications in environmental and geophysical engineering.This study explores the impact of Navier slip conditions on exchange flows within a long channel connecting two large reservoirs of differing salinity.These horizontal density gradients drive the flow.We modify the recent one-dimensional theory,developed to avoid runaway stratification,to account for the presence of uniform slip walls.By adjusting the parameters of the horizontal density gradient based on the slip factor,we resolve analytically various flow regimes ranging from high diffusion to transitional high advection.These regimes are governed by physical parameters like channel aspect ratio,slip factor,Schmidt number,and gravitational Reynolds number.Our solutions align perfectly with ones in the no-slip limit.More importantly,under the conditions of no net flow across the channel and high Schmidt number(where stratification is concentrated near the channel’s mid-layer),we derive a closed-form solution for the slip parameter,aspect ratio,and gravitational Reynolds number that describes the interface’s behavior as a sharp interface separating two distinct zones.This interface,arising from hydrostatic wall gradients,ultimately detaches the low-and high-density regimes throughout the channel when the gravitational Reynolds number is inversely proportional to the aspect ratio for a fixed slip parameter.This phenomenon,observed previously in 2D numerical simulations with no-slip walls in the literature,is thus confirmed by our theoretical results.Our findings further demonstrate that wall slip leads to distinct and diverse flow regimes.展开更多
Magnesium(Mg)alloys are usually subjected to torsion deformation during processing or manufacturing.However,the torsional behavior remains underexplored at the atomic level compared to uniaxial deformation.In this wor...Magnesium(Mg)alloys are usually subjected to torsion deformation during processing or manufacturing.However,the torsional behavior remains underexplored at the atomic level compared to uniaxial deformation.In this work,atomistic simulations are employed to understand the deformation mechanism during torsion around <1010>and<1120>axes of Mg.We reveal that the onset of plasticity occurs near the surface due to stress-gradient effect and the deformation mechanisms are highly dependent on torsion axis.Specifically,the prismatic and basal slip dominate torsion around[1120]axis.During torsion around[1010]axis,{1121}twinning can be activated,whereas{1011}twinning is formed due to local stress but detwinned eventually.Moreover,extensive cross slip and interactions between basal and prismatic dislocations are observed and the associated mechanisms are discussed.These novel atomic-scale insights provide deeper understanding of the plastic deformation mechanisms of Mg under torsional loading.展开更多
In this study,we employed Bayesian inversion coupled with the summation-by-parts and simultaneousapproximation-term(SBP-SAT)forward simulation method to elucidate the mechanisms behind mininginduced seismic events cau...In this study,we employed Bayesian inversion coupled with the summation-by-parts and simultaneousapproximation-term(SBP-SAT)forward simulation method to elucidate the mechanisms behind mininginduced seismic events caused by fault slip and their potential effects on rockbursts.Through Bayesian inversion,it is determined that the sources near fault FQ14 have a significant shear component.Additionally,we analyzed the stress and displacement fields of high-energy events,along with the hypocenter distribution of aftershocks,which aided in identifying the slip direction of the critically stressed fault FQ14.We also performed forward modeling to capture the complex dynamics of fault slip under varying friction laws and shear fracture modes.The selection of specific friction laws for fault slip models was based on their ability to accurately replicate observed slip behavior under various external loading conditions,thereby enhancing the applicability of our findings.Our results suggest that the slip behavior of fault FQ14 can be effectively understood by comparing different scenarios.展开更多
基金support from the National Natural Science Foundation of China (Grant Nos.51927807,42077267 and 42277174).
文摘A complex geological environment with faults can be encountered in the process of coal mining.Fault activation can cause instantaneous structure slipping,releasing a significant amount of elastic strain energy during underground coal mining.This would trigger strong rockburst disasters.To understand the occurrence of fault-slip induced rockbursts,we developed a physical model test system for fault-slip induced rockbursts in coal mine drifts.The boundary energy storage(BES)loading apparatus and bottom rapid retraction(BRR)apparatus are designed to realize energy compensation and continuous boundary stress transfer of the surrounding rocks for instantaneous fault slip,as well as to provide space for the potential fault slip.Taking the typical fault-slip induced rockburst in the Xinjulong Coal Mine,China,as the background,we conducted a model test using the test system.The deformation and stress in the rock surrounding the drift and the support unit force during fault slip are analyzed.The deformation and failure characteristics and dynamic responses of drifts under fault-slip induced rockbursts are obtained.The test results illustrate the rationality and effectiveness of the test system.Finally,corresponding recommendations and prospects are proposed based on our findings.
基金supported by the International Collaborative Research Program(fundamental research,2021-2023)funded by Korea Institute of Civil Engineering and Building Technology(KICT).
文摘Rock fractures or faults could be reactivated by the thermal stress generated during the decay process of the high-level radioactive waste in deep geological repositories(DGRs).Understanding thermoshearing behavior and its influencing factors are important for the long-term performance assessment of DGRs.We designed multistage mechanical(M)shear tests and thermomechanical(TM)shear tests on three 100 mm-cubic granite specimens,each containing a single inclined sawcut fracture with distinct microroughness of 8-15μm.M test results have shown that the static friction coefficient of the granite fracture decreases in proportion to the increase in the logarithm of the loading rate within the range of 1-15 kPa/s.For the given heating and boundary conditions,thermal loading rate,i.e.,thermal stress increment with heating time,is measured to be around 1 kPa/s in the fractured granite.Thermoshearing can be well predicted by the linear Mohr-Coulomb failure envelope deduced from M shear tests employing a loading rate that is comparable with the thermal loading rate.The granite fractures exhibited two distinct slip patterns during the mechanical shearing,i.e.,stick-slip observed in the smooth fracture and stable sliding in the relatively rough surface.In contrast,the mechanical loading rate(1-15 kPa/s)investigated in this study appears to not influence the slip pattern.Unlike those in M shear tests,thermoshearing in both smooth and relatively rough fractures show stable sliding with a very slow peak velocity of around 0.002μm/s.
基金supported by the National Natural Science Foundation of China(Nos.U24A2088,42177130,42277174,and 42477166).
文摘As coal mining depth increases,the combined effects of high stress,mining stress,and fault structures make dynamic impact hazards more frequent.The reproduction of dynamic impact phenomena is basis for studying their occurrence patterns and control mechanisms.Physical simulation test represents an efficacious methodology.However,there is currently a lack of simulation devices that can effectively simulate two types of dynamic impact phenomena,including high stress and fault slip dynamic impact.To solve aforementioned issues,the physical simulation test system for dynamic impact in deep roadways developed by authors is employed to carry out comparative tests of high stress and fault slip dynamic impact.The phenomena of high stress and fault slip dynamic impact are reproduced successfully.A comparative analysis is conducted on dynamic phenomena,stress evolution,roadway deformation,and support force.The high stress dynamic impact roadway instability mode,which is characterized by the release of high energy accompanied by symmetric damage,and the fault slip dynamic impact roadway instability mode,which is characterized by the propagation of unilateral stress waves accompanied by asymmetric damage,are clarified.On the basis,the differentiated control concepts for different types of dynamic impact in deep roadways are proposed.
文摘This study investigates the development of novel high-entropy alloys(HEAs)with enhanced mechanical properties through an innovative fabrication method of direct energy deposition(DED).The focus is on the creation of metastable core-shell precipitation-strengthened HEAs that exhibit a unique multi-stage terrace-like slip wave toughening mechanism,a novel approach to improving both strength and ductility simultaneously.Mechanical testing reveals that the developed HEAs exhibit superior mechanical proper-ties,including high yield strength,ultimate tensile strength,and exceptional ductility.The improvement in these properties is attributed to the multi-stage terrace-like slip wave toughening mechanism activated by the unique microstructural features.This toughening mechanism involves the sequential activation of slip systems,facilitated by the stress concentration around the core-shell precipitates and the subsequent propagation of slip waves across the material.The terrace-like pattern of these slip waves enhances the material's ability to deform plastically,providing a significant toughening effect while maintaining high strength levels.Furthermore,the study delves into the fundamental interactions between the microstruc-tural elements and the deformation mechanisms.It elucidates how the core-shell precipitates and the matrix cooperate to distribute stress uniformly,delay the onset of necking,and prevent premature failure.This synergistic interaction between the microstructural features and the slip wave toughening mecha-nism is central to the remarkable balance of strength and ductility achieved in the HEAs.The introduction of a multi-stage terrace-like slip wave toughening mechanism offers a new pathway to designing HEAs with an exceptional amalgamation of strength and ductility.
基金the National Natural Science Foundation of China(grant Nos.11988102,52301146,51301173,51531002,52171055,52371037,51601193)the National Key Research and Development Program of China(grant No.2016YFB0301104)+1 种基金the Fundamental Research Funds for the Central Universities(grant No.2023JG007)China Postdoctoral Science Foundation(grant No.8206300226).
文摘Tension-compression asymmetry is a critical concern for magnesium(Mg)alloys,particularly in automo-tive crash structures.This study systematically examines the tension-compression asymmetry of a cast Mg-Gd-Y alloy at various strain rates.Experimental results indicate symmetric yielding stress under both tension and compression at all strain rates,along with a reduction in the tension-compression asym-metry of ultimate stress and plastic strain as the strain rate increases.This trend arises from an unusual strain rate-dependent tension-compression asymmetry,characterized by strain rate toughening in tension and negligible strain rate effect in compression.The differing behavior is linked to the distinct twinning mechanisms under tension and compression.The suppression of twinning under tension contributes to the positive strain rate dependence of pyramidal slip,whereas the activation of abundant twins during compression means that pyramidal slip is unnecessary to accommodate c-axis strain,leading to the ab-sence of a strain rate effect in compression.Abundant twins nucleate consistently from yielding to 2%strain,but only after basal and prismaticslip have mediated microplasticity,suggesting that these slip systems reduce the nucleation stress for twinning during compression,resulting in a lower activation stress for twinning compared to tension.This study provides new insights into micromechanisms of the tension-compression asymmetry in cast Mg-Gd-Y alloys and offers practical guidance for the application of these materials in critical components that must endure both tension and compression under varying strain rates.
基金supported by the Elements Strategy Initiative for Structural Materials(ESISM,No.JPMXP0112101000)the JSP EIG CONCERT-Japan(No.JPMJSC21C6)+5 种基金the Grant-in-Aid for Scientific Research on Innovative Area“High Entropy Alloys”(Nos.JP18H05455 and JP18H05451)the Grant-in-Aid for Scientific Re-search(A)(Nos.JP20H00306 and JP23H00234)the Grant-in-Aid for Research Activity Start-up(No.JP21K20487)the Grant-in-Aid for Early-Career Scientists(No.JP22K14501)the Grant-in-Aid for JSPS Research Fellow(No.JP18J20766)supported by China Scholarship Council(CSC),China.
文摘The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy(RMEA)and its systematic comparison with pure niobium(Nb).Fully-recrystallized specimens were fabricated by cold rolling and subsequent annealing,and uniaxial tensile deformation was applied at room temperature.Slip trace morphologies on the surfaces of the tensile-deformed ma-terials were quantitatively characterized,and the so-calledψand x relationships of the observed slip traces were evaluated by a newly developed method for polycrystalline specimens.Wavy slip traces were observed in most grains in the pure Nb.They consisted of low-indexed slip planes,such as{110},and{112},and high-indexed(or undetermined)slip planes.Some straight slip traces persisting on the low-indexed slip planes were also found in the pure Nb.In contrast,straight slip traces were dominant in the RMEA.The straight slip traces in the RMEA were not parallel to particular slip planes but mostly distributed along the maximum shear stress plane(MSSP),indicating that frequent cross slip in very short intervals occurred.Large deviations of slip planes from the MSSP in a few grains of the RMEA were attributed to the slip transfer from neighboring grains as a characteristic of polycrystalline materi-als.Frequent cross slip in short intervals,attributed to homogeneous slip resistance distribution for screw dislocations in the RMEA originating from the chemical heterogeneity on an atomic scale,was proposed as a novel mechanism responsible for the unique slip behavior and macroscopic deformation behavior.
基金supported by the National Natural Science Foundation of China(No.52171125)the Sichuan Science and Technology Program(No.2024NSFSC0193)。
文摘The grain-scale tension-compression(T-C)asymmetric slip behavior and geometrically necessary dislocation(GND)density in an aged and twin-free Mg-10Y sheet were statistically studied using slip trace analysis and electron backscatter diffraction(EBSD)analysis.A significantly asymmetric slip activity,i.e.,higher tensile slip activity and proportion of non-basal slip,was manifested.Prismatic〈a〉(37.1%)and basal〈a〉(27.6%)slips dominated the tensile deformation,followed by pyramidalⅡ〈c+a〉slip(20.0%).While during compression,basal〈a〉slip(61.9%)was the most active slip mode,and only 6.9% pyramidalⅡ〈c+a〉slip was observed.The critical resolved shear stress(CRSS)ratio was estimated based on~800 sets of the identified slip traces,which suggested that the CRSS_(pyrⅡ)/CRSS_(bas)for compression was~3 times than that of tension.The pyramidalⅡ〈c+a〉slip was more active when the slip plane was under tension than under compression,which was consistent with the calculated asymmetric CRSS_(pyrⅡ)/CRSS_(bas).The activity of multiple slip,cross slip and slip transfer,as well as the GND density were also T-C asymmetric.This work thoughtfully demonstrated the T-C asymmetric slip behavior and plastic heterogeneity in Mg alloys which was believed to be responsible for the macroscopic T-C asymmetry when twinning was absent.The present statistical results are valuable for validating and/or facilitating crystal plasticity simulations.
基金supported by the National Research Foundation of Korea(NRF)grants funded by the Korea government(MSIT)(nos.RS-2024-00351052 and 202300212657).
文摘This study investigates the influence of initial crystallographic texture on the deformation mechanisms during three-point bending of AZ31 Mg alloy sheets.Three distinct orientations are examined by using the following bending specimens:(i)the normal direction(ND)sample,where the c-axes are predominantly aligned along the specimen thickness,(ii)the rolling direction(RD)sample,where the c-axes are mostly aligned along the longitudinal direction,and(iii)the 45 sample,where the c-axes are tilted at approximately 45°from both the thickness and longitudinal directions.The bending properties vary significantly depending on the initial texture,thereby affecting the strain accommodation and dominant deformation modes.The ND sample exhibits the lowest bendability due to its unfavorable orientation for{10–12}extension twinning and basal slip,which results in poor strain accommodation and early crack initiation in the outer tensile side.By comparison,the RD sample demonstrates an approximately 22.1%improvement,with extensive{10–12}extension twinning in the outer tensile zone.Meanwhile,the 45 sample exhibits the highest bendability(approximately 75.7%greater than that of the ND sample)due to sustained activation of both basal slip and{10–12}extension twinning,promoting uniform strain distribution and delaying fracture.Detailed electron backscatter diffraction analysis reveals that the 45 sample retains favorable crystallographic orientations for basal slip throughout bending,minimizing strain localization and enhancing the bendability.These findings highlight the importance of tailoring the initial texture in order to optimize the bending properties of Mg alloy sheets,and provide valuable insights for improving the manufacturability of Mg-based structural components.
基金financially supported by the National Natural Science Foundation of China(Grants 52178124,52478151).
文摘When a coin is tossed to a gravity well,it will spiral instead of falling directly to the center.Inspired by this phenomenon,a gravity well-inspired double friction pendulum system(GW-DFPS)is developed to extend the length of sliding trajectories of bridge superstructures during pulse-like near-fault earthquakes.As a result,a greater amount of energy will be dissipated due to the frictional sliding of the isolators.The GW-DFPS consists of a spherical surface and an outer surface described by a 1/x or logarithmic function to build gravity well.Full-scale isolators were fabricated and their response was characterized considering various parameters such as the friction material of slider,surface roughness of sliding surfaces,and applied vertical loads.Additionally,a finite element model of the isolator was created using the experimental test data.Numerical simulations were performed on a case-study bridge structure isolated using both a conventional DFPS system and the proposed GW-DFPS systems.The experimental results reveal that the proposed isolators exhibit stable response under vertical loads varying from 200 kN to 1000 kN with a negative stiffness response when the isolator slides at the outer sliding surface.The numerical simulations of the selected bridge structure demonstrate that the GW-DFPS significantly extends the sliding trajectory lengths of the superstructure during half of the earthquake pulses,resulting in increased energy dissipation during this interval.The kinetic energies of the bridge isolated by GW-DFPS are consistently lower than those of the bridge isolated by the other two kinds of isolators,resulting lower shear forces on the bridge.
基金Project supported by the National Key Research and Development Program of China(Grant No.2020YFC2201001)the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2019B030302001)+1 种基金the National Natural Science Foundation of China(Grant Nos.12105373,12105374,and 11927812)the Science and Technology Research Project of Jiangxi Provincial Department of Education(Grant No.GJJ2402105).
文摘Accurate thrust assessment is crucial for characterizing the performance of micro-thrusters.This paper presents a comprehensive evaluation of the thrust generated by a needle-type indium field emission electric propulsion(In-FEEP)micro-thruster using three methods based on a pendulum:direct thrust measurement,indirect plume momentum transfer and beam current diagnostics.The experimental setup utilized capacitive displacement sensors for force detection and a voice coil motor as a feedback actuator,achieving a resolution better than 0.1μN.Key performance factors such as ionization and plume divergence of ejected charged particles were also examined.The study reveals that the high applied voltage induces significant electrostatic interference,becoming the dominant source of error in direct thrust measurements.Beam current diagnostics and indirect plume momentum measurements were conducted simultaneously,showing strong agreement within a deviation of less than 0.2N across the operational thrust range.The results from all three methods are consistent within the error margins,verifying the reliability of the indirect measurement approach and the theoretical thrust model based on the electrical parameters of In-FEEP.
基金supported by the National Natural Science Foundation of China(No.52171125)the Sichuan Science and Technology Program(No.2024NSFSC0193)。
文摘This work is intended to further understand the controversial temperature dependencies of various slip modes in Mg alloys,and their effects on the mechanical properties at high temperature(HT).A systematical and statistical investigation on the temperature-dependent macroscopic deformation behavior and the corresponding grain-scale slip activity was performed for both an extruded Mg-10Y(wt.%)sheet and a pure Mg sheet during tension at 25-300℃.The alloy’s strength increased by up to 44 MPa(14.0%)at HT compared to that at 25℃and this was accompanied by decreased pyramidal II(c+a)slip activity;both phenomena were opposite to that for pure Mg.The critical resolved shear stress(CRSS)ratios were estimated based on the~1700 sets of observed slip traces,and a positive temperature-dependent CRSS_(pyr II)/CRSS_(bas)was found in Mg-10Y.Compared to pure Mg,Mg-10Y exhibited pronounced strain hard-ening at HT due to enhanced slip-slip interactions,including multiple slip and cross slip,increased GND accumulation,and Y solute-dislocation interactions.The significant pyramidal II(c+a)slip activity(up to 30%frequency),its thermal hardening and pronounced strain hardening nature are proposed to be the key reasons for the observed anomalous strength increase in Mg-10Y.The grain-scale experimental evidence for(c+a)dislocation activity and its correlation to mechanical properties were revealed in this study and compared to recent atomic-scale simulations.
基金supported by the National Natural Science Foundation of China(No.52171125)the Sichuan Science and Technology Program(No.2024NSFSC0193).
文摘This work investigated the effects of grain size(GS)on individual slip mode activities and the corresponding Hall-Petch coefficients in a rolled basal-textured pure Mg sheet under uniaxial tension using statistical slip trace analysis and electron backscatter diffraction.The studied regions covered a total of 1150 grains,in which 136 sets of slip traces were identified and analyzed in detail.The basalslip always dominated the deformation,whose frequencies decreased(from 81.0%to 62.5%)with increasing GS(from 10 to 85μm).The prismaticslip activity increased from 10.8%(10μm)to 27.5%(85μm),while that for pyramidal II<c+a>slip was almost constant.Critical resolved shear stress(CRSS)ratios were estimated based on the identified slip activity statistics,and then the Hall-Petch coefficients(k)of individual slip modes were calculated.The k value for prismaticslip(194 MPa·μm^(1/2))was lower than that for pyramidal II<c+a>slip(309 MPa·μm^(1/2)),which implies that pyramidal II<c+a>slip was more GS sensitive.Twinning activity exhibited a positive correlation with GS,though it remained limited partly due to the unfavorable loading direction.The macroscopic Hall-Petch relationship was divided into two regions,i.e.,the k value(753 MPa·μm^(1/2))for the coarse-grain region(30-85μm)was significantly larger than that(118 MPa·μm^(1/2))of the fine-grain region(10-30μm),which could be attributed to the transition of predominant deformation mechanisms from slip to slip combined twinning with increasing GS.This work provides detailed and quantitative experimental data of the GS effects on individual slip activities of Mg and provides new insights into the Hall-Petch relationship for individual slip modes.
基金the National Key Research and Development Program(2023YFB3710903)the National Natural Science Foundation of China(U2167213)+1 种基金the Fundamental Research Funds for the Central Universities(N25GFZ006)the Xingliao Talent Plan Program(XLYC2203202).
文摘In this study,the typical Mg-14Gd-0.3Zr alloy was rolled at the high-temperature range of 450–500℃.The rolled Mg alloy plate with thickness of 30 mm exhibits an ultra-high ultimate tensile strength of 428 MPa and elongation of 3.4%,which has rarely been reported,and the strong fiber texture played a critical role in strengthening.The mechanisms underlying the evolution of texture during rolling were systematically investigated.At the early stage of rolling,alloys(450℃and 475℃)exhibited a[10.10]texture due to twinning assisted by Prismaticslipping.At 500℃,the alloy underwent nearly complete dynamic recrystallization(DRX)process.With increasing the rolling reduction,the DRX occurred in the whole temperature range,exhibiting the typical[10.10]–[11.20]double fiber texture.For continuous DRX,Prismaticdislocations accumulate to form grains with 30°[0001]grain boundaries,which exhibit a[10.10]fiber texture.During discontinuous DRX,Prismaticslip induced grain rotation around the[0001]axis,stabilizing either the<10.10>//RD(rolling direction)or<11.20>//RD orientations,leading to the formation of[10.10]–[11.20]double fiber texture.TEM observations confirmed that Prismaticdislocations can accumulate to form sub-grain lamellae,which gradually transform into high-angle grain boundaries by absorbing more Prismaticdislocations.First-principle calculation demonstrated that with increasing Gd content,the unstable stacking fault energy of prismatic slipping significantly decreases,promoting the activation of Prismaticslipping.These findings elucidate the critical role of twinning and Prismaticdislocations in texture evolution and the DRX process during thick plate rolling of the high-Gd content Mg-Gd-Zr alloy.
基金funded by the National Key Research and Development Program of China(Grant No.2023YFC3804205)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant No.KYCX24_2706)the Graduate Innovation Program of China University of Mining and Technology(Grant No.2024WLKXJ203).
文摘Massive fracturing fluid injection in reservoir stimulation can alter the fluid pressure field,potentially inducing the faults to slip in an aseismic or seismic phenomenon.In this work,laboratory friction experiments were performed on split-cutting granite fracture to investigate the effect of fluid pressure on injection-induced slip behavior.The injection experiments spanned a fluid pressure range of 1-20 MPa,which was up to half of the confining pressure.The laboratory results demonstrated that an increase in confining pressure led to a marginal reduction in the friction coefficient,decreasing from a range of 0.70-0.80 at 10 MPa to 0.71-0.75 at 40 MPa.Friction constitutive parameters in experiments with fluid pressure above 10 MPa exhibited a transition from velocity-strengthening to velocity-weakening behavior,while remaining consistently velocity-strengthening below this threshold.Similarly,measurements of dilatancy and critical slip distance exhibited a similar evolution,first increasing and then becoming approximately constant,independent of fluid pressure.The observed microstructural evolution of the split-cutting fractures during slip testing supported these mechanical responses.Post-shear slip,a decrease in the fracture roughness and asperity distribution of the split-cutting fracture was noted,with the decrease in amplitude being more pronounced at high confining pressure.Research may provide a prospect on slip-on faults with fluid pressure.
文摘Steel-concrete composite beams,due to their superior mechanical properties,are widely utilized in engineering structures.This study systematically investigates the calculation methods for internal forces and load-bearing capacity of composite beams based on elastic theory,with a focus on the transformed section method and its application under varying neutral axis positions.By deriving the geometric characteristics of the transformed section and incorporating a reduction factor accounting for slip effects,a computational model for sectional stress and ultimate load-bearing capacity is established.The results demonstrate that the slip effect significantly influences the flexural load-bearing capacity of composite beams.The proposed reduction factor,which considers the influence of the steel beam’s top flange thickness,offers higher accuracy compared to traditional methods.These findings provide a theoretical foundation for the design and analysis of composite beams,with significant practical engineering value.
基金funded by the National Key Research and Development Program of China,(Grant No.2022YFE0128300)the Natural Science Foundation of China(Grant No.52379113)+1 种基金the Fundamental Research Funds for the Central Universities of China(Grant No.2024-10945)the Postgraduate Research&Practice Innovation Program of Jiangsu Province of China.
文摘The thermal effect has a significant impact on the activation and slip characteristics of fractures.In this study,four pairs of granite fractures were treated by temperatures T ranging from 25℃to 900℃.The fractures were then employed to carry out triaxial unloading-induced shear slip experiments.The step unloading of confining pressure σ_(3) was used as a disturbed stress to activate fractures that were in a near-critical stress state.The slip characteristics,frictional behaviors,as well as damage modes of fractures with different T,were systematically investigated.The results show that at T=25℃ and 300℃,no stick-slip events were observed,and the slipping process of the fractures was characterized by aseismic slip and creep,respectively.For T=600℃ and 900℃,the fractures slipped stably,with occasional interruptions by episodic stick-slip events.Ultimately,they entered the dynamic slip stage after a series of consecutive stick-slip episodes.With increasing T,the number of sheared-off asperities increases due to thermal damage,which in turn leads to an increase in the occurrence of stick-slip events.The slip modes of the fractures transited from friction strengthening to friction weakening.As T increased from 300℃to 900℃,a considerable quantity of generated gouge layer acted as a lubricant for the slipping of fractures.This resulted in a notable increase in the proportion of aseismic slip,which rose from 24%to 54%.As the temperature increased from 25℃to 900℃,the crack length increased exponentially from 2.975 mm to 45.349 mm.For T=600℃ and 900℃,the duration between stick-slip events decreased as stick-slip events occurred more frequently.
基金financially supported by the National Natural Science Foundation of China(No.52475341)the Natural Science Foundation of Heilongjiang Province(No.JQ2022E004)。
文摘Given the limitations of traditional hot extrusion methods in improving the microstructure and mechanical properties of magnesium(Mg)alloys,this paper attempts to treat AZ31 Mg alloy billet by pre-upsetting continuous variable cross-section direct extrusion(U-CVCDE).The effects of dynamic recrystallization behavior and slip system activity on texture evolution and mechanical properties of CVCDE Mg alloys with different pre-upsetting amounts were systematically analyzed.The results indicate that the introduction of the pre-upsetting process promotes dynamic recrystallization during the CVCDE process.The recrystallization proportion shows a trend of first rising and then decreasing with the increase of the pre-upsetting amount.Among them,the proportion of recrystallization grains in the U2-CVCDE-formed structural parts is as high as 88.3%.The average grain sizes of U1-CVCDE,U2-CVCDE,and U3-CVCDE were 6.01μm,4.90μm,and10.45μm,respectively.In addition,following U-CVCDE,the pyramidal slip of each forming component consistently maintains a high level of activation and opening and dominates,making more grains deflect in the axial extrusion direction of C to varying degrees,which is conducive to the uniform distribution of stress in more grains during plastic deformation.The synergistic effect of dynamic recrystallization behavior and the high activity of the pyramidal slip system significantly weakened the(0001)basal texture strength,and the maximum basal texture strength showed a gradually decreasing trend,among which the base surface texture strength of U3-CVCDE formed parts was only 9.9.The U-CVCDE process is employed to achieve deep modification of Mg alloy,and excellent comprehensive mechanical properties are obtained;among them,the yield and tensile strength of U2-CVCDE are as high as 243.4 MPa and 317.5 MPa,respectively,and the elongation after breaking is up to 21.3%.This study introduces a practical new idea for investigating the extrusion forming technology of high-performance Mg alloys.
文摘The variable salinity in stored reservoirs connected by a long channel attracts the attention of scientists worldwide,having applications in environmental and geophysical engineering.This study explores the impact of Navier slip conditions on exchange flows within a long channel connecting two large reservoirs of differing salinity.These horizontal density gradients drive the flow.We modify the recent one-dimensional theory,developed to avoid runaway stratification,to account for the presence of uniform slip walls.By adjusting the parameters of the horizontal density gradient based on the slip factor,we resolve analytically various flow regimes ranging from high diffusion to transitional high advection.These regimes are governed by physical parameters like channel aspect ratio,slip factor,Schmidt number,and gravitational Reynolds number.Our solutions align perfectly with ones in the no-slip limit.More importantly,under the conditions of no net flow across the channel and high Schmidt number(where stratification is concentrated near the channel’s mid-layer),we derive a closed-form solution for the slip parameter,aspect ratio,and gravitational Reynolds number that describes the interface’s behavior as a sharp interface separating two distinct zones.This interface,arising from hydrostatic wall gradients,ultimately detaches the low-and high-density regimes throughout the channel when the gravitational Reynolds number is inversely proportional to the aspect ratio for a fixed slip parameter.This phenomenon,observed previously in 2D numerical simulations with no-slip walls in the literature,is thus confirmed by our theoretical results.Our findings further demonstrate that wall slip leads to distinct and diverse flow regimes.
基金supported by the National Natural Science Foundation of China—Excellent Young Scientists Fund(Overseas)Partial support came from the Fundamental Research Funds for the Central Universities,Jilin University.
文摘Magnesium(Mg)alloys are usually subjected to torsion deformation during processing or manufacturing.However,the torsional behavior remains underexplored at the atomic level compared to uniaxial deformation.In this work,atomistic simulations are employed to understand the deformation mechanism during torsion around <1010>and<1120>axes of Mg.We reveal that the onset of plasticity occurs near the surface due to stress-gradient effect and the deformation mechanisms are highly dependent on torsion axis.Specifically,the prismatic and basal slip dominate torsion around[1120]axis.During torsion around[1010]axis,{1121}twinning can be activated,whereas{1011}twinning is formed due to local stress but detwinned eventually.Moreover,extensive cross slip and interactions between basal and prismatic dislocations are observed and the associated mechanisms are discussed.These novel atomic-scale insights provide deeper understanding of the plastic deformation mechanisms of Mg under torsional loading.
基金the Graduate Innovation Program of China University of Mining and Technology,the Fundamental Research Funds for the Central Universities(Grant No.2023WLKXJ017)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX23_2776)the Shandong Energy Group(Grant No.SNKJ2022BJ03-R28)。
文摘In this study,we employed Bayesian inversion coupled with the summation-by-parts and simultaneousapproximation-term(SBP-SAT)forward simulation method to elucidate the mechanisms behind mininginduced seismic events caused by fault slip and their potential effects on rockbursts.Through Bayesian inversion,it is determined that the sources near fault FQ14 have a significant shear component.Additionally,we analyzed the stress and displacement fields of high-energy events,along with the hypocenter distribution of aftershocks,which aided in identifying the slip direction of the critically stressed fault FQ14.We also performed forward modeling to capture the complex dynamics of fault slip under varying friction laws and shear fracture modes.The selection of specific friction laws for fault slip models was based on their ability to accurately replicate observed slip behavior under various external loading conditions,thereby enhancing the applicability of our findings.Our results suggest that the slip behavior of fault FQ14 can be effectively understood by comparing different scenarios.
