Plastic strain in polycrystalline metals is highly localized in grain boundaries(GBs),slip bands(SBs)and twins.While extensive research has focused on intra-granular deformation mechanisms such as slip and twinning,st...Plastic strain in polycrystalline metals is highly localized in grain boundaries(GBs),slip bands(SBs)and twins.While extensive research has focused on intra-granular deformation mechanisms such as slip and twinning,strain localization at GBs has been largely overlooked.In this study,high-resolution digital image correlation(HRDIC)was employed to capture the strain distribution and its evolution during tension in an extruded pure Mg sheet.Particular attention was paid to strain localization at GBs and its governing factors.Results reveal that,at 3%applied strain,approximately 10%of GBs were categorized as extremely-high-strain GBs(defined as the GB where at least 20 data points have an effective shear strain(ε_(eff))value exceeding the 99th percentile of the overallεeff distribution),and the majority(84%)of them were observed to deform at even 0.5%applied strain.This suggests that early-stage deformation plays a critical role in subsequent GB strain localization.The mean strain value and grain boundary sliding(GBS)displacement of GBs increased significantly with applied strain,with progressively accelerating increasing rates observed in most instances.Most(~62%)GBs exhibiting slip transfer showed low strain,while a small fraction(~8%)of them exhibited extremely high strain.This indicates that slip transfer can mitigate GB strain localization in most cases.However,complex local conditions are also critical,and case-by-case analysis is essential.Moreover,GBs with misorientation angles ranging from 50°to 80°were found to be more likely to exhibit extremely high strain.This work provides valuable insights into GB strain localization,which is critical for further understanding the plastic deformation of polycrystalline Mg.展开更多
The shallow slip deficit(SSD)during strike-slip earthquakes raises a question of how the strain budget is accommodated over multiple cycles.However,the origin of variable SSD observed in different earthquakes is still...The shallow slip deficit(SSD)during strike-slip earthquakes raises a question of how the strain budget is accommodated over multiple cycles.However,the origin of variable SSD observed in different earthquakes is still under debate because each earthquake has its unique initial stress condition.Here,we derive the slip model of the 2021 M W 7.4 Maduo earthquake in Qinghai,China,using multi-track radar images.Our results revealed that,in contrast to the large SSD on segments close to the epicenter,a much smaller SSD was observed at the west terminus of the rupture,where aftershock distribution indicates that the fault changes dip direction at 6 km depth.The 2021 Maduo earthquake thus represents an extraordinary case of significant along-strike SSD variation.After accounting for interseismic,postseismic,and diffuse off-fault deformation,we find that this variation is likely contributed by the along-dipping geometrical variation,implying that a multi-segment earthquake may leave heterogeneous stress condition on the fault with different amounts of SSD.展开更多
An MW6.0 earthquake struck Jishishan County in Linxia Prefecture,Gansu Province,on December 18,2023.In this research,Sentinel-1A satellite radar observations were used to obtain the field of coseismic deformation of t...An MW6.0 earthquake struck Jishishan County in Linxia Prefecture,Gansu Province,on December 18,2023.In this research,Sentinel-1A satellite radar observations were used to obtain the field of coseismic deformation of the Jishishan earthquake in 2023,and the geometric and fine slip distribution of the seismogenic fault were inverted using this as a constraint.The results show that the earthquake is characterized by thrust movement.The coseismic slip distribution results show that the maximum slip of this earthquake is 0.3 m.The Coulomb stress distribution shows that the whole section of the southern edge of Lajishan fault,the NWW trending segment of the northern edge of Lajishan fault and its NNW trending segment to the south of the epicenter,the northern edge of the West Qinling fault and the segment to the east of the epicenter of the Daotanghe Linxia fault are under stress loading,which indicates an increase in the potential risk of earthquakes.This research discussed the seismogenic characteristics of earthquakes and the tendency of faults.We speculate that the Jishishan earthquake is the result of the joint action of regional faults and tectonic stress.Based on the observation of seismic data,geodesy,and other geological and geophysical data,we believe that the earthquake was caused by the activation of weak areas under the crust by the local stress from the driving mechanism of the northeast expansion of Qinghai-Xizang Plateau.The seismogenic fault of this earthquake is more likely to be northeast dipping under the comprehensive consideration of various factors,which occurred on the concealed fault belonging to the eastern edge of the Jishishan fault zone.展开更多
Quantitative assessment of microscale slip activities and plastic localizations is essential for understanding the complex deformation mechanisms in crystalline materials.However,few experimental studies have been abl...Quantitative assessment of microscale slip activities and plastic localizations is essential for understanding the complex deformation mechanisms in crystalline materials.However,few experimental studies have been able to dynamically measure the deformation fields of rapidly evolving slip activities at the microscale.In this study,we used the Sampling Moire?Method(SMM)to directly measure the dynamic deformation fields of slip activities in Nickel-Based Single-Crystal(NBSC)superalloy under in-situ tensile test,and the strain and displacement fields under the evolving microplastic events with intense slip activities around the notch of the NBSC superalloy specimen were obtained for the first time.The dynamic evolution of slip bands was quantitatively characterized through detailed statistical analysis of strains and displacements under different loads.The locations of the initial appearance of slip traces were successfully predicted by the regions of plasticity localization.The results show that the deformation fields exhibit both high spatial and temporal resolutions,enabling the capture of nanometer-scale displacement fields and visualization of the dynamic fluidity of slip accumulation.This method demonstrates the superiority of the dynamic characterization of the plastic deformation field at the microscale and the promise of its application for characterizing the slip activities of various crystalline metals.展开更多
This study investigates the plastic deformation behaviour of the AZ31 magnesium alloy under various uniaxial loading conditions using in-situ neutron diffraction,the crystallite group method(CGM),and crystal plasticit...This study investigates the plastic deformation behaviour of the AZ31 magnesium alloy under various uniaxial loading conditions using in-situ neutron diffraction,the crystallite group method(CGM),and crystal plasticity modelling.A key novelty of this work is the direct,model independent determination of resolved shear stress(RSS)values for individual slip and twinning systems,as well as their critical values(CRSS),derived from lattice strains in grains with preferred orientations.The experiment was extended beyond the conventional loading paths along the normal direction(ND)and rolling direction(RD)to include compression at angles of 30°and 60°from the ND(referred to as NDC30 and NDC60 tests),which had not been investigated in previous studies.Notably,the NDC30 test,combined with diffraction measurements,was specifically designed to activate basal slip in the majority of grains while minimizing twinning,enabling clear identification of this slip system and accurate determination of its CRSS.For the first time,hardening parameters were determined by comparing the model predicted values of RSS with those obtained from diffraction measurements for each active system.These data,together with the results of macroscopic tests,were used to calibrate an elastic-plastic self-consistent(EPSC)model,which accurately reproduced stress partitioning under applied load,texture evolution,and twin activity.The integrated methodology enhances the reliability of CRSS input and improves the modelling of anisotropic plasticity in magnesium alloys by tuning intergranular interactions based on a modified Eshelby inclusion approach.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
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
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
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
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
基金supported by the National Natural Science Foundation of China(Nos.52571157,52171125 and 52301152)Sichuan Science and Technology Program(No.2024NSFSC0193).
文摘Plastic strain in polycrystalline metals is highly localized in grain boundaries(GBs),slip bands(SBs)and twins.While extensive research has focused on intra-granular deformation mechanisms such as slip and twinning,strain localization at GBs has been largely overlooked.In this study,high-resolution digital image correlation(HRDIC)was employed to capture the strain distribution and its evolution during tension in an extruded pure Mg sheet.Particular attention was paid to strain localization at GBs and its governing factors.Results reveal that,at 3%applied strain,approximately 10%of GBs were categorized as extremely-high-strain GBs(defined as the GB where at least 20 data points have an effective shear strain(ε_(eff))value exceeding the 99th percentile of the overallεeff distribution),and the majority(84%)of them were observed to deform at even 0.5%applied strain.This suggests that early-stage deformation plays a critical role in subsequent GB strain localization.The mean strain value and grain boundary sliding(GBS)displacement of GBs increased significantly with applied strain,with progressively accelerating increasing rates observed in most instances.Most(~62%)GBs exhibiting slip transfer showed low strain,while a small fraction(~8%)of them exhibited extremely high strain.This indicates that slip transfer can mitigate GB strain localization in most cases.However,complex local conditions are also critical,and case-by-case analysis is essential.Moreover,GBs with misorientation angles ranging from 50°to 80°were found to be more likely to exhibit extremely high strain.This work provides valuable insights into GB strain localization,which is critical for further understanding the plastic deformation of polycrystalline Mg.
基金the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project under Grant 2024ZD1000500。
文摘The shallow slip deficit(SSD)during strike-slip earthquakes raises a question of how the strain budget is accommodated over multiple cycles.However,the origin of variable SSD observed in different earthquakes is still under debate because each earthquake has its unique initial stress condition.Here,we derive the slip model of the 2021 M W 7.4 Maduo earthquake in Qinghai,China,using multi-track radar images.Our results revealed that,in contrast to the large SSD on segments close to the epicenter,a much smaller SSD was observed at the west terminus of the rupture,where aftershock distribution indicates that the fault changes dip direction at 6 km depth.The 2021 Maduo earthquake thus represents an extraordinary case of significant along-strike SSD variation.After accounting for interseismic,postseismic,and diffuse off-fault deformation,we find that this variation is likely contributed by the along-dipping geometrical variation,implying that a multi-segment earthquake may leave heterogeneous stress condition on the fault with different amounts of SSD.
基金National Natural Science Foundation of China(Grant Nos.41930101 and 42101096)the China Postdoctoral Science Foundation(No.2019M660091XB)+8 种基金the Key Research and Development Project of Ecological Civilization Construction in Gansu Province(No.24YFFA054)the Natural Science Foundation of Gansu Province(Grant Nos.23JRRA857,23JRRG0015,and 21JR7RA317)the Gansu Province Higher Education Institutions Young Doctor(2024QB-046)the Open Fund of Wuhan,Gravitational Field and Solid Tides,National Field Observation and Research Station(WHYWZ202403)the National Cryosphere Desert Data Center(No.E01Z790201/2021kf07)the Lanzhou Talent Innovation and Entrepreneurship(No.2022-RC-73)the Experimental Teaching Reform Project of Lanzhou Jiaotong University(2024002)the Undergraduate Teaching Reform Project of Lanzhou Jiaotong University(JGY202416)"Young Scientific and Technological Talents Supporting Project"Project of Gansu Province(Li Wei)。
文摘An MW6.0 earthquake struck Jishishan County in Linxia Prefecture,Gansu Province,on December 18,2023.In this research,Sentinel-1A satellite radar observations were used to obtain the field of coseismic deformation of the Jishishan earthquake in 2023,and the geometric and fine slip distribution of the seismogenic fault were inverted using this as a constraint.The results show that the earthquake is characterized by thrust movement.The coseismic slip distribution results show that the maximum slip of this earthquake is 0.3 m.The Coulomb stress distribution shows that the whole section of the southern edge of Lajishan fault,the NWW trending segment of the northern edge of Lajishan fault and its NNW trending segment to the south of the epicenter,the northern edge of the West Qinling fault and the segment to the east of the epicenter of the Daotanghe Linxia fault are under stress loading,which indicates an increase in the potential risk of earthquakes.This research discussed the seismogenic characteristics of earthquakes and the tendency of faults.We speculate that the Jishishan earthquake is the result of the joint action of regional faults and tectonic stress.Based on the observation of seismic data,geodesy,and other geological and geophysical data,we believe that the earthquake was caused by the activation of weak areas under the crust by the local stress from the driving mechanism of the northeast expansion of Qinghai-Xizang Plateau.The seismogenic fault of this earthquake is more likely to be northeast dipping under the comprehensive consideration of various factors,which occurred on the concealed fault belonging to the eastern edge of the Jishishan fault zone.
基金supported by the Natural Science Foundation of China(No.12372176)the National Science and Technology Major Project of China(No.J2019-IV-0007-0075)。
文摘Quantitative assessment of microscale slip activities and plastic localizations is essential for understanding the complex deformation mechanisms in crystalline materials.However,few experimental studies have been able to dynamically measure the deformation fields of rapidly evolving slip activities at the microscale.In this study,we used the Sampling Moire?Method(SMM)to directly measure the dynamic deformation fields of slip activities in Nickel-Based Single-Crystal(NBSC)superalloy under in-situ tensile test,and the strain and displacement fields under the evolving microplastic events with intense slip activities around the notch of the NBSC superalloy specimen were obtained for the first time.The dynamic evolution of slip bands was quantitatively characterized through detailed statistical analysis of strains and displacements under different loads.The locations of the initial appearance of slip traces were successfully predicted by the regions of plasticity localization.The results show that the deformation fields exhibit both high spatial and temporal resolutions,enabling the capture of nanometer-scale displacement fields and visualization of the dynamic fluidity of slip accumulation.This method demonstrates the superiority of the dynamic characterization of the plastic deformation field at the microscale and the promise of its application for characterizing the slip activities of various crystalline metals.
基金founded by the National Science Centre,Poland(NCN),under grant no.UMO-2023/49/B/ST11/00774The research(neutron diffraction experiments)leading to this result has been co-funded by the project NEPHEWS under grant agreement no.101131414 from the EU Framework Programme for Research and Innovation Horizon Europe+6 种基金Views and opinions expressed are however those of the author(s)only and do not necessarily reflect those of the European Union.Neither the European Union nor the granting authorities can be held responsible for them.Measurements were carried out at the CANAM infrastructure of the NPI CAS Rez.The employment of the CICRR infrastructure supported by MEYS project LM2023041 is acknowledgedThe Ministry of Education,Youth and Sports of the Czech Republic(MEYS),support of large research infrastructures LM2023057K.M.acknowledges support of the Czech Grant Agency under project no.25-16210SP.K.acknowledges support from the European Union's Horizon 2020 research and innovation program under the NOMATEN teaming grant agreement no.857470the European Regional Development Fund via the Foundation for Polish Science International Research Agenda Plus Program grant no.MAB PLUS/2018/8the Ministry of Science and Higher Education's initiative“Support for the Activities of Centers of Excellence Established in Poland under the Horizon 2020 Program”under agreement no.MEiN/2023/DIR/3795K.W.was partly supported by the program“Excellence initiative-research university”for the AGH University of Krakow.
文摘This study investigates the plastic deformation behaviour of the AZ31 magnesium alloy under various uniaxial loading conditions using in-situ neutron diffraction,the crystallite group method(CGM),and crystal plasticity modelling.A key novelty of this work is the direct,model independent determination of resolved shear stress(RSS)values for individual slip and twinning systems,as well as their critical values(CRSS),derived from lattice strains in grains with preferred orientations.The experiment was extended beyond the conventional loading paths along the normal direction(ND)and rolling direction(RD)to include compression at angles of 30°and 60°from the ND(referred to as NDC30 and NDC60 tests),which had not been investigated in previous studies.Notably,the NDC30 test,combined with diffraction measurements,was specifically designed to activate basal slip in the majority of grains while minimizing twinning,enabling clear identification of this slip system and accurate determination of its CRSS.For the first time,hardening parameters were determined by comparing the model predicted values of RSS with those obtained from diffraction measurements for each active system.These data,together with the results of macroscopic tests,were used to calibrate an elastic-plastic self-consistent(EPSC)model,which accurately reproduced stress partitioning under applied load,texture evolution,and twin activity.The integrated methodology enhances the reliability of CRSS input and improves the modelling of anisotropic plasticity in magnesium alloys by tuning intergranular interactions based on a modified Eshelby inclusion approach.
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 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.
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.
