The reaction of Mg^(2+)and 5-{1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl}terephthalic acid(H_(2)L)leads to two metal-organic frameworks,[Mg(L)(DMF)_(2)(H_(2)O)_(2)]_(2)·5DMF·2H_(2)O(1)with a 1D structure and...The reaction of Mg^(2+)and 5-{1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl}terephthalic acid(H_(2)L)leads to two metal-organic frameworks,[Mg(L)(DMF)_(2)(H_(2)O)_(2)]_(2)·5DMF·2H_(2)O(1)with a 1D structure and[Mg_(2)(L)_(2)(DMSO)_(3)(H_(2)O)](2)with a 2D(4,4)-net structure.Interestingly,the two compounds exhibit distinct luminescent responses to external mechanical stimuli.1 exhibited exceptional resistance mechanical chromic luminescence(RMCL),which can be attributed to the predominant hydrogen bonds and the presence of high-boiling-point solvent molecules within its structure.2 had a reversible MCL property,which can be attributed to the dominantπ-πweak interactions,coupled with the reversible destruction/restoration of its crystallinity under grinding/fumigation.CCDC:2410963,1;2410964,2.展开更多
The accepted doping ion in Ti^(4+)-site of PbZr_(y)Ti_(1–y)O_(3)(PZT)-based piezoelectric ceramics is a well-known method to increase mechanical quality factor(Q_(m)),since the acceptor coupled by oxygen vacancy beco...The accepted doping ion in Ti^(4+)-site of PbZr_(y)Ti_(1–y)O_(3)(PZT)-based piezoelectric ceramics is a well-known method to increase mechanical quality factor(Q_(m)),since the acceptor coupled by oxygen vacancy becomes defect dipole,which prevents the domain rotation.In this field,a serious problem is that generally,Qm decreases as the temperature(T)increases,since the oxygen vacancies are decoupled from the defect dipoles.In this work,Q_(m) of Pb_(0.95)Sr_(0.05)(Zr_(0.53)Ti_(0.47))O_(3)(PSZT)ceramics doped by 0.40%Fe_(2)O_(3)(in mole)abnormally increases as T increases,of which the Qm and piezoelectric coefficient(d_(33))at room temperature and Curie temperature(TC)are 507,292 pC/N,and 345℃,respectively.The maximum Qm of 824 was achieved in the range of 120–160℃,which is 62.52%higher than that at room temperature,while the dynamic piezoelectric constant(d_(31))was just slightly decreased by 3.85%.X-ray diffraction(XRD)and piezoresponse force microscopy results show that the interplanar spacing and the fine domains form as temperature increases,and the thermally stimulated depolarization current shows that the defect dipoles are stable even the temperature up to 240℃.It can be deduced that the aggregation of oxygen vacancies near the fine domains and defect dipole can be stable up to 240℃,which pins domain rotation,resulting in the enhanced Q_(m) with the increasing temperature.These results give a potential path to design high Q_(m) at high temperature.展开更多
Graphene nanoplatelets(GNPs)have attracted tremendous interest due to their unique properties and bonding capabilities.This study focuses on the effect of GNP dispersion on the mechanical,thermal,and morphological beh...Graphene nanoplatelets(GNPs)have attracted tremendous interest due to their unique properties and bonding capabilities.This study focuses on the effect of GNP dispersion on the mechanical,thermal,and morphological behavior of GNP/epoxy nanocomposites.This study aims to understand how the dispersion of GNPs affects the properties of epoxy nanocomposite and to identify the best dispersion approach for improving mechanical performance.A solvent mixing technique that includes mechanical stirring and ultrasonication was used for producing the nanocomposites.Fourier transform infrared spectroscopy was used to investigate the interaction between GNPs and the epoxy matrix.The measurements of density and moisture content were used to confirm that GNPs were successfully incorporated into the nanocomposite.The findings showed that GNPs are successfully dispersed in the epoxy matrix by combining mechanical stirring and ultrasonication in a single step,producing well-dispersed nanocomposites with improved mechanical properties.Particularly,the nanocomposites at a low GNP loading of 0.1 wt%,demonstrate superior mechanical strength,as shown by increased tensile properties,including improved Young's modulus(1.86 GPa),strength(57.31 MPa),and elongation at break(4.98).The nanocomposite with 0.25 wt%GNP loading performs better,according to the viscoelastic analysis and flexural properties(113.18 MPa).Except for the nanocomposite with a 0.5 wt%GNP loading,which has a higher thermal breakdown temperature,the thermal characteristics do not significantly alter.The effective dispersion of GNPs in the epoxy matrix and low agglomeration is confirmed by the morphological characterization.The findings help with filler selection and identifying the best dispersion approach,which improves mechanical performance.The effective integration of GNPs and their interaction with the epoxy matrix provides the doorway for additional investigation and the development of sophisticated nanocomposites.In fields like aerospace,automotive,and electronics where higher mechanical performance and functionality are required,GNPs'improved mechanical properties and successful dispersion present exciting potential.展开更多
The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique natu...The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique nature of this soil type.In this study,a series of unconfined compression tests were carried out on unsaturated CWG soil in an underground engineering site,and the effects of varying the environmental variables on the main undrained mechanical properties were analyzed.Based on the experimental results,a novel constitutive model was then established using the damage mechanics theory and the undetermined coefficient method.The results demonstrate that the curves of remolded CWG specimens with different moisture contents and dry densities exhibited diverse characteristics,including brittleness,significant softening,and ductility.As a typical indicator,the unconfined compression strength of soil specimens initially increased with an increase in moisture content and then decreased.Meanwhile,an optimal moisture content of approximately 10.5%could be observed,while a critical moisture content value of 13.0%was identified,beyond which the strength of the specimen decreases sharply.Moreover,the deformation and fracture of CWG specimens were predominantly caused by shear failure,and the ultimate failure modes were primarily influenced by moisture content rather than dry density.Furthermore,by comparing several similar models and the experimental data,the proposed model could accurately replicate the undrained mechanical characteristics of unsaturated CWG soil,and quantitatively describe the key mechanical indexes.These findings offer a valuable reference point for understanding the underlying mechanisms,anticipating potential risks,and implementing effective control measures in similar underground engineering projects.展开更多
[Objective]Traditional structural geology textbooks often provide outdated treatments of joints and veins,failing to reflect the significant advances made in the past three decades.This review seeks to address part of...[Objective]Traditional structural geology textbooks often provide outdated treatments of joints and veins,failing to reflect the significant advances made in the past three decades.This review seeks to address part of this gap by highlighting the significance of barren joints and veins in reconstructing both the directions and magnitudes of geological paleostresses.[Conclusion]Conjugate shear joints not only indicate the orientation of the three effective principal stresses but also imply differential stresses at least four times greater than the tensile strength of the brittle host rock.Exfoliation joints form under stress states ofσ_(1)≈σ_(2)>0>σ_(3),whereas polygonal columnar joints in sedimentary rocks reflectσ_(1)^(*)>>σ_(2)^(*)=σ_(3)^(*),allowing the tensile strength of rocks to be estimated.Tensile joints in brittle strong beds interlayered with ductile soft layers are primarily driven by tensile stresses transferred from interfacial shear stresses between the hard and soft layers,with joint saturation mainly controlled by tectonic strain.Under natural strain-rate conditions,the Weibull modulus and tensile strength of the strong layers,as well as the shear-flow strength of the ductile layers,can be inferred from the nonlinear relationship between joint spacing and bed thickness.Ladder-like orthogonal joints,which form under a stress state ofσ_(1)^(*)>>σ_(2)^(*)>σ_(3)^(*),divide strata into blocky units and,after weathering and erosion,give rise to characteristic castle-and tower-like landforms.Veins,as mineral-filled joints,provide spacing and thickness data that allow estimates of layer strain.Moreover,the nonlinear relationship between vein spacing and bed thickness permits quantification of the extent to which mineral precipitation restores the tensile strength of rock beds.The absence of ladder-like orthogonal veins is attributed to this strength recovery.[Significance]Collectively,these observations demonstrate the critical role of joints and veins in constraining both the magnitudes and orientations of geological paleostress fields.展开更多
The effects of different warm rolling(WR)reductions on the microstructure and mechanical properties of low-Cr FeCrAl alloys at both room and elevated temperatures were investigated.The study revealed that when the WR ...The effects of different warm rolling(WR)reductions on the microstructure and mechanical properties of low-Cr FeCrAl alloys at both room and elevated temperatures were investigated.The study revealed that when the WR reduction is small,it effectively refines the grains and forms a large number of subgrains in the matrix,while also inducing the dissolution of the Laves phase.This enhances the mechanical properties of FeCrAl alloys primarily through grain refinement and solid solution strengthening.Conversely,with larger WR reductions,the grain refinement effect diminishes,but a significant number of Laves phases form in the matrix,strengthening the alloys primarily through precipitation strengthening.WR exhibited a remarkable enhancing effect on the comprehensive mechanical properties at both room and high temperatures,with a signi-ficant enhancement in ductility at high temperatures.Notably,a 10%WR reduction resulted in the optimal overall mechanical properties at both room and elevated temperatures.展开更多
The aim of this study is to address the issues associated with traditional magnetorheological fluid(MRF)dampers,such as insufficient damping force after power failure and susceptibility to settlement.In order to achie...The aim of this study is to address the issues associated with traditional magnetorheological fluid(MRF)dampers,such as insufficient damping force after power failure and susceptibility to settlement.In order to achieve this,a bidirectional adjustable MRF damper was designed and developed.Magnetic field simulation analysis was conducted on the damper,along with simulation analysis on its dynamic characteristics.The dynamic characteristics were ultimately validated through experimental testing on the material testing machine,thereby corroborating the theoretical simulation results.Concurrently,this process generated valuable test data for subsequent implementation of the semi-active vibration control system.The simulation and test results demonstrate that the integrated permanent magnet effectively accomplishes bidirectional regulation.The magnetic induction intensity of the damping channel is 0.2 T in the absence of current,increases to 0.5 T when a maximum forward current of 4 A is applied,and becomes 0 T when a maximum reverse current of 3.8 A is applied.When the excitation amplitude is 8 mm and the frequency is 2 Hz,with the applied currents varying,the maximum damping force reaches 8 kN,while the minimum damping force measures at 511 N.Additionally,at zero current,the damping force stands at 2 kN,which aligns closely with simulation results.The present paper can serve as a valuable reference for the design and research of semi-active MRF dampers.展开更多
Design a precision electroplating mechanical structure for automobiles based on finite element analysis method and analyze its mechanical properties.Taking the automobile steering knuckle as the research object,ABAQUS...Design a precision electroplating mechanical structure for automobiles based on finite element analysis method and analyze its mechanical properties.Taking the automobile steering knuckle as the research object,ABAQUS parametric modeling technology is used to construct its three-dimensional geometric model,and geometric simplification is carried out.Two surface treatment processes,HK-35 zinc nickel alloy electroplating and pure zinc electroplating,were designed,and the influence of different coatings on the mechanical properties of steering knuckles was compared and analyzed through numerical simulation.At the same time,standard specimens were prepared for salt spray corrosion testing and scratch method combined strength testing to verify the numerical simulation results.The results showed that under emergency braking and composite working conditions,the peak Von Mises stress of the zinc nickel alloy coating was 119.85 MPa,which was lower than that of the pure zinc coating and the alkaline electroplated zinc layer.Its equivalent strain value was 652×10^(-6),which was lower than that of the pure zinc coating and the alkaline electroplated zinc layer.Experimental data confirms that zinc nickel alloy coatings exhibit significant advantages in stress distribution uniformity,strain performance,and load-bearing capacity in high stress zones.The salt spray corrosion test further indicates that the coating has superior corrosion resistance and coating substrate interface bonding strength,which can significantly improve the mechanical stability and long-term reliability of automotive precision electroplating mechanical structures.展开更多
Mechanical activation (MA) is a significant pretreatment technique for enhancing the dissolution of mineral;however, its promotion effect on the role of pyrite during chalcopyrite bioleaching has not been elucidated u...Mechanical activation (MA) is a significant pretreatment technique for enhancing the dissolution of mineral;however, its promotion effect on the role of pyrite during chalcopyrite bioleaching has not been elucidated up to now. In this study, the effect of MA on the role of pyrite on chalcopyrite bioleaching mediated by Acidithiobacillus ferroxidans was investigated by X-ray diffraction, scanning electron microscopy, particle size distribution analysis, and electrochemical measurement. The results showed MA could significantly reduce the minerals particle size, and increase the specific surface area and surface energy of minerals. For example, the d50 of chalcopyrite reduced from 13.40 to 0.31 μm after MA. The copper extraction of mixed MA-chalcopyrite and MA-pyrite system was 63.4%, which exhibited a 51.8% enhancement compared to the non-activated mixed system. Electrochemical experiments identified that the strengthening effect of pyrite on chalcopyrite dissolution was negligible before MA. After MA, the dissolution mechanism of chalcopyrite was not changed, and pyrite could not only provide additional oxidants (acids and iron) but also act as the cathode in the galvanic couple. In this case, the bioleaching of chalcopyrite was accelerated. Therefore, a model of the promotion effect of mechanical activation on the role of pyrite on chalcopyrite bioleaching was proposed.展开更多
High-entropy alloys(HEAs)with multi-component elements have attracted significant interest since they exhibit numerous superior properties compared to traditional ones.These properties include significant energy relea...High-entropy alloys(HEAs)with multi-component elements have attracted significant interest since they exhibit numerous superior properties compared to traditional ones.These properties include significant energy release,remarkable fracture toughness,and high strength,making them promising candidates as energetic structural materials(ESMs).This paper summarizes the energy release mechanisms under dynamic impact and the mechanical behavior of TiZr-based HEAs,TiNb-based HEAs,andWbased HEA,including velocity threshold for energy release,chamber quasi-static pressure curve,energy release efficiency,interface reactions,and"self-sharpening".In addition,we propose future research directions for their energy release and mechanical behavior.展开更多
This work aimed to(i)understand conventional and pulse gas tungsten arc welding(GTAW)of AZ31B,and(ii)explore high frequency welding(100 Hz-1500 Hz).GTA welding with alternating current(AC)and direct current electrode ...This work aimed to(i)understand conventional and pulse gas tungsten arc welding(GTAW)of AZ31B,and(ii)explore high frequency welding(100 Hz-1500 Hz).GTA welding with alternating current(AC)and direct current electrode positive(DCEP)polarities yielded crack-free partial penetration welds for6 mm thick AZ31B alloy sheet.Welding under direct current electrode negative(DCEN)polarity with identical parameters as that for AC and DCEP resulted in full penetration welds that had microcracks.Defect-free full-penetration welds could be accomplished with pulse GTA welding using DCEN polarity at a pulse frequency of 1 Hz with a pulse duration ratio of 1:1.The resultant DCEN P 1:1 weld metal had a microstructure finer than the conventional DCEN weld.Welds produced with pulse duration ratios of 1:2and 1:4 lacked penetration but had a much finer microstructures because of the lower heat input.The arc constriction by the high frequency pulsing in the Activ Arc■-High frequency(AA-HF)mode welding was responsible for deeper penetration.Welds produced under DCEN pulsing and AA-HF conditions had hardness higher than conventional DCEN,DCEP and AC GTA welds,attributed to the finer microstructure.AA-HF GTA welding produced defect free deeper penetration welds with good microstructural features/mechanical properties and also gave an advantage of 50%enhanced productivity when welded at1500 Hz.展开更多
In this study,a series of triaxial tests are conducted on sandstone specimens to investigate the evolution of their mechanics and permeability characteristics under the combined action of immersion corrosion and seepa...In this study,a series of triaxial tests are conducted on sandstone specimens to investigate the evolution of their mechanics and permeability characteristics under the combined action of immersion corrosion and seepage of different chemical solutions.It is observed that with the increase of confining pressure,the peak stress,dilatancy stress,dilatancy stress ratio,peak strain,and elastic modulus of the sandstone increase while the Poisson ratio decreases and less secondary cracks are produced when the samples are broken.The pore pressure and confining pressure have opposite influences on the mechanical properties.With the increase of the applied axial stress,three stages are clearly identified in the permeability evolution curves:initial compaction stage,linear elasticity stage and plastic deformation stage.The permeability reaches the maximum value when the highest volumetric dilatancy is obtained.In addition,the hydrochemical action of salt solution with pH=7 and 4 has an obvious deteriorating effect on the mechanical properties and induces the increase of permeability.The obtained results will be useful in engineering to understand the mechanical and seepage properties of sandstone under the coupled chemical-seepage-stress multiple fields.展开更多
In this study,the interaction between deformation and precipitates during multiple equal channel angular pressing(ECAP)deformations and inter-pass aging combination and its effect on the mechanical properties of 7050 ...In this study,the interaction between deformation and precipitates during multiple equal channel angular pressing(ECAP)deformations and inter-pass aging combination and its effect on the mechanical properties of 7050 aluminum alloy are studied.The result show that ECAP induces numerous substructures and dislocations,effectively promoting the precipitation of theηʹphase exhibiting a bimodal structure during inter-pass aging.Following inter-pass aging and subsequent ECAP,the decrease in grain size(4.8μm)is together with the increase in dislocation density(1.24×10^(15) m^(−2))due to the pinning effect of the precipitated phase.Simultaneously,the dislocation motion causes the second phase particles to become even finer and more diffuse.The synergistic effects of precipitation strengthening,fine grain strengthening,and dislocation strengthening collectively enhance the high strength of aluminum alloys,with ultimate tensile strength and yield strength reaching approximately 610 and 565 MPa,respectively.Meanwhile,ductility remains largely unchanged,primarily due to coordinated grain boundary sliding and the uniform and fine dispersion of second phase particles.展开更多
The undercurrent research survey explores the roles of nonlocality and strain gradient size dependencies in nonlinear asymmetric buckling of shallow nanoscale arches having dissimilar end conditions through a numerica...The undercurrent research survey explores the roles of nonlocality and strain gradient size dependencies in nonlinear asymmetric buckling of shallow nanoscale arches having dissimilar end conditions through a numerical analysis.The arches,made from a functionally graded graphene nanofiller reinforced composite(FG-GNRC),are subjected to discretional radial concentrated loads along with converting of temperature.To account for the size dependencies,the exploration is carried out stemming from the nonlocal strain gradient theory(NSGT)in the sense of a quasi-2D parabolic shear flexible concept of curved beam.The material properties of the contemplated FG-GNRC sandwich are determined using the modified Halpin-Tsai micromechanics model.Subsequently,an extended isogeometric analysis(XIGA)is manipulated comprising insertion plus multiplication of knots to achieve the demanded lower continuity allocated to the integration between flexural and tangential reflexes.It is perceived that the both softening and stiffening concomitants assigned to the salient concentrated radial loads obtained by the developed NSGT-based XIGA diminish from the first upper limit to the second one,and then likewise from the first lower limit to the second one.Although,by becoming the upsurge in temperature higher,these softening and stiffening concomitants get more remarkable.展开更多
Gypsum rocks are highly susceptible to mechanical deterioration under the coupled effects of wet-dry(W-D)cycles and flow rates,which significantly influence the stability of underground excavations.Despite extensive r...Gypsum rocks are highly susceptible to mechanical deterioration under the coupled effects of wet-dry(W-D)cycles and flow rates,which significantly influence the stability of underground excavations.Despite extensive research on the effects of W-D cycles,the coupling influence of flow rates and W-D cycles on gypsum rocks remains poorly understood.This study investigates the mechanical behavior and deterioration mechanisms of gypsum rocks subjected to varying W-D cycles and flow rate conditions.Axial compression tests,along with nuclear magnetic resonance(NMR)techniques,were employed to analyze the stress-strain response and microstructural changes.Based on the disturbed state concept(DSC)theory,a W-D deterioration model and a DSC-based constitutive model were developed to describe the degradation trends and mechanical responses of gypsum rocks under different conditions.The results demonstrate that key mechanical indices,elastic modulus,cohesion,uniaxial compressive strength(UCS),and internal friction angle,exhibit logarithmic declines with increasing W-D cycles,with higher flow rates accelerating the deterioration process.The theoretical models accurately capture the nonlinear compaction behavior,peak stress,and post-peak response of gypsum specimens.This study provides valuable insights for predicting the mechanical behavior of gypsum rocks and improving the stability assessments of underground structures under complex environmental conditions.展开更多
This study investigates the shear mechanical responses and debonding failure mechanisms of anchoring systems comprising three anisotropic media and two anisotropic interfaces under controlled boundary conditions of co...This study investigates the shear mechanical responses and debonding failure mechanisms of anchoring systems comprising three anisotropic media and two anisotropic interfaces under controlled boundary conditions of constant normal load(F_(s)),constant normal stiffness(K),and shear rate(v).A systematic analysis of shear mechanical properties,the evolution of maximum principal strain field,and damage characteristics along shear failure surface is presented.Results from direct shear tests demonstrate that initial shear slip diminishes with increasing F_(s)and K,attributed to the normal constraint strengthening effect,while an increase in v enhances initial shear slip due to attenuated deformation coordination and stress transfer.As F_(s)increases from 7.5 to 120 kN,K from 0 to 12 MPa/mm,and v from 0.1 to 2 mm/min,the peak shear load increases by 210.32%and 80.16%with rising F_(s)and K,respectively,while decreases by 38.57%with increasing v.Correspondingly,the shear modulus exhibits,respectively,a 135.29%and 177.06%increase with rising F_(s)and K,and a 37.03%decrease with larger v.Initial shear dilation is identified as marking the formation of shear failure surface along anisotropic interfaces,resulting from the combined shear actions at the resin bolt interface,where resin undergoes shear by bolt surface protrusions,and the resin-rock interface,where mutual shear occurs between resin and rock.With increasing F_(s)and K and decreasing v,the location of the shear failure surface shifts from the resin-rock interface to the resin-bolt interface,accompanied by a transition in failure mode from tensile rupture of resin to shear off at the resin surface.展开更多
In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition...In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition(LDED).The effects of ultrasonic vibration(UV)and tempering treatment on microstructure evolution,microhardness distribution and mechanical properties of deposition layer were studied in detail.The microstructure of UV assisted LDED sample after tempering is mainly composed of tempered sorbite(TS).Due to the improvement of microstructure inhomogeneity and grains refinement,UV assisted LDED sample with tempering treatment obtains excellent mechanical properties.The ultimate tensile strength(UTS),yield strength(YS)and elongation after breaking(EL)reach 765 MPa,657 MPa and 19.5%,the increase ratios of UTS and YS are 14.5%and 33.8%while maintaining plasticity compared to original LDED sample,respectively.It is obvious that ultrasonic vibration combined with tempering is a potential and effective method to obtain uniform microstructure and excellent mechanical properties in metal laser directed energy deposition field.展开更多
In order to analyze the influences of storage aging on the safety of typical elemental explosives,the aged cyclotrimethylene trinitramine(RDX)and cyclotetramethylene tetranitramine(HMX)were prepared by isothermal agin...In order to analyze the influences of storage aging on the safety of typical elemental explosives,the aged cyclotrimethylene trinitramine(RDX)and cyclotetramethylene tetranitramine(HMX)were prepared by isothermal aging tests.The reaction thresholds of aged RDX and HMX under any ignition probability were studied by Langlie-Optimal D method.The thermal decomposition characteristics of RDX and HMX after aging were analyzed by DSC and ARC.Experimental results showed that compared with unaged RDX and HMX,on the one hand,the critical impact energy and critical friction of RDX and HMX aged for 14,28,and 56 days are significantly reduced at an explosion probability of 50%,0.01%,and 0.0001%,respectively.With the increase of aging time,the mechanical sensitivity of RDX and HMX increases obviously.On the other hand,the initial decomposition temperature of RDX and HMX after 56 days of aging decreases,the decomposition heat decreases,the activation energy increases,and the reaction difficulty increases.展开更多
High-entropy alloy composites(HEACs)have attracted significant attention due to their exceptional mechanical properties and chemical stability.By adjusting the content of reinforcing particles in the high-entropy allo...High-entropy alloy composites(HEACs)have attracted significant attention due to their exceptional mechanical properties and chemical stability.By adjusting the content of reinforcing particles in the high-entropy alloy and by employing advanced additive manufacturing techniques,high-performance HEACs can be fabricated.However,there is still considerable room for improvement in their performance.In this study,CoCrFeMnNi HEA powders were used as the matrix,and NiCoFeAlTi high-entropy intermetallic powders were used as the high-entropy reinforcement(HER).CoCrFeMnNi/NiCoFeAlTi HEACs were fabricated using selective laser melting technology.The study results indicate that after aging,the microstructure of HEACs with HER exhibits Al-and Ti-rich nano-oxide precipitates with an orthorhombic CMCM type structure system.After aging at 873 K for 2 h,HEACs with HER achieved excellent overall mechanical properties,with an ultimate tensile strength of 731 MPa.This is attributed to the combined and synergistic effects of precipitation strengthening,dislocation strengthening,and the high lattice distortion caused by high intragranular defects,which provide a multi-scale strengthening and hardening mechanism for the plastic deformation of HEACs with HER.This study demonstrates that aging plays a crucial role in controlling the precipitate phases in complex multi-element alloys.展开更多
In order to obtain high-density dual-scale ceramic particles(8.5 wt.%SiC+1.5 wt.%TiC)reinforced Al-Mg Sc-Zr composites with uniform microstructure,50 nm TiC and 7μm SiC particles were pre-dispersed into 15−53μm alum...In order to obtain high-density dual-scale ceramic particles(8.5 wt.%SiC+1.5 wt.%TiC)reinforced Al-Mg Sc-Zr composites with uniform microstructure,50 nm TiC and 7μm SiC particles were pre-dispersed into 15−53μm aluminum alloy powders by low-speed ball milling and mechanical mixing technology,respectively.Then,the effects of laser energy density,power and scanning rate on the density of the composites were investigated based on selective laser melting(SLM)technology.The effect of micron-sized SiC and nano-sized TiC particles on solidification structure,mechanical properties and fracture behaviors of the composites was revealed and analyzed in detail.Interfacial reaction and phase variations in the composites with varying reinforced particles were emphatically considered.Results showed that SiC-TiC particles could significantly improve forming quality and density of the SLMed composites,and the optimal relative density was up to 100%.In the process of laser melting,a strong chemical reaction occurs between SiC and aluminum matrix,and micron-scale acicular Al_(4)SiC_(4) bands were formed in situ.There was no interfacial reaction between TiC particles and aluminum matrix.TiC/Al semi-coherent interface had good bonding strength.Pinning effect of TiC particles in grain boundaries could prevent the equiaxial crystals from growing and transforming into columnar crystals,resulting in grain refinement.The optimal ultimate tensile strength(UTS),yield strength(YS),elongation(EL)and elastic modulus of the SiC-TiC/Al-Mg-Sc-Zr composite were~394 MPa,~262 MPa,~8.2%and~86 GPa,respectively.The fracture behavior of the composites included ductile fracture of Al matrix and brittle cleavage fracture of Al_(4)SiC_(4) phases.A large number of cross-distributed acicular Al_(4)SiC_(4) bands were the main factors leading to premature failure and fracture of SiC-TiC/Al-Mg-Sc-Zr composites.展开更多
文摘The reaction of Mg^(2+)and 5-{1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl}terephthalic acid(H_(2)L)leads to two metal-organic frameworks,[Mg(L)(DMF)_(2)(H_(2)O)_(2)]_(2)·5DMF·2H_(2)O(1)with a 1D structure and[Mg_(2)(L)_(2)(DMSO)_(3)(H_(2)O)](2)with a 2D(4,4)-net structure.Interestingly,the two compounds exhibit distinct luminescent responses to external mechanical stimuli.1 exhibited exceptional resistance mechanical chromic luminescence(RMCL),which can be attributed to the predominant hydrogen bonds and the presence of high-boiling-point solvent molecules within its structure.2 had a reversible MCL property,which can be attributed to the dominantπ-πweak interactions,coupled with the reversible destruction/restoration of its crystallinity under grinding/fumigation.CCDC:2410963,1;2410964,2.
基金National Natural Science Foundation of China(U2241242)National Key R&D Program of China(2023YFB3812000,2021YFA0716502)。
文摘The accepted doping ion in Ti^(4+)-site of PbZr_(y)Ti_(1–y)O_(3)(PZT)-based piezoelectric ceramics is a well-known method to increase mechanical quality factor(Q_(m)),since the acceptor coupled by oxygen vacancy becomes defect dipole,which prevents the domain rotation.In this field,a serious problem is that generally,Qm decreases as the temperature(T)increases,since the oxygen vacancies are decoupled from the defect dipoles.In this work,Q_(m) of Pb_(0.95)Sr_(0.05)(Zr_(0.53)Ti_(0.47))O_(3)(PSZT)ceramics doped by 0.40%Fe_(2)O_(3)(in mole)abnormally increases as T increases,of which the Qm and piezoelectric coefficient(d_(33))at room temperature and Curie temperature(TC)are 507,292 pC/N,and 345℃,respectively.The maximum Qm of 824 was achieved in the range of 120–160℃,which is 62.52%higher than that at room temperature,while the dynamic piezoelectric constant(d_(31))was just slightly decreased by 3.85%.X-ray diffraction(XRD)and piezoresponse force microscopy results show that the interplanar spacing and the fine domains form as temperature increases,and the thermally stimulated depolarization current shows that the defect dipoles are stable even the temperature up to 240℃.It can be deduced that the aggregation of oxygen vacancies near the fine domains and defect dipole can be stable up to 240℃,which pins domain rotation,resulting in the enhanced Q_(m) with the increasing temperature.These results give a potential path to design high Q_(m) at high temperature.
基金the Puncak RM for the project under the grant 6733204-13069 to carry out the experiments。
文摘Graphene nanoplatelets(GNPs)have attracted tremendous interest due to their unique properties and bonding capabilities.This study focuses on the effect of GNP dispersion on the mechanical,thermal,and morphological behavior of GNP/epoxy nanocomposites.This study aims to understand how the dispersion of GNPs affects the properties of epoxy nanocomposite and to identify the best dispersion approach for improving mechanical performance.A solvent mixing technique that includes mechanical stirring and ultrasonication was used for producing the nanocomposites.Fourier transform infrared spectroscopy was used to investigate the interaction between GNPs and the epoxy matrix.The measurements of density and moisture content were used to confirm that GNPs were successfully incorporated into the nanocomposite.The findings showed that GNPs are successfully dispersed in the epoxy matrix by combining mechanical stirring and ultrasonication in a single step,producing well-dispersed nanocomposites with improved mechanical properties.Particularly,the nanocomposites at a low GNP loading of 0.1 wt%,demonstrate superior mechanical strength,as shown by increased tensile properties,including improved Young's modulus(1.86 GPa),strength(57.31 MPa),and elongation at break(4.98).The nanocomposite with 0.25 wt%GNP loading performs better,according to the viscoelastic analysis and flexural properties(113.18 MPa).Except for the nanocomposite with a 0.5 wt%GNP loading,which has a higher thermal breakdown temperature,the thermal characteristics do not significantly alter.The effective dispersion of GNPs in the epoxy matrix and low agglomeration is confirmed by the morphological characterization.The findings help with filler selection and identifying the best dispersion approach,which improves mechanical performance.The effective integration of GNPs and their interaction with the epoxy matrix provides the doorway for additional investigation and the development of sophisticated nanocomposites.In fields like aerospace,automotive,and electronics where higher mechanical performance and functionality are required,GNPs'improved mechanical properties and successful dispersion present exciting potential.
基金Project(42202318)supported by the National Natural Science Foundation of ChinaProject(252300421199)supported by the Natural Science Foundation of Henan Province,ChinaProject(2024JJ6219)supported by the Hunan Provincial Natural Science Foundation of China。
文摘The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique nature of this soil type.In this study,a series of unconfined compression tests were carried out on unsaturated CWG soil in an underground engineering site,and the effects of varying the environmental variables on the main undrained mechanical properties were analyzed.Based on the experimental results,a novel constitutive model was then established using the damage mechanics theory and the undetermined coefficient method.The results demonstrate that the curves of remolded CWG specimens with different moisture contents and dry densities exhibited diverse characteristics,including brittleness,significant softening,and ductility.As a typical indicator,the unconfined compression strength of soil specimens initially increased with an increase in moisture content and then decreased.Meanwhile,an optimal moisture content of approximately 10.5%could be observed,while a critical moisture content value of 13.0%was identified,beyond which the strength of the specimen decreases sharply.Moreover,the deformation and fracture of CWG specimens were predominantly caused by shear failure,and the ultimate failure modes were primarily influenced by moisture content rather than dry density.Furthermore,by comparing several similar models and the experimental data,the proposed model could accurately replicate the undrained mechanical characteristics of unsaturated CWG soil,and quantitatively describe the key mechanical indexes.These findings offer a valuable reference point for understanding the underlying mechanisms,anticipating potential risks,and implementing effective control measures in similar underground engineering projects.
文摘[Objective]Traditional structural geology textbooks often provide outdated treatments of joints and veins,failing to reflect the significant advances made in the past three decades.This review seeks to address part of this gap by highlighting the significance of barren joints and veins in reconstructing both the directions and magnitudes of geological paleostresses.[Conclusion]Conjugate shear joints not only indicate the orientation of the three effective principal stresses but also imply differential stresses at least four times greater than the tensile strength of the brittle host rock.Exfoliation joints form under stress states ofσ_(1)≈σ_(2)>0>σ_(3),whereas polygonal columnar joints in sedimentary rocks reflectσ_(1)^(*)>>σ_(2)^(*)=σ_(3)^(*),allowing the tensile strength of rocks to be estimated.Tensile joints in brittle strong beds interlayered with ductile soft layers are primarily driven by tensile stresses transferred from interfacial shear stresses between the hard and soft layers,with joint saturation mainly controlled by tectonic strain.Under natural strain-rate conditions,the Weibull modulus and tensile strength of the strong layers,as well as the shear-flow strength of the ductile layers,can be inferred from the nonlinear relationship between joint spacing and bed thickness.Ladder-like orthogonal joints,which form under a stress state ofσ_(1)^(*)>>σ_(2)^(*)>σ_(3)^(*),divide strata into blocky units and,after weathering and erosion,give rise to characteristic castle-and tower-like landforms.Veins,as mineral-filled joints,provide spacing and thickness data that allow estimates of layer strain.Moreover,the nonlinear relationship between vein spacing and bed thickness permits quantification of the extent to which mineral precipitation restores the tensile strength of rock beds.The absence of ladder-like orthogonal veins is attributed to this strength recovery.[Significance]Collectively,these observations demonstrate the critical role of joints and veins in constraining both the magnitudes and orientations of geological paleostress fields.
文摘The effects of different warm rolling(WR)reductions on the microstructure and mechanical properties of low-Cr FeCrAl alloys at both room and elevated temperatures were investigated.The study revealed that when the WR reduction is small,it effectively refines the grains and forms a large number of subgrains in the matrix,while also inducing the dissolution of the Laves phase.This enhances the mechanical properties of FeCrAl alloys primarily through grain refinement and solid solution strengthening.Conversely,with larger WR reductions,the grain refinement effect diminishes,but a significant number of Laves phases form in the matrix,strengthening the alloys primarily through precipitation strengthening.WR exhibited a remarkable enhancing effect on the comprehensive mechanical properties at both room and high temperatures,with a signi-ficant enhancement in ductility at high temperatures.Notably,a 10%WR reduction resulted in the optimal overall mechanical properties at both room and elevated temperatures.
文摘The aim of this study is to address the issues associated with traditional magnetorheological fluid(MRF)dampers,such as insufficient damping force after power failure and susceptibility to settlement.In order to achieve this,a bidirectional adjustable MRF damper was designed and developed.Magnetic field simulation analysis was conducted on the damper,along with simulation analysis on its dynamic characteristics.The dynamic characteristics were ultimately validated through experimental testing on the material testing machine,thereby corroborating the theoretical simulation results.Concurrently,this process generated valuable test data for subsequent implementation of the semi-active vibration control system.The simulation and test results demonstrate that the integrated permanent magnet effectively accomplishes bidirectional regulation.The magnetic induction intensity of the damping channel is 0.2 T in the absence of current,increases to 0.5 T when a maximum forward current of 4 A is applied,and becomes 0 T when a maximum reverse current of 3.8 A is applied.When the excitation amplitude is 8 mm and the frequency is 2 Hz,with the applied currents varying,the maximum damping force reaches 8 kN,while the minimum damping force measures at 511 N.Additionally,at zero current,the damping force stands at 2 kN,which aligns closely with simulation results.The present paper can serve as a valuable reference for the design and research of semi-active MRF dampers.
文摘Design a precision electroplating mechanical structure for automobiles based on finite element analysis method and analyze its mechanical properties.Taking the automobile steering knuckle as the research object,ABAQUS parametric modeling technology is used to construct its three-dimensional geometric model,and geometric simplification is carried out.Two surface treatment processes,HK-35 zinc nickel alloy electroplating and pure zinc electroplating,were designed,and the influence of different coatings on the mechanical properties of steering knuckles was compared and analyzed through numerical simulation.At the same time,standard specimens were prepared for salt spray corrosion testing and scratch method combined strength testing to verify the numerical simulation results.The results showed that under emergency braking and composite working conditions,the peak Von Mises stress of the zinc nickel alloy coating was 119.85 MPa,which was lower than that of the pure zinc coating and the alkaline electroplated zinc layer.Its equivalent strain value was 652×10^(-6),which was lower than that of the pure zinc coating and the alkaline electroplated zinc layer.Experimental data confirms that zinc nickel alloy coatings exhibit significant advantages in stress distribution uniformity,strain performance,and load-bearing capacity in high stress zones.The salt spray corrosion test further indicates that the coating has superior corrosion resistance and coating substrate interface bonding strength,which can significantly improve the mechanical stability and long-term reliability of automotive precision electroplating mechanical structures.
基金Project(GZC20233199) supported by the Postdoctoral Fellowship Program of CPSF,ChinaProject(2022YFC2105300) supported by the National Key Research and Development Program of China。
文摘Mechanical activation (MA) is a significant pretreatment technique for enhancing the dissolution of mineral;however, its promotion effect on the role of pyrite during chalcopyrite bioleaching has not been elucidated up to now. In this study, the effect of MA on the role of pyrite on chalcopyrite bioleaching mediated by Acidithiobacillus ferroxidans was investigated by X-ray diffraction, scanning electron microscopy, particle size distribution analysis, and electrochemical measurement. The results showed MA could significantly reduce the minerals particle size, and increase the specific surface area and surface energy of minerals. For example, the d50 of chalcopyrite reduced from 13.40 to 0.31 μm after MA. The copper extraction of mixed MA-chalcopyrite and MA-pyrite system was 63.4%, which exhibited a 51.8% enhancement compared to the non-activated mixed system. Electrochemical experiments identified that the strengthening effect of pyrite on chalcopyrite dissolution was negligible before MA. After MA, the dissolution mechanism of chalcopyrite was not changed, and pyrite could not only provide additional oxidants (acids and iron) but also act as the cathode in the galvanic couple. In this case, the bioleaching of chalcopyrite was accelerated. Therefore, a model of the promotion effect of mechanical activation on the role of pyrite on chalcopyrite bioleaching was proposed.
基金the funding from the Overseas Young Talents Program(22GAA00842)the Hebei Natural Science Foundation(E2024105032)+4 种基金the Youth Academic Startup Program at Beijing Institute of Technology(RCPT-6120210286)the"National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact(No.WDZC2022-1)""National Natural Science Foundation of China(No.52271141)"the support of"National Natural Science Foundation of China(Grant No.12222204 and 12072045)"the support of"National Natural Science Foundation of China(Grant No.52331006)".
文摘High-entropy alloys(HEAs)with multi-component elements have attracted significant interest since they exhibit numerous superior properties compared to traditional ones.These properties include significant energy release,remarkable fracture toughness,and high strength,making them promising candidates as energetic structural materials(ESMs).This paper summarizes the energy release mechanisms under dynamic impact and the mechanical behavior of TiZr-based HEAs,TiNb-based HEAs,andWbased HEA,including velocity threshold for energy release,chamber quasi-static pressure curve,energy release efficiency,interface reactions,and"self-sharpening".In addition,we propose future research directions for their energy release and mechanical behavior.
文摘This work aimed to(i)understand conventional and pulse gas tungsten arc welding(GTAW)of AZ31B,and(ii)explore high frequency welding(100 Hz-1500 Hz).GTA welding with alternating current(AC)and direct current electrode positive(DCEP)polarities yielded crack-free partial penetration welds for6 mm thick AZ31B alloy sheet.Welding under direct current electrode negative(DCEN)polarity with identical parameters as that for AC and DCEP resulted in full penetration welds that had microcracks.Defect-free full-penetration welds could be accomplished with pulse GTA welding using DCEN polarity at a pulse frequency of 1 Hz with a pulse duration ratio of 1:1.The resultant DCEN P 1:1 weld metal had a microstructure finer than the conventional DCEN weld.Welds produced with pulse duration ratios of 1:2and 1:4 lacked penetration but had a much finer microstructures because of the lower heat input.The arc constriction by the high frequency pulsing in the Activ Arc■-High frequency(AA-HF)mode welding was responsible for deeper penetration.Welds produced under DCEN pulsing and AA-HF conditions had hardness higher than conventional DCEN,DCEP and AC GTA welds,attributed to the finer microstructure.AA-HF GTA welding produced defect free deeper penetration welds with good microstructural features/mechanical properties and also gave an advantage of 50%enhanced productivity when welded at1500 Hz.
基金Projects(12072102,12102129)supported by the National Natural Science Foundation of ChinaProject(DM2022B01)supported by the Key Laboratory of Safe Mining of Deep Metal Mines,Ministry of Education,ChinaProject(JZ-008)supported by the Six Talent Peaks Project in Jiangsu Province,China。
文摘In this study,a series of triaxial tests are conducted on sandstone specimens to investigate the evolution of their mechanics and permeability characteristics under the combined action of immersion corrosion and seepage of different chemical solutions.It is observed that with the increase of confining pressure,the peak stress,dilatancy stress,dilatancy stress ratio,peak strain,and elastic modulus of the sandstone increase while the Poisson ratio decreases and less secondary cracks are produced when the samples are broken.The pore pressure and confining pressure have opposite influences on the mechanical properties.With the increase of the applied axial stress,three stages are clearly identified in the permeability evolution curves:initial compaction stage,linear elasticity stage and plastic deformation stage.The permeability reaches the maximum value when the highest volumetric dilatancy is obtained.In addition,the hydrochemical action of salt solution with pH=7 and 4 has an obvious deteriorating effect on the mechanical properties and induces the increase of permeability.The obtained results will be useful in engineering to understand the mechanical and seepage properties of sandstone under the coupled chemical-seepage-stress multiple fields.
基金Project(52275350)supported by the National Natural Science Foundation of ChinaProject(0301006)supported by the International Cooperative Scientific Research Platform of SUES,China。
文摘In this study,the interaction between deformation and precipitates during multiple equal channel angular pressing(ECAP)deformations and inter-pass aging combination and its effect on the mechanical properties of 7050 aluminum alloy are studied.The result show that ECAP induces numerous substructures and dislocations,effectively promoting the precipitation of theηʹphase exhibiting a bimodal structure during inter-pass aging.Following inter-pass aging and subsequent ECAP,the decrease in grain size(4.8μm)is together with the increase in dislocation density(1.24×10^(15) m^(−2))due to the pinning effect of the precipitated phase.Simultaneously,the dislocation motion causes the second phase particles to become even finer and more diffuse.The synergistic effects of precipitation strengthening,fine grain strengthening,and dislocation strengthening collectively enhance the high strength of aluminum alloys,with ultimate tensile strength and yield strength reaching approximately 610 and 565 MPa,respectively.Meanwhile,ductility remains largely unchanged,primarily due to coordinated grain boundary sliding and the uniform and fine dispersion of second phase particles.
基金supported by projects VEGA 1/0307/23 and APVV-23-0204 of Scientific Grant Agency of the Ministry of Education,Research,Development and Youth of the Slovak Republic.
文摘The undercurrent research survey explores the roles of nonlocality and strain gradient size dependencies in nonlinear asymmetric buckling of shallow nanoscale arches having dissimilar end conditions through a numerical analysis.The arches,made from a functionally graded graphene nanofiller reinforced composite(FG-GNRC),are subjected to discretional radial concentrated loads along with converting of temperature.To account for the size dependencies,the exploration is carried out stemming from the nonlocal strain gradient theory(NSGT)in the sense of a quasi-2D parabolic shear flexible concept of curved beam.The material properties of the contemplated FG-GNRC sandwich are determined using the modified Halpin-Tsai micromechanics model.Subsequently,an extended isogeometric analysis(XIGA)is manipulated comprising insertion plus multiplication of knots to achieve the demanded lower continuity allocated to the integration between flexural and tangential reflexes.It is perceived that the both softening and stiffening concomitants assigned to the salient concentrated radial loads obtained by the developed NSGT-based XIGA diminish from the first upper limit to the second one,and then likewise from the first lower limit to the second one.Although,by becoming the upsurge in temperature higher,these softening and stiffening concomitants get more remarkable.
基金Projects(52378392,52478390)supported by the National Natural Science Foundation of ChinaProject(2024J08213)supported by the Natural Science Foundation of Fujian Province,China+1 种基金Project(00387088)supported by the“Foal Eagle Program”Youth Top-notch Talent Project of Fujian Province,ChinaProject(GY-Z23072)supported by the Scientific Research Foundation of Fujian University of Technology,China。
文摘Gypsum rocks are highly susceptible to mechanical deterioration under the coupled effects of wet-dry(W-D)cycles and flow rates,which significantly influence the stability of underground excavations.Despite extensive research on the effects of W-D cycles,the coupling influence of flow rates and W-D cycles on gypsum rocks remains poorly understood.This study investigates the mechanical behavior and deterioration mechanisms of gypsum rocks subjected to varying W-D cycles and flow rate conditions.Axial compression tests,along with nuclear magnetic resonance(NMR)techniques,were employed to analyze the stress-strain response and microstructural changes.Based on the disturbed state concept(DSC)theory,a W-D deterioration model and a DSC-based constitutive model were developed to describe the degradation trends and mechanical responses of gypsum rocks under different conditions.The results demonstrate that key mechanical indices,elastic modulus,cohesion,uniaxial compressive strength(UCS),and internal friction angle,exhibit logarithmic declines with increasing W-D cycles,with higher flow rates accelerating the deterioration process.The theoretical models accurately capture the nonlinear compaction behavior,peak stress,and post-peak response of gypsum specimens.This study provides valuable insights for predicting the mechanical behavior of gypsum rocks and improving the stability assessments of underground structures under complex environmental conditions.
基金Projects(52174092,42472338,51904290)supported by the National Natural Science Foundation of ChinaProject(BK20220157)supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(2022YCPY0202)supported by the Fundamental Research Funds for the Central Universities,China。
文摘This study investigates the shear mechanical responses and debonding failure mechanisms of anchoring systems comprising three anisotropic media and two anisotropic interfaces under controlled boundary conditions of constant normal load(F_(s)),constant normal stiffness(K),and shear rate(v).A systematic analysis of shear mechanical properties,the evolution of maximum principal strain field,and damage characteristics along shear failure surface is presented.Results from direct shear tests demonstrate that initial shear slip diminishes with increasing F_(s)and K,attributed to the normal constraint strengthening effect,while an increase in v enhances initial shear slip due to attenuated deformation coordination and stress transfer.As F_(s)increases from 7.5 to 120 kN,K from 0 to 12 MPa/mm,and v from 0.1 to 2 mm/min,the peak shear load increases by 210.32%and 80.16%with rising F_(s)and K,respectively,while decreases by 38.57%with increasing v.Correspondingly,the shear modulus exhibits,respectively,a 135.29%and 177.06%increase with rising F_(s)and K,and a 37.03%decrease with larger v.Initial shear dilation is identified as marking the formation of shear failure surface along anisotropic interfaces,resulting from the combined shear actions at the resin bolt interface,where resin undergoes shear by bolt surface protrusions,and the resin-rock interface,where mutual shear occurs between resin and rock.With increasing F_(s)and K and decreasing v,the location of the shear failure surface shifts from the resin-rock interface to the resin-bolt interface,accompanied by a transition in failure mode from tensile rupture of resin to shear off at the resin surface.
基金Project(2021YFC2801904) supported by the National Key R&D Program of ChinaProject(KY10100230067) supported by the Basic Product Innovation Research Project,China+3 种基金Projects(52271130,52305344) supported by the National Natural Science Foundation of ChinaProject(ZR2022QE073) supported by the Natural Science Foundation of Shandong Province,ChinaProject(AMGM2021F01) supported by the Science Fund of Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai,ChinaProject(KY90200210015) supported by Leading Scientific Research Project of CNNC,China。
文摘In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition(LDED).The effects of ultrasonic vibration(UV)and tempering treatment on microstructure evolution,microhardness distribution and mechanical properties of deposition layer were studied in detail.The microstructure of UV assisted LDED sample after tempering is mainly composed of tempered sorbite(TS).Due to the improvement of microstructure inhomogeneity and grains refinement,UV assisted LDED sample with tempering treatment obtains excellent mechanical properties.The ultimate tensile strength(UTS),yield strength(YS)and elongation after breaking(EL)reach 765 MPa,657 MPa and 19.5%,the increase ratios of UTS and YS are 14.5%and 33.8%while maintaining plasticity compared to original LDED sample,respectively.It is obvious that ultrasonic vibration combined with tempering is a potential and effective method to obtain uniform microstructure and excellent mechanical properties in metal laser directed energy deposition field.
基金supported by the National Key Laboratory of Energetic Materials, China (Grant No. 2023-LB-036-09).
文摘In order to analyze the influences of storage aging on the safety of typical elemental explosives,the aged cyclotrimethylene trinitramine(RDX)and cyclotetramethylene tetranitramine(HMX)were prepared by isothermal aging tests.The reaction thresholds of aged RDX and HMX under any ignition probability were studied by Langlie-Optimal D method.The thermal decomposition characteristics of RDX and HMX after aging were analyzed by DSC and ARC.Experimental results showed that compared with unaged RDX and HMX,on the one hand,the critical impact energy and critical friction of RDX and HMX aged for 14,28,and 56 days are significantly reduced at an explosion probability of 50%,0.01%,and 0.0001%,respectively.With the increase of aging time,the mechanical sensitivity of RDX and HMX increases obviously.On the other hand,the initial decomposition temperature of RDX and HMX after 56 days of aging decreases,the decomposition heat decreases,the activation energy increases,and the reaction difficulty increases.
基金Project supported by ClassⅢPeak Discipline of Shanghai-Materials Science and Engineering(High-Energy Beam Intelligent Processing and Green Manufacturing),China。
文摘High-entropy alloy composites(HEACs)have attracted significant attention due to their exceptional mechanical properties and chemical stability.By adjusting the content of reinforcing particles in the high-entropy alloy and by employing advanced additive manufacturing techniques,high-performance HEACs can be fabricated.However,there is still considerable room for improvement in their performance.In this study,CoCrFeMnNi HEA powders were used as the matrix,and NiCoFeAlTi high-entropy intermetallic powders were used as the high-entropy reinforcement(HER).CoCrFeMnNi/NiCoFeAlTi HEACs were fabricated using selective laser melting technology.The study results indicate that after aging,the microstructure of HEACs with HER exhibits Al-and Ti-rich nano-oxide precipitates with an orthorhombic CMCM type structure system.After aging at 873 K for 2 h,HEACs with HER achieved excellent overall mechanical properties,with an ultimate tensile strength of 731 MPa.This is attributed to the combined and synergistic effects of precipitation strengthening,dislocation strengthening,and the high lattice distortion caused by high intragranular defects,which provide a multi-scale strengthening and hardening mechanism for the plastic deformation of HEACs with HER.This study demonstrates that aging plays a crucial role in controlling the precipitate phases in complex multi-element alloys.
基金Project(2022J318)supported by the Natural Science Foundation of Ningbo,ChinaProject(2021A1515110525)supported by the Guangdong Basic and Applied Basic Research Foundation,ChinaProject(2022QN05023)supported by the Inner Mongolia Natural Science Foundation Youth Project,China。
文摘In order to obtain high-density dual-scale ceramic particles(8.5 wt.%SiC+1.5 wt.%TiC)reinforced Al-Mg Sc-Zr composites with uniform microstructure,50 nm TiC and 7μm SiC particles were pre-dispersed into 15−53μm aluminum alloy powders by low-speed ball milling and mechanical mixing technology,respectively.Then,the effects of laser energy density,power and scanning rate on the density of the composites were investigated based on selective laser melting(SLM)technology.The effect of micron-sized SiC and nano-sized TiC particles on solidification structure,mechanical properties and fracture behaviors of the composites was revealed and analyzed in detail.Interfacial reaction and phase variations in the composites with varying reinforced particles were emphatically considered.Results showed that SiC-TiC particles could significantly improve forming quality and density of the SLMed composites,and the optimal relative density was up to 100%.In the process of laser melting,a strong chemical reaction occurs between SiC and aluminum matrix,and micron-scale acicular Al_(4)SiC_(4) bands were formed in situ.There was no interfacial reaction between TiC particles and aluminum matrix.TiC/Al semi-coherent interface had good bonding strength.Pinning effect of TiC particles in grain boundaries could prevent the equiaxial crystals from growing and transforming into columnar crystals,resulting in grain refinement.The optimal ultimate tensile strength(UTS),yield strength(YS),elongation(EL)and elastic modulus of the SiC-TiC/Al-Mg-Sc-Zr composite were~394 MPa,~262 MPa,~8.2%and~86 GPa,respectively.The fracture behavior of the composites included ductile fracture of Al matrix and brittle cleavage fracture of Al_(4)SiC_(4) phases.A large number of cross-distributed acicular Al_(4)SiC_(4) bands were the main factors leading to premature failure and fracture of SiC-TiC/Al-Mg-Sc-Zr composites.
