In order to solve the problem of poor formability caused by different materials and properties in the process of tailor-welded sheets forming,a forming method was proposed to change the stress state of tailor-welded s...In order to solve the problem of poor formability caused by different materials and properties in the process of tailor-welded sheets forming,a forming method was proposed to change the stress state of tailor-welded sheets by covering the tailor-welded sheets with better plastic properties overlapping sheets.At the same time,the interface friction effect between the overlapping and tailor-welded sheets was utilized to control the stress magnitude and further improve the formability and quality of the tailor-welded sheets.In this work,the bulging process of the tailor-welded overlapping sheets was taken as the research object.Aluminum alloy tailor-welded overlapping sheets bulging specimens were studied by a combination of finite element analysis and experimental verification.The results show that the appropriate use of interface friction between tailor-welded and overlapping sheets can improve the formability of tailor-welded sheets and control the flow of weld seam to improve the forming quality.When increasing the interface friction coefficient on the side of tailor-welded sheets with higher strength and decreasing that on the side of tailor-welded sheets with lower strength,the deformation of the tailor-welded sheets are more uniform,the offset of the weld seam is minimal,the limit bulging height is maximal,and the forming quality is optimal.展开更多
This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the pre...This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the prepared surfaces are placed on top of each other and by rolling with reduction more than 50%,the bonding between layers is established.In this research,the roll bonding process was done at room temperature,without the use of lubricants and with a 70%thickness reduction.Then,the final thickness of the Ag/Al bilayer sheet reached 350μm by several stages of cold rolling.Before cold rolling,it should be noted that to decrease the hardness created due to plastic deformation,the roll-bonded samples were subjected to annealing heat treatment at 400℃for 90 min.Thus,the final samples were annealed at 200,300 and 400℃for 90 min and cooled in a furnace to examine the annealing temperature effects.The uniaxial tensile and microhardness tests measured mechanical properties.Also,to investigate the fracture mechanism,the fractography of the cross-section was examined by scanning electron microscope(SEM).To evaluate the formability of Ag/Al bilayer sheets,forming limit curves were obtained experimentally through the Nakazima test.The resistance of composites to failure due to cracking was also investigated by fracture toughness.The results showed that annealing increases the elongation and formability of the Ag/Al bilayer sheet while reduces the ultimate tensile strength and fracture toughness.However,the changing trend is not the same at different temperatures,and according to the results,the most significant effect is obtained at 300℃and aluminum layers.It was also determined that by increasing annealing temperature,the fracture mechanism from shear ductile with small and shallow dimples becomes ductile with deep cavities.展开更多
The formation of an embedded electron current sheet within the magnetotail plasma sheet has been poorly understood.In this article,we present an electron current layer detected at the edge of the magnetotail plasma sh...The formation of an embedded electron current sheet within the magnetotail plasma sheet has been poorly understood.In this article,we present an electron current layer detected at the edge of the magnetotail plasma sheet.The ions were demagnetized inside the electron current layer,but the electrons were still frozen in with the magnetic field line.Thus,this decoupling of ions and electrons gave rise to a strong Hall electric field,which could be the reason for the formation of the embedded thin current layer.The magnetized electrons,the absence of the nongyrotropic electron distribution,and negligible energy dissipation in the layer indicate that magnetic reconnection had not been triggered within the embedded thin current layer.The highly asymmetric plasma on the two sides of the current layer and low magnetic shear across it could suppress magnetic reconnection.The observations indicate that the embedded electric current layer,probably generated by the Hall electric field,even down to electron scale,is not a sufficient condition for magnetic reconnection.展开更多
A novel laser-based additive manufacturing approach of metal additive manufacturing using powder sheets(MAPS)has been introduced recently.The method utilizes polymer-bound powder sheets for metal AM as a feedstock,ins...A novel laser-based additive manufacturing approach of metal additive manufacturing using powder sheets(MAPS)has been introduced recently.The method utilizes polymer-bound powder sheets for metal AM as a feedstock,instead of loose powders.Conventional laser beam powder bed fusion(LPBF)additive manufacturing(AM)is among the most widespread 3D printing technologies.However,LPBF faces challenges related to safety and the impracticality of changing materials due to its reliance on loose powders.Thus,MAPS demonstrates the capability to overcome the limitations of LPBF by offering enhanced safety and the ability to print multi-material structures without the risk of material cross-contamination.As a part of developing processes,we investigate the effects of polymeric binder content on the printability and microstructural characteristics of MAPS-printed stainless steel 316 L.The results indicate that the average layer thickness of solidified material improves as the scanning speed decreases from 1000 mm/s to 50 mm/s across three different polymeric binder contents:10 wt%,20 wt%,and 30 wt%PCL.Additionally,a higher polymeric binder content(i.e.20 wt%and 30 wt%)in the powder sheets reduces the likelihood of crack formation.Electron backscatter diffraction(EBSD)analysis reveals that an increase in scanning speed promotes the formation of more equiaxed grains,while an increase in polymer content results in a reduction in grain size.These findings provide valuable insights into optimizing MAPS configurations for enhanced productivity and functionality in metal component manufacturing.展开更多
Fe–Ga sheets with large magnetostriction are required for improving the conversion efficiency under the ultra-high frequencymagnetic field. Trace Tb element doping can simultaneously improve the magnetostriction and ...Fe–Ga sheets with large magnetostriction are required for improving the conversion efficiency under the ultra-high frequencymagnetic field. Trace Tb element doping can simultaneously improve the magnetostriction and ductility of Fe–Ga alloy. However, the im-pact of trace Tb doping on the microstructure and magnetostriction of Fe–Ga thin sheets is an open question. In this paper, the effects oftrace Tb addition on the secondary recrystallization and magnetostriction of Fe–Ga thin sheets are systematically studied by comparing thecharacteristics evolution of precipitation, texture, and nanoinclusions. The results indicate that trace Tb addition accelerates the secondaryrecrystallization of Goss texture due to the combined action of the bimodal size distributed precipitates, smaller grains, and more HEGBsin primary recrystallization. After quenching at 900℃, the magnetostriction value in 0.07 at %Tb-doped Fe_(81)Ga_(19) thin sheets increases by 30% to that of Fe_(81)Ga_(19) thin sheets. The increase in magnetostriction is attributed to the decrease in the number of Tb-rich precipitates andthe higher density of the nanometer-sized modified-D0_(3) inclusions induced by the dissolving of trace Tb elements after quenching. Theseresults demonstrate a simple and efficient approach for preparing Fe–Ga thin sheets with a large magnetostrictive coefficient by a combin-ation of trace RE element addition and conventional rolling method.展开更多
This study focuses on the risks associated with the on-balance sheet recognition of data resources.At the legal level,disputes over ownership often arise due to unclear data property rights,while privacy protection,cy...This study focuses on the risks associated with the on-balance sheet recognition of data resources.At the legal level,disputes over ownership often arise due to unclear data property rights,while privacy protection,cybersecurity,and cross-border data flows create additional compliance challenges.In terms of recognition,the subjectivity of traditional valuation methods,the lack of active markets,and the rapid depreciation of data value caused by technological iteration hinder reliable measurement.With respect to disclosure,organizations face a dilemma between transparency and confidentiality.Collectively,these issues exacerbate audit risks.It is therefore imperative to establish an appropriate legal,accounting,and auditing framework to mitigate such risks and remove barriers to the proper recognition of data assets on balance sheets.展开更多
Edge cracking is one of the most serious problems in the rolling process of magnesium alloy sheets,which limits its application.In this work,the edge cracking behavior of different initial AZ31 alloy sheets,including ...Edge cracking is one of the most serious problems in the rolling process of magnesium alloy sheets,which limits its application.In this work,the edge cracking behavior of different initial AZ31 alloy sheets,including as-cast(AC),as-rolled(AR)and as-extruded(AE),was systematically investigated and compared under the online heating rolling(O-LHR)process with a single-pass reduction of 50% at 250℃.The results show that both AC and AR sheets exhibit severe edge cracking behavior after the O-LHR.Among them,the AR sheet exhibits the severest edge cracking behavior on the rolling plane(RD-TD)and longitudinal section(RD-ND),which is attributed to the strong basal texture and extremely uneven microstructure with shear bands.While no visible edge crack appears in the AE rolled sheet,which is mainly related to the tilted texture and the more dynamic recrystallization during rolling process.Moreover,it is also found that the micro-cracks of the AC rolled sheet are mainly generated in the local fine-grained area and the twins where recrystallization occurs.In the AR rolled sheet,micro-cracks mainly develop inside the shear bands.Meanwhile,the micro-crack initiation mechanism of AC and AR rolled sheets was also discussed.展开更多
The deformation behavior of hot-rolled AZ31 magnesium(Mg)alloy sheet was analyzed when subjected to uniaxial tension along its normal direction at temperatures ranging from 100 to 400℃and strain rates ranging from 0....The deformation behavior of hot-rolled AZ31 magnesium(Mg)alloy sheet was analyzed when subjected to uniaxial tension along its normal direction at temperatures ranging from 100 to 400℃and strain rates ranging from 0.5 to 100 mm/min.Based on the stress−strain curves and the dynamic material model,the hot processing map was established,which demonstrates that the power dissipation factor(η)is the most sensitive to strain rate at 400℃via absorption of dislocations.At 400℃,sample at 0.5 mm/min possessesηof 0.89 because of its lower kernel average misorientation(KAM)value of 0.51,while sample at 100 mm/min possessesηof 0.46 with a higher KAM value of 1.147.In addition,the flow stress presents a slight decrease of 25.94 MPa at 10 mm/min compared to that at 100 mm/min and 100℃.The reasons are twofold:a special~34°texture component during 100℃-100 mm/min favoring the activation of basal slip,and dynamic recrystallization(DRX)also providing softening effect to some extent by absorbing dislocations.Difference in activation of basal slip among twin laminas during 100℃-100 mm/min results in deformation inhomogeneity within the grains,which generates stress that helps matrix grains tilt to a direction favorable to basal slip,forming the special~34°texture component.展开更多
Microcirculation imaging is crucial in understanding the function and health of various tissues and organs.However,conventional imaging methods suffer from fluorescence label dependency,lack of depth resolution,and qu...Microcirculation imaging is crucial in understanding the function and health of various tissues and organs.However,conventional imaging methods suffer from fluorescence label dependency,lack of depth resolution,and quantification inaccuracy.Here,we report a light-sheet dynamic light-scattering imaging(LSHDSI)system to overcome these shortcomings.LSH-DSI utilizes selected plane illumination for an optical sectioning,while a time-frequency analysis method retrieves blood flow velocity estimates from dynamic changes in the detected light intensity.We have performed imaging experiments with zebrafish embryos to obtain angiographs from the trunk and head regions.The results show that LSH-DSI can capture label-free tomographic images of microvasculature and three-dimensional quantitative maps of local blood flow velocities.展开更多
During the construction of bank slopes involving pile driving,ensuring slope stability is crucial.This requires the design of appropriate support systems and a thorough evaluation of the failure mechanisms of pile str...During the construction of bank slopes involving pile driving,ensuring slope stability is crucial.This requires the design of appropriate support systems and a thorough evaluation of the failure mechanisms of pile structures under dynamic loading conditions.Based on the Huarong Coal Wharf project,various support schemes are analyzed using numerical simulation methods to calculate and compare slope stability coefficients.The optimal scheme is then identified.Under the selected support scheme,a numerical model of double-row suspended steel sheet piles is developed to investigate the dynamic response of the pile structures under pile driving loads.A time-history analysis is performed to assess the slope’s dynamic stability.The results show that the maximum displacements of the upper and lower steel sheet pile rows are 2.51 and 3.14 cm,respectively.The maximum principal stresses remain below 20 MPa in both rows,while the maximum von Mises stresses are 20.85 MPa for the upper row and 25.40 MPa for the lower row.The dominant frequencies of the steel sheet pile structures fall between 30 and 35 Hz,with a frequency bandwidth ranging from 0 to 500 Hz.The stability coefficient of the pile structures varies over time during the pile driving process,ultimately reaching a value of 1.26—exceeding the required safety threshold.This research provides practical guidance for designing support systems in wharf piling projects and offers a reliable basis for evaluating the safety performance of steel sheet piles in bank slopes.展开更多
With the generation of both localised thermal and vibration in incremental sheet forming(ISF)by novel tool designs,rotational vibration assisted ISF(RV-ISF)can achieve significant force reduction and material softenin...With the generation of both localised thermal and vibration in incremental sheet forming(ISF)by novel tool designs,rotational vibration assisted ISF(RV-ISF)can achieve significant force reduction and material softening.However,the combined thermal and vibration softening in RV-ISF is unclear.By evaluating the similarities and differences of friction stir ISF(FS-ISF)and RV-ISF,this study develops a novel approach to decouple and quantify the thermal and vibration softening effects in RV-ISF of AZ31B-H24,providing new insights into underlying thermal and vibration softening mechanism.Experimental results reveal that in RV-ISF of AZ31B-H24 the thermal softening due to frictional heating dominates with 45∼65%of softening,while the vibration effect only contributes up to 15%of softening,from the conventional ISF,depending on the tool designs and tool rotational speed.The double-offset tool(T2)produces greater vibration softening than the three-groove tool(T3)owing to the higher vibration amplitude of the T2 tool.An increase in tool rotational speed primarily enhances thermal softening with only marginal changes to the vibration effect.Microstructural analysis suggests that with average grain size of 0.94μm at the top layer,RV-ISF with T3 and 3000 rpm is more effective for microstructure refinement than that by FS-ISF,especially on the tool-sheet contact surface,which confirms the occurrence of surface shearing.This refinement is a result of the reduced recrystallisation degree,71.8%at the top bottom layer.Compared with FS-ISF,RV-ISF can lead to not only higher geometrically necessary dislocation density,but also higher fraction of low-angle grain boundaries,indicating that softening mechanism due to localised vibration effect is resulted from the enhanced rearrangement and annihilation of dislocations.These findings contribute to new understanding of the thermal and vibration softening effects in RV-ISF of AZ31B-H24 and offer a theoretical foundation for the tool design and process optimisation.展开更多
The objective of this work is to investigate the dynamics of a self-propelled undulating sheet in a non-Newtonian electrolyte solution inside a wavy channel under the electroosmotic effect.The electrolyte solution,whi...The objective of this work is to investigate the dynamics of a self-propelled undulating sheet in a non-Newtonian electrolyte solution inside a wavy channel under the electroosmotic effect.The electrolyte solution,which is non-Newtonian,is modeled as a Carreau-Yasuda fluid.The flow generated by a combination of an undulating sheet and electroosmotic effect is obtained by solving the continuity and momentum equations.The electroosmotic body force term is derived using the Poisson-Boltzmann equation for the electric potential.A fourth-order ordinary differential equation for the stream function is solved under the Stokes flow regime.The dynamics of the undulating sheet’s speed and the energy dissipation it,are investigated.The combined effects of electroosmosis and the viscoelastic properties of the ambient fluid on the undulating sheet are discussed.展开更多
An analytical model for contact area and contact stress considering the loading history in incremental sheet forming(ISF)was established.Then,by integrating with the directional characteristics of friction force and h...An analytical model for contact area and contact stress considering the loading history in incremental sheet forming(ISF)was established.Then,by integrating with the directional characteristics of friction force and horizontal force in the process,a friction test method reflecting the forming characteristics of ISF was proposed.Friction coefficients during the forming processes of parts with different wall angles were measured under various plane curves,process paths,and lubrication conditions.Furthermore,the accuracy of the analytical model,as well as the measured friction coefficients and their variation trends,was verified through comparative analysis with experimental results,simulation data,and outcomes from other existing models.The results indicate that the influence of the plane curve characteristics and process paths of parts on the friction condition is not significant.Under the lubrication conditions of L-HM46 oil,MoS_(2)grease,graphite powder,and dry friction,the friction coefficient shows a gradually increasing trend.Notably,when the wall angle is≤40°,the friction coefficient remains relatively constant;however,when the wall angle exceeds 40°,the friction coefficient increases progressively.展开更多
Elevation change monitoring of the Antarctic ice sheet has been a key issue in global change research.Satellite altimetry has been proven to be effective in detecting ice sheet variations. With the development of ICES...Elevation change monitoring of the Antarctic ice sheet has been a key issue in global change research.Satellite altimetry has been proven to be effective in detecting ice sheet variations. With the development of ICESat-2, many elevation observations can be used to derive elevation changes. However, the large amount of multitemporal data may include anomalous data points, increasing the uncertainty of the results. In this work, we improved the traditional repeat track method by introducing the Institute of Geodesy and Geophysics Ⅲ(IGGⅢ) method to obtain high-accuracy estimates of elevation change. The improved method was applied to analyze elevation changes along the transect from Zhongshan Station to Dome A in East Antarctica via ICESat-2 satellite altimetry data. The results show that the improved and traditional methods yield consistent numerical and spatial elevation change distributions. The elevation change calculated via the traditional method is 0.033 ± 0.131 m/yr, whereas the elevation change estimated via the IGGⅢ robust estimation method is 0.033 ± 0.109 m/yr from March 2019 to December 2021.In terms of spatial distribution, elevation changes in inland areas remain close to equilibrium, whereas regions with steeper ice sheet margins exhibit positive accumulation trends in elevation changes. The improved method reduces the standard error of the adjustment function from 0.975 to 0.691 m/yr. The improvement is particularly remarkable in the area between 72°S and 77°S. The results demonstrate that the IGGⅢ method effectively reduces errors caused by the inclusion of anomalous data and maintains the high data utilization rate of repeat-orbit methods.展开更多
In this work,AZ31B extruded sheets with mixed-grain microstructures were prepared through extrusion.Samples of mixed-grain microstructure with different morphologies were selected from the AZ31B extruded sheets(referr...In this work,AZ31B extruded sheets with mixed-grain microstructures were prepared through extrusion.Samples of mixed-grain microstructure with different morphologies were selected from the AZ31B extruded sheets(referred to as M1 and M2 samples,respectively).The creep tests were performed on these samples at the temperature range of 150-200℃,and the stress level range of 50-100 MPa.The creep properties and fracture behavior of AZ31 extruded sheets with mixed-grain microstructures were studied.Results showed that the creep properties of the M2 sample always outperformed that of the M1 sample and M1 and M2 samples’creep was dominated by dislocation movement.The creep rate of M2 samples(1.5×10^(-7)±1.1×10^(-10) s^(-1))is an order of magnitude lower than that of M1 samples(4.8×10^(-6)±8.1×10^(-10) s^(-1))at 200℃under 50 MPa The high activity of basal slip and softening mechanism in the M1 sample significantly accelerated creep,resulting in a relatively high creep rate.Moreover,the stress concentration within the M1 sample caused by deformation incompatibility,increased the initiation and propagation of voids,ultimately leading to fracture and poorer creep performance.However,the numerous<10µm fine grains surrounding deformed coarse grains in the M2 sample facilitated better coordination of deformation through dislocation slip,effectively slowing down the initiation of voids during the creep process.Meanwhile,the strain was uniformly distributed within each grain,mitigating stress concentration,inhibiting voids propagation,and contributing to the superior creep resistance of the M2 sample.展开更多
In this study,AZ31 Mg alloy sheets were processed by a severe plastic deformation(SPD)technique called forging-bending repeated deformation(FBRD).The effect on the microstructure and microhardness of AZ31 Mg alloy thr...In this study,AZ31 Mg alloy sheets were processed by a severe plastic deformation(SPD)technique called forging-bending repeated deformation(FBRD).The effect on the microstructure and microhardness of AZ31 Mg alloy through FBRD was investigated with increasing temperature treatment and a 90°cross route.The results reveal that the effective strain increases with the number of passes.The flow uniformity is effectively enhanced due to alterations in shear deformation direction.After four passes of deformation,the average grain size is refined by 79.3%compared to the initial specimen.The grain refinement mechanism predominantly originates from the synergistic effects of discontinuous dynamic recrystallization(DDRX),continuous dynamic recrystallization(CDRX),and twinning-induced recrystallization(TDRX).The formation of{1012}extension twins(ET)significantly contributes to coarse grain subdivision and plastic deformation coordinated.Furthermore,pyramidal<c+a>slip activation effectively enhances the plasticity of Mg alloys.By post four-pass processing,the alloy exhibits a microhardness of 81.9HV,primarily governed by fine grain strengthening and dislocation strengthening mechanisms.展开更多
The influence of geometric configuration on the friction characteristics during incremental sheet forming of AA5052 was analyzed by integrating surface morphology and its characteristic parameters,along with plastic s...The influence of geometric configuration on the friction characteristics during incremental sheet forming of AA5052 was analyzed by integrating surface morphology and its characteristic parameters,along with plastic strain,contact pressure,and area.The interface promotes lubrication and support when wall angles were≤40°,a 0.5 mm-thin sheet was used,and a 10 mm-large tool radius was employed.This mainly results in micro-plowing and plastic extrusion flow,leading to lower friction coefficient.However,when wall angles exceed 40°,significant plastic strain roughening occurs,leading to inadequate lubrication on the newly formed surface.Increased sheet thickness and decreased tool radius elevate contact pressure.These actions trigger micro-cutting and adhesion,potentially leading to localized scuffing and dimple tears,and higher friction coefficient.The friction mechanisms remain unaffected by the part’s plane curve features.As the forming process progresses,abrasive wear intensifies,and surface morphology evolves unfavorably for lubrication and friction reduction.展开更多
BACKGROUND Dental follicle stem cell(DFSC)sheets demonstrate strong extracellular secretion capabilities and efficacy in periodontal regeneration.However,existing methods for producing DFSC sheets lack a comprehensive...BACKGROUND Dental follicle stem cell(DFSC)sheets demonstrate strong extracellular secretion capabilities and efficacy in periodontal regeneration.However,existing methods for producing DFSC sheets lack a comprehensive discussion on the most efficient and cost-effective approaches at the good manufacturing practice(GMP)level.AIM To investigate the culture condition of GMP-compliant DFSC sheets and to compare the properties of DFSC sheets and cell suspensions.METHODS This study explored the optimal conditions for culturing GMP-compliant DFSC sheets,focusing on four key factors:Cell passage,cell concentration,L-ascorbic acid content,and culture duration.We evaluated the characteristics of the cell sheets under varying culture conditions,including cell viability,cell count,appearance,osteogenesis,chondrogenesis,odontogenesis,aging,relative telomere length,and extracellular matrix secretion.A comparison was also made between the periodontal regeneration,osteogenesis,and paracrine capacity of cell sheets cultured under optimal conditions and those of the cell suspensions.RESULTS The GMP-compliant DFSC sheets cultured from passage 4 cells exhibited the highest viability(≥99%,P<0.05)and optimal osteogenic differentiation capacity(optical density≥0.126,P<0.05).When cultured for 10 days,DFSC sheets demonstrated maximal expression of osteogenic,chondrogenic and periostin genes[alkaline phosphatase,Runt-related transcription factor 2,collagen type I,osteopontin,cartilage associated protein,and PERIOSTN(P<0.001);osteocalcin(P<0.01)].Concurrently,they showed the lowest senescent cell count(P<0.01)with no progression to late-stage senescence.At a seeding density of 2500 cells/cm^(2),GMP-compliant DFSC sheets achieved better osteogenic differentiation(P<0.01)and maximal osteogenic,chondrogenic and periostin gene expression(P<0.001),coupled with the highest hydroxyproline secretion(P<0.001)and moderate sulfated glycosaminoglycan production.No statistically significant difference in senescent cell count was observed compared to DFSC sheets at a seeding density of 5000 cells/cm^(2).Supplementation with 25μg/mL L-ascorbic acid significantly enhanced osteogenic gene expression(P<0.001)and elevated hydroxyproline(P<0.01)and sulfated glycosaminoglycan secretion to high ranges.Compared with the cell suspension,the cell sheet demonstrated improved osteogenic,paracrine,and periodontal regenerative capacities in Sprague-Dawley rats.The optimized DFSC sheets demonstrated significantly higher levels of vascular endothelial growth factor and angiopoietin-1(P<0.001)compared to DFSC suspensions,along with enhanced osteogenic induction outcomes(optical density=0.1333±0.01270 vs 0.1007±0.0005774 in suspensions,P<0.05).Following implantation into the rat periodontal defect model,micro-computed tomography analysis revealed superior bone regeneration metrics in the cell sheet group compared to both the cell suspension group and control group(percent bone volume,trabecular thickness,trabecular number),while trabecular spacing exhibited an inverse pattern.CONCLUSION Optimized DFSC sheets cultured under the identified conditions outperform DFSC suspensions.This study contributes to the industrial-scale production of DFSC sheets and establishes a foundation for cell therapy applications.展开更多
This study investigates the effects of the ultrasonic surface rolling process(USRP)on the surface microstructure,texture,and wear behavior of commercial AZ31 magnesium alloy sheet.The application of USRP induces a dep...This study investigates the effects of the ultrasonic surface rolling process(USRP)on the surface microstructure,texture,and wear behavior of commercial AZ31 magnesium alloy sheet.The application of USRP induces a depth-dependent gradient microstructure characterized by a gradual transition from fine-grained surface layers to coarser-grained regions.Severe plastic deformation at the surface significantly enhances surface microhardness,with values increasing from 63.8 HV in the untreated specimen to 132.9 HV after USRP-4 passes.The thickness of the plastic deformation layer exhibits process-dependent behavior,growing from 200μm(two passes)to 250μm(four passes).Wear test results indicate that the wear resistance of the material is significantly enhanced after USRP treatment.This improvement is primarily attributed to the combined effects of the following factors:surface grain refinement,the role of dislocation-induced twinning,increased hardness,the formation of nanoscale secondary phases,introduction of residual compressive stresses,weakened surface texture,and reduced surface roughness.Notably,both friction coefficients and wear volumes show a direct dependence on the number of rolling passes.This study systematically elucidates the underlying mechanisms linking USRP-induced microstructural evolution to enhanced wear performance,providing critical insights for optimizing surface engineering strategies in magnesium alloys.展开更多
Bending is a crucial deformation process in metal sheet forming.In this study,the microstructural evolution of a highly ductile Mg–Er–Zr alloy sheet was examined in various bending regions under different bending st...Bending is a crucial deformation process in metal sheet forming.In this study,the microstructural evolution of a highly ductile Mg–Er–Zr alloy sheet was examined in various bending regions under different bending strains using electron backscatter diffraction and optical microscopy.The results show that the Mg–Er–Zr extruded sheet has excellent bending properties,with a failure bending strain of 39.3%,bending yield strength,and ultimate bending strength of 75.1 MPa and 250.5 MPa,respectively.The exceptional bending properties of the Mg–Er–Zr extruded sheets are primarily due to their fine grain size and the formation of rare-earth(RE)textures resulting from Er addition.Specifically,the in-grain misorientation axes(IGMA)and the twinning behaviors in various regions of the specimen during bending were thoroughly analyzed.Due to the polarity of the tensile twins and their low activation stress,a significant number of tensile twins are activated in the compression zone to regulate plastic deformation.The addition of Er weakens the basal texture of the sheet and reduces the critical resolved shear stress difference between non-basal slip and basal slip.Consequently,in the tensile zone,the basal and non-basal slips co-operate to coordinate the plastic deformation,effectively impeding crack initiation and propagation,and thereby enhancing the bending toughness of the Mg–Er–Zr sheet.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.52075347,51575364)and the Natural Science Foundation of Liaoning Provincial(No.2022-MS-295)。
文摘In order to solve the problem of poor formability caused by different materials and properties in the process of tailor-welded sheets forming,a forming method was proposed to change the stress state of tailor-welded sheets by covering the tailor-welded sheets with better plastic properties overlapping sheets.At the same time,the interface friction effect between the overlapping and tailor-welded sheets was utilized to control the stress magnitude and further improve the formability and quality of the tailor-welded sheets.In this work,the bulging process of the tailor-welded overlapping sheets was taken as the research object.Aluminum alloy tailor-welded overlapping sheets bulging specimens were studied by a combination of finite element analysis and experimental verification.The results show that the appropriate use of interface friction between tailor-welded and overlapping sheets can improve the formability of tailor-welded sheets and control the flow of weld seam to improve the forming quality.When increasing the interface friction coefficient on the side of tailor-welded sheets with higher strength and decreasing that on the side of tailor-welded sheets with lower strength,the deformation of the tailor-welded sheets are more uniform,the offset of the weld seam is minimal,the limit bulging height is maximal,and the forming quality is optimal.
基金Project(4013311)supported by the National Science Foundation of Iran(INSF)。
文摘This article examines the influence of annealing temperature on fracture toughness and forming limit curves of dissimilar aluminum/silver sheets.In the cold roll bonding process,after brushing and acid washing,the prepared surfaces are placed on top of each other and by rolling with reduction more than 50%,the bonding between layers is established.In this research,the roll bonding process was done at room temperature,without the use of lubricants and with a 70%thickness reduction.Then,the final thickness of the Ag/Al bilayer sheet reached 350μm by several stages of cold rolling.Before cold rolling,it should be noted that to decrease the hardness created due to plastic deformation,the roll-bonded samples were subjected to annealing heat treatment at 400℃for 90 min.Thus,the final samples were annealed at 200,300 and 400℃for 90 min and cooled in a furnace to examine the annealing temperature effects.The uniaxial tensile and microhardness tests measured mechanical properties.Also,to investigate the fracture mechanism,the fractography of the cross-section was examined by scanning electron microscope(SEM).To evaluate the formability of Ag/Al bilayer sheets,forming limit curves were obtained experimentally through the Nakazima test.The resistance of composites to failure due to cracking was also investigated by fracture toughness.The results showed that annealing increases the elongation and formability of the Ag/Al bilayer sheet while reduces the ultimate tensile strength and fracture toughness.However,the changing trend is not the same at different temperatures,and according to the results,the most significant effect is obtained at 300℃and aluminum layers.It was also determined that by increasing annealing temperature,the fracture mechanism from shear ductile with small and shallow dimples becomes ductile with deep cavities.
基金the National Natural Science Founda-tion of China(NSFC,Grant No.42174181)and the Key Research Program of Frontier Sciences,CAS(Grant No.QYZDJ-SSW-DQC010).
文摘The formation of an embedded electron current sheet within the magnetotail plasma sheet has been poorly understood.In this article,we present an electron current layer detected at the edge of the magnetotail plasma sheet.The ions were demagnetized inside the electron current layer,but the electrons were still frozen in with the magnetic field line.Thus,this decoupling of ions and electrons gave rise to a strong Hall electric field,which could be the reason for the formation of the embedded thin current layer.The magnetized electrons,the absence of the nongyrotropic electron distribution,and negligible energy dissipation in the layer indicate that magnetic reconnection had not been triggered within the embedded thin current layer.The highly asymmetric plasma on the two sides of the current layer and low magnetic shear across it could suppress magnetic reconnection.The observations indicate that the embedded electric current layer,probably generated by the Hall electric field,even down to electron scale,is not a sufficient condition for magnetic reconnection.
基金supported by PoSAddive–Powder Sheet Additive Manufacturing(co-funded by EIT Raw Materials,Grant No.22021)the AML in Trinity College Dublin.EIT Raw Materials is supported by EIT,a body of the European Union.
文摘A novel laser-based additive manufacturing approach of metal additive manufacturing using powder sheets(MAPS)has been introduced recently.The method utilizes polymer-bound powder sheets for metal AM as a feedstock,instead of loose powders.Conventional laser beam powder bed fusion(LPBF)additive manufacturing(AM)is among the most widespread 3D printing technologies.However,LPBF faces challenges related to safety and the impracticality of changing materials due to its reliance on loose powders.Thus,MAPS demonstrates the capability to overcome the limitations of LPBF by offering enhanced safety and the ability to print multi-material structures without the risk of material cross-contamination.As a part of developing processes,we investigate the effects of polymeric binder content on the printability and microstructural characteristics of MAPS-printed stainless steel 316 L.The results indicate that the average layer thickness of solidified material improves as the scanning speed decreases from 1000 mm/s to 50 mm/s across three different polymeric binder contents:10 wt%,20 wt%,and 30 wt%PCL.Additionally,a higher polymeric binder content(i.e.20 wt%and 30 wt%)in the powder sheets reduces the likelihood of crack formation.Electron backscatter diffraction(EBSD)analysis reveals that an increase in scanning speed promotes the formation of more equiaxed grains,while an increase in polymer content results in a reduction in grain size.These findings provide valuable insights into optimizing MAPS configurations for enhanced productivity and functionality in metal component manufacturing.
基金financially supported by the National Natural Science Foundation of China (No. 52004164)the Funding Program of Science and Technology Department of Liaoning Province, China (No. 2023-MSLH-249)the Funding Program of Education Department of Liaoning P rovince, China (No. LMGD2023018)。
文摘Fe–Ga sheets with large magnetostriction are required for improving the conversion efficiency under the ultra-high frequencymagnetic field. Trace Tb element doping can simultaneously improve the magnetostriction and ductility of Fe–Ga alloy. However, the im-pact of trace Tb doping on the microstructure and magnetostriction of Fe–Ga thin sheets is an open question. In this paper, the effects oftrace Tb addition on the secondary recrystallization and magnetostriction of Fe–Ga thin sheets are systematically studied by comparing thecharacteristics evolution of precipitation, texture, and nanoinclusions. The results indicate that trace Tb addition accelerates the secondaryrecrystallization of Goss texture due to the combined action of the bimodal size distributed precipitates, smaller grains, and more HEGBsin primary recrystallization. After quenching at 900℃, the magnetostriction value in 0.07 at %Tb-doped Fe_(81)Ga_(19) thin sheets increases by 30% to that of Fe_(81)Ga_(19) thin sheets. The increase in magnetostriction is attributed to the decrease in the number of Tb-rich precipitates andthe higher density of the nanometer-sized modified-D0_(3) inclusions induced by the dissolving of trace Tb elements after quenching. Theseresults demonstrate a simple and efficient approach for preparing Fe–Ga thin sheets with a large magnetostrictive coefficient by a combin-ation of trace RE element addition and conventional rolling method.
文摘This study focuses on the risks associated with the on-balance sheet recognition of data resources.At the legal level,disputes over ownership often arise due to unclear data property rights,while privacy protection,cybersecurity,and cross-border data flows create additional compliance challenges.In terms of recognition,the subjectivity of traditional valuation methods,the lack of active markets,and the rapid depreciation of data value caused by technological iteration hinder reliable measurement.With respect to disclosure,organizations face a dilemma between transparency and confidentiality.Collectively,these issues exacerbate audit risks.It is therefore imperative to establish an appropriate legal,accounting,and auditing framework to mitigate such risks and remove barriers to the proper recognition of data assets on balance sheets.
基金financially supported by the National Natural Science Foundation of China(Nos.52071036,U2037601)the Guangdong Major Project of Basic and Applied Basic Research,China(No.2020B0301030006)+1 种基金the Independent Research Project of State Key Laboratory of Mechanical Transmissions,China(Nos.SKLMT-ZZKT-2022Z01,SKLMT-ZZKT-2022M12)the Chongqing Science and Technology Commission,China(No.CSTB2022TIAD-KPX0021)。
文摘Edge cracking is one of the most serious problems in the rolling process of magnesium alloy sheets,which limits its application.In this work,the edge cracking behavior of different initial AZ31 alloy sheets,including as-cast(AC),as-rolled(AR)and as-extruded(AE),was systematically investigated and compared under the online heating rolling(O-LHR)process with a single-pass reduction of 50% at 250℃.The results show that both AC and AR sheets exhibit severe edge cracking behavior after the O-LHR.Among them,the AR sheet exhibits the severest edge cracking behavior on the rolling plane(RD-TD)and longitudinal section(RD-ND),which is attributed to the strong basal texture and extremely uneven microstructure with shear bands.While no visible edge crack appears in the AE rolled sheet,which is mainly related to the tilted texture and the more dynamic recrystallization during rolling process.Moreover,it is also found that the micro-cracks of the AC rolled sheet are mainly generated in the local fine-grained area and the twins where recrystallization occurs.In the AR rolled sheet,micro-cracks mainly develop inside the shear bands.Meanwhile,the micro-crack initiation mechanism of AC and AR rolled sheets was also discussed.
基金Project(52005362) supported by the National Natural Science Foundation of ChinaProjects(202303021221005,202303021211045) supported by the Natural Science Foundation of Shanxi Province,China+1 种基金Project(202402003) supported by the Patent Commercialization Program of Shanxi Province,ChinaProject supported by the Key Research and Development Plan of Xinzhou City,China。
文摘The deformation behavior of hot-rolled AZ31 magnesium(Mg)alloy sheet was analyzed when subjected to uniaxial tension along its normal direction at temperatures ranging from 100 to 400℃and strain rates ranging from 0.5 to 100 mm/min.Based on the stress−strain curves and the dynamic material model,the hot processing map was established,which demonstrates that the power dissipation factor(η)is the most sensitive to strain rate at 400℃via absorption of dislocations.At 400℃,sample at 0.5 mm/min possessesηof 0.89 because of its lower kernel average misorientation(KAM)value of 0.51,while sample at 100 mm/min possessesηof 0.46 with a higher KAM value of 1.147.In addition,the flow stress presents a slight decrease of 25.94 MPa at 10 mm/min compared to that at 100 mm/min and 100℃.The reasons are twofold:a special~34°texture component during 100℃-100 mm/min favoring the activation of basal slip,and dynamic recrystallization(DRX)also providing softening effect to some extent by absorbing dislocations.Difference in activation of basal slip among twin laminas during 100℃-100 mm/min results in deformation inhomogeneity within the grains,which generates stress that helps matrix grains tilt to a direction favorable to basal slip,forming the special~34°texture component.
基金supported by the following funding sources:Ministry of Education-Singapore MOE2019-T2-2-094 Ministry of Education-Singapore Tier I R-397-000-327-114 ScienceTechnology Project of Jiangsu Province(Grant No.BZ2022056)Biomedical and Health Technology Platform,National University of Singapore(Suzhou)Research Institute.
文摘Microcirculation imaging is crucial in understanding the function and health of various tissues and organs.However,conventional imaging methods suffer from fluorescence label dependency,lack of depth resolution,and quantification inaccuracy.Here,we report a light-sheet dynamic light-scattering imaging(LSHDSI)system to overcome these shortcomings.LSH-DSI utilizes selected plane illumination for an optical sectioning,while a time-frequency analysis method retrieves blood flow velocity estimates from dynamic changes in the detected light intensity.We have performed imaging experiments with zebrafish embryos to obtain angiographs from the trunk and head regions.The results show that LSH-DSI can capture label-free tomographic images of microvasculature and three-dimensional quantitative maps of local blood flow velocities.
基金sponsored by Natural Science Research Project of Anhui Educational Committee(GrantNo.2022AH050810),NationalNatural Science Foundation of China(GrantNos.42402276,41972286,42072309,42102329)State Key Laboratory of Precision Blasting and Hubei Key Laboratory of Blasting Engineering,Jianghan University(No.PBSKL2023A1)the Open Fund of National Center for International Research on Deep Earth Drilling and Resource Development(No.DEDRD-2023-02).
文摘During the construction of bank slopes involving pile driving,ensuring slope stability is crucial.This requires the design of appropriate support systems and a thorough evaluation of the failure mechanisms of pile structures under dynamic loading conditions.Based on the Huarong Coal Wharf project,various support schemes are analyzed using numerical simulation methods to calculate and compare slope stability coefficients.The optimal scheme is then identified.Under the selected support scheme,a numerical model of double-row suspended steel sheet piles is developed to investigate the dynamic response of the pile structures under pile driving loads.A time-history analysis is performed to assess the slope’s dynamic stability.The results show that the maximum displacements of the upper and lower steel sheet pile rows are 2.51 and 3.14 cm,respectively.The maximum principal stresses remain below 20 MPa in both rows,while the maximum von Mises stresses are 20.85 MPa for the upper row and 25.40 MPa for the lower row.The dominant frequencies of the steel sheet pile structures fall between 30 and 35 Hz,with a frequency bandwidth ranging from 0 to 500 Hz.The stability coefficient of the pile structures varies over time during the pile driving process,ultimately reaching a value of 1.26—exceeding the required safety threshold.This research provides practical guidance for designing support systems in wharf piling projects and offers a reliable basis for evaluating the safety performance of steel sheet piles in bank slopes.
基金the financial support received from the UK Engineering and Physical Sciences Research Council(EPSRC)through project grants EP/W010089/1 and EP/T005254/1.
文摘With the generation of both localised thermal and vibration in incremental sheet forming(ISF)by novel tool designs,rotational vibration assisted ISF(RV-ISF)can achieve significant force reduction and material softening.However,the combined thermal and vibration softening in RV-ISF is unclear.By evaluating the similarities and differences of friction stir ISF(FS-ISF)and RV-ISF,this study develops a novel approach to decouple and quantify the thermal and vibration softening effects in RV-ISF of AZ31B-H24,providing new insights into underlying thermal and vibration softening mechanism.Experimental results reveal that in RV-ISF of AZ31B-H24 the thermal softening due to frictional heating dominates with 45∼65%of softening,while the vibration effect only contributes up to 15%of softening,from the conventional ISF,depending on the tool designs and tool rotational speed.The double-offset tool(T2)produces greater vibration softening than the three-groove tool(T3)owing to the higher vibration amplitude of the T2 tool.An increase in tool rotational speed primarily enhances thermal softening with only marginal changes to the vibration effect.Microstructural analysis suggests that with average grain size of 0.94μm at the top layer,RV-ISF with T3 and 3000 rpm is more effective for microstructure refinement than that by FS-ISF,especially on the tool-sheet contact surface,which confirms the occurrence of surface shearing.This refinement is a result of the reduced recrystallisation degree,71.8%at the top bottom layer.Compared with FS-ISF,RV-ISF can lead to not only higher geometrically necessary dislocation density,but also higher fraction of low-angle grain boundaries,indicating that softening mechanism due to localised vibration effect is resulted from the enhanced rearrangement and annihilation of dislocations.These findings contribute to new understanding of the thermal and vibration softening effects in RV-ISF of AZ31B-H24 and offer a theoretical foundation for the tool design and process optimisation.
文摘The objective of this work is to investigate the dynamics of a self-propelled undulating sheet in a non-Newtonian electrolyte solution inside a wavy channel under the electroosmotic effect.The electrolyte solution,which is non-Newtonian,is modeled as a Carreau-Yasuda fluid.The flow generated by a combination of an undulating sheet and electroosmotic effect is obtained by solving the continuity and momentum equations.The electroosmotic body force term is derived using the Poisson-Boltzmann equation for the electric potential.A fourth-order ordinary differential equation for the stream function is solved under the Stokes flow regime.The dynamics of the undulating sheet’s speed and the energy dissipation it,are investigated.The combined effects of electroosmosis and the viscoelastic properties of the ambient fluid on the undulating sheet are discussed.
基金the National Key R&D Program of China(No.2023YFB3407003)the National Natural Science Foundation of China(No.52375378).
文摘An analytical model for contact area and contact stress considering the loading history in incremental sheet forming(ISF)was established.Then,by integrating with the directional characteristics of friction force and horizontal force in the process,a friction test method reflecting the forming characteristics of ISF was proposed.Friction coefficients during the forming processes of parts with different wall angles were measured under various plane curves,process paths,and lubrication conditions.Furthermore,the accuracy of the analytical model,as well as the measured friction coefficients and their variation trends,was verified through comparative analysis with experimental results,simulation data,and outcomes from other existing models.The results indicate that the influence of the plane curve characteristics and process paths of parts on the friction condition is not significant.Under the lubrication conditions of L-HM46 oil,MoS_(2)grease,graphite powder,and dry friction,the friction coefficient shows a gradually increasing trend.Notably,when the wall angle is≤40°,the friction coefficient remains relatively constant;however,when the wall angle exceeds 40°,the friction coefficient increases progressively.
基金supported by the National Key Research and Development Program of China under grant number 2023YFC2809103the Fundamental Research Funds for the Central Universities under grant numbers 2042022kf1204, 2042022kf1069, 2042023gf0012, 2042022dx0001+1 种基金the Hubei Provincial Natural Science Foundation of China under grant number 2022CFB081the State Key Laboratory of Geodesy and Earth's Dynamics, Innovation Academy for Precision Measurement Science and Technology under grant number SKLGED2023-2-6
文摘Elevation change monitoring of the Antarctic ice sheet has been a key issue in global change research.Satellite altimetry has been proven to be effective in detecting ice sheet variations. With the development of ICESat-2, many elevation observations can be used to derive elevation changes. However, the large amount of multitemporal data may include anomalous data points, increasing the uncertainty of the results. In this work, we improved the traditional repeat track method by introducing the Institute of Geodesy and Geophysics Ⅲ(IGGⅢ) method to obtain high-accuracy estimates of elevation change. The improved method was applied to analyze elevation changes along the transect from Zhongshan Station to Dome A in East Antarctica via ICESat-2 satellite altimetry data. The results show that the improved and traditional methods yield consistent numerical and spatial elevation change distributions. The elevation change calculated via the traditional method is 0.033 ± 0.131 m/yr, whereas the elevation change estimated via the IGGⅢ robust estimation method is 0.033 ± 0.109 m/yr from March 2019 to December 2021.In terms of spatial distribution, elevation changes in inland areas remain close to equilibrium, whereas regions with steeper ice sheet margins exhibit positive accumulation trends in elevation changes. The improved method reduces the standard error of the adjustment function from 0.975 to 0.691 m/yr. The improvement is particularly remarkable in the area between 72°S and 77°S. The results demonstrate that the IGGⅢ method effectively reduces errors caused by the inclusion of anomalous data and maintains the high data utilization rate of repeat-orbit methods.
基金supported by the National Natural Science Foundation of China(52474419,52374395)Natural Science Foundation of Shanxi Province(20210302123135,202303021221143)+3 种基金Scientific and Technological Achievements Transformation Guidance Special Project of Shanxi Province(202104021301022,202204021301009)Central Government Guided Local Science and Technology development projects(YDZJSX20231B003,YDZJSX2021A010)The Ministry of Science and Higher Education of the Russian Federation for financial support under the Megagrant(No.075-15-2022-1133)the National Research Foundation(NRF)grant funded by the Ministry of Science and ICT(2015R1A2A1A01006795)of Korea through the Research Institute of Advanced.
文摘In this work,AZ31B extruded sheets with mixed-grain microstructures were prepared through extrusion.Samples of mixed-grain microstructure with different morphologies were selected from the AZ31B extruded sheets(referred to as M1 and M2 samples,respectively).The creep tests were performed on these samples at the temperature range of 150-200℃,and the stress level range of 50-100 MPa.The creep properties and fracture behavior of AZ31 extruded sheets with mixed-grain microstructures were studied.Results showed that the creep properties of the M2 sample always outperformed that of the M1 sample and M1 and M2 samples’creep was dominated by dislocation movement.The creep rate of M2 samples(1.5×10^(-7)±1.1×10^(-10) s^(-1))is an order of magnitude lower than that of M1 samples(4.8×10^(-6)±8.1×10^(-10) s^(-1))at 200℃under 50 MPa The high activity of basal slip and softening mechanism in the M1 sample significantly accelerated creep,resulting in a relatively high creep rate.Moreover,the stress concentration within the M1 sample caused by deformation incompatibility,increased the initiation and propagation of voids,ultimately leading to fracture and poorer creep performance.However,the numerous<10µm fine grains surrounding deformed coarse grains in the M2 sample facilitated better coordination of deformation through dislocation slip,effectively slowing down the initiation of voids during the creep process.Meanwhile,the strain was uniformly distributed within each grain,mitigating stress concentration,inhibiting voids propagation,and contributing to the superior creep resistance of the M2 sample.
基金Project(52174362)supported by the National Natural Science Foundation of ChinaProject(2023JJ10020)supported by the Natural Science Foundation of Hunan Province,China+2 种基金Project(2024RC7002)supported by the Science and Technology Innovation Program of Hunan Province,ChinaProject(2024CY2-GJHX-71)supported by the Shaanxi Provincial Key R&D Program,ChinaProject supported by the Yancheng“Talent Plan of Yellow Sea Pearl”for Leading Talent Project,China。
文摘In this study,AZ31 Mg alloy sheets were processed by a severe plastic deformation(SPD)technique called forging-bending repeated deformation(FBRD).The effect on the microstructure and microhardness of AZ31 Mg alloy through FBRD was investigated with increasing temperature treatment and a 90°cross route.The results reveal that the effective strain increases with the number of passes.The flow uniformity is effectively enhanced due to alterations in shear deformation direction.After four passes of deformation,the average grain size is refined by 79.3%compared to the initial specimen.The grain refinement mechanism predominantly originates from the synergistic effects of discontinuous dynamic recrystallization(DDRX),continuous dynamic recrystallization(CDRX),and twinning-induced recrystallization(TDRX).The formation of{1012}extension twins(ET)significantly contributes to coarse grain subdivision and plastic deformation coordinated.Furthermore,pyramidal<c+a>slip activation effectively enhances the plasticity of Mg alloys.By post four-pass processing,the alloy exhibits a microhardness of 81.9HV,primarily governed by fine grain strengthening and dislocation strengthening mechanisms.
基金the support of the Key Research and Development Program of Shaanxi Province,China(No.2021GXLH-Z-049)。
文摘The influence of geometric configuration on the friction characteristics during incremental sheet forming of AA5052 was analyzed by integrating surface morphology and its characteristic parameters,along with plastic strain,contact pressure,and area.The interface promotes lubrication and support when wall angles were≤40°,a 0.5 mm-thin sheet was used,and a 10 mm-large tool radius was employed.This mainly results in micro-plowing and plastic extrusion flow,leading to lower friction coefficient.However,when wall angles exceed 40°,significant plastic strain roughening occurs,leading to inadequate lubrication on the newly formed surface.Increased sheet thickness and decreased tool radius elevate contact pressure.These actions trigger micro-cutting and adhesion,potentially leading to localized scuffing and dimple tears,and higher friction coefficient.The friction mechanisms remain unaffected by the part’s plane curve features.As the forming process progresses,abrasive wear intensifies,and surface morphology evolves unfavorably for lubrication and friction reduction.
基金Supported by National Key Research and Development Program of China,No.2021YFA1100600 and No.2022YFA1104400.
文摘BACKGROUND Dental follicle stem cell(DFSC)sheets demonstrate strong extracellular secretion capabilities and efficacy in periodontal regeneration.However,existing methods for producing DFSC sheets lack a comprehensive discussion on the most efficient and cost-effective approaches at the good manufacturing practice(GMP)level.AIM To investigate the culture condition of GMP-compliant DFSC sheets and to compare the properties of DFSC sheets and cell suspensions.METHODS This study explored the optimal conditions for culturing GMP-compliant DFSC sheets,focusing on four key factors:Cell passage,cell concentration,L-ascorbic acid content,and culture duration.We evaluated the characteristics of the cell sheets under varying culture conditions,including cell viability,cell count,appearance,osteogenesis,chondrogenesis,odontogenesis,aging,relative telomere length,and extracellular matrix secretion.A comparison was also made between the periodontal regeneration,osteogenesis,and paracrine capacity of cell sheets cultured under optimal conditions and those of the cell suspensions.RESULTS The GMP-compliant DFSC sheets cultured from passage 4 cells exhibited the highest viability(≥99%,P<0.05)and optimal osteogenic differentiation capacity(optical density≥0.126,P<0.05).When cultured for 10 days,DFSC sheets demonstrated maximal expression of osteogenic,chondrogenic and periostin genes[alkaline phosphatase,Runt-related transcription factor 2,collagen type I,osteopontin,cartilage associated protein,and PERIOSTN(P<0.001);osteocalcin(P<0.01)].Concurrently,they showed the lowest senescent cell count(P<0.01)with no progression to late-stage senescence.At a seeding density of 2500 cells/cm^(2),GMP-compliant DFSC sheets achieved better osteogenic differentiation(P<0.01)and maximal osteogenic,chondrogenic and periostin gene expression(P<0.001),coupled with the highest hydroxyproline secretion(P<0.001)and moderate sulfated glycosaminoglycan production.No statistically significant difference in senescent cell count was observed compared to DFSC sheets at a seeding density of 5000 cells/cm^(2).Supplementation with 25μg/mL L-ascorbic acid significantly enhanced osteogenic gene expression(P<0.001)and elevated hydroxyproline(P<0.01)and sulfated glycosaminoglycan secretion to high ranges.Compared with the cell suspension,the cell sheet demonstrated improved osteogenic,paracrine,and periodontal regenerative capacities in Sprague-Dawley rats.The optimized DFSC sheets demonstrated significantly higher levels of vascular endothelial growth factor and angiopoietin-1(P<0.001)compared to DFSC suspensions,along with enhanced osteogenic induction outcomes(optical density=0.1333±0.01270 vs 0.1007±0.0005774 in suspensions,P<0.05).Following implantation into the rat periodontal defect model,micro-computed tomography analysis revealed superior bone regeneration metrics in the cell sheet group compared to both the cell suspension group and control group(percent bone volume,trabecular thickness,trabecular number),while trabecular spacing exhibited an inverse pattern.CONCLUSION Optimized DFSC sheets cultured under the identified conditions outperform DFSC suspensions.This study contributes to the industrial-scale production of DFSC sheets and establishes a foundation for cell therapy applications.
基金supported by the National Natural Science Foundation of China(Nos.52271107 and 52301164)Natural Science Foundation of Shandong Province(No.ZR2021ME241)supported by Young Talent of Lifting engineering for Science and Technology in Shandong,China(SDAST2025 QTA034).
文摘This study investigates the effects of the ultrasonic surface rolling process(USRP)on the surface microstructure,texture,and wear behavior of commercial AZ31 magnesium alloy sheet.The application of USRP induces a depth-dependent gradient microstructure characterized by a gradual transition from fine-grained surface layers to coarser-grained regions.Severe plastic deformation at the surface significantly enhances surface microhardness,with values increasing from 63.8 HV in the untreated specimen to 132.9 HV after USRP-4 passes.The thickness of the plastic deformation layer exhibits process-dependent behavior,growing from 200μm(two passes)to 250μm(four passes).Wear test results indicate that the wear resistance of the material is significantly enhanced after USRP treatment.This improvement is primarily attributed to the combined effects of the following factors:surface grain refinement,the role of dislocation-induced twinning,increased hardness,the formation of nanoscale secondary phases,introduction of residual compressive stresses,weakened surface texture,and reduced surface roughness.Notably,both friction coefficients and wear volumes show a direct dependence on the number of rolling passes.This study systematically elucidates the underlying mechanisms linking USRP-induced microstructural evolution to enhanced wear performance,providing critical insights for optimizing surface engineering strategies in magnesium alloys.
基金supported by the National Natural Science Foundation of China(No.52071037).
文摘Bending is a crucial deformation process in metal sheet forming.In this study,the microstructural evolution of a highly ductile Mg–Er–Zr alloy sheet was examined in various bending regions under different bending strains using electron backscatter diffraction and optical microscopy.The results show that the Mg–Er–Zr extruded sheet has excellent bending properties,with a failure bending strain of 39.3%,bending yield strength,and ultimate bending strength of 75.1 MPa and 250.5 MPa,respectively.The exceptional bending properties of the Mg–Er–Zr extruded sheets are primarily due to their fine grain size and the formation of rare-earth(RE)textures resulting from Er addition.Specifically,the in-grain misorientation axes(IGMA)and the twinning behaviors in various regions of the specimen during bending were thoroughly analyzed.Due to the polarity of the tensile twins and their low activation stress,a significant number of tensile twins are activated in the compression zone to regulate plastic deformation.The addition of Er weakens the basal texture of the sheet and reduces the critical resolved shear stress difference between non-basal slip and basal slip.Consequently,in the tensile zone,the basal and non-basal slips co-operate to coordinate the plastic deformation,effectively impeding crack initiation and propagation,and thereby enhancing the bending toughness of the Mg–Er–Zr sheet.
