A new unified constitutive model was developed to predict the two-stage creep-aging(TSCA)behavior of Al-Zn-Mg-Cu alloys.The particular bimodal precipitation feature was analyzed and modeled by considering the primary ...A new unified constitutive model was developed to predict the two-stage creep-aging(TSCA)behavior of Al-Zn-Mg-Cu alloys.The particular bimodal precipitation feature was analyzed and modeled by considering the primary micro-variables evolution at different temperatures and their interaction.The dislocation density was incorporated into the model to capture the effect of creep deformation on precipitation.Quantitative transmission electron microscopy and experimental data obtained from a previous study were used to calibrate the model.Subsequently,the developed constitutive model was implemented in the finite element(FE)software ABAQUS via the user subroutines for TSCA process simulation and the springback prediction of an integral panel.A TSCA test was performed.The result shows that the maximum radius deviation between the formed plate and the simulation results is less than 0.4 mm,thus validating the effectiveness of the developed constitutive model and FE model.展开更多
The impacts of asymmetric rolling(ASR)and cold rolling(CR)on the creep-aging behavior of AA2219 alloys were revealed by creep deformation experiments,tensile tests,electron backscattered diffraction(EBSD)and transmiss...The impacts of asymmetric rolling(ASR)and cold rolling(CR)on the creep-aging behavior of AA2219 alloys were revealed by creep deformation experiments,tensile tests,electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM).The ASR specimens under creep stress condition of 1.2σ0.2(σ0.2 is the yield strength)displayed a 50%higher creep strain than the CR specimens.At a creep stress of 0.5σ0.2,the ASR specimens demonstrated remarkably mechanical properties,with a tensile strength of 525 MPa,a yield strength of 338 MPa,and an elongation of 15.2%.This enhancement can be ascribed to the effective grain refinement and promotion of recrystallization after ASR.Notably,ASR resulted in the formation of higher cube textures and a denser forest dislocation structure compared with CR.Additionally,ASR specimens demonstrated a higher density of dispersive,smallerθ′precipitates and larger average Taylor factors compared with CR specimens.展开更多
The influence of electropulsing on the creep behaviour,strength,and microstructure of an Al−Cu−Li alloy during creep ageing was investigated.Electropulsing assisted creep ageing(ECA)and conventional creep ageing(CCA)w...The influence of electropulsing on the creep behaviour,strength,and microstructure of an Al−Cu−Li alloy during creep ageing was investigated.Electropulsing assisted creep ageing(ECA)and conventional creep ageing(CCA)were carried out under various stress levels and time conditions.Applying electropulsing results in a noteworthy change of creep behaviour,including a variation in creep curves,an increased creep rate in early stage,and an improved creep strain.The ECA specimen experiences a shorter time to the peak strength,and an increase in elongation by~17.4% without loss of the peak-aged strength compared with CCA specimen.The ultrafine nano-size subgrains are observed to form under electropulsing,which can result in an increased creep strain by increasing grain-boundary sliding.The enhancement of both dislocation interactions and solute diffusion under electropulsing is considered as a primary cause of disappearance of a platform stage during early creep ageing.Some of T1 precipitates around the grain boundary are observed in the peak ECA sample,resulting in an occurrence of transgranular fracture,which is further responsible for an increased elongation of the ECA specimen.展开更多
A unified constitutive model is presented to predict the recently observed“multi-stage”creep behavior of Al−Li−S4 alloy.The corresponding microstructural variables related to the yield strength and creep deformation...A unified constitutive model is presented to predict the recently observed“multi-stage”creep behavior of Al−Li−S4 alloy.The corresponding microstructural variables related to the yield strength and creep deformation of the alloy during the creep ageing process,including dislocations and multiple precipitates,have been characterized in detail by X-ray diffraction(XRD)and transmission electron microscopy(TEM).For the yield strength,the model considers the multiphase strengthening behavior of the alloy based on strengthening mechanisms,which includes shearable T1 precipitate strengthening,non-shearable T1 precipitate strengthening andθ′precipitate strengthening.Based on creep deformation mechanism,the“multi-stage”creep behavior of the alloy is predicted by introducing the effects of interacting microstructural variables,including the radius of multiple precipitates,dislocation density and solute concentration,into the creep stress−strain model.It is concluded that the results calculated by the model are in a good agreement with the experimental data,which validates the proposed model.展开更多
The viscous damping coefficient （VDC） of hydraulic actuators is crucial for system modeling, control and dynamic characteristic analysis. Currently, the resear- ches on hydraulic actuators focus on behavior assessme...The viscous damping coefficient （VDC） of hydraulic actuators is crucial for system modeling, control and dynamic characteristic analysis. Currently, the resear- ches on hydraulic actuators focus on behavior assessment, promotion of control performance and efficiency. However, the estimation of the VDC is difficult due to a lack of study. Firstly, using two types of hydraulic cylinders, behaviors of the VDC are experimentally examined with velocities and pressure variations. For the tested plunger type hydraulic cylinder, the exponential model B = αν-β （α 〉 0, β 〉 0） or B = α1e-β1ν＋α2e-β2ν（α1, α2 〉 0, β1,β2 〉 0）, fits the relation between the VDC and velocities for a given pressure of chamber with high precision. The magnitude of the VDC decreases almost linearly under certain velocities when increasing the chamber pressure from 0.6 MPa to 6.0 MPa. Furthermore, the effects of the chamber pressures on the VDC of piston and plunge type hydraulic cylinders are different due to different sealing types. In order to investi- gate the VDC of a plunger type hydraulic actuator drasti- cally, a steady-state numerical model has been developed to describe the mechanism incorporating tandem seal lubrica- tion, back-up ring related friction behaviors and shear stress of fluid. It is shown that the simulated results of VDC agreewith the measured results with a good accuracy. The pro- posed method provides an instruction to predict the VDC in system modeling and analysis.展开更多
Adding numerous dislocations into metallic materials before the forming stage significantly enhances their deformability.However,this beneficial effect of dislocation defects may not have a simple monotonic relationsh...Adding numerous dislocations into metallic materials before the forming stage significantly enhances their deformability.However,this beneficial effect of dislocation defects may not have a simple monotonic relationship with increased dislocation density during electroplastic deformation.This is due to the complex interactions among the drifting electrons,dislocations and solute atoms.This study explores the effect of diverse initial dislocation densities on creep deformation during electrically aided creep aging of an aluminum-lithium alloy.Surprisingly,we discovered a threshold value for the dislocation density that affects electroplastic creep,i.e.,an enhanced effect from dislocations weakens when exceeding this density threshold(an anomalous response to creep).Microstructural data also reveal that such an anomalous response originates mainly from differences in various dislocation density-tailored configurations,which can influence the dislocation motions and precipitation kinetics of the strengthening T1precipitates under the same action of pulsed currents.This study provides important insights into the dislocation density-mediated electroplastic creep of an aluminum-lithium alloy.展开更多
The distribution of nuclei produced in the^(40)Ar+^(232)Th reaction has been studied at the gas-filled recoil separator(SHANS2)at the China Accelerator Facility for Superheavy Elements(CAFE2).The bombardment was carri...The distribution of nuclei produced in the^(40)Ar+^(232)Th reaction has been studied at the gas-filled recoil separator(SHANS2)at the China Accelerator Facility for Superheavy Elements(CAFE2).The bombardment was carried out at a beam energy of 205 MeV with the detection system installed at the focal plane.Forty-four isotopes heavier than 208Pb were observed.These isotopes were identified as the transfer reaction(or target-like)products,and their relative cross-sections were extracted.Based on the mass distribution of these products,we exclude the possibility that they were produced by fusion-fission reactions;thus,they may originate from quasi-fission of the^(40)Ar+^(232)Th reaction.展开更多
A new multi-detector array named HALIMA(Hybrid Array for LIfetime MeAsurement)has been developed at Lanzhou for nuclear structure studies in fission.The array comprises eight BGO-shielded High-Purity Germanium detecto...A new multi-detector array named HALIMA(Hybrid Array for LIfetime MeAsurement)has been developed at Lanzhou for nuclear structure studies in fission.The array comprises eight BGO-shielded High-Purity Germanium detectors and twenty fast Ce-doped Lanthanum Bromide[LaBr_(3)(Ce)]detectors shielded with CsI(Tl).HALIMA is further complemented by two ancillary detector systems:fission fragment(FF)detectors and β detectors.This configuration enables precise sub-nanosecond lifetime measurements using the fourfold FF/β-Ge-LaBr_(3)(Ce)-LaBr_(3)(Ce)coincidence technique.The performance and specifications of the detectors,associated electronics,and the data acquisition system are presented in detail.The advantage of FF selectivity is emphasized,which significantly enhances sensitivity to specific fission channels.Using this approach,the lifetimes of the nuclear excited states populated in the spontaneous fission of^(252)Cf were measured,showing good agreement with the established literature values.展开更多
基金supported by the National Key R&D Program of China(No.2021YFB3400900)the National Natural Science Foundation of China(Nos.52175373,52205435)+1 种基金Natural Science Foundation of Hunan Province,China(No.2022JJ40621)the Innovation Fund of National Commercial Aircraft Manufacturing Engineering Technology Center,China(No.COMACSFGS-2022-1875)。
文摘A new unified constitutive model was developed to predict the two-stage creep-aging(TSCA)behavior of Al-Zn-Mg-Cu alloys.The particular bimodal precipitation feature was analyzed and modeled by considering the primary micro-variables evolution at different temperatures and their interaction.The dislocation density was incorporated into the model to capture the effect of creep deformation on precipitation.Quantitative transmission electron microscopy and experimental data obtained from a previous study were used to calibrate the model.Subsequently,the developed constitutive model was implemented in the finite element(FE)software ABAQUS via the user subroutines for TSCA process simulation and the springback prediction of an integral panel.A TSCA test was performed.The result shows that the maximum radius deviation between the formed plate and the simulation results is less than 0.4 mm,thus validating the effectiveness of the developed constitutive model and FE model.
基金financial supports from the National Key Research and Development Program of China(No.2021YFB3400900)the National Natural Science Foundation of China(Nos.U22A20190,U2341273,52205435)+2 种基金the Natural Science Foundation of Hunan Province,China(No.2022JJ40621)the Science and Technology Innovation Program of Hunan Province,China(No.2020RC4001)the Project of State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University,China(No.ZZYJKT2022-07)。
文摘The impacts of asymmetric rolling(ASR)and cold rolling(CR)on the creep-aging behavior of AA2219 alloys were revealed by creep deformation experiments,tensile tests,electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM).The ASR specimens under creep stress condition of 1.2σ0.2(σ0.2 is the yield strength)displayed a 50%higher creep strain than the CR specimens.At a creep stress of 0.5σ0.2,the ASR specimens demonstrated remarkably mechanical properties,with a tensile strength of 525 MPa,a yield strength of 338 MPa,and an elongation of 15.2%.This enhancement can be ascribed to the effective grain refinement and promotion of recrystallization after ASR.Notably,ASR resulted in the formation of higher cube textures and a denser forest dislocation structure compared with CR.Additionally,ASR specimens demonstrated a higher density of dispersive,smallerθ′precipitates and larger average Taylor factors compared with CR specimens.
基金the financial supports by the National Key R&D Program of China(No.2017YFB0306300)the National Natural Science Foundation of China(Nos.51601060,51675538).
文摘The influence of electropulsing on the creep behaviour,strength,and microstructure of an Al−Cu−Li alloy during creep ageing was investigated.Electropulsing assisted creep ageing(ECA)and conventional creep ageing(CCA)were carried out under various stress levels and time conditions.Applying electropulsing results in a noteworthy change of creep behaviour,including a variation in creep curves,an increased creep rate in early stage,and an improved creep strain.The ECA specimen experiences a shorter time to the peak strength,and an increase in elongation by~17.4% without loss of the peak-aged strength compared with CCA specimen.The ultrafine nano-size subgrains are observed to form under electropulsing,which can result in an increased creep strain by increasing grain-boundary sliding.The enhancement of both dislocation interactions and solute diffusion under electropulsing is considered as a primary cause of disappearance of a platform stage during early creep ageing.Some of T1 precipitates around the grain boundary are observed in the peak ECA sample,resulting in an occurrence of transgranular fracture,which is further responsible for an increased elongation of the ECA specimen.
基金the National Key R&D Program of China(No.2017YFB0306300)the National Natural Science Foundation of China(Nos.51675538,51601060)+1 种基金the State Key Laboratory of High-performance Complex Manufacturing,China(No.ZZYJKT2018-18)the Fundamental Research Funds for the Central Universities of Central South University,China(No.2018zzts151).
文摘A unified constitutive model is presented to predict the recently observed“multi-stage”creep behavior of Al−Li−S4 alloy.The corresponding microstructural variables related to the yield strength and creep deformation of the alloy during the creep ageing process,including dislocations and multiple precipitates,have been characterized in detail by X-ray diffraction(XRD)and transmission electron microscopy(TEM).For the yield strength,the model considers the multiphase strengthening behavior of the alloy based on strengthening mechanisms,which includes shearable T1 precipitate strengthening,non-shearable T1 precipitate strengthening andθ′precipitate strengthening.Based on creep deformation mechanism,the“multi-stage”creep behavior of the alloy is predicted by introducing the effects of interacting microstructural variables,including the radius of multiple precipitates,dislocation density and solute concentration,into the creep stress−strain model.It is concluded that the results calculated by the model are in a good agreement with the experimental data,which validates the proposed model.
基金Supported by National Basic Research Development Program of China(Grant No.2011CB706802)Hunan Provincial Foundation for Postgraduate of China(Grant No.CX2013B062)Innovation Driven Program of Central South University of China(Grant No.2015CX002)
文摘The viscous damping coefficient （VDC） of hydraulic actuators is crucial for system modeling, control and dynamic characteristic analysis. Currently, the resear- ches on hydraulic actuators focus on behavior assessment, promotion of control performance and efficiency. However, the estimation of the VDC is difficult due to a lack of study. Firstly, using two types of hydraulic cylinders, behaviors of the VDC are experimentally examined with velocities and pressure variations. For the tested plunger type hydraulic cylinder, the exponential model B = αν-β （α 〉 0, β 〉 0） or B = α1e-β1ν＋α2e-β2ν（α1, α2 〉 0, β1,β2 〉 0）, fits the relation between the VDC and velocities for a given pressure of chamber with high precision. The magnitude of the VDC decreases almost linearly under certain velocities when increasing the chamber pressure from 0.6 MPa to 6.0 MPa. Furthermore, the effects of the chamber pressures on the VDC of piston and plunge type hydraulic cylinders are different due to different sealing types. In order to investi- gate the VDC of a plunger type hydraulic actuator drasti- cally, a steady-state numerical model has been developed to describe the mechanism incorporating tandem seal lubrica- tion, back-up ring related friction behaviors and shear stress of fluid. It is shown that the simulated results of VDC agreewith the measured results with a good accuracy. The pro- posed method provides an instruction to predict the VDC in system modeling and analysis.
基金financially supported by the National Natural Science Foundation of China(Nos.U22A20190 and 52274404)the National Key R&D Program of China(No.2021YFB3400903)。
文摘Adding numerous dislocations into metallic materials before the forming stage significantly enhances their deformability.However,this beneficial effect of dislocation defects may not have a simple monotonic relationship with increased dislocation density during electroplastic deformation.This is due to the complex interactions among the drifting electrons,dislocations and solute atoms.This study explores the effect of diverse initial dislocation densities on creep deformation during electrically aided creep aging of an aluminum-lithium alloy.Surprisingly,we discovered a threshold value for the dislocation density that affects electroplastic creep,i.e.,an enhanced effect from dislocations weakens when exceeding this density threshold(an anomalous response to creep).Microstructural data also reveal that such an anomalous response originates mainly from differences in various dislocation density-tailored configurations,which can influence the dislocation motions and precipitation kinetics of the strengthening T1precipitates under the same action of pulsed currents.This study provides important insights into the dislocation density-mediated electroplastic creep of an aluminum-lithium alloy.
基金Supported by the Gansu Key Project of Science and Technology(23ZDGA014)the National Key R&D Program of China(2023YFA1606500)+5 种基金the Guangdong Major Project of Basic and Applied Basic Research(2021B0301030006)the CAS Project for Young Scientists in Basic Research(YSBR-002)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2023439,2020409)the National Natural Science Foundation of China(12365016)the National Key Research and Development Program of China(2024YFE0110400,W2412040)the Natural Science Foundation of Guangxi(2023GXNSFAA026016)。
文摘The distribution of nuclei produced in the^(40)Ar+^(232)Th reaction has been studied at the gas-filled recoil separator(SHANS2)at the China Accelerator Facility for Superheavy Elements(CAFE2).The bombardment was carried out at a beam energy of 205 MeV with the detection system installed at the focal plane.Forty-four isotopes heavier than 208Pb were observed.These isotopes were identified as the transfer reaction(or target-like)products,and their relative cross-sections were extracted.Based on the mass distribution of these products,we exclude the possibility that they were produced by fusion-fission reactions;thus,they may originate from quasi-fission of the^(40)Ar+^(232)Th reaction.
基金supported by the National Natural Science Foundation of China(Nos.12275321,12121005,12475129,and 12335009)the Natural Science Foundation of Guangdong Province,China(No.2025A1515012112)+5 种基金the International Atomic Energy Agency Coordinated Research Project F41034(No.28649)the computational resources from Sun Yat-sen University the National Supercomputer Center in Guangzhouthe Open Project of Guangxi Key Laboratory of Nuclear Physics and Nuclear Technology(No.NLK2023-08)the Central Government Guidance Funds for Local Scientific and Technological Development,China(No.Guike ZY22096024)the Guangdong Major Project of Basic and Applied Basic Research(No.2021B0301030006)Young Scientists Fund of the National Natural Science Foundation of China(No.12405144)the National Key Research and Development Program(MOST 2022YFA1602304).
文摘A new multi-detector array named HALIMA(Hybrid Array for LIfetime MeAsurement)has been developed at Lanzhou for nuclear structure studies in fission.The array comprises eight BGO-shielded High-Purity Germanium detectors and twenty fast Ce-doped Lanthanum Bromide[LaBr_(3)(Ce)]detectors shielded with CsI(Tl).HALIMA is further complemented by two ancillary detector systems:fission fragment(FF)detectors and β detectors.This configuration enables precise sub-nanosecond lifetime measurements using the fourfold FF/β-Ge-LaBr_(3)(Ce)-LaBr_(3)(Ce)coincidence technique.The performance and specifications of the detectors,associated electronics,and the data acquisition system are presented in detail.The advantage of FF selectivity is emphasized,which significantly enhances sensitivity to specific fission channels.Using this approach,the lifetimes of the nuclear excited states populated in the spontaneous fission of^(252)Cf were measured,showing good agreement with the established literature values.
