Manipulating the expression of synaptic plasticity of neuromorphic devices provides fascinating opportunities to develop hardware platforms for artifi-cial intelligence.However,great efforts have been devoted to explo...Manipulating the expression of synaptic plasticity of neuromorphic devices provides fascinating opportunities to develop hardware platforms for artifi-cial intelligence.However,great efforts have been devoted to exploring biomimetic mechanisms of plasticity simulation in the last few years.Recent progress in various plasticity modulation techniques has pushed the research of synaptic electronics from static plasticity simulation to dynamic plasticity modulation,improving the accuracy of neuromorphic computing and providing strategies for implementing neuromorphic sensing functions.Herein,several fascinating strategies for synap-tic plasticity modulation through chemical techniques,device structure design,and physical signal sensing are reviewed.For chemical techniques,the underly-ing mechanisms for the modification of functional materials were clarified and its effect on the expression of synaptic plasticity was also highlighted.Based on device structure design,the reconfigurable operation of neuromorphic devices was well demonstrated to achieve programmable neuromorphic functions.Besides,integrating the sensory units with neuromorphic processing circuits paved a new way to achieve human-like intelligent perception under the modulation of physical signals such as light,strain,and temperature.Finally,considering that the relevant technology is still in the basic exploration stage,some prospects or development suggestions are put forward to promote the development of neuromorphic devices.展开更多
Network fault diagnosis methods play a vital role in maintaining network service quality and enhancing user experience as an integral component of intelligent network management.Considering the unique characteristics ...Network fault diagnosis methods play a vital role in maintaining network service quality and enhancing user experience as an integral component of intelligent network management.Considering the unique characteristics of edge networks,such as limited resources,complex network faults,and the need for high real-time performance,enhancing and optimizing existing network fault diagnosis methods is necessary.Therefore,this paper proposes the lightweight edge-side fault diagnosis approach based on a spiking neural network(LSNN).Firstly,we use the Izhikevich neurons model to replace the Leaky Integrate and Fire(LIF)neurons model in the LSNN model.Izhikevich neurons inherit the simplicity of LIF neurons but also possess richer behavioral characteristics and flexibility to handle diverse data inputs.Inspired by Fast Spiking Interneurons(FSIs)with a high-frequency firing pattern,we use the parameters of FSIs.Secondly,inspired by the connection mode based on spiking dynamics in the basal ganglia(BG)area of the brain,we propose the pruning approach based on the FSIs of the BG in LSNN to improve computational efficiency and reduce the demand for computing resources and energy consumption.Furthermore,we propose a multiple iterative Dynamic Spike Timing Dependent Plasticity(DSTDP)algorithm to enhance the accuracy of the LSNN model.Experiments on two server fault datasets demonstrate significant precision,recall,and F1 improvements across three diagnosis dimensions.Simultaneously,lightweight indicators such as Params and FLOPs significantly reduced,showcasing the LSNN’s advanced performance and model efficiency.To conclude,experiment results on a pair of datasets indicate that the LSNN model surpasses traditional models and achieves cutting-edge outcomes in network fault diagnosis tasks.展开更多
Based on energy equilibrium,a new procedure called the Membrane Factor Method is devel- oped to analyze the dynamic plastic response of plates with deflections in the range where both bending mo- ments and membrane fo...Based on energy equilibrium,a new procedure called the Membrane Factor Method is devel- oped to analyze the dynamic plastic response of plates with deflections in the range where both bending mo- ments and membrane forces are important.The final deflection of a simply -supported circular rigid-plastic plate loaded by a uniformly distributed impulse is obtained.In comparison with other approximate solutions, the present results are found to be simpler and in better agreement with the corresponding experimental values reoorded by Florence.展开更多
Study on the dynamic response, and especially the nonlinear dynamic response of stiffened plates is complicated by their discontinuity and inhomogeneity. The finite element method (FEM) and the finite strip method are...Study on the dynamic response, and especially the nonlinear dynamic response of stiffened plates is complicated by their discontinuity and inhomogeneity. The finite element method (FEM) and the finite strip method are usually adopted in their analysis. Although many useful conclusions have been obtained, the computational cost is enormous. Based on some assumptions, the dynamic plastic response of clamped stiffened plates with large deflections was theoretically investigated herein by a singly symmetric beam model. Firstly, the deflection conditions that a plastic string must satisfy were obtained by the linearized moment-axial force interaction curve for singly symmetric cross sections and the associated plastic flow rule. Secondly, the possible motion mechanisms of the beam under different load intensity were analysed in detail. For structures with plastic deformations, a simplified method was then given that the arbitrary impact load can be replaced equivalently by a rectangular pulse. Finally, to confirm the validity of the proposed method, the dynamic plastic response of a one-way stiffened plate with four fully clamped edges was calculated. The theoretical results were in good agreement with those of FEM. It indicates that the present calculation model is easy and feasible, and the equivalent substitution of load almost has no influence on the final deflection.展开更多
The rigid, perfectly plastic dynamic response of a free-free beam subjected to impact by a projectile at any cross-section is studied. The instantaneous deformations of the beam are given through an analysis of the ...The rigid, perfectly plastic dynamic response of a free-free beam subjected to impact by a projectile at any cross-section is studied. The instantaneous deformations of the beam are given through an analysis of the complete solution for rigid plastic structures. The in?uence of some parameters such as the input energy and mass ratio on the plastic deformation, travelling plastic hinge position and energy partitioning of the beam are discussed.展开更多
Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high...Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization展开更多
This paper studies intensively the problems of ship-platform collision. The ship and platform are treated as one structural system connected with spring elements and then motion equation of the collision system is est...This paper studies intensively the problems of ship-platform collision. The ship and platform are treated as one structural system connected with spring elements and then motion equation of the collision system is established. A nonlinear force-displacement relationship is derived for the simulation of local dent in a hit member and the yield surface of a dented tubular section is developed to consider the reduction of load carrying capacity of hit members. Large deformations, plasticity and strain-hardening of the beam-column element are taken into account by combining the elastic large displacement analysis theory with the plastic node method. The effect of the hydrodynamic forces acting on the platform, the rubber fender the property of the local dent and the buckling behavior of beam-column on collision are analyzed. The numerical simulation of the nonlinear dynamic response is carried out by Wilson theta method with updated Newton-Raphson iteration. And the numerical example of the dynamic response of a offshore platform in ship-platform collision is also present.展开更多
In the present paper, experimental studies on dynamic plasticbuckling of circular cylindrical shells under axial impact are carried out. Hopkinson bar and drop hammer apparatus are used for dynamic loading. Three grou...In the present paper, experimental studies on dynamic plasticbuckling of circular cylindrical shells under axial impact are carried out. Hopkinson bar and drop hammer apparatus are used for dynamic loading. Three groups of circular cylindrical shells made of copper are tested under axial impact. From the experiments, the first critical velocity corresponding to the axi-symmetric buckling mode and the second critical velocity corresponding to the non-axisymmetric buckling mode are determined. The present results come close to those of second critical velocity given by Wang Ren[4–6]. Two different kinds of non-axisymmetric buckling modes oval-shaped and triangle shaped are founded. The buckling modes under two loading cases, viz. with small mass but high velocity and with large mass and low velocity using Hopkinson bar and drop hammer, are different. Their critical energies are also discussed.展开更多
This paper concerns the dynamic plastic response of a circular plate resting on fluid subjected to a uniformly distributed rectangular load pulse with finite deformation. It is assumed that the fluid is incompressible...This paper concerns the dynamic plastic response of a circular plate resting on fluid subjected to a uniformly distributed rectangular load pulse with finite deformation. It is assumed that the fluid is incompressible and inviscous, and the plate is made of rigid-plastic material and simply supported along its edge. By using the method of the Hankel integral transformation, the nonuniform fluid resistance is derived as the plate and the fluid is coupled. Finally, an analytic solution for a circular plate under a medium load is obtained according to the equations of motion of the plate with finite deformation.展开更多
A theoretical analysis is presented for the dynamic plastic behavior of a simply supported rigid, perfectly plastic circular plate in damping medium with finite-deflections subjected to a rectangular pressure pulse. A...A theoretical analysis is presented for the dynamic plastic behavior of a simply supported rigid, perfectly plastic circular plate in damping medium with finite-deflections subjected to a rectangular pressure pulse. Analytical solutions of every moving stage under both medium and high loads are developed.展开更多
The large deflection dynamic plastic response of fully clamped square plates with stiffeners under blast load is analyzed in detail in this paper. Various relevant motion patterns and criterions are presented. The for...The large deflection dynamic plastic response of fully clamped square plates with stiffeners under blast load is analyzed in detail in this paper. Various relevant motion patterns and criterions are presented. The formulas of maximum permanent deformation of the plates with stiffeners are derived. The results of calculation are compared with those of experiment in [3], with good agreement shown in most cases.展开更多
By using the energy criterion in [3], the impact torsional buckling for the rigid plastic cylindrical shell is studied. The linear dynamic torsional buckling equations for the rigid plastic shell is drived, and the cr...By using the energy criterion in [3], the impact torsional buckling for the rigid plastic cylindrical shell is studied. The linear dynamic torsional buckling equations for the rigid plastic shell is drived, and the critical impact velocity is given.展开更多
Recent investigations indicated that metals can be effectively strengthened by numerous twin boundaries (TBs) with twin/matrix lamellar thicknesses in the nanometer regime.Superior strength-ductility synergies have be...Recent investigations indicated that metals can be effectively strengthened by numerous twin boundaries (TBs) with twin/matrix lamellar thicknesses in the nanometer regime.Superior strength-ductility synergies have been achieved with the nano-twin strengthening mechanism.In this talk,the novel nano-twin strengthening will be applied to austenite steels including 316L stainless steel and a Fe-Mn steel in order to optimize their strength-ductility combinations.The steels are processed by means of dynamic plastic deformation(DPD,i.e.,plastic deformation at high strain rates).Single-phased(austenite) bulk nanostructured steel specimens were prepared,consisting of nano-sized grains embedded with nano-scale twin bundles.The as-prepared nanostructured samples were annealed at various conditions,resulting in partial recrystallization of the nanostructures and forming a mixture structure of coarse-grains embedded with nano-twin bundles.Strength and ductility of the austenite steels with different amount of nano-twin bundles are analyzed.Measurements showed the nano-twin strengthen austenite steels can be superstrong (with yield strength above 1 GPa) together with a considerable ductility(elongation-to-failure >20%).展开更多
In this paper the problem of a circular beam subjected to radial impact by a rigid mass at its lip in its own plane is investigaleil on the basis of rigid-perfectly plastic assumption. The analytical solution of the p...In this paper the problem of a circular beam subjected to radial impact by a rigid mass at its lip in its own plane is investigaleil on the basis of rigid-perfectly plastic assumption. The analytical solution of the particle velocities is obtained as the junction of travelling plastic hinge location. Ky analysing the solution, some special properties oj circular beam problem are found.展开更多
Molecular dynamics simulation is employed to study the tension and compression deformation behaviors of magnesium single crystals with different orientations.The angle between the loading axis and the basal direction ...Molecular dynamics simulation is employed to study the tension and compression deformation behaviors of magnesium single crystals with different orientations.The angle between the loading axis and the basal direction ranges from 0° to 90°.The simulation results show that the initial defects usually nucleate at free surfaces,but the initial plastic deformation and the subsequent microstructural evolutions are various due to different loading directions.The tension simulations exhibit the deformation mechanisms of twinning,slip,crystallographic reorientation and basal/prismatic transformation.The twinning,crystallographic reorientation and basal/prismatic transformation can only appear in the crystal model loaded along or near the a-axis or c-axis.For the compression simulations,the basal,prismatic and pyramidal slips are responsible for the initial plasticity,and no twinning is observed.Moreover,the plastic deformation models affect the yield strengths for the samples with different orientations.The maximum yield stresses for the samples loaded along the c-axis or a-axis are much higher than those loaded in other directions.展开更多
The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to hig...The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to high-stress corrosion cracking(SCC)sensitivity due to the formation of high-density precipitates at grain boundaries(GBs).So far,it is still challenging to improve the strength of Al-Mg alloys without re-ducing SCC resistance.Herein,a nanostructured Al-5Mg-3 Zn alloy with a good yield strength of 336 MPa and good elongation was successfully produced.By dynamic plastic deformation and appropriate anneal-ing treatment,near-equiaxed nanograins were introduced in the nanostructured Al-5Mg-3 Zn alloy with a high proportion(71%)of the low-angle grain boundary.TEM statistical investigations show that the pre-cipitation of active T’phase at GBs has been greatly suppressed in the nanostructured Al-5Mg-3 Zn alloy at sensitized conditions,and the area fraction of GB precipitates is reduced from 72%to 21%,which sig-nificantly decreases the SCC susceptibility.This study provides guidance for developing advanced Al-Mg alloy with high SCC resistance.展开更多
The microstructures and hardness of pure Al samples subjected to plastic deformation with different tem- peratures and strain rates were investigated. The results showed that the strain-induced grain refinement is sig...The microstructures and hardness of pure Al samples subjected to plastic deformation with different tem- peratures and strain rates were investigated. The results showed that the strain-induced grain refinement is significantly benefited by increasing strain rate and reducing deformation temperature. The saturated size of refined subgrains in Al can be as small as about 240 nm in cryogenic dynamic plastic deformation (DPD). Grain boundaries of the DPD Al samples are low-angle boundaries due to suppression of dynamic recovery during deformation. Agreement of the measured hardness with the empirical Hall-Petch relation extrapolated from the coarse-grained Al implies that the low-angle boundaries can contribute to strengthening as effective as the conventional grain boundaries.展开更多
By means of dynamic plastic deformation (DPD) followed by thermal annealing, a mixed structure of micro-sized austenite grains embedded with nano-scale twin bundles (of about 20% in volume) has been synthesized in...By means of dynamic plastic deformation (DPD) followed by thermal annealing, a mixed structure of micro-sized austenite grains embedded with nano-scale twin bundles (of about 20% in volume) has been synthesized in a 316L stainless steel (SS). Such a 316L SS sample exhibits a tensile strength as high as 1001 MPa and an elongation-to-failure of about 23%. The much elevated strength originates from the presence of a considerable number of strengthening nano-twin bundles, while the ductility from the recrystallized grains. The superior strength-ductility combination achieved in the nano-twins-strengthened austenite steel demonstrates a novel approach for optimizing the mechanical properties in engineering materials.展开更多
A pure Cu (99.995 wt%) has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding h...A pure Cu (99.995 wt%) has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy (TEM) assisted by convergent beam electron diffraction (CBED) analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries (〈15°) that are spaced in the nanometer scale, whereas most deformation twins are deviated from the perfect ∑3 coincidence (60°/〈111〉) up to the maximum angle of 9°. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship.展开更多
Lamellar nanostructures were induced in a plain martensitic low-carbon steel by using dynamic plastic deformation at room temperature.The nanostructured steel was hardened after annealing at 673 K for20 min,with a ten...Lamellar nanostructures were induced in a plain martensitic low-carbon steel by using dynamic plastic deformation at room temperature.The nanostructured steel was hardened after annealing at 673 K for20 min,with a tensile strength increased from 1.2 GPa to 1.6 GPa.Both the remained nanostructures and annealing-induced precipitates in nano-scale play key roles in the hardening.展开更多
基金financial support from the National Natural Science Foundation of China(Nos.62104017 and 52072204)Beijing Institute of Technology Research Fund Program for Young Scholars.
文摘Manipulating the expression of synaptic plasticity of neuromorphic devices provides fascinating opportunities to develop hardware platforms for artifi-cial intelligence.However,great efforts have been devoted to exploring biomimetic mechanisms of plasticity simulation in the last few years.Recent progress in various plasticity modulation techniques has pushed the research of synaptic electronics from static plasticity simulation to dynamic plasticity modulation,improving the accuracy of neuromorphic computing and providing strategies for implementing neuromorphic sensing functions.Herein,several fascinating strategies for synap-tic plasticity modulation through chemical techniques,device structure design,and physical signal sensing are reviewed.For chemical techniques,the underly-ing mechanisms for the modification of functional materials were clarified and its effect on the expression of synaptic plasticity was also highlighted.Based on device structure design,the reconfigurable operation of neuromorphic devices was well demonstrated to achieve programmable neuromorphic functions.Besides,integrating the sensory units with neuromorphic processing circuits paved a new way to achieve human-like intelligent perception under the modulation of physical signals such as light,strain,and temperature.Finally,considering that the relevant technology is still in the basic exploration stage,some prospects or development suggestions are put forward to promote the development of neuromorphic devices.
基金supported by National Key R&D Program of China(2019YFB2103202).
文摘Network fault diagnosis methods play a vital role in maintaining network service quality and enhancing user experience as an integral component of intelligent network management.Considering the unique characteristics of edge networks,such as limited resources,complex network faults,and the need for high real-time performance,enhancing and optimizing existing network fault diagnosis methods is necessary.Therefore,this paper proposes the lightweight edge-side fault diagnosis approach based on a spiking neural network(LSNN).Firstly,we use the Izhikevich neurons model to replace the Leaky Integrate and Fire(LIF)neurons model in the LSNN model.Izhikevich neurons inherit the simplicity of LIF neurons but also possess richer behavioral characteristics and flexibility to handle diverse data inputs.Inspired by Fast Spiking Interneurons(FSIs)with a high-frequency firing pattern,we use the parameters of FSIs.Secondly,inspired by the connection mode based on spiking dynamics in the basal ganglia(BG)area of the brain,we propose the pruning approach based on the FSIs of the BG in LSNN to improve computational efficiency and reduce the demand for computing resources and energy consumption.Furthermore,we propose a multiple iterative Dynamic Spike Timing Dependent Plasticity(DSTDP)algorithm to enhance the accuracy of the LSNN model.Experiments on two server fault datasets demonstrate significant precision,recall,and F1 improvements across three diagnosis dimensions.Simultaneously,lightweight indicators such as Params and FLOPs significantly reduced,showcasing the LSNN’s advanced performance and model efficiency.To conclude,experiment results on a pair of datasets indicate that the LSNN model surpasses traditional models and achieves cutting-edge outcomes in network fault diagnosis tasks.
基金The project supported by a fund from the National Educational Committee.
文摘Based on energy equilibrium,a new procedure called the Membrane Factor Method is devel- oped to analyze the dynamic plastic response of plates with deflections in the range where both bending mo- ments and membrane forces are important.The final deflection of a simply -supported circular rigid-plastic plate loaded by a uniformly distributed impulse is obtained.In comparison with other approximate solutions, the present results are found to be simpler and in better agreement with the corresponding experimental values reoorded by Florence.
文摘Study on the dynamic response, and especially the nonlinear dynamic response of stiffened plates is complicated by their discontinuity and inhomogeneity. The finite element method (FEM) and the finite strip method are usually adopted in their analysis. Although many useful conclusions have been obtained, the computational cost is enormous. Based on some assumptions, the dynamic plastic response of clamped stiffened plates with large deflections was theoretically investigated herein by a singly symmetric beam model. Firstly, the deflection conditions that a plastic string must satisfy were obtained by the linearized moment-axial force interaction curve for singly symmetric cross sections and the associated plastic flow rule. Secondly, the possible motion mechanisms of the beam under different load intensity were analysed in detail. For structures with plastic deformations, a simplified method was then given that the arbitrary impact load can be replaced equivalently by a rectangular pulse. Finally, to confirm the validity of the proposed method, the dynamic plastic response of a one-way stiffened plate with four fully clamped edges was calculated. The theoretical results were in good agreement with those of FEM. It indicates that the present calculation model is easy and feasible, and the equivalent substitution of load almost has no influence on the final deflection.
基金Project supported by the National Natural Science Foundation of China (No.10272011).
文摘The rigid, perfectly plastic dynamic response of a free-free beam subjected to impact by a projectile at any cross-section is studied. The instantaneous deformations of the beam are given through an analysis of the complete solution for rigid plastic structures. The in?uence of some parameters such as the input energy and mass ratio on the plastic deformation, travelling plastic hinge position and energy partitioning of the beam are discussed.
文摘Recrystallized grains, less than 200 nm in diameter were observed in heavily shear zones of a high strength low alloy steel and a Ni-based alloy, and Also grain refinement, less than 3 μm in diameter was made in high purity aluminum by ECAE at ambient temperature. The experimental results showed that high strain rate and large deformation could induce dynamic recrystallization.Based on dislocation dynamics and grain orientation change enhanced by plastic deformation,a model for the recrystallization process is developed. The model is used to explain the ultra fine grains which are formed at a temperature still much lower than that for the conventional recrystallization
文摘This paper studies intensively the problems of ship-platform collision. The ship and platform are treated as one structural system connected with spring elements and then motion equation of the collision system is established. A nonlinear force-displacement relationship is derived for the simulation of local dent in a hit member and the yield surface of a dented tubular section is developed to consider the reduction of load carrying capacity of hit members. Large deformations, plasticity and strain-hardening of the beam-column element are taken into account by combining the elastic large displacement analysis theory with the plastic node method. The effect of the hydrodynamic forces acting on the platform, the rubber fender the property of the local dent and the buckling behavior of beam-column on collision are analyzed. The numerical simulation of the nonlinear dynamic response is carried out by Wilson theta method with updated Newton-Raphson iteration. And the numerical example of the dynamic response of a offshore platform in ship-platform collision is also present.
基金The project is supported by the National Natural Science Foundation of China(19672039)the Foundation for Returned Scholar from Abroad of Shanxi Province
文摘In the present paper, experimental studies on dynamic plasticbuckling of circular cylindrical shells under axial impact are carried out. Hopkinson bar and drop hammer apparatus are used for dynamic loading. Three groups of circular cylindrical shells made of copper are tested under axial impact. From the experiments, the first critical velocity corresponding to the axi-symmetric buckling mode and the second critical velocity corresponding to the non-axisymmetric buckling mode are determined. The present results come close to those of second critical velocity given by Wang Ren[4–6]. Two different kinds of non-axisymmetric buckling modes oval-shaped and triangle shaped are founded. The buckling modes under two loading cases, viz. with small mass but high velocity and with large mass and low velocity using Hopkinson bar and drop hammer, are different. Their critical energies are also discussed.
文摘This paper concerns the dynamic plastic response of a circular plate resting on fluid subjected to a uniformly distributed rectangular load pulse with finite deformation. It is assumed that the fluid is incompressible and inviscous, and the plate is made of rigid-plastic material and simply supported along its edge. By using the method of the Hankel integral transformation, the nonuniform fluid resistance is derived as the plate and the fluid is coupled. Finally, an analytic solution for a circular plate under a medium load is obtained according to the equations of motion of the plate with finite deformation.
文摘A theoretical analysis is presented for the dynamic plastic behavior of a simply supported rigid, perfectly plastic circular plate in damping medium with finite-deflections subjected to a rectangular pressure pulse. Analytical solutions of every moving stage under both medium and high loads are developed.
文摘The large deflection dynamic plastic response of fully clamped square plates with stiffeners under blast load is analyzed in detail in this paper. Various relevant motion patterns and criterions are presented. The formulas of maximum permanent deformation of the plates with stiffeners are derived. The results of calculation are compared with those of experiment in [3], with good agreement shown in most cases.
基金Project supported by the National Natural Science Foundation of China
文摘By using the energy criterion in [3], the impact torsional buckling for the rigid plastic cylindrical shell is studied. The linear dynamic torsional buckling equations for the rigid plastic shell is drived, and the critical impact velocity is given.
文摘Recent investigations indicated that metals can be effectively strengthened by numerous twin boundaries (TBs) with twin/matrix lamellar thicknesses in the nanometer regime.Superior strength-ductility synergies have been achieved with the nano-twin strengthening mechanism.In this talk,the novel nano-twin strengthening will be applied to austenite steels including 316L stainless steel and a Fe-Mn steel in order to optimize their strength-ductility combinations.The steels are processed by means of dynamic plastic deformation(DPD,i.e.,plastic deformation at high strain rates).Single-phased(austenite) bulk nanostructured steel specimens were prepared,consisting of nano-sized grains embedded with nano-scale twin bundles.The as-prepared nanostructured samples were annealed at various conditions,resulting in partial recrystallization of the nanostructures and forming a mixture structure of coarse-grains embedded with nano-twin bundles.Strength and ductility of the austenite steels with different amount of nano-twin bundles are analyzed.Measurements showed the nano-twin strengthen austenite steels can be superstrong (with yield strength above 1 GPa) together with a considerable ductility(elongation-to-failure >20%).
文摘In this paper the problem of a circular beam subjected to radial impact by a rigid mass at its lip in its own plane is investigaleil on the basis of rigid-perfectly plastic assumption. The analytical solution of the particle velocities is obtained as the junction of travelling plastic hinge location. Ky analysing the solution, some special properties oj circular beam problem are found.
基金supported by the National Natural Science Foundation of China(No.11372032)The Open Project of Key Laboratory of Computational Physics in China
文摘Molecular dynamics simulation is employed to study the tension and compression deformation behaviors of magnesium single crystals with different orientations.The angle between the loading axis and the basal direction ranges from 0° to 90°.The simulation results show that the initial defects usually nucleate at free surfaces,but the initial plastic deformation and the subsequent microstructural evolutions are various due to different loading directions.The tension simulations exhibit the deformation mechanisms of twinning,slip,crystallographic reorientation and basal/prismatic transformation.The twinning,crystallographic reorientation and basal/prismatic transformation can only appear in the crystal model loaded along or near the a-axis or c-axis.For the compression simulations,the basal,prismatic and pyramidal slips are responsible for the initial plasticity,and no twinning is observed.Moreover,the plastic deformation models affect the yield strengths for the samples with different orientations.The maximum yield stresses for the samples loaded along the c-axis or a-axis are much higher than those loaded in other directions.
基金This research was financially supported by the National Nat-ural Science Foundation of China(Grant No.52171088)the Young Elite Scientists Sponsorship Program by CAST(grant No.2022QNRC001).We thank X.Si for assistance in sample prepara-tion.
文摘The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to high-stress corrosion cracking(SCC)sensitivity due to the formation of high-density precipitates at grain boundaries(GBs).So far,it is still challenging to improve the strength of Al-Mg alloys without re-ducing SCC resistance.Herein,a nanostructured Al-5Mg-3 Zn alloy with a good yield strength of 336 MPa and good elongation was successfully produced.By dynamic plastic deformation and appropriate anneal-ing treatment,near-equiaxed nanograins were introduced in the nanostructured Al-5Mg-3 Zn alloy with a high proportion(71%)of the low-angle grain boundary.TEM statistical investigations show that the pre-cipitation of active T’phase at GBs has been greatly suppressed in the nanostructured Al-5Mg-3 Zn alloy at sensitized conditions,and the area fraction of GB precipitates is reduced from 72%to 21%,which sig-nificantly decreases the SCC susceptibility.This study provides guidance for developing advanced Al-Mg alloy with high SCC resistance.
基金support from the National Natural Science Foundation of China (Grants Nos. 50971122, 50431010,50621091, 50890171)Shenyang Science & Technology Project (No. 1071107-1-00)the Ministry of Scienceand Technology of China (2005CB623604)
文摘The microstructures and hardness of pure Al samples subjected to plastic deformation with different tem- peratures and strain rates were investigated. The results showed that the strain-induced grain refinement is significantly benefited by increasing strain rate and reducing deformation temperature. The saturated size of refined subgrains in Al can be as small as about 240 nm in cryogenic dynamic plastic deformation (DPD). Grain boundaries of the DPD Al samples are low-angle boundaries due to suppression of dynamic recovery during deformation. Agreement of the measured hardness with the empirical Hall-Petch relation extrapolated from the coarse-grained Al implies that the low-angle boundaries can contribute to strengthening as effective as the conventional grain boundaries.
基金the National Natural Science Foundation of China (Grants Nos. 50971122, 50431010,50621091 and 50890171)the Ministry of Science and Technology of China (2005CB623604) are acknowledged
文摘By means of dynamic plastic deformation (DPD) followed by thermal annealing, a mixed structure of micro-sized austenite grains embedded with nano-scale twin bundles (of about 20% in volume) has been synthesized in a 316L stainless steel (SS). Such a 316L SS sample exhibits a tensile strength as high as 1001 MPa and an elongation-to-failure of about 23%. The much elevated strength originates from the presence of a considerable number of strengthening nano-twin bundles, while the ductility from the recrystallized grains. The superior strength-ductility combination achieved in the nano-twins-strengthened austenite steel demonstrates a novel approach for optimizing the mechanical properties in engineering materials.
基金the Danish National Research Foundation and the National Natural Science Foundation of China (Grant No. 50911130230)for the Danish-Chinese center for Nanometals, within which this study was performedsponsored by MOST international S&T project(2010DFB54010), SRF for ROCS, SEM, and the Young Merit Scholar of Institute of Metal Research, Chinese Academy of Science, China
文摘A pure Cu (99.995 wt%) has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy (TEM) assisted by convergent beam electron diffraction (CBED) analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries (〈15°) that are spaced in the nanometer scale, whereas most deformation twins are deviated from the perfect ∑3 coincidence (60°/〈111〉) up to the maximum angle of 9°. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship.
基金Financial supports from the National Basic Research Program of China(Grant No.2012CB932201)the National Natural Science Foundation of China(Grant No.51371172)+1 种基金Bosch (China) Investment Ltd.,the MOST of China(2010DFB54010)the CAS International Cooperation Project(GJHZ1033)
文摘Lamellar nanostructures were induced in a plain martensitic low-carbon steel by using dynamic plastic deformation at room temperature.The nanostructured steel was hardened after annealing at 673 K for20 min,with a tensile strength increased from 1.2 GPa to 1.6 GPa.Both the remained nanostructures and annealing-induced precipitates in nano-scale play key roles in the hardening.