With the rapid development of heavy haul railway transportation technology,tunnel foundation defects and their effects on structural performance have attracted wide attention.This paper systematically investigates the...With the rapid development of heavy haul railway transportation technology,tunnel foundation defects and their effects on structural performance have attracted wide attention.This paper systematically investigates the evolution mechanism of tun-nel foundation defects in heavy haul railway tunnels and their impact on structural stiffness degradation through experiments and numerical simulations.A heavy haul train-ballasted track-tunnel basement-surround rock dynamic interaction model(TTTR model)is constructed.Firstly,the study reveals the four-stage evolution process of initial defects in the tunnel base-ment under complex environmental conditions.Experiments were conducted to measure the load-bearing capacity and stiff-ness degradation of the tunnel basement structure under different defect states.It is found that foundation defects,especially under the coupling of loose fill in the basement with the water-rich environment of the surrounding rock,significantly reduce the stiffness of the tunnel bottom structure and increase the risk of structural damage.Then,based on refined simulation of wheel-rail interaction and multi-scale coupled modeling technology,the TTTR dynamic interaction model was successfully constructed,and its validity was proven through numerical validation.A time-varying coupling technique of constrained boundary substructures(CBS technique)was adopted,significantly improving computational efficiency while ensuring calculation accuracy.The study also analyzes the effects of different degrees of void defects on the dynamic behavior of the train and the dynamic characteristics of the tunnel structure.It finds that foundation defects have a significant impact on the train’s operational state,track vibration displacement,and vibration stress of the tunnel lining structure,especially under the coupling effect of basement voids and the water-rich environment,which has the greatest impact.The research results of this paper provide a theoretical basis and technical support for the maintenance and reinforcement of tunnel foundation structures.展开更多
Nickel-based single crystal superalloys have become the main structural materials of the aero-engines due to excellent high-temperature strength.The micro defects evolution of nickel-based single crystal superalloys u...Nickel-based single crystal superalloys have become the main structural materials of the aero-engines due to excellent high-temperature strength.The micro defects evolution of nickel-based single crystal superalloys under shear deformation was investigated by molecular dynamics(MD)simulations in the present study.It is found that the interfacial dislocations decompose into Shockley dislocations under low shear stress,resulting in the plastic deformation of the Ni phase.The initial plastic deformation of the Ni3Al phase is caused by Shockley dislocations cutting into the Ni3Al phase.The following deformation from low temperature to medium temperature is controlled by dislocation slip,but the deformation at high temperature is changed.It is also found that the microvoid evolution can be divided into void growth and coalescence during shear deformation.The microvoid could prevent dislocation entanglement,accelerate dislocation decomposition,and promote earlier plastic deformation under relatively low temperatures.展开更多
Defect existing form and its evolution play an important role in the thermoelectric transport process. Here different forms of Pb into the Sn Se system were introduced in order to improve the thermoelectric and mechan...Defect existing form and its evolution play an important role in the thermoelectric transport process. Here different forms of Pb into the Sn Se system were introduced in order to improve the thermoelectric and mechanical properties of Sn Se. Pb/Sn Se samples were fabricated by vacuum melting, solid phase diffusion,spark plasma sintering and annealing treatment. The element valence mapping diagram and the X-ray photoelectron spectra(XPS) characteristic peaks of Pb show that a certain amount of elemental Pb exists in the initial state, and evolves into Pb^(2+)ion after annealing treatment. The micro-structure evolution leads to significant enhancement of the power factor and the ZT value. The power factor(PF) and the ZT value for Pb/Sn Se increases to 623 μW/m/K^(2) and 1.12 at 773 K after annealing treatment, respectively.Compared with Sn Se matrix, the hardness and fracture toughness of Pb/Sn Se samples increased by about40% and 10%, respectively. Reasonable control of microstructure evolution is expected to be a design idea to improve thermoelectric and mechanical properties of Sn Se.展开更多
The surface morphology, cross-sections, and joint break force（JBF） of joints welded under different electrode forces were studied. The defects, such as electrode sticking, notch, and excessive expulsions, were obser...The surface morphology, cross-sections, and joint break force（JBF） of joints welded under different electrode forces were studied. The defects, such as electrode sticking, notch, and excessive expulsions, were observed in the joints. No desirable joints were achieved with the consideration of weld geometries and joint performances. From the cross-sectional morphology, the joint evolution during the RMW of Pt alloy and 316 LVM SS wires was developed, which involved cold collapse and heat promoted set-down of Pt alloy wire, unbalanced heating at interface, molten phase squeezed out, and defect formation. Finally, the defect formation was also discussed.展开更多
The defect evolution in InP with the 75 keV H^(+)and 115 keV He^(+)implantation at room temperature after subsequent annealing has been investigated in detail.With the same ion implantation fluence,the He^(+)implantat...The defect evolution in InP with the 75 keV H^(+)and 115 keV He^(+)implantation at room temperature after subsequent annealing has been investigated in detail.With the same ion implantation fluence,the He^(+)implantation caused much broader damage distribution accompanied by much higher out-of-plane strain with respect to the H^(+)implanted InP.After annealing,the H^(+)implanted InP did not show any blistering or exfoliation on the surface even at the high fluence and the H2 molecules were stored in the heterogeneously oriented platelet defects.However,the He molecules were stored into the large bubbles which relaxed toward the free surface,creating blisters at the high fluence.展开更多
I_(1)stacking faults(SFs)in Mg alloys are regarded as the nucleation sites of<c+a>dislocations that are critical for these alloys to achieve high ductility.Previously it was proposed that the formation of I_(1)S...I_(1)stacking faults(SFs)in Mg alloys are regarded as the nucleation sites of<c+a>dislocations that are critical for these alloys to achieve high ductility.Previously it was proposed that the formation of I_(1)SFs requires the accumulations of a large number of vacancies,which are difficult to achieve at low temperatures.In this study,molecular dynamics(MD)and molecular statics(MS)simulations based on empirical interatomic potentials were applied to investigate the deformation defect evolutions from the symmetric tilt grain boundaries(GBs)in Mg and Mg-Y alloys under external loading along<c>-axis.The results show the planar faults(PFs)on Pyramidal I planes first appear due to the nucleation and glide of(1/2 c+p)partial dislocations from GBs,where p=1/3(1010).These partial dislocations with pyramidal PFs interact with other defects,including pyramidal PFs themselves,GBs,and ppartial dislocations,generating a large amount of I_(1)SFs.Detailed analyses show the nucleation and growth of I_(1)SFs are achieved by atomic shuffle events and deformation defect reactions without the requirements of vacancy diffusion.Our simulations also suggest the Y clusters at GBs can reduce the critical stress for the formation of pyramidal PFs and I_(1)SFs,which provide a possible reason for the experimental observations that Y promotes the<c+a>dislocation activities.展开更多
Sintered silver nanoparticles(AgNPs)arewidely used in high-power electronics due to their exceptional properties.However,the material reliability is significantly affected by various microscopic defects.In this work,t...Sintered silver nanoparticles(AgNPs)arewidely used in high-power electronics due to their exceptional properties.However,the material reliability is significantly affected by various microscopic defects.In this work,the three primary micro-defect types at potential stress concentrations in sintered AgNPs are identified,categorized,and quantified.Molecular dynamics(MD)simulations are employed to observe the failure evolution of different microscopic defects.The dominant mechanisms responsible for this evolution are dislocation nucleation and dislocation motion.At the same time,this paper clarifies the quantitative relationship between the tensile strain amount and the failure mechanism transitions of the three defect types by defining key strain points.The impact of defect types on the failure process is also discussed.Furthermore,traction-separation curves extracted from microscopic defect evolutions serve as a bridge to connect the macro-scale model.The validity of the crack propagation model is confirmed through tensile tests.Finally,we thoroughly analyze how micro-defect types influence macro-crack propagation and attempt to find supporting evidence from the MD model.Our findings provide a multi-perspective reference for the reliability analysis of sintered AgNPs.展开更多
The stability of small vacancy clusters including divacancy,trivacancy and tetravacancy has been studied in body-centered cubic high-entropy alloy Nb_(0.75)ZrTiV_(0.5) in structures of random solid solution and short-...The stability of small vacancy clusters including divacancy,trivacancy and tetravacancy has been studied in body-centered cubic high-entropy alloy Nb_(0.75)ZrTiV_(0.5) in structures of random solid solution and short-range order by first-principles calculations and molecular dynamics simulations.Different from conventional body-centered cubic metals,the tightly bound configurations have a lower structural stability and are not preferred energetically in the studied high-entropy alloy.Instability of vacancy configurations leads to vacancy-atom exchanges that favor less compact configurations.The formation energy of small vacancy clusters is much smaller than its constituent elements of Nb and V due to the large structural adjustment induced by severe local lattice distortion.The difference in local lattice distortion and elemental arrangement in the vacancy neighborhood leads to significant site-to-site variation in vacancy cluster energy and configuration.The formation energy has a strong correlation with the local energy state of the vacancy configuration and the extent of structural relaxation.Compared to random solid solution,the structure of short-range order has a higher stability for the most compact cluster configurations and tends to have higher vacancy cluster formation energy.According to classical molecular dynamics simulations of cluster diffusion at high temperature,the studied high-entropy alloy has a higher probability of cluster dissociation compared to Nb and V.The unconventional energetics of small vacancy clusters is expected to have a profound impact on their generation,diffusion,dissociation,coalescence,as well as the defect microstructure evolution during irradiation.展开更多
Tungsten has promising applications in high-radiation,high-erosion and high-impact environments.Laser peening is an effective method to enhance the surface mechanical properties of tungsten materials.However,the ultra...Tungsten has promising applications in high-radiation,high-erosion and high-impact environments.Laser peening is an effective method to enhance the surface mechanical properties of tungsten materials.However,the ultrafast dynamic mechanism of defect evolutions induced by laser shockwave in tungsten lattice is unclear.Here,we investigated the evolutions and interactions of various defects under ultrafast compressive process in tungsten lattice using molecular dynamic method.The results confirm the brittleness of tungsten and reveal that void can reduce the yield strain and strength of the tungsten lattice by accelerating defect mesh extension and promoting the dislocation nucleation around itself.Dislocation density is increased with compressive strain rate.Meanwhile,dislocation multiplication and motion reduce the elastic stage and play a dominant role during the plastic deformation of tungsten lattice.Additionally,void can disrupt the dislocation displacement and promote the pinning effect on dislocations by defect mesh extension.展开更多
The phase transition process of a photocatalytic system from NaBiO_(3)·2H_(2)O to BiO_(2−x) has been investigated to understand the important factors that affect photocatalytic performance in a composite system. ...The phase transition process of a photocatalytic system from NaBiO_(3)·2H_(2)O to BiO_(2−x) has been investigated to understand the important factors that affect photocatalytic performance in a composite system. It is found that a proper amount of BiO2−x on the surface of NaBiO_(3)·2H_(2)O could effectively suppress the electron/hole recombination and increase the exposed reactive sites for photocatalytic reaction. A fully covered BiO2−x on NaBiO3·2H2O results in a dramatical decrease of photocatalytic degradation of dye. An over long hydrothermal process can result in BiO_(2−x) with reduced oxygen vacancies, which degrades the photocatalytic activity. Furthermore, the photocatalytic reduction ability of CO_(2) conversion has been investigated, indicating that the surface activity to different reactants also directly affects the catalytic performance. The investigation of the gradient phase transition process presents a clear guidance to construct a desired photocatalytic system, in addition to selecting gradient materials with suitable bandgap structure and a morphology with different fraction and distribution of each component. The defect evolution of each component during construction of a composite is also an important factor that should be optimized and considered in making a composite to achieve high photocatalytic efficiency.展开更多
基金funded by the National Natural Science Foundation of China (Grant No. 52178402 & 52378468)the Open Foundation of MOE Key Laboratory of Engineering Structures of Heavy Haul Railway (Central South University) (Grant No. 2022JZZ01)+1 种基金the National Engineering Research Center for High-Speed Railway Construction Technology for their project supportthe support from the MOE Key Laboratory of Engineering Structure of Heavy Haul Railway (Central South University)
文摘With the rapid development of heavy haul railway transportation technology,tunnel foundation defects and their effects on structural performance have attracted wide attention.This paper systematically investigates the evolution mechanism of tun-nel foundation defects in heavy haul railway tunnels and their impact on structural stiffness degradation through experiments and numerical simulations.A heavy haul train-ballasted track-tunnel basement-surround rock dynamic interaction model(TTTR model)is constructed.Firstly,the study reveals the four-stage evolution process of initial defects in the tunnel base-ment under complex environmental conditions.Experiments were conducted to measure the load-bearing capacity and stiff-ness degradation of the tunnel basement structure under different defect states.It is found that foundation defects,especially under the coupling of loose fill in the basement with the water-rich environment of the surrounding rock,significantly reduce the stiffness of the tunnel bottom structure and increase the risk of structural damage.Then,based on refined simulation of wheel-rail interaction and multi-scale coupled modeling technology,the TTTR dynamic interaction model was successfully constructed,and its validity was proven through numerical validation.A time-varying coupling technique of constrained boundary substructures(CBS technique)was adopted,significantly improving computational efficiency while ensuring calculation accuracy.The study also analyzes the effects of different degrees of void defects on the dynamic behavior of the train and the dynamic characteristics of the tunnel structure.It finds that foundation defects have a significant impact on the train’s operational state,track vibration displacement,and vibration stress of the tunnel lining structure,especially under the coupling effect of basement voids and the water-rich environment,which has the greatest impact.The research results of this paper provide a theoretical basis and technical support for the maintenance and reinforcement of tunnel foundation structures.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52175306,52205347)the Natural Science Foundation of Shandong Province(Grant No.ZR2021QE181)the China Postdoctoral Science Foundation(Grant No.2022M712432)。
文摘Nickel-based single crystal superalloys have become the main structural materials of the aero-engines due to excellent high-temperature strength.The micro defects evolution of nickel-based single crystal superalloys under shear deformation was investigated by molecular dynamics(MD)simulations in the present study.It is found that the interfacial dislocations decompose into Shockley dislocations under low shear stress,resulting in the plastic deformation of the Ni phase.The initial plastic deformation of the Ni3Al phase is caused by Shockley dislocations cutting into the Ni3Al phase.The following deformation from low temperature to medium temperature is controlled by dislocation slip,but the deformation at high temperature is changed.It is also found that the microvoid evolution can be divided into void growth and coalescence during shear deformation.The microvoid could prevent dislocation entanglement,accelerate dislocation decomposition,and promote earlier plastic deformation under relatively low temperatures.
基金financially supported by the National Natural Science Foundation of China (No. 51772176)the Science and Technology Development Project of Shandong Province (No.2019JZZY010303)the Shandong Natural Science(No. ZR2015EM013)。
文摘Defect existing form and its evolution play an important role in the thermoelectric transport process. Here different forms of Pb into the Sn Se system were introduced in order to improve the thermoelectric and mechanical properties of Sn Se. Pb/Sn Se samples were fabricated by vacuum melting, solid phase diffusion,spark plasma sintering and annealing treatment. The element valence mapping diagram and the X-ray photoelectron spectra(XPS) characteristic peaks of Pb show that a certain amount of elemental Pb exists in the initial state, and evolves into Pb^(2+)ion after annealing treatment. The micro-structure evolution leads to significant enhancement of the power factor and the ZT value. The power factor(PF) and the ZT value for Pb/Sn Se increases to 623 μW/m/K^(2) and 1.12 at 773 K after annealing treatment, respectively.Compared with Sn Se matrix, the hardness and fracture toughness of Pb/Sn Se samples increased by about40% and 10%, respectively. Reasonable control of microstructure evolution is expected to be a design idea to improve thermoelectric and mechanical properties of Sn Se.
基金Funded by the National Natural Science Foundation of China(No.51365044)the State Key Laboratory for Mechanical Behavior of Materials(No.20111203)the State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology(No.AWJ-M13-09)
文摘The surface morphology, cross-sections, and joint break force（JBF） of joints welded under different electrode forces were studied. The defects, such as electrode sticking, notch, and excessive expulsions, were observed in the joints. No desirable joints were achieved with the consideration of weld geometries and joint performances. From the cross-sectional morphology, the joint evolution during the RMW of Pt alloy and 316 LVM SS wires was developed, which involved cold collapse and heat promoted set-down of Pt alloy wire, unbalanced heating at interface, molten phase squeezed out, and defect formation. Finally, the defect formation was also discussed.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFE0131300)the National Natural Science Foundation of China(Grant Nos.61874128,61851406,and 11705262)+3 种基金Frontier Science Key Program of Chinese Academy of Sciences(Grant Nos.QYZDY-SSW-JSC032 and ZDBS-LYJSC009)Chinese–Austrian Cooperative R&D Project(Grant No.GJHZ201950),Program of Shanghai Academic Research Leader(Grant No.19XD1404600)K.C.Wong Education Foundation(Grant No.GJTD-2019-11)NCBiR within the Polish–China(Grant No.WPC/130/NIR-Si/2018).
文摘The defect evolution in InP with the 75 keV H^(+)and 115 keV He^(+)implantation at room temperature after subsequent annealing has been investigated in detail.With the same ion implantation fluence,the He^(+)implantation caused much broader damage distribution accompanied by much higher out-of-plane strain with respect to the H^(+)implanted InP.After annealing,the H^(+)implanted InP did not show any blistering or exfoliation on the surface even at the high fluence and the H2 molecules were stored in the heterogeneously oriented platelet defects.However,the He molecules were stored into the large bubbles which relaxed toward the free surface,creating blisters at the high fluence.
基金supported by the U.S.Department of Energy,Office of Basic Energy Sciences,Division of Materials Sciences and Engineering under Award DE-SC0008637 as part of the Center for PRedictive Integrated Structural Materials Science(PRISMS Center)at University of Michigan。
文摘I_(1)stacking faults(SFs)in Mg alloys are regarded as the nucleation sites of<c+a>dislocations that are critical for these alloys to achieve high ductility.Previously it was proposed that the formation of I_(1)SFs requires the accumulations of a large number of vacancies,which are difficult to achieve at low temperatures.In this study,molecular dynamics(MD)and molecular statics(MS)simulations based on empirical interatomic potentials were applied to investigate the deformation defect evolutions from the symmetric tilt grain boundaries(GBs)in Mg and Mg-Y alloys under external loading along<c>-axis.The results show the planar faults(PFs)on Pyramidal I planes first appear due to the nucleation and glide of(1/2 c+p)partial dislocations from GBs,where p=1/3(1010).These partial dislocations with pyramidal PFs interact with other defects,including pyramidal PFs themselves,GBs,and ppartial dislocations,generating a large amount of I_(1)SFs.Detailed analyses show the nucleation and growth of I_(1)SFs are achieved by atomic shuffle events and deformation defect reactions without the requirements of vacancy diffusion.Our simulations also suggest the Y clusters at GBs can reduce the critical stress for the formation of pyramidal PFs and I_(1)SFs,which provide a possible reason for the experimental observations that Y promotes the<c+a>dislocation activities.
基金supported by the China Scholarship Council (CSC) (No.202206020149)the Academic Excellence Foundation of BUAA for PhD Students,the Funding Project of Science and Technology on Reliability and Environmental Engineering Laboratory (No.6142004210106).
文摘Sintered silver nanoparticles(AgNPs)arewidely used in high-power electronics due to their exceptional properties.However,the material reliability is significantly affected by various microscopic defects.In this work,the three primary micro-defect types at potential stress concentrations in sintered AgNPs are identified,categorized,and quantified.Molecular dynamics(MD)simulations are employed to observe the failure evolution of different microscopic defects.The dominant mechanisms responsible for this evolution are dislocation nucleation and dislocation motion.At the same time,this paper clarifies the quantitative relationship between the tensile strain amount and the failure mechanism transitions of the three defect types by defining key strain points.The impact of defect types on the failure process is also discussed.Furthermore,traction-separation curves extracted from microscopic defect evolutions serve as a bridge to connect the macro-scale model.The validity of the crack propagation model is confirmed through tensile tests.Finally,we thoroughly analyze how micro-defect types influence macro-crack propagation and attempt to find supporting evidence from the MD model.Our findings provide a multi-perspective reference for the reliability analysis of sintered AgNPs.
基金support from the National Key Research and Development Program of China(Grant no.2019YFA0209900)the National Natural Science Foundation of China(Grant nos.12075179 and 12105219)+2 种基金the China Postdoctoral Science Foundation(Grant no.2021M702583)the Innovative Scientific Program of China National Nuclear Corporation,the Innovation Program of Nuclear Power Institute of China(No.KJCX-2022-1-04)the LiYing Program of the Institute of Mechanics,Chinese Academy of Sciences(Grant no.E1Z1011001).
文摘The stability of small vacancy clusters including divacancy,trivacancy and tetravacancy has been studied in body-centered cubic high-entropy alloy Nb_(0.75)ZrTiV_(0.5) in structures of random solid solution and short-range order by first-principles calculations and molecular dynamics simulations.Different from conventional body-centered cubic metals,the tightly bound configurations have a lower structural stability and are not preferred energetically in the studied high-entropy alloy.Instability of vacancy configurations leads to vacancy-atom exchanges that favor less compact configurations.The formation energy of small vacancy clusters is much smaller than its constituent elements of Nb and V due to the large structural adjustment induced by severe local lattice distortion.The difference in local lattice distortion and elemental arrangement in the vacancy neighborhood leads to significant site-to-site variation in vacancy cluster energy and configuration.The formation energy has a strong correlation with the local energy state of the vacancy configuration and the extent of structural relaxation.Compared to random solid solution,the structure of short-range order has a higher stability for the most compact cluster configurations and tends to have higher vacancy cluster formation energy.According to classical molecular dynamics simulations of cluster diffusion at high temperature,the studied high-entropy alloy has a higher probability of cluster dissociation compared to Nb and V.The unconventional energetics of small vacancy clusters is expected to have a profound impact on their generation,diffusion,dissociation,coalescence,as well as the defect microstructure evolution during irradiation.
基金financially support from the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA25040201)the National Natural Science Foundation of China(Grant No.51727901)support provided by the Deanship of Scientific Research(DSR)at King Fahd University of Petroleum&Minerals(KFUPM)(Grant No.DF201020)
文摘Tungsten has promising applications in high-radiation,high-erosion and high-impact environments.Laser peening is an effective method to enhance the surface mechanical properties of tungsten materials.However,the ultrafast dynamic mechanism of defect evolutions induced by laser shockwave in tungsten lattice is unclear.Here,we investigated the evolutions and interactions of various defects under ultrafast compressive process in tungsten lattice using molecular dynamic method.The results confirm the brittleness of tungsten and reveal that void can reduce the yield strain and strength of the tungsten lattice by accelerating defect mesh extension and promoting the dislocation nucleation around itself.Dislocation density is increased with compressive strain rate.Meanwhile,dislocation multiplication and motion reduce the elastic stage and play a dominant role during the plastic deformation of tungsten lattice.Additionally,void can disrupt the dislocation displacement and promote the pinning effect on dislocations by defect mesh extension.
基金This research was supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science,ICT and Future Planning(2017R1D1A1B03032265 and 2019R1A2C1086881)SEM characterization in this research was supported by Nano-material Technology Development Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science,ICT and Future Planning(2009-0082580)。
文摘The phase transition process of a photocatalytic system from NaBiO_(3)·2H_(2)O to BiO_(2−x) has been investigated to understand the important factors that affect photocatalytic performance in a composite system. It is found that a proper amount of BiO2−x on the surface of NaBiO_(3)·2H_(2)O could effectively suppress the electron/hole recombination and increase the exposed reactive sites for photocatalytic reaction. A fully covered BiO2−x on NaBiO3·2H2O results in a dramatical decrease of photocatalytic degradation of dye. An over long hydrothermal process can result in BiO_(2−x) with reduced oxygen vacancies, which degrades the photocatalytic activity. Furthermore, the photocatalytic reduction ability of CO_(2) conversion has been investigated, indicating that the surface activity to different reactants also directly affects the catalytic performance. The investigation of the gradient phase transition process presents a clear guidance to construct a desired photocatalytic system, in addition to selecting gradient materials with suitable bandgap structure and a morphology with different fraction and distribution of each component. The defect evolution of each component during construction of a composite is also an important factor that should be optimized and considered in making a composite to achieve high photocatalytic efficiency.
