When a metal is subject to cyclic loading with cyclic stress values much lower than its tensile strength,fatigue occurs due to accumulative and irreversible damages developed in the microstructure,causing service fail...When a metal is subject to cyclic loading with cyclic stress values much lower than its tensile strength,fatigue occurs due to accumulative and irreversible damages developed in the microstructure,causing service failure of the metal workpiece or even fatal disaster in the worst cases.To develop materials with higher fatigue limit and longer fatigue life relies on reducing or suppressing展开更多
Plastic-deformation behaviors of gradient nanotwinned(GNT)metallic multilayers are investigated in nanoscale via molecular dynamics simulation.The evolution law of deformation behaviors of GNT metallic multilayers wit...Plastic-deformation behaviors of gradient nanotwinned(GNT)metallic multilayers are investigated in nanoscale via molecular dynamics simulation.The evolution law of deformation behaviors of GNT metallic multilayers with different stacking fault energies(SFEs)during nanoindentation is revealed.The deformation behavior transforms from the dislocation dynamics to the twinning/detwinning in the GNT Ag,Cu,to Al with SFE increasing.In addition,it is found that the GNT Ag and GNT Cu strengthen in the case of a larger twin gradient based on more significant twin boundary(TB)strengthening and dislocation strengthening,while the GNT Al softens due to more TB migration and dislocation nucleation from TB at a larger twin gradient.The softening mechanism is further analyzed theoretically.These results not only provide an atomic insight into the plastic-deformation behaviors of certain GNT metallic multilayers with different SFEs,but also give a guideline to design the GNT metallic multilayers with required mechanical properties.展开更多
Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong, Chinagrains to a^1-martensite nanograins with bimodal grain size distribution for lower strain rates to nanotwins ...Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong, Chinagrains to a^1-martensite nanograins with bimodal grain size distribution for lower strain rates to nanotwins in the ultrafine/coarse grained austenite phase for higher strain rates. Meanwhile, we will further address the mechanism-based plastic models to describe the yield strength, strain hardening and ductility in nanostructured metals with bimodal grain size distribution and nanotwinned polycrystalline metals. The proposed theoretical models can comprehensively describe the plastic deformation in these two kinds of nanostructured metals and excellent agreement is achieved between the numerical and experimental results. These models can be utilized to optimize the strength and ductility in nanostructured metals by controlling the size and distribution of nanostructures.展开更多
文摘When a metal is subject to cyclic loading with cyclic stress values much lower than its tensile strength,fatigue occurs due to accumulative and irreversible damages developed in the microstructure,causing service failure of the metal workpiece or even fatal disaster in the worst cases.To develop materials with higher fatigue limit and longer fatigue life relies on reducing or suppressing
基金the National Natural Science Foundation of China(Grant Nos.51621004,11572118,51871092,and 11772122)the National Key Research and Development Program of China(Grant No.2016YFB0700300)。
文摘Plastic-deformation behaviors of gradient nanotwinned(GNT)metallic multilayers are investigated in nanoscale via molecular dynamics simulation.The evolution law of deformation behaviors of GNT metallic multilayers with different stacking fault energies(SFEs)during nanoindentation is revealed.The deformation behavior transforms from the dislocation dynamics to the twinning/detwinning in the GNT Ag,Cu,to Al with SFE increasing.In addition,it is found that the GNT Ag and GNT Cu strengthen in the case of a larger twin gradient based on more significant twin boundary(TB)strengthening and dislocation strengthening,while the GNT Al softens due to more TB migration and dislocation nucleation from TB at a larger twin gradient.The softening mechanism is further analyzed theoretically.These results not only provide an atomic insight into the plastic-deformation behaviors of certain GNT metallic multilayers with different SFEs,but also give a guideline to design the GNT metallic multilayers with required mechanical properties.
基金supportedby the Chinese Ministry of Science and Technology of China (2012CB932203)the Research Grants Council of the Hong Kong Special Administrative Region of China(CityU8/CRF/08 and GRF/CityU519110)the Croucher Foundation CityU9500006 and PolyU Postdoctoral Fellowship Project (G-YX3S)
文摘Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong, Chinagrains to a^1-martensite nanograins with bimodal grain size distribution for lower strain rates to nanotwins in the ultrafine/coarse grained austenite phase for higher strain rates. Meanwhile, we will further address the mechanism-based plastic models to describe the yield strength, strain hardening and ductility in nanostructured metals with bimodal grain size distribution and nanotwinned polycrystalline metals. The proposed theoretical models can comprehensively describe the plastic deformation in these two kinds of nanostructured metals and excellent agreement is achieved between the numerical and experimental results. These models can be utilized to optimize the strength and ductility in nanostructured metals by controlling the size and distribution of nanostructures.
