The Experts below are selected from a list of 126 Experts worldwide ranked by ideXlab platform
Fuping Yuan - One of the best experts on this subject based on the ideXlab platform.
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Tensile deformation mechanisms of the hierarchical structure consisting of both twin-free grains and nanotwinned grains
Philosophical Magazine Letters, 2014Co-Authors: Fuping Yuan, Ping ChenAbstract:A series of large-scale molecular dynamics simulations have been performed to investigate the tensile properties and atomistic deformation mechanisms for the nanostructured Cu with three typical microstructures: the hierarchical structure consisting of both twin-free grains (d = 70 nm) and grains with bundles of smaller nanotwins (d = 70 nm, λ = 10 nm), the fully nanograined structure and the fully nanotwinned structure. The Average Flow Stress of the hierarchically structure is found to be higher than that calculated by rule of mixture. As compared with that of fully nanograined structure, the strength for the twin-free grains in the hierarchical structure is promoted and gives extra hardening due to the increased dislocation density and dislocation behaviours. It is also found that the nanotwin bundles are more deformable than the twin-free grains in the hierarchical structure according to the deviatoric strain invariant contour. This indicates that the fully nanograined structure cannot only be strengt...
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twin boundary spacing effects on shock response and spall behaviors of hierarchically nanotwinned fcc metals
Journal of Applied Physics, 2014Co-Authors: Fuping Yuan, Liu Chen, Ping JiangAbstract:Atomistic deformation mechanisms of hierarchically nano-twinned (NT) Ag under shock conditions have been investigated using a series of large-scale molecular dynamics simulations. For the same grain size d and the same spacing of primary twins lambda(1), the Average Flow Stress behind the shock front in hierarchically NT Ag first increases with decreasing spacing of secondary twins lambda(2), achieving a maximum at a critical lambda(2), and then drops as lambda(2) decreases further. Above the critical lambda(2), the deformation mechanisms are dominated by three type strengthening mechanisms: (a) partial dislocations emitted from grain boundaries (GBs) travel across other boundaries; (b) partial dislocations emitted from twin boundaries (TBs) travel across other TBs; (c) formation of tertiary twins. Below the critical lambda(2), the deformation mechanism are dominated by two softening mechanisms: (a) detwinning of secondary twins; (b) formation of new grains by cross slip of partial dislocations. Moreover, the twin-free nanocrystalline (NC) Ag is found to have lower Average Flow Stress behind the shock front than those of all hierarchically NT Ag samples except the one with the smallest lambda(2) of 0.71 nm. No apparent correlation between the spall strength and lambda(2) is observed in hierarchically NT Ag, since voids always nucleate at both GBs and boundaries of the primary twins. However, twin-free NC Ag is found to have higher spall strength than hierarchically NT Ag. Voids can only nucleate from GBs for twin-free NC Ag, therefore, twin-free NC Ag has less nucleation sources along the shock direction when compared to hierarchically NT Ag, which requiring higher tensile Stress to create spallation. These findings should contribute to the understandings of deformation mechanisms of hierarchically NT fcc metals under extreme deformation conditions. (C) 2014 AIP Publishing LLC.
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Scaling laws and deformation mechanisms of nanoporous copper under adiabatic uniaxial strain compression
AIP Advances, 2014Co-Authors: Fuping YuanAbstract:A series of large-scale molecular dynamics simulations were conducted to investigate the scaling laws and the related atomistic deformation mechanisms of Cu monocrystal samples containing randomly placed nanovoids under adiabatic uniaxial strain compression. At onset of yielding, plastic deformation is accommodated by dislocations emitted from void surfaces as shear loops. The collapse of voids are observed by continuous emissions of dislocations from void surfaces and their interactions with further plastic deformation. The simulation results also suggest that the effect modulus, the yield Stress and the energy aborption density of samples under uniaxial strain are linearly proportional to the relative density ρ. Moreover, the yield Stress, the Average Flow Stress and the energy aborption density of samples with the same relative density show a strong dependence on the void diameter d, expressed by exponential relations with decay coefficients much higher than -1/2. The corresponding atomistic mechanisms...
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Size effects of primary/secondary twins on the atomistic deformation mechanisms in hierarchically nanotwinned metals
Journal of Applied Physics, 2013Co-Authors: Fuping YuanAbstract:A series of large-scale molecular dynamics simulations have been performed to investigate the tensile properties of nanotwinned (NT) copper with hierarchically twinned structures (HTS). For the same grain size d and the same spacing of primary twins λ1, the Average Flow Stress first increases as the spacing of secondary twins λ2 decreases, reaching a maximum at a critical λ2, and then decreases as λ2 becomes even smaller. The smaller the spacing for λ1, the smaller the critical spacing for λ2. There exists a transition in dominating deformation mechanisms, occurring at a critical spacing of λ2 for which strength is maximized. Above the critical spacing of λ2, the deformation mechanisms are dominated by the two Hall-Petch type strengthening mechanisms: (a) partial dislocations emitted from grain boundaries (GBs) travel across other GBs and twin boundaries (TBs); (b) partial dislocations emitted from TBs travel across other TBs. Below the critical spacing of λ2, the deformation mechanism is dominated by the two softening mechanisms: (a) Partial dislocations emitted from boundaries of the primary twins travel parallel to the TBs of the secondary twins, leading to detwinning of the secondary twins; (b) Boundaries of the primary twins shift entirely, leading to thickening in one part of primary twins and thinning in the other part of primary twins. The present results should provide insights to design the microstructures for reinforcing the mechanical properties in the NT metals with HTS.
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Shock response of nanotwinned copper from large-scale molecular dynamics simulations
Physical Review B, 2012Co-Authors: Fuping YuanAbstract:A series of large-scale molecular dynamics simulations have been performed to investigate the shock response of nanotwinned (NT) Cu, including shock-induced plasticity, strength behind the shock front, and spall behaviors. In this study, two configurations were investigated at an impact velocity of 600m/s, i.e., the practical NT polycrystalline Cu with an Average grain size of 10 nm and the simple NT single-crystalline Cu with an impact direction of [11 (2) over bar]. In the NT polycrystalline Cu, the Average Flow Stress behind the shock front first increases with decreasing twin-boundary spacing (TBS), reaching a maximum at a critical TBS, and then decreases as the TBS become even smaller. This trend of the Average Flow Stress with decreasing TBS is due to two competitive dislocation activities under shock loading, with one being inclined to the twin boundaries (the dislocation-twin boundary intersecting) and the other parallel to the twin boundaries (detwinning with twin-boundary migration). Since voids always nucleate near the grain boundary (GB) junctions and then grow along the GBs to create spallation, no apparent correlation between the spall strength and TBS is observed in the NT polycrystalline Cu. However, the spall strengths of the NT single-crystalline Cu are found to increase with decreasing TBS. Two partial dislocation slips initiated from each twin boundary create voids at the intersections between the partial dislocation slips and twin boundaries. The smaller TBSs result in a larger number of twin boundaries and provide more nucleation sites for voids, requiring a higher tensile Stress to create spallation in the NT single-crystalline Cu. These findings should provide insights for understanding the deformation physics of the NT metals subjected to shock loading.
Liang Fang - One of the best experts on this subject based on the ideXlab platform.
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Quantifying the effect of twin boundaries on grain boundary activities in nanotwinned copper: A molecular dynamics simulation
Mechanics of Materials, 2020Co-Authors: Meng Zhang, Liang FangAbstract:Abstract Twin boundaries (TBs) play an important role in work hardening of nanotwinned metals. However, the effect of TBs on grain boundaries (GBs) activities in nanotwinned metals has not given detailed analysis due to the limited spatial and temporal resolution of experimental technique and the unrealistic model with flat GBs in simulation. Therefore, the nanotwinned copper with more natural GBs was created in this study by using phase field model for molecular dynamics (MD) simulation. In addition, a novel code was developed to quantitatively analyze the GB activities including deformation and rotation in the initial deformation stage. The results show that the Average Flow Stress in nanotwinned copper is larger than that in the twin-free model and the Stress increases with decreasing twin spacing. From the statistical results of GB activities, we can find that the rotation of GBs seems to be not affected by the TBs, but the deformation of GBs will be detained by TBs which finally results in improving Stress concentration on GBs. Hence, with decreasing twin spacing, the deformation mechanism shifts from partials gliding on different slip systems to partials gliding on the adjacent plane of TBs due to the Stress concentration.
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Constructing initial nanocrystalline configurations from phase field microstructures enables rational molecular dynamics simulation
Computational Materials Science, 2019Co-Authors: Meng Zhang, Kun Sun, Liang FangAbstract:Abstract The phase field method is used to create the nanocrystalline (nc) copper film with more physical and natural grain boundaries (GBs) for molecular dynamics (MD) simulation. The results show that the Average Flow-Stress and ductility for the phase field model (PFM) is larger than that for the regular-hexagonal model (RHM) due to large fraction of twinning in the PFM during the tensile deformation. Multiple twins are generated by the evolution of stacking faults (SFs). But, the conversion rate (hexagonal-close-packed (HCP) → twinning boundaries (TBs)) for the PFM is smaller than that for the RHM because the deformation can be mediated by the curved GBs of PFM to reduce the Stress-concentration.
Meng Zhang - One of the best experts on this subject based on the ideXlab platform.
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Quantifying the effect of twin boundaries on grain boundary activities in nanotwinned copper: A molecular dynamics simulation
Mechanics of Materials, 2020Co-Authors: Meng Zhang, Liang FangAbstract:Abstract Twin boundaries (TBs) play an important role in work hardening of nanotwinned metals. However, the effect of TBs on grain boundaries (GBs) activities in nanotwinned metals has not given detailed analysis due to the limited spatial and temporal resolution of experimental technique and the unrealistic model with flat GBs in simulation. Therefore, the nanotwinned copper with more natural GBs was created in this study by using phase field model for molecular dynamics (MD) simulation. In addition, a novel code was developed to quantitatively analyze the GB activities including deformation and rotation in the initial deformation stage. The results show that the Average Flow Stress in nanotwinned copper is larger than that in the twin-free model and the Stress increases with decreasing twin spacing. From the statistical results of GB activities, we can find that the rotation of GBs seems to be not affected by the TBs, but the deformation of GBs will be detained by TBs which finally results in improving Stress concentration on GBs. Hence, with decreasing twin spacing, the deformation mechanism shifts from partials gliding on different slip systems to partials gliding on the adjacent plane of TBs due to the Stress concentration.
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Constructing initial nanocrystalline configurations from phase field microstructures enables rational molecular dynamics simulation
Computational Materials Science, 2019Co-Authors: Meng Zhang, Kun Sun, Liang FangAbstract:Abstract The phase field method is used to create the nanocrystalline (nc) copper film with more physical and natural grain boundaries (GBs) for molecular dynamics (MD) simulation. The results show that the Average Flow-Stress and ductility for the phase field model (PFM) is larger than that for the regular-hexagonal model (RHM) due to large fraction of twinning in the PFM during the tensile deformation. Multiple twins are generated by the evolution of stacking faults (SFs). But, the conversion rate (hexagonal-close-packed (HCP) → twinning boundaries (TBs)) for the PFM is smaller than that for the RHM because the deformation can be mediated by the curved GBs of PFM to reduce the Stress-concentration.
Yutian Ding - One of the best experts on this subject based on the ideXlab platform.
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Effects of grain size and temperature on mechanical properties of nano-polycrystalline Nickel-cobalt alloy
Journal of Materials Research and Technology, 2020Co-Authors: Changyu Dong, Xin Guo, Junqiang Ren, Hongtao Xue, Fuling Tang, Yutian DingAbstract:Abstract Influences of grain size and temperature on the mechanical properties of nano-polycrystalline Ni-Co alloy were investigated with molecular dynamics simulations. It is found that the critical grain size of Hall-Petch relationship is 4.3 nm, at which the maximum Flow Stress of 4.83 GPa is obtained. In samples with the d > 4.3 nm, the Average Flow Stress increases with the decrease of d, according with the Hall-Petch relationship, caused by the dislocation glide and growth of deformation twin with the breaking of individual grain boundaries. For samples with the d
Hanspete Seife - One of the best experts on this subject based on the ideXlab platform.
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dynamic study of contact damping in martensitic stainless steels using nano indentation
Mechanics of Materials, 2020Co-Authors: Roma Mougino, Philippe Spätig, Hanspete SeifeAbstract:Abstract The study was undertaken to gain insight into the micro-mechanisms controlling plasticity at the micrometer scale of elastic-plastic metallic alloys. Dynamic nano-indentation tests, where a small harmonic force amplitude is superimposed during loading, referred to as continuous stiffness measurement (CSM), were performed to study contact damping in martensitic stainless steels with different heat treatments. The nano-indentation experiments were analyzed according to a specific protocol developed in this study, which results from a careful dynamic characterization done over a wide range of materials with significant different plastic Flow properties, to separate the effect of the instrument from those of the material. The method was then applied to the tempered martensitic steel Eurofer97 in different tempering conditions. Based on the dynamic contact analysis developed for visco-elastic materials, we propose a new interpretation of the damping coefficient for materials like Eurofer97 dominated by an elastic-plastic behavior. The loss factor and the nano-hardness were correlated with the propensity of the material to plastic deformation, characterized by the Average Flow Stress determined from tensile tests.
