摘要：
Nanopowder consolidation under high strain rate shock compression is a potential method for synthesizing and processing bulk nanomaterials, and a thorough investigation of the deformation and its underlying mechanisms in consolidation is of great engineering significance. We conduct non-equilibrium molecular dynamics (NEMD) simulation and X-ray diffraction (XRD) simulation to systematically study shock-induced deformation and the corresponding mechanisms during the consolidation of nanopowdered Mg (NP-Mg). Two different deformation modes govern the shock consolidation in NP-Mg, i.e., deformation twinning at u p ≤ 1.5 km s −1 and structural disordering, at u p ≥ 2.0 km s −1 . They accelerate the collapse of nanopores and void compaction, giving rise to the final consolidation of NP-Mg. Three types of deformation twinning are emitted in NP-Mg, i.e., the extension twinning for { 11 2 ¯ 1 } 〈 1 ¯ 1 ¯ 26 〉 , and { 1 1 ¯ 02 } 〈 1 1 ¯ 01 〉 , and the compression { 11 2 ¯ 2 } 〈 1 ¯ 1 ¯ 23 〉 twinning. They are prompted via coupling atomic shuffles and slips. Deformation twinning prefers to occur within the grains as shock along 〈 11 2 ¯ 0 〉 or its approaching direction (A- and B-type grains), originated from the high-angle grain boundaries (HAGB) at compression stage. They are inhibited within the ones as shocking along 〈 0001 〉 and the approaching ones (C- and D -type grains). The release and tension loading facilitates the reversible and irreversible detwinning, for the extension and compression twinning, respectively, within the A- and B-type grains. It also contributes to a compression-tension asymmetry for twinning, i.e., release and tension induced extension twinning within the C- and D -type grains. The subsequent spallation is mediated by GB sliding and GB-induced stacking faults at u p ≤ 1.5 km s −1 , and structural disordering at u p ≥ 2.0 km s −1 .
Nanopowder consolidation under high strain rate shock compression is a potential method for synthesizing and processing bulk nanomaterials, and a thorough investigation of the deformation and its underlying mechanisms in consolidation is of great engineering significance. We conduct non-equilibrium molecular dynamics (NEMD) simulation and X-ray diffraction (XRD) simulation to systematically study shock-induced deformation and the corresponding mechanisms during the consolidation of nanopowdered Mg (NP-Mg). Two different deformation modes govern the shock consolidation in NP-Mg, i.e., deformation twinning at u p ≤ 1.5 km s −1 and structural disordering, at u p ≥ 2.0 km s −1 . They accelerate the collapse of nanopores and void compaction, giving rise to the final consolidation of NP-Mg. Three types of deformation twinning are emitted in NP-Mg, i.e., the extension twinning for { 11 2 ¯ 1 } 〈 1 ¯ 1 ¯ 26 〉 , and { 1 1 ¯ 02 } 〈 1 1 ¯ 01 〉 , and the compression { 11 2 ¯ 2 } 〈 1 ¯ 1 ¯ 23 〉 twinning. They are prompted via coupling atomic shuffles and slips. Deformation twinning prefers to occur within the grains as shock along 〈 11 2 ¯ 0 〉 or its approaching direction (A- and B-type grains), originated from the high-angle grain boundaries (HAGB) at compression stage. They are inhibited within the ones as shocking along 〈 0001 〉 and the approaching ones (C- and D -type grains). The release and tension loading facilitates the reversible and irreversible detwinning, for the extension and compression twinning, respectively, within the A- and B-type grains. It also contributes to a compression-tension asymmetry for twinning, i.e., release and tension induced extension twinning within the C- and D -type grains. The subsequent spallation is mediated by GB sliding and GB-induced stacking faults at u p ≤ 1.5 km s −1 , and structural disordering at u p ≥ 2.0 km s −1 .
摘要：
The dynamic mechanical properties and deformation/damage mechanisms of face centered cubic polycrystalline nickel are investigated systemically via plate impact experiments and molecular dynamics (MD) simulations. The Hugoniot equation of state and spall strength at peak shock stress up to 20 GPa are deduced from free surface velocity histories. The elastic–plastic transition is obscure with no evident Hugoniot elastic limit. The polycrystalline Ni exhibits low spall strength ( ∼ 1.6–2.0 GPa). Given the postmortem characterizations, plastic deformation is mainly achieved via dislocation glides. Ductile spallation is the main damage mode, and void nucleation occurs mostly at grain boundaries and triple junctions. The MD simulations reveal that intense shock compression can induce a 〈 110 〉 texture involving stacking faults, deformation twins and minor solid–solid phase transition. Due to the intense slip–GB intersections, intergranular damage are also predominant at different impact velocities. The evolution of the internal three-dimensional void damage characteristics are also analyzed. The present research provides valuable insights into impact response (mechanical properties and deformation mechanisms) and relationships between the microstructure characteristics and mechanical properties upon shock loading for polycrystalline Ni via both experiments and simulations.
The dynamic mechanical properties and deformation/damage mechanisms of face centered cubic polycrystalline nickel are investigated systemically via plate impact experiments and molecular dynamics (MD) simulations. The Hugoniot equation of state and spall strength at peak shock stress up to 20 GPa are deduced from free surface velocity histories. The elastic–plastic transition is obscure with no evident Hugoniot elastic limit. The polycrystalline Ni exhibits low spall strength ( ∼ 1.6–2.0 GPa). Given the postmortem characterizations, plastic deformation is mainly achieved via dislocation glides. Ductile spallation is the main damage mode, and void nucleation occurs mostly at grain boundaries and triple junctions. The MD simulations reveal that intense shock compression can induce a 〈 110 〉 texture involving stacking faults, deformation twins and minor solid–solid phase transition. Due to the intense slip–GB intersections, intergranular damage are also predominant at different impact velocities. The evolution of the internal three-dimensional void damage characteristics are also analyzed. The present research provides valuable insights into impact response (mechanical properties and deformation mechanisms) and relationships between the microstructure characteristics and mechanical properties upon shock loading for polycrystalline Ni via both experiments and simulations.
作者机构：
[Shang, Min; Shang, M] Hunan Agr Univ, Coll Sci, Changsha 410128, Hunan, Peoples R China.;[Tian, Ze'an] Hunan Univ, Coll Comp Sci & Elect Engn, Changsha 410082, Peoples R China.;[Tian, Ze'an] Guizhou Univ, Sch Big Data & Informat Engn, Guiyang 550025, Peoples R China.;[Wang, Liang] Peac Inst Multiscale Sci, Chengdu 610207, Sichuan, Peoples R China.
通讯机构：
[Shang, M ] H;Hunan Agr Univ, Coll Sci, Changsha 410128, Hunan, Peoples R China.
摘要：
We systematically study the plasticity and melting behavior in shock loading, as well as their dependence on porosity (ϕ) and specific surface area (γ) for nanoporous copper (NPC), by conducting large-scale non-equilibrium molecular dynamics simulations. During shock compression, the plasticity (i.e., dislocation slips) is dominant at lower impact velocities, while melting is governing at higher impact velocities. With increasing ϕ, both the plasticity and melting undergo the transitions from “heterogeneity” to “homogeneity” along the transverse directions. The increase in γ prompts an apparent heat release and gives rise to the transition from local plasticity to uniform solid disordering at lower impact velocities, while accelerates the melting at higher impact velocities, by converting more surface energy into internal energy. Upon impact, shock-induced pores collapse accelerates the consolidation of NPCs and is controlled by two mechanisms, i.e., the shearing ligament, prompted by plasticity, under low-velocity impact, and the internal micro-jetting facilitated by melting under high-velocity impact.
作者：
Li, B.;Liu, M. T.;Luo, B. Q.;Fan, C.;Cai, Y.;...
期刊：
Journal of Applied Physics,2024年135(14):145902 ISSN：0021-8979
通讯作者：
Fan, C;Wang, L
作者机构：
[Li, B.; Liu, M. T.; Fan, C.; Luo, B. Q.] China Acad Engn Phys, Inst Fluid Phys, Mianyang 621999, Sichuan, Peoples R China.;[Cai, Y.; Wang, L.] Peac Inst Multiscale Sci, Chengdu 610207, Sichuan, Peoples R China.;[Zhao, F.] Chengdu Univ, Inst Adv Study, Chengdu 610106, Sichuan, Peoples R China.;[Zhao, F.] Chengdu Univ, Inst Adv Mat Deformat & Damage Multiscale, Chengdu 610106, Sichuan, Peoples R China.;[Wang, L.] Hunan Agr Univ, Coll Sci, Changsha 410128, Hunan, Peoples R China.
通讯机构：
[Fan, C ] C;[Wang, L ] P;China Acad Engn Phys, Inst Fluid Phys, Mianyang 621999, Sichuan, Peoples R China.;Peac Inst Multiscale Sci, Chengdu 610207, Sichuan, Peoples R China.;Hunan Agr Univ, Coll Sci, Changsha 410128, Hunan, Peoples R China.
摘要：
With large-scale non-equilibrium molecular dynamics simulations and in situ x-ray diffraction analysis, we conducted a systematic investigation into the effects of pre-existing shear strain (gamma(xy)) on the shock response of single crystal iron. Our findings reveal significant effects of gamma(xy) on the deformation of the crystal structure during shock loading, leading to noticeable alterations in the propagation of shock waves. Specifically, during the elastic stage, the presence of gamma(xy) results in a reduction of shock strength, consequently diminishing the magnitude of elastic lattice strain (epsilon(e)). In the plastic stage, gamma(xy) stimulates the alpha- epsilon phase transformation, and structure deformation undergoes a transition from the sequential activity of dislocation-to-transformation to the synchronous activity of dislocation and transformation. This transition inhibits the propagation of plastic waves and consequently broadens the elastic regime. Additionally, the introduction of gamma(xy) activates different slip systems, as it alters the corresponding resolved shear stress. Concurrently, the presence of gamma(xy) triggers the activation of different high-pressure phase variants. Our investigation sheds light on the fundamental physics of iron under shock compression and the influence of pre-existing shear strain on its behavior. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(https://creativecommons.org/licenses/by/4.0/).
作者机构：
[Wang, Mingyang; He, Debing; Wang, Liang] Hunan Agr Univ, Coll Sci, Changsha 410128, Hunan, Peoples R China.;[Bi, Wenbo; Bi, WB] China Acad Engn Phys, Grad Sch, Beijing 100193, Peoples R China.
通讯机构：
[Wang, L ] H;[Bi, WB ] C;Hunan Agr Univ, Coll Sci, Changsha 410128, Hunan, Peoples R China.;China Acad Engn Phys, Grad Sch, Beijing 100193, Peoples R China.
摘要：
Consolidating nanopowder metals via impact loading is a potentially significant method for synthesizing and processing bulk nanocrystalline materials. However, until now, the microstructural features, plastic deformation during consolidation, and corresponding mechanisms have been seldom revealed. Using molecular dynamics (MD) simulations, we have studied the plastic deformation, densification, spallation, and micro-jetting in nanopowder titanium (np-Ti) during shock. Upon impact, np-Ti undergoes a transition from heterogeneous plasticity, including basal stacking faults (SFs) and {1012} twinning, to homogeneous disordering, as the impact velocity increases. Then the nanopowder structure evolves into a bulk nanostructure after the final densification, contributed by pore collapse. The subsequent detwinning arises during the release and tension stage, conducing to a partial structural recovery. When the impact velocity up >= 1.0 km s-1, the spallation is following, prompted via GB-sliding and disordering. Upon shock impact, it also facilitates micro-jetting owing to the presence of nanopores, contributing to the pressure gradient and transverse velocity gradient. The plasticity and GB-sliding at lower velocities, and melt-induced the flow deformation at the higher velocities, contribute to the shock consolidation of nanopowder Ti.
期刊：
Chemical Engineering Journal,2023年452:139313 ISSN：1385-8947
通讯作者：
Zou, Rui(zourui@mail2.sysu.edu.cn)
作者机构：
[Cao, Lu-Yu; Guo, Xiao-Xuan; Liu, Bo-Mei; Huang, Lin; Wang, Jing] Sun Yat Sen Univ, Sch Chem, State Key Lab Optoelect Mat & Technol, Minist Educ,Key Lab Bioinorgan & Synthet Chem, Guangzhou 510275, Peoples R China.;[Zou, Rui] Sun Yat Sen Univ, Affiliated Hosp 3, Dept Nucl Med, 600 Tianhe Rd, Guangzhou 510630, Peoples R China.;[Zhou, Zhi] Hunan Agr Univ, Coll Sci, Hunan Opt Agr Engn Technol Res Ctr, Changsha, Hunan, Peoples R China.
通讯机构：
[Rui Zou] D;[Zhi Zhou] C;[Jing Wang] M;Department of Nuclear Medicine, The Third Affiliated Hospital of Sun Yat-Sen University, 600 Tianhe Road, Guangzhou 510630, China<&wdkj&>College of Science, Hunan Optical Agriculture Engineering Technology Research Center, Hunan Agricultural University, Changsha City, Hunan 10128, China<&wdkj&>Ministry of Education Key Laboratory of Bioinorganic and Synthetic Chemistry, State Key Laboratory of Optoelectronic Materials and Technologies, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, China
关键词：
Ni;NIR spectroscopy;NIR-II luminescence;Phosphor-converted LED
作者机构：
[Liu, Bo-Mei; Huang, Lin; Wang, Jing] Sun Yat Sen Univ, Sch Mat Sci & Engn, Guangzhou 510275, Peoples R China.;[Gu, Si-Min; Wang, Jing] Sun Yat Sen Univ, Sch Chem, State Key Lab Optoelectron Mat & Technol, Minist Educ,Key Lab Bioinorgan & Synthet Chem, Guangzhou 510275, Peoples R China.;[Zhou, Rong-Fu] Foshan Univ, Sch Environm & Chem Engn, Foshan 528225, Peoples R China.;[Zhou, Zhi] Hunan Agr Univ, Coll Sci, Hunan Optic Agr Engn Technol Res Ctr, Changsha 10128, Hunan, Peoples R China.;[Ma, Chong-Geng] Chongqing Univ Posts & Telecommunicat, Sch Optoelectron Engn CQUPT BUL Innovat Inst, Chongqing 400065, Peoples R China.
通讯机构：
[Rui Zou] D;[Jing Wang] S;School of Materials Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China<&wdkj&>Ministry of Education Key Laboratory of Bioinorganic and Synthetic Chemistry, State Key Laboratory of Optoelectronic Materials and Technologies, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, China<&wdkj&>Department of Nuclear Medicine, The Third Affiliated Hospital of Sun Yat-Sen University, 600 Tianhe Road, Guangzhou 510630, China
作者机构：
[Jonathan R.Adsetts; 杨柳青; 丁志峰; Darshil Patel; Kenneth Chu; Brian L.Pagenkopf; 张丛洋] Department of Chemistry, Western University;湖南农业大学化学与材料科学学院;凯莱英医药集团(天津)股份有限公司北京分公司;[覃晓丽] Department of Chemistry, Western University<&wdkj&>湖南农业大学化学与材料科学学院;[王鑫] Department of Chemistry, Western University<&wdkj&>凯莱英医药集团(天津)股份有限公司北京分公司
作者机构：
[Deng, HuiQiu; Wen, ShuLong] Hunan Univ, Sch Phys & Elect, Changsha 410082, Peoples R China.;[Zhang, XingMing] Hunan Agr Univ, Coll Sci, Changsha 410128, Peoples R China.;[Pan, Min] Southwest Jiao Tong Univ, Superconduct & New Energy R&D Ctr, Key Lab Adv Technol Mat, Minist Educ, Chengdu 610031, Peoples R China.
通讯机构：
[HuiQiu Deng; Min Pan] S;School of Physics and Electronics, Hunan University, Changsha 410082, People’s Republic of China<&wdkj&>Superconductivity and New Energy R&D Center, Key Laboratory of Advanced Technology of Materials (Ministry of Education), Southwest Jiao Tong University, Chengdu 610031, People’s Republic of China
期刊：
International Journal of Plasticity,2022年155:103329 ISSN：0749-6419
通讯作者：
Fei Gao<&wdkj&>Huiqiu Deng
作者机构：
[Guo, Long; Hu, Wangyu; Liu, Beibei; Wang, Kun] Hunan Univ, Coll Mat Sci & Engn, Changsha 410082, Peoples R China.;[Xiao, Shifang; Chen, Yangchun; Deng, Huiqiu; Guo, Long] Hunan Univ, Sch Phys & Elect, Changsha 410082, Peoples R China.;[Wang, Liang] Hunan Agr Univ, Coll Sci, Changsha 410128, Peoples R China.;[Gao, Ning] Shandong Univ, Inst Frontier & Interdisciplinar Sci, Qingdao 266237, Shandong, Peoples R China.;[Gao, Fei] Univ Michigan, Dept Nucl Engn & Radiol Sci, Ann Arbor, MI 48109 USA.
通讯机构：
[Fei Gao] D;[Huiqiu Deng] S;School of Physics and Electronics, Hunan University, Changsha 410082, China<&wdkj&>Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Michigan 48109, United States
通讯机构：
[Wang, YM ] H;Hunan Agr Univ, Dept Appl Math, Changsha 410128, Peoples R China.
关键词：
Julia sets;Buried component;Singular perturbations;Cantor set of circles
摘要：
Let f be a hyperbolic rational map with degree
$$d\ge 2$$
whose Julia set is connected. We give an elementary approach to prove that there exists a rational map g with degree
$$\le 7d-2$$
such that g contains a buried Julia component which is homeomorphic to the Julia set of f.
