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Mechanical properties of 2D hierarchical re-entrant cellular structures with Voronoi sub-structures

EPL 2018年第1期123卷 16002-16002页

作者： Liu, Lu Li, Dong Dong, Liang Northeastern Univ Coll Sci Shenyang 110819 Liaoning Peoples R China Univ Virginia Mat Sci & Engn Charlottesville VA 22904 USA

In this study, 2D hierarchical re-entrant cellular structures with Voronoi substructures were proposed. Their Poisson's ratios and energy absorption capacities (in-plane) were studied using the finite-element method. The effects of geometric parameters (Voronoi sub structure irregularity, k, concave angle, theta, ratio of cell wall thickness to cell height, omega) on the lattice mechanical properties were investigated. Results showed that Poisson's ratio first decreased and then increased with an increasing theta when k is less than 0.5. A minimum Poisson's ratio of approximately 0.315 was achieved when k = 0.5 and theta = 60 degrees. The 2D hierarchical re-entrant lattice structure exhibited a maximum energy absorption capacity when k = 0.2 and omega = 1/3, which is 3.9 times higher than that of the traditional re-entrant structure with solid ribs and of identical relative density. Copyright (C) EPLA, 2018

关键词： Poisson's ratio structural modeling: serial-addition models, computer simulation Powders, porous materials

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Cation distribution of Mn-Zn ferrite nanoparticles using pair distribution function analysis and resonant X-ray scattering

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EPL 2018年第5期124卷 56001-56001页

作者： Ichikawa, Rodrigo U. Parra, Joao P. R. L. L. Vallcorba, Oriol Peral, Inma Yoshito, Walter K. Saeki, Margarida J. Turrillas, Xavier Martinez, Luis G. Nucl & Energy Res Inst Mat Sci & Technol Ctr IPEN CNEN Av Lineu Prestes 2242 BR-05508000 Sao Paulo SP Brazil Sao Paulo State Univ Inst Biosci UNESP IBB Via Domingos SartorKm 4 BR-18618970 Botucatu SP Brazil LBA Synchrotron Carrer Llum 2-26 Barcelona 08290 Spain Univ Luxembourg Fac Sci Technol & Commun 6 Rue Richard Coudenhove Kalergi L-1359 Luxembourg Luxembourg Luxembourg Inst Sci & Technol 5 Ave Hauts Fourneaux L-4362 Luxembourg Luxembourg CSIC Dept Crystallog ICMAB Campus UAB Barcelona 08193 Spain

Mn-Zn ferrite nanoparticles were synthesized by chemical co-precipitation method and analysed using X-ray synchrotron diffraction data. Pair distribution function (PDF) analysis was used to probe the local structure and revealed that the first-neighbour distances of Fe-Fe and Mn-Zn in the 3.0 up to 3.5 angstrom range are different from the ones usually reported in the literature. For the sample with the best magnetic behaviour, resonant X-ray scattering (RXS) using three energies close to the absorption edges of Mn, Zn and Fe was applied to determine the cation distribution which explained the previous result from PDF analysis. Copyright (C) EPLA, 2018.

关键词： X-ray diffraction Nanocrystals structural modeling: serial-addition models, computer simulation

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Optimizing the primary knock-on atom for simulating particle radiation-induced structural damage in Zr-based metals

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EPL 2017年第1期117卷 16001-16001页

作者： Cai, Guang-Bo Yang, Liang Guo, Gu-Qing Nanjing Univ Aeronaut & Astronaut Coll Mat Sci & Technol Dept Nucl Sci & Engn Nanjing 210016 Jiangsu Peoples R China

Molecular dynamics (MD) can simulate the production of radiation-induced point defects in materials. However, the initial conditions of one "hypothetical" primary knock-on atom (PKA) which starts the MD simulation usually are simplified. In the present work, we aim to obtain the optimized initial conditions of PKA by using the Geant4 software which can simulate the passage of particles through matter. We find that the spectra of kinetic energies of PKAs are similar with each other among pure Zr, Zr2Cu, and Zr2Ni. This indicates that adopting simplified structural models can approximate the atomic-level structural damage in some corresponding served nuclear materials, such as Zr-based and Fe-based alloys. In addition, it is revealed that the moving directions of PKAs strongly relate to the kinetic energies of neutrons, and the corresponding preferred scattering angles of PKAs could be estimated. These findings are helpful for optimizing the initial conditions of MD simulation, and extend our understanding on simulating structural damage in nuclear materials accordingly.

关键词： Neutron radiation effects structural modeling: serial-addition models, computer simulation Neutron transport: diffusion and moderation

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Inversion symmetric vs. asymmetric excitations and the low-temperature universal properties of Ar:N₂ and Ar:N₂: CO glasses

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EPL 2015年第5期109卷

作者： Gaita-Arino, A. Gonzalez-Albuixech, V. F. Schechter, M. Univ Valencia Inst Ciencia Mol Paterna 46980 Spain Ben Gurion Univ Negev Dept Phys IL-84105 Beer Sheva Israel

The bias energies of various two- level systems ( TLSs) and their strengths of interactions with the strain are calculated for Ar:N-2 glass. Unlike the case in KBr: CN, a distinct class of TLSs having weak interaction with the strain and untypically small bias energies is not found. The addition of CO molecules introduces CO flips which form such a class of weakly interacting TLSs, albeit at much lower coupling than that at which they are typically observed in solids. We conclude that because of the absence of a distinct class of weakly interacting TLSs, Ar:N-2 is a non- universal glass, the first such system in three dimensions and in ambient pressure. Our results further suggest that Ar:N-2:CO may show universal properties, but at temperatures lower than approximate to 0.1K, much smaller than the typical temperature approximate to 3K associated with universality, because of the untypical softness of this system. Our results thus shed light on two long- standing questions regarding the low- temperature properties of glasses: the necessary and sufficient conditions for quantitative universality of phonon attenuation, and what dictates the energy scale of approximate to 3 K below which universality is typically observed. Copyright (C) EPLA, 2015

关键词： Glasses Theories and models of crystal defects structural modeling: serial-addition models, computer simulation

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Improving stochastic reconstructions by weighting correlation functions in an objective function

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EPL 2015年第5期111卷 56002-56002页

作者： Gerke, Kirill M. Karsanina, Marina V. CSIRO Land & Water Glen Osmond Glen Osmond SA 5064 Australia Univ Melbourne Dept Infrastruct Engn Parkville Vic 3010 Australia Russian Acad Sci Inst Geosphere Dynam Moscow 119334 Russia Russian Acad Sci Inst Phys Earth Moscow 107031 Russia

Spatial correlation functions (CFs) are prominent descriptors of any structure. In this letter, we show for the first time how proper weighting of CFs in an objective function can lead to significant improvements in reconstruction accuracy and in the likelihood of convergence. We develop a simple weighting scheme and display its effectiveness on two- and three-dimensional structures utilizing up to 27 CFs in one set. Proper weighting of the objective functions led to completely accurate reconstructions not achievable by conventional unweighted approaches. The proposed approach combining numerous CFs can potentially characterize and reconstruct structures of any complexity. Copyright (C) EPLA, 2015

关键词： structural modeling: serial-addition models, computer simulation Classical statistical mechanics Powders, porous materials

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Atomistic two-temperature modelling of ion track formation in silicon dioxide

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EPL 2015年第1期110卷

作者： Leino, A. A. Daraszewicz, S. L. Pakarinen, O. H. Nordlund, K. Djurabekova, F. Univ Helsinki Helsinki Inst Phys FI-00014 Helsinki Finland Univ Helsinki Dept Phys FI-00014 Helsinki Finland UCL Dept Phys & Astron London WC1E 6BT England UCL London Ctr Nanotechnol London WC1E 6BT England

We study swift-heavy-ion track formation in a-quartz using the two-temperature molecular dynamics (2T-MD) model realised as a concurrent multiscale scheme. We compare the simulated track radii to the existing experimental ones obtained from small-angle X-ray scattering and Rutherford backscattering experiments. The 2T-MD model provides an explanation of the origin of the track radii saturation at high electronic stopping power. Furthermore, we study the track structure and show that defects formed outside the region of density fluctuations after a swift-heavy-ion impact may explain the conflicting track radii produced by the two experimental techniques. Copyright (C) EPLA, 2015

关键词： Ion radiation effects structural modeling: serial-addition models, computer simulation

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Improving pattern reconstruction using directional correlation functions

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EPL 2014年第6期106卷 66002-66002页

作者： Gerke, Kirill M. Karsanina, Marina V. Vasilyev, Roman V. Mallants, Dirk CSIRO Land & Water Glen Osmond Glen Osmond SA 5064 Australia Russian Acad Sci Inst Geosphere Dynam Moscow 119334 Russia AIR Technol Moscow 119234 Russia Moscow MV Lomonosov State Univ Geol Fac Moscow 119234 Russia

In this letter we introduce a new method to calculate correlation functions in four principal directions (i.e. two orthogonal and two diagonal) and separately utilize them for image reconstruction. We show that this method is particularly suitable for anisotropic porous media but that it also improves image reconstruction for isotropic structures. Based on the analysis of numerous reconstructions of four binary patterns using different sets of two-point probability and linear (for both phases) correlation functions, we quantify the accuracy of each set. Averaging of correlation functions in all directions almost always results in poorer reconstructions. addition of separate directions significantly improves the quality of replicas with only a minor increase in computational effort. Copyright (C) EPLA, 2014

关键词： structural modeling: serial-addition models, computer simulation Classical statistical mechanics Powders, porous materials

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structural origin of the different devitrification behaviors between ZrCu and ZrPd metallic glasses

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EPL 2014年第6期107卷 66002-66002页

作者： Huang, Po Zou, De-Hui Guo, Gu-Qing Yang, Liang China Acad Engn Phys Inst Nucl Phys & Chem Mianyang 621900 Peoples R China China Acad Engn Phys Key Lab Neutron Phys Mianyang 621900 Peoples R China Nanjing Univ Aeronaut & Astronaut Coll Mat Sci & Technol Dept Nucl Sci & Engn Nanjing 210016 Jiangsu Peoples R China

The microstructures of Zr70Pd30 and Zr70Cu30 metallic glasses (MGs) were investigated via the synchrotron radiation techniques combined with the reverse Monte Carlo simulations. It is revealed that, compared with Zr70Cu30, Zr70Pd30 has more fruitful icosahedral-like clusters, which have a relatively high geometrical regularity closer to that of the ideal icosahedron. Therefore, clusters in Zr70Pd30 are prone to change into the structural units of icosahedral quasicrystal phase. This should be the structural origin of the amorphous-to-quasicrystal transformation found in Zr70Pd30 while such phase change never appears when heating Zr70Cu30 MG. This work provides an understanding of the devitrification mechanism from the atomic level in this class of glassy materials. Copyright (C) EPLA, 2014

关键词： X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. Amorphous semiconductors, metals, and alloys structural modeling: serial-addition models, computer simulation

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Loop punching and bubble rupture causing surface roughening - A model for W fuzz growth

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EPL 2014年第2期105卷 25002-25001页

作者： Lasa, A. Tahtinen, S. K. Nordlund, K. Univ Helsinki Dept Phys Assoc Euratom Tekes FI-00014 Helsinki Finland

We develop a multi-scale computational model for studying tungsten fuzz formation under low-energy He irradiation. The molecular dynamics and kinetic Monte Carlo results show that the W fuzz growth mechanism is the following: the He atoms are trapped in W, forming bubbles and causing growth by loop punching. The bubbles close to the surface rupture. The balance between these processes leads to a stochastic surface growth, causing the surface roughness and fuzz thickness growth to scale as root t. The growth rates agree with the experimental results. Copyright (c) EPLA, 2014

关键词： Plasma-material interactions, boundary layer effects Materials structural modeling: serial-addition models, computer simulation

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Topological correlations of grain faces in polycrystal with experimental verification

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EPL 2013年第5期104卷 56006-56005页

作者： Li, Wenwen Liu, Guoquan Wang, Hao Zhang, Hao Luan, Junhua Ullah, Asad Univ Sci & Technol Beijing Sch Mat Sci & Engn Beijing 100083 Peoples R China Univ Sci & Technol Beijing State Key Lab Adv Met & Mat Beijing 100083 Peoples R China Univ Alberta Dept Chem & Mat Engn Edmonton AB T6G 2V4 Canada City Univ Hong Kong Dept Mech & Biomed Engn Ctr Adv Struct Mat Hong Kong 999077 Hong Kong Peoples R China Karakoram Int Univ Gilgit Baltistan Dept Math Gilgit 15100 Pakistan

How grain faces are arranged in three-dimensional grain structures is one of the outstanding problems in physics, biology and materials science. Based on the topological analysis of 477 real pure iron grains and 6093 Monte Carlo simulated grains, two forms of topological correlations are studied. The first correlation is Rivier's relation (Philos. Mag. B, 52 (1985) 795), in which the average number of edges M-f(e) of faces neighboring to e-edged faces on f-faceted grains is related to e and f;and the second correlation is the one derived in the current paper, in which a typical e-edged face in a polycrystal is a function of the average number of edges of its neighboring faces M(e). Both correlations are verified by experimental and simulation data. Copyright (C) EPLA, 2013

关键词： Equations of state of pure metals and alloys Theory and models of crystal growth, physics and chemistry of crystal growth, crystal morphology, and orientation structural modeling: serial-addition models, computer simulation

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