The Experts below are selected from a list of 63540 Experts worldwide ranked by ideXlab platform
Xizhong An - One of the best experts on this subject based on the ideXlab platform.
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three dimensional mpfem modelling on isostatic pressing and solid phase sintering of tungsten powders
Powder Technology, 2019Co-Authors: Xizhong AnAbstract:Abstract Particulate scale three-dimensional CIP and solid phase sintering of tungsten powder in powder metallurgy process was numerically reproduced using MPFEM method. The effects of initial Packing Structures on the densification behavior of the tungsten powders during CIP and sintering were systematically investigated. Various macroscopic and microscopic properties including relative density, overall/local stress distributions, deformation status, pore filling behavior as well as densification mechanisms were characterized and analyzed. The results indicate that the initial Packing Structure before CIP plays an important role in determining the properties of both green compact and sintered part after compaction and sintering. Detailed analyses of individual particles revealed that the particles with larger deformation tend to generate greater stress concentration during CIP and sintering; meanwhile, the stress distribution in different location of each particle also demonstrated that a close relationship exists between the stress concentration/release process of individual particles and their initial Packing Structure before CIP.
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three dimensional mpfem modelling on isostatic pressing and solid phase sintering of tungsten powders
Powder Technology, 2019Co-Authors: Xizhong AnAbstract:Abstract Particulate scale three-dimensional CIP and solid phase sintering of tungsten powder in powder metallurgy process was numerically reproduced using MPFEM method. The effects of initial Packing Structures on the densification behavior of the tungsten powders during CIP and sintering were systematically investigated. Various macroscopic and microscopic properties including relative density, overall/local stress distributions, deformation status, pore filling behavior as well as densification mechanisms were characterized and analyzed. The results indicate that the initial Packing Structure before CIP plays an important role in determining the properties of both green compact and sintered part after compaction and sintering. Detailed analyses of individual particles revealed that the particles with larger deformation tend to generate greater stress concentration during CIP and sintering; meanwhile, the stress distribution in different location of each particle also demonstrated that a close relationship exists between the stress concentration/release process of individual particles and their initial Packing Structure before CIP.
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two dimensional multiparticle finite element modeling on the cold isostatic pressing of al powder
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2018Co-Authors: Anliang Lu, Xizhong AnAbstract:In this article, the cold isostatic pressing (CIP) of Al powders with different initial Packing Structures was numerically simulated in two dimensions using the multiparticle finite element method from particulate scale. The effects of external pressure and initial Packing Structures on the Packing densification and performance of the compacts were systematically studied. Various macro/micro properties (such as relative density and distribution, local stress and distribution, and particle deformation behavior) and the densification dynamics/mechanisms were characterized and analyzed. Corresponding modeling on die compaction was also conducted for comparison. The results show that the relative displacement of particles is much less and the particle shape is more regular for CIP of ordered initial Packing Structure than those for CIP of random initial Packing Structure, and the distributions of relative density and local stress in the compact for the former case are more homogeneous. Compared with die compaction, the formability of CIP is much better; also, the compact has higher relative density and more uniform density and stress distributions. The normal stresses are transmitted in all directions in the compact during CIP because the external load is applied uniformly to the outer surface of the rubber mold from all directions in the entire process, while the normal stresses are directional along the loading path during die compaction.
Toshikazu Miyoshi - One of the best experts on this subject based on the ideXlab platform.
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chapter 14 Structure and molecular dynamics of semicrystalline polymers as studied by solid state nmr
2019Co-Authors: Zhaoxi Zheng, Kun Wang, Fan Jin, Toshikazu MiyoshiAbstract:Chain-level Structure of semicrystalline polymers in melt- and solution-grown crystals has been debated over the past several decades. Recently, 13C–13C double quantum (DQ) NMR spectroscopy and spin-dynamics simulation have been applied to trace chain trajectory and Packing Structure of 13C labeled polymers in melt- and solution-grown crystals. We highlight recent NMR studies for (i) Packing Structure, (ii) chain trajectory, (iii) conformation of the folded chains, (iv) nucleation mechanisms in the early stage of crystallization, and (v) deformation mechanism at the molecular scale of semicrystalline polymers.
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chain trajectory chain Packing and molecular dynamics of semicrystalline polymers as studied by solid state nmr
Polymers, 2018Co-Authors: Shijun Wang, Youlee Hong, Shichen Yuan, Wei Chen, Wenxuan Zhou, Kun Wang, Xu Min, Takashi Konishi, Toshikazu MiyoshiAbstract:Chain-level Structure of semicrystalline polymers in melt- and solution-grown crystals has been debated over the past half century. Recently, 13C⁻13C double quantum (DQ) Nuclear Magnetic Resonance (NMR) spectroscopy has been successfully applied to investigate chain-folding (CF) Structure and Packing Structure of 13C enriched polymers after solution and melt crystallization. We review recent NMR studies for (i) Packing Structure, (ii) chain trajectory, (iii) conformation of the folded chains, (iv) nucleation mechanisms, (v) deformation mechanism, and (vi) molecular dynamics of semicrystalline polymers.
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Stoichiometry and Packing Structure of Poly(lactic acid) Stereocomplex as Revealed by Solid-State NMR and 13C Isotope Labeling
2018Co-Authors: Wenxuan Zhou, Shijun Wang, Shichen Yuan, Wei Chen, Kun Wang, Takashi Konishi, Toshikazu MiyoshiAbstract:Poly(l-lactic acid) (L)/poly(d-lactic acid) (D) blends form a stereocomplex (SC) at a mixing ratio of 7/3–3/7. The stoichiometry and Packing Structure of L/D in the SC are controversial topics because the SC is semicrystalline and because the enantiomeric pair has the same chemical Structure. In this study, both the stoichiometry and Packing Structure of 33% 13C CH3-labeled (l) L/nonlabeled D blends at mixing ratios of 7/3–3/7 were investigated by using solid-state (SS) NMR. The 13C CO signals in natural abundance provided the fractions of the SC (ΦSC), α, and amorphous regions of l-L/D blends. Moreover, the 33% 13CH3-labeled signals could determine the fraction of only l-L in the SC (ΦL) and amorphous region. These two data sets allowed us to determine the stoichiometry of l-L/D in the SC (ΦL‑SC/ΦD‑SC) to be 1/1. 13C–13C double-quantum (DQ) buildup curves of l-L in the SC followed one universal curve even at different mixing ratios. Comparison of the experimental and simulated DQ curves led to the conclusion that all SC crystals adopt a regular Packing Structure at varied mixing ratios
Yixiang Gan - One of the best experts on this subject based on the ideXlab platform.
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the effects of Packing Structure on the effective thermal conductivity of granular media a grain scale investigation
International Journal of Thermal Sciences, 2019Co-Authors: Weijing Dai, Dorian A H Hanaor, Yixiang GanAbstract:Abstract Structural characteristics are considered to be the dominant factors in determining the effective properties of granular media, particularly in the scope of transport phenomena. Enhancing heat management requires an improved fundamental understanding of thermal transport in granular media. In this study, the effects of Packing Structure on heat transfer in granular media are evaluated at macro- and grain-scales. At the grain-scale, a gas-solid coupling heat transfer model is adapted into a discrete-element-method to simulate this transport phenomenon. The numerical framework is validated by experimental data obtained using a plane source technique, and the Smoluchowski effect of the gas phase is found to be captured by this extension. By considering Packings of spherical SiO2 grains with an interstitial helium phase, vibration induced ordering in granular media is studied, using the simulation method developed here, to investigate how disorder-to-order transitions of Packing Structure enhance effective thermal conductivity. Grain-scale thermal transport is shown to be influenced by the local neighbourhood configuration of individual grains. The formation of an ordered Packing Structure enhances both global and local thermal transport. This study provides a Structure-based approach to explain transport phenomena, which can be applied in properties modification for granular media.
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the effects of Packing Structure on the effective thermal conductivity of granular media a grain scale investigation
arXiv: Soft Condensed Matter, 2018Co-Authors: Weijing Dai, Dorian A H Hanaor, Yixiang GanAbstract:Structural characteristics are considered to be the dominant factors in determining the effective properties of granular media, particularly in the scope of transport phenomena. Towards improved heat management, thermal transport in granular media requires an improved fundamental understanding. In this study, the effects of Packing Structure on heat transfer in granular media are evaluated at macro- and grain-scales. At the grain-scale, a gas-solid coupling heat transfer model is adapted into a discrete-element-method to simulate this transport phenomenon. The numerical framework is validated by experimental data obtained using a plane source technique, and the Smoluschowski effect of the gas phase is found to be captured by this extension. By considering Packings of spherical SiO2 grains with an interstitial helium phase, vibration induced ordering in granular media is studied, using the simulation methods developed here, to investigate how disorder-to-order transitions of Packing Structure enhance effective thermal conductivity. Grain-scale thermal transport is shown to be influenced by the local neighbourhood configuration of individual grains. The formation of an ordered Packing Structure enhances both global and local thermal transport. This study provides a Structure approach to explain transport phenomena, which can be applied in properties modification for granular media.
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Computer simulation of Packing Structure in pebble beds
Fusion Engineering and Design, 2010Co-Authors: Yixiang Gan, Marc Kamlah, J. ReimannAbstract:In HCPB blankets, pebble beds are composed of nearly spherical particles in the state of random closed Packing. The Packing Structure is important to understand responses of pebble beds, e.g., mechanical stresses and effective thermal conductivity. In this paper, an algorithm for random close Packing of polydisperse particles is presented which can be used for arbitrary pebble bed containing geometries. The microStructure of a packed bed in both the bulk and near-wall regions can be determined. Computer-generated samples are compared to recent X-ray tomography results of non-compressed pebble beds, including the Packing factors and coordination number. Moreover, initial configurations obtained by this method can be used in discrete element simulations of random configurations of pebbles to investigate the overall behaviour of pebble beds under fusion-relevant conditions.
Kohji Tashiro - One of the best experts on this subject based on the ideXlab platform.
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factors governing the 3 dimensional hydrogen bond network Structure of poly m phenylene isophthalamide and a series of its model compounds 2 computer simulation of crystal Structures of aromatic amide compounds and comparison with x ray analyzed stru
Journal of Physical Chemistry B, 2002Co-Authors: Kohji Tashiro, Piyarat Nimmanpipug And, Orapin RangsimanAbstract:Crystal Structures have been predicted by using a software Polymorph Predictor and compared with those analyzed by X-ray method for a series of low-molecular-weight aromatic amide compounds as models of poly(m-phenylene isophthalamide) and poly(p-phenylene terephthalamide). For most of the compounds investigated here, the predicted crystal Structure of the lowest or the next lowest Packing energy has been found to be in good agreement with the X-ray analyzed Structure. However, the energy difference was not very large between these energetically most plausible Structures and the other less stable candidates, indicating a difficulty of unique prediction of 3D molecular Packing Structure and a possibility of existence of various types of crystal modification.
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comparison of crystal Structure between low and high temperature phases of diethyl z z muconate a trial to investigate the reasons why the solid state polymerization reaction is ceased at low temperature
Polymer Journal, 2001Co-Authors: Seishi Saragai, Kohji Tashiro, Toshiya Kamae, Akikazu Matsumoto, Shinsuke Nakamoto, Takashi TsubouchiAbstract:Diethyl (Z,Z)-muconate (EMU) shows the topotactic polymerization reaction in the solid-state by an irradiation of light. This reaction occurs quite rapidly at room temperature but reduces its rate gradually at lower temperature and does not occur at all below −45°C, where the 1st-order phase transition occurs. In order to clarify the reasons why the reaction is ceased in the low-temperature phase, the X-Ray structural analysis was made at −80°C by using an imaging plate system. The molecular Packing Structure was found to be slightly different from that at room temperature. If the reactivity is affected quite sensitively by such a slight difference in Packing Structure, we have to say that the solid-state polymerization of EMU can be induced for the first time when the molecular Packing mode satisfies the quite narrow and limited geometrical condition. But, this idea is difficult to be accepted at the present stage judging from the small structural difference between the two phases. As seen typically for the case of polydiacetylenes, the solid-state polymerization or in more general the topochemical reactions had been discussed so far in terms of such Packing geometry as the inter-atomic distance, the molecular orientation in the crystal lattice, etc. But this rule is considered to be too simple to interpret the remarkable difference in the polymerization reactivity at high- and low-temperatures of EMU. In other words, this example of EMU brings up a very important warning about the conventionally-made discussion on the factors governing the solid-state polymerization reaction.
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structural change in the topochemical solid state polymerization process of diethyl cis cis muconate crystal 1 investigation of polymerization process by means of x ray diffraction infrared raman spectra and dsc
Macromolecules, 1999Co-Authors: Kohji Tashiro, Toshiya Kamae, Masamichi Kobayashi, Akikazu Matsumoto, Katsutaka Yokoi, Shuzo AokiAbstract:Structural change occurring in the light-induced solid-state polymerization of diethyl cis,-cis-muconate crystal has been investigated by means of the X-ray diffraction, infrared and Raman spectra, and DSC. The infrared and Raman spectral changes during this polymerization reaction could be interpreted on the basis of a simple two-component system consisting of monomer and polymer molecules. This apparent observation may originate from the high sensitivity of the vibrational spectra to the local Structure. The time-resolved X-ray diffraction measurement, however, showed that the lattice spacings changed continuously in the process of polymerization, indicating that the strain to the crystal lattice, due to the coexistence of the different chemical species of monomer and polymer with various lengths or volumes, changed in this reaction. But this strain was quite small, and the crystal lattice could be maintained more or less during the polymerization reaction. It was also found that the polymerization did not occur at a low temperature below -40 °C, where the phase transition occurred and the Packing Structure of monomer molecules changed, as indicated by the large change in the X-ray diffraction pattern. This good correlation between the reactivity and the crystal Structure indicates that the polymerization reaction is governed sensitively by the Packing Structure of monomer molecules; i.e., this reaction is just the lattice-controlled polymerization.
Yiik Diew Wong - One of the best experts on this subject based on the ideXlab platform.
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the influence of aggregate shape properties on aggregate Packing in porous asphalt mixture pam
Construction and Building Materials, 2020Co-Authors: Dana Mutiara Kusumawardani, Yiik Diew WongAbstract:Abstract Aggregate shape properties is one of the factors that determine the Packing conditions of asphalt mixtures. The influence of aggregate shape properties was evaluated by utilising aggregates in three shapes, namely cubical, blade, and disk. Three shape parameters, namely sphericity, shape factor, and roundness, were defined to quantify the shape properties of the aggregates. Herein, the influence of aggregate shape on the Packing of porous asphalt mixture (PAM) was evaluated via comparative studies of PAM’s mechanical properties in laboratory measurements versus discrete element method (DEM) algorithmic simulations. PG-76 binder was used in the PAM, with compaction by a gyratory compactor. Simulation models of PAMs were built in Particle Flow Code in 3 Dimensions (PFC3D) algorithm simulation. The results showed that aggregate Packing Structure is greatly affected by aggregate shape properties, in terms of volumetric properties and mechanical properties. Statistical analysis results indicated that cubical shape is the recommended shape to optimise the quality of aggregate Packing Structure of PAM. The research provided in-depth analysis of PAM Packing Structure, in terms of volumetric and mechanical properties. The results of these experiments indicated that DEM simulation is an appropriate method to evaluate aggregate Packing Structure of PAM.
