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DEM investigation of strength and critical state behaviours of granular materials under true triaxial loadings

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Particuology 2024年第2期85卷 198-212页

作者： Minyi Zhu Guobin Gong jun xia Stephen Wilkinson Department of Civil Engineering Xi'an Jiaotong-Liverpool UniversityChina Department of Civil Engineering and Industrial Design University of LiverpoolLiverpoolUK Faculty of Engineering and Information Sciences University of Wollongong in DubaiUnited Arab Emirates

This paper investigates the strength and critical state(CS)behaviours of granular materials via DEM simulations of true triaxial drained tests under three different loading modes including constant b(in-termediate stress ratio)tests with constantσ'1(major principal stress),constant p(mean pressure)and constantσ'3(minor principal stress)*** this end,a series of samples are generated with the same particle size distribution,and with the confining stresses ranging from 100 kPa to 900 *** CS is achieved for all *** the macroscopic behaviours and the microscopic behaviours are examined and compared considering different loading modes,confining stresses and intermediate stress ratios(b).The critical state lines(CSLs)are found to be unique and independent of the loading modes,but dependent on the b *** CSLs with b=0 and b=1 form the two boundaries of CSLs respectively beyond which CSLs under all other b tests cannot go *** different strength criteria are examined and compared in terms of both peak and CS *** Mohr-Coulomb strength criterion is found to be only suitable for axisymmetric loading *** Lade-Duncan criterion is only suitable for describing peak strengths,which is dependent on the loading modes and confining *** Satake criterion and Matsuoka-Nakai criterion are the more appropriate strength criteria for describing CS failures,indicating that the CS values of both the Satake parameter and the Matsuoka-Nakai parameter describe an inherent property that characterizes the CS failure for a given type of *** CS mechanical coordination number is fitted by a curved line for a given b value,which is unique regardless of the loading *** peak and CS values of both major and minor principal fabric tensors decrease with increasing b values,while they increase with increasing b values for the intermediate principal fabric tensor.

关键词： Discrete element method Intermediate stress ratio Dilation Critical state Failure criterion

Numerical simulations for radon migration and exhalation behavior during measuring radon exhalation rate with closed-loop method

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Nuclear Science and Techniques 2024年第1期35卷 81-95页

作者： Ming xia Yong-jun Ye Shu-Yuan Liu School of Resources Environment and Safety Engineering University of South ChinaHengyang 421001China Key Discipline Laboratory for National Defense for Biotechnology in Uranium Mining and Hydrometallurgy University of South ChinaHengyang 421001China

Accurate measurements of the radon exhalation rate help identify and evaluate radon risk regions in the *** these measurement methods,the closed-loop method is frequently ***,traditional experiments are insufficient or cannot analyze the radon migration and exhalation patterns at the gas–solid interface in the accumulation *** CFD-based technique was applied to predict the radon concentration distribution in a limited space,allowing radon accumulation and exhalation inside the chamber intuitively and *** this study,three radon exhalation rates were defined,and two structural ventilation tubes were designed for the *** consistency of the simulated results with the variation in the radon exhalation rate in a previous experiment or analytical solution was *** effects of the vent tube structure and flow rate on the radon uniformity in the chamber;permeability,insertion depth,and flow rate on the radon exhalation rate and the effective diffusion coefficient on back-diffusion were *** on the results,increasing the inser-tion depth from 1 to 5 cm decreased the effective decay constant by 19.55%,whereas the curve-fitted radon exhalation rate decreased(lower than the initial value)as the deviation from the initial value increased by approximately 7%.Increasing the effective diffusion coefficient from 2.77×10^(-7) to 7.77×10^(-6) m^(2) s^(-1) made the deviation expand from 2.14 to 15.96%.The conclusion is that an increased insertion depth helps reduce leakage in the chamber,subject to notable back-diffusion,and that the closed-loop method is reasonably used for porous media with a low effective diffusion coefficient in view of the back-diffusion *** CFD-based simulation is expected to provide guidance for the optimization of the radon exhalation rate measurement method and,thus,the accurate measurement of the radon exhalation rate.

关键词： Radon exhalation Numerical simulation Accumulation chamber

Optimal band structure for thermoelectrics with realistic scattering and bands

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npj Computational Materials 2021年第1期7卷 388-396页

作者： junsoo Park yi xia Vidvuds Ozoliņš Anubhav Jain Energy Technologies Area Lawrence Berkeley National LaboratoryBerkeleyCAUSA Department of Materials Science and Engineering Northwestern UniversityEvanstonILUSA Department of Applied Physics Yale UniversityNew HavenCTUSA Energy Sciences Institute Yale UniversityWest HavenCTUSA

Understanding how to optimize electronic band structures for thermoelectrics is a topic of long-standing interest in the *** models have been limited to simplified bands and/or scattering *** this study,we apply more rigorous scattering treatments to more realistic model band structures—upward-parabolic bands that inflect to an inverted-parabolic behavior—including cases of multiple *** contrast to common descriptors(e.g.,quality factor and complexity factor),the degree to which multiple pockets improve thermoelectric performance is bounded by interband scattering and the relative shapes of the *** establish that extremely anisotropic“flat-and-dispersive”bands,although best-performing in theory,may not represent a promising design strategy in ***,we determine optimum bandwidth,dependent on temperature and lattice thermal conductivity,from perfect transport cutoffs that can in theory significantly boost zT beyond the values attainable through intrinsic band structures *** analysis should be widely useful as the thermoelectric research community eyes zT>3.

关键词： bands parabolic apply

Effect of squeeze casting process on microstructures and flow stress behavior of Al-17.5Si-4Cu-0.5Mg alloy

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Journal of Iron and Steel Research International 2017年第9期24卷 957-965页

作者： Yuan-ji Shi Lan-ji Liu Lei Zhang Li-jun Zhang Li Zheng Run-xia Li Bao-yi Yu School of Materials Science and Engineering Shenyang University of TechnologyShenyang 110870LiaoningChina

The effects of squeeze casting process on microstructure and flow stress behavior of Al-17.5Si-4Cu-0.5Mg alloy were investigated and the hot-compression tests of gravity casting and squeeze casting alloy were carried out at 350-500°C and *** results show that microstructures of Al-17.5Si-4Cu-0.5Mg alloys were obviously improved by squeeze *** to the decrease of coarse primary Si particles,softα-Al dendrite as well as the fine microstructures appeared,and the mechanical properties of squeeze casting alloys were ***,when the strain rate rises or the deformation temperature decreases,the flow stress increases and it was proved that the alloy is a positive strain rate sensitive *** was deduced that compared with the gravity casting alloy,squeeze casting alloy（solidified at 632 MPa）is more difficult to deform since the flow stress of squeeze casting alloy is higher than that of gravity casting alloy when the deformation temperature exceeds 400°*** stress behavior of Al-17.5Si-4Cu-0.5Mg alloy can be described by a hyperbolic sine form with Zener-Hollomon parameter,and the average hot deformation activation energy Q of gravity casting alloy and squeeze casting alloy is 278.97 and 308.77kJ/mol,respectively.

关键词： Squeeze casting Al-Si-Cu-Mg alloy Hot compression deformation Flow stress Constitutive equation

Kinetics and thermal stability of the Ni_(62)Nb_(38–x)Ta_x(x=5, 10, 15,20 and 25) bulk metallic glasses

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Science China(Physics,Mechanics & Astronomy) 2017年第7期60卷 70-75页

作者： MengKe He yi Zhang Lei xia Peng Yu College of Physics and Electronic Engineering Chongqing Normal University School of Communication & Information Engineering University of Electronic Science and Technology of China

We studied thermal stability and its relationship to the glass-forming ability （GFA） of the Ni62Nb38-xTax （x=5, 10, 15, 20, 25） bulk metallic glasses （BMG） fi＇om a kinetic point of view. By fitting the heating-rate dependence of glass transition temperature （Tgonsct） and crystallization temperatures （Txonset and Txpcak） of the Ni62Nb38_xTax BMG using the Vogel-Fulcher-Tammann （VFT） equation, we obtained the ideal glass transition and crystallization temperatures （Tg0 and Tx2） and the fragility parameter （m）, and also constructed continuous heating transition （CHT） diagrams for crystallization of the BMG. The CHT diagrams of the BMG indicate enhanced thermal stability by Ta addition; the Tg~ as well as the Tx~ also illustrates this improved stability limit. The compositional dependence of m, which agrees well with that of the reduced glass-transition temperature, indicates a strong correlation between liquid fragility and glass-forming ability in the present alloy system. These results provide new evidence for understanding thermal stability, liquid fragility, and GFA in BMG.

关键词： bulk metallic glasses thermal stability kinetics glass-forming ability

Comparative Study of the Magnetic Properties and Glass-Forming Ability of Fe-Based Bulk Metallic Glass with Minor Mn, Co, Ni, and Cu Additions

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Acta Metallurgica Sinica(English Letters) 2016年第9期29卷 834-839页

作者： Md Anisur Rahman Yun-Zhuo Lu Qiang Luo Shou-Jiang Qu Feng-xia Ye yi-Xuan Wu jun Shen School of Materials Science and Engineering Tongji University School of Materials Science and Engineering Dalian Jiaotong University

Fe43MsCra5Mo14C15B6Y2 （M = Mn, Co, Ni, and Cu in at.%） bulk metallic glasses （BMGs） are synthesized using the suction casting technique, and the glass-forming ability （GFA）, microstructure, and thermal and magnetic properties of these glasses are extensively examined using X-ray diffraction, differential scanning calorimeter, and vibrating sample magnetometer techniques. Among the four BMG alloys, Fe43NisCr15Mo14C15B6Y2 exhibits the lowest coercivity and the highest saturation magnetization, Curie temperature, effective magnetic moment, and GFA. By contrast, Fe43MnsCrlsMo14C15B6Y2 presents the poorest magnetic properties, such as the highest coercivity and the lowest saturation magnetization, Curie temperature, and effective magnetic moment. Fe43Cu5Cr15MolaC15B6Y2 demonstrates the lowest thermal stability and GFA. The observed thermal, structural, and magnetic properties of these BMG alloys are discussed in terms of the kinetics of BMG synthesization and the formation of different ferromagnetic, ferrimagnetic, and antiferromagnetic phases.

关键词： Bulk metallic glasses Saturation magnetization Effective magnetic moment Coercivity Glass-forming ability

Metal distribution characteristic of MSWI bottom ash in view of metal recovery

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Journal of Environmental Sciences 2017年第2期29卷 178-189页

作者： yi xia Pinjing He Liming Shao Hua Zhang State Key Laboratory of Pollution Control&Resource Reuse Tongji UniversityShanghai 200092China Institute of Waste Treatment and Reclamation Tongji UniversityShanghai 200092China Center for the Technology Research and Training on Household Waste in Small Towns&Rural Area Ministry of Housing and Urban-RuralDevelopment of China(MOHURD)Shanghai 200092China

Bottom ash is the major by-product of municipal solid waste incineration（MSWI）, and is often reused as an engineering material, such as road-base aggregate. However, some metals（especially aluminum） in bottom ash can react with water and generate gas that could cause expansion and failure of products containing the ash; these metals must be removed before the ash is utilized. The size distribution and the chemical speciation of metals in the bottom ash from two Chinese MSWI plants were examined in this study, and the recovery potential of metals from the ash was evaluated. The metal concentrations in these bottom ashes were lower than that generated in other developed countries. Specifically, the contents of Al,Fe, Cu and Zn were 18.9–29.2, 25.5–32.3, 0.7–1.0 and 1.6–2.5 g/kg, respectively. Moreover,44.9–57.0 wt.% of Al and 55.6–75.4 wt.% of Fe were distributed in bottom ash particles smaller than 5 mm. Similarly, 46.6–79.7 wt.% of Cu and 42.9–74.2 wt.% of Zn were concentrated in particles smaller than 3 mm. The Fe in the bottom ash mainly existed as hematite, and its chemical speciation was considered to limit the recovery efficiency of magnetic separation.

关键词： Municipal solid waste incineration Bottom ash Metal speciation Metal recovery Size distribution

Fluorinated graphite nanosheets for ultrahigh-capacity lithium primary batteries

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Rare Metals 2021年第7期40卷 1708-1718页

作者： xiao-xia Yang Guan-jun Zhang Bao-Sheng Bai Yu Li yi-xiao Li Yong Yang xian Jian Xi-Wen Wang Tianjin Lishen Special Power Supply Science and Technology Joint-Stock Co. Tianjin 300393China Tianjin Lishen Battery Joint-Stock Co. LtdTianjin 300384China School of Materials Science and Engineering Tianjin UniversityTianjin 300354China State Key Laboratory for Physical Chemistry of Solid Surface Department of ChemistryCollege of Chemistry and Chemical EngineeringXiamen UniversityXiamen 361005China School of Materials and Energy University of Electronic Science and Technology of ChinaChengdu 611731China

For better performances of Ni-based catalysts at low temperatures,Ni/SiC catalyst doped with a little amount of additive La was successfully *** catalytic CO methanation activity tests showed that 3%La-Ni/SiC catalyst was excellent at a low reaction temperature(95.9%CO conversion and 85.1%CH4 selectivity at250℃)with a superior stability compared with Ni/SiC(3.4%CO conversion and 0%CH4 selectivity at 250℃).This can be attributed to that the addition of La can markedly improve the dispersibility of active metal Ni and reduce the particle sizes of Ni nanoparticles or clusters,and can also regulate the interaction between active components and ***,the high thermal conductivity and thermal stability could avoid the generation of hot spots in the catalyst *** results will promote the development of highly active Ni-based catalysts for the low-temperature methanation reaction.

关键词： Graphite nanosheets Carbon fluoride Primary battery Electrolyte Soft pack battery

Some Convergence Properties for Weighted Sums of Martingale Difference Random Vectors

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Acta Mathematica Sinica,English Series 2024年第4期40卷 1127-1142页

作者： yi WU Xue jun WANG School of Big Data and Artificial Intelligence Chizhou UniversityChizhou 247000P.R.China School of Big Data and Statistics Anhui UniversityHefei 230601P.R.China

Let{X_(ni),F_(ni);1≤i≤n,n≥1}be an array of R^(d)martingale difference random vectors and{A_(ni),1≤i≤n,n≥1}be an array of m×d matrices of real *** this paper,the Marcinkiewicz-Zygmund type weak law of large numb... 详细信息

关键词： Martingale difference random vectors weighted sums Marcinkiewicz–Zygmund type weak law of large numbers complete convergence strong law of large numbers multivariate simple linear regression model