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Effect of Particle Size on Mechanical Properties and Fracture Behaviors of Age-Hardening SiC/Al–Zn–Mg–Cu Composites

Acta Metallurgica Sinica(English Letters) 2021年第10期34卷 1447-1459页

作者： Guonan ma Dong Wang Bolv Xiao Zongyi ma Institute of Metal research Chinese Academy of SciencesShenyang 110016China School of materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China

15 vol.% SiC/Al-6.5Zn-2.8 Mg-1.7 Cu(wt%) composites with varying particle sizes(3.5, 7.0, 14 and 20 μm), i.e., C-3.5, C-7.0, C-14, and C-20, respectively, were fabricated by powder metallurgy(PM) method and subjected to microstructural examination. The effect of particle size on mechanical properties and fracture behaviors of the T6-treated composites was revealed and analyzed in detail. Element distribution and precipitates variations in the composites with varying particle sizes were emphatically considered. results indicated that both tensile strength and plasticity of the T6-treated composites increased first and then decreased with particle size decreasing. The C-7.0 composite simultaneously exhibited the highest ultimate tensile strength(UTS) of 686 MPa and best elongation(El.) of 3.1%. The smaller-sized SiC particle would introduce more oxide impurities, which would react with the alloying element in the matrix to cause Mg segregation and depletion. According to strengthening mechanism analysis, the weakening of precipitation strengthening in the T6-treated C-3.5 composite was the main cause of the lower tensile strength. Additionally, the larger SiC particle, the more likely to fracture, especially in the composites with high yield strength. For the T6-treated C-20 composites, more than 75% SiC particles were broken up, resulting in the lowest plasticity. As decreasing particle size, the fracture behaviors of the T6-treated composites would change from particle fracture to matrix alloy fracture gradually.

关键词： Metal matrix composites Mechanical properties Particle size Fracture behaviors Strengthening mechanisms

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QUANTIZATION COMMUTES WITH rEDUCTION,A SUrVEY

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Acta mathematica Scientia 2021年第6期41卷 1859-1872页

作者： Xiaonan ma Institut de mathématiques de Jussieu-Paris rive Gauche Universitéde ParisUFR de MathématiquesCase 701275205Paris Cedex 13France

We review the themes relating to the proposition that“quantization commutes with reduction”([Q,r]=0),from symplectic manifolds to Cauchy-riemann manifolds.

关键词： index theory Dirac operator geometric quantization

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Anisotropy of the Wear Behavior for Carbon Nanotube-reinforced 6061Al Composites

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Acta Metallurgica Sinica(English Letters) 2023年第5期36卷 814-826页

作者： X.N.Li J.F.Zhang W.H.Xue k.ma P.Y.Li Z.Y.Liu B.L.Xiao D.r.Ni Q.Z.Wang D.Wang Z.Y.ma School of materials Science and Engineering University of Science and Technology of ChinaShenyang110016China Shi-Changxu Innovation Center for Advanced materials Institute of Metal ResearchChinese Academy of SciencesShenyang110016China

Carbon nanotube(CNT)-reinforced 6061Al(CNT/6061Al)composites with directionally aligned CNT were fabricated,and their wear behavior was *** results indicate that the wear properties of CNT/6061Al composites exhibited a significant anisotropy.A certain CNT concentrations(1 wt%and 2 wt%)could effectively improve the wear resistance of CNT/6061Al composites along the CNT circumferential and CNT radial directions for the load transfer,grain refinement and self-lubrication effect of *** Brass{011}and{112}textures inhibited the load transfer effect of CNT along the CNT radial direction,resulting in a better wear resistance along CNT circumferential direction than CNT radial *** the CNT axial direction,the weak deformability of composites caused by the intensifyingfiber texture was the main reasons for the poor wear resistance of CNT/6061Al composites with increasing CNT concentration.

关键词： Carbon nanotube Metal matrix composite Wear Anisotropy

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Microstructure and mechanical properties of double-side friction stir welded 6082Al ultra-thick plates

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Journal of materials Science & Technology 2020年第6期41卷 105-116页

作者： C.Yang J.F.Zhang G.N.ma L.H.Wu X.M.Zhang G.Z.He P.Xue D.r.Ni B.L.Xiao k.S.Wang Z.Y.ma Shenyang National Laboratory for materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China CrrC Changchun railway Vehicles Co. Ltd.Changchun 130062China School of Metallurgical Engineering Xi’an University of Architecture and TechnologyXi’an 710055China

In the present work,80 mm thick 6082Al alloy plates were successfully double-side welded by friction stir welding(FSW).The relationship between the microstructures and mechanical properties was built for the double-side FSW butt joint with more attention paid to the local characteristic *** was shown that a phenomenon of microstructural inhomogeneity existed in the nugget zone(NZ)through the thickness *** grain size presented an obvious gradient distribution from the top to the bottom for each single-pass weld,and the microhardness values decreased from both surfaces to the middle of the *** lowest hardness zone(LHZ)exhibited a"hyperbolical"-shaped distribution extending to the middle of the *** tensile properties were obtained in the three sliced specimens of the FSW joint,and the joint coefficient reached about 70%which achieved the same level as the conventional FSW Al alloy *** element modeling proved that the"hyperbolical"-shaped heat affected zone(HAZ)was beneficial to resisting the strain concentration in the middle layer specimen which helped to increase the tensile *** on the analysis of the hardness contour map,tensile property and microstructural evolution of the joints,an Isothermal Softening Layer(ISL)model was proposed and established,which may have a helpful guidance for the optimization on the FSW of ultra-thick Al alloy plates.

关键词： Ultra-thick aluminum alloy plates Double-side friction stir welding Finite element model Microstructural inhomogeneity Mechanical properties

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Temporal and spatial distribution of microfractures in granites of different structures under triaxial compression and its significance in seismology

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Chinese Science Bulletin 1999年第14期44卷 1321-1325页

作者： Liqiang Liu Shengli ma Jin ma Xinglin Lei k. kusunose O. Nishizawa L. Jouniaux China Seismol Bur Inst Geol Beijing 100029 Peoples R China Geol Survey Japan Tsukuba Ibaraki 305 Japan Ecole Normale Super Geol Lab F-75231 Paris France CNrS URA 1316 Paris France

The temporal and spatial distribution of microfracturing activity in two kinds of granite under triaxial compression has been studied by using a new acoustic emission system. For Inada granite, there is no clear clustering of acoustic emission events in time and space, thus it is difficult to exactly deduce the time and position of the major fracturing. While for mayet granite,acoustic emission events are clustered in time and space, so the time and position of the major fracturing can be exactly predicted according to microfracturing process. Such a difference may result from the difference in deformation mode caused by different rock structures.

关键词： rock structure acoustic emission microfracturing temporal and spatial distribution seismicity.

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Animal diversities and characteristics of environmental change revealed by skeletons unearthed at Zhongba Site of Chongqing City,China

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Chinese Science Bulletin 2008年第S1期53卷 74-86页

作者： ZHU Cheng ma ChunMei OUYANG Jie LI ZhongXuan YIN Qian SUN ZhiBin HUANG YunPing r.k.FLAD LI Lan LI YuMei School of Geographic and Oceanographic Sciences of Nanjing University Nanjing 210093China Cultural relic and Archaeology research Institute of Sichuan Province Chengdu 610041China Faculty of Archaeology and Museology Peking UniversityBeijing 100871China Department of Anthropology Peabody MuseumHarvard UniversityCambridgeMA 02138USA Graduate University of Chinese Academy of Sciences Beijing 100049China

Nearly 200000 animal skeletons are unearthed in the Unit T0202 from Zhongba Site of Zhongxian *** to the analysis of 129165 specimens,these skeletons may be classified into 5 kinds, namely,mammalia,Osteichthys,Aves,Amphibian and reptilia,which belong to 13 orders,28 families and 42 *** this paper,based on archeological dating and AMS 14 C data,through statistically analyzing the unearthed skeletons and studying the change of the smallest individual numbers,these research results detected the following:1)In almost all the time of 2370―200 BC,in Zhongba region, some animals distributed widely,such as Muntiacus sp,Elaphodus cephalophus and Muntiacus sp. inhabiting in glade and grassland,Scrofa *** Canis familiaris raised by the ancient people,rodentia rabbit and rattus rattus,which suggested that a fairly good ecological environment of forest and grassland was preserved at that period and the predecessors began to raise domestic animals from 1750 to 1000 BC,which has lasted until today.2)rhinoceros only lived during 2000―1750 BC,1000― 700 BC and 700―500 BC,which indicates that the ecological environment of grassland and wetland might be better in these phases.3)macaca *** Ursus arctos appeared only after 1750―1000 BC, which may show that the forest condition is better for animals to live during 1750―200 BC.4)The smallest individual numbers of Bublus sp.,bos *** otters emerged during about 2370―1750 BC, which perhaps infers that water area during the early period was wider than that of the late period.5) Since skeletons of rhinoceros are discovered in strata of Zhongba Site during 2000―1750 BC and 1000―500 BC,according to the climate and ecology environment which rhinoceros live in now,the average annual temperature and precipitation during 2000―1750 BC and 1000―500 BC are supposed to be probably higher than that of *** Zhu kezhen considered that the first low temperature period in the past 5000 years of China was between 1100 BC a

关键词： Zhongba Site animal skeletons animal diversity climate and ecological environment change 2370 BC—200 BC

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Modeling of terahertz pulse generation from LT-GaAs ultrafast photoconductive switches

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Journal of Systems Engineering and Electronics 2011年第3期22卷 373-380页

作者： Zhe ma ongmei ma Chuntao Yang keming Feng Beijing Institute of radio Metrology and Measurement Beijing 100854P.R.China eijing Institute of Electronic System Engineering Beijing 100854P.R.China

The technique of terahertz pulses generated from the photoconductive switches has been applied in the ultrafast electrical pulse metrology recently.A lumped-element theoretical model is established to describe the performance of the LT-GaAs ultrafast photoconductive switch used in the ultrafast pulse *** carrier transport processes of the photoexcited semiconductor,the attenuation and dispersion during terahertz pulse propagating are considered in the theoretical *** to the experimental parameters,the waveforms of the generated terahertz pulses are calculated under optical excitations with different wavelengths of 840 nm and 450 nm,*** comparisons between the theoretical results and the experimental results are carried out.

关键词： terahertz pulse photoconductive switch coplanar waveguide LT-GaAs.

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A Similitude Method and the Corresponding Blade Design of a Low-Speed Large-Scale Axial Compressor rotor

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Journal of Thermal Science 2014年第2期23卷 145-152页

作者： YU Chenghai ma Ning WANG kai DU Juan Van den Braembussche r.A. LIN Feng key Laboratory of Advanced Energy and Power Institute of Engineering ThermophysicsChinese Academy of Sciences Graduate School of Chinese Academy of Sciences von karman Institute for Fluid Dynamics Turbomachinery and Propulsion DepartmentWaterloose steenweg721640 Sint-Genesius-RodeBelgium

A similitude method to model the tip clearance flow in a high-speed compressor with a low-speed model is presented in this *** first step of this method is the derivation of similarity criteria for tip clearance flow,on the basis of an inviscid model of tip clearance *** aerodynamic parameters needed for the model design are then obtained from a numerical simulation of the target high-speed compressor *** to the aerodynamic and geometric parameters of the target compressor rotor,a large-scale low-speed rotor blade is designed with an inverse blade design *** order to validate the similitude method,the features of tip clearance flow in the low-speed model compressor are compared with the ones in the high-speed compressor at both design and small flow rate *** is found that not only the trajectory of the tip leakage vortex but also the interface between the tip leakage flow and the incoming main flow in the high-speed compressor match well with that of its low speed *** results validate the effectiveness of the similitude method for the tip clearance flow proposed in this paper.

关键词： Similitude method Low-speed model Tip clearance flow TLF/MF interface

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Friction Stir Welding of Discontinuously reinforced Aluminum matrix Composites:A review

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Acta Metallurgica Sinica(English Letters) 2014年第5期27卷 816-824页

作者： D.Wang B.L.Xiao D.r.Ni Z.Y.ma Shenyang National Laboratory for materials Science Institute of Metal ResearchChinese Academy of Sciences

Friction stir welding （FSW） is considered a promising welding technique for joining the aluminum matrix composites （AMCs） to avoid the drawbacks of the fusion welding. High joint efficiencies of 60%-100% could be obtained in the FSW joints of AMCs. However, due to the existence of hard reinforcing particles in the AMCs, the wearing of welding tool during FSW is an unavoidable problem. Moreover, the low ductility of the AMCs limits the welding process window. As the hard materials such as Ferro-Titanit alloy, cermet, and WC/Co were applied to produce the welding tools, the wearing of the tools was significantly reduced and the sound joints could be achieved at high welding speed for the AMCs with low reinforcement volume fraction. In this article, current state of understanding and development of welding tool wearing and FSW parameters of AMCs are viewed. Furthermore, the factors affecting the microstructure and mechanical properties of the joints are evaluated in detail.

关键词： Metal matrix composite Friction stir welding Particle, microstructure Wear

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Stationary distribution and long-time behavior of COVID-19 model with stochastic effect

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International Journal of Biomathematics 2023年第2期16卷 85-114页

作者： C.Gokila M.Sambath k.Balachandran Yong-ki ma Department of mathematics Periyar University Salem 636011India Department of mathematics Bharathiar University Coimbatore 641046India Department of Applied mathematics Kongju National University.Chungcheongnam-do 32588Republic of Korea

The coronavirus disease(COVID-19)is a dangerous pandemic and it spreads to many people in most of the *** this paper,we propose a COVID-19 model with the assumption that it is affected by *** positivity,we prove the global existence of positive solution and the system exhibits extinction under certain parametric ***,we establish the stability region for the stochastic model under the behavior of stationary *** stationary distribution gives the guarantee of the appearance of infection in the population,Besides that,we find the reproduction ratio r for prevail and disappear of infection within the human *** the graphical representation,we have validated the threshold conditions that define in our theoretical findings.

关键词： COVID-19 model extinction threshold value stationary distribution

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