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A set of microstructure-based constitutive equations in hot forming of a titanium alloy

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Journal of University of Science and Technology Beijing 2006年第5期13卷 435-441页

作者： Xiaoli li Miaoquan li College of Materials Science ＆ Engineering Northwestern Polytechnical University Xi＇an 710072 China

A physical model of microstructure evolution including dislocation density rate and grain growth rate was established based on the deformation mechanism for the hot forming of a class of two-phase titanium alloys. Further, a set of mechanism-based constitutive equations were proposed, in which the microstructure variables such as grain size and dislocation density were taken as internal state variables for characterizing the current material state. In the set of constitutive equations, the contributions of different mechanisms and individual phase to the deformation behavior were analyzed. The present equations have been applied to describe a correlation of the flow stress with the microstructure evolution of the TC6 alloy in hot forming.

关键词： titanium alloy constitutive equations microstructure evolution grain size dislocation density

A well-posed Euler-Bernoulli beam model incorporating nonlocality and surface energy effect

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Applied Mathematics and Mechanics(English Edition) 2019年第11期40卷 1561-1588页

作者： Xiaowu ZHU li li School of Statistics and Mathematics Zhongnan University of Economics and LawWuhan 430073China State Key Laboratory of Digital Manufacturing Equipment and Technology School of Mechanical Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074China

This study shows that it is possible to develop a well-posed size-dependent model by considering the effect of both nonlocality and surface energy,and the model can provide another effective way of nanomechanics for *** a practical but simple problem (an Euler-Bernoulli beam model under bending),the ill-posed issue of the pure nonlocal integral elasticity can be ***,a well-posed governing equation can be developed for the Euler-Bernoulli beams when considering both the pure nonlocal integral elasticity and surface ***,closed-form solutions are found for the deflections of clamped-clamped (C-C),simply-supported (S-S) and cantilever (C-F) nano-/*** effective elastic moduli are obtained in terms of the closed-form solutions since the transfer of physical quantities in the transition region is an important problem for span-scale modeling *** nonlocal integral and surface elasticities are adopted to examine the size-dependence of the effective moduli and deflection of Ag beams.

关键词： nonlocal integral elasticity bending size-dependence effect surface elasticity

Theoretical Analysis of Cooperative Driving at Idealized Unsignalized Intersections

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Tsinghua Science and Technology 2024年第1期29卷 257-270页

作者： Shen li Jiawei Zhang Zhenwu Chen li li Department of Civil Engineering Tsinghua UniversityBeijing 100084China Department of Automation Tsinghua UniversityBeijing 100084China Shenzhen Urban Transport Planning Center Co. Ltd.Shenzhen 518000China

Cooperative driving is widely viewed as a promising method to better utilize limited road resources and alleviate traffic *** recent years,several cooperative driving approaches for idealized traffic scenarios(i.e.,uniform vehicle arrivals,lengths,and speeds)have been ***,theoretical analyses and comparisons of these approaches are *** this study,we propose a unified group-by-group zipper-style movement model to describe different approaches synthetically and evaluate their *** derive the maximum throughput for cooperative driving plans of idealized unsignalized intersections and discuss how to minimize the delay of *** obtained conclusions shed light on future cooperative driving studies.

关键词： cooperative driving connected and automated vehicles unsignalized intersection

Traceability model based on improved witness mechanism

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CAAI Transactions on Intelligence Technology 2022年第3期7卷 331-339页

作者： li li Tao li School of Information and Computer Engineering Northeast Forestry UniversityHarbinChina

Traceability system is one of the popular applications of graphic ***,there are centralisation problems and a long time for final consistency confirmation in the graphic *** addition,the blockchain system in the traceability application scenario has the problem of insufficient ***,a witness-based graphic blockchain consensus mechanism is *** the consensus mechanism,a verifiable random function is used to screen the publishers of the unit;an SM2 threshold signature is used to sign the unit information to improve the non-repudiation of the traceability information uploaders to the unit information under the supervision of the *** improved consistency algorithm cancels the process of finding a stable main chain and makes relatively many nodes to participate in the consensus *** experimental results show that the graphic blockchain using the improved witness mechanism can reduce the degree of centralisation,shorten the time for new units to reach consensus,and greatly ensure the security and scalability of the blockchain system.

关键词： mechanism witness signature

Introduction to holographic superconductor models

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Science China(Physics,Mechanics & Astronomy) 2015年第6期58卷 1-46页

作者： CAI RongGen li li li liFang YANG RunQiu State Key Laboratory of Theoretical Physics Institute of Theoretical PhysicsChinese Academy of Sciences Crete Center for Theoretical Physics Department of PhysicsUniversity of Crete State Key Laboratory of Space Weather Center for Space Science and Applied ResearchChinese Academy of Sciences

In the last years it has been shown that some properties of strongly coupled superconductors can be potentially described by classical general relativity living in one higher dimension,which is known as holographic *** paper gives a quick and introductory overview of some holographic superconductor models with s-wave,p-wave and d-wave orders in the literature from point of view of bottom-up,and summarizes some basic properties of these holographic models in various *** competition and coexistence of these superconductivity orders are also studied in these superconductor models.

关键词： holographic duality superconductivity classical theories of gravity conformal field theory

Wheel-rail Profiles Matching Design Considering Railway Track Parameters

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Chinese Journal of Mechanical Engineering 2010年第4期23卷 410-417页

作者： CUI Dabin li li JIN Xuesong li ling School of Mechanical Engineering Southwest Jiaotong University Chengdu 610031 China State Key Laboratory of Traction Power Southwest Jiaotong University Chengdu 610031 China

The profile of wheel/rail has great concern with the vehicle running safety, the wheel/rail wear and the rolling contact fatigue between wheel and rail, due to its severer impact on the dynamic behavior of both the railway vehicle/track, and the wheel/rail rolling contact status. However, recent studies in this respect are mainly explored in reverse methods, where track parameters are predetermined and invariable during the optimizing process. This paper attempts to propose a wheel-rail profiles matching design method considering multi-parameter, through optimizing wheel/rail profile under different rail cants and track gauges, based on the existed optimization technology for the normal gap of wheel/rail. The method presented in this paper can also, compared with the prior reverse methods, be called ＂forward solution method＂ in which the riding comfort, wheel unloading rate and wheel/rail contact stress of the speed-up railway passenger car are calculated by means of a vehicle-track coupling dynamic model, with the range of the rail cant varying from 1/20 to 1/40 and the rail gauge from 1 433 mm to 1 441 mm. These results show that the distribution status of the pairs of contact points can be obviously improved and the contact stress can be reduced significantly; a great influence is exposed by the rail cant and track gauge on the dynamic behavior of the high speed passenger car, and an optimal vehicle dynamics behavior are obtained with the optimized wheel/rail profile when the rail cant is 1/30 and the track gauge is 1 435 mm. This research can provide important references for the investigation of the wheel-rail profiles matching design method considering multi-parameter.

关键词： wheel profile optimization dynamic behavior rail cant track gauge

Comparison of Travel Mode Choice Between Taxi and Subway Regarding Traveling Convenience

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Tsinghua Science and Technology 2018年第2期23卷 135-144页

作者： li li Shuofeng Wang Meng li Jiyuan Tan Department of Automation BNRist Tsinghua University Department of Automation Tsinghua University Department of Civil Engineering Tsinghua University Beijing Key Laboratory of Urban Road Intelligent Traffic Control North China University of Technology

In this study, we investigate travel mode choice behavior between taxi and subway with an emphasis on the influence of traveling convenience. In the first stage, we examine the Origin-Destination(OD) points of Beijing taxi trips and compare these locations with the respective nearest subway station. Statistics reveal several interesting conclusions. First, for approximately 24.89% of all trips, no convenient subway connections exist between the OD pairs. As such, a taxi becomes the only viable choice. Second, for 80.23% of the remaining 75.11%of trips(equivalent to 60.26% of all trips), access distance from either the origin or the destination to the nearest subway station is greater than 500 meters. This phenomenon indicates that walking distance plays an important role in travel mode choice. In the second stage, we examine groups of taxi trips with similar travel distances and travel times to reveal common features. We establish a preference rule in terms of travel distance and travel *** determines whether an individual driver will take a taxi or the subway, using a pairwise comparison-based preference regression model. Tests indicate that more than 95% of taxi trips can be correctly predicted by this preference rule. This conclusion reveals that traveling convenience dominates the travel model choice between taxi and subway. All these findings shed light on the factors that influence travel mode choice behavior.

关键词： travel mode choice behaviors taxi subway preference modeling

Mg-13li-X薄板的拉伸性能与残余应力

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稀有金属材料与工程 2006年第12期35卷 2014-2016页

作者：栗丽周铁涛李焕喜陈昌麒邬秋林章清泉傅祖明北京航空航天大学北京100083 北京首钢冶金研究院北京100088

对一种实验镁锂新合金进行了室温轧制,轧出厚度为1.0mm的薄板,并对其进行了拉伸性能和残余应力测试。结果表明,随轧制变形量的增加,板材强度增加,塑性降低;经过适当退火处理后,板材延伸率可达到39%,强度保持在180MPa。冷轧板材残余应力... 详细信息

对一种实验镁锂新合金进行了室温轧制,轧出厚度为1.0mm的薄板,并对其进行了拉伸性能和残余应力测试。结果表明,随轧制变形量的增加,板材强度增加,塑性降低;经过适当退火处理后,板材延伸率可达到39%,强度保持在180MPa。冷轧板材残余应力值为–3.8MPa,对合金强度基本没有影响。

关键词：镁锂合金冷轧拉伸性能残余应力

The Infiltration Process and Texture Transition of 2D C/C Composites

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Journal of Materials Science & Technology 2009年第1期25卷 109-114页

作者： Hejun li Guozhong Xu Kezhi li Chuang Wang Wei li Miaoling li Carbon/carbon Composites Research Center Key Laboratory of Ultrahigh Temperature Composites Northwestern Polytechnical University Xi＇an 710072 China

2D needle-punched fiber felt was infiltrated by a kind of rapid isothermal chemical vapor infiltration technique. The infiltration process and texture transition of the infiltrated C/C composites were investigated. The porosity and the variations of the cumulative pore volume were determined by mercury porosimetry. The texture of matrix carbon was studied under a polarized light microscope. The results show that the relative mass gain of the sample increases directly as the infiltration time at the initial stage until 20 h, and subsequently the increasing rate of the relative mass gain decreases gradually with the prolonging of infiltration time. Three layers of pyrocarbon were formed around fibers. Low-textured pyrocarbon was obtained at the initial stage. With the densification going on, high-textured pyrocarbon was formed on the surface of low-textured pyrocarbon. Then, low-textured pyrocarbon was produced again during the final stage of densification. The texture transition is ascribed to the variation of the ratio of cumulative inner surface area to volume of pores and the gas partial pressure in pores.

关键词： C/C composites Isothermal chemical vapor infiltration (ICVI) Pyrocarbon Mercury porosimetry Polarized light microscope