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Size Effect on Onset and Subsequent Evolution of Adiabatic Shear Band:Theoretical and Numerical Analysis

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Acta Mechanica Solida Sinica 2020年第3期33卷 294-306页

作者： Jiejian liu Tao Suo Fenghua Zhou yulong li School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China Shaanxi Key Laboratory of Impact Dynamics and Its Engineering Application Xi'an 710072China Joint International Research Laboratory of Impact Dynamics and Its Engineering Application Xi'an 710072China The Faculty of Mechanical Engineering and Engineering Mechanics Ningbo UniversityNingbo 315211China

The adiabatic shear instability of ductile materials has attracted more and more attentions of researchers and groups,who have been sparing no effort in further understanding of the underlying mechanism since the first experimental depiction of adiabatic shear instability by Zener and *** for the adiabatic shear instability,many factors account for its occurrence,including heat conduction,inertia effect,microstructure effect and so ***,lots of experimental evidence has shown that metal materials display a strong size effect when the characteristic length scale is in the order of *** size effect has also been observed in the analysis of shear band in the ductile materials because the order of the bandwidth stays within the microscale ***,a comprehensive understanding of the whole process of adiabatic shear banding(ASB),including the early onset and the subsequent evolution,is still *** this work,a gradient plasticity model based on the Taylor-based nonlocal theory feasible for the linear perturbation analysis and convenient for numerical calculation is proposed to investigate the strain gradient on the onset of ASB and the coupling effect of heat conduction,inertia effect and strain gradient at the early stage,as well as on the subsequent evolution process at later *** for the onset of ASB,the linear perturbation method is used to consider the effect on the initial formation of *** the investigation of the onset of *** characteristic line method is applied to describe the subsequent nonlinear evolution process of *** stages of ASB evolution are clearly depicted during the evolution process,and the significance of size effect on the ASB nonlinear evolution process of ASB at different stages is *** the help of linear perturbation analysis and characteristic line method,a comprehensive description of the role of strain gradient in the ASB from the early onset to the end of the evolution is provided.

关键词： Adiabatic shear band Strain gradient Nonlinear evolution process linear perturbation method Characteristic line method

Variation of Out-of-Plane Constraint and Its Effects on Fracture

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上海交通大学学报 2004年第z2期38卷 212-216页

作者： Fei Xu yulong li Wanlin Guo Department of Mechanical Engineering Tokyo University of Science Noda2788510 Japan School of Aeronautics Northwestern Polytechnical University Xi''an710072 P. R. China School of Aeronautics Northwestern Polytechnical University Xi''an710072 P. R. China School of Aeronautics and Astronauts Nanjing University of Aeronautics and AstronautsNaniing210016 P.R.China

The limitations of using one-parameter to describe the crack-tip fields have prompted investigators to consider better descriptions of the crack tip fields. The two-parameter descriptions, such as J-Q theory, have been an important development in this field. But under the consideration of plane strain and three-dimensional problem, the effects of the out-of-plane stress can not be neglected In this paper, effects of the in-plane constraint as well as the out-of-plane constraint are studied by aid of the finite element method on the plane strain condition. It is obvious that both the in-plane constraint (Q factor) and the out-of-plane constraint (Tz = σzz/(σxx + σyy) ) affect the crack tip *** important features of the out-of-plane constraint are described out based on the simulation results. At the end of this paper, a three-parameter formulation is proposed, in which both the in-plane constraint and the out-of-plane constraint are considered. Comparing with the results of the FEM numerical simulation, the three-parameter description can provide a better prediction near the crack tip.

关键词： in-plane constraint out-of-plane constraint three-parameter formulation crack tip field elastic-plastic

Numerical Investigation of Jet Impingement Cooling with Supercritical Pressure Carbon Dioxide in a Multi-Layer Cold Plate during High Heat Flux

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Journal of Thermal Science 2023年第1期32卷 237-253页

作者： WEN Yaming li yulong li Jingqi YU Xin-Gang National Key Laboratory of Science and Technology on Aero Engines Aero-Thermodynamics&Collaborative Innovation Center for Advanced Aero-Engine School of Energy and Power EngineeringBeihang UniversityBeijing 100191China Beijing Institute of Spacecraft System Engineering Beijing 100094China

Jet impingement cooling with supercritical pressure carbon dioxide in a multi-layer cold plate during the heat flux of 400 W/cm_(2) is investigated *** generation and distribution of pseudocritical fluid with the high specific heat of supercritical pressure carbon dioxide and the mechanism of the heat transfer enhancement led by the high specific heat are *** a given nozzle diameter,the effects of the geometric parameters of a multi-layer cold plate such as the relative nozzle-to-plate distance,relative plate thickness,and relative upper fluid thickness on the average heat transfer coefficient are *** results show that the target surface is cooled effectively with supercritical pressure carbon dioxide jet impingement *** the radial distance is less than 6 mm,the maximum wall temperature is 368 K,which is 30 K lower than the maximum junction temperature for a silicon-based insulated gate bipolar transistor,a typical electronic power *** is a pseudocritical fluid layer near the target surface,where specific heat reaches above 34 kJ/(kg·K)*** drastic rise of the specific heat leads to obvious heat transfer *** a certain range,the local heat transfer coefficient and the specific heat are linearly correlated and Stanton number remains constant over this *** heat transfer coefficient is at a maximum when the relative nozzle-to-plate distance is *** the relative plate thickness increases from 0.5 to 3.5 or the relative upper fluid thickness increases from 0.5 to 2.5,the average heat transfer coefficient decreases monotonically.

关键词： high heat flux jet impingement cooling supercritical pressure carbon dioxide heat transfer enhancement

Tribological mechanisms of slurry abrasive wear

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Friction 2023年第6期11卷 1079-1093页

作者： yulong li Paul SCHREIBER Johannes SCHNEIDER Christian GREINER Institute for Applied Material(IAM) Karlsruhe Institute of Technology(KIT)Karlsruhe76131Germany KIT IAM-ZM MicroTribology Center(μTC) Karlsruhe76131Germany

Abrasive wear mechanisms—including two-body and three-body abrasion—dominate the performance and lifespan of tribological systems in many engineering fields,even of those operating in lubricated *** steel(100Cr6)pins and discs in a flat-on-flat contact were utilized in experiments together with 5 and 13 μm Al_(2)O_(3)-based slurries as interfacial media to shed light on the acting *** results indicate that a speed-induced hydrodynamic effect occurred and significantly altered the systems'frictional behavior in tests that were performed using the 5 μm *** experiments revealed that a speed-dependent hydrodynamic effect can lead to a 14% increase in film thickness and a decrease in friction of around 2/3,accompanied by a transition from two-body abrasion to three-body abrasion and a change in wear mechanism from microcutting and microploughing to fatigue ***,no correlation could be found between the total amount of wear and the operating state of the system during the experiment;however,the wear distribution over pin and disc was observed to change *** paper studies the influence of the hydrodynamic effect on the tribological mechanism of lubricated abrasive wear and also highlights the importance to not only consider a tribological systems'global amount of wear.

关键词： abrasive wear two-body abrasion three-body abrasion hydrodynamic effect steel

Dynamic Biaxial Compression of CFRP Laminates Using Electromagnetic Loading

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Acta Mechanica Solida Sinica 2022年第5期35卷 891-900页

作者： Huaipu Kang Jintao liang Yi li Hao Cui yulong li NPU Yangtze River Delta Research Institute Suzhou215400China School of Aeronautics Northwestern Polytechnical UniversityXi’an710072China School of Civil Aviation Northwestern Polytechnical UniversitySuzhou215400China

The dynamic biaxial compression test for carbon-fiber-reinforced polymer(CFRP)laminates was carried out via synchronous electromagnetic loading in this *** the experiments,four stress pulses transmitted along four incident bars,loading the square specimen simultaneously from four directions to keep the center of the specimen *** dynamic mechanical behavior of CFRP was obtained employing the one-dimensional wave propagation theory,and the deformation and failure processes of the specimens were recorded by a high-speed *** effects of various biaxial stresses on the compressive strength were investigated in three biaxial and one uniaxial loading *** the CFRP laminates,the dynamic transverse compressive stress showed little effect on the longitudinal ultimate compressive *** simulations were performed to understand the dynamic stress wave *** showed that the employed loading device could guarantee good biaxial loading conditions until the ultimate failure of the *** approach allows for the dynamic biaxial compression testing of various materials,which is of great significance in evaluating the dynamic impact performance of aeronautical composites.

关键词： Carbon-fiber-reinforced polymer(CFRP) Dynamic loading Biaxial testing Electromagnetic loading

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外啮合液压齿轮马达输出特性的统一简约式

机械传动 2024年第4期48卷 90-94页

作者：刘萍李玉龙侯鑫宇章丽华宿迁学院机电工程学院江苏宿迁223800 四川五环石化装备有限公司四川成都641300

为正确认识任意侧隙大小/偏置卸荷槽不同类型下齿轮马达的输出特性,基于啮合齿廓/输出特性不同的啮合线区间,以衡量侧隙大小的类型值和双卸荷槽对称线与齿轮副中心线的偏置值为变量,构建出转速/转矩等输出特性的统一简约式。结果表明,... 详细信息

为正确认识任意侧隙大小/偏置卸荷槽不同类型下齿轮马达的输出特性,基于啮合齿廓/输出特性不同的啮合线区间,以衡量侧隙大小的类型值和双卸荷槽对称线与齿轮副中心线的偏置值为变量,构建出转速/转矩等输出特性的统一简约式。结果表明,输出转速/转矩曲线可以由啮合齿廓的啮合转速/转矩曲线,通过输出特性啮合线区间的截取而直接得到;对称卸荷槽类型下的均值转速最小,均值转矩最大,转速/转矩的脉动系数最小;小侧隙较大的卸荷槽偏置范围和调速/调矩范围更大;小侧隙和对称卸荷槽类型的均值转速更小,均值转矩更大,转速/转矩的脉动系数更小;马达转矩脉动式与齿轮泵流量脉动式完全一致;转矩脉动系数略小于转速脉动系数,大齿数情况下可近似为相等;追求高转速时,应选用大侧隙和卸荷槽极限偏置的类型组合;追求大转矩或高输出脉动质量时,应选用小侧隙和对称卸荷槽的类型组合等。得出的输出特性的获取方法更简单、原理更清晰、形式更简洁、结果更可靠。

关键词：外啮合齿轮马达侧隙卸荷槽啮合线区间转速/转矩脉动系数

基于前因因素的建筑工人安全行为评价模型与应用

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安全与环境工程 2024年第2期31卷 62-70页

作者：李国良姚子旸杨晓严章密李玉龙昆明理工大学建筑工程学院云南昆明650500 中央财经大学管理科学与工程学院北京100081

建筑项目中的事故主要与建筑工人的不安全行为有关,因此对建筑工人安全行为进行事前评价是预防事故发生的关键。首先通过文献可视化分析初步筛选建筑工人安全行为前因因素,结合专家意见构建建筑工人安全行为评价的指标体系;然后采用群... 详细信息

建筑项目中的事故主要与建筑工人的不安全行为有关,因此对建筑工人安全行为进行事前评价是预防事故发生的关键。首先通过文献可视化分析初步筛选建筑工人安全行为前因因素,结合专家意见构建建筑工人安全行为评价的指标体系;然后采用群决策改进的层次分析法确定各评价指标的综合权重,并建立可拓物元评价模型;最后对某施工项目建筑工人安全行为进行评价与分析,以验证模型的合理性和可靠性。结果表明:建筑工人安全行为评价指标中安全意识所占权重较高,是事故预防的重要因素;实例应用结果表明该项目建筑工人总体安全行为等级处于“Ⅲ级”为一般安全,说明该项目施工作业人员整体处于比较安全的水平;建筑工人个体安全行为的维度指标评价结果为正态分布或偏正态分布,表明该评价模型能够有效识别建筑工人的安全行为水平,可为建筑安全管理的研究和实践提供参考。

关键词：建筑工人安全行为评价群决策可拓物元模型前因因素

A numerical model for bird strike on sidewall structure of an aircraft nose

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Chinese Journal of Aeronautics 2014年第3期27卷 542-549页

作者： liu Jun li yulong Gao Xiaosheng Yu Xiancheng School of Aeronautics Northwestern Polytechnical University Department of Mechanical Engineering The University of Akron

In order to examine the potential of using the coupled smooth particles hydrodynamic （SPH） and finite element （FE） method to predict the dynamic responses of aircraft structures in bird strike events, bird-strike tests on the sidewall structure of an aircraft nose are carried out and numerically simulated. The bird is modeled with SPH and described by the Murnaghan equation of state, while the structure is modeled with finite elements. A coupled SPH-FE method is developed to simulate the bird-strike tests and a numerical model is established using a commercial software PAM-CRASH. The bird model shows no signs of instability and correctly modeled the break-up of the bird into particles. Finally the dynamic response such as strains in the skin is simulated and compared with test results, and the simulated deformation and fracture process of the sidewall structure is compared with images recorded by a high speed camera. Good agreement between the simulation results and test data indicates that the coupled SPH-FE method can provide a very powerful tool in predicting the dynamic responses of aircraft structures in events of bird strike.

关键词： Bird strike Experiment Sidewall structure Simulation Smooth particles hydrodynamic (SPH) method

Research on Cooling Effectiveness in Stepped Slot Film Cooling Vane

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Journal of Thermal Science 2016年第3期25卷 273-279页

作者： li yulong WU Hong ZHOU Feng RONG Chengjun National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics Beihang University

As one of the most important developments in air cooling technology for hot parts of the aero-engine, film cool- ing technology has been widely used. Film cooling hole structure exists mainly in areas that have high temperature, uneven cooling effectiveness issues when in actual use. The first stage turbine vanes of the aero-engine consume the largest portion of cooling air, thereby the research on reducing the amount of cooling air has the greatest potential. A new stopped slot film cooling vane with a high cooling effectiveness and a high cooling uniformity was researched initially. Through numerical methods, the affecting factors of the cooling effectiveness of a vane with the stepped slot film cooling structure were researched. This paper focuses on the cooling effectiveness and the pressure loss in different blowing ratio conditions, then the most reasonable and scientific structure parameter can be obtained by analyzing the results. The results show that 1.0 mm is the optimum slot width and 10.0 is the most reasonable blowing ratio. Under this condition, the vane achieved the best cooling result and the highest cooling effectiveness, and also retained a low pressure loss.

关键词： Film cooling Cooling effectiveness Blowing ratio Pressure loss