检索结果-南通市图书馆

INVESTIGATION OF THE M-INTEGRAL IN CRACK-DAmaGED PIEZOELECTRIC CERAMICS

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2006年第2期19卷 167-173页

作者： Wang Defa ma lifeng Shi Junping Department of Civil Engineering Xi＇an University of Technology Xi＇an 710048. China Department of Civil Engineering Xi＇an Jiao Tong UniversityXian 710049China Department of Engineering Mechanics Xi＇an University of Technology Xi＇an 710048 China

The physical interpretation of the M-integral is investigated in the analysis of crackdamaged piezoelectric problems. The relation between the M-integral and the change of the total electric enthalpy （CTEE）, i.e., M = 2CTEE, is derived with a theoretical derivation procedure for two^dimensional piezoelectric problems. It is shown that the M-integral may provide a more natural description of electric enthalpy release due to the formation of the pre-existing microcracks associated with the damaged body, rather than the description of the total potential energy release rate as interpreted for conventional brittle solids. For crack-damaged piezoelectric ceramics, numerical calculation of the M-integral is discussed. Based on the pseudo-traction electric displacement method, M = 2CTEE has also been proved by the numerical results.

关键词： M-integral crack piezoelectric ceramics electric enthalpy damage

Structural Design and Dynamic Characteristics of Overloaded Horizontal Servo Cylinder for Resisting Dynamic Partial Load

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Mechanical Engineering 2019年第1期32卷 103-112页

作者： Linan ma Qingxue Huang lifeng ma Qiangjun ma Wenze Zhang Heyong Han Collaboration Innovation Center of Taiyuan Heavy machinery Equipment Taiyuan University of Science and Technology Taiyuan University of Technology

When an output curve force is applied to a horizontal servo cylinder with a heavy load, the piston rod bears a dynamic partial load based on the installation and load characteristics, which significantly a ects the frequency response and control accuracy of the servo cylinder. Based on this partial load, increased friction can lead to cylinder bore scu ng, leakage, lack of output power, or even system failure. In this paper, a novel asymmetric static-pressure support structure is proposed based on the principle of hydrostatic support. The radial component force of a dynamic partial load is balanced by cooperation between the support oil cushion of the variable hydraulic pressure support structure, oil cushion of the supportive force, and the damper. Adaptive control of the servo cylinder piston rod, guide sleeve, and piston, as well as the cylinder oil film friction between lubricated surfaces is achieved. In this paper, theoretical design and analysis of the traditional hydrostatic bearing structure and novel structure are presented. A hydraulic dynamic shear scissor is used as a research target to derive a structural dynamic model. Comparative simulations are performed using matlab Simulink. Additionally, flow field analysis of the novel structure is performed, which verifies the rationality and feasibility of the proposed structure and system.

关键词： Dynamic partial load Servo cylinder Asymmetrical static-pressure support structure Bearing characteristics

Weapon target assignment problem satisfying expected damage probabilities based on ant colony algorithm

在线全文

学校读者我要写书评

暂无评论

Journal of Systems Engineering and Electronics 2008年第5期19卷 939-944页

作者： Wang Yanxia Qian Longjun Guo Zhi ma lifeng Coll. of Automation Nanjing Univ. of Science and Technology Nanjing 210094 P. R. China

A weapon target assignment （WTA） model satisfying expected damage probabilities with an ant colony algorithm is proposed. In order to save armament resource and attack the targets effectively, the strategy of the weapon assignment is that the target with greater threat degree has higher priority to be intercepted. The effect of this WTA model is not maximizing the damage probability but satisfying the whole assignment result. Ant colony algorithm has been successfully used in many fields, especially in combination optimization. The ant colony algorithm for this WTA problem is described by analyzing path selection, pheromone update, and tabu table update. The effectiveness of the model and the algorithm is demonstrated with an example.

关键词： weapon target assignment ant colony algorithm optimization.

Consensus control of stochastic multi-agent systems: a survey

在线全文

学校读者我要写书评

暂无评论

Science China(Information Sciences) 2017年第12期60卷 5-19页

作者： lifeng ma Zidong WANG Qing-Long HAN Yurong LIU School of Automation Nanjing University of Science and Technology College of Electrical Engineering and Automation Shandong University of Science and Technology Department of Computer Science Brunel University London School of Software and Electrical Engineering Swinburne University of Technology Department of mathematics Yangzhou University

In this article, we provide a review of the consensus control problem for stochastic multi-agent systems(maSs). Recent advances are surveyed according to the method of occurrence of the stochasticity of the maSs. First, the consensus problem is discussed for maSs, wherein individual agents are corrupted by random noises, i.e., the dynamics of agents involve stochasticity in process and/or measurement equations. Both additive noises and multiplicative noises are surveyed in detail and special attention is paid to the maSs whose dynamics are governed by It?o differential equations. Moreover, particular effort is devoted to presenting the latest progress on the consensus problem for a special type of stochastic maS with markovian jump parameters. Subsequently,the relevant research is summarized for maSs with noisy communication environments and stochastic ***, we provide a systematic review of the consensus problems for maSs whose communication topology varies randomly in the process of data propagation among agents. Finally, conclusions are drawn and several potential future research directions are outlined.

关键词： stochastic multi-agent systems consensus control stochastic noises markovian jump systems random topology

Gradient microstructure and superior strength-ductility synergy of AZ61 magnesium alloy bars processed by radial forging with different deformation temperatures

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of materials Science & Technology 2024年第3期170卷 65-77页

作者： Jingfeng Zou lifeng ma Yanchun Zhu Ling Qin Yuan Yuan School of Mechanical Engineering Taiyuan University of Science and TechnologyTaiyuan 030024China Heavy machinery Engineering Research Center of the Ministry Education Taiyuan University of Science and TechnologyTaiyuan 030024China Department of Engineering University of HullCottingham RdHull HU67RXUK National Engineering Research Center for magnesium Alloys Chongqing UniversityChongqing 400044China

Gradient microstructure modification is a cost-efficient strategy for high strength without compromising ductility,which is urgently needed in the fundamental science of engineering *** this study,heterogeneous structures of AZ61 alloy bars with anisotropic gradients(with different grain size distributions from the surface to the center)were observed to exhibit strong strength-ductility synergies under different deformation tem *** results reveal that the grain refinement process under mediumlow temperature deformation conditions(≤350℃)consists of four transition stages along the radial direction,i.e.,twin activations and deformation band formations,dislocation cells and pile-ups,ultrafine sub-grains,and randomly orientated quasi-micron *** deformation temperatures have a great influence on twin activations and deformation band formations,and the high temperature can easily provoke the initiation of non-basal *** deformation bands were determined as a primary nucleation site due to their highly unstable dislocation hindrance *** in combination with the Radial forging(RF)deformation process,the differences of dynamic precipitates can be attributed to microstructural difference and solubility limit of Al at different tem *** summarizing the tensile test results,the sample forged at 350℃exhibited the best strength-ductility synergy,exhibiting the highest elongation(EL)of 23.2%with a 251 MPa yield strength(YS)and 394 MPa ultimate tensile strength(UTS)in center region,and combined with the highest strength value of 256 MPa YS and 420 MPa UTS in the center region,while the EL was slightly degraded to 19.8%.

关键词： Gradient microstructure Radial forging Strength-ductility synergy magnesium alloy Strengthening mechanism

Collinear micro-shear-bands model for grain-size and precipitate-size effects on the yield strength

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Theoretical & Applied Mechanics Letters 2018年第4期8卷 245-251,298页

作者： Yike Qiu Peng Zhang lifeng ma S&V Lab Department of Engineering Mechanics Xi'an Jiaotong University Xi'an Thermal Power Research Institute Co. Ltd

Numerous experimental evidences show that the grain size may significantly alter the yield strength of ***,innickel-based superalloys,the precipitate size also influences their yield ***,how to describe such two kinds of size effects on the yield strength is a very practical *** this study,according to experimental observations,a collinear micro-shear-bands model is proposed to explore these size effects on metal materials’yield *** analytical solution for the simple model is *** reveals that the yield strength is a function of average grain-size or precipitate-size,which is able to reasonably explain size effects on yield *** typical example validation shows that the new relationship is not only able to precisely describe the grain-size effect in some cases,but also able to theoretically address the unexplained Hall-Petch relationship between theprecipitate size and the yield strength of nickel-based superalloys.

关键词： Collinear micro-shear-bands model The Hall-Petch relationship γprecipitate Size effect

Microstructural and mechanical response of ZK60 magnesium alloy subjected to radial forging

在线全文

学校读者我要写书评

暂无评论

Journal of materials Science & Technology 2021年第24期83卷 228-238页

作者： Jingfeng Zou lifeng ma Weitao Jia Qichi Le Gaowu Qin Yuan Yuan Heavy machinery Engineering Research Center Ministry of EducationTaiyuan University of Science and TechnologyTaiyuan030024China School of Mechanical Engineering Taiyuan University of Science and TechnologyTaiyuan030024China Key Laboratory of Electromagnetic Processing of materials Ministry of EducationNortheastern UniversityShenyang110819China Key Laboratory for Anisotropy and Texture of materials Ministry of EducationNortheastern UniversityShenyang110819China National Engineering Research Center for magnesium Alloys Chongqing UniversityChongqing400044China

Radial forging(RF)is an economical manufacturing forging process,in which four dies arranged radially around the workpiece simultaneously act on the workpiece with high-frequency radial *** this study,a ZK60 magnesium alloy step-shaft bar was processed under different accumulated strains by RF at350℃.The deformation behavior,microstructure evolution,and mechanical responses of this bar were systematically investigated via numerical simulations and *** the early deformation stage of forging,the material undergoes pronounced grain refinement but an inhomogeneous grain structure is formed due to the strain gradient along the radial *** grains in different radial parts were gradually refined by increasing the RF pass,resulting in a bimodal grained structure comprising coarse(~14.1μm)and fine(~2.3μm)*** the RF pass increased,the initial micro-sizeβ-phases were gradually crushed and dissolved into the matrix mostly,eventually evolving to form a higher area fraction of nano-sized Zn2 Zr spheroidal particles uniformly distributed through the grain *** texture changed as the RF strain increased,with the c-axes of most of the deformed grains rotating in the ***,excellent mechanical properties including higher values of tensile strengths and ductility were attained after the three RFed passes,compared to the as-received sample.

关键词： ZK60 magnesium alloy Radial forging Microstructure Texture evolution Mechanical properties

Robust control for a class of nonlinear networked systems with stochastic communication delays via sliding mode conception

在线全文

学校读者我要写书评

暂无评论

控制理论与应用（英文版） 2010年第1期8卷 34-39页

作者： lifeng ma Zidong WANG Xuemin CHEN Zhi GUO School of Automation Nanjing University of Science and Technology Nanjing Jiangsu 210094 China Department of Information Systems and Computing Brunel University Uxbridge Middlesex UB8 3PH UK Department of Engineering Technology Texas Southern University Houston TX 77004 USA

This paper deals with the robust control problem for a class of uncertain nonlinear networked systems with stochastic communication delays via sliding mode conception （SMC）. A sequence of variables obeying Bernoulli distribution are employed to model the randomly occurring communication delays which could be different for different state variables. A discrete switching function that is different from those in the existing literature is first proposed. Then, expressed as the feasibility of a linear matrix inequality （LMI） with an equality constraint, sufficient conditions are derived in order to ensure the globally mean-square asymptotic stability of the system dynamics on the sliding surface. A discrete-time SMC controller is then synthesized to guarantee the discrete-time sliding mode reaching condition with the specified sliding surface. Finally, a simulation example is given to show the effectiveness of the proposed method.

关键词： Sliding mode control Nonlinear systems Networked systems Stochastic communication delays

Hot deformation behavior of a novel bimetal consisting of BTW1 and Q345R characterized by processing maps

在线全文

学校读者我要写书评

暂无评论

Frontiers of Mechanical Engineering 2019年第4期14卷 489-495页

作者： Pengtao LIU lifeng ma Weitao JIA Tao WANG Guanghui ZHAO College of Mechanical Engineering Taiyuan University of TechnologyTaiyuan 030024China Shanxi Provincial Key Laboratory of Metallurgical Equipment Design and Technology Taiyuan University of Science and TechnologyTaiyuan 030024China College of Mechanical Engineering Taiyuan University of Science and TechnologyTaiyuan 030024China

Only a few studies have been conducted on the flow behavior of the novel BTW1/Q345R bimetal,which is widely used in coal *** this work,compression tests were conducted on BTW1/Q345R bimetal at a temperature range of 950°C–1200°C and strain rates of 0.05,0.5,5,and 15 s^−1 by using a Gleeble-3800 thermomechanical simulator.A constitutive equation was validated by referring to the Arrhenius equation during the characterization of hot *** computed apparent activation energy of the BTW1/Q345R bimetal was 360 kJ/mol,and processing maps under different strain conditions were *** of the stress-strain relationship revealed that work hardening exerted a dominant effect on the thermal deformation of the BTW1/Q345R *** processing maps predicted that the optimal processing interval will increase with *** showed that thermal deformation of the BTW1/Q345R bimetal should proceed when the temperature range varies from 1182°C to 1200°C and the strain rate interval is from 4.2 to 15 s^−1.

关键词： BTW1/Q345R bimetal constitutive equation processing map work hardening