关键词： Thermal strength test   Aerodynamic heating   Ultimate strength   Al-alloy  

摘要： Determination of mechanical parameters such as the ultimate strength of aerospace materials under the condition of transient heating is critical for reliability evaluation, fatigue life prediction and safety design of high-speed aircrafts including missiles. Al-alloys are widely used as aeronautical materials due to their advantages such as light weight, easy manufacturability and relatively low cost. However, their mechanical properties under transient thermal conditions are not available in the handbooks on material strength, mainly due to the difficulty of simulating the transient thermal conditions for thermal strength test. To solve this problem, a joint thermal-mechanical loading system has been developed in the present investigation to simulate the aerodynamic thermal conditions. The mechanical behaviors of some Al-alloys have been examined with this system. The ultimate strengths and durations of two different types of Al-alloys, i.e. Al7178 and Al2024, under joint thermal-mechanical loading conditions have been tested. Furthermore, their different failure modes and mechanisms under various temperatures have been investigated and compared. These data provide a reliable basis for the study of load bearing capacity and weight reduction of aerospace materials and structures under transient aerodynamic thermal conditions.

关键词： Polymers   Nano composites   Curing   Elastic properties   Rheology  

摘要： A polymer material system has been developed to propose an injectable. UV and in situ curable hydrogel with properties similar to the native nucleus pulposus of intervertebral disc. Neat hydrogels based on Tween (R) 20 trimethacrylates (T3) and N-vinyl-2-pyrrolidone (NVP) and composite hydrogels of same composition reinforced by nano-fibrillated cellulose were synthesized with different T3 concentrations and their curing kinetics was investigated by photorheology using UV light The T3 concentration has an influence on the time of curing and final shear stiffness of the material. NFC does not alter the time of curing but increases the final mechanical performance of the hydrogels for a same chemical composition Hydrogel samples, neat and composite, were then tested in unconfined compression at different hydration stages and in confined compression and their elastic modulus was determined. The amount of fluid present in the network is mostly responsible for the mechanical properties and NFC fibres proved to be an efficient reinforcement. The elastic modulus ranged from 002 to 8 MPa Biocompatibility studies showed that cells are confluent at 90% and do not show any morphology change when in contact with the hydrogel. The present hydrogel can therefore be considered for NP replacement. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Multilayer   Semi-coherent interface   Mechanical and tribological properties   Molecular dynamics  

摘要： Mechanical and tribological properties of multilayers with nanometer thickness are strongly affected by interfaces formed due to mismatch of lattice parameters. In this study, molecular dynamics ( MD) simulations of nanoindentation and following nanoscratching processes are performed to investigate the mechanical and tribological properties of Ni/Al multilayers with semi-coherent interface. The results show that the indentation hardness of Ni/Al multilayers is larger than pure Ni thin film, and the significant strength of Ni/Al multilayers is caused by the semi-coherent interface which acts as a barrier to glide of dislocations during nanoindentation process. The confinement of plastic deformation by the interface during nanoscratching on Ni/Al multilayers leads to smaller friction coefficient than pure Ni thin film. Dislocation evolution, interaction between gliding dislocations and interface, variations of indentation hardness and friction coefficient are studied. (C) 2010 Elsevier B.V. All rights reserved.

关键词： 轮式移动单杆柔性机械手   逆动力学   有限元   频域  

摘要： 针对轮式单杆平面柔性移动机械手逆动力学问题进行系统研究。建立在欧拉—伯努力梁理论基础上,采用铰接—自由端边界条件,并引用Hermit插值函数作为单元形函数对柔性机械手进行有限元离散。综合利用虚功原理和牛顿—欧拉方程并在机械手体坐标系下,以矩阵、矢量简洁的形式构建该移动柔性机械手系统的完整逆动力学模型。在频域下,求解系统驱动力(矩)和弹性构型变量。该方法适用于对移动柔性轻质机械手末端执行器有高精度定位要求的动力学研究,并对系统开环控制和闭环控制的策略构建有着重要参考意义。

关键词： 技术协会   化工机械   成都   会员   中国   常务理事   理事会   选举  

摘要： 中国化工机械动力技术协会第六次会员大会于2010年9月3日至4日在四川成都召开。出席本次大会的代表共103人。大会投票选举产生了第六届理事会,由理事144名组成。在第六届理事会第一次会议上,经投票选举常务理事43名,选举孙腾良同志为理事长,王峰涛、李光、李建平、李韵、

关键词： 机械设计制造   工程学院   重庆市   工程技术研究中心   科技   机械电子工程   教学示范中心   石油装备  

关键词： 农村富余劳动力   农业机械化   中国   第三产业   工业化   城镇化  

摘要： 农业机械化使中国平均每年产生1000万农村富余劳动力，为中国工业化、城镇化和第二、第三产业的发展提供有力支撑。

关键词： 空间机械臂   关节   动力学建模   间隙   啮合误差  

摘要： 关节是空间机械臂的核心部件,是保证空间机械臂安全、平稳运行的关键。为全面反映大型空间机械臂关节的动力学特性并从细节之处优化关节设计,利用集中参数法建立了综合考虑轮齿柔性、啮合阻尼、齿侧间隙、啮合误差等非线性因素的细化关节动力学模型。模型中采用一种基于tanh的连续函数对传统分段线性间隙函数进行近似,从而降低了模型的求解难度。研究了各级齿轮精度、关节转速和负载对关节动力学特性的影响。仿真结果表明,三级齿轮的精度变化会影响关节转速波动的振幅并分别影响高、中、低频特性;转速的增加将提高振动频率和幅值;力矩负载的增大会使关节转速波动幅值显著增大,且在满载时,所有的高阶频率都得到明显激励;惯性负载的增大会减小转速波动,并将能量集中在中频上。

关键词： Emergent quantum mechanics   Diffusion   Superposition principle   Born's rule  

摘要： Based on the modelling of quantum systems with the aid of (classical) non-equilibrium thermodynamics, both the emergence and the collapse of the superposition principle are understood within one and the same framework. Both are shown to depend in crucial ways on whether or not an average orthogonality is maintained between reversible Schrodinger dynamics and irreversible processes of diffusion. Moreover, the said orthogonality is already in full operation when dealing with a single free Gaussian wave packet. In an application, the quantum mechanical "decay of the wave packet" is shown to simply result from sub-quantum diffusion with a specific diffusivity varying in time due to a particle's changing thermal environment. The exact quantum mechanical trajectory distributions and the velocity field of the Gaussian wave packet, as well as Born's rule, are thus all derived solely from classical physics. (C) 2010 Elsevier B.V. All rights reserved.

关键词： Molecular dynamics simulations   Ni-Al bimetallic nanowires   Mechanical properties   Stress-strain curve   Young Modulus  

摘要： We employed molecular dynamics simulations to study mechanical properties of Ni-Al nanowires by calculating the stress-strain response of the wires under various loading conditions. For this purpose, nanowires were subjected to uniaxial strain at different strain rates and temperatures using embedded atom model potential. The behaviour of the wires at lower and higher strain rates was investigated, and the yield and rupture strain values and also Young's Modulus were obtained which are essential factors for the ductility of the wires. This work indicates that how the stress-strain response of the nanowires are affected by varying strain rates and temperatures. (C) 2010 Published by Elsevier B.V.