镍钛记忆合金自补偿磨粒磨损性能研究

研究了高临界温度镍钛记忆合金一维自补偿磨粒磨损特性.结果表明,在一定温度下,镍钛记忆合金在摩擦过程中具有形状恢复能力,从而产生一维磨损自补偿作用.超弹状态镍钛记忆合金具有热弹性马氏体相变、高阻尼、应力感生马氏体、超弹性、高应变硬化指数和时效弥散析出强化等特性,这使得硬度较低的镍钛合金的耐磨性能远优于硬度较高的淬火45#钢.利用超弹状态镍钛记忆合金的磨损自补偿作用可望开发出新型抗磨形状记忆合金产品.     

单轴条件下砂岩三维破裂过程的CT观测

岩石破裂过程研究一直是岩石力学专家关注的重要问题。本文采用特制的三轴压力仪与医用西门子SOMATOM -plusCT扫描仪结合 ,对砂岩进行了室内单轴压缩试验。通过对砂岩的CT图像和密度损伤增量与应力关系曲线分析 ,结果显示 ,砂岩的破裂演化过程可分为初始损伤的压密、裂纹出现—扩展、裂纹归并—分岔、裂纹重分岔—扩展以及裂纹惯通—宏观破坏等五个阶段。在初始损伤的压密阶段 ,砂岩的密度损伤增量为正值 ,速率也为正 ;在裂纹出现—扩展阶段 ,砂岩出现局部密度损伤增量减小 ,并随应力增加而由正值转为负值 ,速率也由正变负 ;在裂纹归并—分岔阶段 ,砂岩的密度损伤增量全为负值 ,速率也变快 ;在裂纹重分岔—扩展阶段 ,砂岩的密度损伤增量继续变负 ,但速率变慢 ;在裂纹惯通—宏观破坏阶段 ,砂岩的密度损伤增量继续变负 ,速率变的更快。     

Rheological characterization of melt processed polycarbonate-multiwalled carbon nanotube composites

In this study polycarbonate/multiwalled carbon nanotube composites were produced with different compositions by diluting a masterbatch using melt mixing in a DACA-Micro-Compounder. The composites were rheologically characterized using an ARES-rheometer in the dynamic mode under nitrogen atmosphere at 280 °C and frequency varying from 100 to 0.056 rad/s.The results showed that the dynamic moduli and the viscosity increased with increasing MWNT content. At a concentration of 0.5 wt.% MWNT, a significant change in the frequency dependence of the moduli was observed which indicates a transition from a liquid like to a solid like behavior of the nanocomposites. This transition can be related to the formation of a combined network between the nanotubes and the polymer chains.     

扁球面网壳的混沌运动研究

在圆形三向网架非线性动力学基本方程的基础上,用拟壳法给出了圆底扁球面三向网壳的非线性动力学基本方程．在固定边界条件下,引入了异于等厚度壳的无量纲量,对基本方程和边界条件进行无量纲化,通过Galerkin作用得到了一个含二次、三次的非线性动力学方程．为求Melnikov函数,对一类非线性动力系统的自由振动方程进行了求解,得到了此类问题的准确解．在无激励情况下,讨论了稳定性问题．在外激励情况下,通过求Melnikov函数,给出了可能发生混沌运动的条件．通过数字仿真绘出了平面相图,证实了混沌运动的存在．     

Numerical Study of Natural Convection Heat Transfer in an Inclined Porous Cavity with Time-Periodic Boundary Conditions

Kalabin et al. (Numer. Heat Transfer A 47, 621-631, 2005) studied the unsteady natural convection for the sinusoidal oscillating wall temperature on one side wall and constant average temperature on the opposing side wall. The present article is on the unsteady natural convective heat transfer in an inclined porous cavity with similar temperature boundary conditions as those of Kalabin et al. The inclined angle of the cavity is varied from 0° to 80°. The flow field is modeled with the Brinkman-extended Darcy model. The combined effects of inclination angle of the enclosure and oscillation frequency of wall temperature are studied for Ra* = 10³, Da = 10⁻³, , and Pr=1. Some results are also obtained with the Darcy–Brinkman–Forchheimer model and Darcy’s law and are compared with the present Brinkman-extended Darcy model. The maximal heat transfer rate is attained at the oscillating frequency f = 46.7π and the inclined angle .     

Al/AlN多层膜的摩擦磨损性能研究

采用柱状靶磁控溅射系统制备Al/AlN纳米多层膜,采用纳米压痕仪测量Al/AlN纳米多层膜的纳米硬度,在UMT-2M型摩擦磨损试验机上评价其摩擦磨损性能.结果表明:当AlN层较厚时,薄膜在很短时间内被磨穿;调节Al/AlN层厚比为2.9/1.1时,薄膜的摩擦磨损性能明显提高;当保持Al/AlN层厚比为2.9/1.1、变化多层膜的调制周期时,薄膜的摩擦系数较低,但硬度较低的薄膜由于承载能力不够,不能够保持优良的摩擦磨损性能.     

Large thermal deflections of Timoshenko beams under transversely non-uniform temperature rise

Geometrically non-linear deformation of axially extensional Timoshenko beams subjected mechanical as well thermal loadings were characterized by a system of 7 coupled and highly non-linear ordinary differential equations, which results in a complicated two-point boundary-value problem. By using shooting method this kind of problem can be numerically solved efficiently. Based on the above-mentioned mathematical formulation and numerical procedure, analysis of large thermal deflections for Timoshenko beams, subjected transversely non-uniform temperature rise and with immovably pinned–pinned as well as fixed–fixed ends, is presented. Characteristic curves showing the relationships between the beam deformation and temperature rise are illustrated. Especially, the effects of shear deformation on the bending and buckling response are quantitatively investigated. The numerical results show, as we know, that shear deformation effects become significant with the decrease of the slenderness and with the increase of the shear flexibility.     

Post-buckling of a hinged-fixed beam under uniformly distributed follower forces

Based on geometrically non-linear theory for extensible elastic beams, governing equations of statically post-buckling of a beam with one end hinged and the other fixed, subjected to a uniformly distributed, tangentially compressing follower forces are established. They consist of a boundary-value problem of ordinary differential equations with a strong non-linearity, in which seven unknown functions are contained and the arc length of the deformed axis is considered as one of the basic unknown functions. By using shooting method and in conjunction with analytical continuation, the non-linear governing equations are solved numerically and the equilibrium paths as well as the post-buckled configurations of the deformed beam are presented. A comparison between the results of conservative system and that of the non-conservative systems are given. The results show that the features of the equilibrium paths of the beams under follower loads are evidently different from that under conservative ones.