Applicability of the Hertz contact theory to rail-wheel contact problems

Summary Rail-wheel contact problems have been analyzed by applying three-dimensional finite element models. Based on these models, the applicability of the Hertz contact theory (HCT) to rail-wheel contact problems is verified in the present paper. Beside a standard rail, also a crane rail and a switching component are considered in the verification. In the case of a contact between the standard rail UIC60 and the standard wheel UICORE, different transverse contact positions are analyzed. Numerically calculated distributions of the contact pressure for different types of rails with respect to different initial contact positions agree with the results from the HCT only if either the contact zone does not spread into a region of changed surface curvature or if plastification does not occur. Finally, the convective part of the dissipation power due to friction is calculated, which cannot be provided directly by the HCT. Received 5 August 1998; accepted for publication 6 May 1999     

Formulation of the Fourier transform in the spectral domain technique

A way to formulate the transform in spectral domain technique is presented.     

智能弗兰克-赫兹实验测量仪的研制

采用AT90S 8535单片机研制了一种智能弗兰克－赫兹实验测量仪，能测量10^-9-10^-12A微电流，提供0－50V线性程控稳压电源，模糊控温，图形液晶显示中英和曲线，曲线数据打印，具有测量快、精度高、体积小、成本低、使用方便等优点。本介绍了该测量仪的硬件组成、典型电路工作原理、软件设计，分析了实验结果。     

力学性能对于原子力显微镜接近曲线的影响

该文基于Derjaguin-Muller-Toporov接触模型,研究了振幅调制原子力显微镜(AM-AFM))成像中,3种典型针尖悬臂系统与四类具有不同力学性能的材料样品在针尖样品接近过程中互作用的响应情况。研究表明相位响应与针尖样品相互作用力作用形式密切相关。通过针尖的振幅曲线可确定针尖与样品间的互作用力的性质是吸引还是排斥,本研究结果有助于在AM-AFM成像实验中优化基准值设置,以避免对样品的损害。     

A novel tactile softness display for minimally invasive surgery

The use of Minimally Invasive Surgery (MIS) in various types of surgical procedures has increased significantly in recent years. However, its scope is limited due mainly to the fact that this procedure does not currently provide tactile feedback without which the surgeon can neither feel nor palpate tissue. In this paper, we describe a new tactile display that reproduces these missing constituent properties of the tissue directly to the surgeon. The softness of different objects is regenerated based on the mechanical properties of those objects and fingertip pulp. The force–displacement non-linear behavior of several different materials is simulated using force feedback and a Proportional-Integral-Derivative (PID) controller for the linear actuator. Experimental tests show that the proposed tactile display can closely regenerate the feeling of softness for different objects by rendering the force–displacement curve to the surgeon’s hand.     

等径圆球组简单压缩下的宏观应力-应变关系

应用虚功原理推导出规则排列等径因球颗粒在赫兹接触规律下简单压缩时宏观应力应变关系，并与TRUBAL程序离散元法模拟结果做了比较．比较发现规则排列模拟结果和理论结果是一致的．进一步模拟研究了随机排列，给出了等径圆球随机排列宏观应力应变关系拟合公式．     

赫兹对经典电磁场理论发展的贡献及其影响

文章根据赫兹的日记、书信和论文集，对赫兹在电磁场理论研究方面的主要论著进行了深入分析，对他在经典电磁场理论发展过程中所起到的重要作用和历史地位给予了更为客观的评价．文章指出，赫兹所发表的电磁学理论研究论文不仅促进了麦克斯韦理论在德国的传播和认同，而且对麦克斯韦方程组的理论基础进行了合理的重建和拓展，并给予更为清晰的逻辑论证，从而对经典电磁场理论的发展和最终完善起到了重要作用．文章还指出，赫兹在电磁场理论研究方面的成就对洛伦兹电子论的建立起到了一定的启发作用，对爱因斯坦早期物理学研究也产生了直接的影响。     

也论电磁波的预言及其发现过程

文章根据麦克斯韦的著作和赫兹的《综合文集》、《电波》和《回忆、书信和日记》以及相关文献，对麦克斯韦预言电磁波的问题和赫兹实验发现电磁波的过程进行了仔细考察，指出麦克斯韦没有明确预言电磁波的存在，麦克斯韦的理论不是赫兹电磁学实验研究的直接指导思想．文章认为亥姆霍兹为普鲁士科学院所提出的1879年悬赏课题对赫兹发现电磁波起到了直接的引导作用，而电磁波的发现则主要归因于赫兹精湛的实验技能和敏锐的观察力．     

基于高频轮轨作用的波浪型磨损研究

对高频轮轨相互作用下轨道的波浪形磨损问题进行了考察。通过引入轮轨的灵敏度，得到了轮轨间蠕滑力的波动同轨道表面不平顺幅值和表面曲率的波动关系；通过引入摩擦功计算了轨道表面的磨损，得到了磨损率的计算公式。结果表明，钢轨的磨损率同轨道的垂向动力行为密切相关；轨道表面不同点在不同激振频率下的磨损率不同。     

Uniaxial deformation of a random packing of particles

Summary Mechanical behavior of dense packing spheres with small irregularities is investigated in this paper. A generalization of the hertzian contact model for surfaces of the form x ^k yields a normal contact force F _n , which is proportional to ζ^{1+1/ k} , with the normal displacement ζ. For oblique forces, the frictional force can be calculated, [10]. Different load cases are explained in detail. It is shown that the stress-strain curve during initial loading of the packing is identical with the force-displacement relation at the contact point, using an appropriate constant. The results for uniaxial loading, unloading and reloading are illustrated. As experimentally observed, the axial pressure in unloading is smaller than during loading, while the lateral pressure increases. The stress-strain relation is compared with well-known empirical relations of rock and soil mechanics, and the wave velocity for spherical irregularities agrees with earlier geomechanical theories for random packing of smooth spheres. Received 19 July 1998; accepted for publication 19 October 1998