静电微电机微转子接触动力学特性分析

提出静电微电机中转子和固定轴承间相互接触的数学模型，对微尺度下的接触应力和应变 特性进行理论推导，分析静电微电机几何参数、静电力、材料特性及加载电压对接触宽度、 应力和应变特性的影响，对比研究不同工况下接触宽度、接触应力和应变的变化，并就相同 的问题进行有限元分析，探讨摩擦系数对接触区von Mises应力、应变和接触压力 的影响，结果表明有限元模拟所得接触应力和应变分布与数学 模型的解析值较为相似.     

Detachment of a rigid solid from an elastic wavy surface: Theory

The mechanics of detachment between a wavy elastic half space and a rigid solid is considered. Solutions for the axisymmetric problem of a rigid sphere and the plane strain problem of a rigid cylinder detaching from a wavy surface are developed. The interacting solids are taken to be in complete contact over a finite area initially. It is shown that the surface waviness makes the detachment process unstable, with the interface separating in alternating stable and unstable segments. Each unstable segment dissipates mechanical energy, leading to an increase in the total work of separation compared to that of a flat surface. Further, waviness causes the maximum separation force or the pull-off force to increase during detachment, resulting in an apparent toughening of the interface. This mechanism provides an alternative explanation to the experimental observations in the literature that roughness can sometimes lead to increase in pull-off force. It also illustrates the role of roughness in the attachment capability of several insect feet possessing soft pads. The basic solution presented here can be used to analyze the detachment of surfaces with multiple scale roughness as well. The solution also suggests strategies to improve reversible adhesion of a soft material by designing optimal surface topographies.     

Squeeze flow of Bingham fluids under slip with friction boundary condition

This paper develops a theoretical analysis of a Bingham fluid in slipping squeeze flow. The flow field decomposition consists in combining a central extensional flow zone in the plane of symmetry and shear flow zones near the plates. It is also considered that the slipping zone is located around a central sticking zone as previously shown from experiments. It is assumed that the shear stress at the plates is constant in the slipping zone and equals a fixed friction yield value. The squeeze force required to compress a Bingham fluid under the slipping behaviour as well as the radial evolution of the transition point between both sticking and slipping zones are finally determined.     

高g值冲击下存储测试电路模块缓冲保护研究

为了采用弹载存储测试技术记录弹体高速侵彻硬目标过程中的加速度—时间曲线,必须对存储测试电路模块进行缓冲保护。本文利用非线性缓冲理论、技术,选择较理想的缓冲材料,设计出缓冲器件-泡沫铝试件,进行了静态压缩,得到应力-应变曲线,采用LS-DYNA模拟了空气炮冲击实验中泡沫铝试件的缓冲效果,并对应用于某型号弹侵彻混凝土靶的存储测试电路模块进行了缓冲保护,提高了数据的捕获率和电路模块的重复使用次数。通过试验证明了所设计缓冲器件对电路模块具有保护效果。     

AFM稳定性研究

“突跳”现象严重影响着原子力显微镜(AFM)的性能。根据W igner-Seitz模型微观连续介质理论,建立了AFM针尖同试样面接触力包含斥力的数学模型;由分析力学的稳定平衡条件,发现了引起AFM“突跳”的本质是不稳定平衡点的存在;通过增加AFM悬臂梁刚度,提出了一种避免AFM“突跳”现象发生的方法,并给出仿真结果。     

Bending of Composite Plates under Static and Dynamic Loading

The stationary bending of a two-dimensional elastic system of joined rectangular plates with different mechanical properties and boundary conditions is studied. A technique for solving the corresponding problem is proposed. It is based on approximate approaches in combination with a generalization of the force method. It is established that the static strain state of the system is essentially dependent on the difference between the elastic moduli of the constituent plates. It is also shown that with certain boundary conditions, the dependence of the first resonant frequency on the relative position of plates along the contact line is nonmonotonic__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 1, pp. 77–84, January 2005.     

机载导弹惯性制导装置生产测试工艺研究

从机载导弹惯性制导装置的工厂生产测试的实际情况出发，提出了使用自由方位惯性坐标系作为静止导航测试中的导航参考坐标系，证明了它和以发射点地理坐标系为基础的惯性坐标系的等效性，论证了测试平台所需的调平精度，给出了确定测试指标的算法。这种方法的应用，可节省测试场地的建设经费，提高生产效率。     

Inter-contact force analysis of impacted disk assembly by dynamic caustics

The caustic method was utilized to study the contact force transmission in disk assemblies under impact load. The mapping equations were obtained based on the first invariant of the stress components in the disk subject to a normal concentrated force, and a characteristic dimension of the maximum size in the caustic curve was proposed to evaluate the contact force between the disks. Transient patterns of the caustic shadows were recorded by means of a high-speed camera of off-focus imaging, then the histories of the inter-contact forces among the disks were obtained with respect to the conditions of different masses and heights of the falling hammers. The influence of the impact loading and impulsive velocity was analyzed with respect to the force responses of the disk assembly, the double-peak phenomenon with comparison to the initial masses, and the energy dissipation of the systems under impact of different momentums. The project supported by the National Natural Science Foundation of China (10125211)     

Applicability of normal and shear stress cells embedded in cohesionless materials

A normal stress cell and a shear stress cell have been designed and tested under very varied conditions including permanent strain. Results pooled from nine different tests with the cells embedded in cohesionless materials (sand and wheat) showed that the coefficient of variation of the normal stress-cell sensitivity was 0.04, while it was 0.10 for the shear cell. The agreement between predicted and measured sensitivity was considered to be good for the normal stress cell and reasonably good for the shear stress cell. The shear cell showed a systematic dependence, within acceptable limits, of the total stress state in the surrounding material. A qualitative explanation of this phenomenon is given. Paper was presented at the SEM VI International Congress on Experimental Mechanics held in Portland, OR in June 6–10, 1988.     

Beitrag zur Prüfung metallischer Werkstoffe im Torsionsversuch

Zusammenfassung Der Torsionsversuch eignet sich zur Untersuchung des plastischen Verhaltens von Metallen bei erhöhten Temperaturen, wenn die Fließspannung stark von der Umformgeschwindigkeit abhängt. Aus der gemessenen Drehmoment-Drehwinkel-Kurve wird die Fließkurvek _f () berechnet. Hierfür wird ein Fließkriterium benötigt, dessen Unsicherheit im allgemeinen größer ist als alle Meßfehler. Diese Unsicherheit geht aber nicht in die berechnete Dehngeschwindigkeitsempfindlichkeit ein, die somit als Hauptergebnis des Versuches anzusehen ist.Um die Bedingungen technischer Warmumformung zu simulieren, wird die Verwendung extrem kurzer Proben (flacher Scheiben) empfohlen, womit sehr hohe Umformgeschwindigkeiten erreicht werden können. Für die Auswertung derartiger Versuche ist die wirksame Länge der kurzen Proben — experimentell oder semiempirisch — zu bestimmen und die Kerbwirkung zu berücksichtigen. Im Gegensatz zur herkömmlichen Vorgehensweise wird empfohlen, die örtliche Spannung und Verzerrung nicht für die Mantelfläche der Probe zu berechnen, sondern für einen kritischen Radialabstand im Innern der Probe, für den die Schiebung von der Kerbwirkung unabhängig ist, so daß sich die zuverlässigsten Werte ergeben.

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Summary The torsion test is often used for studying the plastic deformation of metals at elevated temperatures when stress depends strongly on the strain rate. From the measured torque-twisting angle curve, the stress-strain curvek _f () has to be calculated. For this purpose a yield criterion has to be used the uncertaintly of which normally exceeds all experimental errors. This uncertaintly, however, does not propagate into the calculated strain rate sensitivity which therefore may be considered as the main result of the torsion test.For simulating the conditions of technical hot forming processes, the use of extremely short test pieces (flat discs) by which very high strain rates can be obtained is recommended. For evaluating the test data the efficient lenght of short specimens has to be determined. In opposition to the conventional procedure of test evaluation, it is recommended not to calculate stress and strain for the surface of the specimen but for a critical radius for which strain is independent of the notch effect so that the most reliable values are obtained.

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