压水堆堆内构件异种材料螺纹联接件在热循环载荷下的疲劳试验分析研究

压水堆电厂的反应堆堆内构件中的螺纹联接件与一般联接件不同,在高温、辐照环境中工作,除承受机械载荷外,还承受由于水流以及地震等引起的动态载荷。而在寿命期内反复的冷-热-冷循环,会使异种材料联接件产生交变循环热应力,甚至会使预紧力松弛,因此预紧力合适与否将直接影响联接件联接的可靠性。对通过模拟实际联接结构的联接件进行热循环试验和分析,研究热循环载荷对预紧力和联接结构的影响。     

航空结构的连接件内力分析探讨

航空结构疲劳分析的难点在于计算细节疲劳额定强度(DFR)计算,而结构的细节疲劳额定强度关键在于准确地得到紧固件载荷分布,找到最危险铆钉位置及R/P值。使用解析法能得到较准确的结果,但只能对简单、规则连接件进行计算。采用有限元方法,则可以对绝大多数连接件进行模型简化,通过单元的准确模拟,精确地得到内力分布。     

Contact and non-contact approaches in load monitoring applications using surface response to excitation method

Surface response to excitation (SuRE) method is a low-cost alternative to electromechanical impedance based structural health monitoring (SHM) technique. The SuRE method uses one piezoelectric transducer to excite the surface of a structure with a sweep sine wave. Piezoelectric sensors or scanning laser vibrometer can be used to monitor the dynamic response of structure.In this study, the performance of the SuRE method was evaluated with the conventional piezoelectric elements and scanning laser vibrometer used as contact and non-contact sensors, respectively, for monitoring the presence of loads on the surface. In order to determine the accuracy and reliability of both monitoring approaches in detecting changes in level of applied load, three different experimental setups were studied. Response of a system in the presence of a single ​load applying and multiple loads applying and its performance in detecting tightness in a nut and bolt system were investigated. The spectrum of the dynamic response is collected at the optimal operating condition. Any significant change of the spectral characteristics may indicate defects, improper loading or loose fasteners. The performance of the SuRE method using contact and non-contact sensors indicated that both variations of the method could be successfully used in load monitoring applications.     

径向受载型金属垫片法兰密封结构的力学特性研究

介绍了一种径向受载型金属垫片法兰密封结构,分析了其受力特点和密封机理。利用有限元分析方法对它的力学特性进行了研究,计算了不同的法兰锥形张角在不同轴向压缩量下的轴向力、径向力以及密封面上的最大von Mises应力,分析了其规律及对密封结构装配特性、密封特性的影响。与普通轴向受载型金属垫片法兰密封结构相比,其所需的紧固载荷较小,用较轻的法兰及较小的螺栓载荷即能实现密封作用,尤其适用于装配空间小、装配时间要求短、有辐射、需远距离操作等场合。     

Conductors and Contact Connections in Megaampere-Current Electric Circuits

The operation of conductors and contact connections in electric circuits transmitting megaampere-current pulses with durations of tens of microseconds is considered. The permissible conductor-current density is determined from the condition of thermal stability of the high-voltage polymeric insulation. Operating conditions of demountable contact connections for megaampere pulse currents are described, and design examples of such connections operating at a linear current density as high as 80 kA/cm are given. Methods for providing mechanical stability against the action of electrodynamic forces that occur during the passage of megaampere-current pulses are considered.     

变化环境下的超声导波结构健康监测研究进展

超声导波结构健康监测(Structural health monitoring,SHM)在大规模板和管结构的缺陷诊断中是一个极具吸引力的检测技术。不同研究者均证实环境和操作条件变化,特别是温度和外加载荷变化会掩盖由缺陷引起的信号变化从而限制SHM系统的性能。分别就环境变化中温度和外加载荷对SHM系统中超声导波传播机理的影响进行综述:环境温度的变化会引起样本热膨胀系数和弹性模量的改变,进而影响超声导波在结构中的传播,且相比于超声纵向导波,横波对温度的敏感度较低;外加载荷对导波传播的影响主要体现在时移、幅值及相位的变化上。针对温度变化对导波结构健康监测造成的影响,详细阐述温度补偿法的研究进展,为更好地辨识由缺陷引起的变化和由周围环境引起的良性变化奠定理论基础,为后续超声导波SHM的研究指明方向。     

钛合金紧固件在机械加工中存在的问题及措施

钛合金紧固件在机械生产加工当中使用范围广泛,构件的精准度和强度很高,各方面综合性能优越,能够运用到机械加工当中的各个领域,是一种加工生产的好材料。在钛合金紧固件使用的时候,也存在一定缺陷,这些缺陷直接影响了产品使用过程当中加工的质量,使加工存在一定的问题。本文从钛合金紧固件在机械加工当中存在问题及其改进措施进行探讨分析。     

Identification of external forces in mechanical systems by using LifeCycle model and stress-stiffening effect

This paper presents an optimization-based inverse procedure for the determination of external loads applied to a given mechanical structure, by using information concerning the dynamic behavior of the system and its corresponding finite element model. The influence of the stress-stiffening effect on the dynamic characteristics of structural systems is used to establish a relation between the dynamic responses and the applied external forces. An optimization problem is formulated in which the objective function represents the difference between the measured modal characteristics of the loaded structure and their finite element counterparts. The loading parameters (magnitude, position and direction) assumed as being unknown, are considered as design variables. The identification procedure is illustrated by means of numerical simulations and experimental tests, in which a heuristic technique known as LifeCycle model was used.     

机械式拖拉机导向探测装置

拖拉机自动导向能提高行驶轨迹的精度,提高行间作业质量,减轻驾驶员劳动强度。机械式拖拉机自动导向利用田间的作物、秸秆或垄沟等进行接触探测,机构简单、成本低、易维护。设计针对玉米秸秆行间作业的低成本机械式导向探测装置。通过对导向探测器具有的特点进行分析,确定触杆的对称结构和偏心半椭圆形状特征,在对触杆进行受力分析的基础上确定触杆形状的关键参数即偏心矩。经过试验表明这种形式的导向探测装置及角位移传感器能实现拖拉机在秸秆行间的导向探测,并对秸秆无破坏。     

EXPERIMENTAL RESEARCH ON EVALUATING STRUCTURE DAMAGE WITH PIEZOELECTRIC DYNAMIC IMPEDANCE

A dynamic impedance-based structural health monitoring technique is introduced. According to the direct and the converse piezoelectric property of piezoelectric materials, the piezoceramic ( PZT ) can be used as an actuator and a sensor synchronously. If damages like cracks, holes, debonding or loose connections are presented in the structure, the physical variations of the structure will cause the mechanical impedance modified. On the basis of introducing the principle and the theory, the experiment and the analysis on some damages of the structure are studied by means of the dynamic impedance technique. On the view of experiment, kinds of structural damages are evaluated by the information of dynamic impedance in order to validate the feasibility of the method.     

PRINCIPLES AND PARAMETER DESIGN FOR AC-DC THREE-DEGREE FREEDOM HYBRID MAGNETIC BEARINGS

To simplify the mechanical structure, decrease the overall system size of the 3-degree freedom axial-radial magnetic bearings and reduce the manufacturing costs as well as operating costs, an innovated AC-DC 3-degree freedom hybrid magnetic bearing is proposed, which is driven by a DC amplifier in axial direction and a 3-phase power converter in radial directions respectively, and the axial and radial bias magnetic fluxes are provided with a common radial polarized permanent magnet ring. The principle producing magnetic suspension forces is introduced. By using equivalent magnetic circuit method, the calculation formulas of magnetic suspension forces and the mathematics models of the system are deduced. Nonlinearities of suspension forces and cross coupling between different degree freedoms are studied further by calculating the suspension forces at different displacements and control currents to validate the feasibility of the mathematics model. Then based on the mathematics models of the bearing, a control method of this novel bearing is designed. Lastly, the methods on parameter design and calculations of the bearing are presented, and an applicable prototype is simulated to analyze the magnetic path by using finite element analysis. The theory analysis and simulation results have shown that this magnetic bearing incorporates the merits of 3-phase AC drive, permanent magnet flux biased and axial-radial combined control, and reduces overall system size and has higher efficiency and lower cost. This innovated magnetic bearing has a wide application in super-speed and super-precision numerical control machine tools, bearingless motors, high-speed flywheels, satellites, etc.     

紧固件横向振动试验台的研制

详细介绍了紧固件横向振动试验台的原理、组成及各部分主要结构。该试验台具有试验周期短、可试验项目多、结构简单和成本低等优点。实践证明,该试验台能有效测试螺纹联接的防松性能。     

Experimental investigation on monitoring interelectrode gap of ECM with six-axis force sensor

To realize on-line monitoring interelectrode gap, six-axis force sensor was embedded into main spindle of machine tool to measure force signals on cathode exerted by electrolyte. The force signals, three forces, and three moments in X, Y, Z directions, respectively, are considered as research parameters. On one hand, the forces exerted on the tool cathode by electrode are measured with six-axis force sensor as electrolyte flow system is activated and electrode is deactivated. On the other hand, the forces are tested when electrolyte flow system and electrode are both activated. Then, the relation between six force components and interelectrode gap are analyzed. Machining experiments using three types of tool, e.g., plane tool, slant tool, and blade tool, have been carried out to deduct experiential equations between six force components and gap according to least squares method. Furthermore, the experimental data with blade tool are put into experiential equation with slant tool to examine validity of measuring gap in ECM. The relation of parameters in equations is analyzed and a conclusion is drawn: in the range of 15% error, machining experiential equation with slant tool can be used to on-line measure the interelectrode gap in ECM.     

Experimental Technique to Study Tangential-to-Normal Contact Load Ratio

This paper considers the mechanical interaction due to surface roughness and examines the surface theories using the classical definition of coefficient of friction: the tangential-to-normal load ratio. The postulation for maximum static friction is used to experimentally evaluate the contact models. For this purpose, a pin-on-disk test apparatus is employed with the capability of measuring tangential and normal forces for a frictional contact. The tests involve pairs of disks and specimens, that is, steel-on-steel and aluminum-on-aluminum contacts. In each case, profilometer measurements are performed on the disk and the Greenwood and Williamson parameters, are determined. Using the parameters, the theoretical estimates of normal and tangential loads are obtained. The theoretical values of tangential-to-normal contact load ratios are compared with those obtained from measurements for various applied normal loads. The tests utilizing a pin-on-disk apparatus showed a partial agreement between the experimentally obtained load ratios and the predicted upper limit confidence interval using the theoretical elastic and elastic-plastic contact. The result suggested that the elastic-plastic formulations provide better predictions of load ratios than the elastic contact formulations.     

基于压阻原理的磁流变减振器阻尼力传感器设计

为实现磁流变减振器运行中的健康状态监测并满足轿车磁流变减振器控制器阻尼力的需要,设计了一种可同时测量磁流变减振器压缩和复原行程中动态阻尼力的压阻式力传感器。根据汽车磁流变减振器的工作特性和压阻式压力传感器的设计原则,对阻尼力传感器进行了整体结构设计;采用理论计算与有限元仿真相结合的方法,以达到设计量程、获得较大灵敏度和固有频率为设计目标,确定了传感器芯片尺寸;通过分析论证,确定了传感器芯片型式、制作材料;研究了压阻系数与晶向的关系,确定了电阻排布方向和位置、电阻条尺寸、电阻条折弯数,完成了芯片的版图设计。     

弹性梁式构件的运动稳定性分析

结构－控制耦合系统是一种机械负载与驱动控制器相互作用的动态反馈系统。将机械系统和控制系统统一考虑,将驱动机械负载的驱动力也看成是结构－控制耦合系统的内力,则可采用处理力学上保守系统的方法使建模和分析大大简化。采用能量方法对无重力状态下弹性梁运动的相对平衡状态进行分析,得出了系统相对平衡的稳定条件。以此稳定条件作为系统运动的控制参数,有利于使弹性梁的动能转化为驱动－控制系统的电磁势能,这样一方面会加速驱动系统的制动,另一方面会迅速衰减弹性梁的振动。研究工作的结果是为弹性梁提供了一种非常简单有效的实时控制方法,该方法已在多种弹性梁试验系统上得到证实。     

A lumped-parameter transducer model for piezoelectric and ferroelectret polymers

We have developed a model to describe the sensor operation of piezoelectric and ferroelectret polymer materials. The lumped-parameter model for the sensors describes the interaction between a mechanical motion and an electrical signal. The differences in material properties are considered in the model, and especially, the effects of dynamic and static forces and temperature to the electrical output signals provided by the sensors constructed from the materials are discussed.     

Automatic control of mechanical forces acting on cell biomembranes using a vision-guided microrobotic system in computer microscopy

A prototype for automatic control of mechanical forces acting on cell biomembranes is proposed in this paper. This prototype consists of vision-guided position control of the holder and micro-force sensor, automatic mechanical property characterization of cell biomembranes and automatic control of mechanical forces acting on cell biomembranes. A template-free calibration method and autofocusing of multiple objects are introduced in the vision-guided position control to minimize external biological contamination and position the cell, holder and micro-force sensor into the same focal plane, respectively. A third-order polynomial modified from biomembrane point-load model describing the relationship between the measured mechanical force and the deformations of biomembranes is proposed. This simplified model is easily identified and inversed to facilitate the automatic control of mechanical forces. Experimental results based on zebrafish embryos demonstrate the feasibility of the proposed prototype.     

Limit state of a stringer panel with a periodic set of cracks

The process of crack propagation in an isotropic panel reinforced by supporting stiffeners is examined. It is assumed that the panel is weakened by a periodic set of straight cracks and there are areas where the crack edges interact with each other. The boundary problem on equilibrium of a periodic set of straight cracks with connections between crack edges in the case of external tensile loads and forces in the connections reduces to a nonlinear singular integrodifferential equation. Using the criterion of limit stretching of connections, the relationship for the residual strength of the panel is obtained.     

Friction Coefficient Measurement of an In Vivo Murine Cornea

Ocular tear film mucins and lipids promote lubricity of the corneal surface during ocular movements. The mechanisms of this lubricity are difficult to model and to measure due to the delicate nature of the film itself and the conditions under which it exists. This study describes a kinetic friction coefficient measured between a glass probe and a living mouse eye. A portable custom micro-tribometer was used to prescribe sliding motions and record normal and frictional forces. Friction coefficient measured over both sliding directions resulted in µ = 0.068 under a pressure of approximately 12 kPa. In vivo measurements may enhance the understanding of corneal friction response, as well as provide an empirical friction coefficient for more complex mechanical models.