Solution of transient thermoelastic contact problems by the fast speed expansion method

Thermoelastic expansion due to frictional heating causes significant changes in contact pressure and temperature in energy dissipation systems such as brakes and clutches. Finite element analysis of such systems tends to be extremely computer-intensive. We here present an alternative implementation of the transient problem, based on the expression of the temperature and stress fields as modal expansions. For its implementation, the method depends upon the availability of solutions of the eigenvalue problem related to thermoelastic instability (TEI). It is demonstrated that computational efficiencies can be achieved by performing the eigenvalue analysis at a limited number of speeds and then using a suitable interpolation procedure. However, care must be taken in the interpolation process, because eigenvalues of the problem tend to be clustered, which complicates the process of identifying corresponding eigenfunction pairs. The method is validated by convergence tests and illustrated by an example of a multidisc clutch.     

A study on the differential gearing device with the faculty of a limited slip differential

The limited slip differential (LSD) is a device which enables the driving force to be transmitted from one slipping wheel to another by temporarily restraining the differential function when unwanted slipping occurs on muddy or icy roads. Many types of LSDs were developed such as the mechanical lock, disk clutch, viscous coupling, Torsen and multiple clutch type. This study designed a new type of differential gearing device with the faculty of a limited slip differential, and then evaluated its performance.     

湿式多片式制动器带排转矩研究

针对一种重型车辆采用的湿式多片式制动器,分析研究了其在分离状态下的带排转矩,讨论了转速,润滑油温,润滑油流量对带排的影响,最后提出了改进措施。     

Thermomechanical finite element analysis of slider-disk impact in magnetic storage thin film disks

Oblique impact of a slider with a rotating disk in a hard disk drive was analyzed using the finite element method. A three dimensional, thermomechanical, impact model was developed to study the mechanical and thermal response during the impact of a spherical slider corner with a rotating disk. The model was validated by comparing the finite element results with analytical solutions for a homogeneous glass substrate disk. Impact penetration, stress and incurred flash temperature were obtained for various normal impact velocities. The effects of material layers on the disk were also investigated by introducing layers with different material properties and thicknesses. It was found that for a rounded slider corner and a critical normal impact velocity of 0.03 m/s studied in this work, the layers have insignificant effects on the mechanical response and small but predictable effects on the flash temperature.     

Influence of surface topography on friction characteristics in wet clutch applications

In heavily loaded wet clutches, such as in limited slip differentials, sintered friction materials are sometimes used due to their resilience at high loads and high temperatures as well as their competitive cost in comparison to alternative friction materials.During the lifetime of the clutch, changes in the friction materials’ topography occur. These changes will influence the friction characteristics of the clutch, and therefore affect the anti-shudder performance of the transmission system. This paper investigates the influence of, and classifies, changes in the topography of the sintered friction material.The topography is measured by utilizing vertical scanning interferometry. Different parameters are investigated in order to find relevant parameters correlating to the wear of the material.Results show that changes in the topography of the friction material do indeed influence the friction characteristics of the clutch and that it is possible to calculate relevant topography parameters that describe the amount of wear the material has been subjected to.     

Effects of the structure and properties of ice and snow on the friction of aircraft tyres on movement area surfaces

At winter-contaminated movement areas, the interfacial materials—snow and ice—cause the major operational problem related to aircraft performance. The central issue is how to evaluate the attainable friction force between the aircraft tyre(s) and the pavement and relate that to aircraft performance. In wintertime the operational window for aircraft movements can change rapidly and so a frequent reporting service of the surface conditions is warranted. Friction is both material and system dependent. An ongoing Joint Winter Runway Friction Measurement Program (JWRFMP) addresses this issue in an international effort to produce reliable data on friction at winter-contaminated movement areas in potentially slippery conditions. The traditional approach has been to measure the friction with tribometers to generate μ, the “friction number”. The substantial question is: what are these friction numbers? JWRFMP encourage a broad multidisciplinary approach to solve this question and to provide the international aviation industry with the best information attainable. The goal is to provide an International Runway Friction Index (IRFI) that comprises the relevant information to be used for the pilot/aircraft system. This IRFI should be based upon sound basic physics and an analytic approach to understanding and to solving the tribological problems involved. In this paper the interaction of aircraft wheel(s) on travelled winter surfaces of a movement area is outlined by a tribosystem and the operational envelope for the system is described.     

新型湿冷系统的应用探讨与热力特性研究

针对模块式小型压水堆的特点,提出了新型湿冷系统,并介绍其相应的结构组成、不同型式及运行方式。针对新型湿冷系统的运行特点,建立了新型湿冷系统直流部分与二次循环部分热负荷比例分配的数学模型。结合某电厂ACP100核电机组,对新型湿冷系统进行热力特性分析可知,直流冷却负荷百分比的变化对二次循环流量、凝汽器进口水温、凝汽器压力、以及净微增功率的影响显著。应用新型湿冷系统的优化计算方法,对循泵耗功进行计算可知,循泵耗功不仅受到循泵运行方式的影响,还与新型湿冷系统的运行方式,以及直流冷却负荷百分比有关。     

The effect of slip amplitude and test time on fretting wear in metal-metal contact

A study was conducted to determine the effect of amplitude and test time on surface damage in metal-to-metal contact under lubricated conditions. The test set up consisted of a ball loaded against a flat disc, with an external drive imparting a linear oscillatory motion to the ball on the flat. The materials were steel AISI 52100/AISI 52100, and the lubricant was ISO VG 220. Damage characteristics were defined for amplitudes in the range of 5 to 50 microns and for test times of 10 to 360 min.     

The influence of temperature and humidity on the sensitivity of torque transducers

This paper presents a study of the effect of temperature and relative humidity on the sensitivity and the characteristics of torque transducers such as residual zero torque, reversibility and creep. Temperature and humidity coefficients of the sensitivity take positive as well as negative values. Linear dependence is found between the influence of temperature/relative humidity and the applied load. For some torque transducers, under temperature change the sensitivity has a transient overshoot reaching up to 3 times the steady amplitude. Also there is a small effect of temperature/relative humidity on the transducer’s parameters such as residual zero torque, reversibility and creep. Equations are presented to predict the effect of temperature/relative humidity changes on the sensitivity of torque transducers.     

多孔金属结合剂金刚石砂轮研究综述

介绍了目前利用通电烧结、热等静压和真空烧结等方法制造多孔金属结合剂金刚石砂轮的主要技术及其性能。讨论了目前多孔金属结合剂金刚石砂轮研究中的问题 ,并对今后的发展方向做了展望     

The influence of underlying tension on partial slip in complete and nearly complete contacts

Solutions are given for the partial slip regime present under a square ended punch, a punch having a flat plus rounded profile (and, for completeness, a Hertzian contact), when subjected to a monotonically increasing proportional shear force and bulk tension. Particular attention is paid to the effect of the tension in stabilising the partial slip regime in cases where there is an abrupt transition from near adhesion to sliding, and to the various partial slip regimes which can exist.     

扭力转向对麦弗逊悬架前驱车的影响分析

扭力转向是麦弗逊悬架前轮驱动车的一种常见现象。本文介绍了扭力转向对麦弗逊悬架前轮驱动车的影响,对扭力转向产生的机理和各种原因逐一进行了说明,并分析了降低扭力转向的办法,最后进行了实例验证。其结论对解决车辆的实际扭力转向问题及在整车开发前期设计优化都具有借鉴意义。     

Choice of electrical motor and transmission in mechatronic applications: The torque peak

This paper deals with the effect of the torque peak on the choice of electrical motor and transmission suitable for moving a joint. We propose a method that allows us to explain the general form of the resolving diagram and to identify the load conditions that are directly responsible for it. In consequence, this method permits the designer to obtain the equation of this curve and to find analytically the admissible motors and the corresponding transmission ratio ranges.     

Thermal stability of synthetic oils in aviation applications

The thermal decomposition of selected synthetic base fluids has been investigated. The effects of temperature and time on the rate and extent of thermal degradation were studied in a modified steel bomb test device. The effects of chain length and branching are important factors in the thermal stability of hydrocarbons and similar fluids. In order to overcome the 350°C limit of thermal stability, other classes of chemical have to be used.     

Analysis and measurement of torque hysteresis of pivot bearing in hard disk drive applications

During hard disk drive (HDD) operation in the track-following, short seek and seek settling modes, the motion of the actuator, which is supported by a pivot bearing cartridge, has very small amplitudes. The effect of hysteresis friction from the pivot bearing becomes significant, impacting servo performance. Often such effects are not well understood and thus, it is not being taken into consideration during servo design. A study of the hysteresis friction behaviour of pivot bearings is presented. An integrated test apparatus for pivot bearing analysis was designed and built where a Laser Doppler Vibrometer (LDV) was used to accurately measure the displacement and velocity of the actuator for feedback control. Using this test apparatus, the hysteresis friction behaviour in both frequency and time domain was analysed. The effects of pre-load, oscillating magnitude and oscillating frequency were investigated. The results obtained can now be used for servo design and pivot bearing evaluation.     

湿式摩擦离合器摩擦片油槽对瞬态传热的影响

计算了湿式摩擦离合器摩擦片的热流密度和对流换热系数,建立了考虑油槽结构的摩擦片三维瞬态热传导有限元模型.借助ANSYS软件,分析了不同油槽宽度摩擦片的瞬态温度场,给出了摩擦片最高温度随时间的变化曲线和径向温度分布规律.结果表明,摩擦片最高温度出现在结合时间段中间附近,随油槽宽度增加摩擦片最高温度略有降低;由于油槽的影响,摩擦片径向温度呈阶跃分布,结合完成后摩擦片表面出现椭圆形热斑.     

Analysis of interface temperature,forward slip and lubricant influence on friction and wear in cold rolling

To improve cold rolling processes, it is necessary to understand and to optimise contact at roll–strip interface. Thus a simulation test has been developed in our laboratory. The upsetting rolling test (URT) enables to study friction and iron fines pollution by the reproduction of the main industrial contact conditions such as plastic strain, normal and tangential stresses and forward slip. On the basis of the URT, a new experimental protocol has been developed to reproduce industrial lubrication regime. Moreover, a new heating system has been designed to simulate interface temperature which has a decisive effect on lubricant behaviour. These optimisations permit to analyse contact temperature, forward slip and lubricant influence on friction, iron fine pollution and surface aspects. A great influence of temperature and lubricant on friction and wear has been put forward. Actually an increase of the Coulomb friction coefficient associated with a decrease of the iron fines quantity have been shown with an increase of temperature. These results seem to indicate more adhesive wear when temperature increases.     

差动电荷转移式原油含水率测量仪的研究

本文介绍了利用差动电荷转移法测量小电容变量及特点,在此基础上研制出具有高分辨率的原油含水测量仪。给出了传感器电路的实验模型及实验结果。     

“太阳能加热”有限元分析在太阳能热性能试验中的应用

通过"太阳能加热"有限元分析模块与全玻璃真空太阳集热管闷晒试验数据对比,验证"太阳能加热"有限元分析的正确性、吻合性,并对其应用作简要介绍,为太阳能热性能试验提供了一种新的思路。     

平板传热对气膜冷却的影响

对不同平板厚度的圆柱孔平板气膜冷却模型进行了数值研究,其中冷却空气入射角均为35°,湍流模型采用Standardk-ε湍流模型。所研究的模型分为单孔模型和排孔模型,板的厚度分为4mm、2mm及0mm。文章的重点在于分析平板的传热对气膜冷却效果的影响,研究结果显示气膜冷却效率沿主流方向逐渐降低,当吹风比为0.8时冷却效率最高,平板内部导热对气膜冷却效率及平面温度分布有较大影响。