基于ANSYS/LS-DYNA的B-1416滚针轴承动力学仿真与分析

为了研究滚针轴承的动态特性,在UG软件中建立滚针轴承的几何模型,然后导入ANSYS/LS-DYNA软件中,建立有限元模型,对外圈外表面施加局部载荷,空心轴施加转速,得到了滚针轴承的接触应力、转速及振动速度、加速度的变化规律。其中,利用该模型获得的滚动体自转、公转速度与理论值一致性良好,说明采用的分析方法是可行的,为以后研究滚针轴承的磨损和寿命等提供参考。     

专用圆柱滚子轴承功率损失计算模型的建立

轴承的损坏多数情况下是由于温度过高造成的，功率损失是轴承发热的主要来源，研究轴承功率损失，降低轴承失效。     

同极型和异极型磁轴承的磁场分布和功率损耗分析

采用有限元软件ANSYS详细分析了同级型和异极型2种结构磁悬浮轴承的磁场分布,给出了2种结构磁轴承的二维磁力线分布图和磁场分布图,并分析了同级型磁轴承二维磁场矢量分布和三维磁通密度矢量分布。详细计算了在不同频率下2种结构磁轴承的功率损耗,给出了功率损耗随交变电流频率变化拟合曲线。分析结果表明,同极型磁轴承磁力线分布在同一方向,全部平行于转子的轴线,因而耦合效应小,功率损耗小,在应用上具有更加明显的优越性。     

滚针轴承套圈内底面至挡边支持面距离的测量方法探析

采用间接测量法,用辅助标准件和辅助量台的误差综合反映出被测套圈内底面至套圈挡边支持面的尺寸及误差;或用与套圈结构相同的组合标准件进行比较测量。     

Frictional behaviour of Pb‐Sn thin‐film lubrication

The frictional properties of lead‐tin thin films (thickness of 0.05–0.19 μm) with two types of copper interlayer were investigated. The thin film and the interlayer were formed on a silicon wafer surface by vacuum deposition. Friction tests were carried out using a ball‐on‐disc apparatus in a vacuum chamber. The thin copper interlayer reduced the friction coefficient and prolonged the film life. The effect of load on the friction coefficient is explained by an equation derived using the Hertzian contact area between a sphere and a plate. The thicker copper interlayer did not reduce the friction coefficient but markedly extended the life of the film. In this case, the dependence of the friction coefficient on the load is explained by an equation derived using the Hertzian contact area between a sphere with surface roughness of second order and a plate.     

Analysis of load application on idler roller bearing of belt conveyor in different dynamic models

The work presents an analysis of the loading conditions of an idler roller journal bearing of a belt conveyor based on different dynamic models (linear and nonlinear with elastic and frictional elements). It is established using computer simulation that the correct choice of the elastic and viscous characteristics of the damping components used in the support bearing design makes it possible to substantially reduce the dynamic loads on the latter.     

On the feasibility of using cryo‐treatment as a tool to enhance the abrasive wear behaviour of solid‐lubricated polymeric composites

Cryo‐treatment, a bulk modification technique, is fast emerging as a way with which to improve the wear resistance of metals. This technique has also shown the ability to enhance significantly the abrasive wear performance of some polymers and their short glass‐fibre reinforced composites. In this work, short carbon‐fibre reinforced composites of some heat resistant polymers, such as polyetherimide, polyethersulphone, polyamide 6,6, polyetheretherketone, and polytetrafluoroethylene, were selected to explore the potential of cryo‐treatment. The selected materials were cryogenically treated by cooling them to the temperature of liquid nitrogen. The abrasive wear tests were carried out at ambient temperature in single pass conditions at various loads, on a pin‐on‐disc machine, using silicon carbide paper as a counterface. The investigations revealed that this technique has definite potential to increase the wear performance of carbon‐fibre reinforced composites. An increase in hardness due to cryo‐treatment was thought to be responsible for an observed improvement in wear performance. However, the extent of improvement in the wear performance was not matched by an increase in the hardness value. Scanning electron microscopy proved useful in examining the morphological changes in the composites due to cryo‐treatment.     

Frictional and load‐carrying behaviours of micro‐textured sector shape pad thrust bearing incorporating the cavitation and thermal effects

Frictional and load‐carrying behaviours of micro‐textured sector shape pad thrust bearing have been explored and reported herein. The textured pad surfaces have been generated employing different cross‐sectional shapes (circular, square, trapezoidal and triangular) of grooves. Based on the thermohydrodynamic lubrication analysis, it is observed that when the adopted texture pattern is placed on the pad towards the entry region, it produces substantial reduction in friction coefficient. The texture involving the square cross‐sectional shape of grooves has yielded substantial reductions in the friction coefficient in comparison with the conventional plain pad. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance characteristics of oil‐in‐water mixtures in a journal bearing using different bearing materials

Oil‐in‐water (o/w) mixtures have an interesting property that has attracted the attention of tribologists, namely, that they can form thicker hydrodynamic films than those inferred from their rheological properties. The oil phase is believed to separate out on the metal surface in concentrated contacts lubricated with o/w mixtures. In this paper the performance characteristics of water‐based oils have been systematically explored for their film‐generating capabilities. The lubrication properties of o/w lubricants are studied and compared in a journal bearing rig assembly with different bearing materials. The rig is run under increasing loads and speeds in conditions pertinent to hydrodynamic lubrication. The rig has been able to operate with o/w mixtures at a concentration as low as 10 vol.%. However, the results have shown that the bearings exhibited signs of high eccentricities with o/w mixtures compared to Engineering Sciences Data Unit (ESDU) predictions. This behaviour has been attributed to shear rate effects on water‐based lubricants.     

Dynamic characteristics of spiral groove bearing spindles: comparison between rotating‐shaft and fixed‐shaft designs

In this paper, two types of spiral groove bearing (SGB) spindles, a rotating‐shaft spindle and a fixed‐shaft spindle, are analysed, and the dynamic characteristics of these two types of spindles are tested and compared. The effects of lubricants on the dynamic characteristics and power consumption of the spindles are considered. It is found that the dynamic characteristics of the fixed‐shaft spindle are much better in terms of non‐repeatable run out than those of the rotating‐shaft spindle. The lubricants are found to have significant effects on both the dynamic characteristics and power consumption of the spindles. Copyright © 2006 John Wiley & Sons, Ltd.     

Frictional performance of lithium 12‐hydroxystearate greases with different soap fibre structures in sliding contacts

The effect of the fibre structure of the grease on the frictional performance of lithium 12‐hydroxystearate greases with different fibre lengths was investigated in face, line, and point contact sliding tests. At high sliding speeds where the lubrication regime was practically hydrodynamic, the coefficient of friction of the base oil alone was lower than that of the greases. The coefficient of friction was roughly estimated as follows: base oil < long‐fibre grease < medium‐fibre grease < short‐fibre grease. The supply or replenishing capability of the grease played a critical role in maintaining hydrodynamic lubrication. At high contact pressures, the short‐fibre grease was superior in frictional performance to the long‐fibre grease due to the firm fibre network structure of the latter. In mixed and boundary lubrication regimes, the greases were superior in frictional performance to the base oil, since the soap fibres of the greases had a superior load‐carrying capacity. The long‐fibre grease, with a firm fibre structure, offered better frictional performance than the short‐fibre one.     

Non‐Newtonian and thermal effects in constant flow valve compensated symmetric hole‐entry hybrid journal bearing

Every high speed machine, demanding high level of perfection, can operate successfully through a precise design of bearings. Such a design can be formulated after carefully studying both static and dynamic characteristics of the journal bearing. The present paper described the study of static and dynamic performance of a hole‐entry hybrid journal bearing system compensated with constant flow valve restrictor by considering the combined influence of thermal effects and non‐Newtonian behaviour of the lubricant. The variation of the viscosity due to the non‐Newtonian behaviour of the lubricant and temperature rise has been considered in the study. The numerical solution of the generalized Reynolds equation governing the flow of the lubricant, having variable viscosity along with the energy and heat conduction equations, was obtained using finite element method. The non‐Newtonian lubricant has been assumed to follow the cubic shear stress law. The study included the performance of a double row symmetric hole‐entry hybrid journal bearing configuration containing 12 holes per row. The results presented in this paper indicate that change in viscosity of lubricant affects the performance of the hole‐entry hybrid journal bearing system quite significantly. Copyright © 2007 John Wiley & Sons, Ltd.     

Performance of synthetic oils in the hydrodynamic regime ‐ II. Generalisation

In Parti I the results of an extensive experimental investigation of the performance of environmentally adapted oils in the hydrodynamic regime were reported. Four oils were tested in a tilting‐pad thrust bearing for different combinations of load, shaft speed, and supply oil temperature. In this second part, details of a generalisation procedure are described. A number of parameters representing the physical properties of an oil, such as viscosity and viscosity‐temperature coefficient, are adopted. The influence of each of these parameters on minimum oil film thickness, maximum temperature rise, and bearing power loss is then analysed. It is shown that viscosity measured at the supply oil temperature is the most important parameter. The effects of the viscosity‐temperature coefficient and oil thermal conductivity are less pronounced and yet significant. It is also shown that it is not possible to select an optimum oil that yields maximised oil film thickness, minimised temperature rise, and minimised power loss at the same time.     

A study of thermal effects in an offset‐halves journal bearing profile using different grade oils

The Reynolds equation has been solved simultaneously along with the energy equation and heat conduction equation by finite difference method to find pressure and temperature distribution for circular and offset‐halves journal bearings. Numerical solution of energy equation was achieved using parabolic temperature profile approximation technique for faster computation. A comparative study for the rise in oil temperatures, thermal pressures and load‐carrying capacity for the three different commercially available oils namely Hydrol 68, Mak 2T and Mak Multigrade (Bharat Petroleum Corporation Limited [BPCL], Mumbai, India) has been carried out. With an increase in speed, the oil temperature, the thermal pressure and the load‐carrying capacity rose for all the grade oils under study. The rise in computed oil temperature, thermal pressures as well as load‐carrying capacity has been found maximum for Mak Multigrade oil and minimum for Mak 2T oil. The nature of temperature profiles and load‐carrying capacity has been found to be in good agreement with those available in the literature. Copyright © 2011 John Wiley & Sons, Ltd.     

Elasto‐aerodynamic lubrication analysis of a self‐acting air foil journal bearing

Nowadays, air foil bearings find widespread use in very high speed, lightly loaded oil‐free rotating turbomachineries such as compressors and microgas turbines because they have theoretically no speed limitations and they are environmentally benign. In the design of such bearings, it is of cardinal importance to enhance their steady‐state and dynamic performance characteristics for the safety operation, especially against the external dynamic excitations. Most of elasto‐aerodynamic approaches under dynamic conditions proposed in the technical literature include only the static pressure induced deformation of foils. This paper presents a theoretical investigation on the effects of both static and dynamic deformations of the foils on the dynamic performance characteristics and stability of a self‐acting air foil journal bearing operating under small harmonic vibrations. For the dynamic deformations of foils to be taken into account, the perturbation method is used for determining the gas‐film stiffness and damping coefficients for given values of excitation frequency, compressibility number and compliance factor of the bump foil. The rotor‐dynamic coefficients serve as input data for the linear stability analysis of rotor‐bearing system. The nonlinear stationary Reynolds' equation is solved by means of the Galerkin's finite element formulation, whereas the finite differences method are used to solve the first‐order complex dynamic equations resulting from the perturbation of the transient compressible Reynolds' equation. As a first approximation, the corrugated subfoil is modelled as a simple elastic foundation, i.e. the stiffness of a bump is uniformly distributed throughout the bearing surface. It was found that the dynamic properties and stability of the compliant finite length journal bearing are significantly affected by the compliance of foils especially when the dynamic deformation of foils is considered in addition to the static one by applying the principle of superposition. Copyright © 2012 John Wiley & Sons, Ltd.     

Some aspects of rolling friction resistance in a complex tribological pair – the bicycle wheel bearing

Bicycles are an important means of transport — over 20 million are manufactured worldwide each year, and, because their source of motive energy is human, their energy conversion, as measured by their resistance to motion, is critical. The bearings used in bicycles are rolling bearings, but are normally of different materials and construction quality to the roller bearings used in other applications. The present paper is intended to provide an indication of the phenomena influencing the resistance to motion and loss of energy of these bearings, and is based on a rolling bearing test stand designed by the author. A mathematical model derived from experimental observation is presented, and the theoretical results compared with experimental results.     

Thermohydrodynamic studies based on different grade oils in offset‐halves journal bearing

This work presents theoretical and experimental investigations on offset‐halves bearing to access the temperature rise at oil–bush interface with three different grade commercial oils namely Mak 2T, Hydrol 68 and Mak Multigrade at different loads. The Reynolds equation was solved simultaneously along with the energy equation and heat conduction equations by the finite difference method to find the pressure and temperature distribution for offset‐halves journal bearing. The energy equation was solved using parabolic temperature profile approximation technique for faster computation. A comparative study for oil temperatures and thermal pressures for three grade oils was carried out vis‐à‐vis the effect of speed and eccentricity ratio. The temperatures in the oil film were observed to be lowest for Mak 2T oil and highest for Mak Multigrade oil. Copyright © 2011 John Wiley & Sons, Ltd.     

The osteogenic effects of swimming on bone mass,strength, and microarchitecture in rats with unloading‐induced bone loss

The effect of nonweight‐bearing exercise on osteoporotic bones remains controversial and inconclusive. The purpose of this study was to evaluate the effects of swimming on osteoporotic tibias of rats submitted to hindlimb suspension. Initially, 20 Wistar rats were used to confirm a significant bone loss following 21 days of unloading. Thirty rats were then divided into 3 groups and followed during 51 days: CON (nonsuspended rats), S + WB (suspended rats for 21 days and then released for regular weight‐bearing) and, S + Swim (suspended rats for 21 days and then released from suspension and submitted to swimming exercise). We observed that swimming exercise was effective at fully recovering the bone deterioration caused by suspension, with significant increments in BMD, bone strength and bone volume. On the other hand, regular weight‐bearing failed at fully restoring the bone loss induced by unloading. These results indicate that swimming exercise may be a potential tool to improve bone density, strength, and trabecular volume in tibias with bone loss induced by mechanical unloading in suspended rats. We conclude that this modality of activity could be beneficial in improving bone mass, strength, and architecture in osteoporotic individuals induced by disuse, such as bed rest or those exposed to microgravity, who may not be able to perform weight‐bearing exercises. Microsc. Res. Tech. 78:784–791, 2015. © 2015 Wiley Periodicals, Inc.