齿轮跑合的磨损机制研究

通过齿轮副跑合的模拟试验,得出齿轮副在跑合过程中磨损形式的转化规律。     

Experimental study on the chaotic attractor evolvement of the friction vibration in a running-in process

Running-in wear experiments were conducted on a pin-on-disk tester. The attractors of friction vibration were investigated by applying the chaos theory, and the evolvement mechanism of the friction vibration chaotic attractors in the running-in process was analyzed. The experimental results indicate that the friction vibration has a chaotic nature, and the chaotic attractor in the phase space is an always open trajectory with a specific hierarchy and structure. The chaotic attractor of the friction vibration gradually converges and tends toward a balanced state in the running-in process. The evolvement of the friction vibration chaotic attractors indicated that the wear state changes from the running-in stage to the stable wear stage.     

On the nature of running-in

The terms run-in, break-in, and wear-in are related but not identical. All of them concern special cases within the general subject of tribological transitions. Tribological transitions can be induced by imposed changes in operating conditions or they may occur naturally as the system ages, without external intervention. Transitions can occur as an inherent consequence of design, as in the case of a piston ring and cylinder system. The attributes of frictional running-in include the overall trend in friction force with time, the duration of characteristic features in the friction/time curve, and the instantaneous level of frictional fluctuations superimposed on the general trend. Changes in friction and wear that occur during running-in are more than a consequence of surface roughness alterations alone. Depending on the tribosystem, they can also include changes in surface composition, microstructure, and third-body distribution. Examples of how factors like contact alignment and surface pre-conditioning affect the form of friction/time curves are given. Friction and wear relationships during running-in are discussed, as are scale effects whose relative influence also changes with time. Initial running-in behavior can be subject to the influence of nanometer-sized films and progress to the scale of micrometer-sized asperities and larger-sized surface structures as sliding proceeds. Piecewise models for friction during running-in should include the effects of wear since wear affects the surface topography as well as the formation of transfer films, mechanically mixed layers, and third-body agglomerates.     

Wear volume determination during running-in for PEHL contacts

The relation of wear volume and the change of average surface roughness under the “zero-wear” condition was derived, with the assumption that the original profiles of the surface below the wear plane remain exactly the same as before, i.e. no plastic deformation. The flattening of asperities on an engineering rough surface was simulated with numerical techniques. The variation in wear volume and average surface roughness with the depth of wear was studied. The pattern and the correlation length of rough surface were checked and found to have no effect on the relation of wear volume and change of average roughness. The simulated results show that the variation of wear volume and the change of average roughness can be described by a second order polynomial. The model was also validated with experimental results obtained by using a two-disc wear machine.     

磨合表面形貌的分形模拟研究

采用分形插值法模拟磨合期的45钢表面轮廓,并计算相关的模拟参量,得出模拟出的表面轮廓与实测的表面轮廓有统计相似性,因而可用模拟出的轮廓预测实际磨合匹配表面可能有的形貌。     

The combined effects of ZDDP, surface texture and hardness on the running-in of ferrous metals

The effects of surface characteristics including roughness, lay direction and hardness of rubbing pairs on the antiwear performance of secondary short chain ZDDPs under a boundary lubrication condition are studied experimentally. The antiwear performance of the ZDDPs is evaluated by the duration of running-in periods recorded in wear tests of specially prepared specimens. A running-in period is defined as the time interval from the beginning of a wear test to the time at which the contact resistance between the rubbing pair approaches infinity. The shorter running-in period yields the better antiwear performance. The wear tests were conducted with a reciprocating sliding contact made by flat-on-flat specimens which were made from grey cast iron, quenched medium carbon steel and bearing steel. Two lay directions of the surface texture, namely, parallel and perpendicular to the sliding direction were ground, which made four possible combinations in a rubbing action. The CLA roughness of the specimens ranged from 0.35 μm to 0.04 μm. It is found that to obtain a shorter running-in period and to enhance the antiwear performance of ZDDPs, the following rules should be obeyed. If the hardness numbers of the two rubbing members are near the same, the combination of their lay directions should be both in parallel but perpendicular to the sliding direction and, the roughness values should be smaller than 0.09 μm. If the hardness number of one member is much greater than that of the other, the soft member should be the smaller one and the surface of the hard member should be as smooth as possible. Under any circumstance, the smaller members should be chamfered.     

Experimental Study of Lubricant Film Thickness Behavior in the Vicinity of Real Asperities Passing through Lubricated Contact

This article presents an experimental study of the influence of real surface micro-geometry on the film thickness in a circular elastohydrodynamic (EHD) contact formed between a real, random, rough surface of steel ball and smooth glass disk. Phase shifting interferometry was used to measure in situ initial undeformed rough surface profiles, whereas thin film colorimetric interferometry provided accurate information about micro-EHD film thickness behavior over a wide range of rolling speeds. Two real roughness features were studied in detail—a 56-nm-high ridge and a 90-nm-deep groove, both transversely oriented to the direction of surface motion. It was shown that the ridge is heavily deformed in a loaded contact and its height increases with increasing rolling speed. The asperity tip film thickness behavior is quite similar to the contact average film thickness when the film thickness is higher than the undeformed ridge height. However, below this limit the film is thicker than what the EHD theory predicts. For the groove, a local reduction in film thickness at the leading edge was observed. When the groove is passing through the EHD conjunction, it maintains its undeformed shape. The behavior of both roughness features studied shows good agreement with previous experimental observations conducted using an artificially produced ridge and groove.     

New cylinder liner surfaces for low oil consumption

Anticipated emission legislation and reduced fuel consumption are the main driving forces when developing new engines. Optimization of the active surfaces in the piston system is one possible way to meet the above demands. In this study the effects of surface topography and texture direction of the ring/liner contact on oil film thickness and friction were simulated and experimentally tested. “Low wear” results from the experimental wear tests with “glide honed” smooth liner surfaces supported the “low friction” simulation results. In addition a new wear volume sensitive surface roughness parameter, R_ktot, based on the Abbot–Firestone bearing area curve was introduced.     

Experimental and numerical investigation on the behavior of transverse limited micro-grooves in EHL point contacts

This study presents experimental and numerical investigations on the effects of transverse limited micro-grooves on the behavior of film thickness and friction in EHL point contacts. The tribological performance has been compared for smooth and textured surfaces in sliding and reciprocating motion and under starvation. The measurements were conducted by using a ball-on-disk tribometer equipped with a high speed camera and torque sensor. The results show that the transverse shallow micro-grooves with a length less than the diameter of the Hertzian contact are efficiently able to enhance the film thickness under different operating conditions. The beneficial effect under starved lubrication requires a mechanism for filling the depleted micro-grooves entering the contact with fresh lubricant. This mechanism can be attributed to the capillary effect in the inlet zone under starvation. The numerical simulation of the transient behavior of transverse limited micro-grooves shows agreement with experimental results. On the other hand, introducing micro-grooves as closed texture cells on one of rubbing surfaces results in a friction reduction in the reciprocating motion. The reduction of friction is substantially attributed to the film thickness enhancement.     

A mixed EHL model with asymmetric integrated control volume discretization

A transient, non-Newtonian, mixed elastohydrodynamic lubrication model is proposed for heavily loaded point contacts of rough surfaces. An asymmetric integrated control volume (AICV) scheme is used to achieve faster solutions with reduced discretization errors. A unified approach is adapted to handle asperity contacts and the fast Fourier transforms are used to compute elastic deformation. Model predictions with the AICV scheme are compared with a conventional discretization scheme to demonstrate its benefits. Accuracy of this model is verified through comparisons to published experiments. An example contact is analyzed under varying conditions to demonstrate the capabilities of this model.     

Experimental and theoretical investigation of needle contact behavior of wafer level probing

Wafer probing technique is important for testing integrated circuit devices. For the safety of measured chips, the probe card must be examined to verify the performance before online testing as it must avoid the defect of the pad edge excursion and the excessive scrub length. In addition, during wafer testing the oxidized layer of pad has to be pierced to gain the stable testing by the needle, which should have sufficient force. Therefore, a well-designed probing system is significantly important for wafer testing. In this paper, the simple and accurate theoretical method is established, which benefits to design an appropriate probing system rapidly. Moreover, the finite element method is also developed for analyzing the contact behavior between the needle and the aluminum pad during wafer testing. The results, which are determined by using the theoretical analysis, the finite element method and the experiment, are consistent. Finally, the parameters of a well-designed probing system for testing smaller chips are investigated.     

Experimental Investigation of Elastohydrodynamic (EHD) Film Thickness Behavior at High Speeds

At very high speeds, elastohydrodynamic (EHD) films may be considerably thinner than is predicted by classical isothermal regression equations such as that due to Dowson and Hamrock. This may arise because of viscous dissipation, shear thinning, frictional heating or starvation.

In this article, the contact between a steel ball and a glass disc over an entrainment speed ranging from 0.05 m s^?1 to 20 m s^?1 was studied. Two sets of tests were performed. In the preliminary testing, the disc was driven at speeds of up to 20 m s^?1 and the ball was driven by tractive rolling against the disc, its speed being determined using a magnetic method. After all possible explanations for the reduction in film thickness at high speeds were considered, it was shown that the results, which fall well below classical predictions, are consistent with inlet shear heating at the observed sliding speeds.

Another set of tests was then performed, with both disc and ball driven separately, so that the accuracy of the shear heating theory for different types of oils and at different sliding conditions could be assessed. It was found that the thermal correction factor predicts the trend of film thickness behavior well for the oils tested and is particularly accurate at certain slide–roll ratios (depending on the type of oil). Experimental data were also used to obtain improved coefficients for the correction factor for different types of oil to achieve better prediction of film thickness at high speed throughout the whole range of slide–roll ratios.     

Oxidation Characteristics of MoS2 and Other Solid Lubricants

Thermogravimetric oxidation data are presented for fifteen refractory metal dichalcogenides. Interpretation of these data is supported by oxidation thermograms of the chalcogens and the refractory metals and by X-ray diffraction analysis of the oxidized products. The effects of humidity, heating rate, and particle size on oxidation of the dichalcogenides are presented. Thermogravimetric analysis is shown to be helpful in detecting impurities, such as unreacted elements, in commercial samples. Some dichalcogenides are shown to retain the same relative oxidation stability, when bonded in thin films with a ceramic, as for pure powder samples. A table is presented summarizing these oxidation characteristics together with information from the literature on crystal structures, electrical resistivities, and densities.     

Experimental and theoretical investigation of brake squeal with disc brakes installed in rail vehicles

The squealing of brakes is a very unpleasant noise because of its frequency content and high sound level. As a preliminary measure to clarify the matter, a literature review was carried out to summarize the present state of knowledge of experimental and theoretical investigations. Starting from this base, the structure-borne and air-borne noise of brake squeal was measured in two series of bench tests with parameter variations. In addition, a simulation model was developed which determines the stability of parameter-excited vibrations. This permits investigation of the parameter effects of an actual braking system.     

Experimental and theoretical investigation on the sealing performance of the combined seals for reciprocating rod

Sealing performance of the combined seals at supply oil pressure of 40MPa was experimentally and theoretically investigated. An experimental setup of combined seals for reciprocating piston rods was established in Shanghai Jiao Tong University. Two combined seals were chosen for studies, e.g. C-shape and T-shape (Fig. 1). A theoretical model based on one-dimensional Reynolds equation was made for obtaining the oil film distribution between the rod and the combined seals. Finite element method was used to calculate the contact pressure between the rod and the combined seals. The sealing performance of combined seals was analyzed in terms of the contact pressure, the back-pumping ability, the fluid transport and the net leakage under the conditions of varying the inlet pressure, the frequency of the pressure and the velocity of the rod. The experimental results demonstrated that the velocity of the rod significantly influences the sealing performance of the combined seals. Furthermore, the theoretical analysis on the influence of the rod velocity on the fluid transport was in good agreement to the experimental measurements.     

斜齿轮渐进性磨损对齿轮振动特性的影响分析

目前,研究磨损对齿轮动力学特性的影响大多采用传统的Archard磨损模型,并未考虑齿轮的润滑特性,且主要研究对象多为直齿轮。为了弥补斜齿轮研究方面的不足,数值模拟了混合弹流润滑状态下斜齿轮的磨损过程,建立了一个8自由度斜齿轮动力学模型,研究齿面磨损对斜齿轮动态特性的影响。在斜齿轮试验台上进行了齿轮疲劳试验,对数值仿真结果进行验证。结果表明,齿面磨损主要发生在靠近齿根和齿顶部分,且由于齿根处较高的滑滚比导致其磨损更加严重。根据齿轮啮合频率及其谐波幅值的变化可知,磨损导致齿轮的振动增加。试验分析与数值仿真有较好的一致性,说明该研究可以为斜齿轮磨损的预测和故障诊断提供可靠的理论依据。     

An Experimental Validation of the Recently Discovered Scale Effect in Generalized Newtonian EHL

New quantitative numerical simulations of the elastohydrodynamic lubrication (EHL) film forming ability of generalized Newtonian liquids have elucidated a previously unrecognized property of EHL films. The dependency of the film thickness on the scale of the contact is greater when the viscosity is shear dependent within the inlet. Measurements of film thickness were performed in a ball on disc experiment using balls ranging from 5.5 to 35 mm in diameter. Three liquids were investigated with varying shear dependence in the range of stress important to film forming. The experimental results confirm the previous analytical findings. Numerical simulations using the measured viscosities show that the increased scale sensitivity is substantially the result of shear-thinning. However, the smallest scales produced films thinner than even the shear-dependent prediction, possibly indicating molecular degradation. It is quite likely that some machine components, which were designed using the effective viscous properties derived from a larger scale film thickness measurement, are operating with substantially lower film thickness than the designer had intended.     

Basics of EHL for practical application

Elastohydrodynamic lubrication (EHL) is present in all lubricated components whose elements roll together, including gears, rolling bearing, cams and constant velocity joints. These are characterised by having very localised and thus very high pressure contact, of order 1 to 3 GPa, between the elements. Two important practical properties of EHL contacts are the lubricant film thickness and the friction, and lubricant and machine designers and users need to be able to predict both of these. In principle, they can be determined from full numerical solution of the elastohydrodynamic problem. However, this is quite difficult and time‐consuming and requires detailed knowledge of the rheology of the lubricant film at high pressure and shear rate. This paper is aimed at practising engineers and describes alternative approaches, i.e. how EHL can be applied to predict film thickness and friction in practical applications. Copyright © 2014 John Wiley & Sons, Ltd.