基于拓展有限元的齿轮点蚀磨粒形态学特征模拟

疲劳点蚀是齿轮摩擦副的典型固有磨损特征,其产生的点蚀磨粒已经被用于理解疲劳磨损的发生和发展机理,由于缺乏理论模拟,基于磨粒特征的疲劳磨损机理判断还停留在经验分析层面。为此,拟通过齿轮接触疲劳点蚀的数值模拟,研究点蚀磨粒形态特征,为在线磨粒特征表征磨损状态的方法提供理论探索。在考虑弹流润滑的条件下,建立齿轮副局部接触模型,并采用拓展有限元法(Extended finite element method,XFEM)模拟表面萌生裂纹的拓展过程。进一步分析工况与点蚀磨粒形态特征的关系,结果表明,点蚀磨粒长轴尺寸随初始萌生裂纹的长度增加而增大,随载荷的增加而减小;点蚀磨粒的厚度随初始萌生裂纹的深度增加而增大。通过与已发表的试验结果进行对比,该模型所得到的点蚀形貌尺寸和形状与试验得到的点蚀形貌基本一致,从而验证了该模型的有效性。     

Optimum carburization in external spur gears

In order to determine the surface durability of case-hardened gears and the optimum design conditions required to prevent spalling fatigue, an analytical model was developed which correlates the subsurface shear stress produced by the transmitted load with the material strength of the gear. Consequently, it was made clear that there is an optimum case depth for the required surface durability and that the crack initiation depth of spalling coincides quite well with the depth where the subsurface shear stress exceeds the material shear strength. The implications of the model for optimizing the carburizing process and preventing gear spalling fatigue are discussed.     

Macroscopic and microscopic changes in the surface layers of annealed and case-hardened steel rollers due to rolling contact

Measurements of the residual stress and observations of the microstructure at the surface and in the subsurface of rollers were performed during rolling contact fatigue tests of annealed 0.45% carbon steel and case-hardened nickel-chromium steel rollers. Compressive residual stresses in annealed rollers were induced by the rolling contact. With case-hardened rollers they were induced by heat treatment prior to the rolling contact fatigue tests. After the rolling contact fatigue tests the compressive residual stresses on the surface of the annealed rollers and in the subsurface of the case-hardened rollers relaxed; a characteristic substructure was formed by the stress cycles, which caused surface failure. It was confirmed that the microcracks leading to surface failure initiate on the surfaces of annealed rollers and in the subsurface of case-hardened rollers.     

Surface failure of soft and surface-hardened steel rollers in rolling contact

To study the mechanism of rolling contact fatigue failure, annealed thermally refined 0.43% carbon steel and case-hardened nickel chromium steel rollers were tested under conditions of pure rolling and sliding/rolling. The failure mechanism was examined by fractographic observation and by calculation of the amplitudes of the ratio of stress to strength.It was found that pitting cracks initiated on the roller surface and were induced by the normal stress in the circumferential direction of the roller or by the maximum principal stress. Spalling cracks initiated beneath the surface and were induced by the orthogonal shear stress.     

The lubricant-coating interaction in rolling and sliding contacts

The research presented in this paper was aimed at elaboration of a new technology for heavy-loaded machine elements, lubricated with ecological oils.The tribological experiments were performed using four-ball tester (scuffing resistance), cone-three balls pitting tester (fatigue life), as well as gear test rig (resistance of lubricated gears to scuffing). The tribosystems were lubricated with various base oil and vegetable-based eco-oil.The tested components were coated with standard single coatings (TiN, CrN) and low-friction coatings (a-C:H:W, MoS₂/Ti). The results obtained confirm that low-friction a-C:H:W coating has a great potential for application in heavy-loaded machine components. Under extreme-pressure conditions this coating can take over the functions of anti-wear/extreme-pressure (AW/EP) additives and through this it is possible to minimise the application of toxic lubricating additives and achieve “ecological lubrication”.     

Thermal aspects of lubrication of concentrated contacts

Deterioration of gears occurs by abrasive wear, pitting (surface fatigue) or severe adhesive wear (scuffing). The effects of the latter mode may be mitigated by the use of extreme pressure (EP) additives but these sometimes accentuate the risk of pitting-type failure. Accordingly, EP lubricants are not recommended for industrial gearing. The introduction of elastohydrodynamic lubrication theory has demonstrated that it is possible to operate gears without physical contact between the interacting tooth faces. Under conditions of pure rolling (at the pitch point) there is good agreement between theory and experiment, but when relative sliding occurs the measured film thickness is lower than calculated. A recently derived theory, taking into account the effect of the heating arising from relative sliding on the hydrodynamic film thickness, has been applied to a set of industrial gears, from which it is deduced that the effect on load-carrying capacity of the gear is not serious. The theory has also been applied to some results obtained on the Institution of Automobile Engineers lubricant-testing machine.     

APPLYING REGRESSION AND STOCHASTIC TIME SERIES ANALYSIS TO THE PREDICTION OF PITTING FATIGUE LIFE FOR GEARS

ＡＰＰＬＹＩＮＧＲＥＧＲＥＳＳＩＯＮＡＮＤＳＴＯＣＨＡＳＴＩＣＴＩＭＥＳＥＲＩＥＳＡＮＡＬＹＳＩＳＴＯＴＨＥＰＲＥＤＩＣＴＩＯＮＯＦＰＩＴＴＩＮＧＦＡＴＩＧＵＥＬＩＦＥＦＯＲＧＥＡＲＳＡＰＰＬＹＩＮＧＲＥＧＲＥＳＳＩＯＮＡＮＤＳＴＯＣＨＡＳＴＩＣＴＩ...     

Gear Lubrication in Inert Gas Atmospheres

An investigation was made of the effect of inert gas atmospheres on the gear load-carrying capacity of lubricants. The experiments were performed in two types of gear test machines, using case-hardened AMS-6260 steel test gears. It was found that two mineral oils (a solvent-extracted turbine oil base stock and a USP grade white mineral oil), as well as the same oils fortified with different extreme-pressure additives, all exhibited a decided increase in load-carrying capacity when the gears were operated in an atmosphere of nitrogen or argon instead of air. On the other hand, the response of synthetic lubricants was not found to be necessarily similar. In fact, only one of the six synthetic fluids tested showed any significant increase in load-carrying capacity when the gears were operated in a nitrogen atmosphere.     

Effect of Running-In (Load and Speed) on Surface Characteristics of Honed Gears

The initial running-in cycles alter the surface integrity characteristics and influence gear performance. This article shows how the surface characteristics of honed spur gears evolved due to the combined effect of running-in load (0.9 or 1.7?GPa) and speed (0.5 or 8.3 m/s) in Forschungsstelle fur Zahnräder und Getriebebau tests. Running-in affected the surface layers to a depth of 5 µm. High running-in load promoted plastic deformation of asperities, created microstructural changes associated with surface cracks, and relaxed residual stresses. It also enhanced the amount of phosphorous from extreme pressure (EP) additives at the surface. The surface contact fatigue failure—that is, micropitting—was promoted by running-in speed rather than load.     

Evaluation of surface fatigue performance of gear oils

The effect of additive chemistry on the surface fatigue of gears was investigated using an FZG gear tester and fluids based on an API GL-5 grade gear oil. Surface fatigue lives were determined as a function of load and additive chemistry. At 1.52 GPa, the removal of the primary extreme pressure (EP) additive from the fully formulated gear oil decreased the fatigue life of gears slightly (4%). However, the removal of the primary antiwear (AW) additive decreased the fatigue life of gears significantly (83%). At 1.86 GPa, the removal of the EP additive from the fully formulated gear oil decreased the gear fatigue life by 27%. However, the removal of the primary AW additive decreased the fatigue life of gears significantly (75%). Micro-pitting was the dominant surface morphology in the dedendum of the gears tested with two oils at load stage eleven: one using the complete additive package, and a second where the EP additive had been removed. However, spalling was the primary failure mode of gears tested without an AW additive, independent of whether an EP agent was present. Surface analysis of the pinion gears showed the formation of a mixed phosphate/phosphite—oxide layer on the surface of gears tested with fluids containing an AW additive. Formation of this layer seems to be the key to a long fatigue life.     

Effect of sursulf treatment on the performance of 0.14% C steel gears

Sursulf-treated low carbon steel gears were tested in a back-to-back gear test rig. The failure of the gears is by pitting and the contact stress-pitting life curve has been established. Wear particle analysis of the lubricating oil was carried out to analyse the nature of the failure. The study reveals that Sursulf treatment on low carbon steel gears considerably improves their performance. The cumulative wear particle concentration at the pitting limit has been suggested as a basis for predicting the onset of failure of the gears.     

多级多工况传动载荷处理方法及应用

在单级设计载荷法的基础上,考虑传动系统各部件所选材料、载荷和循环次数的影响,提出多级设计载荷法.以混凝土运输车搅拌桶减速器为例,描述从载荷测试到编制减速器传动系统的全工况载荷谱和齿轮疲劳载荷谱的过程.根据齿轮的疲劳载荷谱,分别用单级设计载荷法和多级设计载荷法计算各齿轮的弯曲当量转矩和接触当量转矩,并用两种方法计算的当量...     

极限载荷工况下滚珠丝杠副疲劳弹性寿命研究

滚珠丝杠副因高精度、高可靠性等特点,被广泛应用于机械、航空航天及核工业等领域.传统滚珠丝杠副寿命计算方法是以疲劳点蚀为失效判定依据,而在航空航天等极限载荷工况下,滚珠丝杠副需要在短时间内承受几近额定静载荷的负载,其主要失效形式将变为塑性变形失效.因此,基于疲劳点蚀的疲劳寿命理论和计算方法不再适用.基于滚珠丝杠副的塑性接...     

Effect of sursulf treatment on fatigue life of medium carbon steel spur gears

Medium carbon steel gears untreated as well as Sursulf treated were tested in a back-to-back gear test rig. The failure of the test gears was by pitting. The contact stress-pitting life curves have been established for both untreated and Sursulf treated conditions. Sursulf treated gears exhibited low wear compared to untreated. Wear particle analysis of lubricating oil was carried out to analyse the nature of failure. Cumulative wear particle concentration at pitting limit has been suggested as a basis for predicting the onset of the failure in the gears.     

Lubricant and additive effects on spur gear fatigue life

Spur gear endurance tests were conducted with six lubricants using a single batch of consumable-electrode vacuum melted (CVM) AISI 9310 spur gears. The sixth lubricant was divided further into four batches, each of which had a different additive content. Lubricants tested with a phosphorus-type load carrying additive showed a statistically significant improvement in life over lubricants without this type of additive. The presence of sulphur-type antiwear additives in the lubricant did not appear to affect the surface fatigue life of the gears. No statistical difference in life was produced with those lubricants of different base stocks but with similar viscosity, pressure-viscosity coefficients and antiwear additives. Gears tested with a 0.1 wt % sulphur and 0.1 wt % phosphorus EP additives in the lubricant had reactive films that were 200 to 400 Å (0.8 to 1.6 μin) thick.     

A re-examination of rolling contact fatigue experiments by Clayton and Su with suggestions for surface durability calculations

A re-interpretation of recent RCF experiments by Clayton and Su (C&S) [Wear 200 (1996) 63] under water lubricated rolling/sliding conditions, with careful measurements of ratchetting strains, and their comparisons with experimentally observed lives, seems to confirm the validity of ratchetting failure (RF) mechanism and Kapoor’s “critical ratchet strain” as a material property. However, the complexity of modelling the ratchetting phenomenon and the uncertainties on the material’s critical ratchet strain, suggests that perhaps a more realistic alternative is the use of empirical Wöhler-like life curves similarly to currently used for the contact fatigue evaluation in gears design and standards. In particular, it is found that the “pitting” fatigue limit at 10⁷ cycles suggested by the gears standard is reasonably accurate also for the C&S experiments on various typical rail steels. Since the gears life factor suggested for gears turns out quite conservative at shorter lives, it seems a single new life factor could be suggested, at least for all pearlitic and bainitic steels tested by C&S under water lubrication.     

The influence of oil additives on spread cracks in silicon nitride

The properties of ceramic materials (high hardness, high-temperature capability, low coefficient of thermal expansion) are of interest to rolling element materials. One of the most interesting materials is silicon nitride.The paper presents an experimental study of the influence of oil additives (Cl, S, P, cerium dioxide (CeO₂)) on spread cracks in silicon nitride. The additives Cl, S, P are bound in molecules in liquid form soluble in the base oil. The CeO₂ is purely in powder form in suspension. The use of CeO₂ powder was made based on the good results of polishing of silicon nitride. A ceramic angular contact ball bearing was modelled using a four-ball machine. Silicon nitride, -in diameters balls were artificially damaged with pre-cracks. Ring formed pre-cracks were propagated on the ball surface by a blunt impact load using a tungsten carbide ball under five various impacts.Rolling contact fatigue failure modes were studied under high contact stresses and speed. The surface of silicon nitride balls before and after failure was examined using scanning electron microscopy.The research of the present paper shows that fatigue failure under rolling contact loading is markedly sensitive on the size of pre-cracks and oil additives. Propagations of surface pre-cracks takes place under fatigue load. Primary and secondary surface crack propagation are described.     

润滑和载荷状态对聚甲醛齿轮服役性能的影响

基于齿轮耐久性能试验台开展了一系列干接触/油润滑下POM(聚甲醛)-POM齿轮副承载能力试验,并测量了服役过程中的轮齿温度、磨损量、齿廓精度和齿面形貌.试验发现,POM齿轮失效形式与载荷和润滑方式有关.通过对齿面微观形貌和磨屑表征,确认干接触下POM齿轮主要磨损模式为黏着磨损与磨粒磨损,而油润滑下POM齿轮失效形式为接...     

Load‐carrying capacity of WC/C‐coated gears lubricated with a low‐viscosity oil

The application of low‐friction coatings on the surfaces of gear teeth is primarily motivated by the increasing demands for load‐carrying capacity or the rolling‐contact fatigue life. Despite the costs of manufacturing being higher, better performance is an important consideration for many demanding applications. In the present study, we have investigated the load‐carrying capacity of WC/C‐coated gears that were lubricated with an oil blend that was formulated in‐house. A significantly higher load‐carrying capacity was found for the WC/C‐coated gears lubricated with a tailored, low‐viscosity oil in comparison with the case‐carburised gears lubricated with a conventional gear oil of a similar viscosity. The carburised gears failed due to scuffing on the pinion tip, while coating thinning on the pinion face and coating fracture in the wheel‐root area are the dominant failure mechanisms for WC/C‐coated gears. An approximately 40% lower roughness was found on the coated gear flanks. Copyright © 2015 John Wiley & Sons, Ltd.     

Contact fatigue life prediction of a bevel gear under spectrum loading

Rolling contact fatigue (RCF) issues, such as pitting, might occur on bevel gears because load fluctuation induces considerable subsurface stress amplitudes. Such issues can dramatically affect the service life of associated machines. An accurate geometry model of a hypoid gear utilized in the main reducer of a heavy-duty vehicle is developed in this study with the commercial gear design software MASTA. Multiaxial stress–strain states are simulated with the finite element method, and the RCF life is predicted using the Brown–Miller–Morrow fatigue criterion. The patterns of fatigue life on the tooth surface are simulated under various loading levels, and the RCF S–N curve is numerically generated. Moreover, a typical torque–time history on the driven axle is described, followed by the construction of program load spectrum with the rain flow method and the Goodman mean stress equation. The effects of various fatigue damage accumulation rules on fatigue life are compared and discussed in detail. Predicted results reveal that the Miner linear rule provides the most optimistic result among the three selected rules, and the Manson bilinear rule produces the most conservative result.