The evaluation of the micro-tracks and micro-dimples on the tribological characteristics of thrust ball bearings

One of the primary remedies for tribological problems is surface modification. The reduction of the friction between the ball and the raceway of bearings is a very important goal of the development of bearing technology. A low friction has a positive effect in terms of the extension of the fatigue life, avoidance of a temperature rise, and prevention of premature failure of bearings. Therefore, this research sought to investigate the effects of micro-tracks and micro-dimples on the tribological characteristics at the contact point between the ball and the raceway of thrust ball bearings (TBBs). The ultrasonic nanocrystal surface modification (UNSM) technology was applied using different intervals (feed rates) to the TBB raceway surface to create micro-tracks and micro-dimples. The friction coefficient after UNSM at 50 microm intervals showed marked sensitivity and a significant reduction of 30%. In this study, the results showed that more micro-dimples yield a lower friction coefficient.     

Contribution of industrial composite parts to fatigue behaviour simulation

The dimensioning of composite structures presents the problem of behaviour modelling. This problem comes not only from the specific nature of the involved materials, but also from the reproducibility of the process both on the series scale as well as on the specimen characterisation level, which enables determination of the modelling parameters. In the case of static dimensioning with or without damage, the reproducibility of the mechanical parameters is satisfactory overall, regardless of the implemented experimental procedure. In fatigue dimensioning, the two aspects; process influence and procedure of identification play a major role in the application of the lifetime predictive models. This research has, as a medium-term objective, to partially answer the problems raised previously. The damage model used is based on generalised standard material thermodynamics. This model, coupled with the finite element method, allows simulation of the fatigue behaviour of composite parts.     

Investigation of rolling contact fatigue cracks in ball bearings

Rolling contact fatigue in a ball bearing is studied using the experimental method. Fatigue pits and spallings on the rolling surface are investigated, and the strain-hardening beneath the contact surface is studied using the microhardness profile. Moreover, surface and subsurface crack layouts and the effect of inclusions on crack nucleation are studied by optical and electron microscopy. Additionally, a simulated model is used to study the influences of the crack inclined angle and the inclusion’s hardness on fatigue damage in bearings.     

Wälzverschleiß und -ermüdung von Bauteilen und Maßnahmen zu ihrer Einschränkung

Wear and Fatigue at Rolling contacts and Counter Measures Machine parts subjected to rolling contact fatigue, i.e. gears or rolling element bearings, are exposed to a very particular stressing condition. No comparable condition will occur for other technical applications. These typical conditions and their effects on the material behaviour are described comprehensively. An introductional overview for this are of technical knowledge is given, in particular for engineers not so much experienced with respect to this matter. The most important phenomena influencing the behaviour of parts subjected to rolling contact fatigue are presented as well as the physics of damage initiation and the appearance of damaged parts. It is demonstrated exemplarily, how the analysis of the damaging processes can be used to take counter measures. The referencing to the public literature has been done in a way to enable the reader to easily find material for a further improvement of his knowledge for particular items.     

On-line surveillance of lubricants in bearings by means of surface acoustic waves

The acoustic wave propagation in bearings filled with lubricants and driven by pulsed excitation of surface acoustic waves has been investigated with respect to the presence and the distribution of different lubricants. Experimental setups, which are based on the mode conversion between surface acoustic waves and compression waves at the interface between a solid substrate of the bearing and a lubricant are described. The results of preliminary measurements at linear friction bearings, rotation ball bearings and axial cylinder roller bearings are presented.     

Lager wie geschmiert

Friction reduction in ball bearings by nanodyn® ‐plasma coating Without ball bearings engines wouldn't operate. On the other hand by friction and wear in bearings a certain amount of material and energy is lost. For bottling plants, packaging machines and machine tools such bearings are indispensable as well as for gears, and motors in pumps in the automotive and aviation areas. To minimize friction and wear in bearings different types of lubricants are in use. Nevertheless a part of the kinetic energy will be transformed in heat and wear and corrosion might happen. Enhanced friction properties are gained on bearings from the company of Cerobear after applying the nanodyn® coatings deposited on all parts of the bearings by the Fraunhofer Institute for Interfacial engineering and Biotechnology. The friction is reduced by more than 50%. In addition the corrosion is reduced as well and cleaning becomes easier. In conclusion, this project contributes to resource efficient production in Germany by the development of plasma coatings for enhanced wetting of lubricants, reduced friction and wear and for minimized corrosion of ball bearings.     

Thrust cone bearings provide increased efficiency for helical gear units at moderate speed levels

Thrust cone bearings are an elegant option to handle the axial forces generated by the torque transmission in helical-toothed gear stages. They have proven as an efficient and reliable bearing concept for integrally geared compressors but are nearly unknown in other fields of gearbox engineering. The presented investigations consider three aspects which appear relevant to extend the field of possible applications for thrust cones towards gearboxes constructed with roller bearings. Based on simulations and experiments design parameters were identified, which enable a significant reduction of the necessary velocity for full film lubrication. For a single stage test gearbox noticeable increases in efficiency were achieved by replacing tapered roller bearings with a combination of thrust cone and ball bearings, especially during partially loaded operation. The resistance to wear and the determination of limits for the bearable loads under mixed friction conditions for various thrust cone design configurations are investigated in a third test series. It appears that the few limit values known so far might be exceeded significantly for future applications.     

Analysis of an Angular Contact Ball Bearing Failure and Strategies for Failure Prevention

Bearing failures are one of the most common failure modes in the rotating machinery and equipment. Angular contact ball bearings are widely used considering their ability to carry the loads in both axial and radial directions, durability and low friction. The smooth functioning of these bearings greatly depends on the bearing load rating, material, type of fit with which it is assembled, the operating temperature and proper installation in the assembly. This paper presents the analysis of a failure of an angular contact ball bearing used in the gas motor system of an electrohydraulic control actuator used for launch vehicle attitude control. Detailed investigation of the failure is carried out by thermal and structural modeling of the bearing assembly, and the failure cause is identified as the combination of design error, hardware deviations and improper assembly operation which led to bearing misalignment and very high loading of the first row of balls resulting in excessive heating. The failure theory explains all the observations on the parts of the failed bearing. The physics of failure is understood, corrective actions to avoid the failure are addressed, and the strategies for prevention of similar failures are evolved.     

An expert system for the design and selection of ball bearing parameters

Artificial Intelligence (AI) is an emerging technology. Research in Al is focused on developing computational approaches to intelligent behaviour.The computer programs with which AI could be associated are primarily processes associated with complexity, ambiguity, indecisiveness, and uncertainty. One of these computer programs is referred to as Knowledge-based Expert System (KBES) as it represents knowledge acquired from various experts in a particular field of interest to the user. The expert system emulates human behaviour in solving problems thought to require experts for their solution by utilizing computer programs that incorporate experts' heuristic reasoning. In this paper, the application of KBES to aid the design of ball and roller bearing is discussed. The precision rolling-element bearing of the twentieth century is a product of exacting technology and sophisticated science. A bearing supports radial and axial loads, at the same time allowing relative motion between two elements of a machine. Various requirements and steps in the design of ball and roller bearings are discussed. Equations are developed for the relevant design parameters and input into the expert system shell called VP-Expert. The expert system rules are also provided.     

Damage behaviour of laminated composites during fatigue loading

This study deals with the modelling of damage evolution in the carbon/epoxy laminated composites under static and fatigue loading. A cumulative damage model is developed on the basis of damage evolution due to static and fatigue during cyclic loading. A continuum damage mechanics (CDM)‐based damage model coupling with the micromechanics has been utilized to predict the fatigue behaviour of laminate composites. A multicriterion approach has been introduced to predict the damage behaviour in the longitudinal, transverse, and shear direction at the ply scale. Extensive experimental results on T300/EPL1012 carbon/epoxy laminates are prepared to characterize under static and fatigue loading and to evaluate the proposed model in different conditions. The obtained results show that at the beginning of the cyclic loading, the damage grows suddenly and increases until final failure, which justifies the proposed method is able to predict the evolution of the damage due to static and fatigue loading separately during cyclic loading. The obtained results show that considering damage due to static loading leads to more accurate results, particularly in low‐cycle fatigue.     

PVD‐beschichtete Wälzlager im Trockenlauf

Under extreme operating conditions like vacuum or high temperature, lubrication of rolling bearings is unwanted or even impossible. As a result of dry running conditions bearing components are exposed to high tribological stress. Thus, alternative material solutions are necessary to achieve acceptable lifetimes under these conditions. Using hybrid rolling bearings with PVD coated races might be a possible solution. Therefore, PVD coated bearings were analyzed under different test conditions to assess their characteristics. Potentials of dry running PVD coated hybrid roller bearings regarding wear and friction reduction are shown. Additionally, main damage characteristics are analyzed.     

High temperature low cycle fatigue

Fatigue at high temperature is a complex phenomenon as it is influenced by a number of time-dependent processes which become important at elevated temperatures. These processes include creep, oxidation, phase instabilities and dynamic strain ageing (DSA), acting either independently or synergistically influence fatigue behaviour, often lowering the fatigue life. Current design approaches employ linear summation of fatigue and creep damage with suitable factors on permissible damage to take care of uncertainties in interaction between cyclic and time-dependent processes. It is, therefore, important to develop a deeper understanding of the processes that occur during high temperature fatigue so that realistic life predictions could be made. Results on the high temperature fatigue behaviour of austenitic stainless steels, ferritic steels and nickel base alloys are presented here. The important mechanisms of interaction of high temperature time-dependent processes with fatigue under various conditions are discussed in detail. Emphasis is placed on cyclic stress response, fatigue life, deformation substructure and fracture behaviour. This is followed by a review of important life prediction techniques under combined creep-fatigue loading conditions. Life prediction techniques considered here include linear damage summation, strain range partitioning, ductility exhaustion approach, frequency modified and frequency separation methods, techniques based on hysteresis energy and damage rate models, and methods based on crack-cavitation interation models.     

Cumulative fatigue damage of stress below the fatigue limit in weldment steel under block loading

To investigate the cumulative fatigue damage below the fatigue limit of multipass weldment martensitic stainless steel, and to clarify the effect of cycle ratios and high‐stress level in the statement, fatigue tests were conducted under constant and combined high‐ and low‐stress amplitude relative to stress above and below the fatigue limit. The outcomes indicate that neither modified Miner's nor Haibach's approach provided accurate evaluation under repeated two‐step amplitude loading. Moreover, effect of cycle ratios has been determined. Additionally, the cumulative fatigue damage saturated model is established and validated. Cumulative fatigue damage contributed by low‐stress below the fatigue limit in high stress of 700 MPa is higher than that with 650 MPa at identical conditions (fatigue limit 575 MPa). Thus, high stress affects fatigue damage behaviour below the fatigue limit. A new predicted approach has been proposed based on Corten‐Dolan law, whose accuracy and applicability have been proven.     

Comparison of different statistical models for description of fatigue including very high cycle fatigue

In this paper the fatigue behaviour of welded joints and helical compression springs are analysed using two different statistical models. The data consist of results from low cycle, high cycle and very high cycle fatigue and different number of investigated specimens. In particular, the software program ProFatigue is used for derivation of the probabilistic S–N field from experimental fatigue data. The program, based on a former regression Weibull model, allows the estimation of the parameters involved in the S–N field model, providing an advantageous application of the stress based approaches in the fatigue design of mechanical components. The results obtained are compared with the customary Wöhler-curve, represented as a straight line in a double-logarithmic scale. Application to probabilistic assessment of cumulative damage and further program enhancement can be now envisaged.     

Inclined standing contact fatigue

An experimental method is presented, in which a sphere is repeatedly pressed against a surface with an inclined contact load. The method is a development of the normally loaded standing contact fatigue test. Experiments are performed for three inclination angles below the angle of friction and the results are compared to those of the normally loaded standing contact fatigue test. The influence of tangential load on endurance limit load, number of cycles to crack initiation, contact mark appearance and crack behaviour in the surface as well as in cut views are evaluated. The surface crack behaviour outside the contact mark is analysed based on the cyclic contact stresses in the test specimen. The trajectories of the largest principal stresses are followed in both the surface view and in the cut view on the symmetry plane. These stress trajectories are compared to the experimental crack results. The connection between the inclined standing contact fatigue cracks and surface distress micro‐cracks is also discussed.     

Fatigue crack propagation in rocker and roller-rocker bearings of railway steel bridges

In this work, a method is proposed for rolling contact fatigue crack propagation analysis using contact and fracture theories in conjunction with fatigue laws. The proposed method is used in the fatigue analysis of rocker and roller-rocker bearings of a railway open web girder bridge which is instrumented with strain gages. Using a contact algorithm based on the minimum energy principle for bodies in rolling contact with dry friction, the normal and tangential pressure distribution are computed. It is seen that the most critical location of a crack in bearings is at a point very close to the contact region, as expected.     

Thermoelastic Phase Analysis (TPA): a new method for fatigue behaviour analysis of steels

In literature, there are already well‐established thermal methods which allow for the estimation of fatigue limit, in particular for metallic materials such as austenitic steels. These methods are based on heat source generation analysis or on surface temperature evaluation of material subjected to different types of cyclic loading. General application of methodology found limitation in those cases in which temperature changes on material related to fatigue damage were very low and, furthermore, thermal methods require high‐performance equipment and a difficult setup. This is the case, for instance, with brittle materials (such as martensitic steels), welded joints and aluminium alloys. In this work, a new thermal method named Thermoelastic Phase Analysis is used to evaluate the fatigue limit of martensitic steels. This thermal method is based on an empirical approach. The main idea is that phase of thermoelastic response of the material subjected to fatigue loading is influenced by the presence of a heat source due to dissipative phenomena related to damage. Monitoring of the phase parameter provides a more stable setup and an independent means of identifying the fatigue limit of material. The method has also proven to be potentially one order of magnitude faster than traditional thermal methods.     

Contact Fatigue Failure of a Tapered Roller Bearing Used in a Lorry Wheel

Tapered roller bearings, which are also known as angular-contact bearing, are suitable for supporting radial and axial loads. The more frequent types of defects in such bearings are caused by contact fatigue in these machine components, and this examination focuses on a contact fatigue failure in a tapered rolling bearing. The examination included visual inspection, microscopic analysis (optical and scanning electron microscope), and microhardness measurements. These measurements were conducted to help understand the failure mechanisms. Based on the results of visual examination and microstructure and fracture surface analysis, it was determined that the tapered roller bearing failed by contact fatigue that was caused by overloading of the bearing.     

Thermal and mechanical fatigue analysis of CFRP laminates

[0°/90°]_s and [±45°]_s CFRP laminated plates were analysed using a finite element formulation for their fatigue behaviour. A fatigue criterion which is based on the laminate interlaminar stresses and the basic lamina fatigue parameters was used. Thermal effects were included in the formulation. In particular, initial thermal stresses resulting from the curing of the laminate were also included in the analysis. The results showed that both laminates had predicted S-N behaviour similar to that from experiments of past investigators. Also, the fatigue behaviour for the [±45°]_s laminate between room temperature and the curing temperature were found to be the same. However, in the case of the [0°/90°]_s laminate the fatigue strength at high temperatures was found to be lower than that at low temperatures.     

新型钢滚轴及混合隔震结构地震模拟振动台试验研究

针对一种新型钢滚轴隔震支座进行研究,分别设计制作了一组钢滚轴隔震支座和一组摩擦摆隔震支座,并完成了某两层钢框架的固结、纯滚轴隔震、滚轴+MR被动阻尼器混合隔震和摩擦摆隔震模型的振动台试验。研究了各模型在地震加速度峰值为0.10 g、0.20 g的3条地震波作用下的结构响应,试验结果表明:新型钢滚轴隔震支座的隔震效果优于摩擦摆隔震支座,纯滚轴隔震模型和滚轴+MR被动阻尼器的混合隔震模型均可降低结构加速度反应56.1%～80.8%,且合理的优化混合阻尼隔震体系的阻尼值可使隔震效果更佳。同时,采用MR阻尼器的混合隔震模型较纯滚轴隔震模型可降低隔震层位移反应58.7%～87.4%,且随着阻尼值的增大其控制效果更好。因此,将新型钢滚轴隔震支座与阻尼装置配套使用的方法有效可行,在充分发挥滚轴隔震支座隔震效果的同时避免了结构隔震层位移过大的问题。