Bearing Fatigue Research Articles

Modelling micropit formation in rolling contact fatigue of bearings with a crystal plasticity damage theory coupled with cohesive finite elements

Modelling micropit formation under rolling contact fatigue (RCF) is a big challenge due to strong dependence on microstructure. A RCF damage model was developed based on combined crystal plasticity theory and cohesive zone to study the crack growth and micropit formation. The results showed the crack growth is driven by shear stress, but affected by crystal orientation. Cracks would rather propagate transgranularly in the shear stress-dominant region as the damage accumulates inside grains faster than at grain boundaries. They changes to intergranular beyond the stress-dominated region becasue there is no enough driving force. The modelling results agree well the experiment.

The effect of friction on surface crack initiation in rolling contact fatigue considering damage accumulation

AbstractSurface initiated rolling contact fatigue (RCF) of gears and rolling bearings can lead to premature failure in mechanical transmission systems. The orientation of surface crack initiation closely depends on surface tractive force, while the mechanism leading to this dependence is still obscure. In this work, a numerical model is proposed to investigate the effect of friction on surface crack initiation in RCF. An inhomogeneous contact solver based on semi‐analytical method (SAM) is developed by combining the damaged‐coupled constitutive relation and the Eshelby's equivalent inclusion method. The damage accumulation and concurrent degradation of material properties are modeled with continuum damage mechanics (CDM). The effect of surface tractive force on the orientation of surface crack initiation is simulated and analyzed. Results indicate that the progressive evolution of damage under the cyclic loading is accompanied by the stress variation around the damaged area. The damaged area increases, and the crack initiation life decreases with an increasing coefficient of friction.

Influence of Tribolayer on Rolling Bearing Fatigue Performed on an FE8 Test Rig—A Follow-up

The tribological contact between raceways and rolling elements is essential for rolling bearing performance and lifetime. The geometrical description of these contacts is well known and can be used in several mechanical simulation tools. The material description, especially of the near-surface volume after interaction with lubricants, is not as simple. In particular, the Schaeffler FE8-25 test with cylindrical roller thrust bearings exhibits different failure modes depending on the lubricant chemistry. The main failure mechanisms of this test are sub-surface fatigue damage due to WECs (White Etching Cracks) and/or surface-induced fatigue damage (SIF). The harsh test conditions with mixed friction at high speeds and multiple slip conditions over the raceway width additionally provides different tribological conditions on a small area. This leads finally to the formation of certain tribological layers on the raceway because of the interaction of the surface with the lubricant chemistry under local frictional energies, which are worth investigating. The characterization of the layers was performed by the two less time-consuming, spatially resolved analysis methods of µXRF and ATR FTIR microscopy adapted by Schaeffler. This paper shows the results of this research and offers new approaches to optimizing rolling bearing testing and predicting the risk of early failures.

Quantitative analysis and validation using computational approach for hollow spherical roller bearing 22212E

A bearing is a part of the machine that lowers friction between moving parts by limiting relative motion to only the desired motion. Bearing debility is affected by a several factors, also the roller–raceway interfaces are the most significantly stressed areas in a bearing, minimizing the Hertz contact stresses there has been a main objective. The analytical and finite element approaches have been used to evaluate the deformation, contact stress and contact pressure of spherical roller bearings 22212E. It has been observed that the acquired results employing the theoretical and FE Analysis methods have quite a 9 percent variation. Based on results, confirming the FEA for solid spherical bearing with a theoretical approach using the same operating parameters. Furthermore, the finite element approach has been employed to analyse how the hollow spherical rolling element enhanced the bearing performance. In ANSYS, multiple hollowness percentages ranging from 0% to 90% of the external diameter of the spherical roller were analysed in order to determine the optimal hollowness for bearing service life. It has been discovered that bearings with a hollowness of roughly 62 percent have the lowest contact stress, which extends the bearing's fatigue life.

Overview of existing methods of asynchronous motor diagnostics

The paper provides a review, analysis and research of existing diagnostic methods such as a vibroacoustic method based on the analysis of damped oscillations arising from dynamic loads of the system in friction nodes, the thermal method based on the analysis of thermal fields created by the object under study and the acoustic emission method, which includes an assessment of acoustic emission occurring in metals and welded joints. The advantages and disadvantages are identified and the conditions and areas of use of these methods are described. The applicability of these methods to such an electromechanical system as an asynchronous motor is also described. Vibroacoustic diagnostics can be used to assess shaft fatigue and wear of rolling bearings; thermal diagnostics can be used to diagnose the operation of the cooling system and assess the degree of aging of the insulation of the windings; the acoustic emission method is applicable in cases where it is necessary to assess the progressive wear of the shaft and bearing assemblies, as well as fatigue of gear elements in the gearbox.

The Grease Life Factor concept for ball bearings

Bearing fatigue life is calculated using a so called basic rating life equation L10=CPp where the operating load is translated into an equivalent load P and divided by the bearing capacity. This makes it possible to test the bearing capacity C under an arbitrary load and therefore on almost any test rig. For grease life such a concept does not exist. Grease life is specified by a number of hours running on standardized test rigs and conditions. A similar concept as for bearing life is introduced in this paper for lubricating grease, called the ‘Grease Life Factor’ (GLF) concept. It is based on a grease life model for axially loaded grease lubricated ball bearings and makes it possible, similar to bearing life, to quantify the life properties of a grease using ‘any’ grease life test rig. It also implies that there is no longer a need to specify grease life for standardized test rigs. The validity is illustrated with test data obtained from the most widely used test methodologies: FE9 and R0F.

Research on Bearing Fatigue Life of New Type Tire Unloader based on Ncode DesignLife

The new tire unloading machine is used for unloading and turning over the giant radial tire (weighing 6t). During the turning process, due to the huge inertial force of the tire and the collision force between the plywood and the tire, the tire unloading machine bearing is subjected to complex alternating stresses. It is difficult to predict the fatigue life of a bearing. To this end, the paper combines Ncode DesignLife, ADAMS and Workbench numerical analysis platform to predict the fatigue life of tire unloading machine bearings. At the same time, the ISO bearing life standard calculation method is used to evaluate the bearing life and compare the two calculation results. The research results show that the simulation prediction of the bearing life at the lowermost rocker arm of the tire unloader is 2190.56h, and the bearing life of the uppermost guide wheel bearing is 2025.56h. Accordingly, the ISO prediction results are 1717.12h and 1128.44h, which are basically in the same order of magnitude. It shows that the simulation method of bearing life prediction used in the article is reasonable. The research can provide theoretical guidance for the bearing type matching and service life of the giant tire unloader.

The influence of type of dispersed phase on rolling contact fatigue of lubricating greases on mineral base oil

The paper discusses the influence of type dispersed phase on value of rolling contact fatigue of bearings lubricated with selected lubricating compositions. The compositions, which were produced on the mineral base oil were thickened of lithium stearate, calcium stearate, aluminum stearate, lithium complex soap and modified silica, montmorillonite, and polytetrafluoroethylene were evaluated.
 Were carried out the investigations of rolling contact fatigue (pitting) of bearings, which were lubricated of the compositions prepared on the above-mentioned thickeners. Then was evaluated the influence of various thickeners on changes of rolling contact fatigue. The tribological tests were carried out using T-03 four-ball machine under high load conditions.
 On the basis of obtained results it may be concluded, that used of thickeners such as: modified amorphous silica, montmorillonite and polytetrafluoroethylene to produce of lubricating compositions, positively affected on the change of rolling contact fatigue of tribosystems lubricated with the above-mentioned compositions in comparison to the compositions, when as a dispersed phase were used a soap thickeners.

Studies on the Influence of Residual Stresses on the Fatigue Life of Rolling Bearings in Dependence on the Production Processes

The production process significantly influences the surface properties of rolling element bearings raceways. Deep rolling can induce a depth dependent residual stress state. Previous numerical and experimental studies have shown that rolling bearings fatigue life can be positively influenced by high compressive residual stress to a depth of around 300 µm from the surface. By extending the components life, the resource efficiency of machine components can be increased. In order to determine the influence of the residual stress state in bearing fatigue life, a calculation method was developed for predicting the bearing fatigue life. This method was validated for hard-turning and subsequent deep rolling by experiments on a test rig in four-bearing configuration under radial load. An increase of the L10 bearing life by a factor of 2.5 has been achieved by inducing residual stresses on the bearing’s inner ring. Due to similar process control, the manufacturing steps turning and deep rolling were combined. Bearings were manufactured combining the processes hard-turning and deep rolling (called turn-rolling). The heat from the hard machining has an effect on the residual stresses in the bearing subsurface, thus further altering the magnitude and maximum depth of the residual stress influencing the microstructure. With these bearings, the additional fatigue life was determined experimentally and compared to the results of the bearings produced by hard-turning and subsequent deep rolling. It could be shown, that the process of hard turning and subsequent deep rolling has highest potential to achieve improved bearing fatigue life. These findings were transferred to a “Tailored Forming” shaft with integrated raceway in a second step. In this case, a shaft made of mild steel is combined with a cladding layer of high strength bearing steel to be used as a bearing raceway.

Enhancement of roller bearing fatigue life by innovative production processes

Purpose The efficient and economical use of natural resources is a big issue. Machine elements with a rolling contact are highly relevant because of their wide application in technical systems and a large production quantity. Innovative hard machining can reduce the friction and increase the fatigue strength of rolling element bearings. The purpose of this study is to focus on the surface properties of such parts. Design/methodology/approach A new model to predict bearing fatigue life is presented which takes compressive residual stresses in the bearing subsurface area into consideration. The investigated bearings were machined by the processes of hard turning, hard turning with subsequent deep rolling and a combination of hard turning and deep rolling (turn-rolling) in one process step. Changes in the residual stress state during bearing fatigue tests were investigated and the influence of residual stresses on the bearings fatigue life was researched. Findings Both combinations including the deep rolling process decrease the surface roughness and induce compressive residual stresses. As a result, the L10 fatigue life of roller bearings was increased by the factor of 2.5. Owing to the developed models, this effect can be considered within the design process. Originality/value In the context of the research program “Resource efficient Machine Elements (SPP1551),” machining processes of bearings were investigated regarding the bearing fatigue life. By inducing beneficial residual stresses on the bearings’ subsurface area, the fatigue life could be increased. Thus higher resource efficiency was achieved. To increase the productivity, a combination of hard turning and deep rolling was evaluated.

Strength Computation of Bearing Test Station

The test station is used to determine the fatigue of bearings in passenger cars. The influence of prestressing or axial clerance, the reliability of the locking elements for the axial adjustment, the quality of the seating of the outer ring and the change in the type, quantity or distribution of the lubricant can also be examined. The test station consists of a test unit for the simultaneous testing of two test bearings. The misalignment of the wheel contact point and the center of the bearing is fixed by means of mountable parts. The test bearings are clamped between the flanges at both ends of the test shaft, which is supported by two auxiliary bearings. The numerical simulation with finite element method (FEM) deals with the analysis of the bearing test station, which will be loaded by axial and radial loads.

Reuse of Zeolite By-Products Derived from Petroleum Refining for Sustainable Roads

The reduction in consumption of natural resources (fuel, gas, etc.) and contaminant emissions (CO2, CO, NOx, etc.) during the production of asphalt mixtures has become one of the main challenges in road engineering. Warm mix asphalts (WMAs) have been developed in order to achieve this objective while ensuring the mechanical performance and durability of traditional hot mix asphalts (HMAs). However, these materials are commonly manufactured using additives or products whose production could reduce both their environmental benefits and cost effectiveness. This paper presents a research study that aims to analyse the reuse of zeolite wastes derived from petroleum refining in the production of warm mix asphalts. For this purpose, two different types of zeolite wastes were analysed as additives for the manufacture of two warm mix asphalts, whose mechanical performance was compared with conventional WMA and hot mix asphalt. The results indicate that zeolite wastes with a lower particles size presented higher capacity to absorb water, while its dosage at 0.3% allows for producing warm mix asphalts at temperatures around 145°C, with comparable workability and densification to conventional HMA at 165°C without reducing its bearing capacity, fatigue life, and resistance to water action and plastic deformation.

A model for hybrid bearing life with surface and subsurface survival

Hybrid bearings have rings made of steel and rolling elements made of bearings grade silicon nitride ceramic. Due to the higher modulus of elasticity of ceramic compared to steel, the ellipse of the Hertzian contact is slightly smaller than that in a conventional bearing. This results in about a 12% increase in the contact pressure between the ceramic ball and the raceway. Following the standard Rolling Contact Fatigue theory, a higher contact pressure leads to a reduction of the dynamic load-carrying capacity and service life of the bearing. However, long experience in the use of hybrid bearings shows that, in most applications, hybrid bearings clearly outperform traditional bearings made entirely out of steel.This paper addresses this issue by applying a novel approach to Rolling Contact Fatigue. Central to the new method is the survival probability of the raceway surface which is explicitly formulated into the basic life equations of the rolling contact. This allows tailoring the contribution of the stress system close to the rolling surface to better represent the ceramic-steel interaction, which has been proven to be substantially more favourable in the case of a hybrid ceramic-steel contact. The comparison between experimentally obtained hybrid bearings fatigue lives and lives predicted using the new calculation model indicates good agreement.It is found that an increase of the fatigue resistance of the raceway surface of hybrid bearings can, in most cases, compensate for the additional stress present in the subsurface region of the rolling contact. The new methodology, by providing a direct account of the survival probability of the ceramic-steel interface gives a better representation of the expected performance of hybrid bearings, opening new opportunities for the reliable use of this type of bearing in modern machinery.

The relationship between 100Cr6 steelmaking, inclusion microstructure and rolling contact fatigue performance

A processing-microstructure-performance approach is followed to study three bearing steel samples manufactured from the most frequently used continuous casting routes. The inclusion microstructures of the samples were altered by varying the metallurgy and hot working conditions. Inclusion size distribution information is obtained, showing the steel-making route that results in the highest cleanliness. 3D analysis of inclusion morphologies using electrolytic extraction indicates the irregularities on the surface to be favourable sites for crack nucleation under RCF. Flat-washer and ball-on-rod tests were conducted to study the rolling contact fatigue life of the steels, with the results from the flat-washer testing method being more representative for bearing life. This research suggests that early fatigue of bearings is governed by silicate fragmentation and late fatigue by TiN inclusions.

Inversion Effect of Asphalt Pavement with Two Courses of Semi-Rigid Base

To study the combination principles of structural design and material design in asphalt pavement with semi-rigid bases, the software BISAR3.0 was used to analyze the load responses in asphalt pavement with two layers of semi-rigid base courses, and its inversed structure. Then composite beam specimens composed of two kinds of cement-treated macadam with different cement contents were then fabricated, and four-point bending strength and fatigue tests were conducted. Results indicated that the lower semi-rigid base layer (lower base) undertakes greater tensile stress than the upper semi-rigid base layer (upper base), and the fatigue life of the pavement structure is dependent on the lower base. Therefore, using inferior materials for the lower base and superior materials for the upper base is unreasonable. The inversed structure can fully utilize each material, and its bearing capacity and fatigue resistance were considerably improved. Thus, pavement structural design should be combined with material design according to the tensile stress state in pavement layers.

A short review on fretting wear behaviour of Al7075

Generally, matting components are great in dealing with a surface of friction in contacting area gripping and is focusing the service life of the mating materials. In applied components, service life can also be measured in terms of wear. Due to their higher bearing capacity and fatigue resistance, the aluminium (Al) based alloys are preferred in high-end applications. Nevertheless, due to weakened tribological strengths, many researchers explore the possible wear mechanisms existing in worn surfaces of Al based alloys to enhance the strength. Fretting is one of the primary failure mechanisms which promote severe damage to the matting of metal parts especially in Al7075 is revealed recently by the researchers. In general, damage severity during the wear is analysed through fretting which could be the result of synergy of rubbing with matting parts and vibrations. The fretting regime represents many primary wear mechanisms. Fretting map support the cause analysis of wear from the worn morphology. The present survey dealt the utilisation of fretting regime to explore the possible wear mechanisms and factors caused the wear damages from the research outcome of leading tribo research groups.

Stress Analysis and Fatigue Behaviour of PTFE-Bronze Layered Journal Bearing under Real-Time Dynamic Loading

The present paper is based on experimental studies and numerical simulations on the surface fatigue failure of the PTFE-bronze layered journal bearings under real-time loading. ‘Permaglide Plain Bearings P10’ type journal bearings were experimentally tested under different real time dynamic loadings by using real time journal bearing test system in our laboratory. The journal bearing consists of a PTFE-bronze layer approximately 0.32 mm thick on the steel support layer with 2.18 mm thick. Two different approaches have been considered with in experiments: (i) under real- time constant loading with varying bearing widths, (ii) under different real-time loadings at constant bearing widths. Fatigue regions, micro-crack dispersion and stress distributions occurred at the journal bearing were experimentally and theoretically investigated. The relation between fatigue region and pressure distributions were investigated by determining the circumferential pressure distribution under real-time dynamic loadings for the position of every 10° crank angles. In the theoretical part; stress and deformation distributions at the surface of the journal bearing analysed by using finite element methods to determine the relationship between stress and fatigue behaviour. As a result of this study, the maximum oil pressure and fatigue cracks were observed in the most heavily loaded regions of the bearing surface. Experimental results show that PTFE-Bronze layered journal bearings fatigue behaviour is better than the bearings include white metal alloy.

Jacobian free Newton-GMRES method for the solution of elastohydrodynamic grease lubrication in line contact using wavelet based pre-conditioners

Jacobian Free Newton-GMRES (JFN-GMRES) method is used in the present study for the analysis of isothermal, steady and incompressible elastohydrodynamic lubrication line contact problem. The lubricant is grease, described by Herschel–Bulkley constitutive equation. The problem is investigated for smooth surface as well as surface with asperity. Governing equations are discretized on uniform grid. The resulting system of algebraic equations is solved using JFN-GMRES method for wide range of parameters of interest. For the convergence of restarted GMRES wavelet based pre-conditioners are used. Pressure profiles, film shapes and details of Petrusevich pressure spikes are given for moderate to high load and speed. The proposed scheme is stable and fast converging. Results presented in tables and graphs confirm these findings. The minimum film thickness increases for decrease in n, a parameter characterizing grease lubricant, with other parameters held constant. There is a noticeable decrease (in height as well as spread) of pressure spike for small values of n, which arrests bearings fatigue life.

THE INFLUENCE OF DIFFERENT VEGETABLE DISPERSION PHASES ON THE ROLLING CONTACT FATIGUE OF BIODEGRADABLE LUBRICATING GREASES

The paper discusses the influence of the vegetable dispersion phase on the rolling contact fatigue of bearings lubricated with ecological lubricating compositions. Four vegetable oils were used for the production of lubricating greases: rapeseed, sunflower, soybean, and castor. For comparison purposes, the synthetic and mineral oils were used as well. The rolling contact fatigue (pitting) of bearings lubricated with particular compositions were investigated and evaluated for each base oil. The tribological tests were carried out using T-03 four-ball machine under high load conditions. Based on the obtained results, it may be concluded that vegetable oils, such as rapeseed, sunflower and castor, as the base of lubricating grease positively affected the rolling contact fatigue of tribosystems lubricated with the above-mentioned compositions in comparison to the control lubricated with greases based on mineral or synthetic oil. There is no favourable change in rolling contact fatigue of tribosystems lubricated with greases based on soybean oil.

Modeling the Compression Stiffness Degradation in Circular Elastomeric Bearings due to Fatigue

AbstractLaminated rubber, or elastomeric, bearings fatigue when subjected to repeated cycles of loading. Fatigue in these elements is characterized by the formation of cracks typically originating at the interface of the steel-rubber laminae at the outermost edge of the laminate then propagating at an inclination toward the center of the bearing under subsequent cycling. The presence of fatigue cracks alters the bulging surface of the rubber layers, thereby degrading the stiffness properties of the bearings. Past experimental studies have shown the stiffness degradation of laminated rubber bearings can be significant, i.e., reductions on the order of 20–30%. To date, much of the analytical and experimental research has been focused on the determination of the initiation of fatigue cracking to establish replacement schedules for elastomeric bearing components in aerospace and rail applications. However, in bridge applications elastomeric bearings are likely to fatigue while in service and the level of stif...