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In this study, finite element method (FEM) is applied to investigate the effect of material defect orientation on subsurface crack initiation in rolling bearings. First, the history of stress intensity factors (SIFs) of a subsurface cubic material defect is calculated. SIFs calculation is conducted when it is parallel to the rolling surface of a bearing ring ( φ = 0 ∘ ) under a ball rolling on the ring. Then, the effect of defect orientation, varying from φ = 0 ∘ to φ = 30 , 45 and 60 ∘ , on the history of SIFs is investigated. It is deduced that changing the defect orientation results in a threefold increase in the equivalent SIF range compared to parallel orientation. [ABSTRACT FROM AUTHOR]

In this study, finite element method (FEM) is applied to investigate the effect of material defect orientation on subsurface crack initiation in rolling bearings. First, the history of stress intensity factors (SIFs) of a subsurface cubic material defect is calculated. SIFs calculation is conducted when it is parallel to the rolling surface of a bearing ring ( φ = 0 ∘ ) under a ball rolling on the ring. Then, the effect of defect orientation, varying from φ = 0 ∘ to φ = 30 , 45 and 60 ∘ , on the history of SIFs is investigated. It is deduced that changing the defect orientation results in a threefold increase in the equivalent SIF range compared to parallel orientation. [ABSTRACT FROM AUTHOR]

This experimental research work is conducted to determine statistical models of wear evolution and surface roughness components in a misaligned contaminated EHL rolling contact. To achieve this goal, experiments were realized on an original test rig representing the real operating conditions of gears or roller bearings. In fact, the rolling contact tests are carried out using the contact between two steel disks with the presence of misalignment defect and solid contaminants within lubricant oil. In order to investigate the influence of four operating input variables like misalignment angle (α), rotational velocity (V), load (Q), and contaminant concentration (C) on the studied responses (i.e., wear (W) and surface roughness components (Ra, Rt, and Rz)), the Box-Behnken design (BBD) was adopted. Thereafter, the results obtained were analyzed using both response surface methodology (RSM) and analysis of variance (ANOVA). It is found that the rotational velocity (V) is the most significant factor affecting the wear (W) and the surface roughness components (Ra, Rt, and Rz) of a misaligned contaminated EHL rolling contact with 75.51%, 79.2%, 89.07%, and 59.65% of contributions, respectively, whereas load (Q), misalignment angle (α), contaminant concentration (C), and two-level interaction effect (α × C and C × Q) are significant factors but have a lesser effect on the wear variability with 8.23%, 5.57%, 2.42%, 2.68%, and 2.62% contributions, respectively. It is also deduced that the misalignment angle (α) is statistically significant when studying the mean depth roughness (Rz) with 15.67% of contributions. Finally, it is revealed that the obtained higher values of determination coefficient (more than 90%) show clearly the reliable of the implemented quadratic models. [ABSTRACT FROM AUTHOR]

This research paper reviews the recent works on the rolling contact fatigue of rail wheels. The topic covered includes the mathematics equations of rail-wheel contact stress and fatigue, RCF defects in the rail, the development of cracks, and the strategies used to reduce the rate of RCF defects. Therefore, the main understandings of RCF as they currently stand are crucial for the improvement and mitigation on rail fatigue failures in the future. This research paper has not been published yet and has not been discussed yet by the Malaysia Railway Network. [ABSTRACT FROM AUTHOR]

Rolling bearings are machine elements found in a wide field of applications. They are reliable even under the toughest conditions. When bearings fail to meet their expected life, the consequences are increased down time, loss of revenue and missed delivery. Hence, it is important to know the bearing theoretical fatigue life. However, unfortunately, it sometimes happens that a bearing does not attain its calculated rating life. There may be many reasons for this—heavier loading than has been anticipated, inadequate or unsuitable lubrication, careless handling, ineffective sealing, improper mounting and improper clearance. This article describes the failure of a conveyor bearing in rolling contact fatigue. The investigation consists of visual observation, chemical analysis, characterization of microstructures using optical microscopes and hardness test. The study also calculates the bearing fatigue life (L10) under these operating conditions. Surface-initiated rolling contact fatigue, leading to spalling, is a life-limiting failure mode in bearings. Ferrography test, discussed in this paper, indicates fatigue spalling. Analysis suggested that the conveyor bearing failed near its calculated fatigue life and the failure occurred in rolling contact fatigue. Periodic schedule, after calculating L10 life, for changing the bearing and scheduled ferrography checks can eliminate this type of unplanned breakdown. [ABSTRACT FROM AUTHOR]

To manufacture semi-finished hybrid workpieces with tailored properties, a finite element simulation assisted process chain design was investigated. This includes the process steps of cross wedge rolling, hot geometry inspection, induction hardening, and fatigue testing. The process chain allows the utilisation of material combinations such as high-strength steels with low-cost and easy to process steels. Here, plasma transferred arc welding is applied to supply the process chain with hybrid specimen featuring different steel grades. An overview of the numerical approaches to consider the various physical phenomena in each of the process steps is presented. The properties of the component behaviour were investigated via the finite element method (FEM) and theoretical approaches. At first, the manufacturing of a hybrid workpiece featuring a near net shape geometry with improved mechanical properties due to recrystallising the weld was computed, using the example of a cross wedge rolling process. The rolling process was designed by means of FEM to determine suitable process parameters and to reduce experimental testing. An optical multi-scale geometry inspection of the hot workpiece is meant to be carried out after each manufacturing step to detect potential undesired forming or cooling-induced deformations. Due to the heat transfer from the hot component to the ambient medium, an optical measurement is affected by the developing inhomogeneous refractive index field in air. To gain a basic understanding of the refractive index field and induced light deflection effects, computations were conducted using heat transfer and ray tracing simulations. According to the proposed process route, a subsequent local heat treatment of the hybrid component is required to adapt the mechanical properties by a spray cooling assisted induction hardening. The heat treatment step was computed via a 2D FEM calculation. After finishing by machining, the hybrid material shafts are examined in fatigue tests under load conditions. To predict the component's lifetime under rolling contact fatigue, a damage accumulation model was combined with an FE simulation. The resulting residual stress state after quenching and the geometry after the finishing process were used as input data for the fatigue life calculations. [ABSTRACT FROM AUTHOR]

In this paper, the rolling contact fatigue crack growth in the presence of multiple cracks and their interactions is studied. The proposed formulation is based on linear elastic fracture mechanics and singular integral equations. The body under the rolling contact is modeled by a half-plane weakened by a set of surface, subsurface and surface–subsurface cracks. Rolling contact is simulated by translational motion of an elliptically distributed force along the half-plane boundary. Several parameters, such as the distance between cracks, the value of initial crack lengths, the value of the friction coefficient, and the initial angle between cracks and the boundary of the half-plane are studied. Results obtained from this investigation are in good agreement in a special case with those reported in the literature. It is observed that in the system of two parallel surface and subsurface cracks with equal lengths, changing the distance between the cracks changes the growth paths, and when this distance increases to a critical value, the cracks grow independently. In addition, in the case of two parallel surface cracks when the left crack is shorter, the cracks have a stronger tendency to join together, which leads to pitting phenomena on the contact surface. Furthermore, in the system of two parallel subsurface cracks, it is seen that fast fracture occurs sooner when the initial angle of the cracks increases. In the system of parallel surface and subsurface cracks, the dominant failure mode is spalling. [ABSTRACT FROM AUTHOR]

The application of coating gets exceptional importance since it improves the tribological properties of the contacting surfaces. Different input parameters like coating deposition processes, coating material properties and its thickness, use of lubricant and its additives, surface roughness and temperature affect the tribological properties and the rolling contact fatigue (RCF) life of coated rolling and sliding contact elements. In this paper, an attempt has been made to review for the clear understanding of the effect of these input parameters on the RCF life and tribological performance of coated rolling and sliding contact elements. It has been observed that coating deposition process must be chosen based on technical and economic aspects. Among the different techniques, thermal spraying technique is cost effective, and it also provides better bonding strength, which improves the RCF life in comparison with other techniques. Similarly, the effect of other input parameters has been reviewed and possible combination of the input parameters that help improve the performance of coated contacting elements summarized. Furthermore, the current status of research and the scope of future work to be carried out, in this area, have been outlined. [ABSTRACT FROM AUTHOR]

Failed bearings of various aero-engines were subjected to investigations. The bearing of cooling turbine of aircraft designated as B-1 was found to fail due primarily to misalignment and overloading. Bulk fatigue and permanent dimensional changes also accelerated the failure. The center main bearing of another aero-engine designated as CMB-1 was found nonfunctional because of 'Brinelling' action. Lack of lubrication caused over heat and deformation of rollers by metal to metal contact, and this resulted in formation of untempered martensite, leading to failure of center main bearings referred as CMB-2 of another helicopter engine. Stationary race and rotating race of thrust bearing of positive displacement reciprocating hydraulic pump bearing denoted as EDP-1 failed by abrasive action of foreign particles and oxidized metallic particles. In contrast, balls of the same bearing failed because of abrasive action of oxidized metal debris and rolling contact fatigue. [ABSTRACT FROM AUTHOR]

The relatively recent appearance of formerly rare vertical split rim wheel failures provides a good case study of how a shift in failure mode occurs when a material improvement is made to solve an existing problem. The mode of railroad wheel failures have changed three times over the past 40 years when the dominate failure mode has been identified and corrected. When the principal failure mode has been corrected the service life increases, but a new or previously minor failure mode assumes the role of principle failure cause. Because of the large population of railroad wheels in North American service, failure trends can be easily observed. This paper will discuss the evolution of failure mode with successive material and structural improvements. [ABSTRACT FROM AUTHOR]

Since the accurate prediction of fatigue life has a significant value, many researchers have attempted to develop a reliable fatigue life model. Recently, rolling contact fatigue life models incorporating machining impact were developed. These models have contributed to a significant improvement in prediction accuracy as compared with earlier models, thus representing a major step forward in the modeling effort. This paper compares the prediction accuracy of these models with that of the prediction method in International Standards. When α is set to 0.25, the observed improvement of prediction accuracy as measured by variance of prediction errors due to these models over that due to prediction method in International Standards is statistically significant. Impact analyses of such improvement are conducted to illustrate its value. It is further noted that while difference was observed between the variance of prediction errors due to the crack initiation life model based on a dislocation model and that due to the crack initiation life model based on a local stress-life curve, the observed difference is not statistically significant. [ABSTRACT FROM AUTHOR]

The rolling contact fatigue cracks (RCF), produced at the surface of the rail tracks, can be detected using a magnetooptical (MO) sensor. Rail tracks are carbon steels with pearlite microstructure. This microstructure has a lamellar texture composed of alternating layers of ferrite and cementite. Both phases are soft ferromagnetic materials at room temperature. If an external magnetic field is applied on the surface of a rail track, the reduced magnetic permeability causes a magnetic leakage field above the cracks. When the external magnetic field is removed, in most cases, a residual stray magnetic field remains above the cracks. When a MO sensor is placed on the surface of the rail track, the sudden change of the stray remanent magnetic field near a crack, yields a significant rotation of the polarization plane of the reflected light, resulting in high MO contrast, exactly above the cracks. Using a polished surface and a cross-section from the head of the rail track, we succeeded in visualizing the RCF cracks in the laboratory. The RCF cracks can also be detected on the surface of the rail track, in field measurements, using a portable commercial polarized light microscope equipped with a MO sensor. Finally, we use computer vision methods, to automatically detect the RCF cracks, using video recorded by displacing the portable microscopy with the MO sensor, on the surface of the rail tracks. We tested an unsupervised automatic crack detection algorithm, which exploits the tubular contrast of the RCF cracks to pinpoint the pixels that correspond to them. [ABSTRACT FROM AUTHOR]