Papers by Keyword: Rolling Contact Fatigue

Abstract: Rolling and sliding contacts are common tribological interactions between surfaces in high-speed rotating components such as bearings, gears, and rail wheels. If the bearing is operated under mixed/boundary lubrication conditions, the major failure mechanism would be micro-pitting and wear, and its extent depends on the percentage slide between the contact pairs. This work compares the rolling contact fatigue (RCF) behavior of AISI 4140 steel under pure rolling (zero slip) and slip conditions by using base lubricant and formulated lubricant with graphene nanoadditives. Rolling contact fatigue performance under pure rolling and slip conditions shows a significant improvement with graphene lubrication compared to base lubrication. Under pure rolling conditions, the RCF L₁₀ life improved 3-fold with graphene lubricant compared to base lubricant. Similarly, under the slip condition, a significant improvement in the anti-wear performance was observed for the graphene lubrication compared with the base lubrication. A detailed wear track analysis was performed using scanning electron microscopy and Raman spectroscopy. The results reveal that the formation of tribo-films on the surface is the major reason for the improved anti-wear performance with graphene nanolubrication. According to the working conditions, the physical tribo-film was observed under pure rolling conditions, and the chemical tribo-film was observed under slip conditions.

Abstract: The objective of this research is to study the surface damage of train wheels and rail under applied loads. The simulation of this damage was predicted and calculated using finite element method (FEM), specially with the ABAQUS program. According to the EN13674-1 (R350HT) and EN13262 standard for train rail and wheel, respectively, the train wheel and rail were modeled to create a suitable mesh and to simulate stress and deformation. The distribution of stress and deformation were first analyzed when the interaction between wheel and rail occurred. In this research the simulated damage was further discussed in the context of both rolling and non-rolling wheels on the rail. The simulated results showed that the maximum stress was distributed beneath the surfaces of wheels and rails, leading to initiation and propagation of crack. The continuous crack beneath the surface led to the surface fatigue, resulting in material loss. The fatigue life of surface was also evaluated and calculated based on these predicted stresses. The effect of plastic deformation occurring on the surface due to rolling fatigue were further discussed in this work.

Abstract: Maintenance due to the replacement of damaged wheels and rails due to rolling contact fatigue (RCF) and wear has been found to be the major problem to rail operating companies. This problem tends to lead to unavailability of railway networks. To solve this problem, costly wear simulators are developed to predict the wear behaviour of the rails and wheels to improve the preventive maintenance in pursuit of operational efficiency. Therefore, more studies that simulate a combination of rolling and sliding wear, together with RCF, are required, specifically for the Southern African, where good and cost-effective rail wear simulators are not readily available. The problem with wear and RCF simulators is high production costs, so this work aims to solve this problem by developing a cost-effective wear test rig that is capable of simulating RCF, sliding and rolling wear as experienced by the train wheel while moving along railway tracks. For this work, it was decided that twin-disc concept would be used, since literature clearly shown that the method was able to simulate the three damage mechanisms mentioned. The developed twin-disc wear simulator was able to simulate both rolling and sliding wear and parameters including contact load and slip ratio could be changed with ease so to simulate the actual contact conditions between the wheel and rail. Outputs such as coefficient of friction and wheel disc temperature were obtained. The results showed that the severity of wear is heavily dependent on slip ratio i.e., increased with slip ratio, with both coefficient of friction and wear rate increasing with slip ratio.

Abstract: Rolling Contact Fatigue (RCF) caused crack propagation, flaking, and wear. We focused on the wear in the present study because in recent years it was found that PPS thrust bearings under the RCF in water caused wear. The RCF test was performed under a thrust load of 2300 N in water to investigate the effect of the number of cycles on surface roughness in detail. We obtained the experimental results that R_a and R_z values decrease with the number of cycles. This means the bottom surface is worn down at the early stage of wear fatigue.

Abstract: Rolling bearings are important mechanical parts. They are used for the transmission of rotational motion. In this study, we focused on surface roughness of the polymer thrust bearing under rolling contact fatigue. Surface roughness of the groove bottom was measured when small pitting around shoulder and crack occurred. Thrust bearings were loaded with thrust loads of 2300 N, 2400 N, 2500 N, and 2600 N. The surface in the rolling contact area was worn during the rolling contact fatigue test. We concluded that surface roughness values ranged from 0.49 μm to 0.18 μm, under thrust loads of 2300 N, 2400 N, 2500 N, and 2600 N when small pitting occurred.

Abstract: Bearings are important in moving machinery. Today machines are used in varied fields, including environments where metals are not ideal materials. Industrial polymers are a possible alternative due to their mechanical properties, and the thermoplastic polymer Polyether ether ketone (PEEK) is suitable in many varied conditions. The failure mechanisms of PEEK are not fully understood, so the purpose of this study is to continue examining the relationship between load and rotation speed in rolling contact fatigue of PEEK thrust bearings in water conditions, to evaluate fatigue strength and life.

Abstract: The sectional observations of 13Cr-2Ni-2Mo and SUS 440C stainless steel ball bearings were done. Two features were found from the observations: parabolic-shaped cracks generated the flaking failure of 13Cr-2Ni-2Mo stainless steel bearing; jellyfish-shaped wear affected the flaking failure of SUS 440C stainless steel bearing.

Abstract: The rolling contact fatigue (RCF) tests of 13Cr-2Ni-2Mo and SUS440C stainless steels were carried out in water. Their groove surfaces and the flaking failures were observed. Some hair cracks, wear and high roughness area were found. While the flaking depth of SUS440C was shallower than that of 13Cr-2Ni-2Mo stainless steel, the RCF life of the latter was longer than the former one. The flaking depth did not influence the RCF life.

Abstract: In order to explore influence on tribological behavior of PEEK composite film layer in PEEK-PTFE composite radial alumina ball bearings, rolling contact fatigue tests were performed by using the PEEK bearing’s inner rings with the artificial defects in dry condition. When rotation speed and applied load were 600 rpm and 98 N, the number of cycles of the PEEK-PTFE bearings reached 1.0×10⁷ fatigue cycles. The artificial defects with 0.02 mm depth on the raceway surface of the PEEK inner ring was covered with PEEK composite film accumulation.

Abstract: In this study, in order to evaluate the progress of internal cracks in PPS thrust bearings under rolling contact fatigue in water, cracks were observed by a full-cross-section observation method using a lathe machining. “Main subsurface crack” initiated at the surface toward the inside, then grew in a direction parallel to the surface. They connected with many “Semi-circular cracks” initiating at the surface from the opposite side to the inside, to from a semi-ellipsoidal flaking damage. It was found that the “Semi-circular cracks” and the “Main subsurface crack” dominated the flaking destruction.