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The clarification of uncertain factors of rolling contact fatigue (RCF) life variation is expected to lead us to better understanding of the RCF mechanism and further improvement of the service life of bearings. The objective of this study is to clarify the effect of defect location on RCF life. Artificial cavities, pores, and drilled holes were introduced to the specimens as a flaking origin under RCF for simplification on the presumption that their physical properties and interfacial rubbing between cavity and matrix were ignorable. The RCF test resulted in flakings initiated from the pore located right below the center of the track, when a specimen included numerous pores. Their RCF lives were simply determined by fracture mechanical parameters, size of pore, and orthogonal shear stress range parallel to rolling direction. On the other hand, RCF life was prolonged when the drilled hole in a specimen was located near the contact edge, although the resultant flakings appear the same irrespective of defect location. Therefore, defect location is one of the important factors for RCF life variation. The following were found through a further verification experiment and finite-element analysis: (1) A crack initiates from a drilled hole surface because of principal tensile stress at early stages of RCF irrespective of location of the hole. (2) Both of the orthogonal shear stresses, parallel and perpendicular to rolling direction, lead to the three-dimensional propagation of crack. (3) The weakening/damaging effect from a hole near the contact edge is less than that from a hole near the center of the contact track.
Many of the engineering problems of particular importance to railways arise at interfaces and the safety-critical role of the wheel/rail interface is widely acknowledged. Better understanding of wheel/rail interfaces is therefore critical to improving the capacity, reliability and safety of the railway system. Wheel-rail interface handbook is a one-stop reference for railway engineering practitioners and academic researchers. Part one provides the fundamentals of contact mechanics, wear, fatigue and lubrication as well as state-of-the-art research and emerging technologies related to the wheel/rail interface and its management. Part two offers an overview of industrial practice from several different regions of the world, thereby providing an invaluable international perspective with practitioners’ experience of managing the wheel/rail interface in a variety of environments and circumstances. This comprehensive volume will enable practising railway engineers, in whatever discipline of railway engineering – infrastructure, vehicle design and safety, and so on – to enhance their understanding of wheel/rail issues, which have a major influence on the running of a reliable, efficient and safe railway. One-stop reference on the important topic of wheel rail-interfaces Presents the fundamentals of contact mechanics, wear, fatigue and lubrication Examines state-of-the-art research and emerging technologies related to wheel-rail interface and its management
A number of competing failure mechanisms are involved in bearing failure initiation. For well manufactured bearings operating under clean and well controlled running conditions, sub-surface initiated fatigue is the classical initiation form. Three mechanisms dominate the concept of subsurface induced initiation and growth: (i) The well documented slow structural breakdown of the steel matrix due to accumulation of fatigue damage in a process superficially similar to tempering, (ii) stress induced generation of butterflies by a process enabling the growth of butterfly micro-cracks and accompanying wings at non-metallic inclusions, and (iii) surface induced hydrogen intrusion causing hydrogen-enhanced fatigue damage accumulation in the matrix. The development of butterflies as a function of contact stress, over-rolling, and non-metallic inclusion characteristics is presented, and the influence of metallurgical cleanliness and processing history on this progression is discussed. The results of laboratory conducted tests are compared to results from field applications where premature spallings have occurred. The progression from butterfly micro-cracks to extending cracks with non-etching borders has been studied. Special interest has been paid to the interaction between the non-metallic inclusion composition and morphology and their propensity to generate butterfly wing formations, as this may affect the way that inclusion harmfulness should be judged in rolling bearing steel quality assurance efforts. Complex oxy-sulfides are the main butterfly initiators in today's bearing steels.
The bearings used in various industrial machines need to have good rolling contact fatigue resistance. It is known that the fatigue resistance in clean lubricating oil is decreased when there is a nonmetallic inclusion in the bearing steel. For this reason, various studies to reduce the size and quantity of inclusions have been carried out. On the other hand, to obtain a new approach to suppress the influence of the nonmetallic inclusions, it is important to understand the influence of each nonmetallic inclusion type on the rolling contact fatigue resistance. Therefore, we have worked on evaluations of the fracture initiation and propagation on the rolling contact fatigue in bearing steels. In the previous symposium, we reported that we had created an oxide type inclusion controlled steel (OTICS) using the melting furnace in our laboratory. This steel has an excellent rolling contact fatigue life. In this paper, we will report fracture initiation and propagation on the rolling contact fatigue in OTICS and conventional steel evaluated using an ultrasonic test and an acoustic emission test. We have investigated the defects under the rolling contact surface by the ultrasonic test, with loadings applied at certain times in the thrust-type rolling contact fatigue test. During the test, we also measured the acoustic emissions generated when a fracture occurred. From the ultrasonic test, we succeeded in detecting nonmetallic inclusions with the fractures. Furthermore, the time before defects were detected in the OTICS was longer compared to conventional steel. The same tendency was observed in the acoustic emission test. Longer load times were required before acoustic emissions were detected in OTICS. According to these results, it can be considered that OTICS has a greater rolling contact fatigue life than conventional steel due to the inhibition of the fracture initiation from the nonmetallic inclusion.
Rolling Bearing Tribology: Tribology and Failure Modes of Rolling Element Bearings discusses these machine elements that are used to accommodate motion on or about shafts in mechanical systems, with ball bearings, cylindrical roller bearings, spherical roller bearings, and tapered roller bearings reviewed. Each bearing type experiences different kinds of motion and forces with their respective raceway, retainers and guiding flanges. The material in this book identifies the tribology of the major bearing types and how that tribology depends upon materials, surfaces and lubrication. In addition, the book describes the best practices to mitigate common failure modes of rolling element bearings. Discusses important tribological implications surrounding the performance and durability of rolling element bearings Describes how the different types of roller bearings work Explores the reasons behind the failure of roller bearings and presents information on how to mitigate those failures
This book comprises the select proceedings of Structural Damage Modelling and Assessment (SDMA 2020) presented online on 4–5 August 2020. It discusses the recent advances in fields related to damage modelling, damage detection and assessment, non-destructive testing and evaluation, structure integrity and structural health monitoring. The conference covers all research topics and applications relevant to structural damage modelling and assessment using theoretical, numerical and experimental techniques. This book is useful to scientists and engineers in academia and industry who are interested in the field of structural damage and integrity.