PSI - Issue 57

Yuri Kadin et al. / Procedia Structural Integrity 57 (2024) 236–249 Kadin et. al / Structural Integrity Procedia 00 (2023) 000 – 000

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failure and the reduction of service life is linked to these imperfection, meaning that each ceramic roller has to be inspected. The non-destructive inspection aims to reject components, containing relatively large surface defects which during bearing operation can trigger Rolling Contact Fatigue (RCF), manifested e.g. by the crack propagation and spalling. Multiple experimental and theoretical studies were conducted in SKF in attempt to develop engineering criteria for the rejection of imperfect rolling elements based on the size and type of surface imperfection, material characteristics and bearing loading conditions. Most of these studies targeted the imperfections located on the raceway which is undoubtedly acceptable for balls, while in the case of roller the situation is more complex. This is because in rollers the defect criticality is also dependent on their location. Indeed, the imperfections located on the roller raceway are subjected to different loading conditions compared to the ones located at the chamfer (see Fig. 1). Firstly, the edge imperfections are typically beyond the rolling contact, and therefore it can be reasonably considered that these imperfections are less risky compared to the imperfections located on the regular zone – raceway. Secondly, the stress field at the chamfer is quite different from the stress at the raceway zone, as result of the free face (the roller end-face) effect. This means that the models, previously developed for the raceway imperfections (see e.g. Zolotarevskiy et. al (2020), Lai et. al (2018), Kadin et. al (2012) ) cannot be directly applied to the edge features.

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Contact pressure

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Fig. 1. Schematic of a ceramic roller containing the two types of imperfections: Missing Material (MM) and surface cracks. Differently from the imperfections located on the raceway, the edge imperfections (located at the roller chamfer) are beyond the rolling contact zone, thus intuitively these imperfections are associated with lower RCF risk. Recently, the numerical study on ceramic rollers with imperfect chamfer was presented by Kadin et. al (2022), focusing on the feature, termed as a “Missing Material” (MM). This imperfection was modelled as a surface cavity of ellipsoidal shape, and since no crack linked to MM was experimentally observed, the defect criticality was assessed in terms of stress criterion. Obviously, this work did not cover all possible types of edge imperfections, and cannot be applied for the features associated with cracks. For cracks, optical inspection technique combined with fluorescent penetrant inspection and cross-sectioning were used to characterize the crack size and geometry. In such case (as the crack is explicitly present) the stress based failure criterion is not reasonable, while the fracture mechanics criterion should be used instead. The current work can be seen as the continuation of the previous activity, because similar solution strategy, combining the Finite Elements (FE) modelling of defect with the semi-analytical evaluation of contact pressure, is used. Like in the previous study, challenging contact conditions (high contact load + misalignment) are assumed here, in order to consider the worst case scenario. Few geometrical configurations of edge crack are considered for the fracture mechanics analysis, aiming to compute the Stress Intensity Factors (SIF) distribution along the crack front. Eventually, the main goal of the work is the development of the engineering specifications to be used for the inspection of ceramic rollers.