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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2. Experimental study The edge imperfections on ceramic rollers are mainly due to the grinding and finishing operations. These can be MMs or imperfections of other type associated with visible cracks. The imperfections incorporating cracks retain fluorescent penetrant, which is different from MMs which may or may not retain this liquid. Several rollers containing edge imperfections were received from the product line for analysis. Observation under optical microscope showed that most of the edge imperfections are confined within the chamfer region of rollers, however some of them extend into the raceway or to the end-face region. Examples of optical observations are given in Fig. 2. The two types of surface imperfections are illustrated in this figure: MMs (studied in our previous work) and the surface cracks, which are the subject of the current study.

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Surface cracks

Fig. 2. Optical observations related to the imperfect roller chamfer. MMs (left) where studied before by Kadin et. al (2022), and surface cracks (right) are the subject of the current study.

Based on the current observations, cracks of three types were identified due to their orientation with respect to the raceway. Based on some idealization the orientations are defined as following (see Fig. 3): 90º (vertical crack), 0º (horizontal) and 45º (inclined). The crack orientation may have effect on the crack propagation criticality, and therefore this parameter is included into the parametric study of the current work. Additional parameter defining the crack morphology correspond to the crack size. Obviously, the imperfection criticality pertains to its size: regarding the current feature, SIF is proportional to the square root of crack length (or any other crack dimension), and eventually, SIF governs the crack propagation behavior (see e.g. Anderson (2017)). 50 rollers of size 11 × 12 and 24 × 30 ( D w × L , where D w is the roller diameter and L its length – see Fig. 1) containing cracks at chamfers, had been collected to characterize the crack size and geometry (see Fig. 3). Few of these rollers were cross-sectioned in order to determine the 3D cracks shape and their depth (see Fig. 5 and 6).