PSI - Issue 2_A

Y. Nakai et al. / Procedia Structural Integrity 2 (2016) 3117–3124 Nakai, Shiozawa, Kikuchi, Obama, Saito, Makino, Neishi/ Structural Integrity Procedia 00 (2016) 000–000

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5. Conclusions

In the present study, 4D observations of the formation and propagation of the rolling contact fatigue (RCF) tests were performed on a high-strength steel by combining a newly developed compact rolling contact fatigue test machine with synchrotron radiation computed laminography (SRCL), and the effects of inclusion size and orientation on the RCF process were examined. The following results were obtained. 1. An increase in the sulfur concentration, i.e. , an increase of inclusion length, resulted in an increase in the variation of flaking life, and materials with horizontal inclusion showed large variation compared to those with vertical inclusion while the average flaking lives were almost identical. 2. The observations of flaking process showed as follows. First, cracks those were perpendicular to the rolling surface and rolling direction forms from an inclusion that was adjacent to the rolling surface. Then the cracks propagated vertically in the depth direction under normal stress. After the vertical crack propagated to a critical depth, a horizontal crack formed, which was parallel to the rolling surface. Finally, the horizontal crack propagated to form flaking under shear stress. 3. Although the variation of initiation lives of vertical and horizontal cracks, and propagation life of vertical crack were large, the variation of propagation life of horizontal crack was minimal. Then, the effect of inclusion size and orientation on flaking life should be responsible to the effect of these parameters on vertical crack initiation and propagation along inclusion. Acknowledgments The synchrotron radiation experiments were performed at beam line BL46XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) under proposal numbers 2014A1562, 2014A1770, 2014A1770, 2014B1602, 2014B1890, 2015A1668, 2015A1973, and 2015B1592. The authors are grateful for the technical support of Dr. K. Kajiwara (JASRI). References Adams, R., Bischof, L., 1994. Seeded region growing, IEEE Transactions on Pattern Analysis and Machine Intelligence, 16, 641 – 647. Gondrom S., Zhou J., Maisl M., Reiter H., Kroning M., Arnold W., 1999. X-ray computed laminography: An approach of computed tomography for applications with limited access, Nuclear Eng. Design, 190, 141-147. Goshima, T., Ueda, K., Shimizu, M., Ishihara, S., 1988. Crack growth path emanating from an inclusion and fatigue life prediction due to repeated rolling/sliding contact, Trans. Japan Soc. Mech. Eng. A, 54, 190-197. Grabulov, A., Zandbergen, H.W., 2007. Investigation of microstructural changes within white etching area (‘butterfly”) under rolling contact fatigue (RCF) using TEM and 3D crack reconstruction by focus ion beam (FIB), in: E. Allison, J.W. Jones, J.M. Larson, and R.O. Ritchie (Eds.), Fourth International Conference on Very High Cycle Fatigue, The Metallurgical Society, Warrendale, Pennsylvania, 219-226. Makino T., Neishi Y., Shiozawa D., Fukuda, Y., Nakai, Y., 2014. Evaluation of rolling contact fatigue crack path in high strength steel with artificial defects, Int. J. Fatigue, 68, 168-177. Murakami, Y., Shimizu, 1988. M., Effects of non-metallic inclusions, small defects and cracks on fatigue strength of metals, Trans. Japan Soc. Mech. Eng. A, 54, 413-425. Nakai, Y., Shiozawa, D., Kikuchi, S., Sato, K., Obama, T., Makino, T., Neishi, Y., 2014. In situ Observation of Rolling Contact Fatigue Cracks by Laminography Using Ultra-bright Synchrotron Radiation, Frattura ed Integrità Strutturale, 34 267-275. Shiozawa, D., Nakai, Y., Fukuda, Y., Neishi, Y., Makino, T., 2012. Observation of cracks in carbon steel under contact rolling fatigue by micro CT imaging using ultra-bright synchrotron radiation, Proc. 15th Int. Conf. Exp. Mech., CD-ROM, 2635. Shiozawa, D., Makino, T., Neishi, Y., Nakai, Y., 2014. Observation of rolling contact fatigue cracks by laminography using ultra-bright synchrotron radiation, Procedia Materials Science, 3, 154-164. Stiénon, A., Fazekasa, A., Buffi?rea, J.-Y., Vincenta, A., Daguierb, P., Merchi, F., 2009. A new methodology based on X-ray micro-tomography to estimate stress concentrations around inclusions in high strength steels, Materials Sci. Eng. A, 513-514, 376-383. Stiénon, A., Fazekat, A., Buffi?rea, J.-Y., Daguierb, P., Merchi, F., Vincent, A., 2010. A new methodology for predicting fatigue properties of bearing steels: From X-Ray micro-tomography and ultrasonic measurements to the bearing lives distribution, J. ASTM Int., 7. Uhrus, L.O., 1963. Through-hardening steels for ball bearings-effect of inclusions on endurance, Proc. Conf. on Clean Steels, Ir on and Steel Institute., 77, 104.