Issue34

Y. Nakai et alii, Frattura ed Integrità Strutturale, 34 (2014) 246-254; DOI: 10.3221/IGF-ESIS.34.26 253 Rolling direction Surface Extended inclusion Surface Surface (1)Vertical crack initiation (2)Vertical crack growth (3)Shear type crack initiation (4)Shear type crack growth and flaking Figure 10 : Model of flaking mechanism from extended inclusion. The following results were obtained. 1. To observe RCF cracks and inclusions in a plate specimen, SRCL imaging was carried out at the BL46XU beam line of SPRing-8, which is the brightest synchrotron radiation facility in Japan. Cracks existing beneath the contact surface could be detected with high resolution. Thus, SRCL imaging is a powerful technique for elucidating the crack initiation and propagation behaviors of RCF. 2. RCF tests using the newly developed compact testing machine and SRCL imaging were carried out successively to observe the crack initiation and propagation behaviors. Using this technique, the formation of tensile-type vertical cracks, and shear-type horizontal cracks, and the flaking process were successfully observed. 3. A shear-type horizontal crack initiated after the vertical crack, whose face was perpendicular to the rolling direction and rolling surface, and initiated and propagated along an inclusion. Therefore, the formation of a vertical crack must affect shear-type crack formation and flaking, where the shape and length of the inclusion also affect the initiation and propagation of the vertical crack. A CKNOWLEDGMENTS he 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, 2014B1602, and 2014B1890. The authors are grateful for the technical support of Dr. K. Kajiwara (JASRI). R EFERENCES [1] Murakami, Y., Shimizu, M., Effects of non-metallic inclusions, small defects and cracks on fatigue strength of metals, Trans. Japan Soc. Mech. Eng. A, 54 (1988) 413-425. [2] Goshima, T., Ueda, K., Shimizu, M., Ishihara, S., Crack growth path emanating from an inclusion and fatigue life prediction due to repeated rolling/sliding contact, Trans. Japan Soc. Mech. Eng. A, 54 (1988) 190-197. [3] Grabulov, A., Zandbergen, H.W., 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, (2007) 219-226. [4] Gondrom, S., Zhou, J., Maisl, M., Reiter, H., Kroning, M., Arnold, W., X-ray computed laminography: An approach of computed tomography for applications with limited access, Nuclear Eng. Design, 190 (1999) 141-147. T