In situ observation of rolling contact fatigue cracks by laminography using ultrabright synchrotron radiation

Y Nakai,S Kikuchi,D Shiozawa,K Sato,T Obama

doi:10.3221/igf-esis.34.26

Abstract

In rolling contact fatigue (RCF), cracks usually initiate from inclusions beneath the surface and propagate to the contact surface. In the present study, synchrotron radiation computed laminography (SRCL) imaging was performed to observe flaking defects during the RCF of a high-strength steel. Specially fabricated inclusion-rich steel plate specimens were employed in the experiments. For the in situ observation of crack propagation, a compact RCF testing machine was developed, and a 4D analysis scheme was applied to the data obtained by SRCL. RCF tests were carried out near the measurement hatch of the beam line used SRCL to enable the successive observation of crack initiation and growth behaviors. Specimens before and after the occurrence of flaking were observed by SRCL, and flaking defects and cracks under the surface were successfully detected. As a result, details of the crack initiation and flaking process in RCF could be discussed. Shear-type horizontal cracks were found to initiate after the initiation and propagation of tensile-type vertical cracks along inclusions, where the face of the vertical cracks was perpendicular to the rolling direction and rolling surface. Therefore, the formation of vertical cracks is considered to affect shear-type crack formation and flaking, where the shape and length of inclusions also affect the initiation and propagation of vertical cracks.

Highlights

I n rolling contact fatigue (RCF), cracks usually initiate from inclusions beneath the surface, and they propagate to form flakes [1, 2]
Stiénon et al [5],[6] calculated the stress field around nonmetallic inclusions in bearing steels in RCF tests using 3D shapes obtained by synchrotron radiation micro computed tomography imaging (SRCT), which was conducted at the European Synchrotron Radiation Facility (ESRF)
For successive SRCT imaging of the RCF process, samples must be sufficiently small to allow the transmission of X-rays, and the crosssection must be smaller than 500 μm × 500 μm

Summary

Introduction

I n rolling contact fatigue (RCF), cracks usually initiate from inclusions beneath the surface, and they propagate to form flakes [1, 2]. Since this method is destructive, the crack propagation behavior is difficult to observe, and synchrotron radiation micro computed tomography imaging (SRCT) has been applied for nondestructive observation [4]. Stiénon et al [5],[6] calculated the stress field around nonmetallic inclusions in bearing steels in RCF tests using 3D shapes obtained by SRCT, which was conducted at the European Synchrotron Radiation Facility (ESRF) They used SRCT imaging for the observation of samples with flaking damage and RCF cracks [7], [8]. A compact RCF testing machine, which enables simultaneous RCF tests and SRCL observation, was developed, and the crack initiation and propagation behaviors are discussed

Results

Discussion

Conclusion