Threshold Maps for Inclusion-Initiated Micro-Cracks and White Etching Areas in Bearing Steel: The Role of Impact Loading and Surface Sliding

Abstract

Wind turbine gearbox (WTG) bearings can fail prematurely, significantly affecting wind turbine operational availability and the cost of energy production. The current most commonly accepted theory of failure mechanism is that the bearing subsurface is weakened by white etching crack (WEC ) networks that eventually lead to the flaking away of material from the bearing surface. Subsurface damage due to rolling contact fatigue (RCF) is thought to be the main cause of premature failure, resulting from the initiation of micro-cracks, often at non-metallic inclusions or other material defects, which then propagate to the bearing surface. This study proposes a hypothesis that impact loading together with high levels of surface traction and contact pressure are important factors contributing to the initiation of micro-cracks and white etching areas (WEAs) at non-metallic inclusions which may lead to the formation of WEC networks. Both repeated impact and twin-disc RCF tests were designed to investigate inclusion-initiated micro-cracks and WEAs at subsurface in order to test this hypothesis. This led to the recreation of inclusion-initiated micro-cracks and WEAs in tested specimens, similar to the subsurface damage observed at inclusions in failed WTG bearing raceways. Tests were carried out to determine threshold levels of contact pressure, surface traction, and impact loading required for the formation of inclusion-initiated micro-cracks and WEAs.

Recognition of Crack-Rubbing Coupling Fault of Bearing under High Water Pressure Based on Polar Symmetry Mode Decomposition

“…In order to better understand inertial manifolds and nonlinear Galerkin method, the concept of central manifolds is first introduced [9].…”

A combined experimental and analytical method to determine the EHL friction force distribution between rollers and outer raceway in a cylindrical roller bearing

“…On the one hand, local friction force on the raceway surface caused by abnormal sliding will aggravate the wear of the surface [3][4][5]. On the other hand, the tangential friction force induces subsurface cracks of raceways to propagate towards to the surface and finally leads to material peeling [6,7]. In rolling element bearings, the local tangential friction force varies greatly at different azimuths of roller-raceway contact [8], which is called friction force distribution in this paper.…”

“…Fig 6. Measured strain signals from all of the sensing locations on the outer ring of the test bearing during a test (test conditions: shaft speed 4,000 r/min, applied load 12 kN, and lubricant oil 5W-30).…”

A vision-based approach for rolling contact fatigue evaluation in twin-disc tests on a railway wheel steel

“…Twin-disc tests are used for studying damage phenomena in various fields of application. For instance, twin-disc tests were used for studying rolling contact fatigue (RCF) in surface hardened materials, such as steels for bearings or gears [1][2][3][4][5][6]. In these cases, RCF usually develops through the nucleation and propagation of cracks from surface or subsurface defects, which lead to localized severe damage due to the removal of large material flakes.…”

“…The destructive measurements consist essentially in cutting the specimens at the end of the tests, observing the subsurface microstructure and crack morphology by optical or scanning electron microscopy, and measuring the hardness on these sections or on the contact surface [1,4,6,[8][9][10][11][12][13][14][15]17,[19][20][21]. In [2], even residual stress measurements were done by means of X-ray diffraction and deep-hole drilling (DHD).…”