Finite element simulation of subsurface initiated damage from non-metallic inclusions in wind turbine gearbox bearings

The premature failure of wind turbine gearbox bearings significantly affects the reliability of wind turbine operation and energy production. Damage initiated from non-metallic inclusions known as White Etching Cracks (WECs) has been identified as the dominant initiation mechanism that causes the premature failure under the influence of transient events. In this study, the factors affecting the initiation of subsurface damage from non-metallic inclusions were investigated by finite element modelling. It was found that the direction of surface traction and loading-unloading cycle had a detrimental effect on stress concentration at the tips of the de-bonded non-metallic inclusions in bearing steel

Initiation of sub-surface micro-cracks and white etching areas from debonding at non-metallic inclusions in wind turbine gearbox bearing

In this study, a failed planetary bearing from a wind turbine gearbox was destructively examined to investigate the initiation of micro-cracks and butterflies at non-metallic inclusions, and the effect of debonding between these inclusions and the steel matrix. The butterflies were scanned using Atomic Force Microscopy (AFM) to show the topography that could not be assessed by using other microscopy techniques. Nano-indentation was conducted across a butterfly wing and a non-metallic inclusion to measure the hardness at the interface with the steel matrix. It was found that the White Etching Areas (WEA) in the region of the butterfly wing was a damaged material that showed tearing at the debonding gap between the inclusion and steel matrix. This study highlighted the effect of debonding on the initiation of micro-cracks, WEA and inclusion cracking. A direct relationship was found between the size of inclusions and the total length of inclusions and micro-cracks or butterfly wings. The depth of the observed sub-surface damage was correlated with the sub-surface stress distribution and these results suggested that surface traction could be an important contributing factor to the subsurface damage initiation

From rifting to spreading in the eastern Gulf of Aden : a geophysical survey of a young oceanic basin from margin to margin

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