Fatigue Assessment of a Low Speed Wind Turbine Shaft
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AH Gears Ltd are specialists in quality gear cutting, hobbing and grinding, CNC machining, gearbox parts, repair and maintenance. Their specialist gear services including straight cut, planetary, worm, bevel, splines and helical gears.
Matrix undertook a fatigue assessment of a low speed shaft which is to be installed in a wind turbine. The scope of the analysis commissioned by AH Gears was to check if the addition of service hatchways to the shaft would cause fatigue failure under cyclic loading.
The initial hatchway design was a rectangular cut out with corner fillet radii to reduce stress concentrations. A finite element model was developed with MSC.Patran and solved using MSC.Nastran. MSC.Fatigue was used to perform the fatigue calculations.
The hatchway was placed in a region of the shaft with a relatively low nominal stress and on first glance it seemed unlikely to be a real issue. However the shaft failed the fatigue assessment due to the large stress concentrations in the radii of the cut out.
A second design iteration used a circular cut out with an equivalent working area. The finite element model was modified to include the new cut out and subsequent fatigue assessment performed.
This assessment concluded the new shaft design would have a satisfactory fatigue life. The image below shows the shaft and detail of the much higher stress (red) in the rectangular cutout - and the acceptable stress levels with a circular cutout.
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