US Patent 7270518 Steep angle turbine cover buckets having relief grooves

Steam turbine bucket covers have forward and aft clearance surfaces on a pressure side edge of the cover, a contact surface between the clearance surfaces and an undercut fillet between the forward clearance surface and the contact surface. The adjoining bucket cover has forward and aft clearance surfaces, a contact surface between the clearance surfaces and an outside radius between the forward clearance surface and the contact surfaces along the suction side edge of the cover. The undercut fillet includes two different radii to minimize or eliminate fretting damage caused by high stresses in the interference fit between the contact surfaces of adjacent covers.