Improved Three-Dimensional Crowning Profiles for Dovetail Attachments

Dovetail attachments in gas turbines are subject to fatigue failures. These fatigue failures occur as a result of large fluctuations in hoop stresses near the edges of contact in attachments. The high hoop stresses available for fluctuating are, in turn, the result of high contact stress peaks near the edges of contact. One means of alleviating these stresses is via crowning. Such crowned configurations are inherently three-dimensional and consequently present some challenges to obtaining convergent contact stresses with finite elements. Such challenges are met in the work of Beisheim and Sinclair (2008, "Three-Dimensional Finite Element Analysis of Dovetail Attachments With and Without Crowning," ASME J. Turbomach., 130, pp. 021012-1-021021-8), and crowning is shown to reduce contact stresses by about 40%. The crowning profile used in that paper is the natural Hertzian profile of a segment of an ellipsoid. This note investigates an alternative profile with a view to increasing the area of contact, and thereby further reducing contact stresses. Converged contact stresses are obtained for both profiles, and demonstrate that the alternative profile can indeed reduce contact stresses by an additional 10%.