Contact Stresses in Dovetail Attachments: Alleviation via Precision Crowning

Abstract

Previous studies of contact stresses in dovetail attachments provide verified finite element stresses as well as some simple physical models of such stresses. Generally there is good agreement between the finite element analysis and the simple physical models. Together the two identify a pinching mechanism as leading to large fluctuations in hoop stresses at the edges of contact. These fluctuating hoop stresses can be expected to be a major contributor to the fatigue of dovetail attachments. The present study investigates a method of alleviating the fluctuating hoop stresses. This method entails crowning of the contacting flat on a blade. Such crowning is in two orthogonal directions on the blade flat. Two-dimensional finite element analyses are made in both directions. These analyses indicate that significant reductions in fluctuating hoop stresses can be achieved by the method, provided the crowning is controlled sufficiently precisely.