Stresses in a Splineless Drive for Aero-Engines

Abstract

This paper describes an alternative to splines for connecting turbine discs to shafts. The trilobe shape consists of six smoothly blending 60° circular arcs of two alternating radii; it is between a circle (both radii equal) and a triangle (smaller radius zero, larger radius infinite). Frozen-stress, photoelastic models of a realistic disc and a tubular shaft have been designed, made and loaded centrifugally, under static torsion and under combined torsion and rotation. The results show that the greatest centrifugal stresses in the disc occur in the bore at the tips of the trilobe and the greatest contact stresses occur near the transition from the larger to the smaller radius. The centrifugal stress concentrations due to the trilobe were small. Bore deformation and backlash due to differential centrifugal expansion were measured and found to be acceptable for a similar ceramic or nickel alloy disc.