Finite element analysis of fir-tree region in turbine discs

Comprehensive 2D and 3D finite element analysis is undertaken of the fir-tree region in aeroengine turbine disc assemblies. The study examines the effect of the critical geometrical features, such as the number of teeth, flank length and flank angle upon the stress field in the disc. The two-dimensional finite element predictions are verified using photoelastic-stress-freezing technique. The study is further extended to account for the effect of the skew angle and the interfacial friction between the disc and attached blades upon the resulting contact stresses at the interface and through the disc thickness. The results reveal that aeroengine disc designers must treat the two-dimensional finite element results with caution. This is due to the fact that two-dimensional results do not account for the large stress variations at the contact region and through the thickness due to the presence of skew slots in the disc.