Modelling and characterization of the thermo-mechanical behaviour of firtree roots in turbine disc assemblies

We conducted three-dimensional finite element (FE) analysis of the coupled thermo-mechanical contact behaviour of firtree joints in aviation turbine discs with the focus of the work being the effect of the geometrical features of the joint on the contact stresses and load sharing among firtree teeth. The 3D FE model of disc/blade assembly is developed using an existing preprocessor, and the contact behaviour at the firtree roots is described using penalty parameters. Convergence tests were conducted to overcome both the mesh size dependency of our simulations and the selection of an appropriate penalty parameter on the accuracy of our results. Furthermore, nickel-based alloy Inconel 718 is chosen for the turbine disc assembly with temperature-dependent properties. The importance of performing the current coupled thermo-mechanical analysis is reflected in the significant discrepancy between the coupled and the uncoupled models, where the mechanical and thermal loads are applied independently. The study is further extended to include the influence of friction on the state of stress at disc/blade interface and the resulting shear stresses. Contact stresses and interfacial disc/blade stresses have a direct impact on the structural integrity of the turbine disc and ultimately the safety of the entire gas turbine engine.