Modeling of Residual Stresses After Shot Peening and the Effect of Accounting Their Influence on the Stress State of Turbine Blade Fir Tree Roots

To ensure the strength reliability of gas turbine engine parts such as turbine blades, technological methods of surface hardening are widely used, the application of which leads to the formation of residual stresses in the surface layer of these parts.

In this paper, we describe methods for modeling the residual stresses arising in the process of shot peening hardening and their accounting for the calculation of the stress-strain state of the elements of turbine blade root locking joints. A method for calculating the residual stress field and cold hardening is developed. It is based on finite element simulation of the collisions of a shot with the sample surface in an elastoplastic formulation. The simulation results using the proposed method are the diagrams of the residual stress components and equivalent plastic deformation. Identification of mathematical model parameters is based on experimentally determined residual stress diagrams obtained on nickel alloy samples with varying shot peening modes.

An approach to the calculation of the stress-strain state and the cyclic durability of the turbine blade root is described. The calculation of the turbine impeller model loaded with a non-uniform temperature field and centrifugal forces is performed, taking into account componentwise residual stress diagrams determined using the developed method. A comparison of the values of the residual stress tensor components for the surface of the turboprop blade roots, determined experimentally and predicted numerically, showed satisfactory agreement. The effect of the form of residual stress diagrams calculated using various shot peening parameters on the stress-strain state of the turbine blade root and the values of its cyclic durability is estimated.

The use of the developed method of shot peening modeling will allow engineers to assign the parameters of the method of the blade root strengthening based on operating conditions of turbine impellers in order to form the most favorable residual stress diagram for ensuring the necessary cyclic durability of the product.