Fatigue Crack Growth of Turbine Disc Part Considering Effect of Shotpeen Nonlinear Stress Gradients Using Finite Element Based and Numerical Methods

Abstract

Abstract Crack growth in mechanical components is affected by the residual stress gradient around the crack zone. Shot peen is one of the cold working processes used to generate compressive residual stress layer on gas turbine engine parts. The aerospace industry frequently uses shot peening to increase the fatigue life of mechanical components. In this study, mechanical properties of disc part made of nickel-base super alloy material are modified by applying shot peen residual stress parameters. Three-dimensional residual stress modification is transformed to finite element model of the uncracked area. Then, surface semi-elliptical crack introduced in the finite element model on the maximum principal stress orientation on the surface. One of the most recent, adaptive remeshing capabilities are used during simulations by using Ansys SMART. Crack front element division and incremental crack advance in each step of FEM are fine-tuned by different parameter sets. After each simulation step, new crack front is calculated, and finite element model is updated consequently. Then, crack growth is calculated using mixed-mode maximum circumferential stress criterion until the failure. Similar procedure is performed to create a numerical weight function solution by employing empirical formulas. Shot peen effect is converted into the residual stress intensity factor by using weight function method. Yau’s weight function formulation was used to calculate residual stress intensity values with Newman-Raju surface crack solution. This residual stress intensity profile mostly affects the stress distribution in a compressive stress manner causing lower crack growth rates. This yields a variation on SIF around the crack tip zone. At that point, fatigue crack growth is also calculated by numerical solutions. Results are compared with FEM based mixed-mode crack growth and differences in results are highlighted. Applicability of FEM based crack growth method on shot peen application is investigated. The role of the shot peen operations and consequence of surface residual stress during crack growth is emphasized.