Fracture mechanics on critical rotor component in turbojet engine

Abstract

The occurrence of crack initiation in a rotor component within turbo-engines poses a substantial threat, given the potential for severe engine failure due to the high-speed rotation and harsh operational conditions. To enhance engine durability and safety, a comprehensive understanding of fracture mechanics is necessary. The thesis incorporates a triple-pronged approach to calculating crack fatigue life and related fracture mechanics parameters such as stress intensity factor and J-Integral. In the first approach, a compact tension test (CTT) specimen was investigated in terms of both Linear Elastic Fracture Mechanics (LEFM) and Elastic Plastic Fracture Mechanics (EPFM) by using 2D and 3D analysis methods. These analysis results were compared with empirical formulations available in the literature. The main goal of first study is creating a baseline for third study. In the second approach, a turbine geometry with firtree structure was drawn by utilizing NACA airfoils as a baseline. After geometry adaptation, Finite Element Method (FEM) is leveraged using ANSYS In the analysis model, Linear Elastic Fracture Mechanics was deployed with linear material model. To ascertain stress values in proximity to the crack tip, a static structural analysis with elastic material properties is conducted, considering rotational velocity loading. In the third approach, a parametric study was conducted by using the same compact tension test specimen in first approach by changing geometric parameters such as plate thickness, specimen width, load values using ANSYS Mechanical. After having 250 different solution combination of the analysis, these parameters were exported as a data file in order to use in a machine learning model. A linear regression machine learning model was deployed by using sklearn's machine learning libraries. In the final stages of the study, the results gathered from both the ANSYS simulation and the numerical method are rigorously compared, providing a nuanced understanding of the agreement and discrepancies between these analytical approaches. This comparative analysis not only validates the robustness of the chosen methodologies but also contributes to a deeper comprehension of the factors influencing crack propagation in turbine blades within the specified operational contexts.