13th International Conference on Fracture June 16–21, 2013, Beijing, China Crack Growth Life Assessment on Turbine Component under Combined Fatigue Loading Dianyin Hu1,*, Rongiqao Wang1, Huawei Liu1, Jiaming Wei1 1 School of Energy and Power Engineering, BeiHang University, Beijing 100191, China * Corresponding author: hdy@buaa.edu.cn Abstract This paper focuses on a crack growth life assessment method for a turbine component under high-low combined cycle fatigue (HLCCF) loading through experimental and numerical methods. Crack growth tests under HLCCF loading on five full scale turbine components, attached to actual turbine discs, were conducted at elevated temperature by using a Ferris wheel combined fatigue system to simulate the stress under HLCCF loading and temperature distributions. Then, the fracture mechanics (FM) analysis was utilized to simulate crack growth of the turbine component to implement crack growth. The experimental life data agrees well with the crack growth life prediction for the turbine component. In summary, this paper provides a new way to estimate the crack growth lifetime criterion of the turbine components under HLCCF loading through experimental and numerical investigations. Keywords High-low combined cycle fatigue, Crack growth life, Turbine component, Elevated temperature 1. Introduction The turbine blades of an aero-engine are generally attached to the disc by means of a fir-tree design, a typical multiple load path structure, to allow for different rates of expansion between the disc and the blade while still holding the blade firmly against centrifugal loads. During operation, the fir-tree attachments are subjected to significant tensile stresses due to centrifugal loading and during the flight cycle may experience aerodynamically induced vibrations, leading to additional stresses. The amplitude of the vibrational loading is typically much smaller than that due to centrifugal loading and hence vibration is generally thought to give rise to high cycle fatigue (HCF). In contrast, the effect of centrifugal loading is frequently considered to be low cycle fatigue (LCF). Under the overall high-low combined cycle fatigue (HLCCF) loading, the fatigue damage of the turbine attachments is largely increased[1,2,3,4]. These effects may be responsible for the unscheduled crack failures in service of the mortise on a certain aeroengine second turbine disc. Conventional life assessment methods of blade-disc connections of gas turbines are almost based on finite element analysis [5] and the experimental data of specimens and component-like specimens instead of actual components so as to reduce experimental costs [6,7,8]. However, the actual crack growth and fracture failure of the mortise teeth are not only determined by the characteristics of the material, but are also affected by the structure, dimension, and the teeth space of the mortise. Furthermore, the differences in crack growth lives between laboratory specimens and full scale components can arise from some characteristics, such as geometry, volume and manufacture process, and therefore influences the accuracy of life assessment. To overcome the above shortcomings, the crack growth life prediction method of the blade-disc connection based on experimental life data of a full scale turbine blade attached to actual turbine disc in conjunction with the fracture mechanics (FM) analysis, is more accurate, since the components own the same manufacture process with real flight turbine components. The only way to accurately predict the life of a fir-tree contact is to perform fatigue test on a full scale turbine blade attached to an actual turbine disc. For this study, the most challenge work is how to simulate operating conditions of actual turbine attachments in laboratory, especially under -1-
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