Fatigue Life Prediction And Reliability Analysis For The Fan Shaft Of Aircraft Engine

Fan shaft is the major component and one of the most important rotor components of the aircraft engine. During the working process of aircraft engine with a large speed, it encounters complex loading conditions, such as rotating moment, axial force vibrating moment, bending moment and so on, which have a great effect on the safety and reliability of aircraft engines. In order to ensure enough safety and reliability of aircrafts, it is of critical importance and necessity to carry out fatigue life prediction and reliability analysis of the fan shaft in aircraft engines based on its material properties and failure characteristics. Referring to the fan shaft of a certain aircraft engine as the research object, this thesis investigates its fatigue life by means of elastic finite element analysis and elastic-plastic finite element analysis, and then predicts the fatigue life based on critical plane method and strain-based method during the process. After that, the fatigue life reliability is performed with Monte Carlo simulation method.The main contents and contributions of this thesis are shown as follows:(1) The 3D model and the finite element analysis model of 3D are established by adopting softwares on the 3D modeling and finite element analysis.Firstly, the 3D model is build up using Siemens NX Version 8.0 based on the actual dimensions of aircraft engine’s fan shaft, then the 3D model is imported to the ANSYS Workbench Version 14.5 and the finite element analysis model of 3D is constructed.(2) The elastic and elastic-plastic finite element analysis methods are performed under the multi-loading conditions, in order to obtain the information of stress, strain and dangerous parts with fatigue failures.The elastic finite element analysis is carried out considering the loading conditions of bending moment, rotating moment, axial force, vibrating moment and so on. The results of show that the plastic deformation of the engine’s fan shaft has occurred, which leads to a further elastic-plastic finite element analysis. Due to the fact, we obtained such information as total deformation, the stress state and the strain state of fan shaft in the aircraft engine, while recognizing two dangerous places of fatigue failure, i.e. root of the spline and the shoulder of the largest radius changing closer to the shaft.(3) Based on the results of elastic-plastic finite element analysis, the multiaxial fatigue life prediction of the aircraft engine fan shaft is performed.The multiaxial fatigue life prediction of the aircraft engine’s fan shaft is investigated by adopting critical plane methods(Wang-Brown model, Fatemi-Socie model and SWT-Bannantine model, respectively) and strain-based methods(methods based on maximum shear stain, based on Von Mises principle and method based on range of maximum principal strain). We realized that the predicting results are different according to different methods, and among them, the method based on range of maximum principal strain has a better performance.(4) The problem of fatigue reliability is studied for the life of fan shaft with Monte Carlo simulation method, with the results of the distribution types and reliability functions of fatigue life for engine’s fan shaft.Combining the multiaxial fatigue life prediction model(the method based on range of maximum principal strain) and the distribution types of model parameters, the reliability function of fatigue life for the fan shaft in aircraft engines is established by means of Monte Carlo simulation method. which concludes that the exponential distribution fits well for the fatigue life conditions of engine’s fan shaft. Then the probabilistic distributions of fatigue life and the reliability function can be obtained.