Fatigue Life Calculation And Analysis Of Aircraft Engine Low-pressure Turbine Shaft

The fatigue life of airplane is directly affected by the reliability fatigue life of aircraft engine, which is a power source of the airplane. The fatigue life of aircraft engine depends to a great extent on the fatigue life of its main components. Research on the fatigue life confirming for aircraft engine main components starts late, there is no standardized procedure and standards for fatigue life confirming. Therefore, as a fracture critical of aircraft engine parts, low-pressure turbine shaft’s reliability fatigue life research takes important implications for the reliability of military equipment and the fatigue life confirming of aircraft engine.The main failure modes of the low-pressure turbine shaft include fatigue, wear, deformation, ductile and brittle fracture, among which fatigue failure is the most important failure mode. The low-pressure turbine shaft is subjected to combined loads during operation, which mainly includes load torque, axial force, bending moment and vibration torque. And torque and axial force produce high cycle fatigue damage, while bending and vibration torque produce low cycle fatigue damage.In order to accumulate experience and data setting for research on the fatigue life confirming of aircraft engine main components, and to promote procedure and standards of the fatigue life confirming of aircraft engine main components, this thesis comes out of the research project "The fatigue life confirming of aircraft engine" to carry out the fatigue life confirming research work by taking aircraft engine low-pressure turbine shaft as a research object. The main research work includes:(1) Through the statistical analysis of the measured load spectrum, obtaining the computation load spectrum required in the fatigue life confirm. In order to obtain the corresponding maximum nominal stress, the local stress and strain of the fatigue damage dangerous region, the stress and strain are analyzed by using the finite element method and simulating the actual work environment of the low-pressure turbine shaft under load and boundary conditions. Based on the analysis, by calculating the average stress values on minimum cross-section of dangerous parts, we can determine the stress concentration factors.(2) In order to calculate turbine shaft fatigue damage under different loads, firstly, fatigue damage assessment is predicted by using the nominal stress method and local stress-strain method in the condition of the low-pressure turbine shaft at high and low cycle load case alone. And then, cumulative damage of low-pressure turbine shaft in composite load is obtained and the safety life cycle is calculated with Miner linear cumulative damage method.(3) Considering the importance of fatigue test verification and the necessity to fatigue life confirming, fatigue test load spectrum of low-pressure turbine shaft is calculated. Depending on the standard load cycle of low-pressure turbine shaft, the fatigue test load is determined through calculating multi term correction coefficient of the load by using the load dispersion coefficient method. Finally, a complex load spectrum is developed for fatigue testing by identifying test frequency of high and low cyclic load, and data analysis method of the fatigue test of low-pressure turbine is analyzed and studied.