Research on the Analysis Technology of Random Sonic Fatigue of High-Temperature Alloy Thin-Walled Structure

As to the sonic fatigue problem of aeronautical thin-walled structure, this thesis mainly studies the vibration response calculation and analysis as well as the fatigue life estimation of an aero-engine combustor liner high-tempreture alloy structure under random acoustic loads. Mainly by theoretical research and numerical analysis, the emphasis is put on how to obtain probability density function (PDF) of stress cycles from the wide-band random vibrational stress response and then to estimate the random sonic fatigue life of structure.1. The curve fitting method for three kinds of fatigue life models, i.e three-parameter Weibull model, Langer model and Basquin model is studied. The method for solving the three models parameters is studied, and the implamentation process by programming is given, the S-N curve fitting effects are comparetively analyzed by numerical examples.2. The probability distribution of Von Mises stress process of structure under band-limited Gaussian white noise is studied. Suggesting that the stress progress accord approximately with double-parameter Weibull distribution, the formula for calculating Weibull parameters are given, as a result, the probability density function and the peak probability density function of Von Mises process can be determined. Based on the Palmgren-Miner linear fatigue damage cumulative rule, the method for predicting the random sonic fatigue life based on the stress probability density and power spectrum density (PSD) is proposed, and the model for fatigue life prediction is established. The fatigue life is estimated by using the model. Considering the influence of the wide frequency band, the calculated results are modified, then an effective method for predicting the fatigue life of structure under random loads is obtained.3. The model of an aero-engine combustion chamber liner thin-walled structure is built. Using the coupled finite element and boundary element method, the displacement and stress response of the structure in diffusion field under different sound pressure level band-limited Gaussian white noise and the measured combustion chamber inner acoustic loads are calculated, and the vibrational response characteristics of the structure under acoustic loads are analyzed. By applying the power spectrum density method and so called the method of probability density function of Von Mises stress respectively, the sonic fatigue life of the aero-engine combustor liner structure is estimated. Furthermore, the influence of acoustic loads and modal frequencies to vibration response and fatigue life is analyzed.The method for calculating the vibrational response and estimating the fatigue life, as well as the calculated results of aeronautical thin-walled structure subjected to random acoustic loads presented in this paper are of important applied values to analyze and solve the random sonic fatigue problem and to improve anti-fatigue strength design of thin-walled structure.