Stiffness Analysis And Fatigue Life Prediction Of Metal Bellows Used For Aerospace Engine Gas Valve

Gas valve bellows is one of the most essential parts of aerospace engine components.As one of the most important component, gas valve is of high failure probability due to itsextreme work condition of high pressure and high temperature. The metal bellows, which isan axisymmetric cylindrical shell, is the core part of gas valve. Thus, studies on strengthcalculation, stability check and fatigue life prediction of metal bellows are of very highpractical significance. In this thesis, focusing on the reliability problems of gas valvebellows, a finite element model is established in accordance with the bellows’ formingprocess, and the axial stiffness, the pressure stability and the fatigue life of bellows aredeeply studied. The main contents of this thesis are as follows:Based on bellows’ forming principle, technological level, wall thinning theory andfinite element theory, a finite element model is established of exponential thinning forbellows’ wall. The model takes into account bellows’ wall thinning caused by processingtechnology, and its applicability and reasonability is verified by comparing with bellows’international standard thinning method.Based on the established model of exponential thinning for bellows’ wall, bellow’saxial stiffness and stability of internal and external pressure is further studied. On theresults of stiffness analysis, a suitable wall thinning exponent x is determined to controlaxial stiffness error within2%. As for the instability problem of internal and externalpressure, suitable judgment methods are established respectively.Based on Miner’s linear cumulative fatigue damage theory, the uniaxial fatigue theoryand multiaxial fatigue theory, studies on bellows’ fatigue life are further conducted.Bellows’ fatigue life is predicted by using multiaxial fatigue model and Manson-Coffinequation after mean stress correction. Through fatigue life data comparison of both fatiguemodels’ applicability for bellows, a suitable life prediction model for bellows is finallyestablished.Based on the established model of exponential thinning for bellows’ wall, deepanalysis is presented on the effect of bellows’ structural parameters on the stressdistribution under axial displacement load and stress load. Results of analysis can thenprovide references for both the design and the use of bellows.By using ANSYS and APDL, a program is developed on bellows’ parametric modelingand analysis. With this program, effective analytical investigation is achieved on bellows of different size, plies, materials, forming processes and working conditions.