Dynamic Stress Calculation And Analysis Of High Temperature Alloy Thin-walled Structures Under Thermo-acoustic Laods

With the improvement of the advanced aircraft performance,hypersonic vehicle are exposed to high intensity acoustic excitations from Aero Engine jet noise impingement or boundary layer pressure fluctuations during flights,the sound pressure level is as high as 180dB.Moreover,the surface panels of aero craft are roughly exposed to elevated temperature in the range of 1000?-3000? due to aerodynamic heating and solar radiation etc.Very severe elevated temperature and high intensity acoustic loads will cause the thin-walled structures of aircraft to respond in a strong nonlinear large deflection vibration characteristics,and leading to premature fatigue failure of the structure.Therefore,in this paper,the dynamic stress responses of thin-walled structures are investigated using theory analysis and numerical simulation method,and according to stress response calculated above,the improved rain flow cycling counting method and the linear damage accumulation method are employed to calculate the fatigue life of the thin-walled structure under combined thermo-acoustic loads,and influences of the fatigue life on thermal loads are analyzed emphatically.Firstly,according to the Von Karman large deflection theory,the nonlinear large deflection governing equation of thin-walled structures under thermo-acoustic loadings is founded,and the relations of displacement,stress and strain are more deeply understood.In this paper,because thermo-acoustic responses are calculated using finite element numerical stimulation method,finite element equations of motion of thin-walled structure are also founded.Secondly,the critical thermal buckling temperatures and modal frequencies of simply-supported rectangular thin-walled flat panel and simply-supported thin-walled cylindrical shell under thermal loads with linear temperature gradient,the dynamic responses of them under thermo-acoustic loads,are obtained using finite element numerical stimulation,and using time-domain analysis(Time history),frequency-domain analysis(Power Spectral Density)and Root Mean Square of the dynamic responses of different types of thin-walled structures under thermo-acoustic loads are investigated emphatically.Finally,being aimed at the stress time histories of different types of thin-walled structures with simply-supported boundary condition under thermo-acoustic loads,mean stress models are applied for them to obtain the equivalent amplitude stress with zero mean stress,and then,the improved rain flow cycling counting method and the linear damage accumulation method are employed to calculate the rain flow cycling matrix and the rain flow cycling damage matrix of different types of thin-walled structures under combined thermo-acoustic loads,and the fatigue life of different types of thin-walled structures under combined thermo-acoustic loads are estimated and analyzed.High temperature noise fatigue,which is a serious problem,and must be considered in the design of aircraft structure.Especially,the thin-walled structures of aircraft.Consequently,in this paper,the calculation and analysis of the dynamic response and fatigue life of thin-walled structures can provide a preliminary basis for the anti-fatigue design of thin-walled structures.