Estimation Of The Random Fatigue Life Of Composite Thin-walled Structures Under Thermo-acoustic Loadings

The acoustic fatigue of High-speed aircraft thin-walled structures has become an importance issue in the field aerospace.The structures subjected to high intensity acoustic and serious thermal loading.The acoustic loads as high as 170dB,while the temperature could reach 30000?.Complex stresses in structures can decrease the fatigue life seriously.Therefore need to analyze the stress,strain,displacement and modal of composite thin-walled structures.According to the complexity of the dynamic response of composite thin-walled structures under thermo-acoustic loading,and futher analysis of composite fatigue failure criteria.In this paper,theory analysis and numerical simulation are employed to obtained the nonlinear response of composite thin-walled structures under thermal-acoustic loadings.The improved model of rainflow cycle counting(RFC)method,S-N curves are combined by means of damage accumulation theory to predict fatigue life of panel.Firstly,according to the Von Karman large deflection theory and laminated plate theories,the large deflection governing equation of thin-walled under thermo-acoustic loading is calculated based on the elasticity theory.The Galerkin method is employed to transform the equation of motion in physical DOF into equation of motion in modal coordinates,and the stress,dispacecment expressed by modal displacement for the simply-supported.Secondly,the nonlinear response of carbon-carbon composite thin-walled structures for the simply-supported are obtained under thermal-acoustic loading.Under certain thermo-acoustic loading conditions,a dynamic instability will give rise to buckling and then snap-thoughs response.The maximum stress and displzcement position of composite thin-walled structures are obtained by analyzing.The dynamic response of composite thin-walled structures are calculated by time domain Monte Carlo method.Include displacement time history,stress time history,displacement power spectral density and probability density function.Finally,according to the theory of fatigue analysis combine composite damage theory,and the dynamics characteristics of thin-walled structures under thermal-acoustic loadings.The stress time history is calculated by improved model of rainflow cycle counting(RFC)method,S-N curves are combined by means of damage accumulation theory to predict fatigue life under different thermal-acoustic loadings.The calculation methods and theoretical analysis of nonlinear response of thin-walled under high intensity acoustic and serious thermal loading in this paper.It plays an important basic role on estimating the acoustic fatigue life of High-speed aircraft thin-walled structures.