Nonlinear Aerothermoelastic Research Of Composite Cylindrical Shells In Supersonic Flow

Cylindrical shell is a common structure of aerospace vehicle,such as aircraft fuselage,missile body,etc.With the increasing requirement of lightweight structure and flight speed of modern aircraft,its design is faced with the requirement of structural lightweight design,which not only meets the strength requirement,but also meets the stiffness requirement of structure under aerodynamic and aerothermal effects caused by high-speed flight.In other words,it is necessary to consider the non-linear thermo-aeroelastic problems caused by the coupling of aerodynamic,aerothermal,elastic and inertial forces.Fiber reinforced composites have become an advanced material for structural design of modern high-speed and lightweight aircraft.The overall stiffness will be affected by the laying angle and the laying mode of the composite material,and the mechanical properties of the material will change at high temperature.The thermo-aeroelastic problem of the thin shell structure with this kind of material under the combined influence of aerodynamics and aerothermal is more complex.The existing theories and methods can not solve these problems very well,and new theories and methods need to be developed.In this paper,the cylindrical shell structure composed of fiber reinforced composites has been considered,and the effects of different fiber layers and angles on the thenno-aeroelasticity of the cylindrical shell under the combined action of aerodynamic force and aerothermal force,i.e.the basic stiffness design of the thermo-aeroelasticity of the cylindrical shell made of fiber reinforced composites,are studied.The research will help to develop the corresponding basic theory.And the method has a certain significance of scientific and practical application.In this paper,the basic problems of thermo-aeroelastic stiffness and stability design of fiber reinforced composite cylindrical shells are studied,including thermo-elastic static stability,i.e.thermal buckling,thermo-elastic dynamics,i.e.thermal mode,thermo-aeroelastic dynamic stability i.e.thermal flutter.Aiming at the first two problems,the effects of geometric parameters,composite laying angle and laying mode on buckling temperature,buckling mode and vibration mode were studied by numerical analysis method.For the thermo-aeroelastic stability problem,based on the non-linear strain-displacement relationship,considering the thermal stress effect and the temperature non-linear effect of material properties,the first-order piston theory is used to calculate the unsteady aerodynamic force.The flutter boundary and flutter frequency of composite cylindrical shells under the influence of temperature are analyzed.At the same time,the time history and phase diagrams of flutter are obtained by solving in time domain.The effects of anisotropy of composites,temperature effect of material properties and non-uniform temperature distribution on flutter amplitude and mode of vibration are discussed.The main conclusions are as follows:the in-plane thermal stress produced by aerodynamic heating will reduce the overall stiffness of the cylindrical shell structure,and then reduce the static and dynamic stability of the cylindrical shell,resulting in thermal buckling phenomenon,as well as the linear reduction of natural frequency and flutter boundary,and the increase of flutter amplitude;the temperature gradient has little influence on flutter frequency,and has little influence on the dynamic stability of the cylindrical shell.The existence of temperature gradient will improve the flutter stability when the temperature at the front of the cylindrical shell is higher;the stability change caused by the change of mechanical properties can not be neglected;the change of thermal expansion coefficient has greater influence on the flutter aerodynamic force,while the elastic modulus has greater influence on the flutter frequency;increasing the 90 degree layer can obviously increase the flexural stiffness of the cylindrical shell and improve the stability and vibration of the cylindrical shell.The flutter boundary can be increased by increasing the dynamic frequency,especially when the 90 layer is placed outside,when the temperature gradient is large or the peak temperature is located at the front end of the cylindrical shell.By studying the influence of the laying angle of composite cylindrical shells on the static and dynamic instability of the cylindrical shells in thermal environment,it can provide guidance for the overall design of composite cylindrical shells in high-speed airflow,the optimization of the geometrical shape design of cylindrical shells,the selection of materials and the design of composite layers.