Optimum Design Of Thermo-mechanical Coupling Buckling Of Stiffened Shells With Functionally Graded Material Thermal Barrier Coating

The grid stiffened shell is usually used as the load-carrying structure of heavy-lift launch vehicle due to its high strength and stiffness efficiency.At present,the metal alloy materials are mainly used in the grid stiffened shell of the launch vehicle.The ceramic foam is usually pasted on the outer surface of the stiffened shell,in order to prevent the stiffened shell from ablation or thermal buckling failure during the rocket launching.The physical properties of the metal alloy and ceramic foam are quite different,so there is a large stress concentration at the interface between the two materials in high temperature environment,which often produce cracks or delamination at the interface,resulting in the serious consequences.In this paper,the Functionally Gradient Materials(FGM)thermal barrier coating is used as a part of the skin of the grid stiffened shell.The stability loadcarrying capacity of the stiffened shell is simulated and studied in the uniform and linear temperature field.Smeared Stiffener Method(SSM)and the exact model are used to analyze the stability of the stiffened shell with FGM thermal barrier coatings in the uniform and linear steady temperature field.In the SSM method,the grid structure of ribs is equivalent to a continuous plate based on the homogenization principle with the same overall stiffness performance and the same height as ribs.The skin with FGM coating is simplified as a transverse isotropic laminated plate by using the delamination method.The stiffness matrix of the skin and the ribs is superimposed,and the position of neutral layer is adjusted.Then,the critical buckling load of the stiffened shell with FGM thermal barrier coating in thermal environment is derived by using the nonlinear geometric equation,the constitutive equation and the stability equation.In the exact model,the shell element is used to establish the numerical model of the stiffened shell,and the linear buckling and nonlinear buckling methods are used to solve the overall critical buckling load and the collapse load of the stiffened shell,respectively.The first eigenmode-shape imperfection and single dimple-shape imperfection are introduced to calculate the ultimate load of the stiffened shell and draw the imperfection sensitivity curve,and the influence of the imperfection amplitude on the load-carrying capacity of the stiffened shell is analyzed.The stiffened shell is optimized by genetic algorithm,and the single-objective and multiobjective optimization results based on the maximum critical buckling load and the minimum weight are obtained.The numerical analysis results show that the critical buckling load of the stiffened shell with FGM skin is 104.86 % higher than that of the pure metal stiffened shell without FGM.For the uniform and linear temperature rise,the load-carrying performance of the stiffened shell with FGM skin is greatly improved compared with that of the pure metal stiffened shell.The results of single-objective optimization of the maximum critical buckling load and minimum weight of FGM stiffened shells also prove this conclusion.It is foreseeable that the stiffened shell containing FGM will have a huge application prospect.