The Investigation On The Stability Problem Of Composite Thin-shell

For improving the performance and competitiveness of engineering structures, It is necessary to reduce the weight, improve the reliability, maintainability, viability and service life as well as reduce life cycle cost. The application of composites is one of the best ways to achieve these requirements because of its high strength and modulus, strong design characteristics and anti fatigue performance. Since 1970s, China has begun to research the advanced composite materials. Then the composites was applied into the aerospace field in the 80s. Nowadays, composite laminated plate and shell structures have been widely used in the aerospace, transportation, oil and chemical industry, construction and other fields. Meanwhile, it gave rise to study the mechanical behaviors of the composites structures. Especially, the buckling failure has been taken place for the plate and shell composites structures subjected to the excessive load. Therefore, it is necessary to investigate the buckling behavior and its stability for the composites structure.In this work, based on the classical laminated plate theory, Donnell flat shell theory and Flugge shell theory, the buckling loads were deduced for the composites thin-plate and cylindrical thin-shell subjected to the external loads without the reinforcement and with the orthogonal grid reinforcement. In addition, the finite element analysis software were used to verify the theoretical solutions. The main research contents are as follows.(1) The calculation method of the critical buckling load was studied systematically for of the composites rectangular thin-plate subjected to the uniaxial compressive load. And the maximum relative error was less than 5%.(2) The stability analysis was carried out for four types composites stiffened rectangular plates subjected to the uniaxial compressive loading.(3) Implanting a new displacement function and based on the Donnell flat shell theory and Flugge shell theory, the calculation formulation of the buckling critical load was constructed for the composites cylindrical thin-shell with the arbitrary layer form subjected to the external pressure. The modified coefficient was 1.11, which was verified by the finite element solution.(4) The critical buckling load expression was derived for the composites orthogonal grid reinforced cylindrical shell subjected to the external pressure, which was also verified by the finite element solution:the modified coefficient was 1.15 when it was reinforced outside; the modified coefficient was 1.12 when it was reinforced inside.The research results show that the analytical and numerical solutions were accurate and reliable. Especially for the complex structures, the numerical solution became an important tool to calculate the critical buckling load when the analytical one cannot be obtained. In addition, the effect of stiffness coefficient D16 and D26 on the buckling load should be taken into consider for the composites cylindrical shell when the length to diameter ration L/R is more than or equal to 1. For more than 8 layers skew symmetric equilibrium laying orth-grid stiffened cylindrical shell, the effect of stiffness coefficient D16 and D26 on the buckling load could be ignored.