Imperfection Sensitivity Of Composite Cylindrical Shell Under External Pressure

Laminated composite cylindrical shells have been widely used in the aerospace,ship and other fields due to their high specific strength and stiffness to weight ratios.As a typical thin-walled structure,the loading capacity of the cylindrical shell structure is very sensitive to the initial imperfections of the structure,which leads to the fact that the actual loading capacity of the cylindrical shell is much smaller than the ultimate loading capacity based on the theoretical or numerical prediction methods of the perfect model.The initial imperfections mainly include the initial geometric imperfections and material defects,in which delamination is the most important material defect.In this paper,the effect of initial geometric imperfections and delamination on the loading capacity of composite cylindrical shells under external pressure is studied by VCCT numerical technique.Based on the surrogate-based model optimization method,a new method for predicting the knockdown factor of cylindrical shell under external pressure is established.This method has strong defect coverage and robustness of design.The main works of this paper are as follows:(1)Based on the B-R criterion,a method to determine the instability of composite cylindrical shell under external pressure is established,and the limit load of the composite cylindrical shell is obtained.The geometrical imperfections sensitivity of the composite cylindrical shell are analyzed by introducing the dimple-shape imperfection,multiple dimple-shape imperfection,eigenmode-shape imperfection or measured imperfection into the perfect cylindrical shell.(2)The finite element model of the composite cylindrical shell with a rectangle delamination is established by using the finite element software ABAQUS.Based on the VCCT numerical technique,the delamination growth behavior is simulated.The effect of delamination sizes,delamination height positions,delamination depth positions on the loading capacity of composite cylindrical shell is studied.(3)Based on the surrogate-based model optimization method,a new method for predicting the external pressure knockdown factor is established.The method can cover the influence of the material defects and geometric imperfections on the loading capacity of the composite cylindrical shell.Compared with NASA SP-8007 and ASME 2007 design guidelines,the method of this paper can improve the value of the knockdown factor to a certain extent,and the increase of knockdown factor is reasonable.In paper,the method for predicting the knockdown factor of cylindrical shell under external pressure is higher than the existing methods.