Optimization for buckling loads of grid stiffened composite panels

An improved smeared method is developed to model the buckling problem of an isogrid stiffened composite cylinder. In this model the stiffness contributions of the stiffeners is computed by analyzing the force and moment effect of the stiffener on a unit cell. The equivalent stiffness of the stiffener/shell panel is computed by superimposing the stiffness contribution of the stiffeners and the shell. The equivalent stiffness parameters are then used to calculate the buckling load of the stiffened cylinder. A 3-D finite-elements model is also built that takes into consideration the exact geometric configuration and the orthotropic properties of the stiffeners and the shell. Experimental analysis is also performed to compliment the two analytical methods used to determine the buckling load of the stiffened cylinder. Results of the three types of analyses methods are compared. Finally a parametric study is carried out and general conclusions are drawn regarding optimum configurations of the different parameters of the grid-stiffened cylinder.