ANALYSIS AND OPTIMUM DESIGN OF COMPOSITE GRID STRUCTURES

An integrated equivalent stiffness model is developed to describe a gr id structure with or without laminate skins. The in-plane bending and shear of ribs are included without introducing any extra degree of fre edom so that Mindlin's plate theory can still be adopted. As a result, the model can be directly incorporated with the existing FEM techniqu e and take advantage of commercial codes. The proposed model is demons trated to be efficient and reasonably accurate. If high precision is r equired, the equivalent stiffness model can be incorporated with the e xact FEM modeling to obtain a refined stress analysis. Hygrothermal be havior and local buckling are also taken into account. Using the model as a tool, the performance of composite grid structures can be compar ed to traditional laminates, sandwich plates and metal grid structures . A method of optimum design is established to design a grid structure with or without laminated skins. Multiple loads and multiple failure mechanisms are considered. Discrete design is also included. Furthermo re, the method can be easily incorporated with FEM to perform structur al optimization. The optimization code is demonstrated to be a very po werful design tool. Finally, a user-friendly computer code is develope d to perform the above tasks.