DESIGN AND STIFFNESS OPTIMIZATION OF QUADRI-DIRECTIONAL COMPOSITE GRID LATTICE STRUCTURES

Abstract

Composite grid structures are rib stiffeners connected to each other rigidly in a pattern or a lattice such that the whole grid pattern has certain smeared stiffness property and has a certain structural behavior. The main focus of this thesis is to design the geometric pattern of a Quadri-directional composite grid lattice such that it has the prescribed stiffness moduli. The research is divided into three phases, in the first phase, the equation for stiffness moduli, the reduced stiffness matrix [Q] and the laminate stiffness matrices [ABD] of the grid pattern is derived for Quadri-directional grid panels. In the second phase, two methods are developed and discussed to obtain maximum stiffness moduli from the grid structure. • The explicit stiffness moduli equations of the grid structure is solved to obtain the design variables by giving the required stiffness moduli as the resultant vector. • Multi-objective genetic algorithm is used to optimize the design variables in the given range such that vital stiffness moduli is maximized. A MATLAB code is generated for both the methods and the values of the design variables is extracted to be developed as a latticed structure. In the third phase, a Finite Element Model is developed in Hypermesh order to validate the results obtained from the code and analyze the behavior of the grid structure in both the cases.