H Shahsavari Alavijeh - Graduate student,
S Sadeghnejad Limouei - Graduate student
M Sadighi - Associate Professor, Department of Mechanical Engineering, Amirkabir University of Technology, Hafez Ave., Tehran, Iran

Grid Stiffened Composite Structures are the most attractive lightweight which their optimal design would lead to a stretching dominated structure. Due to possibility of usage of various forms of grids in manufacturing process of lattice composite structures, it is necessary to have a deeper knowledge of the unit cells of these grids. In this article, different kinds of grids known as, Bi-Grid with two stacks of struts, Tri-Grid with three stacks of struts and Quadri-Grid with four stacks of struts have been investigated. Three different kinds of unit cell with different dimensions for mentioned grids with equal area and mass have been assumed. Iso-grid as a special case of Tri-grid has also been studied. Then stiffness matrix has been developed theoretically and the results have been compared to each other. The analysis has been developed in accordance with the equivalent continuum method and coordinates transformation by considering the anisotropic properties of the stiffness of lattice grid composites. Also, numerical investigation is followed using ANSYS FEM code to verify the analytical results. In addition of the comparison of the results, a parametric study is discussed to check the geometrical parameters’ effects on the stiffness matrix for different kinds of mentioned grids.

Grid Stiffened; Quadri-Grid; stiffness matrix; Bi-Grid; equivalent continuum method