The resistance to macrocrack propagation in two-dimensional periodic cellular
materials subjected to uniaxial remote stresses is improved by redistributing the
material of the solid phase. The materials are represented by beam lattices with
regular triangular or hexagonal patterns. The purpose of the design is to minimize
the maximum tensile stress for all possible crack locations allowed by the material
microstructure. Two design cases are considered. In the cell design case material is
redistributed between the otherwise uniform elements of the repetitive cell. In the
element design case the shape of identical elements is optimized. The analysis of such
infinite trellis with an arbitrary macroscopic crack is enabled by an efficient exact
structural analysis approach. It is shown that the fracture toughness of the triangular
layout can be significantly increased by redistribution of the material between the
elements with uniform cross sections while for the case of hexagonal lattice the
effect is achieved mainly by using identical elements with variable thickness
distribution.