Introducing the new lattice structure based on the representative element double octagonal bipyramid

This study introduced a new lattice structure based on the representative volume element of a double octagonal bipyramid. The stiffness matrix of the lattice structure was extracted based on the superposition principal method using Euler-Bernoulli beam theory equations in this model. Analytical relationships were validated using the finite element and the stiffness matrix methods. In addition, the elasto-plasto-damage behavior was implemented into FE model which tracks the nonlinear response of considered structures. The lattice structure was experimentally fabricated using 3D printing technology. Its mechanical properties were studied using quasi-static compression and tensile tests and digital image correlation (DIC), which were consistent with each other. For this purpose, tensile and compressive coupon tests were printed and the load-unload tensile and compressive tests have been carried out. The new unit cell, based on the square unit cells due to its 32 inclined struts and 16 node connections, exhibited a higher stiffness and yield strength than the lattice structures. The results indicated that the different amounts of the elastic modulus could be achieved in the two directions and improved by another repeating arrangement of micro-architectures. Moreover, the optimal distribution of the mechanical properties was achieved by evaluating three lattice structures with the different percentages of functionally graded material (FGM) analytically. Finally, the geometric parameters affecting the mechanical properties of the lattice structure were analyzed.