Beam Finite Element Model Modification Considering Shear Stiffness: Octet-Truss Unit Cell with Springs

This study investigates the effects of modifying a beam model for octet-truss lattice structures to calculate the homogenized material properties using the average stress method. While alignment is observed at low relative densities, the unmodified beam model derives underestimated results at higher relative densities, reaching up to 40% and 30% for elastic and shear modulus values, respectively, for a relative density of 0.5. Beam model modification achieved by increasing strut stiffness at the joints is investigated in detail, and we conclude that both modulus values cannot fit the solid model’s results with this type of modification. This study proposes a novel modification method involving seven spring elements with two constants to capture both the elastic and shear moduli. This study concludes by compensating differences between the solid and beam models’ moduli with the inserted springs, providing an analytical solution for the linear elastic system. The performance of the unit cell models is tested by solving two lattice structures at which the elastic modulus and shear modulus were dominant, respectively, on the mechanical behavior. The results converge to a constant value when the number of unit cells is six, and the beam with a spring model achieved a performance that was close to that of the solid model for the shear-modulus-dominant lattice structure.