Numerical and experimental study on the collapse of a triangular cell under compression

Lattice materials can be described as arrangements of cell walls such as beams with joints of high stiffness. Loads on the macroscopic level of the lattice material can cause a loss of structural stability on the microscopic level and lead to buckling of cell walls. In this study the buckling and post-buckling deformation of a triangular cell with elasto-plastic material behavior is investigated in finite element (FE) analyses under compressive loading. The triangular cell is discretized with beam elements and the outcome is compared to simulations using a fine mesh of continuum elements. Both discretizations are investigated in nonlinear FE simulations since regular linear stability analysis cannot consider elasto-plastic material behavior and contact. In addition, the collapse of the triangular cells is studied experimentally with selective laser melted samples. The beam element model is capable of predicting the collapse behavior as well as the reaction force determined in the experiments and FE analyses with continuum elements. By applying eigenmodes from buckling analyses as initial imperfection to the triangular cell the beam element model is able to predict mode changes in the post-buckling regime. The magnitude of imperfection is thereby in agreement with the geometrical deviation of the samples introduced by the selective laser melting (SLM) process. The outcome of the study is a methodology for investigating lattice materials computationally efficient with FE analyses and taking multiple nonlinearities into account. Consequently, it can be used to study two- or three-dimensional lattice structures with a large number of cell walls, nonlinear parent material and instability effects.