High Strain Rate Response of Additively-Manufactured Plate-Lattices: Experiments and Modeling

Plate-lattices are a new emerging class of isotropic cellular solids that attain the theoretical limits for the stiffness of porous materials. For the same mass, they are significantly stiffer than random foams or optimal truss-lattice structures. Plate-lattice structures of cubic symmetry are fabricated from stainless steel 316L through selective laser melting. A special direct impact Hopkinson bar system is employed to perform dynamic compression experiments at strain rates of about 500/s. In addition, tensile specimens are manufactured for characterizing the stress-strain response of the additively-manufactured cell wall material for strain rates ranging from 10(-3) to 10(3)/s. The results show that plate-lattices of a relative density of 23% crush progressively when subject to large strain compression. Their specific energy absorption increases by about 8% when increasing the applied strain rate from 0.001 to 500/s, which is primarily attributed to the strain rate sensitivity of the base material. Good quantitative and qualitative agreement between the experiments and the simulations is observed when using a detailed finite element model of the plate structures in conjunction with a modified Johnson-Cook model. The comparison of the simulation results for plate- and truss-lattices of the equal-density reveal a 45% increase in specific energy absorption. Compression experiments on Ti-6Al-4V lattices revealed a low energy absorption due to the early fracture of the additively-manufactured cell wall material.