Design and evaluation of 3D printed polymeric cellular materials for dynamic energy absorption

The design freedom to create complex shapes and parts is one of the major benefits offered by the 3D printing manufacturing process. The aim of this study is to utilize this advantage to tailor and optimize cellular materials for impact energy-absorbing applications. The energy-absorbing performance of two types of lattice structure, namely, octagonal and Kelvin lattices, is investigated numerically and compared to the out-of-plane performance of the traditional honeycomb, under two different loading conditions. Firstly, the relative density of the three structures is kept constant and each structure is subjected to three different compression loading rates. Secondly, the three structures are designed to have the same stress threshold of 1MPa at a loading rate of 3.5m/s produced at the maximum energy-absorbing efficiency strain epsilon eta max, and they are subjected to an impact mass and an initial velocity of 1.75kg and 3.5m/s, respectively. For the second condition, an empirical relationship is established to relate the design parameters of each structure to the peak stress produced at the epsilon eta max. Compression experiments are performed on the standard specimens of the thermoplastic base material at different strain rates to characterize its dynamic properties and rate sensitivity, for the numerical modeling. The finite element approach is validated against experimental results of published studies. The numerical results show that when the relative density is kept constant, the out-of-plane energy absorption of the traditional honeycomb, which is known for its high-energy absorption, significantly outperforms the two lattices for all loading rates. However, when the stress threshold is kept constant, the results show that both lattices can provide better energy-absorbing performance than the honeycomb. Finally, a methodology is developed to improve the energy absorption of the octagonal lattice and the traditional honeycomb; this enhances their energy-absorbing efficiency significantly, from 57 to 63% and from 44 to 61%, respectively.