Assessing Impact Performance of an Elastomeric Cubic + Octet Lattice Structure

Impacts are seen across a wide variety of scenarios and depending on the rates and severity of these collisions there are harmful effects that can occur to structures, humans, and surroundings. Materials such as lattice structures, foams, and honeycombs have been used and continue to be developed and studied to mitigate impact forces. Studies focus on energy absorption and material stiffness of these structures to determine what is needed to mitigate the impact. One metamaterial, a cubic + octet lattice structure, has been shown to have a high stiffness-to-weight ratio which may be promising as an impact mitigating material. Previous studies with this lattice structure were conducted by 3D printing the cubic + octet structure with an elastomer material and testing at low and high rates of compression replicating a wide range of impacts. However, the material properties were not identified in these efforts. The goals of this thesis are to assess the mechanical properties of this lattice structure by quantifying the properties of its constitute material, creating and validating a constitutive model of the material in a simulation environment, and using modeling to explore how adjustments to various components will change the performance of the cubic + octet structure. The first part of this thesis explores the mechanical properties of an elastomeric material via experimental dogbone testing at various rates of loading. These properties were fit to an Ogden hyperelastic constitutive model based on the experimental data. Finally, the constitutive model was implemented into a simulated tensile dogbone test to validate the material against the experimental results. The second part of this thesis involved implementing the elastomeric material into a computational model of a puck based on the cubic + octet lattice. Simulations of the puck were compared to experimental compression tests of a puck for both low rate and high rate impacts. Other parameters associated with the fabrication of the puck, such as the density and thickness of the lattice puck, were explored in the simulation to create a comparable simulated mass to the experimental lattice pucks. Due to the high rate nature of the impact tests, the introduction of airflow within the lattice was necessary to create a buildup of air pressure that is seen in experimental testing. Lastly, the lattice puck components were explored by modifying attributes such as height, width, holes, and thicknesses to see how this would affect the performance of the structure. Generalized equations for the stress and mass of the lattice puck were also formulated to go along with the future adjustments without the need to run simulations for these results. This research creates a framework for validating and adjusting the cubic + octet lattice puck components to optimize impact responses for the specific use of the structure.