Modeling 3D-Printed Composite Honeycomb Structures with the Representative Lattice Element Method

The goal of our research was to develop and validate a method for predicting the mechanical behavior of Additively Manufactured multi-material honeycomb structures. Multiple approaches already exist in the field for modeling the behavior of cellular materials, including the bulk property assumption, homogenization and strut level characterization [1]. With the bulk property approach, the structure is assumed to behave according to what is known about the material in its bulk formulation, without regard to its geometry or scale. With the homogenization technique, the specimen that is being tested is treated as a solid material within the simulation environment even if the physical specimen is not. Then, reduced mechanical properties are assigned to the specimen to account for any voids that exist within the physical specimen. This approach to mechanical behavior prediction in cellular materials is shape dependent. In other words, the same model cannot be used from one specimen to the next if the cell shapes of those lattices differ in any way. When using the strut level characterization approach, a single strut (the connecting member between nodes constituting a cellular material) is isolated and tested. With this approach, there tends to be a significant deviation in the experimental data due to the small size of the isolated struts. Yet it has the advantage of not being shape sensitive, at least in principle. The method that we developed, and chose to test lies within the latter category, and is what we have coined as the Representative Lattice Element (RLE) Method. This method is modeled after the well-established Representative Volume Element (RVE) method [2]. We define the RLE as the smallest unit over which mechanical tests can be conducted that will provide results which are representative of the larger lattice structure. In other words, the theory is that a single member (or beam in this case) of a honeycomb structure can be taken, tests can be conducted on this member to determine the mechanical properties of the representative lattice element and the results will be representative of the mechanical behavior whole structure. To investigate this theory, we designed specimens, conducted various tensile and compression tests, analyzed the recorded data, conducted a micromechanics study, and performed structural simulation work using commercial Finite Element Analysis software.