Deformation and fracture of PLA honeycomb samples under dynamic loading

The search for and investigation of new porous materials with a bionic honeycomb structure is an urgent scientific problem due to the active development of additive technologies. The aim of this study is to examine the effect of the morphology of PLA (polylactide, C3H4O3) samples with a honeycomb structure based on a triply periodic minimal surface, namely the Schwarz-Diamond surface, on their impact resistance under dynamic (ballistic) loading. To produce samples with the Schwarz-Diamond surface, a software, which generates G-Code using surface equations, is developed. The honeycomb samples are manufactured from PLA filaments via fusion deposition modeling (FDM) using a Picasso 3D printer. The dimensions of the cells in the samples vary from 1 to 5 mm, which corresponds to the large honeycomb morphology. Ballistic tests are conducted on an experimental test setup comprising a Crossman 2100 classic BB pneumatic pump air rifle, a device for recording the velocity of a spherical projectile (ball), and a pocket to arrange a test sample and to catch the ball and fragments. The analysis of deformation and fracture of the PLA samples reveals that the fracture pattern after ballistic impact tests is dependent on density and exhibits a transition from ductile to quasi-brittle behavior. Quasi-brittle fracture behavior is observed in the samples with the highest density (0.93 g/cm³). The mechanical properties of the Schwarz-Diamond surface structures are found to be moderate. Therefore, such structures can be used as reinforcement in various applications, including building materials, aerospace components, and automotive parts.