Structure–Property Relationships and Energy Absorption of FFF-Manufactured PETG Honeycomb-Type Structures for Automotive Applications

This study explores the quasi-static and dynamic responses of irregular, honeycomb-like topologies made from glycol polyethylene terephthalate (PETG) with various sparse infill densities, using fused filament fabrication (FFF) manufacturing technology. Both tensile and flexural tests revealed a linear increase in Young’s modulus and sample strength as infill density increased, under constant printing and testing conditions. Below 50% infill, this trend remained unchanged, despite cells being irregular and fracture mechanics differing. Low-velocity impact tests were conducted at a velocity of 1.5 m/s, equivalent to an incident energy of 6.2 J. Regarding dynamic responses, irregular honeycomb-like structures use 12.5–25% of the nominal pendulum energy during complete fracture in Charpy tests, and 74.3–98.3% of total available energy during low-impact crushing. Samples with infill densities of 15% and 25% revealed higher absorbed energy values of around 6.5 and 6.1 J, respectively, compared with denser samples. Although they exhibit more favorable mass-specific energy absorption, these samples collapse more quickly than their stiffer 50–100% counterparts. The findings provide valuable insights into irregular, honeycomb-like structures and open up perspectives for optimization and component-level assessment, with potential applications as impact-resistant, secondary/non-structural components for the automotive industry.