Dynamic fracture behaviour of additively manufactured polymers and composites under ballistic impact

Recent technological advancements led to active research in the field of additive manufacturing (AM) thanks to its ability to fabricate complex structures with reduced material waste. While many studies focused on quasi-static performance of AM materials and structures, investigations on the dynamic performance of these materials are still limited, especially for polymers and composites. The aim of this research is to investigate the dynamic fracture behaviour of AM polymer composites under ballistic impact. Nylon reinforced with short carbon fibres was selected, and fused deposition modelling was used to fabricate solid quasi-isotropic structures. Quasi-static tensile and compression tests were carried out based on ASTM standards to characterise the elastic-plastic properties of the manufactured material. Based on these tests, the material’s deformation and fracture behaviour can be considered elastic-brittle. Further, dynamic mechanical analysis was conducted under a frequency sweep at room temperature to examine the viscoelastic properties; the material exhibited high elastic behaviour. Then, ballistic impact tests were performed on solid plates using a gas gun with 9 mm spherical steel projectiles at velocities ranging from 95 m s^-1 to 120 m s^-1. Post-experimental observation revealed the complete target perforation, with a circular hole at the front of the plates and delamination at the back. The dynamic experimental conditions were reproduced within the finite-element simulations, employing Hashin damage criteria via a user subroutine. A similar perforation was achieved at the front of the plate.