Dynamic fracture of additively manufactured continuous-fibre composites under ballistic impact: experimental and numerical study

The ability to manufacture complex geometries with additive manufacturing (AM) has led to a significant increase in research in this field. Thermoplastic polymer-matrix composites are mostly fabricated using fused deposition modelling, and the addition of fibres demonstrated a considerable increase in strength and stiffness of resultant composites. Dynamic deformation and fracture of AM structures are investigated to optimise architectures for biomedical, industrial, and civil applications. This study focuses on the dynamic-fracture behaviour of AM continuous-carbon-fibre-reinforced composites with nylon polymer-matrix under ballistic impact. The mechanical behaviour of these composites exhibits brittle fracture under tension and ductile deformation under compression. Compared to short-carbon-fibre-reinforced AM composites with similar carbon content, the continuous-fibre composite had higher tensile and compressive moduli. Although the tensile strength was also found to be significantly higher than that of composites with short fibres, the elongation at break in tension and the compressive strength was lower. A ballistic test on a solid unidirectional plate was carried out using a 9 mm steel bullet at 100 – 120 m s−1. Complete perforation was achieved, with a circular hole at the front of the target and a delaminated damaged area at the back. The impact boundary conditions were replicated in finite-element simulations at 100 m s⁻¹. The material's linear elastic behaviour was modelled based on in-house mechanical characterisation tests, and a VUMAT of Hashin damage model was used for the description of impact damage with cohesive-surface modelling of the delamination failure. The simulation showed a good agreement with the experimentally observed damaged areas at the front and the back of the plate, indicating that traditional composite-material and damage models can be used to predict the dynamic impact fracture of AM composites.