Interlaminar shear behaviour of additively manufactured continuous fibre-reinforced composites using MWCNT-coated filaments

The unsatisfactory interlaminar performance in additively manufactured continuous fibre-reinforced composites (CFRCs) remains a major challenge inherent to the printing process. Incorporating multi-walled carbon nanotubes (MWCNTs) has improved interlaminar performance in traditionally manufactured laminates. However, the use of MWCNTs in additively manufactured CFRCs has received little attention to date. This study investigates the interlaminar shear behaviour of additively manufactured CFRCs enhanced via coating MWCNTs on the surface of continuous fibre filaments. An automatic layer-by-layer coating process was developed to coat two types of fibre filament materials: glass fibre filaments (GFF) and carbon fibre filaments (CFF). Multilayer MWCNTs were deposited onto the filaments by sequentially adsorbing positively charged polyethyleneimine (PEI) and negatively charged MWCNTs via electrostatic self-assembly process. The automated process promoted uniform MWCNT coating through precise control of the filament speed. The redesigned coating baths allowed the filament to pass over a thin layer of solution without contacting rollers, thereby avoiding mechanical damage associated with the previous roller-based system. MWCNTs were successfully deposited on both GFF and CFF. The contribution of MWCNTs to the interlaminar shear properties differed between CFF and GFF in terms of tangent modulus, maximum load and ultimately the short beam strength. With a single layer of MWCNTs, the maximum short beam shear load improved by 4% and 14% for CFF and GFF composites, respectively. The addition of 1–5 MWCNT layers enhanced the tangent modulus across all tested configurations, ranging 12–20% for CFF and 30–96% for GFF. The effects of MWCNTs on the stiffness were more pronounced for GFF samples than stiffer CFF samples. The integration of MWCNTs into additively manufactured CFRCs would facilitate the production of customised lightweight components with improved interlaminar performance.