Influence of geometry, reinforcement, and sterilisation on the dimensional accuracy of additively manufactured carbon fibre-reinforced nylon composites

Dimensional accuracy is a critical quality metric in manufacturing, particularly for medical devices subjected to sterilisation and disinfection. While additive manufacturing (AM), especially fused filament fabrication (FFF), facilitates the production of complex geometries, challenges such as void formation, surface deformation, and mechanical instability persist. This study evaluated the impact of sterilisation (autoclaving) and disinfection (ethanol) on the dimensional stability of 3D-printed carbon fibre-reinforced polymer (CFRP) parts. Two geometries - representing standard ASTM D3039 and complex non-standard designs - were printed using carbon fibre nylon-based composites with and without continuous carbon fibre (CCF) reinforcement. Dimensional accuracy and void fraction were assessed using micro-CT imaging and geometrical comparison analysis. While sterilisation (p = 0.247) and disinfection treatments (p > 0.05) had negligible overall effects on dimensional stability and void fraction, geometric design (p = 0.0036) and CCF inclusion (p = 0.0042) significantly influenced shape fidelity. The inclusion of CCF reinforcement enhanced resistance to deformation under external stressors, though its efficacy varied with design complexity. A significant interaction between geometry and CCF inclusion (p < 0.0001) demonstrated the dependency of void formation on design complexity and reinforcement. Additionally, maximum surface deviation was independently influenced by geometry (p = 0.0139) and CCF reinforcement (p = 1.1 × 10⁻⁴). This study highlights the strategic imperative of design optimisation and informed material selection to increase precision in additive manufacturing. By addressing the confluence of manufacturing constraints and stringent regulatory mandates, this research reinforces the viability of additive manufacturing for medical device fabrication, advocating for customised methodologies to harmonise functionality with compliance requirements.