The effect of 3D printing parameters on the mechanical properties of material extrusion-printed carbon fiber reinforced nylon

Abstract

Material Extrusion (MEx) Additive Manufacturing, particularly with Fiber Reinforced Polymer (FRP) composites, such as carbon fiber-reinforced (CFR) nylon, is increasingly used to produce functional parts. However, the mechanical properties of parts produced on widely available desktop systems are highly anisotropic and dependent on process parameters. This thesis investigates the effect of two key slicer parameters, infill orientation and the number of wall contours, on the tensile properties and fracture behavior of MEx-printed CFR Nylon 12. ASTM D638 Type V tensile specimens and custom notched-bar samples were manufactured on a desktop MEx printer. Four infill orientations (0°, 90°, 45°, and alternating 45°/135°) and two contour settings (0 and 3 contours) were tested. Tensile testing was performed using an Instron machine, with strain data captured via Digital Image Correlation (DIC). Fracture analysis was conducted on the notched samples. The results demonstrate that both parameters significantly influence the material's tensile strength and modulus. The 90° infill orientation (parallel to the loading direction) exhibited the highest tensile strength, approximately 1.8 times greater than the 0° (perpendicular) orientation. The addition of three wall contours consistently increased the maximum load and stress at failure across all infill directions compared to samples with zero contours. Fracture analysis of notched bars confirmed that failure paths followed the weakest direction, parallel to the infill lines, a behavior that was mitigated by the inclusion of contours. This study quantifies the significant impact of infill and contour settings on the mechanical performance of desktop-printed carbon fiber nylon, highlighting the critical importance of design-for-manufacturing in MEx and the consistency challenges of hobby-level equipment for engineering applications.