Open Hole Tension of 3D Printed Aligned Discontinuous Composites

Abstract

This paper explores the use of Discontinuous Aligned Fibre Filament (DcAFF), a novel discontinuous fibre reinforced thermoplastic filament for 3D printing, to produce structural complex parts. Compared to conventional composite manufacturing, 3D printing has great potential in steering fibres around small structural features. In this current study, the initial thin carbon fibre (CF)-poly(L-lactic acid) (PLA) tape, produced with the High Performance Discontinuous Fibre (HiPerDiF) technology, is now reshaped into a circular cross-section filament, the DcAFF, using a bespoke machine designed to be scalable to high production rates rather than using a labour-intensive manual moulding method as in previous work. The filaments are then fed to a general-purpose 3D printer. Tensile and open-hole tensile tests were considered in this paper for mechanical and processability of DcAFF. The 3D printed specimens fabricated with the DcAFF show superior tensile properties compared to other PLA-based 3D printed composites, even those containing continuous fibres. Curvilinear open-hole tensile test samples were fabricated to explore the processability and performances of such material in complex shapes. The mechanical performance of the produced specimens was benchmarked against conventionally laid-up specimens with a cut hole. Although the steered specimens produced have lower strength than the fully consolidated samples, the raster generated by the printing path has turned the failure mechanism of the composite from brittle to ductile.

Mechanical performance of carbon fiber‐reinforced polymer cellular structures manufactured via fused filament fabrication

“…This anisotropy results from a combination of fusion effects described above and the strengthening due to the preferential orientation of the fibers along the printing lines (see Figure 3). Such alignment of the fibers results in enhanced strength and modulus in the direction of alignment, 41,42 as well as superior performance in more complicated loading geometries such as open hole tension 43 …”

“…Such alignment of the fibers results in enhanced strength and modulus in the direction of alignment, 41,42 as well as superior performance in more complicated loading geometries such as open hole tension. 43 While the FFF process does not have the means to control the fiber orientation directly, it induces rotations due to shear flow as the thermoplastic goes through the nozzle orifice. 44,45 We observed through microscopy that the fibers in the as-received filament are also primarily aligned towards the filament axis due to the extrusion process employed in manufacturing.…”

Steering Potential for Printing Highly Aligned Discontinuous Fibre Composite Filament

“…A dry-aligned discontinuous fibre preform (approximately 24-26 g/m 2 ) produced using the HiPerDiF method was impregnated with a thin PLA tape (62 g/m 2 ). The composite tape was reshaped into a circular cross section filament using a bespoke filament-forming machine [24]. The filament This paper aims to explore routes for improving the FFF printing accuracy of DcAFF material.…”

“…The high level of fibre alignment and the use of short fibres, which are longer than the critical fibre length, leads to high mechanical performance that matches continuous fibre composites while providing better formability [23]. The DcAFF is obtained by reshaping a thin HiPerDiF tape to a circular cross section (0.8 mm diameter) using a purpose-designed machine [24]. When combined with poly(L-lactic acid), or PLA, as the matrix, the DcAFF-PLA mechanical performance is superior to other PLA composite 3D printed materials reported in the literature [24,25].…”

“…The DcAFF is obtained by reshaping a thin HiPerDiF tape to a circular cross section (0.8 mm diameter) using a purpose-designed machine [24]. When combined with poly(L-lactic acid), or PLA, as the matrix, the DcAFF-PLA mechanical performance is superior to other PLA composite 3D printed materials reported in the literature [24,25]. However, the printability of DcAFF has not been broadly studied.…”