SAMPE Journal - November/December 2021 - 57

INTRODUCTION
Lightweight composite structures are ubiquitous
in diverse industrial domains such as aerospace,
marine, automotive and construction sectors1,2
.
Moreover, composites are playing an important
role in achieving improved performance to weight
ratio in transport vehicles which can directly
impact fuel consumption and therefore help reduce
CO2 emissions3
. Carbon reinforced composites
are not only lightweight but they also display a
range of interesting mechanical properties such
as high specific tensile modulus and strength4,5
.
Besides their lower weight compared with metal
or ceramics, composites also can achieve greater
durability and resist corrosion and wear6
. All these
properties combined make them suitable for
lightweight structural applications.
Traditional composite manufacturing
technologies are limited by the high cost of tooling
(e.g. molds), complex setups and poor control
over fiber placement7
. Continuous fiber additive
manufacturing (CFAM) offers an innovative
solution to these shortcomings. As an additive
manufacturing technique, it is based on melt
extrusion of thermoplastic polymer filaments with
the added ability to locally deposit and orient fibers
where mechanical reinforcement is needed8,9
. It is
similar to automated tape laying but it offers greater
freeform possibilities allowing the creation of more
detailed and complex components. Additionally,
the mechanical properties can be tuned by making
smart use of the fiber placement based on how the
components will be used (i.e. loading conditions)10
.
Combining freeform designs with optimum fiber
placement promises additional weight gains
making components potentially much lighter.
In this work we aim to investigate the properties
of 3D printed continuous carbon fiber reinforced
parts as a function of composition and fiber layout.
We show the experimentally obtained mechanical
behavior of CFAM components under tension
and flexion compared with theory or numerical
models. Finally, we explore the manufacturing of a
complex design, namely a bike lug, using the here
EXPERIMENTATION
Materials and Printing Process
All 3D printing was performed using an Anisoprint
Composer A4 printer. This printer is equipped with
a thermoplastic polymer extrusion nozzle as well
as a composite nozzle that combines a continuous
carbon fiber filament and a thermoplastic
polymer filament. Continuous carbon fiber (CCF)
was obtained from Anisoprint, glycol-modified
polyethylene terephthalate (PETG) filament
(HDGlass) and short carbon fiber (sCF) filled
PET-G filament (CarbonFil) was obtained from
FormFutura BV. The printing temperature was
240°C for the HDGlass and 265°C for CarbonFil due
to its higher viscosity.
Printing and Mechanical Testing of Flat Beams
For flexural testing, rectangular beams of 50 x 10 x
2 mm were printed, with a nominal layer thickness
of 0.34 mm. For tensile testing, rectangular beams
of 250 x 15 x 1.6 mm were used, with a nominal
layer height of 0.32 mm. In all cases, incorporated
carbon fiber were placed parallel to the long axis
of the beam. For samples with maximum fiber
content, carbon fibers were spaced evenly in all
layers of the sample (see Figure 1). For samples
with less fiber content, fibers were either placed
in layers alternated with layers of unfilled PETG
(sandwich layout), or placed on the sides of the
sample in each layer (perimeter layout). Fiber
volume fraction was calculated based on the use
of PETG and CCF material in the printing process.
Mentioned fiber fractions refer to pure carbon fiber
content, corresponding to 60 vol% of CCF.
Tensile strength and Young's moduli were
determined using an Instron machine with a 100
kN force cell. The test speed was 1 mm/min until
sample break; the modulus is determined up to
0.25% stain.
Dynamic flexural moduli were determined
Figure 1. Schematic representation of the fiber layout in the test geometries: (left) maximum fiber
content, (middle) sandwich layout, i.e. vertically distributed, (right) perimeter layout, i.e. horizontally
distributed.
presented technique and evaluate its performance
with respect to a conventionally manufactured
carbon fiber lug.
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SAMPE Journal - November/December 2021

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