ArticlePDF Available

Abstract and Figures

Additive manufacturing (i.e., 3D printing) has rapidly developed in recent years. In the recent past, many researchers have highlighted the development of in-house filaments for fused filament fabrication (FFF), which can extend the corresponding field of application. Due to the limited mechanical properties and deficient functionality of printed polymer parts, there is a need to develop printable polymer composites that exhibit high performance. This study analyses the actual mechanical characteristics of parts fabricated with a low-cost printer from a carbon fibre-reinforced nylon filament. The results show that the obtained values differ considerably from the values presented in the datasheets of various filament suppliers. Moreover, the hardness and tensile strength are influenced by the building direction, the infill percentage, and the thermal stresses, whereas the resilience is affected only by the building direction. Furthermore, the relationship between the mechanical properties and the filling factor is not linear.
Content may be subject to copyright.
machines
Article
Investigation of the Mechanical Properties
of a Carbon Fibre-Reinforced Nylon Filament
for 3D Printing
Flaviana Calignano 1, * , Massimo Lorusso 2, Ignanio Roppolo 3and Paolo Minetola 1
1
Department of Management and Production Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24,
10129 Turin, Italy; paolo.minetola@polito.it
2Istituto Italiano di Tecnologia, Center for Sustainable Future Technologies IIT@Polito, Corso Trento 21,
10129 Turin, Italy; massimo.lorusso@iit.it
3Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi 24,
10129 Turin, Italy; ignazio.roppolo@polito.it
*Correspondence: flaviana.calignano@polito.it; Tel.: +39-011-090-7218
Received: 19 July 2020; Accepted: 2 September 2020; Published: 4 September 2020


Abstract:
Additive manufacturing (i.e., 3D printing) has rapidly developed in recent years.
In the recent past, many researchers have highlighted the development of in-house filaments
for fused filament fabrication (FFF), which can extend the corresponding field of application. Due to
the limited mechanical properties and deficient functionality of printed polymer parts, there is a need
to develop printable polymer composites that exhibit high performance. This study analyses the actual
mechanical characteristics of parts fabricated with a low-cost printer from a carbon fibre-reinforced
nylon filament. The results show that the obtained values dier considerably from the values
presented in the datasheets of various filament suppliers. Moreover, the hardness and tensile strength
are influenced by the building direction, the infill percentage, and the thermal stresses, whereas
the resilience is aected only by the building direction. Furthermore, the relationship between
the mechanical properties and the filling factor is not linear.
Keywords:
additive manufacturing; 3D printing; fused filament fabrication; carbon fibre;
mechanical testing
1. Introduction
Additive manufacturing (i.e., 3D printing) is constantly evolving due to open source technologies [
1
3
]
and the possibility of producing complex geometries with lower costs, faster production times, and less
waste [
4
6
] than traditionally manufactured parts [
7
]. Moreover, with the increase in available materials,
3D printing has found applications in the aerospace and architectural industries (e.g., creating complex
lightweight and structural models) [
8
,
9
], art fields [
10
,
11
], and medical fields (e.g., printing tissues
and organs) [
12
,
13
]. However, most plastic 3D printed products are still used primarily as conceptual
prototypes rather than functional components because of the poor mechanical and functional
properties of the neat polymer used in 3D printing. The development of polymer composites solves
these problems [
14
]. The incorporation of fibre and nanomaterial reinforcements into polymers
allows the manufacture of polymer matrix composites, which are characterized by high mechanical
performance and excellent functionality [
14
,
15
]. One process that has been extensively utilized in
the fabrication of polymeric 3D printed parts is fused deposition modelling (FDM), which was
developed by Stratasys Inc. In 2009, Stratasys’s FDM printing patent expired, opening up the market
for low-cost FDM 3D printers. For non-Stratasys 3D printers, this process is usually referred to as fused
filament fabrication (FFF). In FFF, a thin filament wire is extruded through a heated nozzle (Figure 1).
Machines 2020,8, 52; doi:10.3390/machines8030052 www.mdpi.com/journal/machines
Machines 2020,8, 52 2 of 13
The FFF head moves in the x and y directions, whereas the platform moves in the z direction. The part
is manufactured by the sequential build-up of these layered depositions, during which each new layer
fuses with material that has already been deposited. The final strength, quality, cost and production
time of the parts fabricated by FFF are influenced by some process parameters, such as layer thickness,
infill pattern, extruder uniformity and/or build-bed temperature, and by the presence of reinforcing
materials (e.g., carbon fibres, glass fibres [16]).
Machines 2020, 8, x FOR PEER REVIEW 2 of 13
fabrication (FFF). In FFF, a thin filament wire is extruded through a heated nozzle (Figure 1). The FFF
head moves in the x and y directions, whereas the platform moves in the z direction. The part is
manufactured by the sequential build-up of these layered depositions, during which each new layer
fuses with material that has already been deposited. The final strength, quality, cost and production
time of the parts fabricated by FFF are influenced by some process parameters, such as layer thickness,
infill pattern, extruder uniformity and/or build-bed temperature, and by the presence of reinforcing
materials (e.g., carbon fibres, glass fibres [16]).
Figure 1. Fused filament fabrication process.
Some researchers have correlated the build orientation (Figure 2b) to the mechanical properties
of the part [17–22]. The variations in quality of the melt between adjacent filaments results in a
degradation in mechanical properties (tensile strength, compressive strength, flexural strength,
hardness, and elastic modulus), especially for parts tested perpendicular to the direction of layer
construction. In addition to the orientation of the part on the building platform, the mechanical
properties of FFF parts are also significantly influenced by the process parameters of inherent
layering (Figure 2a,c), such as the layer thickness, raster angle, raster width, infill pattern and air gap
[17,22–25]. Ahn et al. [23] determined that both the air gap and the raster orientation had significant
effects on the resulting tensile strength, whereas these factors did not affect the compressive strength.
A similar study was carried out by Sood et al. [17] with varying factors of layer thickness, build
orientation, raster angle, raster width, and air gap: the tested factors influenced the mesostructural
configuration of the built part and the bonding and distortion within the part. Lužanin et al. [26]
studied the effects of layer thickness, deposition angle and infill percentage on the maximum flexural
force in FFF specimens made of polylactic acid (PLA) and concluded that layer thickness has the
maximum effect on the flexural strength followed by the interaction between the deposition angle
and the infill percentage. Despite its advantages over conventional manufacturing processes, FFF
parts often exhibit low mechanical properties. One of the possible methods to improve the strength
of FFF parts is adding reinforcing materials, such as carbon fibres, into pure thermoplastic matrix
materials to form carbon fibre-reinforced thermoplastic composites [27–29]. Several studies have been
conducted related to FFF and carbon fibre (CF) composites. A list of various studies of FFF with
chopped fibre-reinforced thermoplastics is given in Table 1.
Figure 1. Fused filament fabrication process.
Some researchers have correlated the build orientation (Figure 2b) to the mechanical properties of
the part [
17
22
]. The variations in quality of the melt between adjacent filaments results in a degradation
in mechanical properties (tensile strength, compressive strength, flexural strength, hardness, and elastic
modulus), especially for parts tested perpendicular to the direction of layer construction. In addition
to the orientation of the part on the building platform, the mechanical properties of FFF parts are
also significantly influenced by the process parameters of inherent layering (Figure 2a,c), such as
the layer thickness, raster angle, raster width, infill pattern and air gap [
17
,
22
25
]. Ahn et al. [
23
]
determined that both the air gap and the raster orientation had significant eects on the resulting
tensile strength, whereas these factors did not aect the compressive strength. A similar study was
carried out by Sood et al. [
17
] with varying factors of layer thickness, build orientation, raster angle,
raster width, and air gap: the tested factors influenced the mesostructural configuration of the built part
and the bonding and distortion within the part. Lužanin et al. [
26
] studied the effects of layer thickness,
deposition angle and infill percentage on the maximum flexural force in FFF specimens made of
polylactic acid (PLA) and concluded that layer thickness has the maximum effect on the flexural strength
followed by the interaction between the deposition angle and the infill percentage. Despite its advantages
over conventional manufacturing processes, FFF parts often exhibit low mechanical properties. One of
the possible methods to improve the strength of FFF parts is adding reinforcing materials, such as
carbon fibres, into pure thermoplastic matrix materials to form carbon fibre-reinforced thermoplastic
composites [
27
29
]. Several studies have been conducted related to FFF and carbon fibre (CF) composites.
A list of various studies of FFF with chopped fibre-reinforced thermoplastics is given in Table 1.
Machines 2020, 8, x FOR PEER REVIEW 3 of 13
Table 1. A summary of some studies on FFF with chopped fibres.
Reinforcement Matrix
Material
Investigated
Properties Limitations References
Carbon fibres ABS Tensile strength and
tensile modulus
Porosity, weak interfacial adhesion
between the fibres and the matrix
and fibre breakage
[27]
Vapour-grown
carbon fibres ABS Tensile strength and
tensile modulus
Interlayer fusion, intralayer fusion,
and a change from ductile to brittle
behaviour
[28]
Carbon fibres ABS
Strength, stiffness,
thermal properties,
distortion, and
geometric tolerances
[30]
Carbon fibres ABS
Tensile strength,
Young’s modulus,
and flexural
properties
Decreases in toughness, yield
strength and ductility and increases
in porosity with increased carbon
fibre content
[31]
Carbon fibres PLA Tensile strength and
tensile modulus [32]
Carbon fibres PLA Fracture properties
Critical factors for the fracture
toughness: bead layup sequence,
fiber pullout, interfacial de-bonding,
and void formation
[33]
Carbon fibres PLA Tensile strength Tensile strength increases with infill
density and low layer thickness [34]
Carbon fibres Nylon Charpy impact
testing
Toughness results show a severe
anisotropy in
toughness and high dependence on
the infill strategy
[35]
Figure 2. Examples of (a) infill percentage, (b) build orientation and (c) infill pattern.
Love et al. [30] showed that filaments made from CFs and acrylonitrile butadiene styrene (ABS)
polymer significantly increase the strength and stiffness of the final parts: the tensile strength and
stiffness of the composite sample were 70.69 MPa and 8.91 GPa, respectively, whereas these values
for the pure ABS sample were 29.31 MPa and 2.05 GPa, respectively. They also demonstrated that the
addition of CFs decreased the distortion of the printed ABS/CF, which was attributed to the 124%
increase in thermal conductivity compared to unfilled ABS. Ning et al. [31] investigated the material
properties of ABS polymer matrices with different CF contents. They concluded that compared with
pure ABS specimens, adding CFS into ABS could increase the tensile strength and Young’s modulus
but may decrease the toughness, yield strength and ductility. Porosity became the most severe in the
specimens with a 10 wt% carbon fibre content. Ivey et al. [32] analysed specimens produced using a
Figure 2. Examples of (a) infill percentage, (b) build orientation and (c) infill pattern.
Machines 2020,8, 52 3 of 13
Table 1. A summary of some studies on FFF with chopped fibres.
Reinforcement Matrix Material Investigated Properties Limitations References
Carbon fibres ABS Tensile strength
and tensile modulus
Porosity, weak interfacial
adhesion between the fibres
and the matrix
and fibre breakage
[27]
Vapour-grown
carbon fibres ABS Tensile strength
and tensile modulus
Interlayer fusion, intralayer
fusion, and a change from
ductile to brittle behaviour
[28]
Carbon fibres ABS
Strength, stiness, thermal
properties, distortion,
and geometric tolerances
[30]
Carbon fibres ABS
Tensile strength,
Young’s modulus,
and flexural properties
Decreases in toughness,
yield strength and ductility
and increases in porosity with
increased carbon fibre content
[31]
Carbon fibres PLA Tensile strength
and tensile modulus [32]
Carbon fibres PLA Fracture properties
Critical factors for the fracture
toughness: bead layup
sequence, fiber pullout,
interfacial de-bonding,
and void formation
[33]
Carbon fibres PLA Tensile strength
Tensile strength increases with
infill density and low layer
thickness
[34]
Carbon fibres Nylon Charpy impact testing
Toughness results show a severe
anisotropy in toughness
and high dependence on
the infill strategy
[35]
Love et al. [
30
] showed that filaments made from CFs and acrylonitrile butadiene styrene
(ABS) polymer significantly increase the strength and stiness of the final parts: the tensile strength
and stiness of the composite sample were 70.69 MPa and 8.91 GPa, respectively, whereas these values
for the pure ABS sample were 29.31 MPa and 2.05 GPa, respectively. They also demonstrated that
the addition of CFs decreased the distortion of the printed ABS/CF, which was attributed to the 124%
increase in thermal conductivity compared to unfilled ABS. Ning et al. [
31
] investigated the material
properties of ABS polymer matrices with dierent CF contents. They concluded that compared with
pure ABS specimens, adding CFS into ABS could increase the tensile strength and Young’s modulus
but may decrease the toughness, yield strength and ductility. Porosity became the most severe in
the specimens with a 10 wt% carbon fibre content. Ivey et al. [
32
] analysed specimens produced
using a commercial polylactic acid (PLA) filament and a PLA filament reinforced with short-carbon
fibres (PLA/CF). The tensile properties of the PLA and PLA/CF filaments showed that the addition of
carbon fibres to the PLA filament led to a significant increase in the elastic modulus of the FFF samples.
The fracture properties (stress intensity factor and energy release rate) of PLA and its short CF reinforced
composites have been studied by Papon and Haque [
33
]. Dierent CF concentrations were printed with
two bead lay-up orientations using PLA and CF/PLA composite filaments. The most critical factors
for the fracture toughness seem to be the bead layup sequence, fiber pullout, interfacial de-bonding,
and void formation. Higher fiber contents did not show improvement in fracture toughness due to
higher intra-bead voids, microcracks, and poor interfacial bonding. Yasa [
35
] pointed out that the build
orientation has a significant influence of carbon-reinforced tough nylon. The impact toughness of
specimens built vertically was reduced by 90% in comparison to other directions where the impact
was not received in between deposited layers. In 2014, MarkForged
©
developed the first continuous
carbon fibre composite 3D printer. Printed samples generated with MarkForged
©
printers have
been characterized in previous studies [
36
39
]. A summary of some studies focused on the FFF of
Machines 2020,8, 52 4 of 13
continuous fibre-reinforced polymers is given in Table 2. These studies observed some discontinuities
in the construction of samples: the carbon fibres were not completely continuous. Experiments showed
that discontinuities in the fibres led to premature failure in areas where the fibres were absent, severely
reducing the tensile strength of the sample.
Table 2. A summary of some studies on FFF with continuous fibres.
Reinforcement Matrix Material Investigated
Properties Limitations References
Carbon fibres Nylon Tensile properties Discontinuities of
the fibres and porosity [36]
Carbon, glass
and Kevlar fibres Nylon Tensile properties Poor bonding
and porosity [37]
Carbon, glass
and Kevlar fibres Nylon
Tensile and flexural
properties
Weak bonding
and porosity [38]
Carbon fibres PLA Flexural strength
and modulus None reported [39]
This study investigated the performance of parts produced with an FFF 3D printer from chopped
carbon fibre-reinforced nylon filaments (nylon-carbon). This filament is composed of nylon 612 with
20% carbon fibres. Nylon 612 (Polyamide 612) gives high resistance to the filament (high impact strength;
good resistance to greases, oils, fuels, hydraulic fluids, water, alkalis and saline; good stress cracking
resistance; low coecients of sliding friction; high abrasion resistance; and high tensile and flexural
strength [
40
]), a relatively low water absorption and a high dimensional stability. The CFs add stability
and rigidity, which makes the parts less likely to warp than standard nylon. Due to these characteristics,
this filament is ideal for engineering parts, custom end-use production parts, functional prototyping
and testing, structural parts, jigs, fixtures, and other tooling. Although the extrusion of preimpregnated
fibres does not allow changes in the fibre volume fraction, this approach eliminates the problems
associated with poor fibre/matrix interfaces if the impregnation is good and if adequate process
parameters are selected. However, the high values of mechanical properties (e.g., tensile modulus
of 500–8000 MPa, tensile strength of 54–110 MPa, and hardness of 110 MPa) found in the material
datasheets from various manufacturers do not specify the construction conditions, i.e., orientation
and filling. This is because some data is obtained by building specimens with other technologies,
such as injection molding. In the last year alone, filament manufacturers have been trying to provide
mechanical test data by making the specimens using FFF technology. Therefore, the purpose of
this study is to analyse the actual mechanical characteristics of a nylon-carbon filament using a
low-cost printer.
2. Materials and Methods
2.1. Fabrication of Samples
In this study, a nylon-carbon filament produced by Fiber Force Italy [
41
], which had a standard
diameter of 1.75 mm, was used for 3D printing. The nylon-carbon filament is composed of nylon
612 with 20% carbon fibres (chopped fibres with a random orientation). Each fibre is approximately
10
µ
m in diameter and 30
µ
m in length. A Sharebot Next Generation printer with a 0.4 mm nozzle was
used to print tensile and Charpy impact test specimens with a layer thickness of 0.20 mm and three
dierent values of infill, 15%, 80%, and 100%, in two dierent planes, XY and XZ (Figure 3). Many of
the samples produced on the ZX plane showed defects during construction due to problems regarding
adhesion on the building platform. For this reason, these samples were not analysed. Choosing an
infill pattern depends on the kind of model, the desired structural strength, and the print speed.
In general, rectilinear, linear and honeycomb infill patterns are preferred. From a study conducted by
Akhoundi and Behravesh [
42
], honeycomb was found to be the least favourable pattern at a filling
Machines 2020,8, 52 5 of 13
percentage of 100, whereas it provided better properties at a low filling percentage. The honeycomb
pattern is more susceptible to creating small voids in the matrix, leading to a significant reduction
in the specific tensile strength [
42
]. Therefore, filling with 15% of the material was realized with a
honeycomb structure. The first four layers and the last four layers that enclose the part are filled
with a solid layer. Linear filling was used for the samples with filling percentages of 80% and 100%.
Table 3shows the parameters of the 3D printing process.
r
Figure 3. (a) Sample building direction, (b) linear filling at 100%, and (c) honeycomb filling at 15%.
Table 3. 3D printing process parameters.
3D Printer Filament Value
Sharebot Next Generation
Diameter 1.75 mm
Extruder temperature 230 C
Bed temperature 40 C
Perimeter print speed 35 mm/s
Infill and support print speed 40 mm/s
Layer height 0.20 mm
2.2. Mechanical Testing
The mechanical properties relevant for the sports, automotive and aerospace industries, such as
the hardness, tensile and resilience of 3D printed nylon-carbon specimens, are evaluated via
mechanical testing.
During the Brinell hardness test (ISO 2039-1, DIN 53456), an indenter comprising a hardened steel
ball (diameter: 5 mm) is pressed into the top surface of the sample for a standard length of time (30 s)
under a standard load of 49 N [
43
]. After removing the load, the circular indentation is then measured
in two mutually perpendicular directions, taking the average of the two readings. The hardness
H [N/mm2] is the ratio between the applied load and the surface area of the impression.
Tensile tests were conducted in accordance with ASTM D638 using an Instron 3366 dynamometer,
which was equipped with a 10 kN load cell, at a strain rate of 10 mm/min. Five specimens for each set
were tested, and the final results were obtained by averaging the data.
Charpy impact tests were performed with a Charpy Zwick Roell B513E to study the energy
absorption of the dierent samples. The test was carried out in accordance with ISO179-1,
and the unnotched specimen dimensions were 80
×
10
×
4 mm. The distance between the supports was
40 mm. Five samples for each set were tested. After the test, each sample was inspected, and the fracture
surface was photographed.
Machines 2020,8, 52 6 of 13
3. Results and Discussion
3.1. Hardness and Tensile Properties
In Table 4, the hardness values are reported. The results showed that the samples produced in
the XY plane have a higher hardness than the samples produced in the XZ plane. This discrepancy is
evident for the samples with 100% filling, whereas for the other samples with 15% and 80% filling,
the eect is not as clear. The samples built in the XZ plane with 80% and 100% filling have similar
hardness. Increasing the filling percentage results in an increase in the hardness in the XY plane but
also increases material costs and lengthens production times.
Table 4. Hardness values in N/mm2.
Number Indentation Filling Percentage and Building Direction
15%, XY 15%, XZ 80%, XY 80%, XZ 100%, XY 100%, XZ
1 14.4 10.1 55.6 48.5 80.1 51.1
2 10.3 9.2 54.7 49.3 80.9 45.4
3 13.0 11.5 53.5 52.2 78.3 52.2
4 10.3 13.0 48.2 53.7 75.3 41.3
5 8.5 10.0 55.9 45 81.9 43.4
Average 11.3 10.8 53.6 49.7 79.3 46.7
Std. dev. 2.4 1.5 3.1 3.4 2.6 4.8
In Table 5and Figure 4, the results from the tensile tests are reported. The results show that,
in general, the specimens built in the XZ direction are stier than those built in the XY direction;
the former exhibit higher Young’s modulus and higher stress at break. In contrast, the energy at break
is higher for the samples built in the XY direction.
Table 5. Tensile test results for the specimens printed on a Sharebot printer from a 1.75 mm filament.
Sample Young’s Modulus E [MPa] σY[MPa] σUTS [MPa] σbreak [MPa] Elongation at Break [%] Energy at Break [mJ]
15%, XY 930 ±77 17 ±0.3 22 ±0.7 21 ±0.7 2.0 ±0.2 202 ±50
15%, XZ 1467 ±21 26 ±0.8 31 ±0.6 25 ±0.6 1.5 ±0.1 76 ±15
80%, XY 1552 ±60 35 ±0.4 44 ±1.2 37 ±1.2 2.2 ±0.1 625 ±194
80%, XZ 2294 ±154 36 ±1.8 57 ±4.1 44 ±4.1 2.6 ±0.5 361 ±119
100%, XY
1625 ±64 39 ±1.4 45 ±1.9 38 ±1.9 2.0 ±0.1 464 ±209
100%, XZ
2403 ±95 42 ±1.7 56 ±3.9 45 ±3.9 2.8 ±1.0 163 ±89
Machines 2020, 8, x FOR PEER REVIEW 7 of 13
Figure 4. Stress-strain curves.
As previously reported by Rodriguez et al. [44], this means that building in the XZ direction
leads to stiffer and more fragile components, whereas when an object is built in the XY direction, the
object is softer but more resistant to failure.
Regarding the filling factor, as the filling percentage increases, the specimen stiffness increases.
The choice of the type of infill pattern can influence the behaviour of the material, leading to a
nonlinear relationship between the mechanical properties and the filling factor. For instance, the
Young’s modulus of the samples with a filling factor of 15% (honeycomb infill pattern) is
approximately 60% of the average Young’s modulus of the specimens with a filling factor of 100%
(linear infill pattern), independent of the building direction. The modulus values with a filling factor
of 80% (linear infill pattern) increase by up to 95%. A similar trend could be evidenced for the tensile
strength at break σbreak (53% for a 15% filling factor and 97% for an 80% filling factor). This finding
means that once the stiffness requirements for a component are established, important weight
reductions could be implemented by using only the amount of material sufficient to satisfy the criteria
and the most suitable infill pattern. On the other hand, the use of an exceeding amount of material
could be even detrimental: the more material there is, the more defects generated during the printing
process, leading to a decrease in the mechanical properties. Although 100% fill density can provide
maximum strength, it can negatively affect the overall cost by increasing the print time and the
amount of material consumed. For certain applications, it is not necessary to use a fill density of 100%
due to the nature of the application itself, for example in the case of components not subjected to
loads or stresses of certain amounts. Therefore, determining the required fill density based on the
nature and application of the product would be very important for large-scale production lines to
optimize resources. Obviously, the load capacity of the printed parts is a function of the filling
density, the fraction of the volume of the fiber to the matrix and the quality of the chemical and
mechanical bond between droplets/layers. Low fill densities can lead to an increase in gaps within
the structure (i.e., an increase in porosity) and this can cause the strength of the part to decrease [45].
A filling percentage of 100% can cause raster overlap or a negative air gap size, which, in turn,
negatively influences the strength of the material.
Regarding the mechanical properties in the XZ orientation, a filling percentage of 80% improves
the material characteristics, among which the hardness slightly increases and the energy at break
increases more substantially. In the XY orientation, the difference between the samples produced
with the 15% honeycomb strategy and those produced with higher filling percentages (linear filling)
is more consistent in terms of hardness than stiffness. This finding confirms that the combination of
filling percentage and filling strategy has a high effect on the mechanical properties. Fernández-
Vicente et al. [46] carried out a study that analysed the influence of the pattern and infill percentage:
the density of the infill was a decisive factor in tensile strength, and the combination of a rectilinear
pattern and a 100% filling percentage provided the greatest tensile strength. This result was not fully
found in the present case. Samples with 80% and 100% filling percentages exhibited similar values
Figure 4. Stress-strain curves.
Machines 2020,8, 52 7 of 13
As previously reported by Rodriguez et al. [
44
], this means that building in the XZ direction leads
to stier and more fragile components, whereas when an object is built in the XY direction, the object is
softer but more resistant to failure.
Regarding the filling factor, as the filling percentage increases, the specimen stiness increases.
The choice of the type of infill pattern can influence the behaviour of the material, leading to a nonlinear
relationship between the mechanical properties and the filling factor. For instance, the Young’s modulus
of the samples with a filling factor of 15% (honeycomb infill pattern) is approximately 60% of the average
Young’s modulus of the specimens with a filling factor of 100% (linear infill pattern), independent of
the building direction. The modulus values with a filling factor of 80% (linear infill pattern) increase
by up to 95%. A similar trend could be evidenced for the tensile strength at break
σbreak
(53% for
a 15% filling factor and 97% for an 80% filling factor). This finding means that once the stiness
requirements for a component are established, important weight reductions could be implemented by
using only the amount of material sucient to satisfy the criteria and the most suitable infill pattern.
On the other hand, the use of an exceeding amount of material could be even detrimental: the more
material there is, the more defects generated during the printing process, leading to a decrease in
the mechanical properties. Although 100% fill density can provide maximum strength, it can negatively
aect the overall cost by increasing the print time and the amount of material consumed. For certain
applications, it is not necessary to use a fill density of 100% due to the nature of the application itself,
for example in the case of components not subjected to loads or stresses of certain amounts. Therefore,
determining the required fill density based on the nature and application of the product would be
very important for large-scale production lines to optimize resources. Obviously, the load capacity of
the printed parts is a function of the filling density, the fraction of the volume of the fiber to the matrix
and the quality of the chemical and mechanical bond between droplets/layers. Low fill densities
can lead to an increase in gaps within the structure (i.e., an increase in porosity) and this can cause
the strength of the part to decrease [
45
]. A filling percentage of 100% can cause raster overlap or a
negative air gap size, which, in turn, negatively influences the strength of the material.
Regarding the mechanical properties in the XZ orientation, a filling percentage of 80% improves
the material characteristics, among which the hardness slightly increases and the energy at
break increases more substantially. In the XY orientation, the dierence between the samples
produced with the 15% honeycomb strategy and those produced with higher filling percentages
(linear filling) is more consistent in terms of hardness than stiness. This finding confirms that
the combination of filling percentage and filling strategy has a high eect on the mechanical properties.
Fern
á
ndez-Vicente et al. [
46
] carried out a study that analysed the influence of the pattern and infill
percentage: the density of the infill was a decisive factor in tensile strength, and the combination of a
rectilinear pattern and a 100% filling percentage provided the greatest tensile strength. This result was
not fully found in the present case. Samples with 80% and 100% filling percentages exhibited similar
values for the Young’s modulus and stress at break with dierences of 4% and 5% in the XY and XZ
planes, respectively. The greatest deviation is observed for energy at break: samples with 80% filling
exhibited higher values (+35% and +121% in the XY and XZ planes, respectively) than those built with
100% filling. This finding can be explained by considering the following factors: thermal stresses during
construction, random orientation of the fibres and filling percentage. Residual stresses induced in
the layer-by-layer fabrication process of additive manufactured parts have a significant impact on their
mechanical properties and dimensional accuracy [
23
,
47
]. Based on the coecient of thermal expansion
(CTE), the material is prone to shrinkage, which induces internal stresses due to the evolving material
stiness upon solidification and the bonds between the beads constraining the material. A fraction of
these stresses is released due to viscoelastic relaxation and material deformations. During cooling,
the crystallization reaction introduced additional strains that promote internal stresses and partial
deformations. The combined behaviour of these factors simultaneously influences the mechanical
properties. The random orientation of the fibres aects the thermal properties in dierent directions.
Therefore, the fibres significantly increase the conductivity in the bead direction and other directions.
Machines 2020,8, 52 8 of 13
The thermal conductivity of the carbon fibres helps the already cooled bottom beads soften again
after a hot bead is deposited on their upper surfaces, leading to improved packing and smaller gaps.
This assertion would explain the smaller gap between the results for hardness and stiness in the XZ
plane for the two infill percentages of 80% and 100%. In the XY direction, the heating of the plate
and the lower number of layers reduces the thermal stress, making the eect of the filling more
obvious, thereby highlighting a greater dierence in hardness between 80% and 100% infills and a
lesser dierence in the Young’s modulus and stress at break. A 20% reduction in the infill percentage
(from 100% to 80%) led to greater energy at break in both construction directions.
A comparison of the obtained values with those found in the material datasheets from the supplier
and other manufacturers is shown in Table 6. The FFF samples exhibited higher mechanical property
values than pure thermoplastic material (nylon) [
48
,
49
] but lower mechanical property values than
the injection moulded samples [
50
]. Comparing the values reported for Nylon 12CF [
48
] with those
obtained in this study with the same percentage of filling, it can be observed that the increase in carbon
fibres from 20% (nylon-carbon) to 35% (Nylon 12CF) with the same construction orientation allows an
increase in the tensile properties. Considering instead a reduction of 5% (CF112) [
51
] of the percentage
of carbon fiber, the mechanical properties are reduced except the elongation at break considering what
is declared by the manufacturer. The percentages and type of filling and orientation of the samples
are not indicated. The values reported by the Fiber Force manufacturer show a certain dierence
compared to what was found in this study. The datasheet does not show the data relating to the type
of infill used. The other process parameters used are the same as in this study. This therefore focuses
on the fact that with the same filament and process parameters, the results determined with a tensile
test are also conditioned by the geometry of the tested specimen. The ISO 527-1/-2 and ASTM D638
(used in the scientific literature) standards define test methods for tensile tests. Although technically
equivalent, the tests carried out according to these standards do not provide fully comparable results,
as the shape of the specimens, the test speed, and the determination of the results are dierent from
each other in several respects [52,53].
Table 6. Comparison of the tensile test results.
Manufacturer Data Young’s Modulus E [MPa] σy[MPa] σbreak [MPa] Elongation at
Break [%]
Energy at
Break [J]
Injection moulded–Nylon Carbon
6000 100 - - -
Nylon 12CF (Stratasys) 7515 63.4 76 1.9 -
(100%, XZ) (100%, XZ) (100%, XZ) (100%, XZ)
Nylon Carbon (Fiber Force)
1844
-
33.7 5.7 5.45
(15%, XY) (15%, XY) (15%, XY) (15%, XY)
2758 66.3 6.7 12.2
(100%, XY) (100%, XY) (100%, XY) (100%, XY)
CF112 (Fillamentum) 2200 52.4 37.7 8 -
Nylon (Stratasys) 1282 32 46 3.0 -
(100%, XZ) (100%, XZ) (100%, XZ) (100%, XZ)
Nylon (Fiber Force)
881.9
-
20.7 13.94 10.48
(15%, XY) (15%, XY) (15%, XY) (15%, XY)
1529.0 41.1 31.30 49.70
(100%, XY) (100%, XY) (100%, XY) (100%, XY)
Nylon (Markforged) 940 54
3.2. Resilience
Figure 5shows the test results for the specimens built on the XY plane and the XZ plane for each
filling ratio. In general, the samples constructed on the XY plane have a resilience that is approximately
4.6 times, 3.1 times, and 2.9 times that of the samples built on the XZ plane with filling factors of 15%,
80%, and 100%, respectively.
Machines 2020,8, 52 9 of 13
Machines 2020, 8, x FOR PEER REVIEW 9 of 13
(100%, XY) (100%, XY) (100%, XY) (100%, XY)
CF112
(Fillamentum) 2200 52.4 37.7 8 -
Nylon
(Stratasys)
1282
(100%, XZ)
32
(100%, XZ)
46
(100%, XZ)
3.0
(100%, XZ) -
Nylon
(Fiber Force)
881.9
(15%, XY)
1529.0
(100%, XY)
-
20.7
(15%, XY)
41.1
(100%, XY)
13.94
(15%, XY)
31.30
(100%, XY)
10.48
(15%, XY)
49.70
(100%, XY)
Nylon
(Markforged) 940 54
3.2. Resilience
Figure 5 shows the test results for the specimens built on the XY plane and the XZ plane for each
filling ratio. In general, the samples constructed on the XY plane have a resilience that is
approximately 4.6 times, 3.1 times, and 2.9 times that of the samples built on the XZ plane with filling
factors of 15%, 80%, and 100%, respectively.
Figure 5. Charpy impact test results.
The filling factor does not have a strong influence on the resilience. The resilience of samples
manufactured in the XY plane with a filling percentage of 100% is only 4% higher than the resilience
of samples built on the same plane with a filling percentage of 15%. The resilience of samples built
on the XZ plane with a filling percentage of 100% is 29% higher than that of samples with a filling
percentage of 15%. It is evident that the effect of the building direction is more important than the
influence of the filling factor. This finding indicates that if the layers are parallel to the mechanical
test direction, the mechanical properties are lower than in the sample where the layers are
perpendicular to the mechanical test direction.
Figure 6a shows that the fracture surface of the samples built on the XZ plane corresponds to the
interlayer part. During the test, two samples constructed on the XY plane with a filling percentage of
15% were not broken: the last four layers were bent (Figure 6b,c), and the samples passed through
the supports. The samples that did not break during the test were not considered in the evaluation of
resilience.
From the images of the fracture section (Figure 6), it is possible to observe greater compactness
between the first and last layer and filling of samples in the XZ plane at 80% and 100% with respect
to the XY plane. This may be due to the very principle of the additive process. Additive processes
develop in layers. If it considers, for example, the specimen for Charpy tests, the number of layers
varies from 20 layers for the XY plane to 50 layers for the one built in the XZ plane. Therefore,
Figure 5. Charpy impact test results.
The filling factor does not have a strong influence on the resilience. The resilience of samples
manufactured in the XY plane with a filling percentage of 100% is only 4% higher than the resilience
of samples built on the same plane with a filling percentage of 15%. The resilience of samples built
on the XZ plane with a filling percentage of 100% is 29% higher than that of samples with a filling
percentage of 15%. It is evident that the eect of the building direction is more important than
the influence of the filling factor. This finding indicates that if the layers are parallel to the mechanical
test direction, the mechanical properties are lower than in the sample where the layers are perpendicular
to the mechanical test direction.
Figure 6a shows that the fracture surface of the samples built on the XZ plane corresponds to
the interlayer part. During the test, two samples constructed on the XY plane with a filling percentage
of 15% were not broken: the last four layers were bent (Figure 6b,c), and the samples passed through
the supports. The samples that did not break during the test were not considered in the evaluation
of resilience.
Machines 2020, 8, x FOR PEER REVIEW 10 of 13
considering that the first and last 4 layers are solid, the specimen constructed on the XY plane will
have 2.4 mm of infill at 15%, 80% or 100% and 1.6 mm (0.8 mm in the first 4 layers and 0.8 mm in the
last 4 layers) of 100% filling; while the one built on the XZ plane will have 8.4 mm of filling at 15%,
80% or 100% and always 1.6 mm of full. Therefore, in the case of hardness and resilience, the
components in the XY plane have higher values than those in the XZ plane having a reduced number
of layers which reduces the percentage of defects. In the case of tensile test, on the other hand, the
specimen has a thin section in the useful area that reverses the condition, i.e., it has more layers but
with a reduced filling value, also considering the effects in the contour that decrease the percentage
of votes in the transition area between outline and fill. The contours scanned around the part to be
filled in every layer limited these porosities. Due to the fact that the specimens were quite thin, the
effect of dense contours probably contributes to a higher Young’s modulus [54].
Figure 6. (a) Fracture surfaces from the Charpy impact test samples: (b) side view and (c) top view of
the sample built on the XY plane with a filling percentage of 15% that has not been broken.
4. Conclusions
Although short fibre-reinforced composites offer better mechanical performance than their
unreinforced counterparts, there is still a certain gap between the mechanical properties of
preimpregnated fibre and conventionally manufactured fibre-reinforced polymer composites.
Furthermore, the weight percentage of the carbon fibres and the selected process parameters can
greatly influence the mechanical characteristics, as reported in the literature.
Based on the experimental results of this study, the following conclusions may be drawn:
o The samples produced in the XY plane have higher hardness than the samples built in the XZ
plane. The samples built in the XZ plane with 80% and 100% filling have similar hardness values.
Figure 6.
(
a
) Fracture surfaces from the Charpy impact test samples: (
b
) side view and (
c
) top view of
the sample built on the XY plane with a filling percentage of 15% that has not been broken.
Machines 2020,8, 52 10 of 13
From the images of the fracture section (Figure 6), it is possible to observe greater compactness
between the first and last layer and filling of samples in the XZ plane at 80% and 100% with respect to
the XY plane. This may be due to the very principle of the additive process. Additive processes develop
in layers. If it considers, for example, the specimen for Charpy tests, the number of layers varies from
20 layers for the XY plane to 50 layers for the one built in the XZ plane. Therefore, considering that
the first and last 4 layers are solid, the specimen constructed on the XY plane will have 2.4 mm of
infill at 15%, 80% or 100% and 1.6 mm (0.8 mm in the first 4 layers and 0.8 mm in the last 4 layers)
of 100% filling; while the one built on the XZ plane will have 8.4 mm of filling at 15%, 80% or 100%
and always 1.6 mm of full. Therefore, in the case of hardness and resilience, the components in the XY
plane have higher values than those in the XZ plane having a reduced number of layers which reduces
the percentage of defects. In the case of tensile test, on the other hand, the specimen has a thin section
in the useful area that reverses the condition, i.e., it has more layers but with a reduced filling value,
also considering the eects in the contour that decrease the percentage of votes in the transition area
between outline and fill. The contours scanned around the part to be filled in every layer limited these
porosities. Due to the fact that the specimens were quite thin, the eect of dense contours probably
contributes to a higher Young’s modulus [54].
4. Conclusions
Although short fibre-reinforced composites offer better mechanical performance than their
unreinforced counterparts, there is still a certain gap between the mechanical properties of preimpregnated
fibre and conventionally manufactured fibre-reinforced polymer composites. Furthermore, the weight
percentage of the carbon fibres and the selected process parameters can greatly influence the mechanical
characteristics, as reported in the literature.
Based on the experimental results of this study, the following conclusions may be drawn:
The samples produced in the XY plane have higher hardness than the samples built in the XZ plane.
The samples built in the XZ plane with 80% and 100% filling have similar hardness values.
At a filling percentage of 100%, the samples built in the XZ plane exhibit much lower hardness
than those constructed in the XY plane.
The specimens built in the XZ direction are stier than those built in the XY direction, in which
the former exhibits higher Young’s modulus and higher stress at break. In contrast, the energy at
break is higher for the samples built in the XY direction. Furthermore, the relationship between
the mechanical properties and filling factor is not linear.
The ISO 527-1/-2 and ASTM D638 standards, although technically equivalent, do not provide
fully comparable results
The filling factor does not have a strong influence on the resilience on the XY plane.
Author Contributions:
Conceptualization, F.C.; methodology, F.C.; validation, F.C., M.L., and I.R.; formal analysis,
F.C., M.L., and I.R.; investigation, F.C., M.L., and I.R.; writing—Original draft preparation, F.C., M.L., I.R., and P.M.
All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Acknowledgments:
The authors gratefully acknowledge Arturo Donghi of Sharebot Company for having supplied
the FFF printer and the 1.75 mm nylon-carbon filament for printing the test specimens.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Kostakis, V.; Niaros, V.; Giotitsas, C. Open source 3D printing as a means of learning: An educational
experiment in two high schools in Greece. Telemat. Inform. 2015,32, 118–128. [CrossRef]
2.
Rayna, T.; Striukova, L.; Darlington, J. Co-creation and user innovation: The role of online 3D printing
platforms. J. Eng. Technol. Manag. 2015,37, 90–102. [CrossRef]
Machines 2020,8, 52 11 of 13
3.
West, J.; Kuk, G. The complementarity of openness: How MakerBot leveraged Thingiverse in 3D printing.
Technol. Forecast. Soc. Change 2016,102, 169–181. [CrossRef]
4.
Boschetto, A.; Bottini, L. Design for manufacturing of surfaces to improve accuracy in Fused Deposition
Modeling. Robot. Comput. Integr. Manuf. 2016,37, 103–114. [CrossRef]
5.
Yang, S.; Tang, Y.; Zhao, Y.F. A new part consolidation method to embrace the design freedom of additive
manufacturing. J. Manuf. Process. 2015,20, 444–449. [CrossRef]
6.
Domingo-Espin, M.; Puigoriol-Forcada, J.M.; Garcia-Granada, A.A.; Llum
à
, J.; Borros, S.; Reyes, G. Mechanical
property characterization and simulation of fused deposition modeling Polycarbonate parts. Mater. Des.
2015,83, 670–677. [CrossRef]
7.
Baumers, M.; Dickens, P.; Tuck, C.; Hague, R. The cost of additive manufacturing: Machine productivity,
economies of scale and technology-push. Technol. Forecast. Soc. Change 2016,102, 193–201. [CrossRef]
8.
Kroll, E.; Artzi, D. Enhancing aerospace engineering students’ learning with 3D printing wind-tunnel models.
Rapid Prototyp. J. 2011,17, 393–402. [CrossRef]
9.
Wong, K.V.; Hernandez, A. A Review of Additive Manufacturing. ISRN Mech. Eng.
2012
,2019, 7–31.
[CrossRef]
10.
Short, D.B. Use of 3D printing by museums: Educational exhibits, artifact education, and artifact restoration.
3D Print. Addit. Manuf. 2015,2, 209–215. [CrossRef]
11. Walters, P.; Davies, K. 3D Printing for Artists: Research and Creative Practice. Rapport 2010,1, 12–15.
12.
Murphy, S.V.; Atala, A. 3D bioprinting of tissues and organs. Nat. Biotechnol.
2014
,32, 773–785. [CrossRef]
[PubMed]
13.
Chen, H.; Yang, X.; Chen, L.; Wang, Y.; Sun, Y. Application of FDM three-dimensional printing technology in
the digital manufacture of custom edentulous mandible trays. Sci. Rep.
2016
,6, 19207. [CrossRef] [PubMed]
14.
Wang, X.; Jiang, M.; Zhou, Z.; Gou, J.; Hui, D. 3D printing of polymer matrix composites: A review
and prospective. Compos. Part B Eng. 2017,110, 442–458. [CrossRef]
15.
Mohammadizadeh, M.; Fidan, I.; Allen, M.; Imeri, A. Creep behavior analysis of additively manufactured
fiber-reinforced components. Int. J. Adv. Manuf. Technol. 2018,99, 1225–1234. [CrossRef]
16.
Mohan, N.; Senthil, P.; Vinodh, S.; Jayanth, N. A review on composite materials and process parameters
optimisation for the fused deposition modelling process. Virtual Phys. Prototyp.
2017
,12, 47–59. [CrossRef]
17.
Sood, A.K.; Ohdar, R.K.; Mahapatra, S.S. Parametric appraisal of mechanical property of fused deposition
modelling processed parts. Mater. Des. 2010,31, 287–295. [CrossRef]
18.
Bagsik, A.; Schöppner, V.; Klemp, E. FDM Part Quality Manufactured with Ultem*9085. In Proceedings of
the 14th International Scientific Conference on Polymeric Materials, Halle, Germany, 15–17 September 2010;
N.M.Emanuel Institute of Biochemical Physics, Russian Academy of Sciences: Moscow, Russia, 2010.
19.
Torrado Perez, A.R.; Roberson, D.A.; Wicker, R.B. Fracture surface analysis of 3D-printed tensile specimens
of novel ABS-based materials. J. Fail. Anal. Prev. 2014,14, 343–353. [CrossRef]
20.
Ziemian, C.; Sharma, M.; Ziemian, S. Anisotropic Mechanical Properties of ABS Parts Fabricated by Fused
Deposition Modelling. In Mechanical Engineering; Intech Open: London, UK, 2012.
21.
Zaldivar, R.J.; Witkin, D.B.; McLouth, T.; Patel, D.N.; Schmitt, K.; Nokes, J.P. Influence of processing
and orientation print eects on the mechanical and thermal behavior of 3D-Printed ULTEM
®
9085 Material.
Addit. Manuf. 2017,13, 71–80. [CrossRef]
22.
Mohamed, O.A.; Masood, S.H.; Bhowmik, J.L. Experimental Investigations of Process Parameters Influence on
Rheological Behavior and Dynamic Mechanical Properties of FDM Manufactured Parts. Mater. Manuf. Process.
2016,15, 1983–1994. [CrossRef]
23.
Ahn, S.H.; Montero, M.; Odell, D.; Roundy, S.; Wright, P.K. Anisotropic material properties of fused deposition
modeling ABS. Rapid Prototyp. J. 2002,8, 248–257. [CrossRef]
24.
Wu, W.; Geng, P.; Li, G.; Zhao, D.; Zhang, H.; Zhao, J. Influence of layer thickness and raster angle on
the mechanical properties of 3D-printed PEEK and a comparative mechanical study between PEEK and ABS.
Materials 2015,8, 5834–5846. [CrossRef] [PubMed]
25.
Tymrak, B.M.; Kreiger, M.; Pearce, J.M. Mechanical properties of components fabricated with open-source
3-D printers under realistic environmental conditions. Mater. Des. 2014,58, 242–246. [CrossRef]
26.
Lužanin, O.; Movrin, D.; Plan, M. Eect of Layer Thickness, Deposition Angle, and Infill on Maximum
Flexural Force in Fdm-Built Specimens. J. Technol. Plast. 2014,39, 49–58.
Machines 2020,8, 52 12 of 13
27.
Tekinalp, H.L.; Kunc, V.; Velez-Garcia, G.M.; Duty, C.E.; Love, L.J.; Naskar, A.K.; Blue, C.A.; Ozcan, S.
Highly oriented carbon fiber-polymer composites via additive manufacturing. Compos. Sci. Technol.
2014
,
105, 144–150. [CrossRef]
28.
Shofner, M.L.; Lozano, K.; Rodr
í
guez-Mac
í
as, F.J.; Barrera, E.V. Nanofiber-reinforced polymers prepared by
fused deposition modeling. J. Appl. Polym. Sci. 2003,89, 3081–3090. [CrossRef]
29.
Karsli, N.G.; Aytac, A. Tensile and thermomechanical properties of short carbon fiber reinforced polyamide 6
composites. Compos. Part B Eng. 2013,51, 270–275. [CrossRef]
30.
Love, L.J.; Kunc, V.; Rios, O.; Duty, C.E.; Elliott, A.M.; Post, B.K.; Smith, R.J.; Blue, C.A. The importance of
carbon fiber to polymer additive manufacturing. J. Mater. Res. 2014,29, 1893. [CrossRef]
31.
Ning, F.; Cong, W.; Qiu, J.; Wei, J.; Wang, S. Additive manufacturing of carbon fiber reinforced thermoplastic
composites using fused deposition modeling. Compos. Part B Eng. 2015,80, 369–378. [CrossRef]
32.
Ivey, M.; Melenka, G.W.; Carey, J.P.; Ayranci, C. Characterizing short-fiber-reinforced composites produced
using additive manufacturing. Adv. Manuf. Polym. Compos. Sci. 2017,3, 81–91. [CrossRef]
33. Papon, E.A.; Haque, A. Fracture toughness of additively manufactured carbon fiber reinforced composites.
Addit. Manuf. 2019,26, 41–52. [CrossRef]
34.
Rao, V.D.P.; Rajiv, P.; Geethika, V.N. Eect of fused deposition modelling (FDM) process parameters on
tensile strength of carbon fibre PLA. Mater. Today Proc. 2019,18, 2012–2018.
35.
Yasa, E. Anisotropic impact toughness of chopped carbon fiber reinforced nylon fabricated by
material-extrusion-based additive manufacturing. Anadolu Univ. J. Sci. Technol. Appl. Sci. Eng.
2019
,20,
195–203.
36.
Der Klift, F.; van Koga, Y.; Todoroki, A.; Ueda, M.; Hirano, Y.; Matsuzaki, R. 3D Printing of Continuous
Carbon Fibre Reinforced Thermo-Plastic (CFRTP) Tensile Test Specimens. Open J. Compos. Mater.
2016
,6, 18.
[CrossRef]
37.
Melenka, G.W.; Cheung, B.K.O.; Schofield, J.S.; Dawson, M.R.; Carey, J.P. Evaluation and prediction of
the tensile properties of continuous fiber-reinforced 3D printed structures. Compos. Struct.
2016
,153, 866–875.
[CrossRef]
38.
Dickson, A.N.; Barry, J.N.; McDonnell, K.A.; Dowling, D.P. Fabrication of continuous carbon, glass and Kevlar
fibre reinforced polymer composites using additive manufacturing. Addit. Manuf.
2017
,16, 146–152.
[CrossRef]
39.
Tian, X.; Liu, T.; Yang, C.; Wang, Q.; Li, D. Interface and performance of 3D printed continuous carbon fiber
reinforced PLA composites. Compos. Part A Appl. Sci. Manuf. 2016,88, 198–205. [CrossRef]
40.
McKeen, L.W. The Eect of Long Term Thermal Exposure on Plastics and Elastomers; William Andrew:
Norwich, NY, USA, 2013; ISBN 9780323221085.
41.
Fiber Force Italy. Available online: http://www.fiberforce.it/wp-content/uploads/2019/07/TDS_NY-CARBON_
REV-2.1.pdf (accessed on 23 August 2020).
42.
Akhoundi, B.; Behravesh, A.H. Eect of Filling Pattern on the Tensile and Flexural Mechanical Properties of
FDM 3D Printed Products. Exp. Mech. 2019,59, 883–897. [CrossRef]
43.
ASTM International. ISO/ASTM52900-15 Standard Terminology for Additive Manufacturing—General
Principles—Terminology; ASTM International: West Conshohocken, PA, USA, 2015.
44.
Rodr
í
guez, J.F.; Thomas, J.P.; Renaud, J.E. Mechanical behavior of acrylonitrile butadiene styrene fused
deposition materials modeling. Rapid Prototyp. J. 2003,9, 219–230. [CrossRef]
45.
Abeykoon, C.; Sri-Amphorn, P.; Fernando, A. Optimization of fused deposition modeling parameters for
improved PLA and ABS 3D printed structures. Int. J. Light. Mater. Manuf. 2020,3, 284–297. [CrossRef]
46.
Fernandez-Vicente, M.; Calle, W.; Ferrandiz, S.; Conejero, A. Eect of Infill Parameters on Tensile Mechanical
Behavior in Desktop 3D Printing. 3D Print. Addit. Manuf. 2016,3, 183–192. [CrossRef]
47.
Torrado, A.R.; Roberson, D.A. Failure Analysis and Anisotropy Evaluation of 3D-Printed Tensile Test
Specimens of Dierent Geometries and Print Raster Patterns. J. Fail. Anal. Prev.
2016
,16, 154–164. [CrossRef]
48.
Fused Deposition Modelling (FDM) Parts on Demand. Available online: https://www.stratasysdirect.com/
materials/fused-deposition-modeling (accessed on 20 September 2001).
49.
Markforged, Material. Available online: https://markforged.com/materials/composites/(accessed on
20 August 2020).
50.
Products-Maker—Fiberforce. Available online: http://www.fiberforce.it/products-maker/(accessed on
20 August 2020).
Machines 2020,8, 52 13 of 13
51.
Data Sheets Fillamentum. Available online: https://fillamentum.com/pages/data-sheets (accessed on
22 August 2020).
52.
Garc
í
a-Dom
í
nguez, A.; Claver, J.; Camacho, A.M.; Sebasti
á
n, M.A. Considerations on the applicability of
test methods for mechanical characterization of materials manufactured by FDM. Materials.
2020
,13, 28.
[CrossRef] [PubMed]
53.
Friday, M.J. A comparison of tension test data using ASTM D 638 and ISO 527. In ASTM Limitations of Test
Methods for Plastics; ASTM International: West Conshohocken, PA, USA, 1999.
54.
Yasa, E.; Ersoy, K. Dimensional Accuracy and Mechanical Properties of Chopped Carbon Reinforced Polymers
Produced by Material Extrusion Additive Manufacturing. Materials 2019,12, 3885. [CrossRef]
©
2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).
... Yasa et al. [13] showed that there was a severe level of anisotropy in the mechanical properties for the modulus of elasticity caused by insufficient adhesion between the layers deposited in the construction direction of the parts made from chopped carbon-reinforced polymers. Another study [14] on nylon filaments reinforced with carbon fiber indicated that the hardness and the tensile strength are influenced by the construction direction of the part, the infill density, and the thermal stresses, while the resilience is influenced only by the construction direction, and the relationship between the mechanical properties and the infill factor is not linear. In a study [15], the effects of the process conditions on the manufacture of polymer composites reinforced with short carbon fiber made by the material extrusion process were investigated at micro and macro levels. ...
... Polymers 2022,14, 2923 ...
... Polymers 2022, 14, 2923 ...
Article
Full-text available
Additive manufacturing, through the process of thermoplastic extrusion of filament, allows the manufacture of complex composite sandwich structures in a short time with low costs. This paper presents the design and fabrication by Fused Filament Fabrication (FFF) of composite sandwich structures with short fibers, having three core types C, Z, and H, followed by mechanical performance testing of the structures for compression and bending in three points. Flatwise compression tests and three-point bending have clearly indicated the superior performance of H-core sandwich structures due to dense core structures. The main modes of failure of composite sandwich structures were analyzed microscopically, highlighting core shear buckling in compression tests and face indentation in three-point bending tests. The strength–mass ratio allowed the identification of the structures with the best performances considering the desire to reduce the mass, so: the H-core sandwich structures showed the best results in compression tests and the C-core sandwich structures in three-point bending tests. The feasibility of the FFF process and the three-point bending test of composite wing sections, which will be used on an unmanned aircraft, have also been demonstrated. The finite element analysis showed the distribution of equivalent stresses and reaction forces for the composite wing sections tested for bending, proving to validate the experimental results.
... The specimen geometries in the stl format were created with the software CREO ® and the Ultimaker Cura software was used for the slicing process. The mechanical properties of the printed carbon nylon used for the numerical simulations were retrieved from the filament producer [25,26], where the results of the experimental tests are available. ...
... The mechanical behavior of the lattice structures was simulated with an elastoplastic material law, namely *MAT_PIECEWISE_LINEAR_PLASTICITY. In accordance with [26], the Young modulus and the yield limit were 3510 MPa and 20 MPa, respectively, and the plastic field was described with the stress deformation curve reported in [26]. It must be noted that the mechanical properties of the printed parts depend on the microstructure of the filament. ...
... The mechanical behavior of the lattice structures was simulated with an elastoplastic material law, namely *MAT_PIECEWISE_LINEAR_PLASTICITY. In accordance with [26], the Young modulus and the yield limit were 3510 MPa and 20 MPa, respectively, and the plastic field was described with the stress deformation curve reported in [26]. It must be noted that the mechanical properties of the printed parts depend on the microstructure of the filament. ...
Article
Full-text available
In this work, an experimental and numerical analysis of a lattice structure for energy absorption was carried out. The goal was to identify the most influencing parameters of the unit cell on the crushing performances of the structure, thus guiding the design of energy absorbers. Two full factorial plans of compression tests on cubic specimens of carbon nylon produced by fused deposition modeling (FDM) were performed. The factors were the beam diameter and the number of unit cells. In the first factorial plan, the specimen volume is constant and the dimensions of the unit cell are varied, while the second factorial plan assumes a constant size of the unit cell and the volume changes in accordance with their number. The results showed that the specific energy absorption increases with the diameter of the beam and decreases with the size of the unit cell. Based on these results, a crash absorber for the segment C vehicle was designed and compared with the standard component of the vehicle made of steel. In addition to a mass reduction of 25%, the improved crushing performances of the lattice structure are shown by the very smooth force-displacement curve with limited peaks and valleys.
... The printing process took about 12 min (without waiting for the sample to heat up and then to cool down). Researchers agree that the parameters for the 3D FDM printing process have a significant influence on the properties of the printed element [68][69][70][71][72][73]. Due to the fact that the print parameters are crucial, the parameters used for depositing plastics with 3D FDM printing to metal are presented in Table 3. Table 3. Manufacturing parameters for 3D-printed samples. ...
... Due to the fact that the print parameters are crucial, the parameters used for depositing plastics with 3D FDM printing to metal are presented in Table 3. Table 3. Manufacturing parameters for 3D-printed samples. Researchers agree that the parameters for the 3D FDM printing process have a significant influence on the properties of the printed element [68][69][70][71][72][73]. Due to the fact that the print parameters are crucial, the parameters used for depositing plastics with 3D FDM printing to metal are presented in Table 3. ...
Article
Full-text available
Nowadays, the replacement of a hip joint is a standard surgical procedure. However, researchers have continuingly been trying to upgrade endoprostheses and make them more similar to natural joints. The use of 3D printing could be helpful in such cases, since 3D-printed elements could mimic the natural lubrication mechanism of the meniscus. In this paper, we propose a method to deposit plastics directly on titanium alloy using 3D printing (FDM). This procedure allows one to obtain endoprostheses that are more similar to natural joints, easier to manufacture and have fewer components. During the research, biocompatible polymers suitable for 3D FDM printing were used, namely polylactide (PLA) and polyamide (PA). The research included tensile and shear tests of metal–polymer bonds, friction coefficient measurements and microscopic observations. The friction coefficient measurements revealed that only PA was promising for endoprostheses (the friction coefficient for PLA was too high). The strength tests and microscopic observations showed that PLA and PA deposition by 3D FDM printing directly on Ti6Al4V titanium alloy is possible; however, the achieved bonding strength and repeatability of the process were unsatisfactory. Nevertheless, the benefits arising from application of this method mean that it is worthwhile to continue working on this issue.
... Similar results were postulated by Travieso-Rodriguez et al. [42]. Afonso [43] et al. studied the influences of the fused filament fabrication parameters process on the mechanical properties for printed polylactic acid (PLA) parts. They found that the greatest influence parameter in the fabrication process is the extrusion temperature. ...
... This paper analyses the effect of heat treatment at three different temperatures on the physical and tensile behavior of two types of filaments printed by using two infill densities and two patterns infill. The percentages of porosities shown correlated with densities and patterns of infill; this is due to differences in thermal expansion of the filament which affects interfacial bonding between filament layers, the other reason for the porosity is the lack in filling to complete the geometric space between filaments in case of the small density (70%) [43]. It is clear from Figure 3 that there is a large space between the filaments in the case of density infill 70%, while the filaments are very close to each other in the case of density infill 100%. ...
Article
Full-text available
This work investigated the effects of heat treatment on the tensile behavior of 3D-printed high modules carbon fiber-reinforced composites. The manufacturing of samples with different material combinations using polylactic acid (PLA) reinforced with 9% carbon fiber (PLACF), acrylonitrile butadiene styrene (ABS) reinforced with 9% carbon fiber (ABSCF) were made. This paper addresses the tensile behavior of different structured arrangements at different% of densities between two kinds of filaments. The comparison of the tensile behavior between heat treated and untreated samples. The results showed that heat treatment improves the tensile properties of samples by enhancing the bonding of filament layers and by reducing the porosity content. At all structure specifications, the rectilinear pattern gives higher strength of up to 33% compared with the Archimedean chords pattern. Moreover, there is a limited improvement in the tensile strength and modulus of elasticity values for the samples treated at low heat-treatment temperature. The suggested methodology to evaluate the tensile behavior of the pairs of materials selected is innovative and could be used to examine sandwich designs as an alternative to producing multi-material components using inexpensive materials.
... (a) Percentage infill; (b) 3D printed dog bone specimen at different plane; (c) Different infill patterns.62 ...
Article
Full-text available
Fused deposition modeling (FDM) is one of the leading emerging technologies of Industry 4.0, which has been employed to develop sustainable engineering products, customized implants and sophisticated biomedical devices. However, the mechanical strength and durability of 3D printed parts is still lower than its conventional counterparts, which restrict its widespread use. In this regard, the use of short fibres (i.e. natural or artificial) and advanced nanomaterials to reinforce the existing polymer matrix has been drastically increased to improve the load bearing capacity of FDM printed parts. Hence, this article aims to provide a systematic review on thermoplastic composite structure prepared through FDM technology and summarizes the current knowledge about the use of various additives to improve the overall quality FDM parts. Moreover, the common defects associated with FDM printed composite structures and the methods required to improve the quality of FDM composite parts are discussed in this article.
... However, these kinds of flaws might compromise the structural integrity of the part [3,4]. Some studies, through a design of experiment (DOE) approach, showed that process parameters like the number of layers, the hatch distance, the build orientation, air gap, raster width and infill strategy have a deep influence on the porosity of the part, affecting the resulting mechanical properties [5][6][7][8]. Therefore, the characterization of these defects could improve the fabrication process itself because they strongly depend on the process parameters. ...
Article
Recently, the popularity of 3d printing for industrial and consumer use has spread across many different sectors. For this reason, quality assurance of 3d printed parts is becoming increasingly important. The extrusion and layer-by-layer deposition of a polymer filament on the print bed can introduce defects such as pores and voids into the internal structure of 3d printed parts. The relation between 3d printing defects and tensile performance of 3d printed samples is studied in this paper. The study considers tensile specimens of acrylonitrile butadiene styrene (ABS) that were 3d printed by varying the infill strategy and percentage to simulate different levels of strength for the part. Before the tensile tests, the ABS samples were inspected by X-ray tomography to identify the presence of internal voids generated by the 3d printing process. For each sample, data and statistics about the internal defects were used for determining a relation with the tensile test results. The local deformation of the sample and the position of the final fracture were observed using a digital camera and digital image correlation (DIC). In most cases, the experimental results confirmed the matching between the presence of internal voids and the areas of high deformation. However, the position of the specimen fracture did not always coincide with the largest defects. Nevertheless, this study highlights the importance of non-destructive inspection in quality assurance of 3d printed parts when in-situ monitoring of the 3d printing process is not applied.
... Before printing and within the slicing settings the user should define the layer height, the infill percentage, and the infill path among other printing parameters. Different infill strategies directly influence the mechanical performance of a 3d printed component [5][6][7][8]. Therefore, it is of paramount importance for the user to know in advance how the choice of slicing parameters will influence the part resistance. ...
Article
Fused Deposition Modelling (FDM), also known as 3d printing, is one of the most widespread Additive Manufacturing (AM) technologies based on the extrusion of a thermoplastic filament. This layerwise technology allows lightweight products to be built using different infill strategies and percentages. Furthermore, by varying other parameters, such as temperature, printing speed or layer thickness, it is possible to obtain components with different characteristics. Polylactic Acid (PLA) is one of the cheapest and most sustainable materials for 3d printing because it is a biobased and biodegradable plastic. Its use in 3D printing is widely spread among hobbyists and in the communities, such as the ones of Fablabs or the Makers movement. Nevertheless, to reduce the number of uncompliant parts that may fail into operation since they do not meet the expectations of the user, it is important to know in advance the mechanical performance that different 3d printing strategies can ensure for PLA parts. In this paper, Design of Experiment (DOE) is applied to investigate how main 3D printing parameters influence the tensile strength of PLA products. For this purpose, a 3x3 factorial plane with one replication was constructed and used for 3d printing tensile specimens of PLA Tough material using a Makerbot Replicator machine. The tensile test results show that the layer thickness is more significant than the infill percentage for the resistance of PLA products. A regression model is also proposed to allow the user to predict the ultimate tensile strength of PLA products depending on the values of those two parameters.
... Investigations on the mechanical properties of 3D printed carbon fiber reinforced nylon filament were conducted by Flaviana et al. (13) . This review investigation the genuine mechanical attributes of parts created with a minimal expense printer from a carbon fiber-supported nylon fiber. ...
Article
Thermoplastic is one of the most popular materials used in additive manufacturing (AM). As the adoption of AM technologies has been rapidly increasing, the feasibility of recycling AM waste and the quality of recycled materials need to be investigated to facilitate closed-loop material flow and cleaner production. In current literature, studies have been performed to compare material property changes before and after recycling, and a certain level of mechanical degradation has been observed. Some material properties such as molecular weight distribution have not yet been investigated in AM recycling. In addition, the recyclability of waste materials under multiple rounds of recycling has not yet been well studied. These knowledge gaps indicate a research need for AM material recyclability evaluation and improvement. In this research, an assessment framework is proposed and implemented to evaluate the recyclability of acrylonitrile butadiene styrene in extrusion-based AM, providing guidelines for quantifying variations of molecular weight distribution, material density, fabrication quality, and mechanical properties under multiple rounds of recycling. Different process parameters and their impact on material recyclability in each round are also studied. Experimental results indicate that the ultimate tensile strength degradation after each recycling round varies from 27% to over 50%; surface roughness increases 29.54% after three rounds of recycling; molecular weight distribution of recycled materials demonstrates obvious shifts, and the polydispersity is decreased by 13.16% after three rounds of recycling. The results of this research will help AM users better understand and implement waste recycling, causing a positive impact towards achieving cleaner production and enhancing the material efficiency and environmental sustainability of AM.
Article
In the last years, with the development of Additive Manufacturing processes, the research on the mechanical behaviour of lattice structures has gained significant attention. Depending on the application, the mechanical properties of the unit cell can be modified by varying its geometry. The cell geometry is generally designed through Finite Element Analyses. However, the simulation of the mechanical response of components made of lattice structures can be rather complex, due to the long computation time. Therefore, efficient simplified models should be employed, but, in this case, an experimental validation is required. In the paper, experimental compression tests are carried out on cubic specimens in lattice structures produced with a carbon nylon filament through a Fused Deposition Modeling process and with an AlSi10Mg alloy through a Selective Laser Melting process. The tests on carbon nylon specimens are carried out to assess the cell geometry ensuring the highest energy absorption among five selected cell geometries. Subsequently, a Finite Element (FE) model of the lattice structure specimens is created by using 1D beam elements and experimentally validated with the results obtained by testing manufactured specimens. The activity in the paper proves the effectiveness of models with 1D elements for the simulation of the mechanical response of the lattice structures and the importance of validating FE models to assess their real failure mode.
Article
Full-text available
3D printing is a popular technique for fabricating three-dimensional solid objects from a digital design. In order to produce high quality 3D printed parts, the appropriate selection of printing parameters is crucial. This research is focused on studying the properties of 3D printed specimens (i.e., mechanical, thermal and morphological) with varying processing conditions such as infill pattern, infill density and infill speed, and also with different printing materials. A number of testing techniques such as tensile, bending, compression, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), thermal imaging, and scanning electron microscopy (SEM) were used for performing a comprehensive analysis. The results showed that Young’s modulus of the printed parts increased with the increase of infill density. Parts with 100% infill density obtained the highest Young’s modulus of 1538.05 MPa. Of the tested infill speeds from 70-110 mm/s; 90 mm/s infill speed gave the highest Young’s modulus. Meanwhile, there was a slight difference of Young’s modulus between low speeds (70 mm/s and 80 mm/s) and high speeds (100 mm/s and 110 mm/s) compared to the commonly used infill speed of 90 mm/s. The level of crystallinity of the 3D printed PLA specimens did not directly influence the mechanical properties as was confirmed by the DSC results. SEM images showed that the strength of the printed samples was dependent upon the arrangement of their layers. Furthermore, it was found that the most appropriate processing temperature and infill speed for PLA filament are 215 °C and 90 mm/s, respectively. Carbon fibre reinforced PLA (CFR-PLA) gave the highest Young’s modulus of 2637.29 MPa at 90 mm/s. Voids inside the matrix and the gaps between layers lead to initiation of cracks of the specimens. Overall, 100% infill density, 90 mm/s infill speed, 215 °C of set nozzle temperature, and the linear fill pattern were the possible optimal process settings for the most improved performance of the five different printing materials used in this study.
Article
Full-text available
The lack of specific standards for characterization of materials manufactured by Fused Deposition Modelling (FDM) makes the assessment of the applicability of the test methods available and the analysis of their limitations necessary; depending on the definition of the most appropriate specimens on the kind of part we want to produce or the purpose of the data we want to obtain from the tests. In this work, the Spanish standard UNE 116005:2012 and international standard ASTM D638-14:2014 have been used to characterize mechanically FDM samples with solid infill considering two build orientations. Tests performed according to the specific standard for additive manufacturing UNE 116005:2012 present a much better repeatability than the ones according to the general test standard ASTM D638-14, which makes the standard UNE more appropriate for comparison of different materials. Orientation on-edge provides higher strength to the parts obtained by FDM, which is coherent with the arrangement of the filaments in each layer for each orientation. Comparison with non-solid specimens shows that the increase of strength due to the infill is not in the same proportion to the percentage of infill. The values of strain to break for the samples with solid infill presents a much higher deformation before fracture.
Article
Full-text available
Fused Filament Fabrication (FFF), classified under material extrusion additive manufacturing technologies, is a widely used method for fabricating thermoplastic parts with high geometrical complexity. To improve the mechanical properties of pure thermoplastic materials, the polymeric matrix may be reinforced by different materials such as carbon fibers. FFF is an advantageous process for producing polymer matrix composites because of its low cost of investment, high speed and simplicity as well as the possibility to use multiple nozzles with different materials. In this study, the aim was to investigate the dimensional accuracy and mechanical properties of chopped carbon-fiber-reinforced tough nylon produced by the FFF process. The dimensional accuracy and manufacturability limits of the process are evaluated using benchmark geometries as well as process-inherent effects like stair-stepping effect. The hardness and tensile properties of produced specimens in comparison to tough nylon without any reinforcement, as well as continuous carbon-reinforced specimens, were presented by taking different build directions and various infill ratios. The fracture surfaces of tensile specimens were observed using a Scanning Electron Microscope (SEM). The test results showed that there was a severe level of anisotropy in the mechanical properties, especially the modulus of elasticity, due to the insufficient fusion between deposited layers in the build direction. Moreover, continuous carbon-reinforced specimens exhibited very high levels of tensile strength and modulus of elasticity whereas the highest elongation was achieved by tough nylon without reinforcement. The failure mechanisms were found to be inter-layer porosity between successive tracks, as well as fiber pull out.
Article
Full-text available
This research study reports the creep behavior analysis of the new composite materials manufactured by 3D printing technology. Nylon was used as a polymer matrix, and carbon fiber, Kevlar, and fiberglass were used as reinforcing agents. Since the properties of 3D-printed components are usually insufficient for robust engineering applications, adding reinforcing fibers improves the performance of these components for several engineering applications. Fiber-reinforced additive manufacturing (FRAM) is an almost 4-year-old technology. Additionally, there is not sufficient research on the behavior of FRAM components specifically at high temperatures. Therefore, the investigation of the high-temperature behavioral analysis of FRAM components was focused on in this study. Creep properties of the composite specimens reinforced by different fibers were measured by the dynamic mechanical thermal analysis system. The statistical analyses were conducted to analyze the experimental data using mathematical models. The microstructural analysis was performed to further investigate parts’ morphology, 3D printing quality, and fracture mechanisms. The results indicated that the creep compliance of reinforced composite specimens was significantly improved in comparison with pure nylon. Overall, this paper presents quantitative creep analysis results demonstrating the capabilities of FRAM components to be used for several engineering applications.
Article
In this work the effect of FDM parameters, viz., layer thickness, print temperature, and infill pattern on tensile strength of Carbon fibre PLA is studied. The printing process is done by considering three levels for each parameter and a full factorial design of experiments (3³) are conducted. The tensile test data is analyzed by conducting ANOVA and results indicate that the interactions between layer thickness-infill pattern, and infill pattern-extrusion temperature have significant effect on tensile strength. The highest tensile strength of 26.59 MPa is obtained for a layer thickness of 0.1 mm, extrusion temperature of 225 °C and cubic infill pattern.
Article
This experimental study investigates the effect of filling pattern on tensile and flexural strength and modulus of the parts printed via fused deposition modeling (FDM), 3D printer. The main downside of the printed products, with an FDM 3D printer, is the low strength compared to the conventional processes such as injection molding and machining. The issue stems from the low strength of thermoplastic materials and the weak bonding between deposited rasters and layers. Selection of proper filling pattern and infill percentage could highly influence the final mechanical properties of the printed products that were experimentally explored in this research work. Concentric, rectilinear, hilbert curve, and honeycomb patterns and filling percentage of 20, 50 and 100 were the variable parameters to print the parts. The results indicate that concentric pattern yields the most desirable tensile and flexural tensile properties, at all filling percentages, apparently due to the alignment of deposited rasters with the loading direction. Hilbert curve pattern also yielded a dramatic increase in the properties, at 100% filling. The dramatic increase could be mainly attributed to the promotion of strong bonding between the rasters and layers, caused by maintaining a high temperature of rasters at short travelling distances of nozzle for the hilbert curve pattern. Scanning electron microscopy (SEM) examination revealed the strong bonding between rasters and sound microstructures (less flaws and voids) for concentric and hilbert curve pattern at a high filling percentage of 100. Besides, SEM examination revealed large voids in honeycomb pattern, deemed to be responsible for its lower strength and modulus, especially at the filling percentage of 100.
Article
The fracture properties (stress intensity factor and energy release rate) of additively manufactured (AM) polylactic acid (PLA) and its short carbon fiber (CF) reinforced composites have been studied. The effects of CF reinforcement, nozzle geometry and bead lay-up orientations in fracture properties, void contents, and interfacial bonding were investigated. The fused filament fabrication (FFF)-based AM specimens using both circular and square shaped nozzle were printed and compared with the conventional compression molded (CM) samples. Compact tension (CT) specimens with different CF concentrations (0 wt.%, 3 wt. %, 5 wt.%, 7 wt.% and 10 wt.%) were printed with two bead lay-up orientations (45⁰/-45⁰ and 0⁰/90⁰) using PLA and CF/PLA composite filaments. The results show significant improvement in fracture toughness and fracture energy for CF/PLA composites in comparison to neat PLA. The fracture toughness was increased by 42% for 0⁰/90⁰ and 38% for 45⁰/-45⁰ bead orientations, respectively with 5% CF loading. The increase in fracture energy was observed to be about 77% for 0⁰/90⁰ and 88% for 45⁰/-45⁰ bead orientations, respectively for the same fiber reinforcement (5 wt. %). Such improvement in fracture properties is expected to be higher for all 90⁰ bead orientations. The samples printed by square-shaped nozzle showed enhanced fracture toughness with less inter-bead voids and larger bonded areas in comparison to the circular-shaped nozzle. Although the fracture toughness showed very negligible differences between 0⁰/90⁰ and 45⁰/-45⁰ specimens, distinguishable variation may be seen in the case of 0⁰ and 90⁰ bead orientations. The crack propagation path and fracture mechanisms were studied using optical microscopy (OM) and scanning electron microscopy (SEM) examinations. Fractography revealed different modes of failure with a very high fiber orientation along the printing direction and a relatively higher void contents for 7 and 10 wt. % fiber reinforcement.
Article
Material extrusion additive manufacturing (MEAM), a sub-branch of three- dimensional (3D) printing is growing in popularity. Test specimens were 3D-printed using commercial polylactic acid (PLA) filament, and PLA filament reinforced with short-carbon fibers (PLA/CF). As-printed specimens and specimens that were annealed at three different temperatures, then subjected to tensile testing. The internal microstructures of the samples were also examined. The effects of the short- carbon fiber fillers on the mechanical properties of 3D-printed PLA were investigated, and the effects of the annealing process on polymer crystallinity and mechanical properties. The annealing process was shown to increase the crystallinity of both sample groups, though no statistically significant effect of annealing on mechanical properties was observed. The tensile properties of the PLA and PLA/CF filaments showed that the addition of carbon fibers to the PLA filament led to a significant increase in elastic modulus of the MEAM sample
Article
This study evaluated the performance of continuous carbon, Kevlar and glass fibre reinforced composites manufactured using the fused deposition modelling (FDM) additive manufacturing technique. These nylon composites were fabricated using a Markforged Mark One 3D printing system. The mechanical performance of the composites was evaluated both in tension and flexure. The influence of fibre orientation, fibre type and volume fraction on mechanical properties were also investigated. The results were compared with that of both non-reinforced nylon control specimens, and known material property values from literature. It was demonstrated that of the fibres investigated, those fabricated using carbon fibre yielded the largest increase in mechanical strength. Its tensile strength values were up to 6.3 times that obtained with the non-reinforced nylon polymer. As the carbon and glass fibre volume fraction increased so too did the level of air inclusion in the composite matrix, which impacted on mechanical performance. As a result, a maximum efficiency in tensile strength was observed in glass specimen as fibre content approached 18%, with higher fibre contents (up to 33%), yielding only minor increases in strength.