Journal of Materials Processing Technology 238 (2016) 218225 [623418]

Journal of Materials Processing Technology 238 (2016) 218–225
Contents lists available at ScienceDirect
Journal of Materials Processing Technology
jo ur nal home p ag e: www.elsevier.com/locate/jmatprotec
Rapid prototyping of continuous carbon fiber reinforced polylactic
acid
composites by 3D printing
Nanya Li, Yingguang Li∗, Shuting Liu
College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China
a r t i c l e i n f o
Article history:
Received
24 March 2016
Received in revised form 11 July 2016
Accepted
15 July 2016
Available online 18 July 2016
Keywords:3D printing
Continuous
carbon fiber
Polylactic
acid compositesa b s t r a c t
The continuous carbon fiber reinforced polylactic acid composite was manufactured by the rapid pro-
totyping approach of three-dimensional (3D) printing. In order to analyze the improvement of this new
method, the comparison experiments of printed samples with or without preprocessed carbon fiber bun-
dle were performed. The mechanical strength and thermodynamic properties were measured by using
the electronic testing machine and Dynamic Mechanical Analyzer (DMA). The novel nozzle and path
control methods were designed to satisfy the demands of continuous carbon fiber printing. Through the
experiment and analysis, the preprocessed carbon fiber with polylactic acid sizing agent could effectively
increase the interfacial strength between carbon fiber and resin. The experimental results demonstrated
that the tensile strength and flexural strengths of modified carbon fiber reinforced composites were
13.8% and 164% higher than original carbon fiber reinforced samples. The Scanning Electron Microscope
(SEM) scan results indicated that the preferable bonding interfaces were achieved of modified carbon
fiber reinforced composite.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
In recent years, the biodegradable composites draw many
attentions in aerospace applications, as the increasingly seri-
ous environmental pollution problems caused by thermosetting
composites. Mohanty et al. (2000) reviewed the application of
biopolymers and considered that the biopolymers offer envi-
ronmental benefits including biodegradability, renewability and
less greenhouse gas emissions. Polylactic acid (PLA) is a kind
of biodegradable material derived from renewable resource and
possesses good mechanical properties, which makes it promis-
ing an ecologically friendly material for composite applications.
Drumright et al. (2000) and Garlotta (2001) reported that the degra-
dation occurs by hydrolysis to lactic acid and fully disappeared
within one month. However, Semba et al. (2006) exhibited that
the PLA is brittle, and limiting its uses in aerospace field with high
performance requirements. Some improvements have been made
by Oksman et al. (2003) who proposed to use fiber materials as
reinforcement.
3D printing method is widely investigated in processing the
thermoplastic resin of PLA due to the good characteristics of strong
∗Corresponding author.
E-mail address: [anonimizat] (Y. Li).operation, low cost and no need of tooling or mold (Lipson and
Kurman, 2013 ). But it is still a big challenge to rapidly obtain the
fiber reinforced PLA composites of excellent mechanical proper-
ties by 3D printing. The printing techniques of polymer materials
mainly include the Stereo Lithography Apparatus (SLA) and Fused
Deposition Modelling (FDM). Melchels et al. (2009) and Sarment
et al. (2002) developed the SLA technologies with better fabrica-
tion accuracy, but the high costs of facilities and photo-sensitive
resin materials restrict its applications.
The fused deposition modeling with low costs of printing device
and thermoplastic materials is a better choice for industrial pro-
duction. Various devices and parts have been printed by the FDM.
Leigh et al. (2012) and Czy˙zewski et al. (2009) demonstrated the
printing of micro-scale of electronic sensors and carbon nanofibers,
separately. Hutmacher et al. (2001) and Ahn et al. (2002) investi-
gated the mechanical strengths and anisotropic material properties
of FDM manufactured parts. For the FDM printing of carbon fiber
reinforced composite material, Van Der Klift et al. (2015) employed
the Mark One 3D printer to evaluate the 3D printing production
capabilities of carbon fiber reinforced thermoplastic. Tekinalp et al.
(2014) and Ning et al. (2015) studied the 3D manufacturing of short
carbon fiber (0.2–0.4 mm) and carbon fiber powder reinforced com-
posites with the microstructures and mechanical performances
being tested. Matsuzaki et al. (2016) proposed that the continuous
fiber reinforced composites could be fabricated by the 3D print-
http://dx.doi.org/10.1016/j.jmatprotec.2016.07.025
0924-0136/© 2016 Elsevier B.V. All rights reserved.

N. Li et al. / Journal of Materials Processing Technology 238 (2016) 218–225 219
ing and the technique has potential to become the next-generation
composite fabrication methodology. Mori et al. (2014) printed a
sandwich structure with carbon fibers placed between lower and
upper plastic plates and heated after 3D printing to bond the car-
bon fibers with the plastics. These printing methods mention above
can manufacture continuous carbon fiber reinforced thermoplastic
composites. However, the curved printing path can be printed, and
the weak infiltration between fiber and resin reduced the perfor-
mance of printed composites.
To develop the 3D printing of continues carbon fiber rein-
forced polylactic acid composites with curved structures and higher
mechanical strength for practical applications, we proposed a pro-
totyping approach for the rapid and continuous printing. The novel
extrusion nozzle and path control methods were designed to print
curved composite structures. And mechanical properties of tensile
strength and flexural strength were tested to make the comparison
between printed samples with or without carbon fibers. The car-
bon fiber reinforced composite exhibits better mechanical property
than that of PLA but weak interface bonding between carbon fiber
and PLA. Thus, the modification of carbon fiber bundles was intro-
duced by infiltration in the PLA sizing agent before printing, for
further improvement of the composite mechanical properties. It is
indicated that the interfacial strength of the modified carbon fiber
composite was increased substantially from experimental results of
mechanical tests combined with the analysis of scanning electron
microscope (SEM). Thermodynamic properties of glass-transition
temperature and loss modulus were also tested to analyze the
glass-transition temperature and loss modulus of printed samples.
2. Experimental
2.1. Material preparation
The carbon fiber bundle is made up of 1000 single carbon fibers
(HtA40 H13, Toho Tenax Co., Ltd.), and the purity of polylactic acid
resin is 98% (NatureWorks). For purpose of continuous extrusion of
PLA resin with the carbon fiber, the PLA wire rod is processed by
using screw-type extruder (Wellzoom-B). The framework of FDM
printer is assembled by using mature commercial modules and the
main controller board can connect to the CURA open source 3D
printer software. This modified 3D printer can manufacture the
composite components in three axis position control. Four stepping
motors are responsible for the nozzle-path control, Z-axis, X-axis
and Y-axis. The control accuracy of the stepping motors is about
±0.2 mm.
2.2. Design of extrusion nozzle
The nozzle of 3D printer is designed to print continuous carbon
fiber and curved path, as shown in Fig. 1. Continuous PLA wire and
carbon fiber bundle mix in the guide pipe through heating the PLA
resin to melting temperature. The heat sink at the entrance of guide
pipe is to ensure the solid state of PLA wire. To uniformly mix the
carbon fiber and PLA resin, the conical nozzle is employed. During
the printing process, the already extruded carbon fiber reinforced
PLA filaments stick on the panel and provide persistent traction
force to pull the carbon fiber cladded by PLA out of the nozzle.
The printing processes of continuous carbon fiber reinforced PLA
composite parts are shown in Fig. 2. The printing mainly includes
the straight (shown in Fig. 2(a)) and curve (shown in Fig. 2(b)) paths,
both of which can be effectively conducted by the designed nozzle.
Because the port on the nozzle for material extrusion is circular, no
obstacles occur in the direction changing process. Furthermore, the
PLA resin cladding the carbon fiber reduces the friction force of the
nozzle.
Fig. 1. Schematic of the designed extrusion device to printing continuous carbon
fiber
reinforced PLA.
2.3. Printing path control
The printing path of unidirectional flat part, hollow-out aerofoil
and circle part are shown in Fig. 3. The start point, end point and
printing direction of a single layer printing path are presented in the
figure. With regard to the flat part shown in Fig. 3(a), the printing
path
changes 180◦at both ends of the length direction and the mov-
ing nozzle speeds down at the corner. The hollow-out aerofoil has
different start point and path control methods. The small straight
lines are applied to fit and interpolate the curve paths, just as the
G code method used in numerical control machines. As shown in
Fig. 3(b), the path starts from the inside to the outside of the part
and goes forward clockwise. When the path nears to the start point
of the first printing path, the nozzle changes direction to the sec-
ond path and the printing process circulates until reaching the end
point of the single layer. For the circle part, the printing path con-
trol is the same as the wing profile, as shown in Fig. 3(c). In more
detail, the nozzle feed speed, stopping time of extrusion when fiber
is turning around and path programming to avoid fiber interlacing
were taken into account. The material stacking along the thickness
direction of each composite part follows the printing path of single
layer. By taking these printing path control methods, the 3D printer
efficiently achieved the aim of rapid prototyping of continuous car-
bon fiber reinforced PLA composites part. Every single fiber path are
uniformly compacted by employing an appropriate space between
the nozzle and heating panel.
2.4. Carbon fiber modification
Considering the weak bonding interface between carbon fiber
and PLA resin reported by Yu et al. (2010) , the surface modification
of carbon fiber bundle is conducted before the printing process to
improve the interfacial strength, as shown in Fig. 4. The methy-
lene dichloride solution is added and the PLA particles (8% mass
fraction) partially dissolved after 30 min magnetic stirring. High-
speed dispersing and emulsification machine (DE-100LB) work
on 8000 r/min to shear and emulsify the filtrate of PLA resin in
methylene dichloride solution. The surface active, emulsifying and
antifoaming agents are added in the deionized water with 1% mass
fraction of total solution. Then slowly add the deionized water to
process the aqueous PLA sizing agent and modify the surface con-
dition of carbon fibers.

220 N. Li et al. / Journal of Materials Processing Technology 238 (2016) 218–225
Fig. 2. 3D printing process of the continuous carbon fiber reinforced composite. (a) printing the straight area of composite sample, (b) printing the corner of composite
sample.
Fig. 3. 3D printing path of continuous carbon fiber reinforced PLA composite parts. (a) unidirectional flat part, (b) hollow-out aerofoil and (c) circle part.
Fig. 4. Surface preprocessing modification of carbon fibers.
2.5. Mechanical and thermal analysis
Mechanical properties, thermodynamics testing and morphol-
ogy analysis were carried out to characterize the performance ofthis novel 3D printing of continuous carbon fiber composite. Three
different samples of PLA, carbon fiber reinforced PLA and modified
carbon fiber reinforced PLA were characterized by tensile strength,
flexural strength and DMA properties respectively, by using the
same process conditions (resin volume fraction, path control and
printing speed).
The tensile strength and flexural strength were tested by an
electron material testing machine (MTS CMT5504). The sizes of
samples were 110 mm long, 27 mm width and 2.3 mm thick, and
55 mm long, 12 mm width and 2.3 mm thick for tensile and flex-
ural strength test, respectively. The HITACHI DMS 6100 dynamic
mechanical analyzer was employed to characterize the glass tran-
sition temperature of continuous modified carbon fiber reinforced
polylactic acid composite and polylactic acid samples. The size of
sample was 35 mm long, 12 mm width and 2.3 mm thick and the
storage modulus and mechanical loss tangent were evaluated by
a single cantilever tool. The tests were achieved for three kinds of
different samples in three-point bending mode at a frequency of
1 Hz, and amplitude of 50 um. The temperature range from 23◦C to
250◦C at a heating rate of 5◦C/min.
2.6. Morphological studies
The surface morphology of 3D printed carbon fiber/PLA compos-
ites were measured using Olympus CX31 microscope. The electron
microscope samples with dimensions of 4 mm × 4 mm × 2 mm

N. Li et al. / Journal of Materials Processing Technology 238 (2016) 218–225 221
Fig. 5. Surface morphology of 3D printed carbon fiber/PLA composite. (a) micrograph of carbon fiber bundle and PLA resin, (b) micrograph of PLA width between carbon
fibers,
(c) schematic of the uneven distribution of PLA.
were fixed to the substrate and coated with a 40 nm thickness gold
layer to improve the resolution ratio. The Carl Zeiss EVO18 Scanning
Electron Microscope (SEM) with thermionic gun and accelerating
voltage of 10 kV was used to scan the SEM images of the samples.
3. Results and discussions
3.1. Morphological analysis
Before measuring the mechanical properties of printed com-
posite, the morphological analysis was conducted. The surface
morphology of printed carbon fiber reinforced PLA composite is
shown in Fig. 5. The modified carbon fiber bundle and PLA resin can
be clearly distinguished from the micrographs shown in Fig. 5(a)
and (b). The width of extruded carbon fiber bundle and resin is
about 600 um. During the printing process, the distance between
the nozzle and heating panel (or the already printed composite
layer under the nozzle) is controlled less than the diameter of the
extruded material. Thus, the nozzle and heating bed (or the already
printed composite layer) can squeeze the composite material into
flat banding The PLA resin is coated on the fiber and extruded to the
two sides of fiber banding from figure, and the maximum width is
about 500 um. As shown in Fig. 5(a), the surface of 3D printed car-
bon fiber reinforced PLA composite is flattened by the nozzle and
the good fusion quality between PLA resins is achieved. Fig. 5(b)
exhibits that there is different width of the PLA between carbon
fibers, the mechanism of this phenomenon is analyzed in Fig. 5(c).
The PLA has uneven distribution at the two sides of carbon fiber
banding after extrude from the nozzle, the back and forth printing
path may not change the distribution of PLA. Thus, the width of PLA
change from about 300 um to 500 um between carbon fibers during
printing.In order to check the voids and fiber volume content of the
printed composite, the optical micrographs of the cross section of
3D printed specimen are shown in Fig. 6. The profile of straight and
corner areas of the printed composite are compared and analyzed.
The modified carbon fiber bundles are marked in white circles in
Fig. 6(a) and (b), two printing layers are observed in the cross sec-
tion. And the amplification of the straight and corner areas are
shown in Fig. 6(c) and (d), respectively. The voids of printed com-
posite specimens are marked in blue circles and the micrographs
exhibit that the corner area has much more voids than the straight
area. This result may attribute to the deformation of carbon fiber in
the corner area. The amplified graphs indicate that modified carbon
fiber and PLA resin joint closely for both two kinds of specimens.
Based on the microscopic testing method of the fiber volume frac-
tion measurement for unidirectional composite materials, the fiber
volume fraction of printed samples can obtain in Fig. 6(a) and (b).
The printed carbon fiber reinforced composite samples have unidi-
rectional carbon fiber bundle and the microscopic of cross section
can clearly distinguish the carbon fiber and resin areas. The carbon
fiber areas only have PLA sizing agent (can be ignored) and gather
into bundles. And the cross section areas of carbon fibers are ellip-
tical circles, because of the nozzle and heating bed (or the already
printed composite layer) squeezed the material into flat banding.
The area in the yellow lines is one of the periodic structure areas
of the specimen. That means the fiber volume fraction calculated
by those areas can represent the printed composite samples. The
cross section area of carbon fiber is defined as Afand the total mea-
suring area is defined as A. The fiber volume fraction Vfof printed
composite can be calculated according to the equation below.
Vf=Af
A× 100% (1)

222 N. Li et al. / Journal of Materials Processing Technology 238 (2016) 218–225
Fig. 6. The optical micrographs of the cross section of 3D printed specimen. (a) and (b) straight and corner areas of the printed composite, (c) and (d) amplification of the
straight
and corner areas.
By means of calculating the dimensions of pixel, the area in
the yellow lines (total measuring area) is about 0.7 mm2and the
area of white circle in the yellow line (carbon fiber area) is about
0.24 mm2. Thus, the fiber volume fraction Vfis about 34% of the
printed composite specimen. The calculated fiber volume fraction
value is almost the same as the feeding volume ratio of carbon fiber
and PLA resin.
3.2. Mechanical properties
The tensile strength and flexural strength were both tested by
fixtures on the universal testing machine. In order to ensure the
repeatability of the test results, each of the properties were tested
by using three samples. A testing speed of 2 mm/min is applied
during the tensile test, as shown in Fig. 7(a). The tensile strength of
sample can be calculated by:
/ESCt=F
bd(2)
Where F is the stretching load (N), b is the width of the test sample
(mm), d is the thickness (mm). The flexural strength test is con-
ducted on the same testing machine but only the fixture is changed
to the three-point bending type, as shown in Fig. 7(b). The diameter
of the load indenter was adjusted to 5 mm and its descent veloc-
ity was 2 mm/min. The flexural strength was determined using the
equation:
/ESCf=3P · l
2b · d2(3)
Where the P is the bending load (N), l is the length (mm) of the sam-
ple. The tensile and flexural strength curves of three different kinds
of material are shown in Fig. 8. As illustrated in this figure, the whole
tensile process can be divided into three different phases. The dif-
ferent slope of curves shown in Fig. 8 at the beginning are observed
in both two kinds of test results. The duration periods are from 0 to
10 s and 0 to 50 s for the tensile and flexure strength, respectively.
Fig. 7. Test of tensile and flexure strength of 3D printed composite parts. (a) tensile
test, (b) flexure test using three-point bending fixture.
The PLA resin of the contact area which between the sample and
the test fixtures may bear the load firstly. Therefore, those periods
exhibit lower strength and slope of curves than the follow-up test
stages. Owing to a better interface adhesion, the modified carbon
fiber reinforced sample’s curve transforms to linear elastic defor-
mation stage earlier than the original carbon fiber reinforced one.
During the elastic deformation stage, there is a slight drop of slope
for both two carbon fiber reinforced samples. The reason proba-
bly is that a part of fiber-matrix interface debond when the load
is up to the limit value of interface strength. However, on account
of a better interface between the modified carbon fiber and PLA
matrix, the reducing is smaller than the unmodified one. Finally,
the two kinds of carbon fiber reinforced composite material and

N. Li et al. / Journal of Materials Processing Technology 238 (2016) 218–225 223
Fig. 8. Mechanical properties of three different materials printed by the same process condition, (a) Tensile strength of PLA, carbon fiber reinforced PLA and modified carbon
fiber reinforced PLA, (b) flexure strength of PLA, carbon fiber reinforced PLA and modified carbon fiber reinforced PLA.
Fig. 9. SEM micrographs of printed composites, (a) fiber-matrix interface of carbon fiber reinforced PLA specimen, (b) carbon fiber reinforced PLA specimen after tensile test,
(c)
fiber pull-out of specimen after tensile test, (d) fiber-matrix interface of modified carbon fiber reinforced PLA specimen, (e) modified carbon fiber reinforced PLA specimen
after
tensile test and (f) fiber pull-out of modified carbon fiber reinforced PLA specimen after tensile test.
Table 1
Statistic
results of tensile and flexure strength of three different samples.
PLA Carbon fiber
reinforced
PLAModified carbon
fiber
reinforced
PLA
Tensile strength (Mpa) 28 80 91
Flexure
strength (Mpa) 53 59 156
PLA resin reaches the yield point and fracture. The carbon fiber
reinforced samples are completely snapped by the external load
and most of the fiber-matrix interface are damaged too. Consider-
ing the extreme loading capacity, it is apparent that the maximum
tensile strength of two different carbon fiber reinforced sample are
significantly higher than the PLA one.
Compared to the short carbon fiber reinforced thermoplastic
matrix material which are manufactured by Tekinalp et al. (2014)
and Ning et al. (2015) , the tensile strength of continuous car-
bon fiber reinforced composite manufactured in this experiment
is much higher. Precisely, the maximum value of short carbon fiber
reinforced part is only 68 Mpa, but the continuous carbon fiber
reinforced ones reach up to 91 Mpa (Table 1).
As shown in Fig. 8(b), the flexural property of the original carbon
fiber printed sample is much closer to the PLA sample. However,
the modified carbon fiber printed PLA sample has much higherflexural strength than the original carbon fiber printed one, and
about 164% improvement is achieved for the modified carbon fiber
printed sample. This can be attributed to the reason that the inter-
facial strength between matrix and reinforcement has a significant
influence on three-point bending test and flexural property. As can
be seen in Fig. 8(b), the first marked circle of carbon fiber rein-
forced samples corresponds to the process of load change from
resin to fiber, which means plastic deformation of PLA. At the yield
point, the PLA polymer chains generate plastic elongation and the
stretched polymer chains lead to a continued load bearing after the
broken of carbon fibers.
The SEM micrographs of carbon fiber and modified carbon fiber
reinforced composite samples are shown in Fig. 9. Fig. 9(a)–(c)
demonstrate the fiber-matrix interface, interface structure after
tensile test and the morphology of fiber pull-out the original car-
bon fiber reinforced sample, respectively. Also, the micrographs
of Fig. 9(d)–(f) correspond to the modified carbon fiber reinforced
composite samples. Comparing the micrograph of Fig. 9(a) and (d),
homogeneous distribution of PLA between fibers and nearly void-
free microstructure can be found in modified carbon fiber samples,
which indicates a better wetting and stronger interface of the mod-
ified carbon fiber samples.
As shown in Fig. 9(b), many voids between carbon fibers can
be identified, and poor infiltrate of PLA and fibers are founded. The

224 N. Li et al. / Journal of Materials Processing Technology 238 (2016) 218–225
Fig. 10. Storage modulus and loss tangent of three kinds of printed materials.
small bridges marked by the red circle in micrograph Fig. 9(b) suffer
and transfer the load between the fibers. On the contrary, the mod-
ified carbon fiber reinforced PLA composite has higher fiber-matrix
interfacial bonding strength as the good infiltration, the stripe and
scaly structures are observed. Those structures are broken from the
coated carbon fibers and the main load is transferred by the dense
PLA matrix distributed among the carbon fibers. Furthermore, the
fracture surface of two kinds of printed composite is compared. As
shown in Fig. 9(c) and (f), the carbon fibers put-out from the ten-
sile fracture surface. The more evident comparison results between
original and modified carbon fiber reinforced PLA composites are
analyzed. For the fracture surface of original carbon fiber sample,
there is very little PLA resin cover the cracked carbon fibers, or some
fibers are completely exposed. Conversely, in the case of modified
carbon fiber sample, plentiful PLA resin clad among the cracked
fiber, and there is no prominent separation of fiber and matrix. This
explains the significant difference of flexure strength of the modi-
fied carbon fiber and the original carbon fiber printed composites.
All the micrographs indicate that the better fiber-matrix interfacial
strength has been achieved by adopting the method of modifying
the carbon fiber before the printing process.
3.3. Analyzing of DMA results
The dynamical mechanical characteristics of three kinds of dif-
ferent samples were measured based on DMA. The dynamic storage
modulus (E/prime) and loss tangent (tan ı) are analyzed in Fig. 10. The loss
tangent is the ratio of loss modulus and storage modulus, which
indicate the viscosity and elastic properties of material, respec-
tively. As shown in Fig. 10, the storage modulus of three specimen
reach the maximum value at the beginning of the testing and
decrease as the temperature raising. The peak of loss tangent curve
appears and can be defined as the glass transition temperature (Tg)
of material. This can be attributed to the promotion of the molecular
mobility of the thermoplastic PLA resin. Comparing with the stor-
age modulus of different specimens at the beginning of the test, a
remarkable increase can be found of the modified carbon fiber rein-
forced PLA specimen. The reason can be explained as the stiffness of
the specimen raised by applying the modified fiber reinforcement,
and most of the stress is transferred to the carbon fiber through the
fiber-matrix interface. What makes the result unforeseen is that the
initial storage modulus of original carbon fiber reinforced specimen
is lower than the PLA. This behavior is quite similar to the result
of flexural test. This may associate with the infiltration quality of
carbon fiber and melting PLA matrix during the printing process.
Without the PLA sizing agent, the carbon fiber can hardly be infil-Table 2
The
storage modulus, loss tangent and Tgof different printed materials.
PLA Carbon fiber
reinforced
PLAModified carbon
fiber
reinforced
PLA
Storage modulus (GPa) 1.22 0.72 3.25
Loss tangent 2.32 1.52 1.32
Tg(◦C) 63.6 65.2 66.8
trated by the PLA resin and the fibers lead to weak connection or
even defects for the printed composite structure.
The statistic results of storage modulus, loss tangent and Tgof
different printed materials are shown in Table 2. It is observed that
the modified carbon fiber reinforced PLA samples have highest stor-
age modulus and Tgthan other two samples, and the loss tangent
is the lowest. That means that the modified carbon fiber reinforced
PLA has a better interfacial bond and strength, which lead to a more
effective stress transfer between the fiber bundle. The storage mod-
ulus of modified carbon fiber reinforced samples are higher than
the PLA and original fiber reinforced samples for about 166% and
351%, respectively. Considering the Tgvalue, obviously, the thermal
stability of composites improves by being reinforced with contin-
uous carbon fiber. The much better heat conduction ability and
fiber-matrix interfacial bond contribute to this experiment results.
4. Conclusions
The rapid printing technologies of continuous carbon fiber rein-
forced polylactic acid composite was presented in this paper. The
nozzle was design to uniformly mix the carbon fiber and PLA resin.
The straight and curve paths for 3D printing of continuous car-
bon fiber reinforced composites can be achieved. Considering the
weak bonding interface between carbon fiber and PLA resin, the
preprocessing of carbon fibers was realized to improve the inter-
facial strength. The experimental results indicated that the tensile
strength and flexural strengths of modified carbon fiber reinforced
composites were 13.8% and 164% higher than original carbon fiber
reinforced samples. The storage modulus of the modified carbon
fiber reinforced samples were also higher than the PLA and original
fiber reinforced samples for about 166% and 351%, respectively. The
SEM scan results indicated better fiber-matrix bonding interface
of the carbon fiber preprocessed printing technology. This rapid
prototyping technology for the continuous carbon fiber composite
is a potential technology to manufacturing the complex and high
performance composite part, especially for the complex aircraft
structures.
Acknowledgements
This project is supported by National Natural Science Founda-
tion of China (Grant no. 51575275 and 51305195), jointly sup-
ported by the “Outstanding Talents Cultivation Fund” (NE2012003)
of Nanjing University of Aeronautics and Astronautics. The authors
sincerely appreciate the continuous support provided by our indus-
trial collaborators.
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