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TSpace Research Repository tspace.library.utoronto.ca
Carbon Nano Fibers Reinforced Composites Origami Inspired Mechanical Metamaterials
with Passive and Active Properties
Mohamed Ali E. Kshad, Clement D’Hondt, and Hani E. Naguib
Version Post-print/accepted manuscript
Citation
(published version)
Kshad, M. A. E., D’Hondt, C., & Naguib, H. E. (2017). Carbon nano
fibers reinforced composites origami inspired mechanical metamaterials with passive and active properties. Smart Materials and Structures,
26(10), 105039.
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accepted for publication/published in Smart Materials and Structures. IOP Publishing Ltd is not responsible for any errors or
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10.1088/1361-665X/aa8832.
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1
Carbon Nano Fibers Reinforced Composites Origami Inspired Mechanical
Metamaterials with Passive and Active Properties
Mohamed Ali E. Kshad1, Clement D’Hondt1, and Hani E. Naguib* 1,2,3
1 Department of Mechanical and Industrial Engineering, 5 King’s College Road, Toronto, ON,
M5S 3G8, Canada, University of Toronto, Canada 2 Department of Materials Science and Engineering, University of Toronto, Canada
3 Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada
* Corresponding author: naguib@mie.utoronto.ca
Abstract
Core panels used for compression or impact damping are designed to dissipate energy and to reduce the
transferred force and energy. They are designed to have high strain and deformation with low density.
The geometrical configuration of such cores plays a significant role in redistributing the applied forces to
dampen the compression and impact energy. Origami structures are renowned for affording large
macroscopic deformation which can be employed for force redistribution and energy damping. The
material selection for the fabrication of origami structures affects the core capacity to withstand
compression and impact loads.
Polymers are characterized by their high compression and impact resistance; the drawback of polymers is
the low stiffness and elastic moduli compared with metallic materials. This work is focused on the study
of the effect of Carbon Nano Fibers (CNF) on the global mechanical properties of the origami panel cores
made of polymeric blends. The base matrix materials used were Polylactic Acid (PLA) and Thermoplastic
Polyurethane (TPU) blends, and the percentages of the PLA/TPU were 100/0, 20/80, 65/35, 50/50, 20/80,
and 0/100 as a percentage of weight. The weight percentages of CNF added to the polymeric blends were
1%, 3%, and 5%. This paper deals with the fabrication process of the polymeric reinforced blends and the
origami cores, in order to predict the best fabrication conditions. The dynamic scanning calorimetry and
the dynamic mechanical analyzer were used to test the reinforced blended base material for
thermomechanical and viscoelastic properties.
The origami core samples were fabricated using per-molded geometrical features and then tested for
compression and impact properties. The results of the study were compared with previous published
results which showed that there is considerable enhancement in the mechanical properties of the origami
cores compared with the pure blended polymeric origami cores. The active properties of the origami unit
cell made of composite polymers containing a low percentage of CNF were also investigated in this
study, in which the shape memory effect test conducted on the origami unit cell.
2
1. INTRODUCTION
Presently, mechanical metamaterials; materials that gain their properties from their structure rather than
from the base material composition, have received increasing interest in research due to their superior
properties that can be exploited for designing novel materials with high-end functionalities composition
[1-3]. These materials have enormous potential use for sandwich and lightweight structures in aerospace
industry and other applications, because of their attractive properties such as negative Poisson’s ratio (i.e.
auxetic materials), negative compressibility, vanishing shear modulus, etc. [1–3]. Origami-inspired
metamaterials are auxetic meta-materials, in which the material is arranged in certain patterns creating
3D-tessellation. These auxetic properties have enabled the design of new structural materials with
superior properties based on the arrangement of the structural elements [4–6]. Origami based
metamaterials, inspired by the Art of folding papers, have received particular interest for engineering
applications, such as foldable solar panels, medical stents, and sandwich core applications [7,8]. The
design of the pattern of the origami tessellations affects the auxetic properties of the resultant 3D cores
[2]. Indeed, the creation of rigidly folded 3D geometric tessellations from 2D sheets, in which, rigid faces
joined by hinges, shows a great promise for those applications by offering good mechanical properties for
low-weight and low amount of used material [9,10].
Apart from these geometric tessellations is the Miura origami structure, which was first presented by
Miura in the 1970s for sandwich core applications and solar panel deployment in space [7,8]. Miura
origami is one of the origami patterns that attracted attention due to its geometric simplicity, its wide
range of possible configurations, and its intriguing mechanical properties, which lead to great elastic
energy absorption and force redistribution. [7, 8, 11, 12]. The mechanical properties of fold core
structures and origami cores have got wide attention in the literature, Kayumov et al. [13] introduced a
mathematical model to describe the behavior of chevron type sandwich panel cores. The study of the
impact of Z-crimp structure parameters on the strength under different loading conditions were
investigated in [14], Xiang Zhou et. al. studied the mechanical properties of Miura folded cores. Heimbs
et al. [15] investigated the behavior of the sandwich made of textile-reinforced composite. Based on
Miura origami pattern, You et al.[16] examined morphing sandwich mechanisms. Numerous of research
has been done in the investigating the mathematical and geometrical parameters of foldable core
structures [17–20]. Active origami structures also get interest in the resent years, in which active materials
can be employed for folding and unfolding process [21–24].
The aim of this study is to investigate the effect of CNF on the mechanical properties of origami
structures made of multiphase polymeric blends by using pre-molded process. The material blends used
were PLA and TPU, the weight percentages of the compositions used were 100/0, 20/80, 65/35, 50/50,
20/80, and 0/100, and the reinforcement weight percentages of CNF were 1%, 3%, and 5%. The
3
polymeric blends were compounded with the CNF, and then the compounded compositions were used for
fabricating the origami structures, by using compression molding.
The compression test was conducted for the fabricated cores to measure the compression and the strength
moduli of the origami cores; also, a drop mass impact test was performed to predict the transferred force
and the damped energy by the origami cores. The results demonstrated that the compression moduli
increased as a result of the increase in the CNF content; these values showed that there is large
enhancement in the moduli of compression and strength of the composite origami cores, compared with
the cores made of pure blends; while the amount of damped energy during the impact event was reduced
by the increase in the CNF percentage.
The folding/unfolding operation of origami structure is important in some origami-based applications to
be externally produced [21]. At very small, large and in remote applications, self-folding origami made of
active materials that convert various forms of energy to mechanical work, have proven their usefulness
use in many of these potential applications [25–30]. Shape memory polymers (SMP) are active materials
that have high shape memory recoverability, that can be employed in many active applications
[11,21,25,26,31,32]. This work also includes an investigation of active properties (shape memory effect)
of origami unit cell made of composite polymers. The shape memory effect test showed that there is high
recovery ratio in the PLA with low percentage of CNF samples.
2. EXPEREMENTAL WORK
2.1 MATERIALS
The goal of the use of the origami cores is to transform kinetic energy into elastic strain energy through
the elastic deformation of the core structure; therefore, the materials used to fabricate the origami
structures are the key to the global mechanical properties of the origami cores, for target applications. The
materials must be compliant to allow for the free motion of the structure. Also, since the cores should
withstand the bending loading, the material must allow the faces’ connections to deform elastically, while
also providing enough stiffness in the panels to resist bending. Therefore, two polymers were selected to
produce the material blends which are used as a matrix reinforced with Carbon Nano-Fibers (CNFs) as a
filler to enhance the mechanical properties of the material blends.
Polylactic Acid (PLA) grade (3052D) was obtained from Natureworks, LLC (USA), and Thermoplastic
polyurethane (TPU) grade (55D) was obtained from Lubrizol Engineering Polymers (USA).
PLA is a bio-based polymer which has advantageous mechanical properties, is also a bio-degradable
material, which requires low energy processability [33]. PLA is blended with (TPU) which is
characterized by strength, ductility, impact resistance and toughness [34]. Previous studies showed that
both polymers are compatible, and it is easy to compound the two material phases. Table 1, lists the
4
physical properties [28], the tensile test results, and the DSC results of the base materials used in the
experimental work.
The Carbon Nanofibers CNFs used were Pyrograf, PR-19-XT-PS, with an average diameter of 150 nm,
which are available in their fiber form or as a master-batch composed of 85% of PLA and 15% of
nanofibers. The use of the master-batch is preferred for safety reasons, but the CNF fiber form can be
manipulated under fume hoods in a designated laboratory with safety equipments. The PLA/TPU weight
percentages used are similar to the previous study done for the pure blends [35], which were (100/0,
80/20, 65/35, 50/50, 20/80, 0/100), and the CNF weight percentages added to the blends were (1%, 3%,
and 5%). A twin screw micro-compounder (DSM; Geleen, Netherlands) (MICRO15) was used to produce
the material blends, by melting and mixing the pellets at a temperature range of (180 °C – 195°C) with
the screw speed of 30 rpm for 10 min; then the blends were extruded and pelletized.
Carbon Nanofibers are fillers used in polymers when multifunctional properties are needed [36,37]. In our
case, the properties that we need to improve are mainly the strength of the origami cores and the thermal
properties (for active properties).
Al-Saleh et al. [38,39] introduced multiple reviews on CNF/polymer composites’ properties that outline
the various improved properties, taking in the consideration the optimal method to prepare those
composites. The fibers need to be well dispersed and distributed in the polymer matrix to minimize the
stress concentration, and to improve the uniformity of the stress distribution. One important factor is the
fiber diameter, which improves the tensile properties due to a diminution of the number of defects, the
contact area between fillers and polymer increases, as well as the fiber flexibility. The flexibility allows
the fibers to keep their aspect ratio increasing the stress transfer, and enhancing its mechanical properties.
It has also been proven that the CNF increases the complex viscosity, storage modulus and loss modulus
of the matrix polymer. CNF could also change the polymer crystallinity and affect the transition
temperatures. Al-Saleh et al. [38,39] also considered how to blend polymers and CNF by melt-spinning to
get a good dispersion, and to maintain the aspect ratio of the fibers.
Table 1. The physical, mechanical and the thermal properties used to fabricate origami cores
Material Density (g/cm3) E (MPa) Melting Temperature Tg (C)
PLA 1.24 1060 145 - 160
TPU 1.16 34.0 ~ 181
2.2 MATERIAL BLENDS MICROSTRUCTURE
Small samples from the composite blends were frozen by using liquid nitrogen and fractured for imaging
the cross section. The samples were prepared and placed on stubs, and then they were coated with
5
platinum ions using SC7620 Sputter Coater, Polaron, for 3 minutes. The microstructure images were
obtained by using scanning electron microscope micro-scope (JSM-6060, JEOL) (SEM).
The SEM images of the blended composites are illustrated in figure 1, in which figures a, b and c, show
the SEM images of PLA with 1, 3 and 5 wt.% of CNF respectively, it is clear that, the CNF fibers were
homogeneously distributed in the polymeric matrix. Figures 1 d, e, and f, show the SEM images of the
80/20 PLA/TPU with 5 wt.% CNF, 50/50 PLA/TPU with 5 wt.% CNF, and neat TPU with 5 wt.% CNF,
the images show that the CNF were uniformly distributed in matrix in both 80/20 and 50/50 PLA/TPU
composites, while there is slight CNF agglomeration in the case of neat TPU.
Figure 1. SEM micrographs of composite blends, magnification factor 20000X, a) PLA with 1 wt% CNF, b) PLA with 3wt% CNF, c) PLA with 5 wt% CNF, d) 80/20 PLA/PTU with 5 wt% CNF, e) 50/50
PLA/PTU with 5 wt% CNF, f) TPU with 5 wt% CNF.
2.3 FABRICATION PROCESS
To fabricate the origami core structures, a special compression mold was used; the mold was designed to
transfer the geometrical features of the origami structure, to the fabricated cores (see figure 2) [35]. The
pelletized material blends were uniformly spread in the mold to ensure the homogeneous distribution of
the material, and to avoid bubbles occurring in the samples; the mold was initially coated with silicon
based mold-release spray, in order to easily remove the samples. The upper and the lower parts of the
mold were set at a temperature of 20C above the melting temperature of the material blends for 30
6
minutes, allowing the blended material to melt. Then, after the upper and lower temperatures were
stabilized, the mold was sealed using fiber reinforced rubber, and was closed without applying pressure
for 15 minutes; in this stage, the melted material flowed through the geometrical features of the origami.
In the next stage, a pressure of (3 - 3.5) tons was applied to the compression mold for 15 minutes; and
then finally, the pressure was released and the mold was immersed in a cold-water bath for the
recrystallization process. The melting temperatures of the material blends were experimentally measured
using DSC. Table 2 lists the fabrication parameters used for each material blend. In this process, it was
noticed that with the higher amount of CNF the material blends get more viscous and more material
leakage was observed; therefore, thicker sealing rubber was used to reduce the material leakage. The
values of the molding temperatures were taken to be about 20 °C above the melting range of the
composites, because the large mold size cannot allow the prediction of the temperature of the mold center.
Six samples from each composition were fabricated to be used for compression and impact tests. Figure 2
shows the fabricated origami core sample. For blended material compositions, a dog-bone shaped samples
and rectangular samples were produced according to ASTM 638 and ASTM D638 standards using
injection molding process. Those samples were used for the tensile testing and the DMA to investigate the
mechanical and the dynamic mechanical properties of the blended compositions.
Figure 2. a) Multi-stage compression mold used to fabricate origami cores, b) Composite origami
structures made by molding process
2.4 DIFFERENTIAL SCANNING CALORIMETRY (DSC) TEST
Differential scanning calorimetry provided by TA Instruments (Q50 TGA) was used to characterize the
thermal properties of the blended materials’ composition. Small material masses, ranging between 10 -
15g, were cut from each material blend composite and panned in aluminum pans; the temperature cycle
covered the range of -50 C to 180 C, the cooling/heating rate was 10C/min, and heat/cool/heat cycles
were conducted to predict the thermal properties of the tested samples.
b) a)
)
7
2.5 DYNAMIC MECHANICAL ANALYSIS (DMA) TEST
Dynamic mechanical analyzer provided by TA Instruments (DMA Q800) was used to test the viscoelastic
properties of the blended composite materials. The test was carried out on the rectangular samples
prepared by injection molding according to the ASTM D638 standard. A sinusoidal load with a frequency
of 5 Hz is applied under a temperature ramp from 30°C to 85°C. The storage and the loss moduli
were measured for each sample.
2.6 PASSIVE PROPERTIES OF COMPOSITE ORIGAMI CORES
2.6.1 COMPRESSION TEST OF COMPOSITE ORIGAMI CORES
To measure the capacity of withstanding the compression loads, the fabricated composite origami cores
were tested in compression, using a compression machine. Three samples from each composition were
prepared and tested. The samples were placed between two thick-rigid plates connected to the testing
machine to ensure the uniform distribution of the compressive load (figure 3). The load was applied
gradually at the rate of 5mm/min (ASTM D1621/94 standard), and the load deformation values were
recorded; then, the elasticity moduli and the compressive strength moduli were obtained.
Figure 3. Composite origami cores placed between thick-rigid plates in the compression test
2.6.2 IMPACT TEST OF COMPOSITE ORIGAMI CORES
For the impact event, a custom drop-weight impact setup was used to measure the impact force received
in the other side of the origami sandwiched cores, during the impact event (figure 4).
The test setup has a dynamic load sensor (Dytran, 1060V) placed in the lower side of the testing plate.
This load sensor is connected to the data acquisition system, allowing the recording of the force-time
values of the impact event, and then the force and energy transferred were obtained. In the test, the impact
weight used was 1.104 Kg, and the height was 66.5cm.
8
Figure 4. a) Composite origami core sandwiched between two plates, b) Impact test setup.
2.7 ACTIVE PROPERTIES
In order to investigate the active properties of the origami unit cell, the origami core made of PLA with
0.1% CNF was fabricated, and the unit cell was split for shape test. The shape memory test started with
compressing the origami unit cell using Instron (5848) testing machine, with a strain rate of 5mm/min as
per ASTM D695. The test was done at a temperature of 80C, which represents the glass transition
temperature of the composite material. Then the relaxation test was run under the same thermal conditions
to remove the residual stresses from the samples, from which the stress-time relation was recorded. After
relaxation test, the deformed origami unit cell sample was fixed. Finally, the deformed sample was kept
under a uniform temperature of 80 C, allowing the origami unit cell geometry to recover; the changing
height versus time recorded and the recovery factor was calculated.
3. RESULTS AND DISCUSSION
3.1 THERMAL PROPERTIES OF COMPOSITE MATERIAL BLENDS
3.1.1 DIFFERENTIAL SCANNING CALORIMETRY (DSC)
Figure 5 shows the heat flow curves of the composite blends, which were obtained using DSC. The
curves show the thermal behavior of the material tested. The glass transition temperature range (Tg), and
the melting temperatures of the composites were taken from the test, to decide the fabrication conditions
of the composite blends. Table 2 lists the values of the Tg, the melting temperature ranges of blended
composites Tm, and the molding temperature ranges used in the fabrication process.
The DSC results show that the addition of CNF in the base polymer matrix does not significantly change
the glass transition temperature of the TPU, which ranges from -36°C to -31°C or of PLA, which ranges
from 56°C to 60°C. The general behavior is that these temperatures increase with a higher PLA
composition in the PLA/TPU polymer blend, and a higher CNF composition in the composite.
a) b)
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Table 2. The DSC Results of the Material blends
CNF
(w%)
Material Blends Composition
(PLA/TPU) w%
Glass Transition
Temperature Range Tg (C)
Molding Temperature
range (C)
1% 100/0, 80/20,65/35, 50/50, 20/80, 0/100 (-34.55 – 58.65) 210 - 230
3% 100/0, 80/20,65/35, 50/50, 20/80, 0/100 (-32.35 – 59.30) 210 - 220
5% 100/0, 80/20,65/35, 50/50, 20/80, 0/100 (-31.85 – 58.9) 200 - 210
a) Composite blends with 1 w% CNF b) Composite blends with 3 w% CNF
c) Composite blends with 5 w% CNF
Figure 5. Thermal behavior of composite blends with CNF
3.1.2 DYNAMIC MECHANICAL ANALYSIS (DMA)
DMA results show the mechanical viscoelastic properties of the composite polymeric blends; those
results are illustrated in figure 6, which shows the storage and the loss moduli of the composite blends. At
low temperature, the macromolecules remain stiff, and do not resonate with the sinusoidal load, while at
high temperature; the molecular segments become mobile and then resonate with the load. By analyzing
the curve, we can clearly see the glass transition of PLA between the energy elastic state and the energy
10
entropy state shown by the sudden drop in storage modulus and the pronounced peak for loss modulus.
The behavior of PLA/TPU blends shows that, PLA dominates the viscoelastic response up to 50/50
PLA/TPU composition, and then deviates to TPU behavior. The glass transition of PLA has major
consequences on the viscoelastic properties for high PLA composition up to 50/50 PLA/TPU. Moreover,
CNF tends to increase the storage moduli in a significant way, from 1% to 3% CNF, while the loss
moduli are only slightly improved. From the experiments on 5% CNF, 80/20 PLA/TPU shows
significantly improved moduli, while there seems to be a stagnation starting at 65/35 PLA/TPU
composition and below. For 50/50 PLA/TPU, the DMA results do not show a significant variation in
dynamic moduli, but the 5% CNF loss modulus seems inferior to the 3% CNF. With the actual results for
20/80 PLA/TPU and Neat TPU, there was no significant improvement of the DMA moduli with the
addition of CNF.
a) PLA/TPU Blends with 1% CNF b) PLA/TPU Blends with 1% CNF
c) PLA/TPU Blends with 3% CNF d) PLA/TPU Blends with 3% CNF
11
e) PLA/TPU Blends with 5% CNF f) PLA/TPU Blends with 5% CNF
Figure 6. Storage and loss moduli of PLA/TPU blends with CNF
3.2 PASSIVE PROPERTIES
3.2.1 COMPRESSION TEST RESULTS
The results of the modulus of elasticity of the CNF reinforced blended composite parent materials are
shown in figure 7. The compression tests results of the origami composite cores are shown in figures 8 –
10, in which figure 8 shows a comparison of the modulus of elasticity values of the composite origami
cores. It is clear that, the 5% CNF samples have the highest values of the elastic modulus in the 20/80,
65/35, and 50/50 PLA/TPU samples, while it overlaps with the values of 3% CNF in the case of pure
PLA, pure TPU and the 20/80 PLA/TPU samples. The 1% CNF samples always have the lowest modulus.
The strength of composite origami cores is illustrated in figure 9, which clearly shows that the 5%
samples have the highest strength values compared with the other compositions, similarly to the behavior
of the elastic modulus.
In figure 10, the toughness of the origami cores is illustrated, and it is obvious that, samples with high
percentages of CNF absorbed higher energy than the samples with low CNF content, but with plastic
deformation and fracture through the crease lines, as observed in the samples with high PLA (100% and
80%), while samples with lower PLA percentage showed elastic behavior during the compression test,
and were able to recover after releasing the load.
In general, the elastic modulus and the strength of the composite origami cores decrease in response to the
increase of the TPU composition, which is compatible with the behavior of pure blended origami results
[35]. Samples with high PLA content tend to fracture at the crease lines, while the samples with high TPU
content have the lower elasticity modulus and able to withstand high strains without fracturing.
Comparing these results with previous results of pure polymeric blends origami [35], it can clearly
observe a significant improvement of the strength and the modulus of the origami cores by the increase of
12
the CNF, Figures 8 and 9 show comparison of the compressive modulus of elasticity and the strength of
origami cores made of composite blends and pure blends [35].
Figure 7. modulus of elasticity of the CNF reinforced
blended composite parent materials
Figure 8. Comparison the modulus of elasticity of the
pure blended origami [35] with composite origami cores
Figure 9. Comparison the strength of pure blended
origami [35] with composite origami cores.
Figure 10. Toughness of composite origami cores
3.2.2 IMPACT TEST RESULTS
The study in the previous section showed that the addition of the CNFs to the PLA/TPU blends improves
the elastic modulus, and the strength of the composite origami cores. In the case of impact event, the
higher strength altered the ability of the base material to work as a compliant mechanism, and thus
decreases the absorbed force and diminishes the energy absorption by the cores, compared to pure
PLA/TPU cores. Origami cores with high percentage of CNF tend to fracture more than those of pure
polymer blends. Most of the samples made of high PLA/CNF composition break under the impact point
(figure 11), and it is observed that the fracture propagated through the crease lines, which is the weakest
region in the origami structures. Some PLA with high percentage of CNF samples, which are more rigid
and brittle were fractured even through the rigid faces of the origami structures (figure 11C).
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Figure 11. (a) Fractured PLA+1%CNF sample under the point of impact, (b) Propagation of the fracture
through crease line on a PLA+1%CNF sample, (c) fractured PLA+3%CNF sample
Composite origami core samples with 80/20 PLA/TPU also experienced fracture through the crease lines,
when they were tested multiple times. This can be an indicator for the existence of internal micro-
fractures during the tests. Figure 12 shows a sample of force-time response curve, which was used to
calculate the transferred energy. The presented results in figure 13 show the higher maximum force
transferred proportional with the higher amount of the CNF. These values of the maximum force
transferred are still lower than the values of force transferred by steel, or polycarbonate plates tested in the
same conditions, which proves the efficiency of origami core structures in distributing the impact loads
through its unique geometrical features.
The behavior of the composite origami cores seems to present two different zones, with the 65/35
PLA/TPU being in the middle. The samples above this composition showed brittle behavior. Samples
with neat PLA showed fractures and 80/20 PLA/TPU might have internal fracture as explained above.
This explains that these samples transferred forces to the bottom side until they got facture, which
decreased the transferred force they might transmit during the impact event, and the slight difference in
the force transmitted between neat PLA and 80/20 PLA/TPU, because of the small amount of TPU
allowed the distribution of the impact force before fracture.
The samples with PLA/TPU below 65/35 showed a flexible behavior allowed them to distribute the
incoming impact force through the origami structure, and as a result transferred less force to the other
sandwich side. The neat TPU samples showed a slightly higher transferred force than the 20/80
PLA/TPU, because of the rubbery behavior of the TPU that allows the cores to densify and transfer force.
The 65/35 PLA/TPU composition benefits from the rigid behavior without showing fracture and then
transferred more force to the bottom side of the core. In Figure 14 the maximum impact energy
transferred by the composite origami cores is illustrated. It shows a higher value with the increased
14
amount of CNF, which might act against the brittle fracture of the samples. Moreover, the samples that
seem to transfer the least energy are 20PLA/80TPU, due to their high flexible behavior, allowing
compliant mechanisms on the creases, but preventing a high deformation of the faces. Neat TPU with
CNF seems to be the composition that transfers the most energy, as explained before, due to the rubbery
behavior, causing it to endure important elastic deformation without any fracture and transfer force on a
large scale of time compared to the other compositions. The decreasing transferred energy for TPU with
increasing amount of CNF might be due to the improvement of the samples’ rigidity. The results of the
impact testing showed that the addition of CNF increases the force transferred by the origami cores and
decreases the damping efficiency of the cores. Figures 13 and 14 illustrate the comparison of impact force
and impact energy transferred by origami cores made of composite origami and pure blended origami
[35]. Table 3 lists a comparison values of the maximum force transferred by composite origami cores and
the maximum force transferred by plane polycarbonate and steel plats tested in the same condition [35].
Figure 12. Sample of impact force-time response
Figure 13. Comparison of the max. force
transferred by pure blended origami cores [35]
with composite origami cores
Figure 14. Comparison of maximum impact
energy transferred by pure blended origami
cores[35] with composite origami cores
15
Table 3. Comparison between the maximum force transferred by composite origami cores and other
plane materials
CNF (w%) Material Blends Composition
(PLA/TPU) w% Maximum force transferred (N)
1% 100/0, 80/20,65/35,
50/50, 20/80, 0/100 (2574.26 – 3559.76)
3% 100/0, 80/20,65/35,
50/50, 20/80, 0/100 (3019.65 - 3829.513)
5% 100/0, 80/20,65/35,
50/50, 20/80, 0/100 (3184.39 - 4094.45)
Polycarbonate (11432.9) [35]
Steel (20852.0) [35]
3.3 ACTIVE PROPERTIES
3.3.1 SHAPE MEMORY EFFECT
The four steps of the shape memory test were performed on the composite origami unit cell, the samples
with high percentages of CNF showed no recovery during the shape memory test, the 1%, 3%, and the
5% CNF composite samples have showed no response during the recovery test. This can be explained
because of the existence of the carbon fibers which does not allow the material to flow during the heating
process, even when the material reaches the glass transition temperature. The amount of fibers affects the
flow of the polymer particles, and increasing the stiffness of the composites which resist the activation
force required to move the part.
In addition, the CNF affected the compression resistance when the samples heated during the
compression stage of the shape memory test, in which crack has been observed along the crease lines on
the origami unit cell (figure 15). The samples with small amount of CNF (0.1 wt %) showed high
response and high recovery ratio, due to the thermal response of the composite and the less amount of the
CNFs, the unite cell faces were able to move during the recovery test. Figure 16 shows a compressed
composite origami unit cell made of PLA + 0.1 wt % CNF after shape fixing.
The compression-relaxation test results are shown in figure 17; the figure shows the maximum stress
reached by the origami unit cell was 0.348 MPa, and the tested sample relaxed in about 300 sec. The
recovery test showed that the sample was able to recover its original height in about 63 sec. Figure 18
shows the height recovery versus time, and figure 19 shows the unit cell height recovery during time. This
results show that there is an enhancement in the recovery time compared with the recovery time of the
16
pure PLA samples tested in our previous work[40], in which the pure PLA origami sample toke more
than 450 sec to recover 85% from its original height.
Figure 15. Cracked composite Origami unit cell made
of (PLA + 3wt % CNF) Figure 16. Deformed composite origami unit cell made
of low percentage of CNF (PLA + 0.1wt % CNF)
Figure 17. Stress relaxation test of composite
origami sample made of PLA + 0.1wt% CNF
Figure 18. Recovery shape of composite origami
sample made of PLA + 0.1wt % CNF
Figure 19. The origami unit cell recovery (height)
From the same material composition (PLA + 0.1 wt % CNF), origami samples were fabricated and tested
for compression and impact resistance. The results demonstrated that the elastic modulus was 8.55 MPa,
and the maximum force transferred by impact was 419 .5 95 N. These results are comparable with the
values obtained from the PLA+CNF samples.
4. CONCLUSION
The way the origami metamaterial can redistribute compression and impact forces make it qualified for
potential use in future applications, as a light-weight sandwich core. The use of CNF with the material
blends to fabricate composite origami structures significantly enhances the overall mechanical properties
17
of the origami cores in compression, in which the compressive modulus and the strength of the origami
cores were increased by the increase of the CNF. By noting that samples with high PLA content face
fracture through the crease lines, while low PLA samples showed more elastic behavior. The impact
testing showed a higher transferred force and energy for higher carbon nanofiber compositions, because
of the increasing in the rigidity of the samples. 65PLA/35TPU showed the highest transferred force
because of the coupling effect of rigidity, flexibility and fiber reinforcement, while the higher PLA
composition samples showed major brittle behavior and the lower PLA composition samples showed
flexible behavior. The DSC test results showed an improvement in glass transition for both TPU and PLA
with the increasing amount of CNF, and the DMA results showed a significant increasing of the storage
modulus and a slight improvement of the loss modulus. Active composite origami structures showed
fractures along crease lines and low recovery ratio, composite origami with low CNF percentages (0.1%)
showed good stress relaxation behavior and high recovery ratio.
ACKNOWLEDGMENTS
The authors would like to acknowledge the following agencies for financial support: The Natural Science
and Engineering Research Council (NSERC) of Canada, the Canada Research Chair Program, the Libyan
Ministry of Higher Education and scientific research, Tripoli.
REFERENCES
[1] Zadpoor A A 2016 Mechanical meta-materials Mater. Horizons 3 371–81
[2] Lim T-C 2015 Auxetic Materials and Structures (Singapore:Springer) (https://doi.org/10.1007/978-
981-287-275-3)
[3] Eidini M and Paulino G H 2015 Unraveling metamaterial properties in zigzag-base folded sheets Sci.
Adv. 1 e1500224–e1500224
[4] Florijn B, Coulais C and Van Hecke M 2014 Programmable mechanical metamaterials Phys. Rev.
Lett. 113 1–5
[5] Blumenfeld R and Edwards S F 2012 Theory of strains in auxetic materials J. Supercond. Nov. Magn.
25 565–71
[6] Brunck V, Lechenault F and Reid A 2016 Elastic theory of origami-based metamaterials Phys. Rev. E
93 033005
[7] Miura K 1972 Zeta-core sandwich-its concept and realization Inst. Sp. Aeronaut. Sci. Univ. Tokyo
480 137–64
18
[8] Miura K 1985 Method of packaging and deployment of large membranes in space Institute of Space
and Astronautical Science AA10632072
[9] Lv C, Krishnaraju D, Konjevod G, Yu H and Jiang H 2014 Origami based mechanical metamaterials
Sci. Rep. 4 5979
[10] Silverberg J L et al 2014 Using origami design principles to fold reprogrammable mechanical
metamaterials Science 345 647–50
[11] Jianguo C, Xiaowei D and Jian F 2014 Morphology analysis of a foldable kirigami structure based
on Miura origami Smart Mater. Struct. 23 094011
[12] Wei Z Y, Guo Z V, Dudte L, Liang H Y and Mahadevan L 2013 Geometric mechanics of periodic
pleated origami Phys. Rev. Lett. 110 215501
[13] Kayumov R a., Zakirov I M, Alekseev K P, Alekseev K a. and Zinnurov R a. 2007 Determination of
load-carrying capacity in panels with chevron-type cores Russ. Aeronaut. (Iz VUZ) 50 357–61
[14] Dvoeglazov I V and Khaliulin V I 2013 A Study of Z-Crimp Structural Parameters Impact on
Strength under Transverse Compression and Longitudinal Shear Russ. Aeronaut. 56 15–21
[15] Heimbs S, Cichosz J, Klaus M, Kilchert S and Johnson A F 2010 Sandwich structures with textile-
reinforced composite foldcores under impact loads Compos. Struct. 92 1485–97
[16] Gattas J M and You Z 2015 Geometric assembly of rigid-foldable morphing sandwich structures
Eng. Struct. 94 149–59
[17] Schenk M and Guest S D 2013 Geometry of Miura-folded metamaterials Proc. Natl. Acad. Sci. 110
3276–81
[18] Wonoto N, Baerlecken D, Gentry R and Swarts M 2013 Parametric design and structural analysis of
deployable origami tessellation Comput. Aided. Des. Appl. 10 939–51
[19] Alekseev K a., Zakirov I M and Karimova G G 2011 Geometrical model of creasing roll for
manufacturing line of the wedge-shaped folded cores production Russ. Aeronaut. (Iz VUZ) 54
104–7
[20] Schenk M 2011 Folded Shell Structures (PhD. thesis, Clare College University of Cambridge)
[21] Peraza-Hernandez E A, Hartl D J, Malak Jr R J and Lagoudas D C 2014 Origami-inspired active
structures: a synthesis and review Smart Mater. Struct. 23 094001
19
[22] Onal C D, Wood R J and Rus D 2013 An origami-inspired approach to worm robots IEEE/ASME
Trans. Mechatronics 18 430–8
[23] Lee D Y, Jung G P, Sin M K, Ahn S H and Cho K J 2013 Deformable wheel robot based on origami
structure Proc. - IEEE Int. Conf. Robot. Autom. 5612–7
[24] Guo W, Li M and Zhou J 2013 Modeling programmable deformation of self-folding all-polymer
structures with temperature-sensitive hydrogels Smart Mater. Struct. 22 115028
[25] Tcharkhtchi Abbas, Abdallah-Elhirtsi Sofiane, Ebrahimi Kambiz, Fitoussi Joseph, Shirinbayan
Mohammadali and Farzaneh Sedigheh 2014 Some New Concepts of Shape Memory Effect of
Polymers Polymers (Basel). 6 1144–63
[26] Lendlein A, Behl M, Hiebl B and Wischke C 2010 Shape-memory polymers as a technology
platform for biomedical applications. Expert Rev. Med. Devices 7 357–79
[27] Lendlein A and Langer R 2002 Biodegradable, elastic shape-memory polymers for potential
biomedical applications. Science 296 1673–6
[28] Song J J, Chang H H and Naguib H E 2014 Design and characterization of porous biocompatible
shape memory polymer (SMP) blends with a dynamic porous structure Polymer (Guildf). 56 82–
92
[29] Small W, Singhal P, Wilson T S and Maitland D J 2010 Biomedical applications of thermally
activated shape memory polymers. J. Mater. Chem. 20 3356–66
[30] Tobushi H, Hara H, Yamada E and Hayashi S 1996 Thermomechanical properties in a thin film of
shape memory polymer of polyurethane series Smart Mater. Struct. 5 483–91
[31] Behl M, Razzaq M Y and Lendlein A 2010 Multifunctional shape-memory polymers Adv. Mater. 22
3388–410
[32] Tolley M T, Felton S M, Miyashita S, Aukes D, Rus D and Wood R J 2014 Self-folding origami:
shape memory composites activated by uniform heating Smart Mater. Struct. 23 094006
[33] Jie Ren 2013 Biodegradable Poly lactic acid Synthesis, Modification, Processing and Applications
vol 53 (Shanghai, China: Springer)
[34] HUNTSMAN 2010 A guide to thermoplastic polyurethanes (TPU)
[35] Kshad M A E and Naguib H E 2016 Development and modeling of multi-phase polymeric origami
inspired architecture by using pre-molded geometrical features Smart Mater. Struct. 025012
[36] Xie X, Mai Y and Zhou X 2006 Dispersion and alignment of carbon nanotubes in polymer matrix : a
20
review Mater. Sci. Eng. R 49 89–112
[37] Anwer M A S and Naguib H E 2016 Study on the morphological , dynamic mechanical and thermal
properties of PLA carbon nano fi bre composites Compos. Part B 91 631–9
[38] Al-saleh M H and Sundararaj U 2011 Composites : Part A Review of the mechanical properties of
carbon nanofiber / polymer composites Compos. Part A 42 2126–42
[39] Al-saleh M H and Sundararaj U 2008 A review of vapor grown carbon nanofiber / polymer
conductive composites Carbon N. Y. 47 2–22
[40] Ali M, Kshad E and Naguib H E 2017 Characterization of origami shape memory metamaterials
(SMMM) made of bio-polymer blends Proc. SPIE 9800 98000H
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