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Thermomechanical Analysis of the Shape Memory Effect of a Polyurethane Composite Used to Create Deployable Space Structures

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ISSN 1063-7850, Technical Physics Letters, 2019, Vol. 45, No. 5, pp. 453–456. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Author(s), 2019, published in Pis’ma v Zhurnal Tekhnicheskoi Fiziki, 2019, Vol. 45, No. 9, pp. 32–35.
Thermomechanical Analysis of the Shape Memory Effect
of a Polyurethane Composite Used
to Create Deployable Space Structures
T. A. Shalyginaa,b*, S. Yu. Voroninaa,b, A. Yu. Vlasova, K. A. Pasechnika,b, and I. V. Obvertkina,b
a Reshetnev
b
Siberian State University of Science and Technology, Krasnoyarsk, 660037 Russia
Federal Research Center “Krasnoyarsk Scientific Center,” Siberian Branch of the Russian Academy of Sciences,
Krasnoyarsk, 660036 Russia
*e-mail: [email protected]
Received January 28, 2019; revised February 12, 2019; accepted February 12, 2019
Abstract—The possible applicability of a three-point bending clamp of a thermomechanical analyzer to study
the shape memory effect of a structural polyurethane composite is studied. The viscoelastic properties of the
sample in the region of the transition from the glass to the highly elastic state are studied. The parameters
affecting recovery rate Rr of the original shape and fixation rate Rf of the temporary shape are determined.
Deformation and cooling conditions that allow one to achieve the values Rr = 99.98% and Rf = 99.70% are
established for the polyurethane composite.
DOI: 10.1134/S1063785019050171
Some problems of space technology involve the use
of large special-purpose structures (antennas of modern satellite communications, sun-protection spatial
structures, solar cell systems, etc.). The delivery of
objects of such dimensions to near-earth orbit gives
rise to many problems, the solution of which affects
various fields of science. In this regard, new materials
with a shape memory effect (SME) are being actively
studied for the manufacture of transformable structures with the possibility of giving them a temporary
compact shape on Earth and restoring their unfolded
(original) shape in outer space [1]. The use of polymer
materials (PMs) in this case is determined by the low
cost and reduced weight of the structures, the suitable
temperature range of implementation, and the low initiation temperature of the SME (about 100°C) [2].
Thermoplastic polyurethane with SME is a PM that
possesses the above advantages and is used as a binder
in the creation of polymer composite materials [3].
To simulate the process of deployment of transformable structures, one needs to study the physical
principles of the algorithm for the free recovery of frozen deformation of the used material with SME.
Therefore, this paper presents the results of studying
the SME in a structural polyurethane composite
(SPC) used for the manufacture of components
(frames) of large-sized transformable reflectors of
space antennas [4]. The aim of the work was to study
the possible applicability of a three-point bending
clamp in the mode of uniaxial controlled bending load
of a thermomechanical analyzer (TMA) for studying
the SME in SPC under conditions that are close to
real operating conditions. In addition, special attention in this study was paid to determining the most
appropriate deformation mode from the points of view
of the effective fixation (packing) of the temporary
shape and of the accuracy of restoration (deployment)
of the original shape of SPC.
An SPC sample composed of a Diaplex MP5510
polyurethane matrix (Japan) with a glass transition
temperature of Tg = 55°C [5] and St 12073 carbon
cloth (Russia) served as an object for studying. The
sample was fabricated by contact molding at the
Resource Center for Collective Use Spacecraft and
Space Systems of the Reshetnev Siberian State University of Science and Technology.
Thermomechanical (TM) studies of the viscoelastic properties of SPC with an SME were performed
using a Q800 dynamic mechanical analyzer (DMA)
manufactured by TA Instruments (United States). The
complex Young’s modulus (E*) of the sample was
measured using a three-point bending clamp in the
mode of linear temperature scanning with heating
from 0 to 100°C at a rate of 5°C/min. The frequency of
dynamic loading of the composite was 1 Hz, and the
relative deformation is no more than 0.1%. The SPC
sample was a plate with a size of 30 × 12.5 × 0.65 mm.
The Tg value was determined from the inflection point
of the temperature dependence of the elastic modulus,
E'(T), in the glass transition region, according to
453
454
SHALYGINA et al.
shape when the sample is heated to a temperature
above the glass transition temperature, Trec (recovery
temperature) (Fig. 1).
The studied SPC sample was considered as a TM
device used in transformable space structures—therefore, control over σm was the most appropriate programming mode. When using a three-point bending
clamp in TMA, the maximum value of the force
applied to the SPC sample was 1.2 N (σm ≈ 15 MPa) at
a maximum deformation value of εm ≈ 20%. To determine the most effective Tprog value from the point of
view of shape recovery, we used the results of studying
the TM cycle of the SME in a SPC at Tprog = 55, 65,
and 80°C. At the same time, temperature Trec must be
20–30°C higher than Tprog; Tlow ≈ 23°C. The TM studies of the SME were carried out without exposure
(tH = 0) of the sample to the preset σm stress and under
curing for tH1 = 10 min at the end of Stage 1 in the
highly elastic state and for tH2 = 10 min at the end of
Stage 2 in the glass state for one TM cycle (tH12 = tH1 +
tH2 = 20 min). Switching temperature TSW (switching
temperature) at which a critical change in the sample
shape occurs upon the free recovery of the frozen
deformation was determined as the inflection point of
the recovery curve (dependence ε(T)) upon heating
from Tlow to Trec at Stage 4 of a TM analysis of the
SME.
Shape recovery rate Rr is a determining parameter
of the SME, which shows the proportion of reversible
deformations that occur as a result of mechanical
action on the sample in its highly elastic state and
expressed as follows:
Tprog m
Tlow
Bending
Cooling
(1)
(2)
Cycle
(3)
Recovery
Trec
(4)
Unloading
Tlow
Fig. 1. Schematic representation of a cyclic thermomechanical study of the shape memory effect in a structural
polyurethane composite using a three-point bending
clamp.
GOST (State Standard) R 56753–2015 (ISO 6721-11:
2012).
The TM cycle of the SME of SPC was studied
using a three-point bending clamp of a TMAQ400EM
thermomechanical analyzer manufactured by TA
Instruments (United States). The measurements were
performed in the mode of adjustable bending load and
temperature varying according to a given program
with simultaneous measurement of the longitudinal
movement of the sample. The SPC sample was a bar
with a size of 10 × 1.22 × 0.72 mm.
The method of a cyclic TM study of the SME,
which was described in 1992 in [6], entailed the presence of the following four stages: Stage 1, which
included the heating of the sample to a temperature of
Tprog (programming temperature), during which the
sample was deformed; Step 2, which consisted in the
creation of a frozen deformed state in the process of
cooling to a temperature below the glass transition
range, Tlow (low temperature), at a constant value of
the σm stress (maintaining); Stage 3, in which the sample was completely unloaded; and Stage 4, which
included the subsequent restoration of the original
εm − ε p
(1)
× 100%,
εm
where εm is the total deformation value determined as
a sum of the instantaneous (εl) and delayed (εc) highly
elastic deformations (εm = εl + εc), while εp is the irreversible plastic deformation. Along with Rr, shape fixation rate Rf determining the proportion of fixed
deformations, i.e., the ability of the material to “memorize” the temporary shape, is an important parameter
of the SME:
Rr =
εu
(2)
× 100%,
εm
where εu is the deformation established as a result of
instantaneous restoration of a certain part of the structural units after removing the εm load at Stage 3.
The DMA curves of the E* value (Fig. 2) describe
the viscoelastic behavior of an SPC sample in the
temperature range from 0 to 105°C. Curve 1 clearly
shows the region in the temperature range from 20 to
90°C, in which the dynamic elastic modulus, E',
decreases from 26 to 2.7 GPa and indicates the transition of the binder of the composite from the glass to
the highly elastic state. When using a loading freRf =
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THERMOMECHANICAL ANALYSIS OF THE SHAPE MEMORY EFFECT
455
0.4
30
3
1
0.3
3
4
52.2
0.2
2
E'', GPa
20
tanδ
−0.4
53.5 63.6
E', GPa
∂E'/∂T, GPa/°C
−0.2
10
−0.6
0.1
1
2
52.0
0
20
40
60
80
0
100
T, °C
Fig. 2. Thermomechanical curves of the temperature dependences of the (1) dynamic elastic modulus E', (2) mechanical loss
modulus E", (3) partial temperature derivative ∂E'/∂T, and (4) mechanical loss tangent tanδ of a shape memory polyurethane
composite. The numbers around the curves correspond to the temperature of the maxima and minima of the signals.
quency of 1 Hz, the maximum of the tanδ peak shifts
to the high-temperature region by 5–15°C [7]. Therefore, we determined the Tg values for SPC samples as
the inflection points on the E'(T) curve, which are
close to the maximum peak of the E"(T) curve and the
minimum on the ∂E'/∂T(T) curve [8]. The initial SPC
sample had a glass transition temperature of Tg =
52.2°C, which is 3°C lower than the glass transition
temperature of the unreinforced polyurethane matrix.
Starting from the 13th minute (t = 13 min), a
delayed highly elastic deformation (εc) can be
observed on the ε(t) TM curve, which describes the
relaxation nature of the PM deformation (Figs. 3a,
3b). During cooling, molecular chains that are still in
the highly elastic state experience chaotic collisions
under thermal motion, which give rise to changes in
the conformational states with a simultaneous
decrease in the εu value, which leads, in turn, to a
decrease in the Rf value. Exposure of the sample to a
constant σm stress in the glass state leads to a decrease
in the proportion of instantaneous reversible deformation that occurs after the sample is unloaded, while the
Rf value increases. Therefore, aging of the sample at
the end of Stage 1 is not an effective tool for improving
the fixation of the temporary shape.
The ε(T) TMA curves show that the TSW value
barely depends on the σm and tH values, but strongly
depends on the Tprog value (Figs. 3c, 3d). Increases in
the Tprog value by 10 and 25°C leads to shifts in the TSW
value toward the high-temperature region by 5 and
9°C, respectively. An increase in the Tprog value also
leads to an expansion of the temperature range of the
frozen deformation recovery by 15–20°C on average.
The εm, εp, and εu parameter values required for the
calculation of Rf and Rr (see Table 1) were determined
using the TMA data (Fig. 3). The maximum value,
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Rr = 99.98%, was obtained at a temperature of Tprog =
65°C and tH = 0 min, and the maximum value, Rf =
99.70%, was obtained at Tprog = 55°C and tH12 =
20 min. An increase in the Tprog temperature to 80°C
leads to decreases in the Rf and Rr values to 93.90 and
94.60%, respectively.
The shape recovery effect deteriorates because of a
substantial displacement of the PM molecular segments during deformation. This occurs as a result of
weakening of the intermolecular bonds, which fixed
the molecular segments in a certain spatial position
before. Thus, if the sample is rapidly cooled after
deformation, thereby decreasing the proportion of
highly elastic deformation, then it is possible to prevent a substantial rearrangement of the structural units
and, thereby, to increase the Rr value. At the same
time, if we maintain the material at a constant σm value
in the glass state, then the quality of fixation (packing)
of the sample can be improved by leaving the Rr value
(deployment) at a high level.
Table 1. Experimentally obtained values of the shape memory effect parameters for structural polyurethane composite
Tg, °C
52.2 ± 1
E', GPa Tprog, °C TSW, °C
26
55 ± 1
65 ± 1
80 ± 1
55 ± 1
65 ± 1
80 ± 1
Rr, %
tH = 0 min
57.3
98
62.4
99.9
66.5
99.8
tH12 = 20 min
57.3
96 (96.8)*
62.2 96.9 (97.2)*
66.4 94.6 (97.5)*
Rf, %
95.4
97.8
93.9
99.7
99.3
99.1
* The values obtained in the case in which temperature Trec is
45°C higher than temperature Tprog.
SHALYGINA et al.
60
(3)
εu
Trec
100
Tprog
8
Tlow
0
10
20
60
25
20
Time, min
3
2
30
20
35
0
(c)
Displacement:
1—(–2.5%)
2—(–2.0%)
10
20
30
40
Time, min
3
16
8
TSW
2
12 1
50
10
20
60
(d)
Displacement:
1—(–4.0%)
2—(–1.5%)
8
4
TSW
0
0
20
εp(4)
Tlow
20
12 1
4
4
Strain, %
Strain, %
16
15
εp(4)
[
4
5
15
] Stress, MPa
10
σm
[
Tprog
8
15
εc
16 (1)
εl
12
(b)
140
(2)εm
] T, °C
100
Strain, %
Trec
(3)εu
] Stress, MPa
(2)εm
σm
20
] T, °C
εc
16 (1)
εl
12
(a)
140
[
Strain, %
20
[
456
40
60
T, °C
80
100
20
40
60
T, °C
80
100
Fig. 3. Thermomechanical curves of the deformation, temperature, and stress as functions of time for a shape memory polyurethane composite deformed at Tprog = 80°С and (a) tH = 0 and (b) tH12 = 20 min; the temperature dependences of the deformation
at (c) tH = 0 and (d) tH12 = 20 min for Tprog values of (1) 55, (2) 65, and (3) 80°C.
This study shows the possibility of using a threepoint bending clamp for a thermomechanical analysis
of the shape memory effect of a structural polyurethane composite used in the production of deployable
space structures. It is established that the maximum Rr
value (99.98%) for the SPC sample was obtained
under controlled bending load (F = 1.2 N) at Tprog =
65°C and tH = 0 min. It is shown that a 10-min exposure of the polyurethane composite sample in the glass
state to a constant load can increase the Rf value to
99.70%. It is revealed that increases in deformation
temperature Tprog by 10 and 25°C give rise to shifts in
temperature of the critical change of the sample
shape TSW toward the high-temperature region by
5 and 9°C, respectively, and to the free recovery of the
frozen deformation.
FUNDING
This work was supported by the Ministry of Education and Science of the Russian Federation under contract no. 02.G25.31.0147.
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TECHNICAL PHYSICS LETTERS
Translated by O. Kadkin
Vol. 45
No. 5
2019