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THERMALLY AND DIMENSIONALLY STABLE STRUCTURES
OF CARBON-CARBON LAMINATED COMPOSITES FOR SPACE APPLICATIONS
V.I. Slyvynskyi, Dr. Tech. Sci., “Ukrainian Research Institute for Machine-building
Technology” PJSC, Dnipropetrovsk, Ukraine,
E-mail: honeycom@ua.fm
.F. Sanin, Dr. Tech. Sci., O. Honchar Dnipropetrovsk National University,
Dnipropetrovsk, Ukraine
.. Kharchenko, O. Honchar Dnipropetrovsk National University,
Dnipropetrovsk, Ukraine
.V. Kondratyev, Cand. Tech. Sci., N.. Zhukovsky National Aerospace University “KhaI”,
Kharkov, Ukraine, E-mail: kondratyev_a_v@mail.ru
It is well known that panel and shell sandwich structures with skins made of polymeric composite
materials based on carbon fibers are widely used for the equipment items meant for long-term operation
in the near-earth orbits, that is, items for telecommunication, remote sensing systems and for use as di-
mensionally stable supports of highly-sensitive transceivers, and in future they are to be used in orbits of
other planets as well.
Structural designs with carbon honeycomb plastic (CHP) are finding ever-widening applications.
CHP when compared to other types of honeycombs features the highest specific indices of strength and
stiffness, in combination with minimal linear thermal expansion coefficients (LTEC) which provide for
high level of dimensional stability at cyclic effects of temperature within the limits of r70q .
However, polymeric binder in the structures of that class not always satisfies ever-increasing re-
quirements to the range of their operating temperatures. Therefore, analysis of opportunities of using car-
bon-carbon composite materials in such structures is of great practical interest.
The paper reveals the preconditions of using carbon-carbon composite materials of laminated
structure which are obtained by processing of finished products of carbon fiber reinforced plastic by car-
bonization in the furnace with non-oxidizing medium at high temperatures. It is shown that obtained
items get an opportunity of operation in the temperature range corresponding to and considerably exceed-
ing the conditions of operation of objects in near-earth orbits with the allowable level of change in their
shape and pre-stress providing for specified service life.
We synthesized the approximate dependencies of physical-mechanical and strength characteris-
tics of obtained carbon-carbon composite material on the basis of the theory of reinforcement of polymer-
ic composites’ mechanics, with the use of which finite-element analysis of the degree and the nature of
change of thermal and dimensional stability of polymeric composite structure after its carbonization and
turning into carbon-carbon composite material has been carried out.
With the use of approximated criteria of optimization of carbon-carbon composite material struc-
ture ensuring its maximum dimensional stability, the package with orientation of the group of thermo-
nonequilibrium layers of (0º,±45º,90º) has been investigated compared to analogs of carbon fiber rein-
forced plastic, which provides for high bearing capacity and service life thereof. Shape stability of skins
of carbon-carbon composite materials is also higher than that in their analogs of carbon fiber reinforced
plastic.
Pre-stress, thermal non-equilibrium state and shape stability of skins of panels made of carbon-
carbon composite materials compared to analogs of carbon fiber reinforced plastic have been analyzed. It
is found that pre-stress of skins of carbon-carbon composite materials both for various structures and for
various thicknesses of monolayers is considerably lower compared with that of carbon fiber reinforced
plastic.
Introduction
Analysis of the methods which allow to
ensure precision accuracy of functioning of
highly-sensitive transceivers mounted on the
satellite devices operating in the near-earth
orbits for a long time, shows that the effi-
cient means to achieve this objective is the
use of sandwich carbon-fiber reinforced
skins with carbon honeycomb plastic (CHP)
[1 – 3].
Polymeric composite materials based on
carbon fibers (carbon fiber composites –
CFC) feature the highest specific physical-
mechanical characteristics (PhMC), strength
properties and minimal linear thermal ex-
pansion coefficients (LTEC) providing for
high level of dimensional and shape stability
at the temperature impacts. However, poly-
meric binder in the structures of that class
not always satisfies ever-increasing re-
quirements to the range of their operating
temperatures. In connection with it, analysis
of opportunities of using carbon-carbon
composite materials (CCC) in such struc-
tures is of great practical interest. Since the
first reports about CCC, this material be-
came unsurpassed in the structures of space
vehicles for their erosion protection, resis-
tance to high-speed heat actions (thermal
impacts) and provision of actually maximum
realization of physical-mechanical and
strength properties of carbon fibers [4]. For
that purpose, wide range of multi-directional
structures of CCC has been developed,
formed as this class of composites from the
beginning. At the same time, the interest is
given to the formation of structures for
space applications which are made of lami-
nated CFC and are subject to carbonization
after manufacture, according to present prac-
tices of obtaining CCC.
The recent reports of Ultracor corpora-
tion [5 – 7] state that this company has de-
veloped and now produces carbon-carbon
honeycomb panels which were already used
on the GOCE satellite and other products.
Below given are the results of joint stu-
dies carried out by the group of authors in
order to create thermally and dimensionally
stable CCC structures for space applica-
tions which would allow to effectively in-
crease the temperature range of their opera-
tion and accuracy of data transmission by
transceiver systems and devices of the Earth
remote sensing from the orbiters.
Analysis of creation of thermally
and dimensionally stable space structures
of carbon-carbon composite materials
CCC represents carbon-containing or
graphite matrix reinforced by carbon or gra-
phite fibers. This matrix has the properties
of the monolithic graphite and fiber compo-
sites.
There are two basic methods of receiv-
ing the carbon matrix: gas-phase deposition
of pyro-carbon formed during the thermal
decomposition of hydrocarbons in the pores
of carbon-fiber frame, and carbonization of
polymeric matrix in previously molded
blank part of CFC and its high-temperature
treatment in non-oxidizing medium [8, 9].
The first method provides for obtaining
of parts of CCC with the higher perfor-
mance properties, however, it cannot be
used for the case of finished product of
CFC, including those of sandwich structure
with CHP and carbon fiber reinforced plastic
skins. In order to implement this structure,
2D structures based on two-dimensional
carbon cloth can be used. For such items, it
is possible to analyze the efficiency of its
carbonization only, i.. high temperature
treatment (over 2100q ) in non-oxidizing
medium of inert gas by turning polymeric
binder into coke with the weight loss, shrin-
kage and formation of large amount of
pores.
For the case of carbonization of the fi-
nished structure of CFC, apparently, it is not
possible to expect as high performance cha-
racteristics as can be achieved with multiple
impregnation of the polymeric composite
and subsequent carbonization thereof. How-
ever, one of the objectives of obtaining such
products is low density and low LTEC, en-
suring high level of dimensional stability
with the moderate strength and stiffness cha-
racteristics at high temperatures. Characte-
ristics of CCC [10] are given in Table 1
below.
It should be noted that CCC, which
properties are stated in p.p. 2 – 3 of Table 1,
are suitable to a greater or lesser extent for
the products discussed here.
Analysis of the experience of obtaining
CCC [9, 11] shows that carbon fibers in
the process of carbonization, in particular, in
a single stage, which is typical for the consi-
dered class of sandwich structures of carbon
fiber reinforced plastic with CHP, retain
their PhMC and strength properties.
At the same time, carbonization of the
binder turning it into coke changes its prop-
erties completely; thermal destruction the-
reof occurs, which is characterized by
weight loss, shrinkage and pore formation.
Properties of 1-D and 2-D CCC based
on laminated structures are little known to us,
since this class of composites appeared and
developed exactly for high-strength and heat-
resistant space products of 3-D type and
components close thereto by the operational
requirements.
Nevertheless, the work [8] gives some in-
formation which is of interest for laminated
CCC of the class of structures concerned as
well. It includes dependencies of density
CCC
U
on the number of carbonization cycles
(Fig. 1).
Table 1 – Characteristics of carbon-carbon and carbon-graphite materials
No. Method for
obtaining
Density
U
, kg/m3
Tensile
strength
1
F
, P
Compres-
sive
strength
1
F
, P
Modulus
of elastici-
ty
1
, GP
Heat con-
ductivity
O
,
Wt/(m)
LTEC
D
10-6,
1/
Matrix
structure,
type
1
CCC
b
ased on
high-modulus fi-
bers (gas-phase
deposition)
1750 75 200 30 6…8 2…3
3D-woven,
pyro-
carbon
2
CCC
b
ased on
low-modulus fi-
bers (impregna-
tion at low
pressure)
1500 80 185 23 5 6
Cloth.
phenol
resin
3
CCC
b
ased on
high-modulus fi-
bers (impregna-
tion in gasostat)
1700 91 99 31 3,8 2,6
Cloth.
phenol
resin
4
CCC
b
ased on
high-modulus fi-
bers (gas-phase
deposition)
1800 100 200 10 10 4
4D-woven,
pyro-
carbon
5 Graphite – 1960 13 75 110…130 110…130 3,4 -
As it follows from the graphs, at one
cycle of carbonization typical for the consi-
dered class of structures of CCC, its densi-
ty is 1000…1100 kg/m3, i.e. 1,4 – 1,55 times
lower than that of starting unidirectional car-
bon fiber reinforced plastic
(CFC
U
=1400…1550 kg/m3, [12]).
Figure 1 – Dependence of CCC density on
the number of cycles n of the process:
1 – impregnation under pressure;
2 – carbonization at atmospheric pressure
Fig. 2 shows the dependence of CCC
density on its porosity [8]. It follows from
the figure that at density of CCC equal to
CCCM
U=1000…1100 kg/m3 porosity
makes 30..35 %.
It is known that porosity plays the nega-
tive role both in the aspect of PhMC and
strength properties of CFC, and in terms of
reduction of the bearing capacity of compo-
site parts in operation at static loads and, in
particular, at their multi-cycle loading with
the force and temperature impacts because
of occurring residual stresses of the material
in the area of pores. However, for the consi-
dered class of structures high level of po-
rosity (relative volume content of pores)
T
plays the definite positive role as well, de-
creasing the CCC density in these prod-
ucts ( CCCM
U
) considerably.
Figure 2 – Changing of the nature
of porosity () of the material type 3
based on carbon-carbon matrix, depending
on density
The mass balance equation for CCC
components can be written as:
fcoke
f
coke CCCM
CCCM CCCM CCCM
VVV
VV V
UU[ U
(1)
or
f
f coke coke CCCM
TU T U [ U
, (2)
where , ,
fcoke
TT
- relative volume content
of carbon fibers, coke and pores in CCC.
Here , , ,
f coke CCCM
VV VV - volumes of
fibers, coke, pores and total fixed volume of
CCC;
[
- coefficient of volume shrin-
kage of coke in the fixed volume equal to
the product of linear shrinkage coefficients
along axes ,
X
Y and
Z
.
For the considered class of 2D CCC:
2
()
xyz x y
[ [[[ [ [
, (3)
where linear shrinkage coefficients
x
[
and
y
[
are determined by formulas given in [13].
Taking into account the absence of
shrinkage in carbon fibers
1
1
coke coke f
x
f
fcoke f
E
EE
[T
[TT
; (4)
11 1
f f f coke coke
ycoke f
ff coke f
EE
EE
TP P
[[ T TT
ªº
«»
«»
¬¼
(5)
400
1200
1400
800
CCCM
U
, kg/m3
0 2 4 6 n
2
1
600
1000
1400
CCCM
U
, kg/m3
020 40 ,%
Formulas for approximated determina-
tion of PhMC and strength properties of un-
idirectional structure of CCC can be ob-
tained from the relevant ratios for CFC [13]
with replacement of the included multiplier
1
f
[
by
f
F
[
, where
1
F
.
This multiplier reflects the fact that in
CCC with high content of pores the unit is
not equal to the sum of relative volume con-
tents of fibers and the binder, as it takes
place in CFC, but it means three components
of the material 1
fcoke
TT
or
1
fcoke
TT F
. (6)
Taking into account the above, PhMC of
unidirectional CCC, accordingly, in the
direction of fibers and across the reinforcing
fibers take the form:
1-
CCCM
f
fcoke f
EEE
TFT
; (7)
2
f
CCCM
f
f
f
coke
E
EE
E
|
TFT
; (8)
12
1
0,5
CCCM
fcoke
f f coke coke coke f
GEE
EE
FT FP FP T
| u
ªº
u
¬¼
;(9)
1
f
f f coke coke f
CCCM
f f coke f
EE
EE
DT D F T
DTFT
; (10)
21
1
CCCM CCCM
ff ff f
CCCM
coke f coke f f
DDTPTDD
DFTPFTDD
,(11)
while the CCC ultimate strength in main
axes can be approximately determined by
formulas [13]
()
() ()
1
f
ff f
CCCM coke
f
F
FEE
E
TFT
ªº
¬¼
; (12)
() ()
2
22
2
2
4
44
16
CCCM coke
f
f
f
f
FF
arctg
S
T
ST
SS
ST
ST
§·
u
¨¸
©¹
§·
¨¸
u
¨¸
©¹
; (13)
12
12
f
CCCM
f f coke f
f
F
FGG
Gªº
¬¼
TFT
. (14)
Here () ()
,
f
coke
FF
- tensile and compres-
sive strengths of carbon fibers and coke;
12
f
F - carbon fiber shear strength.
Stress-strain behavior of the orthogonal
and angle-plied CCC is determined by
formulas of laminated CFC mechanics [13]
taking into account the fact that PhMC of
unidirectional CCC in main axes are ex-
pressed by dependencies (7) – (11).
Therefore, to a first approximation the
total set of CCC PhMC is determined
which allows to find stress-strain behavior
(SSB) of the given structures under the op-
erational loads on the structure made of
these materials.
Obtained results can be taken as the ba-
sis of comparative analysis of the efficiency
of products of the given class made of
CCC with relation to structures of CFC
with CHP.
Analysis of the degree and nature of the
change of thermal and shape stability
of polymeric composite structure after its
carbonization
Our work [14] describes optimization of
the polymeric composite structure with the
orientation of monolayers 0 , 45 , 90
nml
r
DDD
of
the constant total thickness of the pack
'
=9 mm at changing of the relative thick-
ness of ,nm
''
and l
'
monolayers’
groups. As the criteria for optimization of
bi-axial dimensional stability, we have of-
fered two target functions:
11min
y
xpr pr
x
red
D
DD D
§·
o
¨¸
©¹
; (15)
2
2
2
21min
y
xpr pr
x
red
D
DD D
§·
o
¨¸
©¹ , (16)
where ,
x
y
DD
– LTEC along the axes
X
and Y of optimized CFC structure;
pr
– coefficient of priority of directions of
minimal dimensional stability defined by the
conditions of structure operation
01
pr
dd. It is evident that the function
(15) corresponds to the requirement of min-
imum average change of the structure shape
in its plane, defined by the values
x
D
and
y
D
, while the function (16) meets the re-
quirement of minimal root mean square (di-
agonal) distortion of its shape.
It is supposed that CFC structure consi-
dered in [14] at volume content of fibers
T
=0,65 was subjected to carbonization turn-
ing it into CCC. In this case, PhC of
carbon fibers featured no change being equal
to:
f
=163,9 GP;
f
G=65,6 GP;
f
P
=0,25;
f
D=-3,0610-61/q.
Fiber strength values are as follows: ten-
sile strength 1
f
F=1475 P, compressive
strength 1
f
F=1147 P, and shear strength
12
f
F=123 MP.
The binder turned into coke with the fol-
lowing characteristics: coke
=2 GP;
coke
P
=0,3; coke
G=0,77 GP; coke
D
=510-61/q;
coke
F=15 P; coke
F=80 P.
CCC PhMC and its LTEC in the direc-
tions of main axes 1 and 2 calculated by
formulas (7) – (11) at porosity
3
=0,35
(
F
=0,65) are equal to:
1
CCCM
=98,4 GP; 2
CCCM
=34,9 GP;
12
CCCM
G=18,5 GP; 1
CCCM
D
=-3,0510-6 1/q;
2
CCCM
D
= - 1,5910-6 1/q.
The attention should be given to nega-
tive LTEC in two directions, which does not
take place for CFC structures.
Results of optimization of CCC structure
on the considered criteria 1red
D
and 2red
D
at
various pr
are given in Table 2. The patterns
of change of 1red
D
and 2red
D
with pr
are
shown in Fig. 3. These graphs represent the re-
levant values of
x
D
and y
D
as well.
Analysis of results of optimization of the
levels of thermal and dimensional stability
of CCC structure under study revealed the
following.
Figure 3 – Change in optimal LTEC of
CCC depending on the value
of the coefficient of priority of directions
of minimal dimensional stability
1. Some deterioration of the thermal and
dimensional stability of the CCC structure
compared with CFC is observed. However,
undeniable advantage of CCC is not only its
operating temperature range 5 – 10 times ex-
ceeding that of CFC but a potential reduction
product weight as well, which is in the range
of CFC CCCM
U
U
=1,24…1,33, where
CCCM
U
=1050 kg/m3 corresponds to single
stage carbonization at atmospheric pressure.
2. Rational thicknesses of the groups of
layers and their relative thicknesses corres-
ponding to minimal LTEC 1red
D
and 2red
D
at
all coefficients of priority of direction pr
have the same values as the initial CFC sub-
jected to carbonization.
3. Levels of minimal LTEC 1red
D
prede-
termining the degree of thermal and shape sta-
bility in structures of CFC and CCC re-
mains the same from 0
pr
to 0, 4
pr
d,
and further it increases to the ratio
11
CCCM CFC
red red
DD
=1,3 at 1
pr
. The similar pat-
tern takes place also for the levels of minimal
LTEC 2red
D
, but in this case the increase of
CCC LTEC with regard to CFC LTEC is
observed in all pr
range, reaching at
1
pr
the value of 22
CCCM CFC
red red
DD
=1,3, equal
to their ratios for the criterion 1red
D
.
x
D
y
D
p
r
6
10
2red
D
1re d
D
Table 2 – Results of optimization of CCC structure on the criteria of reduced LTEC
Orientation of the
group of layers i
M
within the structure of
the pack
Initial thickness of the group
of layers i
G
, mm, and their
relative thickness
Rational thickness of the group of layers
i
G
, mm and their relative
thickness
on the criterion
1red
D
on the criterion
2red
D
0
pr
0 1,5 (0,167) 0,9 (0,1) 0,9 (0,1)
±45 6 (0,666) 1,8 (0,2) 1,8 (0,2)
90 1,5 (0,167) 6,3 (0,7) 6,3 (0,7)
x
D
-1,7610-6 1/deg. -1,0910-6 1/deg. -1,0910-6 1/deg.
y
D
-0,86210-6 1/deg. -0,18310-61/deg. -0,18310-61/deg.
red
D
0,86210-6 1/deg. 0,18310-6 1/deg. 0,18310-6 1/deg.
0,5
pr
0 1,5 (0,167) 0,9 (0,1) 0,9 (0,1)
±45 6 (0,666) 1,8 (0,2) 1,8 (0,2)
90 1,5 (0,167) 6,3 (0,7) 6,3 (0,7)
x
D
-1,7610-6 1/deg. -1,0910-6 1/deg. -1,0910-6 1/deg.
y
D
-0,86210-6 1/deg. -0,18310-61/deg. -0,18310-61/deg.
red
D
1,3110-6 1/deg. 0,63610-6 1/deg. 0,55210-6 1/deg.
1, 0
pr
0 1,5 (0,167) 0,9 (0,1) 0,9 (0,1)
±45 6 (0,666) 4 (0,444) 4 (0,444)
90 1,5 (0,167) 4,1 (0,444) 4,1 (0,444)
x
D
-1,7610-6 1/deg. -1,3710-6 1/deg. -1,3710-6 1/deg.
y
D
-0,86210-6 1/deg. -0,4510-61/deg. -0,4510-61/deg.
red
D
1,7610-6 1/deg. 1,3710-6 1/deg. 1,3710-6 1/deg.
Pre-stress and shape stability of skins of pa-
nels of carbon-carbon composite of complex
structure at the thermal loading
Peculiar feature of composite skins is
one or another level of SSB arising in the
process of their manufacture and operation –
stress
\
reducing the bearing capacity of
the structure at the force and temperature
impacts. SSB of multilayer skin depends on
the method of its molding. For the cold cur-
ing, absence of technological SSB and dis-
turbance of geometrical characteristics of
skin is typical. At operational loads, stress
\
and shape stability W are determined by
operational external impacts, boundary con-
ditions, external geometry of the structure
and characteristics of material distribution
,
ii
G
M
only.
For the hot curing, technological SSB is
determined by the conditions of curing
(T
'
), characteristics of monolayer material
and distribution of material i
M
.
In the course of operation, SSB of the
product is composed of sum of three SSB:
technological t
V
which is present in the
structure at absence of any external impacts
thereon, being the result of technological
process of obtaining the product, force oper-
ational
f
V
and force thermal
f
V
.
Process effect at hot curing can be mod-
elled by uniform cooling of the structure by
temperature drop T
'
from the molding
temperature to normal temperature.
Below given is the analysis of pre-stress,
thermal non-equilibrium state and shape sta-
bility of skins of CCC obtained by single-
stage carbonization of these structural ele-
ments of CFC, described in our work [15].
We considered the skin of 500×500 mm
size consisting of two monolayers of
G
=0,12 mm, subjected to cooling by tem-
perature of T
'
=100q. Stress factor is the
numerical value of the Hill strength crite-
rion:
22 2
2
12121
yxyxy
x
FFF F
VWVV
V
\
§·§·§ ·
¨¸¨¸¨ ¸
©¹©¹© ¹ , (17)
where , ,
x
yxy
VVW
and 1212
,,FF Fare, ac-
cordingly, stresses acting in axes of ortho-
tropy of CCC and limits of strength of un-
idirectional monolayer along and across the
reinforcement in its plane.
As an indicator (level) of shape stability,
we adopted the maximum linear movement
in transverse direction W.
CFC replacement by CCC was carried
out following the pattern described above.
Modelling was performed with the use
of finite element pack, with multilayer four-
node elements.
1. As the basic structure of skin, place-
ment of monolayers at angles of
M
=0q, 90q
is considered. Thickness of the adhesive
layer is not taken into account. Maximum
stress factors
\
and shape stability levels
W in double-layer skin at various angles of
monolayer placement in pre-deformed (with
the tool) state and released state (hereinafter
referred to as fixing on all degrees of free-
dom in the central node) are given in Ta-
ble 3 while the patterns of deforming are
shown in Fig. 4.
b
Figure 4 – Pattern of strained state of CCC
skin at various angles of placement
of monolayers subjected to cooling
by temperature of T
'
=100q:
–
M
= 0q, 90q; b –
M
= r45q
Table 3 – Maximum stress factors and levels
of shape stability of double-layer skin at var-
ious angles of monolayer placement in pre-
deformed state and free state
Angles of
placement
Pre-deformed
state Free state
max
\
max
W,
mm max
\
max
W,
mm
0q, 90q 0,00034
0
0,00014 11,77
r15q 0 0 12,32
r30q 0,00022 0,00013 20,6
r45q 0,00029 0,00015 23,45
2. Effect of monolayer thickness on
technological SSB of skin
As the basic structure, we considered the
monolayers’ placement at angles of
M
=0q,
90q.
Table 4 gives maximum stress factors
and levels of shape stability at various
thicknesses of monolayers of double-layer
skin in pre-deformed state and free state.
Table 4 – Maximum stress factors and levels
of shape stability of double-layer skin at
various thicknesses of monolayers in pre-
deformed state and free state
Monolayer
thickness,
mm
Pre-deformed
state Free state
max
\
max
W,
mm max
\
max
W,
mm
0,06 0,00034
0
0,00015 22,85
0,12 0,00034 0,00014 11,77
0,2 0,00034 0,00014 7,09
3. Effect of skin size on its technological
SSB.
3.1. As the basic structure of skin, we
considered monolayer thickness of
G
=0,12
mm, and placement of monolayers at angles
of
M
=0q, 90q.
For the panel of 500500 mm in size, we
obtained:
– in pre-deformed skin maximum
stress factor was
\
=0,00034 (W=0);
– in released state of skin
\
=0,00014;
W=11,77 mm.
For the panel of 10001000 mm in size
the values were as follows:
– in pre-deformed skin maximum
stress factor was
\
=0,00034 (W=0);
– in released skin
\
=0,00014;
W=47,31 mm.
3.2. For the skin of 500×500 mm in size
consisting of six monolayers of
G
=0,12 mm
and subjected to cooling by temperature of
T
'
=100q, with monolayer placement at
angles of
M
=45q, -45q, 0q, 90q-45q, 45q we
obtained:
– in pre-deformed skin maximum
stress factor was
\
=0,0003 (W=0);
– in released skin
\
=0,0003; W=0,55
mm;
– for skin freely supported by edges
(assembly on the frame)
\
=0,033;
W=0,015 mm.
Comparison of obtained results with
those given for skins of CFC [15] allows
drawing the conclusions below.
1. Maximum stress factors for all ana-
logs of double-layer skins of CFC in the
course of composite turning into CCC was
more than two orders of magnitude lower,
being the evidence of actually not pre-
stressed skin.
For example, for structures with the an-
gles of fiber placement equal to, according-
ly, 0q, 90q, r30q and r45q, the ratio
max max
CCCM CFC
\\
= 0,0065; 0; 0,0055; 0,006.
For double-layer skin with various thick-
nesses of monolayers (0,06 mm; 0,12 mm and
0,2 mm) the ratio max max
CCCM CFC
\
\
remained con-
stant, equal to 0,0065.
Skin size as in the case with CFC has no
effect on its pre-stress; besides, the ratio
max max
CCCM CFC
\
\
=0,0065 is maintained in pre-
deformed state and 0,0042 in released state,
in any case, for the pattern of layer place-
ment of (0q, 90q); thickness of the monolay-
er is
G
=0,12 mm for sizes of 500×500 mm
and 1000×1000 mm.
For the skin of 500×500 mm in size con-
sisting of six monolayers with the angles of
placement of (45q, -45q, 0q, 90q, -45q, 45q),
monolayer thickness
G
=0,12 mm in pre-
deformed state max max
CCCM CFC
\
\
=0,0016, in re-
leased state – 0,0061.
However, for the skin freely supported
by edges (assembly on the frame), the ratio
max max
CCCM CFC
\
\
increases considerably, be-
coming equal to 0,313.
Analysis of pre-stress of skins of CCC
prove their considerably higher bearing ca-
pacity or increased service life at specified
operating mode in orbit, compared with their
analogs of CFC.
2. Shape stability of skins of CCC
CCCM
W in free state is more than by the order
of magnitude higher than that of analogs of
CFC. For example, CCCM CFC
WWratio for
skins with angles of placement of 0q, 90q;
r15q; r30q and r45q is equal to: 0,03; 0,032;
0,053 and 0,03, accordingly.
The same order is valid for that ratio in
other variants of skins of CCC which are
considered above as well, when analyzing
their pre-stress values.
However, finite element analysis of the
efficiency of replacement of the monolithic
housing of scanner of CFC [16] by CCC
allows revealing also some of its negative
aspects.
As the basic model of scanner housing
of CFC of high resolution we took the finite
element model in which multilayer three-
node shell elements were used. Elements
were generated in the automatic mode, with
the element sizing 10 mm. Finite element
model was represented by 22904 elements
(Fig. 5).
Figure 5 – Finite element model
of scanner housing
As a material, we used unidirectional carbon
fiber reinforced plastic with the characteristics
below: 1
E 150 GP; 2
E 8 GP;
12
G 4 GP; 12
P
0,3;
U
1520 kg/m3;
1
D
-210-6 1/deg.; 2
D
210-5 1/deg.;
1
F 1300 P; 1
F 1300 P;
2
F 40 P; 2
F 100 P; 12
F 60 P.
Characteristics of CCCM obtained by
these PhMC and strength properties CC
according to formulas (7) – (11) are equal
to:
1
CCCM
E 148,4 GP; 2
CCCM
E 36,5 GP;
12
CCCM
G 19,3 GP; 1
CCCM
D
-2,710-6 1/deg.;
2
CCCM
D
-1,3710-5 1/deg.; 1CCCM
F 1289 P;
1CCCM
F 1286 P; 2CCCM
F 15,75 P;
2CCCM
F 84 P; 12CCCM
F 59,4 P.
Thicknesses of the box and the rear face
G
18 mm, front face
G
20 mm. As the
loading, uniform heating of the housing till
the temperature of +50q was chosen. Fix-
ing in the nodes was made at the place of
location of mounting brackets of the hous-
ing. Results of finite element analysis are
given in Table 5.
Table 5 – Results of finite element analysis
of the model of scanner housing made of
CFC and CCC at
'
=50q
CFC CCC
Weight, kg 30,98 23,83
Maximum value of result-
ing linear movement
rez
u,mm
0,0247 0,0856
Value of angular move-
ment with regard to fitting
plane of the mirror
'M
,
ang.s
0,859 5,37
Maximum value of Hill
energy fracture criterion,
\
0,026 0,522
Comparison of obtained data gives the
evidence that CFC replacement by CCC
caused the expected weight reduction of the
base model of scanner housing (1,3 times),
but the value of maximum resulting linear
movement has grown 3,47 times, maximum
angular movement with regard to the fitting
plane of the mirror
'M
– 6,25 times, and
maximum value of pre-stress according to
the Hill criterion 20 times (from 0,026 to
0,522) which confirmed the noticeable re-
duction of probable service life of the prod-
uct at its long-term operation in orbit.
We also carried out the numerical expe-
riments at increasing of the operating tem-
perature drop to
'
=200q (at which CFC
cannot function any longer). In this case, we
considered the opportunity of reducing the
porosity by two-stage (
3
=0,25) and three-
stage carbonization (
3
=0,18). Results of
analysis are summarized in Table 6.
Table 6 – Characteristics of the model of
scanner housing made of CCC
at
'
=200q
Porosity
3
, %
Weight,
kg
rez
u,
mm
\
'M
,
ang.s
25 26,5 0,362 0,909 16,28
18 29,55 0,36 0,332 13,35
As it is seen from Table 6, characteris-
tics of linear movements increased 4,2
times, while those of angular movements
were higher at
3
=0,25 and decreased at
3
=0,18.
Therefore, the above results prove the
possible restrictions on operation of prod-
ucts of CCC type under study and the ne-
cessity of separate task-oriented research.
Conclusions
1. The paper investigates the opportuni-
ties of creating thermally and dimensionally
stable structures for space applications made
of carbon-carbon composite materials allow-
ing to effectively increase the accuracy of
data transmission by transceiver systems and
devices of the Earth remote sensing from the
orbiters.
2. The paper reveals the preconditions
for using the laminated CCC obtained by
processing of finished products of CFC by
their carbonization in the furnace with non-
oxidizing medium at high temperatures: it is
shown that resulting products get an oppor-
tunity to operate in the temperature range
corresponding to and considerably exceed-
ing the conditions of operation of objects in
the near-earth orbits with the allowable level
of change in their shape and pre-stress
which provides for specified service life.
3. We synthesized the approximate de-
pendencies of PhMC and strength properties
of the obtained CCC on the basis of the
theory of reinforcement of polymeric com-
posites’ mechanics, with the use of which
finite-element analysis of the degree and the
nature of change of thermal and dimensional
stability of polymeric composite structure
after its carbonization and turning into
CCC has been carried out.
4. With the use of approximated criteria
of optimization of CCC structure ensuring
its maximum dimensional stability at vari-
ous coefficient of priority of its direction,
the package with orientation of the group of
thermo-nonequilibrium layers of (0º,±45º,
90º) has been investigated compared to ana-
logs of carbon fiber reinforced plastic,
which provides for high bearing capacity
and service life thereof. Shape stability of
skins of carbon-carbon composite materials
is also higher than that in their analogs of
carbon fiber reinforced plastic (0q, r45q,
90q) compared with analogs of CFC. It was
found that the level of thermal and dimen-
sional stability of CFC and CCC struc-
tures under study remains the same up to the
value of coefficient of priority 0, 4
pr
d,
and then it is 1,3 timed reduced in CCC.
However, CCC undeniable advantage re-
mains as potential decrease in the product
weight (1,24…1,33 times) and providing the
operating temperature range unachievable
for CFC.
5. We analyzed pre-stress and shape sta-
bility of skins of CCC panels compared
with their analogs of CFC. It was found that
pre-stress of skins of CCC both for vari-
ous structures (0q, 90q; r15q; r30q; r45q)
and for various thicknesses of monolayers
(0,06 mm; 0,12 mm; 0,2 mm) was more than
two orders of magnitude lower than in CFC
(max max
CCCM CFC
\
\
=0,0055…0,0065), which
provided thereto high bearing capacity and
service life. Shape stability of skins of
CCC is also higher than that in their ana-
logs of CFC, making their ratio in the range
of CCCM CFC
WWd0,053.
6. However, the finite element analysis
of the efficiency of replacement of mono-
lithic CFC housing of scanner of high reso-
lution by CCC revealed, along with the
expected effect of 1,3 weight reduction, also
the negative fact of increase in the maxi-
mum linear movement 3,47 times and max-
imum angular movement with regard to the
fitting plane of the mirror 6,25 times, and
growth of maximum pre-stress 20 times,
which prove the probable deterioration of
the conditions of product operation in orbit.
The revealed facts prove the necessity of
separate in-depth studies of the scale and
limits of the efficiency of using CCC in
the components of orbiters.
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