THE STATIC STRUCTURAL TEST ON SARA SUBORBITAL THERMOSTRUCTURAL
SUBSYSTEM
Eduardo Henrique de Castro Biase(1), Luís Eduardo V. Loures da Costa (2)
(1)
Instituto Tecnológico de Aeronáutica, Pça. Marechal Eduardo Gomes, 50, Vila das Acácias, 12.228-900, São José
dos Campos – SP, Brasil
+55 12 39474691, Email:[email protected]
(2)
Instituto de Aeronáutica e Espaço, Pça. Marechal Eduardo Gomes, 50, Vila das Acácias, 12.228-900, São José dos
Campos – SP, Brasil
+55 12 39474628, Email:[email protected]
ABSTRACT
This paper presents the results of the static structural
test on the SARA Suborbital Thermostructural
Subsystem. The SARA Suborbital is a suborbital
platform developed at the Department of Space Systems
(ASE) of the Institute of Aeronautics and Space (IAE)
to be launched with a VS40 sounding rocket from the
Alcantara Launch Site in Brazil. The static structural
test was carried out to verify and validate the structural
requirements of the thermostructural subsystem. A set
of strain-gages were bounded on the outer surface to
evaluate the maximum strain levels. To investigate the
displacement and deflection magnitude were used
LVDTs sensors mounted external the cone part.
1.
SARA SUBORBITAL
The SARA Suborbital project aim to develop,
manufacture and qualify a recoverable suborbital
platform to carry out scientific and technological tests
under microgravity conditions until december 2012 [1].
The suborbital platform is under development at the
Department of Space Systems (ASE) of the Institute of
Aeronautics and Space (IAE) and a group of Brazilian
aerospace industries. The suborbital platform will
increase the Brazilian microgravity research capability,
providing means for the development of medications
for cancer and diabetes for instance. The project goals
include the launch with the VS40 Brazilian sounding
rocket (Fig. 1) from the Alcantara Launch Site in Brazil
and the recovery at the sea. The SARA Suborbital will
provide the experiments with near 10 minutes of
microgravity conditions, and after recovery, it will be
re-used for future launchings (Fig. 2). The SARA
Suborbital payload is composed of a thermostructural
subsystem, an on-board electronic subsystem, an
experimental module, a recovery subsystem and a
payload support subsystem [2].
Figure 2. SARA Suborbital trajectory.
2.
SARA SUBORBITAL
THERMOSTRUCTURAL SUBSYSTEM
The Sara Suborbital Thermostructural Subsystem (Fig.
3) consists of a composite nose cap followed by a 678
mm tall composite cone and a metallic cylindrical ring
with 1015 maximum diameter (Fig.4). The cone fairing
(Fig. 5) is made of an 8-layer composite laminate
covered by a 4 mm thickness ablative composite cork
[3].
Figure 1. VS-40 launching vehicle.
_________________________________________________
Proc. ‘20th ESA Symposium on European Rocket and Balloon Programmes and Related Research’
Hyère, France, 22–26 May 2011 (ESA SP-700, October 2011)
Figure 5. Upper ring and composite cone fairing.
Figure 3. SARA Suborbital Thermostructural subsystem.
The composite nose cap is composed of two parts, the
internal one is made of aluminium and the external part
is manufactured of quartz-phenolic. The nose cap is
connected to the nose ring with fasteners. To bond the
metallic rings to the composite cone is applied a
thixotropic paste adhesive which cures at room
temperature.
The other three metallic parts: sealing ring, sealing plate
and aft skirt shown below are connected with bolts and
nuts.
Figure 6. Sealing ring, Sealing plate and Aft Skirt
The metallic structures mentioned above are made with
aluminium. The resulting Thermostructural Subsystem
weights 76 kg and is designed to resist both the ascend
loads and the water impact. Another function of this
subsystem is the provision of thermal protection during
the atmospheric re-entry.
3.
Figure 4. SARA Suborbital Thermostructural subsystem
dimensions.
STATIC TEST
During the atmospheric flight the SARA Suborbital
would be subjected to inertial and aerodynamics loads
acting in longitudinal and lateral direction
simultaneously. Thus, the static test was planned to
verify the structural requirements and integrity. The
load magnitude used on the static test were determined
based on the resulting load distribution throughout the
VS-40 vehicle. More details can be seen in [4]. The
structural requirements for the static qualification test
define a safety factor of 1.5 [3]. Thus, the applied load
designed for the static tests exceeded the worst case
dynamic flight conditions with an added safety factor of
50%. The calculated load magnitudes are 70.2 kN for
the axial force and 9.37 kN for the lateral force [5].
Based on the assessment of the load diagrams the
position for the load application in the static test were
defined. The lateral load was applied in seven different
regions of the structure. The height and the magnitude
of each individual load application is presented on Fig.
10, considering the bottom of the aft skirt as reference.
Figure 9. Axial static test configuration.
4.
Figure 7. Lateral static test configuration.
Test apparatus design
A custom wide strap apparatus was designed and
manufactured to transmit the lateral loads to the fairing.
The straps were made of steel with 0.04 inch of
thickness and 50 mm of width. The strap apparatus is
comprised by seven horizontal straps and four vertical
straps tied with rivets. This tooling was also used to
prevent localized load peaking on the composite skin.
The straps were designed to embrace the cone skin and
the aft skirt in same positions previously shown on Fig.
10. The face inside the belts was covered with rubber to
protect the structure.
Figure 8. VS-40 Lateral load distribution.
Figure 10. The custom wide strap apparatus.
5.
TEST CONFIGURATION
The test was carried out in three different loading
conditions: Axial loads; lateral loads; axial and lateral
loads simultaneously. In all loading cases the force was
applied following an increasing sequence until
maximum amplitude is reached. The following table
shows the load amplitudes increasing sequence used on
the static test. During the experiment, force, strain, and
displacement data were acquired for each load
amplitude for further comparison and analysis.
The SARA Thermostructural Subsystem was mounted
on a steel support using a separation clamp. The support
is composed by a steel plate and an adapter skirt as
shown on Fig. 11. The assembly was fixed on the
laboratory floor using bolts.
ii. To measure representative strain levels for the
applied loads.
iii. To measure overall structural displacement
under the applied loads.
Table 1. Increasing of the Load Amplitudes of the static
test
Percentage
Axial Load
Amplitude
(N)
Lateral Load
Amplitude
(N)
0 (0%)
0
0
1 (20%)
14160
1875
2 (40%)
28320
3750
3 (60%)
42480
5625
4 (65%)
46020
6093,75
5 (70%)
49560
6562,5
6 (75%)
53100
7031,25
7 (80%)
56640
7500
8 (85%)
60180
7968,75
9 (90%)
63720
8437,5
10 (95%)
67260
8906,25
11 (100%)
70800
9375
12 (0%)
0
0
Figure 11. Static test support.
6.
Figure 12. A photo of the SARA Suborbital
Thermostructural Subsystem mounted on the
Laboratory floor.
The major objectives of these two tests were the
following:
i.
To observe and confirm that the structure could
resist the applied loads without damage.
INSTRUMENTATION
For this static test two load cells were used, the first one
fixed on the axial actuator, is the Load Cell MTS, model
661.20E-03, serial number 121451, load capacity 100
kN. The second, Load Cell MTS, model 661.20E-01,
serial number 108118, load capacity 25 kN is mounted
on the lateral actuator. Both load cells were mounted to
the shaft of each actuator to monitor the load amplitude.
In addition 24 strain gages manufactured by Toyo Sokki
Kenkyujo, model FLA-350-17, gauge factor 2.13, 350
Ohm and 24 displacement transducers were used on the
instrumentation suite for this static test operation.
Complementarily, three parallel horizontal planes were
defined to place eight straingages, which were bonded
at 00, 450, 900, 1350, 1800, 2250, 2700 and 3150 azimuths
from the direction of lateral load application. For the
deflection measurement six parallel horizontal planes
were chosen to place four displacement transducers and
they were place at 00, 900, 1800 and 2700 from the
direction of the bending load application. The position,
the planes and the angular locations of the strain gages
and displacement transducers are shown on Fig. 13 and
Fig. 14 respectively.
The loading system is comprised by a loading control
hardware MTS model Aero 90, a hydraulic actuator
MTS model 204.52, load capacity of 10 kN and a
second hydraulic actuator MTS model 243.20T, load
capacity of 100 kN. The lateral loading was applied
according the reference direction depicted on Fig. 15.
The hydraulic actuators were mounted in a steel frame
structure fixed on the Laboratory ground and the load
angle was measured with a digital inclinometer. The
strain and displacement data will be used to correlate
and correct finite element analysis developed on
commercial package Abaqus. During the experiment a
continuous digital video of critical fairing regions were
recorded to visually capture a potential failure or
debonding interface.
Figure 15. Lateral Load reference direction.
7.
RESULTS
On the first load case (lateral load, Fig. 16), the highest
negative strain level were obtained by the straingage
located at 00 azimuth from the direction of lateral load
application -89µε. The peak positive strain was +72.6 µε
located at 900 from the reference direction of the
bending load. The maximum deflection was -0.34 mm
positioned 2700 from the direction of the load. The
strain results behave linear with the load application as
can be seen examining the data diagram from the
negative and the positive highest strain, curve blue and
red, respectively Fig. 17.
Figure 13. Strain gage position and location.
Figure 16. Static test photo during the Lateral Loading.
Figure 14. Displacement transducers position and
location.
On the second test with axial load (Fig. 18), the top
negative strain level were obtained by the straingage
locate at 00 and was -363.27µε. The top deflection was
0.22 mm at 900. The strain response as shown on the
chart depicted in Fig.19 was not fully linear.
The aft skirt has a region of diameter reduction which
occurrence results in a region with high stress
concentration and consequentially also high strain
levels. As expected, this mechanical response was
confirmed with the data results. In both axial and lateral
loads the highest strain values occurred in Plane B,
located close to the diameter reduction of the aft skirt, in
comparison with the two others parallel planes, ie.
planes A and C.
8.
In this work, static structural tests have been performed
in the SARA Suborbital Thermostructural Subsystem.
All the objectives were reached and after the tests
execution the structure was carefully examined. It was
notice that no crack or debonding has occurred on the
entire structure. Besides, the maximum amplitudes of
the strain and displacement were low, demonstrating
that the SARA Suborbital Thermostructural Subsystem
is capable to withstand the resulting loads from the
liftoff and ascendant flight.
9.
Figure 17. Strain versus force diagram.
Figure 18. Static test photo - Axial Loading.
Figure 19. Strain versus force diagram.
During the combined load test very little bending was
observed. The negative peak strain levels was -466.08
µε at 00 azimuth from the reference direction. The
maximum lateral deflection measured was -0.49 mm at
900 from the reference direction.
CONCLUSIONS
REFERENCES
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