21 November 2017 Stability study of MMC tubes and advanced assemblies for telescope structures
Author Affiliations +
Proceedings Volume 10569, International Conference on Space Optics — ICSO 2000; 105691L (2017) https://doi.org/10.1117/12.2307925
Event: International Conference on Space Optics 2000, 2000, Toulouse Labège, France
Abstract
This paper presents new advances concerning the development of an Aluminum Matrix Composite for dimensionally stable satellite structures. Feasibility of thermally stable thin-walled tubes have been acquired through microstructure observation and Coefficient of Thermal Expansion measurement.

In order to fit the thermo-mechanical stability domain of tubes on specifications, 3 thermal cycles have been tested, regarding to relaxation of internal stress and changes in macroscopic thermo-mechanical properties. Experimental expansion curves and microstructure observation show that thermal treatments permitts such a good fitting. For a better understanding of physical internal phenomena, internal stress has been measured by neutron diffraction on tube samples after each thermal treatment. Results show a significant decrease of stress due to cycling in cold temperature.

In order to decrease the absolute value of CTE of assemblies, a new concept of thermo-mechanical stable linkage has been developped, which consists in a common alumlinum infiltration of superposed carbon preforms. Structural bonding, which usually affects stability properties and impose surface treatments and polymerization, can so be avoided.

The study has been achieved through CNES (Centre National d’Etudes Spatiales) and French Ministry of Defense (DGA) supports.

1-

Introduction :

Carbon fiber reinforced aluminum alloy is the Metal Matrix Composite (MMC) which properties suit best for thermally stable satellite structures : no moisture instability (compared to Carbon/Resin), high stiffness (compared to Carbon/Carbon), optimized coefficient of thermal expansion (CTE) to near-zero value (compared to SiC).

2–

Material choice :

Fiber and matrix have been chosen accordingly to previous studies performed for small plates :

  • - reinforcement with UltraHighModulus pitch-based carbon fabric.

  • - matrix composed of aluminum alloy with a low solidification temperature, so as to ensure a low time of contact between fibers and liquid aluminum during infiltration.

3-

Feasibility of near-zero CTE MMC thin-walled tubes :

The lay-up has been defined with the two following criteria :

  • - a symetric lay-up with 0° angles

  • - a minimized calculated CTE value.

In order to reduce overall dimensions of small truss structures, thermally stable thin-walled (1.6mm) tubes with low diameter (32mm) have been manufactured by pressure infiltration casting.

Concerning the feasibility of thin-walled tubes, critical points are identified by comparison with already made thick-walled (5mm) tubes with large diameter (60mm) :

  • - Preform manufacturing : the thinner is the tube, the more difficult is the compaction of dry fabric, necessary to obtain the 60% fiber content.

  • - Infiltration parameters : the ratio length/diameter has been decreased, so that thermal behaviour should differ during infiltration.

  • - Material health : swelling of fabric in the mould could cause waving of fibers, which could increases standard deviation of CTE values. Moreover, fiber content is measured in different points to control homogeneity along the tube.

Preform manufacturing :

Rolling of fabrics on the mandrel

00407_PSISDG10569_105691L_page_3_1.jpg

Preform in the mould before closing (With titane sheet)

00407_PSISDG10569_105691L_page_3_2.jpg

Infiltration parameters :

  • - aluminum T°C : 720°C

  • - preform T°C : 700°C

  • - pressure : 60 bars

  • - cooling rate : about –50°C/min

Micrography :

Titane sheet defect

00407_PSISDG10569_105691L_page_4_1.jpg

Conclusion :

The two steps of manufacturing of carbon fiber reinforced aluminum alloys (wrapping and infiltration) are now well-mastered for single shape elements (tubes, plates,..) either thin or thick.

2.3-

CTE measurement

LVDT sensor

00407_PSISDG10569_105691L_page_5_1.jpg

Equipped samples

00407_PSISDG10569_105691L_page_5_2.jpg

Experimental curves

00407_PSISDG10569_105691L_page_5_3.jpg

Conclusion :

CTE = 0.1 +- 0.24 μm/m/°C on [+20°C;+50°C] (3 cycles, 2 samples).

3–

Internal stress

3.1–

Framework

00407_PSISDG10569_105691L_page_6_1.jpg

3.1 –

Expansion curves

Experience principle

00407_PSISDG10569_105691L_page_6_2.jpg

Experimental curves on as-received samples

00407_PSISDG10569_105691L_page_7_1.jpg

Micrography :

-40°C heat-treated

00407_PSISDG10569_105691L_page_7_2.jpg

-100°C heat-treated

00407_PSISDG10569_105691L_page_7_3.jpg

3.2 –

Internal stress measurement

measurement principle

00407_PSISDG10569_105691L_page_8_1.jpg

Axial measurement

00407_PSISDG10569_105691L_page_8_2.jpg

Radial measurement

00407_PSISDG10569_105691L_page_8_3.jpg

Results :

  • - Axial stress is always tensile, while radial and hoop stress are compressive

  • - Thermal cycling decreases internal stress (axial, radial and hoop)

  • - the lower is the cold temperature, the more internal stress is relaxed

3.3–

MicroYield Stress measurement

Sample in the Global Device

00407_PSISDG10569_105691L_page_9_1.jpg

Coupling beetwen applied stress (alternatively tensile and compressive) and residual strain

00407_PSISDG10569_105691L_page_9_2.jpg

Effect of 2 high level of repeated tensile/compressive stress

00407_PSISDG10569_105691L_page_10_1.jpg

Conclusion :

  • - tensile and compressive MicroYield Strenght are low : the material is hysteretic

  • - tensile / compressive MicroYield Strenght is just sufficient for stable structure : 56 MPa

  • - no effect of strength hardening or strength softening

3.4

Conclusion

MicroYield Strenght should be increase by thermal cycling. Experience is planned in the beginning of 2001.

4-

Linkage studies

4.1–

Feasibility of a new stable linkage

tube-plate superposition principle

Feasibilty has been acquirred.

00407_PSISDG10569_105691L_page_11_1.jpg

4.2–

Gluing MMC / metal

Results have shown delamination of MMC in each case. It has been shown that shear stress concentration in the glue due to the different stiffness of MMC and metal can cause delamination. The further is the ratio of stiffnesses from 100%, the earlier happens delamination of MMC.

4.3–

Friction betwwen MMC and metal (or MMC)

Results have shown that friction coefficient is low (about 0.1) compared to classical metal / metal interface (about 0.2). This can be sensitively improved by an adequat surface treatment

© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Martine Nivet-Lutz, Martine Nivet-Lutz, Gilles Pommatau, Gilles Pommatau, } "Stability study of MMC tubes and advanced assemblies for telescope structures", Proc. SPIE 10569, International Conference on Space Optics — ICSO 2000, 105691L (21 November 2017); doi: 10.1117/12.2307925; https://doi.org/10.1117/12.2307925
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