Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
1998-11-13
2001-03-06
Weisberger, Richard (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S293700, C428S539500, C428S294400, C442S228000, C442S376000
Reexamination Certificate
active
06197411
ABSTRACT:
DESCRIPTION
1. Technical Field
The invention relates to an elongated part, of a composite material including an aluminium or magnesium-based metal matrix, as well as continuous carbon fibres arranged in superimposed sheet form.
Throughout the present text, the expression “continuous fibres” designates long fibres, which extend without any discontinuity from one end to the other of the part or over its entire periphery, in accordance with the orientation given to the fibres within the part.
The expression “elongated part” designates any part (plate, rod, tube, etc.) having a larger dimension in a given direction, called the “longitudinal direction”, in which stresses are to be transmitted.
The term “sheet” designates by convention any layer of woven or unwoven fabrics, no matter the way in which it is made (draping, winding, etc.).
The composite, metal matrix material part according to the invention is particularly appropriate for uses in the space industry and, more generally, for any use involving a high dimensional stability.
2. Prior Art
The different structural parts of satellites, probes and other craft to be used in space are subject to particularly severe, more especially mechanical and thermal stresses.
Thus, during assembly and testing on the ground, very careful monitoring is required of the effects of gravity, humidity and temperature.
During the launch phase, the launcher transmits to the spacecraft intense vibrations and thrust forces.
Finally, when the craft is operational, it is subject to very significant temperature changes, depending on whether or not its different faces are illuminated by the sun. To this is added the placing under vacuum of the craft, which can lead to moisture being given off.
In the presence of all the aforementioned stresses and constraints, the production of structural parts causes a difficult problem, particularly when they are used for supporting high precision equipment, such as mirrors belonging to optical systems.
In this context, at present there is no material which, in itself, has an adequate dimensional stability and rigidity to produce structural parts able to withstand the aforementioned stresses, whilst still ensuring the requisite positioning precision. This is why heat regulators of varying complexity are sometimes associated with such parts.
Thus, metal parts always have a non-zero expansion coefficient, which leads to a positioning instability when the part undergoes temperature variations. The rigidity of purely mechanical parts is also generally inadequate for the considered application.
Composite, metal matrix material parts are much less sensitive to temperature variations and can have a high rigidity in the longitudinal direction of the part. However, they suffer from the important disadvantage that when entering vacuum, they progressively desorb the water which they had adsorbed when on earth. This progressive desorption leads to dimensional variations in the part. It requires the following of very prejudicial procedures during the manufacture of the spacecraft. It also leads to the equipping of said craft with devices of varying complexity permitting the repositioning of high precision equipment, when in space. However, these are difficult and energy-consuming operations, which can affect the reliability of the craft and reduce its service life.
The use of composite metal matrix material parts makes it possible, due to the presence of continuous fibres, to significantly increase the rigidity compared with purely metal parts. Moreover, the problems of dimensional variations due to desorption in vacuum are eliminated. These advantages are more particularly described in the article “High Stable Advanced Materials For Space Telescope, An Application of Metal Matrix Composites” by C. Désagulier et al., IAF-96-I.3.01, in the case of composite carbon-aluminium and carbon-magnesium fibres. More specifically, this article recommends the use of ultra-high modulus carbon fibres and states that a sheet or element “ply” having a longitudinal, thermal expansion coefficient &agr;L of 1.10
−6
/° C. (magnesium matrix) or 1.27.10
−6
/° C. (aluminium matrix) and a longitudinal tension modulus EL of 280 GPa (magnesium matrix) or 302 GPa (aluminium matrix) could be obtained.
However, no procedure is suggested with regards to the production of a thick part (group of sheets) having to have longitudinal thermal expansion coefficient &agr;L of virtually zero, i.e. whose absolute value is preferably below 0.2.10
−6
/° C.
DESCRIPTION OF THE INVENTION
The invention specifically relates to a composite, metal matrix material part, whose original design makes it possible to have both a high rigidity and a high dimensional stability, so as to be usable in space, in order to support there high precision equipment.
According to a first embodiment of the invention, this result is obtained by means of a composite, metal matrix material part, which is elongated in a given direction, characterized in that it comprises 35 to 45 volume % of an aluminium-based alloy matrix and, respectively, 65 to 55 volume % of continuous carbon fibres arranged as successive sheets parallel to said direction, at least approximately 90% of the carbon fibres being ultra-high modulus fibres, said ultra-high modulus fibres being oriented at 0°±5° in approximately 25% to approximately 60% of the sheets, and beteween±20° and±40° in the other sheets, with respect to said direction.
In this case, the aluminium-based alloy matrix is preferably of an AG10-type alloy, containing approximately 10 vol. % magnesium.
Advantageously, the ultra-high modulus fibres are then oriented at 0°±5° in 45 to 55% of the sheets and preferably in approximately 50% of the sheets.
Moreover, the ultra-high modulus fibres are advantageously oriented at approximately±25° in the other sheets.
According to a second embodiment of the invention, the sought features are obtained by means of a composite, metal matrix material part, elongated in a given direction, characterized in that it comprises, respectively, 35 to 45 volume % of a magnesium-based alloy matrix and 65 to 55 volume % of continuous carbon fibres, arranged in successive sheets parallel to said direction, at least approximately 90% of the carbon fibres being ultra-high modulus fibres, said ultra-high modulus fibres being oriented at 0°±5° relative to said direction in at least 90% of the sheets.
In this case, the magnesium-based alloy matrix is preferably a GA9Z1-type alloy, containing approximately 9 vol. % aluminium.
Advantageously, the ultra-high modulus fibres are then oriented at 0°±5° in approximately 100% of the sheets.
In both embodiments, the parts have a virtually perfect stability, at least in the longitudinal direction. Thus, as with all metal parts or those having a metal matrix, there is no moisture adsorption on the ground, so that these dimensions do not change when the part is placed in a vacuum. Moreover, due to the characteristics inherent in the material according to the invention, the thermal expansion coefficient &agr;L in the longitudinal direction is substantially zero. Thus, its absolute value is below 0.2.10
−6
/° C., or close thereto.
A part according to the invention also has a high specific rigidity in the aforementioned longitudinal direction. More specifically, the specific rigidity in said direction being defined as the ratio between the longitudinal tension modulus EL and the relative density &rgr;, in most cases said ration exceeds 100 MPa.
Preferably, at least some of the sheets are fabrics, e.g. of the taffeta type, comprising approximately 90% warp yarns, constituted by the continuous carbon fibres with an ultra-high modulus and approximately 10% weft yarns, constituted by other continuous carbon fibres with a lower modulus. The weft yarns have the particular function of holding or maintaining the warp yarns.
In the preferred embodiments of the invention, the ultra-high modulus fibres have a tension modulus at least equal to approximat
Billaud Laetitia
Gaudin Jocelyn
Nivet Lutz Martine
Poncy Joël
Aerospatiale - Societe Nationale Industrielle
Burns Doane , Swecker, Mathis LLP
Weisberger Richard
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