Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Patent
1997-11-20
2000-04-18
Weisberger, Richard
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
428373, 428374, 428408, 156148, 156151, 156229, 156276, 57 3, 57 5, 57 9, 57 10, 57 11, 57 13, D02G 316
Patent
active
060513136
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to fabricating fiber preforms for composite material parts, and in particular it relates to a yarn for such fabrication.
One field of application of the invention is that of fiber preforms for composite material friction disks such as clutch disks, and principally brake disks.
Carbon-carbon (C--C) composite material brake disks are currently used in racing cars and, on a much larger scale, in rotor and stator multiple-disk brake systems for aircraft.
The manufacture of composite C--C brake disks comprises fabricating fiber preforms of carbon fibers and densifying the preforms with a carbon matrix which fills the majority of the initially accessible internal pores in the preforms.
Densification is conventionally carried out by chemical vapor infiltration or by chemical liquid infiltration, i.e., impregnation with a liquid carbon precursor and transformation of the carbon precursor by heat treatment.
Fiber preforms can currently be manufactured by superposing plies formed from a two-dimensional fiber fabric and interconnecting the plies by needling. The two-dimensional fiber fabrics can be in the form of woven fabrics or pre-needled unidirectional sheets. The plies are needled as they are stacked, preferably keeping a constant needling depth as described in French patent FR-A-2 584 106. The plies can be stacked flat and needled to obtain flat slabs from which annular brake disk preforms are cut. In order to avoid wasting a large amount of material, the plies can be formed from juxtaposed annular sectors cut from the two-dimensional fiber fabric, the lines separating the sectors being offset from one ply to the next.
Two-dimensional fiber fabrics in the form of woven fabrics or unidirectional sheets made of carbon yarns are not suitable for needling. Indeed, the needles showing barbs or forks have a tendency to break the continuous or twisted carbon filaments which constitute the yarns, rather than taking the fibers to place them transversely to the superposed plies. One way of solving this problem is to associate a web of carbon fibers with the two-dimensional fabric, which web provides fibers which can be entrained by the needles. Another solution consists of needling two-dimensional fabrics formed by fibers which are not of carbon but of a carbon precursor which is much more suitable for needling. The carbon precursor is transformed by applying heat treatment to the needled preform.
European patent EP-A-0 489 637 describes making two-dimensional fiber fabrics for fabricating preforms from a yarn composed essentially of discontinuous fibers (staple) which are parallel to one another and not twisted, the integrity of the yarn being ensured by a covering yarn of sacrificial material. Eliminating the covering yarn by dissolving or by heating frees the discontinuous fibers and allows needling even when the fibers are in the carbon state. Further, freeing the fibers allows them to expand into the entire volume of the preform, resulting in pores which are more easily and more uniformly accessible to the matrix material during the densification stage. Densification is thus more complete and more uniform.
For brake disks, the nature and the origin of the fibers constituting the preforms, the structure of the two-dimensional fabrics used to fabricate the preforms, the way in which the plies formed by these fabrics are connected together, in particular the needling parameters, the heat treatments to which the preforms can be subjected before densification, the nature of the matrix, and the mode of densification, are all factors which significantly influence the mechanical and tribological properties of the disks.
Particularly in the case of aircraft brakes, the disks used must not only have mechanical properties which enable them to withstand stresses both when hot and when cold, but they must also have tribological properties which enable them to behave satisfactorily in different situations: braking while taxiing cold (taxiing on runways before take-off), braking while taxiing hot (tax
Coupe Dominique
Duval Renaud
Olry Pierre
Zerdouk Amina
Societe Nationale D'Etude et de Construction de Moteurs D'Aviati
Weisberger Richard
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