Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1999-04-14
2002-04-02
Jones, Deborah (Department: 1772)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S037000, C428S066200
Reexamination Certificate
active
06365257
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to continuous fiber preforms for reinforced composites and composites containing such preforms. More particularly, this invention relates to carbon fiber preforms comprising continuous tows of carbon fiber disposed as chords of a circle to form a near net shape part.
BACKGROUND OF THE INVENTION
The present invention is particularly concerned with improved carbon-carbon fiber composites intended for use in applications where severe shear stresses will be encountered, for example, by being subjected to circumferential stress. A prime example of such use is a friction disc employed in a disc brake. Such discs are essentially annular in shape, having at least one surface of each disc being provided with a friction-bearing surface. Braking is accomplished through contact between the friction-bearing surfaces of the discs, thereby converting the mechanical energy of the rotating brake to heat. In addition to withstanding the shearing stresses, the discs also are required to act as heat sinks, absorbing high heat loads. Because of its strength, density, heat capacity, thermal conductivity, coefficient of friction and stability to its sublimation temperature (about 3600° C.), carbon has been particularly attractive for use in constructing such disc brakes, particularly where weight is a major consideration such as in aircraft. Strength and stiffness of a composite are controlled by the orientation of the reinforcement fibers in the matrix. When reinforcement fibers are straight and continuous, the stresses are efficiently transferred through the composite in the direction of the fiber. If the reinforcement fibers are crimped or discontinuous, efficiency drops as the stresses are transferred out of the reinforcement and through the matrix.
In the prior art, composites have generally been fabricated by orienting or directionally aligning the carbon fiber component, which generally has been thought necessary in order to take advantage of fiber strength and enhance mechanical properties of the composite. Fabricating the composite with the desired fiber orientation is more readily accomplished by use of continuous carbon fiber, and such fiber has been preferred over discontinuous fiber for these applications. The primary forms of continuous fiber employed in composite fabrication include woven textile fabric or unidirectional tapes for use in lay-up structures, and continuous fiber yarn or tow, which are used for filament winding of hollow cylindrical shapes and in braided structures.
For example, in U.S. Pat. No. 4,790,052 to Orly carbon composite brakes are produced using a quasi-isotropic layup of uni-directional webs as the reinforcement. These webs are layered so that angles of around 0°/−60°/+60° are formed between the filaments of successive layers of the structure. Though the total web stack is quasi-isotropic, each web is an extremely unbalanced reinforcement which must withstand multi-dimensional forces being transferred through a uni-directionally reinforced web. At load points such as the lugs of a brake disc, very high interlaminar stresses are generated and may cause failure through delamination. To resist these stresses, a very high degree of needlefelting is used to add reinforcement through the stack which will crimp the reinforcement fibers and reduce their effectiveness. The Orly method has economic and performance drawbacks as well. The method is complex and leads to poor material utilization because unidirectional webs which are rectangular are used to make annular shaped parts.
An improvement in the Orly method was made in U.S. Pat. No. 5,184,387 to Lawton. In Lawton, a unidirectional layer of filaments is subjected to needlefelting to provide dimensional stability. The layer is then cut into a plurality of arc-shaped segments and those segments are assembled side by side to produce the annular shape. This method—similar to that used in the garment industry—reduces the wastage of material and permits the layer to be cut so that the filaments run radially in some segments and circumferentially in others. This method yields a 0/90° layup in that the filaments in a superimposed layer of segments is disposed at a 90° angle to those filaments of a lower layer of segments. The resulting composite is less isotropic than Orly and also requires a high degree of needlefelting to prevent delaminations.
Still another method is disclosed in U.S. Pat. No. 5,217,770 to Morris et. al. This method uses an annular braid web to form a mat which is then needlefelted to form a 3-D structure. The braid contains helical fibers woven at approximately 40 degrees and unidirectional fibers which become circumferential during laydown. One or more braids are used to fill the brake annulus which is then needlefelted. This method achieves a near net-shaped part with fibers oriented to handle circumferential and shear loads. However, using braids to build the structure is a complex textile operation that adds to the cost. In addition, the helical fiber volume and angle is not uniform throughout the annulus due to the use of a tubular braid to form an annulus. When a straight braid is curved into an annulus the fibers in the braid are forced closer together at the inner periphery of the annulus and pulled apart at the out periphery of the annulus changing their angles and fiber density.
As noted, needlefelting is widely used in the textile arts to strengthen stacked fabric structures and improve structural integrity. Generally described, needlepunching operations are carried out by forcing barbed needles normally through the stack layers in the thickness direction. A portion of the fiber within the fabric layers is gathered by the barbs and repositioned in the thickness direction, reinforcing the individual fabric layers as well as the stack. If the fibers making up the layers are continuous, the needlepunching operation necessarily breaks individual filaments when re-orienting them. To avoid or at least minimize such breakage, improved processes wherein staple fiber is included within the structure, either as part of the fabric layer or as alternating layers of staple fiber sheet, have been used to supply staple fiber to the needles for re-orienting in the needlepunching operation. Needlepunching operations have been employed in the art with carbon fiber sheet and tape to provide preform structures having good integrity for use in the production of carbon-carbon fiber reinforced composites.
The high degree of fiber alignment within the structure of these prior art composites is intended to take advantage of the strength and dimensional stability of the carbon fiber. However, composites having the entire fiber content aligned in a single direction are highly anisotropic in character, exhibiting a high degree of strength and dimensional stability in the fiber direction while suffering greatly reduced strength properties and poor dimensional stability in the transverse direction. To ensure that the strength of the composite, as well as its heat transfer characteristics and other important properties, are reasonably uniform and to minimize unidirectional shrinkage which may cause warping and distortion, the fiber direction is varied throughout the prior art structures, imparting some isotropic character to the composite. The lamina, however, still suffers from anisotropic effects. When using more costly fabric or the like, the fabricator still has had to resort to varying fiber orientation between successive layers of the structure, for example, using a 0/90° orientation in one layer, +/−45° in the next, and so on, thereby providing a composite having less anisotropic characteristics at the lamina level and being nearly quasi-isotropic overall. As described above, three-dimensional weaving, needlepunching and similar operations are often employed to add through-thickness fiber orientation and improve interlayer strength properties to accommodate these anisotropic stresses. However, a preform with isotropic character throughout the stru
BP Corporation North America Inc.
Chevalier Alicia
Hall Jennifer M.
Jones Deborah
LandOfFree
Chordal preforms for fiber-reinforced articles and method... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Chordal preforms for fiber-reinforced articles and method..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chordal preforms for fiber-reinforced articles and method... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2901279