Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Reexamination Certificate
1999-08-23
2001-08-21
Dixon, Merrick (Department: 1774)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
C264S171290, C264S087000, C264S029200, C264S510000, C264S532000
Reexamination Certificate
active
06277313
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to a structure of woven fiber and discontinuous fiber immersed in a ceramic matrix, and in particular to the construction of such a structure having a sandwich-configuration with an upper length of woven fiber and a lower length of woven fiber in alignment with each other and having disposed therebetween a substantially uniform distribution of discontinuous fibers within a ceramic resin matrix optionally containing a filler material.
BACKGROUND OF THE INVENTION
Employment of a ceramic based structure for the fabrication of certain components that require the chemical and mechanical properties of such construction is well recognized and non-limitedly exemplified in thin ceramic armor. One such structure that could be beneficial is a cured sandwich configuration comprising an upper length of ceramic-resin impregnated woven fiber and a lower length of ceramic-resin impregnated woven fiber in alignment with each other and having disposed therebetween discontinuous fibers optionally including filler material within a ceramic resin.
However, the present method of fabricating a combination of woven and discontinuous fibers unfortunately yields an inherently stressed end product that is not properly usable in many applications. The introduction of stress is caused by fabrication techniques which include laying a number of ceramic precursor resin-wetted woven fabric plies in a mold, adding a quantity of a mixture of discontinuous fibers, precursor resin, and, as desired, filler powders to the mold, and compressing the mold to form a green-state structure for subsequent ceramic conversion of the matrix by pyrolysis. Because the exposed surface of the fabric is uneven and erratic due to the weave at the bottom of the mold, the mixture containing the discontinuous fibers does not flow smoothly during compression of the mold, thereby resulting in both a nonuniform distribution of the mixture and a clumping of mixture at certain sites while causing degradation of mechanical properties of a finished part. Where clumping occurs, more pressure is placed on the woven fabric to thereby enhance non-uniformity of fiber volume and thickness of the woven section so affected. Second, and again due to non-uniformity of the mixture coupled with high molding pressures, a substantial number of internal stress points are introduced within the mixture in its green state. The stresses can cause warpage of the structure during pyrolytic curing and thereby substantially reduce utility of the structure for component fabrication.
In view of the above prior art construction methodology and resultant end product, it is apparent that a need is present for methodology and consequent end product wherein a continuous woven fiber and a discontinuous ceramic fiber can be coupled in a ceramic matrix to produce an end product having favorable properties for ceramic structural applications. Accordingly, a primary object of the present invention is to provide methodology for fabricating a precursor ceramic preimpregnated composite material comprising a continuous woven fiber and a discontinuous fiber combined with a ceramic precursor resin with or without filler powders for subsequent curing and non-stressed component construction.
Another object of the present invention is to provide methodology for fabricating, as well as an end product of, a woven-fiber and discontinuous-fiber ceramic matrix composite structure for subsequent component construction.
Yet another object of the present invention is to provide a cured woven-fiber and discontinuous-fiber ceramic matrix composite structure having uniform distribution of discontinuous fibers within a ceramic resin.
These and other objects of the present invention will become apparent throughout the description thereof which now follows.
SUMMARY OF THE INVENTION
The present invention is a method of fabricating a ceramic structure as well as a precursor ceramic preimpregnated composite material comprising a continuous woven fiber and a discontinuous fiber combined with a ceramic precursor resin with or without a filler material for subsequent curing and component construction. The method comprises preparation of a mixture of discontinuous fibers with or without filler particles and a ceramic precursor resin where the precursor resin is present in a quantity sufficient to substantially saturate subsequently adjacent woven fiber lengths, and thereafter introducing the mixture to a situs between an upper length of single or multiple-ply woven fiber and a lower length of single or multiple-ply woven fiber in alignment with each other while effectuating linear movement of these woven fiber lengths and moving the lengths toward each other. The opposing upper and lower lengths of woven fiber, with the mixture of discontinuous fibers, with or without a filler material, and a ceramic precursor resin therebetween, are compressed and retained in a sandwich configuration to thereby substantially saturate the woven fiber with ceramic precursor resin and fabricate a preimpregnated composite material for subsequent component fabrication.
The resultant preimpregnated composite material yields a part-fabrication material from which parts requiring ceramic properties can be manufactured. Such a material provides an upper length of pre-ceramic resin impregnated woven fiber and a lower length of pre-ceramic resin impregnated woven fiber in alignment with each other with a substantially uniform distribution therebetween of discontinuous fibers with or without filler material within a pre-ceramic resin. The material is cut to size in accord with the configuration of the part to be manufactured, and then is formed via conventional polymer composite forming techniques non-limitedly exemplified by vacuum form, compression mold, etc. to provide a green-state structure. The structure then is cured by pyrolysis in accord with conventional techniques to produce a finished-product whose characteristics show a substantially uniform distribution of discontinuous fibers and filler material if present within the ceramic matrix to thereby provide a substantially internally stress-free end product.
REFERENCES:
patent: 4752313 (1988-06-01), Allaire et al.
patent: 4810442 (1989-03-01), Hilling et al.
patent: 5019308 (1991-05-01), Pratt et al.
patent: 5488017 (1996-01-01), Szweda et al.
Marsh William James
Schwindler Robert Allan
Strasser Thomas Edward
Anderson Terry J.
Dixon Merrick
Hoch, Jr. Karl J.
Northrop Grumman Corporation
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