Reinforced composite articles and method of making same

Details Reinforced composite articles and method of making same Reinforced composite articles and method of making same

1990-04-24

2001-12-04

Tudor, Harold J. (Department: 3641)

Power plants

Internal combustion engine with treatment or handling of...

Material from exhaust structure fed to engine intake

C138S044000, C138S132000, C138S172000, C239S265110, C239SDIG001, C428S036900

Reexamination Certificate

active

06324833

ABSTRACT:

The present invention relates generally to composite articles such as nozzles and polar bosses for rocket motors which are reinforced by yarns of fibrous material impregnated with a matrix material.
A rocket motor nozzle usually consists of one or more bodies of revolution which may be generally described as having a non-cylindrical tubular shape which converges from a large diameter entrance to a reduced diameter throat and then diverges to a large diameter exit end. Because of the high exposure temperature during rocket motor operation, nozzle components are frequently constructed from allotropes of carbon or other materials appropriately resistant to such environments. Composite materials have also been used in which two or more fractions are combined to produce attributes not attainable otherwise.
One such composite material type, known as carbon-carbon, is constructed from a reinforcement fraction consisting of carbon or graphite yarns or rods and a matrix fraction which fills interior space not occupied by reinforcement. Construction of such a composite is performed in sequential steps, the first consisting of creating the desired yarn architecture, and subsequent steps consisting of creating the matrix from liquids such as pitch or various resins or from gases such as methane, or from a combination of liquid and gaseous approaches. Composites of the same type may also be constructed using silicon carbide, hafnium carbide, or other high temperature resistant materials in either the reinforcement or matrix fractions or both, using analogous approaches.
An example of such a composite material is disclosed in U.S. Pat. No. 4,519,290 to Inman et al, which patent is assigned to the assignee of the present invention and which patent is hereby incorporated herein by reference. Inman et al describes a nozzle component consisting of a triaxial braid of carbon fibers built up on a mandrel which supports a plurality of carbon rods positioned in rows and extending radially from the mandrel surface over generally the depth of the composite material of the article to be formed. The radial rods anchor the yarns of the triaxial braid in place as the material is being laid onto the mandrel. Inman et al further describes a process of constructing the matrix fraction of the composite using pitch, consisting of repeated exposures to high temperature, which process may be called “densification” because each cycle increases the density of the composite.
Another example of a carbon-carbon composite is one which has a three dimensional yarn architecture which uses yarns in the radial, circumferential, and axial or meridional directions of the component. For such a three dimensional yarn architecture, the anchoring function of the radial yarns protruding from the mandrel is much more important than in the four dimensional braided construction of Inman et al wherein the braided preform may be sufficiently stable if the component thickness is small.
While such a process as described in Inman et al is considered generally satisfactory, the radial rods in either the three dimensional or four dimensional architecture do not serve a substantial useful function in the completed article and also undesirably act as constraints on yarn architecture. These radial rods also generally erode faster than other yarns leading to increased erosion of nozzle throat inserts. Reduction of such throat erosion may advantageously allow the nozzle expansion ratio, the ratio of areas at the nozzle exit and nozzle throat, to be better maintained, with no change in specific gravity, for better motor performance. These radial rods may also disadvantageously result in increased article thickness and weight for the same amount of yarn in the principal directions of the component membrane. Thus, both increased yarn fraction and increased erosion resistance may be advantageously obtained by eliminating the radial rods. However, if such radial rods are eliminated, it may be necessary to provide an alternative means of holding the yarns in place during the lay-up process.
When the nozzle throat component uses curved meridional yarns, whether with three-dimensional or four-dimensional yarn architectures, operational problems early during burn of the rocket motor may occur while the inner surface, exposed to the exhaust gases, is substantially hotter than regions of the cross-section farther from the heat source. Thermal expansion of the innermost meridional yarns, which because of their curvature tend to displace inward from the rest of the component cross-section, must be restrained by radial tension in the matrix fraction of the composite in order for the component to remain intact. The radial yarns are of little help in this regard because of their insufficient embedment in near-inner-surface material at high temperature to receive any substantial load. Tensile fracture of the matrix fraction, and the resulting buckling of meridional yarns, can produce undesirably high erosion of the throat, spalling, and motor performance losses. It is therefore desirable to eliminate the curvature in such meridional yarns.
A polar boss, which may be used for example to attach and transmit load between the nozzle or an ignition device to the case of a rocket motor or to attach other functional features to a pressure vessel, also may have a non-cylindrical tubular shape which may be described similarly as the nozzle is described. The manufacture of a polar boss would not normally require the densification process typically required for high performance nozzle components, but a polar boss may instead be composed of a cured matrix material impregnating the yarns thereof. The performance of composite polar bosses has been limited by manufacturing processes and non-optimal fiber orientation for sustaining the imposed loads, i.e., curved yarns therein may tend to straighten under load so that the composite may not provide the strength which a metal boss may provide and thus may not be competitive in performance therewith. However, composite polar bosses, if they have adequate strength, may desirably be used in rocket motors and other pressure vessels to reduce the weight thereof.
It is therefore an object of the present invention to permit elimination of unnecessary anchoring yarns or members from a non-cylindrical composite tubular article such as a nozzle, nozzle throat insert, or polar boss so that the resulting article may have more efficient yarn architecture, be lighter, take up less volume, be less expensive, have diminished nozzle erosion, or any desired combination of these features.
It is also an object of the present invention to permit reduction or elimination of curvatures in the load-bearing yarns in the axial direction for increased tensile or compression strength and to reduce radial tension, yarn buckling, and spalling.
In accordance with the present invention, a ply of the article comprises a plurality of straight yarns which extend from one end portion to the other end portion and which are impregnated by a matrix material in which cure may be accomplished or initiated by actinic radiation such as ultraviolet radiation to anchor the yarns in place as they are applied to the mandrel. Plies of circumferential or helical yarns or cloth may be interleaved between plies of straight yarns. If the article is to comprise a carbonizable material impregnating the yarns, the anchoring matrix material is selected to have a sufficiently high char yield to continue to anchor the yarns after it is carbonized or charred and before densification cycles thereof, and the yarns for this purpose need not be straight but may be braided or the like. Other objects, features, and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments thereof which should be read in connection with the accompanying drawings.


REFERENCES:
patent: 3534908 (1970-10-01), Coleman et al.
patent: 4063684 (1977-12-01), O'Brien et al.
patent: 4477024 (1984-10-01), O'Driscoll et al.
patent: 4519290 (198

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