[1]3 @ 8 - 3 7 9 9 8 5 Ullited States Patetit Office Patented Sept. 24, 1974 1 2 3,837,985 MULTI-DIRECITONAL REINFORCED COMPOSITEI AND METHOD OF MAKING THE SAME Vance A. Chase, Poway, Calif., assignor to Whittaker Corporation Filed Feb. 24, 1972, Ser. No. 228,929 5 Int. Cl. B32b 7108 U.S. -Cl. 161-55 16 Claims ABSTRACT OF THE DISCLOSURE 10 An improved composite is fabricated by laying up a thickness of fibers bearing an uncured resin matrix di-iving a series of spaced cured resin impregnated reinf@reing elements at least partially through the lay-up at an angle, and then fully curing the resulting composite to bond the 15 reinforcing elements into the lay-up. BACKGROUND Field of the Invention 20 The present invention generally relates to resin impregnated composites and more parlicularly relates to reinforced resin impregnated fibrous composites and an improved method of making the same. Prior Art 25 Resin impregnated fibrous composites have been fabricated in a number of ways. In those composites requiring special multi-directional strength characteristics, for exc omposites have been used to an increasing extent. One method of fabricating such a composite employs a complicated and expensive weaving process, wherein fi brous threads !are woven in three directions, i.e. longit udinally, transversely and normal to the surface of the 3 5 p reform. However, in those instances where the thickness o f the preform must be substantial, as in heat shields which are of the order of 1/2 inch thick, the weaving p roblems are considerable. So also is the problem of molding quality composites therefrom after impregna4 0 ti on of the woven preform. This is particularly true where t hermosetting matrices employing phenolic, polyimide, p olyquinoxaline, polybenzimidazole or similar resins are u sed. Considerable difficulty is also encountered in maint aining the fibrous reinforcement of such three-dimen4 5 si onal preforms in straight aligninent. In this regard, wrinkling and buckling of the fiber orientation both duri ng the preform weaving and durin.- the composite moldi ng process frequently occur. In the areas where nonuniform alignment of the reinforcing fibers is thus cre5 0 a ted, the resin matrices must withstand initial stress until t he fibers become straightened sufficiently to assume the l oad. Subjecting the resin matrices to such stress may res ult in resin cracking or crazing or more serious struct ural damage, so that the composite may fail. 5 5 More recently in an attempt to overcome the disadv antage,s of the woven preforming approach to the threed imensional fiber reinforced composite requirements, such c omposites have been fabricated by a technique which i nvolves laying up of the fibrous material onto a radial 6 0 fi ber brush so that the radial fiber reinforcing bundles a re orthogonally disposed durin.- the fabrication of the woven body. However, in order to achieve optin-iutn t ensile strength throughout the thickness of the resulting mold it is necessary to use small diameter closely spaced 6 5 r adial fiber bundles which are not practical in many inst ances from a fabrication standpoint. Unless the crosss ectional area of the radial fiber bundle is adjusted such t hat tensile failure and bond failure between the radial fi ber and the remainder of the composite occur almost 7 0 si multaneously, maximum efficiency and utility for the c omposite is not achieved. In addition, laying up or winding of the fibrous material on to the radial brush in this technique tends to be tech-@iically complex. Accordingly, it would be desirable to provide a simplifi@-d, inexpensive commercially practical method of fabricatiiig reinforced fibrous composites having a three-dimensiona 1 fiber alignment for reinforcement and strength. SUMMARY The present invention satisfies the foregoing needs and is substantially as set forth in the Abstract above. In accordance with the present method, any number of reinforced elements can be spaced at atiy number of angles thi-ou,-h any portion of the layup of resin impregnated fibrous material before curing of the layup to lock in the reinforcing elements. Any suitable means can be used for driving the cured reinforcing elements into the lay-up and in one embodiment of the invention the elements are placed in spaced groups which group contains a plurality of elenients of each group being at different angles to more effectively slipport the composite a.-ainst tensional stress, shearing, bending, compression and the like. DRAWINGS FIG. I is a schematic perspective view of a preferred embodiment of the improved multi-dimensional reinforced composite of the invention utilizing a four-dimensionalpattern; FIG. 2 is a schematic perspective view of another embodiment of the improved multi-dimensional reinforced pattern; and FIG. 3 is a top plan view of the compo site of FIG. 2. D E T A I L E D D E S C R I P T I O N In accordance with the method of the present application, an improved multi-dimensional reinforced unitary composite of fibrous material is fabricated. The method includes laying up uncured resin impregnated fibrous material. In this regard, the fibrous material may be, for example, glass fibers, leached silica fibers, carbon fibers, graphite fibers or mixtures thereof or otber types of fibers arranged in the form of woven cloth, roving, tape, single strands or the like. Such fibers are impregnated with resin of the thermosetting type, for example, polyimide, polyquinoxaline, polybenzimidazole and the like, and are in an uncured, that is, an A-staged or B-staged form. Sheets or plies of the resin impregnated fibrous material can be stacked to the desired thickness and shape. Alternatively, roving, tape, etc. can be laid up on a forming surface. In any event, after the lay-up is made it is reinforced by driving at least partially therethrough reinforcing elements fabricated of cured resin impregnated material such as C-staged thermosetting resin-impregnated fibrous reinforcements wherein the fibers are the same as or dissimilar from the above-mentioned fibers. The reinforcing elements contain resin which is compatible with the resin of the lay-up and are in relatively stiff self-supporting form capable of being easily driven into the lay-up, as by mechanical, pneumatic or the like driving means. In accordance with the method of the present invention, a plurality of the reinforcing elements are driven into the lay-tip with the elements spaced in accordance with a predetermined pattern and disposed into the lay-ui) at a predetermined angle. V,7ith this procedtire, a three-(fimensional composite reinforced in a given pattern is provided upon curing of the lay-up, i.e. Cstaging to bond the reinfoi-cing elements to the lay-up components to provide a unitary structtire. Preferably, a second series of spaced cured resin impregnated reinforcing elements of the same or dissimilar typ@-s are driven into the lay-up at a second angle differin.from the'first angle and in a predetermined pattern to further reinforce the composite and provide the composite ample, re-entry heat shields, so-called "three-dimensional"' go composite of the invention utilizing a five-dimensional
[2]with a four-dimensional array. If such second series is used, it is introduced into the layup before the described curing of the lay-up occurs. Althou.-h it is possible to drive the reinforcing elements into the lay-up at an angle normal to the surface of the layup to, in effect, duplicate existing three-dimensional composites in an improved less expensive manner, it is preferred that the present method be utilized to provide either a three-dimensional composite having reinforcing elements disposed at an angle other than that normal to the surface of the lay-up or, if normal to the lay-up, to additionally provide a second series of reinforcing elements introduced into the lay-up at an angle differedt from the first angle so that the described four-dimensional pattern can be achieved. Five-dimensional and greater dimensional patterns can be effected by varying the angle of additional series of reinforcing elements introduced to the lay-up, if desired, all before curing of the lay-up. In accordance with a preferred embodiment of the present method, a plurality of series of the reinforced elements disposed at angles differing from one another are introduced into the lay-up in groups with each group comprising at least one reinforcing element of each of the series so that a pattem is developed in the lay-up of multidimensional groups serving as foci for improved resistance, to bending, torsion and other dimensional stresses. It is obvious that this technique of grouping may be provided in any suitable pattern with or without interposed nongroup oriented reinforcing elements at one or more an,@ies in the lay-up. In any event, whatever the means and sequences of introducing the reinforcing elements, after such introduction is completed the reinforcing elements are bonded to the lay-up by the curin-, step of the method usually involving heating with or without the application of superatmospheric pressure. Moreover, durin.- such curing, the reinforced lay-up can be disposed, if desired, within a suitable n-lold so as to be coi@fl.- Ured to the desired finished or semifinished shape, depending upon the intended ultimate use thereof. Alternatively, if the lay-up is initially made on or in a shapeimparting means, e.g. a mandrel, subsequent molding usually will be obviated. The placement of the reinforcing elements is such as to not in any way interfere with the curing procedure and any molding which may be employed. Accordingly, an improved composite is obtained with multi-di - mensional reinforcements by a method which is simplified, inexpensive, rapid and reproducible. The method results in undistorted composites which can incorporate specialized areas, as needed, of particularly high resistance to stress. In this regard, the method of the invention can be tailored to the particular need of the end product in an improved simplified way. The laminated reinforced composite of the invention is illustrated schematically in FIGS. I to 3 of the accompanying drawings. In this regard, FIG. 1 depicts a fourdimensional pattern in the composite. Thus, a reinforced composite 8 is shown comprising a stack of plies 10 of resin impregnated fiber material with the plies Cstaged bonded together and to spaced pairs of reinforcing elements 12. Elements 12 are disposed entirely through the stack of plies 10 at a 45' angle from horizontal (plane of the stack), the elements 12 of each pair being at a 90' angle from each other nad overlapping at their mid-points. Each reinforcing element 12 is generally cylindrical in configuration and comprises C-staged resin impregnated @fibers. Accordingly, multidimensional strength is achieved. @In F'IGS. 2 and 3, an improved composite 18 is shown comprisin.- a stack of plies 20 with reinforcing elements 22 therein. Each ply 20 is fabricated of C-staged resinimpregnated fibrous material and plies 20 are bonded tO elements 22. The latter are generally cylindrical are fabricated of C-staged re sin-impregnated fibrous material. Elements 22 are arranged in spaced groups of three elements each. The elements 22 of each group are disposed 31837,985 4 ed down through the stack of plies 20 so that their midpoints overlie one another at about the mid-point of the stack. FIG. 3 shows this array in schematic outline. Accordingly, a five-dimensional reinforced composite is provided. The following Examples further illustrate certain features of the present invention: EXAMPLE I 10 An ablative re-entry heat shield having good ablation characteristics, low thermal conductivity and high strength in the wall thickness direction is fabricated in the following manner: A lay-up is made of the basic shape and size of the heat shield by tape wrapping over a mandrel 15 in a conventional manner carbon fiber tape impregnated with B-staged phenolic resin. The tape is wrapped on the mandrel during the wrapping process at a 20' angle to the surface of the mandrel to provide a "shingle effect." The wrapping procedure is continued until a wall thickness 20 of about 0.500 inch in obtained. After completion of the tape wrapping procedure and while the resulting lay-up is still in a B-staged condition and on the mandrel, a mechanical impact tool is used to drive C-staged reinforcing elements through the wall 25 thickness at an angle normal to the plane of the surface of the lay-up. Each reinforcing element comprises a shaft fabricated of layers of carbon fibers impregnated with phenolic resin and C-staged under heat and pressure. A plurality of the reinforcing elements are cut from a stack 30 of the C-staged carbon fiber laminate such that the plies of the stack run the length of each element. Each element is cut and then machined to a square configuration with a diameter of about 0.050 inch and a length of about 0.500 inch. To facilitate introduction of each reinforcing 35 element into the lay-up on the mandrel, the introducing end of the element is slightly tapered. The reinforcing elements are driven through the lay-up by the mechanical tool until the outer end of each reinforcing element is Rush with the outer surface of the lay-up, i.e. until each 40 element extends through the lay-up. The reinforcing elements are distributed throughout the lay-up in a uniform pattern such that each reinforcing element is approximately 0.200 inch away from the next adjoining reinforcing elements in the pattern. Thereafter, the lay-up with the 45 reinforcing elements dispersed therein is C-staged at approximately 100 p.s.i. and 350' F. in an autoclave to fully cure the resulting heat shield and lock and permanently bond the reinforcing elements to the lay-up. EXAMPLE 11 50 The procedure set forth in Example I is duplicated except that the pattem of reinforcing elements is substantially that indicated in FIG. 2 of the accompanying drawings. FIG. 2, however, represents the pattern as viewed 55 in a flat plane or stack rather than the curved lay-up configuration for the heat shield. The reinforcing elements are driven into the lay-up in a pattern to provide spaced groups of three elements each, with the angle ofinclination of the elements to the lay-up surface being about 60 45' and with the angle between adjacent elements in each group being about 120'. Each group of elements thus formed provides reinforcement in five directions. The spacing between groups of elements is approximately 0.200 inch. 65 EXAMPLE III The procedure of Example I is followed except that the reinforcing elements are spaced apart approximately 0.400 inch, are approximately 0.100 inch in diameter and the angle at which the elements are driven through the wall 70 of the heat shield is approximately 45' to the plane of the surface of the shield at the point of entry. EXAMPLE IV Successful composites fabricated in accordance with the in triangular array at 120' from each other and are slant75 procedures of Examples 1, 11 and III are provided utiliz-
[3]3)837)985 6 ing flbrous material such as fiber glass, graphite, silica and high temperature plastic flbers in roving, tape, single fiber windings, cloth and the like, together with phenolic, polyimide, polybenzimidazole and other high temperaturethermosetting resin matrices. Laminates are made utilizing a plurality of types of fibrous materials and/or resin rnatrices. Thus, fiber glass-phenolic resin composites, fiber glass-polyimide resin composites, graphite fiber-phenolic resin composite andmulti-component laminates including fiber glass, carbon and graphite fibers in interleaved and overlapping areas with various types of thermosetting resins are employed, all with successful results. In further tests, yarn, roving and tow are utilized in separate fabrication procedures by winding the same upon mandrels of suitable size and shape to provide the desired initial fiber rendition. In one instance, for a conical shape in fabricating a re-entry heat shield a fiber rendition is provided for a helix pattern where the fiber material is wound from the base to the tip of the cone at one angle and reversed to wind from the tip to the base at the same winding rate and angle. Reinforcing elements in all instances are introduced in preforms patterned in accordance with the previous techniques. In one instance the groups of reinforcing elements are introduced into a stack of plies of re sin-impregnated fibrous cloth with two elements per grotip, each element being forced into the stack at an angle approximately 45' to the plane of the surface of the stack and the two elements being aligned to provide an angle therebetween of about 90' with the elements substantially overlapping each other at the mid points thereof, substantially as is shown in FIG. I of the accompanying drawings, to provide a four-dimensional configuration. In the fabrication of filament wound radomes and the like high strength and stiffness in both the axial and hoop directions is achieved by winding strands of phenolic resin impregnated fiber on to a male mandrel in an alternating hoop and axial winding pattern and then reinforcing the resulting lay-up by forming groups of two reinforcing elements each, the elements of the group being disposed at intersecting angles and locations to provide a fourdimensional reinforced composite structure having a good balance of strength in the axial, hoop and radial directions. After insertion of the reinforcing elements (by pneumatic hammer means) the resulting-reinforced lay-up is cured at about 120 p.s.i. and about 340'. Pressure is applied from both the exterior and the interior surfaces, the latter by means of a pressurized flexible diaphragm disposed on the surface of the male mandrel. In all of the above instances, unitary multi-directional 5( different from said first and second angles before said reinforced composites are provided in an improved simcuring. plified manner with areas of special strength developed to 12, The method of claim 11 wherein series of reinforcfacilitate improved durability and performance in use. ing rods in addition to said third series are driven at least What is
