CA1098329A - Composite tubular element and methods for making same - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A composite tubular drive shaft is diclosed in which a plurality of layers of laminated sheet material is circumferentially disposed on a tubularcore such that the thickness along the tube is preater at the mid-section.

Description

~Q~8~9

2 _eld of the Invention

3 This invention relates ~ improved rotating ele-

4 ments especially useful for transmitting forces, and for sustaining axial and torque bearing forces~
6 Prior Art 7 Conventional rotating elements intended for trans-8 m~ssion of forces 8uch as rotors or drive shafts are gener-9 ally made of metal since these metal rotors or drive shafts are believed generally to possess great durability. More re-11 cently, however, there has been a considerable interest in re-12 ducing the weight of such rotating elements, particularly in 13 vehicles, thereby increasing the fuel efficiencies at which 14 those elements are driven. Thus, the design of a rotor or drive shaft of lighter weight has gained considerable interest 16 from a fuel efficiency viewpoint However, the design of a 17 rotor or drive shaft, not only of lighter weight but also of 18 greater axial stiffness, additionally would permit the use 19 of such shaft in higher critical speed environments than presently possible with an all metal shaft.
21 In the past, some attempts have been made to de-22 sign a lighter drive shaft For example, it is known to re-23 inforce metal tubes with helically wound filaments which are 24 subsequently impregnat~d with a resin such as an epoxy resin, thereby forming a composite structure which has a metal por-26 tion and a plastic portion reinforced with continuous fila-27 ment windings. Composite structures of this type have been 28 capable of withstanding h~gh circumferential speeds; however, 29 they suffer from other disadvantages~ For example, such heli-'~' lOq8329 cally wound rotors have inadequate axial stiffness for drive shaft applications.
As is pointed out in U.S. patent 4,173,670, in order to get the requisite performance from a rotor or drive shaft which is fabricated from both a fiber-reinforced resin and a tubular metal shaft, the two essential load bearing materials, i.e. the metal and the fiber, must be combined in such a way as to operate harmonious-ly in adsorbing and transmitting substantial torsion and bending loads. Accordingly, improved tubular composites for transmitting torsion and bending loads are disclosed in the aforementioned patent application in which the axial loads primarily are borne by unidirectional reinforcing fiber filaments. These fiber filaments are embedded in a resin matrix. The primary torque loads are borne by a metal tube. The metal and fibers provide a composite structure in which the fibers are oriented at a predetermined angle of orientation so as to compensate for the significant differences in the physical properties of the fiber-reinforced resin and the physical properties of the metal tube, such as, for example, the difference in the thermal coefficient of expansion of the metal tube and the thermal coefficient of expansion of fiber of the fiber-reinforced resin. Thus, in the aforementioned patent, there is described a tubular composite structure which comprises a metal tubular core, preferably of aluminum, having a layer of structural metal adhesive on the exterior surface of the metal core. On top of the structural adhesive layer are alternating laminae of resin impregnated unidirectional reinforcing fibers, 32~9 1 particularly carbon or graphite fibers, and of woven fiber-2 glass, beginning with a layer of woven fiberglass followed 3 by a lamina of resin-impregnated continuous unidirectional 4 reinforcing fibers and continuing in alternating fashion but ending with a final layer of resin-impregnated continuous 6 unidirectional reinforcing fibers.~Each successive layer of 7 resin-impregnated continuous unid~rectional reinforcing fibers 8 has the fibers oriented at an angle of between about 5 to 9 20 with respect to the longitudinal axis of the metal tube and in opposite orientation with respect to the next preced-11 ing layer. Such a tube is fabricated by preferentially wrsp-12 ping around the metal core a generally quadrangular laminate 13 of such fiber-reinforcing materials 80 as to provide a sub-14 stantially cylindrical composi~e ~haft having a uniform thick-ness of fiber-reinforced resin on the surface of the core.
16 SUMMARY OF THE rNVENTION
17 It has now been discovered that the fiber-rein-18 forced layer of such a composite tubular shaft doe~ not have 19 to be of uniform thickness along the length of the shaft in order to achieve ~he requisite mechanical properties with re-21 spect to transmitting torsion and bending loads; but rather 22 the greatest aunt of fiber-reinforced resin is needed sub-23 stantially in the center portion of the tubular composite and 24 less reinforcing material is required at the extremities thereof.
26 Thus, generally speaking, the present invention 27 provides an improved tubular composite for transmitting sub-28 stantial torsion and bending loads which comprises a metal 29 tubular core, preferably of aluminum, having a layer of struc-lOq8329 1 tural metal adhesive on the exterior surface of the core. On 2 top of the structural adhesive layer are alternating laminae 3 of resin-impregnated unidirectional reinforcing fibers, partic-4 ularly carbon or graphite fibers, and of woven fiberglass, beginning with a layer of woven fiberglass followed by a lam-6 ina of resin-impregnated unidirectional reinforcing fibers 7 and continuing and alternating fashion but ending with a 8 final layer of resin-impregnated continuous unldirectional 9 reinforcing fibers. Each successive layer of resin-impreg-nated con~inuous unidirectional fibers has the fibers oriented 11 at an angle of between about 5 to 20 with respect to the 12 longitudinal axis of the metal tube and in opposite orienta-13 tion with respect to the next preceding layer. The fibers in 14 the woven fiberglass layer are oriented at 0 and 90 with respect to the longitudinal axis of the metal tubular core.
16 Most importantly, the number of layers disposed along the 17 length of the tubular core varies such that the wall thickness 18 along the length of the tubular metal shaft hss its greatest 19 thickness at substantially the mid-section o~ the shaft.
These and other embodiments of the present inven-21 tion will become readily apparent upon a reading of the de-22 tailed descriptio~ which follows in con~unction with the 23 drawings.
24 BRIEF DESCRIPTIO~ OF 1~ DRAWINGS
Figure 1 is an isometric drawing partly in perspec-26 tive and partly cut away showing the relation~hip of the al-27 ternating sheets of glass fibers in unidlrectional resin-28 impregnated fiber-reinforcing layers to the metal core.
29 Figure 2 is a top plan view of the preferred geo-1~8329 1 metrical shape of the laminate employed in the practice of 2 the pre~ent invention.
3 Figure 3 is a top plan view of an alternate geo-4 metric shape of the laminate used in the practice of the present invention.
6 Figure 4 is yet another ~op plan view of another 7 alternate shape of laminate used in the practice of the 8 present invention.
9 Figure 5 is a vertical cross-section of the pre-ferred laminate taken along lines 5-5 of Figure 2.
11 Figure 6 is an exaggerated view, partially in 12 perspective, of a tubular shaft of the present invention 13 which also is partially cut away, exposing the fibers in the 14 reinforcing layer.
DETAILED DESCRIPTION OF THE INVENTION
16 Referring now to the drawing~, it should be noted 17 that like reference characters designate corresponding parts 18 throughout the several drawings and vicw~.
19 The drive shaft of the present invention has a metal core 25 in ~he form of a cylindrical hollow tube as is 21 shown in Figure 1. In order that the drive shaft will have 22 the requisite strength and weight, it i8 preferred that the 23 metal core be fabricated from aluminum or magne~ium alloys.
~4 Indeed, it is particularly preferred that core 25 be fabri-cated from the following aluminum alloys: 2024, 7075, 7078 26 and 6061. me foregoing numerical designations refer, of 27 course, to U, SO Alloy Compositions. It is particularly pre-28 ferred that these alloys have a T-6 temper. Aluminum alloys 29 having the foregoing compositions and temper are articles of 8 3~9 1 trade and readily available and can be shaped into tubular 2 articles by standard ~echniques, such as drawing or extruding 3 heavy walled cylindrical billets to the required dimensions.
4 In fabricating the composite tubular element of the present invention, it is important that the metal core 6 25 be completely clean. To avoid any possible surface con-7 taminants, the final cleaning of metal core 25 generally is 8 made with a msterial such as alcohol or chlorofluorocarbons 9 to remove traces of lubricants, grease, etc.
M~tal core 25 of the present invention is encased 11 in a sheath of resin-impregnated continuous unidirectional 12 reinforcing fibers and glass fiber fabric which is bonded to 13 core 25 so that it is substantially integral therewith. This 14 sheet of resin impregnated fiber material i8 actually fabri-cated from varlous layersof materials; however, it is partic-16 ularly preferred that the two layers of fiber-reinforced 17 resin sheet material are ultimately bonded one to the other 18 by curing of the resin cont~ined therein.
19 In fabricating composite tubular elements, a lam-inate is first prepared by combining in proper sequan e a num-21 ber of individual laminate of substantially the same pattern.
22 Thus, a lamina such a8 lamina 26 is cut from a sheet of uni-23 directional continuous fiber-reinforcing fibers impregnated 24 w~th a plastic resin. Preferably the fibers in such fiber-reinforcing sheet material are carbon or graphite fib~rs and 26 for convenience such fibers will be hereinafter referred to 27 as graphite fibers. As is shown in the figures, this lamins 28 26 is cut to a predetermined pattern, the length of which 29 preferably is slighly long~r than the axial length of the 3 ~ 9 1 fiber-reinforced layer in the final composite tubular element.
2 The reason for this slight oversizing is for ease of manufac-3 ture which will become apparent upon a further reading of the 4 detailed description. As can be seen from Figures 1 and 2, the preferred geometric pattern for the laminate (designated 6 generally as 10) and hence each lamina is substantially tri-7 angular with end tabs 28 and 30 extending outwardly from the 8 base of the triangle. The widths of the tabs 28 and 30 are 9 equal to about twice the circumference of tubular core 259 thereby providing for substantially two full wraps of laminate 11 material around core 25. Ihe width of the fiber-impregnated 12 sheet material as measured from the apex of the triangle to 13 the base thereof will be sufficient that it can be di~ided 14 for a plurality of wraps around the circumference of metal core 25. Pre~erably the width of the fiber-impregnated sheet 16 msterial will be equal to about 6 times the circumference of 17 the metal tube 25.
18 As is shown in Figures 3 and 4, alternate patterns 19 can be employed in fabri~ating the laminate and ultimately ~0 the composite rotor. Indeed, each lamina can be cut lnto the 21 desired pattern or the desired pattern can be achieved by com-22 b~ning different geometric shapes~ Thus, the pattern 10 of 23 Figure 2 can be obtained by combining rectangular and tri-24 angular shapes, cut and arranged in alternating fashion. The pattern 11 of Figure 3 can be obtained by using a multiple of 26 rectangular shapes, each succeeding shape be~ng slightly 27 shorter than ~he preceding rectangle. Figure 4 can be ob-28 tained by combining a trapezoid and a re~ctangle, and desig-29 nated generally as 12, for example ~aqs3~s 1 Referring again to lamina 26, the resin material 2 impregnating the graphite fibers 22 of lamina 26 is a thermo-3 setting resin. Indeed, the resin in all the resin-impregnated 4 laminae is a thermosetting resin. Suitable thermosetting resins include epoxy and polyester resins.
6 The epoxy resins or polyepoxides, which are well 7 known condensation products, are compounds containing oxirane 8 rings with compounds containing hydroxyl groups or active hy-9 drogen atoms such as amines and aldehydes. The most common epoxy resin compounds are those of epichlorohydrin and bis-11 phenol and it~ homologs.
12 The polyester resin is a condensation product of 13 polybasic acids with polyhydric alcohols. Typical polyesters 14 include polyterephthalates such as polyethylene terephthalate.
As is well known in the art, these thermosetting 16 resins include modifying agents such as hardeners and the 17 like. Forming such compounds i~ not a part of the present in-18 vention. Indeed, the preferred dified epoxy resin impreg-19 n~ted graphite fibers are commercially available materials.
2~ For example, modified epoxy pre-impregnated graphite fibers 21 are sold under the trade ~ of Rigidite 5209 and Rigidite 22 5213 by the Narmco Division of Celanese Corporation, New York, 23 M.Y. Other commercial sources of resin pre-impregnated gr~ph-24 ite fibers are known in the industry.
In general, the resin-impregnated sheet material 26 26 will have a thickne~s of about 0.007 to 0.01 inches and 27 contain from about 50 volume % to about 60 volume % of graph-28 ite fibers in the thermoset resin matrix~ Preferably the 29 sheet m~terial 26 used in the present invention has 54 volume 1 ~ Q ~ 3 ~

1 % to 58 volume % of continuous unidirectional graphite fibers 2 in an epoxy resin matrix. Indeed, it is especially preferred 3 that the graphite fibers have a Youngs modulus of elasticity 4 in the range of 30 x 106 to 50 x 106 psi and a tensile strength in the rsnge of about 200,000 to about 400,000 psi.
6 Turning again to the drawings, woven g~ass fabric 7 layers or laminae designated generally as 24 and 27 are also 8 provided. These laminae 24 and 27 of woven fiberglass have 9 the same dimensions and geometric pattern as the resin-im-pregnated fiber-reinforcing lamina 26. m e sheets of woven 11 fiberglass 24 and 27 will have a thickness of about 0.001 to 12 about 0.002 inches and will consist of woven glass fabric, 13 preferably a fiberglass fabric known in the trade as fiber-14 glass scrim. An especially useful fiberglass scrim is Style 107 sold by Burlington Glass Fabrics Company, New York, N Y.
16 As can be seen, the fibers 21 of the woven fiberglass fabric 17 are at angles of 0 and 90 with respect to the msjor longi-18 tudinal axis of the sheet material 24 and 27.
19 As can be seen in the cutout of Figure 1, the uni-direct~onal graphite fibers 22 in lamina 26 are oriented at 21 a specific predetermined angle el with respect to the longi-22 tudinal axis of layer 26. In the next layer of resin-impreg-23 nated unidirectional continuous graphite fibers, i.e. layer 24 28, the unidirectional graphite fibers 20 are oriented at a negative predetermined specific angle e2 with respect to the 26 longitudinal axis of layer 28. Such angle is preferably the 27 same dimension and of course opposite sign of the angle of 28 orientation to the fibers in the first layer 26.
29 In fabricating the composite shaft, a multiplici~y ~0~83~9 l of layers of resin-impregnated continuous graphite fibers of 2 woven fiberglass are cut from stock material to the desired 3 flat pattern. Each layer is cut to the same size and shape.
4 As is indicated above, the marginal edges of the ends of tabs 28 and 30 are sufficiently wide so as to accommodate st least 6 two complete turns around the tubul~r metal core 25. Also, 7 as indicated previously, the ma~or axis generally will be de-8 termined by the desired length of the shaft, and preferably 9 the major axis is slightly longer in length than the longi-tudinal length of the ultimate composite tubular element.
11 The various layers of sheet material are arranged 12 in alternating sequence starting, for example, with a bottom 13 layer of resin-impregnated graphi~e fibers followed by a 14 layer of fiberglass, followed still by another layer of resin-impregnated graphite fibers, which in turn is followed by 16 another layer of fiberglass. In Figure 1, for example, there 17 is provided a glass layer 24 and 27 and graphite fibers 18 layers 26 and 28 in alternating ~equence.
19 In each successive lamina of resin-impregnated unidirectional reinforcing fibers, however, it should be 21 noted that the reinforcing fibers are oriented at a prede-22 termined a~gle of orientation with respect to the ma~or axis 23 of that layer. Generally, this angle of orientation will 24 range between about 5 to about 20 and preferably this angle of orientation will be about 10. It is particularly pre-26 ferred that the angle of orientation of the graphite fibers 27 in each succeeding layer of resin-impregnated graphite sheet 28 material be of the same magnitude but opposite orientation 29 from ~he next preceding layer. Thus, with reference to 1~83~9 1 Figure 1, fibers 22 in sheet 26 are seen being oriented at 2 angle ~1 and ~ibers 20 of sheet material 28 are oriented st 3 an angle ~2 with respect to the length of the lamina. As 4 indicated hereinabove, it is particularly preferred that the S magnitude of ~1 and ~2 be the same and that ~1 and ~2 merely 6 be oppositç in sign, thereby, in effect, providing for a 7 cross-ply of fibers.
8 In arranging the individual lamina in forming the 9 laminate, it is particularly preferred to form a ply of sheet material consisting of a layer of resin-impregnated 11 graphite fiber lamina hsving 8 woven fiberglass lamina on 12 top of the graphite lamina. Then the plies are placed on top 13 of the sther.
14 As can be seen from Figures 1 and S, the first ply lS comprises a layer of resin-impregnated graphite fiber sheet 16 material 26 on which i8 ~uperimposed a fiberglass layer 27.
17 Next is provided a layer of resin-impregnated sheet material 18 28 on which i8 superimposed a fiberglass sheet material 31.
19 It should be noted that the embodiments shown in Figures 1, 2 and 5 include a rectangularly shaped layer 19.
21 Layer 19 is a metal adhesive. The width of the rectangular 22 layer 19 is sufficient to provide one full wrap around corc 23 25. It is particularly important in the practice of the 24 present invention that a metal adhesive layer be employed to bond the resin of the resin-impregnated sheet materisl to 26 the tubular core 25. The metal adhesive msterial employed 27 in the practice of the present invention is one typically 28 employed for bonding plastics to metals such as elastomeric 29 modified epoxy and elastomeric modified phenol-urea type lQ~83~9 1 resins. An example of one type of adhesive is a polysulfide 2 elastomer modified epichlorohydrin-bis-phenol resin. Msny 3 str~ctural adhesives are commercially available, one of which is known as ~etlbond 1133 which is an elastomer modi-fied epoxy material sold by the Narmco Division of Celanese 6 Corporation, New York, N.Y. Another is FM123-2 ~old by 7 American Cyanamid, Wayne, N.J. The structursl metal adhesive 8 can be applied to the top side of the fiberglass sheet mater-9 ial if the physical consi~tency of the adhesive permits. It c~n also be brushed or sprayed, for example, on the circum-11 ference of the metal core 25. In the practice of the present 12 invention, it is particularly preferred to employ adhesive 13 in the form of a thin film of sheet material such as sheet 14 material 19 in Figures 1, 2 and 5.
Additionally, it has been found to be particularly 16 advantageous to also apply, by brushing or ~praying, a solu-17 tion of the same adhesive used in layer 19 to the exterior 18 of metal core 25 after the metal core has been adequately 19 cleaned In general, the weight of structural metal layer 21 employed in the practice of the present inve~tion ~hould be 22 kept in the range of about 0.020 to about 0.040 lb/ft2, and 23 indeed it is particularly preferred that the weight of the 24 adhesive layer 19 be kept to about 0.030 lb/ft2. Apparently the amount of adhesive that i8 employed i8 important in 26 assuring not only the proper bonding of the plastic resin to 27 the metal core but also a&suring the cooperation of the tor-28 s~onal rigidity of the metal tubing w~th the long~tudinal 29 stiffness oi ~he graphite fiber reinforcement.

a83~9 1 In any event, a polyagonal sheet of laminated 2 material consisting of a structural adhesive layer 19, resin-3 impregnated graphite fibers and glass fabric are wound around 4 the circumference of metal core 25. It should be noted, of course, that the adhesive layer is placed in contact with the 6 tubular metal core 25 and that the continuous unidirectional 7 graphite fibers are arranged at sngles between +5 to +20 8 with respect to the longitudinal axis of the metal core, 9 whereas the woven fiberglass layers sre arranged at angles of between 0 and 90 with respect to the longitudinal axis 11 of the metal core 25. After wrapping the metal core with 12 the requisite layers of mESerial, these materials can be held 13 in place by means of cellophane tape, for example. Al-14 ternstively, the assembly of core and external res~n-impreg-nated graphite fiber reinforcing material can be held in 16 place by a wrapping of polypropylene heat shrinkable film 17 (not shown) which serves in effect as a mold and which is 18 sub~equently removed as hereinafter described.
19 After wrapping the metal core with the rçquisite number of layers of material, the assembly is placed in an 21 oven and heated to a temperature sufficient to cause a bond-22 ing of the separate layers and the various convolutions to 23 each other. The temperature at which the assembly i8 heated 24 depends upon a number of factors including the resin wh~ch i~ used to impregnate the graphite fibers. These tempera-26 tures are well known. Typically for a modified epoxy resin 27 impregnated graphite fiber, the temperature wil} be in the 28 range of about 100C. to about 180DC. and preferably about 29 140C.

lQ~83~9 1 If an external polypropylene wrapping film is used2 to hold the various layers around ~he core, this can be re~
3 movet very 8imply by manually peeling it away from the sur-4 face of ~he shaft. Surface imperfections, if there are any S on the sha~t, can be remove~ by sanding or grinding or the 6 like. If so desired, the shaft can be painted.
7 In view of the fact that it i8 not always possible ~ to get a perfectly flat butt edge in the composite tubular 9 material, as indicated before it is generally preferable to use a laminated sheet material which i8 ~lightly larger in 11 length than the requisite length of the ultimate composite 12 tubular element~ In this way, any rounded æhoulder such as 13 shoulder 6 in Figure 6 can be eliminated merely by making a 14 radial cut through the tube behind the shoulder, thereby providing a perfectly straight butt edge if this i~ required 16 for the composite tubular elementt 17 The invention has been described wlth particular 18 reference to composite shafts for transmitting substan~ial 19 torsion and bending loads, irrespective of the applications of such shafts.
21 To further illustrate the present lnvention, refer-22 ence i8 now made herein to a typical composite shaft for a 23 truck. In such an application, ~he metal core 25 typically 24 will be in the range of 4 to 10 feet long and have an I.D.
in the ran8e of 2 inches to 4-1/2 inches and an O.D. in the 26 range of 2 inches to 5 inches. The shaft will have a layer 27 of structural metal adhesive in the rsnge from about 0.020 28 to 0.040 lb/ft2. On top of the structural metal adhesive 29 layer will be bonded thereto two plies of fiberglass scrim 10'a83~9 1 and the epoxy impregnated unidirectional continuous graphite 2 fiber sheet material~ each ply consisting of a layer of scrim 3 snd a layer of fiberglass sheet material. The orientation 4 of the woven glass fiber layers will be at 0 and 90 with respect to the longitudinal axis of the shaft and the orient-6 ation of the continuous graphite fibers. Each succeeding 7 layer of graphite fiber will be about 10, but in opposite 8 direction to the next preceding layer. Thus, the gr~phite 9 fiber is said to be oriented at +10 with respect to the longitudinal axis. AB can be seen in Figure 6, such a drive 11 shaft has a first end portion 42 and a second end portion 43 12 and two intermediate portions are also present, namely por-13 tions 44 and 45, respectively. Finally, there i8 a gener-14 ally central portion 46. The fiber-reinforcing sheath in the area of the first ent 42 and second end 43 provides for two 16 full wraps around core 25. ~he number of wraps, however, 17 that are di~posed along the length of the tubular shaft varies 18 in number such that the wall thickness along the length 19 varie~ with the greatest thickness being disposed at substan-tially the mid-section of the shaft. In the truck shaft men-21 tioned hereln, the height of the substantially triangular 22 portion of the pattern employed in preparing the laminated 23 sheet material provides for substantially six or ~even wraps 24 around the central portion 46 of the tubular shaft snd with decreasing wraps in the intermediste portions 44 and 45 along 26 the length of the shaft.
27 In contrast thereto, a typical standard size auto-28 mobile composite drive shaft of the present invention would 29 have an aluminum core having a length between sbout 40 inches 83~9 1 to 72 inches and an O.D. between 2-1i2 inches to 3 inches 2 and an I.D. between 2-1/4 inches to 2-3/4 inches. Such com-3 posite drive shaft would have generally about 2 plies of 4 woven fiberglass and continuous graphite fiber8 impregnated with an epoxy resin, each ply consisting of a layer of fiber-6 glass and a layer of resin-impregnated fibers. As with the 7 drive shaft of the truck, the graphite fibers are oriented 8 at +10 with respect to the longitudinal axis of the ~haft 9 and the glaS8 fibers are oriented at 0 and 90 with respect to the longitudinal axis of the shaft. Additionally, the 11 shaft will have interposed between the metal core and the 12 reinforcing layer a layer of structural metal adhesive.
13 As indicated hereinabove, one of the dificulties 14 ~ssociated with forming a composite tubular element for tran~-mittal of axial and torque loads is that there is a vast dif-16 ference in the physlcal properties of the metal core and the 17 fiber-reinforced resin layer such that each res~n layer tends 18 to operate in opposition to the other. Various components of 19 this composite structure are achieved via the proper orienta-tion of the graphite fiberglass in the reinforcing material 21 and in the layer of structural metal adhesive between the 22 metal core and the continuous graphite fiber layer. Decrease 23 in weight with no concomitant loss of strength is achieved 24 by putting the ma~imum amount of fiber reinorcement at the point where the stresses are the greatest. Thus, the gradu-26 stion of the fiber reinforcement from the first end toward 27 the middle and increasing amounts and then decreasing down-28 wardly to the second end of the tube ~s of great significance.
29 As should be appreciated, broad latitude and modi-`` lQq83~9 fication or substitution are intended in the foregoing dis-2 closure. Accordingly, it is appropriatç that the appended 3 claims be construed broadly and in a manner con~istent with 4 the spirit and ~cope of the invention herein.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A tubular composite structure for transmitting substantial torsion and bending loads comprising:
a tubular metal core;
a layer of structural metal adhesive on the exterior surface of the metal core;
a plurality of superimposed layers of resin-impregnated unidirectional continuous reinforcing fibers circumferentially wrapped around said tubular metal core, each layer of said resin impregnated fibers having the fibers oriented at an angle of be-tween about 5° to 20° with respect to the longitudinal axis of the metal core and in opposite orientation with respect to the next preceding layer of said resin-impregnated fibers;
a layer of woven fiberglass cloth interposed between each superimposed layer of said resin-impregnated reinforcing fibers; and a layer of woven fiberglass cloth interposed between said layer of structural metal adhesive and said superimposed layer of said resin-impregnated reinforcing fibers;
each of said plurality of superimposed layers of resin-impregnated unidirectional continuous reinforcing fibers and said layers of woven fiberglass cloth being shaped such that when circum-ferentially wrapped around the said tubular metal core the thickness of said layers wrapped around said core will vary along the length of the tubular core with the maximum wall thickness being substan-tially at the mid-section of the core and the minimum thickness being at the first end and the second end of said core.

2. The structure of claim 1 wherein the resin is a thermoset resin.

3. The structure of claim 2 wherein the reinforcing fibers are selected from carbon and graphite and wherein said fibers are oriented with respect to the longitudinal axis of the tubular metal core at an angle of about 10°.

4. The structure of claim 3 wherein the woven fiber-glass cloth is oriented so that the fibers therein are at 0° and 90° with respect to the longitudinal axis of the tubular metal core.

5. The structure of claim 4 wherein the metal core is selected from alloys of aluminum.

6. The structure of claim 5 wherein the structural metal adhesive is present in an amount ranging from about .020 to .040 lb/ft2.

7. A composite shaft for transmitting forces com-prising:
a tubular metal core having a layer of structural metal adhesive on the circumference of the tubular metal core in an amount ranging from about 0.020 to 0.040 lb/ft2, said tubular metal core having a first end and a second end and a mid-section;
a plurality of layers of laminated sheet material being circumferentially disposed around said metal core, said plurality of layers of laminated sheet material varying in num-ber along the length of the tubular core so that the wall thick-ness along the length of the tubular core varies with the great-est thickness being disposed at substantially the mid-section of the core and decreasing in thickness outwardly to the first end and said second end of said core, said plurality of layers of said laminated sheet material consisting of alternating layers of woven fiberglass cloth and resin-impregnated unidirec-tional continuous reinforcing fibers, the fibers in said fiber-reinforcing sheet material being selected from carbon and graphite fibers, each layer of said resin-impregnated fibers being disposed in opposite angled relationship with respect to the next adjacent layer, said angle of orientation being between about 5° and 20° with respect to the longitudinal axis of the tubular metal core, but in opposite orientation with respect to the next adjacent layer, said layers of woven fiberglass cloth being oriented at 0° and 90° with respect to the longitudinal axis of the tubular metal core.

8 In a composite rotating element for transmitting forces haying a tubular metal core encased in a fiber-reinforced resin sheet wherein the fiber-reinforced resin sheet consists essentially of alternating layers of woven glass fabric and con-tinuous unidirectional fibers selected from carbon and graphite, and wherein said woven glass fabric is oriented at 0° and 90°
with respect to the longitudinal axis of the metal core and the continuous unidirectional reinforcing fibers are oriented at an angle of between +5° and +20° with respect to the longitudinal axis of the tubular metal core, the improvement comprising varying the thickness of said fiber-reinforced resin sheet along the length of the tubular metal core, said thickness gradually increasing from the first end of said tubular metal core to the mid-section of said tubular metal core and then gradually decreasing at the same rate from said mid-section of said metal core toward said second end of said tubular metal core.