Construction of hollow, continuously wound filament load-bearing structure

Hollow continuously wound filament integral structures having integral filament and resin interleafs, integral sleeves, and integral end fittings to transfer all loads, their method, and apparatus of manufacture, all center on the making and use of the filament and resin interleafs. In a preferred embodiment each interleaf has spaced leafs, arranged parallel, i.e. at a zero angle, to the longitudinal axis of each hollow continuously wound filament integral structure, of a length to extend from respective ends of the structure, over and well beyond the respective turnaround zones of the continuous filament and resin windings, so all types of loads will be fully transferred. Also each interleaf has circumferential filament and resin root wraps, wound at ninety degrees to the longitudinal axis of each hollow continuously wound filament integral structure, holding the spaced leafs in place and maintaining a circumferential strength to prevent harmful radial expansion of any integrally wound filaments and resin during their transfer of loads, to thereby keep the integral end fittings in place when they are transferring loads.

BACKGROUND OF THE INVENTION 
Hollow filament wound structures, which exhibit advantages over metal 
structures, such as being lighter in weight, more resistant to corrosion, 
stronger, and more inert, have been manufactured for several years such 
as: 
the tubular fiber reinforced composite shaft with metallic connector 
sleeves mounted by a polygon surface interlock, as disclosed in U.S. Pat. 
No. 4,236,386, in 1980; 
the tubular fiber reinforced composite shaft with metallic connector 
sleeves mounted by a knurl interlock, as disclosed in U.S. Pat. No. 
4,238,539, in 1980; 
the tubular fiber reinforced composite shaft with metallic connector 
sleeves mounted by a connector ring interlock, as disclosed in U.S. Pat. 
No. 4,238,540, in 1980; 
the hollow filament wound spar structure having integral fitting for 
rotational hub mounting, as disclosed in U.S. Pat. No. 4,260,332, in 1981; 
the tubular fiber reinforced composite shaft with metallic connector 
sleeves mounted by longitudinal groove interlocks, as disclosed in U.S. 
Pat. No. 4,265,951, in 1981; and 
the wound graphite epoxy or fiberglass driveshaft joined to a metal end 
member as disclosed in U.S. Pat. No. 4,289,557, source in 1981. 
As stated in prior patents, U.S. Pat. Nos. 4,236,386 and 4,238,539, 
previous proposals for mounting sleeves, i.e. end fittings, by employing 
adhesives or by wrapping the filament bundles around circumferential 
grooves on the end fitting periphery, could not be relied upon to provide 
a connection of the requisite strength and durability. Then the 
disclosures of these patents, like the other patents, illustrated and 
described how end fittings were positioned in the ends of hollow 
continuously wound filament integral structures for the transmission of 
torque loads. 
In these prior patents there were not any direct discussions of how hollow 
continuously wound filament integral structures with end fittings could 
sustain large tension or compression loads as well as sustaining large 
torque loads, Moreover, there were no direct discussions of how hollow 
continuously wound filament integral structures could be reduced in 
diameter at their ends and integrally receive end fittings, which under 
large tension, compression, or torque loads, would remain securely in 
place within the hollow continuously wound filament integral structure. 
There remained a need for creating hollow continuously wound filament 
structures having integral end fittings firmly held in place under all 
types of severe loads, wherein: the wound structure was completed in one 
overall winding operation; the diameter at the respective ends of the 
wound structure did not become greater and preferably remained smaller 
during the winding operation; and the loads carried through the respective 
turnaround zones of the windings were, whenever necessary, equal to the 
maximum loads capable of being transmitted throughout the remaining 
portions of the hollow continuously wound filament integral structure. 
SUMMARY OF THE INVENTION 
Hollow continuously wound filament integral structures, having integral 
filament and resin interleafs, integral sleeves, and integral end fittings 
are manufactured in many embodiments to transfer all types of loads 
throughout an extensive range of load requirements. These structures do 
not have mechanical fasteners, later relied upon, to hold their components 
together, after the one overall winding operation is completed. The 
filament and resin windings may be selected to avoid galvanic and 
electrical problems. The strengths of the filament and resin windings 
directed under and over and around the integral filament and resin 
interleafs in conjunction with the strengths of the interleafs, insures 
there will be sufficient multiple plane or layer bonding to avoid peeling 
and to fully transfer maximum loads of all types, throughout the entire 
length of these hollow continuously wound filament integral structures. 
High production is obtained at comparatively low tooling costs, without 
any substantial loss of material, and with many specific product 
requirements being quickly met by comparatively easily accomplished 
production method changes. The production apparatus and methods insure the 
availability of many selective sizes of well balanced efficient hollow 
continuously wound filament integral structures, each having their 
specific interleafs of a preselected number and of a preselected 
arrangement, to overcome any strength deficiencies, otherwise to be 
located in the respective turnaround zones of the respective continuously 
wound filament and resin. The integral interleafs are readily and 
selectably made in various sizes to respectively assist in carrying 
various types of loads. The integral end fittings and integral sleeves, 
often threaded, are readily and selectably made in various sizes to 
respectively carry the various types of loads. The overall continuous 
filament and resin windings are selected to create balanced layers of 
respective angle windings to withstand specified loads of all types. 
Therefore there are now available hollow continuously wound filament 
integral structures which may be used in many more ways to transmit loads 
of all types.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Utilizing the Best Load Transferring Capabilities of Wound Filament and 
Resin to Tailor by Design Many Hollow Continuously Wound Filament Integral 
Structures Created by Using Only One Overall Filament and Resin Winding 
Operation 
As illustrated and indicated in prior patents such as those patents 
referred to in the background of this invention, and as shown in FIGS. 1 
through 7 of this application, there are installations in aircraft, 
spacecraft, and other vehicles, where fiber reinforced composite products, 
herein specifically referred to as hollow continuously wound filament 
integral structures, are used, or could be designed to be used, because 
they exhibit advantages over metallic parts, being lighter in weight, more 
resistant to corrosion, stronger, and more inert. 
The hollow continuously wound filament integral structures created by 
utilizing just one overall filament and resin winding in the method, 
inclusive of the related apparatus, as illustrated and described herein, 
in addition to the previously noted advantages: do not require the use of 
mechanical fasteners after they are integrally wound, beyond generally 
providing internal threads in the end fittings for the securement of other 
fittings upon installations in vehicles; do not establish the source of 
any galvanic or other electrical faults; do not require high cost tooling; 
do not involve any appreciable loss of the source materials such as the 
high cost filament and resin pre pregnated filament tape, also known as 
filament tow; do not interfere with any high production precedures; and do 
not present any unforeseen structural failures such as caused by peeling, 
because each hollow continuously wound filament integral structure is 
tailored by design to successfully meet all of the specifications 
pertaining to a specific filament and resin wound product having end 
fittings integrally wound therein. 
The Interleafs are the Load Carrying and Bonding Components Integrally 
Wound in the Hollow Continuously Wound Filament Integral Structures Which 
Underlie the Successful Tailoring by Design of These Structures 
When hollow continuously wound filament integral structures with integral 
end fittings are to be wound during one overall winding operation, there 
has always been a necessity to try to determine what strength loss may 
later be expected in regard to the windings occurring in the turnaround 
zone. The filament and resin, i.e. meaning the filaments bearing a 
non-hardened resinous material, i.e. an uncured thermosetting resin, being 
wound in the turnaround zone are wrapped at such angles to the 
longitudinal axis of the hollow structure being formed, that their ability 
to continue to participate in the transmission of axial loads is 
critically diminished. Moreover, even though the filament and resin are 
circumferentially wound during the dwell times, there also remained a 
necessity to try to determine what strength could be expected in 
circumferentially holding an end fitting in place. 
Therefore to be assured of what axial loads could be transmitted and that 
integral end fittings would not pull out of the hollow continuously wound 
filament structure, interleafs are tailored to meet the overall tailored 
design of the hollow continuously wound filament integral structures. They 
are integrally used in such structures in selectable multiple numbers and 
various embodiments. The end objective of each overall tailored design is 
to create a hollow continuously wound filament structure, which if 
strength tested would break well above its designed load requirements and 
break in the middle of its longitudinal length. 
The interleafs have spaced, initially parallel leafs of a length to extend 
over and well beyond the turnaround zone of the filament and resin 
windings. Also each interleaf has a root wrap which extends around the 
ends of the leafs to hold them in place. Each overall root wrap may 
comprise several wrappings to create the circumferential strength 
necessary to keep the end fittings in place. The number of leafs in each 
interleaf and the number of interleafs nestled together are determined by 
axial loads which are to be carried through turnaround zone essentially by 
the interleafs. 
The collective cross sectional areas of the filaments, adjusted downwardly 
in respect to the percentage of resin content are utilized with the 
manufacturers' strength specifications to determine both the capability of 
the collective leafs to transmit tension or compression, and the 
capability of the collective root wraps to withstand tension and thereby 
compressively retain end fittings in place. 
At all times there must be sufficient bonding areas of the leafs and root 
wraps so the bonding strengths will remain high enough to avoid peeling. 
Then the tension or compression loads will be thoroughly transmitted 
through and by the tailor designed hollow continuously wound filament 
integral structures. 
End Fittings and Outer Sleeves, i.e. End Bolts or Inserts and Nuts 
The hollow continuously wound filament integral structures have end 
fittings which are preformed from materials that will meet the 
specifications of an overall installation. Some strong plastics, metals, 
and combinations thereof may be used in the end fittings. In the 
illustrations and description metal end fittings are disclosed. To meet 
the most universal demand, these end fittings have inside threads. Because 
of their use and placement, the end fittings are also considered as 
serving as rod ends or inserts. 
When interleafs are considered, the end fittings have outside threads to 
receive outer sleeves which are also considered as serving as nuts, and 
they have inside threads. Both the end fittings and the outer sleeves have 
flared ends which are cooperatively used in positioning the respective 
root wraps of the interleafs. The flaring is limited in the final diameter 
and enroute it is gradual or tapered so the leafs of the interleafs and 
the filament and resin windings in passing over the flaring are not 
required to excessively change their direction, which otherwise would 
cause a substantial reduction in their axial load carrying capabilities. 
Installations and Uses of the Hollow Continuously Wound Filament Integral 
Structures 
The hollow continuously wound filament integral structures 40 have many 
uses such as the aircraft 42, and spacecraft, installations illustrated 
and/or indicated by FIGS. 1 through 5, or in the drawings of vehicle 
components shown in the background patents. Other uses are for control 
rods, containers, ducts, panel inserts, torque tubes, etc. 
In the drawings, FIG. 1 illustrates an aircraft 42, wherein the 
considerations of weight reductions have led to the design of hollow 
continuously wound filament integral structure 40, as shown in FIGS. 6, 7 
and 8, having integral end fittings 44, often with inside threads 46, to 
receive other attachment fittings 48 often specified by the designers of 
the aircraft 42, having outside threads 50, and fastener receiving 
couplers 52. The integral structure 40 so equipped with fittings 48 
becoming as assembly 54 as shown in FIG. 6, is, for example, designed for 
use as columns in the overall floor supports 56 illustrated in FIGS. 2, 3 
and 4. Also as shown in FIG. 5, some similar but longer assemblies 58 of 
these integral structures 40 with their added fittings 48 are designed to 
be installed as diagonal bracing members 58, in overall floor supports 59. 
In the exploded view of FIG. 7, with the liberty taken of not unwinding any 
portions but cutting away some to illustrate the positions of the 
interleafs 60, the eventual general arrangement of the metal parts is 
indicated of the key integral components of the hollow continuously wound 
filament integral structure 40. Their general arrangement is also 
indicated in FIG. 8, in a partial enlarged cross section, showing the 
assembled and integrally filament and resin wound positions of the 
interleafs 60 with their leafs 62, and root wrap 64, the end fitting 44 
with its flared end 66, and the outer sleeves 68 with their flared ends 
70, also referred to as flared nuts 68. The root warps 64 of the 
interleafs 60 are positioned between the flared ends 70 of the sleeves 68 
or the flared end 66 of the end fitting 44. 
As illustrated in FIGS. 7 and 8 the metal parts, i.e. end fittings 44 and 
sleeves 68 are positioned with respect to the leafs 62 of the interleafs 
60, so the longitudinal axis directed loadings, in tension or compression, 
are fully transmitted between them. Moreover, the root wraps 64 of the 
interleafs 60 are strong enough and positioned very well to prevent any 
expansion of any wound filament and resin, which might otherwise allow the 
unwanted pull out of any sleeve 68 and/or end fitting 44. 
Preferred Methods of Making the Interleafs and Related Apparatus. 
In FIGS. 9 through 14, preferred methods of making the filament and resin 
interleafs 60 are illustrated in conjunction with related apparatus. In 
FIGS. 9 and 10 a rotatable mandrel 72 is shown having two longitudinal 
slots 74. Adjacent each slot 74 a double back adhesive strip 76 is adhered 
to the mandrel 72. The rest of the mandrel cylindrical surface is covered 
by a release film 78. A narrower filament and resin strip 80 to later 
serve as a root wrap 64 is adhered to the double back adhesive strip 76. 
Radial pins 82 are positioned on the ends 84 of the mandrel 72 to receive 
tight circular winds of continuous wider filament and resin strip 86 which 
later, after cutting to length, serves as leafs 62 of interleafs 60. After 
its starting securement to the radial pins 82, and upon rotation of the 
mandrel 72, the castered guide wheel 88 in moving the length of the 
mandrel 72 distributes the continuous strip 86 in many circular windings, 
as shown in FIG. 9. The mandrel is also designed as a larger mandrel 90 
with more slots 74 and radial pins 82, as shown in FIG. 11. 
After the wider filament and resin strip 86 has been fully wound along and 
on the mandrel 72 or mandrel 90, localized heat is applied by moving a 
heater roller 92 over the portions of the strip 86 where it makes the 
numerous contacts with the one or more narrower filament and resin strips 
80, thereby creating a bond between them at these crossover locations. 
Thereafter spaced longitudinally positioned cuts are made across the wider 
filament and resin strip 86 by using a blade 93, which is passed along and 
into the slots 74. Thereafter with or without making any transverse cuts, 
planar arrangements 94 of the bonded together narrower strips 80 and the 
wider strips 86 are removed from the mandrels 72 or 90, as shown in FIG. 
12. 
These planer arrangements 94 are thereafter made into interleafs 60 
appearing as grass skirts, as shown in FIG. 14, by using the apparatus 
illustrated in FIG. 13. Windings of the narrower filament and resin strip 
80 of a selected number depending on the overall tailoring design 
specifications are wound up and down about the rotatable flared mandrel 
96. It is driven by an electric motor 98 through a drive system, not 
shown, positioned in housing 100. The narrower filament and resin strip 80 
is guided over a pulley 102 and past a heating element 104 which are both 
supported on the hand held applicator 106. 
The planar arrangement 94 is then turned about the flared mandrel 96 
generally making two revolutions. Thereafter additional windings of the 
narrower filament and resin strip 80 are made. Then another planar 
arrangement 94 is rotated in place, followed by more windings of strip 80 
and an interleaf 60 appearing as a grass skirt is formed, as illustrated 
in FIG. 14. Tailored designs may call for more planar arrangements 94 and 
more windings of strip 80 to be made to complete another embodiment of an 
interleaf 60. For higher production other apparatus is used; however, the 
basic method of making interleafs is illustrated in these FIGS. 9 through 
14. 
One Method of Making a Mandrel to be Used in a Filament Winding Machine 
Mandrels used in filament winding machines 108, shown in FIG. 20, are made 
of many materials and in many overall shapes the latter being determined 
by the product to be manufactured. The hollow continuously wound filament 
integral structure 40, illustrated in FIGS. 2 through 8, preferably has 
reduced diameter ends 110, where the windings of the filament and resin 
are turned around and dwelled during the operations of a filament and 
resin winding machine 108. One of the lower cost ways of producing a 
mandrel, which must be reduced in size to be withdrawn out of such reduced 
diameter ends of filament wound products, is to make a bonded sand mandrel 
112, as shown in FIG. 17. It is later soaked in water while inside the 
product to eliminate the binding from between the grains of sand. 
Thereafter, the sand may be emptied from within the hollow continuously 
wound filament integral structure 40. 
The forming of the bonded sand mandrel 112 is commenced as 96 parts by 
weight of sand and 4 parts by weight of sodium silicate solution are mixed 
and then compacted into place within an assembled split mold 114, as shown 
in FIG. 15. Throughout its center and extending beyond each end, is a 
hollow rod 116 with internal threads 118 at each end and with spaced 
radial orifices 120 throughout its length. The bottom is fitted with a 
tapered entry liner 122 to form the reduced diameter end 124 of the bonded 
sand mandrel 112. The compacting of the sand 126 with the solution is 
undertaken by moving a hollow handle 128, with a partial circular ram 130 
attached to its end, up and down the hollow rod 116. When the compacted 
sand reaches a given level, then after removal of the ram 130, the other 
reduced diameter end 124 of the bonded sand mandrel 112 is formed by 
driving down another tapered entry liner 122. 
Then carbon dioxide is directed down through the hollow rod 116 and out the 
orifices 120 in the sand 126. The reaction of the carbon dioxide with the 
sodium silicate solution bonds the sand grains together. Thereafter, the 
bonded sand mandrel 112 with its hollow center rod 116 is removed from the 
split mold 114, in the form shown in FIG. 17, which is to be the form of 
the interior of the hollow continuously wound filament integral structure 
40. 
The Assembly of the Mandrel, its Center Rod, Release and Barrier Film, 
Seals, End Fittings, Chucking Fittings, Interleafs, and Outer Sleeves in 
Preparing for the Overall Filament and Resin Winding Operations. 
In the pre-assembly view of FIG. 18, the respective preplacements are shown 
of various parts. When they are assembled, with some parts later requiring 
adjustments during the winding operations, they are then mounted in a 
filament and resin winding machine 108, as illustrated in figure 20. The 
parts are: the bonded sand mandrel 112, its hollow center rod 116 with 
threaded ends 118, a release and barrier film 132 in a tube form, seals 
134 and 136, one set of chucking fittings 138, end fittings 44, multiple 
outer sleeves 68, multiple interleafs 62, and another set of chucking 
fittings 140. In respect to one end, some of the assembled parts are 
illustrated in FIG. 19, to show the placement of the seal 134 and the 
release and barrier film 132, the sand mandrel 112, its hollow center rod 
116, the end fitting 44, the chucking fitting 138, and the chucking 
fitting 140. 
The Operation of the Filament and Resin Winding Machine 
After the assembly of the parts, as illustrated in FIGS. 18 and 19 is 
completed, this overall assembly 146 is rotatably and removably secured to 
a filament and resin winding machine 108, as shown in FIGS. 20, 21, and 
22. Four tensioned alike sources 148 of combined filament and resin 
filaments 159 are arranged on mounting 152 located purposefully at quite a 
distance from the traveling head 154 of the filament winding machine 108 
which supports the various filament pulley guide wheels 156, their pivot 
support 158, and the filament caster guide wheels 160, which direct the 
filaments 150 into contact with the revolving mandrel 112 and its 
accumulating windings of filaments 150. 
As indicated schematically in FIG. 22, the traveling head 154 at each 
location is respectively pivoted to distribute the filament windings so 
very little of a so called dog bone or piling on effect is created, when 
the four filaments 150 are being wound on the mandrel 112 at the same 
winding time. This distribution of the windings and the reduced diameter 
ends together serve in the manufacture of a strong filament wound integral 
product having a good appearance, by avoiding the excessive dog bone 
configuration. 
The Traveling Zones of the Winding Operations Along the Length of the 
Mandrel Revolving in a Filament Winding Machine 
In FIG. 23A, the initial dwell zone 162 of anchoring circumferential 
windings in reference to one filament is schematically illustrated. Then 
as shown in FIG. 23B the traveling head, not shown in the figure, has 
moved across the mandrel 112 through a translating speed increasing zone 
called a turnaround zone 164, then on through a constant translating speed 
zone 166 across the mandrel 112 at a comparatively high speed, and then 
through a translating speed decreasing zone, again called a turnaround 
zone 168. As indicated in FIG. 23C, circumferential windings are again 
undertaken in a dwell zone 170 to anchor the filament windings, before the 
return travel is undertaken, as indicated in FIG. 23D. During the next 
sequence of over and back filament windings the angle of winding with 
respect to the longitudinal axis of the mandrel 112 will be selectively 
changed. The follow on layers of windings ar kept balanced in the 
descriptive comparison of the balanced laminations of plywood. 
The Placement of the Interleafs in Respect to the Flared Portions of the 
End Fittings and Outer Sleeves 
FIG. 24 indicates how the first interleaf 60 at one end is positioned so 
its root wrap 64 is about the flared end 66 of the end fitting 44. FIG. 25 
illustrates how the outer sleeve 68 is moved into position so its flared 
end 70 covers the root wrap 64 of the first interleaf. The collective 
leafs 62 of the resulting grouping of interleafs extend through the 
turnaround zone and beyond to ably transfer the axially directed loads, to 
be carried to the interleafs by the filament windings wound at smaller 
angles to the longitudinal axis of the mandrel. The filament windings 
wound at larger angles are so wound to help position, through bonding and 
their presence, the other windings wound at smaller angles, so they will 
not buckle or otherwise move, under axial loads. 
Preparation of the Uncured Hollow Continuously Wound Filament Integral 
Structure With its Mandrel for Curing in an Autoclave 
After the overall assembly 146 of the parts placed in the filament winding 
machine 108 is removed from this machine 108, and some chucking fittings 
are removed, the resulting overall assembly 172 is wrapped using a tube 
form of a release and barrier film 174 which is sealed by seal 176 at one 
end, and folded over and held by clamp 178 at the opposite end. 
Thereafter, as illustrated in FIG. 27, a resilient heat resistant sock 180 
is inserted into a vacuum apparatus 182 and expanded to the size of the 
interior cylinder 184, which has numerous orifices 186 through which the 
air is withdrawn upon operation of the air impeller 188. With the sock 180 
expanded, the wrapped overall assembly 172 is placed inside the sock 180. 
As the vacuum is reduced and withdrawn the resilient sock 180 tightly 
surrounds the wrapped and sealed overall assembly 172. Later during the 
curing operation this sock protects the overall assembly 172 and also 
helps in forming a better outside appearance of the then cured filament 
windings. The wrapped, sealed and socked overall assembly 172, is then 
withdrawn from the vacuum apparatus 182. 
Curing of the Uncured Hollow Continuously Wound Filament Integral Structure 
in its Wrapped, Sealed and Socked Assembly Within an Autoclave 
The wrapped, sealed, and socked overall assembly 172, while still supported 
by its center rod 116 of the mandrel 112 and a cover 190 used at the 
vacuum apparatus 182, is moved to an autoclave 192 and so supported there, 
as shown in FIG. 28. The autoclave 192 is operated through cycles of 
temperatures reaching 350.degree. F. and with the pressure reaching 100 
p.s.i., in accordance with procedures established by the respective 
manufacturers of the respective filaments 150, of filament and resin, that 
are used in the continuous filament winding of the hollow integral 
structure 40 with integral end fittings 44. 
Removal of the Sand Mandrel From the Interior of the Hollow Continuously 
Wound Filament Integral Structure 
After the curing of the overall assembly 172 heated in the autoclave 192, 
this assembly is removed and taken back to the vacuum apparatus 182 to 
remove the resilient sock 180. Then the release and barrier film 174 is 
unclamped, unsealed, and removed. Thereafter other chucking fittings are 
removed leaving the hollow continuously wound filament integral structure 
40, its sand mandrel 112, and center rod 116 as the resulting assembly 
194. It is then placed in a tubular water bath 196, as illustrated in FIG. 
29, and the soaking action effectively removes the binder. 
As shown in FIG. 30, with the sand grains being freed of the binder and 
with the center rod 116 being cleared away, and with the nearly completed 
product being tilted, the sand leaves the interior space of the hollow 
continuously wound filament integral structure 40, and its manufacture is 
completed. 
Information Regarding a Specific Sized Embodiment of the Hollow 
Continuously Wound Filament Integral Structure Which Provided An Ultimate 
Tensile Load Over Thirty Two Thousand Pounds 
A hollow continuously wound filament integral structure 40 in a specific 
sized embodiment provided an ultimate tensile load over thirty two 
thousand pounds. The integral winding arrangement of all the components 
was like the arrangement illustrated particularly in FIGS. 7 and 8. At 
each reduced diameter end 110, two interleafs 60, and three outer sleeves 
68, i.e. flared nuts, were installed in conjunction with the flared end 
fitting 44. The internal diameter was determined by using a mandrel having 
an outside diameter of 1.875 inches. The wound wall thickness throughout 
the uniform winding length was 0.054 inches and the overall length was 
thirty two inches. 
All the winding tapes consisted of continuous filaments of graphite 
impregnated with a high temperature curing resin. In the root wraps 64 of 
the interleaf 60, graphite resin impregnated tapes of a 6,000 filament 
count were used having a width of 0.070 inches, and a thickness of 0.005 
inches. The theoretical tensile strength attributable only to the graphite 
filaments was 200,000 pounds per square inch. The maximum resin solid 
content was 35%, with the minimum being 29%. In the leafs 62 of the 
interleafs 60, and also in all the tapes wound by the filament winding 
machine, graphite resin impregnated tapes of a 15,000 filament count were 
used having a width of 0.128 inches, and a thickness of 0.010 inches. The 
theoretical tensile strength was also 200,000 pounds per square inch, and 
the maximum resin solid content was 35%. 
In reference to the tailored design of the two interleafs 60 used in this 
specific sized embodiment of the hollow continuously wound filament 
integral structure 40, the tensile filament strength of each interleaf 60 
at its ninety degree root wraps was 2184 pounds. The derivation of this 
circumferential tensile load carrying capacity is as follows: 0.070 inches 
width, times 0.005 inches thickness, times sixteen wraps, i.e. eight wraps 
in each direction, with three such layers of sixteen wraps, times the 
2000,000 pounds per square inch tensile strength, reduced by the 35% for 
the resin content, i.e. or multiplied by 65% to reflect the graphite 
filament content. By numerals only: 
(0.070.times.0.005).times.16.times.3.times.200,000.times.0.65=2184 pounds 
of circumferential strength for one root wrap of one interleaf, or 4368 
pounds for two interleafs which were integrally wound into this 
embodiment. This circumferential tensile strength avoids the pullout of 
the end fittings 44 by keeping all the filaments in place. 
The tensile filament strength of each interleaf 60 in regard to the so 
called zero degree leafs, which are spaced to be spread out upon 
installation, was 14,976 pounds. The derivation of this longitudinal 
tensile load carrying capacity is as follows: 0.128 inches width, times 
0.010 inches thickness, times 45 leafs per original planar arrangement 94, 
times two, for two such arrangements, i.e. two partial skirts, are used in 
making each interleaf 60, times 200,000 pounds per square inch tensile 
strength, reduced by the 35% for the resin content, i.e. or multiplied by 
65% to reflect the graphite filament content. By numerals only: 
(0.128.times.0.010).times.(45.times.2).times.200,000.times.0.65=14,976 
pounds of longitudinal tensile strength for one interleaf, or 29,952 
pounds for the two interleafs which were integrally wound into this 
embodiment. This longitudinal tensile strength of the two interleafs 60, 
insures the transmission of the overall axial tensile loading of this 
embodiment through the turnaround winding zone, which zone, even without 
interleafs is capable of withstanding over 10,000 pounds of longitudinal 
tensile forces. 
In addition to these tensile strengths, the bonding strengths must be 
considered, because they must remain great enough to avoid any peel back 
or other unbonding of the filaments, thereby keeping the tensile loaded 
filaments in their best load carrying positions in the hollow continuously 
wound filament integral structure 40. In respect to the resin or matrix 
adhesion or bond or peel strength of the ninety degree root wraps 64 of 
the interleafs 60, there are eight adjacent wraps of the narrower tape of 
graphite filaments and resin, each being 0.070 inches wide and extending 
about a circumference of a 1.25 inch diameter, and there are a total of 
four of these eight wide circumferential root wrap areas, because each 
interleaf has two wound in place planar arrangements, i.e. skirts, and the 
bond or peel strength is 3500 pounds per square inch. Then by numerals 
only: 8.times.0.070.times.1.25.times.3.14.times.4.times.3500=30,772 pounds 
per interleaf. For the two interleafs the ninety degree total root wrap 
bond strength is 61,544 pounds. 
In respect to the resin or matrix adhesion, or bond, or peel strength of 
zero degree leafs 62 of the interleafs 60, consideration must be given to 
the formation of the end windings on the hollow continuously wound 
filament integral structure 40. During the filament winding machine 
operations, there is both deceleration and acceleration movements of the 
carriage, or traveling head, while the mandrel is being rotated at a 
constant speed, therefore the resulting respective filament paths at the 
ends of the product being wound go from a desired winding angle of say a 
selected seven degrees to a winding angle of ninety degrees, and then back 
to the desired winding angle. This end filament winding surface area at 
each end is called the turnaround area, which is also described as the dog 
bone area. 
The length of the leafs 62 in their essential zero degree arrangement in 
respect to the longitudinal axis is 21/2 inches and at least the ends 
nearest the center of the filament wound product, i.e. inboard ends, are 
in contact with the load carrying filament fibers being wound by the 
winding machine. It was judged, however, in this tested product 40, that 
the last inch of these leafs, i.e. the zero degree fibers, were in contact 
and doing work with the load carrying fibers being wound by the winding 
machine 108. Therefore a one inch length at a diameter of 1.75 inches 
times 3.14 or 5.49 square inches, times two surfaces, i.e. inner and outer 
surfaces, per interleaf, times two interleafs, times 3500 pounds bonding 
strength per square inch, equals an overall bonding strength of 76,969 
pounds at each end. By numerals: 
1.times.1.75.times.3.14.times.2.times.2.times.3500=76,969 pounds. 
During the winding operations on the filament and resin winding machine the 
layers were wound at the following angles: 7 degrees across and back, 
referred to as plus and minus 7 degrees; then .+-.37 degrees; and an 
interleaf was inserted with an outer sleeve, then back to .+-.7 degrees; 
then across and back again at 7 degrees; and another interleaf was 
inserted with another outer sleeve, then .+-.37; and then .+-.7; to 
complete the filament winding of this specific sized embodiment of the 
hollow continuously wound filament integral structure. During all these 
winding times four bands of 6000 filament tape were being laid down at a 
width totalling 0.289", and a thickness of 0.005". 
All the filament tapes could be obtained without the pre-pregnation of the 
resin, and their pregnation considered as part of the method of making 
these hollow continuously filament wound integral products. Production 
runs of all manufacturers, currently are not precisely uniform in respect 
both to the filament fibers and/or their pre pregnation. Upon delivery, 
specific specifications are included by the manufacturer. Therefore care 
must by taken, when practicing this method, to refer to the current 
specifications, which include the tensile strengths and bonding strengths. 
Each manufacturer of filament and resin also furnishes instructions as to 
an autoclave cure cycle. A typical example is: 
1. raise the autoclave temperature from room temperature to 250.degree. F. 
at 2.degree. to 5.degree. per minute; 
2. hold the temperature at 250.degree. F. for 15 minutes; 
3. then apply 100 p.s.i., holding at 250.degree. F.; 
4. hold at 250.degree. F. and 100 p.s.i. for 45 minutes; 
5. raise the temperature to 350.degree. F. at 2.degree. to 5.degree. per 
minute; 
6. hold the temperature at 350.degree. F. for 2 hours; and 
7. cool under pressure to below 175.degree. F. 
Throughout the curing the heating must be reasonably uniform requiring the 
circulation of heated air inside the autoclave. 
Further Comments Concerning the Interleafs and Resulting Products in Which 
They are Used 
Throughout, the preceding description the interleafs of filament and resin 
were discussed in conjunction with carrying axial loads, via their leafs, 
through the turnaround zone and on to end fittings generally made of 
metal, so these loads would not be diminished by the poorer load carrying 
capacities of the filament and resin tapes being distributed by the 
filament winding machine in the turnaround zones. These interleafs were 
also discussed in conjunction with carrying circumferential tension loads, 
via their root wraps which surrounded the filament and resin tapes being 
distributed by the filament winding machine, and which also surrounded the 
end fittings and outer sleeves. 
The leafs were referred to as being directed axially or in the zero degree 
direction to distinguish them as being primarily directed to transferring 
axial loads. However, as indicated by their manufacture and use, the 
leafs, which are spaced in their initial skirt portions, when applied in 
reducing diameter and/or tapering portions, flare out and are not always 
specifically axially aligned or at a zero degree direction. 
Moreover, where torque was to be transmitted rather than axially directed 
loads, the leafs of the interleafs are laid at selected cross angles to 
more efficiently carry the torque loads through the turnaround zone. 
The interleafs were discussed as being preformed, whereby their root wraps 
were described as being initially bonded to the leafs in the initial skirt 
portions. Thereafter, additional root wraps were often made to these 
skirts of preformed interleafs. 
However, it is to be understood these interleafs are also made in situ at 
the time when the overall winding operation is undertaken. When the 
mandrel is stopped, selective leafs are specifically laid in place over 
filament and resin tape windings in the turnaround zone at each end of the 
mandrel. Their inherent adhesion holds them in place. Then the mandrel is 
turned as selective root wraps are circumferentially laid in place over 
the leafs and over portions of the filament and resin tape windings in the 
turnaround zone at each end of the mandrel. 
In addition, these interleafs serve the same useful functions of carrying 
full loads, either axial or torque loads, without the presence of end 
fittings and/or outer sleeves. An entire product is manufactured using 
only filament and resin tapes wound about a mandrel. Again the leafs in 
their selected directions improve the overall load carrying capacity of 
all the filament and resin tape windings in the turnaround zone and 
beyond, and the root wraps improve the circumferential tensile strength 
keeping all the filament and resin tapes in place in the turnaround zone. 
Also the overall placement and windings of the filament and resin tapes 
may be controlled at the turnaround zones, so openings are created to 
receive components, at a later time, which secure this 100% filament wound 
product at its place of use. 
In respect to all the variations of the method steps to tailor these 
respective hollow filament wound integral structures, they require just a 
one time rotational mounting in the winding machine. This advantage has 
been previously described as requiring just one overall filament and resin 
winding operation.