Partially split external barrier for composite structures

A liquid or gaseous impervious barrier is disclosed for use in composite structures, such as pressure vessels or the like, which include a juncture at which a first filament wound laminate meets a second member, such as a second laminate or a fixed boss or fitting. The juncture is capable of separating upon flexing of the first and second laminates or members. The barrier includes a flexible member disposed between the first and second laminates at the juncture thereof, with the barrier member being sealed, as by bonding, to the first and second laminates to prevent moisture penetration about the barrier member. The barrier member is split from the exterior thereof partially therethrough to accommodate any separation at the juncture due to flexing of the first and second laminates. A folded film sheet is disposed in the split in the barrier member to prevent the split portions thereof from adhering to each other. A resilient member, such as an O-ring is disposed in the fold of the film sheet and fits into an enlarged portion formed at the base of the split in the barrier member, for holding the film sheet within the barrier member.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to an external barrier means for composite 
structures, for instance for use in the juncture between filament wound 
laminates of a pressure vessel or the like. 
Heretofore, barrier coats have been applied to the external surfaces of 
composite structures such as filament wound pressure vessels, rocket motor 
cases or the like, to retard moisture or other adverse environment 
penetration into the composite case. Extended exposures in high humidity 
and elevated temperature environments can considerably degrade the 
strength of unprotected composites. 
However, existing techniques utilizing barrier coats do not provide 
protection at the termination of the barrier coat where the composite case 
is attached to fittings, such as polar bosses, or other fixed members. 
Other problem areas where existing techniques utilizing barrier coates are 
deficient include areas where laminate skirt portions of a pressure vessel 
join a cylindrical portion of the vessel; e.g. a juncture between first 
and second laminate portions comprising the skirt and cylinder of a rocket 
motor case. 
In such instances as described above, the juncture is capable of separating 
due to flexing of the adjacent components, such as under pressurization of 
the vessel. The external barrier coats also separate at the junctures, 
leaving a gap which is prone to moisture penetration. 
The present invention is directed to an external barrier means for 
composite structures such as pressure vessels, rocket motor cases, or the 
like, to solve the above problems relating to moisture or gaseous 
penetration into the composite case. 
The barrier means of the present invention is disclosed herein for use in a 
gap between the composite and a non-yielding member, such as a polar boss, 
of a pressure vessel during pressurization. The invention also is shown 
for use at the juncture between a skirt portion and a cylinder portion of 
a pressure vessel, such as a rocket motor case. However, it is to be 
understood that the barrier means of the present invention is equally 
applicable for use at junctures of a wide variety of vessels or casings 
where the juncture is capable of separating to create a gap which is prone 
to moisture penetration. 
In the exemplary embodiment of the invention, the barrier means includes a 
flexible barrier member, such as rubber or the like, disposed between 
first and second components of a composite structure at a juncture which 
is capable of separating. The barrier member is sealed, as by bonding, to 
the components to prevent moisture penetration around the flexible barrier 
member. The barrier member further is split from the exterior thereof 
partially therethrough to accommodate separation of the components at the 
juncture there between. An enlarged portion is formed at the base of the 
split in the barrier member to preclude any stress-riser affect at the 
base of the split, thereby preventing the split from increasing inwardly 
upon any such separation at the juncture. 
Preferably, a film sheet, such as Teflon or the like, is folded onto itself 
and disposed in the split in the barrier member to prevent the split 
portions thereof from adhering to each other. The fold in the film sheet 
is disposed generally at the base of the split in the barrier member, and 
a resilient member, such as an O-ring, is disposed in the fold and sized 
to fit into the enlarged portion of the split in the barrier member to 
hold the film sheet in place. 
Thus, it can be seen that a new and improved barrier means is provided for 
use in a juncture between yieldable components of a composite structure to 
retard moisture or gas penetration into the composite structure where 
existing techniques utilizing barrier coats are deficient. 
Other objects, features and advantages of the invention will be apparent 
from the following detailed description taken in connection with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings in greater detail, and first to FIG. 1, a 
composite structure in the form of a pressure vessel, generally designated 
10, is shown and includes a pair of end fittings in the form of polar 
bosses 12. Pressure vessel 10 includes a filament wound composite forming 
a cylindrical portion 14 and a pair of dome shaped ends 16. The composite 
is wound about polar bosses 12, creating junctures therebetween wherein 
barrier means, generally designated 18, is disposed in accordance with the 
present invention. 
An external barrier coat 20 surrounds the filament wound composite to 
provide protection for the filament windings thereof. The barrier coat may 
be of various materials, including metallic materials. The barrier coat 
retards moisture penetration into the composite case. In addition, the 
barrier coat may perform various other functions, such as protection 
against radiation, lightning strike, or EMI protection. 
An internal barrier member or liner 22, which is fabricated of rubber or 
like material, is disposed about the interior of the composite case to 
separate the contents of the case from the filament wound composite 
thereof. Barrier means 18 of the present invention is incorporated 
directly into portions of the internal barrier 22 which extend about and 
through the juncture between the dome shaped portions 16 of the composite 
and the polar bosses 12. However, it should be understood that this is a 
preferred embodiment of the invention, and separate barrier means may be 
employed as shown in FIGS. 3 and 4 which will be described in detail 
hereinafter. 
With composite structures such as the pressure vessel 10 described above in 
relation to FIG. 1, the utilization of barrier coats, such as barrier coat 
20, does not provide moisture penetration protection at the termination of 
the barrier coat at the juncture of the composite case with polar bosses 
12. In particular, a gap will open during pressurization of the vessel 
between the filament wound composite and the non-yielding polar bosses 
which often times are fabricated of metal or like rigid material. As these 
gaps form during pressurization of the vessel, moisture can penetrate past 
barrier coat 20 at the termination of the composite around polar bosses 
12. The barrier means of the present invention is designed to prevent 
moisture penetration in these areas. 
More particularly, referring to FIG. 2, barrier means 18 of the present 
invention includes a flexible barrier member 24 fabricated of rubber or 
other resilient material. As stated above, in the embodiment of the 
invention shown in FIGS. 1 and 2, the flexible barrier member 24 forms a 
continuation of the internal barrier means or liner 22. Barrier member 24 
is sealed, as by bonding, to adjacent surfaces 26 and 28 of polar boss 12 
and filament wound composite 16, respectively. This prevents moisture 
penetration around the barrier member. In addition, the barrier member has 
an external flange 30 overlying barrier coat 20 and bonded thereto. 
In order to accommodate any separation, as during pressurization of the 
vessel, between polar boss 12 and composite 16 at the juncture 
therebetween, barrier member 24 is split, as at 32. The split in barrier 
member 24 extends from the exterior of the barrier member and partially 
therethrough. Therefore, the barrier member sort of acts as a hinge to 
accommodate any separation between the polar boss and the composite case. 
Referring to FIG. 2A, an enlargement of the base of split 32 in barrier 
member 24 is shown to illustrate particularly the base of the split. More 
particularly, an enlarged portion 36 is formed at the base of split 32 to 
preclude any stress-riser affect at the base of the barrier member to 
thereby prevent the split from increasing or "growing" upon any separation 
at the juncture between the polar boss and the composite case. This is 
particularly important in the event that the split becomes contaminated by 
environmental elements. 
Means also is provided to prevent the split portions of barrier member 24 
from adhering to each other, particularly when such materials as rubber 
are utilized. To prevent this adherence, a thin film sheet 38 of 
non-adhering material, such as Teflon or the like, is folded over onto 
itself and disposed within the split 32 in barrier member 24. This film 
sheet prevents the split portions of the barrier member from adhering to 
each other. In order to hold film sheet 38 within the split in the barrier 
member, a resilient O-ring 40 is disposed within the fold of the film 
sheet and is sized to press fit into the enlarged portion 36 at the base 
of split 32. 
It is readily apparent that the barrier means 18 shown in conjunction with 
the pressure vessel 10 as described in relation to FIGS. 1-2A, provides an 
effective means for retarding moisture penetration into the composite case 
of the pressure vessel at the junctures between the composite case and 
polar bosses 12 or other similar fittings. 
Referring to FIG. 3, a rocket motor case, generally designated 42, is shown 
and incorporates barrier means in accordance with the present invention. 
The rocket motor case includes a filament wound composite having a 
cylindrical portion 44 and opposite dome shaped end portions 46. An 
internal barrier means or liner 48 is employed similar to that described 
in relation to FIGS. 1 and 2. End fittings or polar bosses 50 are shown at 
the ends of the rocket motor case. Although not shown in the drawings, 
barrier means may be provided around polar bosses 50 in accordance with 
the present invention. Such barrier means is not shown in FIGS. 3 and 4 so 
as not to detract from a clear showing of the barrier means in other areas 
of the rocket motor case. 
With rocket motor case 42 shown in FIG. 3, the cylindrical composite 
portion 44 is fabricated of a filament wound laminate which is joined by a 
pair of end skirt portions 52 comprising second laminates joining the case 
at junctures 54. An external barrier coating 56 surrounds the entire 
rocket motor case including cylindrical portion 44, domed end portions 36 
and skirt portions 52. The skirt portions normally are utilized to connect 
one rocket motor case to another in a stage-to-stage fashion. When rocket 
motor case 42 is pressurized, cylindrical portion 44 tends to spread 
outwardly while the domed end portions 46 tend to rotate inwardly under 
pressure. Consequently, junctures 54 tend to separate because of this 
relative movement. In order to compensate for the differential movement 
and prevent disruption of the continuous external barrier system 
comprising barrier coat 56, barrier means, generally designated 58, is 
provided at junctures 54 in accordance with the present invention. 
More particularly, and referring to FIG. 4, barrier means 58 includes a 
continuous, annular flexible barrier member 60 of rubber or like resilient 
material, disposed in junctures 54 between skirt portion 52 and 
cylindrical portion 44 of the composite filament wound motor case. As with 
barrier means 18 in FIGS. 1-2A, barrier member 60 is bonded to adjacent 
surfaces 62 and 64 of the motor case and of skirt portion, respectively. 
This seals the barrier member to prevent moisture penetration thereabout 
from the exterior and into the composite case. Barrier member 60 is split, 
as at 66, from the exterior thereof and partially therethrough to 
accommodate any separation at juncture 54 as described above. Thus, as 
with barrier member 24 in FIGS. 1-2A, barrier member 60 performs as a 
hinge to accommodate separation at juncture 54. 
Barrier member 60 also includes an enlarged portion 68 at the base thereof 
to preclude any stress-riser affect at the base of split 66. This prevents 
the split from increasing or "growing" inwardly upon any separation at 
juncture 54. Barrier means 58 also includes a film sheet 70 of Teflon or 
like material which, like film 38 in FIG. 2A, is folded over onto itself 
with the fold being disposed generally at the base of split 55. A 
resilient O-ring member 72 is disposed within the fold of film sheet 70 
and is sized to press fit within the enlarged portion 68 at the base of 
split 66. Thus, film sheet 70 prevents the split portions of barrier 
member 60 from adhering to each other, and O-ring 72 holds the film sheet 
in place. 
Although the invention is shown herein as utilized as barrier means 18 in 
FIGS. 1-2A about polar bosses 12 of a pressure vessel 10, and is shown in 
FIGS. 3 and 4 for use at junctures 54 between a rocket motor case and 
laminate skirts 52, it is to be understood that the barrier means of the 
present invention is readily applicable for use in many other similar 
areas where juncture or joint separation is prevalent, for retarding 
moisture or gaseous penetration thereat. 
It will be understood that the invention may be embodied in other specific 
forms without departing from the spirit or central characteristics 
thereof. The present examples and embodiments, therefor, are to be 
considered in all respects as illustrative and not restrictive, and the 
invention is not to be limited to the details given herein.