U.S. patent application number 11/432027 was filed with the patent office on 2006-09-14 for method for making a fiber reinforced composite rivet having an upset head.
Invention is credited to Thomas R. Adams, Gary R. Wittman.
Application Number | 20060200967 11/432027 |
Document ID | / |
Family ID | 34652593 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060200967 |
Kind Code |
A1 |
Adams; Thomas R. ; et
al. |
September 14, 2006 |
Method for making a fiber reinforced composite rivet having an
upset head
Abstract
A method for making a composite rivet and upsetting the
composite rivet after the rivet has been inserted through (e.g.,
composite) structural members to be held together. The rivet
includes a core having continuous and unidirectionally extending
fibers that are reinforced by a thermoplastic resin. The core is
surrounded by a braided jacket having fibers arranged in a
criss-cross weave. A forming die guide having a containment opening
extending therethrough is positioned so that the upstanding end of
the composite rivet is received within the containment opening. A
heated forming die having a forming cavity is moved into the
containment opening of the forming die guide so as to lie in axial
alignment with the upstanding end of the rivet. A ram forces the
heated forming die through the containment opening so that the
upstanding end of the rivet is softened and upset within the
forming cavity. The ability of the upstanding end of the rivet to
spread out under the heat and pressure generated by the heated
forming die is limited by the containment opening of the forming
die guide.
Inventors: |
Adams; Thomas R.;
(Huntington Beach, CA) ; Wittman; Gary R.; (Costa
Mesa, CA) |
Correspondence
Address: |
MORLAND C FISCHER
2030 MAIN ST
SUITE 1050
IRVINE
CA
92614
US
|
Family ID: |
34652593 |
Appl. No.: |
11/432027 |
Filed: |
May 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10704276 |
Nov 10, 2003 |
|
|
|
11432027 |
May 11, 2006 |
|
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Current U.S.
Class: |
29/525.06 |
Current CPC
Class: |
Y10T 29/49943 20150115;
B29C 66/0242 20130101; B29C 66/8322 20130101; B29K 2081/04
20130101; Y10T 29/49938 20150115; B29C 66/80 20130101; B29C 66/71
20130101; B29C 66/81431 20130101; Y10T 29/49908 20150115; B21J
15/08 20130101; F16B 5/04 20130101; B29C 66/43 20130101; B29C
66/72141 20130101; B29K 2105/06 20130101; Y10T 29/49956 20150115;
F16B 19/06 20130101; B29K 2071/00 20130101; B29C 66/721 20130101;
B29C 66/71 20130101; B29C 66/7212 20130101; B21J 15/02 20130101;
B29C 66/81429 20130101; B29K 2071/00 20130101; B29K 2307/04
20130101; B29K 2309/08 20130101; B29C 65/601 20130101; B29K 2081/04
20130101; B29C 66/7212 20130101; B29C 66/1122 20130101; B29C
66/7392 20130101; B29C 66/7212 20130101; B29C 65/08 20130101; B29C
66/71 20130101; B29C 66/81831 20130101; B29C 66/81423 20130101 |
Class at
Publication: |
029/525.06 |
International
Class: |
B21J 15/02 20060101
B21J015/02 |
Claims
1-10. (canceled)
11. A method for making a composite rivet having an enlarged rivet
head at one end and an upset head at the opposite end for holding
structural members together, said method comprising the steps of:
providing a rivet preform including a composite core having a
plurality of unidirectional fibers running continuously
therethrough; locating said rivet preform in an insert having a
forming cavity such that a first end of said rivet preform projects
into said forming cavity; heating said insert and said rivet
preform located therein; applying pressure to the first end of said
heated rivet preform for softening and shaping said first end
within the forming cavity of said insert to form said enlarged
rivet head; cooling said rivet preform to produce said composite
rivet with said enlarged rivet head having a shape corresponding to
the shape of the forming cavity of said insert and then removing
said composite rivet from said insert; inserting said composite
rivet through the structural members to be held together such that
the enlarged rivet head of said composite rivet lies at one side of
the structural members and the upstanding end of said composite
rivet opposite the enlarged rivet head projects outwardly from the
structural members to the opposite side thereof; and forming said
upset head by applying heat and pressure to the upstanding end of
said composite rivet.
12. The method for making recited in claim 11, including the
additional step of surrounding the composite core of said rivet
preform with a braided jacket comprising fibers arranged in a
criss-cross weave.
13. The method for making recited in claim 11, including the
additional steps of locating a forming die within the forming
cavity of said insert so as to lie in axial alignment with the
first end of said heated rivet preform; and moving said forming die
into contact with said first end for applying said pressure to said
first end for softening and shaping said first end within the
forming cavity of said insert.
14. The method for making recited in claim 13, including the
additional step of heating said forming die before the step of
moving said forming die into contact with the first end of said
heated rivet preform for applying said pressure thereto.
15. The method for making recited in claim 14, including the
additional steps of positioning said heated insert, said heated
rivet preform located in said insert, and said heated forming die
located within the forming cavity of said insert within a preheated
mold base of a press; and closing said press against said heated
forming die for moving said heated forming die into contact with
the first end of said heated rivet preform for applying said
pressure thereto.
16. The method for making recited in claim 11, wherein said step of
forming said upset head includes the additional steps of: locating
an upsetting die guide having a containment opening extending
therethrough so that the upstanding end of the composite rivet is
received in said containment opening; moving an upsetting die
having an upsetting cavity into the containment opening of said
upsetting die guide for applying said pressure to the upstanding
end of the composite rivet; softening and shaping the upstanding
end of the composite rivet within the upsetting cavity of said
upsetting die; and cooling the upstanding end of the composite
rivet to form said upset head having a shape corresponding to the
shape of said upsetting cavity.
17. The method for making recited in claim 16, wherein said step of
forming said upset head by applying heat to the upstanding end of
said composite rivet includes heating said upsetting die for
softening and shaping said upstanding end within the upsetting
cavity of said upsetting die.
18. The method for making recited in claim 17, including the
additional steps of coupling a ram to said heated upsetting die;
and moving said ram toward said upsetting die guide for forcing
said heated upsetting die against the upstanding end of the
composite rivet and thereby applying said pressure to said
upstanding end when said upstanding end is softened and shaped
within the upsetting cavity of said heated upsetting die.
19. The method for making recited in claim 16, including the
additional step of forming an indentation within the upset head of
the composite rivet.
20. The method for making recited in claim 19, including the
additional step of forming said indentation within said upset head
when said upsetting die is moved into the containment opening of
said upsetting die guide by means of a tip carried by said
upsetting die and projecting from within said upsetting cavity
thereof.
21. The method for making recited in claim 11, wherein the step of
forming said upset head includes the additional steps of:
positioning a forming die guide having a containment opening
extending therethrough such that the upstanding end of the
composite rivet is located in said containment opening; heating a
forming die having a forming cavity at one end thereof and a tip
projecting from said forming cavity; moving said heated forming die
towards said forming die guide such that the upstanding end of the
fiber-reinforced composite rivet is received within the forming
cavity of said heated forming die at the containment opening of
said forming die guide so as to soften the upstanding end of the
fiber-reinforced composite rivet within said forming cavity and
prevent the softened end from spreading outside the containment
opening of said forming die guide, the tip projecting from said
forming cavity making an indentation in the softened rivet end for
controlling the direction of the continuous fibers with which the
rivet is reinforced; and cooling the upstanding end of the
fiber-reinforced composite rivet to form said upset head having a
shape corresponding to the shape of said forming cavity where the
continuous fibers flow around the indentation and into the upset
head to maximize the strength of the composite rivet and said upset
head thereof.
22. The method for upsetting a composite rivet recited in claim 21,
including the additional step of heating said forming die in a
furnace for softening the upstanding end of the fiber-reinforced
composite rivet within the forming cavity of said forming die.
23. The method for upsetting a composite rivet recited in claim 21,
including the additional step of applying pressure to said forming
die when the upstanding end of the fiber-reinforced composite rivet
is softened within the forming cavity of said forming die.
24. The method for upsetting a composite rivet recited in claim 23,
including the additional steps of coupling a ram to said forming
die; and moving said ram towards said forming die guide so as to
force said forming die against the upstanding end of the
fiber-reinforced composite rivet for applying said pressure to said
forming die when the upstanding end of the composite rivet is
softened within the forming cavity of said forming die.
25. The method for upsetting a composite rivet recited in claim 24,
including the additional step of coupling said ram to said forming
die by way of a guide pin projecting outwardly from said ram for
receipt by said forming die.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a fiber reinforced composite rivet
and to a method for upsetting one end thereof by means of compact,
easy to use upsetting tools.
[0003] 2. Background Art
[0004] Plastic and metal rivets are well known fasteners for
connecting opposing structural members to one another. However, in
certain applications, particularly those related to the aerospace
industry, the weight associated with the conventional rivet can not
be ignored. For example, when a very large number of rivets is used
in an aircraft, the total weight of the aircraft is typically
increased and the efficiency of operation is typically reduced.
[0005] To overcome the aforementioned weight problem and to provide
a reliable, high strength means for connecting together opposing
structural members, rivets made from a composite material have been
proposed. In this case, a free upstanding end of the composite
rivet must be upset during the assembly process in the field.
Unfortunately, no compact, easy to use tool is known by which to
enable a workman at a job site to upset the upstanding end of a
composite rivet after the rivet has first been inserted through the
structural members to be connected together.
SUMMARY OF THE INVENTION
[0006] In general terms, a fiber reinforced composite rivet is
disclosed that is capable of being upset so as to reliably connect
together opposing (e.g., composite) structural members once the
rivet has been inserted through the members. A rivet preform is
initially positioned in an insert that is held by a mold base of a
force generating press. The rivet preform is formed by continuous
(e.g., carbon, quartz, glass, etc.) fibers that run
unidirectionally (i.e., longitudinally) through the preform. The
fibers are reinforced by a thermoplastic (e.g., PEEK or PPS) resin.
The rivet preform is surrounded by an outer fiber braided jacket
comprising continuous fibers that are arranged in a criss-cross
weave. The fibers of the braided jacket are also reinforced by a
thermoplastic resin.
[0007] A first end of the fiber preform projects upwardly into a
female cavity of the insert within which the preform is positioned.
The rivet preform and insert are heated in an oven, and the mold
base is preheated within the press. The heated preform and insert
are removed from the oven and located in the preheated mold base.
The press is closed to apply pressure to the first end of the
heated fiber preform, whereby the first end is softened and shaped
by the female cavity of the insert so as to establish a composite
rivet having a (e.g., flat) head. Once the preform has cooled down,
the press is opened and the insert is removed from the mold base
and cooled in water. The composite rivet is then pushed out of the
insert and deflashed.
[0008] The composite rivet is now inserted through the opposing
structural members to be connected together such that the newly
formed head of the rivet lies at one side of the members and the
upstanding core of the rivet projects to the other side of the
members. A forming die guide is positioned so that the upstanding
core of the composite rivet is received within a containment
opening that is formed in the forming die guide. A heated forming
die having a forming cavity at one end thereof is moved into the
containment opening of the forming die guide so as to be axially
aligned with the upstanding core. A ram is coupled to the heated
forming die located within the containment opening of the forming
die guide. The ram generates a pressure to cause the heated forming
die to move towards and into contact with the upstanding core of
the composite rivet, whereby the core is softened and shaped (i.e.,
upset) by the forming cavity of the forming die. The ability of the
upset head to spread out during formation is restricted by the
containment opening of the forming die guide which surrounds the
upstanding core. A pointed tip within the forming cavity of the
forming die leaves a depression in the upset head which directs the
unidirectional fibers to the periphery of the upset head in order
to improve the ability of the composite rivet to withstand tensile
loads.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a braided fiber preform having the preferred
continuous, unidirectional fiber orientation prior to manufacture
of the composite rivet of this invention;
[0010] FIG. 2 shows the fiber preform of FIG. 1 located within a
heated insert so as to receive a force generated by a press during
formation of the composite rivet;
[0011] FIG. 3 shows the composite rivet after it has been formed
and removed from the insert of FIG. 2;
[0012] FIG. 4A is an exploded view illustrating the upsetting tools
by which the upstanding core of the composite rivet of FIG. 3 is
upset following insertion of the rivet through opposing structural
members to be connected together;
[0013] FIG. 4B shows the upsetting tools of FIG. 4A coupled to one
another and with the upstanding core of the composite rivet;
[0014] FIG. 4C shows the upsetting tools applying pressure to the
upstanding core to provide the composite rivet with an upset
head;
[0015] FIG. 4D shows the upset head of the composite rivet after
the upsetting tools of FIG. 4C have been removed; and
[0016] FIG. 5 illustrates the fiber orientation of the composite
rivet of FIG. 4D having an upset head.
DETAILED DESCRIPTION
[0017] FIG. 1 of the drawings shows a rivet preform 1 which will be
subject to heat, compression and solidification in order to form a
fiber reinforced composite rivet 30 (of FIG. 3) that can be upset
(as shown in FIG. 4) by means of compact and easy to use tools so
that a pair of opposing (e.g., planar) composite structures can be
reliably connected together. The rivet preform 1 (e.g., a
pulltruded rod segment) includes a plurality of resin impregnated
fibers 3. For maximum strength and reliability, the fibers running
through the rivet preform 1 are both continuous and unidirectional
(i.e., longitudinal) rather than chopped or random. By way of
example, the fibers 3 of the rivet preform 1 are manufactured from
carbon, quartz, glass, or the like. The fibers 3 are reinforced by
a suitable thermoplastic resin such as, for example, that known as
PEEK, PPS, or the like. A thermoplastic resin is preferable so as
to enable one end of a composite rivet to be upset in a manner that
will be explained in greater detail hereinafter when referring to
FIG. 4.
[0018] The rivet preform 1 is surrounded by an outer braided jacket
5. The braided jacket 5 may be applied over and fused to the
preform 1 by means of a conventional braiding machine. For purposes
of efficiency, the application and fusing of the braided jacket 5
to the preform 1 may be completed during a single step. Like the
rivet preform 1, the braided jacket 5 includes a plurality of
continuous fibers 7 that are reinforced by a suitable thermoplastic
resin. The braided jacket 5 surrounds the rivet preform 1 in a
criss-cross weave as shown in FIG. 1.
[0019] FIG. 2 of the drawings shows the braided composite rivet
preform 1 of FIG. 1 being retained within an insert 10 of the kind
that is typically installed in a mold base 12. The mold base 12 is
preferably manufactured from aluminum to facilitate cooling during
the manufacture of the headed rivet 30 shown in FIG. 3. In general,
an elongated braided rod (not shown) is first produced (i.e.,
pulltruded), and the rod is then cut into smaller preform sections
like that shown in FIG. 1 for receipt by the insert 10 of FIG. 2. A
first end of the rivet preform 1 projects upwardly into a female
cavity 14 at the top of insert 10. A male die 16 which cooperates
with a conventional press (not shown) is supported above the female
cavity 14 at the top of insert 10 so as to lie in spaced axial
alignment with the first end of the rivet preform 1. A plug 18 is
positioned within the mold base 12 so as to communicate with the
bottom of insert 10. The plug 18 includes a pin 20 that projects
upwardly within the insert 10 so as to lie in spaced axial
alignment with the opposite end of the rivet preform 1.
[0020] The steps by which the rivet preform 1 of FIG. 1 is headed
in order to produce the fiber reinforced composite rivet 30 of FIG.
3 are now described while continuing to refer to FIG. 2. The rivet
preform 1 is pressed into the insert 10 so that the first end of
preform 1 projects upwardly into female cavity 14, as shown. The
insert 10, the rivet preform 1 and the male die 16 are all
initially preheated to about 780 degree F. in a suitable oven. The
mold base 12 and the bottom plug 18 are heated within the press to
a temperature of approximately 500 degrees F. The heated preform 1,
insert 10, and male die 16 are removed from the oven and placed in
the preheated mold base 12 within the press.
[0021] The press is now closed to apply approximately 1,500 pounds
of pressure for about three minutes to the first end of the heated
rivet preform 1 by way of the heated male die 16. The corresponding
pressure applied by male die 16 causes the composite material at
the first end of preform 1 to soften and flow into the female
cavity 14 of heated insert 10, such that a relatively wide and flat
head (designated 32 in FIG. 3) is formed after cooling. The
extension 20 of plug 18 applies holding pressure to the opposite
end of the rivet preform 1 to prevent the preform from being
extruded out of the bottom of the insert 10 during the formation of
the head 32. While the head 32 is shown as being flat, other shapes
are contemplated depending upon the shape of the female cavity 14
within which the composite material of preform 1 is forced.
[0022] Once the headed fiber preform has cooled down and solidified
within the insert 10, the press is opened and the male die 16, mold
base 12, insert 10, and preform 1 are all removed therefrom and
turned upside down. Next, the combination of the male die 16,
insert 10 and headed preform are separated from the mold base 12
and cooled in water, or the like, to a temperature preferably below
200 degrees F. The cooled combination is then placed in a
well-known arbor press which pushes the male die 16 and the headed
rivet preform 1 out of the insert 10. At this point, the male die
16 is simply pulled off and separated from the headed preform.
[0023] FIG. 3 of the drawings shows a fiber reinforced composite
rivet 30 having a head 32 at one end thereof after the male die 16
has been separated from the preform 1 and the rivet 30 has been
deflashed. The headed rivet 30 is characterized by the same
continuous and unidirectional (i.e., longitudinally extending)
fibers 3 and braided jacket 5 that were first described when
referring to FIG. 1. In this same regard, FIG. 5 of the drawings
more clearly illustrates the continuous and unidirectional fiber
orientation as well as the braided jacket of the fiber reinforced
composite rivet 30 after the end thereof that lies opposite the
head 32 has been upset in a manner that will now be disclosed.
[0024] To this end, and turning to FIG. 4 of the drawings, the
steps are described by which the opposite end of the fiber
reinforced composite rivet 30 of FIG. 3 is upset. As indicated
above, the composite rivet 30 has particular application for
securing opposing composite structural members together. By way of
example, FIG. 4A shows the composite rivet 30 inserted through a
pair of axially aligned holes that are formed in a pair of
composite plates 34 and 36 that are stacked one above the other.
The head 32 at the first end of rivet 30 is positioned at one side
of the plates 34 and 36, and the upstanding core 38 of rivet 30
extends through the plates 34 and 36 to the opposite side
thereof.
[0025] The upstanding end of core 38 of composite rivet 30 is upset
after being inserted through plates 34 and 36 by means of a forming
die 40 and a forming die guide 50. The forming die 40 and the
forming die guide 50 are preferably manufactured from heat treated
tool steel. The leading end of forming die 40 includes a generally
bowl-shaped forming cavity 44 and a central pointed tip 46
projecting outwardly past the forming cavity 44. The pointed tip 46
at the leading end of forming die 40 is important for directing the
flow of continuous fibers at the upset end of the fiber reinforced
composite rivet 30 in a manner to be described while referring to
FIG. 5 so as to advantageously maximize the ability of rivet 30 to
withstand tensile loads. The trailing end of forming die 40 lying
opposite the forming cavity 44 and pointed tip 46 includes a recess
48 extending axially therewithin.
[0026] A ram 52 having a guide pin 54 projecting outwardly
therefrom is spaced above the forming die 40 so that the guide pin
54 can be moved towards and into receipt by the recess 48 that is
formed in the trailing end of forming die 40. In this way, the
guide pin 54 can be moved to accurately position the forming die 40
relative to the upstanding end of the core 38 of the fiber
reinforced composite rivet 30 that is to be upset.
[0027] FIG. 4B shows the guide pin 54 of ram 52 located within the
recess 48 at the trailing end of forming die 40 so that the pointed
tip 46 of forming die 40 is moved into contact with the upstanding
end of core 38 of composite rivet 30. In this case, the forming die
guide 50 is laid over the composite plates 34 and 36 to be
connected together such that the upstanding end of core 38 of rivet
30 projects upwardly into a containment opening 58 that is formed
in the forming die guide 50. In this same regard, the forming die
40 is positioned by the guide pin 54 of ram 52 so as to project
downwardly into the containment opening 58 and thereby engage the
upstanding end of core 38. With each of the forming die 40 and the
upstanding end of core 38 of rivet 30 axially aligned with one
another within the containment opening 58 and surrounded by the
forming die guide 50, the ability of the core 38 to spread outside
the containment opening 58 of forming die guide 50 will be blocked
during the formation of an upset head (designated 60 in FIGS. 4C
and 4D).
[0028] The details for forming the upset head 60 at the upstanding
end of the core 38 of the fiber reinforced composite rivet 30 are
now described while referring to FIG. 4C. Initially, the forming
die 40 is placed into an oven and heated to about 1200 degrees F.
The precise temperature to which the forming die 40 is heated will
depend upon the composite material from which the rivet 30 is made.
Once the forming die 40 has been heated, it is removed from the
oven and coupled to the guide pin 54 of ram 52, as shown. With the
upstanding end of the core 38 of composite rivet 30 extending
through the composite plates 34 and 36 and projecting into the
containment opening 58 in the forming die guide 50, the ram 52
pushes the heated forming die 40 downwardly through the containment
opening 58 against the upstanding end of core 38. The ram 52
generates approximately 100-200 pounds of pressure for about 15 to
30 seconds to cause the upstanding end of core 38 to soften and
flow into the forming cavity 44 (best shown in FIG. 4A) at the
leading end of forming die 40, whereby to shape the upset head 60.
In the alternative, the upstanding end of the core 38 can be
softened by conventional ultrasonic techniques or other rapid
heating techniques, such as induction heating.
[0029] It is to be understood that a backing force or pressure (not
shown) must be applied to the lower composite plate 34 to oppose
the pressure that is generated by the ram 52 and thereby prevent
the core 38 of rivet 30 from being pushed downwardly and outwardly
from the composite plates 34 and 36 that are to be connected
together. Moreover, the ram 52 is preferably manufactured from a
heat conductive metal (e.g., aluminum) so as to draw heat away from
the forming die 40 during the formation of the upset head 60 so as
to facilitate a rapid cooling.
[0030] After the upset head 60 of composite rivet 30 has cooled and
solidified under pressure, the ram 52 is raised and the forming die
40 is lifted off the upset head. As indicated above, the forming
die guide 50 surrounds both the upstanding end of core 38 and the
forming die 40 to prevent the fibers of the composite rivet from
spreading outside the containment opening 58 of guide 50 under the
pressure that is generated by the ram 52 during the formation of
the upset head 60. Accordingly, and as is best shown in FIG. 4D, a
fiber reinforced composite rivet 30-1 is produced having a
generally bowl shaped upset head 60 formed above the upper plate 36
and a flat head 32 that is flush with the lower plate 34, whereby
to reliably hold the pair of composite plates 34 and 36 together.
Because the upset rivet 30-1 as well as the plates 34 and 36 that
are held together by rivet 30-1 are all manufactured from a
composite material, each will have the same or substantially
similar coefficient of thermal expansion. Thus, the upset composite
rivet 30-1 will be able to completely fill the hole through
composite plates 34 and 36 during changing thermal conditions so as
to establish a more reliable connection therebetween.
[0031] The upset head 60 of the composite rivet 30-1 of FIG. 4D has
an indentation 62 that is created by the pointed tip 46 which
projects from the leading end of forming die 40 into the upstanding
end of core 38 while the core is softened, shaped and cooled within
the forming cavity 44. As previously described, the pointed tip 46
directs the flow of the unidirectional (i.e., longitudinally
extending) fibers that run through the fiber reinforced composite
rivet 30-1. More particularly, and referring now to FIG. 5 of the
drawings, the fiber orientation of the composite rivet 30-1 is
shown after the upset head 60 has been formed. The composite rivet
30-1 is shown in a double flush connection in FIG. 5 having the
flat head 32 thereof positioned flush with the bottom composite
plate 34 and the opposite upset head 60 positioned flush with the
lower composite plate 36. However, the rivet 30-1 may also be
connected to plates 34 and 36 in a single flush configuration as
shown in FIG. 4D or in other rivet configurations such as, for
example, a protruding head configuration (not shown).
[0032] The resin impregnated fibers 3 are shown in FIG. 5 running
continuously and unidirectionally through the rivet 30-1. The
indentation 62 that is created in the upset head 60 by the pointed
tip 46 of forming tool 40 splits the flow and directs or flares the
fibers 3 outwardly to the periphery of the upset head 60 to
maximize the strength thereof. The strength of the composite rivet
30-1 is further increased by virtue of the braided jacket 5 which
surrounds the core 38. That is, because of the ability of the
braided jacket 5 to expand and contract, the orientation of the
fibers 3 is more likely to follow the contour of the rivet 30-1 to
maximize the tensile strength thereof. In addition, during
expansion, the braided jacket 5 aids in directing the
unidirectional fibers 3 to the periphery of the upset head 60 so as
to help achieve optimal tensile characteristics.
* * * * *