Blind fastener with reinforced containment sleeve

A blind fastener for fastening panels, especially panels made of composite materials, comprises a fastener body received within aligned openings in the panels and a cylindrical stem passing through the fastener body. The stem has an enlarged stem head spaced from an inner end of the fastener body which projects inwardly beyond the inner surface of the inner panel. A deformable sleeve mounted on the stem between the stem head and the inner end of the fastener body is a two-piece sleeve comprising a forming sleeve and a containment sleeve. The forming sleeve is made of a relatively soft, deformable material, whereas the containment sleeve is made of a relatively hard, nondeformable material. When the stem moves outwardly through the fastener body during setting of the fastener, the forming sleeve deforms to a fully set condition in overlying contact with the inner surface of the inner panel, forming a large bearing area that does not damage the composite material of the panels. However, the containment sleeve remains substantially undeformed, allowing the fastener to apply and maintain high clamping loads.

BACKGROUND OF THE INVENTION 
This invention relates to blind fasteners for use in fastening two panels 
together in overlapping outer and inner relation and, more particularly, 
to a blind fastener for fastening panels made of composite or other 
relatively soft materials. 
Blind fasteners are used in a variety of applications in which access to 
the blind side surface of panels being connected together is extremely 
limited or in some cases not possible. For example, in the construction of 
aerodynamic designs, including aircraft and the like, a substantially 
flush surface usually is desired on the accessible side of the panels, 
while access to the blind side may not be possible. Such aerospace 
fasteners must meet or exceed stringent requirements. In particular, the 
fasteners must securely fasten the panels and resist losing their gripping 
power under the stresses, vibrations, and temperatures imposed upon them 
by the harsh environment in which they are used. 
One type of blind fastener that satisfies these requirements comprises an 
internally threaded fastener body for insertion into aligned holes of the 
two panels, and an externally threaded cylindrical stem passing in 
threaded engagement through the fastener body. The inserted end of the 
stem has an enlarged stem head, and the outer end of the stem has a wrench 
engaging portion. Upon turning motion of the stem relative to the fastener 
body, the stem is moved in an axial outward direction through the fastener 
body. This axial outward movement causes a deformable sleeve around the 
stem and abutting against the stem head to deform around a tapered nose on 
the fastener body to a fully set condition against the inner panel. The 
stem further may be provided with a localized weakened region or break 
groove adapted to shear the stem at a predetermined torque. The break 
groove is preferably located axially along the stem such that the stem 
twists off in a substantially flush relation to the outer portion of the 
fastener body, i.e., the fastener body head, after the fastener is fully 
set. The fastener body head normally is received in a countersunk, flush 
relationship to the outer panel, thus providing an aerodynamic surface 
after the fastener is set. 
Special considerations arise when blind fasteners are used to secure panels 
made of composite or other relatively soft or lightweight materials. When 
the deformable sleeve of a blind fastener reaches its fully set condition, 
it applies very high and localized stresses against the inner panel. 
Panels made from composite materials normally are unable to withstand 
these high localized stresses. As a result, the panels usually are crushed 
and damaged. To help alleviate these problems, when fastening panels made 
of composite materials, a deformable sleeve constructed from relatively 
soft material is used. In addition, the deformable sleeve usually is 
configured so that it will bulge laterally when being set against the 
inner panel to provide a large bearing area and distribute compression 
forces over a wider surface area of the inner panel. 
In general, blind fasteners having the foregoing type of deformable sleeve 
provide a satisfactory area of engagement with the blind side of the inner 
panel, even though the deformable sleeve is made from a softer and, 
therefore, weaker material than blind fasteners used to set panels made 
from steel or other high strength materials. However, in some applications 
with stress sensitive panel materials, such as composite materials, a high 
strength deformable sleeve is desired, yet it cannot be used since it will 
tend to crush or damage the panel material. 
Accordingly, there has existed a definite need for a blind fastener having 
a deformable sleeve that provides a large area of engagement with the 
blind side of the inner panel, yet provides the strength advantages of a 
deformable sleeve made from a harder material. The present invention 
satisfies this need and provides further related advantages. 
SUMMARY OF THE INVENTION 
The present invention comprises a blind fastener for mounting in an opening 
in a workpiece and, more particularly, for connecting two panels in 
overlapped outer and inner relation. The fastener is especially adapted 
for use in securing panels made of composite or other relatively soft or 
lightweight materials. For this purpose, the fastener employs a special 
two-piece deformable sleeve having a construction which produces a large 
bearing area for clamping against the workpiece, yet provides 
high-strength clamping characteristics. The fastener of the present 
invention provides these advantages by using a first sleeve made of a 
relatively soft, deformable material that produces a large area of 
engagement with the blind side of the panel, and by using a second sleeve 
made of a relatively hard, nondeformable material that provides the 
strength component, all without damage to the panel surface. 
The fastener comprises an internally threaded generally tubular fastener 
body received within the openings in the panels. The fastener body has an 
inner end in the form of a tapered nose projecting inwardly beyond the 
inner panel, and an enlarged body head for engagement with the outer 
panel. An externally threaded cylindrical stem passes in threaded 
engagement through the fastener body. The stem has an enlarged stem head 
spaced from the tapered nose of the fastener body, and an outer portion 
extending outwardly beyond the fastener body head, which is provided with 
a wrenching surface for engagement by a fastener installation tool. 
Turning motion of the stem relative to the fastener body in one direction 
moves the stem in an axially outward direction through the fastener body, 
moving the stem head toward the tapered nose of the fastener body. 
In accordance with the invention, a two-piece deformable sleeve is mounted 
on the stem between the stem head and the tapered nose of the fastener 
body. The deformable sleeve comprises a forming sleeve made of a 
relatively soft, deformable material surrounding the stem. A containment 
sleeve made of a relatively hard, nondeformable material surrounds a 
portion of the forming sleeve adjacent to the stem head. Movement of the 
stem outwardly through the fastener body during setting of the fastener 
deforms the forming sleeve over the tapered nose to a fully set condition 
in overlying contact with the inner surface of the panel or workpiece. 
However, the containment sleeve remains substantially undeformed and 
applies the highest possible clamping loads against the panels without 
crushing or damaging them. 
The forming sleeve preferably is constructed from an annealed steel 
material, such as 304 stainless steel. The containment sleeve preferably 
is constructed from an age hardened steel material, such as A-286 CRES 
which has been heat treated. 
In one aspect of the invention, the forming sleeve, which is substantially 
cylindrical, includes a portion of reduced diameter on its outer surface, 
forming a neck at the inner end of the forming sleeve adjacent to the stem 
head. A shoulder on the forming sleeve separates the normal outer surface 
of the forming sleeve from the reduced diameter neck. This neck is 
designed to receive the containment sleeve, such that the containment 
sleeve is held in a position on the stem between the stem head and the 
shoulder of the forming sleeve. In the preferred embodiment, the 
containment sleeve, which is also substantially cylindrical, includes a 
shoulder at its inner end projecting radially inward. This shoulder is 
designed to abut the stem head and the inner end of the forming sleeve. 
In another aspect of the invention, the forming sleeve further includes a 
counterbore at its outer end for receiving a deformable plastic sleeve. 
This plastic sleeve, which is optional, may be used when it is necessary 
to provide sealing of the hole through which the blind fastener is 
mounted. 
Other features and advantages of the present invention will become apparent 
from the following detailed description, taken in conjunction with the 
accompanying drawings, which illustrate, by way of example, the principles 
of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in the exemplary drawings, the present invention is embodied in a 
blind fastener, generally referred to by the reference numeral 10, for use 
in connecting two panels together in overlapped outer and inner relation. 
The fastener is provided with a two-piece deformable sleeve that produces 
a large bearing area for clamping against the inner panel, yet provides 
high strength clamping characteristics. This fastener construction has 
special utility when fastening panels made of composite materials, since 
the sleeve's large bearing area prevents crushing and damaging of the 
panels, while still providing the strength advantages associated with 
fasteners normally used to connect panels made from steel or other high 
strength materials. 
Referring to FIG. 1, the blind fastener 10 of the present invention is 
shown in position for connecting two panels 12 and 14 together in 
overlapped outer and inner relation, with the outer panel 12 having an 
accessible outer surface 16 and the inner panel 14 having inaccessible or 
blind inner surface 18. The fastener 10 comprises an internally threaded, 
generally tubular fastener body 20 received within aligned openings 22 in 
the two panels 12 and 14. The fastener body 20 has a tapered nose 24 
projecting inwardly beyond the inner surface 18 of the inner 14 panel and 
an enlarged body head 26 received in a substantially flush, countersunk 
relationship to the outer surface 16 of the outer panel 12. Enlarged body 
heads of the non-flush, protruding head type also may be used. 
An externally threaded cylindrical stem 28 passes in threaded engagement 
through the fastener body 20. The inner end of the stem 28 has an enlarged 
stem head 30, and the outer end of the stem has a pair of wrenching flats 
32 for engagement by an installation tool (not shown). If desired, a 
localized weakened region or breakgroove 34 may be provided at an axial 
location along the stem 28 such that, after the fastener 10 is fully set, 
the stem will shear at a point substantially flush with the outer surface 
of the fastener body head 26. In most cases, the stem 28 will twist off 
within a range of approximately one-eighth of an inch above or below the 
outer surface of the fastener body head 26. 
In accordance with the invention, a two-piece deformable sleeve 36 is 
positioned on the stem 28 between the stem head 30 and the tapered nose 24 
of the fastener body 20. This two-piece 36 sleeve comprises a forming 
sleeve 38 and a containment sleeve 40. 
FIG. 2 shows one embodiment of the two-piece deformable sleeve 36 in 
greater detail. The forming sleeve 38 is substantially cylindrical and has 
an inner end 42 and an outer end 44. The inner end 42 of the forming 
sleeve 38 includes a portion of reduced diameter on its outer surface 
forming a neck 46. This neck 46 extends from an external shoulder 48 to 
the inner end 42 of the forming sleeve 38. The inner surface of the 
forming sleeve 38 also has a counterbore 50 extending from an internal 
shoulder 52 to the outer end 44 of the forming sleeve. 
The containment sleeve 40 is substantially cylindrical and has an inner end 
54 and an outer end 56. In the preferred embodiment, the inner end 54 of 
the containment sleeve 40 has a shoulder 58 projecting radially inward a 
short distance. The containment sleeve 40 is designed to fit over the neck 
46 such that the outer end 56 of the containment sleeve 40 abuts the 
external shoulder 48 on the forming sleeve 38, with the inner end 42 of 
the forming sleeve 38 in abutment with the shoulder 58 of the containment 
sleeve 38. This fit between the containment sleeve 40 and the neck 46 
preferably is a frictional-type fit so that the containment sleeve 40 is 
held in position on the forming sleeve 38 after assembly. 
The outer dimensions of the forming sleeve 38 and the containment sleeve 
40, as well as the outer dimensions of the fastener body 20 and stem head 
30, are substantially the same, but are slightly less than the diameters 
of the openings 22 in the two panels 12 and 14. This sizing of the 
fastener 10 permits insertion of the fastener through the openings 22 in 
the two panels 12 and 14 to enable the fastener to perform its clamping 
function on the blind side 18 of the inner panel 14, as explained in more 
detail below. Alternatively, the fastener 10 may be sized to provide an 
interference fit between the fastener and the aligned openings 22 in the 
panels 12 and 14. 
In the preferred embodiment, the forming sleeve 38 is constructed from a 
relatively soft, deformable material, such as an annealed steel material. 
For example, annealed 304 stainless steel is one such preferred material. 
The containment sleeve 40 preferably is constructed from a relatively 
hard, nondeformable material, such as an age hardened, heat treated steel 
material. For example, heat treated, age hardened A-286 CRES is one such 
preferred material. The remaining components of the fastener 10, including 
the fastener body 20 and stem 28, preferably are constructed from 
stainless steel alloys, titanium or the like. For example, the fastener 
body 20 and stem 28 preferably are constructed from stainless steel 
materials. 
FIG. 3 shows another embodiment of the two-piece deformable sleeve 36, in 
which a cylindrical plastic insert 60 is positioned within the counterbore 
50 of the forming sleeve 38. The plastic insert 60 is optional and may be 
used when it is desired to seal the openings 22 in the panels 12 and 14 
being fastened. 
To set the fastener 10 and clamp the two panels 12 and 14 together, the 
stem 28 is turned in one direction relative to the fastener body 20. The 
turning of the stem 28 relative to the fastener body 20 preferably is 
accomplished by applying a torque to the stem while holding the fastener 
body against rotational movement. Various conventional power driven 
installation tools having wrench bits may be used for setting and 
installing the fastener 10 in the appropriate manner. 
To cause turning of the stem 28, the wrenching flats 32 are engaged by the 
rotary wrench bit of an installation tool (not shown). Of course, 
wrench-engaging means other than flats 32 may be provided on the stem 28, 
as desired. To prevent turning of the fastener body 20 within the panels 
12 and 14 while the stem 28 is being turned, a drive nut 62 may be mounted 
on the stem 28 in abutment with the fastener body head 26. The drive nut 
62 has an outer surface 64 for engagement by a non-rotating fitting on the 
installation tool (not shown). Engagement between the contacting surfaces 
of the drive nut 62 and the fastener body head 26 prevents rotation of the 
fastener body 20 while the drive nut 62 is being held stationary by the 
installation tool. Alternatively, when a drive nut 62 is not used, the 
installation tool may engage recesses 66 in the fastener body head 26 to 
hold it against rotation. 
To install the fastener 10 of the present invention, the fastener is 
inserted into the aligned openings 22 in the two panels 12 and 14 until 
the fastener body head 26 is received against the outer surface 16 of the 
outer panel 12. The installation tool is moved axially onto the fastener 
10, with the non-rotating fitting engaging either the drive nut 62 or the 
fastener body recesses 66 to hold the fastener body 20 against rotation, 
and with the rotary wrench bit engaging the wrenching flats 32 and turning 
the stem 28 in one direction to set the fastener. As the stem 28 is 
rotated, the stem is moved in an axial outward direction through the 
fastener body 20. As the stem 28 moves axially outwardly, the stem head 30 
also urges the two-piece deformable sleeve 36 outwardly, causing the outer 
end 44 of the forming sleeve 38 to engage the tapered nose 26 and deform 
over the fastener body 20. Once the outer end 44 of the forming sleeve 38 
engages the blind side 18 of the inner panel 14, the forming sleeve 38 is 
bulged laterally until it reaches a fully set condition. 
In the fully set condition, shown in FIG. 4, the forming sleeve 38 is fully 
deformed against the inner panel 14, providing a relatively large bearing 
area of engagement. This large bearing area distributes compression forces 
over a wider surface area of the inner panel 14, to help prevent crushing 
or damage to the panel surface 18. The circumstance that the forming 
sleeve 38 is constructed from a relatively soft, deformable material also 
helps prevent damage to the panel surface 18, since the outer end 44 of 
the forming sleeve 38 more easily deforms to a set condition against the 
panel's inner surface 18. The counterbore 50 in the outer end 44 of the 
forming sleeve 38 also provides a thinner, more easily deformable 
structure that further helps prevent panel damage. 
Throughout setting of the fastener 10, however, the containment sleeve 40 
remains substantially undeformed. Since the containment sleeve 40 remains 
substantially undeformed and is constructed from high-strength materials, 
it can apply the highest possible clamping loads against the panels 12 and 
14. 
Thus, the use of the forming sleeve 38, which produces a large bearing area 
for wide distribution of compression forces against the panels 12 and 14 
using a relatively soft, deformable sleeve material, in combination with 
the containment sleeve 40, which applies high-strength clamping forces 
against the panels 12 and 14 by using a relatively hard, nondeformable 
sleeve material, enables the highest clamping loads to be applied against 
the panels without damage. 
From the foregoing, it will be appreciated that the present invention 
provides a blind fastener 10 for securing panels 12 and 14 made of 
composite or other relatively soft or lightweight materials in which high 
clamping loads may be achieved without damage to the panel surface. During 
setting of the fastener 10, the relatively soft forming sleeve 38 provides 
a large bearing area of engagement with the panel surface 18 to provide a 
wide distribution of compression forces. However, the containment sleeve 
40 does not deform, thereby providing the fastener 10 with the ability to 
apply the highest possible clamping loads to the panels 12 and 14. Thus, 
the fastener 10 of the present invention offers desirable features 
associated with the fastening of panels 12 and 14 made of composite 
materials, with the added features associated with fasteners ordinarily 
used only to fasten panels made of high strength materials. 
While a particular form of the invention has been illustrated and 
described, it will be apparent that various modifications can be made 
without departing from the spirit and scope of the invention. Accordingly, 
it is not intended that the invention be limited, except as by the 
appended claims.