Textured sleeves for fasteners

Abstract

A fastener adapted to be installed in a hole of a composite structure includes a sleeve, a pin member, and a locking member. The sleeve has an outer surface having an outer diameter. The outer surface of the sleeve is textured. The outer diameter of the tubular portion is less than an inner diameter of the hole of the structure. The pin member has a shank portion. The sleeve is adapted to expand radially over the shank portion of the pin member to form an interference fit between the outer surface of the sleeve and the hole of the structure so as to provide an installed position of the fastener. When the fastener is in the installed position, the texture of the outer surface of the tubular portion deforms to engage with voids of the composite material present on the inner surface of the hole.

Claims

1. A fastener, comprising: a sleeve having a tubular portion and an enlarged head at a first end of said tubular portion, said tubular portion having an inner surface having an inner diameter and an outer surface having an outer diameter, said outer diameter of said tubular portion being less than an inner diameter of a hole of a structure in which the fastener is adapted to be installed, said outer surface of said tubular portion being textured; a pin member having a first end, a second end opposite said first end of said pin member, an enlarged pin head at said first end of said pin member, a locking portion at said second end, and a shank portion between said first and second ends of said pin member, said shank portion having a diameter greater than said inner diameter of said sleeve; and a locking member adapted to fit over said locking portion of said pin member, wherein said sleeve is adapted to expand radially over said shank portion of said pin member to form an interference fit between said outer surface of said sleeve and the hole of the structure so as to provide an installed position of said fastener, wherein when said fastener is in said installed position, said texture of said outer surface of said tubular portion of said sleeve engages with voids present within the inner surface of the hole, and wherein said textured outer surface of said tubular portion of said sleeve has a surface roughness that is greater than or equal to about 1.4microns.

2. The fastener of claim 1, wherein said structure comprises a composite maters, and wherein said engagement of said texture of said outer surface of said tubular portion with the voids of the composite material displaces sealant from the voids of the composite material.

3. The fastener of claim 1, wherein said textured outer surface of said tubular portion of said sleeve has a surface roughness that is about 1.4 micron.

4. The fastener of claim 1, wherein said sleeve has a core hardness in a range from about 30 to about 35 on a Rockwell C hardness scale.

5. The fastener of claim 1, wherein said sleeve has an electrical conductivity that is greater than about 20% of an International Annealed Copper Standard.

6. The fastener of claim 1, wherein said sleeve has an anodic index less than about 0.65 V.

7. The fastener of claim 1, wherein said inner surface of said tubular portion comprises a low-friction coating, and wherein, when said fastener is in said installed position, a first coefficient of friction exists between said inner surface of said tubular portion of said sleeve and said shank portion of said pin member, a second coefficient of friction exists between said outer surface of said tubular portion of said sleeve and the inner surface of the hole of the structure, and said first coefficient of friction remains less than said second coefficient of friction when said shank portion of said pin member is moved within said sleeve.

8. The fastener of claim 1, wherein said locking member is a collar.

9. The fastener of claim 8, wherein said locking member includes a counterbore portion that is adapted to fit over said locking portion of said pin member and compress said sleeve around said pin member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an embodiment of a fastener including a pin member, a textured sleeve, and a collar;

(2) FIG. 2 illustrates the fastener shown in FIG. 1 installed within a plurality of work pieces;

(3) FIG. 3 is an isometric view of the exemplary textured sleeve of FIG. 1;

(4) FIG. 4 is a secondary electron imaging (“SEI”) photograph of an outer surface of the exemplary textured sleeve of FIG. 3;

(5) FIG. 5 is a photograph illustrating surface topography of an outer surface of the exemplary textured sleeve of FIG. 3;

(6) FIGS. 6A and 6B are SEI photographs illustrating intimate contact between the exemplary textured sleeve of FIG. 3 and a composite structure, while also illustrating the absence of micro-voids between the sleeve and the composite structure;

(7) FIG. 7 is a SEI photograph showing individual carbon fiber imprints on the outer surface of the exemplary textured sleeve of FIG. 3 illustrating micro-level conformance between the textured sleeve and the composite structure as the sleeve is deformed to fill the microscopic machining induced voids; and

(8) FIG. 8 is a SEI photograph of an outer surface of the exemplary textured sleeve of FIG. 3 after a lightning strike test.

DETAILED DESCRIPTION OF THE DRAWINGS

(9) Referring to FIGS. 1 and 2, in an embodiment, a fastener 10 includes a pin member 12, a textured sleeve 14, and a collar 16. In other embodiments, the fastener 10 may include a nut instead of a collar 16. In an embodiment, the fastener 10 is adapted to secure a plurality of work pieces 18, 20 to one another, and is adapted to be installed within aligned holes 22, 24 in such work pieces 18, 20. In an embodiment, the work pieces 18, 20 are formed of a composite material. In an embodiment, and except as noted herein, the fastener 10 has a structure and function that are, or are similar to, the structure and function of the fasteners disclosed in U.S. Pat. No. 7,695,226 to March et al., the entirety of which is incorporated by reference herein.

(10) In an embodiment, the textured sleeve 14 has a generally uniform tubular portion 26 that terminates in an enlarged flanged shaped head 28 to receive a head 30 of the pin member 12. In an embodiment, the sleeve 14 has an outer surface 32 and an inner surface 34. In an embodiment, the inner surface 34 has an internal diameter 36 that is greater than the outer diameters of a threaded portion 38 and a frangible portion 40 of the pin member 12, but less than the diameter of a smooth cylindrical shank portion 42 of the pin member 12. In an embodiment, the inner surface 34 of the sleeve 14 is coated with a low-friction coating. In an embodiment, the low-friction coating of the inner surface 34 provides a coefficient of friction between the inner surface 34 and the shank portion 42 of the pin member 12 that is less than a coefficient of friction between the outer surface 32 of the sleeve 14 and inner surfaces of the holes 22, 24 of the workpieces 18, 20.

(11) Referring to FIGS. 3, 4 and 5, in an embodiment, the outer surface 32 of the textured sleeve 14 is textured. In certain embodiments, the outer surface 32 of the sleeve 14 is textured in a variety of ways, such as by mechanical grit blasting, chemical etching, or a combination of both. In an embodiment, the following process is used to obtain a desired surface texture of the outer surface 32 of the textured sleeve 14: (1) Start with a sleeve. In an embodiment, the initial sleeve is a cold drawn A286 sleeve. (2) Grit blast the outer surface 32 of the sleeve 14. In an embodiment, the grit blasting utilizes fine grit glass bead media (100-170 mesh). In an embodiment, the grit blasting is performed until there is full coverage of the outer surface 32 of the sleeve 14. In an embodiment, the grit blasting is performed for about one minute. In another embodiment, the grit blasting is performed for at least one minute. In an embodiment, the grit blasting step is performed twice. (3) Chemical etch the sleeve 14. In an embodiment, the chemical etching utilizes 50/50 HCL. In an embodiment, the chemical etching is performed for about 30 minutes. (4) Rinse the sleeve 14. In an embodiment, the sleeve 14 is rinsed with distilled water for about 15-20 seconds. (5) Dry the sleeve 14. In an embodiment, the sleeve 14 is dried with forced, room-temperature air for approximately 1 to 2 minutes.
In certain embodiments, the textured sleeve 14 has the following characteristics: a) Surface roughness (Sa): greater than or equal to 1.4 micron. In another embodiment, the Sa is about 1.4 micron. b) Core hardness: in the range of 30 to 35 HRC on Rockwell C scale; c) Electrical conductivity: high electrical conductivity (higher than 20% of the International Annealed Copper Standard); and d) Corrosion resistance: galvanically compatible to composite structure (anodic index less than 0.65V).

(12) As the textured sleeve 14 is installed in the holes 22, 24 of the work pieces 18, 20, the textured sleeve 14 deforms into any small voids that are created during drilling of the composite work pieces 18, 20. As the textured sleeve 14 deforms into the voids, it displaces the entrapped sealant during installation of the fastener 10. The insertion of the pin member 12 causes the excess sealant to be extruded outside the sleeve/composite interface. Thus, the textured sleeve 14 excavates excess entrapped sealant during installation of the fastener 10 while bringing the textured sleeve 14 in intimate contact with the work pieces 18, 20 of the composite structure. The finished texture of the outer surface 32 of the textured sleeve 14 is adjusted to provide a surface micro-roughness (Sa) value greater than or equal to 1.4 micron in order to increase the level of conformity and mechanical interlocking.

(13) FIG. 3 shows an isometric view of the textured sleeve 14 including the textured outer surface 32 as described above. FIG. 4 shows a photograph of the textured outer surface 32 of the textured sleeve 14, taken using a scanning electron microscope in the secondary electron imaging (“SEI”) detection mode. FIG. 5 shows the surface topography of the textured outer surface 32 of the textured sleeve 14. As can be seen, the textured outer surface 32 of the textured sleeve 14 exhibits a substantially rough finish.

(14) Table 1 below lists the direct lightning test results obtained from the textured fasteners, which demonstrate that no evidence of arcing was detected with the textured exemplary sleeve fasteners:

(15) TABLE-US-00001 TABLE 1 Sleeve Fastener Fastener Fastener Fastener condition #2 #7 #12 #17 Textured OD No spark No spark No spark No spark surface

(16) FIGS. 6A and 6B are SEI photographs showing the non-existence of micro-voids between the textured sleeve 14 and the composite structure. Additionally, FIG. 7 is an SEI photograph illustrating imprints of individual carbon fibers clearly visible on the outer surface 32 of installed textured sleeves 14 indicating micro-level conformance and mechanical interlocking between the textured sleeve 14 and the panel hole as a result of micro level deformation of the textured sleeve 14. In an embodiment, the textured sleeve 14 provides intimate contact between the sleeve 14 and individual carbon fibers as it deforms to fill the microscopic machining induced voids. As the sleeve 14 deforms into the voids, it also displaces any sealant trapped inside these voids and gaps and brings the textured outer surface 32 of the textured sleeve 14 in intimate contact with the composite structure. This increased electrical contact along the textured outer surface 32 of the textured sleeve 14 decreases the current density and the voltage potential across the sleeve/composite interface by encouraging the current to be shared along the all contact surface. This allows a non-sparking current transfer from the fastener 10 to the structure and minimizes the dielectric effect caused by the sealant, thus mitigating the possibility of arcing between the textured sleeve 14 and the composite structure.

(17) Thus, the textured sleeved 14 can: 1—Minimize fastener arcing during lightning strikes; 2—Provide electrical contact between carbon fibers and fastener surface; 3—Provide gap filling and mechanical interlocking capabilities; and 4—Improve the conforming capabilities of fastener sleeve to the hole surface.

(18) It should be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention.