FASTENING DEVICE AND METHOD FOR COMPOSITE STRUCTURES

Abstract: Fastener installation in a composite panel, such as a graphite epoxy structure, having a longitudinal conductivity substantially greater than the transverse conductivity is achieved in a manner providing increased conductivity between fastener assembly and thepanel to which it is attached. A coned nut (30) and a counter-sink fastener (22) are utilized in a double countersink installation for electrically connecting two graphite epoxy laminate structures (12, 14) together, each countersink providing electrical connection to the longitudinal plies of the respective laminate structures.

Description: FASTENING DEVICE AND METHOD FOP COMPOSITE STRUCTURES This invention relates to improved fastener arrangements for composite structures such as shown in U.S. Patent Application Serial No. 333,248 filed September 30, 1981 and assigned to The Boeing Company. Graphite epoxy laminates are electrically aniso- trophic with electrical conductivity increasing in the direction of the fibers (longitudinally). Continuous fibers are available in a number of structures includinσ yarns or tows containing 400 to 160,000 individual fila¬ ments. Um-directional tapes and bi-directional fabrics at selected fiber orientations comprise a variety of graphite epoxy laminates. Efforts to electically con- nect m a transverse direction to the aforementioned laminate structures is generally precluded by the trans¬ verse electrical properties with resistance 200 to 1,^0 times greater than resistance in the longitudinal direc¬ tion of the laminate structure. Heretofore as shown in aforementioned U.S. Patent Application Serial No. 333,248, an insert device and locking nut were threaded on the shank portion of a fastener utilized to secure together a composite panel structure comprising a pair of graphite epoxy laminate panel members. It is, accordingly, an object of this invention to provide a locking nut structure for -threading to the shank portion of a fastener which locking nut structure mcludes a coned surface portion forming an angle of between 85° to about 150°. It is a further object of the present invention to provide means integral with a locking nut for making countersunk contact with a graphite epoxy laminate structure. It is yet another object of the present invention to provide a countersunk insert device having an integral locking nut portion for utilization in a double countersink fastener installation. It is still a further object of the present inven¬ tion to provide a coned locking nut having a cone angle of about 100° for utilization in making electrical con¬ tact between the shank portion of a fastener and a graphite epoxy laminate surface. A. full understanding of the invention, and of its further objects and advantages and the several uniσue aspects thereof, will be had from the following description when taken in conjunction with the acco - panymg sheet of drawings in which: FIGURE 1 is illustrative of a fastening device an method for composite structures as shown in π.s. Patent Application Serial No. 333,248 filed September 30, 1981 FIGURE 2 is a sectional view illustrative of an apparatus and method in accordance with a preferred embodiment of the present invention for providing increased conductivity between fastener and composite structure; FIGURE 3 is a top view of the self-locking coned nut shown in the composite assembly of FIGURE 2; OMPI r FIGURE 4 is a sectional view of the self-locking coned nut taken along the lines 4-4 of FIGURE 3; FIGURE 5 is a side view of the self-locking coned nut shown in FIGUPES 3 and 4, more clearly showing the angle made by the coned side surface portions of the self-locking coned nut; and, FIGURE 6 is a bottom view of the self-locking coned nut shown n FIGUPES 3, 4 and 5. Turning now to FIGURE 1, and comparing with FIGUPFS 2 and 4 of aforementioned U.S. Patent Application Serial No. 333,248, a countersunk insert device 20 is utilized to provide increased and improved conductivity between the shank portion 16 of a fastener and composite panel structure 12. Countersunk insert device 20, shown in FIGURE 1 of the present application and FIGURES 2 and 4 of the a orementioned patent application, are of tubular shape about the hole and comprise an upper frustro conical shaped portion and a lower shaped flange-like portion. A locking nut 18 is utilized to complete the securing of shank portion 16 of the fastener assembly to the graphite epoxy structure viz. panel member 12. Turning now to FIGURE 2, it will be noted that in a double countersunk fastener installation shown, the shank portion 16 of countersunk fastener 2? is secured to panel member 12 of a pair of composite panel members 12 and 14 instead of by means of insert device 20 and locking nut 18 as seen in FIGURE 1 by a locking nut 30 having a top-shaped hexagonal cross section portion 33 as seen also in FIGURE 3 to which a driving tool is attached for torquing during the installation process. It will also be seen that nut 30 includes a bottom coaxial frustro conically shaped body portion 35 (as also can be seen in FIGURE 5). It can be seen in FIGURE 5 that coaxial frustro conically shaped body portion 35 has external surfaces which are inclined at an angle of about 50° with respect to the central axis 60 of coaxial frustro conically shaped body portion 35. The total angle subtended by the inclined side surface portions of coaxially disposed frusto conically shaped body portion 35 subtend an angle of 100°. The angle subtended in FIGURE 5, while shown as 100°, may range from about ° to about 150°. The bottom surface 38, as seen in FIG¬ URES 4, 5 and 6, provides a tapered return surface to hexagonal cross-sectionally shaped driven end 33 of coned nut 30 m the present illustrative embodiment. It can, therefore, be seen that the present improved coned nut 30 is an improvement over the insert 20 and nut 1 °- m terms of minimum parts count and a provision for one less electrical interface for current flow. Phantom current flow lines are shown for the present coned nut embodiment of FIGURE 2 and also for the nut 18 and insert 20 assembly of FIGURE 1. As recognized earlier, and further recognized in co-pending Application Serial No. 333,248, electrical connection to the longitudinal plies of advanced ' composite panel structures such as graphite epoxy laminate panel members 12 and 14 is of cricital importance due to the transverse electrical electrical properties (200 to 1,000 times worse than longitudinal connection) as herein accomplished throuσh utilization of self-locking hexagonal self-aligning coned nut structure 30. A further distinct feature of the present embodiment includes the overcoming of the difficulty with respect to the critical countersink depth, denoted 100 in FIGURE 1, which is critical in that, if the depth is too great, then cylindricaily shaped flange-like portion 101 will have an inner sur¬ face which does not make contact with the lower surface of laminate panel member 12. This difficulty is over- come in the present embodiment coned nut structure 30 as seen m FIGURE 2. OMPI

Claims: What is claimed is: 1. In combination, an electrical connection between the shank portion of a fastener having a central axis extending in a first direction and conductive fibers of a composite structure extend- ing in a plane perpendicular to said central axis, said electrical connection comprising: a self-locking nut having a coaxial frusto conically shaped portion, said frustro conically shaped portion having an outer surface abutting said conductive fibers of said conductive structure. 2. The invention according to claim 1 wherein said outer surface of said coaxial frustro coni¬ cally shaped portion has an angle of inclination of about 50° with respect to the central axis of said coaxial frustro conically shaped portion. 3. The invention according to claim 1 wherein the opposite side surface portions of said coaxial frustro conically shaped portion subtend and angle between 85° and 100°. 4. A double countersink fastener installation for securing an electrical connection between first and second graphite epoxy laminate panel structures comprising in combination: o:..?l a fastener having a countersunk head disposed in said first graphite epoxy laminate panel struc¬ ture, said fastener having a titanium shank portion extending through said first and second graphite epoxy laminate panel structures, and a self-locking nut disposed about said titanium shank portion, said self-locking nut having a frustro conically shaped outer wall portion abutting an inner surface portion of said second graphite epoxy laminate panel structure. OY-FI _

Inventors: OLSON GLENN OLIVER, OLSON, GLENN, OLIVER
Applicants: BOEING CO, THE BOEING COMPANY
Application year: 1982
Main classification: H01R4
IPC codes: B64D45, H01R4