GB2180905A - Attaching fasteners to composite laminated members - Google Patents

Abstract

A fastener 10 for attachment to composite laminated panel 11 comprises a sleeve 27 with an expansible outer end 33 and a straight knurl 34 spaced from the outer end 33. A washer 12 of sintered metal powder has a knurled opening 35 complementary receiving the knurl 34 of the sleeve to prevent relative rotation of the sleeve 27 and washer 12. The end 37 of the knurl 34 of the sleeve 27 is expanded over the washer 12 to retain the washer 12 to the sleeve 27. An adhesive 48 secures the washer 12 to the panel 11. The density of the sintered metal powder may be greater at the knurl 35 to provide locally increased strength, and lesser outwardly of the knurl 35 to improve permeation of the adhesive 48 into the washer 12. <IMAGE>

Description

SPECIFICATION Fastener for aftachmentto a composite laminated member Frequently in the construction of aircraft and aerospace vehicles, as well as in many other items, it is necessary to attach a fastener to a workpiece, such as a panel. An example of this is found in U.S. patent No. 3,695,324, which provides a floating nut retained by a basket member, which is fixed to the workpiece by means of a sleeve that extends through an opening in the workpiece and is flared outwardlyto form a retaining flange. Rotation is prevented by a straight knurl on the outside of the sleeve, which embeds itself into the surface of the workpiece around the opening as the sleeve isforced into the opening.This is satisfactory for metal workpieces, but is not suitable when the workpiece is of a non-metallic composite laminated material, such as a panel made of graphite and fibre laminations. The cutting of the wall ofthe opening in the panel bythe knurl ofthe fastener is not acceptable because it will tend to cause delamination and will resultin a prematurefailure.Therefore,a problem has existed in attaching fasteners to composite laminated panels or other composite laminated members.

The aim of the present invention is to provide a strong and simple arrangementfor attaching a fastenerto a composite laminated member, overcoming the difficulties ofthe prior art.

According to one aspect of this invention, a fastenerfor attachment to a composite laminated member comprises; a screw threaded element; a sleeve attached to and extending away from the screw threaded element, the sleeve being adapted to extend through an opening in the member and having an outwardly bendable end adapted to form a flange for engaging the memberononesidethereof, and abutment means spaced from the end; and awasherofsintered metal adapted to be bonded to the member on the other side thereof, the washer having an opening receiving the sleeve, and having, at its opening abutment means engaging the abutment means of the sleeve to prevent rotation ofthe sleeve relative to the washer.

The invention also consists, according to another of its aspects in a non-metallic laminated member having an opening therein in combination with a fas tenerfixed to the member, the fastener comprising; a fastener element, a washer, having an opening in registry with the opening in the non-metallic laminated member, the fastener element and the washer including interengaged abutment means preventing rotation ofthe fastener element relative to the washer, and adhesive means securing the washerto the memberto prevent rotation of the washer and hence of the fastener element relative to the member.

The abutment means may comprise a straight knurl which is provided in the opening ofthewasher and is complementary to a knurl on the sleeveoron the fastener element. Therefore, when the fastener sleeve or element is inserted into the washer, itwill not rotate relative to the washer.

Rotation of the fastener assembly is precluded by the bonding or other adherence of the washer to laminated member. This may be accomplished through the use of an epoxy resin, which securely holds the washerto the laminated member so that the washer cannotturn. This will prevent rotation of a nut part of the fastener when a bolt is inserted into the fastener.

To provide resistance to elevated temperatures, as well as adequate strength, it is desirable to use titanium as the material forthewasher. However, itis quite difficult to bond titanium because it is very resistantto etching and general chemical attack by the bonding materials. This may be overcome by making the washer of sintered powdered metal. The resulting porosity enables itto acceptthe bonding material and form a secure attachment to it. In making the washer of powdered titanium, it is preferred to provide a relatively high density of metal particles around the opening, where the knurl or other abutment means ofthe washer is located, and a lower density at peripheral locations remote from the abutment means.The higher density portion of the washer will betterwithstand the torque imposed upon it when the fastener is in service. On the other hand, the lower density portions of the washer, outwardly of the abutment area, are especially porous and receptive to the adhesive, helping to provide a particularly strong attachment and torque resistance as the washer is bonded to the laminate member.

An example of a fastener in accordance with the invention is illustrated in the accompanying drawings, in which; Figure 1 is an exploded perspectiveviewofthefas- tener and of a panel to which the fastener is to be fixed; Figure2 is a longitudinal sectional view to a larger scale of the fastener fixed to the panel; Figure 3 is a fragmentary sectional view to a still larger scale showing part of the fastener fixed to the panel; Figure4is aviewsimilarto Figure 3, but showing a slightly different part of the fastener and panel; and FigureS is a fragmentary perspective view of a washerforming part of the fastener.

In the example given, a fastener loins secured to a panel 11 and held against rotation by a washer 12.

The panel 11 is a composite material, such as a graphite fibre laminate as used in high performance aircraft. The fastener 10 is a floating rivetless nutplate of the type disclosed in U.S. patent No. 3,695,324.

This fastener includes a basket 13, having a flat base 14through which is a central circular opening 15. Op posed upstanding flangesl6and 17projectfromthe base 14 and are provided with slots 18 and 19.

The fastener 10 also includes a nut21, having a threaded bore 22 and a base 23 from which project tabs 24 and 25. The latter elements are dimensioned to fitwithin the slots 18 and 19 in the flanges 16 and 17 with some clearance, which allows the nut 10to float a limited distance relative to the basket 13.

Beneath the nut 21 is a sleeve 27, which has a flat head 28 at one end that overlaps the base 14 of the basket. Tabs 30 and 31 project from opposite edges of the head 28, entering the slots 18 and 19 beneath the tabs 24 and 25 ofthe nut 21. This prevents substantial relative rotation of the sleeve 27 and basket 13. The cylindrical portion 32 of the sleeve 27 extends through the opening 15 in the base 14 of the basket.

The outer end portion 33 of the sleeve has a relatively thin wall to permit itto be flared outwardly in securing thefastenerto the panel, as explained below.

Adjacent to head 28, the wall ofthe sleeve is thicker and on the outside is provided with a straight knurl 34. The lobes of the knurl 34 may be rounded.

The washer 12 is ofsintered powdered titanium. It includes a central opening 35, which, rather than being circular, is contoured to define a straight knurl complementary to the knurl 34 on the sleeve 27.

Rounded lobes of the knurl avoid stress risers. On oneface 36 ofthewasher 12, around the opening 35, is a narrow shallow indentation, providing an an nularradialsurface37 (Figures3and5).

Outwardly ofthe opening 35, the washer 12 has opposite parallel straight side edges 38 and 39, and parallel end edges 40 and 41,which are atrightan- glesto the edges 38 and 39. At the corners ofthe washer 12 are outwardly projecting ears 42,43,44 and 45 which are rounded on their outer edges. The side edges 38 and 39 ofthe washer are longerthan the end edges 40 and 41,so that the washer is slightly elongated in one direction.

The washer 12 is assembled with the fastener 10 by extending the cylindrical part 32 of the sleeve 27 through the opening 35 ofthe washer. The parts are aligned sothatthe longer dimension ofthewasher extends between the flanges 16 and 17 of the basket 13. The knurl 34 of the sleeve 27 fits closely within the complementary opening 35 of the washer 12. The indentation 37 ofthe washer is positioned on the outer side, facing awayfrom the basket 13. With the washer 12 engaging the undersurface of the base 14 of the basket 13, the end of the knurl 34 of the sleeve 27 extends a short distance beyond the radial surface ofthe indentation 37 ofthewasher, as seen in Figure 4.In order to proviee a unitary fastener assembly and assure thatthe fastener and washer staytogether, the end ofthe knurl 34then is expanded outwardly to slightly overlap the recessed surface ofthe indentation 37 ofthe washer, as shown in Figure 5. This holds the washer 12 to the fastener 10. The expanded knurl end does not project past the principal flatsurface 36 ofthewasher.

The panel 11 is provided with an opening 46, gene rally complementary to the outer end portion ofthe sleeve 27 beyond the knurl 34. A countersink 47 is provided at one end ofthe opening 44.

Priorto attachmentofthefastenerandwasherto the panel 11, a quantity of adhesive 48, such as catalyzed epoxy resin, is applied to the undersurface of the washer 12. The outer portion of the sleeve 27 then is extended through the opening 46 and its end is flared outwardlyto form a flange 49 that overliesthe countersink 47 and secures the sleeve to the panel.

As this is done, an axial force is imposed on the fastener assembly, pressuring the base 14 of the basket 13 againstthe washer 12 and the washer, in turn, againstthe panel 11. This may be accomplished by the use of a tool such as disclosed in U.S. patent No.

3,665,581,which has a pullerthatengagesthethrea- ded bore ofthe nut while the bending of the flange of the sleeve takes place. This provides a clamping action as the flange is bent, which assures that a strong bond takes place between the washer 12 and the panel 11 as the adhesive 48 cures. No auxiliary clamping device is required. Excess, adhesive squeezes out from underthe washer and lies along the edges of the washer, as seen in Figure 2.

The resulting arrangement is a very effective means of securing a fastenerto a workpiece such as a composite laminated panel, without in anyway dam- aging the panel All of the torque forces imposed on the fastener are transmitted through the knurled areas of the fastener and the washer. Thus, the two knurls form abutments that will not permit rotation of the fastener relative to the washer. Atthe sametime, the bonded connection between the washer 12 and the panel 11 prevents rotation of the washer relative to the panel under even the most severe load conditions.

The effectiveness of the bonding and the resistance to torque-out forces can be enhanced by controlling the density of the powdered metal the makes up the washer 12. The density of powdered metal particles is greater around the opening 35 atthe area ofthe knurl than it is at the peripheral parts ofthe washer. This means that the washer 12 is particularly strong at the knurl wheretorque loads are applied when a bolt enters the nut 21. At the same time, the peripheral parts of the washer have greater porosity resuiting from the lesser density of powdered metal.

This promotes the penetration ofthewasherbythe adhesive to effect a strong bond. The maximum adhesion of the washer 12 to the panel 11 thus is provided at locations outwardly of where the torque loads are applied, where resistance to rotation ofthe washer is most effective. The outwardly projecting ears 42,4344 and 45 space attaching areas of the washer away from the central openings to maximize torque resistance while minimizing the weight of the washer.

Claims (17)

1. Afastener for attachment to a composite laminated member, the fastener comprising; a screwthreaded element; a sleeve attached to and extending away from the screwthreaded element, the sleeve being adapted to extend through an opening in the member and having an outwardly bendable end adapted to form a flange for engaging the member on one side thereof, and abutment means spaced from the end; and awasherofsintered metal adapted to be bonded to the member on the other sidethereof, the washer having an opening receiving the sleeve, and having, at its opening abutment means engaging the abutment means ofthe sleeve to prevent rotation ofthe sleeve relative to the washer.

2. Afastener according to claim 1, in which the washer is ofsinteredtitanium.

3. Afastener according to claim 2, in which the sintered titanium is of greater density at its abutment means than it is remote from its abutment means.

4. Afasteneraccording to any one of claims 1 to 3, in which the abutment means of the sleeve is a straight knurl, and the abutment means ofthe washer is a straight knurl complementaryto the straight knurl of said sleeve, the knurl of the sleeve having an end which extends beyond the opening in the washer on one side of the washer and is expanded outwardly over the washer for retaining the washerto the sleeve.

5. Afastener according to claim 4, in which the washer has a principal flat surface on its one side, and a recessed surface inwardly of the principal flat surface, the end of the knurl of the sleeve being expanded overthe recessed surface so the expanded part of the knurl ofthe sleeve does not project beyond the principal flat surface.

6. A non-metallic laminated member having an opening therein in combination with a fastenerfixed to the member, the fastener comprising a fastener element, a washer, having an opening in registry with the opening in the non-metallic laminated member, the fastener element and the washer including interengaged abutment means preventing rotation ofthe fastener element relative to the washer, and adhesive means securing the washer to thememberto prevent rotation of the washer and hence of the fastener element relative to the member.

7. The combination according to claim 6, in which, to form the abutment means, the washer has a non-circular opening, and the fastener element includes a portion extending into the opening in the washer, the portion being non-circular and com plementarytotheopening in the washer.

8. The combination according to claim 7, in which the wall of the non-circular opening in the washer is formed as a straight knurl, and the portion of the fastener element extending into the opening in the washer includes a straight knurl meshed with the knurl ofthewasher.

9. The combination according to claim 8, in which the knurls have rounded lobes.

10. The combination according to claim 8 or claim 9 in which the fastener element has a surface engaging one side of the non-metallic laminated member adjacent its opening, the knurl ofthe fastener element extending beyond the face of the washer remote from the element and being displaced outwardly over said surface of the washer toretain the washerto the fastener element.

11. The combination according to any one of claims 6 to 10, in which the washer is made of sintered powdered metal.

12. The combination according to claim 11, in which the metal is titanium.

13. The combination according to claim 11 or claim 12, in which the washer has a greater density of metal particles at the abutment means thereof than it has remote from the abutment means.

14. The combination according to any one of claims 6 to 13, in which the adhesive means is an epoxy resin interposed between the washer and the member.

15. The combination according to anyone of claims 6 to 14, in which thewasher hasoutwardly projecting portions on its outer edge.

16. Afastener according to claim 1, substantially as described with reference to the accompanying drawings.

17. The combination according to claim 6, sub stantiallyas described with reference to theac- companying drawings.