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Title:
FASTENER AND METHOD OF ATTACHING HARDWARE TO FIBER REINFORCED PLASTIC/HONEYCOMB CORE PANELS
Document Type and Number:
WIPO Patent Application WO/2007/146108
Kind Code:
A3
Abstract:
A fastener insert for use with fiber reinforced plastic honeycomb core panels eliminates the need for potting compounds to retain the insert within the panel. Instead, the insert utilizes structural components which engage the top and bottom fiber reinforced panel skins, resulting in high shear and pull-out values for the panel construction. The fastener insert comprises a cap member, a plug member, and a connector member which may float laterally to allow for fastener misalignment. The cap member is adhesively attached to the upper surface of the bottom skin of the composite panel. The plug member fits and slides into the cap member. The plug member attaches to the cap member, such as by utilizing pressure activated adhesives. Upon installation, the plug member attaches to the top skin of the composite panel. These members may comprise pressure activated adhesive for bonding the members to the panel skin or to each other. The configuration of the plug member and the cap member may allow the installed height of the apparatus to adjust as required variations in overall panel thickness typical of the FRP/honeycomb panel construction.

Inventors:
PINEIROS VICTOR M (US)
WAITS BOBBY LAMAR (US)
SCHEPERGERDES WILHELM (US)
Application Number:
PCT/US2007/013485
Publication Date:
October 23, 2008
Filing Date:
June 07, 2007
Export Citation:
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Assignee:
PINEIROS VICTOR M (US)
WAITS BOBBY LAMAR (US)
SCHEPERGERDES WILHELM (US)
International Classes:
F16B37/04
Foreign References:
US3434261A1969-03-25
US3179143A1965-04-20
Attorney, Agent or Firm:
DUNCAN, James, M. (DeNatale Goldner, Cooper, Rosenlieb & Kimball, LLP,P.O. Box 1117, Bakersfield CA, US)
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Claims:
What is claimed is:

1. An apparatus for providing a hardened attachment point in a fiber reinforced plastic honeycomb core panel, the panel comprising a top skin and a bottom skin in parallel spaced apart facing relation, the panel further comprising a honeycomb core structure bounded between the bottom surface of the top skin and the upper surface of the bottom skin, the panel further comprising a blind aperture penetrating through the top skin, said blind aperture extending through the honeycomb core structure and terminating at the upper surface of the bottom skin, the apparatus comprising: a cap member, the cap member comprising an abutment end and a receiving end, the receiving end comprising an opening, and the abutment end comprising a first surface which abuts the upper surface of the bottom skin upon installation of the apparatus into the blind aperture, the first surface comprising an adhesive for bonding the cap member to the upper surface of the bottom skin; a plug member, the plug member comprising a cap attachment end and a top skin attachment end, the plug member further comprising an axial opening extending from the cap attachment end to the top skin attachment end, wherein the cap attachment end is received by the opening in the receiving end of the cap member, the cap attachment end comprising means for attaching to the cap member and the top skin attachment end comprising means for attaching to the top skin; and a connector member, the connector member comprising threads for attachment of a threaded fastener, the connector member retained within the axial opening of the plug member with retaining means, said retaining means

allowing limited lateral movement of the connector member with respect to the plug member.

2. The apparatus of claim 1 wherein the means for attaching the cap attachment end of the plug member to the cap member comprises a pressure activated adhesive.

3. The apparatus of claim 1 wherein the plug member is generally cylindrical in shape.

4. The apparatus of claim 3 wherein the exterior wall of the plug member has a first diameter at the cap attachment end and a second diameter at the top skin attachment end.

5. The apparatus of claim 4 wherein the first surface comprises a rib member.

6. The apparatus of claim 5 wherein the top skin attachment end comprises a peripheral attachment surface which abuts the bottom surface of the top skin upon installation of the apparatus.

7. The apparatus of claim 6 wherein the means for attaching the top skin attachment end of the plug member to the top skin comprises an adhesive which, when cured, bonds the peripheral attachment surface to the bottom surface of the top skin.

8. The apparatus of claim 6 wherein the top skin attachment end further comprises a sleeve member bounding the peripheral attachment surface, the sleeve member extending through the top skin.

9. The apparatus of claim 1 wherein the connector member comprises internal threads configured to receive a male fastener.

10. The apparatus of claim 1 wherein the connector member comprises external threads configured to receive a female fastener.

11. The apparatus of claim 1 wherein the receiving end of the cap member comprises a plurality of locking members.

12. The apparatus of claim 11 wherein the plug member comprises two or more axially extending engagement members which each engage a respective locking member.

13. The apparatus of claim 12 wherein the connector member comprises laterally extending ear members which are each respectively bounded by the axially extending engagement members thereby limiting rotation of the connector member with respect to the plug member.

14. The apparatus of claim 1 wherein the cap attachment end of the plug member comprises two or more axially extending engagement members, wherein each engagement member comprises a laterally extending clip member.

15. The apparatus of claim 14 wherein the receiving end of the cap member comprises an inwardly facing lip member which engages the laterally extending clip members thereby allowing axial movement of the plug member with respect to the cap member but inhibiting withdrawal of the plug member from the cap member once the cap engagement end of the plug member has been placed within the cap member.

16. An apparatus for providing a hardened attachment point in a fiber reinforced plastic honeycomb core panel, the panel comprising a top skin and a bottom skin in parallel spaced apart facing relation, the panel further comprising a honeycomb core structure bounded between the bottom surface of the top skin and the upper surface of the bottom skin, the panel further comprising a blind aperture penetrating through the top skin, said blind aperture extending through the honeycomb core structure and terminating at the upper surface of the bottom skin, the apparatus comprising: a cap member, the cap member comprising an abutment end and a receiving end, the receiving end comprising an opening, and the abutment end comprising a first surface which abuts the upper surface of the bottom skin upon installation of the apparatus into the blind aperture, the first surface comprising an adhesive for bonding the cap member to the upper surface of the bottom skin, the receiving end of the cap member comprising an inwardly facing lip member; a plug member, the plug member comprising a cap attachment end and top skin engagement end, the plug member further comprising an axial opening extending from the cap attachment end to the top skin attachment end, wherein the cap attachment end is received by the opening in the receiving end

of the cap member, the top skin attachment end comprising means for attaching to the top skin; the cap engagement end comprising two or more axially extending engagement members, wherein each engagement member comprises a laterally extending clip member, wherein once the plug member has been inserted into the cap member, the inwardly facing lip member of the cap member limits axial movement of the plug member with respect to the cap member by engaging the axially extending engagement members; and a connector member, the connector member comprising threads for attachment of a threaded fastener, the connector member retained within the axial opening of the plug member with retaining means, said retaining means allowing limited lateral movement of the connector member with respect to the plug member.

17. The apparatus of claim 16 wherein the cap attachment end of the plug member comprises a pressure activated adhesive which, when cured, affixes the plug member to the cap member thereby preventing axial movement of the plug member with respect to the cap member.

18. The apparatus of claim 16 wherein the plug member comprises a axially extending cavity outwardly concentric to the axial opening.

19. A method of creating a hardened attachment point in a fiber reinforced plastic honeycomb core panel, the panel comprising a top skin and a bottom skin in parallel spaced apart facing relation, the panel further comprising a honeycomb core structure

bounded between the bottom surface of the top skin and the upper surface of the bottom skin, the method comprising the steps of: creating a blind aperture in the panel, wherein the blind aperture penetrates through the top skin, extends through the honeycomb structure, and terminates at the upper surface of the bottom skin; removing any debris from the blind aperture; placing an apparatus into the blind aperture, the apparatus comprising: a cap member, a plug member and a connector member assembled in cooperative arrangement, wherein the cap member comprises a pressure activated adhesive which, when cured, bonds the cap member to the upper surface of the bottom skin, and the plug member comprises members which, upon insertion of the apparatus into the aperture, extend outwardly and engage the bottom surface of the top skin; manipulating the apparatus as necessary to provide the necessary relative movement between the cap member, the plug member and the connector member to adjust for the thickness of the panel; and allowing sufficient time for the pressure activated adhesive to cure.

Description:

PATENT APPLICATION TITLE: Fastener and Method of Attaching Hardware to Fiber Reinforced Plastic/Honeycomb Core Panels

INVENTORS: Victor M. Pineiros; Bobby Lamar Waits; Wilhelm Schepergerdes Cross-Reference To Related Application: U.S. Provisional Application No.

60/811,928 for this invention was filed on June 8, 2006 for which the inventors claim domestic priority.

BACKGROUND OF THE INVENTION

[0001 ] The present invention relates to an apparatus and method for creating hardened attachment points for fiber reinforced plastic (FRP) honeycomb core panels. Such panels may comprise a sandwich structure having top skin and a bottom skin with an intermediate honeycomb core. Among other places, such honeycomb sandwich panels are disclosed in United States Patent Nos. 6,267,838 Bl and 6,743,497 B2.

[0002] Hardened attachment points are often necessary for composite panels typically found on overhead stow bins, galleys or lavatories in commercial aircraft. For example, attaching a hinged access door to an overhead bin made out of composite panel requires such a hardened attachment point for hinges or latching mechanisms. However, the presently disclosed apparatus and method is not limited to such application but may also be used in aerospace construction where it is necessary to attach hardware to a FRP honeycomb core panel construction. Floating inserts feature a threaded connector component which moves to compensate for misalignment of the corresponding fastener.

[0003] In aircraft, inserts are potted or mechanically installed in sandwich material, like honeycomb, to allow fabrication of interior secondary structures of the aircraft, such as stow bins, galleys, and lavatories. Floating inserts feature a nut component that can move to compensate for misalignment of the screw.

[0004] A current practice for providing hardened attachment points is to utilize metallic or non-metallic inserts which are potted in composite panels. The potting compound is typically a two part epoxy type filler material which is soft and pliable in the as-mixed condition, but cures and hardens at room temperature or at elevated temperatures if it is oven cured. After a hole has been drilled into the FRP/Honeycomb core panel, debris is removed and the hole is partially filled with potting compound. The insert is then pressed into the partially filled hole and additional potting compound injected into the cavity until potting compound extrudes from the out-gassing holes of the insert. The insert is held in place during the potting and curing cycles by means of an adhesive tab glued to the outer skin of the panel.

[0005] The potting process is time consuming and unreliable because it depends on the operator's ability to completely fill a cavity invisible from the outside. The curing cycle causes additional problems because it is an exothermic process and generated gases escape from the mixture. In many instances the out-gassing pressures are high enough to push the inserts out of position, causing rejections and rework.

SUMMARY OF THE INVENTION

[0006] The presently disclosed apparatus and method eliminate the need for potting compounds to create hardened attachment points. Instead, the disclosed apparatus and method utilize features in which components of the insert engage the top and bottom fiber reinforced panel skins, resulting in high shear and

pull-out values for the panel construction. The disclosed apparatus and method takes advantage of the typical FRP/honeycomb panel construction which has fiber reinforced resin composite top and bottom skins with a honeycomb core sandwiched between the skins. The high mechanical properties of the panels are mostly derived from the strength of the top and bottom skins being structurally spaced by the honeycomb core.

[0007] The apparatus comprises three basic elements, being the cap member, the plug member, and the connector member which may float laterally to allow for fastener misalignment. The cap member is adhesively attached to the upper surface of the bottom skin of the composite panel. The plug member fits and slides into the cap member. The plug member attaches to the cap member, such as by utilizing various adhesives, such as a pressure activated adhesives. Upon installation, the plug member attaches to the top skin of the composite panel. For example, structural members of the plug member may snap under the top skin of the composite panel. These members may further comprise adhesive which bonds the plug member to the top skin of the panel. In an embodiment of the apparatus, the relationship between the plug member and the cap member, and geometry of these two elements allows the apparatus to adjust its installed height to compensate for variations in overall panel thickness typical of the FRP/honeycomb panel construction. [0008] The apparatus further comprises a threaded connector member, which may be either male or female and which may float within the apparatus. The threaded connector member is located between the plug member and the cap member and structurally retained while floating within the assembly. The threaded connector member receives and engages a corresponding sleeve nut or screw. The capacity of

the threaded connector member to float within the assembly compensates and adjusts for location tolerances or mismatch between the structural elements being joined.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 shows a perspective view of an embodiment of the components of the apparatus showing internal detail of the cap member.

[0010] Figure 2 shows a perspective view of an embodiment of the components of the apparatus showing detail of the plug member.

[0011] Figure 3 shows a perspective view of an embodiment of the components of the apparatus wherein the connector member has male threads.

[0012] Figure 4 shows a perspective view of an embodiment of the three components of the apparatus in an assembled configuration.

. [0013] Figure 5 shows a sectional view of the embodiment shown in

Figure 4.

[0014] Figure 6 shows a sectional view of an embodiment of the assembled apparatus having internal threads installed within a FRP/honeycomb panel.

[0015] Figure 7 shows a sectional view of an embodiment of the assembled apparatus having external threads installed within a FRP/honeycomb panel.

DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION [0016] Referring to Figure 1 and Figure 2, an embodiment 10 of the apparatus comprises a cap member 12, a plug member .14, and a connector member 16. The materials used for fabrication of these components should be of the type suitable for application in FRP/honeycomb panels utilized in aircraft, such as thermoplastic materials. As shown in the sectional views in Figure 6 and Figure 7,

these panels comprise a top skin 18 and a bottom skin 20 in parallel spaced apart facing relation. The panels further comprise a honeycomb core structure 22 bounded between the bottom surface 18 ' of the top skin 18 and the upper surface 20' of the bottom skin 20. The term "top" used herein references the side of the panel which is utilized for placement of the hardened attachment point, with other terms used with respect to the "top" as defined. The panel further comprises a blind aperture 24 which penetrates through the top skin 18 and extends through the honeycomb core structure 22 and terminates at the upper surface 20' of the bottom skin 20. One feature of the disclosed apparatus is that the components of the insert engage both the top and the bottom fiber reinforced panel skins.

[0017] Cap member 12 comprises an abutment end 26 and a receiving end 28, which comprises an opening. The abutment end 26 comprises a first surface 30 which, upon installation of the apparatus into the blind aperture 24 of a panel, abuts the upper surface 20' of the bottom skin 20, as shown in Figure 6 and Figure 7. The first surface 30 comprises an adhesive which bonds the cap member 12 to the upper surface 20' of the bottom skin 20. Suitable adhesives comprise pressure activated adhesives, light activated adhesives, heat activated adhesives and two-part adhesives. Cap member 12 may be a molded component of a cylindrical shape. As shown in Figure 5, abutment end 26 may comprise a rib structure 40 to provide the necessary spacing for a pre-applied or otherwise placed pressure activated adhesive.

[0018] As shown Figure 1 , the receiving end 28 of the cap member 12 is shaped to receive and mate with the plug member 14. The receiving end 28 has an opening which is dimensioned to receive the male portion of the plug member 14, the male portion hereinafter referred to as the cap attachment end 32. The dimensions of the mating portions of cap member 12 and plug member 14 are configured to allow

adjustment of the overall length of the assembly to correspond to the thickness of the sandwich panel during the installation process. The end of the plug member 14 opposite from the cap attachment end 32 is referred to herein as the top skin attachment end 34. As shown best in Figure 1 and Figure 2, the plug member 14 may comprise two or more two or more axially extending engagement members 48. The axially extending engagement members 48 may further comprise laterally extending clip member 50. The receiving end 28 of the cap member 12 may comprises an inwardly facing lip member 52 which engages the laterally extending clip member 50 thereby allowing axial movement of the plug member with respect to the cap member but inhibiting withdrawal of the plug member 14 from the cap member once the cap attachment end 32 of the plug member has been placed within the cap member. [0019] When installed in a panel, the top skin attachment end 34 will be generally flush with the top skin 18. The plug member 14 has an axially-aligned opening 36 extending from the cap attachment end 32 to the top skin attachment end 34. The cap attachment end 32 attaches to the cap member 12. The means for attachment may be made mechanically with an interference fit between the cap attachment end 32 and the receiving end 28 of the cap member. Preferably, the internal surfaces of the cap member 12 may utilize an adhesive such that the cap member 12 and the plug member 14 are solidly joined together when the adhesive cures. Suitable adhesives comprise pressure activated adhesives, light activated adhesives, heat activated adhesives and two-part adhesives. The internal surfaces of the cap member 12 and/or plug member 14 may have air venting slots to prevent hydraulic lock of the adhesive during installation.

[0020] The plug member 14 may be a molded component of a cylindrical shape with an axially extending concentric cavity 42 within the cylinder

which allow deflection of the outside cylinder wall to allow sufficient flexibility for the assembly to pass through the internal diameter of the aperture 24 and then spring back and snap in place to permanently captivate the entire assembly 10 between the top skin 18 and a bottom skin 20 of the sandwich panel. The axially extending cavity 42 is outwardly concentric to axially-aligned opening 36 and is best shown in Figure 5 and Figure 6. The captivation may be improved by utilizing a pre-applied pressure activated adhesive on top skin attachment end 34 which comes in intimate contact with the bottom surface 18' of the top skin 18. The internal portion of the plug member is configured to accommodate and capture a floating threaded connector member 16.

[0021] As shown in Figure 1 and Figure 2, plug member 14 may have a first diameter at the cap attachment end 32 and a second diameter at the top skin attachment end.34, such that the plug member has a tapered configuration. The top skin attachment end 34 may comprise a peripheral attachment surface 38 which abuts the bottom surface 18' of the top skin 18 upon installation of the apparatus. Suitable adhesives, such as a pre-applied pressure activated adhesive, may be pre-applied to the peripheral attachment surface 38. The top skin attachment end 34 may further comprise a sleeve member 40 which bounds the peripheral attachment surface 38. As best shown in Figure 5, the sleeve member 40 may comprise axially extending slots 44 to increase the flexibility of the plug member 14. As shown in Figure 6, sleeve member 40 extends through the top skin 18 and may be flush with the exterior surface of the top skin.

[0022] The threaded connector member 16 is of either male or female configuration depending on the particular embodiment of the invention. As shown in Figure 1 , the threaded connector member 16 may have internal threads 46 for

receiving a male fastener. Alternatively, as shown in Figure 3, the threaded connector member 16' may have external threads 46' for receiving a fastener 48 having internal threads (not shown). The connector member 16 is retained within the axially-aligned opening 36 of plug member 14. The connector member 14 has sufficient free lateral movement or "float" necessary to compensate for location tolerances or mismatch of the elements being attached to the invention. As best shown in Figure 2, the connector member 16 may comprise laterally extending ear members 54. The ear members 54 are bounded by the axially extending engagement members 48 which limit rotation of the connector member 14 with respect to the plug member 14. [0023] Installation of the disclosed apparatus requires a that a blind aperture be created in the FRP/honeycomb core panel by drilling or other means. If the aperture is created by drilling or similar means, debris is removed from the cavity and then the apparatus inserted into the aperture. Fastener insertion can be accomplished by hand or by means of an installation tool capable of applying the driving force necessary to introduce the fastener in to the hole, provide relative movement between the components to adjust for panel thickness variations, snap it in place and complete the installation. When the installation is completed, the fastener shall be allowed sufficient time for any adhesives bonding the various components of the apparatus to cure and harden. Creation of the hole, debris removal and placing of the fastener can be an automatic process by using current CNC machining technology.

[0024] While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. Thus the scope of the invention should not be limited according to these factors, but according to the claims to be filed in the forthcoming utility application.