In the construction of aircraft, fuselage and skin panels must be connected to aircraft frame struc¬ tures. Traditionally, this has been done by means 5 ^" of rivets. In order to strengthen these skin panels as well as reduce their weight and radar cross section, they have been fabricated from advanced composite materials, such as graphite and epoxy. Such a composite is made up from epoxy impregnated 0 graphite fibers, and during panel assembly the boring αf rivet holes in such materials weakens the fiber structure and decreases the composite panel strength and fatigue resistance. _ .

In order to avoid this problem, the prior art has included methods for attaching composite panels to aircraft frame structures which involve expensive adhesive bonding. Although adhesives have been for¬ mulated to perform satisfactorily, the expense is considerable and the attachment procedures are time 0 consuming. Accordingly, it is desirable to provide the aircraft industry with a more expeditious and inexpensive means for connecting composite panels than currently available.

The present invention is directed to a con- 5 nector fabricated of memory metal alloy for attaching first and second members, which comprises a bifurcated edge having cross-sectional tines for engaging a mating enlarged edge of the first member during a first temperature condition and contracting during a Q second temperature condition thereby clamping the enlarged edge therebetween and an edge opposite the bifurcated edge for fastening the second member thereto.

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Furthermore, the present invention provides a method for securing a panel to a structural member comprising the steps of forming an enlarged edge on the panel and forming a bifurcated edge on a connector made of memory metal alloy for receiving the enlarged edge of the panel when subjected to a first temperature condition. Thereafter the method includes subjecting the- connector to a second temperature condition causing contraction of the bifurcated edge thus clamping the enlarged panel edge thereto and fastening the structural member to the connector.

The present invention utilizes connectors fabricated from memory metal .alloys to achieve a clamping connection between advanced composite materials and structural frame members.

Memory metal alloys are currently available and typically include brass alloys with high yield strength of over 50,000 psi, and Ni-Ti alloys of over 100,000 psi. The inventive connector may be charac- terized as an extruded rail of memory metal alloy having an elongated flange which is appropriately connected to an aircraft frame structure while a free bifurcated edge- is thermally deformed to engage and clamp a mating enlarged edge of a composite panel. Upon thermal defor- mation of the memory metal rail, the enlarged edge of the panel becomes securely clamped within the bifurcated edge of the memory metal connector to ensure a strong, sealed and more fatigue-resistant connection achieved in an expedient and inexpensive manner. Accordingly, the present invention offers a superior alter¬ native to riveting or adhesive bonding as practiced by the prior art.

It is to be emphasized that, although the present invention is discussed in terms of application to aircraft, the invention is not so limited. The connection device of the present invention has wide application for connect- ing panel-like members to frame support members of various types.

The above-mentioned advantages of the present invention will be more clearly understood when considered in conjunction with the accompanying drawings, in which: Figure 1 is a cross-sectional view of the present invention indicating the positional relationship between a panel and a structural member to which the panel is to be connected via the connection device of the invention; Figure 2 is a cross-sectional view similar to that of Figure 1 but illustrating the inventive connection device in its secured connection after thermal deformation.

Referring to Figure 1, a section of an aircraft skin panel 12 is illustrated. Typically, such a panel may be fabricated from layers of a graphite-epoxy composite material built up from overlaying layers of composite fabric. Such materials are commercially available from sources such as CIBA-GEIGY or Hercules Corp. and have been used extensively in the fabrication of aircraft skin panels. Of significance to the invention is the enlarged buildup of panel 12 at flared edge 10 to resemble a bulbous enlargement in cross-section. This edge 10 forms a first mechanical connection means for achieving the purposes of the invention. The extruded rail 14 is fabricated from memory metal alloy and achieves a connection between the aircraft skin panel and the structural frame members.

In securing an aircaft skin panel 12 to a structural frame member 13, the present clamping con¬ nector 14 is positioned between the panel 12 and the frame member 13. More specifically, the connector 14, which may be characterized as an extruded rail, has the right-illustrated edge connected to the frame member 13 by suitable fasteners such as rivets 15. The- opposite end of the connector 14 is bifurcated and includes elongated tines 16 and 17 having a C-

1.0 shaped ^" cross section for engaging the enlarged edge 10 αf panel 12. As previously explained, the connector 1.4 iεr fabricated from a commercially available memory metal alloy and manufactured by a number of sources including Ray-Chem, Ltd. of London, England, and

1 Memory Metals, Inc. of Stamford, Connecticut. These metal alloys are typically brass alloys with high yield strength of 50,000 psi or may include Ni-Ti alloys having high yield strengths in excess of 100,000 psi. Typically, memory metal alloys assume a first dimensional •

20 ^* state in a first temperature range, and depending upon the alloy training, will shrink or expand when subjected to temperatures outside the normal temperature range. Accordingly, the deformation of the tines 16 and 17 is possible by subjecting an appropriate memory metal to

25- temperature conditions which will achieve contraction. To initiate assembly, the connector 14 is positioned between the panel 12 and frame member 13 as shown in Figure 1. The tines 16 and 17 are maintained in an expanded state by exposing the memory metal alloy

30 connector 14 to sufficiently low temperature. Upon engagement between the enlarged edge 10 and tines 16

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and 17, the connector 14 is heated, which causes the memory metal alloy to contract thereby resulting in the clamping of the enlarged edge 10 between tines .16 and 17, as shown in Figure 2. A memory metal alloy connector will maintain its strong clamping pressure on the panel 12 thereafter through the normal operating temperatures of an aircraft. The rivet connection shown in Figure 1 may be replaced by employing a second bifurcated edge on the rϊght side of connector 14 if the confronting frame member edge is flared as is the enlarged edge 10 of panel 12. The result of the metal deformation, as shown in Figure 2, resembles the result that would be achieved by forging. Connector 14 may be formed by extrusion or, alternatively, may be formed integrally with the structure frame; and the bifurcated end of the con¬ nector 14 may be configured to accommodate a wide variety of curvatures on edge 10.

In summary, the present invention utilizes memory metal alloys in a new fashion, namely, as a material for a rail-like connector which is thermally deformed along one edge thereof to clamp the mating edge of a panel, while an opposite edge of the con¬ nector is fastened to a structural frame member. This avoids the necessity of expensive and time- consuming prior art adhesive bonding between a panel and structural member. The invention is also superior to the utilization of prior art rivet fastening between panel and structural members which, in the event of fiber-containing composite panel materials, evidences a severing of the fibers when rivet holes

are formed which reduces the strength of the composite material.

It should be understood that the invention is not limited to the exact details of construction shown and described herein for obvious modifications will occur to persons skilled in the art.

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