Abstract:
One leg of a connector connector is embedded inside a slot cut in a base panel structure. Adjacent laterally extensive legs overlap and are bonded to the face sheet of the base panel structure. Structural members can be attached to the remaining leg(s) of the connector. The legs bonded to the base panel structure enable loads to be transferred to or from the panel structure, and enable peel-off loads to be distributed through the base panel structure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation in part of U.S. Pat. No. 09/861,995, filed May 21, 2001, to Franklin et al., now abandoned. 

   BACKGROUND 
   1. Technical Field 
   The present invention relates to connector-less attachments for structural members, and more particularly to a connection between a base substrate of sandwich construction and a load supporting “take-off” member, where large transverse loads can be applied to the base substrate for a wide range of service temperatures, including cryogenic temperatures. 
   2. Description of the Related Art 
   Structural connections between a sandwich or honeycomb substrate and another structural member are well known in the prior art. As an example, U.S. Pat. No. 4,671,470 to Jonas discloses a connection between sandwich skin panels and aircraft frame elements using an “H”-shaped woven composite connector. A groove is formed in the panel, and lateral extensions of the connector mid-portion are positioned over adjacent lateral surface regions of the substrate. A structural foam filler is positioned between the lower leg portions of the connector before it is inserted in the groove in the panel. After being positioned in the panel groove, the connector is secured using a bonding agent. The structural foam filler serves the purpose of backing up the connector legs to insure that they make broad area contact with the walls of the groove and enhancing its ability to transfer the shear load across the groove. 
   Other devices for transferring loads to and from sandwich panel structures include those taught by U.S. Pat. No. 4,800,643 to Higgins (teaches a method for mounting a fastener in a sandwich panel to support a bolt for holding auxiliary structures to the panel), and U.S. Pat. No. 5,093,957 to Do and U.S. Pat. No. 4,981,735 to Rickson (both teach mounting upper and lower disks with co-linear bores in a sandwich panel for the purpose of attaching external structure to the panel via the bores). Other similar devices are disclosed by U.S. Pat. No. 3,510,916 to Phelan, U.S. Pat. No. 3,892,099 to Worgan et al., and U.S. Pat. No. 3,305,996 to Shapiro. 
   The cruciform of the present invention facilitates easier installation into the sandwich panel as compared with existing art technologies. Installation of the cruciform requires only cutting a slot through the face sheet and core of the sandwich panel. This slot can be accomplished in a single cutting operation that can be performed after the sandwich structure is fabricated. Cutting the slot after the sandwich structure is fabricated provides the flexibility to accurately locate the cruciform on the sandwich panel at a later stage in the assembly process, thereby reducing the effect of assembly and manufacturing tolerance buildup. 
   By comparison, Jonas, U.S. Pat. No. 4,671,470, discloses a design which requires that a finite-width strip of face sheet and core be removed from the sandwich panel to form a groove for installing the H-shaped connector, or that a groove be prefabricated into the sandwich panel. Removing a strip of core to form a groove is difficult because removal requires that the core strip be severed from the inner face sheet. This operation increases the risk of damage to the inner face sheet. Prefabricating a groove into the panel significantly increases the complexity of the sandwich panel tooling and manufacturing process and greatly reduces the: capability of the design to accommodate the buildup of manufacturing and assembly tolerances. 
   Embodiments of the present invention avoid these drawbacks and difficulties as herein described. 
   Against this background, the applicant has developed a novel apparatus and method for securing a structural member to a sandwich panel that will allow transverse take-off loading through the fastener. 
   SUMMARY 
   In one embodiment, a structural member is connected to a sandwich panel structure to allow transverse take-off loading without damaging the sandwich panel structure, while overcoming many of the disadvantages and drawbacks of similar apparatus known in the art. 
   In another embodiment, a method for attaching a structural member to a sandwich panel distributes load on the structure member into the core of the sandwich panel in addition to distributing flat-wise tension is provided. 
   In another embodiment, an article of manufacture includes a load structural member attached to an underlying sandwich panel-base. A slot is cut in the base panel, and a connector is inserted and secured in the slot. The structural member can be secured to the connector. 
   Other advantages and features of embodiments of the invention will become more apparent, as will equivalent structures, which are intended to be covered herein, with the teaching of the principles of the disclosure in the specification, claims and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  depicts a cross-sectional view of an embodiment of a connector for an article of manufacture. 
       FIG. 2  depicts a cross-sectional view of another embodiment of a connector for an article of manufacture. 
       FIG. 3  depicts a cross-sectional view of yet another embodiment of a connector for an article of manufacture. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The following description is provided to enable any person skilled in this or any related arts to make and use embodiments of the present invention, and sets forth the best modes contemplated by the inventor of carrying out embodiments his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of embodiments of the present invention have been defined herein specifically to provide a novel connection and method of connecting a structural member to an underlying sandwich panel that encompasses many long sought after features that make such connections extremely easy and far less expensive to fabricate. 
   In some embodiments, a load transfer or structural member is secured to a base sandwich panel, which will allow large transverse or “pull-off” loads to be applied or transmitted to the base panel while distributing “peel-off” loads across the skin of the sandwich panel. The combination of connector with panel is effective through a wide range of temperatures, including cryogenic temperatures. 
   Prior techniques use “wet-layups” or precured and bonded “Pi” clips, “T clips” or H-shaped connectors to introduce loads to the adjacent facesheet of the base sandwich structure. Large peel-off loads quickly cause adhesives to fail. Cryogenic applications suffer because of loss of ductility in the adhesive resulting in lower pull strength. 
   Embodiments of the present invention overcome the drawbacks of the known techniques through the arrangement shown in  FIG. 1  of the drawings, in which a slot or groove  102  is cut or formed in a base sandwich panel structure  104 , and a woven composite connector  150  is inserted and secured within slot  102  via a suitable bonding agent  110 , such as an adhesive, which is applied to surfaces of connector  150  that contact base panel structure  104  including the sides of slot  102 . 
   In some embodiments, connector  150  has the configuration of a “+” sign, and includes a first leg  152  which is adapted to be disposed in the panel slot  102 , a second leg  154  extending coextensive with the first leg  152  adapted to be connected to a structural member  112 . Third and fourth legs  156 ,  158  extend laterally and normal to the first and second legs. Third and fourth legs  156 ,  158  of connector  150  are adapted to be connected to face sheet  160  of base panel structure  104  to transmit shear loading thereto. Connector  150  can be fabricated using woven composite materials, plastics, metal, or other suitable material. Legs  152  through  158  of connector  150  can have bending stiffness to reduce peel loading. 
     FIG. 2  shows another embodiment of connector  150  that includes additional legs  154  to accommodate attachment of additional structural members  112 . Note that connector  150  can include fewer or additional legs  154  than shown in  FIG. 2 . When two or more legs  154  are included with connector  150 , legs  154  can extend at an angle with respect to base legs  156 ,  158 , and with respect to each other leg  154 . The angles between legs  154  do not have to be the same, but rather can differ depending on the structure to be fabricated using connector  150 .  FIG. 3  shows yet another embodiment of connector  150  with legs  154  substantially perpendicular to legs  156  and  158 . The length and thickness of legs  152 ,  154 ,  156 , and  158  can be adjusted to provide the desired structural strength and stiffness. The distance between legs  154  can also vary depending on the article to be fabricated using connector  150 . 
   Slot  102  can be cut into face sheet  160  and core  162  of the base sandwich panel structure  104  to allow insertion of the first leg  152  into core  162 . First leg  152  is bonded to core  162  in slot  102  to provide a means to transfer transverse pull-off loads into core  162 . An advantage is that slot  102  can be cut in a single operation after base panel structure  104  is fabricated. The single cutting operation reduces manufacturing complexity. Performing the cut after panel structure  104  is fabricated and installed avoids the build-up of assembly tolerances and increases the accuracy of locating the woven composite connector  150 . Face sheet  160  and core  162  can be comprised of any suitable material, or combination of materials. 
   Structural member  112  can be any suitable structure, such as, for example, a panel or beam element. Structural member  112  can be secured to connector  150  using any suitable method such as bonding or mechanical fasteners. Once slot  102  has been formed in base panel structure  104 , attachment of connector  150  can act as a bonded doubler so that structural strength is not dramatically reduced by cutting slot  102 . Connector  150  transfers load from structural member  112  to legs  152  through  158 . The thermal expansion coefficients of face sheet  160 , core  162 , and connector  150  can be matched. 
   In some embodiments, edges of legs  154 ,  156 , and/or  158  can be chamfered as shown in  FIG. 1  to provide a smooth transition between face sheet  160  and connector  150 , and/or between structural member  112  and connector  150 . Any exposed portion of bonding agent  110  can also be applied to blend with the chamfered edge of connector  150  to further smooth the transition between face sheet  160  and connector  150 . 
   Embodiments of connector  150  permit distribution of both sheer and tensile loads on structural member  112  into face sheet  160  and core  162  of base panel structure  104 . 
   Those skilled in the art will appreciate that various adoptions and modifications of embodiments of the invention as described above can be configured. Therefore, it is to be understood that, within the scope of the appended claims, embodiments of the invention may be practiced other than as specifically described herein. In the claims, unless otherwise indicated the article “a” is to refer to “one or more than one”.