Abstract:
A torque tube includes a composite body and an end fitting. The composite tube includes a body having a body interior diameter, wall thickness, an end having an edge, and a set of grooves. Each groove of the set of grooves passes through the wall thickness. Each groove of the set of grooves begins at the edge and ends in the body. The end fitting includes a sleeve configured to mate with the body interior diameter and a set of ribs configured to mate with the set of grooves.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure generally relates to fabrication of composite items. More particularly, the present disclosure pertains to a configuration for joining a composite tube to an end fitting of a dissimilar material. 
       BACKGROUND 
       [0002]    Composite materials have been used increasingly in a variety of industries, including the automotive, marine and aerospace industries. In these applications, composites often include strong fibrous materials, such as carbon, aramid, glass or quartz, bonded together with a resin, such as an epoxy. Composite materials generally possess a high strength to weight ratio in comparison to metals and plastics. These attributes enable composite items to be made lighter and/or stronger than conventional metal parts. 
         [0003]    However, fabrication of composite items is relatively more complicated than metal fabrication. Generally, composite items are built up, layer upon layer on a mold or the fiber component is placed and then impregnated with resin. Afterward the item is cured and removed from the mold. While some shapes are relatively easy to generate in this manner, others are not. In addition, while composites are quite strong, they are generally not as tough as metals. Conventionally, when dissimilar qualities are to be combined in a single component, two materials are welded, glued, or otherwise joined together. For example, a dense plastic film may be glued to a foamed plastic to form a light, abrasion resistant material. Unfortunately, conventional adhesives and joining methods may not form adequate bonds when joining high strength carbon fiber composites to metals. Furthermore, many safety-critical bonded structures, such as primary aircraft structures, may be required to have redundant load paths which allow the structure to continue performing even if the primary adhesive bond fails. 
         [0004]    Accordingly, it is desirable to provide a hybrid composite item that includes dissimilar materials joined together, where this joint is capable of overcoming the disadvantages described herein at least to some extent. 
       SUMMARY 
       [0005]    The foregoing needs are met, to a great extent, by embodiments the present disclosure, wherein in one respect a joint and method is provided that in some embodiments facilitates joining dissimilar materials together. 
         [0006]    An embodiment relates to a fail-safe torque tube for an aircraft. The torque tube includes a composite body and an end fitting. The composite tube includes a body having a body interior diameter, wall thickness, an end having an edge, and a set of grooves. Each groove of the set of grooves passes through the wall thickness. Each groove of the set of grooves begins at the edge and ends in the body. The end fitting includes a sleeve configured to mate with the body interior diameter and a set of ribs configured to mate with the set of grooves. 
         [0007]    Another embodiment pertains to a fail-safe torque tube for an aircraft. The torque tube includes a composite body and an end fitting. The composite tube includes a body having a body interior diameter, wall thickness, an end having an edge, and a set of grooves. Each groove of the set of grooves is disposed through a portion of the wall thickness. Each groove of the set of grooves begins at the edge and ends in the body. The end fitting includes a sleeve configured to mate with the body interior diameter and a set of ribs configured to mate with the set of grooves. 
         [0008]    Yet another embodiment relates to a method of providing a fail-safe load path for a torque tube in an aircraft. In this method, a torque tube is provided, a fist end of the torque tube is secured to a first aircraft component in a load path and a second end of the torque tube is secured to a second aircraft component in the load path. The torque tube includes a composite body and a pair of end fitting. The composite tube includes a body having a body interior diameter, wall thickness, an end having an edge, and a set of grooves. Each groove of the set of grooves passes through the wall thickness. Each groove of the set of grooves begins at the edge and ends in the body. The end fittings includes a sleeve configured to mate with the body interior diameter and a set of ribs configured to mate with the set of grooves. 
         [0009]    There has thus been outlined, rather broadly, certain embodiments of the disclosure in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments that will be described below and which will form the subject matter of the claims appended hereto. 
         [0010]    In this respect, before explaining at least one embodiment in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The disclosed device and method is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
         [0011]    As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the various embodiments. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the various embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is an exploded view of a torque tube in accordance with an embodiment. 
           [0013]      FIG. 2  is a partial cutaway view of the torque tube according to  FIG. 1 . 
           [0014]      FIG. 3  is a cross-sectional view of the torque tube according to  FIG. 1 . 
           [0015]      FIG. 4  is a hidden line view of a torque tube in accordance with another embodiment. 
           [0016]      FIG. 5  is a cross-sectional view of the torque tube according to  FIG. 4 . 
           [0017]      FIG. 6  is an exploded view of a torque tube in accordance with another embodiment. 
           [0018]      FIG. 7  is a cross-sectional view of the torque tube in accordance with another embodiment. 
           [0019]      FIG. 8  is a cross-sectional view of the torque tube in accordance with another embodiment. 
           [0020]      FIG. 9  is a cross-sectional view of the torque tube in accordance with another embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    The present disclosure provides a device and method for providing a fail-safe torque tube to transmit torque along a load path of an aircraft. The torque tube device includes a composite tube body secured to metal end fittings. The composite tube body is relatively lighter than current metal tube bodies. The metal end fittings provide a durable connection between the torque tube and components attached to the torque tube. To join the composite tube body to the end fitting an improved joint conformation is utilized. As described herein, an embodiment of this improved joint provides an efficient fail-safe connection between the torque tube and the end fitting. For the purpose of this disclosure, the term, “fail-safe” refers to a device, system, and method having a redundant feature. For example, as used herein, the term “fail-safe torque tube” refers to a torque transmission device with a redundant load path. As such, in the event of a failure in one load path, a second load path is configured to transmit torque. 
         [0022]    In an aircraft, a torque tube may be utilized to transmit torque from a motor or other such actuator to a control surface actuator. The control surface actuator modulates the attitude of a control surface on the wing, for example, and is therefore of critical importance to the operation of the aircraft. As such, it is an advantage of embodiments described herein that a primary and secondary load path for the transmission of torque is provided. 
         [0023]    The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout.  FIG. 1  is an exploded view of a torque tube  10  in accordance with an embodiment. As shown in  FIG. 1 , the torque tube  10  includes a tube body  12  and end fittings  14  and  16 . 
         [0024]    The tube body  12  may include any suitable material. Examples of suitable materials include fiber reinforced plastics, metal foil and/or film reinforced plastics, and the like. Particularly suitable materials include, for example, carbon fiber reinforced plastic. The plastic matrix includes any suitable polymer such as, for example, epoxy and the like. The tube body  12  includes a first end  18  and a second end  20 . The ends  18  and  20  include respective sets of grooves  22  and  24 . The end fittings  14  and  16  include respective sets of ribs  26  and  28 . For the sake of clarity, in the following description, an example will be made with reference to the end fitting  14  and end  18 . It is to be noted that the following description of the end fitting  14  and end  18  may pertain to the end fitting  16  and end  20 . 
         [0025]      FIG. 2  is a partial cutaway view of the torque tube  10  according to  FIG. 1 . As shown in  FIG. 2 , the set of grooves  22  is configured to mate with the set of ribs  26 . Also shown in  FIG. 2 , the torque tube  10  includes an adhesive  30  to affix the tube body  12  to the end fitting  14 . The adhesive  30  may provide a primary load path from the tube body  12  to the end fitting  14 . In the event the adhesive bond from the tube body  12  to the end fitting  14  via the adhesive  30  is compromised, the interface between the set of grooves  22  and the set of ribs  26  may provide a secondary load path from the tube body  12  to the end fitting  14 . 
         [0026]    It is another advantage of the torque tube  10  that the joint or interface between the set of grooves  22  and the set of ribs  26  may augment the adhesive bond. For example, in the event that a portion of the adhesive bond delaminates, the ribs  26  to either side of the delaminating portion may prevent or reduce the likelihood that the bond delamination may propagate to other portions of the adhesive bond. 
         [0027]      FIG. 3  is a cross-sectional view A-A of the torque tube  10  according to  FIG. 1 . As shown in  FIG. 3 , the set of grooves  22  includes grooves  22   a  to  22   n . Also shown, the set of ribs  26  includes ribs  26   a  to  26   n . Although four grooves  22   a  to  22   n  and four corresponding ribs  26   a  to  26   n  are shown in the particular example, in other examples, any suitable number from one to about ten grooves and corresponding ribs may be included in the torque tube  10 . 
         [0028]    The adhesive  30  is configured to bond the end fitting  14  to the tube body  12 . As such, in response to torque being applied to the end fitting  14 , the resulting load is translated through the adhesive  30  to the tube body  12  and the tube body  12  is urged to rotate as indicated by arrow  32 . This adhesive bond may thus be considered the primary load path. In the event the primary load path is compromised, the torque tube  10  includes a secondary load path shown in inset B. As shown in inset B, groove  22   a  includes bearing surfaces  34   a  and  34   b  and the rib  26   a  includes corresponding bearing surfaces  36   a  and  36   b . The bearing surface  34   a  is configured to bear upon the bearing surface  36   a . Similarly, the bearing surface  34   b  is configured to bear upon the bearing surface  36   b . In this manner, torque may be translated between the tube body  12  and end fitting  14 . 
         [0029]    Also shown in inset B, the groove  22   a  may be fabricated slightly larger relative to the rib  26   a . For example, to account for machining tolerances, a small gap may be anticipated. This gap may be preferable to binding caused by the groove  22   a  being relatively smaller than the rib  26   a . The small gap between the bearing surfaces  36   b  and  34   b  may be filled with the adhesive  30  or any suitable shimming material. Examples of suitable shimming materials include metal and polymer shims, epoxy, epoxy thickened with cut fibers or powders, and the like. The expected loads exerted upon the adhesive  30  and/or shimming material disposed between the bearing surfaces  36   b  and  34   b  are compressive loads. As such, with regard to the secondary load path, the adhesive qualities of the adhesive  30  and/or shimming material disposed between the bearing surfaces  36   b  and  34   b  are unimportant. That is, failure of the adhesive  30  and/or shimming material disposed between the bearing surfaces  36   b  and  34   b  will not affect the integrity of the secondary load path. 
         [0030]      FIG. 4  is a hidden line view of the torque tube  10  in accordance with another embodiment. As shown in  FIG. 4 , the end fitting  14  includes an outer wall or sheath  38 . The sheath  38  is configured to augment or strengthen the joint between the tube body  12  and end fitting  14 . For example, by covering the portion of the tube body  12  between the grooves  22   a  to  22   n , the sheath  38  acts to prevent the end of the tube body  12  from splaying outwardly. In addition, as shown in  FIG. 5 , the sheath  38  substantially doubles the adhesive area. 
         [0031]      FIG. 5  is a cross-sectional view C-C of the torque tube  10  according to  FIG. 4 . As shown in  FIG. 5 , the tube body  12  is sandwiched between the sheath  38  and an inner wall or sleeve  40  of the end fitting  14 . As shown in inset D, by sandwiching the tube body  12  thusly, a second layer of the adhesive  30  may be utilized to affix the tube body  12  to the end fitting  14 . It is an advantage of this embodiment that the joint is approximately twice as strong as a joint formed by a single layer of the adhesive  30 , all other factors being equal. In addition, depending upon a variety of factors such as joint failure characteristics, empirical data, and the like, it may be another advantage of this embodiment that the length of the set of grooves  22  and set of ribs  26  may be reduced as a result of the increased area of adhesion. 
         [0032]      FIG. 6  is an exploded view of the torque tube  10  in accordance with another embodiment. As shown in  FIG. 6 , the set of grooves  22  are helically shaped. Accordingly, although not shown in  FIG. 6 , the corresponding set of ribs  26  are configured to mate with the helically shaped set of grooves  22 . It is an advantage of this embodiment that the assembled torque tube  10 , may be utilized to also transmit axial loads. In a particular example, the torque tube  10  may be utilized to exert a pushing or pulling axial load instead of, or in addition to, a torsion load. If the tube body  12  and end fitting  14  are restrained from turning relative to one another, the helically interlocking set of grooves  22  and set of ribs essentially lock the tube body  12  and end fitting  14  together. 
         [0033]      FIG. 7  is a cross-sectional view C-C of the torque tube  10  in accordance with another embodiment. As shown in  FIG. 7 , the torque tube  10  includes three grooves  22   a  to  22   c  and three corresponding ribs  26   a  to  26   c . In addition, the grooves  22   a  to  22   c  pass through a portion of the tube body  12 . That is, the grooves  22   a  to  22   c  do not pass through the wall of the tube body  12 . Instead, the grooves  22   a  to  22   c  pass through about 50% of the wall thickness of the tube body  12 . In other embodiments, the grooves  22   a  to  22   c  pass through from about 5% to about 90% of the wall thickness of the tube body  12 . Accordingly, the ribs extend outwardly a corresponding amount. 
         [0034]    Furthermore, the grooves  22   a  to  22   c  of  FIG. 7  are shown extending into the wall of the tube body  12  from an interior surface of the tube body  12 . However, in this or other embodiments, the grooves  22   a  to  22   c  may extend into the wall of the tube body  12  from an exterior surface of the tube body  12 . 
         [0035]      FIG. 8  is a cross-sectional view C-C of the torque tube  10  in accordance with another embodiment. As shown in  FIG. 8 , the torque tube  10  includes the grooves  22   a  to  22   c  that pass through a portion of the tube body  12  and the torque tube  10  includes the sheath  38 . 
         [0036]      FIG. 9  is a cross-sectional view C-C of the torque tube  10  in accordance with another embodiment. As shown in  FIG. 9 , the torque tube  10  includes the grooves  22   a  to  22   e  and corresponding ribs  26   a  to  26   e . In addition, the grooves  22   a  to  22   e  of  FIG. 9  are shown extending into the wall of the tube body  12  from an exterior surface of the tube body  12 . However, in this or other embodiments, the grooves  22   a  to  22   e  may extend into the wall of the tube body  12  from an interior surface of the tube body  12 . As shown in inset E of  FIG. 9 , the adhesive  30  and/or a suitable shim material may be utilized to fill gaps between the groove  22   a  and rib  26   a.    
         [0037]    The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.