Abstract:
An apparatus and method for a composite structural aircraft transmission support link having an integral energy-absorbing feature is disclosed. The link is a two-force member that can carry structural loads up an ultimate load. When loaded beyond ultimate load the design allows sections of the link to fail in a controlled and progressive manner, so that energy is absorbed over a defined stroking distance.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    This technology as disclosed herein relates generally to two force members and, more particularly, to a link having an energy absorbing component. 
         [0003]    2. Background 
         [0004]    Current solutions for providing an energy absorbing link, are limited or not in practice at all. One possible example of a current practice is the use of metallic solutions such as corrugated and slotted tubes, however, these solutions are typically heavy and are not typically capable of absorbing a sufficient amount of energy. Energy-absorbing bearings are feasible but have a limited stroking distance to absorb an amount of energy that is adequate for what is needed. Fluid-filled struts are in practice for energy absorbing links. 
         [0005]    An energy-absorbing link structure that attenuates the energy produced by heavy mass items is needed that is lighter in weight than prior solutions and that has a longer stroke length during maximum load conditions. 
       SUMMARY 
       [0006]    The technology as disclosed herein is a method and apparatus for a two force structural member that is utilized as a link between two heavy structures comprising an energy absorbing tab adjacent a mounting hole of a link member. One embodiment of the technology is a composite structural transmission support link which has a novel integral energy-absorbing feature. The link can be a two-force member that can carry structural loads up an ultimate load. When loaded beyond ultimate load, such as in a crash event, features in the design allow sections of the link to fail in a progressive manner to absorb energy over a defined stroking distance. The energy absorbing link technology as disclosed can be utilized to connect or link two heavy structures. 
         [0007]    A link can be designed to support a heavy mass during normal operations of the heavy mass components up to an ultimate load. When this load is exceeded, for example, during a crash event, the energy absorbing technology as disclosed is designed to attenuate energy of the heavy mass by means of controlled failure through a defined stroke distance—which acts to shed energy of the system, for example, an aircraft system. After completion of the stroke of the mass over a defined distance, the link remains intact and imparts a reduced force to the heavy structure, such as an airframe, during the stroke. 
         [0008]    In one implementation of the technology as disclosed, a slot can be machined or formed into a link to form a weak region under a bushing area. With one implementation, the weak region can be positioned between two thru-holes used to attach the link between two heavy structures, which can absorb compression loads. With another implementation, the weak region can be position on a far side of a thru-hole between the thru-hole and the end of the link, which can absorb tension loads (tensile loads). 
         [0009]    When the component is loaded in compression, the slot can absorb the energy via progressive failure. Ply drops serve as sacrificial components that will fail when stressed beyond maximum capacity, thereby reducing the initial load spike. Ply drops (ply drop-offs) are thickness variations in the laminate composite accomplished by dropping or eliminating plies along the length where, in this case, the ply drops are designed as fail points forming a weak region. This invention has significant weight advantages over a fluid filled strut, with similar energy absorbing capabilities. 
         [0010]    One implementation for the basic design of a link can include a composite tube with a rectangular shaped cross section. Cutouts can be formed on each end of the link to act to form a clevis joint. Metallic bushings can be installed through the thru-holes in each arm of the clevis. 
         [0011]    The technology as disclosed can be a two-force structural member that is loaded double-shear when subjected to a tensile or compressive load. A novel feature of this technology is a weak area designed into a section of the link on each clevis arm face, adjacent to the thru-hole, through which the clevis pin is inserted. The material in this area can form a slot with a width that roughly matches the outer diameter of the bushing installed through each clevis arm thru-hole. This feature is positioned so that, when the part is loaded in compression, the pin bushing fails and the composite material in the slot area and the ensuing crushing action absorbs energy. 
         [0012]    The combination of the length of the slot and depth of the clevis arms define the stroke distance for energy absorption. The layup of the composite material in the slot can be configured to fail through progressive crushing at a relatively constant load, while the link stays intact during the failure event. The slot feature can be formed by a variation in the composite ply layup compared to the link layup, which may include: composite ply drop-offs; composite ply breaks; or, a machined taper in the slot. Ply breaks are when the fibers in a single composite ply are intentionally cut or a gap is left between two different plies. 
         [0013]    An energy-absorbing (EA) slot can be integral to the link and can be designed to fail by crushing during a max-load event, thereby attenuating the energy of a heavy mass. One (1) EA slot at each end of link can effectively double the stroking distance and energy absorbed. A slot can be machined or formed into the EA link to form a ‘weak’ region adjacent a bushing bearing area when loaded in compression. If the bushing bearing is appropriately spaced from the end of the link, a slot can be formed in the EA link between the thru-hole and the end of the link to form a weak region adjacent a bushing area when loaded in tension. The slot can absorb energy by the crushing of the material of the slot. The slot can be formed of a composite material. 
         [0014]    In another implementation, a gradual variation in the number of plies (ply drops) can be utilized to act as sacrificial components that will fail when stressed beyond maximum capacity to initiate crushing and reduce an initial load spike. The thickness and layup orientation of composite material in the slot can be tuned for a required energy attenuation. 
         [0015]    One implementation of a two-force member energy-absorbing link structure can include an elongated structural member having first and second opposing ends and a lengthwise extending central axis where at least the first and second opposing ends of the elongated structural member is constructed of a primary material having a strength characteristic sufficient to link together two structures. A thru-hole can extend substantially orthogonally with respect to the central axis and through one or more of the first and second ends. 
         [0016]    A section of the elongated structural member constructed of a secondary material and having a lesser strength characteristic than the strength characteristic of the material sufficient to link the two structures can be adjacent the thru-hole. The section can extend a lengthwise distance substantially along a direction that the lengthwise extending central axis extends and the section can extend from a point of the material proximate and adjacent the thru-hole. In one implementation, the elongated structural member can be a tubular elongated member, and one or more of the first and second opposing distal ends can have a u-shaped clevis structure with opposing first and second prong members forming the u-shaped clevis structure. 
         [0017]    One implementation of the technology as disclosed herein can be a two-force member energy-absorbing link structure including an elongated structural member having first and second opposing distal ends and a lengthwise extending central axis where at least the first and second opposing distal ends of the elongated structural member are constructed with a primary material thickness having a strength characteristic sufficient to link together two structures. A thru-hole can extend substantially orthogonally with respect to the central axis and through one or more of the first and second distal ends. A recessed cutaway slot section of the elongated structural member, i.e. the link, can be constructed having a lesser thickness and lesser strength characteristic than the strength characteristic of the material sufficient to link the two structures, wherein the section extends a lengthwise distance substantially along a direction that the lengthwise extending central axis extends and wherein the section extends from a point of the material proximate and adjacent the thru-hole. 
         [0018]    The level of energy absorbed can be adjusted through a combination of the design of the layup and form features. Composite materials can be utilized to enhance the performance parameters of the design. The benefits of a design using high performance composite materials is that very high levels of specific-sustained crush stress (per unit energy-absorption, in Joules/gm) may be obtained throughout a relatively large stroke distance, compared to metallic designs. This is particularly useful approach where the structural members also have the ability to attenuate the energy of heavy mass items, such as a rotorcraft transmission during a crash, for virtually no weight penalty. 
         [0019]    The features, functions, and advantages that have been discussed can be achieved independently in various implementations or may be combined in yet other implementations, further details of which can be seen with reference to the following description and drawings. 
         [0020]    These and other advantageous features of the present technology as disclosed will be in part apparent and in part pointed out herein below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    For a better understanding of the present technology as disclosed, reference may be made to the accompanying drawings in which: 
           [0022]      FIG. 1A  is an illustration of two heavy mass structures being connected by links; 
           [0023]      FIG. 1B  is a magnified view of an encircled portion of  FIG. 1A  illustrating two links, which can be used to connect two heavy mass structures; 
           [0024]      FIG. 2A  is a sectional view of a clevis of a link; 
           [0025]      FIG. 2B  is another sectional view of a clevis and bushing bearing of a link; 
           [0026]      FIG. 3A  is a front sectional view of a clevis of a link; 
           [0027]      FIG. 3B  is a perspective view of a clevis of a link; 
           [0028]      FIG. 3C  is a magnified view of a portion of  FIG. 3B , providing a sectional perspective view of a slot area; 
           [0029]      FIG. 4A  is a magnified view of one end of a link prior a controlled failure; and 
           [0030]      FIG. 4B  is a magnified view of one end of a link after a controlled failure. 
       
    
    
       [0031]    While the technology as disclosed is susceptible to various modifications and alternative forms, specific implementations thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description presented herein are not intended to limit the disclosure to the particular implementations as disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present technology as disclosed and as defined by the appended claims. 
       DESCRIPTION 
       [0032]    According to the implementation(s) of the present technology as disclosed, various views are illustrated in  FIG. 1-4  and like reference numerals are being used consistently throughout to refer to like and corresponding parts of the technology for all of the various views and figures of the drawing. Also, please note that the first digit(s) of the reference number for a given item or part of the technology should correspond to the figure number in which the item or part is first identified. 
         [0033]    One implementation of the present technology as disclosed (comprising an energy-absorbing slot feature) teaches a novel apparatus and method for an energy-absorbing link. 
         [0034]    The details of the technology as disclosed and various implementations can be better understood by referring to the figures of the drawings. Referring to  FIGS. 1A and 1B , an illustration of two heavy mass structures being connected by a link system  106  is shown, and an illustration of two links  108  and  110 , which can be used to link two heavy mass structures, is shown. A two-force member energy-absorbing link structure  110  (see  FIG. 1B ) is shown, which can be connected between to two heavy structures, as illustrated in  FIG. 1A , a first heavy structure  104  and a second heavy structure  102 , (see  FIG. 1A ) of the two structure system  100 . As illustrated in  FIG. 1A , for example, the first heavy structure can be an aircraft main structure  104  and the second heavy structure can be an aircraft drive system  102 . Encircled area  106  is further illustrated in  FIG. 1B . 
         [0035]    Referring to  FIG. 1B , an elongated structural member, which is a link  110 , is shown having first  112  and second  114  opposing ends. The portion of the link system  106  as illustrated shows a first link  108  and a second link  110 . First link  108  does not illustrate the present technology as disclosed herein while second link  110  does. Both the first link  108  and the second link  110  are connected by their respective second opposing ends  114  to a mounting structure  116 . The second link  110  has a lengthwise extending central axis (identified by reference numeral  214  in  FIGS. 2B and 3A ) where at least the first and second opposing ends  112 ,  114  of the link  110  are constructed of a primary material  134  having a strength characteristic sufficient to link together two structures (for example, structures  104  and  102 ). 
         [0036]    A first thru-hole  118  and a second thru-hole  120  can extend substantially orthogonally with respect to the central axis (see item  214  of  FIGS. 2B and 3A ) and through one or more of the first  112  and second  114  opposing ends. A first section  126  and/or a second section  128  of the elongated structural member, which is the second link  110 , can be constructed of secondary material having a lesser strength characteristic than the strength characteristic of the material sufficient to link the first heavy structure and the second heavy structure. The first and second sections  126  and  128  can extend a lengthwise distance substantially along a direction that the lengthwise extending central axis  214  extends. The first and second sections can extend from a location  124  of the material proximate and adjacent the thru-hole. 
         [0037]    In one implementation of the technology, the two-force member energy-absorbing link  110  can be constructed such that the elongated structural member, link  110 , is a tubular elongated member. The two-force member energy-absorbing link  110  as illustrated where one or more of the first  112  and second  114  opposing distal ends have a u-shaped clevis structure with opposing first  132  and second  130  prong members (i.e. arms) forming the u-shaped  122  clevis structure. The first and second thru-holes, as illustrated at  118  and  120 , can extend through one or more of the first  130  and second  132  prong members. 
         [0038]    The section, illustrated by  126  or  128 , of the elongated structural member  110  can be constructed of a secondary material and can be an elongated slot  126  or  128  extending a lengthwise distance. The first and second sections of weakened material  126  and  128  of the elongated structural member, link  110 , can be formed in the primary material as a weakened region of the elongated structural member, i.e. the link  110 , to allow the weakened sections  126  and  128  to crush when sufficient compression loads are applied to the elongated structural member in the direction that the lengthwise extending central axis  214  extends. 
         [0039]    Referring to  FIGS. 2A and 2B , a sectional view  200  of first and second arms  130  and  132  of a link is shown. Referring to  FIG. 2B , another sectional view of the clevis arms  130  and  132  and bushing bearing  210  of a link is shown. The section (i.e. slot)  126  can be formed with ply-drops  206  and  208  proximate the thru-hole  118  to act as a weakened area to induce a controlled failure and to initiate crushing of the slot  126  constructed of a secondary material to reduce an initial load spike. The slot  126  comprising the secondary material can also be a recess  202 . With one implementation of the technology as disclosed, the section of secondary material  126 , which can be a recessed slot  202 , can be formed having lengthwise slits  216  (See  FIG. 2B ) extending at least partially from one end of the slot to the opposing end of the slot in the direction that the lengthwise extending central axis extends. 
         [0040]    With one implementation of the technology as disclosed a two-force member energy-absorbing link structure can include an elongated tubular member—i.e. a link  110 . The tubular member can have a rectangular cross section. The link can have first and second opposing distal ends and a lengthwise extending central axis where the elongated structural member is constructed of a primary material having a strength characteristic sufficient to link together two structures. With this implementation a thru-hole can extend substantially orthogonally with respect to the central axis and through one or more of the first and second distal ends. A section  126  of the elongated structural member can be constructed of secondary material  134  having a lesser strength characteristic than the strength characteristic of the material sufficient to link two structures and said section can extend a lengthwise distance  212  substantially along a direction that the lengthwise extending central axis  214  extends and said section extends from a location  124  of the material proximate and adjacent the through hole. 
         [0041]    The first and second opposing ends can have a u-shaped clevis structure  204  with opposing first  130  and second  132  prong members forming the u-shaped clevis structure  204 . The thru-hole  118  extends through one or more of the first and second prong members  130 ,  132 . The section of the elongated structural member constructed of a secondary material is an elongated slot  126  extending a lengthwise distance  212  (see  FIG. 2B ). In one implementation of the technology, the section of the elongated tubular member can be formed in the primary material as a weakened region of the elongated tubular member to allow the section to crush when sufficient compression loads are applied to the elongated tubular member in the direction that the lengthwise extending central axis  214  extends. The section can be formed with ply-drops  206  proximate the thru-hole  118  to act to initiate crushing of the secondary material to reduce an initial load spike. The section can be formed having lengthwise slits  216  extending at least partially in the direction that the lengthwise extending central axis extends. 
         [0042]    Referring to  FIGS. 3A, 3B and 3C , a front sectional view of a clevis of a link is shown, a perspective view of a clevis of a link is shown and a sectional perspective view a slot area is shown. An elongated structural member, i.e. the link  110 , can have first and second opposing ends. The first end  112  is shown in  FIG. 3A . A lengthwise extending central axis  214  can extend in the direction illustrated where at least the first and second opposing ends of the link  110  is constructed having a primary material thickness having a strength characteristic sufficient to link together two structures. 
         [0043]    As can be seen, a thru-hole  118  extends substantially orthogonally with respect to the central axis  214 . A recessed cutaway slot  202  section in the link  110  is shown and can be constructed of a material having a lesser thickness and lesser strength characteristic than the strength characteristic of the material sufficient to link the two structures. The recessed cutaway slot  202  can extend a lengthwise distance substantially along a direction that the lengthwise extending central axis extends and said section can extend from a location proximate and adjacent the thru-hole. 
         [0044]    The first and second opposing ends can have a u-shaped  204  clevis structure with opposing first and second arm members forming the u-shaped clevis structure. The section can be formed with ply-drops  206  proximate the thru-hole  118  to allow for the initiation of the crushing of the secondary material to reduce an initial load spike. The section can be formed having lengthwise slits  216  extending at least partially in the direction that the lengthwise extending central axis extends. 
         [0045]    Referring to  FIGS. 4A and 4B , an illustration is provided for one end of a link before ( FIG. 4A ) and after ( FIG. 4B ) a controlled failure. A view of one end  114  of a link  110  is shown. The link  110  is shown mounted to a structure  116  using the clevis  122  and a mounting bolt  402  and washer  403 . The bolt  402  is shown extending through a thru-hole  120  of the clevis  122  and attaching the link  110  to the structure  116 . The link  110  is constructed of a primary material  134 . The link  110  can have a section of weakened material  128 . The section of weakened material  128  can be an elongated slot  404  that extends lengthwise in the same direction as the central axis  214 . The elongated slot  404  can also have a recess  406  as illustrated where material can be removed further weakening the area.  FIG. 4B  illustrates one end  114  of the link  110  after a controlled failure where the bolt  402  has traversed along the stroke distance  408  and proximately along the same direction as the axis  214 , thereby crushing the section of weakened material  128 , while bolt  402  remains sufficiently intact such that the link  110  is still mounted to the structure  116 . 
         [0046]    The various energy-absorbing link examples shown above illustrate a link between two heavy structures. A user of the present technology as disclosed may choose any of the above implementations, or an equivalent thereof, depending upon the desired application. In this regard, it is recognized that various forms of the subject energy-absorbing link could be utilized without departing from the scope of the present invention. 
         [0047]    As is evident from the foregoing description, certain aspects of the present technology as disclosed are not limited by the particular details of the examples illustrated herein, and it is therefore contemplated that other modifications and applications, or equivalents thereof, will occur to those skilled in the art. It is accordingly intended that the claims shall cover all such modifications and applications that do not depart from the scope of the present technology as disclosed and claimed. 
         [0048]    Other aspects, objects and advantages of the present technology as disclosed can be obtained from a study of the drawings, the disclosure and the appended claims.