Abstract:
An auxetic locking structure can be used as a mechanism for securing two or more members in an assembly or other system. The locking structure has void patterns on its exterior surface which permit the locking structure to reduce its outer diameter upon loading in an axial direction. Once the structure has been sufficiently loaded and the diameter has been sufficiently reduced, the locking structure may be positioned within a bore of an article, the axial load is then reduced, thus causing the locking structure to expand and engage the bore of the article. The locking structure and article are now secured to one another creating an improved assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/792,487, filed Mar. 15, 2013, the contents of which are hereby incorporated in their entirety. 
     
    
     FIELD OF TECHNOLOGY 
       [0002]    A mechanism for securing two members, and more particularly, transformative periodic structures and tunable photonic crystals that may be used as hollow, rolled, spring, or a solid pin. 
       BACKGROUND 
       [0003]    Retaining structures such as pins are used to secure multiple members together so that a combined pinned assembly may be created. Sometimes the combined assembly is to be permanently held together and sometimes it is desirable to disassemble the assembly so that it can be serviced, rebuilt or otherwise repaired. Based upon the design circumstances, it may be difficult to repair certain pinned assemblies due to environmental or physical constraints. 
         [0004]    Pins may be constructed of various materials, including but not limited to metal, polymers, rubber and wood. Such pins have been utilized in numerous products and machinery throughout industry and society. Many of the materials that have been utilized to make pins and other retaining structures have been designed to perform under certain predetermined environmental constraints. However, certain environmental conditions are so severe that traditional constructs of pins structures simply cannot operate under such extreme conditions. 
         [0005]    A pin typically has a longitudinal axis and a radii that defines a part of the geometry of the pin. The geometry of the pin traditionally has a solid construct which lends itself for use in high shear conditions. Based upon the material used, the pin will have varying compression, shear, tension and elastic characteristics. Irrespective of the material used, virtually all materials undergo a transverse contraction when stretched in one direction and a transverse expansion when compressed. The magnitude of this transverse deformation is governed by a material property known as Poisson&#39;s ratio. Poisson&#39;s ratio is defined as the transverse strain divided by the axial strain in the direction of stretching force. Since ordinary materials contract laterally when stretched and expand laterally when compressed, Poisson&#39;s ratio for such materials is positive. Poisson&#39;s ratios, denoted by a Greek nu, n, for various materials are approximately 0.5 for rubbers and for soft biological tissues, 0.45 for lead, 0.33 for aluminum, 0.27 for common steels, 0.1 to 0.4 for cellular solids such as typical polymer foams, and nearly zero for cork. 
         [0006]    Negative Poisson&#39;s ratios are theoretically permissible but have not been successfully observed in real materials. Specifically, in an isotropic material (a material which does not have a preferred orientation) the allowable range of Poisson&#39;s ratio is from −1.0 to +0.5, based on thermodynamic considerations of strain energy in the theory of elasticity (1). It would be helpful to provide a pin structure that exhibits negative Poisson&#39;s ratio. 
         [0007]    Repairing an assembly that utilizes a pin traditionally requires the pin to be driven out of the aperture in which it resides. This can be accomplished by using a driver to force the pin out to the aperture. However, in some circumstances a manufacturer may not want a consumer to repair such assemblies as doing so may invalidate the warranty, or even impact the integrity of the system in which the pinned assembly is being used. For example, if a manufacturer makes a part and that part should only be serviced by an approved repair technician, then it is difficult to monitor circumstances when the consumer may have attempted to repair the pinned assembly themselves. In some instances the consumer may damage a product by taking the repair into their own hands. As such, it would be helpful to provide a locking pin that has features in place that make it difficult for consumers to repair or take apart a manufactured structure, such as a pinned assembly. 
         [0008]    It would also be helpful to provide an improved pin like structure that is made of a process where void configurations are generated in the material directly in a stress free state, whereby the pin like structure can then undergo a loaded condition resulting in a negative Poisson&#39;s ratio behavior. Such process could be used to insert a pin structure into a part, but later allow the part to be serviced again by re-loading the pin structure so as to permit the pin to be removed from the part without damaging the part. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  illustrates a perspective view of a locking pin, in an unloaded state; 
           [0010]      FIG. 2 . illustrates a perspective view of a locking pin, in a loaded state; 
           [0011]      FIG. 3 . illustrates a front view of a sheet of material, depicting a void structure at various strain levels; 
           [0012]      FIG. 4 . illustrates a front view of another sheet of material, depicting an alternative void structure at various strain levels; 
           [0013]      FIG. 5 . illustrates a graph depicting the Poisson&#39;s ratio versus normal strain, for the exemplary locking pin; 
           [0014]      FIG. 6 . illustrates side view of a locking pin installed in a fixture, and the pin is in an unloaded state; 
           [0015]      FIG. 7 . illustrates a side view of a locking pin installed in a fixture, and the pin is under load in the axial direction; 
           [0016]      FIG. 8 . illustrates a side view of a locking pin, in a loaded state and being inserted a bore of a structure; 
           [0017]      FIG. 9 . illustrates an alternative shape for the void structure shown in  FIG. 3 , in which the void structures are in a “double-T” configuration; 
           [0018]      FIG. 10  illustrates a material having void structures in a “double-T” configuration, as shown in  FIG. 9 , and where the placement and configuration of the void structures allows the material to exhibit auxetic properties with areas of minimal stress; and 
           [0019]      FIG. 11  illustrates a material having the configuration of “double-T” void structures as shown in  FIG. 10 , showing the forces acting on the material when compression is applied. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    In an exemplary embodiment a novel locking pin structure is presented. The pin exhibits a negative Poisson&#39;s ratio and is made of a material and construct that reduces its diameter when an axial force is exerted on the longitudinal axis. The material could be a rubber, metal, or others, that easily undergoes shape changes. Another embodiment presents an improved method of inserting an auxetic locking pin into a bore of a structure. The pin may undergo a shape change when axial forces are exerted on the ends of the pin, thus causing the outside diameter of the pin to reduce so as to provide a clearance for the pin to be inserted into the bore of a part. Once the axial force is removed, the diameter of the pin expands thusly engaging the bore of the part causing a locking engagement between the pin and the part. 
         [0021]    Another exemplary embodiment includes a locking pin that could be made of a hollow structure with specific void structures in its surface. The void shapes or structures could be generated in the material directly while it is in a stress-free state, equivalent to collapsed void shapes found in rubber under external load in order to get negative Poisson&#39;s ratio behavior in metal without collapsing a metallic structure in manufacturing. The void&#39;s shapes could be generated in a thick-walled hollow cylinder of the intended size of the pin or the pin can be rolled from sheet metal, in which prior to rolling a void structure has been generated. It will be appreciated that the concepts and void structures that are shown may be employed in areas apart from pins, including but not limited to, combustors, seals, blade tracks, or any components whose functions include maintaining a pressure differential or metering air flow. 
         [0022]      FIG. 1  illustrates an auxetic locking pin  10  that is substantially tubular in shape having a hollow core  12 , a thickness  14 , a length  16 , an outer diameter  18 , an inner diameter  20  and a plurality of surface configurations or voids  22 . The locking pin  10  may be made of rubber, metal, or other material, as is desired for the particular application to which it may be employed. The locking pin  10  is shown in a relaxed, unloaded state, in  FIG. 1 . 
         [0023]    The surface configurations  22 , as depicted in  FIG. 1 , are shown primarily circular in configuration. In an alternative arrangement, the surface configurations are in a “double-T” shape, as shown in  FIG. 9 . In this configuration, the void configurations have a slot with two ends, and a rounded arc disposed on each end of the slot. It will be appreciated that other geometric configurations can be employed. 
         [0024]    The configurations  22  represent apertures that extend through the thickness  14  of the pin  10 . The outer diameter  18  of the pin  10  has configurations that are, in one exemplary embodiment, substantially circular shaped while the inside diameter  20  has a shape  26  that is oval in geometric configuration. The configurations  22  were placed in the surface  24  of the outside diameter  18  while the material forming the pin  10  was in a relaxed, unloaded state.  FIG. 1  illustrates a flat sheet of material  40  ( FIG. 3 ) having a width  16  that may be rolled and the ends welded or otherwise fixed to form the tubular shaped-pin structure assembly that is shown in  FIG. 1 . 
         [0025]    An exemplary configuration  22  includes patterns that consists of horizontal and vertical ellipses arranged on horizontal and vertical symmetry lines in a way that the lines are equally spaced in both dimensions (also Δx=Δy). The center of the ellipses are on the crossing point of the symmetry lines, and vertical and horizontal slots alternate on the vertical and horizontal symmetry lines and any vertical slots is surrounded by horizontal slots along the lines (and vice versa) and the next vertical slots are found on both diagonals. See  FIG. 3 . 
         [0026]    In an alternative arrangement, patterns of horizontal and vertical “double-T” void configurations are disposed on horizontal and vertical symmetry lines in a way that the lines are equally spaced in both dimensions, as shown in  FIG. 10 . Similarly to the configuration shown in  FIG. 3 , the centers of the “double-T” void configurations are on the crossing points of the symmetry lines, and vertical and horizontal “double-T” void configurations alternate on the vertical and horizontal symmetry lines. Any vertical “double-T” void configuration is surrounded by horizontal “double-T” void configurations along both the vertical and the horizontal symmetry lines. 
         [0027]    An ellipse pattern on the outside diameter  18  of the cylindrical component is equivalent to the pattern on the sheet (vertical=axial, horizontal=circumferential). But the ellipse shape on the inside diameter  20  is different due to the different radius of this surface. Axial ellipses have a smaller short axis than on the outside but a larger long axis. Circumferential ellipses have a larger short axis than on the outside but a shorter long axis. 
         [0028]    The material structure illustrated in  FIG. 11  exhibits auxetic properties.  FIG. 11  shows the distribution of the void structures. As shown in  FIG. 11 , the void structures are in a “double-T” configuration, but other configurations could be used. The circular arrows in  FIG. 11  illustrate the forces that act within the material when a compressive force is applied. As can be seen, the material will compress, not only in the direction of the applied force, but also in a direction perpendicular to the applied force. 
         [0029]    Similarly to the material illustrated in  FIG. 11 , the pin  10  has an advantageous behavior of an appeared (macroscopic) negative Poisson&#39;s ratio. The structure of the pin  10  can be made to contract in lateral direction when it is put under axial compression load, without the metal it is made from, having a negative Poisson&#39;s ratio. The behavior is triggered by the void structures  22 , as illustrated in  FIG. 11 . 
         [0030]      FIG. 2  illustrates the  FIG. 1  auxetic locking pin  10  in a loaded state  28 . Loading the locking pin  10  can be effectuated by applying an axial force  30  in the direction of inwardly pointing arrows  36  which causes an inwardly depending force F to be exerted on the distally opposed ends  19 . The exemplary embodiment shown in  FIG. 2  shows an auxetic locking pin  10  having a hole configuration  22 ″ that is different than configuration  22  shown in  FIG. 1 . The hole configuration  22 ″ is but one of many different void structure configurations that could be employed. 
         [0031]    As the axial force  30  is applied to the locking pin  10 , the geometric configuration or structure of the locking pin  10  reacts negatively by causing the surface of the outer diameter  80  of the pin  10  to move inwardly in the direction of arrows  36 . Thus, an inwardly depending force  30 , causes the outer diameter  80  of locking pin  10  to move inwardly in the direction of arrows  36 . The reduction of the outer diameter  80  extends uniformly the entire length  16  of the pin  10 . The greater the axial force  30  that impinges upon the ends  19 , the higher degree of inward defamation of the diameter  80 . They are somewhat directly proportional. The hole configurations  22 ″ are voids in the pin structure that react under pressure to cause a negative Poisson&#39;s ratio like performance of the pin  10 . 
         [0032]      FIG. 3  illustrates a sample of base material  40  that could be employed to manufacture the auxetic locking pin  10  shown in  FIG. 1 . The material  40  could be comprised of a sheet of material that had voids  22  stamped therein while the sheet was in its relaxed state. The material could be rubber, foam, metal, or some other material. The apertures or voids  22  that are shown in the surface of the sheet of material  40 , are formed via stamping, or some other manufacturing process. After the voids  22  have been placed into the sheet  40 , the sheet could undergo a roll forming, or some other process, in order to form the tubular shaped locking pin structure  10  that is depicted in  FIG. 1 . Once the sheet has been placed in its tubular-shaped configuration, any remaining seam may be bonded, welded, or otherwise fixed so as to create a seamless pin like construct. 
         [0033]      FIG. 3  illustrates the sheet of material  40  having gone through three different stages of stressed conditions. Each such stage represents a potential event where the configurations or voids  22  take on a slightly different configuration as a load is applied to the pin  10 . The first step depicts a sheet of material  40  when in an unstrained condition  42  where the sheet  40  of material is primarily unloaded. This is when no axial force F has been applied to the ends  19  of the pin  10 . 
         [0034]    Step 2 illustrates a stage  44  where the sheet  40  of material has been strained, thus causing the oval structure  22 ′ to become oblong along a vertical axis  46 , while becoming narrowed and shortened along the x axis  48 . As the sheet  40  of material becomes more stressed, that is a greater axial force  30  is applied, the oval structures  22  become more disfigured, resulting in the locking pin  10  transforming into a different geometric configuration. At this step the diameter  80  of the pin  10  begins to reduce as the auxetic structure permits a reduction in diameter as the force  30  is applied inwardly. 
         [0035]    Finally, with continued reference to  FIG. 3 , another step  50  occurs as inwardly applied axial force  30  continues to be exerted on the auxetic locking pin  10 . At this step the sheet  40  of material has its oval shaped structures  22 ″ taking on an even more extreme oval geometric configuration where the x axis  48  continues to be shortened, while the y axis  46  continues to elongate. This process may continue until a maximum negative strain level is reached, thus resulting in a minimum diameter  80  being obtained. See  FIG. 2 . 
         [0036]      FIG. 5  illustrates a strain graph  60  that plots the Poisson&#39;s ratio  62  on the y axis, relative to the normal strain  64  on the x axis. This graph depicts the relationship of force  30  being applied to the auxetic pin  10 . For example, with continued reference to  FIGS. 3 and 5 , at step 1 ( 42 ), the sheet  40  may initially take on a slightly positive Poisson&#39;s ratio of approximately 0.2. However, as an axial force  30  continues to be applied to the auxetic pin  10 , the sheet  40  begins to transform the structure to have a negative Poisson&#39;s ratio, such as that depicted at step 2 ( 44 ) where approximately a −0.1 Poisson&#39;s ratio is depicted. This is represented by step 3 ( 44 ), of  FIG. 3 . At this step, the diameter  80  of the locking pin  10  begins to contract in the direction of arrows  36 . 
         [0037]    Finally, as an axial force  30  is continued to be applied to the end  19  of the locking pin  10 , the diameter  80  continues to contract. The void structures at this stage have an elongated configuration  22 ″ as is shown in step 3 ( 50 ) ( FIG. 3 ). By applying the axial force  30  the pin  10  reduces its diameter which may be helpful to load a locking pin  10  into a part. 
         [0038]      FIG. 4  illustrates an alternative pattern arrangement whereby a sheet  40  of material includes a plurality of holes or voids  22  and its surface. The sheet  40  is shown in an unstressed state at first step  42 . It will be appreciated that other geometric configurations  22 , apart from that which is shown in  FIGS. 3 and 4 , are contemplated. 
         [0039]    With continued reference to  FIG. 4 , at step 2 ( 44 ) the pin  10  has had a force  30  applied to the end  19  of the pin. This causes the geometric configuration  22 ′ to deform as it contracts along the longitudinal x axis  48 , and expands along the y axis  46 . 
         [0040]    As force  30  continues to be exerted on the end  19  of the pin  10 , the sheet  40  of material continues to have its void structures deform. This is shown in step 3 ( 50 ) where the material  40  is stressed even further, and the geometric configurations  22 ″ have been further transfigured where the oval shaped openings continue to contract along the x axis  48  and elongate along the y axis  46 . 
         [0041]    It will be appreciated that the auxetic locking pin  10  as illustrated in  FIGS. 1 and 2 , can have various thicknesses  14 , lengths  16 , outside diameters  18 , or inside diameters  20 . Each of which may employ an auxetic structure that is operable to have its structure operate such that when a force is applied on an end  19  of the pin  10 , the diameter  18  contracts, thus allowing the auxetic pin  10  to be loaded into another structure. Applications for this unique concept can be used in industries where it desirable to insert a pin into a boar of an article. 
         [0042]    An exemplary method of manufacturing an auxetic locking pin  10  will be presented. First a sheet  40  of material is provided having a thickness  14  and a length  16 . It may be made of metal, rubber or other material. Next, while the sheet remains in a relaxed state, apertures  22  are stamped or otherwise placed through the thickness  14  of the material  40 . One exemplary pattern is to have alternating shapes along the x axis. One such non-limiting example is to provide an oval shaped pattern where ovals are placed in alternating patterns, such as that shown in  FIG. 3 . Other shapes or void structures are contemplated, including, but not limited to, S-shaped, hook-shaped, J-shaped, and dumbbell-shaped. 
         [0043]    The next step is to roll the sheet  40  of material into a tubular shape as shown in  FIG. 1 . This step creates a pin  10  that has a bore  20  that extends the axial length  16  of the pin  10 . A seam may remain that can be bonded, welded or affixed via other means. Other finishing steps may be employed to complete the exterior surface of the pin. The pin  10  is now ready to be inserted in a part. 
         [0044]      FIGS. 6-8  depict one possible methodology that could be employed for installing an auxetic locking pin  10  into a part  70 . The part  70  could be a device, article, or other structure that needs a pin, barring, shaft, or the like inserted within the part  70 . The part  70  may have a bore  72  that extends the axial length of the part  70 . A fixture or tool  74  may be provided to enhance the process of installing a locking pin  10  into the part  70 .  FIG. 6  illustrates a first step in this process where the part  70  has been loaded onto the shaft  76  of the tool  74 . Once loaded, the part  70  is provided with an inside diameter  78  which is operable to receive a locking pin  10 . The locking pin  10  is shown loaded into the fixture  74  where the end of the shaft  76  impinges upon an end  19  of the locking pin  10 . The locking pin at this stage has a diameter  18 , which is unloaded. 
         [0045]      FIG. 7  illustrates a force  30  being applied by the shaft  76  which results in a load being applied to the locking pin  10 . At this step the diameter  18  of the locking pin  10  begins to contract to where it has a new diameter  80 . The diameter  80  is smaller than the diameter  18 . As the force  30  continues to impinge upon the end  19  of the locking pin  10 , the diameter  80  continues to decrease. This continues until the diameter  80  is less than the inside diameter  72 , of the part  70 . It would be helpful to provide a diameter  80  that is sufficiently less than the diameter  78  of the part  70 , so as to allow a clearance therebetween. 
         [0046]      FIG. 8  illustrates the pin  10  with its diameter  80  held constant while the part  70  is slid axially in the direction of arrow  82  ( FIG. 7 ). The force  30  continues to be maintained on the locking pin  10 , during this step. The part  70  is slid in the direction of arrow  82  until it reaches a point where the pin  10  is centrally located within the bore  72  of the part  70 . 
         [0047]    Once the pin  10  has been fully inserted to the bore  72  of the part  70 , the shaft  76  of the fixture  74  is retracted in the direction opposite of arrow  82 . This allows the locking pin  10  to relax and revert back to its larger diameter  18 , or a size similar thereto. Once the locking pin  10  reverts back towards its diameter  18 , it becomes compressed with the bore  72 , thus causing an interference fit between the outer diameter  18  of the locking pin  10 , and the bore  72  of the part  70 . This interference fit creates a locking engagement, thus firmly securing the pin  10  relative to the part  70 . Due to the larger overlap with the bore, the pin is more securely locked in place. The additional edges  24  from the void structure  22  lead to an additional “keying” with the bore  72 . This creates a locking engagement between the pin  10  and the part  70 . The locking engagement can be unlocked by reversing the aforementioned steps. The pin  10  does not get loose due to external load or vibrations. 
         [0048]    The reverse steps may be employed in order to remove the locking pin  10 , from the part  70 . A force  30  could be applied until the structure of the locking pin  10  begins to transform, thus causing the diameter  18  to decrease. Once the diameter sufficiently decreases, it has a new diameter  80  which results in a clearance between outer diameter  80  and the bore  72  of the part  70 . The pin  10  can then be removed from the part  70 . 
         [0049]    With reference to  FIG. 7 , the part  70  has been separated from the pin  10 . The pin  10  may be removed from the fixture  74 , thus allowing the part  70  to be rebuilt. Likewise, in the event the pin  10  needs to be serviced, the aforementioned steps may be employed to provide a new, or refurbished, pin  10  into a part  70 . Thus, the present method and structure provides for a serviceable part  70  where a new or refurbished pin  10  can be inserted into the part  70 . The present embodiment may be employed in other applications, beyond that disclosed herein, where it is desirable to provide a locking pin  10 , or the like, into a bore of a structure. 
         [0050]    One of the features of an embodiment disclosed herein is that an untrained person, who does not know about the specific properties of the pin  10 , cannot remove the pin  10  without significant damage to the bore  72 , which can be checked for by an OEM during overhaul. If authorized personnel needs to remove the pin  10 , then they can apply the process mentioned above to first compress the pin  10  and then while in the compressed state, slide the pin  10  out without any damage to the bore  72 . This specific property allows the OEM to discover unauthorized manipulation (witness pin), or the OEM can use the pin at a vibration level not bearable for conventional pins in the past. 
         [0051]    It will be appreciated that the aforementioned method and devices may be modified to have some components and steps removed, or may have additional components and steps added, all of which are deemed to be within the spirit of the present disclosure. Even though the present disclosure has been described in detail with reference to specific embodiments, it will be appreciated that the various modification and changes can be made to these embodiments without departing from the scope of the present disclosure as set forth in the claims. The specification and the drawings are to be regarded as an illustrative thought instead of merely restrictive thought.