Patent Publication Number: US-2011064515-A1

Title: Anchor and splice plate assembly for axially split composite duct or pressure vessel

Description:
STATEMENT OF GOVERNMENT INTEREST 
     This invention was made with U.S. Government support under Contract No. N00019-02-C-3003. The Government has certain rights in this invention. 
    
    
     BACKGROUND 
     The present invention relates generally to joint assemblies suitable for use with a segmented duct or pressure vessel. 
     Ducts and pressure vessels are often assembled from a plurality of discrete segments. For example, bypass ducts for gas turbine engines are often made up of axially split duct segments that are secured together at structural joints using bolts and splice plates. However, bypass duct design and assembly presents a number of problems. Access to interior regions of an assembled bypass duct is limited, which reduces access to bolts or other fasteners from the inside of the duct. A number of blind fastener designs are known in the art that allow fasteners to tightened and loosened from exterior locations alone. But those prior art designs have flaws and limitations. For example, certain blind fastener means like caged bolts and nut plates have reliability issues, and if they become worn or damaged during use may make it difficult or impossible to remove. For instance, after use, a caged bolt may begin to spin due to deformation of its retaining cage, making it impossible to loosen a nut attached to the bolt from the exterior of the duct without access to the bolt from inside the duct. Moreover, drilling out a failed caged bolt with a retaining cage that has failed is difficult without access to the interior of the duct. Efforts have been made to utilize composite materials to form bypass duct segments that are lighter (i.e., have less mass) than those made from metallic materials. However, composite materials further limit efforts to structurally join duct segments. For example, it is difficult if not impossible to form composite materials into flanges to make bolted connections between parts. In addition, composite materials themselves are generally unsuitable for forming threads to accept threaded bolts. Blind fastener means like ovalized threaded grommets with threaded inserts can be secured in the composite material, but require a great deal of parent material of the duct to be removed for grommet insertion, in some cases four to five times wider than a diameter of a corresponding bolt to be engaged with the grommet. Extensive parent material removal leads to localized weaknesses in the duct, which present a risk of cracking and other damage. Such grommets are also relatively expensive, heavy, and time consuming to install. 
     The types of problems discussed above all frustrate and complicate efforts to perform maintenance on the bypass duct and other components of the gas turbine engine. Therefore, it is desired to provide a joint assembly for use with ducts and pressure vessels that is relative lightweight, reliable, and easy to install. 
     SUMMARY 
     An assembly according to the present invention includes first and second shell members. An anchor plate includes a body portion, first and second arrays of fastener openings, and anchor plate attachment features extending from a first side of the body portion and each having a fastener opening. Inserts are positioned within each fastener opening of the first array and the second array. A first set of fasteners is secured through the first array of fastener openings in the anchor plate, the first shell member and the splice plate and engaged with a corresponding one of the inserts. A second set of fasteners is secured through the second array of fastener openings in the anchor plate, the second shell member and the splice plate and engaged with a corresponding one of the inserts. A third set of fasteners is secured through the fastener openings of the anchor plate attachment features and the first shell member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a gas turbine engine. 
         FIG. 2  is a perspective view of one embodiment of a joint assembly according to the present invention. 
         FIG. 3  is a cross-sectional view of the joint assembly, taken along line  3 - 3  of  FIG. 2 . 
         FIG. 4  is an elevation view of an additional embodiment of the joint assembly according to the present invention. 
         FIG. 5  is a cross-sectional view of the additional embodiment of the joint assembly, taken along line  5 - 5  of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic cross-sectional view of a gas turbine engine  10  that includes a fan section  12 , a low-pressure compressor (LPC) section  14 , a high-pressure compressor (HPC) section  16 , a combustor section  18 , a high-pressure turbine (HPT) section  20 , and a low-pressure turbine (LPT) section  22 . A centerline C L  is defined by the engine  10 . A generally annular bypass duct  24  extends aftward from the fan section  12 , and is positioned radially outward from a primary flowpath through the LPC section  14 , the HPC section  16 , the combustor section  18 , the HPT section  20  and the LPT section  22 . Airflow through the bypass duct  24  generated by the fan section  12  during operation of the engine  10  helps provide thrust. It should be noted that the illustrated embodiment of the gas turbine engine  10  is provided merely by way of example and not limitation. Aspects of the present invention can be applied to gas turbine engines of any configuration, such as low bypass ratio configurations. The basic operation of gas turbine engines is well known, and therefore further discussion here is unnecessary. 
       FIG. 2  is a perspective view of one embodiment of a joint assembly  30  of the bypass duct  24 , and  FIG. 3  is a cross-sectional view of the joint assembly  30  taken along line  3 - 3  of  FIG. 2 . In the illustrated embodiment, the assembly  30  includes a first duct segment (or shell member)  32 , a second duct segment (or shell member)  34 , an anchor plate  36 , and a splice plate  38 . The first and second duct segments  32  and  34  define adjacent portions of the bypass duct  24  that are axially split from each other (i.e., when assembled together forming a split line that is substantially parallel to the centerline C L ). The first duct segment  32  has an exterior surface  32 E and an opposite interior surface  32 I. Likewise, the second duct segment  34  has an exterior surface  34 E and an opposite interior surface  34 I. 
     In the illustrated embodiment, the anchor plate  36  is positioned against adjacent portions of the interior surfaces  32 I and  34 I of the first and second duct segments  32  and  34 , respectively. The anchor plate  36  includes a body portion  36 B having a substantially rectangular perimeter. A first array of bosses (or collars)  40  and a second array of bosses (or collars)  42  are each arranged in a row extending from the body  36 B of the anchor plate  36 . Each of the bosses  40  and  42  has a substantially cylindrical shape with a central opening in the illustrated embodiment. The central openings of the bosses  40  and  42  are optionally threaded. The first array of bosses  40  is arranged at a portion of the interior surface  32 I of the first duct segment  32 , and the second array of bosses  42  is spaced apart of the first array of bosses  40  and arranged at a portion of the interior surface  34 I of the second duct segment  34 . 
     A plurality of attachment features  44  extend from one edge of the body portion  36 B of the anchor plate  36  in the illustrated embodiment. Each attachment feature  44  has a substantially circular perimeter and defines a central opening. The central openings of the attachment features  44  are optionally threaded. 
     An insert  46  is secured within each opening of the first and second arrays of bosses  40  and  42  and the attachment features  44  to provide a rotationally-fixed blind engagement means between the anchor palate  36  suitable fasteners  48  (e.g., threaded bolts). The inserts  46  can each be configured as a cylinder with threads on both interior and exterior surfaces, with key members positioned along channels formed through the threads on the exterior surface of the insert that are driven down along the channels and through parent material of the corresponding threads of the boss  40  or  42  or attachment feature  44  in which the insert  46  is positioned to rotationally lock the insert  46  relative to the anchor plate  36 . Such a keyed configuration of the inserts  46  provides a relatively reliable and stable rotationally fixed mount. In one embodiment, the inserts  46  are Tridair® brand Keensert® inserts (available from Alcoa Fastening Systems, Torrance, Calif.). Other types of inserts can be utilized in alternative embodiments. 
     The splice plate  38  is positioned generally opposite the anchor plate  36  against adjacent portions of the exterior surfaces  32 E and  34 E of the first and second duct segments  32  and  34 , respectively. The splice plate  38  can define a substantially rectangular perimeter, and can be sized commensurate with a size of the body portion  36 B of the anchor plate  36 . A first array of openings  50  and a second array of openings  52  are defined through the splice plate  38  (only one opening of each array  50  and  52  is visible in  FIG. 2 ). The openings  50  and  52  are arranged to align with the central openings of the first and second arrays of bosses  40  and  42 , respectively, of the anchor plate  36 . The openings  50  and  52  can be circular, or can have other shapes to permit alignment adjustments. The fasteners  48  are engaged to secure the anchor plate  36  and the splice plate  38  together with the first and second duct segments  32  and  34 . 
     In order to fabricate the assembly  30 , the first and second duct segments  32  and  34 , the anchor plate  36 , and the splice plate  38  are provided. In one embodiment, the first and second duct segments  32  and  34  are each made of a fiber reinforced composite material, and the anchor plate  36  and the splice plate  38  are each made of metallic materials. Material of the anchor plate  36  can be removed in between the bosses  40  and  42  (e.g., by machining or other suitable processes) in order to reduce a thickness of the anchor plate  36  and thereby reduce a mass of the assembly  30 . Next, the inserts  46  are secured to the anchor plate  36 . The anchor plate  36  is then attached to the first duct segment  32  using the fasteners  48  engaged to the inserts  46  of the attachment features  44  through suitable openings through the first duct segment  32 . In this way, the anchor plate  36  is secured to the first duct segment  32  in a desired position, allowing the anchor plate  36  to maintain its desired position even as access to interior surfaces  32 I and  34 I of the first and second duct segments  32  and  34  is limited or prevented. 
     Next, the second duct segment  34  is positioned adjacent to the first duct segment  32  in a desired configuration. The splice plate  38  is the positioned adjacent to the first and second duct segments  32  and  34 . The fasteners  48  are then engaged between the first array of openings  50  in the splice plate  38  to the inserts  46  in the first array of bosses  40  of the anchor plate  36 , and between the second array of openings  52  in the splice plate  38  to the insets  46  in the second array of bosses  42  of the anchor plate. The fasteners pass through first and second arrays of openings  52  and  54  in the first and second duct segments  32  and  34 , respectively. This secures the anchor plate  36  and the splice plate  38  together with the first and second duct segments  32  and  34  to form the completed joint assembly  30 . The finished joint assembly  30  provides structural support between the first and second duct segments  32  and  34 . The fasteners  48  are secured in a blind engagement configuration. Because the inserts  46  are rotationally fixed relative to the anchor plate  36 , the fasteners  48  can be engaged and disengaged (e.g., rotationally tightened and loosened) from a location proximate the exterior surfaces  32 E and  34 E of the first and second duct segments  32  and  34  alone, without requiring access to interior regions. 
       FIG. 4  is an elevation view of an additional embodiment of a joint assembly  130 , and  FIG. 5  is a cross-sectional view of the joint assembly  130  taken along line  5 - 5  of  FIG. 4 . The joint assembly  130  includes a first duct segment  32 , a second duct segment  34 , a first anchor plate  136 - 1 , a second anchor plate  136 - 2 , and a splice plate  138 . The first anchor plate  136 - 1  is arranged adjacent to the interior surface  32 I of the first duct segment  32 , and the second anchor plate  136 - 2  is arranged adjacent to the interior surface  34 I of the first duct segment  34 . The splice plate  138  is positioned generally opposite the first and second anchor plates  136 - 1  and  136 - 2  against adjacent portions of the exterior surfaces  32 E and  34 E of the first and second duct segments  32  and  34 , respectively. 
     The first and second anchor plates  136 - 1  and  136 - 2  each have a body portion  136 B. The first anchor plate  136 - 1  includes a first array of bosses  140  extending from the body portion  136 B, and the second anchor plate  136 - 2  includes a second array of bosses  142  extending from the body portion  136 B. In the illustrated embodiment, the first and second arrays of bosses  140  and  142  are each arranged as a pair of parallel, offset rows. Each of the first and second anchor plates  136 - 1  and  136 - 2  further includes a plurality of attachment openings  144 , which are arranged in an offset configuration in the illustrated embodiment. 
     Fabrication and assembly of the joint assembly  130  is generally similar to that described above with respect to the joint assembly  30 . However, in the present embodiment, each of the first and second anchor plates  136 - 1  and  136 - 2  is secured to its respective first and second duct segment  32  and  34  using fasteners  145 , such as rivets, positioned and engaged through the attachment openings  144 . Fasteners  145 B, such as conventional bolts, are then engaged between the splice plate  138  and the first and second anchor plates  136 - 1  and  136 - 2  in blind engagement to inserts  146  in the first and second arrays of bosses  140  and  142 . In the illustrated embodiment, countersunk recesses  147  are provided at the respective exterior surfaces  32 E and  34 E of the each of the first and second duct segments  32  and  34  to accommodate portions of the fasteners  145 , such that the fasteners  145  can be engaged while still allowing the splice plate  138  to be positioned substantially flush with the respective exterior surfaces  32 E and  34 E of the first and second duct segments  32  and  34 . 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. For example, the present invention can be applied to nearly any duct or pressure vessel, such as pipes and conduits used for a variety of applications.