Patent Publication Number: US-2021162698-A1

Title: Large Cell Carbon Core Sandwich Panel and Method of Manufacturing Same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of application Ser. No. 15/878,301, which was filed on 23 Jan. 2018 and entitled “LARGE CELL CARBON CORE SANDWICH PANEL AND METHOD OF MANUFACTURING SAME,” the entire content of which is hereby expressly incorporated by reference. 
    
    
     BACKGROUND 
     In many applications, particularly in the aerospace industry, there is a large demand for thin, strong, lightweight panels, for example, wing skins on aircraft. Wing skins used to be made of thin lightweight aluminum panels and a network of internal structures of the wing carried most of the loads. Later, wing skins were made of carbon fiber sheets with stringers bonded to them to have the skins carry a larger portion of the load. More recently, large cell carbon core technology has enabled aircraft manufacturers to eliminate the stringers in favor of a smooth inner surface of the skins, while improving the structural integrity. As such, the large cell carbon core skins function not just as airfoils, but as structural components of the wing. The smooth inner surface of the panels also significantly simplify fabrication of the panels, and make attachment of internal structures thereto much simpler. 
     Similar to traditional honeycomb sandwich panels, large cell carbon core panels include a pair of laminates bonded to a honeycomb shaped core. However, traditional honeycomb panels are manufactured in a single curing process. That is, when manufacturing a traditional honeycomb sandwich panel, an uncured first laminate, a first layer of adhesive, a honeycomb core, a second layer of adhesive, and an uncured second laminate are all laid-up and the entire panel is co-cured in one operation. With a large cell carbon core panel, the large size of each cell of the core prohibits co-curing because the uncured laminates would sag into the cells, creating a permeable and/or dimpled panel. As such, large cell carbon core sandwich panels are manufactured using pre-cured laminates. Therefore, current large cell carbon core sandwich panels require a minimum of three cure cycles, one for each laminate and one for the whole panel. In addition, these three cure cycles also require three separate sets of tooling for laying up and curing the two laminates and the final panel. The intent of this disclosure is to define methods of co-curing the two laminates and the large cell core in one cure cycle while eliminating the sag, permeability, and/or dimpling of the laminates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique exploded view of components of a large cell carbon core sandwich panel, according to this disclosure. 
         FIG. 2  is cross-sectional side view of a fabrication setup for manufacturing the large cell carbon core sandwich panel of  FIG. 1 . 
         FIG. 3  is an oblique view of a portion of the large sell carbon core sandwich panel of  FIG. 1 . 
         FIG. 4  is a cross-sectional side view of the large cell carbon core sandwich panel of  FIG. 1 . 
         FIG. 5  is a cross-sectional side view of a portion of the manufacturing process of the large cell carbon core sandwich panel shown in  FIG. 2 . 
         FIG. 6  is a cross-sectional side view of the large cell carbon core sandwich panel of  FIG. 1  showing a port sealed with a port cap. 
         FIG. 7  is a cross-sectional side view of the large cell carbon core sandwich panel of  FIG. 1  showing the port sealed with a sealant. 
         FIG. 8  is an oblique side view of an aircraft having a wing with skins made of large cell carbon core sandwich panels, according to this disclosure. 
         FIG. 9  is a cross-sectional side view of the wing of the aircraft of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     In this disclosure, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of this disclosure, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. In addition, the use of the term “coupled” throughout this disclosure may mean directly or indirectly connected, moreover, “coupled” may also mean permanently or removably connected, unless otherwise stated. 
     This disclosure provides a large cell carbon core sandwich panel and a method of manufacturing the same. The panel is generally manufactured by pressurizing the cells within the carbon core to prevent the laminates from sagging into the cells during the curing process. There are several different methods and structures that may facilitate pressurization of the large cell carbon core described below. 
       FIGS. 1-7 . illustrate the components of a panel  100 , according to this disclosure. Panel  100  includes a first laminate  102  with an outer surface  104 , an inner surface  106 , and a depth  108  measured therebetween. Opposite first laminate  102  is a second laminate  110  with an outer surface  112 , an inner surface  114 , and a depth  116  measured therebetween. Outer surface  104  of first laminate  102  and outer surface  112  of second laminate  110  are the faces of finished panel  100 . First laminate  102  and second laminate  110  may be made of one or more layers of woven fiber sheets. For example, first laminate  102  and second laminate  110  may be made of several sheets of woven carbon fiber, fiberglass, or Kevlar. First laminate  102  and second laminate  110  may be pre-impregnated with resin or may have resin added thereto during panel construction. First laminate  102  and second laminate  110  may be different materials and depths  108 , 116  may be equal or unequal. Moreover, depths  108 ,  116  may vary along the length or width of panel  100 . 
     The filling of sandwich panel  100  is a core  118 . Large cell core  118  has a first side  120  facing first laminate  102  and a second side  122  facing second laminate  110 . Core  118  defines a plurality of cells  124  extending from first side  120  to second side  122 . Cells  124  are separated from each other by cell walls  126 . Cell walls  126  are permeable so that gas introduced into one cell  124  may pass through cell wall  126  into an adjacent cell  124 . Each cell  124  has a height  128  measured from first side  120  to second side  122  and a width  130  perpendicular to height  128 . As core  118  is a large cell core, cells  124  preferably have cell widths  130  of at least ½ inch. Core  118  may be made of any material suitable for the intended purpose, for example, core  118  may be made of carbon fiber, fiberglass, Kevlar, aluminum, plastic, etc. Height  128  of cells  124  may be greater than depth  108  of first laminate  102  and depth  116  of second laminate  110 . However, height  128  may be equal to, or less than, either or both depths  108 ,  116 . Moreover, height  128  and width  130  may be variable along the length and width of panel  100 . While shown as having a hexagonal cross-section, cells  124  may have any cross-sectional shape suitable for the intended purpose. 
     A first layer of thermoplastic  132  is located between inner surface  106  of first laminate  102  and first side  120  of core  118 , and a second layer of thermoplastic  134  is located between inner surface  114  of second laminate  110  and second side  122  of core  118 . First and second layers of thermoplastic  132 ,  134  also serve as the bonding agents adhering first and second laminates  102 ,  110  to core  118 . First and second layers of thermoplastic  132 ,  134  may also function as vapor barriers of finished panel  100 . First and second layers of thermoplastic  132 ,  134  may comprise polyetherimide (PEI) or Kapton, or any other material suitable for acting as a gas barrier and a bonding agent. 
     Manufacturing panel  100  is facilitated by increasing the pressure within core  118  to provide a resistance force against inner surface  106  of first laminate  102  and inner surface  114  of second laminate  110  to prevent first and second laminates  102 ,  110  from sagging into cells  124  during the curing process. Pressure within core  118  may be increased by the introduction of a gas  136  through a port  138  extending from outer surface  112  to inner surface  114  of second laminate  110 . Preferably, port  138  is centered over one of cells  124  and port  138  has a diameter  140  that is less than width  130  of cell  124  so that port  138  does not intersect with any of the cell walls  126 , and therefore, port  138  does not affect the structural integrity of core  118 . Port  138  may include a an annular flange  142  extending radially therefrom which may be positioned between the layers of fabric of second laminate  110 . Port  138  may also include a threaded opening  144  therein to facilitate attachment of a nozzle  146  thereto for the introduction of gas  136 . While the embodiment shown illustrates port  138  as an inserted structure, port  138  could simply be an opening created in second laminate  110  by moving fibers to allow nozzle  146  to be inserted through second laminate  110  into core  118 . 
     The method of manufacturing panel  100  is illustrated in  FIG. 2 . First laminate  102  is laid-up on a tooling surface  148 . First laminate  102  is then covered with first layer of thermoplastic  132 . Core  118  is then placed on top of first layer of thermoplastic  132 . Core  118  is then covered with second layer of thermoplastic  134  such that first layer of thermoplastic  132  and second layer of thermoplastic  134  are in contact with each other surrounding a perimeter of core  118 . First layer of thermoplastic  132  is then bonded to second layer of thermoplastic around the entire perimeter of core  118  forming a seal  150 . Seal  150  creates an airtight core pocket  152  between first layer of thermoplastic  132  and second layer of thermoplastic  134 . Second laminate  110  is then placed on top of core pocket  152 . It should be understood that core pocket  152  may be formed after second laminate  110  is placed on second layer of thermoplastic  134 , as long as first layer of thermoplastic  132  and second layer of thermoplastic  134  extend beyond second laminate  110 . 
     After the materials making up panel  100  are laid in position, they are covered with a vacuum bag  154  which is hermitically attached to tooling surface  148 . A vacuum nozzle  156  is inserted through vacuum bag  154  and attached to a vacuum pump  158  via a vacuum hose  160 . Before vacuum pump  158  is activated, nozzle  146  is inserted through port  138 , piercing second layer of thermoplastic  134 , into core pocket  152 . Nozzle  146  is attached to an air compressor  162  by an air hose  164 . Preferably, although not necessarily, vacuum pump  158  and air compressor  162  operate simultaneously to remove both the air from within vacuum bag  154 , thereby increasing the pressure against outer surface  112  of second laminate  110 , and to introduce gas  136  (air) into core pocket  152 , thereby increasing the pressure within core pocket  152 . 
     As shown in  FIG. 5 , cell walls  126  of core  118  are preferably permeable and therefore, permit gas  136  to pass therethrough, allowing an even pressure throughout core pocket  152 . Depending on the degree of permeability and dimensions of core  118 , more than one port  138  may be required to provide substantially equal pressure throughout core pocket  152 . The pressure generated within core pocket  152  should be less than or equal to the pressure applied to outer surface  112  of second laminate  110  by vacuum bag  154 . Otherwise, the higher pressure within core pocket  152  may cause bulging of second laminate  110 . Accordingly, the pressures within vacuum bag  154  and core pocket  152  should both be monitored throughout the curing process. In addition to being internally and externally pressurized, the materials comprising panel  100  should be heated to a desired curing temperature. Heating may be accomplished by placing the setup in an autoclave or an oven. It may be desired to embed temperature probes within panel  100  to monitor internal temperatures of panel  100  during the curing process. The desired internal and external pressures, as well as the desired curing temperature should be maintained for a desired curing duration. 
     After curing is complete, and nozzle  146  is removed from port  138 , it may be desired to seal off port  138 . Sealing port  138  may be accomplished in a variety of ways. For example, as shown in  FIG. 6 , a threaded cap  166  may be inserted therein. Or, as shown in  FIG. 7 , port  138  and the adjoining cell  124  may be filled with a sealant  168 . Sealant  168  may be a foam, epoxy, or resin filled with chopped fiber, or any other material suitable for sealing port  138 . Moreover, port  138  may be removed completely and the resulting opening be patched over. Alternatively, port  138  may remain in place and be used as an anchor point for attaching equipment to panel  100 . 
       FIGS. 8 and 9  illustrate particularly advantageous uses of large cell core sandwich panels.  FIG. 8  illustrates an aircraft  200  with a fuselage  202  and a wing  204  extending bilaterally from fuselage  202 . Coupled to opposite ends of wing  204  are a pair of tiltrotors  206 . Tiltrotors  206  are rotatable between a vertical, helicopter position, (as shown in  FIG. 8 ) and a horizontal, airplane position. The varying forces transmitted from tiltrotors  206  through wing  204  to fuselage  202  require a robust wing structure with a high degree of torsional stiffness. Accordingly, as shown in  FIG. 9 , wing  204  includes a torque box  208  to resist the large forces. Torque box  208  includes a forward spar  210 , an aft spar  212 , a lower skin  214 , an upper skin  216 , and a plurality of ribs  218 . Lower skin  214 , upper skin  216 , and rib  218  are all large cell carbon core sandwich panels cured in a single stage process by pressurizing the cores in accordance with the method described herein. 
     Lower skin  214  includes a first laminate  220  with an outer surface, an inner surface, and a depth measured therebetween. Opposite first laminate  220  is a second laminate  222  with an outer surface, an inner surface, and a depth measured therebetween. As shown, the depth of first laminate  220  is greater than the depth of second laminate  222 . In between first laminate  220  and second laminate  222  is a core  224  bonded in place by a first layer of thermoplastic between first laminate  220  and core  224  and a second layer of thermoplastic between second laminate  222  and core  224 . Lower skin  214  also includes a port  226  plugged with a sealant  228 . 
     Upper skin  216  includes a first laminate  230  with an outer surface, an inner surface, and a depth measured therebetween. Opposite first laminate  230  is a second laminate  232  with an outer surface, an inner surface, and a depth measured therebetween. As shown, the depth of first laminate  230  is greater than the depth of second laminate  232 . In between first laminate  230  and second laminate  232  is a core  234  bonded in place by a first layer of thermoplastic between first laminate  230  and core  234  and a second layer of thermoplastic between second laminate  232  and core  234 . Upper skin  216  also includes a port  236  plugged with a sealant  238 . 
     While the method of manufacturing panels described in this disclosure is particularly useful in manufacturing large cell sandwich panels, it is not so limited. The method described herein may be used to manufacture panels having cells of any size. In addition, formation of a core pocket that facilitates pressurization of core  118  may be created without the use of thermoplastics. For example, first and second laminates  102 ,  110  may undergo B-stage preparation prior to being laid-up. The partial curing of B-stage preparation may provide a sufficient seal to allow pressurization of the  118 . Furthermore, pressurization of core pocket  152  may be accomplished by causing a chemical reaction that releases a gas within core pocket  152 . Core pocket  152  may also be pressurized by filling core pocket  152  with a gas that has a high degree of thermal expansion when heated so that the gas in core pocket  152  expands when the setup is placed in the autoclave. 
     At least one embodiment is disclosed, and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, RI, and an upper limit, R u , is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R l +k*(R u −R l ), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 95 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention. Also, the phrases “at least one of A, B, and C” and “A and/or B and/or C” should each be interpreted to include only A, only B, only C, or any combination of A, B, and C.