Patent Publication Number: US-2022234714-A1

Title: Flat composite panel with tear arrestment and method of making the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/142,767, filed Jan. 28, 2021, and entitled “Flat Composite Panel with Tear Arrestment and Method of Making the Same” which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND INFORMATION 
     1. Field 
     The present disclosure generally relates to composite structures and deals more particularly with a flat composite panel having an integral tear arrestment feature. 
     2. Background 
     Flat composite panels are sometimes subject to impact damage. Designing the panel to arrest impact damage can be challenging, particularly where the panel is relatively thin and requires stiffening features. For example, a flat composite panel may be used in an aircraft to separate pressurized and non-pressurized spaces. One aircraft application of such panels is a pressure deck which separates a flight deck from a nose wheel landing gear well. The pressure deck comprises a composite laminate panel that is reinforced with external stiffeners such as stringers that are co-cured with the panel. Both the stiffeners and the panel are subject to impact damage as a result of debris that may be propelled during takeoffs and landings. 
     Pressure decks of the type described above require specialized tooling to layup, form and co-cure the stiffeners with the panel. Also, impact damage to these pressure decks can be time-consuming and challenging to repair. Damaged stiffeners must be removed and replacement stiffeners must be laid up, formed, and bonded to the panel, following which pull-off tests will be performed to assure that the stiffener are adequately attached to the panel. This repair process becomes even more complicated when the panel itself has been damaged. 
     Accordingly, it would be desirable to provide a flat composite panel having greater stiffness and damage resistance without the use of stiffeners. 
     SUMMARY 
     The disclosure relates in general to composite panels, and more specifically to a pressure deck for aircraft with damage arrestment features. 
     According to one aspect, a composite panel having tear arrestment comprises a base panel, at least a first tear strap and at least a second tear strap. The base panel includes a plurality of base panel plies of a fiber reinforced polymer. The first tear strap extends in a first direction and is integrated into the base plies. The second tear strap extends in a second direction transverse to the first direction and is integrated into the base panel plies. 
     According to another aspect, a pressure deck panel is provided for an aircraft separating a flight deck from a nose wheel well. The pressure deck panel comprises a base panel including a plurality of plies of a fiber reinforced polymer, and a plurality of tear straps integrated into the base panel. 
     According to still another aspect, a method is provided of fabricating a composite pressure deck panel for an aircraft. The method includes laying up a base panel, including laying up a plurality of base panel plies of composite material. The method also includes integrating a plurality of first tear straps into the base panel plies, and integrating a plurality of second tear straps into the base panel plies. Integrating the first and second tear straps includes interspersing them with the base panel plies as the base panel plies are laid up. The method also includes orienting the plurality of second tear straps transverse to the plurality of first tear straps. 
     According to still another aspect, a method is provided of arresting a tear in a composite laminate panel. The method comprises interspersing a plurality of tear straps within plies of the laminate panel, and using the tear straps to arrest a tear in the laminate panel. 
     One of the advantages of the disclosed embodiments is that a flat composite laminate panel can be produced with the necessary stiffness and tear resistance to impacts without the need for stiffener attachments and associated tooling. Another advantage is that the disclosed flat composite laminate panel can be used as a pressure deck for aircraft. Another advantage is that the flat composite laminate panel is less subject to impact impairment as a result of the use of integral tear straps. Still another advantage is that impact impairment of the panel is more easily repaired using commonly used tools and methods. 
     The features, functions, and advantages can be achieved independently in various examples of the present disclosure or may be combined in yet other examples in which further details can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features believed characteristic of the illustrative examples are set forth in the appended claims. The illustrative examples, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative examples of the present disclosure when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an illustration of a perspective view of an aircraft. 
         FIG. 2  is an illustration of a fragmentary, cross sectional view of the nose section of the aircraft shown in  FIG. 1 , the nose landing gear shown in a deployed condition. 
         FIG. 3  is an illustration of the area designated as “ FIG. 3 ” in  FIG. 2 , but showing the nose landing gear in a stowed condition. 
         FIG. 4  is an illustration of a sectional view taken along the line  4 - 4  in  FIG. 2 . 
         FIG. 5  is an illustration of a bottom perspective view of the nose landing gear wheel well section of the airframe, the nose landing gear not shown for clarity. 
         FIG. 6  is an illustration of a top perspective view of the nose section of the airframe, also showing the location of the nose landing gear in both stowed and deployed conditions. 
         FIG. 7  is an illustration of a perspective view of a floor grid assembly forming part of the nose section of the airframe shown in  FIG. 6 . 
         FIG. 8  is an illustration of a cross-sectional view showing how the pressure deck may be attached to beams that reinforce the pressure deck and support the floor grid assembly of  FIG. 7 . 
         FIG. 9  is an illustration of a perspective view of a flat composite panel with integrated tear arrestment. 
         FIG. 10  is an illustration of a top plan view of the flat composite panel shown in  FIG. 9 , integrated tear straps shown in broken lines. 
         FIG. 11  is an illustration of a sectional view taken along the line  11 - 11  in  FIG. 10 . 
         FIG. 12  is an illustration of a sectional view taken along the line  12 - 12  in  FIG. 10 . 
         FIG. 13  is an illustration of a sectional view taken along the line  13 - 13  in  FIG. 10 . 
         FIG. 14  is an illustration of a top plan view of one ply a longitudinal tear strap. 
         FIG. 15  is an illustration of the area designated as “ FIG. 15 ” in  FIG. 14 . 
         FIG. 16  is an illustration of a flow diagram showing a method of making the flat composite panel. 
         FIG. 17  is an illustration of a flow diagram showing a method of making a pressure deck panel. 
         FIG. 18  is an illustration of a flow diagram showing a method of arresting a tear in a composite laminate panel. 
         FIG. 19  is an illustration of a flow diagram of aircraft production and service methodology. 
         FIG. 20  is an illustration of a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIG. 1 , an aircraft  20  comprises a fuselage  22 , wings  24 , horizontal stabilizers  26  and a vertical stabilizer  28 . The aircraft  20  has a nose section  30  that includes a pressurized flight deck  32 , sometimes referred to as a cockpit. 
     Attention is now directed to  FIGS. 2-8  which show additional details of the nose section  30 . The nose section  30  comprises airframe components including bulkheads  62 ,  64 ,  66  ( FIG. 5 ), longitudinally spaced frames  54  ( FIG. 6 ), longitudinal stringers (not shown) and an external skin  52 . A flight deck  32  is located in the nose section  30  and includes a flight deck floor  33  ( FIGS. 3 and 4 ), positioned above a nose landing gear well  40 , sometimes referred to as a landing gear bay. The flight deck  32  is supported by a floor grid assembly  70  ( FIGS. 6 and 7 ) that includes longitudinal beams  72 , and lateral beams  74  connected to the frames  54 . In some examples, the flight deck  32  may be supported on top of a nose landing gear box  68  within a nose landing gear well  40  by stanchions  50  ( FIG. 2 ). The flight deck  32  is a pressurized space  42 , while the nose landing gear well  40  is a non-pressurized space  44 . The pressurized flight deck is separated and sealed from the non-pressurized nose landing gear well  40  by a pressure deck  46 . 
     A nose landing gear  34  is mounted within the nose landing gear well  40  and comprises wheels  36  mounted on a pivoting strut  38 , and other components (not shown) that are normally stowed in the nose landing gear well  40  during flight. In preparation for landing, nose landing gear well doors  48  are swung open, allowing the nose landing gear  34  to pivot downwardly from its stowed position ( FIG. 3 ) to a deployed position ( FIGS. 2 and 4 ). 
     The landing gear box  68  is defined by opposing port and starboard sidewalls  56 ,  58 , forward and aft bulkheads  62 ,  66  and a top wall  60  which includes a pressure deck  46 . As best seen in  FIG. 3 , the pressure deck  46  is upwardly sloped toward the front of the landing gear box  68  in order to provide adequate space for the wheels  36  when stowed. A best seen in  FIG. 3 , the pressure deck  46  is substantially flat and is located at the front of the landing gear box  68 , immediately above the wheels  36  when stowed and is therefore particularly subject to impact by foreign object debris (FOD) hurled into the nose landing gear well  40  during take-off and landings. 
     The pressure deck  46  forms a hermetic seal between the flight deck  32  (pressurized space  42 ) and the nose landing gear well  40  (non-pressurized space  44 ). Pressure in the pressurized space  42 , sometimes referred to a “cabin pressure” P applied to the pressure deck  46 , is a function of the pressure differential that exists between the pressurized space  42  and the external air pressure. This pressure differential increases as the aircraft increases in altitude, consequentially the load on the pressure deck  46  likewise increases. 
     The pressure deck  46  reacts the cabin pressure P applied by the pressurized (cabin) space  42 , while also acting as a structural barrier that prevents any penetration into pressurized space  42  by debris entering the nose landing gear well  40 . The pressure deck  46  may be attached to components of the floor grid assembly  70  by stanchions  50 . For example, as shown in  FIG. 8 , the top of the pressure deck  46  may be attached by fasteners  76  to one or more of pressure deck beams  72   a.    
     Attention is now directed to  FIGS. 9 and 10  which illustrate additional details of a pressure deck  46  that is suitable for the aircraft application described above. It should be noted, however, the principles of the disclosed pressure deck  46  including a flat composite laminate panel may be used in a wide variety of other applications. In the illustrated example, the pressure deck  46  has a generally trapezoidal shape formed by front and rear edges  46   a,    46   b  connected by sides  46   c  having a slight curvature matching the taper of the nose section  30 . However, the pressure deck  46  may have any other shape that is suitable for the application. The thickness T of the pressure deck will depend on the application, including the amount of pressure that must be reacted and the degree of impact tear resistance that is required. 
     The pressure deck  46  comprises a flat composite laminate base panel  75  having a plurality of integrated first tear straps  78 , also referred to herein as longitudinal tear straps  78 , and a plurality of integrated second tear straps  80 , also referred to herein as lateral tear straps  80 . In the illustrated example, seven spaced apart, longitudinal tear straps  78  are shown extending in the longitudinal direction of the aircraft  20  which are spaced apart from each other equal distances, however in other examples the spacing may not be equal, and more or less than seven longitudinal tear straps  78  may be provided. 
     Four equally spaced lateral tear straps  80  are integrated into the base panel  75 , however, in other examples more or less than four lateral tear straps  80  may be provided, and may be irregularly spaced. The longitudinal tear straps  78  and the lateral tear straps  80  extend in directions that are transverse to each other, which in this example are orthogonal. The tear straps  78 , are spaced apart in the thickness T direction of the pressure deck  46  in order to arrest the propagation of cracks (sometimes also referred to herein as “tears”) that may occur anywhere throughout the thickness T. Similarly, the tear straps  78 ,  80  are spaced apart from each other in the longitudinal and lateral directions in order to arrest the propagation of cracks/tears occurring anywhere throughout the length and width of the pressure deck  46 . 
     In the illustrated pressure deck application, orthogonal orientation of the tear straps  78 ,  80  provides the pressure deck  46  with increased bending strength in the lateral and longitudinal directions in order to better react impact loads from FOD, while also providing crack propagation arrestment in both of these directions. The tear straps  78 ,  80  crossover or intersect each other at intersection points  90 . Depending upon the anticipated direction of loading, the directions of the longitudinal tear straps  78  and the lateral tear straps  80  may not be orthogonal, but rather may intersect each other at angles other than 90 degrees, including but not limited to an angular arrangement forming an “X” pattern. In the illustrated example, the longitudinal and lateral tear straps  78 ,  80  are arranged orthogonal to each other in order to arrest cracks/tears propagating in either the longitudinal direction or the lateral direction of the pressure deck  46 . The width W of the longitudinal and lateral tear straps,  78 ,  80  may vary, depending on the application. 
     Referring also to  FIGS. 11-15 , the pressure deck  46  includes a composite laminate base panel  75  comprising a plurality base panel plies  82  of composite material, such as a fiber reinforced polymer plies (FRP), which may be a thermoset, a thermoplastic or a hybrid material system including both a thermoset and thermoplastic. In one example, the base panel plies  82  are carbon fiber epoxy which may be in the form of tape or tows. The fiber orientations of the base panel plies  82  may vary between 0° and 90° and are orthogonal to the fiber orientation of at least one of the longitudinal tear straps and the lateral tear straps  80 . The longitudinal tear straps  78  each comprise one or more longitudinal tear strap plies  86  of unidirectional FRP interspersed in a desired, predetermined order with the base panel plies  82 . In the example shown in  FIG. 12 , four longitudinal tear strap plies  86  shown interspersed between groups of six base panel plies  82 , however, in other examples there may be any number of base panel plies  82  in each group thereof. The base panel plies  82  as well as the lateral and longitudinal tear strap plies  84 ,  86  may be laid up using automatically controlled laminators, such as automatic fiber placement heads (not shown), or they may be laid up manually. In other examples, the lateral and longitudinal tear straps  78 ,  80  may be integrated into the base panel  75  by placing them on either, or both of the outer faces  85  of the base panel  75 . In examples where the tear straps  78 ,  80  are located on the outer faces  85 , they may be arranged such that they respectively extend in directions that are transverse to each other. In still other examples, the tear straps  78 ,  80  may be interspersed within the base panel plies as well as located on either or both of the outer faces  85  of the base panel  75 . 
     While only one longitudinal tear strap ply  86  is shown between the groups of the base panel plies  82  (see  FIG. 12 ), any number of longitudinal tear strap plies  86  may be interspersed between groups of the base panel plies  82 . In other words, groups of the longitudinal tear strap plies  86  may be interspersed between groups of the base panel plies  82 . In the illustrated example, following compaction and curing, the pressure deck  46  will normally have smooth outer faces  85  because of the relatively few number of tear strap plies  84 ,  86  present within the thickness T of the pressure deck  46 . In other examples where the ratio of tear strap plies  84 ,  86  to base panel plies  82  is relatively high, the outer faces  85  may exhibit some degree of rippling or unevenness. 
     In the disclosed pressure deck application however, any unevenness in the outer faces  85  will not adversely affect the performance of the pressure deck  46 . In other applications requiring smooth outer faces, for esthetic or other reasons, a fewer number of tear strap plies  84 ,  86  may be used to achieve a desired smoothness of the outer faces  85 . Furthermore, in the illustrated example, the same number of base panel plies  82  separate the longitudinal tear strap plies  86  from each other, causing them to be evenly spaced within the stack of base panel plies  82 , however in other examples the longitudinal tear strap plies  86  may not be evenly spaced within the stack of base panel plies  82  as a result of using different numbers of base panel plies  82  in each group thereof to separate the longitudinal tear strap plies  86  from each other. Also, in the illustrated example, the longitudinal tear strap plies  86  are of constant width and are vertically aligned in the stack of base panel plies  82 , however, another examples they may have varying widths and may not be aligned as illustrated, depending upon the application, and anticipated loading. The tear straps  78 ,  80  may have any desired thickness. 
       FIG. 11  shows one example of lateral tear strap plies  84  interspersed between groups of four base panel plies  82 . Similar to the description of the longitudinal tear straps  78  discussed above, the lateral tear straps  80  may comprise any number of lateral tear strap plies  84  arranged in any order within the stack of base panel plies  82 . As in the case of the longitudinal tear strap plies  86 , the lateral tear strap plies  84  may be formed of tape or tows of FRP containing unidirectional fibers. Typically, the fiber orientations of the longitudinal tear strap plies  86  and the lateral tear strap plies  84  will be orthogonal to the fiber orientations of the base panel plies  82  which they adjoin in order to enhance the ability of the tear straps  78 ,  80  to arrest the propagation of cracks/tears. The lateral tear strap plies  84  may or may not be vertically aligned, and each may have any width, depending on the application. Also, depending on the application, the number of the lateral tear strap plies  84  may or may not be the same as a number of the longitudinal tear strap plies  86 . For example, in some applications, it may be desirable to provide a greater number of longitudinal tear strap plies  86  than the number of lateral tear strap plies  84  in order to provide the pressure deck  46  with greater strength in the lateral direction than the longitudinal direction, and vice versa. While only one lateral tear strap ply  84  is shown between the groups of the base panel plies  82 , any number of lateral tear strap plies  84  may be interspersed between groups of the base panel plies  82 . In other words, groups of the lateral tear strap plies  84  may be interspersed between groups of the base panel plies  82 . The number of tear straps  78 ,  80  as well as their widths and thicknesses will depend on the application but should be chosen so as to be adequate to arrest cracks/tears throughout the pressure deck  46  without adding unnecessary weight to the pressure deck  46 . 
     Referring to  FIG. 13 , the lateral tear strap plies  84  are arranged in regular, alternating order with the longitudinal tear strap plies  86 , however, in other examples, they may not be arranged in a regular, alternating manner. Depending on the application, and loading, each of the longitudinal tear straps  78 , and lateral tear straps  80  may include any number of lateral tear strap plies  84  and longitudinal tear strap plies  86 , arranged in any order within the stack of base panel plies  82 . While the lateral tear straps  80  comprises  5  tear strap plies  84  separated by 3 base panel plies  820  in the illustrated example, the number of lateral tear strap plies and base panel plies  82  may vary with the application and expected loading. 
     In the illustrated example, the same number of base panel plies  82  separate the lateral tear strap plies  84  from each other, causing them to be evenly spaced within the stack of base panel plies  82 , however in other examples, the lateral tear strap plies  84  may not be evenly spaced within the stack of base panel plies  82  as a result of using different numbers of base panel plies  82  in each group thereof to separate the lateral tear strap plies  84  from each other. Spacing the tear straps  78 ,  80  within the base panel plies  82  provides crack propagation arrestment throughout the thickness of the pressure deck  46 . In some examples, the tear strap plies  84 ,  86  may be more or less concentrated near the outer faces of the base panel  75 , while in other examples, they may be more or less concentrated in the middle of the thickness of the base panel  75 . In some examples, the tear straps  78 ,  80  may be placed on the outer faces of the base panel  75 . 
     Referring to  FIGS. 14 and 15 , the pressure deck may be laid up by hand or using an automatic fiber placement machine (not shown) which layup strips  92  of FRP either in tape form or in tows. Each of the FRP strips  92  contains unidirectional reinforcing fibers  94  held in a polymer matrix  96 , as mentioned earlier. Generally, the fiber orientations of the longitudinal tear straps  78  and the lateral tear straps  80  will be orthogonal to the fiber orientations of the base panel plies  82  that they face in order to better arrest propagation of any cracks beyond the tear strap that might be created within the pressure deck  46 . Moreover, the fiber orientations of the longitudinal and lateral tear straps  78 ,  80  are orthogonal to each other. Consequently, a crack/tear in the base panel  75  propagating in the direction of the fiber orientations of the base panel plies  82  will intersect and be stopped by either the longitudinal tear straps  78  or the lateral tear straps  80 . Although not shown in the drawings, in some examples, the pressure deck  46  may include a core formed of suitable materials sandwiched between the base panel plies  82  in order to enhance the strength and resistance of the pressure deck  46  to impairment due to impacts. 
     As explained earlier, the number, size, and placement of the lateral and longitudinal tear strap plies  84 ,  86 , as well as their separation from each other in the stack of base panel plies  82  will depend on the requirements of the particular application, such as the amount and direction of loading. For example, where higher loading is expected, a greater number of plies  84 ,  86  may be employed. Similarly, where greater loading is expected in the longitudinal direction compared to the lateral direction, a greater number of longitudinal tear strap plies  86  may be used to adequately react the load in the longitudinal direction. Conversely, where greater loading is expected in the lateral direction compared to the longitudinal direction, a greater number of lateral tear strap plies  84  may be used to adequately react the load in the lateral direction. Increasing the number of tear strap plies  84 ,  86  increases bending strength of the pressure deck  46  in order to react the loads imposed on it by the cabin pressure P as well as impacts by FOD. In addition to increasing the bending strength of the pressure deck  46 , the tear straps  78 ,  80  arrest propagation of any interlaminar tears or cracks in the base panel  75  caused by FOD impacts. Cracks or tears are undesirable because they may compromise the ability of the pressure deck  46  to maintain a hermetic seal between the pressurized and non-pressurized spaces  42 ,  44 . Any such cracks or tears propagating in the direction of the fiber orientations of the base panel plies  82  are stopped by the tear straps  78 , which act to interrupt any continuation of such cracks/tears. 
     Attention is now directed to  FIG. 16 , which broadly illustrates the steps of a method of making a composite pressure deck  46 . Beginning at  98 , a base panel is fabricated by laying up base panel plies  82  of composite material, such as an FRP. At  100 , a plurality of first tears straps  78  are integrated into the base panel by interspersing them within the base panel plies  82  as the base panel plies  82  are being laid up. Laying up the first tear straps  78  includes orienting the first tear straps  78  in a first direction, such as for example, a longitudinal direction. At  102 , a plurality of second tear straps  80  are integrated into the base panel by interspersing them within the base panel plies  82  as the base panel plies  82  are being laid up in step  98  above. Laying up the second tear straps  80  includes orienting the second tear straps  80  in a second direction that is transverse to the first direction, such as for example, a lateral direction. Plies  82 ,  84  and  86  may be laid up using an automatic lamination machine, or manually, or by a combination of manual and automatic methods. 
       FIG. 17  broadly illustrates the steps of a method of making a pressure deck  46  for an aircraft  20 . Beginning at  103 , base panel plies  82  are placed, as by laying up one or more plies of a composite material. At  105 , one or more longitudinal tear strap plies  86  are placed by laying up composite material over the base panel plies  82  laid up at  103 . At  107 , additional base panel plies  82  are placed on the longitudinal tear strap plies  86  placed at  105 . At  109 , one or more lateral tear strap plies are placed on the base panel plies  82  placed at  107 . Steps  105  and  109  include orienting the longitudinal tear strap plies  86  and lateral tear strap plies  84  substantially orthogonal to each other. At  111 , additional base panel plies  82  are placed on the lateral tear strap plies  84  placed at  109 . Steps  103 - 111  are repeated until the pressure deck  46  is complete at  113 . 
       FIG. 18  broadly illustrates the steps of a method of arresting a tear in a composite laminate panel. At  115 , a plurality of tear straps  78 ,  80  each comprising one or more tear strap plies are interspersed within plies of a composite laminate panel. At  117 , propagation of a tear in the plies in the panel is arrested using the tear straps  78 ,  80 . 
     Examples of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications, and other application where composite laminate panels, such as pressure decks in aircraft, may be used. Thus, referring now to  FIGS. 19 and 20 , examples of the disclosure may be used in the context of an aircraft manufacturing and exemplary method  104  as shown in  FIG. 19  and an aircraft  106  as shown in  FIG. 20 . Aircraft applications of the disclosed examples may include a variety of flat composite laminate panel structures, but are not limited to pressure decks. During pre-production, exemplary method  104  may include specification and design  108  of the aircraft  106  and material procurement  110 . During production, component and subassembly manufacturing  112  and system integration  114  of the aircraft  106  takes place. Thereafter, the aircraft  106  may go through certification and delivery  116  in order to be placed in service  118 . While in service by a customer, the aircraft  106  is scheduled for routine maintenance and service  120 , which may also include modification, reconfiguration, refurbishment, and so on. The disclosed panel and method may be used in each of at least steps  112 ,  114 , as well as in the nose section  30  and the pressure deck  46 . 
     Each of the processes of exemplary method  104  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 20 , the aircraft  106  produced by exemplary method  104  may include an airframe  122  with a plurality of systems  124  and an interior  126 . Examples of high-level systems  124  include one or more of a propulsion system  128 , an electrical system  130 , a hydraulic system  132  and an environmental system  134 . Any number of other systems may be included. The airframe  122  includes nose section  30 , in which a pressure deck  46  separates and forms a hermetic seal between a pressurized flight deck  32  and a non-pressurized nose landing gear well  40 . Although an aerospace example is shown, the principles of the disclosure may be applied to other industries, such as the marine and automotive industries where a flat composite laminate panel with high stiffness, impact resistance and integrated tear arrestment may be desirable or required. 
     Systems and methods embodied herein may be employed during any one or more of the stages of the aircraft manufacturing and exemplary method  104 . For example, components or subassemblies corresponding to production process  112  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  106  is in service. Also, one or more apparatus examples, method examples, or a combination thereof may be utilized during the production processes  112  and system integration  114 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  106 . Similarly, one or more of apparatus examples, method examples, or a combination thereof may be utilized while the aircraft  106  is in service, for example and without limitation, to maintenance and service  120 . 
     As used herein, the phrase “at least one of”, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of each item in the list may be needed. For example, “at least one of item A, item B, and item C” may include, without limitation, item A, item A and item B, or item B. This example also may include item A, item B, and item C or item B and item C. The item may be a particular object, thing, or a category. In other words, at least one of means any combination items and number of items may be used from the list but not all of the items in the list are required. 
     The description of the different illustrative examples has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the examples in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different illustrative examples may provide different advantages as compared to other illustrative examples. The example or examples selected are chosen and described in order to best explain the principles of the examples, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various examples with various modifications as are suited to the particular use contemplated.