Abstract:
A method of constructing a composite, radius filler noodle for a co-cured spar or stringer used in aircraft construction includes forming a core of the noodle from unidirectional pre-preg tape and stacking pluralities of pre-prep fabric strips in layers surrounding the core.

Description:
This application is a divisional application from application Ser. No. 14/340,982, which was filed on Jul. 25, 2014 and is currently pending. 
    
    
     FIELD 
     This disclosure pertains to a composite, radius filler noodle for a co-cured spar or stringer used in aircraft construction. 
     BACKGROUND 
     In typical constructions of composite spars or stringers for aircraft, two “c” shaped composite channels are brought together back-to-back to form the central web and top and bottom flanges of the spar. The two channels are each constructed of a plurality of fiber-reinforced polymer plies that have been pre-impregnated with a resin, or pre-preg plies. When the two “c” shaped channels are brought together, the radiuses of the channels where the central web transitions into the flanges forms a small v-shaped gap along the centers of the top and bottom flanges. A composite radius filler, commonly called a “noodle” is typically employed to fill these gaps. 
     Noodles have been constructed from unidirectional pre-preg tape. Noodles have also been constructed of pre-preg fabric. However constructed, the noodles are positioned in the gaps in the top and bottom flanges of the composite spar and are co-cured with the channels of the spar. 
     During curing, temperatures typically reach 350 degrees Fahrenheit. The heating of the spar and subsequent cooling to ambient temperature can cause cracking in the noodle. The noodle in the final spar construction can also crack due to mechanical and/or thermal stresses exerted on the spar in use in an aircraft. Cracks in the noodle weaken the entire spar. It is therefore desirable to improve the overall strength of the composite spar by preventing or reducing the propagation of cracks through the noodles employed in constructing the spar. 
     SUMMARY 
     This disclosure pertains to a composite radius filler noodle and its method of construction that prevents the propagation of cracks through the noodle. The noodle is basically constructed from composite unidirectional pre-preg tape and composite pre-preg fabric strips. The tape and strips are brought together according to the method of this disclosure to construct a noodle where, should cracks form in the core of the noodle, the cracks are prevented from propagating to the exterior surface of the noodle and the rest of the spar structure. 
     The noodle core has a triangular cross-section configuration and a length that is determined to fill the length of a gap on the spar with which the noodle is to be used. The triangular configuration of the core gives the core first, second and third exterior surfaces that extend along the length of the core. The core is constructed of unidirectional pre-preg tape that extends along the core length. According to the method of making the noodle, the unidirectional pre-preg tape could be pultruded or otherwise die-formed into the triangular cross-section configuration of the core. 
     A first pre-preg fabric strip covers the core first surface. The first strip has a length that extends completely along the length of the core first surface and a width that extends completely across the core first surface. 
     A second pre-preg fabric strip covers the core second surface. The second strip has a length that extends completely along the length of the core second surface and a width that extends completely across the core second surface. 
     A third pre-preg fabric strip covers the core third surface. The third strip has a length that extends completely along the length of the core third surface and a width that extends completely across the core third surface. 
     A fourth pre-preg fabric strip covers the first strip on the core first surface. The fourth strip has a length that extends completely across the length of the first strip. In one embodiment the fourth strip has a width that is larger than the width of the first strip. In another embodiment the width of the fourth strip is smaller than the width of the first strip. 
     A fifth strip of pre-preg fabric covers the second strip on the core second surface. The fifth strip has a length that extends completely along the length of the second strip. In one embodiment, the fifth strip has a width that is larger than the width of the second strip. In another embodiment the fifth strip has a width that is smaller than the width of the second strip. 
     A sixth strip of pre-preg fabric covers the third strip on the core third surface. The sixth strip of fabric has a length that extends completely along the length of the third strip. In one embodiment, the sixth strip has a width that is larger than the width of the third strip. In another embodiment the sixth strip has a width that is smaller than the width of the third strip. 
     A seventh pre-preg fabric strip covers the fourth strip and the first strip. The seventh strip has a length that extends completely along the length of the fourth strip. In one embodiment, the seventh strip has a width that extends completely across the fourth strip. In another embodiment the seventh strip has a width that is smaller than the width of the fourth strip. 
     An eighth pre-preg fabric strip covers the fifth strip and the second strip. The eighth strip has a length that extends completely along the length of the fifth strip. In one embodiment, the eight strip has a width that extends completely across the width of the fifth strip. In another embodiment the eighth strip has a width that is smaller than the width of the fifth strip. 
     A ninth pre-preg fabric strip covers the sixth strip and the third strip. The ninth strip has a length that extends completely along the length of the sixth strip. In one embodiment, the ninth strip has a width that extends completely across the width of the sixth strip. In another embodiment the ninth strip has a width that is smaller than the width of the sixth strip. 
     In the construction of the noodle described above, the multiple plies of fabric strips on the exterior surface of the noodle core enable the noodle core to be reduced in size, thereby likely reducing the chance of thermally induced matrix cracks forming in the core. The fabric jacket produced by the multiple plies of fabric strips on the exterior surfaces of the core provides a higher fracture toughness material to the core exterior and an arduous crack path to the noodle exterior for the purpose of preventing cracks from propagating out of the noodle core. All of this is accomplished without affecting the configuration of the noodle exterior. The noodle unidirectional core can be produced at a high rate with existing pultrusion machines, and the fabric strips on the core exterior surfaces can be installed on the spar or stringer charges at the same time the unidirectional core is installed. The number and orientation of the fabric strips can be adjusted to achieve a desired level of mechanical strength. Changing the number of fabric strips on the exterior surfaces of the core also enables adjusting the size of the core, which is desirable for achieving an ideally smaller core for the sake of preventing cracks, while maintaining a large enough core to be produced at high rates by pultrusion. The multiple plies of fabric strips can be assembled on the exterior surfaces of the core, or could be assembled on a flat tool in a flat configuration of the strips prior to their being assembled to a surface of the core. 
     The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in other embodiments, further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features of the subject matter of this disclosure are set forth in the following description and drawing figures. 
         FIG. 1  is a flow diagram of aircraft production and service methodology. 
         FIG. 2  is a block diagram of an aircraft. 
         FIG. 3  is a representation of a partial perspective view of the composite radius filler noodle of this disclosure installed in a v-shape gap formed by two back-to-back “c” shaped composite channels. 
         FIG. 4  is a representation of an end elevation view of the noodle that has been constructed according to one method of construction. 
         FIG. 5  is a representation of an end elevation view of layers of pre-preg fabric strips employed in practicing the method of constructing the noodle. 
         FIG. 6  is a representation of an end elevation view of layers of pre-preg fabric strips employed in the method of constructing the noodle. 
         FIG. 7  is a representation of an end elevation view of a variant embodiment of the noodle. 
         FIG. 8  is a representation of a variant embodiment of constructing the noodle. 
         FIG. 9  is a representation of an end view of a variant embodiment of the noodle constructed according to the method of  FIG. 8 . 
         FIG. 10  is a representation of an interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 11  is a representation of an interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 12  is a representation of an interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 13  is a representation of an interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 14  is a representation of an interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 15  is a representation of the interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 16  is a representation of the interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 17  is a representation of the interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 18  is a representation of the interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 19  is a representation of the interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 20  is a representation of the interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
         FIG. 21  is a representation of the interaction between a pair of pre-preg fabric strips meeting along an apex edge of the noodle. 
     
    
    
     DETAILED DESCRIPTION 
     Referring more particularly to the drawings, embodiments of the disclosure may be described in the context of an aircraft manufacturing and service method  10  as shown in  FIG. 1  and an aircraft  12  as shown in  FIG. 2 . During pre-production, exemplary method  10  may include specification and design  14  of the aircraft  12  and material procurement  16 . During production, component and subassembly manufacturing  18  and system integration  20  of the aircraft  12  takes place. Thereafter, the aircraft  12  may go through certification and delivery  22  in order to be placed in service  24 . While in service by a customer, the aircraft  12  is scheduled for routine maintenance and service  26  (which may also include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  10  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 venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on, 
     As shown in  FIG. 2 , the aircraft  12  produced by exemplary method  10  may include an airframe  28  with a plurality of systems  30  and an interior  32 . Examples of high-level systems  30  include one or more of a propulsion system  34 , an electrical system  36 , a hydraulic system  36 , and an environmental system  38 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry. 
     Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method  10 . For example, components or subassemblies corresponding to production process  18  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  12  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  18  and  20 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  12 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  12  is in service, for example and without limitation, to maintenance and service  26 . 
       FIG. 3  is a representation of a partial perspective view of the composite radius filler noodle  40  of this disclosure installed in a v-shaped gap  42  formed by two back-to-back c-shaped composite channels  44 ,  46 . Only upper portions of the c-shaped channels  44 ,  46  are represented in  FIG. 3 . The c-shaped channels  44 ,  46  are used in the typical construction of composite spars or stringers for aircraft. The two channels  44 ,  46  are each constructed of a plurality of pre-preg plies. The two channels  14 ,  16  are brought together back-to-back to form the central web  48  of the spar and the top  50  and bottom flanges of the spar, with only the top flange being shown in  FIG. 3 . As represented in  FIG. 3 , the noodle  40  of this disclosure is constructed to fill the v-shaped gap  42  formed in the top and bottom flanges of the spar. 
     Referring to  FIG. 4 , an end view of the noodle  40  is represented showing details of its construction. The noodle  40  is shown rotated 180° from its orientation represented in  FIG. 3 . The noodle is basically constructed from composite unidirectional pre-preg tape and composite pre-preg fabric strips. The tape and strips are brought together according to the method of this disclosure to construct the noodle  40  where, should cracks form in the core of the noodle the cracks are prevented from propagating to the exterior surface of the noodle. 
     The noodle  40  is constructed with a core  54  having a triangular cross section configuration. The core  54  has a length that is determined to fill the length of the v-shape gap on the spar with which the noodle is to be used. The triangular configuration of the core  54  gives the core first  56 , second  58  and third  60  exterior surfaces. Each of these exterior surfaces extends for the length of the core  54 . The core first surface  56  is flat. This surface will extend across the top of the gap  42  formed at the center of the spar flange  50 . The second  58  and third  60  surfaces are curved. These surfaces will match the curvature of the radiuses formed at the bottom of the v-shaped gap  12 . The core  54  is constructed of unidirectional pre-preg tape that extends along the length of the core. The core  54  fills up the entire region within the layers of strips to be described with the core  54  extending all the way into the apices between the strips of the triangular noodle. No other materials are used in constructing the core  24 . According to a method of making the noodle  10 , the unidirectional pre-preg tape could be pultruded or otherwise die-formed into the triangular cross section configuration of the core shown. 
     A first pre-preg fabric strip  64  covers the core first surface  56 . The first strip  64  has a length that extends completely along the length of the core first surface  56  and a width that extends completely across the core first surface  56 . In the example of the noodle  40  represented in the drawing figures, the width of the first strip  64  is approximately 0.738 inches. 
     A second pre-preg fabric strip  66  covers the core second surface  58 . The second strip  66  has a length that extends completely along the length of the core second surface  58  and a width that extends completely across the core second surface  58 . In the example of the noodle  40  represented in the drawing figures, the width of the second strip  66  is approximately 0.593 inches. 
     A third pre-preg fabric strip  68  covers the core third surface  60 . The third strip  68  has a length that extends completely along the length of the core third surface  60  and a width that extends completely across the core third surface  60 . In the example of the noodle  40  represented in the drawing figures, the width of the third strip  68  is substantially the same as the width of the second strip  66 , 0.593 inches. Thus, the width of the pre-preg fabric second strip, which is 0.593 inches, and the width of the pre-preg fabric third strip, which is 0.593 inches are the same and are smaller than the width of the pre-preg fabric first strip, which is 0.738 inches. 
     A fifth pre-preg fabric strip  74  covers the second strip  66  on the core second surface  58 . The fifth strip  74  has a length that extends completely along the length of the second strip  66 . In the embodiment shown in  FIG. 4 , the fifth strip  74  has a width that is larger than the width of the second strip  66 . In another embodiment the fifth strip  74 ′ has a width that is smaller than the width of the second strip  66 ′. This embodiment is represented in  FIGS. 8 and 9 . 
     A sixth pre-preg fabric strip  76  covers the third strip  68  on the core third surface  60 . The sixth strip  76  has a length that extends completely along the length of the third strip  68 . In the embodiment shown in  FIG. 4 , the sixth strip  76  has a width that is larger than the width of the third strip  68 . In another embodiment the sixth strip  76 ′ has a width that is smaller than the width of the third strip  68 ′. This embodiment is represented in  FIGS. 8 and 9 . 
     A seventh pre-preg fabric strip  80  covers the fourth strip  72  and the first strip  64 . The seventh strip  80  has a length that extends completely along the length of the fourth strip  72 . In the embodiment shown in  FIG. 4 , the seventh strip  80  has a width that is larger than and extends completely across the fourth strip  72 . In another embodiment the seventh strip  80 ′ has a width that is smaller than the width of the fourth strip  72 ′. This embodiment is represented in  FIGS. 8 and 9 . 
     An eighth pre-preg fabric strip  82  covers the fifth strip  74  and the second strip  66 . The eighth strip  82  has a length that extends completely along the length of the fifth strip  74 . In the embodiment shown in  FIG. 4 , the eight strip  82  has a width that is larger than and extends completely across the width of the fifth strip  74 . In another embodiment the eighth strip  82 ′ has a width that is smaller than the width of the fifth strip  74 ′. This embodiment is represented in  FIGS. 8 and 9 . 
     A ninth pre-preg fabric strip  84  covers the sixth strip  76  and the third strip  68 . The ninth strip  84  has a length that extends completely along the length of the sixth strip  76 . In the embodiment shown in  FIG. 4 , the ninth strip  84  has a width that is larger than and extends completely across the width of the sixth strip  76 . In another embodiment the ninth strip  84 ′ has a width that is smaller than the width of the sixth strip  76 ′. This embodiment is represented in  FIGS. 8 and 9 . 
     Although the embodiment of the noodle  40  described above and shown in  FIG. 4  is constructed with three plies of pre-preg fabric strips on each of the three surfaces of the core  54 , the noodle could be constructed with fewer or more plies of fabric. For example, the noodle represented in  FIG. 7  is constructed with four plies of pre-preg fabric strips on each of the three surfaces of the noodle core. 
     Each of the strips of the noodle  40  are cut to size aided by an optical laser template (OLT). The OLT is basically a numerically controlled laser system that is mounted on a gantry above a flat tool surface or above the spar being constructed. The OLT projects the outline of each of the strips onto the tool or part as the strips are cut and then laid down. The strips are laid down onto each projected outline as the strips are stacked. The strip stacks are laid up flat (two, three or four strips high) and installed (either flipped or not flipped) on the c-channel  44 ,  46  surfaces and the spar top flange  50  surfaces that are adjacent the middle cavity or gap  42 . Any overfill of the core  54  is variable based on the width of the unidirectional pre-preg tape used to produce the core. The core  54  can be produced or formed by any method. As stated earlier, pultrusion is the current choice of production based on production rate. The number of strips and the widths of the strips are also variable. This combination allows for more design space than other noodles. For example, results of finite element method (FEM) testing can be used to determine that the core  54  needs to be a certain area to minimize peak stresses. Then the strips can be sized to achieve the proper overfill of the gap  42  and tailor the amount of crack protection (more strips equal more protection) and also the stiffness of the strip laminate (FEM results based on the orientation of the strip laminate can be integrated quickly). Alternatively, it is possible to design two noodles of different sizes that utilize the same core. 
       FIG. 5  is a representation of the stack of strips  64 ,  72 ,  80  that are applied to the core first surface  56 .  FIG. 6  is a representation of the stack of strips  66 ,  74 ,  82  that are applied to the core second surface  58 . The stack of strips  68 ,  76 ,  84  applied to the core third surface  60  would appear the same as the stack shown in  FIG. 6 . In constructing the embodiment of the noodle  40  represented in  FIG. 4 , the strips are first stacked and then flipped over prior to being applied to the respective surfaces  56 ,  58 ,  60  of the core  54 . 
       FIG. 8  is a representation of the cut strips being applied to the surfaces of the core where the widest strips in the stacks are applied to the core surfaces. This produces the embodiment of the noodle  40 ′ represented in  FIG. 9 . 
     The plys of fabric strips that meet along the distal apex edges of the noodle  40  come together in basically three ways. These are represented in  FIGS. 10-21  which show possible interactions between the distal edges of the widest strips of the noodle  40  as they come together at a distal apex edge of the noodle.  FIGS. 10-21  represent examples of the interactions of the edge of the seventh strip  80 ,  80 ′ or the base strip of the noodle with the ninth strip  84 ,  84 ′ or the right side strip of the noodle as shown in  FIGS. 4, 7 and 9 . It should be understood that the interactions of the seventh strip  80 ,  80 ′ or the base strip of the noodle  40  and the eighth strip  82 ,  82 ′ at the left distal end apex of the noodle as shown in  FIGS. 4, 7 and 9  would be a mirror image of the interactions shown in  FIGS. 10-21 . 
     As represented in  FIGS. 10-13 , the end edge of the widest side strip or ninth strip  84 ,  84 ′ interacts with the end edge of the widest base strip or seventh strip  80 ,  80 ′ at a same terminal point  90 . 
     Alternatively, the end edge of the widest side strip or ninth strip  84 ,  84 ′ extends slightly beyond the end edge of the widest base strip or seventh strip  80 ,  80 ′ as represented in  FIGS. 14-17 . 
     Still further, the end edge of the widest base strip or seventh strip  80 ,  80 ′ extends slightly beyond the end edge of the widest side strip or ninth strip  84 ,  84 ′ as represented in  FIGS. 18-21 . 
     For each of the interactions between the end edge of the widest side strip or ninth strip  84 ,  84 ′ and the end edge of the widest base strip or seventh strip  80 ,  80 ′, the strip end edges can be cut at any angle such that the strip end edges end in a beveled edge as represented in  FIGS. 10, 11, 14, 15, 18 and 19 , or squared edges as represented in  FIGS. 12, 13, 16, 17, 20 and 21 . 
     Furthermore, the end edge of the widest side strip or ninth strip  84 ,  84 ′ can meet with the end edge of the widest base strip or seventh strip  80 ,  80 ′ along a small area of co-tangency  92  as represented in  FIGS. 10, 12, 14, 16, 18 and 20 , or the end edges may meet at only a single point  94  as represented in  FIGS. 11, 13, 15, 17, 19 and 21 . 
     In the construction of the noodle described above, the multiple plys of fabric strips on the exterior surface of the noodle core enable the noodle core to be reduced in size, thereby likely reducing the chance of thermally induced matrix cracks forming in the core. The fabric jacket produced by the multiple plys of fabric strips on the exterior surfaces of the core provide a higher fracture toughness material to the core exterior and an arduous crack path to the noodle exterior for the purpose of preventing cracks from propagating out of the noodle core. All of this is accomplished without affecting the configuration of the noodle exterior. The noodle unidirectional core can be produced at a high rate with existing pultrusion machines, and the fabric strips on the core exterior surfaces can be installed on the spar or stringer charges at the same time the unidirectional core is installed. The number, thickness and fiber orientation of the fabric strips can be adjusted to achieve a desired level of mechanical strength. For example, the plurality of first strips could have fibers oriented in different directions and different thicknesses. Additionally, the plurality of second strips could also have fibers oriented in different directions, etc. Changing the number of fabric strips on the exterior surfaces of the core also enables adjusting the size of the core, which is desirable for achieving an ideally smaller core for the sake of preventing cracks, while maintaining a large enough core to be produced at high rates by pultrusion. The multiple plies of fabric strips can be assembled on the exterior surfaces of the core, or could be assembled on a flat tool in a flat configuration of the strips prior to their being assembled to a surface of the core. 
     As various modifications could be made in the construction of the apparatus and its method of construction herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present disclosure should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.