Patent Publication Number: US-8978729-B2

Title: Composite ply stabilizing system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional application of and claims priority to U.S. application Ser. No. 12/638,947 filed on Dec. 15, 2009, and entitled COMPOSITE PLY STABILIZING METHOD, now U.S. Pat. No. 8,491,743, the entire contents of which is expressly incorporated by reference herein. 
    
    
     FIELD 
     The present disclosure relates generally to composite construction and, more particularly, to a system and method of stabilizing composite plies against movement relative to one another. 
     BACKGROUND 
     Composite sandwich structures constructed of honeycomb core or other lightweight core materials provide several advantages over other composite structural arrangements. Sandwich structures typically include the core material bounded on opposing sides of the core by face sheets or laminates comprised of one or more plies of composite material. Due to the relatively light weight of the core, the combination of the core and laminates on opposing sides of the core results in a relatively high stiffness-to-weight ratio as compared to composite structures comprised of laminated plies. In addition, composite sandwich structures have relatively high strength-to-weight ratios due to the relatively low density of the core material. Certain structures such as, without limitation, wing flaps and/or doors of a commercial airliner may benefit from a composite sandwich construction due to the favorable stiffness characteristics and light weight. 
     During the fabrication of a composite structure, pressure and heat are typically applied to a layup of composite materials that make up the structure in order to cure and bond the composite materials. An autoclave may be employed as a means for applying heat and pressure to the composite material layup such as a composite sandwich structure layup. For the above-noted example of a wing flap formed with lightweight core material, the geometry and size of the flap may present challenges regarding the curing and bonding of the composite materials to the core. 
     For example, the wing flap of a commercial airliner may have relatively large core thicknesses (e.g., six inches or larger) with a trend toward increasing core thicknesses in response to ongoing efforts to minimize weight in composite structures. The wing flap may also include one or more chamfers for tapering the core thickness such as along a direction toward the perimeter of the flap. The chamfer angle may exceed 10 degrees and may be as large as 20 degrees or greater depending upon the flap geometry. For such a configuration, the pressure exerted by the autoclave (e.g., approximately 45 psi) may result in the application of a relatively large side load (e.g., up to 4,000 pounds) on the chamfer of the core. The relatively large side load may result in movement or slippage of the plies of the upper and lower laminates relative to one another along a direction from the flap perimeter toward the core chamfer. Furthermore, the heating of the plies between which the core is sandwiched may reduce the viscosity of the resin that is in contact with the core and which may reduce friction and further facilitate ply slippage. The slippage of the plies relative to one another may result in movement of the core causing the core to be compacted or crushed in response to the ply movement. 
     Prior art attempts to prevent core crush include the application of film adhesive and a fiberglass sheet around the border of the composite panel in an effort to stabilize the core from movement during the application of autoclave pressure. Unfortunately, the fiberglass sheet extends across the surface of the core resulting in additional weight to the structure. Other attempts to prevent core crush include the application of tie down straps along the perimeter of the composite layup. The tie down straps may comprise fiberglass straps that may be secured to the tool and extended over and adhered to the uppermost ply of the composite layup. However, such tie down straps may be ineffective against the relatively large side forces exerted on chamfers of large surface area during the application of autoclave pressure. 
     Another approach to preventing ply slippage in composite structures is to septumize or split the core along a horizontal plane at an approximate mid-height of the core. Layers of fiberglass and adhesives may be installed between upper and lower portions of the split core in an attempt to stabilize the core against movement. Unfortunately, the addition of the fiberglass and adhesive layers may eliminate the ability to perform a non-destructive inspection of the composite panel using ultrasonic inspection techniques due to blockage of the ultrasonic signal by the fiberglass layer. Furthermore, the addition of the fiberglass sheet and adhesive may add to the weight of the composite structure. 
     As can be seen, there exists a need in the art for a system and method for stabilizing the plies of a composite structure against movement relative to one another in order to prevent core crush during the application of pressure to the composite structure as may occur during curing and/or consolidation of the structure. Furthermore, there exists a need in the art for a system and method for stabilizing the plies of a composite structure that is effective for relatively thick cores having a chamfer formed at a relatively steep chamfer angle. Finally, there exists a need in the art for a system and method for stabilizing the plies of a composite structure against movement without requiring the addition of materials that may increase the weight of the composite structure. 
     SUMMARY 
     Disclosed is a stabilizing mechanism for resisting relative movement of upper and lower laminates of a composite structure having a core. The upper and lower laminates may be mounted to the core. The stabilizing mechanism may comprise a lower grip strip mounted to the tool and may have an outer surface and may include at least one engagement feature for engaging at least one of the upper and lower laminates. The stabilizing mechanism may include at least one upper grip strip which may have opposing outer surfaces wherein each one of the outer surfaces may include at least one of the engagement features for engaging the lower grip strip and at least one of the upper and lower laminates. 
     Also disclosed is a stabilizing mechanism for resisting relative movement of the upper and lower laminates which may be mounted to a chamfered core of a composite structure to prevent core crush of the chamfered core. The composite structure may be mounted on a tool. Core crush may occur under the application of autoclave force to the chamfer formed in the core. The composite structure may include upper and lower laminates respectively mounted to upper and lower surfaces of the core. The upper and lower laminates may be respectively comprised of upper and lower plies. The composite structure may have a perimeter that may include a trim line defining a trim margin. The stabilizing mechanism may comprise a lower grip strip bonded to the tool within the trim margin and may include a generally elongate metallic sheet member having inner and outer surfaces. The stabilizing mechanism may include a plurality of protrusions extending outwardly from the outer surface. The protrusions from the lower grip strip may engage at least two of the plies for preventing movement relative to the lower grip strip. 
     The stabilizing mechanism may include at least one upper grip strip that may be positioned in substantial alignment with the lower grip strip and may comprise a pair of the sheet members bonded at the inner surfaces in back-to-back arrangement. Each one of the sheet members may have a plurality of the protrusions extending outwardly from the respective outer surfaces. The protrusions from the upper grip strip may engage the lower grip strip for preventing movement relative thereto and may engage at least two of the plies on opposing sides of the upper grip strip for preventing movement of the plies relative to the upper grip strip. At least one tie strap may be mounted to the tool and may overlap a portion of the upper grip strip. A bagging film may seal the composite structure to the tool for applying compressive force on the upper and lower laminates to increase engagement with the upper and lower grip strips. 
     The present disclosure further includes a system for resisting relative movement of upper and lower laminates mounted to a chamfered core of a composite structure to reduce core crush of the chamfered core. The system may comprise a tool for receiving the composite structure and a stabilizing mechanism. The stabilizing mechanism may include a lower grip strip mounted to the tool and which may have an outer surface that includes at least one engagement feature for engaging at least one of the upper and lower laminates. The stabilizing mechanism may include at least one upper grip strip which may have opposing outer surfaces each of which may include at least one engagement feature for engaging the lower grip strip and at least one of the upper and lower laminates. The system may include a force mechanism for applying a compressive force to the upper laminate for increasing the engagement of the upper and lower laminates to the upper and lower grip strips. 
     Also disclosed is a method of resisting relative movement of upper and lower laminates mounted to a chamfered core of a composite structure to reduce core crush in the chamfered core. The method may comprise the steps of mounting a lower grip strip to a tool and laying up a lower laminate on the tool such that the lower laminate engages a portion of the lower grip strip. The method may further comprise placing a core on the lower laminate, positioning an upper grip strip such that a portion thereof engages the lower grip strip, and laying up an upper laminate over the core such that a portion of the upper laminate engages the upper grip strip. 
     In a further embodiment, disclosed is a method of resisting relative movement of upper and lower laminates mounted to a chamfered core of a composite structure to reduce core crush in the chamfered core under the application of autoclave force to the chamfer. The composite structure may be mounted on a tool and may have a perimeter that may include a trim line defining a trim margin. The core may have at least one chamfer. The method may comprise the steps of bonding a lower grip strip to the tool within the trim margin. The lower grip strip may have protrusions extending outwardly from an outer surface thereof. The method may include laying up lower plies of the lower laminate onto the tool such that at least two of the lower plies engage a portion of the lower grip strip. The lower plies may be terminated in staggered relation to one another on the lower grip strip. 
     The method may include positioning the core over the lower laminate within the trim line, positioning at least one upper grip strip in substantial alignment with the lower grip strip and engaging the upper grip strip to a portion of the lower grip strip. The method may include laying up upper plies of an upper laminate over the core such that at least two of the upper plies overlap and engage a portion of the upper grip strip. The upper plies may terminate in staggered relation to one another on the upper grip strip. The method may also include mounting at least one tie strap to the tool and extending the tie strap over at least a portion of the upper grip strip and along a length thereof. A compressive force may be applied to the composite structure to increase engagement of the upper and lower laminates to the upper and lower grip strips. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the present disclosure will become more apparent upon reference to the drawings wherein like numbers refer to like parts throughout and wherein: 
         FIG. 1  is a top view of an aircraft which may include a composite structure for which a stabilizing mechanism preventing ply movement may be implemented; 
         FIG. 2  is a perspective illustration of a layup of a composite structure configured as a wing flap and which is mounted on a tool and further illustrating upper and lower laminates of the composite structure having a core sandwiched therebetween; 
         FIG. 3  is a top view of the composite structure mounted on the tool; 
         FIG. 4A  is a cross-sectional illustration of the composite structure taken along  4 A- 4 A of  FIG. 3  and illustrating ply movement that may occur without the implementation of an embodiment of the stabilizing mechanism; 
         FIG. 4B  is a cross-sectional illustration of the composite structure taken along line  4 B- 4 B of  FIG. 3  and illustrating the stabilizing mechanism for resisting ply movement and wherein the stabilizing mechanism may comprise a lower grip strip mounted to the tool and an upper grip strip engageable to the lower grip strip and to at least one of the upper and lower laminates; 
         FIG. 5A  is a perspective illustration of the upper grip strip in an embodiment formed from a pair of sheet members bonded together in back-to-back arrangement; 
         FIG. 5B  is a perspective illustration of the lower grip strip in an embodiment formed from one of the sheet members; 
         FIG. 6  is a block diagram of the stabilizing mechanism in an embodiment; 
         FIG. 7  is an illustration of a flow diagram for a method for reducing core crush in a chamfered core of a composite structure; 
         FIG. 8  is a flow diagram of an aircraft production and service methodology; and 
         FIG. 9  is a block diagram of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings wherein the showings are for purposes of illustrating preferred and various embodiments of the disclosure only and not for purposes of limiting the same, shown in  FIG. 1  is a plan view of an aircraft  120  as an example of one of a variety of applications where a stabilizing mechanism  72  ( FIGS. 2-3 ) may be implemented for preventing relative ply  32 ,  34  ( FIG. 2 ) movement during fabrication of a composite structure  10 . As can be seen in  FIG. 1 , the aircraft  120  includes a pair of wings  124  extending outwardly from a fuselage  122  from inboard  14  to outboard  16  and having propulsion units  134 . The aircraft  120  may include a tail section  128  having a horizontal stabilizer  130 , a vertical stabilizer  132 , and/or other control surfaces  126 . The aircraft  120  may include other components which may advantageously incorporate the use of the stabilizing mechanism  72  ( FIGS. 2-3 ) as disclosed herein during the fabrication of the composite structures  10 . 
     For example, the aircraft  120  may include one or more wing flaps  136  which may be formed as a composite structure  10  benefiting from the stabilizing mechanism  72  ( FIGS. 2-3 ) in preventing ply  32 ,  34  ( FIG. 2 ) movement and core  20  ( FIG. 2 ) crush during the fabrication process. In this regard, it should be noted that although the stabilizing mechanism  72  as disclosed herein is described with regard to a wing flap  136  as may be used in an aircraft  120 , the stabilizing mechanism  72  may be implemented in the fabrication of a composite structure  10  for any vehicular or non-vehicular application and for use in any industry including, without limitation, the marine and automotive industries. Furthermore, the stabilizing mechanism  72  and method disclosed herein is not limited for use in sandwich panels having a lightweight open cell core such as honeycomb core  20 , but may include the fabrication of any composite structure  10  comprised of layered plies  32 ,  34  ( FIG. 2 ) wherein ply movement may occur. 
     Referring to  FIG. 2 , shown is the composite structure  10  configured as a wing flap  136  and mounted on a tool  50  as may be used for the layup and preparation of the composite structure  10  prior to consolidating and/or curing of the composite structure  10 . Although shown configured as a wing flap  136  in  FIG. 2 , the composite structure  10  may be configured in a variety of alternative shapes, sizes and configurations without limitation and which may benefit from the stabilizing mechanism  72  as disclosed herein. The tool  50  may include tooling fixtures  52  for restraining the composite structure  10  during the fabrication process. The composite structure  10  may be laid on a tool surface  54  of the tool  50  as illustrated in  FIG. 2 . The tool  50  may also be transportable such that the composite structure  10  may be moved from a layup facility to an autoclave facility for the application of heat and/or pressure during cure. 
     As can be seen in  FIG. 2 , the composite structure  10  may include upper and lower laminates  28 ,  30  between which the core  20  may be sandwiched. The composite structure  10  may include a perimeter  48  along which the stabilizing mechanism  72  may be located. The lower laminate  30  may be comprised of lower plies  34  upon which the core  20  may be mounted. The upper laminate  28  may be comprised of upper plies  32  which may be laid over the core  20  and which may also overlap the lower laminate  30  at the edge of the core  20  to form a skin member  12 . The core  20  may be formed of any suitable core  20  material including, but not limited to, metallic materials such as aluminum, aramid, fiberglass or any other suitable material. Likewise, the upper and lower plies  32 ,  34  which respectively comprise the upper and lower laminates  28 ,  30  may be formed of any suitable materials such as, without limitation, pre-impregnated woven fabric or uni-directional tape material. 
     As can be seen in  FIG. 2 , the composite structure  10  may include one or more chamfers  40  which may be formed at any angle. The stabilizing mechanism  72  as disclosed herein may at least substantially prevent ply movement such as along a direction from the perimeter  48  toward the core chamfer  40 . The stabilizing mechanism  72  may be disposed around the perimeter  48  of the composite panel  18  as illustrated in  FIGS. 2 and 3 . The stabilizing mechanism  72  may prevent core crush of the chamfered core  20  under the application of pressure to the composite structure  10  such as during consolidation and/or curing. The process of curing of the composite structure  10  may include bonding of the upper and lower laminates  28 ,  30  to respective ones of the upper and lower surfaces  22 ,  24  of the core  20  material. 
     Referring particularly now to  FIG. 3 , shown is a plan view of the composite structure  10  mounted on the tool  50  and illustrating the perimeter  48  of the composite structure  10  upon which the stabilizing mechanism  72  may be located. As can be seen in  FIG. 3 , the upper laminate  28  may be formed of the upper plies  32  which are illustrated as being partially broken away in  FIG. 3  in order to illustrate the overlap of the upper laminate  28  over the stabilizing mechanism  72 . The stabilizing mechanism  72  may comprise a lower grip strip  78  which may be bonded to the tool  50  at the inner surface or otherwise mounted to the tool  50 . In addition, the stabilizing mechanism  72  may include at least one upper grip strip  76  which may optionally be disposed in substantial alignment with the lower grip strip  78  and may be engaged to the lower grip strip  78 . The upper and lower grip strips  76 ,  78  may be engaged to the upper and lower laminates  28 ,  30  in order to resist, restrict or prevent relative movement of the upper and lower plies  32 ,  34  which make up the upper and lower laminate  28 ,  30 . In this manner, the stabilizing mechanism  72  may resist movement of the core  20  to which the upper and lower laminates  28 ,  30  are mounted within the composite structure  10 . In this manner, the stabilizing mechanism  72  may minimize or eliminate core crush of the core  20 . 
     For example, and referring to  FIG. 4A , shown is a cross-sectional illustration of the composite structure  10  in an embodiment having a tie strap  74  mountable to the tool  50  and extending partially over the plies  32 ,  34 . As can be seen in  FIG. 4A , ply movement  104  occurs in the plies  32 ,  34  resulting in movement of the core  20  causing core crush  100 . The area of core crush  100  is illustrated as having a generally increased density of the individual cells  26  that make up the core  20 . In this regard, core movement  106  and core crush  100  may occur as a result of compaction of the core cells  26  in response to the side force  108  exerted on the chamfer  40  by the autoclave force  112  generated by autoclave pressure  110  or other external pressure applied to the chamfer  40 . As a result, the chamfer  40  portion of the composite structure  10  may exhibit panel sag  102  or deformation. For relatively large thicknesses of the core  20  (e.g., greater than six inches) and for relatively large chamfer angles θ (e.g., greater than 10 degrees), the magnitude of the autoclave force  112  or side force  108  may be sufficient to cause core crush  100  in the absence of a mechanism for restricting movement of the plies  32 ,  34 . 
     Referring now to  FIG. 4B , shown is a cross-sectional illustration of the composite structure  10  having the stabilizing mechanism  72  engaged to the upper and lower laminates  28 , along the perimeter  48  of the structure  10 . The stabilizing mechanism  72  is configured to resist movement of the plies  32 ,  34  along a direction from the perimeter  48  toward the core chamfer  40 . The stabilizing mechanism  72  may resist movement of the plies  32 ,  34  which may resist or prevent movement of the core  20 . As can be seen in  FIG. 4B , the stabilizing mechanism  72  may include at least one upper grip strip  76  and a lower grip strip  78  engaged to the upper grip strip  76 . The lower grip strip  78  may be formed as a sheet member  78   a  and may be mounted to the tool  50  such as by bonding an inner surface  78   b  of the lower grip strip  78  to the tool  50  using an adhesive  92 . However, the lower grip strip  78  may be mounted to the tool  50  by any suitable means including, without limitation, bonding and/or mechanical fastening. The stabilizing mechanism  72  may preferably be located within an edge band  42  of the tool  50  in order to allow for trimming or removal of the stabilizing mechanism  72  upon completion of curing or consolidating of the composite structure  10 .  FIG. 4B  illustrates a trim line  44  defining a trim margin  46  along the perimeter  48  of the composite structure. The stabilizing mechanism  72  is preferably located within the trim margin  46 . 
     Referring still to  FIG. 4B , the lower grip strip  78  may be mounted to the tool  50  and may include an outer surface  78   c  having at least one engagement feature  78   d  such as a protrusion  78   e  for engaging at least one of the upper and lower laminates  28 ,  30 . For example, the lower laminate  30  may include three plies P 1 , P 2  and P 3  which may extend over the lower grip strip  78  in overlapping relation thereto within a ply-strip overlap  94  region. The ply-strip overlap  94  may be provided in any width such as a one inch overlap of each lower ply  34  with the lower grip strip  78 . The amount of ply-strip overlap  94  is preferably sufficient to facilitate engagement of the lower plies  34  to the lower grip strip  78  to resist movement of the lower plies  34 . 
     Although  FIG. 4B  illustrates three plies  34  as being engaged to the lower grip strip  78 , any number of lower plies  34  may be engaged to the lower grip strip  78  and in any amount of ply-strip overlap  94 . In this regard, it is contemplated that only a single ply  34  may be engaged in overlapping relation to the lower grip strip  78 . The amount of overlap of the plies  34  with the lower grip strip  78  may be dictated in part by the width of the lower grip strip  78 . In an embodiment, the lower grip strip  78  may be provided in a width of three inches or in a width of six inches. Likewise the upper grip strip  76  may be provided in a width of three or six inches depending upon material availability. However, the lower grip strip  78  and upper grip strip  76  may be provided in any width or in any combination of widths along the perimeter  48  of the composite structure  10 . 
     Referring still to  FIG. 4B , the upper grip strip  76  is illustrated as being optionally oriented in substantial alignment with the lower grip strip  78 . In this regard, the upper grip strip  76  may be formed of the same or similar material as the lower grip strip  78 . For example, the upper grip strip  76  may be formed as a pair of sheet members  76   a  joined at inner surfaces  76   b  by adhesive  92  ( FIG. 5A ) although the upper grip strip  76  may be formed as a unitary structure of any suitable configuration. In this regard, the upper and lower grip strips  76 ,  78  may be formed of similar or dissimilar materials. The upper grip strip  76  is preferably disposed such that the upper laminate  28  is engaged thereto. More particularly, the upper plies  32  that comprise the upper laminate  28  may be engaged in overlapping relation to the upper grip strip  76 . As can be seen in  FIG. 4B , the plies P 4  and P 5  of the upper laminate  28  may be disposed on opposing sides of the upper grip strip  76 . However, it is also contemplated that the lower laminate  30  and upper laminate  28  may be directly engaged to the upper grip strip  76 . 
     For example, ply P3 of the lower laminate  30  may be engaged to a bottom side of the upper grip strip  76  while ply P 4  of the upper laminate  28  may be engaged to a top side of the upper grip strip  76 . In this regard, the upper grip strip  76  may be formed as a sheet member  76   a  and may have at least one engagement feature  76   d  such as a protrusion  76   e  formed on each one of the outer surfaces  76   c  of the upper grip strip  76  for engaging the lower grip strip  78  and/or for engaging at least one of the upper and lower laminates  28 ,  30 . As can be seen, the arrangement of the upper laminate  28  and lower laminate  30  relative to the upper grip strip  76  provides a variety of configurations for layering the upper plies  32  and lower plies  34  relative to the upper grip strip  76 . Notably, the upper grip strip  76  is engaged along a portion of the lower grip strip  78  and is also preferably engaged to one or more of the upper plies  32  of the upper laminate  28 . 
     Referring still to  FIG. 4B , it can be seen that the upper grip strip  76  overlaps the lower grip strips  78  by the amount indicated as the grip strip overlap  96 . In an embodiment, the grip strip overlap  96  may measure approximately two inches for a grip strip width of approximately six inches. In this regard, the amount of the grip strip overlap  96  may comprise approximately 20% to 40% of the total width available for engagement to the lower grip strip  78 . Likewise, each one of the ply-strip overlaps  94  may comprise approximately 10% to 20% of the total width of the upper and lower grip strips  76 ,  78 . However, the ply-strip overlap  94  and grip strip overlap  96  may be provided in any relative amount and is not limited to that which is illustrated and disclosed herein. 
     It should also be noted that although the stabilizing mechanism  72  is illustrated in  FIG. 4B  as comprising a single one of the upper and lower grip strips  76 ,  78 , any number of upper and lower grip strips  76 ,  78  may be provided in any arrangement relative to one another and to the upper and lower laminates  28 ,  30 . For example, the stabilizing mechanism  72  may comprising a plurality of the upper grip strips  76 ,  78  which may be engaged to one another and to one or more of the upper and/or lower plies  32 ,  34 . One of the upper grip strips  76  may at least partially overlap and engage the lower grip strip  78  which may be mounted to the tool  50 . The upper grip strips  76  may at least partially overlap and engage the lower grip strip  78 . The upper grip strips  76  may additionally at least partially overlap and engage one another in any one of a variety of different arrangements without limitation. 
     Referring briefly to  FIG. 3 , the lower grip strip  78  can be seen as extending underneath the lower plies  34  of the lower laminate  30 . Plies P 1 , P 2  and P 3  are illustrated as terminating in staggered relationship  80  to one P 1 , P 2  and P 3  another such that a portion of at least one of the lower plies  34  is in direct engagement  82  with the lower grip strip  78 . The upper grip strip  76  can be seen as being engaged to an outermost portion of the lower grip strip  78 . Referring still to  FIG. 3 , the upper and lower grip strips  76 ,  78  are illustrated as extending along the perimeter  48  of the composite structure  10 . In addition, the upper and lower grip strips  76 ,  78  are illustrated as extending along a width of the composite structure  10  in a continuous section or length of the material. However, the upper and lower grip strips  76 ,  78  may comprise any number of sections along perimeter  48  of the composite structure  10 . In addition, the upper and lower grip strips  76 ,  78  may extend along portions of the perimeter  48  in a continuous manner or in an arrangement of sections of the upper and lower grip strips  76 ,  78 . 
     Referring to  FIG. 4B , shown is a tie strap  74  which may optionally be mounted to the tool  50  along the tool surface  54  and may be disposed in overlapping relation to the upper grip strip  76 . The tie strap  74  may additionally overlap the uppermost one of the upper plies  32  of the upper laminate  28  by an amount illustrated as a tie strap overlap  98 . The tie strap  74  may provide additional resistance against movement of the upper grip strip  76  relative to the lower grip strip  78 . The tie strap  74  may be mounted to the tool surface  54  by any suitable means including, but not limited to, adhesive  92  bonding and/or by mechanical attachment. 
     The tie strap  74  may comprise individual sections of tape and/or may be formed as a strip of tape which may be extended along a length of the perimeter  48  or a width of the perimeter  48  as illustrated in  FIG. 3 . Referring still to  FIG. 4B , the tie strap  74  may be mounted to the tool  50  and may overlap at least a portion of the upper grip strip  76  along a length thereof such as along the perimeter  48  of the structure  10 . Referring to  FIG. 4B , the lower grip strip  78  may be formed of any suitable material including a substantially thin metallic planar sheet member  78   a  which may include inner and outer surfaces  78   b ,  78   c  as was earlier indicated. In this regard, the lower grip strip  78  may be comprised of a single planar sheet member  78   a  having a generally elongate shape and which may include a plurality of protrusions  78   e  extending outwardly therefrom. 
     The protrusions  78   e  may comprise the engagement feature  78   d  for engaging the upper and/or lower laminates  28 ,  30 . The protrusions  78   e  may extend outwardly to a height sufficient to engage at least one of the upper and lower plies  32 ,  34  of the upper and lower laminates  28 ,  30 . For example, for a woven fiber prepreg having a thickness of approximately 0.007 inch, it is contemplated that the protrusions  78   e  may extend outwardly at least to a height that is substantially equivalent to a thickness of one of the plies  32 ,  34 . In an embodiment, the protrusions  78   e  may have a height of at least approximately 0.010 inch to facilitate engagement to one of the plies  32 ,  34  to an extent sufficient to prevent movement or slippage of the plies  32 ,  34 . 
     Referring to  FIGS. 5A-5B , shown are perspective illustrations of embodiments of the upper and lower grip strips  76 ,  78 . As can be seen in  FIG. 5A , the upper grip strip  76  may comprise a pair of sheet members  76   a . The sheet members  76   a  may be bonded or otherwise fastened together or connected such as at the inner surfaces  76   b  in back-to-back arrangement. As can be seen in  FIG. 5B , the lower grip strip  78  may comprise a single one of the sheet members  78   a . Each one of the sheet members  76   a ,  78   a  of the upper and lower grip strips  76 ,  78  may comprise sheet material formed of any suitable material. In an embodiment, the sheet members  76   a ,  78   a  may include engagement features  76   d ,  78   d  which may comprise a plurality of protrusions  76   e ,  78   e  extending outwardly from the respective outer surfaces  76   c ,  78   c . In an embodiment, each one of the sheet members  76   a ,  78   a  may be formed of relatively thin (e.g., 0.005 inch) material of any composition. For example, the sheet members  76   a ,  78   a  may be formed of metallic material including, but not limited to, aluminum and stainless steel. The protrusions  76   e ,  78   e  may be stamped out of the sheet material such that the protrusions  76   e ,  78   e  are integrally formed with the sheet members  76   a ,  78   a.    
     In this regard, each one of the sheet members  76   a ,  78   a  may include a plurality of perforations (not shown) which may facilitate the evacuation or egression of volatiles and other gasses which may be generated during the application of heat and/or pressure to the composite structure  10  ( FIG. 4B ) such as during consolidating and/or curing. In addition, each one of the upper and lower grip strips  76 ,  78  is preferably configured to facilitate suitable engagement to the upper and lower laminates  28 ,  30  ( FIG. 4B ) to prevent relative movement thereof. For example, the protrusions  76   e ,  78   e  extending outwardly from the upper and lower grip strips  76 , 78  may be configured to have a height sufficient to penetrate a thickness of at least one of the upper and lower plies  32 ,  34  ( FIG. 4B ) of the upper and lower laminates  28 ,  30  ( FIG. 4B ). 
     Referring still to  FIGS. 5A-5B , the sheet members  76   a ,  78   a  from which the upper and lower grip strips  76 ,  78  may be formed may comprise any suitable material in any suitable configuration and are not limited to a metallic construction having protrusions  76   e ,  78   e  integrally formed into the sheet members  76   a ,  78   a . For example, it is contemplated that each one of the sheet members  76   a ,  78   a  may comprise a sheet of grit material (not shown) for frictional engagement of the upper and lower plies  32 ,  34  ( FIG. 4B ) of the upper and lower laminates  28 ,  30  ( FIG. 4B ). In addition, the upper and lower grip strips  76 ,  78  may have a similar configuration which may facilitate interlocking or engagement of the upper grip strip  76  to the lower grip strip  78 . However, the upper and lower grip strips  76 ,  78  may be fabricated of dissimilar materials and may be provided in different sizes, shapes and configurations and are not limited to a configuration where the upper grip strip  76  is formed of a pair of metallic sheet members  76   a  similar to that from which the lower grip strip  78  is formed. Furthermore, the configuration of the upper and lower grip strips  76 ,  78  as shown and described herein in not to be construed as limiting alternative embodiments of the upper and lower grip strips  76 ,  78 . 
     Referring to  FIG. 4B , the upper and lower grip strips  76 ,  78  may further comprise a portion of a system  70  for reducing core crush such as may occur in composite structures  10  having a chamfered core  20 . The system  70  may include a force mechanism  116  which may be provided by an external pressure source such as autoclave pressure  110  or vacuum bag pressure (not shown). The force mechanism  116  may result in the application of compressive force  114  to the upper laminate  28  to increase the engagement of the upper and lower laminates  28 ,  30  to the upper and lower grip strips  76 ,  78 . The application of compressive force  114  can be seen in  FIG. 4B  as acting upon the upper laminate  28  and which may be transmitted to the upper grip strip  76 , lower laminate  30  and lower grip strip  78  in order to improve the engagement therebetween. 
     In this regard, the stabilizing mechanism  72  may provide an additional advantage in that an increase in compressive force  114  such as a result of autoclave pressure  110  may also result in an increase in the compressive force  114  applied to the upper laminate  28  which may, in turn, result in an increase in the engagement of the upper and lower laminates  28 ,  30  to the upper and lower grip strips  76 ,  78 . In this regard, the stabilizing mechanism  72  facilitates an increase in the compressive force  114  applied to the upper laminate  28  in proportion to the increase in side force  108  or autoclave force  112  exerted on the chamfer  40 . It is also contemplated that the force mechanism  116  may result from a vacuum drawn on a bagging film  56  as may be used for sealing the composite structure  10  to the tool  50 . For example, as shown in  FIG. 4B , the bagging film  56  may be secured or sealed to the tool surface  54  of the tool  50  by means of a sealant  58  such as sealant tape. The composite structure  10  may optionally include a breather layer  60 , a bleeder layer  62 , parting film  64  and/or other components associated with the fabrication of composite structures. 
     Referring still to  FIG. 4B , the lower grip strip  78  may be configured such that the protrusions  78   e  extending outwardly therefrom are disposed in overlapping engagement with at least two of the upper plies  32  or lower plies  34 . However, the stabilizing mechanism  72  may be configured such that any number of lower plies  34  may be disposed in overlapping relation to the lower grip strip  78 . Likewise, the upper grip strip  76  may be configured such that at least two of the upper plies  32  or lower plies  34  are engaged thereby. However, as was earlier mentioned, the arrangement of the stabilizing mechanism  72  may be such that the upper grip strip  76  may be engaged to any number of the lower plies  34  and any number of upper plies  32  in addition to engagement with the lower grip strip  78 . 
     Referring to  FIG. 6 , shown is a block diagram of a system  70  for reducing core crush of core  20  of a composite structure  10 . As was indicated earlier, the system  70  may comprise a tool  50  upon which the composite structure  10  may be mounted. The structure  10  may comprise the upper laminate  28  having upper plies  32  and the lower laminate  30  having lower plies  34  and between which the core  20  is sandwiched. The perimeter of the composite structure  10  may be engaged to the stabilizing mechanism  72  having the lower grip strip  78  mounted to the tool  50 . As indicated above, the stabilizing mechanism  72  may be comprised of the lower grip strip  78  having an outer surface including at least one engagement feature  78   d  such as a protrusion  78   e  for engaging at least one of the upper and lower laminates  28 ,  30 . Likewise, the upper grip strip  76  may have opposing outer surfaces  76   c  wherein each of the outer surfaces  76   c  may include at least one engagement feature  76   d  such as a protrusion  76   e  for engaging the lower grip strip  78  and for engaging at least one of the upper and lower laminates  28 ,  30 . In addition, the system  70  may comprise a force mechanism  116  such as autoclave pressure  110  or a bagging film  56  under vacuum pressure for applying a compressive force to the upper laminate  28  in order to increase the engagement of the upper and lower laminates  28 ,  30  to the upper and lower grip strips  76 ,  78 . 
     Referring now to  FIG. 7 , shown is a flow diagram illustrating a methodology for reducing core crush  100  in a chamfered  40  core  20  such as the core  20  of the composite structure  10  illustrated in  FIGS. 2-4B . As illustrated in  FIG. 7 , the methodology may include step  200  of bonding the lower grip strip  78  to the tool  50  within the trim margin  46  as illustrated in  FIG. 4B . The lower grip strip  78  may be mounted to the tool  50  by any means and is not limited to bonding. For example, the lower grip strip  78  may be mechanically fastened to the tool  50 . As was indicated earlier, the lower grip strip  78  may include engagement features such as a plurality of protrusions  78   e  extending outwardly from the outer surface  78   c  of the lower grip strip  78 . Step  202  of the methodology may include laying up lower plies  34  of the lower laminate  30  onto the tool  50 . For example,  FIG. 4B  illustrates plies P 1 , P 2  and P 3  which may comprise the lower plies  34  of the lower laminate  30 . Such plies may be laid up on the tool  50  such that at least two of the lower plies  34  (i.e., P 1  and P 2 ) are in engagement with at least a portion of the lower grip strip  78 . For example, as illustrated in  FIG. 4B , plies P 1 , P 2  and P 3  are disposed in overlapping relation to the lower grip strip  78  such that a portion of the lower grip strip  78  remains exposed. 
     Referring still to  FIG. 7 , step  204  may comprise terminating the lower plies  34  in staggered relation to one another on the lower grip strip  78  such that each ply defines a ply-strip overlap providing a predetermined amount of engagement of each one of the plies with the lower grip strip  78  as illustrated in  FIG. 4B . Step  206  may comprise positioning the core  20  such as the honeycomb core  20  described above over the lower laminate  30 . In this regard, the honeycomb core  20  may be machined to size including forming chamfers in the core  20  for layup of the upper and lower plies  32 ,  34  of the upper and lower laminates  28 ,  30  onto the core. The core  20  is preferably sized within the final shape of the composite structure  10  after addition of the upper and lower laminates  28 ,  30 . Step  208  may comprise positioning the upper grip strip  76  in substantial alignment with the lower grip strip  78 . For example, the upper grip strip  76  is illustrated as having a width similar to the lower grip strip  78  as shown in  FIG. 4B  wherein the upper grip strip  76  is illustrated as being positioned over the lower grip strip  78  within the trim margin  46  of the layup in  FIG. 4B . Step  210  may comprise engaging the upper grip strip  76  to a portion of the lower grip strip  78 . 
     Referring still to  FIG. 7 , step  212  may comprise laying up the upper plies  32  of the upper laminate  28  over the core  20  such that at least two of the upper plies  32  overlap and engage a portion of the upper grip strip  76  as illustrated in  FIG. 4B . For example,  FIG. 4B  illustrate plies P 4  and P 5  disposed on opposing sides of the upper grip strip  76  and in direct contact therewith. In addition, ply P 6  of the upper plies  32  is illustrated in  FIG. 4B  as being in overlapping relation to the upper grip strip  76  on a top side thereof. In this regard, the methodology comprises step  214  of terminating the upper plies  32  in staggered relation to one another on the upper grip strip  76  in order to facilitate attachment of a maximum number of plies to the upper grip strip  76 . 
     Referring to  FIG. 7 , step  216  may comprise mounting at least one tie strap  74  to the tool  50  as illustrated in  FIG. 4B  in order to increase the resistance against ply movement. As indicated above, the tie strap  74  may comprise a material extending along a length of the upper grip strip  76 . The tie strap  74  may comprise a tape-like material which may be applied in sections or as in continuous length along each one of the sides of the composite structure  10  at the perimeter  48  as illustrated in  FIG. 3 . In this regard,  FIG. 4B  illustrates that a portion of the ply is directly engageable to the top of the upper grip strip  76  to provide increased resistance to movement thereof. Step  218  may comprise extending the tie strap  74  over at least a portion of the upper grip strip  76  and along a length thereof. 
     Referring still to  FIG. 7 , step  220  may comprise applying the compressive force  114  to the composite structure  10 . A main result of application of the compressive force  114  may be to consolidate the upper and lower laminates  28 ,  30  and core  20  of the composite structure  10  with a secondary result of increasing engagement of the upper and lower laminates  28 ,  30  to the upper and lower grip strips  76 ,  78 . As indicated above, the application of such compressive force  114  may be facilitated by the placing of the composite structure  10  within a bagging film  56  which may be sealed to the tool surface  54  by means of the sealant  58  as illustrated in  FIG. 4B . A vacuum may be drawn on the bagging film  56  in order to generate the compressive force which is exerted on the stabilizing mechanism  72 . Alternatively, the application of compressive force  114  to the composite structure  10  may also include the application of autoclave pressure on the composite structure  10  such as may occur within during an autoclave operation for consolidation or curing of the composite structure  10  as was described above. 
     The method may further comprise laying up the upper and lower laminates  28 ,  30  such that at least one of the upper and lower plies  32 ,  34  engages both the upper and lower grip strips  76 ,  78 . In this manner, movement of the plies may be reduced or prevented. The method may further comprise laying up the upper laminate  28  over the core  20  such that a portion of the upper laminate  28  overlaps the lower laminate  30  and engages the upper grip strip  76 . As was also indicated above, the upper laminate  28  comprises upper plies  32  which may be terminated to the upper grip strip  76  in staggered relation to one another. Likewise, the lower plies  34  of the lower laminate  30  may be laid up such that at least two of the lower plies  34  are arranged in staggered relation to one another over the lower grip strip  78 . 
     Referring to  FIGS. 8-9 , embodiments of the disclosure may be described in the context of an aircraft manufacturing and service method  300  as shown in  FIG. 8  and an aircraft  302  as shown in  FIG. 9 . During pre-production, exemplary method  300  may include specification and design  304  of the aircraft  302  and material procurement  306 . During production, component and subassembly manufacturing  308  and system integration  310  of the aircraft  302  takes place. Thereafter, the aircraft  302  may go through certification and delivery  312  in order to be placed in service  314 . While in service  314  by a customer, the aircraft  302  is scheduled for routine maintenance and service  316  (which may also include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  300  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. 9 , the aircraft  302  produced by exemplary method  300  may include an airframe  318  with a plurality of systems  320  and an interior  322 . Examples of high-level systems  320  include one or more of a propulsion system  324 , an electrical system  326 , a hydraulic system  328 , and an environmental system  330 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the disclosed embodiments 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  300 . For example, components or subassemblies corresponding to production process  308  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  302  is in service  314 . Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  308  and  310 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  302 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  302  is in service  314 , for example and without limitation, to maintenance and service  316 . 
     Additional modifications and improvements of the present disclosure may be apparent to those of ordinary skill in the art. Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present disclosure and is not intended to serve as limitations of alternative embodiments or devices within the spirit and scope of the disclosure.