Patent Publication Number: US-9851182-B2

Title: Macro fiber for composite articles

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional application of and claims priority to pending U.S. application Ser. No. 13/523,108 filed on Jun. 14, 2012, and entitled BICOMPONENT FIBERS CONTAINING NANO-FILAMENTS FOR USE IN OPTICALLY TRANSPARENT COMPOSITES, the entire contents of which is expressly incorporated by reference herein. 
    
    
     FIELD 
     The present disclosure relates generally to composites and, more particularly, to fiber-reinforced composite articles having improved ballistic and optical performance. 
     BACKGROUND 
     Glass is widely used as a transparency in a variety of applications due to its superior optical qualities. For example, glass is commonly used as a glazing material or as an architectural material for buildings. Glass is also commonly used as a transparency in vehicular applications. Unfortunately, glass is a relatively dense material and is also relatively brittle such that relatively large thicknesses are required to provide sufficient strength for resisting shattering when the glass is impacted by an object such as a projectile. 
     In attempts to avoid the weight penalty associated with glass, transparencies may be fabricated from polymeric materials. For example, transparencies may be formed of optically transparent monolithic polymers such as acrylic which is less dense than glass and which possesses suitable optical properties. Unfortunately, acrylic is a relatively low strength material making it generally unsuitable for many applications where high impact resistance is required. 
     In consideration of the weight penalties associated with glass and the strength limitations associated with monolithic polymers, manufacturers have also fabricated composite transparencies using conventional fibers such as ribbon-shaped fibers embedded in a matrix. Unfortunately, conventional fibers are typically spaced apart from one another in the matrix resulting in a portion of the incident light passing through gaps between the fibers. When there is a mismatch in the refractive index of the matrix and the fibers, there is a deleterious effect on the optics of the transparency due differences in the optical path lengths of the light rays and differences in the resultant angles of the light rays depending on whether the light rays pass through the main portions of the fibers or whether the light rays pass through the side surfaces of the fibers. The consequence of the differences in the optical path lengths and resultant angles is that an object viewed through the transparency may appear blurred. 
     As can be seen, there exists a need in the art for a high-strength transparent composite article having a fiber configuration that provides improved optical performance with reduced optical distortion. 
     BRIEF SUMMARY 
     The above-described needs associated with composite articles are specifically addressed and alleviated by the present disclosure which, in an embodiment, provides a macro fiber for a composite article. The macro fiber includes a plurality of nano-filaments or inner fibers which may each have an inner fiber final cross-sectional size of less than approximately 100 nanometers. The inner fibers may be surrounded by matrix material. 
     In a further embodiment, disclosed is a composite article which may include a plurality of macro fibers. Each one of the macro fibers may include a plurality of inner fibers. Each one of the inner fibers may have an inner fiber final cross-sectional size of less than approximately 100 nanometers. Each macro fiber may include a matrix material surrounding the inner fibers. Each macro fiber may have a predetermined cross-sectional shape. 
     Also disclosed is a method of manufacturing a macro fiber. The method may include the step of forming a plurality of inner fibers each having an inner fiber final cross-sectional size (e.g., a final diameter) of less than approximately 100 nanometers. The method may additionally include surrounding the inner fibers with matrix material to form a macro fiber. The method may also include forming the macro fiber in a predetermined cross-sectional shape. 
     In a further embodiment, disclosed is a method of forming a composite article. The method may include the step of providing a plurality of macro fibers. Each one of the macro fibers may include a plurality of inner fibers surrounded by matrix material. Each one of the inner fibers may have an inner fiber final cross-sectional size of less than approximately 100 nanometers. The method may include reducing a viscosity of the matrix material to cause intermingling of the matrix material among the plurality of the macro fibers, and curing and/or solidifying the matrix material to form a composite article. 
     Also disclosed is a method of using a composite article which may include providing a composite article having a plurality of macro fibers wherein each one of the macro fibers includes a plurality of inner fibers surrounded by matrix material. Each one of the inner fibers may have an inner fiber final cross-sectional size of less than approximately 100 nanometers. The method of using the composite article may include placing the composite article in a non-loaded condition, and placing the composite article in a loaded condition. 
     The features, functions and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the present disclosure will become more apparent upon reference to the drawings wherein like numerals refer to like parts throughout and wherein: 
         FIG. 1  is a perspective view of an embodiment of a composite article in an embodiment comprising a plurality of layers containing inner fibers embedded in matrix material; 
         FIG. 2  is an enlarged perspective view of a portion of the composite article of  FIG. 1  and illustrating the inner fibers; 
         FIG. 3  is perspective view of a plurality of macro fibers in a layup configuration and wherein each macro fiber contains a plurality of the inner fibers; 
         FIG. 4  is a perspective view of the plurality of macro fibers of  FIG. 3  arranged in a stacked configuration prior to heating and/or consolidation; 
         FIG. 5  is a cross-sectional view of an embodiment of one of the macro fibers containing a plurality of inner fibers; 
         FIG. 6  is a cross-sectional view of a macro fiber having an outer sheath comprised of sacrificial material; 
         FIG. 7  is a cross-sectional view of a macro fiber in a sheet configuration; 
         FIG. 8  is a cross-sectional view of a macro fiber in a trapezoid configuration; 
         FIG. 9  is a cross-sectional view of a macro fiber in a triangle configuration; 
         FIG. 10  is a cross-sectional view of a macro fiber in a diamond configuration; 
         FIG. 11  is a side view of a composite article in a layup configuration including a plurality of first and second structural layers; 
         FIG. 12  is a side view of the composite article of  FIG. 11  in a consolidation configuration; 
         FIG. 13  is a perspective view of the composite article illustrating the uppermost first and second structural layer partially cutaway to illustrate the stretched directions of the alternating first and second structural layers; 
         FIG. 14  is a flow chart illustrating one or more operations that may be included in a method of manufacturing a macro fiber; 
         FIG. 15  is a flow chart illustrating one or more operations that may be included in a method of manufacturing a composite article; 
         FIG. 16  is a flow chart illustrating one or more operations that may be included in a method of using a composite article; and 
         FIG. 17  is a perspective illustration of an aircraft which may incorporate the composite article in one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings wherein the showings are for purposes of illustrating preferred and various embodiments of the disclosure, shown in  FIG. 1  is an embodiment of a composite article  100 . The composite article  100  is configured as a composite panel  104  having upper and lower sides  108 ,  110 . The composite article  100  may be fabricated using a plurality of structural layers arranged in a stacked formation  230 . For example, the composite article may be comprised of a plurality of structural layers such as the first and second structural layers  400 ,  420  illustrated in  FIG. 1 . Each one of the first and second structural layers  400 ,  420  may be formed using a plurality of macro fibers  200  as shown in  FIG. 5 . Each one of the macro fibers  200  may be comprised of a plurality of substantially unidirectional inner fibers  300  ( FIG. 5 ) surrounded by matrix material  236  ( FIG. 5 ) as described in greater detail below. The inner fibers  300  may have an inner fiber length  310  ( FIG. 3 ) that may be aligned with the macro fiber length  222  ( FIG. 3 ). 
     Referring to  FIG. 2 , shown is a portion of the composite article  100  of  FIG. 1  and illustrating the inner fibers  300  in first and second structural layers  400 ,  420 . Each one of the first and second structural layers  400 ,  420  has a stretched direction  406 ,  426 . The composite article  100  may be configured such that the stretched direction of the structural layers may be oriented in any direction relative to the stretched direction of any of the other structural layers in the composite article  100 . For example, in  FIG. 2 , the stretched direction  406  of the first structural layer  400  in each couplet  228  is oriented generally perpendicular to the stretched direction  426  of the second structural layer  420  of the couplet  228 . By orienting the stretched direction  406  of a first structural layer  400  in a couplet  228  generally perpendicular to the stretched direction  406  of a second structural layer  420  in a couplet  228 , the ballistic performance of the composite article may be improved as described below. 
     However, the stretched direction  406  of the first structural layer  400  may be oriented at any non-perpendicular angle (not shown) relative to the stretched direction  426  of the second structural layer  420  and which may also result in an improvement in the ballistic performance and/or strength properties of the composite article  100  relative to an embodiment wherein the stretched directions of the structural layers are oriented generally parallel to one another. In this regard, the composite article  100  may also be provided in an embodiment wherein the stretched direction one or more of the structural layers may be oriented generally parallel (not shown) to one another. 
       FIGS. 3-4  illustrate a plurality of macro fibers  200  in a layup configuration  232  during fabrication of the composite article  100 . Each macro fiber  200  has a stretched direction  224  along the macro fiber length  222 . Each macro fiber  200  may be formed with a predetermined cross-sectional shape  208  to facilitate the layup of the macro fibers  200  in the first and second structural layers  400 ,  420 . For example, each macro fiber  200  may be formed in a cross-sectional shape  208  having macro fiber side surfaces  206  and at least one substantially planar macro fiber upper surface  202  and/or a substantially planar macro fiber lower surface  204 . In  FIG. 3 , each macro fiber  200  has a parallelogram  210  cross-sectional shape  208  although the macro fibers  200  may be formed in other suitable cross-sectional shapes that may facilitate the positioning of the macro fibers  200  in relatively close proximity with one another. The macro fiber upper and lower surfaces  202 ,  204  may be substantially parallel and planar which may facilitate placing the macro fibers  200  in intimate contact with the macro fibers  200  of adjacent first and second structural layers  400 ,  420 . 
       FIG. 4  shows the first and second structural layers  400 ,  420  arranged as couplets  228  in a stacked formation  230 . Although three couplets  228  are shown, any number of couplets  228  may be included to form a composite article  100  of any desired thickness. The macro fiber side surfaces  206  may be placed in side-by-side arrangement  226  in relatively close proximity to one another. Once the first and second structural layers  400 ,  420  are arranged in stacked formation  230 , heat (not shown) and/or pressure (not shown) may be applied to reduce the viscosity of the matrix material  236 . The application of heat may reduce the viscosity of the matrix material  236  resulting in the intermingling of the matrix material  236  of adjacent macro fibers  200 . The intermingling of the matrix material  236  may eliminate gaps or voids between the macro fiber side surfaces  206  and/or between the macro fiber upper and lower surfaces  202 ,  204  of adjacent macro fibers  200  as shown in  FIG. 12  and described in greater detail below. The application of pressure may aid in the consolidation, curing, and/or solidification of the matrix material of the composite article  100 . 
     Referring to  FIG. 5 , shown is an embodiment of a macro fiber  200  in a parallelogram  210  cross-sectional shape  208 . Each macro fiber  200  may include a plurality of relatively small cross-sectional size (e.g., small diameter) nano-filaments or inner fibers  300  surrounded by matrix material  236 . The matrix material  236  may be applied substantially simultaneous with the forming of the inner fibers  300 . Advantageously, by co-forming the inner fibers  300  substantially simultaneous with the application of the surrounding matrix material  236 , the time, expense, and complexity associated with the separate application of resin in conventional composites manufacturing may be reduced or avoided. In addition, co-forming the inner fibers  300  with the matrix material  236  may result in a more precise control of the final dimensions (e.g., the overall height or thickness) of the composite article  100  ( FIG. 3 ) and more precise control of the fiber volume fraction of the composite article  100 . More precise control of the geometry and fiber volume fraction may result in improved optical performance and/or improved ballistic performance of the composite article  100 . 
     The inner fibers  300  and the matrix material  236  may be formed of material that is at least partially light-transmissive within a predetermined spectrum of light such as within the visible spectrum and/or infrared spectrum or within other wavelength bands. Each one of the inner fibers  300  may have an inner fiber final cross-sectional size  308 . For non-circular (not shown) inner fiber  300  cross-sectional shapes, the inner fiber final cross-sectional size  308  may be defined as the longest distance across the cross-sectional shape of the inner fiber  300 . 
     The inner fibers  300  may initially have a cross-sectional size that may be greater than their inner fiber final cross-sectional size  308 . Each one of the inner fibers  300  may be stretched along a lengthwise direction during or after formation of the inner fiber  300  which may reduce the cross-sectional size of the inner fiber  300  down to an inner fiber final cross-sectional size  308 . In an embodiment, the inner fiber final cross-sectional size  308  may be less than approximately one-quarter of the wavelength of a lower end of a predetermined range of light to which the composite article  100  may be exposed. For example, for composite articles  100  intended to be substantially optically transparent in the visible spectrum wherein the wavelength range is between approximately 400 nanometers (nm) and 750 nm, each one of the inner fibers  300  may have an inner fiber final cross-sectional size  308  of less than approximately 100 nm. For composite articles configured to be substantially optically transparent in the near-infrared spectrum wherein the wavelength range is between approximately 750 nm to 1.4 microns, each one of the inner fibers  300  may have an inner fiber final cross-sectional size  308  that is less than approximately 190 nm. 
     Advantageously, by providing the inner fibers  300  in an inner fiber final cross-sectional size (e.g., a final diameter) less than approximately one-quarter of the wavelength of light rays incident on the composite article, the refractive index of the inner fibers  300  and the matrix material  236  may not be separable and instead may be defined or characterized by an average of the optical properties of the combination of the inner fibers  300  and the matrix material  236 . For example, the inner fibers  300  may be formed of material having a certain refractive index and a temperature coefficient of refractive index. Likewise, the matrix material  236  may have a refractive index and a temperature coefficient of refractive index that may be different than the refractive index and a temperature coefficient of refractive index of the inner fibers  300 . The optical properties (e.g., the refractive index) of the macro fiber  200  may be defined as a weighted average of the optical properties (e.g., the refractive index) of the matrix material  236  and the inner fiber  300  material. 
     In  FIG. 5 , the inner fibers  300  are shown as having different inner fiber final cross-sectional sizes  308  (e.g., diameters) and being arranged at non-uniform spacings between one another. In this regard, the inner fibers  300  may be arranged in a pseudo-random spacing to minimize potential adverse optical effects that may occur with uniform spacing of the inner fibers  300 . However, one or more macro fibers  200  may be formed having inner fibers  300  that are substantially uniform in diameter and/or wherein the inner fibers  300  are arranged in a substantially uniform (not shown) spacing. Although the inner fibers  300  are shown as having a generally circular cross-sectional shape  304 , one or more of the inner fibers  300  may be provided in specific, non-circular (not shown) cross-sectional shapes to improve the optical performance of the composite article  100  ( FIG. 1 ). For example, one or more of the inner fibers  300  may be provided in cross-sectional shapes having one or more substantially planar surfaces (not shown) which may reduce optical distortion of light passing through the composite article  100 . 
     Each macro fiber  200  ( FIG. 5 ) may be stretched along a stretched direction  224  ( FIG. 3 ) during formation of the macro fiber  200  and/or after formation of the macro fiber  200 . As shown in  FIGS. 3-4 , the stretched direction  224  of the macro fibers  200  in the first and second structural layer  400 ,  420  ( FIG. 3 ) defines the respective stretched direction  406 ,  426  of the first and second structural layer  400 ,  420  as shown in  FIGS. 1-2 . The stretching of each macro fiber  200  may include the stretching of the inner fibers  300  ( FIG. 5 ) and the stretching of the matrix material  236  ( FIG. 5 ). The inner fibers  300  may be stretched to a predetermined stretching ratio to attain a desired strength property such as a desired ultimate tensile strength of the inner fibers  300 . The inner fibers  300  may be stretched prior to forming the macro fibers  200  or the inner fibers  300  may be stretched substantially simultaneous with the forming of the macro fibers  200 . Advantageously, the stretching of the inner fibers  300  may significantly increase the tensile strength and/or tensile modulus of the inner fibers  300 . The increase in the strength properties of the inner fibers  300  due to stretching of the inner fibers  300  may result in an increase in the global strength properties of the composite article  100  such as the specific strength and/or specific stiffness of the composite article  100  ( FIG. 1 ). 
     In  FIG. 5 , the parallelogram  210  cross-sectional shape  208  of the macro fiber  200  includes the macro fiber upper and lower surfaces  202 ,  204  and the macro fiber side surfaces  206 . The macro fiber side surfaces  206  may be oriented non-perpendicularly relative to the macro fiber upper and lower surfaces  202 ,  204 . The non-perpendicular orientation of the macro fiber side surfaces  206  may facilitate alignment of adjacent macro fibers  200  in side-by-side arrangement  226  with one another as shown in  FIGS. 3-4 . The non-perpendicular orientation of the macro fiber side surfaces  206  may also facilitate the intermingling of the matrix material  236  at the macro fiber side surfaces  206  when the viscosity of the matrix material  236  is reduced such as by heating and/or during the application of pressure during consolidation of the first and second structural layers  400 ,  420  ( FIG. 3 ). The macro fiber upper and lower surfaces  202 ,  204  may be oriented substantially parallel to one another which may facilitate the layup of a plurality of macro fibers  200  in substantially close or intimate contact with one another. 
     In  FIG. 5 , each macro fiber  200  has a macro fiber cross-sectional shape  208  that may be comprised of or defined by the matrix material  236 . In this arrangement, each one of the inner fibers  300  in a macro fiber  200  may be set back or spaced away from the perimeter surface of the macro fiber cross-sectional shape  208  such that each one of the inner fibers  300  is fully surrounded by matrix material  236 . However, the macro fiber cross-sectional shape  208  may be defined by a combination of the matrix material  236  and by portions of the inner fiber surface  302  of one or more of the inner fibers  300 . 
     Referring still to  FIG. 5 , each macro fiber  200  has a macro fiber width  218  and a macro fiber thickness  220 . In an embodiment, the macro fiber  200  may be provided with a maximum macro fiber thickness  220  in a range of from approximately 3 microns to 5000 microns. However, the macro fiber  200  may be provided in any macro fiber width  218  or any macro fiber thickness  220 , without limitation. The macro fiber  200  may have a generally elongated cross-sectional shape  208  which is preferably formed at a relatively high aspect ratio to minimize the quantity of individual macro fibers  200  required to span a desired width of the first structural layer  400  ( FIG. 3 ) or second structural layer  420  ( FIG. 3 ) or other structural layers (not shown) during layup of the macro fibers  200 . The macro fiber  200  aspect ratio may be defined as the ratio of the macro fiber width  218  to the macro fiber thickness  220 . In an embodiment, the aspect ratio may be within the range of from approximately 3 to approximately 500 although the macro fiber  200  may be formed in any aspect ratio. 
     Although  FIG. 5  shows the macro fiber  200  in a parallelogram  210  shape, the macro fiber  200  may be provided in any one of a variety of alternative shapes and configurations, without limitation. For example, the macro fiber  200  may be provided as a sheet  242  ( FIG. 7 ), a trapezoidal  212  shape ( FIG. 8 ), a triangular  214  shape ( FIG. 9 ), a diamond shape  216  ( FIG. 10 ), or in other shapes. In addition, the macro fiber  200  is not limited to cross-sectional shapes  208  that are substantially planar but may also include cross-sectional shapes  208  that are at least partially curved. For example, the macro fiber  200  cross-sectional shape  208  may include a circle  306 , a partially-circular shape, a closed semi-circle, a kidney shape, an oval, an ellipsoid, and any one of a variety of other shapes. 
       FIG. 6  shows an embodiment of a macro fiber  200  having an outer sheath  238  applied to the macro fiber  200 . The outer sheath  238  may comprise a sacrificial material  240  applied to the macro fiber  200  to preserve the cross-sectional shape  208  of the macro fiber  200  during formation. The sacrificial material  240  may be applied to the macro fiber  200  substantially simultaneous with the forming of the inner fibers  300  and matrix material  236 . The sacrificial material  240  of the outer sheath  238  may be formed of polymeric material that is complementary to the inner fibers  300  and the matrix material  236 . The sacrificial material  240  may comprise a generally dissolvable material that may be washed away or otherwise removed after formation of the macro fiber  200 . For example, the sacrificial material  240  may be dissolvable in water or in a solvent or the sacrificial material  240  may be removed by other chemical means or by mechanical means. Advantageously, the sacrificial material  240  may improve the dimensional control of the macro fiber  200  during formation by minimizing rounding of the macro fiber  200  surfaces and macro fiber  200  corners due to surface-energy-effects on the cross-sectional shape  208  of the macro fiber  200 . 
       FIG. 7  shows an embodiment of a macro fiber  200  in a sheet  242  cross-sectional shape  208 . The sheet  242  may be provided with a relatively high aspect ratio of macro fiber width  218  to macro fiber thickness  220 . In an embodiment, the sheet  242  may have an aspect ratio of macro fiber width  218  to macro fiber thickness  220  of at least approximately 10. By forming the macro fiber  200  in a sheet  242  embodiment, the total quantity of macro fibers  200  required to form a structural layer may be reduced which may result in a reduced amount of time required to lay up a composite article  100  ( FIG. 1 ). 
       FIG. 8  illustrates a trapezoidal  212  cross-sectional shape  208  of the macro fiber  200  having substantially planar macro fiber upper and lower surfaces  202 ,  204  that may be substantially parallel to one another. The macro fiber side surfaces  206  may be oriented in non-parallel relation to one another. The trapezoidal  212  cross-sectional shape  208  of the macro fiber  200  may be provided in a relatively high aspect ratio which may reduce fabrication time for a composite article  100  ( FIG. 1 ). During the layup of a composite article, a plurality of trapezoidal  212  macro fibers  200  may be positioned in side-by-side arrangement  226  ( FIG. 4 ) in first and second structural layers  400 ,  420  ( FIG. 3 ). A plurality of the first and second structural layers  400 ,  420  and additional structural layers (not shown) may be arranged in a stacked formation  230  ( FIGS. 3-4 ) and may be heated to reduce the viscosity of the matrix material  236  and allow the intermingling of the matrix material  236  of adjacent macro fibers  200 . The layup may be cured and/or solidified to form a composite article  100 . 
       FIG. 9  illustrates a triangular  214  cross-sectional shape  208  of the macro fiber  200  having a macro fiber lower surface  204  and a pair of macro fiber side surfaces  206 . The aspect ratio of the triangular macro fiber  200  is preferably large to reduce the total quantity of macro fibers  200  required to form a structural layer. The triangular macro fiber  200  may facilitate registration or alignment of the macro fibers  200  relative to one another in the first and second structural layers  400 ,  420  ( FIG. 3 ) when laying up a composite article  100 . For example, a first structural layer  400  ( FIG. 3 ) of the triangular  214  macro fibers  200  may be arranged in an upright orientation and in side-by-side arrangement (not shown) to one another. A second structural layer  420  ( FIG. 3 ) of inverted (not shown) triangular  214  macro fibers  200  may be nested between the upright triangular  214  macro fibers  200 . Each pair of first and second structural layers  400 ,  420  may comprise a couplet  228  ( FIG. 3 ). A plurality of the couplets  228  may be arranged in stacked formation  230  ( FIG. 3 ) (not shown) and may be processed in a manner described above to form a composite article  100 . 
       FIG. 10  illustrates a diamond  216  cross-sectional shape  208  of the macro fiber  200  having two pairs of macro fiber side surfaces  206 . A plurality of the diamond  216  macro fibers  200  may be arranged in first and second structural layers  400 ,  420  ( FIG. 3 ) or more structural layers in a manner similar to that described above with regard to the triangular  214  ( FIG. 9 ) macro fibers  200 . Heat and/or pressure may be applied to reduce the viscosity of the matrix material  236  and/or consolidate the first and second structural layers  400 ,  420  followed by curing and/or solidification to form the composite article  100  ( FIG. 1 ). 
       FIG. 11  is side view of a composite article  100  in a layup configuration  232 . The composite article  100  includes a plurality of the first and second structural layers  400 ,  420  forming a plurality of couplets  228 . Each one of the first and second structural layers  400 ,  420  includes macro fibers  200 . The stretched direction  406  of the first structural layers  400  may be oriented perpendicularly relative to the stretched direction  426  of the second structural layers  420 . However, the stretched direction the structural layers may be oriented in any direction relative to the stretched direction of other structural layers to achieve desired strength properties and/or desired ballistic properties of the composite article  100 . For example, the stretched direction one or more of structural layers may be oriented at any non-perpendicular angle (e.g., at 15°, 22.5°, 45°, 60°, 75°, etc.) relative to the stretched direction of one or more of the other structural layers in the composite article. In an embodiment, the stretched directions may by oriented in consideration of the primary structural load path (not shown) in the composite article  100 . 
     In  FIG. 11 , the composite article  100  may be provided in an embodiment wherein the macro fiber side surfaces  206  may be positioned in relatively close proximity to one another or in contact with one another to minimize or prevent the occurrence of voids in the final composite article  100 . The minimizing of the occurrence of voids may improve the strength properties and optical properties of the composite article  100 . The macro fiber upper and lower surfaces  202 ,  204  may also be placed in substantially intimate contact with one another to minimize the occurrence of voids. Heat and/or pressure may be applied to the composite article  100  to reduce the viscosity of the matrix material  236  and allow intermingling thereof. 
       FIG. 12  is a side view of the composite article  100  in a consolidated configuration  234 . The heating of the matrix material  236  and the resulting reduction in viscosity may cause intermingling of the matrix material  236  between adjacent macro fibers  200  ( FIG. 11 ). In this manner, gaps between the macro fiber side surfaces  206  ( FIG. 11 ) may be avoided or eliminated in the final composite article  100 . The prevention or avoidance of gaps in the composite article  100  may minimize or eliminate the occurrence of optical distortions otherwise caused by light rays passing through gaps between conventional fibers (not shown). Pressure may be applied to a layup of the composite article  100  during the heating of the matrix material  236  to consolidate the composite article  100  and eliminate voids in the composite article  100 . In addition, consolidation may improve the intermingling and infusion of the matrix material  236  throughout the composite article  100 . 
       FIG. 13  is a perspective view of the composite article  100  in an embodiment wherein the uppermost first and second structural layer  400 ,  420  are partially cut away to illustrate the stretched direction  406 ,  426  of the alternating first and second structural layers  400 ,  420 . As indicated above, the stretching of the inner fibers  300  may significantly increase the tensile strength or tensile modulus of the inner fibers  300 . The increase in the tensile strength or tensile modulus of the inner fibers  300  may improve the specific strength and/or specific stiffness of the composite article  100 . 
     In any of the embodiments disclosed herein, the inner fibers  300  ( FIG. 13 ) may be formed of any suitable thermoplastic material, thermosetting material, inorganic material, and/or glass material, without limitation. For example, the inner fibers  300  may be formed of a thermoplastic material comprising at least one of the following: acrylics, nylon, fluorocarbons, polyamides, polyethylenes, polyesters, polypropylenes, polycarbonates, polyurethanes, polyetheretherketone, polyetherketoneketone, polyetherimides, stretched polymers and any other suitable thermoplastic material. Likewise, the inner fibers  300  may be formed of a thermosetting material which may include any one of the following: polyurethanes, phenolics, polyimides, bismaleimides, polyesters, epoxies, silsesquioxanes and any other suitable thermoset material. In addition, the inner fibers  300  may be formed of an inorganic material including carbon, silicon carbide, boron, or other inorganic material. Even further, the inner fibers  300  may be formed of a glass material such as E-glass (alumino-borosilicate glass), S-glass (alumino silicate glass), pure silica, borosilicate glass, optical glass, and any other glass material, without limitation. For embodiments where the inner fibers  300  are stretched, the inner fibers  300  may be formed of a thermoplastic material. 
     In any of the embodiments disclosed herein, the matrix material  236  ( FIG. 13 ) may comprise any suitable thermoplastic material or thermosetting material including, but not limited to, any of the above-mentioned thermoplastic or thermosetting materials from which the inner fibers  300  may be formed. Furthermore, in any of the embodiments disclosed herein, the matrix material  236  ( FIG. 13 ) may comprise any suitable metallic material. Although the matrix material  236  and the materials for forming the inner fibers  300  may be substantially optically transparent as mentioned above, the matrix material  236  and/or the inner fibers  300  may be formed of substantially non-transparent material or opaque material. 
     In an embodiment, the matrix material  236  ( FIG. 13 ) may be formed of a material that is different than the material of the inner fibers  300  ( FIG. 13 ). However, the matrix material  236  and the inner fibers  300  may be formed of substantially the same or similar material. In an embodiment, the matrix material  236  and the inner fibers  300  may be formed of substantially the same material but wherein the molecular weight of the inner fibers  300  material may be higher than the molecular weight of the matrix material  236 . The high molecular weight of the inner fiber  300  material may improve the strength properties and the ballistic performance of the composite article  100 . By forming the matrix material  236  and the inner fibers  300  from the same material, the matrix material  236  and the inner fiber  300  material may have substantially equivalent indices of refraction and/or temperature coefficients of refractive index which may improve the optical performance of the composite article  100  relative to an arrangement where the matrix material  236  and the inner fiber  300  are formed of different materials. In an embodiment, the inner fibers  300  and/or the matrix material  236  may be formed of polyethylene due to its favorably high modulus of elasticity. For example, the inner fibers  300  may be formed of ultra-high molecular weight polyethylene such as SPECTRA′ or DYNEEMA™ brand high density polyethylenes. 
     The composite article  100  may be configured in any one of a variety of different shapes, sizes and configurations as is not limited to the composite panel  104  shown in  FIG. 1 . Furthermore, the composite article  100  may be configured for use in any vehicular or non-vehicular application. For example, the composite article  100  may be configured as a transparency of a vehicle such as an aircraft. The composite article  100  may also comprise a windshield or a canopy of an aircraft. The composite article  100  may additionally be configured for use as a window in any vehicular or non-vehicular application. Even further, the composite article  100  may be implemented as a membrane, an armor panel, a structural panel, an architectural panel, a non-structural panel or article, or in any other implementation of the composite article, without limitation. 
       FIG. 14  is a flow chart illustrating an embodiment of a method  500  of manufacturing a macro fiber  200 . Step  502  of the method  500  of  FIG. 14  may include forming a plurality of inner fibers  300  ( FIG. 5 ) each having an inner fiber final cross-sectional size  308  ( FIG. 5 ) of less than approximately 100 nanometers. In an embodiment, the method may initially include selecting a wavelength band of interest to which the composite article  100  ( FIG. 3 ) may be exposed during service. The inner fibers  300  may initially have a cross-sectional size greater than their inner fiber final cross-sectional size  308  and may be stretched during formation or after formation along a lengthwise direction which may reduce the initial diameter down to an inner fiber final cross-sectional size  308  of the inner fiber  300 . In an embodiment, each one of the inner fibers  300  may have an inner fiber final cross-sectional size  308  that may be less than approximately one-quarter of the wavelength at a lower end of the wavelength band of interest. For example, the lower end of the visible spectrum is approximately 400 nm such that the inner fibers  300  may be formed at an inner fiber final cross-sectional size  308  of less than approximately 100 nm. 
     Step  504  of the method  500  of  FIG. 14  may include surrounding the inner fibers  300  ( FIG. 4 ) with matrix material  236  ( FIG. 3 ) to form a macro fiber  200  ( FIG. 3 ). The inner fibers  300  may be oriented generally parallel to the macro fiber length  222  ( FIG. 3 ). The inner fibers  300  may be formed substantially simultaneously with the matrix material  236 . Advantageously, by co-forming the inner fibers  300  with the matrix material  236 , the fiber volume fraction of the composite article  100  ( FIG. 3 ) may be more precisely controlled relative to conventionally-manufactured composite articles. In addition, co-forming the matrix material  236  with the inner fibers  300  may reduce the amount of time required for fabricating composite articles  100 . Furthermore, co-forming the matrix material  236  with the inner fibers  300  may eliminate the need for specialized resin-infusion equipment as may be required for infusing dry fiber preforms (not shown) with resin (not shown) in conventional composites manufacturing. 
     Step  506  of the method  500  of  FIG. 14  may include stretching the inner fibers  300  and the matrix material  236 . For example, the inner fibers  300  and the matrix material  236  may be stretched as the inner fibers  300  and the matrix material  236  are drawn from a nozzle (not shown). However, the inner fibers  300  may be stretched prior to forming the macro fibers  200 . In an embodiment, the inner fibers  300  may be stretched following formation of the inner fibers  300  and prior to forming the macro fibers  200 . Advantageously, the increase in the strength properties of the inner fibers  300  may be controlled by controlling the stretching ratio of the inner fibers  300 . 
     Step  508  of the method  500  of  FIG. 14  may include forming the macro fiber  200  ( FIG. 6 ) in a predetermined cross-sectional shape  208  ( FIG. 6 ). For example, the macro fiber  200  may be formed having a macro fiber upper surface  202  ( FIG. 6 ), a macro fiber lower surface  204  ( FIG. 6 ), and one or more macro fiber side surfaces  206  ( FIG. 6 ). The cross-sectional shape  208  of the macro fiber  200  may be controlled such that the macro fiber upper surface  202  and the macro fiber lower surface  204  may be substantially planar and parallel. However, the macro fiber  200  may be formed in any suitable cross-sectional shape  208  that may facilitate laying up the macro fibers  200  to form structural layers. The macro fiber  200  may be formed in a cross-sectional shape  208  comprising a sheet  242  ( FIG. 7 ), a polygon, a parallelogram  210  ( FIG. 6 ), a trapezoid  212  ( FIG. 8 ), and any one of a variety of other cross-sectional shapes  208 . 
       FIG. 15  is a flow chart illustrating a method  600  having one or more operations that may be included in an embodiment of forming a composite article  100  ( FIG. 1 ). Step  602  of the method  600  may include providing a plurality of macro fibers  200  ( FIG. 5 ) wherein each one of the macro fibers  200  comprises a plurality of inner fibers  300  ( FIG. 5 ) surrounded by matrix material  236  ( FIG. 5 ). In an embodiment where the composite article  100  may be exposed to light in the visible spectrum, each one of the inner fibers  300  may be provided in an inner fiber final cross-sectional size  308  of less than approximately 100 nanometers. In this regard, the inner fibers may be stretched to an inner fiber final cross-sectional size  308  that is less than approximately one-quarter of the wavelength of a lower end of a predetermined range of light to which the composite article  100  may be exposed. However, the inner fibers  300  may be formed at any inner fiber final cross-sectional size, without limitation, based upon the wavelength at the low end of the wavelength band of light to which the composite article  100  may be exposed. 
     Step  604  of the method  600  of  FIG. 15  may include arranging the macro fibers  200  ( FIG. 11 ) in side-by-side arrangement  226  ( FIG. 11 ) with one another in a structural layer. For example, in an embodiment, a plurality of the macro fibers  200  may be arranged in a first structural layer  400  and a plurality of the macro fibers  200  may be arranged in a second structural layer  420 . A plurality of the structural layers may be arranged in a stacked formation. For example, in the embodiment shown in  FIG. 11 , the first and second structural layers  400 ,  420  may be positioned in relatively close proximity to one another such as in substantially intimate contact with one another. 
     Step  606  of the method  600  of  FIG. 15  may include arranging the structural layers in a desired orientation relative to one another. For example, in the embodiment shown in  FIGS. 3-4 , the composite article  100  may be formed of a plurality of first and second structural layers  400 ,  420 . The second structural layer  420  may be arranged such that the stretched direction  426  of the second structural layer  420  is oriented generally perpendicular to the stretched direction  406  of the first structural layer  400  as shown in  FIG. 3 . However, the first and second structural layer  400 ,  420  may be arranged such that the respective stretched directions  406 ,  426  are oriented non-perpendicular to one another by any amount including parallel orientations of the stretched directions. In an embodiment, the stretched directions of one or more of the structural layers may be arranged at specific angles relative to one another to achieve desired strength, ballistic, and/or optical performance in a composite article  100 . 
     Step  608  of the method  600  of  FIG. 15  may include applying heat to the macro fibers  200  ( FIG. 11 ) of the structural layers. Heat may be applied by any suitable means. For example, heat may be applied by one or more heating elements (not shown). Heat may also be applied by radiation heating or by any other means for elevating the temperature of the matrix material  236  ( FIG. 11 ). 
     Step  610  of the method  600  of  FIG. 15  may include reducing the viscosity of the matrix material  236  ( FIG. 12 ) such as due to the application of heat. The reduction in viscosity may allow for intermingling of the matrix material  236  among the macro fibers  200  ( FIG. 12 ). In this regard, the matrix material  236  of each macro fiber  200  may intermingle with the matrix material  236  of adjacent macro fibers  200  such that the structural layers may be formed with substantially no gaps across a width of the structural layers. By forming the composite article  100  ( FIG. 12 ) with no gaps, optical performance may be significantly improved relative to conventional composite articles (not shown) having gaps between fibers. Pressure may optionally be applied during application of heat to promote consolidation of the structural layers. 
     Step  612  of the method  600  of  FIG. 15  may include curing and/or solidifying the matrix material  236  ( FIG. 13 ) to form a composite article  100  ( FIG. 13 ). As indicated above, the composite article  100  may be formed in any one of a variety of different shapes, sizes, and configurations, without limitation. Furthermore, the composite article  100  may be implemented in any one of a variety of vehicular and non-vehicular applications. Non-limiting examples of composite article  100  configurations include a windshield, a canopy, a window, a membrane, an armor panel, a structural panel, an architectural panel, and a non-structural article. 
     Advantageously, the macro fibers  200  ( FIG. 11 ) as described above may facilitate a significant improvement in the optical performance of a composite article  100  ( FIG. 11 ) relative to conventional composite articles using conventional fibers. In addition, the macro fibers  200  may result in more precise control of the fiber volume fraction of the composite article  100  which may improve the specific strength of the composite article  100  and the ballistic performance of the composite article  100 . 
       FIG. 16  is a flowchart of a method  700  of using a composite article  100 . Step  702  of the method  700  may include providing a composite article  100  having a plurality of macro fibers  200 . Each one of the macro fibers  200  may include the plurality of inner fibers  300  surrounded by matrix material  236 . Each one of the inner fibers  300  may have an inner fiber final cross-sectional size  308  of less than approximately 100 nanometers. 
     Step  704  of the method  700  of  FIG. 16  may include placing or maintaining the composite article  100  ( FIG. 1 ) in a non-loaded condition. The non-loaded condition may comprise a static condition of the composite article  100 . For example, the composite article  100  may comprise a portion of a vehicle  801  ( FIG. 17 ) that is static or substantially non-moving. In an embodiment, the vehicle  801  may comprise an aircraft  800  ( FIG. 17 ). 
     Referring to  FIG. 17 , shown is a perspective illustration of an aircraft  800  which may incorporate one or more embodiments of the composite article  100  ( FIG. 1 ) as disclosed herein. The aircraft  800  may include a fuselage  802  having a pair of wings  804  and a tail section  808  which may include a vertical stabilizer  812  and horizontal stabilizers  810 . The aircraft  800  may further include control surfaces  806  and propulsion units  814 . The aircraft  800  may be generally representative of one of a variety of vehicles that may incorporate one or more of the composite articles  100  as described herein. 
     In an embodiment, the composite article  100  ( FIG. 1 ) may comprise a composite panel  104  ( FIG. 1 ). In the non-loaded condition, loads on the composite panel  104  may be limited to static loads such as due to gravitational force acting on a mass of the composite panel  104  or other static loads acting on the aircraft  800  ( FIG. 17 ). An example of a non-loaded condition may include the aircraft  800  fuselage  802  being un-pressurized such as when the aircraft  800  is parked on an airport tarmac. 
     Step  706  of the method  700  of  FIG. 16  may include placing the composite article  100  ( FIG. 1 ) in a loaded condition wherein the vehicle  801  ( FIG. 17 ) may be in motion and/or the composite panel  104  may be subjected to a dynamic load. For example, the vehicle may comprise the aircraft  800  ( FIG. 17 ) in motion on a runway during takeoff. The loaded condition may also comprise the aircraft  800  fuselage  802  being pressurized. In the loaded condition, loads on the composite article  100  may include any one of compression loads, tension loads, shear loads, torsion loads, or any combination thereof. 
     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.