Patent Publication Number: US-2021180225-A1

Title: Multiaxial reinforcing fabric with a stitching yarn for improved fabric infusion

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and any benefit of U.S. Provisional Patent Application No. 62/720,418, filed Aug. 21, 2018, the entire content of which is incorporated herein by reference. 
    
    
     FIELD 
     The general inventive concepts relate to fiber reinforced materials and, more particularly, to systems for and methods of using a stitching yarn as part of a reinforcement fabric with improved infusion properties. 
     BACKGROUND 
     It is known to use fiber reinforced materials, often in the form of a non-woven fabric, to form structural components. The fabric is formed from a multitude of continuous fibers, each of the fibers including many individual continuous filaments. Within the fabric, most of the fibers are arranged side by side and substantially parallel to one another. The fibers are held together with the use of a stitching yarn. Such a fabric is referred to as a non-crimp fabric. 
     The fabric can have a thickness of 0.8 mm to several mm. The fabric can be formed to have almost any practical width. After production, the fabric can be wound up into rolls, each having a length of a couple hundred of meters. 
     As noted above, these fabrics are useful for forming structural components. For example, the fabric can be stacked up or otherwise layered to form a spar cap of a blade of a wind energy turbine. In particular, several layers of cut pieces of the fabric are arranged on top of each other to form the structural component. The pieces are arranged within specific areas and regions of a mold. An infusion process introduces a curable matrix material (a resin) into the mold in order to penetrate the layers of the fabric. A vacuum can be applied to the mold during the infusion process to press the layers of cut pieces together and aid the resin in penetrating the layers. Thereafter, the resin is cured to form the structural component. 
     During formation of the structural component, it is important that the resin fully and uniformly impregnate the fabric. The speed at which the resin can achieve this state for a particular fabric is the rate of infusion of the fabric. 
     It can be a challenge to satisfactorily impregnate certain fabrics at a desired (e.g., an economically acceptable) infusion rate. For example, hybrid fabrics (e.g., formed from glass fibers and carbon fibers) and heavier fabrics (e.g., having an area weight greater than 1,200 g/m 2 ) can be difficult to evenly impregnate and/or can take a relatively long time to do so. Consequently, there is an unmet need for reinforcement fabrics with improved infusion properties. 
     SUMMARY 
     It is proposed herein to provide fiber reinforced materials with improved infusion properties. The fiber reinforced materials are suitable for the production of structural components, such as wind turbine blades. 
     The invention relates generally to a reinforcement fabric, a method of producing the reinforcement fabric, and a composite part formed from the reinforcement fabric. 
     In one exemplary embodiment, a reinforcing fabric is provided. The reinforcing fabric comprises a plurality of first fibers oriented in a first direction; a plurality of second fibers oriented in a second direction; and a stitching yarn maintaining the first fibers and the second fibers in their respective orientations. The first direction is 0 degrees. The second direction is different from the first direction, wherein the second direction is within the range of 0 degrees to 90 degrees. The first fibers constitute between 91 wt. % and 99.5 wt. % of the fabric. The second fibers constitute between 0.5 wt. % and 9 wt. % of the fabric. 
     In some exemplary embodiments, all of the first fibers are glass fibers. In some exemplary embodiments, some of the first fibers are glass fibers. In some exemplary embodiments, none of the first fibers are glass fibers. 
     In some exemplary embodiments, all of the second fibers are glass fibers. In some exemplary embodiments, some of the second fibers are glass fibers. In some exemplary embodiments, none of the second fibers are glass fibers. 
     In some exemplary embodiments, all of the first fibers are carbon fibers. In some exemplary embodiments, some of the first fibers are carbon fibers. In some exemplary embodiments, none of the first fibers are carbon fibers. 
     In some exemplary embodiments, all of the second fibers are carbon fibers. In some exemplary embodiments, some of the second fibers are carbon fibers. In some exemplary embodiments, none of the second fibers are carbon fibers. 
     In some exemplary embodiments, the first fibers include at least two distinct types of fibers. In some exemplary embodiments, the two distinct types of fibers are glass fibers and carbon fibers. In some exemplary embodiments, the at least two distinct types of fibers are selected from the group consisting of glass fibers, basalt fibers, and carbon fibers. 
     In one exemplary embodiment, the stitching yarn constitutes less than 3 wt. % of the fabric. 
     In one exemplary embodiment, the stitching yarn is a polyester yarn. 
     In one exemplary embodiment, the stitching yarn has a linear mass density within the range of 60 dTex to 250 dTex. In one exemplary embodiment, the stitching yarn has a linear mass density greater than 85 dTex. In one exemplary embodiment, the stitching yarn has a linear mass density greater than 200 dTex. In one exemplary embodiment, the stitching yarn has a linear mass density greater than 225 dTex. 
     In one exemplary embodiment, a number of discrete filaments in the stitching yarn is within the range of 20 to 80. In one exemplary embodiment, the number of discrete filaments in the stitching yarn is within the range of 20 to 30. In one exemplary embodiment, the number of discrete filaments in the stitching yarn is within the range of 70 to 80. 
     In one exemplary embodiment, an average diameter of the filaments in the stitching yarn is within the range of 12 μm to 30 μm. In one exemplary embodiment, the average diameter of the filaments in the stitching yarn is greater than 12 μm. 
     In one exemplary embodiment, the stitching yarn has a crimp contraction (CC), prior to stitching, of at least 24%. In one exemplary embodiment, the stitching yarn has a CC, prior to stitching, within the range of 26% to 28%. In one exemplary embodiment, the stitching yarn has a CC, prior to stitching, within the range of 30% to 32%. In one exemplary embodiment, the stitching yarn has a CC, prior to stitching, within the range of 31% to 36%. 
     In one exemplary embodiment, the stitching yarn, after being unstitched from a fabric, has a crimp contraction (CC) less than or equal to 30%. In one exemplary embodiment, the unstitched stitching yarn has a CC within the range of 18% to 24%. In one exemplary embodiment, the unstitched stitching yarn has a CC within the range of 21% to 24%. 
     In one exemplary embodiment, the stitching yarn forms a stitching pattern through the fabric, the stitching pattern being a tricot stitching pattern. 
     In one exemplary embodiment, the stitching yarn forms a stitching pattern through the fabric, the stitching pattern being a symmetric double tricot stitching pattern. 
     In one exemplary embodiment, the stitching yarn forms a stitching pattern through the fabric, the stitching pattern being an asymmetric double tricot stitching pattern. 
     In one exemplary embodiment, the stitching yarn forms a stitching pattern through the fabric, the stitching pattern being a symmetric diamant stitching pattern. 
     In one exemplary embodiment, the stitching yarn forms a stitching pattern through the fabric, the stitching pattern being an asymmetric diamant stitching pattern. 
     In one exemplary embodiment, the stitching yarn defines a stitching length within the range of 3 mm to 6 mm. In one exemplary embodiment, the stitching yarn defines a stitching length of 5 mm. In one exemplary embodiment, the stitching yarn defines a stitching length of 4 mm. 
     In one exemplary embodiment, the stitching yarn is a single strand stitching yarn. In one exemplary embodiment, the stitching yarn is a double strand stitching yarn. In one exemplary embodiment, the stitching yarn is a triple strand stitching yarn. 
     In one exemplary embodiment, the first fibers are glass fibers and the second fibers are glass fibers, wherein a glass composition of the first fibers is the same as a glass composition of the second fibers. 
     In one exemplary embodiment, the first fibers are glass fibers and the second fibers are glass fibers, wherein a glass composition of the first fibers differs from a glass composition of the second fibers. 
     In one exemplary embodiment, the reinforcing fabric further comprises a plurality of third fibers oriented in a third direction, wherein the second fibers are glass fibers and the third fibers are glass fibers, and wherein a glass composition of the second fibers is the same as a glass composition of the third fibers. 
     In one exemplary embodiment, an absolute value of the second direction is equal to an absolute value of the third direction. 
     In one exemplary embodiment, a difference between the first direction and the second direction is greater than or equal to 45 degrees. 
     In one exemplary embodiment, a difference between the first direction and the second direction is greater than or equal to 80 degrees. 
     In one exemplary embodiment, a linear mass density of the first fibers is within the range of 600 Tex to 4,800 Tex. 
     In one exemplary embodiment, the second fibers are glass fibers, wherein a linear mass density of the second fibers is within the range of 68 Tex to 300 Tex. 
     In general, the reinforcing fabric is a non-crimp fabric. In one exemplary embodiment, the reinforcing fabric is a unidirectional, non-crimp fabric. In one exemplary embodiment, the reinforcing fabric is a multidirectional, non-crimp fabric. In general, the reinforcing fabric (as formed) contains no resin, i.e., none of the fibers forming the fabric are pre-impregnated with a resin. 
     In general, the reinforcing fabric has an area weight greater than 600 g/m 2 . 
     In one exemplary embodiment, the reinforcing fabric is a “heavy” fabric having an area weight greater than 1,200 g/m 2 . In one exemplary embodiment, the reinforcing fabric has an area weight greater than or equal to 1,800 g/m 2 . In one exemplary embodiment, the reinforcing fabric has an area weight greater than or equal to 2,000 g/m 2 . In one exemplary embodiment, the reinforcing fabric has an area weight greater than or equal to 2,400 g/m 2 . 
     In one exemplary embodiment, the fabric is infused with a resin that is cured to form a composite article. In one exemplary embodiment, the article is a wind turbine blade or related component (e.g., spar cap). 
     Other aspects, advantages, and features of the inventive concepts will become apparent to those skilled in the art from the following detailed description, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The general inventive concepts, as well as embodiments and advantages thereof, are described below in greater detail, by way of example, with reference to the drawings in which: 
         FIGS. 1A-1D  illustrate a reinforcing fabric, according to an exemplary embodiment of the invention.  FIG. 1A  is a top plan view of the reinforcing fabric.  FIG. 1B  is a bottom plan view of the reinforcing fabric.  FIG. 1C  is a detailed view of the circle A in  FIG. 1A .  FIG. 1D  is a detailed view of the circle B in  FIG. 1B . 
         FIGS. 2A-2E  illustrate several exemplary stitching patterns that can be used in the reinforcing fabric of  FIG. 1 .  FIG. 2A  shows a tricot stitching pattern.  FIG. 2B  shows a symmetric double tricot stitching pattern.  FIG. 2C  shows an asymmetric double tricot stitching pattern.  FIG. 2D  shows a symmetric diamant stitching pattern.  FIG. 2E  shows an asymmetric diamant stitching pattern. 
         FIG. 3  is a diagram illustrating a through thickness infusion speed (TTIS) test for measuring the infusion rate of a fabric. 
         FIGS. 4A-4B  illustrate an in-plane infusion test (IPIT) test for measuring the infusion rate of a fabric. 
         FIG. 5  is a graph illustrating the distribution of crimp contraction (CC) values across eleven (11) different stitching yarns. 
         FIG. 6  is a graph illustrating the results of the IPIT test of  FIG. 4  performed on three (3) different fabrics to measure the infusion rate (in the x-direction) of the fabrics. 
         FIG. 7  is a graph illustrating the results of the IPIT test of  FIG. 4  performed on three (3) different fabrics to measure the infusion rate (in the y-direction) of the fabrics. 
     
    
    
     DETAILED DESCRIPTION 
     While the general inventive concepts are susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the general inventive concepts. Accordingly, the general inventive concepts are not intended to be limited to the specific embodiments illustrated herein. 
     It has been discovered that by using a stitching yarn with a specific combination of features, a reinforcing fabric can be constructed that exhibits improved infusion properties. In particular, by controlling one or more specific product variables including, but not necessarily limited to, fabric area weight, stitching yarn composition, stitching yarn density, stitching yarn filament count, stitching yarn filament diameter, stitching yarn crimp contraction, stitching pattern, and stitching length, a reinforcement fabric can be produced that is an effective reinforcement for structural components (e.g., wind turbine blades) and that exhibits an enhanced rate of infusion. 
     Additionally, embodiments of the reinforcing fabric that include fibers with different moduli oriented in the same direction (e.g., glass fibers and carbon fibers), along with fibers oriented in another (i.e., different) direction may exhibit improved mechanical dampening in certain applications, such as in wind turbine blades. 
     Accordingly, the inventive concepts provide a reinforcement fabric comprising a plurality of fibers. The reinforcement fabric can be readily infused at an acceptable infusion speed, without requiring that the fibers used to form the reinforcement fabric be spread or pre-impregnated with resin. Thus, the inventive fabric provides for an effective one-step (i.e., in the mold) infusion process during composite part formation. The inventive concepts also encompass a method of producing the reinforcing fabric. The inventive concepts also encompass a composite part formed from the reinforcing fabric. 
     In an exemplary embodiment of the invention, a reinforcement fabric  100  is constructed from first reinforcing fibers  102  and second reinforcing fibers  104 , as shown in  FIGS. 1A-1D . For purposes of this illustrative embodiment, the first reinforcing fibers  102  and the second reinforcing fibers  104  are glass fibers. 
     Any suitable glass reinforcing fibers  102 ,  104  can be used in the reinforcement fabric  100 . For example, fibers made from E glass, H glass, S glass, and AR glass types can be used. In some exemplary embodiments, basalt fibers can be used in place of some or all of the glass reinforcing fibers  102 . In general, the glass reinforcing fibers  102 ,  104  have a diameter within the range of 13 μm to 24 μm. Typically, the glass reinforcing fibers  102 ,  104  in the reinforcement fabric  100  are glass fiber strands (fed from one or more glass rovings) made up of many individual glass filaments. 
     The reinforcement fabric  100  is a non-crimp fabric, wherein the fibers  102 ,  104  are arranged in their respective positions/orientations and then held together by a stitching yarn  106 . The stitching yarn  106  is a textured, multifilament yarn comprised of many individual filaments. The stitching yarn  106  may be a single, double, or triple strand yarn. In some embodiments, the stitching yarn  106  is polyester. 
     In some embodiments, the filaments of the stitching yarn  106  are made of a polymer selected from the group consisting of polyester, polyamide, polyethylene, polypropylene, polyactic acid, aramide, and polybutylene succinate. 
     In some embodiments, the stitching yarn  106  has a linear mass density within the range of 70 dTex to 250 dTex. In some embodiments, the stitching yarn  106  has a linear mass density greater than 85 dTex. In some embodiments, the stitching yarn  106  has a linear mass density greater than 200 dTex. In some embodiments, the stitching yarn  106  has a linear mass density greater than 225 dTex. If the stitching yarn  106  comprises multiple strands, the linear mass density is the sum of the densities of the strands. 
     In some exemplary embodiments, the number of discrete filaments in the stitching yarn  106  is within the range of 20 to 80. In some exemplary embodiments, the number of discrete filaments in the stitching yarn  106  is within the range of 20 to 30. In some exemplary embodiments, the number of discrete filaments in the stitching yarn  106  is within the range of 70 to 80. 
     In some exemplary embodiments, an average diameter of the filaments in the stitching yarn  106  is within the range of 12 μm to 30 μm. In some exemplary embodiments, an average diameter of the filaments in the stitching yarn  106  is greater than 12 μm. 
     Another characteristic that was found to impact the infusion rate of a reinforcing fabric is the crimp contraction of a stitching yarn (e.g., the stitching yarn  106 ) used to form the fabric (e.g., the reinforcement fabric  100 ). Crimp contraction refers to the contraction of a texturized filament yarn resulting from the development of crimp, expressed as a percentage of its original length, with the lengths of the contracted and straightened yarns measured under specific conditions, derived from the EN 14621:2005 standard. According to this test, the crimp of a specimen of a texturized filament yarn of known nominal linear density, which is formed into the shape of a loop, is developed by treatment with hot air while the specimen is subjected to a low tensile force. The dimensions of this loop approximate those of the skein described in the EN 14621:2005 standard. After reconditioning, the straightened length of the loop is measured under a high tensile force. After a specified recovery time under application of the low tensile force, the contracted length of the loop, shortened by the effect of the yarn crimp, is measured. Crimp contraction is calculated as the difference between the two length values related to the straightened length. More specifically, the crimp contraction (CC), expressed in percent, is calculated using Equation 1: 
         CC= 100×[( L   0   −L   1 )/ L   0 ](%)  Equation 1
 
     where 
     L 0  is the straightened length; and 
     L 1  is the contracted length. 
     In some exemplary embodiments, the stitching yarn of the present invention (e.g., the stitching yarn  106 ) has a CC, prior to stitching, of at least 24%. In some exemplary embodiments, the stitching yarn has a CC within the range of 26% to 28%. In some exemplary embodiments, the stitching yarn has a CC within the range of 30% to 32%. In some exemplary embodiments, the stitching yarn has a CC within the range of 31% to 36%. 
     In some exemplary embodiments, the stitching yarn, after being unstitched from a fabric (e.g., the reinforcement fabric  100 ), exhibits a reduction in crimp contraction (CC) of no more than 30%. In some exemplary embodiments, the stitching yarn, after being unstitched from a fabric (e.g., the reinforcement fabric  100 ), exhibits a reduction in crimp contraction of no more than 25%. 
     In some exemplary embodiments, the stitching yarn, after being unstitched from a fabric (e.g., the reinforcement fabric  100 ), has a CC in the range of less than or equal to 30%. In some exemplary embodiments, the stitching yarn, after being unstitched from the fabric, has a CC in the range of 18% to 24%. In some exemplary embodiments, the stitching yarn, after being unstitched from the fabric, has a CC in the range of 21% to 24%. In some exemplary embodiments, the stitching yarn, after being unstitched from the fabric, has a CC of approximately 29%. In some exemplary embodiments, the stitching yarn, after being unstitched from the fabric, has a CC of approximately 25%. In some exemplary embodiments, the stitching yarn, after being unstitched from the fabric, has a CC of approximately 22%. In some exemplary embodiments, the stitching yarn, after being unstitched from the fabric, has a CC of approximately 12%. 
     Any stitching pattern suitable to hold the fibers  102 ,  104  of the fabric  100  together can be used. Various exemplary stitching patterns  200  are shown in  FIGS. 2A-2E . A tricot stitching pattern  200  in which reinforcing fibers  202  (e.g., the fibers  102 ,  104 ) are held together by a stitching yarn  206  (e.g., the stitching yarn  106 ) is shown in  FIG. 2A . A symmetric double tricot stitching pattern  200  in which the reinforcing fibers  202  (e.g., the fibers  102 ,  104 ) are held together by the stitching yarn  206  (e.g., the stitching yarn  106 ) is shown in  FIG. 2B . An asymmetric double tricot stitching pattern  200  in which the reinforcing fibers  202  (e.g., the fibers  102 ,  104 ) are held together by the stitching yarn  206  (e.g., the stitching yarn  106 ) is shown in  FIG. 2C . A symmetric diamant (diamond-like) stitching pattern  200  in which the reinforcing fibers  202  (e.g., the fibers  102 ,  104 ) are held together by the stitching yarn  206  (e.g., the stitching yarn  106 ) is shown in  FIG. 2D . An asymmetric diamant (diamond-like) stitching pattern  200  in which the reinforcing fibers  202  (e.g., the fibers  102 ,  104 ) are held together by the stitching yarn  206  (e.g., the stitching yarn  106 ) is shown in  FIG. 2E . The general inventive concepts may encompass other stitching patterns as well.  FIGS. 1C-1D  illustrate a tricot stitching pattern used in the fabric  100 . 
     In general, the stitching pattern  200  is a repeating series of stitches, with transitions between each individual stich portion  220  defining a stitching length  222  (see  FIG. 2A ). The stitching length  222  is another variable that can influence the rate of infusion of the fabric  100 . Typically, the stitching length  222  will be within the range of 3 mm to 6 mm. In some exemplary embodiments, the stitching length  222  is 4 mm. In some exemplary embodiments, the stitching length  222  is 5 mm. 
     The reinforcement fabric  100  is a unidirectional fabric, wherein between 91 wt. % to 99.5 wt. % of the first reinforcing fibers  102 ,  104  are oriented in a first direction and 0.5 wt. % to 9 wt. % of the second reinforcing fibers  102 ,  104  are oriented in one or more other directions (e.g., second and third directions). In some exemplary embodiments, the reinforcement fabric could be a non-unidirectional fabric, such as a biaxial or triaxial fabric. 
     Typically, the first direction will be 0° (lengthwise direction of the fabric). 
     The second direction is different from the first direction. The second direction will generally be within the range of greater than 0° to less than or equal to 90°. 
     The third direction is different from the first direction. The third direction will generally be greater than 0° and less than or equal to 90°. 
     The third direction may be the same as the second direction (such that there are only two distinct fiber orientations in the fabric). Otherwise, the third direction will typically be equal to the negative orientation of the second direction. 
     In the reinforcement fabric  100  shown in  FIGS. 1A-1D , the first direction is 0°, the second direction is 80°, and the third direction is −80°. 
     In some exemplary embodiments, all of the reinforcing fibers oriented in the second direction are glass reinforcing fibers  104 . 
     In some exemplary embodiments, all of the reinforcing fibers oriented in the third direction are glass reinforcing fibers  104 . 
     In some exemplary embodiments, the first glass reinforcing fibers  102  oriented in the first direction include a different glass composition than the second glass reinforcing fibers  104  oriented in the second direction. 
     In some exemplary embodiments, the first glass reinforcing fibers  102  oriented in the first direction include a different glass composition than the second glass reinforcing fibers  104  oriented in the third direction. 
     In some exemplary embodiments, the glass reinforcing fibers  104  oriented in the second direction include the same glass composition as the glass reinforcing fibers  104  oriented in the third direction. 
     As noted above, the reinforcement fabric  100  comprises between 91 wt. % to 99.5 wt. % of the first glass reinforcing fibers  102  and between 0.5 wt. % to 9 wt. % of the second glass reinforcing fibers  104 . The stitching yarn  106  comprises a maximum of 3 wt. % of the fabric  100 . 
     The linear mass density of the first glass reinforcing fibers  102  being fed in the first direction is within the range of 600 Tex to 4,800 Tex. The linear mass density of the second glass reinforcing fibers  104  being fed in the non-first direction (i.e., the second/third directions) is within the range of 68 Tex to 300 Tex. 
     As known in the art, the glass reinforcing fibers  102  and/or  104  may have a chemistry applied thereon during formation of the fibers. This surface chemistry, typically in an aqueous form, is called a sizing. The sizing can include components such as a film former, lubricant, coupling agent (to promote compatibility between the glass fibers and the polymer resin), etc. that facilitate formation of the glass fibers and/or use thereof in a matrix resin. In some exemplary embodiments, the glass reinforcing fibers  102  and/or  104  include a polyester compatible sizing. In some exemplary embodiments, the glass reinforcing fibers  102  and/or  104  include an epoxy compatible sizing. 
     In some exemplary embodiments, the glass reinforcing fibers  102  and/or  104  may also have a post-coating applied thereto. Unlike a sizing, the post-coating is applied after formation of the fibers. 
     The reinforcing fabrics disclosed herein (e.g., the reinforcement fabric  100 ) have combinations of structural components and/or properties that improve the resin infusion rate of the fabrics, even when the reinforcing fibers making up the fabric are not pre-impregnated with resin. As noted above, these components/properties may include the fabric area weight, stitching yarn composition, stitching yarn density, stitching yarn filament count, stitching yarn filament diameter, stitching yarn crimp contraction, stitching pattern, and stitching length used in the reinforcing fabrics. 
     One test for the measuring the resin infusion rate of a fabric is called the through thickness infusion speed (TTIS) test. The TTIS test will be explained with reference to  FIG. 3 . In the TTIS test  300 , multiple layers  302  of a fabric  304  to be tested (e.g., the reinforcement fabric  100 ) are placed on an infusion table  306 . In general, many layers  302  of the fabric  304  are used for the TTIS test  300 . Typically, the number of layers  302  is based on a target “testing thickness.” In some exemplary embodiments, the target thickness is 30 mm. A vacuum foil  308  is placed over the layers  302  on top of the table  306  to form an airtight enclosure  350  (i.e., vacuum bag). 
     A supply  310  of resin  312  is situated below, or otherwise in proximity to, the table  306 , such that the resin  312  can be drawn into the enclosure  350  (e.g., through one or more openings (not shown) in the bottom of the table  306 ) below the layers  302  of the fabric  304 . In some exemplary embodiments, the resin  312  is located remote from the table  306 , but is fed thereto through a supply hose (not shown). An opening  320  in the vacuum bag formed from the foil  308  is interfaced with a hose  322  so that a vacuum source (not shown) can be used to evacuate air from the enclosure  350  and suck the resin  312  through the fabric  304 . 
     In this manner, the resin  312  is pulled from the supply  310  into the enclosure  350  (see arrow  330 ); through the layers  302  of the fabric  304  (see arrows  332 ); and out the opening  320  through the hose  322  (see arrow  334 ). Given the close-fitting dimensions of the layers  302  of the fabric  304  within the enclosure  350 , the only path for the resin  312  to travel is through the layers  302  of the fabric  304 , i.e., through the thicknesses (z-direction) of the layers  302  of the fabric  304 . The TTIS test  300  measures the amount of time it takes until the resin  312  is first visible on an upper surface  340  of a top layer  302  of the fabric  304 . This amount of time (e.g., in minutes) is used as a measure of the rate of infusion of the fabric  304 . The TTIS test  300  can be used to compare the rates of infusion of different fabrics, so long as the other testing parameters are substantially the same. Additionally, for comparison purposes, the fabrics should have similar grammage. 
     Another test for the measuring the resin infusion rate of a fabric is called the in-plane infusion test (IPIT) test. The IPIT test will be explained with reference to  FIGS. 4A-4B . In the IPIT test  400 , five (5) layers of a fabric  404  to be tested (e.g., the reinforcement fabric  100 ) are placed on an infusion table  406 . A vacuum foil  408  is placed over the edges of the layers on top of the table  406 , and sealed to the table  406  (e.g., using tape), to form an airtight enclosure  410  (i.e., vacuum bag). 
     All of the layers of the fabric  404  in the enclosure  410  are aligned with one another so as to face in the same direction (e.g., the first orientation of each layer of the fabric  404  aligns with the first orientation of each other layer of the fabric  404 ) within the enclosure  410 . 
     The vacuum foil  408  (and tape) form the airtight enclosure  410  except for an input opening  412  and an output opening  414  formed near opposite ends of the fabric  404 . 
     A supply of resin  420  is situated adjacent to, or otherwise in proximity to, the input opening  412 . As configured, the resin  420  can be drawn into the enclosure  410  through the input opening  412 . In some exemplary embodiments, the resin  420  is located remote from the table  406 , but is fed thereto through a supply hose (not shown) interfaced with the input opening  412 . The output opening  414 , on the other side of the enclosure  410 , is interfaced with a hose (not shown) so that a vacuum source  422  can be used to evacuate air from the enclosure  410  and suck the resin  420  through the fabric  404 . 
     In this manner, the resin  420  is pulled from the supply into the enclosure  410  (see arrow  430 ); through the layers of the fabric  404  (see arrows  440  in  FIG. 4B ); and out the opening  414  through the hose (see arrow  432 ). Given the close-fitting dimensions of the layers of the fabric  404  within the enclosure  410 , the only path for the resin  420  to travel is through the layers of the fabric  404 , i.e., through the length (x-direction, production direction) or width (y-direction) of the layers of the fabric  404 , depending on the orientation of the fabric  404  between the openings  412 ,  414  of the enclosure  410 . Thus, only the resin channels within the layers of the fabric  404  are used to transport the resin  420 . 
     The IPIT test  400  measures the distance covered by the resin  420  over time. A flow front (distance) of the resin  420  is recorded after 2, 4, 6, 8, 10, 12, 16, 20, 26, 32, 38, 44, 50, 55, and 60 minutes. The current distance that the resin  420  has traveled through the fabric  404  is referred to as the infusion length. The measured amount of time (e.g., in minutes) relative to the infusion length (e.g., in centimeters) is used as a measure of the rate of infusion of the fabric  404 . The IPIT test  400  can be used to compare the rates of infusion of different fabrics, so long as the other testing parameters are substantially the same. Additionally, for comparison purposes, the fabrics should have similar warp grammage. 
     Examples 
     Eleven (11) candidate fabrics, each formed using a different stitching yarn, were identified. An assessment of five (5) of these samples was performed with the results being shown in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Parameter 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 Average 
                   
                   
               
               
                   
                   
                 Approximate 
                 Filament 
                 Crimp 
               
               
                   
                   
                 Filament 
                 Diameter 
                 Contraction 
                 Infusion 
               
               
                 Sample # 
                 dTex 
                 Count 
                 (μm) 
                 (%) 
                 Properties 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 111 
                 38 
                 16.58 
                 23.8 
                 Not Tested 
               
               
                 2 
                 83 
                 39 
                 14.18 
                 22.9 
                 Not Tested 
               
               
                 3 
                 88 
                 25 
                 17.9 
                 31 
                 Good 
               
               
                 4 
                 228 
                 77 
                 16.51 
                 32 
                 High 
               
               
                 5 
                 111 
                 34 
                 17.22 
                 28 
                 Not Tested 
               
               
                 6 
                 84 
                 37 
                 14.66 
                 26.1 
                 Not Tested 
               
               
                 7 
                 112 
                 50 
                 14.45 
                 4.9 
                 Not Tested 
               
               
                 8 
                 170 
                 55 
                 16.9 
                 4.6 
                 Not Tested 
               
               
                 9 
                 170 
                 52 
                 16.9 
                 7 
                 Poor 
               
               
                 10 
                 89 
                 55 
                 12.21 
                 17 
                 Poor 
               
               
                 11 
                 88 
                 27 
                 17.46 
                 27 
                 Good 
               
               
                   
               
            
           
         
       
     
     In particular, infusion performance of the five (5) tested fabrics, i.e., samples #3, 4, 9, 10, and 11, was assessed. These fabrics were essentially the same (i.e., a non-crimp, unidirectional fabric formed from glass fibers (1240 Tex)) except for the use of a different stitching yarn.  FIG. 5  is a boxplot  500  that shows the crimp contraction (CC) values for the stitching yarn used in each of the eleven (11) candidate fabrics. Additional information on the stitching yarns is presented in Table 1. 
     An IPIT test (in the x-direction), an IPIT test (in the y-direction), and a TTIS test were performed on each tested sample to assess its infusion performance. From this data, the IPIT(x) and TTIS test data were used as indicators of infusion performance. Sample #4 exhibited the best performance of the group; samples #3 and 11 exhibited satisfactory performance; and samples #9 and 10 exhibited poor performance. 
       FIG. 6  is a graph  600  that shows the results of the IPIT test  400  performed on samples #3, 4, 10, and 11 to measure the infusion rate (in the x-direction) of those fabrics. 
       FIG. 7  is a graph  700  that shows the results of the IPIT test  400  performed on samples #3, 4, and 11 to measure the infusion rate (in the y-direction) of those fabrics. 
     The results of the TTIS test  300  performed on samples #3, 4, and 11 to further assess the infusion rate of those fabrics are detailed in Table 2. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Sample #3 
                 Sample #4 
                 Sample #11 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Area Weight (g/m 2 ) 
                 1267 
                 1281 
                 1265 
               
               
                   
                 Number of Layers 
                 35 
                 35 
                 35 
               
               
                   
                 Resin Type 
                 Epoxy 
                 Epoxy 
                 Epoxy 
               
               
                   
                 Time for First Spot 
                 30 
                 14 
                 28 
               
               
                   
                 of Resin (min) 
               
               
                   
                   
               
            
           
         
       
     
     From the graphs  600  and  700 , as well as Table 2, it is clear that (1) samples #3 and 11 exhibited a “good” rate of infusion; (2) samples #3 and 11 performed similar to one another; and (3) sample #4 outperformed both of these samples. Conversely, the IPIT test  400  and the TTIS test  300  revealed that samples #9 and 10 exhibited a “poor” rate of infusion, which is believed to be at least partially attributable to one or more properties of the stitching yarns used in those samples. 
     The reinforcing fabrics described herein (e.g., the reinforcement fabric  100 ) can be combined with a resin matrix, such as in a mold, to form a composite article. Any suitable resin system can be used. In some exemplary embodiments, the resin is a vinyl ester resin. In some exemplary embodiments, the resin is a polyester resin. In some exemplary embodiments, the resin is an epoxy resin. In some exemplary embodiments, the resin includes a viscosity modifier. 
     Any suitable composite forming process can be used, such as vacuum-assisted resin transfer molding (VARTM). The composite article is reinforced by the reinforcing fabric. In some exemplary embodiments, the composite article is a wind turbine blade or related component (e.g., spar cap). 
     The above description of specific embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the inventive concepts and their attendant advantages, but will also find apparent various changes and modifications to the structures and concepts disclosed. It is sought, therefore, to cover all such changes and modifications as fall within the spirit and scope of the general inventive concepts, as defined herein and by the appended claims, and equivalents thereof.