Abstract:
A composite shaft formed from a single flag of composite material having variable fiber orientation, and methods of forming said shaft, are disclosed herein. A preferred method includes preparing a sheet of prepreg material, dividing it into segments, deforming the segments, cutting a single flag and constructing a composite shaft from the single flag.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to composite shafts constructed from variable angle plies, or flags, such that the fiber orientation varies along the length of the shafts. 
     2. Description of the Related Art 
     Shafts made from non-metal materials, such as graphite composite, are routinely used with sporting equipment such as golf clubs. Composite shafts typically are constructed from multiple plies, or flags, of composite that are rolled onto a tapered mandrel in a process known as sheet wrapping. Each flag has a fixed fiber orientation relative to the longitudinal axis. In general, the fiber orientations used are 0°, which means the fibers run parallel to the shaft axis, ±45°, and 90°, which means that the fibers extend in a circumferential direction around the shaft. 
     A flag extends over a finite length along a shaft axis from a start position to an end position and is sized for a defined number of wraps about the shaft axis. As shown in  FIG. 2 , most flags are roughly trapezoidal in shape. A unidirectional composite material typically is comprised of fibers oriented along a given direction with resin matrix filler in a thin layer, which forms a configuration known as a prepreg. A prepreg also typically has a backing material to maintain integrity of the ply during handling. 
     For sheet wrapped construction, changing ply orientation along the length of the shaft requires that separate flags, oriented at different angles, be placed along the shaft axis. The flags are made to overlap in this construction to ensure structural continuity and strength. This overlapping configuration is detrimental, however, because it increases the complexity of the sheet wrapping process, adds weight, and creates an uneven thickness distribution in the wall of the shaft. 
     In view of the above, there is a need for thin, lightweight, composite shafts that are capable of resisting the stresses and strains placed upon them during use, particularly when they are used with golf club equipment. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to the use of composite flags having varying fiber orientation along their length to construct shafts with low weight and high structural integrity. One aspect of the present invention is a shaft comprising 0° fiber orientation at its tip end, where high bending stiffness is needed, and 30° orientation at its butt end, wherein more circumferential strength is required. 
     Another aspect of the present invention is a composite shaft comprising a shaft axis, a butt end, and a tip end, wherein the composite shaft is composed of a single composite flag, and wherein the fiber orientation of the flag with respect to the shaft axis varies along the shaft axis. In some embodiments, the fiber orientation of the flag at the tip end may be no less than 0° and no more than 15°, and further may be approximately 0°. In other embodiments, the fiber orientation of the flag at the butt end may be no less than 20° and no more than 45°, and further may be approximately 30°. In some embodiments, the flag may be approximately trapezoidal in shape. In further embodiments, the composite shaft may comprise a golf club head and a grip, wherein the golf club head may be affixed to the tip end and the grip may be affixed to the butt end. In another embodiment, the composite flag may comprise a backing material, which may be composed of an open weave material. 
     Yet another aspect of the present invention is a method of manufacturing a composite shaft, the method comprising the steps of preparing a sheet of prepreg material, dividing the prepreg material into a plurality of segments, deforming each of the plurality of segments by a designated offset to create a deformed prepreg sheet, cutting a single flag from the deformed prepreg sheet, and constructing a shaft from the single flag. In some embodiments, the step of deforming each of the plurality of segments by a designated offset may be accomplished with a table comprising a plurality of parallel bars, wherein each of the parallel bars may be free to move laterally while at the same time staying in contact with each other. In some further embodiments, each bar may grasp the prepreg material, and the individual offset for each bar may be enforced in small increments until the desired offset profile is reached. In further embodiments, each bar may grasp the prepreg material with a device selected from the group consisting of a strap, a clamping bar, and an adhesive. 
     In some embodiments, the shaft may comprise a longitudinal shaft axis, a tip end, and a butt end, the tip end may comprise fibers oriented at no less than 0° and no more than 15° with respect to the shaft axis, and the butt end may comprise fibers oriented at no less than 20° and no more than 45° with respect to the shaft axis. In a further embodiment, the tip end may comprise fibers oriented at approximately 0° with respect to the shaft axis, and the butt end may comprise fibers oriented at approximately 30° with respect to the shaft axis. In some embodiments, the prepreg material may comprise a backing material, which may comprise an open weave construction. In some embodiments, the method may further comprise the step of slitting the backing material perpendicular to the undeformed fiber, and this further step may occur prior to the step of deforming each of the plurality of segments. 
     Another aspect of the present invention is a method of manufacturing a composite shaft, the method comprising the steps of preparing a sheet of prepreg material, the prepreg material comprising a plurality of fibers, a resin material, and a backing material, dividing the prepreg material into a plurality of segments, deforming each of the plurality of segments by a designated offset to create a deformed prepreg sheet using a table comprising a plurality of parallel bars, wherein each of the parallel bars is free to move laterally, and wherein the plurality of parallel bars stay in contact with one another, cutting a single flag from the deformed prepreg sheet, and constructing a shaft from the single flag, wherein the shaft comprises a longitudinal shaft axis, a tip end, and a butt end, wherein the tip end comprises fibers oriented at no less than 0° and no more than 15° with respect to the shaft axis, and wherein the butt end comprises fibers oriented at no less than 20° and no more than 45° with respect to the shaft axis. 
     Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a front, perspective view of a golf club including an embodiment of the present invention. 
         FIG. 2  is a front, plan view of a typical composite ply layout. 
         FIG. 3  is a front, plan view of an idealized section of composite material. 
         FIG. 4A  is a front plan view of a composite segment in an undeformed condition. 
         FIG. 4B  is a front plan view of a composite segment in a pure shear deformation. 
         FIG. 4C  is a front plan view of a composite segment in a combined extension and bending deformation. 
         FIG. 5  is a flow chart showing a method of the present invention. 
         FIGS. 6A-6C  are front plan views of prepreg sheets on an adjustment table having different lateral deformations. 
         FIG. 7A-7C  are front, plan views of a trapezoidal flag cut from a deformed section of prepreg material. 
         FIG. 8  is a chart showing the offset distance versus position in a variable fiber angle composite of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1 , a shaft  10  used with a golf club typically includes a shaft axis  15 , a butt end  12  to which a grip  20  is affixed, and a tip end  14 , at least part of which is inserted into, and in many cases permanently bonded to, the hosel  26  of a golf club head  25  or a shaft sleeve (not shown) for use with an adjustable golf club head  25 . Shafts  10  used with golf club heads  25  typically have a length of 35 to 46 inches, though they may be as short as 18 inches or as long as 48 inches, as desired by the player. Composite shafts  10  are desirable for use with golf club heads  25  because they are strong and lightweight, and free up mass that can be used to incorporate advanced golf club head  25  technology. 
     The present invention is directed to composite shafts  10  having variable composite fiber orientation along their lengths, a configuration that is particularly useful for golf equipment. Composite shafts  10  typically are constructed from multiple plies, or flags  30 , of composite that are rolled onto a tapered mandrel in a process known as sheet wrapping. Each flag  30 , an example of which is shown in  FIG. 2 , has a fixed fiber orientation relative to the longitudinal axis of the resulting shaft  10 . The flag  30  has a length, L, a wrap direction dimension a at its tip end  32 , a wrap dimension b at its butt end  34 , and a fiber angle θ, which is relative to the longitudinal axis x of the flag  30 . 
     In general, the fiber orientations used in a typical flag  30  are 0°, which means the fibers run parallel to the shaft axis, ±45°, and 90°, which means that the fibers extend in a circumferential direction around the shaft  10 . A flag  30  extends over a finite length along the shaft axis  15  from a start position to an end position and is sized for a defined number of wraps about the shaft axis  15 . As shown in  FIG. 2 , most flags  30  are roughly trapezoidal in shape. A unidirectional composite material typically is comprised of fibers  35  oriented along a given direction with resin matrix filler  37  in a thin layer, which forms a configuration known as a prepreg, an idealized section of which is shown in  FIG. 3 . As shown in  FIG. 3 , prepreg also typically includes a backing material  38  that is designed to maintain integrity of the prepreg material during handling. 
     In situations where minimum weight and structural integrity are important, such as with golf equipment, variable fiber orientation is beneficial. Unfortunately, as illustrated in  FIGS. 4A-4C , obtaining variable fiber orientation can be difficult. As shown in  FIG. 4A , a segment  40  of composite material, which makes up a flag  30 , has single fibers  35  along its upper and lower surfaces that contain the resin matrix material  37 . When in pure shear, as shown in  FIG. 4B , the fibers  35  rotate and are aligned with the local slope, dy/dx, but are not subjected to extensional strain because no change in length takes place. Instead, the resin matrix material  37  deforms in shear only and experiences no change in volume. This form of deformation requires very little force because the fibers  35  do not deform and there is no volume change to the resin matrix material  37 . 
     In order to facilitate this deformation process, the backing material  38  typically used for handling composite prepreg can be slit perpendicular to the undeformed fiber  35  direction to allow shear deformation of the flag  30  to take place. Alternatively, another form of shear flexible material, such as an open weave, can be used as backing material  38 . If the composite segment  40  is deformed in general bending and extension, which would occur if overall curvature of a composite flag  30  in the xy-plane were enforced, the segment  40  behaves as shown in  FIG. 4C . In this case, the fibers  35  are subjected to extensional strains and the resin matrix material  37  undergoes a change in volume. Deforming a composite material in this manner is difficult because the fibers  35  are stiff and resist longitudinal deformation. Additionally, changing the volume of the resin matrix material  37  tends to cause the resin to flow. 
     According to a preferred method of the present invention, shown in flow chart form in  FIG. 5 , composite material is transformed into a variable angle flag  30  by gradually deforming the material in transverse shear along its longitudinal axis x according to processes illustrated in  FIGS. 6A-6C . As shown in  FIG. 6A , a sheet of prepreg material  50  first is divided into segments  55  along its longitudinal axis x  100 . Each segment  55  corresponds to a longitudinal position, x i , along the prepreg material  50 . Each of the segments  55  is then deformed by a designated offset, y i    110 , which orients the fibers  35  of the prepreg material  50  at desired angles along the longitudinal axis as shown in  FIG. 6B . As shown in  FIGS. 6A-6C , the deformation step is accomplished using a table  60  with multiple parallel bars  65  that are free to move laterally while at the same time staying in contact with each other. In this embodiment, the prepreg material  50  is held at each bar  65  by a strap, clamping bar, or adhesive, and the individual offset for each bar  65  is enforced in small increments until the desired offset profile is reached. Because the fibers  35  of the prepreg material  50  are continuous and have some flexural stiffness, they do not deform in a piecewise linear manner, and their resulting shape is a smooth curve as shown in  FIG. 6C . 
     Once a piece of prepreg material  50  is deformed as shown in  FIGS. 6A-6C , a trapezoidal flag  30  that will be used to create the shaft  10  is cut  120  from a section of the prepreg material  50  according to the process shown in  FIGS. 7A-7C . Table 1 provides an example of the parameters for a twenty five-inch long flag  30  that has been divided into twenty five equal width segments  55 . Once the flag  30  is cut, a shaft  10  is formed  130  by a process such as sheet wrapping or another process known to a person skilled in the art. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Position  
                 Delta 
                 Offset 
                   
                 Angle 
               
               
                   
                 (in.) 
                 (in.) 
                 (in.) 
                 Slope 
                 (deg) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0.0 
                 0.000 
                 0.000 
                 0.000 
                 0.0 
               
               
                   
                 0.5 
                 0.000 
                 0.000 
                 0.000 
                 0.0 
               
               
                   
                 1.0 
                 0.000 
                 0.000 
                 0.000 
                 0.0 
               
               
                   
                 1.5 
                 0.000 
                 0.000 
                 0.000 
                 0.0 
               
               
                   
                 2.0 
                 0.000 
                 0.000 
                 0.000 
                 0.0 
               
               
                   
                 2.5 
                 0.000 
                 0.000 
                 0.000 
                 0.0 
               
               
                   
                 3.0 
                 0.000 
                 0.000 
                 0.010 
                 0.6 
               
               
                   
                 3.5 
                 0.010 
                 0.010 
                 0.030 
                 1.7 
               
               
                   
                 4.0 
                 0.020 
                 0.030 
                 0.050 
                 2.9 
               
               
                   
                 4.5 
                 0.030 
                 0.060 
                 0.070 
                 4.0 
               
               
                   
                 5.0 
                 0.040 
                 0.100 
                 0.090 
                 5.1 
               
               
                   
                 5.5 
                 0.050 
                 0.150 
                 0.110 
                 6.3 
               
               
                   
                 6.0 
                 0.060 
                 0.210 
                 0.130 
                 7.4 
               
               
                   
                 6.5 
                 0.070 
                 0.280 
                 0.150 
                 8.5 
               
               
                   
                 7.0 
                 0.080 
                 0.360 
                 0.170 
                 9.6 
               
               
                   
                 7.5 
                 0.090 
                 0.450 
                 0.190 
                 10.8 
               
               
                   
                 8.0 
                 0.100 
                 0.550 
                 0.210 
                 11.9 
               
               
                   
                 8.5 
                 0.110 
                 0.660 
                 0.230 
                 13.0 
               
               
                   
                 9.0 
                 0.120 
                 0.780 
                 0.250 
                 14.0 
               
               
                   
                 9.5 
                 0.130 
                 0.910 
                 0.270 
                 15.1 
               
               
                   
                 10.0 
                 0.140 
                 1.050 
                 0.290 
                 16.2 
               
               
                   
                 10.5 
                 0.150 
                 1.200 
                 0.310 
                 17.2 
               
               
                   
                 11.0 
                 0.160 
                 1.360 
                 0.330 
                 18.3 
               
               
                   
                 11.5 
                 0.170 
                 1.530 
                 0.350 
                 19.3 
               
               
                   
                 12.0 
                 0.180 
                 1.710 
                 0.365 
                 20.1 
               
               
                   
                 12.5 
                 0.185 
                 1.895 
                 0.375 
                 20.6 
               
               
                   
                 13.0 
                 0.190 
                 2.085 
                 0.385 
                 21.1 
               
               
                   
                 13.5 
                 0.195 
                 2.280 
                 0.395 
                 21.6 
               
               
                   
                 14.0 
                 0.200 
                 2.480 
                 0.400 
                 21.8 
               
               
                   
                 14.5 
                 0.200 
                 2.680 
                 0.400 
                 21.8 
               
               
                   
                 15.0 
                 0.200 
                 2.880 
                 0.400 
                 21.8 
               
               
                   
                 15.5 
                 0.200 
                 3.080 
                 0.400 
                 21.8 
               
               
                   
                 16.0 
                 0.200 
                 3.280 
                 0.400 
                 21.8 
               
               
                   
                 16.5 
                 0.200 
                 3.480 
                 0.400 
                 21.8 
               
               
                   
                 17.0 
                 0.200 
                 3.680 
                 0.400 
                 21.8 
               
               
                   
                 17.5 
                 0.200 
                 3.880 
                 0.400 
                 21.8 
               
               
                   
                 18.0 
                 0.200 
                 4.080 
                 0.400 
                 21.8 
               
               
                   
                 18.5 
                 0.200 
                 4.280 
                 0.400 
                 21.8 
               
               
                   
                 19.0 
                 0.200 
                 4.480 
                 0.400 
                 21.8 
               
               
                   
                 19.5 
                 0.200 
                 4.680 
                 0.400 
                 21.8 
               
               
                   
                 20.0 
                 0.200 
                 4.880 
                 0.400 
                 21.8 
               
               
                   
                 20.5 
                 0.200 
                 5.080 
                 0.400 
                 21.8 
               
               
                   
                 21.0 
                 0.200 
                 5.280 
                 0.400 
                 21.8 
               
               
                   
                 21.5 
                 0.200 
                 5.480 
                 0.400 
                 21.8 
               
               
                   
                 22.0 
                 0.200 
                 5.680 
                 0.400 
                 21.8 
               
               
                   
                 22.5 
                 0.200 
                 5.880 
                 0.400 
                 21.8 
               
               
                   
                 23.0 
                 0.200 
                 6.080 
                 0.400 
                 21.8 
               
               
                   
                 23.5 
                 0.200 
                 6.280 
                 0.400 
                 21.8 
               
               
                   
                 24.0 
                 0.200 
                 6.480 
                 0.400 
                 21.8 
               
               
                   
                 24.5 
                 0.200 
                 6.680 
                 0.400 
                 21.8 
               
               
                   
                   
               
             
          
         
       
     
       FIG. 8  shows the offset profile and fiber angle profile resulting from the method disclosed herein and illustrated in  FIGS. 6A-6C  and Table 1. In this example, the tip portion of the flag  30  has a fiber orientation of 0°. The fiber angle increases almost linearly in the middle portion to 22° and remains constant at that value for the remainder of the flag. 
     Shear deformation of the prepreg material  50  is a key feature of the method of the present invention because it requires minimal force and keeps the fiber  35  and resin matrix material  37  of the prepreg material  50  intact. This method is most readily applicable to composite prepreg material  50  used in standard hand lay-up and sheet wrap processes. However, the backing material  38  on the prepreg material  50  must be modified to permit shear deformation transverse to the longitudinal axis of the ply. This method may also be adapted to automated tape laying (ATL). In ATL, the tape laying head translates laterally perpendicular to the tape laying path without rotation of the head to produce the desired slope. 
     The method disclosed herein provides a number of benefits for shaft  10  performance. First, the composite fiber remains continuous along the length of the flag  30 , which provides increased strength and stiffness through the elimination of cut fibers, overlap joints, and thickness discontinuities. Furthermore, shaft  10  weight is reduced through the elimination of flag  30  overlap regions and fabrication is simplified, with one flag  30  replacing multiple flags  30  of different fiber angles. 
     In one embodiment of the present invention, the method disclosed herein is used to form a shaft  10  a single composite flag having variable fiber orientation, an example of which is shown in FIGS.  2  and  6 A- 6 C, so that the tip end  14  of the shaft  10 , which requires high bending stiffness, has composite fibers with 0° orientation, and the butt end  12 , which requires more circumferential strength, has composite fibers with 30° orientation. 
     From the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes, modifications and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claims. Therefore, the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claims.