Patent Publication Number: US-2002007897-A1

Title: Mehtod and apparatus for providing through-the-thickness reinforcements in laminated composite materials

Description:
CLAIM OF BENEFIT OF PROVISIONAL APPLICATION  
     [0001] Pursuant to 35 U.S.C. Section 119, the benefit of priority from provisional application No. 60/080,241, with a filing date of Apr. 1, 1998, is claimed for this non-provisional application. 
    
    
     ORIGIN OF THE INVENTION  
     [0002] The invention described herein was made by an employee of the U.S. Government and may be used by or for the government for governmental purposes without the payment of royalties thereon or therefor. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0003] 1. Technical Field of the Invention  
       [0004] The present invention is directed to a method and apparatus for reinforcing laminated composite materials. In particular, the reinforcing entails the insertion of rods through the thickness of laminated composite materials.  
       [0005] 2. Description of the Related Art  
       [0006] A typical laminated composite material is shown in FIG. 1. The laminated composite material  100  is composed of layers or plies of yarns  110 . The yarns  110  are themselves composed of a multitude of fibers  120 . The longitudinal axis of each fiber  120  is substantially aligned with the longitudinal axis of the respective yarn  110 . In prepreg material, the yarns are pre-impregnated with a resin that will harden when cured. In dry fiber preforms the resinous material has not yet been added. The laminated composite material is usually shaped by laying up prepreg material or dry fiber preforms on a support tool that defines the shape of the desired structure, saturating the voids between the yarns with a resin, and curing the resin to form a structure. The hardened resin forms a matrix  130  that holds the yarns together. The strength of the matrix  130  is much less than the longitudinal strength of the yarns  110 . Laminated composite materials  100  are generally made with the yarns  110  in adjacent plies oriented differently. In FIG. 1, the plies have yarn orientations that are rotated 90 degrees with respect to the adjacent plies. The resultant structure has great strength in planes parallel to the plies (the in-plane directions), but are weak in the direction perpendicular to the plies (the interlaminar direction). Other types of laminated composite materials differ in their details, but are still characterized by a matrix material supporting a multitude of fibers oriented substantially parallel to a surface. Specifically, in addition to the dry-fiber preforms and the laid up prepreg material, tow-placed and filament-wound structures are to be considered laminated composite materials herein. Uncured laminated composite material refers to either dry-fiber preforms, laid up prepreg material, tow-placed, filament-wound, or similar fiber-filled materials before the material is cured into a hardened structure, regardless of whether or not the material includes a resinous substance.  
       [0007] Providing through-the-thickness reinforcement in laminated composite materials greatly increases the interlaminar strength, resulting in a more damage-tolerant structure. Under certain conditions through-the-thickness reinforcements also act as miniature crack arresters.  
       [0008] One way of providing through-the-thickness reinforcement consists of stitching the laminates together with yarns. However, Farley and Dickinson [NASA Conference Publication 3176, pp. 123-143, 1992] show that the stitch loop degrades the compressive strength of the resultant material. Tufting is similar to stitching in that a yarn is threaded through the laminates. However, tufting does not leave a stitch loop. When used with prepreg materials both the stitching and tufting processes potentially induce resin-rich regions that can adversely affect structural performance. When stitching and/or tufting is performed on prepreg materials, uncured resin tends to stick to the stitching/tufting needles. This tendency slows the process and results in poor manufacturing economics.  
       [0009] Stitching/tufting has been more successful when applied to dry fiber preforms. However, the process is difficult to use on preforms with compound curvature or those that integrate complex-shaped interconnecting parts. In addition, the need for stitching machinery to access both sides of the preform further complicates the process.  
       [0010] Other techniques have been developed to provide through-the-thickness reinforcing without the need to access both sides of the laminated composite material.  
       [0011] For instance, U.S. Pat. No. 4,808,561 to Boyce et al. describes a process in which reinforcing elements are embedded in a thermally decomposable structure having opposing surfaces. The reinforcing elements extend perpendicular to the opposed surfaces. The thermally decomposable structure is placed on the laminated composite that requires reinforcement and then exposed to elevated temperature and pressure. The thermally decomposable structure collapses under the influence of the elevated temperature and pressure while the reinforcing elements are inserted into the laminated composite. A variation of the process is disclosed in U.S. Pat. No. 5,466,506 to Freitas et al. Here the reinforcing elements are inserted obliquely into the laminated composite. They claim that the obliquely inserted reinforcing elements help prevent against both laminate peeling (mode I failures) and shear-induced (mode II) failures. Both approaches require heat and pressure to insert the reinforcing elements.  
       [0012] Other approaches employ ultrasonic energy to locally heat and soften the composite laminates. In U.S. Pat. No. 5,186,776 to Boyce et al., a reinforcing fiber is fed into an elongated hollow needle that is ultrasonically vibrated and inserted into the composite laminate material. The needle is then retracted, leaving the reinforcing fiber in place. U.S. Pat. No. 5,589,015 to Fusco et al. discloses a hybrid method of inserting through-the-thickness reinforcing elements. A compressible structure with reinforcing elements embedded therein is used in a way similar to the thermally decomposable structure of U.S. Pat. No. 4,808,561. However, instead of using an autoclave to provide heat and pressure, ultrasonic energy and mechanical pressure are applied to the reinforcing elements, thereby compressing the compressible material and inserting the reinforcing elements into the laminated composite structure. A somewhat more sophisticated system for practicing the hybrid method is taught in U.S. Pat. No. 5,800,672 to Boyce et al. All of the approaches that employ ultrasonic energy require bulky equipment and therefore are not well adapted for structures with complex shapes.  
       SUMMARY OF THE INVENTION  
       [0013] The present invention seeks to overcome the difficulties associated with prior techniques of providing through-the-thickness reinforcement. As such, the following objects are important to the present invention.  
       [0014] An object of the present invention is to provide a method for delivering through-the-thickness reinforcement to a laminated composite material. The technique should not compromise in-plane mechanical properties because of the presence of stitching loops, nor should the technique require more than one-sided access to the laminated composite material. The method should be applicable to either dry fiber preforms or prepreg laminated materials. In addition, the method should be quick, portable, and not require bulky nor expensive equipment. The method should enable reinforcements to be inserted over a wide range of angles relative to the surface of the laminated composite material. The technique should be capable of being performed both by hand and under robotic control.  
       [0015] Another object of the invention is to provide a machine for practicing the method of insertion. The machine should be portable and easily adapted to deliver different types and sizes of reinforcement material.  
       [0016] A further object is to provide a method of making a reinforcing rod blank. The rod blank would comprise a plurality of connected reinforcing elements or rods. The rod blank would be capable of being used in the above mentioned machine for delivering through-the-thickness reinforcement.  
       [0017] Yet another object of the invention is to provide a medical implant for reinforcing bone or holding broken bone together while the bone heals. In addition to having structural fibers that add strength to the implant, either the implant&#39;s matrix contains healing and/or analgesic agents, or the implant contains space for containing healing and/or analgesic agents.  
       [0018] Another object is to provide an automotive tire that reduces the risk of delamination of the layers of the tire tread.  
       [0019] The above and numerous other objects are achieved through the use of an impulsive force to drive a rod through an uncured laminated composite material. The rod provides through-the-thickness reinforcement to the cured laminated composite material without substantially compromising in-plane mechanical properties. The impulsive force is preferably delivered with a machine that comprises a rod guide for guiding the reinforcing rod into the uncured composite material and a ram with a hardened tip for thrusting the rod along the rod guide. A blank of rods, suitable for use with the machine are made by placing a mixture of substantially unidirectional fiber material and uncured resin in a mold such that the fibers are generally aligned with the rod axes and then curing the mixture. In other embodiments rods are formed from a supply of continuous rod material. In these embodiments rods of finite length are cut from the continuous supply and then subsequently inserted into the uncured laminate material. An unique application of the rods is for use as a medical implant. The rods comprise structural fibers for strength and a matrix that contains healing and/or analgesic agents. Alternatively, the healing and/or analgesic agents are contained in spaces formed from a conventional matrix. A further application includes using through-the-thickness reinforcement in automotive tires to reinforce the interfaces between the various layers of tire material.  
       [0020] Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0021] In the drawings, fibers are indicated in cross section by dots, and in side view by lines generally aligned with their respective yarns. Although the lines and dots representing the fibers are oriented substantially as they would be in a composite material, the number, density, and length of the fibers shown in the drawings are not necessarily representative of fibers in actual composite materials.  
     [0022]FIG. 1 shows yarns in a typical laminated composite material.  
     [0023]FIG. 2 shows a laminated composite material with a rod providing through-the-thickness reinforcement.  
     [0024]FIG. 3 illustrates a side view of a rod-inserting machine.  
     [0025]FIG. 4 shows a detailed side view of the magazine, the rod loader, the rod guide, the ram and ram actuator. The ram is extended.  
     [0026]FIG. 5 is similar to FIG. 4 except that the ram has retracted and the next rod is loaded into the rod guide.  
     [0027]FIG. 6 provides a perspective view of a ram.  
     [0028]FIG. 7 is a perspective view of a ram housing with internal ram chamber and rod guide.  
     [0029]FIG. 8 illustrates details of an alternate embodiment of the rod-inserting machine. Continuous rod material is cut to length to form individual finite-length rods.  
     [0030]FIG. 9 shows a rod-inserting machine under robotic control.  
     [0031]FIG. 10 is a cross-section view of top and bottom portions of a mold for making a rod blank.  
     [0032]FIG. 11 shows a bottom view of a rod blank with cross fibers.  
     [0033]FIG. 12 shows a cross-section of a rod blank. Although multiple fibers and cross fibers are shown, for clarity, only one of each is indicated.  
     [0034]FIG. 13 shows cross-sections of rods serving as medical implants. FIG. 13A shows a matrix of medicine. FIG. 13B has the conventional matrix and fibers in the central region with the medicine surrounding it. In FIG. 13C, the conventional matrix material and fibers form a C-shape with the medicine contained in the resulting cavity. FIG. 13D shows conventional matrix material in a U-shape with medicine in the remaining area. FIG. 13E shows conventional matrix material and fibers in an X-shape with medicine between the crossed sections.  
     [0035]FIG. 14 shows a cross sectional view of an automotive tire.  
     [0036]FIG. 15 illustrates the corner of an automotive tire with interlaminar reinforcement. 
    
    
     [0037] Reference numerals in the figures correspond to the following items:  
     [0038] 100  laminated composite material  
     [0039] 110  yarn  
     [0040] 120  fiber  
     [0041] 130  matrix  
     [0042] 140  rod  
     [0043] 150  rod blank  
     [0044] 160  robot  
     [0045] 170  ram  
     [0046] 174  ram driving portion  
     [0047] 176  ram driving portion face  
     [0048] 180  ram tip  
     [0049] 190  ram actuator  
     [0050] 200  ram housing  
     [0051] 210  ram chamber  
     [0052] 220  rod guide  
     [0053] 230  rod-guide notch  
     [0054] 240  insertion slot  
     [0055] 250  rod loader  
     [0056] 254  rod-loader spring  
     [0057] 256  rod-loader platen  
     [0058] 260  magazine  
     [0059] 270  continuous rod material  
     [0060] 280  continuous rod material supplier  
     [0061] 290  spool  
     [0062] 300  cutter  
     [0063] 310  robot  
     [0064] 320  mold  
     [0065] 322  bottom portion of mold  
     [0066] 324  top portion of mold  
     [0067] 326  gap between top and bottom portions of mold  
     [0068] 328  semi-circular recesses in mold  
     [0069] 329  cross fiber  
     [0070] 330  medical implant  
     [0071] 340  medicine  
     [0072] 360  rod-inserting machine  
     [0073] 370  handle  
     [0074] 380  trigger  
     [0075] 390  body  
     [0076] 400  tire  
     [0077] 410  tire tread  
     [0078] 420  tire belt  
     [0079] 430  tire bead  
     [0080] 440  tire sidewall  
     [0081] 450  tire body ply  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0082] In FIG. 2, a rod  140  extends through the thickness of the laminated composite material  100 . The presence of the rod  140  improves the interlaminar properties of the laminated composite material  100 . Specifically, the presence of the rod  140  enhances damage tolerance, increases the ability of the material to transfer loads perpendicular to the plane of the plies, and helps retard crack growth. The diameter of the rod  140  is preferably small compared with the diameter of the yarn  110 . For current uses the diameter of the rod  140  is most preferably between 0.005 inches and 0.030 inches, although the size is dependent on the specific use. The use of small rods  140  is preferred because the small size reduces the chance that the rod  140  will promote failure of the laminated composite material  100 . Because failure of a composite structure generally is governed by the largest anomaly inherent in the composite structure, the inclusion of smaller-scale anomalies rarely has a detrimental effect. Typical large-scale anomalies in composite materials include fiber waviness, voids, and resin-rich regions. The scale of these anomalies tend to be at least the yarn diameter of the material, hence rods  140  with diameters less than the yarns  110  are less likely to adversely effect the laminated composite material  100 . Although the use of larger rods degrades the mechanical properties, in some situations, the economies associated with using fewer but larger rods will outweigh the decreased mechanical performance.  
     [0083] A new technique for inserting through-the-thickness reinforcement into a laminated composite material  100  takes advantage of the fact that the strength of the laminated composite material  100  is not compromised substantially by localized damage to fibers, providing that the damaged region is small compared with the scale of largest inherent anomaly. In the new approach, rods  140  for providing through-the-thickness reinforcement are driven into the laminated composite material  100  with an impulsive force. Providing that each rod  140  has a diameter that is smaller than the largest scale anomaly inherent in the laminated composite material  100 , the abrupt introduction of the rod  140  will have little detrimental effect on the structural properties of the final cured material. In fact the presence of the rod  140  will substantially increase the resistance of the laminated composite material  100  to interlaminar failure mechanisms.  
     [0084]FIG. 3 shows a side view of a rod-inserting machine  360 . The rod-inserting machine  360  is similar in many respects to a commercially available nail gun, such as the Stanley Bostitch Model Number BT35-2. Referring to FIGS. 4 and 5, a rod  140  stored in a magazine  260  is loaded into a rod guide  220 , which is located interior to a ram housing  200 . Upon actuation by a trigger  380 , a ram actuator  190  in the body  390  thrusts a ram  170  with a hardened ram tip  180  along a ram chamber  210 . Details of the ram are shown in FIG. 6 and the ram housing  200  with internal ram chamber  210  and rod guide  220  in FIG. 7. The ram  170  is an elongated member terminating at one end in a ram tip  180 . The ram  170  has a ram driving portion  174  that is smaller in cross section than the rest of the ram  170 . Only the ram driving portion face  176  actually contacts the rod  140 . The bulk of the ram  170  provides strength and makes the ram  170  more resistant to buckling than the ram driving portion  174  alone would be. The shape of the ram  170  is a consequence of the shape of the ram chamber  210  and how the ram  170  attaches to the ram actuator  190 . To enable convenient adaptability to differently sized rods, the preferred embodiment of the rod-inserting machine  360  allows the magazine  260 , the ram housing  200 , and the ram  170  to be easily replaced with components suited for differently sized rods  140 . Preferably, each ram  170  has a cross section that is sized and shaped to fit a conventional ram actuator  190  at one end, and is sized and shaped with an appropriate ram driving portion  174  at the other end. The ram driving portion  174  need only extend along the ram length a distance sufficient to transfer the load from the ram driving portion  174  to the remainder of the ram  170  without creating excessive stress concentrations. Typically, a length of 3-5 times the largest linear dimension of the ram driving portion face  176  is sufficient to transfer the load without undue stress. Preferably, the rod guide  220  in the ram chamber  210  has close tolerances so that each rod  140  does not have much play as it is driven down the rod guide  220 . The rod guide  220  must not be too small; otherwise the rod  140  will jam in the rod guide  220 . The rod guide  220  preferably is not be too large, otherwise buckling and subsequent failure of the rod  140  is more likely to occur during rod insertion. As an example of the preferred tolerances, less than  0 . 005  inches of excess space is desired for a rod guide  220  designed for a rod  140  having a diameter between 0.020 inches and 0.025 inches. A rod-guide notch  230  is sized to prevent rod jamming and buckling. Although embodiments with any appropriately sized and shaped ram  170  are possible, preferably a large ram  170  is used. A large ram  170  tends to resist buckling and is more easily adapted to mate conveniently with standard ram actuators  190 .  
     [0085] The ram driving portion face  176  of the ram tip  180  is preferably hardened to work in the rod-inserting machine  360 . Experiments revealed that standard ram tips  180  are not hard enough to withstand the stresses resulting from driving the rods  140  into the laminated composite material  100 . The small diameter rods  140  bear upon a small area of the ram tip  180 , thereby creating large stresses. In addition, the fibers in the rod  140  generally have higher stiffness and hardness than the material of the ram  170 . The impact of materials with disparate stiffnesses damages the less stiff material. Hardening the ram driving portion face  176  of the ram tip  180  reduces and/or eliminates this problem. Preferably the ram driving portion face  176  of the ram tip  180  is hardened by applying a silicon carbide or a diamond coating. Most preferably, the ram driving portion face  176  of the ram tip  180  is hardened by applying a diamond coating.  
     [0086] Referring back to FIG. 4, the operation of a preferred rod loader  250  is explained. The rod loader  250  comprises a rod-loader spring  254  that bears against the bottom of the interior of the magazine  260  and urges a rod-loader platen  256  upward. The three remaining rods  140  of a rod blank  150  are shown above the rod-loader platen  256 . The rod blank  150  is a group of rods  140  temporarily held together for ease of handling. Although in some embodiments individual rods  140  are loaded into the magazine  260 , the rod blank  150  is easier to handle and therefore is preferred. More details of the rod blank  150  are given later. The rod-loader platen  256  pushes upward against the rod blank  150 . In FIG. 4, the ram  170  is still extended in the rod guide  220 , as it would be just after driving the previous rod  140  and before being retracted by the ram actuator  190 . The presence of the ram  170  in the rod guide  220  prevents the rod loader  250  from inserting the next rod  140  into the rod guide  220 . In FIG. 5, the ram  170  is retracted and the next rod  140  is pushed upward through an insertion slot  240  and into the rod guide  220 . Actuation of the ram actuator  190  thrusts the ram  170  forward again. The force of the ram  170  shears the rod  140  from the rod blank  150  and drives the rod  140  through the rod guide  220  and into the laminated composite material  100 .  
     [0087] Because 60 to 100 rods per square inch are typically required to achieve damage-tolerant structures, other embodiments of the rod-inserting machine  360  insert multiple rods per insertion or ram actuation cycle.  
     [0088] To accomodate more rods in a single rod blank, in a further embodiment (not shown), the linear magazine is replaced with a circular magazine where the rod blank is rolled in a spiral around a core. Each time a rod is inserted, the rolled up blank rotates, advancing the end rod into the rod guide. Alternate embodiments feed multiple rod blanks simultaneously into multiple rod guides for simultaneous insertions of the rods.  
     [0089] Another embodiment is shown in FIG. 8. Instead of storing discrete rods  140  in the magazine  260 , continuous rod material  270  is stored on a continuous rod material supplier  280 , which is a spool  290  in this particular embodiment. In other embodiments, other types of continuous rod material suppliers  290  are used. The continuous rod material  270  is fed into the rod guide  220 . A cutter  300  cuts the continuous rod material  270  into a rod  140  of finite length and then retracts. The continuous rod material  270  is sufficiently elastic so that the portion cut returns to a substantially straight configuration after being cut. The ram  170  then drives the rod  140  down the rod guide  220  and into the uncured laminated material. Preferably the motion of the cutter  300  is electrically or pneumatically actuated. Also preferably, the continuous rod material  270  is made by a conventional pultrusion process.  
     [0090]FIG. 9 shows the rod-inserting machine  360  being controlled by a robot  310 . When under robotic control, triggering is preferably done electronically, hence no mechanical trigger  380  is needed.  
     [0091] Insertion of the rod  140  at non-normal incidence to the surface of the laminated composite material  100  is easily accomplished by tilting the rod-inserting machine  360 . Embodiments of the rod-inserting machine  360  with wedges to tilt the rod-inserting machine  360  provide a means of consistantly inserting rods  140  at a specific angle. Wedges are particularly helpful when the rod-inserting machine  360  is manually operated, but are generally unnecessary when the rod-inserting machine  360  is used in conjunction with a robot.  
     [0092] Rods  140  are made from any appropriate material. Preferably metal or composite materials are used. Metallic rod blanks  150  are formed in a similar manner as commercially available metallic brads are produced.  
     [0093] Although the diameter of the rods  140  most preferably ranges between 0.005 and 0.030 inches, larger diameter rods  140  are useful on larger structures, especially in cases in which coarse yarns are used in the laminated composite material. Similarly, although the length of each rod  140  is typically between 0.005 and 1.0 inches, longer rods  140  are appropriate for large structures.  
     [0094] One method for making rod blanks  150  of composite material includes placing unidirectional prepreg material in a mold  320  such that the fiber orientation of the prepreg is aligned with the axis of the rods  140 . FIG. 10 shows bottom  322  and top  324  portions of a mold  320 . In this embodiment, the bottom portion  322  of the mold  320  has approximately semi-circular recesses  328 . Each semi-circular recess  328  will contain material for a single rod  140 . The top portion  324  of the mold  320  is flat. A small gap  326  exists between the flat top portion  324  and the sections that divide the semi-circular recesses  328 . The gap  326  permits some prepreg material to join adjacent semi-circular recesses  328 , thereby joining the resultant rods  140 . Preferably a relatively small number of additional fibers  329  are oriented perpendicular to the rods  140  in the gap  326 . The resultant rod blank  150  is held together better, thereby facilitating handling of the rod blank. After placing the material in the mold  320 , the material is cured. A bottom view of the finished rod blank  150  is shown in FIG. 11. A cross-sectional view of the finished rod blank  150  is shown in FIG. 12. An alternate embodiment employs dry fibers and a separate resin in place of prepreg. The remainder of the process and the resultant product are essentially the same. In another embodiment, the surface of the resultant rods is slightly roughened to improve adhesion between the rod  140  and the laminated composite material  100 . The roughening is performed either after curing the rod blank  150 , or by employing a mold with spaced indentations or a coarse inner surface. However, generally the roughening is not required. The cross fibers  329  are explicitly indicated. In the preferred embodiments, each rod blank is approximately 4 to 6 inches in length, resulting in approximately 200 to 800 rods per blank. Alternate embodiments with differently shaped and sized molds are also appropriate, depending upon the particular application.  
     [0095] Medical implants  330 , as shown in FIGS. 13A through 13D, made from the rods  140  can be used as reinforcements to support broken bones and facilitate proper bone alignment while simultaneously providing a medical delivery vehicle for analgesics and healing agents directly to the damaged area. The term medicine is used to refer to any appropriate combination of analgesic and healing agents. As shown in FIG. 13A, the matrix  130  of the medical implant  330  could be comprised of solidified medicine  340  that dissolves in a time-release fashion, dispensing the medicine  340  to the damaged area as it dissolves. The fibers  120  would remain embedded in the bone after the broken bone reattaches. In one embodiment, the medicine is formulated as a solid at room temperature, but melts at body temperature. To aid in insertion, the stiffness of the medicine matrix is increased by decreasing the temperature of the implant  330  prior to insertion. Because the medicine does not always provide an appropriate matrix material for the fibers  120 , in other embodiments a conventional matrix material, as for example a structural polymer, is used to form a section of the implant  330 , the balance of the implant  330  being filled with medicine  340 . In FIG. 13B, the conventional matrix material  130  is used in a core region, and the medicine  340  encircles the core region. A C-shaped void for the medicine  340  is shown in FIG. 13C. In FIG. 13D, a U-shaped conventional matrix  130  is used, with the medicine  340  filling the remaining area. An X-shaped region of conventional matrix  130  with the gaps between the crossed regions filled with medicine  340  is illustrated in FIG. 13E. In the embodiments of FIGS.  13 B,  13 C,  13 D and  13 E, the medicine fills the spaces in the implant  330  that is not occupied by the fibers  120  nor by the matrix  130 .  
     [0096] Interlaminar reinforcement is also applicable to improved automotive tires. In particular, run-flat tires are designed to be usable even after experiencing a loss of tire air pressure. However, run-flat tires typically have severe speed and drive-duration limitations. After losing air pressure, run-flat tires flex more than usual, thereby increasing heat production. The heating decreases interlaminar strength between the layers of the tire, leading to delamination failures. FIG. 14 illustrates a cross section of a typical tire  490 . The outermost layer of the tire is referred to as the tire outer wall. The tire outer wall is comprised of two portions: the tire tread  410  on the outer circumference, and the tire sidewalls  440  on the side portions of the tire outer wall. The tire tread  410  is typically thicker than the tire sidewall  440 . Proximal to the tire tread  410  are one or more tire belts  420 . Preferably each tire belt  420  is made of steel although other types of puncture-resistant material are usable. Proximal to the tire belts  420  are tire body plies  450 . On the tire sidewall  440 , where the tire belts  420  are not required, the tire body plies  450  are overlain with the tire sidewall  440  portion of the tire outer wall. Tire beads  430  seal the tire  490  to a wheel rim thereby enabling elevated air pressure to be maintained inside the tire. Delamination failures typically occur at geometric discontinuities, such as layer discontinuities and changes in the tire geometry. The junction of the tire tread  410  and the tire sidewall  440  is such an area. The tire belts  420  typically do not continue along the sidewall, therefore the bond between the tire body plies  450  and the tire belts  420  ends and new bonds begin, for instance, between the tire body plies  450  and the tire sidewall  440 . Referring now to FIG. 15, interlaminar reinforcement, such as the introduction of rods  140  through the various layers of the tire, greatly reduces the risk of delamination failure. Rods  140  through the interface of the tire tread  410  and the tire belt or belts  420  are particularly helpful, as are rods  140  through the interface of the tire belt or belts  420  and the tire body ply or plies  450 . Further reinforcement involving rods  140  through the interface of the tire body ply or plies  450  and the tire sidewall  440  are also useful. Although any appropriate type of interlaminar reinforcement is usable, the rods  140  described herein are preferred. Most preferably, composite rods  140  are used. The application of the method for inserting the rods  140  described herein is well suited for the tires. The compound curvature of the tire and the restriction to one-sided access to the plies does not present any special problems.  
     [0097] Compared with prior methods for inserting through-the-thickness reinforcements, the use of an impulsive force to drive rods into uncured laminated composite material is fast, inexpensive, and rapidly adaptable to different shapes and configurations of the underlying composite material. The method of insertion is straightforward to use on complex structures. Only one-sided access to the composite material is required, hence the reinforcement can be inserted while the composite material is lying on its support tool, thereby eliminating the need to provide custom tooling, as is the case for stitching. Damage to the composite material during the insertion process is limited to the very near vicinity of the inserted rod  140 . Such limited damage is in marked contrast to stitching and tufting processes in which the damaged area extends to the diameter of the needle, which is typically much larger than the inserted reinforcement.  
     [0098] Although the description above contains specific examples, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.