Patent Publication Number: US-10316443-B2

Title: Composite braided open structure without inter-yarn bonding, and structures made therefrom

Description:
This non-provisional patent application claims all benefits under 35 U.S.C. § 119(e) of U.S. provisional patent application Ser. No. 62/148,831 filed 17 Apr. 2015, entitled “COMPOSITE BRAIDED OPEN STRUCTURE WITHOUT INTER-YARN BONDING, AND STRUCTURES MADE THEREFROM”, in the United States Patent and Trademark Office, which is incorporated by reference in its entirety herein. 
    
    
     FIELD OF THE INVENTION 
     The invention herein pertains to open architecture composites and particularly pertains to fiber-reinforced composites defining an open architecture or structure formed from large (i.e. high filament number) yarns that are pre-impregnated with an adhesive resin matrix and braided without bonded crossover points into the desired composite structure, such as a spring. 
     DESCRIPTION OF THE PRIOR ART AND OBJECTIVES OF THE INVENTION 
     Braided, lattice structure fiber-reinforced composites can form lightweight seamless truss structures but suffer from the inability to easily form complex shapes and the difficulty of extracting the mandrel for any shape other than those with parallel sides, or those which are conical/pyramidal to some degree. Historically, helical springs are produced from a single coil of torsionally stiff cylindrical elements twisted into a helical coiled shape. The spring structure defines spaces between the coils which either open or close with tension and compression, respectively. These coiled springs rely on the torsional stiffness of the element material for the overall compressional stiffness of the spring. Given the shear modulus of many materials is low compared to the axial stiffness, coil springs typically allow large travel (approx. 90% strain) but low overall stiffness for their weight. The use of braided, fiber-reinforced composite yarns to form structural members is known in the art (see for example, U.S. Pat. No. 8,859,088, entitled “Minimal Weight Composites Using Open Structure”, U.S. Patent Publication No. 2013/0302604, entitled “Robust Pre-Impregnated Yarn for Manufacturing Textile Composites”, and U.S. Patent Publication No. 2015/0056449, entitled “Minimal Weight Composites Using Open Structure”, all belonging to the assignee/applicant of the subject application, the entire disclosures of which are all hereby incorporated by reference). It would be desirable to create a lightweight spring from lightweight composite materials and structures, but most structural composites have a shear modulus that is dependent on the matrix material (typically a polymer) and so cannot make springs of practical stiffness near the size of metal coil springs. 
     Conventional springs also rely on the material and the diameter of the cylindrical element to provide the torsional stiffness. Such springs “bottom out” (i.e. experiences a sudden and dramatic increase in stiffness) when compressed to the extent that successive helical coils of the spring come into contact (called the “solid height”). The typical helical spring further has very low bending stiffness due to the unsupported helix geometry; thus the spring must be constrained by another mechanism to ensure motion only in the axial direction, for example by restraining at least one of the spring ends, relying on standard spring end designs such as “squared” and “ground”, utilizing special spring end anchoring members, enclosing the spring in a cylinder, or inserting a rod inside the substantial length of the spring for use as a cam follower. Because of these and other limitations, they cannot be made very long before buckling instability becomes a concern. 
     It has been discovered that a braided, open structure composite made from large (i.e. high filament number) yarns known as “tows” can be pre-impregnated with an adhering resin or substrate and cured without bonding at the yarn intersections (also known as “crossovers”) and after removal from the mandrel, can be constructed and used as a spring in which the spring constant in bending, torsion, tension or compression can be controlled by the geometry of the braided structure as well as the size of the structural elements. Alternatively or additionally, the spring may be curved in multiple directions and then crossovers can be re-bonded to make more rigid open structure composites that would be difficult or impractical to manufacture by conventional techniques, particularly when considering the logistical difficulties of removing the same from a mandrel. 
     Thus, in view of the problems and disadvantages associated with prior art springs, the present invention was conceived and one of its objectives is to provide a braided, open architecture structure with unbound yarn crossover points sometimes referred to in the art as pics. 
     It is another objective of the present invention to provide an open architecture structure formed from large (i.e. high filament number) prepreg yarns without bonded crossover points. 
     It is still another objective of the present invention to provide an open architecture structure without bonded crossover points formed from yarns containing between fifty thousand and one hundred thousand (50,000-100,000) axially aligned carbon filaments. 
     It is yet another objective of the present invention to provide an open architecture structure without bonded crossover points formed from yarns defining a braid angle from fifty to one hundred degrees (50°-100°). 
     It is a further objective of the present invention to provide an open architecture structure without bonded crossover points formed from a material that produced significant travel comparable to conventional helical springs, preferably seventy-five percent (75%) reduction in unrestrained length for a compression-type spring. 
     It is still a further objective of the present invention to provide an open architecture structure without bonded crossover points formed on a conventional Maypole braiding machine and substantially liner mandrel. 
     It is yet a further objective of the present invention to provide an open architecture structure without bonded crossover points that defines both rigid and flexible sections. 
     It is another objective of the present invention to provide an open architecture structure without bonded crossover points that defines the same spring constant as a coiled spring, but with a much lighter weight. 
     It is still another objective of the present invention to provide a method of forming an open architecture structure without bonded crossover points. 
     It is yet a further objective of the present invention to provide a method of removing an open architecture structure without bonded crossover points from a conventional mandrel. 
     It is a further objective of the present invention to provide a method of forming tubular structures that are curved, bent, or otherwise arcuate over a longitudinal length before curing. 
     Various other objectives and advantages of the present invention will become apparent to those skilled in the art as a more detailed description is set forth below. 
     SUMMARY OF THE INVENTION 
     The aforesaid and other objectives are realized by producing an open structure composite member such as a spring, without bonded crossover points, on a conventional braiding machine. The open structure composite member has a higher strength and stiffness to weight ratio than composite structures made from resin coated fabric, solid filament wound composites, or from other typical spring-construction materials like metal. At least two sets of large pre-impregnated (i.e. prepreg) yarns are braided by a braiding machine, such as a Maypole braiding machine. The sets of yarns are oriented in the opposite pitch direction, and it should be understood that additional sets of yarns may be incorporated as desired. Additionally, or in the alternative, another set of yarns may be deployed in the axial direction to produce a structure with additional structural capabilities. The yarns are spaced widely (relative to the standard braiding configuration for structural members) on a cylindrical or polygonal tapered mandrel, defining an orientation best described as a tubular woven lattice. Precautions are taken to prevent bonding at the yarn crossover points. This produces a spring that is greater in flexibility than the prior art as it pertains to compression, tension, torsion, and bending metrics. The spring may then be conformed into any number of shapes that could not otherwise be manufactured on and removed from on a conventional rigid mandrel. To produce a more structurally rigid section or member, the crossover points may later be cured after the spring is removed from the mandrel surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an elevated plan view of an open architecture composite member, 
         FIG. 2  pictures an elevated plan view of the member of  FIG. 1  after longitudinal contortion, 
         FIG. 3  depicts an elevated plan view of an alternate embodiment of an open architecture composite member, 
         FIG. 4  demonstrates an elevated plan view of an alternate embodiment of an open architecture composite member, and 
         FIG. 5  illustrates an elevated plan view of the member of  FIG. 4  after longitudinal contortion. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT AND OPERATION OF THE INVENTION 
     For a better understanding of the invention and its operation, turning now to the drawings,  FIGS. 1 and 2  demonstrate elevated plan views of preferred open structure composite member  10 . As presented herein, composite member  10  is presented as a cylindrical member deployed as a spring, but it should be understood that the intended use of any composite member disclosed herein should not be construed as a limitation. Further, the figures as drafted present cylindrical embodiments of the various composite members disclosed herein, with a single side represented without the opposing side demonstrated for the sake of visual clarity, but it should be understood that other shapes of composite member are contemplated within the scope of this disclosure. As shown in  FIG. 1 , composite member  10  is preferably formed from a plurality of yarns  11 , referred to in reference to  FIGS. 1-2  as “helical” yarns. The preferred embodiment of yarn  11  is defined by a high number (i.e. greater than 20,000 and preferably between 50,000-100,000) carbon filaments axially aligned and positioned within a jacket, as described by U.S. Pat. No. 8,859,088, entitled “Minimal Weight Composites Using Open Structure”, U.S. Patent Publication No. 2013/0302604, entitled “Robust Pre-Impregnated Yarn for Manufacturing Textile Composites”, and U.S. Patent Publication No. 2015/0056449, entitled “Minimal Weight Composites Using Open Structure”. The preferred embodiment of yarn  11  includes filaments, jackets, or both that have been pre-impregnated with an adhesive resin matrix, for example epoxy, vinyl ester, or other polymeric derivatives. The structural spring represented in  FIGS. 1 and 2  is achieved by braiding two yarns  11  in the opposite pitch direction about a cylindrical or polygonal mandrel (not shown, but typically tapered) with a conventional braiding machine, such as a Maypole braiding machine (not shown), in a biaxial braiding pattern. Yarns  11  preferably define a braid angle from fifty to one hundred degrees (50°-100°) under torsion and at a failure torque of less than twenty (20) inch ounces for an inch length, indicating that the resulting structure is easily deformed in torsion. This indicates that the resulting structure, for example composite member  10 , defines a very low spring constant but possesses excellent multi-directional stiffness. 
     Preferred composite member  10  enjoys structural superiority over the prior art in part due to a surprising compression stiffness imparted between the braided yarns  11 , even without bonding the crossover points of yarns  11  as is taught in the prior art, and obvious solution to impart added rigidity and strength to prior art structures. As used herein, the term “bonded”; “bonding”, and other “bond” derivatives refers to the substantial attachment of two or more proximal yarns  11  as they pass over or under one another in combination with the resin matrix as described. Composite member  10  also enjoys improved bending characteristics by virtue of the crossover points not being bound. The unbound, braided configuration produces a much lighter weight construction than a conventional coiled spring, all while unexpectedly producing similar or identical spring constant and comparable range of travel (up to 75% reduction in unrestrained spring length). The braided nature of composite member  10  also defines exceptional and surprising torsional stiffness and bending stiffness for its weight compared to helical springs because bending and torsion create predominantly axial loads in the individual composite elements. 
     Once yarns  11  are braided, they are laid on the mandrel and spaced widely relative to the yarn spacing typical of a structural component. In the preferred embodiment, yarns  11  define a coverage factor (i.e. the degree of “openness” or exposure between respective yarns) of at least fifty percent (50%), and more preferably of at least seventy-five percent (75%). Yarns  11  may be slightly cured to preserve their orientation and interwoven geometry, but great care is exercised in seeking to limit, and preferably avoid bonding between yarns  11  at any crossover point. The resulting structure may be described as a composite tubular woven lattice. If curing does take place, the resulting composite structure is removed from the mandrel, and any inadvertent crossover point bonding is broken, ensuring that composite structure  10  enjoys the greatest degree of spring flexibility with respect to compression, tension, torsion, and bending. A structure such as composite structure  10  may define unusual and directional properties. For example, composite structure  10  has been shown to exhibit a high resistance to compression relative to a low resistance to tension. When compressed, this compression stiffness increases with increases in length reduction, even prior to contact between the helical elements as is often necessary for conventional coil springs. The difference is particularly stark when viewed from the perspective of resistance to deformation (i.e. high spring constant) as a function of weight, with composite structure  10  having a much lower weight than that of the comparable conventional coil spring.  FIG. 2  illustrates this deformability, as composite member  10  may be deformed into any number of desired shapes or orientations that could not otherwise be made on, or even more likely not removed from, a conventional mandrel. As will be described in further detail below, after composite structure  10  is removed from the mandrel and the final shape or orientation is achieved, bonding may take place at the crossover points with a resin that may vary from low (pliable and elastomeric) to high resistance (stiff as that of the original resin infused in yarns  11  such as epoxy, vinyl esters, polyurethane, bismalemide, or other resin materials as are known in the art). 
       FIGS. 1 and 2  show composite member  10  as defining yarns  11  braided with a variable pitch angle along the longitudinal length of composite member  10 , producing helical structures that alters from high coverage area  12  to low coverage area  13  (i.e. tight spacing between the coils interspersed with wider spacing) which more greatly permit the flexible nature of composite member  10  described above (see  FIG. 2 ). An alternate embodiment of composite structure  10  may include yarns  11  similar in all respect as described but with a uniform pitch angle, producing a repeatable braiding pattern and coverage ratio along the longitudinal length of composite structure  10 . Such an orientation may include desirable structural or functional characteristics different than those defined by the variable pitch angle embodiment, but nonetheless should be construed as within the scope of the present invention. Additionally, or in the alternative, it is envisioned that sections of open structure composite member  10  may be interspersed with sections of rigid composites to provide for moderate shaft flexibility or to compensate for misalignment between structural elements. 
       FIG. 3  presents another alternate embodiment of composite structure  100 , whereby yarns  111 , similar in all respects to yarns  11  as described above, are deployed in substantially the same manner as described to produce composite structure  100  as structure  10 . As should be discerned unlike composite structure  10 , composite structure  100  defines a constant helix angle with a variable diameter component, producing composite structure  100  which defines narrowing section  112 , then widening section  113  in a conical or pyramidal structure. This type of configuration would be impossible to reproducibly braid on a conventional braiding machine, for at least the reason that the associated mandrel could not accommodate the resulting geometry. However, by braiding the structure in the manner disclosed herein, and later curing the crossover points for additional structural integrity as needed, entirely new structural geometries may be achieved that previously have been considered improbable or impractical to manufacture. 
       FIGS. 4 and 5  show elevated plan views of an alternate embodiment of composite structure  200 , braided with yarns  211  that are similar in all respects to yarns  11  as described above. As shown, unlike composite structures  10  and  100 , composite structure  200  is formed via a true triaxial braiding pattern. This pattern (see U.S. Pat. No. 5,899,134, incorporated by reference in its entirety herein), preferably includes axial yarns  211 ′ laid in the axial direction of composite structure  200  which bestows upon composite structure  200  surprising structural, compression, and bending advantages not found in the prior art. 
     A method of producing an open architecture, fiber-reinforced composite formed from large (i.e. high filament number) threads pre-impregnated with resin, formed into yarns, and braided without bonded crossover points into a composite member is also disclosed. A plurality of yarns  11 , defined by a high number (i.e. greater than 20,000 preferably at least 25,000, and more preferably between 50,000-100,000 but intended herein to be limited only by the ability to braid such yarns) of carbon filaments axially aligned and positioned within a jacket, are loaded onto a braiding machine such as a Maypole braiding machine. The yarns  11  are braided about a mandrel into a tubular woven lattice defining a biaxial braiding pattern defining a uniform pitch angle extending along the longitudinal length of the composite member. Alternatively, yarns  11  are braided about a mandrel into a tubular woven lattice defining a biaxial braiding pattern defining a variable pitch angle extending along the longitudinal length of the composite member. Alternatively, yarns  11  are braided about a mandrel into a tubular woven lattice defining a triaxial braiding pattern defining either a uniform or variable pitch angle extending along the longitudinal length of the composite member. In each case, the yarns  11  are spaced widely on the mandrel relative to the yarn spacing typical of a woven structural component, and the yarns may be cured to preserve their orientation and interwoven geometry, but great care is exercised in seeking to limit, and preferably avoid bonding between yarns  11  at any crossover point. In the preferred embodiment of the method, yarns  11  define a coverage factor (i.e. the degree of “openness” or exposure between respective yarns) of at least fifty percent (50%), and more preferably of at least seventy-five percent (75%). 
     The composite member is then removed from the mandrel and utilized as a spring, exhibiting superior compression, torsional, bending, and tension metrics compared to coil springs formed from metal materials. Any inadvertent bonding at crossover points may be broken upon removal to maintain desired flexion capabilities. Alternatively, the composite member may be cured to structurally reinforce the resulting composite member before deploying it as a spring. Alternatively, the composite member may be urged, bent, or otherwise manipulated to assume any number of shapes as desired, shapes that would not otherwise be possible with a mandrel defining a uniform or tapered exterior. An embodiment of one or more composite members as described above may include an exterior sleeve (not shown) formed from a pre-impregnated material as an added structural support without significant weight increase. The resulting composite member, regardless of exterior reinforcement, may then be cured to structurally reinforce the resulting composite member before deploying it as a spring. 
     Example 1 
     A cylindrical open composite structure made on a Maypole braiding machine from large, jacketed prepreg yarns similar to those in U.S. Patent Publication No. 2013/0302604 consists of two opposing sets of helical yarns interwoven in a biaxial pattern to produce an open lattice structure braided spring, in which the yarns were not bonded together at the crossover after curing. The braided structure is restricted in its compression by the necessity for the yarns to bend to accommodate the weave structure during compression. The resulting spring has a spring constant that is larger than the sum of the same number of helical springs made from the same yarn material at the same pitch and arranged in parallel. Unlike a helical spring, the woven structure relies on deformation modes other than torsion or compression of the spring element for development of the spring stiffness. 
     Example 2 
     A cylindrical open composite structure made on a Maypole braiding machine from large jacketed prepreg yarns similar to those in Example 1 consists of two opposing sets of helicals interwoven in a biaxial pattern to produce a braided spring, in which the yarns are slightly bonded together at the crossovers after curing. The lightly bonded structure may be compressed axially to break the bonds at yarn crossovers producing a braid equivalent in stiffness properties to the spring in Example 1. 
     Example 3 
     The spring of Example 1 was bent into a circular shape of twenty-six (26) inches inner diameter and one end threaded inside the other end to make a circular spring which was bonded at the overlapped ends with epoxy, then sprayed with a plasticized PVC and installed on a tire rim to produce a tire in the form of a spring which is suitable for use on a sandy granular surface, like a desert, a beach, a snowy surface, or on the surface of the moon. 
     Example 4 
     A tube was braided with three sets of large prepreg yarns (two helical sets and one set of axial yarns) and cured but without bonding yarn crossovers. The structure was limited in axial compression in the axial direction by the axial cured composite yarns; however, the structure was flexible and spring-like in bending and torsion modes. Such structures have potential as a drive shaft with some limited flexibility. A shaft of interspersed rigid and flexible sections is also envisioned. 
     Example 5 
     A braided open composite structure with two sets of helical yarns was produced using a process similar to Example 2 except that the braided tubular shape is rectangular with rounded corners. A spring with broken joints is formed into a path that may bend to change direction or to pass around obstacles that cause the path to deviate from a straight line. The braided open structure is suitable for a cable tray that is bent into a non-linear shape to follow a sinuous path after the joints are broken. Later the joints may be cured with a glue-like epoxy, with the braid now set and locked into the shape of the path. Alternatively, the cable tray may be mobile to facilitate actuation as is known in the art, for example on industrial automation machinery with cable management to supply a cutting head for a CNC (Computer Numerical Control) router. In either application, cables can now feed into the cable tray. 
     Example 6 
     A braided open structure spring was produced similar to Example 4, except that the axial yarns are not prepreg and do not form fiber-reinforced composite elements after curing. The axials in this case are unimpregnated textile yarns of the high performance fiber such as liquid crystal polymer (LCP), aramid, metal wire, or UHMPE (Ultra-high-molecular-weight polyethylene). The non-impregnated LCP yarns provide stability in bending deformation and in tension, but allow the structure to compress as those from Example 1 and 2. This example should not be considered to limit the type of yarn used for axials members in the respective structures. Other high perfoiniance fibers, including metal or synthetic embodiments, are envisioned as are high compliance fibers, for example elastomers. 
     Example 7 
     A cylindrical open composite structure formed and cured as described above (i.e. with unbonded crossover points), and covered, encased, or otherwise inserted into a sleeve formed from a resin pre-impregnated material (or alternatively, a braided sleeve that is later coated or impregnated with resin). The sleeved structure is then bent into any desired shape and the entire assembly is recurred to produce a stiffened, rib-shaped tubular structure. 
     The illustrations and examples provided herein are for explanatory purposes and are not intended to limit the scope of the appended claims.