Abstract:
A novel composite beam is disclosed. The composite beam may comprise variations in the surface that can be used to create open and closed surfaces for the modulation of natural light. The composite beam may also be optimized for the applied loads by placing the fibers in the direction of the applied loads and/or increasing the fiber density in the regions of higher loads.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 61/587,832 filed on Jan. 18, 2012, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Composite structures comprise high strength fibers held together in a matrix of thermoset or thermoplastic resin. A panel made from these materials is typically 1.5 times stronger and 7 times lighter than the same panel made of steel. It is therefore desirable to have improvements in composite structures to facilitate their increased use in various applications. 
       FIELD OF THE INVENTION 
       [0003]    The present invention relates generally to building materials and, more particularly, to composite beams. 
       SUMMARY 
       [0004]    Embodiments of the present invention provide a novel composite beam that is well-suited for use in construction of building structures. The composite beam is often many times lighter than a beam of conventional materials such as concrete or steel, while offering improved strength characteristics. Beams can be assembled into a series of joined units to form complete long span support systems such as for roofing applications. Each truss can be mass customized allowing variations in the surface that can be used to create open and closed surfaces for the modulation of natural light. Such customized fiber architectures can be optimized for the applied loads by placing the fibers in the direction of the applied loads and/or increasing the fiber density in the regions of higher loads. The system is lighter and stronger than conventional construction systems. 
         [0005]    In one embodiment, a beam is provided, having a first end and a second end, and comprising a plurality of composite tape windings arranged with a varying pitch along the length of the beam. 
         [0006]    In another embodiment, a beam is provided, the beam comprising: a first portion having a first cross section; a second portion having a second cross section; and a third portion having a third cross section, wherein the beam is comprised of multiple composite tape windings. 
         [0007]    In another embodiment, a beam is provided, the beam comprising: a first portion having a first cross section; and a second portion having a second cross section, wherein the beam is comprised of multiple composite tape windings, and wherein the composite tape windings comprise thermoplastic impregnated fibers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings in which: 
           [0009]      FIG. 1  shows a perspective view of a composite beam in accordance with an embodiment of the present invention. 
           [0010]      FIG. 2  shows a detailed view of an alternative embodiment of a composite beam. 
           [0011]      FIG. 3A  shows an end view of the embodiment of  FIG. 2 . 
           [0012]      FIG. 3B  shows detail of  FIG. 3A . 
           [0013]      FIG. 4  shows a view of a composite beam in accordance with an additional embodiment of the present invention. 
           [0014]      FIG. 5  shows a view of a composite beam during the fabrication process. 
           [0015]      FIG. 6A  shows a view of a composite beam in accordance with an additional embodiment of the present invention. 
           [0016]      FIG. 6B  shows an example of a winding mold. 
           [0017]      FIG. 7  shows a view of a composite beam in accordance with an additional embodiment of the present invention. 
           [0018]      FIG. 8  is a flowchart indicating process steps for fabrication of a composite beam in accordance with an embodiment of the present invention. 
           [0019]      FIG. 9  is a block diagram of a system for fabrication of a composite beam in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  shows a perspective view of a composite beam  100  in accordance with an embodiment of the present invention. Beam  100  is comprised of one or more composite tape windings  102 . “Windings” is used herein interchangeably with “strips”. The tape windings may be S-glass tape strips or plies, or any other suitable material. In some embodiments, the composite tape may be translucent. The tape windings are arranged to form a triangular cross-section C. The tape windings may be arranged via Computer Automated Fiber Placement technology (AFP). AFP is a relatively new fabrication process that provides fundamental changes in the way people think about space, structure, and program. Fiber placement machines employ a robotically controlled taping head to lay down fiber reinforced plastic strips on a reusable mold or “mandrel”. Because the forms AFP creates are incredibly strong, rigid, and corrosion resistant, they are also able to handle dynamic mechanical loads without the need for an independent structural armature. 
         [0021]      FIG. 2  shows a detailed view of an alternative embodiment of a composite beam  200 . Reinforcing tape strip  204  travels longitudinally along the beam length, serving as a reinforced edge. Multiple tape windings (indicated as  202 A and  202 B) form the cross-sectional shape of the beam. While the embodiment shown has a triangular cross section, other shapes are possible, such as square, circular, or rectangular, as well as other shapes, all of which are included within the scope of the invention. Some embodiments may have non-constant cross-sections. Each winding is wound with a pitch P, which indicates the spacing between successive windings of the material. In some embodiments, the pitch P may vary over the length of the beam. Each winding is placed with reinforcing angle A, which is the angle of a winding relative to reinforcing tape strip  204 . The pitch P and angle A can be varied to create composite beams for various applications. In some embodiments, a beam may have multiple portions, where each portion may vary the reinforcing angle and/or pitch. In some embodiments, the beam has a first portion with a reinforcing angle ranging from about 72 degrees to about 80 degrees, and a second portion has an angle ranging from about 60 degrees to about 68 degrees. In some embodiments, the beam has a first portion with a pitch ranging from about 0.125 inches to about 1 inch, and a second portion has a pitch ranging from about 1.5 inches to about 2 inches. 
         [0022]    In some embodiments, the width W of winding  202 B may range from about 0.25 inch to about 1 inch. In some embodiments, the pitch P may range from about 3 inches at its maximum to about 0.125 inch at its minimum. In some embodiments, the widest pitch of the beam may be between 3 to 4 times the width W of a winding. In some embodiments, the smallest pitch of the beam may be between 0.1 to 0.5 times the width W of a winding. In some embodiments, the angle A may range from about 45 degrees to about 80 degrees. In some embodiments, the angle A may range from about 65 degrees to about 80 degrees. In some embodiments, the beam  200  may have a constant reinforcing angle A throughout the length of the beam. In other embodiments, the beam may have a reinforcing angle A that varies along the length of the beam. A higher value for reinforcing angle A may be used in conjunction with a narrower pitch P, and a lower value for reinforcing angle A may be used in conjunction with a wider pitch P. For example, a beam may have a first section with a pitch P of 3 inches and a reinforcing angle A of 65 degrees, and a second section with a pitch P of 1 inch and an angle A of 80 degrees. The narrower pitch P and larger angle A result in more tape windings per unit area in the second section, which increases the strength of that section. The wider pitch P and smaller reinforcing angle A result in less tape windings per beam unit area in the first section, which increases the amount of light that can pass through that section of a beam. 
         [0023]      FIG. 3A  shows an end view of the composite beam  200  of  FIG. 2 . In this view, the crossing pattern  306  of two tape strips is visible. The close-up view of  FIG. 3B  shows the pattern  306  creates a void  309  where no winding material exists. Unlike beams of conventional manufacture, where material is actively removed by drilling or punching, beams in accordance with embodiments of the present invention only use the material that is required. Hence, if voids are specified as part of the design of a beam in accordance with embodiments of the present invention, no additional material is wasted to form the desired voids. 
         [0024]    For a given area B, a percentage of the area T is occupied by tape windings  302 , and a percentage of the area V is occupied by voids  309 . The beam tape density, which is the amount of tape per unit area of beam, is defined by T/B, where B is the total unit area, and T is the amount of beam area occupied by tape windings (strips). When a unit area is completely occupied by tape, T=B, and the beam tape density is 1. With more voids, the tape density is less than one. The lower the tape density, the more light is able to pass through that area of the beam. In some embodiments, the tape density of a beam may range from about 0.2 to 1. In other embodiments, the tape density of a beam may range from about 0.4 to about 0.8. When designing a beam, considerations for choosing a beam tape density for a given section of beam include considering the weight support requirements for the beam, and the desired amount of light that can pass through the beam. Ventilation needs may also be considered, as more air can pass through sections of beam with lower beam tape density. 
         [0025]      FIG. 4  shows a view of a composite beam  400  in accordance with an additional embodiment of the present invention. In this embodiment, the pitch varies from a maximum pitch Pmax at each end of beam  400  to a minimum pitch Pmin in the middle of the beam. Hence, the beam can be divided into multiple sections or regions, each having different tape densities (the amount of tape per unit area). End regions  432  and  436  have a wider pitch than middle section  434 . The variation in pitch can be used to achieve certain architectural and/or aesthetic design goals. For example a wider pitch can be used reduce the beam tape density, and allow light to pass through the beam, whereas a smaller pitch (higher beam tape density) can be used when it is desirable to restrict light. Likewise, a smaller pitch may be used where structural load requirements are greater. 
         [0026]    In some embodiments, beam  400  may have three beam tape density regions ( 432 ,  434 , and  436 ). The end regions  432  and  436  may have an average beam tape density that is lower than middle section  434 . In some embodiments, the beam tape density may continuously vary throughout the length of the beam. For example, in beam  400 , the beam tape density increases from a minimum value at end  433  to a maximum value at midpoint  435 , which is equidistant between end  433  and end  437 , and then back to the minimum value at end  437 . In some embodiments, the maximum beam tape density value is 1, meaning completely occupied by tape, with no voids in that area. 
         [0027]      FIG. 5  shows a view of a composite beam during a representative fabrication process. A fabrication system  500  applies individual fiber “tows” or windings using a computer-numerically controlled robotic taping head. Thermoplastic impregnated fibers are melted together by a heating element that travels over a preformed shape. When the part is cooled, it is removed from the mold. Using computer aided design (CAD) data, a part&#39;s fiber orientation can be designed to exact structural specifications. Fabrication system  500  comprises a mandrel  540 . The mandrel is a metal tool or mold used as a surface to lay down the strips of fiber reinforced composite tape  542 . In some embodiments, “shapeable” mandrels may be used to ‘mass customize’ complex forms in a single production run. Altering tape geometries on the fly is another way to produce variable components from a single tool. A robotic gantry mechanism  544  is used to apply the tape  542  to the mandrel  540  as the mandrel is rotated by chuck  548  which is driven by a computer-controlled motor (not shown). Tape is supplied from spool  546 . While  FIG. 5  illustrates an exemplary embodiment, it will be obvious to one skilled in the art that other suitable fabrication means may be used to place suitable reinforcements in the desired patterns to achieve the innovative truss structure. Such other suitable fabrication means include different fiber placement mechanisms and different materials. 
         [0028]      FIG. 6A  shows a view of a composite beam  600  in accordance with an additional embodiment of the present invention. In this embodiment, the widest pitch Pmax is at one end of the beam, indicated by end  607 A. The pitch gradually decreases towards the other end  607 B of the beam, at which point, the pitch is the smallest (Pmin). Increased fiber plies in a section allow for a less densely packed fiber layout in elevation. This strategy of reciprocation also helps reduce surface buckling.  FIG. 6B  shows a winding mold  640  used for making beam  600  of  FIG. 6A . 
         [0029]      FIG. 7  shows a view of a composite beam  700  in accordance with an additional embodiment of the present invention. In this embodiment, the beam has a varying cross section. The beam has three logical regions (portions): end regions  742  and  746 , and middle region  744 . The end regions  742  and  746  have a square cross section, and middle region  744  has a triangular cross-section. The cross-section shape gradually transitions at the intersection of the middle section  744  with each neighboring end section ( 742 ,  746 ). In another embodiment, the middle region  744  is circular instead of triangular. Any feasible shape of each section is included within the scope of the invention. 
         [0030]      FIG. 8  is a flowchart  800  indicating process steps for fabrication of a composite beam in accordance with an embodiment of the present invention. In process step  802 , the path of the tape is computed. This step may be performed via a computer executing a software program. The software program may take in to account various design goals such as cost, required strength, the anticipated load type and direction on the beam, and aesthetic issues such as appearance and translucency. Once the path of the tape is computed, the tape is applied in step  804 , for example, by using a system such as that shown in  FIG. 5 . The tape is applied to a mold or mandrel. Then, once the tape application step  804  is complete, the mold (or mandrel) is removed in process step  806 , leaving the composite beam intact. 
         [0031]      FIG. 9  is a block diagram of a system  900  for fabrication of a composite beam in accordance with an embodiment of the present invention. System  900  comprises a computer  901 . Computer  901  comprises a processor  902  and memory  904 . Memory  904  may comprise flash memory or other non-volatile storage technology. Memory  904  contains machine instructions, that when executed by processor  902 , communicate with tape dispensing system  908  to apply strips of tape to a mandrel or mold. Memory  904  may also contain machine instructions, that when executed by processor  902 , compute the desired path of the tape based on design requirements for the particular beam that is being fabricated. 
         [0032]    Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, certain equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more features of the other embodiments as may be desired and advantageous for any given or particular application.