Minimal weight composites using open structure

Abstract

Preforms for open structured (lattice) composite tubular members manufactured from large (i.e. high filament count) prepreg yarns on a conventional maypole braiding machine, and subsequently cured to produce fiber reinforced composites of high strength and light weight.

Claims

1. An open structure composite member comprised of a plurality of jacketed yarns, each comprised of a plurality of tows pre-impregnated with resin and defining a core formed from at least twenty thousand (20,000) axially aligned filaments, the tows packed within a jacket, wherein the plurality of jacketed yarns are combined and cured to form an open structure composite member, and wherein the open structure composite member is formed at a rate of at least one meter per minute.

2. The composite member of claim 1 further comprising jackets formed from tows pre-impregnated with resin.

3. The composite member of claim 1 whereby the jackets are formed from a material selected from the group consisting of aramids, polyethylene, nylon, polyester, polyolefin, and liquid crystal polymer.

4. The composite member of claim 1 whereby the jackets are formed from one of braiding, yarn wrapping, or thermoplastic extrusion.

5. The composite member of claim 1 further comprising axially aligned filaments selected from the group consisting of carbon fiber, para-aramid, liquid crystal polymer, and glass.

6. The composite member of claim 1 comprising jacketed yarns defining a braiding architecture selected from the group consisting of diamond, twill, hercules, biaxial, triaxial, and true triaxial patterns.

7. An open structure composite member comprised of a plurality of jacketed yarns each comprised of a plurality of tows pre-impregnated with resin and defining a core formed from at least twenty thousand (20,000) axially aligned filaments, the tows hexagonally packed within a jacket, wherein the plurality of jacketed yarns are combined and cured to form an open structure composite member.

8. The composite member of claim 7 further comprising jackets formed from tows pre-impregnated with resin.

9. The composite member of claim 7 whereby the jackets are formed from a material selected from the group consisting of aramids, polyethylene, nylon, polyester, polyolefin, and liquid crystal polymer.

10. The composite member of claim 7 whereby the jackets are formed from one of braiding, yarn wrapping, or thermoplastic extrusion.

11. The composite member of claim 7 further comprising axially aligned filaments selected from the group consisting of carbon fiber, para-aramid, liquid crystal polymer, and glass.

12. The composite member of claim 7 comprising jacketed yarns defining a braiding architecture selected from the group consisting of diamond, twill, hercules, biaxial, triaxial, and true triaxial patterns.

13. A method of forming an open structure composite member comprising the steps of: providing a plurality of jacketed yarns each comprised of a plurality of tows pre-impregnated with resin and that define a core formed from at least twenty thousand (20,000) axially aligned filaments packed within a jacket; combining the plurality of jacketed yarns; and curing the combined jacketed yarns to form an open structure composite member.

14. The method of claim 13 wherein providing a plurality of jacketed yarns includes providing jackets formed from tows pre-impregnated with resin.

15. The method of claim 13 wherein providing a plurality of jacketed yarns includes providing jackets formed from a material selected from the group consisting of aramids, polyethylene, nylon, polyester, polyolefin, and liquid crystal polymer.

16. The method of claim 13 further comprising the step of interlacing the open structure composite member with a yarn, the yarn oriented laterally within said open structure composite member.

17. The method of claim 13 further comprising the steps of: exuding resin from the plurality of pre-impregnated tows; mechanically interlocking the plurality of tows; and bonding the plurality of tows that contact the resin at a crossover joint.

18. The method of claim 14 further comprising the steps of: exuding resin from the plurality of pre-impregnated jackets; mechanically interlocking the plurality of jackets; and bonding the plurality of jackets that contact the resin at a crossover joint.

19. The method of claim 15 further comprising the steps of: partially melting the jackets; and bonding the jackets at a crossover joint.

20. The method of claim 13 further comprising the steps of: reinforcing the open structure composite member with a plurality of braided sleeves; infusing resin into the plurality of sleeves; adding resin at a crossover joint; and curing the open structure composite member with a plurality of braided sleeves.

Description

BRIEF DESCRIPTION OF FIGURES

(1) Figure:

(2) FIG. 1. Drawing of a maypole braiding machine,

(3) FIG. 2. Side view of open structure member with circular cross section and z direction interlaced strengthened joints,

(4) FIG. 3. Cross section of open structure member with circular cross section and z direction interlaced strengthened joints,

(5) FIG. 4. Elevated end view of an open structure member having a true triaxial braid structure,

(6) FIG. 5. Open structure member produced having a true triaxial braid structure,

(7) FIG. 6. 3-D space frame used for human powered vehicle, “moonbuggy”, Multiple open structure members assembled into a much larger truss structure,

(8) FIG. 7. Triangular and hexagonal cross section truss and triangular truss members in perspective view—produced by strategic placement of axial yarns, possibly on a triangular or hexagonal mandrel,

(9) FIG. 8. Formation zone of open structured member on a maypole braiding machine, and

(10) FIG. 9. Open structured member with small yarn stabilization of joints in side view and enlarged side view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT AND OPERATION OF THE INVENTION

(11) The structures of this invention are embodiments of open structure composite tubular members (101) produced on a maypole braiding machine (103) utilizing very large (i.e. high filament count) prepreg yarns (102) with filament (113) counts from 20,000 (20K) up to 100,000 (100 k) or more. Prepreg yarns (102) are jacketed by braiding, yarn wrapping or extrusion of thermoplastic sheath 110. FIG. 1 is a diagram of a typical maypole braiding machine (103), although it will be appreciated by one skilled in the art that such braiding machines are available in a variety of sizes—both physically and in the number of carriers (111) on the machine. Typical carrier (111) numbers on a machine range from 4 up to 1000. Bobbins (104) for carriers (111) range from 3 inches up to 3 feet and more. Tubular members (101) that can be made using this invention and method can be scaled up in size from the examples produced to illustrate this patent. Tubular members (101) in the following reduction to practice are all produced on a 32-carrier or 64-carrier Wardwell maypole horizontal braiding machine

(12) FIG. 2 shows a side view of an open structured tubular member (101) in cylindrical form defining a truss and having eight longitudinally extending and parallel oriented axial yarns (105) and eight helical braided yarns (106), four in each rotational direction. Tubular member (101) was braided on a cylindrical mandrel (108) as shown in FIG. 5 and after curing was removed prior to insertion of four “z” prepreg reinforcing yarns (107), also commonly referred as cross yarns, strut yarns, or through-the-thickness yarns, which were subsequently cured in place. FIG. 3 is a drawing of the cross section of open structured tubular member (101) in FIG. 2.

(13) FIG. 4 is an elevated end view of jacketed yarn 102 exhibiting a true triaxial configuration, in which prepreg filaments 113 (also referred to as “tows” that define a yarn core) are hexagonally packed within jacketed sheath (110). FIG. 5 is an enlarged, elevated side view of an embodiment of jacketed yarn (102) defining a true triaxial configuration, which may be used for to form open structured tubular member (101). This orientation is identified by the interlacing of respective helical yarns (106) at a position “offset” or spaced from from their engagement with axial yarns (105). The “offset” engagement coupled with the over/under interlacing demonstrated in FIGS. 4 and 5 bestows jacketed yarn (102) and any resulting open structured member (101) with improved structural stability and crush-resistance relative to other braided members. In a braiding hierarchy, tows (113) are collected within jacketed sheath (110) and other yarns, for example axial yarns (105) and smaller helical yarns (106), may be braided therearound. Resulting jacketed prepreg yarn (102) may then be braided to form open structure member (101) is described in the examples below.

(14) FIG. 8 shows a picture of the prepreg yarns (102) as they transition from the carrier (111) yarn packages to the braid consolidation point (fell point, not shown) of tubular member (101). One skilled in the art will immediately understand that the size and shape of the braid openings as well as the diameter of tubular member (101) are determined by the number of prepreg yarns (102), the speed of the braiding head, the speed of the take up, and the size of any mandrel (108) inserted into the center of the forming tubular member (101). It will also be understood that the mandrel (108) cross section can be any polygon shape (FIG. 7) or any convex curved elongate shape. The mandrel (108) may also vary in cross sectional size along its length.

Example 1

(15) An embodiment of tubular open structured member (101) was made according to the teaching of this invention, but similar in size and weight per unit length to an energy drink can and similar in size and weight to a prepreg single-layer woven sleeve constructed of carbon fiber and epoxy resin. Open structure member (101) was made from a 36 k assembled prepreg carbon yarn (102) (from TCR Composites and formed from filaments 113 as illustrated in FIG. 4) with eight helical yarns (106) serving as the jacket. The jacket yarns were 200 denier Vectran™ yarns which were braided around the 32K prepreg tow (113) core. Jacket 110 itself is formed from eight helical yarns (106) and eight axial yarns (105) arranged in a true triaxial configuration. The composite open structured member (101) was made on a 32-carrier maypole braider (103) with four helical yarns (106) and four axial yarns (105) in the true triaxial structure (as shown in FIG. 5). In the true triaxial structure, the axial yarns (105) interlace with the helical yarns (106). Crossover joints (112) in open structure member (101), which are defined as positions where two or more yarns contact one another via braiding, were reinforced with additional epoxy resin. Both the aluminum can and the single-layered cured prepreg weave could be easily crushed by hand, but the cured open structure member (101) could not be crushed by hand, demonstrating the superior stiffness and strength of open structure member 101.

Example 2

(16) An embodiment of tubular open structured members (101) similar to that disclosed in Example 1 may be assembled into larger structures like that shown in FIG. 6. FIG. 6 is a drawing of a framework for a human powered vehicle for a student “moonbuggy” competition at NASA's Marshall Space Flight Center. The framework was constructed of cylindrical open structured members (101) defining a plurality of trusses produced in accordance with the teachings of this invention using the z direction reinforcement (107) yarn and crossover joints (112) shown in FIGS. 2 and 3.

Example 3

(17) An embodiment of tubular open structure member (101) may be constructed using jacketed 36k carbon prepreg yarns (102)—namely, three axial (105) and eight helical (106) prepreg yarns—in a true triaxial configuration. A mandrel (108) of triangular cross section was used. Each helical prepreg yarn (106) was flanked by 2 Kevlar™ 1000 denier yarns (109). Open structure member (101) was cured on the mandrel (108) to set the shape and then the smaller Kevlar™ flanker yarns (109) for example shown in FIG. 9, and the crossover joints (112) were coated with resin before curing again. The Kevlar™ flanker yarns (109) were on either side of the cured prepreg yarns (102). The flanking yarns (109) helped to stabilize the crossover joints (112) between respective yarns (105) and (106). The geometry of open structure member (101) is shown in FIG. 9.

Example 4

(18) An embodiment of tubular open structure member (101) may be constructed using 8 axial (105) and 8 helical (106) jacketed 36 k prepreg carbon tows on a maypole braiding machine (103) set up for true triaxial braiding. The mandrel (108) was a 1.5 inch diameter pipe with a 1.5 inch diameter sleeve of braided fiberglass covering the pipe. The open structured member (101) and sleeve were painted with liquid resin and then cured. The structure had significantly greater strength and stiffness than the same open structure member (101) without the added sleeve.

Example 5

(19) An embodiment of tubular open structure member (101) of example 4 was taken before painting with resin and was covered with an non-prepreg embodiment of jacket (110), namely a 1.5 inch diameter braided fiberglass sleeve. The mandrel (108) with its 3 layers was vacuum bagged and vacuum infused with liquid epoxy resin before curing. The composite open structure member (101) was very strong and supported a 200 pound person standing and jumping on the side of the structure (101). In this configuration, as in Example 4, the lattice structure of open structure member (101) with a sleeve can be viewed as rib stiffened cylindrical structure which on larger scale might be useful as a pipe, tank or rocket motor.

Example 6

(20) An embodiment of tubular open structure member (101) was constructed using jacketed prepreg carbon yarns (102) on a maypole braiding machine (103). The structure used four (4) 36 k axials (105) and sixteen (16) helicals (106) (eight (8) 36 k helicals and eight (8) 72 k helicals). The helical yarns (106) were arranged in two (2) sets of four (4) yarns each with the smaller (i.e. 36 k yarns) two in the center and the larger (i.e. 72 k yarns) two flanking either side. The prepreg yarns (102) were braided on a 2.5 inch diameter mandrel (108). The crossover joints 112 were strengthened and reinforced by painting with additional epoxy resin before curing. The product was used as a drive shaft by a student team in a formula style race car for intercollegiate competition. The axials (105) and helicals (106) were interlaced into a titanium gear to transmit the power. The structure had a 75% weight saving over the metal drive shaft it replaced.

REFERENCES

(21) Manual of Steel Construction, 8th Edition, American Institute of Steel Construction, 1987 Hou, A., Gramoll, K., Compressive Strength of Composite Lattice Structures, Journal of Reinforced Plastics and Composites March 1998 17: 462-483 Hou, A., Gramoll, K., Fabrication and compressive strength of the composite attachment fitting for launch vehicles, J of Advanced Materials, 2000, vol. 32, not, pp. 39-45 Jensen, M. J., Jensen, D. W., Howcroft, A. D., Continuous Manufacturing of Cylindrical Composite Lattice Structures, TEXCOMP10 Recent Advances in Textile Composites, edited by Christophe Binetruy, François Boussu, 2010, p. 80-87 Mouritz A., Gellert, E., Burchill, P., Challis, K., Review of advanced composite structures for naval ships and submarines, Composite Structures, 2001 Zhang, Q., Beale, D., Adanur, S., Broughton, R. & Walker, R., Structural Analysis of a Two-dimensional Braided Fabric, Journal of The Textile Institute, Volume 88, Issue 1, 1997, pages 41-52 Wilson, Kipp and Ridges, U.S. Pat. No. 8,313,600: Method and system for forming composite geometric support structures, Nov. 12, 2012 http://www.geostrut.net/home/

U.S. PATENT DOCUMENTS

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(23) A method of forming embodiments of open structure composites members (101) as described above is also provided and may include the steps of providing a plurality of resin pre-impregnated yarns (102) which preferably include a thermoplastic sheath or jacket (110) braided, wrapped, or extruded therearound. Each yarn (102) is formed from a core of resin pre-impregnated filaments (113), sometimes collectively referred to a “tow”. In the preferred embodiment, at least twenty thousand (20,000) filaments (113) are axially aligned and combine to four one or more tows that are packed into jacket (110). The plurality of yarns (102) are then combined, for example by braiding on a maypole braiding machine (103) as described above, and cured so that the braided yarns (102) form an open structure composite member. In some embodiments, jackets (110) include resin pre-impregnated jackets, and these pre-impregnated jackets may themselves be fainted from tows pre-impregnated with resin. The jackets (110) may be formed from a material selected from the group consisting of aramids, polyethylene, nylon, polyester, polyolefin, and liquid crystal polymer.

(24) The pre-impregnated nature of filaments (113), yarns (102), and jackets (110) may be quite advantageous, as the pre-impregnated resin may exude from one or more of filaments (113), yarns (102), and/or jackets (110) during or after the combination of yarns (102) as described above. Particularly in view of the number of filaments (113) at issue, to exude resin after the yarns have passed through the braiding machine is advantageous as to try and utility such yarns with surface-located resin would render the braiding operation practically non-functional. By mechanically interlocking the exterior surfaces, specifically adjacent portions of jackets (110), for example by allowing the resin to harden following a partial melting of the jacket surface, the resulting engagement or “crossover joint” (i.e. where one jacketed yarn (102) intersects or “crosses” another) is significantly more structurally reinforced than it otherwise would be. This similar mechanism may also be used with yarns (102) that do not include jackets (110), and instead exude resin directly from one yarn (102) to another. Additionally, or in the alternative, an open structure composite member (101) may include an additional, laterally-oriented yarn (102) to interlace with said open structure composite member (101) to define a new geometry or reinforce a particular feature of the existing geometry.

(25) Additionally, or in the alternative, one or more open structure composite members (101) may further include an exterior sleeve formed therearound. Such a reinforcing sleeve may be pre-impregnated with resin, or it may be receptive of resin exuded from yarns (102). By infusing resin into the sleeve, for example by exuding the resin from yarns (102) which the sleeve surrounds, additional resin may be imparted on surfaces where the sleeve comes in contact with braided yarns (102), creating a further advantageous structure relative to the prior art.