The invention relates to shaped terminations for composite tension members, as well as methods for creating such shaped terminations.
The leisure marine industry relies upon strong and lightweight tension members for a number of applications, including various types of rigging for sailboats. High-performance sailboats can benefit greatly from the use of tension members that combine high tensile strength, high modulus, resistance to corrosive salt-water environments, light weight, durability, and reduced cross section. However, optimization of these features can involve significant trade-offs, particularly between those affecting light weight and cross section vs. durability.
Carbon fiber based tension members offer an attractive combination of the qualities listed above; however they suffer from the inefficiencies common to many fiber-based tension members including a vulnerability to unequal loading of the component fibers. In applications where the fiber bundle is loaded such that the majority of the load is applied only to a subset of the component fibers, the overall tensile strength of the member is reduced, and an immediate or gradual cascading failure of the fibers can result.
In general, where a consolidated grouping of fibers is bent while under tension, the fibers on the outside of the bend will bear an increasing share of the load, while the innermost fibers will slacken. The application of carbon fiber tension members to sailboat rigging can create regions that are particularly susceptible to uneven loading of the component fibers. Rigging generally also ends in a terminal of some type, in addition to applications where rigging is bent continuously around a structure such as a mast. These terminals, if not thoughtfully designed, may incorporate bends, loops, or knots that result in unequal fiber loading. Accordingly, there have been a number of attempts to address this problem.
A known terminal system for composite tension members is disclosed in U.S. Pat. No. 7,137,617 (Sjostedt). It includes a tension cable comprising a plurality of composite rods bundled together into a composite cable. The ends of this composite cable are splayed out and embedded into a fitting having an internal cavity that flares outwardly, where they are held by adhesives and/or in an interference fit using wedges or plugs adapted to fit the internal cavity of the fitting. However, the anchoring strength of the splayed material is dependent upon the bonding and frictional forces provided by the wedges and/or adhesives. When the included angle of the internal cavity flare is low, the tension member is subject to pulling out if the tensile forces exceed the friction imparted by the wedging forces and/or adhesive. If the included angle of the internal cavity flare is high, excessive stress can be concentrated upon individual components of the splayed material at the angle, increasing the likelihood of successive individual component breakage, and premature failure of the tension member.
Another system for terminating tension members is disclosed in U.S. Pat. No. 3,660,887 (Davis). It includes a tension cable comprising a plurality of fibers. The ends of this cable are spread within a fitting having an internal cavity, and a potting compound is cast in place within the fitting in order to surround the cable with a closely conforming complimentary surface. However, like U.S. Pat. No. 7,137,617, the spread fibers are subject to pull-through and excessive individual stresses.
What is desired therefore is a composite tension member having a terminal with characteristics that address these deficiencies.
It is an object of the invention to provide a shaped terminal to a composite tension member. Ideally, this shaped terminal will be consolidated into a solid mass that is substantially uniform in structure. This arrangement has the advantage of ensuring that the components of the tension member at the terminal are durably fixed into an optimized arrangement for the intended loading configuration, such that unequal stresses are minimized.
Tension members may comprise a thermoplastic rod or bundle of rods comprising a thermoplastic resin and a high strength and high modulus carbon fiber or other fiber.
Objects of the invention are achieved by forming a terminal using heat and pressure to shape and fuse the carbon fiber composite into geometries having favorable loading characteristics. The forming of the terminal geometry can be completed by re-forming existing material, or by adding additional material, which can be the same thermoplastic, epoxy or other resin/fiber composite material in the form of tow, tape material, mat or bulk; to the inside, outside, or throughout the tension member. The fill of the epoxy or thermoplastic can be nano-fibers, chopped fibers, unidirectional fibers, or other fibers. The terminal may be machined and/or thermoformed before and/or after the addition of material.
Terminal geometries can include, but are not limited to: frustum, concave head, convex spherical head, conical taper, eye (e.g. material wrapped around pin and fused back onto itself), threaded (male and female), overlap joint, unidirectional tube overlap joint, laminate, flatten-and-overlap, two-into-one (butt-joint, diagonals onto verticals) and so forth.
The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.
a-c are section views illustrating the steps of inserting materials into a void created in the end of a tension member according to various embodiments of the invention.
a-e are section views illustrating the creation of a void and insertion of materials into the end of a tension member according to an alternative embodiment of the invention.
a-d are section views illustrating the insertion of a material part into the end of a tension member according to an alternative embodiment of the invention.
a-d are section views of various bends and joins of tension members according to an alternative embodiment of the invention.
a-c are section views of the formation of a shaped terminal using two coordinating dies according to an alternative embodiment of the invention.
a-h are section views of example geometries into which shaped terminals may be formed, and corresponding collar shapes which may be used in order to create the geometries.
a-c illustrate an arrangement for creating a shaped terminal by adding material prior to initial consolidation according to an alternative embodiment of the invention.
In all figures and embodiments, second end 4 can be formed into a consolidated shaped terminal (not shown) in the same manner as described for first end 3.
a illustrates a die 31 adapted to accept the split end 29 which is described with respect to
b illustrates a filled end 33 which is created as described with respect to
c illustrates a consolidated shaped terminal 34 created as described with respect to
Here, in a first step 38, a plurality of composite rods, fibers, tow or tape are first arranged to form a bundle having a first end and a second end. In second step 39, the first end is consolidated by placing it into a die and applying heat and pressure to the end while it is within the die to create a consolidated end comprising a substantially unified structure. In an alternate embodiment, the first end is consolidated by wrapping it with a heat-shrink tape prior to placement within the die. In another alternate embodiment, an initial pre-consolidation is applied to the first end where it is compressed and reformed using heat and pressure such that an exterior profile of the bundle is given a smaller cross-section and/or a desired shape, and such that at least some interstitial spaces between the resin/fiber composite rods, fibers, tow or tape are removed or reduced; In other alternative embodiments, the die may also be transported along the length of the bundle to form continuous consolidated regions of arbitrary length, as in the preferred embodiment. In third step 40, the consolidated end is drilled axially to create a drilled consolidated end.
In fourth step 41, a spiked plunger is inserted into the drilled, consolidated end axially to create a voided end having a void by applying heat and pressure. Here, the drill hole may serve as a pilot hole for insertion of the spiked plunger.
In a fifth step, 42, the voided end of the previously consolidated end of the bundle is filled to create a filled end by adding thermoplastic and/or composite material to the void that was created by drilling and plunging. In an alternative embodiment, the material added to the void can comprise a metal or metal alloy, or other suitable material. In a sixth step, 43, the filled end is consolidated by placing the filled end into an appropriately shaped die; and applying heat and pressure to the end while it is within the die to create a shaped terminal that is consolidated and substantially unified in structure, and where the shaped terminal has an outer end disposed toward, or substantially coincident with, the end of the tension member; an inner end disposed toward the center of the tension member; and where the outer end of the shaped terminal has a dimension that is greater than a corresponding dimension of the inner end of the shaped terminal.
a-e illustrate the alternative embodiment of the invention, wherein a void is created in a drilled consolidated end of a tension member using a spiked plunger.
a illustrates a drilled consolidated end 44 of a tension member 45 showing drill hole 46. Drill hole 46 may serve as a pilot hole for the insertion of a spiked plunger 47. Spiked plunger 47 is aligned axially with drilled consolidated end 44 such that it may be plunged axially into drilled consolidated end 44 in order to create a void (not shown).
b illustrates the end 50 of the tension member 45 which is held within a die 48. Spiked plunger 47 has been plunged axially into the end 50 of the tension member such that upon removal, a void (not shown) will have been created in the drilled consolidated end (shown in
c illustrates a voided end 49 of the tension member 45 which is held within die 48. A plunger has previously been applied to the drilled consolidated end (not shown) as described with respect to
d illustrates a filled end 53 of a tension member which is held within die 48. A material has previously been inserted into a voided end as described with respect to
e illustrates a shaped terminal 54 to a tension member which was created as described with respect to
a-d illustrate an alternative embodiment of the invention wherein a preformed material is plunged axially into the tension member. This arrangement, or any portions of this arrangement, may be used in combination with any of the embodiments described herein to replace or compliment steps for adding material to the tension member end.
a illustrates the arrangement of a die 58, a material 59, which may have a spiked shape and in various embodiments may comprise one or more of a thermoplastic and/or composite material, a metal or metal alloy, or other suitable material, and a plunging arm 60, which is adapted to position material 59.
Here, in a first step 63, a plurality of composite rods, fibers, tow or tape are first arranged to form a bundle having a first end and a second end. In second step 64, the first end is consolidated by placing it into a die and applying heat and pressure to the end while it is within the die to create a consolidated end comprising a unified structure. In an alternate embodiment, the first end is consolidated by wrapping it with a heat-shrink tape, and applying heat to the end while it is wrapped with the heat-shrink tape.
In third step 65, the consolidated end is inserted into a thermoplastic or composite part having the shape of a collar or other shape such that the material surrounds the consolidated end to create a surrounded end.
In fourth step 66, the surrounded end is consolidated by placing the surrounded end into an appropriately shaped die; and applying heat and pressure to the end while it is within the die to create a shaped terminal that is consolidated and substantially unified in structure, and where the shaped terminal has an outer end disposed toward, or substantially coincident with, the end of the tension member; an inner end disposed toward the center of the tension member; and where the outer end of the shaped terminal has a dimension that is greater than a corresponding dimension of the inner end of the shaped terminal.
a-f illustrate further embodiments of the invention wherein the consolidation techniques described herein are applied to other sections of the tension member, or to multiple tension members.
a illustrates a tension member 70 comprising a bundle 71 of thermoplastic or composite rods, fibers, tape, or tow, that has been consolidated in one or more mid-span portions 72 by the application of heat and pressure using a die (not shown) as described with respect to
Because a bundle of individual, small-diameter thermoplastic rods is more flexible than a comparatively large-diameter solid thermoplastic rod; in some embodiments, one or more mid-span lengths of tension member 1 can be left as individual, separate thermoplastic rods, while other mid-span lengths are consolidated. This has the advantage of providing one or more bending locations to coil the entire assembly for shipping, storage, or other purposes. In alternate embodiments, heat and pressure can be applied to sections of the bundle, using a die or heat-shrink tape as developed above, using a degree of heat and/or pressure that is lower than that used to fuse and consolidate the bundle. The temperature and/or pressure used are selected such that the thermoplastic rod components of the bundle are not fused. Rather, the components are caused to deform to a degree such that the exterior profile of the tension member is given a smaller cross-section and/or a desired shape, and such that some, or all interstitial spaces between the components are removed. This is performed in such a way that the components of the tension member retain their independent movement and remain under equal tension. This can have the combined advantage of providing a section that is flexible for bending as above, but also exhibits desirable drag and windage characteristics.
b illustrates the use of heat and pressure 73 to join consolidated end portions 74 of two separate tension members 75 such that the joint comprises a consolidated and substantially unified structure.
c illustrates the use of heat and pressure 76 to join the consolidated end portion 77 of one tension member to the consolidated mid-span portion 78 of a separate tension member such that the joint 79 comprises a consolidated and substantially unified structure.
d illustrates the use of heat and pressure 80 to bend an unconsolidated mid-span portion of a tension member 84, having components under equal tension, around a form 82 having a radiused surface 83. This method creates a radiused mid-span portion 81 comprising a consolidated and substantially unified structure. In alternative embodiments, heat and pressure 80 is applied using methods developed herein incorporating a die (not shown) or using heat-shrink tape (not shown). By forming a radiused mid-span portion 81 in this way, the resulting tension member 84 can be fastened around similarly radiused objects such as mast spreader bends with a reduction or substantial elimination of weakening due to imbalanced loading of the composite structure of the tension member at the site of the radius. This can have the advantage of increasing the tensile strength of a tension member used for such applications.
a illustrates an alternative embodiment of the invention where tension member 85 is placed into a die 86, such that the region of tension member 85 closest to tension member end 87 is within the die 86, and a portion of tension member end 87 protrudes from die 86. In
a-h illustrate various example geometries into which consolidated shaped terminals may be formed using the methods described above, and corresponding collar shapes which may be used in order to create these geometries according to alternative embodiments of the invention as described above. These shaped terminal geometries (
a-c illustrates an alternative embodiment of the invention which includes adding material to the tension member end prior to consolidation. This embodiment is similar to the preferred embodiment described above with respect to
a illustrates an arrangement where a plurality of composite rods, fibers, tow or tape are first arranged to form a bundle 97 having a first end 98 and a second end 99. First end 98 is placed within a die 100, and the component materials forming the bundle 97 within the die 100 are arranged in a suitable pattern such as a distributed, conical, or other pattern, such that interstitial spaces exist within the first end 98. The materials may be arranged by feeding them through a disk with a suitable arrangement of holes, a loom, or another suitable method (not shown). Bundle 97 is then tensioned such that its individual components are under equal tension. The tensioning may be achieved through the application of weights to the individual components, or by another suitable method (not shown). A channel 102 is disposed within die 100 such that materials (not shown), which may comprise composites, thermoplastic resins, or other materials, may be added to the interstitial spaces within first end 98.
b, illustrates the arrangement where materials have been added to the interstitial spaces within the first end 98 via channel 102. First end 98 is consolidated by applying heat and pressure to while it is within the die 100 to create a consolidated end comprising a unified structure. Surplus end materials 103 which protrude from the die may subsequently be sliced or removed in a suitable manner from the first end 98 in order to form a shaped terminal (not shown) that is consolidated and substantially uniform in structure.
c illustrates the resulting consolidated shaped terminal 104 formed as described regarding
This application claims priority pursuant to 35 U.S.C. §119(e) and 37 CFR §1.78(a)(4), to provisional Application No. 61/356,992, filed Jun. 21, 2010, the content of which is incorporated herein by reference.
Number | Date | Country | |
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61356992 | Jun 2010 | US |