GB2279085A

GB2279085A - Termination of thermoplastic composite tensile members

Info

Publication number: GB2279085A
Application number: GB9312572A
Authority: GB
Inventors: Michael William Commander
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-06-18
Filing date: 1993-06-18
Publication date: 1994-12-21
Also published as: GB9312572D0

Abstract

A tensile member 1, comprising longitudinally extending, collimated fibres in a thermoplastic resin matrix, is provided with an end fitting by locally heat-softening the matrix and moulding a flored portion within collar 2 by insertion of tool 3. The tool may be left in place and carry end fitting 5. Alternatively, the flored portion may form a solid hemi-sphere (Figs. 2 and 3, not shown). Matrix and fibre materials are disclosed. <IMAGE>

Description

TERMINATION OF THERMOPLASTIC COMPOSITE TENSILE MEMBERS This invention relates to thermoplastic composite tension members, the terminal fittings thereof and the method of forming such terminations.

Tension members used on pieces of infrastructure such as suspension or cable stayed bridges, rigging of sailing vessels and tension leg offshore platforms are usually made from metal in a wire or rod like form. Similarly control cables for such things as brakes (as used on bicycles, motor cycles, cars etc.), and clutch cables are also made from metal in a wire or rod like form. In common with all tethers, be they metal or composite there is the problem of terminating the tension member. In the early days of wire rigging, splicing with or without a thimble was the only way in which a wire could be terminated.Nowadays there are many ways to terminate wires including: swaging; Taluritm / NicopressaM range of swaged ferrules; NorsemanlM / Sta,lokTM swageless end fittings; and of course splicing.

The swaging process squeezes a hollow fitting into the wire under high pressure to 'flow' the fitting material between the strands of wire. Two type of machine may be used to achieve this - roll swaging and rotary hammer. Although the swaging process is commonly used there are a number of problems that may be encountered. For example: residual stresses in the material occur if the fitting has been badly made or overswaged; on the otherhand under-swaging can cause the fitting to work loose while under load; corrosion between the wire and fitting can occur when different grades of material are used; wire fatigue can be a problem on swaged fittings as the wire cannot move once it is in the swage part of the fitting.

The Talurit / Nicopress is similar to the swaging process in as much that a ferrule is squeezed onto the wire under high pressure between the dies.

The ferrule is usually a copper alloy and the system normally incorporates a thimble, either solid or hollow, around which the wire wraps before passing the loose end of the wire back through the ferrule.

The Norseman and Sta-lock are popular swageless end fittings. They consist of a split cone that compresses and holds the wire inside a tapered body. The wire strands must be unravelled to allow insertion of the split cone and then the wire strands can be carefully reformed. An end fitting can then be screwed into the tapered body which has been previously placed over the wire.

Splicing of wires is done in a similar way to splicing ropes and is still a popular method of fixing, particularly for the running rigging of sailing craft.

With all these processes, corrosion - can be a problem and care must always be taken to ensure no dissimilar metals are inadvertently covered in while making the end fitting.

Rods of metal have become more popular in recent years for tension members as they offer low stretch, reduced weight and lower windage.

They consist of solid bars in a range of diameters and materials, including Nitronic 50 (a nickel chromium molybdenum alloy), cobalt and titanium.

There are two ways of terminating metal rods - swaging and cold heading.

Swaging is done in exactly the same way as for wire swaging using the same end fittings. Since the swaged end fitting cannot flow in and around wire strands, the load carrying capability of a swaged fitting on a rod relies solely on the degree of compression set in the fitting.

The cold heading process involves clamping the end of the rod in a special die and applying high pressure to the end of the rod, producing a bulbous head. Before the rod is headed, a machined collar is slid onto the rod. This collar has a cup shaped hole in which the rod is seated - and is threaded internally to allow a machined eye or fork to be screwed into the collar.

Fatigue can be a problem with all such metallic tension members and their associated end fittings. They are also heavy and prone to fatigue and stress corrosion in adverse environments.

One way of overcoming the shortcomings of metallic tension members and their associated end fittings is to use thermoplastic composite materials.

Tension members that are made of continuous fibre reinforced thermoplastic composite, for example employing glass, carbon or aramid fibres in a matrix of thermoplastic polymer such as polyetheretherketone (PEEK), polyphenylene sulphide (PPS), polyethylene (PE) etc., in the form of a rod. The fibres are essentially collimated in the longitudinal direction of the tension member. Such tension members provide a high performance, corrosion resistant solution, are light in weight and have the potential for very high strengths and stiffness.

Terminating such thermoplastic composite rods in the ways described above (cold swaging and cold heading) is not recommended because of the damage that would occur to the fibre, hence reducing the load carrying ability of the tension member.

The reduction of such problems and the provision of a good load transfer path from the composite tension member, through and out of an end fitting, may be achieved in accordance with the invention by hot forming the member to locally increase its size. The load can then be transferred by a shearing action into a mating fitting which may be metallic, composite or made of other appropriate materials.

Thus, according to the invention, an elongate tension member comprises continuous, collimated fibre reinforced thermoplastic composite material wherein the axes of said fibres extend substantially parallel to the longitudinal axis of said member, said member further comprising an integral flared termination.

In one form of tension member according to the invention, said flared termination is substantially a hollow conical shape which tapers towards the remote end of said tension member. Preferably, a generally conical support member is retained in and relative to said termination.

In another form of tension member according to the invention, said flared termination is substantially hemisperical (or conical) in shape and reduces in diameter towards the remote end of said tension member.

Preferably, the tension member according to the invention comprises a hollow, load transfer member, which optionally is segmented or whole, having an internal shape complementary to the shape of said termination whereby, in use, load is transferable in shear from said tension member through said termination and said load transfer member.

If desired the tension member may incorporate sensing fibres for monitoring load etc..

The invention also includes a method of producing a tension member according to the invention, said method comprising surrounding an end of said tension member with a heated die, heating said end to a temperature at which the composite material is formable and applying pressure to said end to flare it and form said termination.

Preferably, a hollow, load-transfer member is located within said die around said end.

Preferably, when said end is flared to a hollow conical shaped termination, a complementary shaped flaring tool is optionally left in place and retained relative to said termination.

Two specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 illustrates a tension member according to a first embodiment and the method of making it; Figure 2 illustrates a tension member acording to a second embodiment and the method of making it; and Figure 3 illustrates the tension member of the second embodiment complete with stemball and coquille fitting.

Referring to Figure 1, a tension member (1) of a continuous collimated fibre reinforced thermoplastic composite material, for example carbon fibre / PEEK composite (available under the trade name APC-2 from ICI Composites Inc., Tempe, USA) has an integral flared termination (1A) surrounded by a collar (2), a hollow, load transfer member. The termination (1A) is a hollow, conical shape tapering towards the remote end of the termination (not shown). By incorporating additional composite material in the flared termination (1A), the wall thickness may kept constant, or varied as required. The collar (2), which optionally is segmented or whole - and may be metallic, composite or some other suitable material - has an internal shape complementary to the shape of the termination (1A).A flaring tool (3) shaped to compliment the internal flare of the the termination (1A) may optionally be left in place as the end fitting (5), a fork or eye, is connected to the collar.

To form such a termination to a tension member an appropriately sized hollow, load transfer member (2) is first slipped over the end of the tension member (1). The tension member, and optionally the flaring tool (3) and hollow, load transfer member (2) , is heated to a temperature at which the composite material is formable. The hollow, load transfer member (2) may be held in place by a die (for a given tension member size) (4). When the assembly is at an appropriate temperature, pressure is applied to the flaring tool (3) which is driven in the direction of arrow 'A'. The effect of temperature and pressure on the composite material of the tension member (1) sufficiently softens the thermoplastic resin allowing the composite to be formed to a conical shape. Upon cooling, a rigid conical structure is formed.

Referring to Figure 2, a tension member (1) of a continuous, collimated fibre reinforced thermoplastic composite material, for example APC-2 composite material, has an integral hemi-spherical termination (1A) surrounded by a hollow, load transfer member (2). The hollow, load transfer member (2), which optionally is segmented or whole - and may be metallic, composite or some other suitable material - has an internal shape complementary to the shape of the termination (1 A).

To form such a termination to a tension member an appropriately sized end fitting must be selected. In this case a stem ball (2), is placed over the end of the tension member (1) which is clamped in a die (for a given size of tension member) (3). The tension member, and optionally the stem ball (2) and die(3) , is heated to a temperature at which the composite material is formable. When the assembly is at an appropriate temperature, pressure is applied to the forming head (4) which is driven in the direction of arrow 'A'. The effect of temperature and pressure on the tension member (1) sufficiently softens the thermoplastic resin allowing the composite to be formed in to a hemi-spherical shape. Upon cooling, a rigid hemi-spherical structure is formed.

Figure 3 illustrates the tension member (1) and stemball (2) inserted into a coquille fitting (5) which may be attached, for example to a mast or other such object.

Claims

1) An elongate tension member comprising continuous, collimated fibre reinforced thermoplastic composite material wherein the axes of said fibres extend substantially parallel to the longitudinal axis of said member, said member further comprising an integral flared termination.

2) A tension member according to claim 1 in which said flared termination is substantially a hollow conical shape which tapers. towards the remote end of said tension member.

3) A tension member according to claim 2 in which a generally conical support member is retained in and relative to said termination.

4) A tension member according to claim 1 in which said flared termination is substantially hemisperical in shape and reduces in diameter towards the remote end of said tension member 5) A tension member according to claim 1 in which said flared termination is substantially conical in shape and reduces in diameter towards the remote end of said tension member.

6) A tension member according to any one of the preceding claims comprising a hollow, load transfer member having an internal shape complementary to the shape of said termination whereby, in use, load is transferable in shear from said tension member through said termination and said load transfer member.

7) A tension member according to any one of the preceding claims which incorporate sensing fibres.

8) An elongate tension member according to claim 1 substantially as herein before described with reference to Figure 1 or to Figures 2 and 3 of the accompanying drawings.

9) A method of producing an elongate tension member as defined in any one of claims 1 to 7 comprising surrounding an end of said tension member with a heated die, heating said end to a temperature at which the composite material is formable and applying pressure to said end to flare it and form said termination.

10) A method according to claim 8 in which a hollow, load-transfer member is located within said die around said end.

11) A method according to claim 8 or claim 9 in which, when said end is flared to a hollow conical shaped termination, a complementary shaped flaring tool is optionally left in place and retained relative to said termination.

12) A method according to claim 8 substantially as herein before described with reference to Figure 1 or Figures 2 and 3 of the accompanying drawings.