IES83965Y1 - A machinery link member - Google Patents

Description

The present invention relates to a construction of machinery link member of a fibre reinforced thermoplastics composite material having at least one connector hole for reception of a load transmitting element. It also relates to a process for manufacturing such a link element and a mould for use in such a manufacturing process.

Such link members are used extensively in all types of machinery. An example is a suspension rocker used in a motorcar, which suspension rocker, for example, may connect together various elements of a rear suspension such as the push rod, anti- roll bar, damper connection, central spring rod and a bearing connection to allow rotation. The dynamic loads applied by some of these elements can be as high as 50 KN in a racing car and the number of cycles imposed on the rocker are of the order of 60,000 cycles. indeed, the operating temperature of the rocker can be as high as 150°C.

There are many other similar link members used in machinery and equipment generally which undergo considerable dynamic loads. Currently, many of such members are made from aluminium or other lightweight metals in order to save weight. It is well known that carbon—fibre reinforced composites can offer stiffnesses and strengths per unit of weight between two and three times that, for example, of aluminium. Lower weight is particularly important for fast—moving elements in many performance equipment. Further, for many robotic equipment and any type of heavily loaded machine element, any reduction in weight and inertia is to be desired. This is particularly a problem, for example, with aircraft where weight saving is of considerable importance. Many other items such as gear selectors, lever arms and actuating bars may also be made.

There are many main areas for application on aircraft. The following lists four main areas for application on aircraft. This is not by any means an exhaustive list. The first group is for lateral wing and empennage structures. These aircraft assemblies contain_.numerous movables or control surfaces such as spoilers, ailerons, flaps or rudders. Every one of these components needs to be attached to the wing or empennage via hinges and actuators. At present, the attachment points are metallic. it these metal parts were replaced directly with a thermoplastics link machinery member, there would be a weight saving. Moreover, the thermoplastics link member could be integrated into the control surface thereby reducing the weight further by eliminating the need for fasteners or adhesives, and issues associated with dissimilar materials.

The second application relates to the centre wing box where the wings are attached to the aircraft fuselage. Typically, this highly loaded region comprises a space frame structure with the top and bottom surfaces connected by a lattice of composite struts.

To date, due to the high loads encountered, the end fittings of these struts have been metallic. The replacement of the metal end fittings with thermoplastic link members would reduce the weight and eliminate issues associated with dissimilar materials.

The third area for consideration is aircraft landing gear components such as side stay fittings or gear ribs. At present, these parts are large aluminium or titanium forgings.

It has been recognised that weight savings could be achieved if composite materials were used. However, for typical aerospace composite materials, the load introduction points would typically be metallic inserts. This reduces the weight advantage of employing composite materials and, as before, introduces issues associated with dissimilar materials. The use of thermoplastic link members would ensure that any weigh reductions were maximised.

The fourth area of application is in aircraft propellers, which are today largely composite structures, adhesively bonded to a metal machined element, which connects the propeller to the engine. The use of the metal connector adds greatly to the weight and inertia of the propeller. Use of a steered fibre thermoplastic connector would -significantly reduce the weight of the entire propeller and improve the performance. A single—piece propeller of thermoplastic composite material is also a possibility.

A further weight critical application is for space vehicles. There are many highly loaded brackets and supports were weight has to be minimised. Typically metallic materials have been used as the service temperature conditions exceed the properties of standard composite materials. Thermoplastics composite machinery members could satisfy both the weight and elevated temperature requirements.

The use of such a lightweight connecting element could be advantageous in space launchers. There are many types of supports, supporting arms, actuators, Such elements are today made from steel, for high stiffness and strength, and from connectors and other machine elements used in rocket launch engines. aluminium and titanium for lighter weight. The ability to decrease weight in the launcher means that increased payloads can be carried without the use of heavier, more powerful engines. The high expense of titanium can be compensated for by the lighter weight and higher operating temperatures, as compared to aluminium.

Such a thermoplastic composite element could be used to reduce weight in such space launcher engines, while providing similar stiffness to steel elements, similar weight savings as titanium, and enhanced temperature resistance, all at a lower cost than titanium. in particular, the type of fibre employed in the element can be varied between high modulus (and lower strength) and high strength (and lower modulus), as required to match stiffness and strength of the element.

Indeed, it is known to use thermoset composite materials or fibre-reinforced thermoplastic composite materials for many such applications. There are, however, certain problems with the use of these composite materials. Firstly, there is considerable difficulty in many of them operating at temperatures of the order of 150°C. Many of them, at this temperature, have long exceeded their glass transition temperature, meaning that their mechanical properties fall off dramatically at that temperature.

A further problem is that composite materials suffer badly in performance terms when the machinery link member has connector holes for reception of a load transmitting element. Such “load-bearing holes”, as they will often be referred to hereunder, suffer badly in performance terms, when the holes are simply machined from the carbon-fibre reinforced composite material. Thus, as mentioned above, there is the necessity to use metal inserts. Such link members are often subjected to alternating tensile and compressive loads which leads to further problems. Thus, a link member of a composite material may operate satisfactorily under tension but buckle and distort under compression.

When designing a composite material to take significant loading around holes, it is suggested that a tailored preform, where the fibres are arranged in such a way as to flow around the load-bearing hole, would offer performance improvements over simply machining the holes. However, it is extremely expensive to manufacture such a preform, and it can only be done in a dry fibre reinforcement, meaning that a further step of introducing the resin in a liquid form into the mould must follow. Further, this liquid—moulding process is only available with a number of resins and there are very few liquid—mouldable resins that can operate at temperatures of 150°C.

A particularly useful form of material is a commingled or co-blended thermoplastic composite yarn, such as has been disclosed in various patent specifications, for example, European Patent Specification No. 0466,618. In this material, both the reinforcing fibre, for example, carbon, glass or aramid, and the polymer matrix, are in the form of fibres which can be manipulated using standard textile techniques. The resulting preform has the consistency, or feel of a rope, which can easily conform to curved and complex mould contours and is thus particularly suitable for wrapping around the core of a mould when that core is used to form a hole. Upon application of heat and pressure, the polymer fibres melt and flow between the reinforcing fibres, thus expelling air from the preform.

The term link member is used broadly in this specification to cover not just a member connecting for example a driving member and a driven member but also a member linked to only one member i.e. the driver member. However all transmit a load such as an aircraft propeller does.

The present invention is directed towards providing a machinery link member of a thermoplastics composite material having at least one connector hole for reception of a load transmitting element, which machinery link member will overcome some of the problems of conventionally constructed machinery link elements of thermoplastic composite material. Further, the invention is directed towards providing a process for manufacturing such a machinery link element of a thermoplastic composite material and finally to a mould for a manufacturing machinery link element.

S1a1ements_o.t_1mu=.n;f.i.Qn According to the invention, there is provided a machinery link member of a fibre reinforced thermoplastics composite material having at least one connector hole for reception of a load transmitting element characterised in that the member comprises: a plurality of sheets of fibre reinforced thermoplastics composite material forming a laminate; and commingled fibres arranged adjacent the periphery of the hole.

The commingled fibres arranged around the periphery of the hole add greatly to the strength of the link member and, in many instances, obviate the need for any metallic reinforcing. in one embodiment of the invention, the commingled fibres arranged around the hole comprise a commingled yarn.

In another embodiment of the invention, the fibres arranged adjacent the hole extend of the order of half of the periphery of the hole. in another embodiment of the invention, the fibres are adjacent that part of the periphery of the hole under load when a tensile force is exerted on the link member.

In a still further embodiment of the invention, a sheet of fibre reinforced thermoplastics material comprises unidirectional fibres to form a unidirectional fibre reinforced thermoplastics tape.

In another embodiment of the invention, the tapes may be arranged with the unidirectional fibres oriented relative to each other to form crossing fibres from tape to tape or alternatively the fibres of at least some of the tapes are aligned at the hole substantially along the axis of the load exerted on the periphery of the hole.

The fibres may be one or more of boron, carbon, glass, aramid, para-aramid, ultra- high molecular weight polyethylene (UHMW PE), metal.

Further, the thermoplastics material may be one or more of PEEK, PEKK, PPS, PEI, PA—6, PA—12, PET, PETI-5, PBT, PP, and PE.

In another embodiment of the invention, the sheet is a woven fabric of commingled yarns.

In another embodiment of the invention, the sheets have different tensile and compressive properties.

Further, the invention provides a process for producing a machinery link member of a thermoplastics composite material having at least one connector hole for reception of a load transmitting element comprising not necessarily sequentially in a mould having a hole forming core for the or each hole: laying sheets of fibre reinforced thermoplastics material in the mould; arranging commingled thermoplastics fibres around the or each core; and applying heat and pressure to mould the link member.

In this latter process, the sheets may comprise unidirectional fibre reinforced thermoplastics tape with the unidirectional fibres of adjacent tapes oriented to cross each other.

In another way of carrying out the invention, the arranging of commingled thermoplastics fibres in the mould comprises laying a commingled yarn around the or each core.

In certain embodiments of the invention, subsequently the or each hole is machined out.

Further, the invention provides a mould for carrying out the process comprising a hole forming core of an outer diameter less than that of the subsequent hole which then has to be machined out.

In another embodiment of the invention, there is provided a mould for carrying out the process of the invention which comprises a hole forming core substantially semicircular in plan. With this latter construction of mould, the upright planar face of the core may be substantially orthogonal to the axis of the application of a subsequent load on the hole and spaced-apait from the part of the subsequent hole under compression.

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The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which: Figs. 1(a) to 1(c) are plan views of three test specimens used in accordance with the invention, Figs. 2 and 3 illustrate the results of some tests on the specimens of Fig. 1, Figs. 4 and 5 are perspective views of a composite rear suspension rocker arm, manufactured in accordance with the invention, Fig. 6 is a schematic view of portion of a mould used to form the rocker arm, Fig. 7 is a plan view showing the orientation of a commingled thermoplastic carbon-fibre yarn in a mould, Fig. 8 is a photograph of the layout of the commingled thermoplastic carbon- fibre yarn in the mould, Figs. 9(a) to (c) are schematic plan views of carbon-fibre reinforced thermoplastic tapes used in accordance with the invention, Fig. 10 is a photograph showing one of the tapes of Figs. 9 in a mould, Fig. 11 is a view showing various stress patterns of the rocker arm, _Fig. 12 illustrates the results of a test on the rocker arm of Figs. 4 and 5.

Figs. 13(a) to (c) show the formation of a push rod in accordance with the invention, Fig. 14 illustrates some compression tests on the push rod, Fig. 15 illustrates some hole tensile strengths on the push rods, and Fig. 16 diagrammatically illustrates the formation of a hole in a machine link element.

In this invention, carbon-fibre reinforced polyetheretherketone (PEEPQ was used.

PEEK is a semi-crystalline thermoplastic polymer which has a glass transition temperature of 145°C. Thus, it can be used at a temperature of 150°C or so, without any serious drop-off in mechanical property. PEEK, however, has a very high melt temperature (343°C) and a high viscosity in the melt, which means it can not be used to liquid mould into a tailored fibre preform, as with more conventional methods.

The process according to the invention is to make the part in a press—moulding process, using a combination of unidirectional pre-impregnated tape (in the flat sections of the rocker), with selective use of commingled fibres around the load- bearing holes. The press moulding was obviously done at an elevated temperature.

The importance of using the commingled fibres is that testing has shown that their use can increase the tensile strength of a composite Ioad—bearing hole by as much as %, as will be described below.

Referring now to Figs. 1(a) to 1(c), three types of link member were moulded in a thermoplastics carbon—fibre nylon material. The holes were all to 20.60mm, the diameter of the highest loaded hole in the rocker arm, described below with reference to the other figures. The edge of the hole was located 3.6mm from the outside of the specimen. Seven test specimens were produced. Two were made where the commingled woven fabric was laid up and the hole was machined postproduction.

Two more were made where the individual commingled fibres were orientated around the pin and two where a commingled rope fabric was laid around the hole. The final specimen had commingled rope fabric orientated around the outside of the specimen with no pin insert and the hole was then machined out. The specimen layups are shown in the drawings.

Four of these specimens were tested in tension and the other three in compression.

The results of these tests are given in Tables 1 and 2 below. In tension, the specimens which had the fibre orientations around the outside of the pin were over % stronger than the woven fabric which had the hole machined out. The specimen which had the rope fibres orientated around the outside edges and the hole then machined out performed as well as the one with the formed hole using the rope fabric. In compression, the specimen that performed best was the one made of woven fabric which had the hole machined out. The specimens with the orientated fibres only had 80% the strength of the specimen with the machined hole, in compression.

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Specimen Layup Type Tensile Bolt Bearing St. (MPa) O1-jor/BB4 Figure 1(a) 107.7 01-jor/BB5 Figure 1(b) 114.1 O1-jor/BB6 Figure 1(c) 76.1 iv O1—jor/BB7 Figure 1(a) 107.4 Iable_2 Specimen Layup Type Compression Bolt Bearing St. (MPa) L O1-jor/BB8 Figure 1(c) 163.0 O1-jor/BB9 Figure 1 (a) 142.0 O1-job/BB1O Figure 1(b) 123.0 Figs. 2 and 3 show the full results.

Referring to Figs. 4 and 5, there is illustrated the composite rear suspension rocker, indicated generally by the reference numeral 1, having holes 2, 3, 4 and 5.

Fig. 6 shows, in diagrammatic form, a mould 10 having cores 11 for the formation of the rocker arm 1.

Fig. 7 shows how commingled yarn is laid around the cores, the yarn is identified by the reference numeral 12 in this drawing.

Fig. 8 shows the commingled yarn 12, again laid around the various cores.

Referring now to Fig. 9, there is illustrated sheets of fibre reinforced PEEK forming tapes, indicated generally by the reference numeral 15, with various patterns of layout of the reinforcing, such as, for example, at 145°, as shown in Fig. 7(a), 120°, as shown in Fig. 7(b) and then at 90° to each other, namely at 0° and 90° in Fig. 7(c).

Fig. 10 shows one of the pre—impregnated unidirectional tapes formed laid again in the mould. To form the rocker arm, a plurality of laminated sheets of carbon—fibre reinforced PEEK, namely tapes 15, are laid in the mould 10 and the commingled fibre and thermoplastic yarn 12 is formed around the various cores 11. Then, the mould is subject to heat and pressure, and the rocker arm 1 was formed.

Fig. 11 illustrates the stresses experienced by the rocker arm 1 in use in an automobile racing engine and Fig. 12 shows the results of the test on the rocker arm 1.

Referring to Fig. 13, there is illustrated various push rods, similar in shape to those of Fig. 13(a) shows commingled CF/PEEK yarn wrapped around a push rod hole and Fig. 13(b) shows Fig. 1, which were formed using CF/PEEK pre—pregnated. commingled CF/PEEK yarn extending into the push rod. Fig. 13(c) shows laminates similar to those of Fig. 9.

The results of the testing push rod hole strengths are given in Tables 3 and 4 below.

It was found that the use of more pre impregnated tapes led to higher compression strength and the significant buckling occurred when the specimens were too thin.

IABLE3 C .|.l Compression No. of layers of No. of layers of No, of layers of Specimen 1 2 3 Max Force (kN) Strength (MPa) Tensile Specimen Max Force (kN) Strenqth (MPa) O1—.lor/BB21 15.1 1241.6 —.Jor/BB22 14.0 939.2 Table 5 below illustrates the test on further push rods of the same construction which were manufactured from 7mm CF/PEEK specimen. It will be seen from Table 4 that the best results were obtained from specimens BB25 and BB26 which had machined holes. These compression tests are illustrated in Fig. 14.

To summarise tables 3 & 5 show the compression results and illustrate that the best compression results are achieved by machining the holes, with no fibre wrapping, of the type shown in either Fig. 13 (a) or Fig. 13 (b) Table 4 shows the high tensile strengths achieved using the fibre wrapping illustrated in Fig. 13 (b) IABLE5 Specimen No. of layers of No. of layers of No. of layers of Max Force (kN) Strength (MPa) Fibre 1flap_ Fibre E@ Presjbreg 01-Jor\BB25 0 0 14 44 4 352 8 01~Jor\BB26 6 6 12 39 5 283 5 01—Jor\BB27 0 12 12 390 2763 O1«.Jor\BB28 6 6 12 39.0 279 6 O1—.lor‘BB29 0 0 14 46.1 328.8 The conclusion to be drawn from the results shown in tables 3, 4 & 5 is that the best results in tension are achieved by fibre wrappings of the type shown in Fig.13 (b), whereas the best results in compression are achieved by maximising the use of prepreg as shown in Fig 13 (c).

Fig. 16 illustrates diagrammatically the formation of the hole in a D-shape, namely, a semi—circular shape. It is proposed that a D-shaped moulded hole as illustrated in Fig (b) and 13(c) which is subsequently machined as a circular shape, would offer maximum tensile and , with reinforcements of the types shown in Fig. 13. compressive properties.

It is envisaged that tape such as illustrated in Fig 13(c) could also be made from what is essentially a woven fabric of false impregnated yarn It will be appreciated that there are many ways of making such fibre impregnated tape such as by heating films and powdered polymers to form sheets. This may be carried out by sandwiching powdered polymer and fibres between polymer sheets and heating to form a cohesive tape.

It is also important to appreciate that many different fibres of different materials such as boron, carbon, glass, aramid, para - aramid, ultra high molecular weight polyethylene (U H M W P E) and many metals may be used. These will be chosen for the properties required of the link member. It is envisaged that the one link member will incorporate many different fibres. For some applications, it may be desirable to mix high modulus of elasticity and high strength fibres together.

In the specification the terms “comprise, comprises, comprised and comprising” or any variation thereof and the terms “include, includes, included and including” or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

The invention is not limited to the embodiment hereinbefore described, but may be varied in both construction and detail.

Claims (3)

1. A machinery link member (1) of a fibre reinforced thermoplastics composite material having at least one connector hole (2, 3, 4, 5) for reception of a load transmitting element characterised in that the member comprises: a plurality of sheets of fibre reinforced thermoplastics composite material forming a laminate; and commingled fibres comprising a commingled yarn (12) arranged adjacent the periphery of the hole (2, 3, 4, 5).

2. A machinery link member (1) as claimed in any preceding claim, in which a sheet of fibre reinforced thermoplastics material comprises unidirectional fibres to form a unidirectional fibre reinforced thermoplastics tape (15), the tapes (15) being arranged with the unidirectional fibres oriented relative to each other to form crossing fibres from tape to tape.

3. A machinery link member (1) as claimed in any preceding claim, in which the fibre is one or more of: boron, carbon, glass, aramid, para-aram id, ultra-high molecular weight polyethylene (UHMW PE), metal and the thermoplastics material is one of: PEEK, PEKK, PPS, PEI, PA—6, PA—12, PET, PETl—5, PBT, PP, and PE. A machinery link member substantially as described herein with reference to and as illustrated in the accompanying drawings. A process for making a machinery link member as claimed in any preceding claim substantially as described herein.