Patent Application
20130004696
The present invention relates to components made of a thermoplastic composite material comprising fibers and thermoplastic polymer.
With the aim of replacing metal parts for weight savings and cost reduction while having comparable or superior mechanical performance, structures based on composite materials comprising a polymer matrix containing a fibrous material have been developed. With this growing interest, fiber reinforced plastic composite structures have been designed because of their excellent physical properties resulting from the combination of the fibrous material and the polymer matrix and are used in various end-use applications. Manufacturing techniques have been developed for improving the impregnation of the fibrous material with a polymer matrix to optimize the properties of the composite structure. In highly demanding applications, such as for example structural parts in automotive and aerospace applications, composite materials are desired due to a unique combination of lightweight, high strength and temperature resistance.
Thermoplastic composite materials are made using a fibrous material, such as non-woven structures, textiles, fibrous battings and combinations thereof, the fibrous material being impregnated with a polymer resin composition. There are various ways of making thermoplastic composite (TPC) materials, including lamination, pre-impregnation and powder impregnation. In the lamination method, layers of fibrous material and layers of polymer film are alternately stacked, to form a stacked structure. This structure is subjected to heat and pressure to result in impregnation of the fibrous material with the polymer. The result in this case is a sheet that is substantially consolidated, i.e. it has very little void content. Such thermoplastic composite materials are typically referred to as laminates.
In the pre-impregnation method, the fibrous material has molten polymer applied to it, for example by dipping, extrusion of a molten film, or by spraying. The result in this case is a less consolidated structure, in which the fibrous material is partially impregnated with polymer.
In the powder impregnation method, layers of fibrous material are constructed with layers of finely powdered solid polymer. The structure is then subjected to heat and pressure, resulting in impregnation of the fibrous material with the polymer. In this case the result is a sheet that is substantially consolidated, i.e. with very little void content.
Thermoplastic composite materials may be used to form components and impart structural strength thereto. In a typical use, the thermoplastic composite material is heated to render the polymer partially molten. It can then be shaped to enable it to be fitted in a mold. As soon as it is placed in the mold, the mold parts are closed, and the same polymer as in the thermoplastic composite material, or another polymer having compatibility with it, is injected into the mold to fully or partially encapsulate the thermoplastic composite material. The result is an overmolded article having the thermoplastic composite material within it to impart structural strength.
Often components made with thermoplastic composite materials need to be attached or fixed to other components, frames, structures, etc. This may be done, for example, by making the component with a hole therein, and inserting a means for connecting, such as a pin, bolt, rod or the like (a “connecting member”) to form a “pin-loaded hole”. Of course the hole and the placement of the connecting member creates an intrinsic weakness in the component, such that when severe stress is encountered, the part will likely fail at or around the hole.
The design of a joint in a thermoplastic composite material component traditionally aims to optimize the pin-loaded hole strength performance by varying the available parameters, such as hole diameter, laminate thickness and laminate lay-up (i.e. orientation of the fibers in the different fiber layers). This allows the designer to determine the most likely failure mode, and hence failure load of the pin-loaded hole. Different failure modes include: net section failure, where the material formed with the hole has a net cross-sectional area less than its area where there is no hole, so that the resulting reduced strength leads to a failure of the material in tension; shear bearing failure, where the connecting member crushes the material against which it bears (most common in isotropic materials and unusual for composite materials which are anisotropic); and rip-through failure, in which the connecting member rips through or tears out the material.
It is often desirable for components of vehicles to fail in a manner providing good energy absorption, because by absorbing energy in a collision less energy is available to damage other vehicle components. Although rip-through failure can provide the best energy absorption of the different failure modes in a pin-loaded joint design, the present inventors have recognised that it is possible to improve energy absorption during rip-through failure.
The present invention provides a component made of a thermoplastic composite material comprising fibers and thermoplastic polymer, the component having a hole defined therein for receiving a member to form a connection, and having reinforcement provided in the region of the hole and arranged to define a predetermined rip-through path to be followed by the member in the event that a failure load is applied.
The disclosure is directed to a component made of a thermoplastic composite material comprising fibers and thermoplastic polymer, the component having a hole defined therein for receiving a member to form a connection, and having reinforcement provided in the region of the hole and arranged to define a predetermined rip-through path to be followed by the member in the event that a failure load is applied.
By providing reinforcement in the region of the hole which defines a predetermined rip-through path to be followed by a connecting member, (such as a bolt, rod, pin or the like) in the event that a failure load is applied, the route of the rip-through path in the thermoplastic composite material of the component can be chosen to provide high energy absorption and give progressive failure of the structure. This is to be contrasted with a rip-through failure in a conventional component, where the failure path is determined by the lowest energy equation, or catastrophic fracture of the bulk structure away from the load introduction point, thereby limiting the energy absorbing potential of such a construction. When possible, the rip-though path will follow the route acquiring the least energy to progress. However, maximum energy absorption takes place when the maximum number of fibers needs to be broken for the ripping of the material to progress. Thus, for example, in an embodiment of the invention, the connecting member may rip through the material along a path breaking fibers which traverse the path resulting in energy absorption with each fiber breakage, the path being chosen to maximize the number of fibers broken along the length thereof. In a conventional construction the path of least resistance (but not of maximum energy absorption) would be one parallel to the fiber direction, or to the main fiber direction where there is more than one.
The connecting member may be suitably shaped to facilitate the rip-through the polymeric material in the event that a failure load is applied. Suitably shaped connecting members may be non-round connecting members having polygonal, square, rectangular or triangular cross-sections along their longitudinal axis. Other shaped connecting members may be connecting members having salient fins that facilitate the rip-through the polymeric material in the event that a failure load is applied. It will be appreciated by the person skilled in the art that the shape of the hole defined in the component should preferably be matched to the shape of the connecting member.
Whilst it is known to design ribs or fiber reinforcement around a hole to support a connecting member and to reduce the local stresses around the hole, thereby increasing the load carrying capability of the joint, these structures do not make provision for predetermining a rip-through path through the material, which can result in sudden catastrophic failure of the structure.
An additional problem is that with the manufacturing of a thermoplastic composite material the fiber placement will not be precisely as theoretically designed due to variations and inaccuracies in manufacturing processes. This can result in varying the failure path in an unpredictable way. This is even more the case when using thermoplastic composite sheets, whereby the final shape of the fabric structure or reinforcement is manufactured in a sheet stamping process. Variations in the failure path could result in deformation of the structure in an unforeseen or undesired way. Again, predetermining a rip-through path through the material can mitigate this problem.
By causing rip-through failure to occur in a preferred manner, energy dissipation can be controlled, and failure can be progressive. For example, in the case of a car seat frame, it is desirable that failure occur in a predictable, preferred manner to protect the passenger as much as possible.
The reinforcement which defines the predetermined rip-through path may be provided by additional fibers or by one or more ribs. The overmolding processes used to make thermoplastic composite materials provide the design freedom to provide such reinforcement. However, that design freedom may be used not just to strengthen the region around the hole, but also to define the failure path when a rip-through failure occurs to maximize energy absorption compared to an uncontrolled rip-through path.
The reinforcement may be arranged close to, but not exactly at a critical region where failure is expected to occur. Thus the rip-through path may be adjacent to the reinforcement. In certain preferred embodiments, the reinforcement is elongate and the rip-through path follows the length of the reinforcement adjacent thereto. An elongate rip-path may be straight or curved.
A pair of reinforcements may define the rip-through path therebetween. This arrangement may provide a clearly defined path in order to maximise the number of fibers broken during failure and the energy absorbed. The pair of reinforcements is preferably generally parallel to each other.
The rip-through path preferably will start at the hole and emanate away therefrom through the thermoplastic composite material. The path may extend radially from the hole. The path may emanate from the periphery of the hole and extend away therefrom in a direction at an angle intermediate between a radial direction extending from the center of the hole to the inner end of the path, and a direction tangential to the periphery of the hole at the inner end of the path. The path may extend in a direction at an angle to this radial direction (i.e. the radial direction extending from the center of the hole to the inner end of the path) which is between 1° and 90° , or 5° and 90°, or 10° and 90°, or 15° and 90°, or 20° and 90° , or 10° and 80°, more preferably between 40° and 50°.
In each case, the route of the path may be designed depending on the arrangement of fibers and in such a way that the maximum number of fibers traverse the path and are broken during failure.
The fibers comprised in the thermoplastic composite material may be staple or continuous fibers, and may be chosen among glass fiber, metal fiber, ceramic fiber, carbon fiber, or aramid fiber.
The fibers comprised in the thermoplastic composite material may be present in the form of one or more fibrous materials.
As used herein, the term “fibrous material” refers to any nonwoven textile, woven textile, knitted textile or non-crimped textile, which may preferably be in-plane with the thermoplastic composite material.
Suitable nonwoven textiles may be chosen from continuous random mats, chopped strand mats, or felts.
Suitable woven textile may be chosen for example, from un-biased weave textiles such as plain or basket weaves, twill or satin weave textiles; or biased weave textiles.
In the case where the fibers are present as a fibrous material such as woven textile, the fibers preferably extend in a first direction and in a second direction perpendicular to the first direction. Suitable non-crimped textiles can be chosen for example from unidirectional, biaxial, or quasi-isotropic textiles.
In a preferred embodiment, the thermoplastic composite material may comprise a combination of multiple layers of fibrous materials, such as for example a combination of nonwoven textile and woven or knitted textile. Examples of such a combination may be a layer of nonwoven textile and a layer of woven or knitted textile, a layer of nonwoven textile and two or more layers of woven or knitted textiles wherein the layer of nonwoven textile is placed between the two layers of woven or knitted textiles.
The component may further comprise a metallic element such as a sheet of metal having a channel, or groove, arranged to define a predetermined rip-through path to be followed by the connecting member in the event that a failure load is applied. Alternatively, the metallic element may also have a series of closely adjacent holes arranged to define a predetermined rip-through path to be followed by the connecting member in the event that a failure load is applied.
Preferably, the channel, groove, or series of closely adjacent holes in the sheet of metal are chosen in a way that the connecting member rips through the composite material along a direction substantially at 45° to the first and second directions of the fiber comprised in the component, such as to maximize the number of fibers broken along the length of said path. The component may further be weakened along the predetermined rip-through path to be followed by the member in the event that a failure load is applied by providing additional, closely adjacent holes along the rip-through path. Such holes may be obtained by drilling, machining or by modifying the mold for the component by, for example, adding pins where the additional holes are to be formed.
Other measures that modify the predetermined rip-through path to be followed by the member in the event that a failure load is applied may be areas in which the fiber comprised in the component is disrupted, i.e. where the fibers are displaced or partially fractured along the predetermined rip-through path such as to locally decrease the fiber content or strength along said rip-through path. Such disruption may be obtained by modifying the mold for the component by adding pins that are retracted mid-way through the molding cycle such that the fiber is disrupted and holes or slots previously occupied by the pins (e.g. pins shaped linear punches or knives) are then filled with polymer during the overmolding process.
Furthermore, at least two tapes of unidirectional textile parallel to each other, may be placed within the thermoplastic composite material along a direction substantially at 45° to the first and second directions of the fiber comprised in the component, such as to maximize the number of fibers broken along the length of the predetermined rip-through path to be followed by the connecting member in the event that a failure load is applied.
In a preferred embodiment, the thermoplastic composite material may have a reduced thickness along the predetermined rip-through path to be followed by the member in the event that a failure load is applied, which may be obtained for example by machining away part of said composite material or by modifying the mold for the component accordingly.
It is desirable to design the component such that the rip-through path starts or initiates at the location on the circumference of the hole where the reinforcement intersects the hole and where the reinforcement defines the predetermined rip-through path from the hole in the component.
There are many component designs which influence the location along the component hole where rip initiation begins. Any such method revolves around controlling the stress levels in the component.
For example, the thickness of the TPC sheet can be modified such that the thickness of the TPC sheet is less at the location where it is desirable for the rip initiation to occur. Rip initiation should then occur where the TPC sheet is thinnest as the TPC sheet will be the most stressed at this location.
The thickness of any overmolded polymer may also be used to effect the location of rip initiation. If the thickness of the overmolded polymer is less at the location where rip initiation is desired, rip initiation should occur where the overmolded polymer is thinnest as the overmolded component will be the most stressed at this location. The thickness of the TPC sheet may also be thinner at the same location that the overmolded polymer is at its least thickness.
The location of rip initiation can also be determined by mixing glass fiber and carbon fiber materials in the component such that in a global carbon fiber component, the area or location around the hole where rip initiation of the component is desired will comprise a lower concentration of glass fibers. During operation of the component, stresses during load introduction will locally exceed the load capacity of the component where the concentration of glass fibers in the component is lowest and force rip initiation to occur at this location. This same concept can be used by using steel cord or steel braid molded into the component structure. The location in the component where rip initiation is desired to progress will not comprise any steel braid or cord.
The thermoplastic composite material may comprise fibers extending in a first direction and fibers extending in a second direction perpendicular to the first direction, and the rip-through path may extend in a direction intermediate between the first and second directions. Thus, rather than failure occurring along a path parallel to one set of fibers and breaking the other set of fibers, it preferably occurs along a path which involves breakage of both sets of fibers. The path may extend in a direction substantially at 45° to the first and second directions.
The fibers extending in the first direction may have a greater fiber concentration than the fibers which extend in the second direction, and the rip-through path may extend in a direction at an angle α to the first direction and at an angle β to the second direction, the angle α being smaller than the angle β. The direction of the rip-through path may be chosen to ensure that fibers extending in both the first and the second directions are broken during failure, rather than the failure path extending parallel to one of the fiber directions.
The disclosure of the present invention could be used in any component made of a thermoplastic composite material where a controlled failure path and/or an increased energy absorption mechanism would be useful, such as components for vehicles, for example, automobiles, trucks, aeroplanes, space vehicles or rail vehicles. It may be useful in vehicle seat frames, lift gates, tail gates, side impact beams, bumper beams, trunks (boots), hoods (bonnets), parcel shelves, doors or any other component which may be critically loaded in a vehicle collision.
Certain preferred embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:
a and 3b respectively show the fibers in a thermoplastic composite material with a rip-through path of minimal energy and a rip-through path of maximal energy; and
a and 4b show another embodiment respectively show the fibers in a thermoplastic composite material with a rip-through path of minimal energy and a rip-through path of maximal energy.
Referring to
The component is shown when in use, with the connecting member 10 passing through the hole 2 to form a bolted joint. The hole 2 can therefore be regarded as a pin-loaded hole. If loading is applied to cause the bolt or rod to tend to rip through the material of the component in a generally upward direction as seen in
a schematically shows a first set of fibers 7 extending in a first direction, and a second set of fibers 8 extending in a second direction. In this case the fibers 7 extend perpendicularly to the fibers 8. The fibers are arranged in a so-called balanced weave, because they are of equal fiber concentration in both directions. A similar arrangement is shown in
b.
In
a and 4b show rip-through paths 5a and 5b similar to those shown in
The components according to the present invention may be used in a wide variety of applications such as for example as components for automobiles, trucks, commercial airplanes, aerospace, rail, hand held devices, recreation and sports, structural components for machines, structural components for buildings, structural components for photovoltaic equipment or structural components for mechanical devices.
Examples of automotive applications include without limitation seating components and seating frames, engine cover brackets, engine cradles, suspension arms and cradles, spare tire wells, chassis reinforcement, floor pans, front-end modules, steering column frames, instrument panels, door systems, body panels (such as horizontal body panels and door panels), tailgates, hardtop frame structures, convertible top frame structures, roofing structures, engine covers, housings for transmission and power delivery components, oil pans, airbag housing canisters, automotive interior impact structures, engine support brackets, cross car beams, bumper beams, pedestrian safety beams, firewalls, rear parcel shelves, cross vehicle bulkheads, pressure vessels such as refrigerant bottles and fire extinguishers and truck compressed air brake system vessels, hybrid internal combustion/electric or electric vehicle battery trays, automotive suspension wishbone and control arms, suspension stabilizer links, leaf springs, vehicle wheels, recreational vehicle and motorcycle swing arms, fenders, roofing frames and tank flaps.
Examples of recreation and sports include without limitation inline-skate components, baseball bats, hockey sticks, ski and snowboard bindings, rucksack backs and frames, and bicycle frames.
This application claims the benefit of priority to U.S. Provisional Application having the Ser. No. 61/503,109, which was filed on Jun. 30, 2011 and which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61503109 | Jun 2011 | US |
