Patent Description:
The pursuit of lightweight structures has driven the advancements and commercial use of composite materials. The high strength-to-weight ratio of composite materials is highly dependent upon the layup direction of the fibres, and quickly starts to lose this characteristic as the fibres deviate from load direction to include more of a transisotropic behaviour (all-around strength).

Among the first proponent of fibre-metal hybrid materials and their use as aerospace grade material was TU Delft where <CIT>) described a composite laminate consisting multiple layers of metal sheets and fibre layers bonded together via an adhesive. The metal sheets are made from aluminum alloys and proposed to have a thickness of. <NUM> to <NUM> and the fibre/adhesive layer is sandwiched between the metal sheets. The laminate structure was proposed to be a suitable material for aircraft skin.

However, in certain examples (like heavily loaded joints), the all-around (in all direction) increase in strength by adding multiple plies bulks up the structure and increase the weight of component thus defeating the purpose of using composite materials for "high strength to weight ratio" gains. <CIT> claims to provide a solution for this problem by proposing the use of metal reinforcements in the heavily joint areas, particularly mechanically fastened joints as a virgin CFRP composite is susceptible to delamination around the fastening holes. The metal reinforcements (layers) are inserted while laying up the multiple plies of a composite panel (or beam) such that the fibres of the panel area (non-joint area) are continuous throughout the joint area, thereby meaning that increase in the joint area thickness is same as the thickness of said reinforcements.

For large-scale production and cost-effectiveness, it is necessary to have low cycle times during production. <CIT> laid down the basic concept for the fast manufacture of multi-material layered structure. It proposed the forming of a metal/reinforced thermoplastic layup through a rapid-stamping process where the metal layer act as clamping support and provides structural integrity during heating, prior to forming into complex 3D shapes. <CIT> discloses a frame of fibre reinforced thermoplastic material with metal plate like fittings.

Current art and general methodology include the addition of composite layers in the critical load-path of a component. General practice is to include multiple layers of fibre/polymer composite in a single direction (UD) or in varying directions to improve planar strength in all directions. To reduce the weight, each layer can be custom cut via laser to add holes or perforations of desired shape. However, this layup philosophy of building each layer as a closed surface geometry leaves some discontinuous fibres in each layer that are not contributing to overall strength and stiffness of the material but rather contributes to bulk mass.

The present invention relates to a reinforcement composite frame (<NUM>) comprising:
at least one-layer set, wherein each layer set comprises:.

In one embodiment each metal sheet (<NUM>) is either on top of each second prepreg strip (<NUM>) at each intersection area (A) or between each first (<NUM>) and second (<NUM>) prepreg strips at each intersection area (A).

In one embodiment each of the second prepreg strips (<NUM>) intersects each of the first prepreg strips (<NUM>), making an angle of <NUM>° and <NUM>° between them, preferably an angle of <NUM>°.

In one embodiment the composite further comprises a discontinuous prepreg layer (<NUM>) laid subsequently to each extremity of each metal sheet (<NUM>).

The present invention also relates to a process for producing the reinforcement composite frame (<NUM>) comprising the steps of:.

In one embodiment each metal sheet (<NUM>) is positioned in a different orientation than each metal sheet (<NUM>) of the subsequent layer set, forming a staggered positioning of the metal sheets (<NUM>).

In one embodiment each metal sheet (<NUM>) is <NUM> to <NUM>% different in size than each metal sheet (<NUM>) of the subsequent layer set, forming a staggered position.

In one embodiment each metal sheet (<NUM>) is either placed on top of each second prepreg strip (<NUM>) at each intersection area (A) or between each first (<NUM>) and second (<NUM>) prepreg strips at each intersection area (A).

In one embodiment a discontinuous prepreg layer (<NUM>) is laid subsequently to each extremity of each metal sheet (<NUM>), depending on the disparity between the prepreg and metal sheet (<NUM>) thickness.

In one embodiment, on top of the frame (<NUM>) is over-molded a bulk-part (<NUM>) made of lightweight formable material selected from thermoplastic sheets or short fibre composite mats, or fabricated via injection moulding using thermoplastic pellets, originating a reinforced part (<NUM>).

The present patent application provides a thermoplastic-based fibre-metal laminate reinforcement composite frame which is an optimal compositional solution for building a lightweight structure. The present patent application also provides the manufacturing process of said reinforcement frame.

For a high production volume application, on top of the frame (<NUM>) is over-molded a bulk-part (<NUM>) made of lightweight formable material selected from thermoplastic sheets or short fibre composite mats, or fabricated via injection moulding using thermoplastic pellets, originating a reinforced part (<NUM>). The reinforcement frame is proposed to be made of single direction (UD) fibre composite. The layup of reinforcement frame (<NUM>)) is at the centre of this invention. Furthermore, an addition of metal layers at the intersection areas is proposed to benefit the attachment hole behaviour. The invention also proposes method of placement of metal layers.

In one main embodiment of the present patent application, it is disclosed herein a reinforcement composite frame that comprises multiple layers of unidirectional thermoplastic prepreg, wherein each prepreg layer is placed on top of each other and arranged in an intersecting pattern so that each layer has an orientation arranged at angle between <NUM> and <NUM>°, preferably <NUM>° to the subsequent layer, thus forming a mesh-like structure or frame, wherein a smaller metal layer / metal sheet is placed after each intersection of prepreg layers in order reinforce those areas that are more prone to suffer multidirectional tensions. In one preferable embodiment, the reinforcement frame disclosed herein is a mesh-like structure. The prepreg layers comprise any fibre suitable for composite construction, for example glass, carbon or aramid fibres. The metal layers comprise at least one of aluminum alloy, steel and magnesium alloy, preferably thin sheets (<NUM> to <NUM>) of aluminum alloy.

The present invention proposes the layers comprised of the reinforcement composite frame to be arranged in a modular fashion, where each unidirectional prepreg strip runs along the entire length or width of the part to be reinforced and creates areas of intersection, thereby creating an intertwined mesh form. Making reference to <FIG> that discloses the simplest embodiment of the present invention, i.e. a layer module, and <FIG> that discloses a reinforcement frame that comprises multiple layer modules, it is disclosed herein a reinforcement frame (<NUM>) comprising at least one layer module of unidirectional composite layers arranged in an alternate succession of at least one first prepreg composite strip (<NUM>) having one first orientation and at least one second prepreg composite strips (<NUM>) having a second orientation arranged at angle between <NUM> and <NUM>°, preferably <NUM>°, to the first prepreg strips (<NUM>) intersecting and contacting each other on at least one intersection area (A), and at least one metal sheet (<NUM>) placed on the at least one intersection area (A), either between each first prepreg strip(<NUM>) and respective subsequent each second prepreg strip (<NUM>) or on top of each intersection between each first prepreg strip (<NUM>) and each second prepreg strip (<NUM>). According to the present application, and for the sake of clarity, the invention disclosed herein refers to "layer module" or "layer set" which can be used interchangeably and are better defined as a set of <NUM> layers where one first layer comprises at least one of first prepreg strip (<NUM>) having a first orientation (and parallel to each other in case of at least two first prepreg strips (<NUM>)), a second layer comprising at least one of second prepreg strips (<NUM>) having an orientation arranged at angle between <NUM> and <NUM>° to the first orientation, wherein each of the second prepreg strips (<NUM>) is fixed to each of the first prepreg strips (<NUM>) in at least one intersection area (A), a third layer comprising a metal sheet (<NUM>) at each intersection area (A) either between each first (<NUM>) and second (<NUM>) prepreg strips or on top of said first (<NUM>) and second (<NUM>) prepreg strips, wherein a reinforced frame (<NUM>) may comprise as many layer modules as necessary.

In one embodiment, and when making reference to a 2D plane, prepreg strips having a first orientation (<NUM>) could be understood as substantially horizontal strips and prepreg strips having a second orientation (<NUM>) could be understood as substantially vertical strips (<FIG>).

Although a hand layup on a flat (2D plane) surface could be performed in the context of the present invention, a preferred embodiment (<FIG>) consists of using automated tape (prepreg strip) lay-up method where the layup is prepared such that two tape-laying heads place first (horizontal) prepreg strips (<NUM>) followed by three tape-laying heads placing second (vertical) strips (<NUM>), followed by placing metal sheet (<NUM>) at each intersection area (A), and these three steps repeated until desired thickness of composite strips is achieved. Again, it is important to emphasize that the terms vertically and horizontally serve to give a positional reference in relation to 2D plane where the layers are being laid up.

<FIG> shows other examples, where a bulk part (<NUM>) is supported by a reinforcement frame (<NUM>) made of unidirectional composite strips (<NUM>, <NUM>) in a mesh form as well as metal sheets (<NUM>) to reinforce the intersection areas (A). The alternate layers in intersection areas bonds firmly during co-forming and a molded reinforcement frame (<NUM>) behaves as a cohesive structure instead of a group of thick strips.

In another main embodiment of the present patent application, it is provided herein a process for producing said reinforcement frame (<NUM>) which includes addition of metal layers. The placement of metal layer during layup is of prime importance. In one example, according to <FIG>, the reinforcement frame (<NUM>), comprises three-layer modules (and one additional layer of first prepreg strips (<NUM>)), i.e. a total of <NUM> layers of first prepreg strips (<NUM>) and <NUM> layers of second prepreg strips (<NUM>) with metal sheets (<NUM>) at each intersection area (A). All the first prepreg strips (<NUM>) run across the length while the second prepreg strips (<NUM>) have dimension equal or more than full width of final component (<NUM>) and run across it. The layup also comprises one metal sheet (<NUM>) at each intersection (A) per layer module. In this example, the metal sheets (<NUM>) are placed on top of each of the second prepreg strips (<NUM>). After placing another set of first prepreg strips (<NUM>) and another set of second prepreg strips (<NUM>), the next set of metal sheets (<NUM>) placed is <NUM> to <NUM>% (preferably <NUM>%) smaller in size compared to metal sheets (<NUM>) of the previous layer module. This size difference allows for staggered position when centered across the intersection area. Similarly, a third metal sheet (<NUM>) layer is placed after another set of first (<NUM>) and second (<NUM>) prepreg strips. From a top-bottom perspective, the top metal sheets (<NUM>) are smaller in size compared to both metal layer beneath it and allows for all metal layers to be placed in staggered fashion.

In one embodiment better illustrated by <FIG> and <FIG> every third layer constitutes both metal and prepreg layer. First prepreg strip (<NUM>) of the first layer module is laid, followed by metal sheets (<NUM>) at the intersection area. Two discontinuous prepreg strips (<NUM>) are placed adjacent to metal sheet (<NUM>), which is followed by a second prepreg strip (<NUM>). This set of <NUM> layers is repeated over the bottom set (subsequent layer module). In the subsequent layer module, the metal sheet is placed in an orientation that is orthogonal to metal sheet of the previous layer module. These two-layer modules are then repeated wherein the respective metal layers are placed at a slight staggered position in relation to the metal layers of the previous layer modules. The two staggered position are within <NUM>-<NUM>% of length of metal sheets. This layup of a set of <NUM> layers is repeated <NUM> more times, each time orienting the metal layer perpendicular to the direction of preceding metal layer. Optionally, a prepreg strip (<NUM>) is laid at the top of the laminate.

For easier understanding of this application, figures are attached in the annex that represent the preferred forms of implementation which nevertheless are not intended to limit the technique disclosed herein.

<FIG> shows a layer module, where the layer of first prepreg strip (<NUM>) is laid and then the layer of second prepreg strip (<NUM>) is laid on top of the layer of first prepreg strip (<NUM>), such that both layers are perpendicular to each other.

The layer module consists of a third layer of metal sheet (<NUM>) placed at each intersection area of the two prepreg strip layers (<NUM>,<NUM>).

Now, preferred embodiments of the present application will be described in detail with reference to the annexed drawings. However, they are not intended to limit the scope of this application.

The present patent application describes a reinforcement composite frame (<NUM>) comprising:
at least one-layer set, wherein each layer set comprises:.

In one embodiment, each metal sheet (<NUM>) is either on top of each second prepreg strip (<NUM>) at each intersection area (A) or between each first (<NUM>) and second (<NUM>) prepreg strips at each intersection area (A).

In one embodiment, each of the second prepreg strips (<NUM>) intersects each of the first prepreg strips (<NUM>), making an angle of <NUM>° and <NUM>° between them, preferably an angle of <NUM>°.

The present patent application also describes the process for producing the reinforcement composite frame as defined above, wherein the process comprises:.

In one embodiment, each metal sheet (<NUM>) is positioned in a different orientation than each metal sheet (<NUM>) of the subsequent layer set, forming a staggered positioning of the metal sheets (<NUM>).

In one other embodiment, each metal sheet (<NUM>) is <NUM> to <NUM>% different in size than each metal sheet (<NUM>) of the subsequent layer set, forming a staggered position.

In one embodiment, each metal sheet (<NUM>) is either placed on top of each second prepreg strip (<NUM>) at each intersection area (A) or between each first (<NUM>) and second (<NUM>) prepreg strips at each intersection area (A).

In one embodiment, a discontinuous prepreg layer (<NUM>) is laid subsequently to each extremity of each metal layer, depending on the disparity between the prepreg and metal sheet (<NUM>) thickness.

Claim 1:
A reinforcement composite frame (<NUM>) characterized in that it comprises:
at least one-layer set, wherein each layer set comprises:
a first layer comprising at least one first prepreg strip (<NUM>) having one first orientation;
a second layer comprising at least one second prepreg strip (<NUM>) having a second orientation arranged at an angle between <NUM>° and <NUM>° to each of the first prepreg strips (<NUM>), wherein each of the second prepreg strips (<NUM>) is fixed to each of the first prepreg strips (<NUM>) in at least one intersection area (A); and
a third layer comprising a metal sheet (<NUM>) at each intersection (A);
wherein each prepreg strip (<NUM>, <NUM>) comprises unidirectional thermoplastic fibre.