PRODUCING THE SAME

FIELD OF THE INVENTION

The present invention relates to a composite article of reinforcing fibers and a curable thermosetting resin composition, which article is readily bonded to other articles. The invention further relates to a method for manufacturing the article. In another aspect, the invention relates to a joined assembly of composite articles in accordance with the invention, and to a method for manufacturing such a joined assembly.

BACKGROUND OF THE INVENTION

Composite materials comprise reinforcing fibers or particles that are embedded in a matrix resin composition, which can either be thermosetting or thermoplastic. Widely used composite materials include glass fibre reinforced unsaturated polyester resin composites and carbon fibre reinforced epoxy resin composites. Both these composite materials use a thermosetting resin composition as matrix, and are therefore often referred to as thermosetting composites.

Uncured thermosetting resin compositions typically comprise constituents such as monomers and a hardener, which react together to produce a cross-linked resin after cure. Other thermosetting resin compositions may comprise oligomer or polymer molecular chains of some length dissolved in a reactive solvent, such as styrene. The reactive solvent combines with the molecular chains when initiated to form a cross- linked network. The thermosetting resin composition may be selected such that curing occurs at room temperature or at higher temperatures, typically ranging between 80 and 200°C. During curing, the constituents of a resin mixture react and the viscosity of the mixture increases to infinity while forming a cross-linked solid resin. After curing, a thermosetting resin exhibits a glass transition temperature, above which considerable softening of the thermosetting resin occurs and the thermosetting resin behaves like a rubber. A post-cure may be used to increase the glass transition temperature. The cross- linked state however is not reversible by increasing temperature for instance, and a thermosetting resin is degraded at a temperature above its degradation temperature. A composite article of reinforcing fibers and a cured thermosetting resin composition has excellent properties since the cross-linked thermosetting matrix resin provides a good support and environmental resistance to the reinforcing fibers. However, once formed (cured), thermosetting composite articles may not be reformed since a thermosetting resin composition cannot be melted and re-solidified by raising and lowering the temperature. This represents a drawback of thermosetting resin

compositions, since large articles of thermosetting composites such as fuselage sections of an airplane for instance need to be produced in one piece. This requires expense manufacturing equipment, such a large autoclaves, as well as expensive logistics, due to the need of a large composite article once manufactured to be transported to its location of use. An alternative solution in which large articles are assembled from smaller components requires connecting the components to each other. Connecting could be done by bonding or by mechanical means, such as by riveting for instance. Making the connections however is time consuming and may not lead to the desired properties, such as (long term) strength.

EP 2730397 Al discloses a method for making composite shell elements. The elements comprise first and second regions in which the resin is cured to different levels. The composite element is not completely cured in first regions, and the shape in the first regions can consequently still be slightly modified without damaging the element. The first regions thus provide deformability to compensate for production dimensional tolerances. US 2014/119813 Al discloses a method for making a composite article of reinforcing fibers and a curable thermosetting resin composition. A first thermosetting resin composition in a first part of the article is substantially fully cured. A second part of the article comprises exposed fibers. This part is obtained by placing a gel in contact with the uncured laminate, forcing the fibers into the gel during cure, and using the gel to displace the first thermosetting resin composition during cure. The gel is then removed to expose the fibers. To bond with another article, two second parts with exposed fibers are mated and an adhesive layer is applied between the two mated second parts. Curing of the adhesive provides a bond between the articles. US 2014/119813 Al does not disclose an article having a second part wherein a second thermosetting resin composition is partially cured to form a bondable surface.

It would be desirable to provide the possibility of manufacturing relatively large composite articles of reinforcing fibers and a curable thermosetting resin composition without at least some of the above stated drawbacks.

SUMMARY OF THE INVENTION

In a first aspect of the invention there is provided a composite article of reinforcing fibers and a curable thermosetting resin composition, wherein the thermosetting resin composition in a first part of the article comprises a first thermosetting resin

composition that is substantially fully cured, wherein the thermosetting resin

composition in a second part of the article comprises a second thermosetting resin composition that is partially cured such that it comprises reactive moieties and forms a bondable second part, adapted to form a functional joint with another article. An advantage of the article is also that the second part of the composite article can still be shaped, if desired. The first and second part of the article form an integrated structure, and reinforcing fibers of the first part extend into the second part and vice versa. The first thermosetting resin composition of the first part of the article is substantially fully cured, which provides the article with a solid first part that has the desired mechanical properties, and is easily handled, transported and the like. The article, by providing a bondable second part thereof, may be joined to other articles whenever this is needed. Since the second thermosetting resin composition is partially cured only and therefore comprises reactive moieties, it can be bonded to another article, preferably to a second part of another similar article, to produce a functional joint between

corresponding reactive moieties. Such bonding may be stronger than provided by a secondary bond, such as the bond between a cured thermoset composite article and an adhesive layer applied to its surface.

Thermosetting composite articles are typically adhered to other articles by adhesive bonding or by mechanical joints, such as bolting, both of which have disadvantages. Adhesive bonding is costly, sometimes hazardous to the environment, and the quality of bonding achieved is generally sensitive to variations in process parameters. The quality of an adhesive bond indeed depends on surface properties and craftsmanship, making it a rather unreliable way of joining composite articles. Extra material is added and surface treatments are generally time consuming and dependent on circumstances. Bolting on the other hand produces holes in the articles to be connected, which gives rise to stress concentrations and possibly premature failure. An article in accordance with the present invention is readily transportable and yet provides a bondable surface that may be joined to (a bondable surface of) another article to produce a functionally joined assembly. An article in accordance with the present invention is readily transportable and yet provides a bondable surface that may be joined to (a bondable surface of) another article to produce a functionally joined assembly.

A functional joint between two articles is meant to represent a joint that enables the object to be useful for at least one of the principal functions for which the object is designed or is used. Two typical functional joints are structural joints and sealing joint that provide liquid or gas tightness.

A structural joint between two articles is meant to represent a joint that contributes to the load bearing capacity of the joined articles, and is able to transfer functional loads between the two articles. Functional loads may be but are not limited to design loads, primary loads and other expected loads which need to be transferred to ensure structural integrity of the assembly. For example, the principal functions of a coupling piece used to connect two liquid transporting pipes is to provide a structural joint (or load bearing capacity) and make it water tight; therefore, a functional joint between two articles is achieved if, at least, it provides sealing or load bearing capacity. According to an embodiment of the invention, a composite article is provided wherein the bondable second part has a surface area available for bonding and a cross sectional area perpendicular to it, and the surface area exceeds the cross-sectional area. In another embodiment, the bondable second part has a surface area available for bonding, the first part of the composite article has a cross-sectional area perpendicular to the bonding area, and the surface area exceeds the cross-sectional area. Such embodiments are particularly adapted to yield a structural joint with another article.

According to the invention, the first thermosetting resin composition is substantially fully cured. A substantially fully cured first thermosetting resin composition can be obtained in accordance with a curing cycle recommended by the supplier of the first thermosetting resin composition, or in accordance with a curing cycle that produces a similar result. A post-cure may be applicable. With the wording 'substantial' or 'substantially' is meant in the context of the present application at least 70% of the indicated property, more preferably at least 80%, even more preferably at least 90%, and most preferably at least 95% of the indicated property. According to the invention, the second thermosetting resin composition is partially cured such that it still comprises reactive moieties. A partial cure is defined as any degree of cure that differs from zero and from a fully cured state. The degree of cure of the thermosetting resin composition may be established according to well known standard practices. A suitable and widely used technique measures (changes in) enthalpy using Differential Scanning Calorimetry (DSC). The degree or extent of cure is defined as the change in enthalpy that has occurred, compared to the total change of enthalpy of a complete reaction (a substantially full cure or 100% degree of cure). The total change of enthalpy involved in completing a curing reaction is determined by using a slow temperature ramp from a low temperature to a temperature close to the onset of thermal degradation. To define the degree of cure of the second thermosetting resin composition in an article according to the invention would involve taking a sample of such resin from the second part, and determining the residual change in enthalpy using a slow temperature ramp from a low temperature to a temperature close to the onset of thermal degradation of the second thermosetting resin. The degree of cure is then defined by the ratio of the total enthalpy change minus the residual enthalpy change, to the total enthalpy change of the resin. Although DSC is the technique of choice in determining degree of cure and therefore a state of partial cure of the second thermosetting resin composition, other techniques may also be used, such as Dynamic Mechanical Analysis (DMA) for instance. An embodiment of the invention provides a composite article wherein the second thermosetting resin composition is B-staged. The wording "B-staged" as employed herein designates that partial curing (partial crosslinking) of the thermosetting resin composition has occurred. The "B-stage" of a thermosetting resin composition is well known to one skilled in the art and is defined by an intermediate stage in the reaction of certain thermosetting resins in which the material softens when heated and swells when in contact with certain liquids, but may not entirely fuse or dissolve. In the B-stage, a thermosetting resin may provide a tacky surface but this is not essential. Second parts of the invented articles may be joined and heated to further cure the second thermosetting resin compositions and create a primary bond between the second parts.

An article according to the invention comprises a first substantially fully cured part and a second part that comprises a partially cured thermosetting resin. In producing such an article, care has to be taken to avoid premature curing of the second thermosetting resin composition while curing the first thermosetting resin composition. One way of achieving this objective is provided by an embodiment of the composite article wherein the second thermosetting resin composition has a curing temperature, and wherein the reactivity of the first thermosetting resin composition is higher than the reactivity of the second thermosetting resin composition at a temperature lower than the curing temperature of the second thermosetting resin composition.

The second part of the article offers a bondable surface for a certain period of time. The time frame that offers a bondable surface depends on a number of parameters including the temperature at which the article is stored. In order to delay the cure of the second thermosetting resin composition, the article may have to be stored at temperatures lower than the temperature at which the curing reaction is initiated. Such a storage

temperature may be below 0°C. In a useful embodiment of the composite article, the second thermosetting resin composition is stable at a temperature of -10°C. In such embodiment, the second resin will not substantially cure (change its degree of cure) at a temperature of -10°C for at least one day, more preferably for at least one week, even more preferably for at least one month, even more preferably for at least three months, and most preferably for at least six months.

In other useful embodiments, the second thermosetting resin composition is stable at a temperature of -5°C, more preferably at a temperature of 0°C, even more preferably at a temperature of 5°C, even more preferably at a temperature of 10°C, even more preferably at a temperature of 15°C.

A particularly preferred embodiment of the composite article according to the invention comprises a second thermosetting resin composition that is stable at room temperature. In such embodiment, the second resin composition will not cure at room temperature for at least one day, more preferably for at least one week, even more preferably for at least one month, even more preferably for at least three months, and most preferably for at least six months. With room temperature is meant a temperature between 15 and 40°C.

In the article of the invention, the first and second thermosetting resin compositions have a different degree of cure. Such difference may be created by first and second resin compositions that comprise the same constituents (monomers and hardeners for instance) but that have been cured to different extents. In another embodiment of the invention, a composite article is provided wherein the monomer composition of the first thermosetting resin composition differs from the monomer composition of the second thermosetting resin composition. The different constituents of both resin compositions allow a straightforward tuning of the reactivity and degree of cure in the article. The volumetric percentage of the first and second parts of the article relative to the article's total volume may be chosen within a wide range. It is possible for instance that the second part of the article comprises as much as 90% by volume of the article. In a preferred embodiment of the composite article, the second part of the article comprises at most 60% by volume of the article, more preferable at most 50% by volume of the article, even more preferably at most 40% by volume of the article, even more preferably at most 30% by volume of the article, even more preferably at most 20% by volume of the article, and most preferably at most 10% by volume of the article. The first part of the article then preferably occupies the remaining volume. In other embodiments, the second part of the article comprises at least 5% by volume of the article, and more preferably at least 10% by volume of the article.

Many composite articles are substantially two-dimensional by which is meant that such articles have two planar dimensions that are substantially larger than a thickness dimension of the article. The above volumetric percentages may in case of planar articles be equated to surface area percentages. As an example, the surface area covered by the second part of the article comprises at most 40% of the total surface area of the article in an embodiment. It should be noted that the second part of the article covers a percentage of the volume or surface area of the article that differs from zero.

In an embodiment of the composite article according to the invention, the first part is continuous across the article and provides dimensional stability to the article and supports the second part or parts. With a continuous first part is meant a first part that extends across the article uninterruptedly. Such a first part may however locally comprise holes etc. as long as a line can be found that runs in the first part from one end of the article to an opposed end of the article in an uninterrupted fashion.

The cured first part of the article in this embodiment provides shape stability to the article, so that it can be transported and handled, even with partly cured second parts. After the first curing cycle (or production step), the articles shape is (substantially) defined and does not need additional supporting structures to be handled. In addition to this, tooling for the second curing cycle can be simplified or even omitted, thanks to the shape stability of the article.

A particularly preferred embodiment of the invention provides a composite article having edges, the second part of the article comprising article edge parts. Article edge parts are defined as parts that extend from a free edge of the article over some distance from said free edge. The distance covered may be governed by the above defined preferred surface area percentages. This embodiment of the invention is useful in joining a plurality of articles from head to tail, such as is required for instance in building pipe lines. The composite article according to the invention would then comprise one or more pipe sections. Another useful embodiment of the invention provides a composite article having a thickness, the second part extending over part of said thickness. This embodiment provides a bondable surface on one side of the article and a solid substantially fully cured surface on an opposite side of the article.

The thermosetting resin compositions of an article in accordance with the invention may be chosen within a wide range of available thermosetting resin compositions. The second thermosetting resin composition is preferably available in a stable partly cured state. In an embodiment of the invention, a composite article is provided wherein the thermosetting resin composition comprises an epoxy, unsaturated polyester, phenolic, polyurethane, or bismaleimide resin/hardener mixture, or combinations thereof, such as two-component systems based on thermosetting urethane. An epoxy and/or unsaturated polyester resin/hardener mixture is particularly preferred. Another useful embodiment of the invention provides a composite article, comprising a coupling part for coupling yet another article by bolting, the coupling part preferably providing a flange for coupling. Such coupling part may for instance be used to provide a pipe with end couplings. The coupling part in such an embodiment may be cylindrical with a first part being formed by an outer cylindrical shell, and a second part being formed by an inner cylindrical shell of the cylindrical coupling part.

In another embodiment of the invention, a composite article is provided comprising first parts that are interconnected by a deformed second part, for instance a folded second part. A typical example of such an embodiment comprises a number of plate shaped first parts that are interconnected along lines by line-shaped second parts. Such a configuration may be easily transported by folding the first parts on top of each other. In such a transportable configuration, the second parts act as plastically deformable joints.

A second aspect of the invention provides a method for manufacturing a composite article in accordance with the invention. The method of the invention comprises combining reinforcing fibers and a first thermosetting resin composition to form a first part of the article, combining reinforcing fibers and a second thermosetting resin composition to form a second part of the article, curing the first thermosetting resin composition to a substantially fully cured stage, and providing the second thermosetting resin composition in a partially cured stage such that it comprises reactive moieties and forms a bondable second part, adapted to form a functional joint with another article.

A joint of two articles with first and second parts may result in a chemical joint (or more specifically a crosslinked joint) between the articles after the second curing cycle has been achieved. Generally, two interfaces in such a joined articles can be identified: a first interface between the first and second parts, and a second interface between second parts of the joined articles. The first interface is generated when the first part of the article is fully cured while the second part is semi-cured only. In case of a same first and second resin, this may be achieved by curing means such as heat, UV, etc. applied in the first part only. The same can be achieved by using two mutually compatible resins with different curing mechanisms (e.g. different curing temperature). When making such an article, the first and second resin come into contact before the first resin is actually cured. This means that the first and second resin potentially interact chemically when the proper resin combination is chosen, and crosslinking between the first and second part of an article can be expected. This is especially the case after the second curing cycle has been completed and both parts are solid. This adds to the strength of a joined assembly. Joining of two articles can be achieved by contacting surfaces of two semi-cured second parts; by contacting surfaces of a semi-cured second part and of an uncured part; or by contacting surfaces of an uncured to another uncured part. When two of such surfaces are brought together and co-cured a joint is formed. If the proper resin combination is chosen, resins will by chemically compatible and will react with each other forming a chemical bond. Therefore, crosslinking between the two articles along the second interface can be expected.

The above means that a functional joint quality may be achieved through the invention by crosslinking between the resins across both the first and the second interface. This is not achieved by the known method in which surfaces are bonded by an adhesive.

The reinforcing fibers may be combined with the thermosetting resin compositions in any known way. Suitable examples include but are not limited to hand lay-up, in which reinforcing fibers are impregnated with a thermosetting resin composition by hand, for instance with a brush or roller; resin infusion methods such as RTM, in which the thermosetting resin is injected or sucked into a closed mold provided with reinforcing fibers, or vacuum infusion; pultrusion, in which reinforcing fibers are led through a thermosetting resin bath and subsequently through a heated die; rotational casing molding in which a thermosetting resin is brought into a rotating mold and pressed through reinforcing fibers provided in the mold by centrifugal force; and filament winding. A method in accordance with a preferred embodiment combines reinforcing fibers and the first and second thermosetting resin compositions to form the first and second part of the article by impregnating the reinforcing fibers with the first and second thermosetting resin composition and filament winding the impregnated reinforcing fibers onto a mandrel having the shape of the article and/or pultruding the impregnated reinforcing fibers through a die.

In a practical embodiment of the method, impregnating the reinforcing fibers with the first and second thermosetting resin compositions is performed by providing first and second thermosetting resin baths and leading the reinforcing fibers through either one of said baths. Leading the reinforcing fibers through a bath comprising the first thermosetting resin composition will produce first parts, whereas leading the reinforcing fibers through a bath comprising the second thermosetting resin composition will produce second parts of the article. The production process need not be interrupted in this embodiment since the reinforcing fibers are contacted with a first or second thermosetting resin by respectively bringing the first or second resin bath in an operable position. Other useful embodiments of the invention relate to a method wherein combining reinforcing fibers and the first and second thermosetting resin compositions to form the first and second part of the article is performed by impregnating the reinforcing fibers with the first and second thermosetting resin composition through vacuum infusion or resin transfer molding (RTM). A preferred embodiment provides a method wherein the resin compositions are injected at different locations of a mould and vented at one location providing a separation between the first and the second resin compositions. A third aspect of the invention relates to a joined assembly of composite articles in accordance with the invention, wherein second parts of said articles at least partly overlap in a bondable area and are substantially fully cured.

A fourth aspect of the invention provides a method for manufacturing such a joined assembly of at least two composite articles having a bondable surface, the method comprising:

a) providing composite articles according to the present invention having a

bondable second part;

b) bringing second parts of said composite articles in overlapping arrangement with each other to form a bondable area;

c) applying a curing means to said bondable area; and

d) curing the second thermosetting resin compositions to a substantially fully cured stage.

In the overlapping arrangement, second parts preferably contact each other over part of their surface area to provide the bond between said parts.

The curing means are preferably external to the articles and are configured to initiate a curing reaction in the second parts of the articles and, optionally to apply a pressure to the bondable area of the second parts. Suitable curing means comprise any tool configured to emit energy waves at an energy level that initiates the curing reaction, such as ultraviolet waves, ultrasonic waves, heat waves, and the like. A preferred embodiment of the method according to the invention makes use of curing means that comprise a heating tool and means for pressurizing the bondable area. Suitable heating tools provide contact heat or radiation heat, and may employ electrical current, hydraulic fluids, magnetic coils, microwaves, and the like to bring the tool and second parts to the desired curing temperature.

A practical embodiment that may for instance be applied in situ for bonding pipe sections to each other head to head and thereby form a pipeline is characterized in that the bondable area is cylindrical (such as provided by end parts of pipe sections) and the heating tool comprises a sleeve configured to be provided around the bondable area, the sleeve being provided with an inflatable pressure pad at an inner surface of the sleeve. The sleeve is in use applied around the bondable area and closed such that it can withstand an inner pressure. The internal pressure pad is then inflated which brings it into contact with an outer surface of one of the articles to be joined and inflated further until the desired pressure is applied to said outer surface. The sleeve is then heated and kept at the curing temperature of the second thermosetting resin until said resin is (fully) cured.

Although the second thermosetting resins in the articles to be joined are preferably the same, they may actually differ from each other as long as the second resins of the articles to be joined may be co-cured to form a cross-linked copolymer.

The method of joining articles having a bondable surface according to the invention may be carried out at any temperature as long as such curing temperature does not substantially exceed the degradation temperature of the first thermosetting resin composition. If such would be the case, the first part of the article may have to be cooled when curing the second thermosetting resin. For practical reasons, the curing temperature of the second thermosetting resin is preferably at or above room

temperature, but more preferably below the glass transition temperature of the first thermosetting resin. In other instances, the curing temperature will be above the glass transition temperature of the partially cured second thermosetting resin.

A fifth aspect of the invention relates to a method for manufacturing a composite product. The method comprises:

a) providing a composite article in accordance with the invention having a first and a second part;

b) deforming a second part of said composite article to a first shape;

c) applying a curing means to said shaped second part; and

d) curing the second thermosetting resin compositions to a substantially fully cured stage to form the composite product.

This embodiment of the invention allows to easily shape thermosetting composite articles.

Yet another embodiment of the invention provides a method comprising: a) providing a composite article in accordance with the invention having a first and a second part;

b) deforming a second part of said composite article to a first shape;

c) transporting the article with the second part in the first shape;

d) deforming the second part to a second shape that differs from the first shape; e) applying a curing means to said shaped second part; and

f) curing the second thermosetting resin compositions to a substantially fully cured stage to form the composite product. A typical example of this embodiment comprises a number of plate shaped first parts that are interconnected along lines by line-shaped second parts. Such a configuration may be easily transported by folding the first parts on top of each other. In such a transportable configuration, the second parts act as plastically deformable joints. Upon arrival at the site of deployment, the first parts are folded out to obtain an elongated structure of interconnected first parts. This structure may be wrapped around a mandrel to produce a pipe for instance. The pipe is stabilized by curing the second parts.

The composite article according to the invention may comprise other articles, such as metal inserts, foam or honeycomb core, thermoplastic of thermosetting articles or films, bonded thereto by other methods than according to the invention, or any other material that can be incorporated as an integral part of such a a thermosetting composite article.

BRIEF DESCRIPTION OF THE FIGURES The invention will now be described in more detail by way of example, without however being limited thereto and with reference to the accompanying figures in which: Figure 1 schematically illustrates an embodiment of an article having a bondable area in accordance with the invention;

Figure 2 schematically represents an embodiment of a method for joining two composite articles as shown in figure 1 to obtain a joined assembly in accordance with the invention;

Figures 3A and 3B schematically show embodiments of a filament wound article in accordance with the invention; Figures 4A and 4B schematically illustrate the use of a heating tool in the method of the invention;

Figure 5 schematically shows a composite article in accordance with another

embodiment of the invention;

Figures 6A-6C schematically represent different steps of another embodiment of a method for joining two composite articles as shown in figure 5 to obtain a joined assembly in accordance with the invention;

Figures 7A and 7B schematically illustrate an embodiment of a method in accordance with the invention in which resin transfer moulding (RTM) is used;

Figures 8 A and 8B schematically represent examples of articles according to the invention;

Figures 9A to 9C schematically illustrate yet another embodiment of a method on accordance with the invention;

Figures 10A to 10E schematically represent examples of other articles according to the invention;

Figure 11 schematically represents an embodiment of a method in accordance with the invention wherein second parts are plastically deformed to shape a composite product; and

Figure 12 schematically represents another embodiment of a method in accordance with the invention wherein second parts are plastically deformed to shape a composite product.

DESCRIPTION OF PREFERRED EMBODIMENTS The invention will be illustrated first with reference to figures 1 and 2 in the context of producing a pipeline of a thermosetting composite material. Such a pipeline may be used for transport of gas or liquids and typically comprises a plurality of pipe sections (3, 3-1, 3-2) that are joined to each other head-to-tail in situ, i.e. at a site of construction. A single pipe section 3 is shown in figure 1, and may conveniently be produced by filament winding reinforcing fibers onto a mandrel, as will be described below. A typical pipe section 3 is cylindrical and exhibits a hollow circular cross-section with a wall thickness sufficient to withstand design loads. A filament wound pipe section 3 is made in a number of steps that involve preparing a mandrel onto which reinforcing fibers impregnated with a thermosetting resin composition are positioned, preparing a liner, an optional calibration of the

impregnation system, the actual winding of reinforcing fibers onto the mandrel, curing of the pipe section 3 and extracting the mandrel after cure.

In producing a pipe section, a cylindrical mandrel (or mold) made of a suitable metal such as aluminum or steel is used. The mandrel is covered with a release film to facilitate the extraction of the filament wound composite pipe section 3 from the mandrel after cure. The release film can be any layer having a low coefficient of friction, such as a layer of wax or a thin sheet of a PET polymer (Mylar® for instance) or a PTFE polymer (Teflon® for instance).

To enhance the sealing and chemical resistance properties of the pipe section 3, a liner is typically applied onto the mandrel. A liner represents a resin rich layer (usually a thermosetting resin) located at the interior of the pipe section and may be composed of different materials depending on the desired properties. In the present example, a glass fiber veil (a mat of randomly oriented glass fibers of relatively low areal weight) was used as lining material, due to its ability to absorb a high amount of resin. The mandrel provided with the resin impregnated liner was rotated until the resin reached its gel point. The gel point of the resin is reached when all monomers of the resin are part of the formed resin network (an infinite molecular weight is reached), but cross-linking is still to be achieved. After gelification of the liner, the mandrel is ready to be used in the filament winding equipment.

To produce a pipe section 3 in accordance with the invention, at least two resin baths need to be present in the filament winding device. A first resin bath contains a first thermosetting resin composition that needs to be fully cured, while a second resin bath contains a second thermosetting resin composition that needs to be cured only partially, or needs to be provided in a partially cured stage, such as a B-stage. After having established the correct fiber configuration (amount, fiber angle, etc.) for a pipe section 3, a calibration run is executed to ensure that the at least two resin baths switch correctly and the fibers impregnated with the first and second resin compositions are positioned in the correct position on the mandrel. The calibration data may be stored in computer memory and used each time the same pipe section 3 is made.

In a next step of the method for producing the pipe section 3, the mandrel is secured between the rotational clamps of a filament winding device and brought in a state of continuous rotation about its central axis. Reinforcing fibers are taken from a creel and positioned onto the outer surface of the mandrel according to a predetermined path. Before placement on the mandrel surface, the reinforcing fibers are impregnated with the first and/or second resin composition, The first and second thermosetting resin baths thereto switch between the two resins during the winding process such that first or second resin impregnated fibres are selectively positioned on the mandrel's surface.

An example of a pipe section 3 thus produced comprises a second part 2 in which the layers of reinforcement fibres are impregnated with a second thermosetting epoxy resin composition that is B-Staged. The second part 2 comprises an edge part of the pipe section 3 that extends from a free edge 4 over a distance of about 20% of the total length 5 of the pipe section 3, and is used to form a bond with a second part 2 of another pipe section 3 to form a larger pipeline of interconnected pipe sections 3. The pipe section 3 further comprises a (major) first part 1 in which the layers of reinforcing fibers are impregnated with a first thermosetting epoxy resin that is fully cured at room temperature. The first epoxy resin in the present example was an Epikote Resin 04434, produced by Momentive, while the second epoxy resin in the present example was an SR121/KTA 315 system, produced by Sicomin. Besides selectively switching from the first epoxy resin to the second B-stage epoxy resin through the length 4 of the pipe section, it may be beneficial according to another embodiment to switch resins while building up the thickness 6 of the pipe section 3, as shown in figure 3B. In the configuration of figure 3B, layers of first epoxy resin impregnated fibers 7 have been positioned between the liner 8 provided onto the mandrel 10, and layers 9 of reinforcing fibers impregnated with B-staged second epoxy resin material. This embodiment increases the stiffness of a joint formed by second parts 2 of two pipe section 3-1- and 3-2, which allows the joint to withstand an optional pressure required for the joining process, thereby avoiding the use of an internal mould. Once the filament winding of the reinforcing fibers is completed the mandrel 10 is allowed to rotate at a constant slow rotational speed while the first epoxy resin is cured to an extent that allows demolding of the pipe section 3. The mandrel 10 is then extracted from the formed pipe section 3 using a hydraulic extraction tool for instance. A typical pipe section 3 is then post-cured in an oven at an elevated temperature of about 150-200°C, depending on the type of first thermosetting resin selected. To avoid curing of the second B -staged thermosetting resin, measures need to be taken to cool the second part 2 during post-cure of the first part 1 of the pipe section 3. A plurality of pipe sections 3 may now be joined together in a head-to-tail fashion to form a pipeline. Figure 2 shows the principle of the invented joining process of two pipe sections 3-1 and 3-2, both sections consisting of a second part 2 that provides a bondable surface for joining to a bondable surface of another pipe section 3. Pipe sections 3-1 an 3-2 are readily handled since their first parts 1 comprise a substantially fully cured thermosetting resin. The pipe sections 3-1 and 3-2 to be joined are brought together such that their second parts 2 at least partly overlap in a jointed configuration. This configuration is also illustrated in figures 4A and 4B. In the jointed configuration, layers of load carrying reinforcing fibers impregnated with a second B-staged resin composition are brought together. The final step in joining the pipe sections 3-1 and 3-2 involves curing the B-staged second thermosetting resins in the overlapping second parts 2 of the pipe sections to a substantially fully cured state. The formed pipeline part 30 comprising two pipe sections 3-1 and 3-1 includes reinforced fibers impregnated with a fully cured thermosetting resin 1. The above described process may be repeated to obtain a pipe line of a plurality of pipe line sections 3. The method can be carried out in-situ using a curing means, an embodiment of which is described below.

Referring to figures 4 A and 4B, a suitable curing tool 20 comprises a metal sleeve 20 that is provided around two mated pipe sections (3-1, 3-2). Interposed between the outer surfaces of the mated pipe sections and the inner surface of the metal sleeve 21 is provided an inflatable member 22 such as a silicon bladder. To mate the pipe sections, a second part 2 of the pipe section on the left is provided with a slightly enlarged cross- section. This produces a female edge part for mating with a male edge part. An enlarged female edge part is easily obtained since the thermosetting resin in the second parts 2 is in a B-stage and therefore deformable. A male edge part of the pipe section on the right of the figure is inserted into the female B-staged edge part of the pipe section on the left of the figure up to a required length. The curing tool 20 is then applied around the area to be jointed. Using air pressure, the silicon bladder 22 of the curing tool 20 is inflated to a pressure ranging from 1-5 bar depending on process requirements. The air pressure provides a substantially uniform radial compaction pressure during curing at an elevated temperature. The temperature is raised by heating the area to be joined locally. This can be done by introducing a heated fluid in the silicon bladder 22 of the curing tool 20, or a heat blanket may be provided. A typical curing temperature ranges from 60°C up to 120°C. The heat provided activates a second step curing of the second B-staged resin composition. The joint is cured for about 30 minutes at 120°C which completes the joint between the pipe sections 3-1 and 3-2. Other methods for joining pipe sections 3 - and other articles - may be used, for instance when dimensions are large and the use of the curing tool 20 is less practical. In such cases, an inflatable pad may be wound around the joint area of the pipe sections. It is also possible to provide at least the jointed area with an internal mold to provide support to the joint and avoid collapse of parts of pipe sections. In a typical method, an inflatable internal mold is inserted in mating pipe sections 3-1 and 3-2 and inflated. The internal mold also serves as an alignment tool. An outside pressure chamber (joining tool) is then positioned around the pipe joint and filled with a heated fluid to pressurize the chamber and heat the surface to cure the joint, making it as strong as the actual cured pipe. A last step involves removing the curing and internal molds from the assembly.

Other large composite structures may also be assembled from sub-assembly composite articles in accordance with the invention. An example is a fiber reinforced thermosetting composite hull of a vessel that is assembled from smaller vessel hull sections, as illustrated in figures 5 and 6A-6C.

Figure 5 shows a schematic representation of a hull section 6 of a vessel. The hull section 6 comprises two second parts 2 that run along two edges 11 of the hull section 6 and extend over some distance 12 from the edges 11. Second parts 2 comprise layers of reinforcing fibers embedded in a second B-staged thermosetting resin. Parts 2 provide bondable areas adapted to form a bond with another hull section 6 to form a larger part of a vessel's hull. The hull section 6 further comprises a central first part 1 that extends between the second parts 2 and in which layers of reinforcing fibers are impregnated with a single cure cycle first thermosetting resin composition that is fully cured.

Figures 6A to 6C schematically show the joining process of two hull sections 6-1 and 6- 2. Two of said sections 6-1 and 6-2 are brought together such that edge parts 2 of each section (6-1, 6-2) are aligned, as show in figure 6 A. The hull sections 6-1 and 6-2 are then brought in overlapping arrangement in which second parts 2 of both sections (6-1, 6-2) overlap in a joint configuration (figure 6B). A final step in the joining of the hull sections 6 is shown in Figure 6C. In this step the overlapping B-staged parts 2 of both sections 6-1 and 6-2 are fully cured by applying heat and, optionally, pressure, to produce a completed hull part 60.

With reference to figures 7A and 7B a method is illustrated wherein combining reinforcing fibers and the first and second thermosetting resin compositions to form the first and second part of an article in accordance with the invention is performed by impregnating the reinforcing fibers with the first and second thermosetting resin composition through resin transfer molding or vacuum infusion. A fiber reinforcement 15 is positioned between an upper mold half 13 and a lower mold half 14. The upper mold half 13 is then brought towards the lower mold half 14 to provide the closed configuration of figure 7B. In case of vacuum infusion, the upper half 14 can be a flexible foil. The first resin composition 16 is injected through an inlet provided in the upper mold half 13 and the second resin composition 17 is injected through a second inlet provided in the upper mold half 13. Both resin compositions (16, 17) travel through the reinforcement 15 and exit through a common venting outlet 18. The common venting outlet 18 defines the border between the first and second part of the article. The lower mold half 14 may be provided with heating/cooling channels 19.

Figures 8A and 8B schematically represent examples of other articles according to the invention. It is shown that the joining technology of the invention may also be used to connect pipes (40-1, 40-2) to auxiliary components such as couplings 41, flanges 42 and local reinforcements. In the figures, the first (substantially cured) parts are invariably referred to as parts 1, whereas the second (partially cured) parts are invariably referred to as parts 2. In the illustrated cases, the substantially cured section 1 has a functional role, such as avoiding collapse of the structure, facilitating transport and handling and/or enabling joining by mechanical means (e.g. bolts, clamps, etc.). Auxiliary components can be used to connect a pipe 40-1 to another component such as, but not limited to, another pipe segment 40-2 with the same partially cured parts 2, substantially cured FRP pipe segments, pipes from other materials such as cast iron, steel, PVC, and the like, and other components such as valves, pumps, etc. The auxiliary components such as flanges or couplings need not necessarily be connected to partially cured pipe sections. For example, flanges 42 having partially cured parts 2 may be used in combination with uncured tubes such that after co-curing (joining) both components, they can be connected to a third component, such as a pipe, a pump, and the like. This provides a fast and reliable method of making a connection with third elements without extra processing steps.

A typically application where such configuration could be used is shown in figures 9A to 9C. The shown technology is referred to as cured-in-place pipes (CIPP), and represents a rehabilitation method used to repair an existing pipeline 43. In the method, a resin saturated uncured or partially cured felt tube 44 made of polyester/fiberglass cloth, or a number of other materials suitable for resin impregnation, is inverted and pulled into the damaged pipe 43. The felt tube 44 that acts as liner may be inverted using water or air pressure 45. An auxiliary component such as flange 42 is provided at an end of the pipe 43. The felt tube 44 is inflated and advanced inside the pipe 43 until it contacts the flange 42 at an inner surface thereof. The partially cured parts 2 of the flange 42 and the tube 44 are then co-cure, for instance by applying hot water, UV light, ambient temperature and/or steam. After cure, a tight-fitting, jointless and corrosion- resistant replacement pipe 46 is formed, having a flange 42 that can be used for connection to other components in the rehabilitated pipe system.

Other possible auxiliary components 51 that can be used with flat or curved panels 53 (see Figure 10E) are shown in figures 10A to 10D. Suitable components 51 may have the function of stiffening the panel 53, adding lugs or bolt holes to the structure or other functional/structural functions. These functions may be incorporated in the cured first part of the article, or it may be provided by an additional component, such as steel insert

50 in figure IOC. The benefit is that the main structure or panel 53 and the additional components 51 can be made in different production processes. For example, stiffeners

51 could be made by a compression molding or pultrusion process and then be co-cured with other larger panels 50 made with vacuum infusion. Joining the auxiliary components 51 to the flat or curved panels 53 is performed by contacting the partially cured parts 2 of the auxiliary components 51 with the panel 53 and curing the partially cured parts 2 of the auxiliary components 51 to form a bond. Yet other embodiments of the invention are shown in figures 11 and 12, in which a composite product is shaped in a step-wise fashion. In such methods, use is made of the possibility of shaping partially cured parts 2 in a composite product, wherein a substantially fully cured part 1 is used for handling. Shaping is possible since the second resin parts are still flexible, at least to some extent. Such a shaping method may for instance be used in a series of products with the same shape except for some small or local variations in shape. This offers the possibility to employ a relatively large main mold to shape the major parts of the products and a number of smaller less expensive molds to provide the small variations in shape. As illustrated in figure 11, a first step of a possible shaping method provides a composite article 52 having a first (substantially fully cured) part 1 and a second (partially cured) part 2. Shaping and impregnation of reinforcing fibers with at least two resins may be performed by any method, such as vacuum assisted RTM, RTM, filament winding, pultrusion, and the like.

In a second step, the shape of the composite article 52 is slightly modified in a region that corresponds with partially cured part 2. The shape modification can be carried out by any suitable method, such as by pressing, rolling, die casting, or other mechanical and manual means.

In a third step, the shape modified article 52 is then fully cured by further curing the partially cured second resin in part 2 to obtain a composite product 53 having a stable geometry.

Curing a composite article in two or more steps can also have transport benefits, particularly in case of large structures. As shown in figure 12, a large tubular structure, such as a storage tank, silo, cooling tower, or cold water pipe for instance can be made from flat or curved composite panels. At a production facility, a composite panel 54 strip is made in which the panel 54 is provided with substantially fully cured parts 1 and relatively small partially uncured portions (2a, 2b). Parts 2a are arranged between first parts 1, whereas parts 2b are arranged along side edges of the panel 54. Folding first parts 1 on top of each other, where the folding lines are formed by parts 2a, allows to transport the panel 54 in a flat state to a final destination. On location, the panel strip 54 is rolled to form a tubular cross section of the structure, as shown in the left part of figure 12. Next, the partially cured areas 2a of the panel strip 54 are cured to fix the shape of the structure. This process can be repeated and several sections may be joined in a lengthwise direction to form a longer structure using partially cured section 2b. Alternatively, the process can be repeated in a circumferential direction to increase the cross sectional dimension of the structure. A joint between panels 54 may also be formed by unrolling panel strips 54 e in a diagonal direction into a tubular structure having a spiral joint.

The method for producing a joined assembly according to the invention may be used for joining any thermosetting composite article, such as plates, panels, profiles and the like, and any combination thereof.

It will be understood that the invention as disclosed in the above detailed description is only given by way of example and that many variations may be envisaged by the skilled person within the scope of the appended claims. It is particularly noted that the skilled person may combine technical measures of the disclosed embodiments of the invention.