CONTOURED STRUCTURAL ELEMENT AND PRODUCTION OF THE CONTOURED STRUCTURAL ELEMENT

Abstract

A contoured structural element (100) for use as a core layer in a curved sandwich composite element, wherein the contoured structural element (100) is formed from a foamed thermoplastic material, in particular PET, wherein the contoured structural element (100) is divided into a plurality of body elements (10) with the exception of a bonding layer (12), and wherein the body elements (10) and the bonding layer (12) are oriented parallel to a base surface (26) of the structural element (100) that is in a flat state. According to the invention, at least one surface layer (16) of the bonding layer (12) and the surface layer of the body elements (10) adjacent thereto (18) comprise at least partially a thermally compacted layer (14), wherein the body elements (10), the bonding layer (12), and the thermally compacted layer (14) are formed from the same material.

Description

CONTOURED STRUCTURAL ELEMENT AND PRODUCTION OF THE CONTOURED STRUCTURAL ELEMENT Field of Invention The present invention relates to a contoured structural element according to the preamble of claim 1, and a method for producing such a contoured structural element. Background of the Invention Generic contoured structural elements are used as a core layer in a curved sandwich composite element, particularly for manufacturing wind turbine blades and / or for applications in the marine sector, specifically for the production of boat hulls and decks, in rail transport, public transportation, and for structural applications in construction where the structural elements have single or double curves or other complex three-dimensional contours. In this case, the contoured structural element is bonded in a curved, sandwich-like state to one or more cover layers, preferably made of fiber-reinforced plastic material, to form a curved sandwich composite element with high flexural stiffness and low weight. Ref. 341099 died at the same time. The applicant's document DE 10 2012 102 689 Al shows a partially welded plate-shaped structural element for use as a middle layer in a sandwich composite element, wherein the plate-shaped structural element is formed from a plurality of body elements welded together made of a thermoplastic material extruded, in particular PET, and wherein the plate-shaped structural element is produced by a thermal element cutting process from a block of extruded plastic. Structural panel elements, intended for use as a core layer in a sandwiched composite element, for example, made of balsa wood or foamed plastic, are characterized by low dead weight, but also by low elasticity and low tensile strength. For this reason, plate-shaped structural elements are only conditionally suitable as a core layer for curved sandwiched composite elements. US patent 3,540,967 A1 describes a structural element suitable and intended for use as a core layer in a curved, sandwiched composite element. The structural element consists of individual body elements or blocks with a rectangular cross-section, connected on one face and at a specified distance from one another by a mesh-like fabric, also called woven material. The woven material, for example, a fiberglass mesh, acts as a hinge between the individual body elements and allows for curvature of the structural element. In production, several plate-like elements of the raw material are cut into individual blocks by a sawing process and then coated on one face with the woven material, the body elements being arranged at a specified distance from one another.This distance or intermediate space between body elements is required, particularly if the structural elements are to be placed with the woven material face in a concave shape. Document DE 10 2015 203 375 A1 describes a method for processing spongy blanks, in which a rotating tool is applied under pressure in a longitudinal motion to a surface of the spongy blank to compact the surface. The spongy blank is processed along the surface with negligible depressions and without material removal, thus creating a watertight surface, particularly against liquids or gases. Therefore, the negligible depressions cannot form an intermediate space with body elements that could bend together in a hinge-like manner. A generic method for applying woven material can involve several costly and time-consuming steps. In this process, a woven material impregnated with adhesive resin is applied to the body parts and aligned. The adhesive resin then hardens, and care must be taken to ensure the body parts do not change their orientation. According to the prior art, an alternative method for applying woven material is also known, in which a woven material with fibers previously embedded in adhesive (hot melt) is applied to a rigid, ungrooved plate using heat and pressure. Subsequently, the plate with the material is grooved or sawn on one side in both a longitudinal and transverse direction. EP 2 483 076 B1 also describes a contoured structural element formed by a plurality of body elements. A woven material is used as a hinge-like joint between the body elements, holding them together and reinforcing a bonding layer between body elements that are not completely separated, such as those partially separated within the structural element by depressions or contours. Generic sponge plastic core materials are held together locally by pores, with the pore walls made as thin as possible to reduce the core material's weight for lightweight construction applications. Due to the reduction in the local cross-section of the material between pores, a sponge plastic exhibits brittle fracture behavior under macroscopic conditions. This is also the case if the plastic exhibits ductile or tough fracture behavior in its unsponged state. For this reason, contoured structural elements made of sponge plastics require a woven material to act as a hinge. Based on the aforementioned prior art, the invention aims to provide a contoured structural element suitable for use as a central layer in a curved sandwich composite element, the composition of which is such that the contoured structural element consists entirely of a spongy thermoplastic and wherein the bonding layer between the body elements is reinforced in such a way as to allow a hinge-like curvature of the body elements relative to each other and can be produced by a simple or less expensive method. Furthermore, the objective is to specify a method for producing such a contoured structural element as well as a curved sandwiched composite element with such a contoured structural element as the middle layer. Summary of the Invention This problem is solved with respect to the contoured structural element with the features of independent claim 1, with respect to the method with the features of claim 13, and with respect to the curved sandwiched composite element with the features of claim 15. The advantageous embodiments are the subject of the dependent claims. According to the invention, a contoured structural element is proposed for use as a core layer in a curved sandwich composite element, wherein the contoured structural element is formed from a foamed thermoplastic material, in particular PET, wherein the contoured structural element is divided into a plurality of body elements with the exception of a bonding layer, and wherein the body elements and the bonding layer are oriented parallel to a base surface of the structural element that is in a flat state. At least one surface layer of the bonding layer and the surface layer of the body elements adjacent thereto comprise at least partially a thermally compacted layer, wherein the body elements, the bonding layer, and the thermally compacted layer are formed from the same material. In this respect, the invention has surprisingly revealed that by inventively strengthening the surface layer of the contoured structural element, particularly in the region of the bonding layer between the body elements, it is possible to replace the use of additional woven material. Furthermore, the inventive manufacturing process allows for the avoidance of the laborious and particularly time-consuming steps involved in applying woven material. This makes it possible to provide, in a particularly advantageous manner, a structural element that, in addition to possessing high mechanical stability, does not require any additional reinforcing material.It has also been found in a particularly unexpected way that the thermally compacted layer formed by different methods for its production or formation is configured low frFRnnn / cznz / E / YiAi in powder or dust-free, for example, by cutting thermal elements, so that the adhesion or bonding properties of the thermally compacted layer, in addition to mechanical stabilization, are particularly good, for example, for connecting, in particular gluing the thermally compacted layer with a cover layer of a sandwiched composite element. The invention has further demonstrated that by thermally compacting a surface of the foamed plastic, some of the pores can be closed and the local cross-section enlarged, so that the ductile fracture behavior can be adjusted similarly to that of a perforated plastic film. Therefore, the thermally compacted layer acts as a woven material that locally reinforces the foamed material, and the reinforcement can be achieved without a significant increase in weight. Furthermore, the invention has proven that the thermally compacted layer not only stabilizes the contoured structural element, but also partially seals the open pores on a surface of the contoured structural element previously processed by a cutting process, so that unnecessary resin absorption can be avoided. The thermally compacted layer is made from the same material as the body elements and, optionally, the adjacent bonding layer. This means that the structural element according to the invention comprises a material that forms the body elements in different spatial areas and, advantageously, the bonding layer in other spatial areas, and which, furthermore, in a thermally compacted state and again in other spatial areas, forms the thermally compacted layer. In general, therefore, the invention results in a core layer, which certainly has several different regions, but only one material, which locally in the compacted layer undergoes a transformation process, namely, a compaction process. According to the invention, at least one surface layer of the bonding layer and the adjacent surface layer of the body elements form the base surface of the contoured structural element, wherein the thermally compacted layer extends across the entire surface of the base surface of the contoured structural element. This embodiment is particularly advantageous if the contoured structural element can be produced by a hot-wire cutting process and the hot-wire cutting process simultaneously thermally compacts the base surface of the contoured structural element and preferably partially thermally seals the pores of the contoured structural element. By means of a cutting process to separate, i.e., separating a plate-shaped structural element from a spongy block or cutting depressions in a plate-shaped structural element, pores are opened in the spongy material, which otherwise preferably has predominantly closed cells, so that an adhesive or laminating resin, in particular a polyester resin, vinyl ester resin, epoxy resin, or phenolic resin, can penetrate the pores of the contoured structural element. Beyond a certain depth of penetration, and therefore a certain amount of penetration, the adhesive resin no longer has a positive effect on the adhesive effect but instead only increases the weight of the contoured structural element, which is disadvantageous for lightweight construction applications where a sandwich component formed with such a contoured structural element is intended to be used as a supporting structural component.However, it should be noted that a smooth, pore-free surface also has a detrimental effect on the adhesion of the adhesive resin, as the adhesive resin cannot anchor itself sufficiently to the contoured structural element. For this reason, a thermally compacted layer according to the invention, which is intended for contact with adhesive resin, is preferably made so that the partially thermally sealed surface has fewer pores for penetration of the adhesive resin than an area where the surface was created by sawing, with the remaining open pores making it possible for the resin to anchor. A partially thermally sealed layer of this type is described in document DE 10 2012 102 689 Al, to which corresponding description is referred in full, the described features of the partially sealed layer are included herein in full in the application as part of the invention within the context of an improvement. In particular, if the contoured structural element is to be sandwiched between two cover layers, it is preferable that a surface of the body elements, opposite the bonding layer, which in the flat state of the contoured structural element is parallel to the base surface, comprises a thermally compacted surface layer, preferably partially sealed. This ensures that the surfaces bonded to the cover layer of a sandwiched composite element are partially sealed, thereby reducing resin absorption and consequently lowering the weight of the sandwiched composite element. It is also preferred that the thermally compacted layer form a flat and / or uniformly strong layer on the flat surface of the contoured structural element, so that the bonding layer is reinforced and partially sealed uniformly on the base surface of the contoured structural element. This prevents mechanical weak points and the potential formation of cracks at these points and their propagation. Furthermore, uniform resin absorption can be achieved, resulting in uniform bond strength to the cover layer of a sandwiched composite element. It is particularly preferred that at least the surfaces intended for contact with the resin material of the contoured structural element be partially heat-sealed. Preferably, the surfaces between the body elements, which can be produced, for example, by cutting a plate, are also partially sealed, thus reducing resin absorption in these areas as well. Preferably, the thickness of the thermally compacted layer is between 0.01 mm and 1.00 mm, preferably between 0.10 mm and 0.70 mm, more preferably between 0.15 mm and 0.60 mm, and preferably between 0.25 mm and 0.35 mm in the flat state of the contoured structural element perpendicular to the base surface. Mechanical stability increases with increasing thickness, while the adhesion of an adhesive resin to the thermally compacted layer decreases with increasing thickness, as the pores of the expanded thermoplastic material become increasingly sealed. A thickness of the thermally compacted layer in accordance with the invention preferably ensures sufficient mechanical stability and, at the same time, sufficient adhesion to a cover layer of a sandwiched composite element. Preferably, the thermally compacted layer completely forms the bonding layer. In this case, the bonding layer does not include any additional brittle foam material, which can break when bent or under light loads. Broken foam material can lead to the formation of dust or loose foam particles that can contaminate a sandwiched composite element and reduce its mechanical properties. For the thermally compacted layer, preferably partially sealed, the gloss value of the thermally compacted surface, measured at 60°C in accordance with DIN 67530-1982, must be between 2 and 10 gloss units. 100 gloss units corresponds to a reference glass body, for example, a flat plate of polished black glass. If the thermally compacted layer is produced by a cutting process using thermal elements, care must be taken when measuring the gloss value to ensure that the direction of irradiation is parallel to the cutting direction of the thermal element.The use of gloss value as a parameter to describe the surface of the thermally compacted layer is based on the idea that a surface with very few pores, particularly a completely sealed one, which has too low a resin absorption, achieves too high a gloss value, which is then accompanied by a poor adhesive effect; and, on the other hand, a surface that is too intensely porous, such as that obtained by sawing, has too low a gloss value, which, although accompanied by good adhesion, nevertheless suffers from too high a resin absorption. In an improved form, the contoured structural element is preferably divided into body elements according to a regular pattern, such as a checkerboard and / or hexagon. This division can be advantageously performed in a two-stage or multi-stage sawing process. This is particularly advantageous if the curved state of the structural element is not predetermined and the contoured structural element is to be used universally for unilateral or bilateral curves and different radii of curvature. Alternatively, the contoured structural element is divided according to the curve of the structural element. For example, by dividing the contoured structural element into a first curved section in a first plurality of body elements and into a second, less curved section in a second plurality of body elements, wherein the second plurality is smaller than the first plurality and preferably comprises a larger cross-section or a greater volume than the first plurality. This means that preferably the size and / or shape and / or volume of the respective body elements can be adapted to the shape, in particular the curvature, required by the structural element. Preferably, the body elements have a rectangular or trapezoidal cross-section. A rectangular cross-section is particularly easy to produce or configure. However, a trapezoidal cross-section can be advantageous if the gaps between the body elements need to be closed in the curved state of the contoured structural element. In an improvement, the body elements are preferably welded to their surfaces in the curved state of the contoured structural element. This consolidates the curved state of the contoured structural element. If the space between the body elements in the curved state of the contoured structural element is not completely closed, then it is preferable that at least the surfaces opposite the base surface of the contoured structural element be welded to each other in a line along the edges towards the depressions, so that the face opposite the base surface of the contoured structural element forms a closed surface to prevent resin material from penetrating the spaces between the body elements. Welding the body elements further increases the stiffness of a curved sandwich composite element. It is particularly convenient that the welding of the body elements be effected by fusing the lateral surfaces of the body elements to be joined, for example, by means of a thermal element or a heating blade, and subsequent joining of the same, the fusion zones hardening by forming surface-to-surface welding seams in the form of intermediate layers of pore-deficient or pore-free plastic, which preferably takes place without additional additives such as adhesive resins, so that the contoured structural element as such is made up exclusively of plastic and, namely, of the synthetic thermoplastic material, in particular PET. In a particularly advantageous embodiment of the invention, the temperature of the thermal element or elements is adjusted and at the same time the relative speed between the thermal element or elements and the body element is selected so that the brightness value is achieved within a range of values ​​between 2 and 10 mentioned above. Furthermore, it is preferred that the thermally compacted layer withstand more than 20, preferably more than 40, more preferably more than 300, and most preferably more than 1000 bending cycles between 0 and 180°, the bending being carried out in such a way as to increase the spacing between the body elements. In the case of a contoured structural element without a thermally compacted layer, the bonding layer breaks on average after fewer than 20 bending cycles. Preferably, the compacted, preferably partially sealed, layer of the contoured structural element is produced by hot-wire cutting. Cutting a contoured structural element by hot-wire cutting advantageously allows for the simultaneous thermal compaction of the cut surfaces of the contoured structural element. The invention also relates to a method for producing a previously described contoured structural element, configured according to the concept of the invention, wherein a plate-shaped structural element is made available, separated from a block of thermoplastic material, preferably extruded, particularly PET. In this case, the separated surfaces are thermally compacted, preferably at least the base surface of the plate-shaped structural element is thermally compacted. Preferably, the thermally compacted surface, or preferably the thermally compacted base surface, can be produced or manufactured by cutting with thermal elements. In principle, however, other methods can also be used. For example, contact with a heated surface can be used to produce the thermally compacted layer. According to the teaching of the invention, it can be envisaged that the thermally compacted layer is formed before the body elements are configured, for example, by cutting, sawing, thermal cutting, milling, or similar processes. This can be particularly advantageous if the generation of the thermally compacted layer occurs simultaneously with the cutting of plate-shaped structural elements from a larger spongy body or spongy block, so that plate-shaped structural elements with thermally compacted surfaces on one or both faces are produced first. From one of these surfaces, with or without a thermally compacted or surface layer, depressions / contours can be created to contour the plate-shaped structural element and divide it into body elements with a bonding layer. However, alternatively, it can also be foreseen that a contoured structural element is formed first, which is then provided with the thermally compacted surface layer(s). The following description of a thermal cutting process for the production of a plate-shaped structural element with a partially heat-sealed layer is set out in DE 10 2012 102 689 Al, and the corresponding description is referenced in its entirety. The content of the description in DE 10 2012 102 689 Al is therefore an integral part of this description. It was found that the temperature of the heating element, particularly a hot wire, is critical for the success of the thermal cutting process, especially in combination with the relative speed of the heating element to a block of fluffed material. Good results with respect to the desired surface texture were achieved with a heating element temperature between 300°C and 700°C, particularly between 400°C and 700°C, and preferably between 500°C and 700°C. This temperature should be set at least at the beginning of the cutting or separating process. Preferably, the temperature is maintained at least approximately the same temperature throughout the cutting or separating process. It is also essential that, in combination with the frFRnnn / cznz / E / YiAi temperature shown above, for separation a relative speed between the thermal element and the block of spongy material is used by moving the thermal element and / or the block of spongy material within a range of values ​​between 50 mm / min and 150 mm / min. The temperature and feed rate values ​​mentioned above apply in particular to a spongy block material having a density (including air pockets) in the range of between 50 kg / m3 and 250 kg / m3, preferably between 60 kg / m3 and 150 kg / m3. It was found that the optimal feed rate for achieving the desired gloss levels depends on the density of the foam block being processed. For a foam block with a density of 60 kg / m³, the feed rate of the heating element is preferably selected from a range of 100 mm / min to 140 mm / min. For a foam block with a density of 100 kg / m³, the feed rate is preferably selected from a range of 65 mm / min to 85 mm / min. For a foam block with a density of 130 kg / m³, the feed rate is preferably selected from a range of 50 mm / min to 70 mm / min. This in turn is due to the fact that the sealing energy frFRnnn / cznz / E / YiAi required per surface to be partially sealed by means of the thermal element depends on the density of the sponged material block. The following functional relationship was found to be valid for calculating energy: E = 1 / 2 x (U x I) / (v x L) E represents the energy that will be introduced per surface to be partially sealed. The electrical energy used is calculated from the product of the electrical voltage U applied to the heating element and the current I flowing through the heating element. This product is divided by the product of the heating element's travel speed v, specifically the hot wire, and the length L of the heating element, measured perpendicular to the direction of travel. The unit of energy is Wh / m², where W is watts, h is hours, and m is square meters. The factor 1 / 2 accounts for the fact that two partially sealed surfaces are produced simultaneously per heating element. Preferably the width of the block of spongy material, measured parallel to the longitudinal extension of the thermal element, corresponds to at least 60%, preferably between 70% and 95% of the length of the thermal element. The optimum brightness values ​​of the surface frPRnnn / cznz / E / YiAi resulting from the corresponding flat side are obtained if an energy per surface to be partially sealed is introduced via the thermal element, in particular the hot wire, which is calculated according to the following functional linear relationship. E [Wh / m ] = m [Whm / kg] x density of spongy block [kg / m3] o + b [Wh / m ] In this case, m is preferably selected from a range of values ​​between +0.12 and +0.20 Whm / kg, and even more preferably from a range of values ​​between +0.12 and +0.18 Whm / kg. At the same time, b is preferably selected from a range of values ​​between -0.5 and +0.5 Wh / m², and particularly preferably between -0.5 and 0.0 Wh / m². For a density of 60 kg / m3, the following preferred limits for the energy / sealing energy introduced per surface result: 6.7 Wh / m2 to 12.5 Wh / m2, in particular 6.7 Wh / m2 to 10.8 Wh / m2. For a density of the foamed material block of 100 kg / m3, preferred energy ranges result between 11.5 Wh / m2 and 20.5 Wh / m2, preferably between 11.5 Wh / m2 and 18.0 Wh / m2. For a sponged material with a density of 130kg / m3, the following preferred limits for the energy introduced are between 15.1 Wh / m2 and 26.5 Wh / m2, preferably between 15.1 Wh / m2 and 23.4 Wh / m2. It was particularly preferred that the diameter of the hot wire, preferably cylindrical, be selected from a diameter value range between 0.25 mm and 2.0 mm, in particular between 0.25 mm and 1.00 mm, preferably between 0.40 mm and 0.80 mm. As already mentioned, the division of the spongy block into the plate-shaped structural element can be followed by production, in particular by cutting depressions on at least one face, in particular the face of the plate-shaped structural element opposite the base surface by sawing, laser engraving, milling or heat cutting process, so that the plate-shaped structural element is divided into a plurality of body elements except for a bonding layer and the inventive contoured structural element is formed. In particular, a laser engraving or heat cutting process can simultaneously thermally compact the cut surfaces of the body elements and further strengthen the bonding layer. However, sawing is preferred due to its faster processing speed. The invention also leads to a sandwiched composite element, in particular for the manufacture of wind turbine blades and / or for applications in the marine sector, in particular for the production of boat hulls and boat decks, in the field of rail transport, in particular for the manufacture of train fronts, roofs, floors, railway wagon wall elements, in public transport on streets, in particular for the manufacture of roofs, floors, bus fronts, for structural applications in the construction sector, e.g., roofs and many other things, wherein the curved sandwiched composite element, in addition to the inventive contoured structural element, comprises at least one cover layer bonded to the contoured structural element, in particular, two cover layers housing the contoured structural element between them,Whereas it is preferred that at least one cover layer be made of fiberglass-reinforced plastic. The invention is preferably suitable for the production of curved sandwich composite elements in the resin infusion process. The fiber composite, in layers or woven form, including the core material, is assembled in a dry state. It is then covered with a vacuum-sealed film and sealed at the edge. A vacuum applied to the film then draws liquid resin from a storage container through the structure and thereby infuses the composite. The curing or reaction of the resin generally takes place at room temperature, but it can also be carried out at elevated temperatures. Therefore, the invention also relates in particular to a curved sandwich composite element, which was produced in the resin infusion process, it being essential that the resin, specifically the laminating resin, be drawn into the layered structure by means of vacuum, it being particularly preferred that the resin connecting the cover layers with the contoured structural element be at the same time the resin of the cover layers with which the layers or fabric of the cover layers are embedded. Brief Description of the Figures Other advantages and details of the invention result from the following description of preferred embodiments of the invention and based on the figures. They show: Figure 1: A perspective view of the contoured structural element consisting of rectangular body elements with a bonding layer and a thermally compacted base surface, Figure 2a: A side elevation view of two body elements in accordance with Figure 1, with a photograph of the corresponding construction component, Figure 2b: a side elevation view in accordance with Figure 2a in a curved state, Figure 3a: A side elevation view of two body elements in accordance with Figure 2a, wherein the body elements have a trapezoidal cross-section, Figure 3b: a side elevation view in accordance with Figure 3a in a curved state, Figures 4a-4c: Side elevation views of two body elements in accordance with Figure 2a, wherein the contoured structural element is represented in three states of curvature between 0 and 180°, Figure 5a: A side elevation view of the contoured structural element, wherein the bonding layer is arranged on the base surface and the opposite surface of the body elements, Figure 5b: a side elevation view of the contoured structural element according to Figure 5a in a doubly curved state, Figure 6a: A side elevation view of two contoured structural elements, which are thermally welded to each other, and Figure 6b: A side elevation view of two contoured structural elements in accordance with Figure 6a in a doubly curved state, which are thermally welded to each other. Identical elements or elements with the same function are provided with the same reference numbers in the figures. Detailed Description of the Invention Figure 1 depicts a contoured structural element 100 for use as a core layer in a curved sandwich composite element consisting of a thermoplastic foam material, wherein the contoured structural element 100 is divided into a plurality of body elements 10 except for a bonding layer 12 of the same material. The contoured structural element 100 is shown in a flat, non-curved state, and the body elements 10 and the bonding layer 12 extend parallel to a base surface 26 of the contoured structural element 100. According to the definition of the present invention, a transition between adjacent body elements 10 is configured, except in the edge regions, by means of a bonding layer 12, which is characterized in Figure 1 by a bonding region A and is delimited by dashed vertical lines. A surface layer 16 of the bonding layer 12 and the adjacent surface layer 18 of the body elements 10 have a thermally compacted layer 14. The thermally compacted layer 14 is of the same material as the body elements 10 and the bonding layer 12. The contoured structural element 100 is preferably divided such that the surface layer 16 of the bonding layer 12 and the surface layer 18 of the body elements 10 form the base surface 26 of the contoured structural element 100. In this case, the entire base surface 26 of the contoured structural element 100 preferably comprises a thermally compacted layer 14 over its entire surface. Advantageously, this thermally compacted layer 14 can be produced over its entire surface by a hot-wire cutting process, in which the entire base surface 26 of the contoured structural element 100 can be compacted in a short time. Advantageously, a surface 24 of the body elements 10 opposite the bonding layer 12, which is oriented parallel to the base surface 26 in the flat state of the contoured structural element 100, also comprises a thermally compacted surface layer 14, preferably partially sealed (see Figure 5a). In particular, if the contoured structural element 100 comes into contact with resin material on both sides, partial thermal sealing of both sides is particularly advantageous. It should be noted that the thermally compacted layer 14 of the contoured structural element 100 refers to a heat treatment of the contoured structural element 100 itself and not to a subsequently applied / bonded thermally compacted layer of an identical or different material. This means that, although there is a transition from a compacted to a non-compacted area within the same connected or single-piece material, there are no bonding surfaces where different layers of material are joined together. In other words, the body elements 10, the bonding layer 12, and the thermally compacted layer 14 are preferably produced from the same material and from a single-piece basic element, for example, a plate-shaped structural element. Alternatively, it is possible that the surface layer 16 of the bonding layer 12 and the surface layer 18 of the body elements 10 adjacent to it may have partially, preferably in a bonding region A, a thermally compacted layer 14, so that in particular the edge region 28 between the bonding layer 12 and the body elements 10 is also stabilized by the thermally compacted layer 14. In the case of a bending stress of the contoured structural element 100, the edge area 28 of the bonding layer 12 may be broken in particular due to the increase in notch stresses, so that the surface layer 18 of the body elements 10 is reinforced at least in the bonding region A. In a flat state of the contoured structural element 100, the thermally compacted layer 14 preferably forms a flat and / or uniformly strong layer, so that the bonding layer 12 is uniformly reinforced over the base surface 26 of the contoured structural element 100. It is also preferred that at least the surfaces of the contoured structural element 100 intended for contact with the resin material be partially heat-sealed. Preferred surfaces of the contoured structural element 100 include, in particular, the base surface 26 of the contoured structural element 100 and the surface 24 of the body elements 10 opposite the base surface 26. Additionally, the surfaces 20 of the body elements 10, which, according to Figures 2a and 2b, face an intermediate space 32, may also be partially heat-sealed. Partial sealing can favorably influence the bonding properties and resin absorption of the surfaces. Furthermore, it can reduce dust, which again improves the properties mentioned above. Preferably, the thickness d of the thermally compacted layer 14 in the flat state of the contoured structural element 100, perpendicular to the base surface 26, is between 0.01 mm and 1.00 mm, preferably between 0.10 mm and 0.70 mm, more preferably between 0.15 mm and 0.60 mm, and most preferably between 0.25 mm and 0.35 mm. This thickness d of the thermally compacted layer 14 preferably ensures sufficient mechanical stability of the bonding layer 12 and sufficient adhesion to a cover layer of a sandwiched composite element. Mechanical stability increases with increasing thickness d. On the other hand, adhesion to a cover layer decreases with increasing thickness d, as more and more pores of the thermoplastic foam material are sealed, so that in a subsequent gluing process or lamination process or vacuum injection process, a resin material cannot anchor itself to the enlarged surface of the pores. The bonding layer 12 can be designed to be formed precisely by the thermally compacted layer 14 itself. For example, the contoured structural element 100 can be sawn up to or just before the thermally compacted layer 14. In this way, it is possible to prevent uncompacted, spongy, and therefore brittle material from remaining between the body elements 10, which can easily break under certain circumstances and contaminate the sandwiched composite element or reduce the mechanical stability of the sandwiched composite element due to loose elements. Alternatively, the non-thermally hardened layer of the bonding layer 12 should preferably be minimized, as otherwise it would limit the bending of the structural element and the hinge effect of the bonding layer 12. For the thermally compacted layer 14, preferably partially sealed, a gloss value of the thermally compacted surface, for example, the thermally compacted base surface 26, should be between 2 and 10 gloss units measured at 60° according to DIN 67530-1982. The contoured structural element 100 is, as shown in Figure 1, preferably divided into body elements 10 according to a regular, checkerboard-like pattern. This subdivision can be advantageously carried out in a two-stage sawing process, in which saw patterns are produced with one or more saws that are preferably arranged at an angle, in particular perpendicular to each other. Additionally or alternatively, the contoured structural element 100 can also be divided into body elements 10 in accordance with a preferably regular hexagonal pattern. As shown in Figure 1 and the detailed view in Figure 2a, the body elements 10 have a preferably rectangular cross-section. This cross-section can be advantageously produced using a two-stage sawing method. In a curved state of the contoured structural element 100, as shown in Figure 2b, it is possible to bend the body elements around the y-axis. A bilateral bend around the x and y axes is also possible, but is not shown here. The body elements 10 are preferably bent toward each other until the inner surfaces 20 of the body elements 10 come into at least partial contact at a contact surface 30. Body elements 10 with a rectangular cross-section are easy to produce, but the contoured structural element 100 then also has gaps 32 in the curved state. These intermediate spaces 32 could be filled with resin material in a subsequent process and thus the weight of the contoured structural element 100 could be increased. The maximum angle of curvature α between two body elements 10 is advantageously between 2° and 3°, so that the slope jumps on the curved surface 26 of the contoured structural element 100 are small enough that the deviation of, for example, an arc of a circle can be compensated for with resin material, so that the slope jumps are not transferred to a cover layer bonded to the curved structural element 100. In the case of strongly curved sandwiched composite elements, it is necessary to increase the number of body elements 10 per unit length accordingly. To prevent the inclusion of resin material in the intermediate space 32, the body elements 10 alternatively have a trapezoidal cross-section according to Figure 3a, such that in the curved state of the contoured structural element 100, the surface 20 of the body elements 10 facing the intermediate space 32 are in contact at least partially, preferably over their entire surface. Figure 3b shows such a curved state, in which the entire intermediate space 32 between the body elements 10 is closed.Preferably, the dimensions of the trapezoidal cross-section are designed according to the curvature angle α, so that the body elements 10 are preferably in full surface contact in the curved state of the contoured structural element 100, for example, by designing an opening angle γ of the intermediate space 32 between the trapezoidal body elements according to the intended curve of the structural element 100. In this, the cross-section of the body elements 10 can adopt a more complex geometry, in case bilateral curvature around the xy axis and around the y axis is required, and the respective curves have different curvature angles. Preferably, a width b of the gap 32 between the body elements 10 and a height h of the contoured structural element 100, or a height of the gap 32 according to the curve of the contoured structural element 100, are selected so that in the curved state of the contoured structural element 100, the surfaces 20 of the body elements 10 facing an gap 32 are at least partially in contact, preferably over the entire surface 20. A closed gap 32 can prevent resin absorption. The subdivision of the contoured structural element 100 can deviate from a regular pattern similar to a chessboard. Furthermore, it would be conceivable to weld the body elements 10 together along the contact surface 30, so as to consolidate the curved state of the contoured structural element 100 and to permanently prevent penetration of resin material into the intermediate spaces 32 of the body elements 10. Preferably, the contact surfaces 30, as shown in Figure 3b, are welded together over their entire surface. In the manipulation of the contoured structural element 100, or for sandwiched composite elements with curves in different directions, it may happen that the contoured structural element 100 bends in such a way that the intermediate space 32 increases compared to the flat state of the contoured structural element 100. Figures 4a-4c represent such curvature of the contoured structural element 100 by an angle β in three states between 0°, a flat contoured structural element 100, and 180°, a contoured structural element 100 with maximum curvature. In Figure 4b, an angle β of approximately 50° is shown, where a non-compacted portion of the bonding layer 12 is broken and the body elements 10 are held together exclusively by the thermally compacted layer 14.The body elements 10 can be bent further to the state shown in Figure 4c without causing a rupture of the thermally compacted layer 14. A bending cycle between 0 and 180° for a contoured structural element 100 having a thermally compacted layer 14 can be repeated more than 20 times, preferably more than 40, particularly preferably more than 300, and very particularly preferably more than 1000 times, without causing a failure of the thermally compacted layer 14. If the thermally compacted layer 14 is not present, the body elements 10 already split in two with an average number of bending cycles of less than 20 cycles. The high fatigue resistance of the thermally compacted layer 14 allows it to replace a woven material, with stability not only being sufficiently guaranteed for a small curvature in a shape, but also for stresses in handling the contoured structural element 100; for example, if the contoured structural element 100 needs to be cut or aligned in a shape. For a contoured structural element 100 with thermally compacted layers 14 on both sides, in accordance with Figure 5a, the bonding layer 10 may extend either along the base surface 26 or along the surface of the body elements 24 opposite the base surface 26. With this subdivision, a contoured structural element 100 can be produced for shapes with changing curve directions. Alternatively, it is also possible to weld one to another two contoured structural elements 100 by way of their lower surfaces 26 in accordance with Figure 6a. This doubly contoured structural element is, as shown in Figure 6b, also suitable for changing curve directions. Preferably, the compacted layer 14, preferably partially sealed, is produced by hot wire cutting. With the hot wire cutting process, the contoured structural element 100 can be cut to size from a block of spongy material, and simultaneously the base surface 26 of the structural element 100, as well as the surface 24 of the body elements 10 opposite the base surface 26, can be compacted and partially sealed. The contoured structural element 100 shown in Figure 1 is produced from a preferably plate-shaped structural element made of extruded, sponged thermoplastic material with preferably thermally compacted surfaces. The plate-shaped structural element is then divided, with the exception of a bonding layer 12, into a plurality of body elements 10, in particular by cutting depressions into at least one face of the plate-shaped structural element by means of sawing, laser engraving, milling, or heat cutting methods. A sandwiched composite element can be produced by fixing a cover layer, in particular of fiberglass-reinforced plastic, preferably by means of a resin, onto the base surface 26 of the contoured structural element 100 and on the surface 24 of the body elements 10 opposite the base surface 26. Preferably, a first cover layer and / or a second cover layer are fixed in the infusion process. The contoured structural element 100 described so far can be altered and modified in many ways without departing from the inventive idea. Thus, for example, it is conceivable to thermally compact the intermediate spaces 32 of the body elements 10 with a hot wire, laser, or hot element tip. For example, the doubly contoured structural element shown in Figure 6a can be produced from a single piece by cutting from two faces into a plate-shaped structural element and then thermally compacting the bonding layer 12, or by thermally compacting the surfaces of the intermediate spaces 32 between the body elements 10 in a laser engraving process or with a hot element (wire, hot tip, or hot blade). List of reference symbols Body element Bonding layer thermally compacted layer Bonding layer surface Surface of the body element Surface of the body element in an intermediate space Surface opposite the base surface Base surface of the contoured structural element Contact surface of body elements Intermediate space between body parts 100 Contoured structural element x,y,z Spatial axes of a Cartesian coordinate system a Angle of curvature β Opening angle between body elements frFRnnn / cznz / E / YiAi γ Opening angle between trapezoidal body elements h Height of the contoured structural element b Width of the intermediate space d Thickness of the thermally compacted layer It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A contoured structural element for use as a core layer in a curved sandwich composite element, wherein the contoured structural element is formed from a thermoplastic, sponged material, in particular PET, wherein, except for a bonding layer, the contoured structural element is divided into a plurality of body elements, and wherein the body elements and the bonding layer are oriented parallel to a base surface of the contoured structural element that is in a flat state, wherein at least one surface layer of the bonding layer and the surface layer adjacent thereto of the body elements have at least partially a thermally compacted layer, wherein the body elements, the bonding layer, and the thermally compacted layer are made of the same material,characterized in that at least one surface layer of the bonding layer and the surface layer of the body elements adjacent to it form the base surface of the contoured structural element, and in that the thermally compacted layer, preferably a partially sealed layer, extends with its entire surface over the base surface of the contoured structural element.

2. Contoured structural element according to claim 1, characterized in that a surface of the body elements opposite the bonding layer which in the flat state of the structural elements is oriented parallel to the base surface also comprises a thermally compacted surface layer, preferably partially sealed.

3. Contoured structural element according to any of claims 1 or 2, characterized in that the thermally compacted layer forms a flat and / or uniformly resistant layer in a flat state of the structural element.

4. Contoured structural element according to any of claims 1 to 3, characterized in that at least the surfaces of the structural element intended for contact with the resin material are partially thermally sealed.

5. Contoured structural element according to any of claims 1 to 4, characterized in that the thickness of the thermally compacted layer in the flat state of the structural element perpendicular to the base surface is between 0.01 mm and 1.00 mm, preferably between 0.10 mm and 0.70 mm, more preferably between 0.15 mm and 0.60 mm, and most preferably between 0.25 mm and 0.35 mm.

6. Contoured structural element according to any of claims 1 to 5, characterized in that the thermally compacted layer forms the bonding layer.

7. Contoured structural element according to any of claims 1 to 6, characterized in that a gloss value of a surface of the thermally compacted layer measured at 60° in accordance with DIN 67530-1982 amounts to between 2 and 10 gloss units.

8. Contoured structural element according to any of claims 1 to 7, characterized in that it is divided into body elements in accordance with a regular pattern in the manner of a chessboard and / or hexagon and / or the body elements have a rectangular cross-section or a trapezoidal cross-section.

9. Contoured structural element according to any of claims 1 to 8, characterized in that in the curved state of the structural element the body elements are preferably thermally welded flat relative to each other.

10. Contoured structural element according to any of claims 1 to 9, characterized in that the compacted layer, preferably partially sealed, is produced by hot wire cutting.

11. A method for producing a contoured structural element according to any of the preceding claims 1 to 10, comprising the steps of: providing a structural element, preferably plate-shaped, made of thermoplastic material extruded by foaming; producing, in particular cutting depressions on at least one face, particularly on the face opposite the base surface of the plate-shaped structural element by sawing, laser engraving, milling, or heat cutting processes, so that the plate-shaped structural element is divided into a plurality of body elements with the exception of a bonding layer; characterized in that producing a thermally compacted layer on at least one surface layer of the bonding layer and at least partially on the adjacent surface layer of the body elements, preferably on the base surface.

12. Method for producing a curved sandwich composite element of one or more faces with a contoured structural element according to any of claims 1 to 10, characterized in that it comprises the steps of: - unilaterally or multilaterally curving the contoured structural element, joining at least one face of the contoured structural element with a coating layer of adhesive resin, in particular a fiber-reinforced plastic, preferably in an infusion process.

13. A unilaterally or multilaterally curved sandwich composite element, in particular for the production of blades for wind power plants and / or for applications in the marine sector and / or in the railway sector and / or in public transport on streets and / or for structural applications in the construction sector, characterized in that it comprises a contoured structural element in accordance with any of claims 1 to 10 as a central layer, wherein on at least one face of the contoured structural element a cover layer is fixed by means of adhesive resin, in particular formed from what comprises a fiber-reinforced plastic.