Method for evaluating composition of composite structure

Abstract

The invention provides a method for evaluating the composition of a composite structure. The composite structure comprises a plurality of layers of fibrous material embedded in a thermoset epoxy resin matrix having a cross-linked network structure. The method includes exposing the composite structure to a treatment fluid to at least partially degrade the thermoset epoxy resin matrix. The treatment fluid comprises formic acid and / or acetic acid. The method further includes temporarily constraining the composite structure during exposure to the treatment fluid to maintain the order and / or orientation and / or number of layers of fibrous material. Further, the method includes separating the one or more layers of fibrous material from the one or more other layers of fibrous material, thereby evaluating the composition of the composite structure.

Description

Technical Field

[0001] The present invention relates to composite structures comprising a plurality of layers of fiber material embedded in a thermosetting epoxy resin matrix and, more particularly, to methods of evaluating components of such composite structures. Background Art

[0002] Composite materials, such as fiber-reinforced plastics, are widely used in many fields due to their superior strength and weight characteristics. A typical example is a composite structure consisting of one or more layers of reinforcement material embedded in a polymer matrix. For example, a composite body such as a composite wind turbine blade shell may comprise multiple layers of fiber material embedded in a thermosetting epoxy resin matrix. In many cases, after manufacturing such a composite structure or body, only the exterior and / or interior surfaces of the structure may be visible. Consequently, visual inspection may not be sufficient to assess the composition of the composite structure.

[0003] Evaluating the components of a composite structure can be useful in many different situations. For example, evaluation can aid in quality control or in investigating the cause of a failure or defect. Furthermore, when repairing a composite structure, such as a wind turbine blade, it can be advantageous to arrange substantially equivalent repair materials in substantially the same order and orientation as the existing materials in the composite.

[0004] In existing methods, evaluating the components of a composite structure often involves significant damage to the composite structure, requiring each layer to be mechanically removed (e.g., by grinding) before evaluating each subsequent layer in the structure. In addition to damaging the composite structure, this method is time-consuming and difficult to control. Furthermore, because layers of fiber material must be ground away to reveal the next layer, accurate and detailed evaluation of each layer and its respective component is difficult, as the fiber material can be damaged or destroyed during the evaluation process. Therefore, there is a need for an improved method for evaluating components of a composite structure.

[0005] The present invention is made in this context. Summary of the Invention

[0006] The present invention provides a method for evaluating constituent components of a composite structure. The composite structure comprises a plurality of fiber material layers embedded in a thermosetting epoxy resin matrix having a cross-linked network structure. The method comprises exposing the composite structure to a treatment fluid to at least partially degrade the thermosetting epoxy resin matrix. The treatment fluid comprises formic acid and / or acetic acid. The method further comprises temporarily restraining the composite structure during exposure to the treatment fluid to maintain the order and / or orientation and / or number of the fiber material layers. The method further comprises separating one or more fiber material layers from one or more other fiber material layers to thereby evaluate the constituent components of the composite structure.

[0007] For example, evaluating the composition of the composite structure may involve evaluating at least one of the orientation of the fiber material, the type of the fiber material, the thickness of the fiber material, the number of layers of the fiber material, and / or the order of the layers of the fiber material.

[0008] In some preferred embodiments, the fiber material may include carbon fibers, glass fibers, aramid fibers, metal fibers and / or polyethylene fibers. Thus, in some embodiments, a composite structure comprising a fiber material embedded in a thermosetting epoxy resin matrix may be described as comprising a fiber-reinforced polymer. Specifically, in some embodiments, the fiber material may include one or more sheets, plies or pads of fiber-reinforced materials. For example, the composite structure may include any one of the following materials: one or more woven reinforcing fiber plies, one or more fiber fabric material plies, one or more unidirectional fiber material plies (i.e., reinforcing fibers extend in one direction), one or more multiaxial fiber material plies (i.e., reinforcing fibers extend in multiple selected directions, such as biaxial or triaxial fiber materials), or one or more chopped fiber pads (e.g., felt or veil felt), to name only some possible non-limiting examples.

[0009] In some examples, the fiber material may include fibers selected from one or more of the following: synthetic fibers, semi-synthetic fibers, regenerated fibers, plant fibers, carbon fibers, rock fibers, glass fibers, and / or metal fibers. In some preferred examples, the fibers may be at least one sheet comprising fibers, for example, at least one sheet comprising fibers embedded in a polymer other than a thermosetting epoxy resin matrix.

[0010] In some examples, the composite structure may include metal-containing components. In examples where the composite structure includes metal, the metal material is preferably in the form of a mesh, a net, a wire, or a sensor. The method can facilitate detection of such metal-containing components in the composite structure by at least partially degrading the thermosetting epoxy resin matrix, thereby releasing the or each metal-containing component from the thermosetting epoxy resin matrix.

[0011] The thermosetting epoxy resin matrix of the composite structure may comprise an epoxy-based polymer and at least one reactive curing agent or catalyst. The epoxy resin may be cured by conventional heating or radiation (e.g., ionization, infrared radiation, electron beam, etc.). Additionally or alternatively, the epoxy resin may be cured by at least one curing agent (e.g., one or more anhydride curing agents, and / or one or more thiol curing agents, and / or one or more amine curing agents). In some preferred embodiments, the thermosetting epoxy resin matrix may not contain disulfide bridging groups. In some preferred embodiments, the thermosetting epoxy resin matrix is ​​an amine-cured thermosetting epoxy resin matrix. Examples of amine-cured thermosetting epoxy resins include Olin Airstone 760, Hexion RIMR035C infusion epoxy resin, and Aditya Birla Recyclamine systems. Such epoxy resin systems allow for separation of the fiber material layers by swelling and / or dissolving in an acidic solution containing formic acid and / or acetic acid under relatively mild conditions. For formic acid, solutions of at least 50 wt% formic acid at ambient temperature and pressure have been found to be very effective. However, increasing temperature, pressure, and concentration can accelerate the reaction rate. In some examples, the composite structure can be described as comprising a composite laminate structure, in that multiple layers of fiber material are laminated together via a thermosetting epoxy resin matrix. Additionally, in some examples, the composite structure can comprise a sandwich structure, in which one or more components (e.g., a lightweight core material or composite layer) are sandwiched between inner and outer layers of the composite structure.

[0012] It should be understood that separating one or more layers of fibrous material from one or more other layers of fibrous material can be described as delaminating the multiple layers of fibrous material of the composite structure. Thus, by exposing the composite structure to the treatment fluid, the composite structure may exhibit delamination, i.e., separation into separate layers or separate components.

[0013] As described above, exposing the composite structure to the treatment fluid at least partially degrades the thermosetting epoxy resin matrix. As used herein, unless otherwise specified, degrading the thermosetting epoxy resin matrix includes disrupting the crosslinked network structure of the thermosetting epoxy resin matrix, causing the epoxy resin to lose structural integrity and thereby be unable to bond the components of the composite structure (i.e., the fiber material layers) together. For example, in some examples, degrading the thermosetting epoxy resin matrix may include dissolving the epoxy resin matrix, thereby releasing (i.e., separating) the fiber material layers from the epoxy resin. Alternatively, in some examples, degrading the thermosetting epoxy resin matrix may include swelling the epoxy resin matrix, thereby releasing (i.e., separating) the fiber material layers from the epoxy resin, as described in more detail below.

[0014] It should be understood that "swelling" and equivalent terms as used herein refer to the process by which a swelling fluid enters (i.e., permeates) a thermosetting epoxy resin matrix, spatially opening or expanding the crosslinked network structure of the thermosetting epoxy resin matrix without completely dissolving the thermosetting epoxy resin matrix, thereby increasing the size and / or mass of the composite structure. Furthermore, "swelling fluid" as used herein should be understood to mean a fluid comprising formic acid and capable of swelling and / or decomposing the thermosetting epoxy resin matrix.

[0015] Exposing the composite structure to a treatment fluid containing formic acid and / or acetic acid causes the thermosetting epoxy resin matrix to swell, which facilitates penetration of the treatment fluid into the thermosetting epoxy resin matrix's network. Over time, the swelling of the thermosetting epoxy resin matrix mechanically disrupts the thermosetting epoxy resin matrix's network, forming a large number of thermosetting epoxy fragments that are released from the fiber material layer, thereby releasing the fiber material layer.

[0016] Thus, the method can include allowing the treatment fluid to infiltrate the composite structure for a sufficient period of time to allow the treatment fluid to mechanically disrupt the network structure of the thermosetting epoxy resin matrix. This period of time may depend on the concentration of the treatment fluid (i.e., the concentration of formic acid and / or acetic acid), the size of the composite structure, and the ambient temperature and pressure to which the composite structure is exposed to the treatment fluid. In some examples, the method can include allowing the treatment fluid to infiltrate the composite structure for up to 144 hours, preferably from 1 hour to 130 hours, more preferably from 10 hours to 100 hours, more preferably from 24 hours to 96 hours, more preferably up to 72 hours, and more preferably up to 48 hours.

[0017] In some preferred embodiments, when the composite structure is exposed to the treatment fluid, the treatment fluid can be at least partially liquid, i.e., in a liquid state. In some embodiments, when the composite structure is exposed to the treatment fluid, the treatment fluid can comprise a mixture of a gaseous fluid and a liquid fluid. However, in some particularly advantageous embodiments, when the composite structure is exposed to the treatment fluid, the treatment fluid can be in a liquid state.

[0018] In some preferred embodiments, the composite structure can be exposed to a treatment fluid having a temperature of up to 100°C, for example, 8°C to 75°C, preferably 10°C to 50°C, more preferably 20°C to 35°C, and even more preferably 22°C to 27°C. The composite structure can be exposed to the treatment fluid at atmospheric or elevated pressure. For example, the composite structure can be exposed to a treatment fluid at a pressure of up to 3 bar, preferably up to 2 bar, and more preferably up to 1.5 bar.

[0019] In some examples, the composite structure can be a complete composite body, i.e., a complete composite part. Thus, the method can include exposing the composite body to the treatment fluid. However, in some other examples, the composite structure can be a sample part. Thus, the method can also include extracting the sample part from the larger composite body.

[0020] The sample portion facilitates evaluation of the composition of a composite without causing excessive damage to the composite. Furthermore, the smaller sample portion allows for examination and evaluation under more tightly controlled conditions, resulting in a more accurate and reliable evaluation. Compared to previous evaluation methods (e.g., determining the composition of a composite by grinding individual layers, as described in the background), using the sample portion exemplified by the methods described herein is less damaging to the existing composite. Furthermore, the method facilitates evaluation of the individual components of the sample portion without damaging the fiber material layers of the sample portion. Consequently, these layers can be evaluated and measured in greater detail, resulting in more reliable and accurate information than using previous methods.

[0021] It should be understood that the "larger complex" in this example is defined relative to the sample portion, i.e., the complex is larger than the sample portion. The sample portion may also be referred to as the sample portion. It is worth noting that the function of the sample / sample portion is to facilitate the evaluation or study of the components of the complex without requiring the entire complex to be tested and / or analyzed. Therefore, it should be understood that the terms "sample portion" and "sample portion" are used interchangeably herein.

[0022] In some examples, the composite object may be at least a portion of a vehicle (i.e., a carrier, such as a floating vessel, aircraft, or road vehicle). In other examples, the composite object may be sports equipment, such as a snowboard, bicycle, helmet, or tennis racket. However, this method is particularly advantageous in examples where the composite object is a component of a wind turbine.

[0023] For example, in some examples, the composite body may be a portion of a wind turbine rotor nose cone, fairing, or hub. Alternatively, the composite body may be a nacelle or shell, or a portion of a wind turbine tower, such as a tower wall, tower platform, or hatch. In some particularly advantageous examples, the wind turbine component may be a wind turbine blade component.

[0024] For example, the wind turbine blade component may be a composite reinforced structural component of a wind turbine blade. In some particularly advantageous examples, the wind turbine blade component may be a composite shell of a wind turbine blade. As will be described in greater detail below, this method is particularly advantageous for evaluating the composition of a composite shell of a wind turbine blade, as most blade repairs are performed on the shell. For example, the evaluation can determine the correct fiber material and / or orientation of such fiber material for repairing a damaged area of ​​a composite wind turbine blade shell.

[0025] In addition to facilitating the assessment of fiber content, type, and orientation, this method can also facilitate the assessment of other characteristics of a composite. For example, in some cases, composites and / or composite structures may contain other components in addition to fiber materials. For example, a wind turbine blade may contain lightning protection components, such as lightning conductors and / or lightning collectors. For example, a composite may contain non-composite components, such as metal mesh. Furthermore, in some cases, components may include sensors, heating elements, non-epoxy coatings, core elements, or other non-fiber components in addition to fiber materials. Furthermore, blades may contain different forms of carbon fiber, such as pre-cured pultrusions with different polymer resin matrices, or spun carbon fiber cured in the same epoxy matrix as the rest of the blade or component. Separating the individual layers of a composite structure allows for a more thorough analysis of the carbon materials. It should be understood that this method can facilitate the analysis of such components of a composite structure—either as part of an initial assessment or as an offline, further analysis of components that were initially inaccessible, such as carbon spar caps or sensors that were not fully explored in the initial assessment.

[0026] In some examples, extracting a sample portion from a larger composite structure can include using a mechanical cutting tool to extract the sample portion from the composite structure. This extraction method can advantageously reduce the risk of damaging or displacing components (e.g., fiber materials) of the composite structure (i.e., the sample portion) during extraction. Furthermore, this method can advantageously minimize damage to the composite structure during extraction. In particular, when the extraction of the sample portion is combined with subsequent repair of the composite structure, this method can enable research without permanently compromising the structural integrity of the composite structure.

[0027] In some examples, the sample portion can be extracted from the composite body using a jigsaw or a multi-purpose tool. In some examples, extracting the sample portion from a larger composite body can include extracting the sample portion from the composite body using a rotating tool. In some examples, such a rotating tool can be a disc tool or a saw blade. In some preferred examples, the rotating tool can include a core drill or a hole saw. Thus, the sample portion can be a core sample. Additionally or alternatively, in some preferred examples, the rotating tool can include a cutting edge or cutting teeth with a diamond and / or carbide tip. Similarly, such a cutting device can help minimize damage to the sample portion and the composite body during the extraction process.

[0028] In some examples, after extracting the sample portion from the larger composite body, the method may include the step of restoring the extracted sample portion to the larger composite body. This may be achieved, for example, by applying an adhesive or resin (e.g., a filling adhesive or an expanding adhesive) to the location where the sample portion was extracted. Optionally, the adhesive or resin may be reinforced with glass fiber sheets or chopped fibers.

[0029] In some examples, a larger composite may include a damaged area. Thus, the method may include extracting a sample portion from a location on the composite that is no more than 1 meter (preferably no more than 0.5 meters) away from the damaged area. Thus, the method may be implemented in particularly advantageous examples to evaluate the composition of a composite near an area requiring repair. Thus, the method may assist in research to determine the correct material to use for repairing a damaged area of ​​a composite. Furthermore, in some advantageous examples, the method may beneficially assist in determining the orientation of fiber material near the damaged area. This helps to ensure that when repairing the composite, the correct repair material (i.e., material that is substantially the same as that present in the existing composite) is arranged in the correct orientation, i.e., in an orientation that is substantially the same as the orientation of the existing material in the composite.

[0030] For example, as previously described, the composite body can be a composite shell, shear web, or other component of a wind turbine blade. Such wind turbine blades may become damaged during use, for example due to erosion, lightning strike, or impact damage (e.g., bird strike). Accordingly, the composite body (e.g., a composite wind turbine blade) can include a damaged region, and the method can include extracting a sample portion from the composite body at a location no more than 1 meter (preferably no more than 0.5 meters) from the damaged region. As generally described above with respect to the composite body, the method described herein facilitates the study and evaluation of the components of a composite wind turbine blade so that the blade can be repaired using materials that are substantially equivalent to the existing materials of the composite wind turbine blade shell and arranged in substantially equivalent directions. This helps ensure that load paths are accurately replaced, rebuilt, or (if necessary) reinforced when repairing the blade.

[0031] Furthermore, by extracting sample sections (i.e., composite structures) from a wind turbine blade shell to investigate the composition of the shell, unnecessary additional damage to the blade composite can be avoided. This means that, after assessing the composition of the composite structure, repairs to the blade shell can be made relatively simply. In contrast, previous repair methods required extensive sanding operations to remove material around the damaged area, often resulting in large chamfered grooves to determine the type and orientation of the fiber material required for the repair. It is therefore clear that the method described herein can minimize this additional damage to the blade, thereby reducing the cost and time required for repairs, while also improving the structural integrity and performance of such repairs.

[0032] In some examples, the width of the sample portion may be between 0.010 and 0.100 meters, preferably between 0.025 and 0.075 meters, and more preferably between 0.04 and 0.06 meters. This helps ensure that the sample portion accurately represents the composition of the composite. For example, a sample portion having a width that meets the aforementioned minimum requirements helps ensure that the sample is large enough to accurately represent the composition of the composite, taking into account any potential variations in the arrangement of the fiber materials in the composite, such as variations in the type and orientation of any fiber materials, variations in the density and / or basis weight of the fiber materials, or any other variations that may occur during the composite manufacturing process. Furthermore, a sample portion having a width that meets the aforementioned maximum requirements helps ensure that the composite is not unnecessarily damaged. Specifically, it limits the size of the sample portion extracted from the composite, helping to ensure that extraction of the sample does not compromise the structural integrity of the composite. In some examples, the width of the sample portion may be 0.050 meters. It should be understood that in some examples, the width of the sample portion may also be referred to as the diameter of the sample portion.

[0033] The size of the sample portion is preferably small relative to the size of the complex being studied. Preferably, the area of ​​the sample portion is less than 2% of the area of ​​the complex, more preferably, the area of ​​the sample portion is less than 1% of the area of ​​the complex, and even more preferably, the area of ​​the sample portion is less than 0.5% of the area of ​​the complex.

[0034] In some examples, the sample portion can have an aspect ratio of less than 1:2, preferably less than 1:1.75, and more preferably less than 1:1.5, where the aspect ratio is defined as the ratio of the width of the sample portion to the height of the sample portion. This helps ensure that the composite structure (i.e., the sample portion) and its components remain stable upon exposure to the treatment fluid and subsequent degradation of the thermosetting epoxy resin matrix, thereby facilitating accurate assessment of the sequence and / or orientation of the components (i.e., the fiber material layers).

[0035] It is worth noting that in examples where the sample portion is substantially cylindrical, such as examples where the sample portion is removed from the composite body using a rotating mechanical cutting tool (e.g., a hole saw or a core drill), the width of the sample portion is the diameter of the sample portion. Therefore, any reference herein to the width of the sample portion should be understood to be equivalent to the diameter of the sample portion.

[0036] In some examples, the treatment fluid may contain at least 20 wt% formic acid, preferably at least 50 wt% formic acid, and more preferably at least 80 wt% formic acid. Formic acid, also known as methanoic acid, is liquid at 20°C and 1 atmosphere. The concentration of formic acid in the treatment fluid may be selected based on the composition and / or crosslink density of the thermosetting epoxy resin matrix.

[0037] Alternatively, in some other examples, the treatment fluid may be a dissolving liquid. For example, the treatment fluid may contain acetic acid and / or formic acid. Thus, exposing the composite structure to the treatment fluid dissolves the thermosetting epoxy resin matrix in the composite structure. For example, the thermosetting epoxy resin matrix may be a chemically decomposable epoxy-type resin, such as It decomposes into soluble epoxy fragments when exposed to treatment fluids containing formic and / or acetic acid. Dissolution of the thermosetting epoxy matrix releases the components of the composite structure for simple evaluation.

[0038] In some examples, the treatment fluid may further comprise one or more additional components in addition to formic acid and / or acetic acid. Thus, the treatment fluid may be an aqueous solution comprising formic acid and / or acetic acid. The additional components of the treatment fluid may include at least one additional organic acid, trifluoroacetic acid, trichloroacetic acid, propionic acid, methanesulfonic acid, trifluoromethanesulfonic acid, performic acid, or anhydrides of any of these organic acids. Additionally or alternatively, the one or more additional components may include at least one inorganic acid, such as hydrochloric acid. Furthermore, in some examples, the one or more additional components may include at least one alcohol, such as methanol, ethanol, propanol, isopropanol, butanol, tert-butanol, or amyl alcohol.

[0039] Still referring to the example where the treatment fluid may include one or more additional components, in some examples, the one or more additional components may include an additional solvent. For example, the treatment fluid may include one or more of the following: tetrahydrofuran (THF), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dichloromethane, chloroform, acetone, acetonitrile, chlorobenzene, diethyl ether, dioxane, ethylene glycol, polyethylene glycol (PEG), glycerol, hexamethylphosphoramide (HMPA), nitromethane, pyridine, trimethylamine, toluene, xylene, benzene, dimethylacetamide (DMAc), dimethoxyethane (DME), diglyme, or ethylene dichloride. The treatment fluid including the additional solvent may be a single-phase or multiphase fluid system.

[0040] In some examples, one or more additional components in the treatment fluid may include at least one dissolved salt, such as NaCl, KCl, CsCl, NaHCO3, KHCO3, CsHCO3, Na2CO3, K2CO3, Cs2CO3, any salt containing a quaternary ammonium cation, or any salt containing a tetrafluoroborate anion or a hexafluorophosphate anion. Furthermore, in some examples, the treatment fluid may include an additional component comprising at least one surfactant, preferably selected from anionic and / or nonionic surfactants, such as sulfates, sulfonates, gluconates, cocamide, ethoxylates, and / or alkoxylates.

[0041] It should be understood that in some examples, the method may include selecting the type and / or amount of at least one additional component based on the components of the composite structure (e.g., the fiber material layers) to ensure that exposing the composite structure to the treatment fluid does not cause any significant dissolution or decomposition of the components.

[0042] It should also be understood that, in other examples, the method may include selecting the type and / or amount of at least one additional component based on a component of the composite structure (e.g., a coating of the composite structure) to ensure that exposing the composite structure to the treatment fluid will result in dissolution or decomposition of the component, particularly when such component can prevent or slow degradation of the epoxy resin matrix by the treatment fluid.

[0043] In some preferred embodiments, the combination of the component and any reactive components does not contain a disulfide bond moiety. In some preferred embodiments, the pH of the treatment fluid is at least 2, for example, the pH of the treatment fluid is between 2.5 and 4.

[0044] In some examples, exposing the composite structure to the treatment fluid can include discretely applying the treatment fluid to the composite structure, such as by spraying, sprinkling, pouring, or smearing the treatment fluid onto one or more exposed surfaces of the composite structure. It should be understood that discretely applying the treatment fluid to one or more exposed surfaces of the composite structure is different from immersing the composite structure in the treatment fluid. Discrete application includes applying the treatment fluid to specific portions of the composite structure in a controlled manner (in some examples, quantitatively) without having to expose the entire structure to the treatment fluid. This application method can better control the degradation process. Therefore, this application method can better control when separating one or more fiber material layers of the composite structure from one or more other fiber material layers.

[0045] In some examples, the method may include the following steps:

[0046] a) discretely applying a treatment fluid to individual exposed surfaces of the composite structure to at least partially degrade the thermosetting epoxy resin matrix, thereby releasing individual layers of fiber material from the composite structure;

[0047] b) subsequently removing the single layer of fibrous material to reveal a newly exposed surface of the composite structure; and

[0048] c) repeating steps a) and b) at least once such that the plurality of fiber material layers in the composite structure are exposed to the treatment fluid, respectively, and subsequently removed from the composite structure layer by layer.

[0049] In some examples, the method may further include an optional step for determining at least one of the ply orientation of the individual fiber material layers, the type of the individual fiber material layers, and the thickness of the individual fiber material layers. For example, in some examples, such determination and / or analysis may be performed prior to step b). Furthermore, step c) may be repeated to determine the number of fiber material layers and / or the order of the fiber material layers in the composite structure.

[0050] In some other examples, exposing the composite structure to the treatment fluid may include immersing the composite structure in the treatment fluid. For example, the method may include immersing the composite structure in a beaker or other suitable container containing the treatment fluid. In some other examples, the method may include arranging the composite structure in a beaker or other suitable container, temporarily constraining the composite structure, and then exposing the composite structure to the treatment fluid by introducing the treatment fluid into the beaker or container. In some preferred examples, immersing the composite structure in the treatment fluid may include completely immersing the composite structure so that the depth of the treatment fluid in the beaker is greater than or equal to the height (or thickness) of the composite structure. In some other examples, only a portion of the composite structure may need to be inspected. Therefore, in some examples, the method may include partially immersing the composite structure in the treatment fluid.

[0051] In some preferred embodiments, the treatment fluid may not be agitated after the composite structure is immersed in the treatment fluid. This helps ensure that the sequence and / or orientation of the fiber material layers in the composite structure remains stable throughout the composite structure's exposure to the treatment fluid, thereby facilitating accurate assessment of the composition of the composite structure.

[0052] In some examples, temporarily restraining the composite structure can include applying a restraining force to an upper surface of the composite structure during exposure to the treatment fluid. For example, in some examples, the density of the treatment fluid can be greater than the density of one or more components in the composite structure. Therefore, when the composite structure is immersed in the treatment fluid, if not restrained, there may be a risk that one or more components may float or otherwise move, resulting in the order and / or orientation of the fiber material layers not being maintained. Therefore, in examples that include submerging the composite structure, it may be advantageous to apply a restraining force to the upper surface of the composite structure to ensure that the order and / or orientation of the fiber material layers are maintained while the thermosetting epoxy resin matrix degrades (i.e., swells or dissolves) to release the components.

[0053] In some preferred embodiments, a restraining force can be applied via one or more pins. This facilitates easy access to the composite structure for exposure to the treatment fluid. Additionally or alternatively, in some embodiments, the composite structure can be exposed to the treatment fluid in a treatment container or beaker. Such a treatment container or beaker can be sized and configured to apply a restraining force (e.g., via the sides of the container) to support the composite structure during exposure, thereby maintaining the order and / or orientation and / or number of fibrous material layers to be analyzed.

[0054] In some preferred embodiments, the restraining force may be a variable restraining force such that the layers of the composite structure are compressed together during degradation of the epoxy resin matrix between the layers. For example, the restraining force may be applied by one or more elastic restraining devices or movable pins.

[0055] In some examples, after separating one or more fibrous material layers from one or more other fibrous material layers, the method may further include rinsing the separated fibrous material layers to remove any treatment fluid on the separation layers. The or each separated fibrous material layer may be rinsed with a rinsing fluid. In some examples, the rinsing fluid may include a surfactant, and in some examples, the surfactant may include an anionic surfactant and / or an amphiphilic surfactant, such as a quaternary ammonium surfactant. In some examples, the rinsing fluid may include a neutralizer to neutralize the pH of the treatment fluid.

[0056] In some examples, the composite structure may further comprise one or more support elements.The method may further comprise separating the or each support element from the plurality of layers of fibre material in the composite structure after exposure to the treatment fluid.

[0057] As used herein, the term "support element" should be understood to refer to any element or feature of a composite structure and / or composite body that does not provide reinforcement during use. For example, such support elements may include filler materials, molding aids, electrical components (e.g., lightning protection components), paint, glue, and / or core materials (e.g., foam and / or wood).

[0058] In some examples, the support element may be made of wood (e.g., balsa wood). Additionally or alternatively, in some examples, the support element may be made of a foamed plastic. The foamed plastic may include at least one of polystyrene (PS), polyurethane (PU), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyolefins (polyethylene (PE) and polypropylene (PP)), or ABS foam. In some preferred examples, the foamed plastic may be rigid.

[0059] In some examples, the fiber material and / or support element may include at least one additional thermoset matrix including cross-linked polyester, polyurethane, vulcanized rubber, cross-linked polyvinyl ester, cross-linked polyimide, cross-linked phenol formaldehyde, cross-linked polybenzoxazine, cured amino resin, cured furan resin, cured maleimide resin, cured silicone, or any combination including at least one of the foregoing thermoset matrix materials.

[0060] The composite structure is preferably exposed to the treatment fluid in a treatment vessel. The treatment vessel is preferably closed or closable. In some examples, exposing the composite structure to the treatment fluid can include arranging the composite structure on a conveyor and conveying it through the treatment vessel, where the treatment fluid is applied to the composite structure, for example, by spraying or sprinkling. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Examples of the present invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0062] Figure 1 is a schematic cross-sectional view of a composite structure comprising a plurality of layers of fiber material embedded in a thermosetting epoxy resin matrix;

[0063] Figure 2 is a schematic cross-sectional view of immersing a composite structure in a treatment fluid to degrade the epoxy resin matrix;

[0064] Figure 3a and 3b is a schematic cross-sectional view of an alternative method of exposing a composite structure to a treatment fluid by discrete applications of the fluid;

[0065] Figures 4a to 4d are schematic cross-sectional views of examples of different methods of temporarily restraining a composite structure during exposure to a process fluid;

[0066] Figure 5a is a schematic perspective view of the complex;

[0067] Figure 5b is a schematic cross-sectional view of a step in a method of extracting a sample portion from a composite; and

[0068] Figure 5c is a schematic perspective view of a sample portion. DETAILED DESCRIPTION

[0069] Figure 1 FIG is a schematic cross-sectional view of a composite structure 10 comprising multiple components. For example, the composite structure 10 comprises multiple fiber material layers 12, wherein these fiber materials are embedded in a thermosetting epoxy resin matrix 14 having a cross-linked network structure. In some examples, the fiber material 12 may include reinforcing fibers, such as glass fiber reinforcement fibers and / or carbon fiber reinforcement fibers. In addition, as shown in FIG. Figure 1 As shown, in some examples, the composite structure 10 may include one or more support elements 16, such as balsa wood or foam plastic, between the fiber material layers 12. Thus, in some examples, the composite structure 10 may have a sandwich structure. Figure 1 18 or the outer surface 20 of the composite structure 10 , the components of the composite structure 10 are generally not identifiable by visual inspection of the inner surface 18 or the outer surface 20 of the composite structure 10 .

[0070] Therefore, an example of a new method of evaluating components of a composite structure 10 will now be described with reference to the remaining figures.

[0071] Preliminary Overview: In each example, the method involves exposing the composite structure 10 to a treatment fluid 22 to at least partially degrade the thermosetting epoxy resin matrix 14. The degradation of the thermosetting epoxy resin matrix 14 releases (i.e., separates) the components of the composite structure 10 (e.g., the fiber material 12) from the epoxy resin 14 that bonds the components together. Consequently, the method also involves separating one or more fiber material layers 12 from one or more other fiber material layers 12. This facilitates the evaluation of each component of the composite structure 10 without damaging the corresponding component, i.e., without damaging the fiber material layers 12.

[0072] First reference Figure 2 , which shows the composite structure 10 after exposure to the treatment fluid 22, which in some examples can be exposed to the composite structure 10 by immersing the composite structure 10 in the treatment fluid 22. As previously described, exposure to the treatment fluid 22 degrades the thermosetting epoxy resin matrix 14, causing the fiber material layers 12 to separate from the epoxy resin 14 and each other, which can then be individually removed for evaluation.

[0073] Alternatively, Figure 3a and 3b As shown, in some other examples, the treatment fluid 22 may be discretely applied to the composite structure 10, such as by spraying, sprinkling, pouring, or painting the fluid onto an exposed surface 24 of the composite structure 10. Thus, the method may involve releasing a single layer of fiber material 12 from the composite structure by applying the treatment fluid 22 to the exposed surface 24 to degrade the thermosetting epoxy resin matrix 14 that bonds the layer 12 to the other layers 12 of the composite structure 10. The single layer 12 may then be removed, thereby presenting a new exposed surface 24 of the composite structure 10, to which the treatment fluid 22 may then be applied to repeat the process, releasing and removing a single layer of fiber material 12 at a time.

[0074] As previously described, in each example, the epoxy matrix 14 is at least partially degraded by exposure to the treatment fluid 22. The treatment fluid 22 includes formic acid and / or acetic acid, which degrades the epoxy matrix 14 by causing the epoxy 14 to swell or dissolve. For example, the thermosetting epoxy matrix 14 may be a conventional type of epoxy resin that may swell when exposed to the treatment fluid 22 including formic acid, thereby decomposing the epoxy 14 into swollen epoxy particles. In other examples, the thermosetting epoxy matrix 14 may be a chemically decomposable epoxy type resin, such as It may decompose into soluble epoxy fragments when exposed to the treatment fluid 22. Therefore, in this case, the treatment fluid 22 may contain acetic acid and / or formic acid to dissolve the epoxy resin 14. In some preferred examples, the treatment fluid 22 may contain at least 50 wt% formic acid.

[0075] To facilitate accurate assessment of the order and / or orientation of the fiber material 12 and / or other components of the composite structure 10 , the method further includes temporarily restraining the composite structure 10 during exposure to the treatment fluid 22 . Figures 4a to 4d Examples of various methods for temporarily restraining composite structure 10 during exposure to treatment fluid 22 are shown. The dimensions of the container are preferably less than twice the dimensions of the composite structure. For example, for a composite structure having a circular cross-section, the diameter of the container is preferably less than twice the diameter of the composite structure. More preferably, the dimensions of the container are 1.2 to 1.8 times the dimensions of the composite structure to ensure stable temporary retention and sufficient treatment fluid volume.

[0076] For example, Figure 4a In some examples shown, composite structure 10 may be arranged in a container 26 or beaker shape to match the shape of composite structure 10. In this manner, container 26 itself, i.e., sides 28 of container 26, may help constrain composite structure 10 and its components during exposure to treatment fluid 22.

[0077] Particularly in instances where the composite structure 10 is immersed in the treatment fluid 22, it may be advantageous to apply a restraining force to the upper surface 30 of the composite structure 10 during exposure to the treatment fluid 22. This may help maintain the order and / or orientation of the components of the composite structure 10 even if those components have a density less than that of the treatment fluid 22 and may float or move when immersed in the treatment fluid 22 and released from the epoxy resin 14 of the composite structure 10. For example, Figure 4b An example is shown in which the restraining force is applied to the upper surface 30 by one or more pins 32 engaging the surface 30; Figure 4c An example is shown where the method involves tying down the composite structure 10 , such as using one or more elastic restraints 34 . Figure 4dAn example of a composite structure 10 having openings through layers 12, resin 14, and support element 16 is shown. In this example, the composite structure can be prepared, for example, using a hole saw with guide holes, the holes of which form the openings. The sample is restrained by pins 35 that pass through the openings in the composite structure, for example, from the bottom of the processing container 26. The pins 35 prevent lateral displacement and mixing of the layers while maintaining good circulation of the processing fluid 22. In addition, the diameter of the pins is preferably close to the diameter of the openings, so that rotation of the layers 12 and support element 16 can be limited or prevented. Alternatively, two or more sets of corresponding guide holes and pins 35 spaced a certain distance apart can prevent the layers 12 from rotating.

[0078] In an alternative example, temporary restraint of the composite structure 10 is achieved by introducing an directional feature into the composite structure 10. For example, this could be a smaller, non-centrally arranged through-hole, or by providing an identifiable mark on the composite structure 10 to identify each layer 12 before it is exposed to the treatment fluid 22. Such an identifiable mark could, for example, be a (wedge-shaped) cutout cut into the side of a rotationally symmetric cylinder. After separation, the relative rotational orientation of the layers 12 can now be determined by aligning the identifiable mark or the layers 12, thereby temporarily restraining the composite structure and making it easier to identify.

[0079] In each example, temporarily restraining the composite structure 10 while the thermosetting epoxy resin matrix 14 degrades helps ensure that the orientation and / or sequence of the fiber material layers 12 is maintained or readily identifiable even if the fiber material layers 12 are released from the binding epoxy resin matrix 14. Thus, inspection and evaluation of the fiber material layers 12 after degradation of the epoxy resin 14 can provide a clear and accurate indication of the type and arrangement of the fiber material 12 within the composite structure 10. Notably, in examples where the composite structure 10 includes a support element 16 (e.g., a balsa or foam plastic core), the method can further include separating the support element 16 from the fiber material layers 12 after exposure to the treatment fluid 22. Thus, the method can also facilitate evaluation of such support elements 16.

[0080] In each of the examples of the methods described herein, after separating one or each layer of fibrous material 12 from another layer or layers of fibrous material 12, the method may further include rinsing or washing the separated layers 12 (not shown). For example, such a rinsing step may advantageously remove any residual treatment fluid 22 from the separated layers 12, thereby facilitating a more thorough and accurate evaluation of the separated layers 12.

[0081] While in some examples, the aforementioned method can be performed on an entire composite body to evaluate its composition, in some examples, such an approach may not be practical. For example, for a larger composite body (e.g., a composite wind turbine blade), immersing the entire blade shell in the treatment fluid 22 or applying the treatment fluid 22 to the entire composite body to evaluate its composition may not be practical. Instead, in some examples, the method preferably includes extracting one or more sample portions 36 from the larger composite body 38 and evaluating the sample portions 36 according to the examples of the method described herein. Therefore, it should be understood that previous references to the composite structure 10 also apply to the sample portion 36 of the composite body 38, i.e., the composite structure 10 can be the sample portion 36.

[0082] Now refer to Figures 5a to 5c Non-limiting examples of a sample portion 36 and its extraction from a larger complex 38 are described.

[0083] First reference Figure 5a , which shows a schematic perspective view of a composite body 38. In this example, the composite body 38 is a composite wind turbine blade shell. However, it should be understood that a composite wind turbine blade shell is only one preferred example of a composite body 38 to which the method described herein is applicable. Therefore, the method is equally applicable to other composite bodies 38, such as kayaks, bicycle frames and other sports equipment, as well as wind turbine components, such as nacelles and platforms. It should be understood that, as Figure 5a As shown, the sample portion 36 is smaller than the larger composite body 38 , and thus, the larger composite body 38 is defined as “larger” relative to the sample portion 36 .

[0084] In some examples, a composite body 38 (e.g., a composite wind turbine blade shell 38) may include a damaged region 40. For a composite blade shell 38, the damaged region 40 may be caused by a lightning strike, impact damage, erosion, or the like. Examples of the methods described herein are particularly suitable for assessing the composition of a composite body 38 as part of a repair or refurbishment method. For example, accurately assessing the composition and its sequence and / or orientation according to examples of the methods described herein may allow substantially equivalent fiber materials to be arranged in a substantially equivalent orientation to existing fiber materials 12 of the composite body 38 when repairing or refurbishing the damaged region 40 of the composite body 38. To accurately indicate the composition and its sequence and / or orientation of the composite body 10, in some preferred examples, a sample portion 36 may be extracted from a location 42 on the composite body 38 that is no more than 1 meter from the damaged region 40.

[0085] Now refer to Figure 5b In some examples, the sample portion 36 may be extracted from the composite body 38 using a mechanical cutting tool 44 , such as a core drill. Figure 5bThe schematic cross-sectional view in this example shows the core drill 44 midway through extracting the sample portion 36 from the composite body 38. The method may further include marking the exposed surface of the composite body 38 at the extraction location 42 prior to extracting the sample portion 36 so that the orientation of the sample portion 36 relative to the composite body 38 can be verified by reference to the mark in the event of any movement of the sample portion 36 (e.g., rotation of the sample portion 36 after the core drill releases the sample portion 36 from the composite body 38). The mark may be, for example, a written or engraved mark on the surface of the sample portion or a smaller hole drilled outside the center position of the core drill.

[0086] Figure 5c An example of a sample portion 36 extracted from a composite body 38 is shown. The sample portion 36 is engraved with markings 46 and a small through-hole 48 for verifying the orientation of the sample portion 36. The width or diameter D of the sample portion 36 is preferably between 0.010 and 0.100 meters to maintain the stability of the sample portion 36 and to facilitate temporary restraint of the sample portion 36 during exposure to the treatment fluid 22 (as previously described). For similar reasons, the aspect ratio (width:height) of the sample portion 36 is preferably less than 1:2.

[0087] It is noted that after the sample portion 36 is extracted from the composite body 38, any of the aforementioned examples of exposing the composite structure 10 to the treatment fluid 22 may be performed on the sample portion 36. Therefore, with brief reference to Figure 2 , the sample portion 36 may be immersed in the processing fluid 22; alternatively, reference Figure 3a and 3b , the treatment fluid 22 can be applied discretely to a single exposed surface 24 of the sample portion 36. Similarly, the sample portion 36 can be applied as previously described with reference to Figures 4a to 4d Alternatively, temporary restraint can be performed by smaller through-holes 48, thereby re-establishing the relative orientation between the layers.

[0088] It should be understood that the above description is intended to illustrate multiple possible examples of the present invention. Features described in any example above can be easily combined with any other features described with reference to other examples without departing from the scope of the present invention as defined in the appended claims.

Claims

1. A method of evaluating a component of a composite structure (10) comprising a plurality of layers of fiber material (12) embedded in a thermosetting epoxy resin matrix (14) having a cross-linked network structure, the method comprising: exposing the composite structure (10) to a treatment fluid (22) comprising formic acid and / or acetic acid to at least partially degrade the thermosetting epoxy resin matrix (14); temporarily constraining the composite structure (10) during exposure to the treatment fluid (22) to maintain the order and / or orientation and / or number of the fiber material layers (12); as well as One or more layers of fibrous material (12) are separated from one or more other layers of fibrous material (12) to thereby evaluate the components of the composite structure (10).

2. The method of claim 1, wherein the composite structure (10) is a sample portion (36), and wherein the method further comprises extracting the sample portion (36) from a larger composite body (38).

3. The method of claim 2, wherein the composite body (38) is a wind turbine component. The method of claim 3 , wherein the wind turbine component is a wind turbine blade component.

5. A method according to any preceding claim, wherein the thermosetting epoxy resin matrix is ​​an amine-cured thermosetting epoxy resin matrix.

6. The method of any one of claims 2 to 5, wherein extracting the sample portion (36) from the larger composite body (38) comprises extracting the sample portion (36) from the composite body (38) using a mechanical cutting tool (44).

7. A method according to any one of claims 2 to 6, wherein the larger composite body (38) comprises a damaged area (40), and wherein the method comprises extracting the sample portion (36) from a location (42) on the composite body (38) not more than 1 meter, preferably not more than 0.5 meters, from the damaged area (40).

8. The method according to any one of claims 2 to 7, wherein the width of the sample portion (36) is 0.010 m to 0.100 m, preferably 0.025 m to 0.075 m, more preferably 0.04 m to 0.06 m.

9. The method according to any one of claims 2 to 8, wherein the aspect ratio of the sample portion (36) is less than 1:2, preferably less than 1:1.75, more preferably less than 1:1.5, wherein The aspect ratio is defined as the ratio of the width of the sample portion to the height of the sample portion.

10. A method according to any preceding claim, wherein the treatment fluid (22) comprises at least 20 wt% formic acid, preferably at least 50 wt% formic acid, more preferably at least 80 wt% formic acid.

11. A method according to any preceding claim, wherein exposing the composite structure (10) to the treatment fluid (22) comprises discretely applying the treatment fluid (22) to the composite structure (10), for example by spraying, sprinkling, splashing or smearing the fluid (22) onto one or more exposed surfaces (24) of the composite structure (10).

12. The method according to claim 11, comprising: a) discretely applying a treatment fluid (22) to a single exposed surface (24) of the composite structure (10) to at least partially degrade the thermosetting epoxy resin matrix (14) to release the single fiber material layer (12) from the composite structure (10); b) subsequently removing the single layer of fibrous material (12) to reveal a new exposed surface (24) of the composite structure (10); as well as c) repeating steps a) and b) at least once such that the plurality of fiber material layers (12) in the composite structure (10) are exposed to the treatment fluid (22) and subsequently removed from the composite structure (10) layer by layer.

13. The method of any one of claims 1 to 10, wherein exposing the composite structure (10) to the treatment fluid (22) comprises immersing the composite structure (10) in the treatment fluid (22).

14. The method of claim 13, wherein temporarily restraining the composite structure (10) comprises applying a restraining force to the upper surface (30) of the composite structure (10) during exposure to the treatment fluid (22).

15. A method according to any preceding claim, wherein After separating the one or more layers (12) of fibrous material from one or more other layers (12) of fibrous material, the method further comprises flushing the separated layers (12) of fibrous material to remove any treatment fluid (22) from the separated layers (12).

16. A method according to any preceding claim, wherein the composite structure (10) further comprises one or more support elements (16), and wherein the method further comprises separating the or each support element (16) from the plurality of layers of fibrous material (12) in the composite structure (10) after exposure to the treatment fluid (22).

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