THERMOSETTING MATERIAL, METHODS AND USES THEREOF

Technical Domain

[0001] The present disclosure refers to textile structures, with sensory capacity, for reinforcing thermosetting matrices, forming a structural composite, which in addition to serving as mechanical reinforcement also allows the monitoring/sensing of the mechanical performance of structural parts (applicable to several sectors such as automotive, aeronautics and aerospace) in order to predict possible structural failures and the need to replace the part (preventive maintenance of components).

Background

[0002] WO2013034964 discloses a composite material comprising a layer of polymeric piezoelectric material, wherein such polymeric piezoelectric layer has a first surface and a second surface opposite to said first surface; a textile substrate; a first electrode disposed on the first surface of the polymeric piezoelectric layer, wherein on the other surface of said textile substrate turned towards the layer of polymeric piezoelectric material, conductors are provided.

[0003] WO1999042643A1 presents a reinforcing carbon fiber base material capable of being formed into a large-sized structure and a composite reinforced with such material, wherein metallic wires are disposed inside the reinforcing carbon fiber base material at 4% in volume, in order to detect strain conditions occurring in the structure and in the reinforced composite.

[0004] US20130048841A1 presents a composite structure having an embedded sensing system, along with systems and methods for monitoring the integrity of a composite structure. The composite structure includes a composite material and an optical fiber disposed within the composite material. [0005] W02006072767A1 discloses a composite material provided with a damage detection system, wherein the composite material comprises a fiber-reinforced polymeric matrix and wherein the reinforcement fibers comprise electrically conductive fibers and the polymeric matrix comprises a thermosetting polymer and a thermoplastic polymer, and wherein the detection system is used for detecting a change in the resistance of the composite material indicating a damaged area of the material.

[0006] These facts are described in order to illustrate the technical problem solved by the embodiments of the present document.

General Description

[0007] One of the objectives of the present disclosure is to describe a composite material with textile fibers with high resistance, wherein the material simultaneously allows the mechanical reinforcement and the monitoring/sensing of the mechanical performance of structural parts in order to predict possible failures and the need to replace the part. Thus, the possibility of preventive maintenance of components/parts is increased.

[0008] The solution presented in this description is based in particular on the fact that the thermosetting composite material comprises one or more textile structures (multilayer textile structure) and thermosetting resin impregnated in the textile structure(s), wherein the textile structure comprises carbon fibers and piezoelectric/piezoresistive fibers/yarns (i.e: piezoelectric fibers, piezoelectric yarns, piezoresistive fibers or piezoresistive yarns).

[0009] One of the aspects of the present disclosure relates to a multilayer textile structure impregnated with a thermosetting resin, wherein the individual textile structures constituting the multilayer textile structure comprise carbon fibers and piezoelectric/piezoresistive fibers/yarns, and wherein the piezoelectric/piezoresistive fibers provide the thermosetting composite with the ability to monitor/sense mechanical stresses/changes. [0010] One of the aspects of the present disclosure describes a thermosetting composite comprising a multilayer textile structure impregnated with a thermosetting resin, comprising a plurality of woven layers wherein at least two layers of the plurality of woven layers comprise carbon fibers and piezoelectric/piezoresistive fibers/yarns, wherein the plurality of woven layers comprises the impregnated thermosetting resin, and wherein the piezoelectric/piezoresistive fibers/yarns are configured to monitor/sense mechanical stresses/changes of the thermosetting composite; wherein the spacing between the piezoelectric/piezoresistive fibers/yarns is of 3 cm maximum.

[0011] Surprisingly, the thermosetting composite of the present disclosure improves the monitorization/sensing of the mechanical stresses/changes in the structure, namely inside structure, along the life of the product and without compromising the performance of the composite.

[0012] In one embodiment, the piezoelectric/piezoresistive fibers/yarns have been woven with the carbon fibers in order to obtain a woven layer and an electrical contact of the piezoelectric/piezoresistive fibers/yarns is exposed. That is, the end of the piezoelectric/piezoresistive fibers/yarns is not impregnated with a resin in order to be able to monitor/sense mechanical stresses/changes in the structure (composite). As a result, the combination of piezoelectric/piezoresistive fibers/yarns woven with the carbon fibers and impregnated with a resin, wherein the spacing between piezoelectric/piezoresistive fibers/yarns is 3 cm maximum, allows to obtain a sensorized composite while maintaining mechanical properties similar to the non-sensorized product.

[0013] In one embodiment, each layer of the plurality of woven layers comprises carbon fibers and piezoelectric/piezoresistive fibers/yarns. [0014] In one embodiment, the carbon fibers are in the warp and/or weft of the woven textile structure.

[0015] In one embodiment, the piezoelectric/piezoresistive fibers/yarns are integrated into the warp and/or weft of the textile structure, preferably in the weft of the textile structure.

[0016] In one embodiment, the number of carbon fiber filaments ranges between 1 K and 24 K, preferably between 6 K and 12 K.

[0017] In one embodiment, the linear density of the carbon fibers ranges from 60 and 1600 tex; preferably 100 - 800 tex.

[0018] In one embodiment, the twist of the carbon fibers ranges between 0 and 100 turns/meter, preferably 0 and 50 turns/meter.

[0019] In one embodiment, the piezoelectric/piezoresistive fibers/yarns comprise 20 - 80% (w/w) polymeric compound with piezoelectric properties and 20 -80% (w/w) conductive polymeric compound; preferably with a linear massranging between 200 and 2000 dtex.

[0020] In one embodiment, the spacing between piezoelectric/piezoresistive fibers/yarns is of 3 cm maximum, preferably 0.1 - 2 cm.

[0021] In one embodiment, the ratio of piezoelectric/piezoresistive fibers to carbon fibers in the weft or warp ranges between lpiezoelectric/piezoresistive fiber/yarn/lcarbon fiber tO lpiezoelectric/piezoresistive fiber/yarn/5carbon fibers; preferably from lpiezoelectric/piezoresistive fiber/yarn/lcarbon fiber tO lpiezoelectric/piezoresistive fiber/yarn/3carbon fibers-

[0022] In one embodiment, the weaving diagram of the plurality of woven layers is selected from: taffeta, twill, satin, or derivatives thereof.

[0023] In one embodiment, the mass per surface unit of the textile structure (fabric) may be between 120 and 1500 g/m ² .

[0024] In one embodiment, the plurality of woven layers comprises 2-20 layers, preferably 2-10 layers, more preferably 3-5 layers. [0025] In one embodiment, the composite material further comprises a fabric layer and/or a coating.

[0026] In one embodiment, the composite material further comprises a fabric layer between the plurality of woven layers.

[0027] In one embodiment, the directions of the fibers on the warp and/or weft of each layer of the plurality of woven layers are aligned to form an angle that ranges from 15° - 60°, preferably 30° - 45°.

[0028] In one embodiment, the pluralities of woven layers are joined together forming a 3D structure, that is, due to the resin impregnation between the layers the composite material surprisingly increases the mechanical strength and properties.

[0029] In one embodiment, the piezoelectric/piezoresistive fibers/yarns are found along the thickness of the composite.

[0030] In one embodiment, the piezoelectric/piezoresistive fibers comprise a protective coating, preferably applied to the ends of each piezoelectric/piezoresistive fiber. The coating is in contact with the conductive core of the fiber in order to make the electrical connection possible. The coating may be in the form of spray, lacquer or paint.

[0031] In one embodiment, the piezoelectric/piezoresistive fibers/yarns comprise a protective coating applied at their end, preferably the coating comprises silver, or combinations thereof.

[0032] In one embodiment, the piezoelectric/piezoresistive fibers/yarns comprise a copper strip, the strip being preferably twisted around the end of the piezoelectric/piezoresistive fiber in order to protect and promote the efficiency of contact.

[0033] In one embodiment, the thermosetting resin is selected from a list consisting of: bisphenol diglycidyl ether groups (preferably bisphenol A or bisphenol F, even more preferably with a molecular weight less than or equal to 700), polyoxypropylene triamine and trimethyl cyclohaxylamine or combinations thereof. [0034] In one embodiment, the piezoelectric/piezoresistive fibers/yarns are encapsulated at their end in order to protect the electrical contacts, wherein the encapsulating material comprises silicone.

[0035] In one embodiment, the thermosetting resin is selected among low viscosity epoxy resins.

[0036] In one embodiment, the thermosetting resin is selected among low viscosity epoxy resins, preferably with viscosity limits equal to or less than 1100-2000 cP at 25 °C, preferably, and curing agent containing at least one amine group, and combinations thereof (for example, SR8200 + SD 720x resin available by the company Sicomin).

[0037] In one embodiment, the thermosetting resin comprises a viscosity equal to or less than 1100 ± 200 cP at 15 °C and a curing agent comprising at least one amine group.

[0038] In one embodiment, the electrical contacts previously coated of the sensory fibers are isolated before the process of impregnating resin in the carbon fabric, through the application of mold release wax, as well as commercial silicone. The latter can be applied in liquid form and solidifies after 24 hours at room temperature.

[0039] The present disclosure describes an article comprising the sensorized composite material described in the present disclosure.

[0040] In one embodiment, the article may be a component of a car in particular the internal trim of the door, car pillar, floor or ceiling, car console, dashboard, instrument panel, glove compartment and/or trunk; a baby stroller component; or an electrical appliance, a stand or door handle.

[0041] Another aspect refers to an article comprising the thermosetting material described above, preferably a structural or fastening component, more preferably a component for an automobile, aeronautical or aerospace equipment.

[0042] In one embodiment, the article can be a structural, fixing, supporting or decorative component, applicable to an automobile (or to other sectors such as aeronautics or aerospace), in particular in the internal trim of the door, bodywork (car pillar , floor or ceiling), car console, dashboard, glove compartment and/or trunk; a baby stroller component; sports equipment components (bicycles, canoes, etc.).

Brief Description of the Figures

[0043] For an easier understanding, figures are herein attached, which represent preferred embodiments which are not intended to limit the object of the present description.

[0044] Figure 1: Schematic representation of a possible embodiment of the textile structure wherein the carbon fibers form a taffeta structure and wherein a periodic insertion of a piezoelectric fiber/yarn into the weft takes place.

[0045] Figure 2: Schematic representation of a possible embodiment of a multilayer textile structure wherein taffeta structures (1) composed of weft carbon yarns (2), warp carbon yarns (3) and piezoelectric/piezoresistive fibers/yarns (4) are disposed parallel to each other, and are connected by a connecting yarn (5).

[0046] Figure 3: Schematic representation of an embodiment of the textile structure with carbon fibers and piezoelectric/piezoresistive fibers/yarns wherein (1) represents the carbon fiber thermosetting composite material with integration of sensory fibers/yarns for monitoring structural performance; wherein (2) represents the piezoelectric/piezoresistive fibers/yarns; and, wherein (3) represents the carbon fibers; wherein (4) represents the outer polymeric layer of the piezoelectric/piezoresistive fiber (based on piezoelectric compounds); wherein (5) represents the conductive core of the piezoelectric/piezoresistive fiber (first electrode); wherein (6) the conductive coating applied to the end of the piezoelectric/piezoresistive fiber; wherein (7) represents the carbon fiber (external electrode).

Figure 4: Schematic representation of an embodiment of the textile structure wherein (a) corresponds to the representation of carbon fiber removal in order to expose the piezoelectric/piezoresistive fibers; (b) application of silver at the end of each fiber and (c) different approaches for encapsulating electrical contact. Detailed Description

[0047] The present invention relates to a thermosetting composite material, method of obtaining and use thereof, comprising a woven textile structure and a thermosetting resin impregnated in the textile structure, wherein the woven textile structure comprises carbon fibers and woven piezoelectric/piezoresistive fibers, and wherein the piezoelectric/piezoresistive fibers are capable of providing the composite material with auto-sensing in volume and/or along the length thereof.

[0048] In one embodiment, the preparation of the composite of the present embodiment by the method of infusion with the encapsulation of the electrical contacts, can be done as follows: in figure 4, image A relates to the preparation of the materials and the encapsulation of the electrical contacts. In the structure containing carbon fibers (1) and piezoelectric fibers/yarns (2), the contacts are encapsulated with silicone (3). Subsequently, the infusion (B) is carried out and the resin (4) impregnates the carbon fibers (1) and the piezoelectric fibers/yarns (2) without impregnating the ends. This process is carried out by applying vacuum between 650 - 900 mbar, which forces the thermosetting resin to flow through the carbon structure. After wetting the entire carbon structure, the composite (C) is cured, the encapsulation (3) is removed and the electrical contact gets exposed (5), allowing for further monitoring/sensing.

[0049] In one embodiment, figure 1 represents a possible embodiment of the textile structure composed of carbon yarns inserted into the warp (1) and carbon yarns inserted into the weft (2) wherein the interlacing thereof forms a taffeta structure and where a piezoelectric/piezoresistive fiber/yarn (3) is inserted periodically, with a maximum spacing of up to 3 cm and which can range, preferably between 0.1 and 2 cm. In addition to this structure, obtaining the thermosetting material of the present disclosure can be achieved with weaving diagrams wherein the carbon yarns of both warp and weft form taffeta, twill, or satin structures or derivatives thereof.

[0050] In one embodiment, figure 2 represents a possible embodiment of a multilayer textile structure used for obtaining the thermosetting material of the present disclosure, wherein the multilayer textile structure is obtained during the weaving process. The textile structures making up the multilayer textile structure are composed of carbon yarns inserted into the warp, carbon yarns inserted into the weft wherein the interlacing thereof forms a taffeta, twill, or satin structure or derivatives thereof and wherein a piezoelectric/piezoresistive fiber/yarn is inserted periodically, with a maximum spacing of 3 cm and which can range preferably between 0.1 and 2 cm.

[0051] In one embodiment, figure 3 represents a possible embodiment of the thermosetting composite material (1) obtained from a fabric with piezoelectric/piezoresistive fibers/yarns (2) integrated in the warp and/or weft of the fabric and carbon fibers (3) integrated into the warp and weft of the fabric. The conductive coating (6) is applied to the end of the piezoelectric/piezoresistive fiber composed by an external polymeric layer of the piezoelectric/piezoresistive fiber (4) and the conductive core of the piezoelectric/piezoresistive fiber (first electrode) (5), actuating the carbon fiber (7) as an external electrode.

Embodiment Examples

Production of "sheath-core" piezoelectric/piezoresistive fibers/yarns

[0052] In one embodiment, bi-component fibers with piezoelectric and piezoresistive response capabilities with sheath-core type cross-sectional geometry are used. The relevance of this geometry is that the conductive part of the fiber is isolated, not allowing contact with carbon in the textile structure.

[0053] This type of fiber allows the monitoring of vibrations, stretching, or flexure in the composite structure (see Figure 3).

Characterization of carbon yarns

[0054] In one embodiment, the number of carbon fiber filaments can be comprised between IK and 24K, preferably 6 - 12 K.

[0055] In one embodiment, the carbon fiber has a linear density of the carbon fiber comprised between 60 and 1600 tex. [0056] In one embodiment, carbon fibers have a torsion level that can range between 0 and 100 turns/meter.

[0057] In one embodiment, carbon fibers have a surface finish that guarantees chemical compatibility with the thermosetting matrix. For example, epoxy.

Production of the textile structure: weaving

[0058] In one embodiment, the textile structures produced are obtained by weaving having a high stability.

[0059] In one embodiment, the textile structures have characteristic weaving diagrams that can be taffeta, twill, satin and variations thereof.

[0060] In one embodiment, Figure 1 represents a possible embodiment of the textile structure wherein the carbon fibers form a taffeta structure and wherein a periodic insertion of a piezoelectric fiber/yarn into the weft takes place.

[0061] In one embodiment, the piezoelectric/piezoresistive fibers/yarns are introduced during the production of the fabric by weaving.

[0062] Insertion of the piezoelectric/piezoresistive fibers/yarns occurs in the weft, with the periodic insertion of the fibers with a spacing that can range between 0.1 and 2 centimeters. This distance allows to enhance the sensitivity of the sensors along the composite structure, and spacings greater than 2 cm can be used, depending on the defined application (e.g.: monitoring of impact, flexure, or vibration of the part).

[0063] In one embodiment, the structures produced have a mass per surface unit between 120 and 1500 g/m ² per layer, preferably 300 and 1000 g/m ² per layer.

[0064] In one embodiment, figure 2 represents a multilayer structure, obtained by weaving, wherein the individual textile structures constituting the multilayer textile structure comprise carbon fibers and piezoelectric/piezoresistive fibers/yarns.

[0065] In one embodiment, the individual textile structures that make up the multilayer textile structure shown in figure 2 are connected through a connecting yarn, during the weaving process. [0066] In one embodiment, subsequently to the manufacturing method, the application of electrical contacts on the sensory yarns follows. Therefore, following the production of carbon textile structures, with taffeta, twill, satins weaving diagrams or derivatives thereof, and with integration of piezoelectric/piezoresistive fibers/yarns, electrical contacts were made on the respective piezoelectric/piezoresistive fibers/yarns.

[0067] In one embodiment, electrical contacts consisted of exposing piezoelectric/piezoresistive fibers/yarns, applying lacquer/silver paint in order to access the conductive core and subsequent applying of copper tape, to protect and promote contact efficiency, as shown in Figure 3.

Contact protection

[0068] In one embodiment, different methodologies for the production of composite materials were evaluated, thus having been verified that infusion is the production method that allows obtaining composites with higher quality. Therefore, this method was selected for the preparation of composites with sensory fibers integrated in the reinforcement structure. In this production method, several layers of fabric with the desired dimensions are superimposed (multilayer structure) and subsequently - through the application of vacuum and the structure being contained in a vacuum bag - impregnated with resin, ensuring a continuous and homogeneous impregnation of the fibers. However, the main limitation in the preparation of composites with sensory fibers integrated in the structure, consists of the need to keep the ends of the sensory fibers not impregnated with resin, that is, dried during and after the production process, in order to maintain the sensing capacity. The electrical contacts were made with silver coatings and subsequent application of a copper tape around the entire piezoelectric fiber in order to protect and promote the efficiency of the contact. It has been found that this coating was not enough, requiring the encapsulation of the contacts with an insulator that was easy to remove after infusing and curing the material. For such, two layers of mold release wax were previously applied and then liquid silicone was applied, then cured for at least 24 hours at room temperature in order to solidify. Then, allow the removal thereof. This method of protection proved to be effective since the sensory fiber ends are not impregnated and maintain their structural integrity after the process of infusion and curing of the composite.

[0069] Another aspect of the present disclosure, describes the method of obtaining a thermosetting material of the present disclosure that allowed to overcome the existing constraints in the processing of the textile structure by the infusion method, and thus achieve the objectives successfully.

[0070] Another limiting aspect in the production of thermosetting composites with this type of integrated sensory fibers is the temperature to which the material is subjected to during the curing cycle, with the possible degradation of the components of these fibers to temperatures above 100 °C and consequent loss of sensing capacity. Thus, it was decided to change the post-cure cycle from 6h at 100 °C to 8h at 80 °C.

[0071] In one embodiment, using the adapted curing cycle and the appropriate contact protection method, composites were produced by the infusion method with a layer of fabric.

[0072] In one embodiment, with the obtained specimens, the effect of the piezoelectric/piezoresistive fibers/yarns integrated in the composite was validated. In this sense, the tested specimens comprised one or more textile structures of carbon fiber and piezoelectric/piezoresistive fibers/yarns impregnated with thermosetting resin. The validation of the sensory properties of the fibers was based on the application of mechanical deformations in the specimens, with the generated electrical signal (e.g., voltage or electrical resistance) acquired by specific monitoring hardware. This type of test was carried out cyclically, evaluating the performance of the sensory fibers over time, allowing to confirm the sensitivity and repeatability of the acquired response.

[0073] The term "comprises" or "comprising" when used herein is intended to indicate the presence of the features, elements, integers, steps and components mentioned, but does not preclude the presence or addition of one or more other features, elements, integers, steps and components, or groups thereof.

[0074] The present invention is of course in no way restricted to the embodiments described herein and a person of ordinary skill in the art can foresee many possibilities of modifying it and replacing technical features with equivalents depending on the requirements of each situation as defined in the appended claims.

[0075] The following claims define additional embodiments of the present description.