RU2800738C2 - Method for manufacturing strain-resistive sensor made in form of a woven fabric from conductive carbon fibers and dielectric fibers - Google Patents

Abstract

FIELD: sensor technology.

SUBSTANCE: invention can be used to control processes occurring in critical products in the aerospace industry. A method for manufacturing a strain-resistive sensor made in form of a woven fabric of conductive carbon fibers and dielectric fibers that provide insulation for the latter is proposed. The assembly and installation of the strain-resistive sensor is carried out during the manufacture of the product, placing parts of the product on each other, represented by pre-woven layers of a conductive fabric, an insulating fabric and a newly conductive fabric, ensuring the mutually perpendicular direction of carbon fibers in the conductive fabrics, then the final assembly of the product is carried out and subsequent joint impregnation of the product and the piezoresistive sensor with ceramic slip or resin mixed with a crosslinking agent, followed by annealing.

EFFECT: possibility of registering mechanical loads inside the product, which allows to track the processes occurring in it and predict product failures.

1 cl, 2 dwg

Description

The invention relates to the field of sensor technology and can be applied when placing a piezoresistive sensor inside critical aerospace products made of polymer composite materials.

Known continuous thin film strain gauge [patent US4104605, THIN FILMSTRAIN GAUGE AND METHOD OF FABRICATION (thin film strain gauge and method for its manufacture), published 01.08.1978]. The thin film strain gauge is made by applying a first film of high temperature insulating material to the surface of a test article, which is coated with a resistive film, a conductive lead at each end of the resistive pattern, and a coating of the resistive film. Parts of the conductive leads are covered with a second film of high temperature insulating material to protect the load cell from corrosion and erosion in the working environment.

A flexible matrix of force or pressure sensors is known, which contains: a substrate including semiconductor strain sensors, in which a plurality of elements formed in a certain matrix template are deformed under the action of force or pressure, two layers of a polymer film in contact with each other and containing a semiconductor a strain gauge, and two layers of signal lines formed on the upper and lower surfaces of the insulating layer, using either of the two layers of polymer film as an insulating layer and connected to the elements of the array to form electrodes, for extracting strain signals outputted to the outside; and two layers of elastomer located on both sides of the substrate [patent US8695441, FLEXBLE FORCE OR PRESSURE SENSOR ARRAY USING SEMCONDUCTOR STRAN GAUGE, FABRICATION (Flexible force or pressure sensor using semiconductors, method of manufacturing it and method of measurement using a flexible sensor), published 15.04 .2014].

Known strain-resistive element [GOST 21616-91 Strain gauges], which contains an elastic element - a strain gauge placed in the housing and a cable connector. The principle of its operation is based on measuring the change in the resistance of strain gauges installed on the product. The product under the action of mechanical loads is deformed and deforms the strain gauges placed in it.

The strain-resistive element can be made either as a separate component mounted on the surface of the product, or in special mesas cut out in the product. In view of this, the mechanical loads transmitted from the product to the strain-sensing element are dissipated on the mounting components of this element, which is a disadvantage of the above analogues.

The strain-resistive element can be made on the surface of the product using plenary technologies, such as electronic photolithography, silkscreen printing [Physical encyclopedia, vol. 5 - M.: Great Russian encyclopedia, p. 70]. In this case, there is no need for special mounting components, however, the strain-resistive element can only be located on the surface of the product and, therefore, it will only respond to processes occurring on the surface of the product, as a result of which the registration of mechanical loads inside the product will not be ensured, thereby the quality of product telemetry has been reduced, which in turn will not allow tracking the processes occurring inside the composite and predicting product failures.

Known materials that change their electrical resistance under the action of external mechanical loads. These include polymer nanocomposites with conductive additives [Deng H, Zhang R, Reynolds CT, Bilotti E, Peijs T., A novel concept for highly oriented carbon nanotubes composite tapes or fibers with high strength and electrical conductivity. Macromol Mater Eng 2009; 294:749-55]. The article describes a multifunctional polymer nanocomposite material that combines high rigidity and strength with good electrical properties, which is structurally made in the form of a two-component tape (or fiber) consisting of a highly oriented polymer core and a shell of a conductive polymer composite based on a polymer with a lower melting point, than the core. The tape is glued to the surface of the product

A composite material is known that exhibits piezoelectric and/or piezoresistive properties during deformation and is used as a strain gauge (patent RU2664290, published on 08/16/2018). The strain sensor is made in the form of a non-layered homogeneous composite foam consisting of a mixture of a highly elastic polymeric material with many pores and a plurality of conductive fillers distributed in the polymeric material. As conductive fillers, conductive nanoparticles and/or conductive stabilizers can be used. The disadvantage of this material is that the strain gauge will not provide registration of mechanical loads inside the product, and the porous morphology leads to low strength of the element.

The prototype is a sensor (sensor) described in patent KR20210048015A, which is used for medical purposes - on the insole of a shoe. The conductive coating of the insole is made of a fabric in which the yarn consists of a conductive fiber and a twisted thread of a non-conductive fiber. The conductive fiber includes two parts, the first part is made of a carbon-containing material (the carbon-based material is selected from the group consisting of carbon nanotubes, fullerenes, graphene, graphite, carbon fibers, carbon black and combinations of two or more of them), the second part contains a thermoplastic resin .

The design of the sensor (sensor) contains sequentially stacked electrodes and a conductive coating, and the conductive coating is made of a fabric into which twisted material is woven from threads made of conductive fibers and threads of non-conductive fibers. The disadvantages of this sensor include the fact that it cannot be used inside a rigid product made of composite material due to the presence of thermoplastic resin. In addition, this pressure sensor responds to an external load, and will not provide registration of mechanical loads inside the product.

The objective of the invention is to ensure the registration of mechanical loads inside the product.

The task is achieved by the fact that in the known method of manufacturing a piezoresistive sensor, made in the form of a woven fabric of conductive carbon fibers and dielectric fibers, providing insulation of the latter, according to the invention, the assembly and installation of the piezoresistive sensor is carried out during the manufacture of the product, placing on top of each other on the part of the assembled the products are pre-woven layers of a conductive fabric, an insulating fabric and a newly conductive fabric to ensure mutually perpendicular direction of carbon fibers in the conductive fabrics, then the product is finally assembled and the product is subsequently impregnated together with a strain gauge sensor with ceramic slip or resin mixed with a crosslinking agent, and annealed.

The technical result, characterized by the possibility of registering mechanical loads inside the product, is ensured by the fact that carbon fibers woven into a woven base made of insulating fibers under the action of mechanical loads will change along the length, which will lead to a change in their resistance, which is measured by a reliable bridge circuit method.

The invention is illustrated in the drawing.

In FIG. 1 shows a strain gauge sensor, FIG. 2 - tensoresistive element with increased information content.

The strain-resistive sensor consists of carbon fibers 1 (black fibers) and dielectric fibers 2. The strain-resistive sensor is made in the form of a woven fabric in which the carbon fibers do not have mutual intersection and are isolated by dielectric fibers.

The strain gauge sensor is made as follows. As piezoresistive fibers, carbon fibers are used, obtained, for example, according to the method described in the patent US2957756, "Filiform graphite and its production method". As dielectric fibers can be used: fiberglass, polymer (guliaramid, polyamide) fibers or natural fibers, or any combination thereof. Using a loom or braiding machine, weaving is performed according to the pattern shown in Fig. 1, insulating conductive carbon fibers with polymeric or natural fibers or glass fibers. Any arrangement of carbon fibers will do, as long as they don't intersect. It is possible to interweave carbon fibers not over the entire surface of the woven base, but in its individual parts.

A better and more reliable response to an external mechanical action is provided by the modification of the carbon fiber surface with carbon nanotubes. To do this, carbon fibers are pre-impregnated with a precursor based on the ammonia complex of nickel sulfate and processed in vapors of carbon-containing compounds according to a well-known method [Bobrinetskii Nevolin V.K., Simunin, M.M. Production of carbon nanotubes by catalytic gas-phase pyrolysis of ethanol // Theoretical Foundations of Chemical Engineering Volume 41, Issue 5, October 2007, Pages 639-643].

To ensure greater information content of control, it is preferable to assemble a strain-resistive sensor from at least two layers of woven fabric with carbon fiber, separated by a layer of woven fabric made of one dielectric fiber (without carbon fiber) (see Fig. 2) simultaneously with the manufacture of a product from PCM . To do this, the sheet 3 is first laid in a pile on the assembled part of the product, according to the type shown in Fig. 1, then web 4 without carbon fiber, then web 5 with carbon fiber, rotated relative to web 3 by 90 degrees. Thus, the webs of woven tensoresistive sensors are stacked with the provision of a mutually perpendicular direction of the carbon filaments in them. This provides reliable isolation of the carbon fiber and topological addressing of the sections of the strain gauge. In this form, the piezoresistive sensor should be installed on the product. To install a strain-resistive sensor inside the product, it is advisable to assemble it directly during the manufacture of the product. The assembled tensoresistive element is connected to a common fabric base of the product, then the rest of the product is laid out, and then it is completely impregnated with ceramic slip or resin - epoxy or polyester with a crosslinking agent. After that, the product is annealed to cure the impregnation. After that, the product is annealed to cure the impregnation. Then, a measuring circuit is connected to the ends of the carbon fibers, according to a pattern determined by the characteristics of the product, which works for each carbon fiber according to the principle of an ohmmeter.

Operation of a strain-resistive sensor based on carbon fibers. When a mechanical load is applied, the carbon fibers that are along the projection of the loading forces will change their dimensions. As a result, at low loads, the resistance of the fibers will change according to the law:

where R ₀ is the resistance of an unloaded fiber, S is the cross section of the fiber, ρ is its electrical resistivity, and - its absolute elongation under the action of mechanical loads on the composite.

The measurement of electrical resistance is carried out by standard methods by connecting a measuring circuit (ohmmeter) to the ends of carbon fibers. The resistance value, depending on the brand of carbon fibers and their length, corresponds to 150 Ohm per centimeter of carbon fiber length, and the measured range is from 0.1 to 1 kOhm.

The use of the proposed method for manufacturing a strain-resistive sensor made in the form of a woven fabric of conductive carbon fibers and dielectric fibers and placed inside the product makes it possible to determine the processes occurring inside the composite, which improves the quality of the telemetry of the product and provides the ability to predict product failures.

Claims (1)

A method for manufacturing a strain-resistive sensor made in the form of a woven fabric of conductive carbon fibers and dielectric fibers that provide insulation for the latter, characterized in that the assembly and installation of the strain-resistive sensor is carried out during the manufacture of the product, placing on top of each other, on a part of the assembled product, pre-woven layers from a conductive sheet, an insulating sheet and a newly conductive sheet, ensuring the mutually perpendicular direction of carbon fibers in the conductive sheets, and then the final assembly of the product is carried out and subsequent impregnation of the product together with a strain-resistive sensor with ceramic slip or resin mixed with a crosslinking agent, and annealing.

Images