Composite material bolt connection structure mixed failure monitoring system and method based on carbon-based piezoresistive sensor

Abstract

The invention belongs to the technical field of composite material monitoring, and particularly discloses a composite material bolt connection structure mixed failure monitoring system and method based on a carbon-based piezoresistive sensor, and the preparation method comprises the steps: preparing carbon-based material piezoresistive sensor ink, manufacturing a resin insulating film, and manufacturing the carbon-based material piezoresistive sensor. The piezoresistive sensor is prepared from the carbon-based material, the conductivity and mechanical property of the sensor are excellent, the preparation process is simple, and the sensor is easy to store; the sensor and the bolt connection structure are integrated in an embedded mode, and the upper surface and the lower surface of the sensor are subjected to insulation treatment through resin films, so that the sensor and the connection structure are integrated, the mechanical property of the connection structure is guaranteed, external interference to the sensor is reduced, and real-time monitoring of the sensor on failure of the connection structure is achieved. According to the method, different layout modes are designed for three failure types, the complexity of sensor design is reduced by dividing modules, and the recognition capability and recognition efficiency are effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of composite material monitoring technology, specifically relating to a hybrid failure monitoring system and method for composite material bolted connection structures based on a carbon-based piezoresistive sensor. Background Technology

[0002] Carbon fiber reinforced polymer (CFRP) composites, with their high specific strength and designable mechanical properties, are widely used in critical equipment fields such as aerospace and rail transportation. As a core component of composite structures, the connection structure directly affects the integrity and reliability of the overall structure. Bolted connections, due to their high load-bearing capacity and convenient maintenance, have become the main connection method for composite structures. However, the inherent characteristics of composite bolted connections, as well as the complexity of the loads and operating environments, present significant challenges to the integrity and durability analysis of composite bolted connections.

[0003] Existing traditional non-destructive testing techniques (such as ultrasonic testing and X-ray flaw detection) are insufficient for real-time dynamic monitoring of failure types and their propagation processes in composite bolted connections, and also cannot quickly assess structural safety and reliability. Therefore, the development of structural health monitoring technology has become an inevitable trend. This technology can effectively monitor and assess the actual condition of composite connection structures in real time throughout their entire lifespan, determine the severity of failures, and provide data support for maintenance decisions.

[0004] Carbon-based materials possess excellent properties such as structural diversity, high conductivity, good selectivity, chemical stability, and environmental friendliness, leading to their widespread application in energy storage and conversion, optics, and biomedicine. Flexible sensors developed based on the piezoresistive effect can accurately sense micro-strain and pressure changes, showing great promise in structural health monitoring. Currently, carbon-based piezoresistive sensors are used in human body monitoring, but integrating them into composite bolted connection structures and constructing a powerful sensor network to meet the diverse monitoring needs of failure modes in composite bolted connection structures and identify different failure types remains a significant technical challenge. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the existing technology and provide a hybrid failure monitoring system and method for composite material bolted connection structures based on carbon-based piezoresistive sensors.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for fabricating a carbon-based piezoresistive sensor includes the following steps:

[0008] (1) Preparation of carbon-based piezoresistive sensor ink: surfactant, carbon-based conductive filler and matrix material are added to anhydrous ethanol, and carbon-based piezoresistive sensor ink is obtained by mechanical stirring, ultrasonic dispersion and magnetic stirring.

[0009] (2) Making resin insulating film: Mix epoxy flow-conducting resin and curing agent in proportion to obtain resin mixture, mold it under high temperature and vacuum conditions, and take it out after curing into film to obtain resin insulating film.

[0010] (3) Fabrication of carbon-based piezoresistive sensor: Repeatedly spray the carbon-based piezoresistive sensor ink obtained in step (1) onto the surface of the resin insulating film obtained in step (2) to isolate the influence of CFRP resistor on the sensor; after each spraying, the upper layer of ink must be dried before the next spraying. After a certain number of spraying layers, a carbon-based sensing film is obtained. Then, conductive silver paste is coated on the surface of the sensing film, wires are led out, and the surface of the sensing film is encapsulated with the insulating film obtained in step (2) to obtain a carbon-based piezoresistive sensor based on carbon-based materials.

[0011] In a preferred embodiment of the present invention, in step (1), the carbon-based conductive filler is a mixture of two of carbon black, carbon nanotubes, and graphene. The surfactant is used to break up the agglomeration of the conductive filler and disperse it, preferably at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and hexadecyltrimethylammonium bromide. The matrix material is a non-conductive flexible nanomaterial, preferably one of polyvinylpyrrolidone, polydimethylsiloxane, and polyimide. The concentrations of the surfactant, carbon-based conductive filler, and matrix material are 0.1-0.9 mg / ml, 2-15 mg / ml, and 30-80 mg / ml, respectively.

[0012] In a preferred embodiment of the present invention, the mass ratio of epoxy flow-conducting resin to curing agent in step (2) is (8-12):(2-4).

[0013] In a preferred embodiment of the present invention, the epoxy flow-conducting resin in step (2) is IN2 and the curing agent is AT30.

[0014] A carbon-based piezoresistive sensor prepared by the above-mentioned method.

[0015] A hybrid failure monitoring system for composite bolted connection structures based on carbon-based piezoresistive sensors.

[0016] A design method for a hybrid failure monitoring system for composite bolted connection structures includes sensor layout, construction of a multi-module piezoresistive sensing network, and integrated sensor network.

[0017] In a preferred embodiment of the present invention, the sensor layout design includes:

[0018] (1) Layout for tensile failure: Since tensile failure occurs along the hole center axis perpendicular to the long side of the specimen, the layout for tensile failure is located on the left side of the screw hole, with electrodes arranged in parallel on both sides of the axis. The overall shape of the sensor area is a quarter-circle ring, and the sensor as a whole is symmetrical about the hole center axis of the long side of the specimen.

[0019] (2) Layout for shear failure: Since shear failure occurs along the hole center axis perpendicular to the short side of the specimen, one of the electrodes in the layout for shear failure is located directly above the screw hole. The overall shape of the sensor area is an eighth of a circle, and the two electrodes are arranged in parallel.

[0020] (3) Layout for extrusion failure: Since extrusion failure occurs at the weak point of the hole edge above the screw hole, the layout for extrusion failure is located directly above the screw hole, with the electrodes arranged in parallel on both sides of the axis, and the overall shape of the sensor area is a hollow quarter ring.

[0021] Since bolted connection failures all occur at stress concentration points around the bolt holes, in order to fit the bolt holes as closely as possible, all three sensor layout methods are circular, and the shortest distance between the sensor and the center of the bolt hole is 7mm-8mm.

[0022] More preferably, in the tensile failure layout, the difference between the inner and outer diameters of the ring is 10-13 mm, and the electrode spacing is 12-16 mm; in the shear failure layout, the difference between the inner and outer diameters of the ring is 10-13 mm, and the electrode spacing is 6-8 mm; in the extrusion failure layout, the difference between the inner and outer diameters of the ring is 10-13 mm, the perforation spacing is 1-2 mm, and the electrode spacing is 12-16 mm.

[0023] In a preferred embodiment of the present invention, the multi-module piezoresistive sensing network is constructed by dividing the layouts for tensile failure, shear failure, and extrusion failure into two monitoring modules, namely monitoring module 1 and monitoring module 2. Monitoring module 1 is used to monitor tensile failure, while monitoring module 2 is used to monitor shear failure and / or extrusion failure. A common electrode is set between monitoring module 1 and monitoring module 2, and a lead wire is led out to integrate the two modules into a whole multi-module piezoresistive sensing network. The integrated sensor monitoring network is a semi-circular ring with a difference of 10mm-13mm between its inner and outer diameters. This integrated sensor monitoring network has multiple electrode connectors, and the monitoring module is selected by connecting different electrode connectors during the monitoring process.

[0024] In a preferred embodiment of the present invention, the sensor network is integrated by embedding it in a CFRP laminate after resin film encapsulation.

[0025] A method for monitoring mixed failures in composite bolted connections based on carbon-based piezoresistive sensors is proposed. This method uses a data acquisition device to collect real-time changes in resistance signals between multiple electrode pairs of each module to determine the occurrence and severity of failures in the bolted connection structure. Different modules are used to identify single failure types that occur simultaneously. Tensile failures are identified based on signals from monitoring module 1, and shear and extrusion failures are distinguished based on signals from monitoring module 2. Mixed failure types (such as tensile-extrusion, shear-extrusion, etc.) are determined by signal feature fusion.

[0026] Because the failure types of composite bolted connections include single failures and mixed failures, single failures include three types: tensile, shear, and compressive failures. When multiple single failures coexist, the failure type presents a mixed failure form. Therefore, determining the specific type of a mixed failure requires accurately identifying the single failure type present when the failure occurs.

[0027] In a preferred embodiment of the present invention, the data acquisition device is a digital source table.

[0028] The specific monitoring test piece consists of two CFRP laminates connected by bolts. The laminates are 135mm long, 36mm wide, 3mm thick, 18mm apart at the ends, and have a hole diameter of 6mm. The monitoring object is a bolted connection structure of carbon fiber composite material, and the monitoring area is a circular area with a radius of 17-20mm centered on the center of the bolt hole.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. This invention uses carbon-based materials to prepare piezoresistive sensors, which have excellent conductivity and mechanical properties, and the preparation process is simple and easy to store.

[0031] 2. This invention integrates the sensor with the bolt connection structure by embedding it, and the upper and lower surfaces of the sensor are insulated with resin film, so that the sensor and the connection structure are integrated into one, ensuring the mechanical properties of the connection structure, reducing the external interference to the sensor, and realizing the sensor's real-time monitoring of connection structure failure.

[0032] 3. This invention designs different sensor network layouts for three types of failures, and divides monitoring module 1 and monitoring module 2 according to the location characteristics of different failure types, which reduces the complexity of sensor design and effectively improves the ability and efficiency of identifying different failure types.

[0033] 4. The hybrid failure monitoring method adopted in this invention determines the single failure type included in the hybrid failure through different modules. The presence of tensile failure is determined by monitoring signal 1, and the presence of extrusion and shear failure types is determined by monitoring signal 2. This method can accurately classify hybrid failures with complex damage propagation characteristics and improve the accuracy of sensor identification of hybrid failure types. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the fabrication process of the carbon-based piezoresistive sensor in Embodiment 1 of the present invention;

[0035] Figure 2 This is a schematic diagram of the monitoring layout of the carbon-based piezoresistive sensor of the present invention for different failure types;

[0036] Figure 3 This is a schematic diagram of the modular layout of the multi-module piezoresistive sensing network of the present invention and the overall monitoring network.

[0037] Figure 4 This is a schematic diagram illustrating the integrated method and monitoring mechanism for combining sensor networks with bolted connection structures. Detailed Implementation

[0038] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0039] Example 1

[0040] A carbon-based piezoresistive sensor is fabricated by spray coating. The specific fabrication process is as follows: Figure 1 As shown, the carbon-based piezoresistive sensor ink was first prepared by sequentially and uniformly adding sodium dodecylbenzenesulfonate (0.0327g), monolayer graphene (0.0874g), carbon nanotubes (0.2622g), and polyvinylpyrrolidone (2g) to 50ml of anhydrous ethanol. After mechanical stirring for 3 hours, ultrasonic stirring for 1 hour, and magnetic stirring for 3 hours at room temperature, a uniformly dispersed sensor ink was obtained. Next, a resin insulating film was prepared by mixing 18g of epoxy conductive resin IN2 and 6g of rapid curing agent AT30 to obtain an epoxy conductive resin mixture. The epoxy conductive resin mixture was then molded into a film using an aluminum plate under vacuum at 100℃. Finally, four layers of sensing ink were repeatedly sprayed onto the prepared resin insulating film to obtain a carbon-based sensing film. After each spraying, the top layer of ink was dried before the next spraying. Electrodes and wires were then installed, and the sensor surface was encapsulated with the resin insulating film to obtain a carbon-based piezoresistive sensor.

[0041] Example 2

[0042] A hybrid failure monitoring system for composite bolted connection structures based on carbon-based piezoresistive sensors, such as... Figure 4 As shown, its design method includes sensor layout, construction of multi-module piezoresistive sensor network and integrated sensor network.

[0043] (1) Sensor layout design for different failure types:

[0044] The sensor obtained in Example 1 was designed with different layouts for different failure types, including layouts for monitoring three failure types. For example... Figure 2 As shown, the layout for tensile failure is located to the left of the screw hole, with electrodes arranged parallel to each other on both sides of the axis. The overall shape of the sensor area is a quarter-circle ring, with a 10mm difference between the inner and outer diameters of the ring and a 14mm electrode spacing. The sensor is symmetrical about the center axis of the hole along the long side of the specimen. In the shear failure layout, one electrode is located directly above the screw hole. The overall shape of the sensor area is a quarter-circle ring, with two electrodes arranged parallel to each other. The difference between the inner and outer diameters of the ring is 10mm, and the electrode spacing is 7mm. In the extrusion failure layout, the electrode is located directly above the screw hole, with electrodes arranged parallel to each other on both sides of the axis. The overall shape of the sensor area is a hollowed-out quarter-circle ring, with a 1mm spacing between the hollowed-out sections, a 10mm difference between the inner and outer diameters of the ring, and a 13mm electrode spacing.

[0045] (2) Construction of a multi-module piezoresistive sensor network for hybrid failure modes:

[0046] In step (1) as follows Figure 2 The layout shown is divided into two monitoring modules for different failure types, and integrated into a whole multi-module piezoresistive sensing network, as follows: Figure 3 As shown, monitoring module 1 is responsible for monitoring tensile failure, and monitoring module 2 is responsible for monitoring shear and / or extrusion failure. Failure monitoring is achieved by measuring the resistance change between different lead wires. The overall sensor network is approximately a semi-circular ring with a 10mm difference between the inner and outer diameters.

[0047] (3) Preparation of carbon fiber composite laminates and integrated sensor network:

[0048] First, cut the carbon fiber prepreg (USN20000 in T300) to a suitable size.

[0049] Next, the prepreg is laid up on an aluminum plate mold coated with Easy-Lease-150 release agent according to the set layup sequence. When the number of orderly layup layers of prepreg reaches 10, the sensor network obtained in step 3 is embedded and the prepreg is laid up to the set number of 20 layers.

[0050] Then, the aluminum plate mold is closed and placed in a high and low temperature alternating test chamber to cure at a vacuum temperature of 105℃ for 3 hours. After curing, the mold is removed after the test chamber has cooled naturally to room temperature.

[0051] Finally, the mold is opened, the cured carbon fiber composite laminate is removed, and post-processing such as cutting and drilling is performed according to assembly requirements.

[0052] Carbon fiber composite laminates are assembled into composite bolt connection structure specimens of a certain size.

[0053] Example 3

[0054] A hybrid failure monitoring method for composite material bolted connection structures based on a multi-module piezoresistive sensing network includes the following steps:

[0055] Failure types in composite bolted connections include single failures and mixed failures. Single failures include three types: tensile, shear, and compressive. When multiple single failures occur simultaneously, the failure type presents a mixed failure form. Therefore, determining the specific type of a mixed failure requires accurately identifying the single failure types present when the failure occurs. This monitoring method uses different modules to determine the simultaneous occurrence of single failure types.

[0056] When a certain hybrid failure occurs, through Figure 4 The digital source meter in the sensor network collects signals. First, it uses the sensor signal characteristics in monitoring module 1 to determine the presence of tensile failure in the mixed failure mode. Then, it uses the sensor signal characteristics in monitoring module 2 to determine the presence of shear failure and compression failure in the mixed failure mode. For example, when a tensile-compression mixed failure occurs, tensile and compression failures occur simultaneously. The sensor signal in monitoring module 1 will show the characteristics of tensile failure, indicating that tensile failure is present in the failure mode. The sensor signal in monitoring module 2 will show the characteristics of compression failure. Thus, the overall sensor signal indicates that the composite bolted connection structure has experienced a tensile-compression mixed failure. When a shear-compression mixed failure occurs, shear and compression failures occur simultaneously. The sensor signal in monitoring module 1 does not show the characteristics of tensile failure, indicating that tensile failure is not present in the failure mode. The sensor signal in monitoring module 2 will show the characteristics of a mixture of compression and shear failures. The overall sensor signal indicates that the composite bolted connection structure has experienced a tensile-compression mixed failure.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fabricating a carbon-based piezoresistive sensor, characterized in that, Includes the following steps: (1) Preparation of carbon-based piezoresistive sensor ink: surfactant, carbon-based conductive filler and matrix material are added to anhydrous ethanol, and carbon-based piezoresistive sensor ink is obtained by mechanical stirring, ultrasonic dispersion and magnetic stirring. (2) Making resin insulating film: Mix epoxy flow-conducting resin and curing agent in proportion to obtain resin mixture, mold it under high temperature and vacuum conditions, and take it out after curing into film to obtain resin insulating film. (3) Fabrication of carbon-based piezoresistive sensor: Repeatedly spray the carbon-based piezoresistive sensor ink obtained in step (1) onto the surface of the resin insulating film obtained in step (2); After each spraying, the top layer of ink needs to be dried before the next spraying. After a certain number of spraying layers, a carbon-based sensing film is obtained. Then, conductive silver paste is coated on the surface of the sensing film, wires are led out, and the surface of the sensing film is encapsulated with the insulating film obtained in step (2) to obtain a carbon-based piezoresistive sensor based on carbon-based materials.

2. The method for preparing the carbon-based piezoresistive sensor as described in claim 1, characterized in that, In step (1), the carbon-based conductive filler is a mixture of two of carbon black, carbon nanotubes, and graphene; the surfactant is at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and hexadecyltrimethylammonium bromide; and the matrix material is a non-conductive flexible nanomaterial. The concentrations of the surfactant, carbon-based conductive filler, and matrix material are 0.1-0.9 mg / ml, 2-15 mg / ml, and 30-80 mg / ml, respectively.

3. The method for preparing the carbon-based piezoresistive sensor as described in claim 1, characterized in that, In step (2), the mass ratio of epoxy superplastic resin to curing agent is (8-12):(2-4).

4. The method for preparing the carbon-based piezoresistive sensor as described in claim 1, characterized in that, In step (2), the epoxy flow-conducting resin is IN2 and the curing agent is AT30.

5. A carbon-based piezoresistive sensor prepared by the method of preparing a carbon-based piezoresistive sensor as described in any one of claims 1-4.

6. A hybrid failure monitoring system for composite bolted connection structures based on carbon-based piezoresistive sensors.

7. A design method for a hybrid failure monitoring system for composite material bolted connection structures based on a carbon-based piezoresistive sensor, characterized in that, This includes sensor layout, construction of multi-module piezoresistive sensor networks, and integrated sensor network architecture.

8. The design method of the hybrid failure monitoring system for composite material bolted connection structures based on carbon-based piezoresistive sensors as described in claim 7, characterized in that, The sensor layout design includes: (1) Layout for tensile failure: Located on the left side of the screw hole, the electrodes are arranged in parallel on both sides of the axis. The overall shape of the sensor area is a quarter-circle ring. The sensor is symmetrical about the hole center axis of the long side of the specimen. (2) Layout for shear failure: One of the electrodes is located directly above the screw hole, the overall shape of the sensor area is an eighth of a circle, and the two electrodes are arranged in parallel. (3) Layout for extrusion failure: The electrodes are arranged in parallel on both sides of the axis, located directly above the screw hole. The overall shape of the sensor area is a hollow quarter-circle.

9. The design method of the hybrid failure monitoring system for composite material bolted connection structures based on carbon-based piezoresistive sensors as described in claim 8, characterized in that, In the tensile failure layout, the difference between the inner and outer diameters of the ring is 10-13 mm, and the electrode spacing is 12-16 mm. In the shear failure layout, the difference between the inner and outer diameters of the ring is 10-13 mm, and the electrode spacing is 6-8 mm. In the extrusion failure layout, the difference between the inner and outer diameters of the ring is 10-13 mm, the perforation spacing is 1-2 mm, and the electrode spacing is 12-16 mm.

10. The design method of the hybrid failure monitoring system for composite material bolted connection structures based on carbon-based piezoresistive sensors as described in claim 8, characterized in that, The multi-module piezoresistive sensing network is constructed by dividing the layouts for tensile failure, shear failure, and extrusion failure into two monitoring modules. The layout for tensile failure is designated as monitoring module 1, used to monitor tensile failure, while the layouts for shear failure and extrusion failure are designated as monitoring module 2, used to monitor shear failure and / or extrusion failure. A common electrode is placed between monitoring module 1 and monitoring module 2, and a lead wire is extended to integrate monitoring module 1 and monitoring module 2 into a whole multi-module piezoresistive sensing network. The integrated sensor monitoring network is a semi-circular ring with a difference of 10mm-13mm between its inner and outer diameters. The integrated sensor monitoring network has multiple electrode connectors, and the monitoring module is selected by connecting different electrode connectors during the monitoring process.

11. The design method of the hybrid failure monitoring system for composite material bolted connection structures based on carbon-based piezoresistive sensors as described in claim 7, characterized in that, The sensor network is integrated by embedding it into a CFRP laminate after being encapsulated in a resin film.

12. A method for monitoring hybrid failure of composite bolted connection structures based on carbon-based piezoresistive sensors, characterized in that, The failure occurrence and severity of bolted connection structures are determined by real-time acquisition of resistance signal changes between multiple electrode pairs of each module using a data acquisition device. The single failure type that occurs simultaneously is determined by different modules. Tensile failure is identified based on the signal of monitoring module 1, shear and extrusion failures are distinguished based on the signal of monitoring module 2, and mixed failure type is determined by signal feature fusion.

13. The method for monitoring hybrid failure of composite bolted connection structures based on carbon-based piezoresistive sensors as described in claim 12, characterized in that, The data acquisition device is a digital source table.

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