Composite material adhesive mechanical hybrid connection joint with self-monitoring function and manufacturing method thereof

Abstract

A mechanical hybrid connection joint of composite materials glue with a self-monitoring function and its manufacturing method belong to the fields of functional composite materials and structural health monitoring. The connection joint fixes multiple composite materials by mechanical connection, and a connection glue layer is filled at the joint between two adjacent composite materials. An MXene / CNT sensor is arranged in the connection glue layer. By means of the arranged MXene / CNT sensor, the curing degree of the reactive adhesive is monitored to realize the preparation monitoring of the connection joint. And after the adhesive is cured, the sensor and the connection structure become an integral structure, and the sensor will continue to provide the function of health monitoring during the service process of the connection structure, including being able to self-detect damage when cracks initiate in the mechanical hybrid connection joint of composite materials glue, so as to give early warning of the damage and prevent the expansion of cracks and the overall failure of the mechanical hybrid connection component of composite materials glue.

Description

Technical Field

[0001] The present invention relates to a composite material adhesive mechanical hybrid connection joint with a self-monitoring function and a manufacturing method thereof, belonging to the technical fields of functional composite materials and structural health monitoring. Background Art

[0002] Traditional composite material connection methods mainly include mechanical connections (riveting, screwing, etc.), adhesive bonding, stitching, and Z-Pin connections. Among them, adhesive bonding cannot be widely used in engineering structures due to poor durability, sensitivity to humid and hot environments, and lack of effective non-destructive testing techniques. Adding mechanical connections to adhesive joints to form a hybrid connection form, as a new design feature, can improve the joint bearing capacity to a certain extent, thus meeting the requirements of the engineering field. The manufacturing process of composite material adhesive mechanical hybrid connection joints is simple, the structure appearance is neat, and it has the advantages of high strength, low cost, fatigue resistance, good environmental resistance, and good stability. It can give full play to the advantages of each component and make up for the deficiencies of each component to a certain extent, becoming a research hotspot for scholars in the composite material field at home and abroad, and receiving more and more attention and applications in fields such as aviation, aerospace, automobiles, ships, and high-speed trains with complex working environments.

[0003] Adhesive mechanical hybrid connection combines adhesive bonding and mechanical connection processes, possessing the advantages of both connection methods. On the one hand, the mechanical connection in the adhesive mechanical hybrid connection structure can increase the anti-peeling performance of the adhesive layer and prevent crack propagation; on the other hand, the adhesive bonding structure in the adhesive mechanical hybrid connection structure has good sealing and mechanical properties, which can improve the strength and stability of the connection structure. As a kind of component connection method, adhesive mechanical hybrid connection has an increasing influence in various engineering fields, and the safety and reliability of composite material adhesive mechanical hybrid connection components have also become a key issue urgently needed to be solved in the industry. For composite material components using adhesive mechanical hybrid connection structures, the connection holes prepared at the connection parts will directly lead to the discontinuity of some reinforcing fibers, resulting in a decrease in the strength of composite material components. In addition, due to the particularity of the composite material structure itself and the complex non-linear coupling factors existing in the adhesive mechanical hybrid connection joint during the load-bearing process, the stress distribution around the connection holes is very complex. Once the hybrid connection structure fails, it will cause huge economic losses and even catastrophic consequences. In order to avoid the above situation to the greatest extent, realizing the real-time health monitoring of composite material adhesive mechanical hybrid connection joints has become an urgent problem to be solved at present.

[0004] At present, there are many sensors capable of monitoring. Among them, the patent CN 201911336931.8, "A Sensor for Monitoring the Liquid Composite Molding Process and Its Preparation Method", discloses a preparation method of MXene / CNT sensors. The MXene / CNT sensors can be arranged at different positions of preforms of composite materials with arbitrary shapes to perform real-time online monitoring during the mold filling process of the LCM process. In the MXene / CNT sensors, there is a MXene-CNT-MXene sandwich structure film composed of transition metal carbides (MXene sheets) and carbon nanotubes (CNT tubes). Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a composite material adhesive mechanical hybrid connection joint with self-monitoring function and its manufacturing method, which can monitor the curing degree of the reaction adhesive through the MXene / CNT sensor arranged in the connection joint, realize the preparation monitoring of the connection joint, and after completing the preparation monitoring task, the adhesive infiltrates into the pores of the MXene-CNT-MXene sandwich structure film in the sensor. Thus, after the adhesive cures, the sensor and the connection structure become an integral structure, and the sensor will continue to provide the function of health monitoring during the service process of the connection structure, including being able to self-detect damage when cracks initiate in the composite material adhesive mechanical hybrid connection joint, thereby giving early warning of the damage and preventing the expansion of cracks and the overall failure of the composite material adhesive mechanical hybrid connection component.

[0006] The technical solution realized by the present invention is as follows:

[0007] A composite material adhesive mechanical hybrid connection joint with self-monitoring function of the present invention is formed by mechanically connecting multiple composite materials and filling a connection adhesive layer at the connection between two adjacent composite materials, and an MXene / CNT sensor is arranged in the connection adhesive layer.

[0008] The mechanical connection is one of rivet connection, screw connection, bolt connection, and stud connection.

[0009] The MXene / CNT sensor uses a MXene-CNT-MXene sandwich structure film as a sensing element, connects it to a circuit, and forms a MXene / CNT sensor.

[0010] The MXene-CNT-MXene sandwich structure film is a multi-porous structure with a porosity of 65 - 80% and a pore size of 30 - 40 nm.

[0011] The composite material is preferably a composite material prepared with continuous fibers as the reinforcing material and resin as the matrix.

[0012] When the joint is affected by the load, the MXene-CNT-MXene sandwich structure film of the MXene / CNT sensor can sense the load and respond in the form of resistance change to achieve the self-monitoring function of the structure.

[0013] The described MXene / CNT sensor can be arbitrarily changed in shape and size according to the layout area.

[0014] The preparation method of the composite material adhesive mechanical hybrid connection joint with self-monitoring function described in the present invention includes the following steps:

[0015] Step 1: Grind and clean the area to be bonded in the composite material laminate to form a grinding area with a surface roughness Ra of 10 - 15 μm; and position the mechanical connection holes.

[0016] Step 2: Uniformly apply the resin adhesive to the grinding areas of the two composite material laminates to be connected, implant the MXene / CNT sensor into the resin adhesive, and then bond the areas to be connected to obtain the bonded component.

[0017] Step 3: Place the bonded component in a hot press, select the pressure and temperature suitable for curing the resin adhesive, perform pressure application and heat preservation curing, and use a resistance measuring instrument to monitor the resistance change of the MXene / CNT sensor in real time during curing. When it is monitored that the resistance of the MXene / CNT sensor shows an increasing trend, it indicates that the MXene / CNT sensor has been impregnated by the resin adhesive and is integrally formed with the bonded component.

[0018] Step 4: Subsequently, the resistance of the MXene / CNT sensor will gradually decrease. When the resistance of the MXene / CNT sensor stabilizes at a fixed value, it indicates that the curing reaction of the resin adhesive is completed. After forming the connection adhesive layer, stop heating, wait for the connected part to cool naturally, and then release the pressure to complete the adhesive connection to obtain the adhesively bonded specimen.

[0019] Step 5: Use a punching machine to punch connection holes at the predetermined positions of the adhesively bonded specimen for mechanical connection to obtain a composite material adhesive mechanical hybrid connection joint with self-monitoring function.

[0020] When the composite material adhesive mechanical hybrid connection joint with self-monitoring function is affected by the load, the MXene / CNT sensor will respond simultaneously and be reflected in the form of resistance change. The damage degree of the specimen is evaluated by analyzing whether there is a step phenomenon in the resistance change rate to judge whether the specimen still has the ability to continue in service.

[0021] In the described Step 1, the composite material laminate is preferably a continuous fiber reinforced resin matrix composite material laminate.

[0022] In the said step 1, grinding is carried out using 100-mesh sandpaper; cleaning is carried out using acetone solution.

[0023] In the said step 2, the shape of the MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor needs to be cut into a circular shape, with a thickness of 10 - 20 μm and a diameter of 3 - 6 mm. The MXene / CNT sensor must be implanted in the stress concentration areas such as the edges of the adhesive layer of the composite adhesive mechanical hybrid joint and around the rivets, screws, bolts or studs used for mechanical connection. It can also be selectively implanted in the non-stress concentration areas according to the connection structure size, shape and special requirements of the monitored component. The distance between the edges of all implanted MXene / CNT sensors and the edges of the mechanical connection holes must be greater than 2 mm to prevent the tube-sheet cross-linked microstructure between the MXene sheets and CNT tubes inside the MXene-CNT-MXene sandwich structure film from being damaged during drilling.

[0024] In the said step 3, further, the glued component is placed in a hot press, and the resistance measuring instrument is connected to the circuit of the MXene / CNT sensor to monitor the resistance change of the MXene / CNT sensor in real time while the resin is curing.

[0025] In the said step 3, the MXene / CNT sensor has the characteristic of being penetrated by the resin adhesive. During the penetration process, the resin adhesive molecules will fill between the MXene sheets and CNT tubes, increasing the tunneling barrier for electrons between adjacent and non-contact MXene sheets and CNT tubes, reducing its quantum tunneling effect. At the same time, some of the overlapping MXene sheets and CNT tubes are separated. The superposition of these two effects affects the transfer of electrons inside the MXene / CNT sensor, thus causing the resistance of the MXene / CNT sensor to increase.

[0026] In the said step 4, the resistance of the MXene / CNT sensor will gradually decrease because the resin molecules penetrated inside the MXene / CNT sensor in step 2 start to crosslink and cure, forming a three-dimensional network macromolecular structure, and the matrix undergoes curing shrinkage, thus shortening the distance between the MXene sheets and CNT tubes, reducing the transfer barrier for electrons between them, and thus the resistance of the MXene / CNT sensor gradually decreases. After the resin is completely cured, the conductive network of the MXene / CNT sensor will tend to be stable, and the resistance will also stabilize at a fixed value at this time.

[0027] In step 5 described above, when the composite adhesive mechanical hybrid connection joint is affected by a load, the MXene-CNT-MXene sandwich structure film integrated with the joint undergoes micro-deformation, resulting in a change in the tube-sheet cross-linked microstructure between the internal MXene sheets and CNT tubes. The resistance of the MXene / CNT sensor will also change, and the degree of influence of the load on the connection structure and the damage failure mode are evaluated through its resistance change rate curve.

[0028] By adopting the above technical solutions, the beneficial effects of the present invention are as follows:

[0029] (1) The advantage of this monitoring method is that the MXene-CNT-MXene sandwich structure film has a multi-porous structure with a porosity of 65-80% and a pore size of 30-40 nm. The adhesive can fully penetrate the pores of the MXene-CNT-MXene sandwich structure film in the sensor. After the adhesive cures, the MXene / CNT sensor and the adhesive mechanical hybrid connection component will become an integral structure. The MXene / CNT sensor can be arranged inside the connection joint without affecting the structural integrity and mechanical properties of the connection joint. The MXene / CNT sensor and the component produce synergistic deformation, so that the debonding and delamination damage inside the joint and at the adhesive layer can be accurately monitored. There is no phenomenon of strain lag and monitoring data response delay caused by the bonding interface between the traditional strain gauge sensor and the structure to be monitored. Moreover, the MXene / CNT sensor also has the function of monitoring the curing process of the adhesive at the bonded joint of the joint.

[0030] (2) The MXene / CNT sensor in the present invention can be integrally formed with the composite adhesive mechanical hybrid connection joint with a self-monitoring function into an integrated self-monitoring structure, and the manufacturing process is simple and easy to operate. Moreover, the MXene / CNT sensor is inexpensive, which can effectively reduce the cost of intelligent structures and obtain higher economic benefits.

[0031] (3) The present invention uses the MXene / CNT three-dimensional tube-sheet cross-linked conductive sensing network to convert the complex mechanical damage invisible to the naked eye generated by the composite material connection structure into visible and intuitive simple electrical signals, realizing real-time online monitoring of the composite adhesive mechanical hybrid connection joint, and can effectively avoid potential accidents caused by damage accumulation and crack propagation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the composite adhesive mechanical hybrid connection joint with self-monitoring function of the present invention;

[0033] Figure 2Self-monitoring results of the composite material adhesive mechanical hybrid connection joint with self-monitoring function in Embodiment 1 of the present invention;

[0034] In the figure, 1 is the MXene / CNT sensor; 2 is the rivet; 3 is the adhesive layer. Specific implementation manners

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings by way of example.

[0036] Embodiment 1

[0037] A schematic diagram of the composite material adhesive mechanical hybrid connection joint with self-monitoring function in the embodiment of the present invention is as Figure 1 shown, and its preparation method includes the following steps:

[0038] Step 1: The area to be adhesively bonded in the continuous glass fiber reinforced epoxy resin based composite laminate is polished with 100-mesh sandpaper to make the contact surface have a certain roughness (Ra is 12.5 μm), then the polished area is cleaned with acetone solution, and the riveting connection hole is positioned.

[0039] Step 2: The polished areas of the two composite laminates to be connected are respectively and evenly coated with epoxy resin adhesive. The MXene / CNT sensor is prepared by using the patent CN 201911336931.8 "A Sensor for Monitoring the Liquid Molding Process of Composite Materials and Its Preparation Method". The MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor is selected to be circular with a diameter of 5 mm and a thickness of 15 μm. In the adopted MXene / CNT sensor, the porosity of the MXene-CNT-MXene sandwich structure film is 70%, and the pore diameter is 35 nm. The distance between the edge of the MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor and the edge of the riveting connection hole is 4 mm. The Figure 1 MXene / CNT sensor is implanted between the epoxy resin adhesive layers, and then the area to be connected is adhered.

[0040] Step 3: Place the adhesively bonded component in a hot press with a pressure of 1.5 MPa and a temperature of 120 °C for pressure application and heat preservation curing. During the curing process, use a resistance measuring instrument to monitor the resistance change of the MXene / CNT sensor in real time. The MXene / CNT sensor has the characteristic of being penetrated by epoxy resin adhesive. During the penetration process, resin molecules will fill between the MXene sheets and CNT tubes, increasing the tunneling barrier for electrons between adjacent and non-contact MXene sheets and CNT tubes, reducing its quantum tunneling effect. At the same time, some mutually overlapping MXene sheets and CNT tubes are separated. The superposition of these two effects affects the transfer of electrons inside the MXene / CNT sensor. When the resistance measuring instrument monitors an increasing trend in the resistance of the MXene / CNT sensor, it indicates that the MXene / CNT sensor has been impregnated with the adhesive and integrally formed with the component.

[0041] Step 4: Subsequently, the resin molecules infiltrated inside the MXene / CNT sensor start to crosslink and cure, forming a three-dimensional network macromolecular structure. The matrix undergoes curing shrinkage, thereby shortening the distance between the MXene sheets and CNT tubes, reducing the transfer barrier for electrons between them, and the resistance of the MXene / CNT sensor will gradually decrease. After the resin is completely cured, the MXene / CNT conductive network will tend to be stable. When the resistance of the MXene / CNT sensor stabilizes at a fixed value, it indicates that the curing reaction of the adhesive layer is completed. Stop heating, and after the connector cools naturally, release the pressure to complete the adhesive bonding connection.

[0042] Step 5: Use a punching machine to punch connection holes at the predetermined positions of the adhesively bonded specimen, and use a riveting gun to complete the riveting to obtain a composite material adhesive mechanical hybrid connection joint with self-monitoring function. When the joint is affected by a load, the MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor integrally formed with the joint undergoes micro-deformation, resulting in a change in the tube-sheet crosslinked microstructure between the internal MXene sheets and CNT tubes. The MXene / CNT sensor will respond simultaneously and be reflected in the form of resistance change. Evaluate the damage degree of the specimen by analyzing the resistance change rate to determine whether the specimen still has the ability to continue serving.

[0043] Figure 2For the structural health monitoring results of the composite adhesive mechanical hybrid connection joint adopting the present embodiment, it can be seen from the figure that when no load is applied, the resistance change rate of the MXene / CNT sensor remains at 0. As the load slowly increases, the resistance change rate of the sensor shows a stable increase. When damage begins to occur in the adhesive mechanical hybrid connection joint, some of the conductive paths of the MXene / CNT sensor are damaged, and a step phenomenon appears in the resistance change rate. As shown in the boxed part 1 in the figure, the resistance change rate signal curve output by the sensor shows the first step, and at this time, debonding failure of the adhesive layer occurs in the composite adhesive mechanical hybrid connection joint. As the load continues to increase, as shown in the boxed part 2 in the figure, the resistance change rate signal curve output by the sensor shows the second step, and at this time, the rivet of the composite adhesive mechanical hybrid connection joint undergoes shear failure, and the joint fails as a whole. According to this phenomenon, the structural health status of the composite adhesive mechanical hybrid connection joint can be self-monitored through the resistance change rate signal curve output by the MXene / CNT sensor.

[0044] Example 2

[0045] A schematic diagram of the composite adhesive mechanical hybrid connection joint with a self-monitoring function in the embodiment of the present invention is as Figure 1 shown, and its preparation method includes the following steps:

[0046] Step 1: Grind the area to be bonded in the continuous basalt fiber-reinforced epoxy resin-based composite laminate with 100-mesh sandpaper to make the contact surface have a certain roughness, then clean the ground area with acetone solution, and position the riveting connection holes.

[0047] Step 2: Apply polyurethane resin adhesive evenly to the ground areas of the two composite laminates to be connected. Prepare the MXene / CNT sensor by referring to the patent CN 201911336931.8 "A Sensor for Monitoring the Liquid Molding Process of Composites and Its Preparation Method". The MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor is selected to be circular with a diameter of 3 mm and a thickness of 10 μm. In the adopted MXene / CNT sensor, the porosity of the MXene-CNT-MXene sandwich structure film is 65%, and the pore diameter is 30 nm. The distance between the edge of the MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor and the edge of the riveting connection hole is 3 mm. Place the Figure 1 MXene / CNT sensor between the polyurethane resin adhesive layers, and then bond the areas to be connected.

[0048] Step 3: Place the glued component in a hot press with a pressure of 2 MPa and a temperature of 60 °C for pressure application and heat preservation curing. During curing, use a resistance measuring instrument to monitor the resistance change of the MXene / CNT sensor in real time. The MXene / CNT sensor has the characteristic of being penetrated by the polyurethane resin adhesive. During the penetration process, resin molecules will fill between the MXene sheets and CNT tubes, increasing the tunneling barrier for electrons between adjacent and non-contact MXene sheets and CNT tubes, reducing its quantum tunneling effect. At the same time, some overlapping MXene sheets and CNT tubes are separated. The superposition of these two effects affects the transfer of electrons inside the MXene / CNT sensor. When the resistance measuring instrument monitors an increasing trend in the resistance of the MXene / CNT sensor, it indicates that the MXene / CNT sensor has been impregnated with the adhesive and is integrally formed with the component.

[0049] Step 4: Subsequently, the resin molecules penetrated inside the MXene / CNT sensor start to crosslink and cure, forming a three-dimensional network macromolecular structure. The matrix undergoes curing shrinkage, thereby shortening the distance between the MXene sheets and CNT tubes, reducing the transfer barrier for electrons between them, and the resistance of the MXene / CNT sensor will gradually decrease. After the resin is completely cured, the MXene / CNT conductive network will tend to be stable. When the resistance of the MXene / CNT sensor stabilizes at a fixed value, it indicates that the curing reaction of the adhesive layer is completed. Stop heating, and after the connector cools naturally, relieve the pressure to complete the adhesive connection.

[0050] Step 5: Use a punching machine to punch connection holes at the predetermined positions of the glued specimen, and use a riveting gun to complete the riveting to obtain a composite adhesive mechanical hybrid connection joint with self-monitoring function. When the joint is affected by a load, the MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor integrally formed with the joint undergoes micro-deformation, resulting in a change in the tube-sheet crosslinked microstructure between the internal MXene sheets and CNT tubes. The MXene / CNT sensor will respond simultaneously and be reflected in the form of resistance change. By analyzing the resistance change rate, evaluate the damage degree of the specimen and determine whether the specimen still has the ability to continue in service.

[0051] For the MXene / CNT sensor, the resistance change rate remains at 0 without applying a load. As the load slowly increases, the resistance change rate of the sensor shows a stable increase. When the adhesive mechanical hybrid connection joint starts to be damaged, some conductive paths of the MXene / CNT sensor are destroyed, and the resistance change rate shows a step phenomenon. Based on this phenomenon, the structural health status of the composite adhesive mechanical hybrid connection joint can be self-monitored through the resistance change rate signal curve output by the MXene / CNT sensor.

[0052] Example 3

[0053] The schematic diagram of the mechanical hybrid connection joint of composite material adhesive with self-monitoring function in the embodiment of the present invention is as follows Figure 1 As shown, the preparation method comprises the following steps:

[0054] Step 1: Use 100-grit sandpaper to polish the area of the continuous glass fiber reinforced phenolic resin-based composite laminate that needs to be bonded to create a certain degree of roughness on the contact surface. Then, use acetone solution to clean the polished area and locate the riveted connection holes.

[0055] Step 2: Evenly apply phenolic resin adhesive to the polished areas of the two composite laminates to be connected, and use patent CN 201911336931.8 "A sensor and preparation method for monitoring the liquid molding process of composite materials" to prepare a MXene / CNT sensor. The MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor is a circular shape with a diameter of 3mm and a thickness of 10μm. In the MXene / CNT sensor used, the MXene-CNT-MXene sandwich structure film has a porosity of 80% and a pore diameter of 35nm. The distance between the edge of the MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor and the edge of the riveted connection hole is 3mm. Figure 1 The MXene / CNT sensor is embedded between the phenolic resin adhesive layers and then bonded to the front connection area.

[0056] Step 3: The bonded component is placed in a hot press at a pressure of 1.2 MPa and a temperature of 160°C for pressurized, heat-insulated curing. During the curing process, a resistance meter is used to monitor the resistance change of the MXene / CNT sensor in real time. The MXene / CNT sensor is susceptible to penetration by the phenolic resin adhesive. This penetration process causes resin molecules to fill the gaps between the MXene sheets and CNT tubes, increasing the tunneling barrier for electrons between adjacent, non-contacting MXene sheets and CNT tubes, reducing quantum tunneling. This also separates some overlapping MXene sheets and CNT tubes. These two combined effects affect electron transport within the MXene / CNT sensor. When the resistance meter detects an increasing resistance trend in the MXene / CNT sensor, it indicates that the MXene / CNT sensor has been impregnated with the adhesive and integrated with the component.

[0057] Step 4: Subsequently, the resin molecules infiltrated inside the MXene / CNT sensor start to crosslink and cure, forming a three-dimensional network macromolecular structure. The matrix undergoes curing shrinkage, thereby shortening the distance between the MXene sheets and the CNT tubes, reducing the electron transfer barrier between them, and the resistance of the MXene / CNT sensor will gradually decrease. After the resin is completely cured, the MXene / CNT conductive network will tend to be stable. When the resistance of the MXene / CNT sensor stabilizes at a fixed value, it indicates that the curing reaction of the adhesive layer is completed. Stop heating, and after the connector cools naturally, relieve the pressure to complete the adhesive connection.

[0058] Step 5: Use a punching machine to punch connection holes at the predetermined positions of the specimens after adhesive bonding, and use a riveting gun to complete the riveting to obtain a composite adhesive mechanical hybrid connection joint with self-monitoring function. When the joint is affected by the load, the MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor integrally formed with the joint undergoes micro-deformation, resulting in a change in the tube-sheet crosslinked microstructure between the internal MXene sheets and the CNT tubes. The MXene / CNT sensor will respond simultaneously and be reflected in the form of resistance change. By analyzing the resistance change rate, the damage degree of the specimen is evaluated to determine whether the specimen still has the ability to continue serving.

[0059] For the MXene / CNT sensor, the resistance change rate remains at 0 without applying load. As the load slowly increases, the resistance change rate of the sensor shows a stable increase. When the adhesive mechanical hybrid connection joint starts to be damaged, some of the conductive paths in the MXene / CNT sensor are destroyed, and a step phenomenon appears in the resistance change rate. According to this phenomenon, the structural health status of the composite adhesive mechanical hybrid connection joint can be self-monitored through the resistance change rate signal curve output by the MXene / CNT sensor.

[0060] Example 4

[0061] The preparation method of the composite adhesive mechanical hybrid connection joint with self-monitoring function in the embodiment of the present invention includes the following steps:

[0062] Step 1: Use 100-mesh sandpaper to polish the area to be adhesively bonded on the continuous basalt fiber-reinforced phenolic resin-based composite laminate to make the contact surface have a certain roughness. Then use acetone solution to clean the polished area and locate the screw connection holes.

[0063] Step 2: Evenly apply epoxy resin adhesive to the polished areas of the two composite laminates to be joined. Prepare the MXene / CNT sensor using the patent CN 201911336931.8, "A Sensor for Monitoring the Liquid Molding Process of Composites and Its Preparation Method". The MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor is selected to be circular with a diameter of 3 mm and a thickness of 10 μm. In the adopted MXene / CNT sensor, the porosity of the MXene-CNT-MXene sandwich structure film is 70%, and the pore diameter is 40 nm. The distance between the edge of the MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor and the edge of the screw connection hole is 3 mm. Place the Figure 1 MXene / CNT sensor into the epoxy resin adhesive layer and then bond the areas to be joined.

[0064] Step 3: Place the adhesively joined component in a hot press with a pressure of 1.5 MPa and a temperature of 120 °C, and perform pressure application and heat preservation curing. During curing, use a resistance measuring instrument to monitor the resistance change of the MXene / CNT sensor in real time. The MXene / CNT sensor has the property of being penetrated by epoxy resin adhesive. During the penetration process, resin molecules will fill between the MXene sheets and CNT tubes, increasing the tunneling barrier for electrons between adjacent and non-contact MXene sheets and CNT tubes, reducing its quantum tunneling effect. At the same time, some overlapping MXene sheets and CNT tubes are separated. The superposition of these two effects affects the transfer of electrons inside the MXene / CNT sensor. When the resistance measuring instrument monitors an increasing trend in the resistance of the MXene / CNT sensor, it indicates that the MXene / CNT sensor has been impregnated with adhesive and integrated with the component.

[0065] Step 4: Subsequently, the resin molecules infiltrated inside the MXene / CNT sensor start to crosslink and cure, forming a three-dimensional network macromolecular structure. The matrix undergoes curing shrinkage, thereby shortening the distance between the MXene sheets and CNT tubes, reducing the transfer barrier for electrons between them, and the resistance of the MXene / CNT sensor will gradually decrease. After the resin is completely cured, the MXene / CNT conductive network will tend to be stable. When the resistance of the MXene / CNT sensor stabilizes at a fixed value, it indicates that the curing reaction of the adhesive layer is completed. Stop heating, and after the connecting piece cools naturally, release the pressure to complete the adhesive bonding.

[0066] Step 5: Use a punch to drill holes at the desired locations on the bonded specimens. Bolts are then used to create a self-monitoring composite adhesive mechanical hybrid joint. When the joint is subjected to load, the MXene-CNT-MXene sandwich film in the MXene / CNT sensor, integrally formed with the joint, undergoes micro-deformation, causing changes in the tube-sheet crosslinking microstructure between the internal MXene sheets and CNT tubes. The MXene / CNT sensor responds, reflecting this change in resistance. Analysis of the resistance change rate assesses the extent of damage to the specimen and determines its continued serviceability.

[0067] When no load is applied, the MXene / CNT sensor's resistance change rate remains at zero. As the load slowly increases, the sensor's resistance change rate steadily increases. However, when damage begins to appear in a self-monitoring mechanical hybrid composite adhesive joint, the MXene / CNT sensor's conductive pathway is partially destroyed, causing a step-like change in resistance rate. This phenomenon allows for self-monitoring of the structural health of the mechanical hybrid composite adhesive joint using the resistance change rate signal curve output by the MXene / CNT sensor.

[0068] Comparative Example 1

[0069] If a strain gauge is used instead of the MXene / CNT sensor, the strain gauge and the composite material glue mechanical hybrid connection joint cannot produce completely coordinated deformation due to the presence of a glue layer interface in the bonding between the strain gauge and the composite material glue mechanical hybrid connection joint. The monitoring results of the strain gauge have strain lag and monitoring data response delay, and in the subsequent monitoring process, the sensitivity is 2-5. Compared with the composite material glue mechanical hybrid connection joint with self-monitoring function in Example 1 of the present invention, its sensitivity is 40-100.

[0070] Furthermore, because the added strain gauges and joints cannot be integrally molded, embedding them within the composite adhesive layer can actually compromise the structural integrity of the joint, affecting its mechanical properties. For these reasons, strain gauges can only be affixed to the surface of mechanically hybrid composite adhesive joints, resulting in low accuracy in monitoring debonding and delamination damage within the joint, particularly in the adhesive layer. Furthermore, strain gauges cannot monitor the curing process of the adhesive within the joint.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. Preparation method of a composite material adhesive mechanical hybrid connection joint with a self-monitoring function, characterized in that, It includes the following steps: Step 1: Grind and clean the areas to be bonded in the composite laminate to form a ground area with a roughness Ra of 10 - 15 μm; and position the mechanical connection holes; Step 2: Uniformly apply resin adhesive to the ground areas of the two composite laminates to be joined, implant the MXene / CNT sensor into the resin adhesive, and then bond the areas to be joined to obtain a bonded component; The MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor has a thickness of 10 - 20 μm and a diameter of 3 - 6 mm; the distance between the edges of all implanted MXene / CNT sensors and the edges of the mechanical connection holes is greater than 2 mm; Step 3: Place the bonded component in a hot press, connect the resistance measuring instrument to the circuit of the MXene / CNT sensor, select the appropriate pressure and temperature for curing the resin adhesive, perform pressure application and heat preservation curing, and use the resistance measuring instrument to monitor the resistance change of the MXene / CNT sensor in real time during curing; when it is monitored that the resistance of the MXene / CNT sensor shows an increasing trend, it indicates that the MXene / CNT sensor has been impregnated with the resin adhesive and is integrally formed with the bonded component; Step 4: Subsequently, the resistance of the MXene / CNT sensor will gradually decrease. When the resistance of the MXene / CNT sensor stabilizes at a fixed value, it indicates that the curing reaction of the resin adhesive is completed. After forming the connection adhesive layer, stop heating, wait for the connecting piece to cool naturally, and then relieve the pressure to complete the bonding connection and obtain a bonded specimen; Step 5: Use a punching machine to punch connection holes at the predetermined positions of the bonded specimen for mechanical connection to obtain a composite material adhesive mechanical hybrid connection joint with self-monitoring function.

2. The preparation method of the composite material adhesive mechanical hybrid connection joint with self-monitoring function according to claim 1, characterized in that, In the above-mentioned Step 1, grinding is carried out using 100-mesh sandpaper; and cleaning is carried out using acetone solution.

3. The composite material adhesive mechanical hybrid connection joint with self-monitoring function obtained by the preparation method according to claim 1, characterized in that, Multiple composite materials are fixed by mechanical connection, and a connection adhesive layer is filled at the joint between two adjacent composite materials, and an MXene / CNT sensor is arranged in the connection adhesive layer.

4. The composite material adhesive mechanical hybrid connection joint with self-monitoring function according to claim 3, characterized in that, The above-mentioned mechanical connection is one of rivet connection, screw connection, bolt connection, and stud connection.

5. The composite material adhesive mechanical hybrid connection joint with self-monitoring function according to claim 3, characterized in that, The above-mentioned MXene / CNT sensor uses the MXene-CNT-MXene sandwich structure film as the sensing element, connects it to the circuit to form the MXene / CNT sensor; determine the shape and size of the MXene-CNT-MXene sandwich structure film in the MXene / CNT sensor according to the layout area situation.

6. The composite material adhesive mechanical hybrid connection joint with self-monitoring function according to claim 5, characterized in that, The above-mentioned MXene-CNT-MXene sandwich structure film is a multi-porous structure with a porosity of 65 - 80% and a pore size of 30 - 40 nm.

7. The composite material adhesive mechanical hybrid connection joint with self-monitoring function according to claim 3, characterized in that, The above-mentioned composite material is a composite material prepared with continuous fibers as the reinforcing material and resin as the matrix.

8. The composite material glue mechanical hybrid connection joint with self-monitoring function according to claim 3, characterized in that, When the composite material adhesive mechanical hybrid connection joint with self-monitoring function is affected by load, the MXene-CNT-MXene sandwich structure film of the MXene / CNT sensor can sense the load and respond in the form of resistance change. By analyzing whether there is a step phenomenon in the resistance change rate, the damage degree of the specimen is evaluated to judge whether the specimen still has the ability to continue serving, so as to realize the self-monitoring function of the structure.

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