A flexible conductivity monitoring system and method for composite material curing performance

Abstract

The present application discloses a flexible conductivity monitoring system for the curing performance of composite materials, which relates to the field of marine composite material performance monitoring, and includes a DSC measuring device, a flexible sensor, a flexible data processor, a data transmission device, and a display device; the DSC measuring device is used to obtain the corresponding relationship between the degree of cure and the glass transition temperature; the flexible sensor includes a flexible substrate and a flexible sensing electrode, the flexible sensing electrode can deform along with the flexible substrate, and the flexible sensing electrode is used to obtain the conductivity signal generated during the curing process in real time; the flexible data processor obtains the curing degree change curve and the glass transition temperature change curve; the data transmission device transmits it to the display device. The system can be tightly attached to a three-dimensional curved surface of any shape to achieve real-time non-destructive monitoring of conductivity, so as to obtain the curing degree and glass transition temperature in situ online, and improve the accuracy and reliability of curing performance monitoring. The flexible conductivity monitoring method disclosed in the present application has the same advantages.

Description

Technical Field

[0001] The present invention belongs to the technical field of marine composite material performance monitoring, and in particular relates to a flexible conductivity monitoring system and method for composite material curing performance. Background Art

[0002] Composite materials have enormous potential for application in the marine sector, and their excellent performance offers significant advantages for marine engineering. First, the high strength of composite materials is one of their core advantages. In marine environments, equipment and structures often need to withstand enormous loads, such as wave impact and seawater pressure. Composite materials, with their exceptional strength, ensure stability even under extreme conditions, meeting the extremely high demands of marine engineering for material strength and safety. Second, composite materials have a low density, making them lightweight, significantly reducing the overall weight of marine vehicles. This not only improves the fuel efficiency of the vehicles and reduces energy consumption, but also enhances their maneuverability and controllability, further improving performance. At the same time, their lightweight nature reduces transportation and installation costs, bringing economic benefits to marine engineering. In the high-salt environment of the ocean, corrosion is a major challenge facing equipment. Composite materials have exceptional corrosion resistance, enabling long-term stable operation and effectively resisting the erosion of seawater. Therefore, they can significantly extend the service life of equipment and reduce maintenance costs. In addition, composite materials also have excellent fatigue resistance. In the marine environment, since equipment is often subjected to repeated impact and stress, the material is required to have fatigue resistance. Composite materials, with their unique structure and properties, can maintain stable performance under repeated impact and stress, thereby reducing maintenance costs and failure rates, and improving the reliability and economy of the equipment.

[0003] In order to ensure that marine composite materials can perform well in the marine environment, it is crucial to monitor the key parameters of the curing process in real time. Among them, the degree of curing and the glass transition temperature are the core indicators for measuring the curing performance of marine composite materials. This degree of curing reflects the degree to which the resin matrix changes from liquid or viscous state to solid state, which can directly affect the mechanical properties and chemical stability of the composite material. As the degree of curing increases, the strength and stability of the composite material also increase, which can better cope with the challenges of the marine environment. The glass transition temperature (T g) is the critical temperature at which the resin matrix transitions from a highly elastic state to a glassy state. Below this temperature, the resin matrix maintains high elasticity and flexibility, adapting to the fluctuations and changes of the marine environment. However, above this temperature, the resin matrix becomes hard and brittle, and the composite's performance deteriorates dramatically. Therefore, real-time monitoring of the curing process to ensure that the resin matrix achieves the appropriate degree of cure and glass transition temperature is crucial for maintaining the excellent performance of marine composites. One existing monitoring solution uses a polyimide (PI) substrate and copper electrodes to fabricate a flexible dielectric sensor. This sensor is then integrated onto a PI circuit board, forming a flexible dielectric monitoring system embedded within the composite material to effectively monitor its curing process. However, due to the PI substrate's poor flexibility and lack of good tensile properties, its embedding into the composite material can, to a certain extent, degrade the composite's internal mechanical properties, thereby reducing its overall reliability. Furthermore, since the flexible dielectric sensor and other processing chips are integrated onto the same PI substrate, they must be embedded into the composite during monitoring, significantly increasing the volume of the embedded sensor, further negatively impacting the composite's mechanical properties. Summary of the Invention

[0004] To address the above-mentioned issues, the present invention provides a flexible conductivity monitoring system and method for the curing performance of composite materials. The system can be tightly attached to a three-dimensional curved surface of any shape, thereby realizing real-time monitoring of the conductivity signal of marine composite materials with arbitrary surface shapes. The degree of curing and glass transition temperature can be obtained in situ online, thereby improving the accuracy and reliability of curing performance monitoring in complex marine environments. Moreover, the system does not need to be embedded in the marine composite material, thereby preventing damage to its internal mechanical properties, improving overall reliability, and realizing non-destructive testing.

[0005] The present invention provides a flexible conductivity monitoring system for composite material curing performance, comprising a DSC measuring device, a flexible sensor, a flexible data processor, a data transmission device and a display device electrically connected in sequence;

[0006] The DSC measuring device is used to obtain the corresponding relationship between the degree of cure and the glass transition temperature of the monitored object;

[0007] The flexible sensor includes a flexible substrate and flexible sensing electrodes wrapped on five sides of the flexible substrate. The flexible sensing electrodes can deform along with the flexible substrate so that the exposed side thereof is completely adhered to the surface of the monitored object. The flexible sensing electrodes are used to obtain in real time the conductivity signal generated by the monitored object during the curing process.

[0008] The flexible data processor is used to obtain a curing degree change curve of the monitored object according to the conductance signal, and obtain a glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship;

[0009] The data transmission device is used to transmit the curing degree change curve and the glass transition temperature change curve to the display device for display.

[0010] Preferably, the flexible conductivity monitoring system for the curing properties of the composite material further includes a flexible circuit board for carrying the flexible data processor and the data transmission device, and the flexible circuit board and the flexible sensor are electrically connected together and packaged into a flexible whole.

[0011] Preferably, in the above-mentioned flexible conductivity monitoring system for the curing properties of the composite material, the flexible circuit board includes a polyimide substrate, a circuit pattern arranged on the polyimide substrate, and electronic components electrically connected and fixed on the polyimide substrate using the circuit pattern, and the electronic components and the circuit pattern constitute the flexible data processor and the data transmission device.

[0012] Preferably, in the flexible conductivity monitoring system for the curing properties of the composite material, the flexible circuit board and the flexible sensor are electrically connected by silver nanowires.

[0013] Preferably, in the flexible conductivity monitoring system for composite material curing performance, the flexible circuit board, the flexible sensor and the silver nanowires are cured using a polydimethylsiloxane solution to encapsulate them into a flexible whole, so that the exposed side of the flexible sensing electrode remains exposed to the outside.

[0014] Preferably, in the flexible conductivity monitoring system for composite material curing performance, the flexible data processor is configured to obtain a curing degree change curve of the monitored object according to the conductivity signal, comprising:

[0015] According to the formula

[0016] ,

[0017] Obtaining the curing degree α of the monitored object at time t, and obtaining a curing degree change curve based on the corresponding relationship between α and t;

[0018] Among them, log(G s ) is the logarithm of the conductivity value of the monitoring object detected at the beginning of curing;

[0019] log(G(t)) is the logarithm of the conductivity value of the monitored object detected at the solidification time t;

[0020] log(G e ) is the logarithm of the conductivity value of the monitored object detected when the degree of curing finally stops changing.

[0021] Preferably, in the flexible conductivity monitoring system for the curing properties of composite materials, the corresponding relationship between the curing degree and the glass transition temperature of the monitored object is obtained by using the DSC measuring device using the following formula:

[0022] ,

[0023] in,

[0024] T gu is the glass transition temperature of the monitored object in liquid state;

[0025] T gcmax The maximum glass transition temperature of the monitored object when the degree of solidification finally stops changing;

[0026] T g is the glass transition temperature of the monitored object at the solidification time t;

[0027] ΔC pu is the thermal capacity difference between the glassy state and the rubbery state of the monitored object in liquid state at the glass transition temperature;

[0028] ΔC pc It is the thermal tolerance difference between the glassy state and the rubbery state of the monitored object at the glass transition temperature when the degree of cure finally stops changing.

[0029] Preferably, in the flexible conductivity monitoring system for composite material curing performance, obtaining the glass transition temperature curve of the monitored object according to the curing degree and the corresponding relationship includes:

[0030] Use the following formula:

[0031] ,

[0032] Obtain the glass transition temperature T of the monitored object at time t g , and according to T g The corresponding relationship between t and t is used to obtain the glass transition temperature change curve of the monitored object.

[0033] Preferably, in the flexible conductivity monitoring system for composite material curing properties, the data transmission device is a Bluetooth transmission device, and the display device is a remote terminal display.

[0034] The present invention provides a flexible conductivity monitoring method for composite material curing performance, using any of the above-described systems, including:

[0035] Taking out a portion of the sample of the monitored object and placing it in the DSC measuring device to obtain the corresponding relationship between the degree of curing and the glass transition temperature of the monitored object;

[0036] Placing the flexible sensor on the surface of the monitored object so that the exposed side of the flexible sensing electrode is completely attached to the surface of the monitored object to obtain a conductivity signal in real time;

[0037] During the curing process of the monitored object, a curing degree α of the monitored object at time t is obtained according to the conductivity signal, and a curing degree variation curve is obtained according to the corresponding relationship between α and t;

[0038] According to the curing degree and the corresponding relationship, the glass transition temperature T of the monitored object at time t is obtained. g , and according to T g The corresponding relationship between t and t gives the glass transition temperature curve;

[0039] transmitting the curing degree change curve and the glass transition temperature change curve to the display device in real time;

[0040] The curing degree change curve and the glass transition temperature change curve are shown.

[0041] From the above description, it can be seen that the flexible conductivity monitoring system for the curing performance of the composite material provided by the present invention includes a DSC measuring device, a flexible sensor electrically connected in sequence, a flexible data processor, a data transmission device and a display device, and the DSC measuring device is used to obtain the correspondence between the curing degree and the glass transition temperature of the monitored object, the flexible sensor includes a flexible substrate and a flexible sensing electrode wrapped on five sides by the flexible substrate, the flexible sensing electrode can follow the deformation of the flexible substrate so that the exposed side is completely attached to the surface of the monitored object, and the flexible sensing electrode is used to obtain the conductivity signal generated by the monitored object during the curing process in real time, so it can be tightly attached to a three-dimensional curved surface of any shape, thereby realizing the monitoring of marine composite materials with any surface shape. Real-time monitoring of the conductivity signal, and since the flexible data processor is used to obtain the curing degree change curve of the monitored object according to the conductivity signal, and obtain the glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship, the data transmission device is used to transmit the curing degree change curve and the glass transition temperature change curve to the display device for display, so the curing degree and glass transition temperature can be obtained in situ online, improving the accuracy and reliability of curing performance monitoring in complex marine environments, and there is no need to embed in marine composite materials, so as not to damage their internal mechanical properties, improve overall reliability, and realize non-destructive testing. After the test is completed, the system can be taken down to continue monitoring the next monitored object, and the monitoring efficiency is higher. The flexible conductivity monitoring method for the curing performance of composite materials provided by the present invention has the same advantages as the above-mentioned system. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0043] Figure 1 This is an overall schematic diagram of an embodiment of a flexible conductivity monitoring system for composite material curing performance provided by the present invention;

[0044] Figure 2 A schematic diagram of an embodiment of a flexible conductivity monitoring method for curing properties of a composite material provided by the present invention;

[0045] Figure 3 Schematic diagram of the preparation process of a flexible circuit board;

[0046] Figure 4Schematic diagram of the connection and packaging between the flexible circuit board and the flexible sensor;

[0047] Figure 5 This is the principle block diagram of the sensor integration system;

[0048] Figure 6 It is the flow chart of the measurement scheme;

[0049] Figure 7 is the measured curing degree change curve of the above composite material;

[0050] Figure 8 is the measured glass transition temperature change curve of the above composite material. DETAILED DESCRIPTION

[0051] The core of the present invention is to provide a flexible conductivity monitoring system and method for the curing performance of composite materials. The system can be tightly attached to a three-dimensional curved surface of any shape, thereby realizing real-time monitoring of the conductivity signal of marine composite materials with arbitrary surface shapes. In this way, the degree of cure and glass transition temperature can be obtained in situ online, improving the accuracy and reliability of curing performance monitoring in complex marine environments. Moreover, it does not need to be embedded in the marine composite material, so it will not damage its internal mechanical properties, thereby improving overall reliability and realizing non-destructive testing.

[0052] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0053] The implementation example of the flexible conductivity monitoring system for composite material curing performance provided by the present invention is as follows: Figure 1 As shown, Figure 1 This is an overall schematic diagram of an embodiment of a flexible conductivity monitoring system for composite material curing properties provided by the present invention, which may include a DSC measuring device 1, a flexible sensor 2, a flexible data processor 3, a data transmission device 4, and a display device 5 electrically connected in sequence;

[0054] The DSC (differential scanning calorimetry) measuring device 1 is used to obtain the corresponding relationship between the degree of cure and the glass transition temperature of the monitored object. In this way, the glass transition temperature can be directly obtained based on the degree of cure at each time point, thereby assisting in obtaining a change curve of the glass transition temperature. It should be noted that the DSC measuring device is a separate device and is not connected to other devices in the system.

[0055] The flexible sensor 2 includes a flexible substrate 21 and a flexible sensing electrode 22 wrapped on five sides by the flexible substrate 21. The flexible sensing electrode 22 can deform along with the flexible substrate 21 so that the exposed side thereof is completely attached to the surface of the monitored object. The flexible sensing electrode 22 is used to obtain the conductivity signal generated by the monitored object during the solidification process in real time. Figure 1 It can be seen that the three-dimensional shape of the flexible sensing electrode 22 can be approximated by a rectangular parallelepiped. The upper surface and the four surrounding surfaces of the flexible sensing electrode 22 can be completely wrapped by the flexible substrate 21, leaving only the bottom surface exposed to the outside and able to contact the monitored object to obtain the conductivity signal. The flexible sensor 2, as the sensing front end of the entire system, has strong flexibility and stretchability, ensuring that it can be closely attached to various curved structures for conductivity measurement without affecting the monitoring accuracy. One side can be a low-potential electrode and the other side can be a high-potential electrode. Through this design, the conductivity signal changes generated during the curing process of the composite material can be effectively captured and transmitted. This not only simplifies the signal acquisition path, but also significantly improves the sensitivity and stability of the system. The target object can be, but is not limited to, marine composite materials.

[0056] The flexible data processor 3 is used to obtain a curing degree change curve of the monitored object based on the conductivity signal, and to obtain a glass transition temperature change curve of the monitored object based on the corresponding relationship between the curing degree and the curing degree and glass transition temperature obtained by the DSC measuring device. Specifically, each curing degree corresponds to a glass transition temperature, and the obtained glass transition temperatures are plotted against time in a coordinate system to obtain the glass transition temperature change curve.

[0057] The data transmission device 4 is used to transmit the curing degree change curve and the glass transition temperature change curve to the display device 5 for display. Figure 1 The dotted line in the figure indicates that there is no need for a physical connection between the data transmission device 4 and the display device 5, but they are connected through wireless communication. This eliminates the need for wiring and makes on-site measurement more convenient. In addition, the above-mentioned flexible data processor 3 can also use the data transmission device 4 to communicate with the DSC measuring device to obtain data including the above-mentioned corresponding relationship from the DSC measuring device. In this case, after the DSC measuring device measures various parameters of the monitored object, it can obtain the corresponding relationship between the curing degree and the glass transition temperature of the monitored object, and then transmit this corresponding relationship to the above-mentioned flexible data processor 3. The flexible data processor 3 can use this corresponding relationship to perform subsequent calculation processes.

[0058] In summary, the system effectively avoids the problems of existing technologies such as reliance on external desktop instruments, cumbersome operation and high cost. The system has the advantages of low cost and easy portability. The flexible data processor therein not only has powerful data processing capabilities, but also can receive and process signals from flexible sensors in real time, and can transmit the processed signals to a display device in real time through a data transmission device. This display device can be a display located in a remote monitoring center or a mobile terminal, realizing remote access and real-time monitoring of data.

[0059] From the above description, it can be seen that in the embodiment of the flexible conductivity monitoring system for the curing performance of the composite material provided by the present invention, since it includes a DSC measuring device, a flexible sensor, a flexible data processor, a data transmission device and a display device electrically connected in sequence, and the DSC measuring device is used to obtain the correspondence between the curing degree and the glass transition temperature of the monitored object, the flexible sensor includes a flexible substrate and a flexible sensing electrode wrapped on five sides by the flexible substrate, the flexible sensing electrode can follow the deformation of the flexible substrate so that the exposed side thereof is completely attached to the surface of the monitored object, and the flexible sensing electrode is used to obtain the conductivity signal generated by the monitored object during the curing process in real time, so it can be tightly attached to a three-dimensional curved surface of any shape, thereby realizing the monitoring of marine composite materials. Real-time monitoring of the conductivity signal, and since the flexible data processor is used to obtain the curing degree change curve of the monitored object according to the conductivity signal, and obtain the glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship, the data transmission device is used to transmit the curing degree change curve and the glass transition temperature change curve to the display device for display, so the curing degree and glass transition temperature can be obtained in situ online, thereby improving the accuracy and reliability of curing performance monitoring in complex marine environments, and there is no need to be embedded in marine composite materials, so as not to damage its internal mechanical properties, thereby improving the overall reliability and realizing non-destructive testing. After the detection is completed, the system can be taken down to continue monitoring the next monitored object, and the monitoring efficiency is higher.

[0060] In a specific embodiment of the flexible conductivity monitoring system for composite material curing performance, continue to refer to Figure 1, and can also include a flexible circuit board 6 for carrying the flexible data processor 3 and the data transmission device 4. The flexible circuit board 6 and the flexible sensor 2 are electrically connected together and packaged into a flexible whole. After forming a flexible and lightweight whole, it is more convenient to carry, and there is no need to use large equipment as in the prior art. Moreover, when it is necessary to monitor a certain monitoring object, the whole can be placed on it, which is more convenient to operate and does not require any on-site connection operations. Furthermore, the flexible circuit board 6 can include a polyimide substrate, a circuit pattern provided on the polyimide substrate, and electronic components (such as) electrically connected to and fixed to the polyimide substrate by the circuit pattern. Figure 1As shown, the electronic components and circuit patterns constitute the flexible data processor 3 and data transmission device 4. Specifically, a polyimide substrate with a thickness of 50 to 300 microns is preferred. In further embodiments, a polyimide substrate with a thickness of 125 microns can be selected, depending on actual needs. The fabrication process is as follows: a uniform copper layer approximately 20 μm thick is deposited on the polyimide (PI) substrate via a precision sputtering process, serving as the foundation for the conductive paths. Subsequently, the copper layer is finely processed using wet etching techniques to form the desired circuit pattern. Before etching, the copper-clad polyimide substrate is thoroughly cleaned and dried to ensure a clean, contaminant-free surface, laying a solid foundation for subsequent processes. During the etching process, a corrosion-resistant solvent is used to protect the copper surface, preventing the etching solution from attacking non-target areas. After etching, various electronic components (including chips, resistors, capacitors, etc.) are precisely soldered to the polyimide substrate using reflow soldering technology, creating a complete flexible circuit board that integrates the data processing module and the data transmission module. Specifically, the resulting flexible data processor 3 can be a microcontroller (MCU). During this process, uniform solder paste application, precise positioning of the electronic components, and the high-temperature melting effect of the reflow oven are crucial to ensure a secure and reliable solder connection and excellent electrical performance. It should also be noted that this microcontroller (MCU) may include a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), input / output (I / O) interfaces, reset and clock circuits, etc., and the MCU is small in size, light in weight, low in power consumption, and has powerful control functions and flexible expansion. There are many options for selecting MCU, such as the STM32 series, ARM Cortex-M series, MSP430 series, etc. The STM32 series includes STM32F2, STM32F4, STM32F7, STM32H7, STM32F0, STM32F1, STM32F3 and the ultra-low power STM32L0, STM32L1, STM32L4; the ARM Cortex-M series includes Cortex-M0, Cortex-M0+, Cortex-M1, Cortex-M3, Cortex-M4, Cortex-M7, Cortex-M23, Cortex-M33; the MSP430 series includes MSP430F1132, MSP430F133, MSP430F149, MSP430F2003, MSP430F2011 and other models. You can choose any MCU model.

[0061] Another specific embodiment provided by this application is based on the embodiment of the flexible conductivity monitoring system for the curing performance of the composite material, and further refers to Figure 1Silver nanowires 7 are used to electrically connect the flexible circuit board 6 and the flexible sensor 2. The specific manufacturing process may include: using double-sided seamless tape to secure the flexible circuit board to a smooth glass plate, then applying PI tape to the remaining portion of the glass plate. Laser cutting is then used to precisely outline the sensor structure and conductive path. After removing the cut portion of the PI tape, a silver nanowire solution is drop-coated onto the exposed glass substrate. Once the solution has completely dried, a highly conductive electrode layer and conductive path are formed. It should also be noted that this silver nanowire can also be replaced by other conductive materials with high flexibility and excellent conductivity, such as carbon-based flexible conductive materials: graphene, carbon nanotubes, carbon fibers, graphene oxide, reduced graphene oxide, titanium carbide, MXenes, etc.; metal-based flexible conductive materials: gold nanowires, copper nanowires, metal foil (copper foil, aluminum foil); polymer-based flexible conductive materials: polystyrene sulfonic acid-doped polystyrene (PEDOT:PSS), polystyrene sulfonic acid-doped poly-p-styrene (PEDOT:PTS), poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), polyacetylene, polyaniline, polypyrrole, polybenzimidazole, polythiophene, etc.; conductive gels, graphite composites, metal-organic frameworks (MOFs), transition metal disulfides (such as molybdenum disulfide, tungsten disulfide), etc.; in terms of preparation technology, it can be processed by laser cutting, screen printing, inkjet printing, physical vapor deposition and other technologies.

[0062] This application also provides another specific embodiment, based on the above-mentioned flexible conductivity monitoring system for composite material curing properties. In this embodiment, a polydimethylsiloxane solution is preferably used to cure the flexible circuit board 6, flexible sensor 2, and silver nanowires 7, thereby encapsulating them into a flexible, integrated structure. This allows the exposed side of the flexible sensing electrode 22 to remain exposed. The specific manufacturing process can be as follows: The flexible circuit board, flexible sensor, and the conductive path (silver nanowires) between them are surrounded by 1 cm thick tape (a 1 mm thickness can be achieved by stacking five 2 mm thick tape layers) to prevent the polydimethylsiloxane solution (PDMS) from flowing. The PDMS solution is then poured, allowed to level in a horizontal position, and cured at a constant temperature to form a durable encapsulation layer. After encapsulation, excess PDMS material is removed using a cutter, allowing the flexible sensor to be flexibly integrated onto complex three-dimensional surfaces, meeting diverse monitoring needs. This flexible, integrated encapsulation structure protects the internal circuitry from environmental corrosion while maintaining the system's flexibility and durability. Of course, in addition to polydimethylsiloxane, the packaging material here can also use other stretchable materials with small elastic modulus and excellent flexibility, such as silicone materials, hydrogel materials, etc., which can be selected according to actual needs.

[0063] It should also be noted that in one of the aforementioned embodiments, the flexible circuit board 6 is fabricated using polyimide (PI) as the base material and copper as the conductive material. The polyimide base, with its excellent high-temperature resistance and flexibility, provides reliable assurance for the stable operation of the flexible circuit board in complex deformation environments. Copper, with its excellent conductive properties, plays a key role in constructing the conductive pathways of the flexible circuit board 6. Furthermore, the flexible sensor 2 is fabricated using a combination of silver nanowires and a polydimethylsiloxane (PDMS) base. These silver nanowires not only possess excellent conductivity, but their unique nanoscale dimensions also give the sensor increased sensitivity. The PDMS base exhibits excellent flexibility, demonstrating significant advantages in multiple applications. In this design for connecting the flexible circuit board 6 to the flexible sensor 2, silver nanowires, made of the same material as the flexible sensor 2, serve as the conductive pathways for the electrode connections. However, achieving an efficient and stable connection between the copper electrodes of the flexible circuit board 6 and the silver nanowire material still presents certain technical challenges. To address these connection challenges, the present application provides a preparation process, which may include the following steps:

[0064] The specific preparation steps are as follows:

[0065] The first step is to construct a lower electrode layer on the PI substrate of the flexible circuit board 6. Specifically, magnetron sputtering technology can be used. This technology uses a magnetic field to confine the movement of electrons in a plasma, significantly improving sputtering efficiency and uniformity of thin film deposition. Under strictly controlled process parameters (including sputtering power, sputtering time, and vacuum level), a uniform circular copper layer (approximately 20 μm thick and 0.5 cm in diameter) is deposited on the PI substrate. This lower electrode layer serves as the foundation for subsequent connection to the silver nanowire electrode material, and its quality and performance are crucial to the stability of the overall connection structure.

[0066] The second step is to prepare an intermediate electrode layer on the surface of the lower electrode layer. Specifically, a simple drop coating method can be used to evenly apply a silver nanowire dispersion to the lower electrode surface. By precisely controlling parameters such as the coating time and solution concentration, the silver nanowires can completely and evenly cover the lower electrode surface, forming a continuous conductive network. After the silver nanowire solution has fully dried, the silver nanowire layer now constitutes the intermediate electrode layer, acting as a bridge in the entire connection structure, achieving a conductive connection between the flexible circuit board 6 and the flexible sensor 2.

[0067] The third step is to prepare an upper electrode layer on the dried silver nanowire intermediate electrode layer. Specifically, magnetron sputtering technology can be used again to deposit a uniform copper layer (approximately 20μm thick and 0.65cm in diameter). The function of this upper electrode layer is to completely encapsulate the intermediate and lower electrode layers, forming a sandwich-like three-layer structure. This structural design greatly enhances the conductivity and bonding between the two different electrode materials. From a microscopic perspective, the copper in the upper electrode layer forms a strong metallurgical bond with the intermediate silver nanowire layer and the copper in the lower electrode layer through atomic interactions, effectively reducing contact resistance and improving electron transfer efficiency. At the same time, the mechanical stability of the sandwich structure is significantly improved, which can better adapt to the mechanical deformations such as bending and stretching that occur during actual use of flexible devices.

[0068] The present application also provides a preferred embodiment, based on the embodiment of the flexible conductivity monitoring system for composite material curing performance, wherein the flexible data processor 3 is configured to obtain a curing degree change curve of the monitored object based on the conductivity signal, and specifically may include:

[0069] According to the formula

[0070] ,

[0071] Obtaining the curing degree α of the monitored object at time t, and obtaining a curing degree change curve based on the corresponding relationship between α and t;

[0072] Among them, log(G s ) is the logarithm of the conductivity value of the monitoring object detected at the beginning of curing;

[0073] log(G(t)) is the logarithm of the conductivity value of the monitored object detected at the solidification time t;

[0074] log(G e ) is the logarithm of the conductivity value of the monitored object detected when the degree of curing finally stops changing.

[0075] Specifically, since the viscosity of the monitored object is closely related to the degree of cure, that is, the greater the viscosity, the higher the degree of cure, and the viscosity is inversely proportional to the ionic conductivity, that is, the greater the viscosity, the lower the ionic conductivity and the higher the degree of cure, based on this, the above formula can be used to accurately obtain the real-time degree of cure based on the conductivity. e), it should be noted here that it is the logarithm of the conductivity value detected when the degree of curing finally stops changing, and the fact that the degree of curing finally stops changing does not mean that the degree of curing reaches 100%, because at each temperature there is a corresponding degree of curing that finally stops changing. For example, at a certain temperature, the degree of curing when it finally stops changing is only 80%, that is, the maximum degree of curing when the monitored object at this temperature finally stops changing can reach 80%, but cannot reach 100%. At this time, the conductivity obtained is G e , and G s It is the conductivity value detected at the beginning of curing, and G(t) is the conductivity value detected after the curing time has passed t time. It should also be noted that when this embodiment performs the above-mentioned curing performance monitoring on a certain monitoring object, it is necessary to go through a curing process from the beginning of curing to the curing degree no longer changing, and obtain the conductivity value from G s , G e And G (t) corresponding to each moment in the curing process, and then the curing degree corresponding to each moment t can be obtained according to the above formula. However, these curing degree values ​​are not obtained in real time during the curing process. After all, G is needed in this formula. e Only after the solidification is completed can this G be obtained e .

[0076] The present application also provides another preferred embodiment, based on the preferred embodiment of the flexible conductivity monitoring system for the curing performance of composite materials described above, the corresponding relationship between the curing degree and the glass transition temperature of the monitored object obtained by using a DSC measuring device can be obtained using the following formula:

[0077] ,

[0078] in,

[0079] T gu is the glass transition temperature of the monitored object in liquid state;

[0080] T gcmax The maximum glass transition temperature of the monitored object when the degree of solidification finally stops changing;

[0081] T g is the glass transition temperature of the monitored object at the solidification time t;

[0082] ΔC pu is the thermal capacity difference between the glassy state and the rubbery state of the monitored object in liquid state at the glass transition temperature;

[0083] ΔC pc It is the thermal tolerance difference between the glassy state and the rubbery state of the monitored object at the glass transition temperature when the degree of cure finally stops changing.

[0084] It should be noted that this is to associate the obtained conductivity signal with differential scanning calorimetry (DSC). A small piece of the monitored object can be selected and measured using this DSC to obtain multiple parameters in the formula. Specifically, through isothermal DSC testing, T at different curing temperatures can be obtained. g and α, and finally calculated T through least squares regression model analysis gu 、T gc , ΔC pu , ΔC pc After all the parameters in the formula are measured, only T g and α are unknown, and the previous embodiment mentioned that the value of α of the monitored object at each moment can be obtained by using the conductivity signal, so T g The above nonlinear relationship with α can be obtained by substituting the previously obtained α value into the formula to obtain the corresponding T g , that is to say, according to α at each moment, we can get the T corresponding to each moment. g .

[0085] The present application also provides another preferred embodiment, based on another preferred embodiment of the flexible conductivity monitoring system for composite material curing performance, wherein obtaining a glass transition temperature curve of the monitored object according to the curing degree and the corresponding relationship may specifically include:

[0086] Use the following formula:

[0087] ,

[0088] Get the glass transition temperature T of the monitored object at time t g , and according to T g The corresponding relationship between and t can be used to obtain the glass transition temperature change curve of the monitored object.

[0089] It can be seen that using this formula, the corresponding curing degree α and glass transition temperature T of the composite material can be obtained according to the conductivity signal obtained at each moment. g The flexible data processor can use this formula to quickly and accurately obtain the glass transition temperature curve according to its corresponding relationship with time, thereby realizing a rapid and direct quantitative analysis of the curing process of the composite material.

[0090] Regarding each of the above formulas, it's important to further clarify that temperature is a key factor influencing the conductivity of a material. Specifically, as temperature rises, the conductivity of a material generally increases. The underlying mechanism is that rising temperature causes atoms or molecules within the material to acquire higher kinetic energy, which in turn increases the movement of electrons within the lattice. As charge carriers, the increased movement of electrons greatly promotes their migration, thereby enhancing the material's electrical conductivity. Therefore, the effect of temperature on conductivity can be further considered to modify the above formulas to some extent.

[0091] In the study of composite materials, accurate monitoring of their degree of cure is crucial. Since the conductivity values ​​at different temperatures are significantly affected by temperature, accurately monitoring the temperature of the material while monitoring the cure of the composite material can help effectively solve the problems faced in the composite material cure monitoring process and significantly improve the accuracy of monitoring. It is particularly noteworthy that compared with traditional constant temperature curing experiments, decoupling temperature and conductivity has obvious advantages. By decoupling temperature and conductivity, it is possible to break through the limitations of constant temperature conditions and achieve effective monitoring of variable temperature curing processes, making this monitoring technology more suitable for practical applications (because in practical applications, the temperature of the material will continue to change with the environment and the heat released by its own curing process), making it able to adapt to more diverse actual working conditions. Based on this, the following formula is proposed:

[0092] ,

[0093] Where G(T) represents the conductivity value at temperature T, G0 represents the initial conductivity value at T0, T0 represents the initial temperature, T represents the temperature at any time, and K is the compensation coefficient. The calculation of K can be obtained by the following formula:

[0094] ,

[0095] Since the conductivity values ​​at different temperatures are significantly affected by temperature, in order to more accurately monitor the degree of cure of the composite material, it is necessary to convert the conductivity values ​​at different temperatures so that they all correspond to the conductivity values ​​at the same temperature. After theoretical derivation and decoupling the relationship between temperature and conductivity, the optimized cure degree formula is obtained as follows:

[0096] ,

[0097] in, is the logarithm of the conductivity value of the monitored object detected at the beginning of curing at temperature T0; It is the logarithm of the conductivity value of the sample that has been cured at temperature T0; It represents the logarithm of the conductivity value of the monitored object detected at the temperature T0 and the curing time t;

[0098] The corresponding relationship between the degree of curing and the glass transition temperature is still:

[0099] ,

[0100] Substituting the above curing degree formula into the corresponding relationship formula between curing degree and glass transition temperature, the glass transition temperature formula can be obtained as follows:

[0101] ,

[0102] To determine the compensation factor K in the above formula, an experiment was designed and conducted. The experiment first focused on the cured composite material, accurately measuring its conductivity at T0. This step provided an important foundational data point for subsequent research. The conductivity of the cured composite material was then measured at T. By comparing the conductivity data at different temperatures, we can initially understand the impact of temperature on conductivity. Finally, these different temperatures and their corresponding conductivity values ​​were substituted into the above formula. Through precise mathematical calculations, the compensation factor K was calculated.

[0103] The specific steps are as follows:

[0104] Select a small piece of cured epoxy resin (composite material) and place it on a heating table at 30°C. First, use a temperature sensor to measure the temperature. When the surface temperature of the epoxy resin stabilizes at 30°C, use an LCR meter to measure it and read the value of the LCR meter at this time.

[0105] Select a piece of cured epoxy resin (composite material) of the same size and place it on a heating table at 60°C. First, measure the temperature with a temperature sensor. When the surface temperature of the epoxy resin stabilizes at 60°C, measure it with an LCR meter and read the value of the LCR meter at this time.

[0106] According to the LCR reading, the conductivity value of epoxy resin at 30°C is G(30) = 2.271pS; the conductivity value of epoxy resin at 60°C is G(60) = 2.953pS. Substituting the obtained value into the compensation coefficient calculation formula, it is obtained that K is 0.0089. In each embodiment of the flexible conductivity monitoring system for composite material curing performance, the data transmission device can be preferably a Bluetooth transmission device. Of course, other types of wireless transmission devices can also be selected, such as any one of wireless radio frequency identification (RFID) devices, ZigBee wireless communication devices, Wi-Fi communication devices, and 4G / 5G mobile communication devices. Moreover, the display device can be preferably a remote terminal display. By using this wireless communication device, long-distance transmission can be achieved, and intuitive curing information during the composite material curing process can be directly displayed on the remote control terminal.

[0107] In summary, the above-mentioned system provided by the present invention has a relatively simple and portable overall structure, does not require complex external measuring instruments, and greatly simplifies the overall equipment for monitoring composite materials. By performing real-time online monitoring of two important parameters in the curing process of composite materials, namely the degree of curing and the glass transition temperature, the mechanical properties of marine composite materials after curing can be effectively improved, making their scope of application more extensive, their stability and reliability more excellent, and able to better cope with the challenges of the marine environment. The system is entirely constructed based on flexible materials, and its sensor part uses fully flexible materials. In terms of material selection, the base material has flexibility, corrosion resistance and high reliability, while the electrode material has both high flexibility and excellent electrical conductivity. This design enables the sensor to fit tightly to any three-dimensional complex surface, thereby breaking through the limitations of traditional plane monitoring and broadening the scope of application. The flexible circuit part of the system also uses flexible materials as its base, thereby reducing the weight of its own circuit, making it more miniaturized and lightweight.

[0108] The implementation example of the flexible conductivity monitoring method for the curing performance of a composite material provided by the present invention is as follows: Figure 2 As shown, Figure 2 This is a schematic diagram of an embodiment of a flexible conductivity monitoring method for composite material curing performance provided by the present invention, which may include the following steps using any of the above systems:

[0109] S1: taking out a portion of the sample of the monitored object and placing it in a DSC measuring device to obtain the corresponding relationship between the degree of curing and the glass transition temperature of the monitored object;

[0110] The specific steps can be as follows:

[0111] 1. Place a small sample of the composite material into a test tube;

[0112] 2. Place the test tube containing the sample on the heater of the differential scanning calorimeter (DSC equipment);

[0113] 3. Set the cavity environment inside the differential scanning calorimeter to air, and use the heat flow sensor of the differential scanning calorimeter to detect the reaction enthalpy of the sample;

[0114] 4. The degree of curing α can be inferred from the reaction enthalpy obtained from the isothermal DSC test, and its expression is: , where H(t) represents the reaction enthalpy of the composite material at time t, and H∞ represents the reaction enthalpy of the composite material at time infinite;

[0115] 5. Perform a non-isothermal test on the test sample, heating the temperature from -50°C to 275°C at a heating rate of 5°C / min. By observing the temperature turning point of the isothermal DSC curve obtained, the glass transition temperature of the test sample can be obtained;

[0116] 6. The ΔC is finally obtained by fitting the curing degree and glass transition obtained at different curing temperatures using the least squares method. pu and ΔC pc , where ΔC pu is the thermal capacity difference between the glassy state and the rubbery state of the monitored object in liquid state at the glass transition temperature, ΔC pc It is the thermal capacity difference between the glassy state and the rubbery state of the monitored object at the glass transition temperature when the degree of cure finally stops changing;

[0117] 7. Obtain T directly from non-isothermal DSC test gu and T gcmax , where T gu is the glass transition temperature of the monitored object in liquid state, T gcmax It is the maximum glass transition temperature of the monitored object when the degree of solidification finally stops changing.

[0118] Substitute the above parameters into the formula,

[0119] ,

[0120] The curing degree α and glass transition temperature T of the monitored object can be obtained g The corresponding relationship between them.

[0121] S2: placing the flexible sensor on the surface of the monitored object so that the exposed side of the flexible sensing electrode is completely attached to the surface of the monitored object to obtain the conductivity signal in real time;

[0122] It should be noted that this flexible sensing electrode can conform to the surface of any shape of the monitored object, ensuring that the conductivity signal of the contact area is fully obtained. It can be seen that this can test the conductivity signal of marine composite materials of various shapes to achieve the monitoring of curing performance.

[0123] S3: During the curing process of the monitored object, the curing degree α of the monitored object at time t is obtained according to the conductivity signal, and a curing degree change curve is obtained according to the corresponding relationship between α and t;

[0124] It can be seen that the conductivity signals at various time points are obtained until the final curing is completed, and then the curing degree can be calculated based on these conductivity signals, so that the curing degree change curve can be drawn using t as the horizontal axis and the curing degree α as the vertical axis.

[0125] S4: According to the curing degree and the corresponding relationship, the glass transition temperature T of the monitored object at time t is obtained. g , and according to T g The corresponding relationship between t and t gives the glass transition temperature curve;

[0126] This correspondence is obtained from the previous step S1. Combined with the data of the curing degree α at each moment obtained in step S3, the glass transition temperature T at each moment can be obtained. g The data is then taken as t on the horizontal axis and T g The glass transition temperature curve can be drawn with θ as the vertical axis.

[0127] S5: transmitting the curing degree change curve and the glass transition temperature change curve to a display device in real time;

[0128] Specifically, wireless communication may be used to transmit the display device at the remote control end to achieve remote monitoring.

[0129] S6: Displays the curing degree change curve and glass transition temperature change curve.

[0130] It should be noted that this allows the remote control end to see the changes in these curves in real time, so as to understand the curing performance in a timely manner.

[0131] The following describes in detail the manufacturing process and measurement process of the flexible conductivity monitoring system for the curing performance of the composite material using a preferred example:

[0132] This example uses an epoxy-based composite material. For the flexible conductivity monitoring system based on the curing properties of this composite material, the sensor utilizes silver nanowire electrodes and a PDMS substrate, fabricated through laser patterning and drop coating. For the flexible circuit design, a PI-Cu substrate is used as the substrate, fabricated through wet etching and reflow soldering. The low-power STM32L0 microcontroller was chosen. For wireless communication, a Bluetooth communication module was selected, offering more stable and secure data transmission due to its low cost.

[0133] refer to Figure 3 , Figure 3 This is a schematic diagram of the preparation process of a flexible circuit board. The flexible circuit board uses a 125μm thick PI film as the substrate 101. A 20μm thick copper layer is plated on the surface of the PI film using sputtering technology as the conductive layer 102 of the circuit board. The copper-plated PI film is cleaned to remove surface dirt and wet-etched. A corrosion-resistant solvent is evenly applied to the surface of the copper layer. After the solution dries, a protective thin layer can be formed on the surface of the copper layer. The desired conductive path pattern is then obtained by exposing and developing it. Finally, the developed PI copper-clad substrate is placed in a copper wet etcher to obtain an etched copper conductive path. After the conductive path etching is completed, the STM32L0 chip, Bluetooth communication chip and other electronic components are integrated on the etched PI copper-clad substrate using reflow soldering technology. First, solder paste is evenly applied to the substrate's solder joints, and the required electronic components are installed at these joints. The assembled circuit board is then placed in a reflow oven, where the high temperature melts the solder paste again, forming a reliable solder joint connection. After reflow is complete, the soldered circuit board is removed from the oven and cooled, forming the final flexible circuit board.

[0134] refer to Figure 4 , Figure 4This is a schematic diagram of the connection and packaging between the flexible circuit board and the flexible sensor. After the flexible circuit board is prepared, the packaging and connection between the flexible circuit board and the flexible sensor are carried out. First, the prepared flexible circuit 103 is fixed to a smooth glass plate 104 using double-sided seamless tape. A 55μm thick, patterned PI tape 105 is attached to the remaining portion of the glass plate. This patterned PI tape is cut using a laser cutter. Subsequently, a silver nanowire electrode solution is dripped onto the cut portion of the PI tape. After the silver nanowire solution dries, the PI tape is removed, thereby forming a conductive path 106 between the flexible sensor and the flexible circuit board, as well as the electrode structure 107 of the flexible sensor. Next, a 1cm thick layer of seamless tape is wrapped around the glass plate to ensure that the flexible circuit board, the flexible sensor, and the conductive path between them are all enclosed. The prepared PDMS solution 108 is poured onto the glass plate, and the glass plate is moved to a horizontal surface and left to rest for 5 minutes to allow the PDMS solution to completely level. After complete leveling, the entire material is placed in a constant temperature oven, set to a curing temperature of 60°C, and cured for 4 hours. The material is then removed, the surrounding tape removed, and the bottom glass plate removed, resulting in the encapsulated flexible circuit board, flexible sensor, and the conductive path connecting them 109. Finally, a cutting machine is used to remove the remaining PDMS encapsulation layer between the flexible sensor and the flexible circuit board, excluding the conductive path, to obtain the main body 110 of the flexible conductivity monitoring system for composite material curing performance.

[0135] The flexible sensor is attached to the surface of the composite material on the three-dimensional curved surface so that the electrode structure 107 directly contacts the surface of the composite material to monitor the signal during the curing process and transmit the data to the computer for processing via the wireless Bluetooth communication module. Figure 5 As shown, Figure 5 This is a block diagram of the sensor integration system. The power module provides power to the system, including a battery module, a power management chip, and an overcurrent protection device. The microcontroller unit (MCU) can embed a real-time algorithm program and is connected to a filtering circuit, a temperature sensor, a flexible sensor, an I / O interface, a data storage module, a clock module, a crystal oscillator module, an AD conversion module, an antenna, an antenna communication module, a driver module, and a signal generation unit. During internal processing, the flexible sensor connects to the I / O interface, transmitting the data collected by the flexible sensor to the MCU. The data is then stored in the MCU's built-in data storage module (ROM / RAM). After being processed by the MCU's embedded real-time algorithm program, the AD conversion module converts the processed data into digital output. Finally, the output data is filtered and transmitted to a remote computer via the communication module.

[0136] refer to Figure 6 , Figure 6The measurement flow chart shows that the program is initialized first, and an excitation signal (i.e., the conductivity signal obtained by the sensor) is applied to the input. After the algorithm processes the data, an ADC conversion is performed. A delay of 1-2 seconds is performed to read and store the ADC value, and then the software loop repeats until the delay time ends. Finally, the excitation signal is removed from the input, and a delay is added before starting the next measurement to ensure that the circuit can operate stably. Finally, the monitored data is uploaded to the PC via Bluetooth, and the final curing degree data and glass transition temperature data are displayed on the PC. Figure 7 and Figure 8 , Figure 7 is the measured curing degree change curve of the above composite material, Figure 8 is the measured glass transition temperature change curve of the above composite material.

[0137] It's also worth noting that the chip portion of the flexible printed circuit board can further integrate edge computing algorithms. The derived conductivity-temperature expressions, curing degree expressions, and glass transition temperature expressions can be precisely written into the chip. In this way, the chip can display the composite material's curing degree and glass transition temperature in real time.

[0138] However, a significant challenge in actual monitoring practice is that low temperatures significantly prolong the curing time of composite materials. This characteristic results in rapid power consumption during long-term monitoring. To address this issue, the program design was optimized, combining the monitoring functions of the flexible sensor and temperature sensor in the hardware with the real-time calculation of the composite material's conductivity, degree of cure, and glass transition temperature in the software. The resulting design incorporates three different operating modes: sleep mode (low-frequency monitoring), normal mode (medium-frequency monitoring), and fast mode (high-frequency monitoring).

[0139] Specifically, by comparing the degree of cure values ​​at different times in real time, the system can automatically and dynamically adjust to the most appropriate operating mode based on the degree of cure's changes. This comparison of degree of cure values ​​is chosen because it provides a direct indicator of the composite's curing status. This approach effectively reduces system energy consumption while ensuring accurate monitoring, achieving a balance between performance and efficiency.

[0140] Program Initialization and Startup: After the program starts, it first undergoes a comprehensive initialization phase. During this initialization phase, the system performs a self-test of each hardware module to ensure that the temperature sensor, flexible dielectric sensor, communication module, and internal chip computing unit are functioning properly. After the self-test is complete, the system applies an excitation signal and enters normal operating mode (default mode). In this mode, the system begins collecting temperature and conductance values ​​from the temperature sensor and flexible dielectric sensor.

[0141] Sensor Selection and Calibration: A high-precision thermistor-type temperature sensor is used, offering a measurement accuracy of ±0.1°C, capable of accurately sensing temperature changes on the composite material surface. A capacitive dielectric sensor is used as the dielectric sensor, achieving a resolution of 0.01pS for conductivity measurements, ensuring the accuracy of conductivity data collection. Before each experiment, the sensor must be calibrated using a standard temperature source and standard samples of known conductivity to eliminate systematic sensor errors.

[0142] Data Acquisition and Processing: After collecting real-time temperature and conductance values, the conductance values ​​are converted using the relationship between temperature and conductance, converting them to values ​​at a specific temperature. This temperature is typically the baseline temperature of the experimental environment, such as 25°C. During data processing, double-precision floating-point arithmetic is used internally on the chip to improve accuracy. The converted data is stored in the chip's internal cache. The resulting conductance value is then used to determine the degree of curing at that point and stored accordingly.

[0143] Working mode judgment and switching:

[0144] Data Reading and Comparison: Repeat the above data acquisition and processing operations, reading the temperature and conductance values ​​of the temperature sensor and dielectric sensor at the next moment. The conductivity and cure degree values ​​are converted and stored again. The cure degree values ​​recorded at the two moments are then compared. During this comparison process, the chip uses high-precision subtraction and absolute value calculation instructions to ensure the accuracy of the comparison results.

[0145] Mode Switching Logic: The system's operating mode is determined by the absolute difference between the previous and next cure values. This conversion and comparison of cure values ​​occurs continuously. If the absolute value of the difference exceeds 1%, this indicates that the composite material's cure process is rapidly changing, and the system immediately switches to Fast Mode. In Fast Mode, the data collection frequency is doubled, primarily to more accurately capture the rapidly changing dynamics of the cure process and provide users with high-resolution monitoring data. If the absolute difference between the previous and next cure values ​​remains greater than 1% after doubling the data collection frequency, the collection frequency is doubled again. If the absolute value of the difference is between 0.1% and 1%, the cure process is relatively stable, and the system remains in Normal Mode. This mode maintains a moderate monitoring frequency, ensuring adequate monitoring accuracy while minimizing energy consumption. If the absolute value of the difference is less than 0.1%, the cure process is nearing completion, with changes occurring very slowly. The system switches to Sleep Mode to reduce unnecessary energy consumption.

[0146] Sampling Frequency Settings: In sleep mode, the system defaults to recording data every three minutes, adjusting the frequency up and down within a certain range as the curing process speeds up or down. This lower sampling frequency effectively reduces system energy consumption during slow curing stages. In normal mode, the system defaults to recording data every one minute, adjusting the frequency up and down within a certain range as the curing process speeds up or down. This frequency ensures data acquisition density during the general curing stage, meeting the monitoring needs of the curing process while avoiding excessive data acquisition. In fast mode, the system defaults to recording data every 15 seconds, still adjusting the frequency up and down within a certain range as the curing process speeds up or down. This high-frequency sampling frequency ensures that no critical information is missed during the fast curing stage. These sampling frequencies have been experimentally verified. By comprehensively considering the curing characteristics of different stages, they can effectively balance the system's energy consumption and monitoring accuracy while meeting the data acquisition frequency requirements of different stages, providing an optimal monitoring solution for composite material curing.

[0147] Glass transition temperature calculation: After switching to real-time mode, the glass transition temperature is calculated in depth. The recorded conductivity and cure values ​​are substituted into the glass transition temperature formula. This process utilizes the chip's powerful complex mathematical unit to perform the calculation. To improve efficiency, optimized algorithms and parallel computing techniques are employed to quickly determine the glass transition temperature of the composite material at that moment. The results are also stored in the chip's internal cache for subsequent transmission and analysis.

[0148] Data Transmission and Display: The communication module is activated, using Bluetooth low energy technology to wirelessly transmit the recorded values ​​to the PC. A dedicated data analysis and display system is designed on the PC to receive and analyze the transmitted data in real time, presenting intuitive charts showing the composite material's degree of cure and glass transition temperature over time. The software interface allows the operator to clearly observe the progress of the curing process.

[0149] Monitoring end judgment: The system will repeat the above steps in sequence and continue monitoring and calculation. When the recorded curing degree value is basically stable, it indicates that the curing process of the composite material has been basically completed. When judging whether the curing degree value is stable, the standard deviation method in statistics is used. The standard deviation of the curing degree value over a period of time is calculated and compared with the set threshold (0.01%). If the standard deviation is less than the set threshold, the system considers that the curing degree value is basically stable. The final stable curing value is compared with 1. If the curing value is close to 1, it means that the curing is complete. At this time, the system will automatically remove the excitation signal and complete the entire curing monitoring process; if the final stable curing value is far less than 1, it means that the curing is not complete, which may be due to unreasonable curing conditions. At this time, a signal will be issued to inform the operator to adjust the curing conditions. At the same time, monitoring will continue until the curing process is completely completed.

[0150] Through the careful optimization of the program and experimental details mentioned above, the above system can work more efficiently and accurately, providing more reliable data support for the research on the curing process of composite materials.

[0151] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A flexible conductivity monitoring system for composite material curing performance, characterized in that: It includes a DSC measuring device, a flexible sensor, a flexible data processor, a data transmission device and a display device which are electrically connected in sequence; The DSC measuring device is used to obtain the corresponding relationship between the degree of cure and the glass transition temperature of the monitored object; The flexible sensor includes a flexible substrate and flexible sensing electrodes wrapped on five sides of the flexible substrate. The flexible sensing electrodes can deform along with the flexible substrate so that the exposed side thereof is completely adhered to the surface of the monitored object. The flexible sensing electrodes are used to obtain in real time the conductivity signal generated by the monitored object during the curing process. The flexible data processor is used to obtain a curing degree change curve of the monitored object according to the conductance signal, and obtain a glass transition temperature change curve of the monitored object according to the curing degree and the corresponding relationship; The data transmission device is used to transmit the curing degree change curve and the glass transition temperature change curve to the display device for display; It also includes a flexible circuit board for carrying the flexible data processor and the data transmission device, and the flexible circuit board and the flexible sensor are electrically connected together and packaged into a flexible whole; The flexible circuit board includes a polyimide substrate, a circuit pattern provided on the polyimide substrate, and electronic components electrically connected to and fixed on the polyimide substrate by the circuit pattern, wherein the electronic components and the circuit pattern constitute the flexible data processor and the data transmission device; The flexible circuit board and the flexible sensor are electrically connected by using silver nanowires; curing the flexible circuit board, the flexible sensor, and the silver nanowires using a polydimethylsiloxane solution to encapsulate them into a flexible whole, so that the exposed side of the flexible sensing electrode remains exposed to the outside; The flexible data processor is an MCU, and the MCU is connected to a temperature sensor; The steps for preparing the electrical connection between the flexible circuit board and the flexible sensor using silver nanowires are as follows: A uniform circular copper layer is deposited on the polyimide substrate of the flexible circuit board using magnetron sputtering technology to construct the lower electrode layer; preparing an intermediate electrode layer on the surface of the lower electrode layer by uniformly applying a silver nanowire dispersion onto the surface of the lower electrode using a drop coating method. By precisely controlling the drop coating time and solution concentration parameters, the silver nanowires are ensured to completely and uniformly cover the surface of the lower electrode, forming a continuous conductive network. After the silver nanowire solution is fully dried, the silver nanowire layer constitutes the intermediate electrode layer. An upper electrode layer is formed on the dried silver nanowire intermediate electrode layer, specifically by again using magnetron sputtering technology to deposit a uniform copper layer, completely encapsulating the intermediate electrode layer and the lower electrode layer to form a sandwich-like three-layer structure that can adapt to the bending and stretching of the flexible device. The copper in the upper electrode layer forms a strong metallurgical bond with the silver nanowires in the intermediate electrode layer and the copper in the lower electrode layer through atomic interactions; Using the formula , where G(T) represents the conductivity value at temperature T, G0 represents the initial conductivity value at T0, T0 represents the initial temperature, T represents the temperature at any time, and K is the compensation coefficient. Focus on the cured composite material, accurately measure the conductivity value of the cured composite material at temperature T0, and then measure the conductivity value of the cured composite material at temperature T. By comparing the conductivity data at different temperatures, we can preliminarily understand the trend of the influence of temperature on conductivity. Finally, substitute these different temperatures and their corresponding conductivity values ​​into the expression , after precise mathematical calculation, the compensation coefficient K is calculated; Using the formula Calculate the degree of cure, where is the logarithm of the conductivity value of the monitored object detected at the beginning of curing at temperature T0; It is the logarithm of the conductivity value of the sample that has been cured at temperature T0; It represents the logarithm of the conductivity value of the monitored object detected at the temperature T0 and the curing time t; The corresponding relationship between the degree of curing and the glass transition temperature is: ， The glass transition temperature is given by the following formula: ， T gu is the glass transition temperature of the monitored object in liquid state; T gcmax The maximum glass transition temperature of the monitored object when the degree of solidification finally stops changing; ΔC pu is the thermal capacity difference between the glassy state and the rubbery state of the monitored object in liquid state at the glass transition temperature; ΔC pc It is the thermal tolerance difference between the glassy state and the rubbery state of the monitored object at the glass transition temperature when the degree of cure finally stops changing.

2. The flexible conductivity monitoring system for composite material curing performance according to claim 1, characterized in that: The data transmission device is a Bluetooth transmission device, and the display device is a remote terminal display.

3. A flexible conductivity monitoring method for the curing performance of composite materials, characterized in that: Utilizing the system according to any one of claims 1 to 2, comprising: Taking out a portion of the sample of the monitored object and placing it in the DSC measuring device to obtain the corresponding relationship between the degree of curing and the glass transition temperature of the monitored object; Placing the flexible sensor on the surface of the monitored object so that the exposed side of the flexible sensing electrode is completely attached to the surface of the monitored object to obtain a conductivity signal in real time; During the curing process of the monitored object, a curing degree α of the monitored object at time t is obtained according to the conductivity signal, and a curing degree variation curve is obtained according to the corresponding relationship between α and t; According to the curing degree and the corresponding relationship, the glass transition temperature T of the monitored object at time t is obtained. g , and according to T g The corresponding relationship between t and t gives the glass transition temperature curve; transmitting the curing degree change curve and the glass transition temperature change curve to the display device in real time; The curing degree change curve and the glass transition temperature change curve are shown.

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