Test method and system based on carbon nanotube sensing fiber flow front

Abstract

The invention belongs to the technical field of composite material liquid forming, and particularly relates to a testing method and system based on a carbon nanotube sensing fiber flow front. According to the invention, the sensor grid is formed by adopting the carbon nanotube sensing fibers, the carbon nanotube sensing fibers expand after absorbing the resin, and the contact resistance between the tubes is obviously improved, so that the carbon nanotube sensing fibers have sensitive resistance response characteristics to resin infiltration. The carbon nano tube sensing fiber is used as a sensor to monitor the liquid flowing front in the composite material liquid forming process, the carbon nano tube sensing fiber is used as a reinforcing fiber of the composite material, adverse effects on the performance of the composite material are avoided, meanwhile, the monitoring sensitivity is high, and the monitoring precision is high. The flow front in the horizontal direction and the flow front in the thickness direction can be monitored in real time only by using the data of the resistance change rate of the carbon nanotube sensing fiber, and meanwhile, the accuracy of calculating the liquid filling area at a certain time is also improved.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material liquid molding, and in particular relates to a testing method and system based on a carbon nanotube sensing fiber flow front. Background Art

[0002] Carbon nanotube materials have excellent mechanical properties, electrical properties and other functional properties. Using different methods to apply them to traditional fiber-reinforced composites plays an important role in improving the mechanical properties and functional properties of composite materials. Adding carbon nanotubes to the resin matrix can significantly improve the modulus and other mechanical properties of the resin matrix. The membrane material prepared by carbon nanotubes can show excellent mechanical properties and electromagnetic shielding properties after being impregnated with resin. In the application process of carbon nanotube materials, it was found that due to its own piezoresistance characteristics and the evolution of different types of carbon nanotube network structures, carbon nanotube materials show good monitoring application potential. Under tensile, compressive, bending loads and even failure damage, carbon nanotube materials show obvious resistance change characteristics. On the one hand, it is because carbon nanotubes themselves have high piezoresistance factors. On the other hand, the contact resistance and tunneling resistance between carbon nanotubes change under the action of external fields. Therefore, it has attracted attention in structural health monitoring and process monitoring. Liquid molding process is a typical low-cost molding process method for composite materials. It prepares composite products by injecting low-viscosity resin into dry fiber preforms and curing them.

[0003] There are many liquid molding process methods, including resin transfer molding, resin film infiltration, vacuum assisted resin infusion, etc., which are widely used in aerospace, energy, shipbuilding and other fields. In the liquid molding process, the fiber composite material products obtained after curing often have local defects, which will lead to the overall performance of the parts and leave safety hazards. The formation of defects is caused by the high permeability diversion medium layer used in the process. Its permeability is usually two orders of magnitude greater than that of the fiber preform. Therefore, during the liquid molding process, the resin solution close to the diversion medium in the thickness direction of the preform will flow faster, and the resin solution away from the diversion medium in the thickness direction of the preform will flow slower, resulting in the formation of a three-dimensional wedge-shaped flow front in the thickness direction of the preform. This phenomenon is called the lead-lag effect.

[0004] In the later stage of resin filling, the existence of the lead-lag effect will make the resin flow front in the flow medium reach the vacuum port first. At this time, the resin liquid will be quickly sucked away by the vacuum port through the flow medium, resulting in the fiber preform within a certain range not being saturated. When the permeability of the preform is affected, it will cause defects in the fiber fabric such as pores and dry spots, which directly threaten the structural health of the part. Therefore, the real-time monitoring technology of the composite material liquid molding resin impregnation process came into being. By monitoring the resin flow behavior at the bottom of the preform, the opening and closing timing of the injection port and the vacuum port can be controlled to optimize the resin injection strategy, reduce the probability of fiber composite material defects, and thus improve the quality of fiber composite products.

[0005] At present, the liquid flow front monitoring technology in the composite material liquid molding process includes optical fiber sensor monitoring technology, CCD camera monitoring technology, thermocouple monitoring technology, pressure sensor monitoring technology and ultrasonic sensor monitoring technology, etc. However, all of the above monitoring technologies require the implantation of foreign substances into the composite material, which has an adverse effect on the performance of the composite material. Summary of the invention

[0006] The purpose of the present invention is to provide a testing method and system for the flow front based on carbon nanotube sensor fibers. The present invention adopts carbon nanotube sensor fibers as sensors to monitor the liquid flow front of the liquid molding process of composite materials. The carbon nanotube sensor fibers, as reinforcing fibers of composite materials, will not have an adverse effect on the performance of the composite materials. At the same time, the monitoring sensitivity is high. Only the data of the resistance change rate of the carbon nanotube sensor fibers can be used to monitor the flow front in the horizontal and thickness directions in real time, and the accuracy of calculating the liquid filling area at a certain time is also improved.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The invention provides an application of a carbon nanotube sensing fiber in monitoring the liquid flow front in a composite material liquid molding process. The carbon nanotube sensing fiber comprises an organic fiber and carbon nanotubes coated on the surface of the organic fiber.

[0009] Preferably, the organic fiber includes one or more of aramid fiber, polyimide fiber and polybenzoxazole fiber;

[0010] In the application, the carbon nanotube sensing fiber is used in the form of a carbon nanotube sensing fiber bundle, and a plurality of carbon nanotube sensing fiber bundles are regularly arranged to form a sensor grid, and the sensor grid includes a plurality of closed micro units, and the plurality of carbon nanotube sensing fiber bundles are insulated from each other.

[0011] The present invention provides a testing system based on the flow front of carbon nanotube sensing fibers, comprising a sensor grid, a connection module, a data collection module and a data processing module;

[0012] The sensor grid is formed by regularly arranging a plurality of carbon nanotube sensing fiber bundles, the sensor grid includes a plurality of closed micro units, the plurality of carbon nanotube sensing fiber bundles are insulated from each other, the carbon nanotube sensing fiber bundles are formed by carbon nanotube sensing fibers, and the carbon nanotube sensing fibers include organic fibers and carbon nanotubes coated on the surface of the organic fibers;

[0013] The connection module is used to connect the sensor grid with the data collection module;

[0014] The data collection module is used to collect resistance data of the carbon nanotube sensing fiber bundle in the sensor grid;

[0015] The data processing module is used to process the resistance data and obtain the test result of the flow front according to the processing result of the resistance data.

[0016] Preferably, the arrangement of the carbon nanotube sensing fiber bundles in the sensor grid includes an orthogonal arrangement or a diagonal mixed arrangement;

[0017] The orthogonal arrangement is: the carbon nanotube sensing fiber bundles are arranged equidistantly along the horizontal direction and the vertical direction respectively;

[0018] The diagonal mixed arrangement is: the carbon nanotube sensor fiber bundles are arranged equidistantly along the horizontal direction or the vertical direction; and at the same time, the carbon nanotube sensor fiber bundles arranged in the horizontal direction or the vertical direction are arranged along the 45° direction starting from the end points of the carbon nanotube sensor fiber bundles arranged in the horizontal direction or the vertical direction.

[0019] Preferably, the connection module comprises conductive silver glue, metal foil and metal wire.

[0020] Preferably, the data collection module includes a resistance testing system;

[0021] The data processing module includes a curve drawing module and a filling area calculation module. The curve drawing module is used to draw a curve of the resistance change rate of the carbon nanotube sensor fiber bundle over time, and the filling area calculation module is used to calculate the filling area of ​​the resin flow.

[0022] The present invention provides a method for testing the flow front of a carbon nanotube sensing fiber, which is tested by using the testing system described in the above technical solution, and includes the following steps:

[0023] Laying fiber fabrics in layers in a forming mold to obtain a fiber preform;

[0024] Providing a sensor grid on the upper surface and / or the lower surface of the fiber preform, and forming the preform in a forming mold;

[0025] The molding mold is sealed to obtain a sealed molding mold, the sealed molding mold is evacuated, and then resin is injected into the sealed molding mold while maintaining the vacuum environment; the initial resistance of each carbon nanotube sensor fiber bundle before the resin is injected is recorded, the moment of resin injection is defined as the injection time zero point, and during the resin injection process, the resistance data of each carbon nanotube sensor fiber bundle that changes with the injection time is continuously collected through a data collection module;

[0026] The resistance data is input into a data processing module, data processing is performed on the resistance data collected by the data collection module, and a test result of the flow front is obtained according to the processing result of the resistance data.

[0027] Preferably, the test result of the flow front includes the arrival position of the resin flow front;

[0028] The test result of the flow front is when the resin flow front reaches the position, and the data processing includes the following steps:

[0029] A curve of the resistance change rate of the carbon nanotube sensor fiber bundle versus the resin injection time is plotted, wherein the resistance change rate is the ratio of the resistance of the carbon nanotube sensor fiber bundle at any resin injection moment to the initial resistance, and a resistance change rate-time curve of the carbon nanotube sensor fiber bundle is obtained; and the arrival position of the resin flow front is obtained according to the mutation point of the resistance change rate on the resistance change rate-time curve of the carbon nanotube sensor fiber bundle.

[0030] Preferably, the test result of the flow front also includes the filling area of ​​the resin flow; the filling area of ​​the resin flow is the total area of ​​a number of closed micro-units filled with resin in the sensor grid, and any one closed micro-unit is filled with resin so that the resistance change rate on the resistance change rate-time curve of all carbon nanotube sensing fiber bundles forming the closed micro-unit has a mutation point;

[0031] When the test result of the flow front also includes the filling area of ​​the resin flow, the data processing further includes the following steps:

[0032] The total area of ​​several closed micro-units filled with resin in the sensor grid is calculated to obtain the filling area of ​​the resin flow.

[0033] Preferably, the fiber fabric comprises glass fiber fabric or carbon fiber fabric;

[0034] The types of the fiber fabric include unidirectional fabric, twill fabric or plain fabric;

[0035] The resin is injected through a glue injection port, and the glue injection port is located at a central position or an eccentric position of the preform.

[0036] The present invention provides a testing system based on the flow front of carbon nanotube sensor fibers, comprising a sensor grid, a connection module, a data collection module and a data processing module; the sensor grid is formed by regularly arranging a plurality of carbon nanotube sensor fiber bundles, the sensor grid comprises a plurality of closed micro-units, the plurality of carbon nanotube sensor fiber bundles are insulated from each other, the carbon nanotube sensor fiber bundles are formed by carbon nanotube sensor fibers, the carbon nanotube sensor fibers comprise organic fibers and carbon nanotubes coated on the surface of the organic fibers; the connection module is used to connect the sensor grid with the data collection module; the data collection module is used to collect resistance data of the carbon nanotube sensor fibers in the sensor grid; the data processing module is used to process the resistance data, and obtain the test result of the flow front according to the processing result of the resistance data. The present invention adopts carbon nanotube sensor fibers to form the sensor grid, the carbon nanotube sensor fibers expand after absorbing resin, and the contact resistance between the tubes is significantly improved, so that the carbon nanotube sensor fibers have sensitive resistance response characteristics to resin infiltration. The present invention arranges the carbon nanotube sensor fiber bundle regularly on the upper surface and / or lower surface of the fiber preform to form a grid structure, which can obtain a sensor grid with high sensitivity in a simple and highly applicable manner, so that a small number of sensors are used to monitor the flow front in the horizontal direction and the thickness direction in real time, and the accuracy of calculating the liquid filling area at a certain time is improved. In summary, the present invention uses carbon nanotube sensor fibers as sensors to monitor the liquid flow front in the composite material liquid molding process. The carbon nanotube sensor fibers, as reinforcing fibers of the composite material, will not have an adverse effect on the performance of the composite material. At the same time, the monitoring sensitivity is high. Only the data of the resistance change rate of the carbon nanotube sensor fiber bundle can monitor the flow front in the horizontal direction and the thickness direction in real time, and the accuracy of calculating the liquid filling area at a certain time is also improved.

[0037] In the present invention, the organic fiber includes one or more of aramid fiber, polyimide fiber and polybenzoxazole fiber. The present invention uses the organic fiber to make carbon nanotube sensing fiber, and then when the sensor grid formed by the carbon nanotube sensing fiber detects the resin flow front, the formed sensor grid has good flexibility, is easy to operate during the laying process, etc., does not affect the sensing effect, and the detection result is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 Aramid fiber tow before and after needle tube drop coating in the preparation process of the carbon nanotube-coated aramid fiber sensor provided in an embodiment of the present invention;

[0040] Figure 2 The glue injection port provided in Example 1 of the present invention monitors the material placement process of the flow front on the upper surface of the glass fiber at the central position;

[0041] Figure 3 The change law of the resistance of the carbon nanotube sensing fiber bundle during the process of monitoring the flow front on the upper surface of the glass fiber at the center position of the glue injection port provided in Example 1 of the present invention;

[0042] Figure 4 A schematic diagram of injection area calculation in the process of monitoring the flow front on the upper surface of the glass fiber at the center position of the injection port provided in Example 1 of the present invention;

[0043] Figure 5 The diagonal mixed arrangement of the sensing fibers provided in Example 2 of the present invention monitors the material placement process of the flow front on the upper surface of the glass fiber;

[0044] Figure 6 The diagonal mixed arrangement of the sensing fibers provided in Example 2 of the present invention monitors the resistance variation of the carbon nanotube sensing fiber bundle during the flow front on the upper surface of the glass fiber;

[0045] Figure 7 A schematic diagram of injection area calculation in the process of monitoring the flow front on the upper surface of glass fiber by the diagonal mixed arrangement of sensing fibers provided in Example 2 of the present invention;

[0046] Figure 8 The material placement process in which the glue injection port provided in Example 3 of the present invention monitors the flow front of the upper and lower surfaces of the glass fiber at an eccentric position;

[0047] Fig. 9 The resistance variation law of the carbon nanotube sensing fiber bundle in the process of monitoring the flow front on the upper surface of the glass fiber at the eccentric position of the injection port provided in Example 3 of the present invention;

[0048] Fig.10 The resistance variation law of the carbon nanotube sensing fiber bundle during the process of monitoring the flow front of the lower surface of the glass fiber at the eccentric position of the injection port provided in Example 3 of the present invention;

[0049] Fig.11 The material placement process in which the glue injection port provided in Example 4 of the present invention monitors the flow front on the upper surface of the carbon fiber at an eccentric position;

[0050] Fig.12 The resistance variation law of the carbon nanotube sensing fiber bundle in the process of monitoring the flow front on the upper surface of the carbon fiber at the eccentric position of the injection port provided in Example 4 of the present invention;

[0051] Fig.13 A schematic diagram of injection area calculation in the process of monitoring the flow front on the upper surface of glass fiber at an eccentric position of the injection port provided in Example 4 of the present invention. DETAILED DESCRIPTION

[0052] The invention provides an application of a carbon nanotube sensing fiber in monitoring the liquid flow front in a composite material liquid molding process. The carbon nanotube sensing fiber comprises an organic fiber and carbon nanotubes coated on the surface of the organic fiber.

[0053] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0054] In the present invention, the method for preparing the carbon nanotube sensor fiber preferably comprises the following steps:

[0055] The carbon nanotube dispersion is drop-coated onto the surface of the organic fiber, and the surface of the organic fiber is coated under capillary action to obtain the carbon nanotube sensing fiber; the organic fiber is suspended horizontally, and the drop-coating is performed at equal intervals.

[0056] In the present invention, the organic fiber preferably includes one or more of aramid fiber, polyimide fiber and polybenzoxazole fiber. The carbon nanotube preferably has a diameter of 20 to 35 nm and a length of less than 10 μm.

[0057] In a specific embodiment of the present invention, the specific preparation method of the carbon nanotube sensor fiber preferably includes the following steps:

[0058] The carbon nanotube coated fiber sensor fiber is prepared by the syringe dropping method. The mass of the carbon nanotube dispersion required to be applied is calculated according to the target coating amount and the mass fraction of the carbon nanotube dispersion. The carbon nanotube dispersion is sucked by a syringe and dripped onto the horizontally suspended organic fiber at equal intervals. The dripping amount at each position is controlled by the syringe. Due to the capillary action of the organic fiber, the liquid will automatically infiltrate both sides of the organic fiber, and the dripping positions of multiple carbon nanotube dispersions should ensure the uniform coating of the carbon nanotubes on the organic fiber as much as possible.

[0059] In the present invention, in the carbon nanotube sensor fiber, the mass of the carbon nanotubes accounts for 5-10% of the mass of the organic fiber, preferably 8-10%.

[0060] In the present invention, during the application, the carbon nanotube sensing fiber is used in the form of a carbon nanotube sensing fiber bundle, and a plurality of the carbon nanotube sensing fiber bundles are regularly arranged to form a sensor grid, and the sensor grid includes a plurality of closed micro units, and the plurality of carbon nanotube sensing fiber bundles are insulated from each other.

[0061] In the present invention, when used, the carbon nanotube sensor fiber is used in the form of a carbon nanotube sensor fiber bundle, and the carbon nanotube sensor fiber bundle is a bundle formed by multiple carbon nanotube sensor fibers. The present invention has no special requirements on the number of carbon nanotube sensor fibers in the carbon nanotube sensor fiber bundle. That is, the sensor grid is formed by regularly arranging multiple carbon nanotube sensor fiber bundles.

[0062] The present invention provides a testing system based on the flow front of carbon nanotube sensing fibers, comprising a sensor grid, a connection module, a data collection module and a data processing module;

[0063] The sensor grid is formed by regularly arranging a plurality of carbon nanotube sensing fiber bundles, the sensor grid includes a plurality of closed micro units, the plurality of carbon nanotube sensing fiber bundles are insulated from each other, the carbon nanotube sensing fiber bundles are formed by carbon nanotube sensing fibers, and the carbon nanotube sensing fibers include organic fibers and carbon nanotubes coated on the surface of the organic fibers;

[0064] The connection module is used to connect the sensor grid with the data collection module;

[0065] The data collection module is used to collect resistance data of the carbon nanotube sensing fibers in the sensor grid;

[0066] The data processing module is used to process the resistance data and obtain the test result of the flow front according to the processing result of the resistance data.

[0067] The testing system based on the flow front of carbon nanotube sensor fibers provided by the present invention includes a sensor grid. In the present invention, the sensor grid is formed by regularly arranging a plurality of carbon nanotube sensor fiber bundles, the sensor grid includes a plurality of closed micro-units, the plurality of carbon nanotube sensor fiber bundles are insulated from each other, the carbon nanotube sensor fiber bundles are formed by carbon nanotube sensor fibers, and the carbon nanotube sensor fibers include organic fibers and carbon nanotubes coated on the surface of the organic fibers. In the present invention, the carbon nanotube sensor fibers in the sensor grid are used in the form of carbon nanotube sensor fiber bundles, the carbon nanotube sensor fiber bundles are bundles formed by a plurality of carbon nanotube sensor fibers, and the present invention has no special requirements on the number of carbon nanotube sensor fibers in the carbon nanotube sensor fiber bundles.

[0068] In the present invention, the sensor grid includes a plurality of closed micro-units, a plurality of carbon nanotube sensing fiber bundles are insulated from each other, the carbon nanotube sensing fiber bundles are formed by carbon nanotube sensing fibers, and the carbon nanotube sensing fibers include organic fibers and carbon nanotubes coated on the surface of the organic fibers. The arrangement of the carbon nanotube sensing fiber bundles in the sensor grid preferably includes an orthogonal arrangement or a diagonal mixed arrangement. In the present invention, the orthogonal arrangement is preferably: the carbon nanotube sensing fiber bundles are equidistantly arranged along the horizontal direction and the vertical direction respectively (that is, the carbon nanotube sensing fiber bundles are equidistantly arranged along the radial direction and the weft direction of the fiber preform respectively). In a specific embodiment of the present invention, the specific method of the orthogonal arrangement is preferably: the carbon nanotube sensing fiber bundles are equidistantly arranged along the radial direction (or weft direction) of the fiber preform to form a first sensing layer; then on the first sensing layer, the carbon nanotube sensing fiber bundles are equidistantly arranged along the weft direction (or radial direction) of the fiber preform to form a second sensing layer; the first sensing layer and the second sensing layer form the sensor grid. An insulating isolation layer is preferably provided between the first sensing layer and the second sensing layer, and the insulating isolation layer is specifically a glass fiber plain weave fabric. The insulating isolation layer achieves insulation between the carbon nanotube sensing fiber bundle in the first sensing layer and the carbon nanotube sensing fiber bundle in the second sensing layer at the overlapped position.

[0069] In the present invention, the diagonal mixed arrangement is preferably: the carbon nanotube sensing fiber bundles are arranged equidistantly along the horizontal direction or the vertical direction; and at the same time, the carbon nanotube sensing fiber bundles arranged in the horizontal direction or the vertical direction are arranged in a 45° direction with the endpoints of the carbon nanotube sensing fiber bundles arranged in the horizontal direction or the vertical direction as the starting point (that is, the carbon nanotube sensing fiber bundles are arranged equidistantly along the radial direction or the weft direction of the fiber preform; and at the same time, the carbon nanotube sensing fiber bundles arranged in the radial direction or the weft direction are arranged in a 45° direction with the endpoints of the carbon nanotube sensing fiber bundles arranged in the radial direction or the weft direction as the starting point). In a specific embodiment of the present invention, the diagonal mixed arrangement is preferably: the carbon nanotube sensing fiber bundles are arranged equidistantly along the radial direction or the weft direction of the fiber preform to form a first sensing layer; and then on the first sensing layer, the carbon nanotube sensing fiber bundles are arranged in a 45° direction with the endpoints of the carbon nanotube sensing fiber bundles arranged in the radial direction or the weft direction in the first sensing layer as the starting point to form a second sensing layer; the first sensing layer and the second sensing layer form the sensor grid. An insulating isolation layer is preferably provided between the first sensing layer and the second sensing layer, and the insulating isolation layer is specifically a glass fiber plain weave fabric. The insulating isolation layer achieves insulation between the carbon nanotube sensing fiber bundle in the first sensing layer and the carbon nanotube sensing fiber bundle in the second sensing layer at the overlapped position.

[0070] The testing system based on the flow front of carbon nanotube sensor fibers provided by the present invention includes a connection module. In the present invention, the data collection module is used to collect the resistance data of the carbon nanotube sensor fiber bundle in the sensor grid. The connection module preferably includes conductive silver glue, metal foil and metal wire. The conductive silver angle is used to fixedly connect the carbon nanotube sensor fiber bundle and the metal foil. The metal foil is specifically copper foil. The metal wire is specifically copper conductive. The present invention preferably fixes the metal foil to the carbon nanotube sensor fiber bundle in the sensor grid respectively, and the fixed connection is preferably fixedly connected using conductive silver glue. The metal foil is welded to the metal wire.

[0071] The carbon nanotube sensing fiber flow front test system provided by the present invention includes a data collection module. In the present invention, the data collection module includes a resistance test system. The resistance test system is specifically a digital multimeter.

[0072] In the present invention, when monitoring the flow front of the liquid molding process, the edge of the carbon nanotube sensing fiber bundle is preferably connected to the copper foil by curing with conductive silver glue, and the other end of the copper foil is preferably connected to the copper wire conductor using solder, and the other end of the copper wire conductor is preferably connected to a digital multimeter.

[0073] The testing system based on the flow front of the carbon nanotube sensing fiber provided by the present invention includes a data processing module. In the present invention, the data processing module includes a curve drawing module and a filling area calculation module, the curve drawing module is used to draw the curve of the resistance change rate of the carbon nanotube sensing fiber bundle over time, and the filling area calculation module is used to calculate the filling area of ​​the resin flow. The filling area calculation module is used to obtain the resin arrival position according to the mutation point appearing on the resistance-time curve of the sensing fiber, and draw and calculate the resin filling area.

[0074] The present invention provides a method for testing the flow front of a carbon nanotube sensing fiber, which is tested by using the testing system described in the above technical solution, and includes the following steps:

[0075] Laying fiber fabrics in layers in a forming mold to obtain a fiber preform;

[0076] Providing a sensor grid on the upper surface and / or the lower surface of the fiber preform, and forming the preform in a forming mold;

[0077] The molding mold is sealed to obtain a sealed molding mold, the sealed molding mold is evacuated, and then resin is injected into the sealed molding mold while maintaining the vacuum environment; the initial resistance of each carbon nanotube sensor fiber bundle before the resin is injected is recorded, the moment of resin injection is defined as the injection time zero point, and during the resin injection process, the resistance data of each carbon nanotube sensor fiber bundle that changes with the injection time is continuously collected through a data collection module;

[0078] The resistance data is input into a data processing module, data processing is performed on the resistance data collected by the data collection module, and a test result of the flow front is obtained according to the processing result of the resistance data.

[0079] The present invention stacks and lays fiber fabrics in a forming mold to obtain a fiber preform. In the present invention, the fiber fabric preferably includes glass fiber fabric or carbon fiber fabric. The type of the fiber fabric preferably includes unidirectional fabric, twill fabric or plain fabric.

[0080] In a specific embodiment of the present invention, the method for preparing the fiber preform preferably comprises: laying the cut fiber fabric layer by layer on the bottom plate of the forming mold.

[0081] After obtaining the fiber preform, the present invention arranges a sensor grid on the upper surface and / or the lower surface of the fiber preform, and forms the preform in a molding die.

[0082] In the present invention, when testing carbon fiber fabric, since the diameter of the carbon fiber forming the carbon fiber fabric is small, the carbon fiber fabric structure is dense, and the permeability is low, the present invention preferably adds a high permeability medium layer on the upper surface of the carbon fiber preform to assist the resin penetration. The high permeability medium layer is preferably a glass fiber fabric with a large permeability and a thickness of less than 0.05 mm. The present invention preferably cuts the high permeability medium material into a size that can cover the carbon fiber preform, obtains a high permeability medium layer and covers the upper surface of the carbon fiber preform, and then sets the sensor grid.

[0083] The present invention cross-lays the carbon nanotube sensing material on the upper surface and / or the lower surface of the fiber preform in a preset order and along a preset direction.

[0084] In a specific embodiment of the present invention, the laying method of the carbon nanotube sensor fiber bundle in the sensor network preferably includes: orthogonal laying or diagonal mixed laying. In the orthogonal laying, the carbon nanotube sensor fiber bundle is laid in the warp and weft directions at equal intervals. In the diagonal mixed laying, the carbon nanotube sensor fiber bundle is first laid at equal intervals in the warp or weft directions, and then laid in parallel along the 45° direction with the two end points in the warp and weft directions as starting points.

[0085] The present invention cross-lays a plurality of carbon nanotube sensing fiber bundles on the surface of a fiber preform, monitors the liquid flow front in real time through the resistivity change thereof, and obtains the resin filling area at different times.

[0086] In the present invention, in order to prevent the carbon nanotube sensor fiber bundles arranged in different directions from overlapping and causing the resistance signal to be difficult to decompose, a layer of glass fiber plain weave fabric is preferably used to insulate and isolate the carbon nanotube sensor fiber bundles arranged in different directions.

[0087] In the present invention, when testing carbon fiber fabrics, a high permeability dielectric layer is preferably added to the upper surface of the carbon fiber preform to assist resin penetration. At this time, the high permeability dielectric layer also serves as insulation between the carbon fiber preform and the sensor grid.

[0088] In the present invention, when testing carbon fiber fabric, when the sensor grid is arranged on the lower surface of the carbon fiber preform, preferably a layer of glass fiber plain fabric is arranged between the lower surface of the carbon fiber preform and the sensor grid for insulation isolation.

[0089] The sensor grid of the present invention is connected to the data collection module through a connection module. In a specific embodiment of the present invention, the two ends of the carbon nanotube sensor fiber bundle of the sensor grid are connected to copper foil by curing with conductive silver glue, and the other end of the copper foil is connected to a copper wire conductor by soldering, and an external digital multimeter is connected; the digital multimeter is connected to a computer.

[0090] After forming a preform in a molding die, the present invention seals the molding die to obtain a sealed molding die, evacuates the sealed molding die, and then injects resin into the sealed molding die while maintaining a vacuum environment; records the initial resistance of each carbon nanotube sensor fiber bundle before resin injection, defines the moment of resin injection as injection time zero, and continuously collects resistance data of each carbon nanotube sensor fiber bundle as injection time changes during the resin injection process through a data collection module. The present invention preferably uses a vacuum bag to seal the preform in the molding die as a whole, and the infusion process mainly relies on vacuum pressure to drive the resin to penetrate along the fabric surface.

[0091] In the present invention, the sealing is preferably: using sealing tape to tightly surround the preform, and using double-layer sealing tape to bond the copper foil and the guide tube to the sealing tape at the joint to avoid leakage problems, using a vacuum bag to seal the molding mold and the preform as a whole, and connecting the guide tube at one end to a liquid collection bottle, and connecting to a vacuum pump through an air pipe.

[0092] In the present invention, before the resin is injected, the present invention first uses vacuum to make the fabric dense, observes the resistance of each conductive path, and after there is no short circuit or other problems, maintains this state for about 5 minutes and the resistance is stable without obvious changes, and then prepares for resin injection.

[0093] In the present invention, the resin is preferably injected through a glue injection port, and the glue injection port is located at a central position or an eccentric position of the preform.

[0094] The present invention preferably compacts the fabric of the fiber preform in the vacuum preform. During the vacuuming, observe the resistance of the conductive path formed by the carbon nanotube sensor fiber bundles, the connection module and the data collection module in each sensor grid (i.e., characterize the resistance of the carbon nanotube sensor fiber bundles). After there is no problem such as short circuit, maintain the vacuum state for about 5 minutes and the resistance is stable and has no obvious change, and then start to prepare for resin injection; after opening the injection port, the resin is injected into the preform under the action of vacuum negative pressure, and flows from the injection port to the surroundings. In this process, the resistance change of the carbon nanotube sensor fiber bundle is collected in real time, and the resistance change rate-time curve is drawn according to the collected data. The mutation point where the resistance responds is taken as the arrival time of the front, and the preform is divided into a number of square micro-areas according to the sensor fibers, and the arrival of the resin at the four sensor fiber bundles surrounding the micro-area is used as the criterion for the resin filling the micro-area. The resin filling area can be obtained by calculating the area of ​​the micro-area.

[0095] The present invention preferably turns on the data collection module to record the resistance change of the carbon nanotube sensor fiber, opens the injection port, and injects the resin into the glass fiber preform under the action of vacuum negative pressure, and flows from the injection port to the surroundings. During the liquid injection process, the liquid injection start time is recorded, and the resistance information is continuously collected to collect a complete resistance change curve. When liquid drips in the liquid collection bottle, the vacuum pump is turned off.

[0096] After the resistance data of the carbon nanotube sensor fiber bundle is obtained, the resistance data is input into the data processing module, the resistance data collected by the data collection module is processed, and the test result of the flow front is obtained according to the processing result of the resistance data.

[0097] In the present invention, the test result of the flow front includes the arrival position of the resin flow front; when the test result of the flow front is the arrival position of the resin flow front, the data processing includes the following steps:

[0098] A curve of the resistance change rate of the carbon nanotube sensor fiber bundle versus the resin injection time is plotted, wherein the resistance change rate is the ratio of the resistance of the carbon nanotube sensor fiber bundle at any resin injection moment to the initial resistance, and a resistance change rate-time curve of the carbon nanotube sensor fiber bundle is obtained; and the arrival position of the resin flow front is obtained according to the mutation point of the resistance change rate on the resistance change rate-time curve of the carbon nanotube sensor fiber bundle.

[0099] In a specific embodiment of the present invention, the method for obtaining the carbon nanotube sensing fiber bundle resistance change rate-time curve preferably includes:

[0100] The present invention first plots the data of the change of the resistance (R) of each carbon nanotube sensor fiber bundle with time t collected by the data collection module into a resistance-time point-line graph, namely, an Rt point-line graph.

[0101] According to the resistance-time point line graph, the resistance change rate-time curve, i.e., the △R / R0-t curve graph, is drawn using Origin software, wherein R0 is the resistance of the carbon nanotube sensing fiber bundle at the initial moment when the test is started; △R=R-R0, which refers to the difference between the resistance at different moments and the initial resistance.

[0102] In a specific embodiment of the present invention, Figure 3 Schematic diagram of the resistance relative change rate-time curve provided in Example 1 of the present invention, see Figure 3 The characteristics of the △R / R0-t curve include a stable baseline and a resistance increase stage. The mutation point where the resistance changes from a stable baseline to a resistance increase stage is taken as the arrival time of the flow front of the permeating liquid. The mutation point is defined as the first time that the resistance change rate is greater than or equal to 1.5%.

[0103] After drawing the △R / R0-t curve, the response time of the test fluid reaching each carbon nanotube sensor fiber bundle is determined according to the resistance change rate mutation point of the △R / R0-t curve, which is s1, s2, s3...s n The mutation point is defined as the first time that the resistance change rate is greater than or equal to 1.5%.

[0104] In the present invention, the test results of the flow front also include the filling area of ​​the resin flow; the filling area of ​​the resin flow is the total area of ​​a number of closed micro-units filled with resin in the sensor grid, and any one closed micro-unit is filled with resin so that a mutation point appears in the resistance change rate-time curve of all carbon nanotube sensing fiber bundles forming the closed micro-unit.

[0105] When the test result of the flow front also includes the filling area of ​​the resin flow, the data processing further includes the following steps:

[0106] The total area of ​​several closed micro-units filled with resin in the sensor grid is calculated to obtain the filling area of ​​the resin flow.

[0107] In a specific embodiment of the present invention, the method for obtaining the filling area of ​​the resin flow comprises the following steps:

[0108] The fiber preform is divided into a plurality of micro-regions according to the carbon nanotube sensing fiber bundles in the sensor grid; the resin reaching the four carbon nanotube sensing fiber bundles surrounding the micro-region is used as a criterion for filling the micro-region, and the resin filling area at the corresponding time is obtained by calculating the area of ​​the micro-region.

[0109] The present invention obtains the resin arrival position according to the mutation point of the sensor fiber resistance-time curve, and draws and calculates the resin filling area.

[0110] In a specific embodiment of the present invention, the method for obtaining the resin filling area specifically comprises the following steps:

[0111] The resin arrival position is obtained according to the mutation point of the sensor fiber resistance-time curve, and the resin filling area is calculated by drawing.

[0112] Taking the mutation point of the resistance response as the front arrival time, the preform is divided into several square micro-areas according to the sensing fiber bundle, such as Figure 4 As shown, the arrival of the resin at the four sensing fiber bundles that form a micro-region is used as a criterion for the resin filling the micro-region, and the resin filling area at the corresponding time can be obtained by calculating the area of ​​the micro-region.

[0113] In summary, the purpose of the present invention is to provide a testing method and system based on the flow front of carbon nanotube sensing fibers. The present invention constructs a sensor grid on the upper surface and / or lower surface of a fiber preform; connects the carbon nanotube sensing fiber bundle in the sensor grid to the data collection module; injects resin into the sealed molding mold through a glue injection port, and records the change of the resistance of the carbon nanotube sensing fiber bundle over time in real time through the data collection module; finds the mutation point of the resistance change rate based on the change of the resistance of the carbon nanotube sensing fiber bundle over time, obtains the liquid arrival position, draws a liquid filling diagram, and calculates the liquid filling area.

[0114] The present invention is based on the testing method of monitoring the flow front by carbon nanotube sensing fibers. The method is simple to operate, highly adaptable, can identify the arrival of the flow front, monitor the change in thickness direction, and obtain more accurate resin filling conditions in real time with fewer sensors. The method has broad application prospects.

[0115] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0116] The sensing fiber used in the following embodiments is prepared using TNWDMC-MC8 multi-walled carbon nanotube aqueous dispersion of Chengdu Zhongke Times Nano Energy Technology Co., Ltd. and aramid fiber (linear density 444 dtex) of China National Bluestar (Group) Co., Ltd., and the final sensor carbon nanotube mass ratio is 10%.

[0117] The epoxy resin used in the following examples was purchased from Dasen (Tianjin) Materials Technology Co., Ltd., product model HJ966.

[0118] In the following embodiments, the carbon nanotube sensing fibers used in the sensor grid are all carbon nanotube sensing fiber bundles.

[0119] Example 1

[0120] This embodiment uses glass fiber plain weave fabric EW100 as the test object, cuts the fabric into 300mm×300mm, and lays it on the mold surface in sequence, with a total of 6 layers of fabric laid. The carbon nanotube sensor fiber bundle is laid on the fabric surface along the warp and weft directions of the fabric, and 4 carbon nanotube sensor fiber bundles with a length of 300mm are laid in sequence in two directions, where the edgemost carbon nanotube sensor fiber bundle is 60mm away from the edge of the layer, and the interval between each carbon nanotube sensor fiber bundle is 60mm. In order to prevent the overlap of the carbon nanotube sensor fiber bundles arranged in the warp and weft directions from causing the resistance signal to be difficult to decipher, a layer of glass fiber plain weave fabric with a thickness of about 60μm is used between the carbon nanotube sensor fiber bundles arranged in the warp and weft directions for insulation isolation. A glue injection port is set in the middle position, which is sealed with a vacuum bag and connected to the equipment. Before the infusion experiment begins, vacuum is first drawn to make the fabric dense, and the resistance of the conductive path of each carbon nanotube sensor fiber is observed. After there is no problem of short circuit, the state is maintained for about 5 minutes and the resistance is stable and has no obvious change. Then the glue injection port is opened, and epoxy resin is used as the test liquid fluid. The resin is injected into the glass fiber preform under the action of vacuum negative pressure and flows from the middle injection port to the surroundings. The flow front is approximately circular. In this process, the resistance change of the carbon nanotube sensor fiber bundle is collected in real time. The resistance change law of the 8 carbon nanotube sensor fiber bundles is as follows Figure 3 As shown in the figure, the resin injection port is opened at about 233s after the resistance data collection starts, and the resin soaks the entire fabric surface for about 320s. The positions of the eight carbon nanotube sensing fibers, such as 1-X and 1-Y, are as follows: Figure 2 shown.

[0121] From the mutation point of the carbon nanotube sensor fiber bundle resistance response, it can be seen that the time for the front to reach 2-X and 3-X is 244s, while the time to reach 1-X and 4-X is 286s and 278s respectively. Correspondingly, in the vertical direction, the 2-Y and 3-Y carbon nanotube sensor fiber bundles respond first, and the corresponding start response times are 242s and 244s respectively. The 1-Y and 4-Y resistance mutation points are generated later, at 276s and 283s respectively. If the glass fiber fabric is divided into 25 60mm×60mm square micro-areas by using carbon nanotube sensor fiber bundles, and the arrival of the resin at the four carbon nanotube sensor fiber bundles that surround the micro-areas is used as the criterion for the resin filling the micro-areas, the injection area of ​​the resin can be monitored by the carbon nanotube sensor fiber bundles. At 244s and 286s after the start of resistance acquisition, the injection area obtained based on the carbon nanotube sensor fiber bundle analysis is 36cm 2 and 324cm 2 .

[0122] Example 2

[0123] Glass fiber plain weave fabric EW100 was used as the test object. The fabric was cut into 300mm×300mm and laid on the mold surface in sequence, with a total of 6 layers of fabric laid. On the fabric surface, the carbon nanotube sensor fiber bundles were first laid in the same direction at intervals of 60mm, and then 6 groups of carbon nanotube sensor fiber bundles were laid in parallel along a 45° direction with the end point of the carbon nanotube sensor fiber bundle as the starting point. The two layers of carbon nanotube sensor fiber bundles were separated by ultra-thin glass fiber fabric to prevent the nodes from contacting each other. Figure 5 As shown. The glue injection port is located at the center of the fabric.

[0124] The resin was injected at t = 96s, and the resistance change curves of each carbon nanotube sensor fiber bundle were obtained as shown in Figure 6 As shown. The arrival times of 2-X and 3-X resins are 107s and 105s, respectively, followed by 1-X and 2-X arrival times of 163s and 150s, respectively. In the 45° carbon nanotube sensing fiber bundle, the liquid front reaches the 4#, 3#, 5#, 2#, 6#, and 1# carbon nanotube sensing fiber bundles in turn, with arrival times of 110s, 116s, 135s, 156s, 204s, and 241s, respectively. Since the resin is point-injected, when the resin reaches the Y-direction or 45° carbon nanotube sensing fiber bundle, it is approximately considered that the semicircular area formed with the central injection point as the center and the carbon nanotube sensing fiber bundle as the tangent is filled with resin, as shown in Figure 7 As shown in the figure, based on this, the injection areas at 11s, 20s, 67s and 145s after the start of resin injection were 28.3cm 2 、56.5cm 2 、254.5cm 2 、508.9cm 2 .

[0125] Example 3

[0126] Glass fiber plain weave fabric EW100 was used as the test object. The fabric was cut into 300mm×300mm and laid on the mold surface in sequence, with a total of 6 layers of fabric laid. Five groups of carbon nanotube sensor fiber bundles were laid uniformly at intervals of 5cm along the X and Y directions above and below the preform, such as Figure 8 As shown, 20 carbon nanotube sensing fiber bundles are laid on the upper and lower surfaces, 10 each. At the same time, the injection method is selected at an eccentric position.

[0127] Fig. 9 is the resistance change result of each carbon nanotube sensor fiber bundle on the patch bag surface (upper surface), Fig. 9It can be seen that the resin preferentially reaches the 2-XT, 3-XT, 3-YT, and 4-YT carbon nanotube sensing fibers, and the arrival time is 336s after the resistance change is recorded. As the resin continues to be injected, the resistance of the 1-XT, 4-XT, 2-YT, 5-XT, 5-YT, and 1-YT carbon nanotube sensing fibers increases in turn, and the change times are 427s, 427s, 454s, 482s, 533s, and 761s, respectively.

[0128] Fig.10 The resistance change results of each carbon nanotube sensor fiber bundle on the mold surface (lower surface) are shown in Figure 2. The time when the resin reaches the 3-XB, 3-YB, 2-XB, and 4-YB carbon nanotube sensor fiber bundles is 340s, 340s, 347s, and 347s after the resistance change is recorded. As the resin continues to be injected, the resistance of the 1-XB, 4-XB, 2-YB, 5-YB, 5-XB, and 1-YB carbon nanotube sensor fiber bundles increases in turn, and the change time is 429s, 433s, 457s, 535s, 604s, and 803s, respectively. The order of the resin arrival time at each point in the film surface and the bag surface is consistent.

[0129] Example 4

[0130] The carbon fiber plain fabric SXTR30S-3K-P20g was used as the test object. The fabric was cut into 270mm×270mm and laid on the mold surface in sequence. A total of 6 layers of fabric were laid, and a high permeability medium layer was added on the upper surface to assist resin penetration.

[0131] Five groups of carbon nanotube sensor fiber bundles were laid on the preform at a uniform interval of 5 cm along the longitude and latitude directions, and the injection method was set to an eccentric position, such as Fig.11 shown. Fig.12 is the resistance change result of each carbon nanotube sensor fiber bundle, Fig.12 It can be seen that the resin first reaches the 2-XT, 3-XT and 3-YT, 4-YT carbon nanotube sensor fiber bundles, and the arrival time is 336s after the resistance change is recorded. As the resin continues to be injected, the resistance of the 1-XT, 4-XT, 2-YT, 5-XT, 5-YT, and 1-YT carbon nanotube sensor fiber bundles increases in turn, and the change time is 427s, 427s, 454s, 482s, 533s, and 761s respectively. Fig.13 As shown in the figure, at 18s, 30s, 43s, 49s, 87s and 99s after the injection was started, the injection areas calculated by analysis were 36cm 2 、108cm 2 、216cm 2 、288cm2 、432cm 2 、576cm 2 .

[0132] It can be seen from the above embodiments that the present invention provides a test method and system for real-time monitoring of the flow front based on carbon nanotube sensor fibers, which can obtain a more accurate resin filling area in a relatively simple manner. The present invention has the following advantages: The present invention uses a carbon nanotube sensor fiber bundle to form a sensor grid, the fiber specifications of the carbon nanotube sensor fiber bundle are adjustable, and the content of carbon nanotubes is controllable. The laying method of the carbon nanotube sensor fiber bundle of the present invention can achieve more accurate monitoring with fewer fiber sensors. The present invention can achieve simultaneous monitoring of the upper and lower surfaces of the fiber preform. The system or method provided by the present invention can identify the arrival of the flow front and determine the resin arrival area at the same time.

[0133] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0134] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. An application of a carbon nanotube sensing fiber in monitoring the liquid flow front in a composite material liquid molding process, wherein the carbon nanotube sensing fiber comprises an organic fiber and carbon nanotubes coated on the surface of the organic fiber.

2. The use according to claim 1, characterized in that: The organic fiber includes one or more of aramid fiber, polyimide fiber and polybenzoxazole fiber; In the application, the carbon nanotube sensing fiber is used in the form of a carbon nanotube sensing fiber bundle, and a plurality of carbon nanotube sensing fiber bundles are regularly arranged to form a sensor grid, and the sensor grid includes a plurality of closed micro units, and the plurality of carbon nanotube sensing fiber bundles are insulated from each other.

3. A testing system based on carbon nanotube sensing fiber flow front, characterized in that: It includes a sensor grid, a connection module, a data collection module and a data processing module; The sensor grid is formed by regularly arranging a plurality of carbon nanotube sensing fiber bundles, the sensor grid includes a plurality of closed micro units, the plurality of carbon nanotube sensing fiber bundles are insulated from each other, the carbon nanotube sensing fiber bundles are formed by carbon nanotube sensing fibers, and the carbon nanotube sensing fibers include organic fibers and carbon nanotubes coated on the surface of the organic fibers; The connection module is used to connect the sensor grid with the data collection module; The data collection module is used to collect resistance data of the carbon nanotube sensing fiber bundle in the sensor grid; The data processing module is used to process the resistance data and obtain the test result of the flow front according to the processing result of the resistance data.

4. The carbon nanotube sensing fiber flow front testing system according to claim 3, characterized in that: The arrangement of the carbon nanotube sensing fiber bundles in the sensor grid includes an orthogonal arrangement or a diagonal mixed arrangement; The orthogonal arrangement is: the carbon nanotube sensing fiber bundles are arranged equidistantly along the horizontal direction and the vertical direction respectively; The diagonal mixed arrangement is: the carbon nanotube sensor fiber bundles are arranged equidistantly along the horizontal direction or the vertical direction; and at the same time, the carbon nanotube sensor fiber bundles arranged in the horizontal direction or the vertical direction are arranged along the 45° direction starting from the end points of the carbon nanotube sensor fiber bundles arranged in the horizontal direction or the vertical direction.

5. The carbon nanotube sensing fiber flow front testing system according to claim 3, characterized in that: The connection module includes conductive silver glue, metal foil and metal wires.

6. The carbon nanotube sensor fiber flow front testing system according to claim 3 or 5, characterized in that: The data collection module includes a resistance testing system; The data processing module includes a curve drawing module and a filling area calculation module. The curve drawing module is used to draw a curve of the resistance change rate of the carbon nanotube sensor fiber bundle over time, and the filling area calculation module is used to calculate the filling area of ​​the resin flow.

7. A method for testing the flow front of carbon nanotube sensing fibers, characterized in that: The test system according to any one of claims 3 to 6 is used for testing, comprising the following steps: Laying fiber fabrics in layers in a forming mold to obtain a fiber preform; Providing a sensor grid on the upper surface and / or the lower surface of the fiber preform, and forming the preform in a forming mold; The molding mold is sealed to obtain a sealed molding mold, the sealed molding mold is evacuated, and then resin is injected into the sealed molding mold while maintaining the vacuum environment; the initial resistance of each carbon nanotube sensor fiber bundle before the resin is injected is recorded, the moment of resin injection is defined as the injection time zero point, and during the resin injection process, the resistance data of each carbon nanotube sensor fiber bundle that changes with the injection time is continuously collected through a data collection module; The resistance data is input into a data processing module, data processing is performed on the resistance data collected by the data collection module, and a test result of the flow front is obtained according to the processing result of the resistance data.

8. The method for testing the flow front based on carbon nanotube sensing fibers according to claim 7, characterized in that: The flow front test results include the resin flow front arrival position; The test result of the flow front is when the resin flow front reaches the position, and the data processing includes the following steps: A curve of the resistance change rate of the carbon nanotube sensor fiber bundle versus the resin injection time is plotted, wherein the resistance change rate is the ratio of the resistance of the carbon nanotube sensor fiber bundle at any resin injection moment to the initial resistance, and a resistance change rate-time curve of the carbon nanotube sensor fiber bundle is obtained; and the arrival position of the resin flow front is obtained according to the mutation point of the resistance change rate on the resistance change rate-time curve of the carbon nanotube sensor fiber bundle.

9. The method for testing the flow front based on carbon nanotube sensing fibers according to claim 8, characterized in that: The test result of the flow front also includes the filling area of ​​the resin flow; the filling area of ​​the resin flow is the total area of ​​a number of closed micro-units filled with resin in the sensor grid, and any one closed micro-unit is filled with resin so that the resistance change rate on the resistance change rate-time curve of all carbon nanotube sensor fiber bundles forming the closed micro-unit has a mutation point; When the test result of the flow front also includes the filling area of ​​the resin flow, the data processing further includes the following steps: The total area of ​​several closed micro-units filled with resin in the sensor grid is calculated to obtain the filling area of ​​the resin flow.

10. The method for testing the flow front based on carbon nanotube sensing fibers according to claim 7, characterized in that: The fiber fabric comprises glass fiber fabric or carbon fiber fabric; The types of the fiber fabric include unidirectional fabric, twill fabric or plain fabric; The resin is injected through a glue injection port, and the glue injection port is located at a central position or an eccentric position of the preform.

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