A test method and system based on carbon nanotube sensing fiber flow front

Abstract

The present application belongs to the technical field of liquid forming of composite materials, and particularly relates to a test method and system based on a carbon nanotube sensing fiber flow front. The present application forms a sensor grid by using carbon nanotube sensing fibers, and the carbon nanotube sensing fibers swell after absorbing resin, so that the contact resistance between the tubes is significantly improved, and thus the carbon nanotube sensing fibers have sensitive resistance response characteristics to resin infiltration. The present application uses carbon nanotube sensing fibers as sensors to monitor the liquid flow front in the liquid forming process of composite materials. The carbon nanotube sensing fibers serve as reinforcing fibers of the composite materials, and do not adversely affect the performance of the composite materials. Meanwhile, the monitoring sensitivity is high, and only the data of the resistance change rate of the carbon nanotube sensing fibers can be 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 also improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of liquid forming of composite materials, and particularly relates to a test method and system based on a flow front of a carbon nanotube sensing fiber. BACKGROUND

[0002] Carbon nanotube materials have excellent mechanical properties and electrical properties and other functional characteristics. The application of carbon nanotube materials in traditional fiber-reinforced composites by different methods plays an important role in improving the mechanical properties and functional characteristics of the composites. Adding carbon nanotubes to the resin matrix can significantly improve the mechanical properties such as modulus of the resin matrix. The film material prepared from carbon nanotubes can exhibit excellent mechanical properties and electromagnetic shielding properties after being impregnated with resin. During the application of carbon nanotube materials, it is found that due to the piezoresistive properties of carbon nanotubes and the evolution of different types of carbon nanotube network structures, carbon nanotube materials exhibit good monitoring application potential. Under the action of tensile, compressive, bending load and even failure and destruction, carbon nanotube materials exhibit obvious resistance change characteristics. On the one hand, carbon nanotubes themselves have a high piezoresistive factor, and on the other hand, the contact resistance and tunneling resistance between carbon nanotubes change under the action of external field. Therefore, carbon nanotube materials have attracted attention in structural health monitoring and process monitoring. Liquid forming process is a typical low-cost forming process for composite materials, which involves injecting low-viscosity resin into a dry fiber preform and curing to prepare a composite product.

[0003] There are many liquid forming processes, including resin transfer molding, resin film infusion, and vacuum-assisted resin infusion process, which are widely used in aerospace, energy, and shipbuilding fields. In the liquid forming process, the fiber composite product obtained after curing often has local defects, which will lead to a decrease in the overall performance of the product and pose a safety hazard. The formation of defects is caused by the use of a high-permeability flow guide medium layer in the process, which has a permeability two orders of magnitude greater than that of the fiber preform. Therefore, during the liquid forming process, the resin solution flow rate near the flow guide medium in the thickness direction of the preform is faster, while the resin solution flow rate away from the flow guide medium in the thickness direction of the preform is slower, resulting in the formation of a three-dimensional wedge-shaped flow front in the thickness direction of the preform, which is known as the advance-lag effect.

[0004] The existence of the leading-lagging effect can make the resin flow front of the flow guide medium reach the vacuum port first in the late resin filling stage, at this time, the resin liquid will be quickly sucked away by the vacuum port through the flow guide medium, resulting in that the fiber preform in a certain range is not saturated and impregnated, when the permeability of the preform is affected, defects such as pores and dry spots will be caused in the fiber fabric, which directly threatens the structural health of the product. Therefore, the real-time monitoring technology for the resin impregnation process of the liquid composite molding is developed, the opening and closing time of the glue injection port and the vacuum port is controlled by monitoring the resin flow behavior at the bottom of the preform, so as to optimize the resin injection strategy, reduce the probability of defects in the fiber composite material, and improve the quality of the fiber composite product.

[0005] At present, the liquid flow front monitoring technology of the liquid composite molding process includes optical fiber sensor monitoring technology, CCD camera monitoring technology, thermocouple monitoring technology, pressure sensor monitoring technology and ultrasonic sensor monitoring technology. However, the above monitoring technologies need to implant exogenous substances into the composite material, which will adversely affect the performance of the composite material. SUMMARY

[0006] The purpose of the present application is to provide a test method and system based on carbon nanotube sensing fiber flow front, which uses carbon nanotube sensing fiber as a sensor to monitor the liquid flow front of the liquid composite molding process. The carbon nanotube sensing fiber is used as a reinforcing fiber of the composite material, which will not adversely affect the performance of the composite material. At the same time, the monitoring sensitivity is high, and only the data of the resistance change rate of the carbon nanotube sensing fiber can be used to monitor the flow front in the horizontal and thickness directions in real time. At the same time, the accuracy of calculating the liquid filling area at a certain time is also improved.

[0007] In order to achieve the above purpose, the present application provides the following technical scheme:

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

[0009] Preferably, the organic fiber comprises 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 carbon nanotube sensing fiber bundle, a plurality of carbon nanotube sensing fiber bundles are regularly arranged to form a sensor grid, the sensor grid comprises a plurality of closed micro units, and the plurality of carbon nanotube sensing fiber bundles are insulated from each other.

[0011] The application provides a test system based on carbon nanotube sensing fiber flow front, 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, and comprises a plurality of closed micro units.

[0013] The connection module is used for connecting the sensor grid with the data collection module.

[0014] The data collection module is used for collecting resistance data of the carbon nanotube sensing fiber bundles in the sensor grid.

[0015] The data processing module is used for data processing of the resistance data, and a test result of the flow front is obtained according to a processing result of the resistance data.

[0016] Preferably, the arrangement mode of the carbon nanotube sensing fiber bundles in the sensor grid comprises orthogonal arrangement or diagonal mixed arrangement.

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

[0018] The diagonal mixed arrangement is that the carbon nanotube sensing fiber bundles are arranged equidistantly along the horizontal direction or the vertical direction, and the end points of the carbon nanotube sensing fiber bundles arranged along the horizontal direction or the vertical direction are taken as the starting points for arrangement along the 45° direction.

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

[0020] Preferably, the data collection module comprises a resistance test system.

[0021] The data processing module comprises a curve drawing module and a filled area calculation module, the curve drawing module is used for drawing a curve of the resistance change rate of the carbon nanotube sensing fiber bundles with time, and the filled area calculation module is used for calculating the filled area of resin flow.

[0022] The application provides a test method based on carbon nanotube sensing fiber flow front, which is tested by using the test system.

[0023] The fiber fabric is stacked and laid in a forming mold to obtain a fiber preform.

[0024] a sensor grid is arranged on the upper surface and / or the lower surface of the fiber preform, and a preform is formed in a molding die;

[0025] The molding die is sealed to obtain a sealed molding die, the sealed molding die is vacuumized, and then resin is injected into the sealed molding die in a vacuum environment; the initial resistance of each carbon nanotube sensing fiber bundle before resin injection is recorded, the moment of resin injection is defined as the zero point of injection time, and the resistance data of each carbon nanotube sensing fiber bundle varying with injection time are continuously collected by a data collection module during resin injection;

[0026] The resistance data are input into a data processing module, the resistance data collected by the data collection module are processed, and the 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 position reached by the resin flow front;

[0028] When the test result of the flow front is the position reached by the resin flow front, the data processing includes the following steps:

[0029] A curve of the resistance change rate of the carbon nanotube sensing fiber bundle varying with resin injection time is drawn, the resistance change rate is the ratio of the resistance of the carbon nanotube sensing fiber bundle at any resin injection moment to the initial resistance, a resistance change rate-time curve of the carbon nanotube sensing fiber bundle is obtained, and the position reached by the resin flow front is obtained according to the sudden change point of the resistance change rate on the resistance change rate-time curve of the carbon nanotube sensing fiber bundle.

[0030] Preferably, the test result of the flow front further includes the filling area of resin flow; the filling area of resin flow is the total area of a plurality of closed micro-units filled with resin in the sensor grid, and the resistance change rate on the resistance change rate-time curve of all carbon nanotube sensing fiber bundles forming any one closed micro-unit filled with resin all have sudden change points;

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

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

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

[0034] The type of the fiber fabric includes a unidirectional fabric, a twill fabric or a plain fabric;

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

[0036] The application provides a test system based on a carbon nanotube sensing fiber flow front, which comprises 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 comprises a plurality of closed micro units, the plurality of carbon nanotube sensing fiber bundles are insulated from each other, the carbon nanotube sensing fiber bundle is formed by a carbon nanotube sensing fiber, the carbon nanotube sensing fiber comprises an organic fiber and a carbon nanotube wrapped on the surface of the organic fiber; the connection module is used for connecting the sensor grid with the data collection module; the data collection module is used for collecting resistance data of the carbon nanotube sensing fiber in the sensor grid; and the data processing module is used for processing the resistance data, and a test result of the flow front is obtained according to the processing result of the resistance data. In the application, the carbon nanotube sensing fiber is used to form the sensor grid, the carbon nanotube sensing fiber expands after absorbing resin, the contact resistance between the tubes is significantly improved, and therefore the carbon nanotube sensing fiber has a sensitive resistance response characteristic to resin infiltration. The grid structure formed by regularly arranging the carbon nanotube sensing fiber bundle on the upper surface and / or the lower surface of the fiber preform can obtain a sensor grid with high sensitivity in a simple and applicable manner, so that the flow fronts in the horizontal direction and the thickness direction can be monitored in real time by using a small number of sensors, and the accuracy of calculating the liquid filling area at a certain time is improved. In conclusion, the carbon nanotube sensing fiber is used as a sensor to monitor the liquid flow front in the liquid forming process of the composite material, the carbon nanotube sensing fiber is used as a reinforcing fiber of the composite material, and the performance of the composite material is not adversely affected, the monitoring sensitivity is high, the resistance change rate of the carbon nanotube sensing fiber bundle can be used to monitor the flow fronts 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.

[0037] Further, in the application, the organic fiber comprises one or more of aramid fiber, polyimide fiber and polybenzoxazole fiber. When the carbon nanotube sensing fiber is made of the above-mentioned organic fiber, and the sensor grid formed by the carbon nanotube sensing fiber is used to detect the resin flow front, the sensor grid has good flexibility, is easy to operate in the process of laying and the like, does not affect the sensing effect, and the detection result is more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative effort.

[0039] Figure 1 The aramid fiber tows before and after needle tube drop coating in the preparation process of the carbon nanotube coated aramid fiber sensor provided by the embodiments of the present application;

[0040] Figure 2 The material laying process of monitoring the flow front on the upper surface of glass fibers in the central position of the glue injection port provided by the embodiment 1 of the present application;

[0041] Figure 3 The resistance change rule of carbon nanotube sensing fiber tows in the process of monitoring the flow front on the upper surface of glass fibers in the central position of the glue injection port provided by the embodiment 1 of the present application;

[0042] Figure 4 The injection area calculation schematic diagram in the process of monitoring the flow front on the upper surface of glass fibers in the central position of the glue injection port provided by the embodiment 1 of the present application;

[0043] Figure 5 The material laying process of monitoring the flow front on the upper surface of glass fibers in the diagonal mixed layout mode of sensing fibers provided by the embodiment 2 of the present application;

[0044] Figure 6 The resistance change rule of carbon nanotube sensing fiber tows in the process of monitoring the flow front on the upper surface of glass fibers in the diagonal mixed layout mode of sensing fibers provided by the embodiment 2 of the present application;

[0045] Figure 7 The injection area calculation schematic diagram in the process of monitoring the flow front on the upper surface of glass fibers in the diagonal mixed layout mode of sensing fibers provided by the embodiment 2 of the present application;

[0046] Figure 8 The material laying process of monitoring the flow front on the upper and lower surfaces of glass fibers in the eccentric position of the glue injection port provided by the embodiment 3 of the present application;

[0047] Figure 9 The resistance change rule of carbon nanotube sensing fiber tows in the process of monitoring the flow front on the upper surface of glass fibers in the eccentric position of the glue injection port provided by the embodiment 3 of the present application;

[0048] Figure 10 The resistance change rule of carbon nanotube sensing fiber tows in the process of monitoring the flow front on the lower surface of glass fibers in the eccentric position of the glue injection port provided by the embodiment 3 of the present application;

[0049] Figure 11 The glue injection port provided for the embodiment 4 of the present application monitors the material laying process of the flow front on the upper surface of the carbon fiber at the eccentric position;

[0050] Figure 12 The glue injection port provided for the embodiment 4 of the present application monitors the resistance change rule 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;

[0051] Figure 13 The injection area calculation schematic diagram in the process of monitoring the flow front on the upper surface of the glass fiber at the eccentric position by the glue injection port provided for the embodiment 4 of the present application. DETAILED DESCRIPTION

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

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

[0054] In the present application, the preparation method of the carbon nanotube sensing fiber preferably comprises the following steps:

[0055] The carbon nanotube dispersion liquid is drop-coated on the surface of the organic fiber, and the surface of the organic fiber is coated under the capillary action to obtain the carbon nanotube sensing fiber; the organic fiber is horizontally suspended, and the drop-coating is equidistant drop-coating.

[0056] In the present application, the organic fiber preferably comprises one or more of aramid fiber, polyimide fiber and polybenzoxazole fiber. The diameter of the carbon nanotube is preferably 20-35 nm, and the length is <10 μm.

[0057] In the specific embodiment of the present application, the specific preparation method of the carbon nanotube sensing fiber preferably comprises the following steps:

[0058] The carbon nanotube coating fiber sensing fiber is prepared by the syringe drop-removing method. According to the target coating amount and the mass fraction of the carbon nanotube dispersion liquid, the required applied mass of the carbon nanotube dispersion liquid is calculated, the carbon nanotube dispersion liquid is taken by a syringe, the carbon nanotube dispersion liquid is drop-coated on the horizontally suspended organic fiber at equidistant intervals, the drop-coating amount at each position is controlled by the syringe, the liquid is automatically infiltrated to both sides of the organic fiber due to the capillary action of the organic fiber, and the drop-coating positions of the multiple carbon nanotube dispersion liquids are ensured to uniformly coat the carbon nanotube on the organic fiber.

[0059] In the present application, the mass percentage of the carbon nanotube in the carbon nanotube sensing fiber is preferably 5-10%, preferably 8-10% of the mass of the organic fiber.

[0060] In the present 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, which includes a plurality of closed micro-units, and the carbon nanotube sensing fiber bundles are insulated from each other.

[0061] In the present 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, which includes a plurality of closed micro-units, and the carbon nanotube sensing fiber bundles are insulated from each other.

[0062] The present application provides a test system based on a carbon nanotube sensing fiber flow front, which includes a sensor grid, a connection module, a data collection module, and a data processing module.

[0063] The sensor grid is regularly arranged by a plurality of carbon nanotube sensing fiber bundles, and the sensor grid includes a plurality of closed micro-units, and the carbon nanotube sensing fiber bundles are insulated from each other, the carbon nanotube sensing fiber bundle is formed by a carbon nanotube sensing fiber, and the carbon nanotube sensing fiber includes an organic fiber and a carbon nanotube coated on the surface of the organic fiber.

[0064] The connection module is used to connect the sensor grid and the data collection module.

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

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

[0067] The test system based on carbon nanotube sensing fiber flow front provided by the application comprises a sensor grid. In the application, the sensor grid is formed by regularly arranging a plurality of carbon nanotube sensing fiber bundles, the sensor grid comprises a plurality of closed micro units, the plurality of carbon nanotube sensing fiber bundles are insulated from each other, the carbon nanotube sensing fiber bundle is formed by carbon nanotube sensing fibers, and the carbon nanotube sensing fiber comprises an organic fiber and a carbon nanotube coated on the surface of the organic fiber. In the application, the carbon nanotube sensing fibers in the sensor grid are used in the form of carbon nanotube sensing fiber bundles, the carbon nanotube sensing fiber bundle is a fiber bundle formed by a plurality of carbon nanotube sensing fibers, and the application does not have special requirements for the number of carbon nanotube sensing fibers in the carbon nanotube sensing fiber bundle.

[0068] In the application, the sensor grid comprises a plurality of closed micro units, the plurality of carbon nanotube sensing fiber bundles are insulated from each other, the carbon nanotube sensing fiber bundle is formed by carbon nanotube sensing fibers, and the carbon nanotube sensing fiber comprises an organic fiber and a carbon nanotube coated on the surface of the organic fiber. The arrangement mode of the carbon nanotube sensing fiber bundle in the sensor grid preferably comprises orthogonal arrangement or diagonal mixed arrangement. In the application, the orthogonal arrangement is preferably that the carbon nanotube sensing fiber bundles are arranged equidistantly along the horizontal direction and the vertical direction respectively (i.e. the carbon nanotube sensing fiber bundles are arranged equidistantly along the radial direction and the weft direction of the fiber preform respectively). In the specific embodiment of the application, the specific method of the orthogonal arrangement is preferably that 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; then on the first sensing layer, the carbon nanotube sensing fiber bundles are arranged equidistantly along the weft direction (or the radial direction) of the fiber preform to form a second sensing layer; and the first sensing layer and the second sensing layer form the sensor grid. An insulating isolation layer is preferably arranged between the first sensing layer and the second sensing layer, and the insulating isolation layer is specifically a glass fiber plain fabric. The insulating isolation layer realizes the insulation of the carbon nanotube sensing fiber bundles in the first sensing layer and the carbon nanotube sensing fiber bundles in the second sensing layer at the lap joint points.

[0069] In the present application, the diagonal mixed arrangement is preferably that the carbon nanotube sensing fiber bundles are arranged equidistantly along the horizontal direction or the vertical direction, and the end points of the carbon nanotube sensing fiber bundles arranged equidistantly along the horizontal direction or the vertical direction are taken as the starting points for arranging the carbon nanotube sensing fiber bundles along the 45° direction (i.e. the carbon nanotube sensing fiber bundles are arranged equidistantly along the radial direction or the weft direction of the fiber preform, and the end points of the carbon nanotube sensing fiber bundles arranged equidistantly along the radial direction or the weft direction are taken as the starting points for arranging the carbon nanotube sensing fiber bundles along the 45° direction). In the specific embodiments of the present application, the diagonal mixed arrangement is particularly preferably that 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 along the 45° direction with the end points of the carbon nanotube sensing fiber bundles arranged equidistantly along the radial direction or the weft direction in the first sensing layer as the starting points to form a second sensing layer, and the first sensing layer and the second sensing layer form the sensor grid. An insulating isolation layer is preferably arranged between the first sensing layer and the second sensing layer, and the insulating isolation layer is particularly a glass fiber plain fabric. The insulating isolation layer realizes the insulation of the carbon nanotube sensing fiber bundles in the first sensing layer and the carbon nanotube sensing fiber bundles in the second sensing layer at the lap joint points.

[0070] The test system based on the carbon nanotube sensing fiber flow front provided by the present application comprises a connecting module. In the present application, the data collection module is used to collect the resistance data of the carbon nanotube sensing fiber bundles in the sensor grid. The connecting module preferably comprises conductive silver paste, a metal foil and a metal wire. The conductive silver paste is used to fixedly connect the carbon nanotube sensing fiber bundles and the metal foil. The metal foil is particularly a copper foil. The metal wire is particularly a copper conductor. The present application preferably fixedly connects the metal foil and the carbon nanotube sensing fiber bundles in the sensor grid by using the conductive silver paste. The metal foil is welded with the metal wire.

[0071] The test system based on the carbon nanotube sensing fiber flow front provided by the present application comprises a data collection module. In the present application, the data collection module comprises a resistance test system. The resistance test system is particularly a digital multimeter.

[0072] In the present application, when monitoring the flow front in the liquid forming process, the edge of the carbon nanotube sensing fiber bundle is preferably fixedly connected with the copper foil by using the conductive silver paste, the other end of the copper foil is preferably connected with the copper wire by using soldering tin, and the other end of the copper wire is preferably connected with the digital multimeter.

[0073] The test system based on the carbon nanotube sensing fiber flow front provided by the application comprises a data processing module. In the application, the data processing module comprises a curve drawing module and a filled area calculation module. The curve drawing module is used to draw a curve of the resistance change rate of the carbon nanotube sensing fiber bundle with time, and the filled area calculation module is used to calculate the filled area of resin flow. The filled area calculation module is used to obtain the resin reaching position according to the mutation point appearing on the sensing fiber resistance-time curve, and draw the calculated resin filled area.

[0074] The application provides a test method based on the carbon nanotube sensing fiber flow front, which is tested by using the test system described in the above technical scheme, and comprises the following steps:

[0075] The fiber fabric is stacked and laid in the forming mold to obtain a fiber preform.

[0076] A sensor grid is arranged on the upper surface and / or the lower surface of the fiber preform to form a preform in the forming mold.

[0077] The forming mold is sealed to obtain a sealed forming mold. The sealed forming mold is subjected to vacuum extraction, and then resin is injected into the sealed forming mold in a vacuum environment. The initial resistance of each carbon nanotube sensing fiber bundle before resin injection is recorded. The time point of resin injection is defined as the zero point of injection time. The resistance data of each carbon nanotube sensing fiber bundle changing with injection time are continuously collected by the data collection module during the resin injection process.

[0078] The resistance data are input into the data processing module. The resistance data collected by the data collection module are subjected to data processing. The test result of the flow front is obtained according to the processing result of the resistance data.

[0079] In the application, the fiber fabric preferably comprises a glass fiber fabric or a carbon fiber fabric. The type of the fiber fabric preferably comprises a unidirectional fabric, a twill fabric or a plain fabric.

[0080] In specific embodiments of the application, the preparation method of the fiber preform preferably comprises: laying the cut fiber fabric on the bottom plate of the forming mold layer by layer.

[0081] After obtaining the fiber preform, a sensor grid is arranged on the upper surface and / or the lower surface of the fiber preform to form a preform in the forming mold.

[0082] In the present application, when testing carbon fiber fabric, due to the small diameter of carbon fiber forming the carbon fiber fabric, the dense structure of the carbon fiber fabric, and the low permeability, the present application preferably increases a high-permeability medium layer on the upper surface of the carbon fiber preform to assist resin permeation. The high-permeability medium layer is preferably a glass fiber fabric with high permeability and a thickness of less than 0.05 mm. The present application preferably cuts the high-permeability medium material to a size that can cover the carbon fiber preform, so that the high-permeability medium layer is laid on the upper surface of the carbon fiber preform, and then the sensor grid is arranged.

[0083] In the present application, the carbon nanotube sensing material is laid on the upper surface and / or lower surface of the fiber preform along the preset direction in the preset order.

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

[0085] In the present application, a plurality of carbon nanotube sensing fiber bundles are laid on the surface of the fiber preform, and the liquid flow front is monitored in real time through the change of resistivity to obtain the resin filling area at different times.

[0086] In the present application, in order to prevent the carbon nanotube sensing fiber bundles arranged in different directions from being overlapped to make it difficult to analyze the resistance signal, a layer of glass fiber plain fabric is preferably used for insulation and isolation between the carbon nanotube sensing fiber bundles arranged in different directions.

[0087] In the present application, when testing carbon fiber fabric, a high-permeability medium layer is preferably added to the upper surface of the carbon fiber preform to assist resin permeation, and at this time the high-permeability medium layer simultaneously serves as an insulating layer between the carbon fiber preform and the sensor grid.

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

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

[0090] After forming the preform in the forming mold, the forming mold is sealed to obtain a sealed forming mold, the sealed forming mold is vacuumized, and then resin is injected into the sealed forming mold in a vacuum environment; the initial resistance of each carbon nanotube sensing fiber bundle before resin injection is recorded, the moment of resin injection is defined as the zero point of injection time, and the resistance data of each carbon nanotube sensing fiber bundle changing with injection time are continuously collected by a data collection module during resin injection. The preform in the forming mold is preferably sealed as a whole by a vacuum bag, and the resin is mainly driven to penetrate along the fabric surface by vacuum pressure during the pouring process.

[0091] In the present application, the sealing preferably tightly surrounds the preform with sealing tape, and double-layer sealing tape is used to bond the copper foil and the flow guide pipe in the middle at the overlapping position of the sealing tape, so as to avoid air leakage. The forming mold and the preform are sealed as a whole by a vacuum bag, and the flow guide pipe at one end is connected to a liquid collection bottle, and the vacuum pump is connected through the air pipe.

[0092] In the present application, before the resin injection, the fabric is first densified by vacuumizing, and the resistance of each conductive path is observed without short circuit and other problems. After maintaining this state for about 5 minutes and the resistance is stable without obvious change, the resin injection is prepared to start.

[0093] In the present application, the resin is preferably injected through a glue injection port, which is located at the center position or eccentric position of the preform.

[0094] The fabric in the vacuumized preform is preferably densified by vacuumizing. After observing the resistance of the conductive path formed by the carbon nanotube sensing fiber bundle, the connecting module and the data collection module in each sensor grid without short circuit and other problems, and maintaining the vacuum state for about 5 minutes and the resistance is stable without obvious change, the resin injection is prepared to start. After opening the glue injection port, the resin is injected into the preform under the action of vacuum negative pressure, and flows from the injection port to the surrounding. The resistance change of the carbon nanotube sensing fiber bundle is collected in real time during this process, and the resistance change rate-time curve is drawn according to the collected data. The mutation point of the resistance response is taken as the front arrival time, the preform is divided into several square microzones according to the sensing fiber, and the four sensing fiber bundles surrounding the microzone are taken as the criterion for resin filling the microzone. The resin filling area can be obtained by calculating the area of the microzone.

[0095] The application preferably opens the data collection module to record the resistance change of the carbon nanotube sensing fiber, opens the resin injection port, and the resin is injected into the glass fiber preform under the action of vacuum negative pressure, flows from the injection port to the surrounding, records the time when the liquid starts to be injected, continuously collects the resistance information, and collects the complete resistance change curve. When the liquid drops in the liquid collection bottle, the vacuum pump is closed.

[0096] After obtaining the resistance data of the carbon nanotube sensing fiber bundle, 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 application, the test result of the flow front includes the position reached by the resin flow front; when the test result of the flow front is the position reached by the resin flow front, the data processing includes the following steps:

[0098] A resistance change rate-time curve of the carbon nanotube sensing fiber bundle is drawn, the resistance change rate is the ratio of the resistance of the carbon nanotube sensing fiber bundle at any resin injection time to the initial resistance, the resistance change rate-time curve of the carbon nanotube sensing fiber bundle is obtained, and the position reached by 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 sensing fiber bundle.

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

[0100] The application first draws the resistance (R) of each carbon nanotube sensing fiber bundle collected by the data collection module against time t into a resistance-time point line graph, that is, an R-t point line graph.

[0101] According to the resistance-time point line graph, an Origin software is used to draw a resistance change rate-time curve, that is, a ΔR / R0-t curve graph, wherein R0 is the resistance of the carbon nanotube sensing fiber bundle at the initial time when the test is started; ΔR=R-R0, which refers to the difference between the resistance at different times and the initial resistance.

[0102] In a specific embodiment of the application, Figure 3 The resistance relative change rate-time curve graph provided for the embodiment 1 of the application is shown in the following figure: Figure 3 The characteristics of the ΔR / R0-t curve graph include a stable baseline and a resistance rising stage. The mutation point when the resistance changes from the stable baseline to the resistance rising stage is taken as the time when the penetrating liquid flow front arrives, and the mutation point is defined as the resistance change rate being greater than or equal to 1.5% for the first time.

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

[0104] In the present application, the test result of the flow front also includes the filling area of resin flow; the filling area of resin flow is the total area of a plurality of closed micro-units filled with resin in the sensor grid, and the resistance change rate of all carbon nanotube sensing fiber bundles forming the closed micro-unit appears a sudden change point on the resistance change rate-time curve.

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

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

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

[0108] The fiber preform is divided into a plurality of micro-zones 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-zone is taken as the criterion for filling the micro-zone, and the resin filling area corresponding to the time is obtained by calculating the area of the micro-zone.

[0109] The present application obtains the resin reaching position according to the sudden change point of the sensing fiber resistance-time curve, and draws the calculated resin filling area.

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

[0111] The resin reaching position is obtained according to the sudden change point of the sensing fiber resistance-time curve, and the calculated resin filling area is drawn.

[0112] The sudden change point of resistance response is taken as the front arrival time, the preform is divided into a plurality of square micro-zones according to the sensing fiber bundle, as shown in Figure 4 The resin reaching the four sensing fiber bundles surrounding the micro-zone is taken as the criterion for resin filling the micro-zone, and the resin filling area corresponding to the time is obtained by calculating the area of the micro-zone.

[0113] In summary, the present application aims to provide a test method and system based on carbon nanotube sensing fiber flow front. The present application constructs a sensor grid on the upper surface and / or lower surface of the 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 the glue injection port, records the resistance change of the carbon nanotube sensing fiber bundle with time in real time through the data collection module; finds the mutation point of the resistance change rate according to the resistance change of the carbon nanotube sensing fiber bundle with time, obtains the liquid arrival position, draws the liquid filling diagram, and calculates the liquid filling area.

[0114] The test method for monitoring flow front based on carbon nanotube sensing fiber of the present application is simple to operate, has strong adaptability, can identify the arrival of flow front, monitor the change in thickness direction, and obtain more accurate resin filling condition in real time with fewer sensors, and has a wide application prospect.

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

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

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

[0118] In the following examples, the carbon nanotube sensing fiber used in the sensor grid is a carbon nanotube sensing fiber bundle.

[0119] Example 1

[0120] The embodiment uses glass fiber plain fabric EW100 as the test object, and cuts the fabric into 300 mm x 300 mm, and sequentially lays the fabric on the mold surface, and a total of 6 layers of fabric are laid. The carbon nanotube sensing fiber bundle is laid on the surface of the fabric along the warp and weft directions of the fabric, and 4 carbon nanotube sensing fiber bundles with a length of 300 mm are sequentially laid in two directions, wherein the edge carbon nanotube sensing fiber bundle is 60 mm away from the edge of the layer plate, and the carbon nanotube sensing fiber bundles are spaced 60 mm apart. In order to prevent the overlap of the carbon nanotube sensing fiber bundles arranged along the warp and weft directions from causing difficulty in analyzing the resistance signal, a layer of glass fiber plain fabric with a thickness of about 60 μm is used for insulation and isolation between the carbon nanotube sensing fiber bundles arranged along the warp and weft directions. A glue injection port is provided at the middle position, and a vacuum bag is used to seal it, and the equipment is connected. Before the experiment starts, first, vacuumize the fabric to make it dense, and then observe the resistance of the conductive path of each carbon nanotube sensing fiber, and there is no problem such as open circuit, and then keep the state for about 5 min and the resistance is stable and does not change significantly, and then open the glue injection port. Epoxy resin is used as the test fluid, and 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 surrounding, and the flow front is approximately circular. The resistance change of the carbon nanotube sensing fiber bundle is collected in real time during the process, and the resistance change law of the 8 carbon nanotube sensing fiber bundles is shown in Figure 3 , wherein the resin injection port opening time is about 233 s after the resistance data starts to be collected, and the resin infiltration time of the entire fabric surface is about 320 s, and the positions of the 8 carbon nanotube sensing fibers 1-X, 1-Y, etc. are shown in Figure 2 .

[0121] From the mutation point of the resistance of the carbon nanotube sensing fiber bundle, it can be seen that the time when the front reaches 2-X and 3-X is 244 s, and the time when it reaches 1-X and 4-X is 286 s and 278 s, respectively. Corresponding to the vertical direction, the carbon nanotube sensing fiber bundles 2-Y and 3-Y respond preferentially, and the corresponding start response times are 242 s and 244 s, respectively, and the resistance mutation points of 1-Y and 4-Y occur later, and the times are 276 s and 283 s, respectively. If the glass fiber fabric is divided into 25 60 mm x 60 mm square microzones by using the carbon nanotube sensing fiber bundle, and the resin reaches the four carbon nanotube sensing fiber bundles surrounding the microzone as the criterion for the resin filling the microzone, then the resin injection area can be monitored by the carbon nanotube sensing fiber bundle, and the injection area zones obtained based on the carbon nanotube sensing fiber bundle at the 244 s and 286 s after the start of resistance collection are 36 cm 2 and 324 cm 2 , respectively.

[0122] Example 2

[0123] Glass fiber plain fabric EW100 was used as the test object, and the fabric was cut into 300 mm x 300 mm and placed on the mold surface in turn, and a total of 6 layers of fabric were placed. The carbon nanotube sensing fiber bundle was laid on the surface of the fabric in the same direction at an interval of 60 mm, and then 6 groups of carbon nanotube sensing fiber bundles were laid in parallel along the 45° direction with the end point of the carbon nanotube sensing fiber bundle as the starting point, and the two layers of carbon nanotube sensing fiber bundles were separated by ultra-thin glass fiber fabric to prevent node contact, as shown in Figure 5 The injection port position was at the center of the fabric.

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

[0125] Example 3

[0126] Glass fiber plain fabric EW100 was used as the test object, and the fabric was cut into 300 mm x 300 mm and placed on the mold surface in turn, and a total of 6 layers of fabric were placed. The carbon nanotube sensing fiber bundle was laid on the surface of the fabric in the same direction at an interval of 60 mm, and then 6 groups of carbon nanotube sensing fiber bundles were laid in parallel along the 45° direction with the end point of the carbon nanotube sensing fiber bundle as the starting point, and the two layers of carbon nanotube sensing fiber bundles were separated by ultra-thin glass fiber fabric to prevent node contact, as shown in Figure 8 The injection port position was at the center of the fabric.

[0127] Figure 9 The resistance change results of each carbon nanotube sensing fiber bundle on the bag surface (upper surface) are shown in Figure 9It can be seen that the resin preferentially reaches the 2-X-T, 3-X-T and 3-Y-T, 4-Y-T carbon nanotube sensing fibers, and the arrival time is 336s after starting to record the resistance change. With the continuous injection of resin, the resistance of 1-X-T, 4-X-T, 2-Y-T, 5-X-T, 5-Y-T, 1-Y-T carbon nanotube sensing fibers increases in turn, and the change time is 427s, 427s, 454s, 482s, 533s, 761s respectively.

[0128] Figure 10 The resistance change results of each road carbon nanotube sensing fiber bundle on the mold surface (lower surface) are as follows: the resin reaches the 3-X-B, 3-Y-B and 2-X-B, 4-Y-B carbon nanotube sensing fiber bundles at 340s, 340s, 347s, 347s after starting to record the resistance change. With the continuous injection of resin, the resistance of 1-X-B, 4-X-B, 2-Y-B, 5-Y-B, 5-X-B, 1-Y-B carbon nanotube sensing fiber bundles increases in turn, and the change time is 429s, 433s, 457s, 535s, 604s, 803s respectively. The resin arrival time of each point on 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, and the fabric was cut into 270mm x 270mm and placed on the mold surface in turn, a total of 6 layers of fabric, and a high permeability medium layer was added on the upper surface to assist resin permeation,

[0131] Five groups of carbon nanotube sensing fiber bundles were placed on the preform at a uniform interval of 5cm along the warp and weft directions respectively, and the injection mode was set to an eccentric position, as shown in Figure 11 Figure 12 The resistance change results of each road carbon nanotube sensing fiber bundle are as follows: Figure 12 It can be seen that the resin preferentially reaches the 2-X-T, 3-X-T and 3-Y-T, 4-Y-T carbon nanotube sensing fiber bundles, and the arrival time is 336s after starting to record the resistance change. With the continuous injection of resin, the resistance of 1-X-T, 4-X-T, 2-Y-T, 5-X-T, 5-Y-T, 1-Y-T carbon nanotube sensing fiber bundles increases in turn, and the change time is 427s, 427s, 454s, 482s, 533s, 761s respectively. As shown in Figure 13 2 , 108cm 2 , 216cm 2 , 288cm​​2 , 432 cm 2 , 576 cm 2 .

[0132] From the above embodiments, the present application provides a test method and system for real-time monitoring of flow front based on carbon nanotube sensing fiber, which can obtain more accurate resin filling area in a relatively simple way. The present application has the following advantages: the present application uses carbon nanotube sensing fiber bundle to form a sensor grid, the fiber specification of the carbon nanotube sensing fiber bundle is adjustable, and the content of carbon nanotube is controllable. The laying method of the carbon nanotube sensing fiber bundle can realize more accurate monitoring with less fiber sensor. The present application can realize simultaneous monitoring of the upper and lower surfaces of the fiber preform. The system or method provided by the present application can identify the arrival of the flow front and determine the resin arrival area at the same time.

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

[0134] The principles and implementation manners of the present application are described by applying specific examples in this paper, and the above embodiment description is only used to help understand the method of the present application and its core idea; at the same time, for the general technical personnel in the art, according to the idea of the present application, the specific implementation manner and application range will be changed. In view of the above, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for testing the liquid flow front during the liquid forming process of composite materials based on carbon nanotube sensing fibers, characterized in that, The test is conducted using a test system, which includes a sensor grid, a connection module, a data collection module, and a data processing module. The sensor grid is formed by regularly arranged bundles of carbon nanotube sensing fibers. The sensor grid includes multiple closed micro-units. The bundles of carbon nanotube sensing fibers are insulated from each other. The bundles of carbon nanotube sensing fibers are formed by carbon nanotube sensing fibers. 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 to the data collection module; The data collection module is used to collect the resistance data of the carbon nanotube sensing fiber bundles in the sensor grid; The data processing module is used to process the resistance data and obtain the test results of the flow front based on the processing results of the resistance data. The testing method includes the following steps: Fiber fabric is layered and laid in a molding die to obtain a fiber preform; A sensor grid is provided on the upper and / or lower surface of the fiber preform to form the preform in a molding die; The molding mold is sealed to obtain a sealed molding mold. The sealed molding mold is then evacuated, and resin is injected into the sealed molding mold while maintaining the vacuum environment. The initial resistance of each carbon nanotube sensing fiber bundle before resin injection is recorded. The moment of resin injection is defined as the zero point of injection time. During the resin injection process, the resistance data of each carbon nanotube sensing fiber bundle as the injection time is continuously collected by the data collection module. The resistance data is input into the data processing module, which processes the resistance data collected by the data collection module, and the test results of the flow front are obtained based on the processing results of the resistance data. The test results of the flow front include the location where the resin flow front arrives. The data processing includes the following steps: plotting the resistance change rate of the carbon nanotube sensing fiber bundle as a function of resin injection time, where the resistance change rate is the ratio of the resistance of the carbon nanotube sensing fiber bundle at any resin injection time to the initial resistance, to obtain the resistance change rate-time curve of the carbon nanotube sensing fiber bundle; and obtaining the location where the resin flow front arrives based on the abrupt change point of the resistance change rate on the resistance change rate-time curve of the carbon nanotube sensing fiber bundle. The test results of the flow front also include the resin flow filling area; the resin flow filling area is the total area of ​​several closed micro-units filled with resin in the sensor grid, and any one closed micro-unit is filled with resin such that the rate of change of resistance on the resistance change-time curve of all carbon nanotube sensing fiber bundles forming the closed micro-unit shows an abrupt change point; the data processing also includes the following steps: calculating the total area of ​​several closed micro-units filled with resin in the sensor grid to obtain the resin flow filling area.

2. The method for testing the liquid flow front in the liquid forming process of composite materials based on carbon nanotube sensing fibers according to claim 1, characterized in that, The arrangement of carbon nanotube sensing fiber bundles in the sensor grid includes orthogonal arrangement or a mixed diagonal arrangement; The orthogonal arrangement is as follows: carbon nanotube sensing fiber bundles are arranged at equal intervals along the horizontal and vertical directions, respectively. The diagonal mixed arrangement is as follows: carbon nanotube sensing fiber bundles are arranged at equal intervals along the horizontal or vertical direction; at the same time, they are also arranged at a 45° direction starting from the endpoints of the carbon nanotube sensing fiber bundles arranged in the horizontal or vertical direction.

3. The method for testing the liquid flow front in the liquid forming process of composite materials based on carbon nanotube sensing fibers according to claim 1, characterized in that, The connection module includes conductive silver paste, metal foil, and metal wires.

4. The test method for liquid flow front based on carbon nanotube sensing fiber monitoring of composite liquid forming process according to claim 1 or 3, characterized in that, The data collection module includes a resistance testing system; The data processing module includes a curve plotting module and a filling area calculation module. The curve plotting module is used to plot the change curve of the resistance 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.

5. The method for testing the liquid flow front in the liquid forming process of composite materials based on carbon nanotube sensing fibers according to claim 1, characterized in that, The fiber fabric includes glass fiber fabric or carbon fiber fabric; The types of fiber fabrics include unidirectional fabrics, twill fabrics, or plain weave fabrics; The resin is injected through a glue injection port, which is located at the center or off-center of the preform.

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