A real-time monitoring method for the entire composite material liquid molding process based on grid-type fiber sensors

Abstract

The present invention discloses a method for real-time monitoring of the entire process of composite material liquid molding based on a grid-type fiber sensor. The method comprises the following steps: S1: placing a grid-type fiber sensor between preform layers, and connecting the two electrodes of the sensor to the excitation and acquisition modules of the monitoring system; S2: during the preforming process, applying pressure to compact the preform in the mold, and collecting the voltage signal changes of the sensor in real time to reflect the compaction state; S3: opening the resin filling channel, injecting resin to impregnate the preform, and at the same time collecting the voltage signal changes of the sensor during the resin injection process in real time to reconstruct the position changes of the flow front during resin filling, and closing the resin inlet and outlet after the filling is completed; S4: during the resin cross-linking molding process, monitoring the real-time molding quality of the composite material by collecting the voltage signal changes of the sensor during the resin cross-linking process. The present invention adopts a grid-type fiber sensor, which can monitor the entire process of composite material liquid molding without affecting the performance of the preform and the flow of resin.

Description

Technical Field

[0001] The invention relates to a real-time monitoring method for the entire composite material liquid molding process based on a grid-type fiber sensor, and belongs to the field of composite materials. Background Art

[0002] Resin-based composite materials are widely used in aerospace, rail transportation, wind power and other fields due to their light weight, high strength and corrosion resistance. Liquid molding of composite materials is an important method for preparing composite materials, which mainly includes three steps: preform compaction, resin injection and resin cross-linking molding. Preform compaction is a crucial step in composite material manufacturing. It involves aligning and pressurizing the fiber preform before molding to improve the mechanical properties and durability of the composite material. The resin filling and cross-linking processes are equally important. Whether the resin filling and impregnation are sufficient and the degree of cross-linking reaction of the resin will directly affect the quality of the product. However, the three main processes of liquid molding are often carried out in a closed environment, which is difficult to observe directly and the molding process cannot be directly monitored, resulting in unstable product quality and difficulty in subsequent process optimization. Therefore, there is an urgent need for a method that can effectively monitor the liquid molding of composite materials.

[0003] Several existing methods for monitoring the liquid molding of composite materials have been proposed. These include monitoring the liquid resin molding process using optical fibers by monitoring changes in their refractive index, or by monitoring changes in the conductivity of reinforcing fibers embedded with conductive carbon nanoparticles. While both methods can monitor the liquid molding of composite materials, optical fibers are susceptible to temperature fluctuations and are unsuitable for continuous monitoring in fluctuating temperatures. Furthermore, the complex and expensive synthesis process for reinforcing fibers coated with conductive carbon nanoparticles makes them unsuitable for industrial production and development.

[0004] With the widespread application of resin-based composite materials in fields such as aviation, automobiles, and new energy, the requirements for the performance of the materials involved are increasing. In this context, composite molding technologies that are simple to operate, provide high quality, and achieve fast molding speeds are gaining increasing attention. Liquid molding of composite materials facilitates rapid molding and improves production efficiency, making real-time molding monitoring data even more crucial for improving product quality. Summary of the Invention

[0005] The present invention aims to provide a method for real-time monitoring of the entire composite material liquid molding process based on a grid-type fiber sensor. This method places a grid-type magnetic fiber sensor within the preform interlayer, aligning the sensor grid fibers parallel to the resin flow direction. During the fiber preform compaction, resin filling, and resin crosslinking processes, the voltage response of the pre-installed grid-type fiber sensor is monitored in real time to monitor the liquid resin flow and the entire molding process. The grid-type fiber sensor and signal output terminal used are compact, stable, and reliable, enabling monitoring of the entire composite material liquid molding process without affecting the preform compaction quality or resin injection.

[0006] Preferably, the method for real-time monitoring of the entire composite material liquid forming process based on the grid-type fiber sensor of the present invention comprises the following steps:

[0007] Step 1: Arrange stress-sensitive amorphous magnetic fibers using a grid model to prepare a grid-type fiber sensor, and use an offline pressure test to determine the stress sensitivity curve of the grid-type fiber sensor;

[0008] Step 2: Layers of fiber cloth are stacked and compacted to form a preform according to the preset molding requirements of the composite material. During the stacking process, the fiber grid sensor obtained in Step 1 is embedded between the two layers of fiber cloth at the location to be monitored and fixed according to the preset monitoring requirements. The preform is then placed in a vacuum bag and the fiber grid sensor is connected to the monitoring system via interface leads.

[0009] Step 3: During the compaction process of the preform vacuum bag, the response voltage of each grid fiber sensor is continuously collected, and the compaction state of the preform near the sensor is calculated based on the stress sensitivity curve of the sensor; after the preform is compacted, vacuum infusion resin is performed, and the response voltage of each position sensor is collected in real time. According to the position information of the sensor and the response time of the corresponding sensor, the time when the flow front reaches each position in the internal space of the preform during the resin flow filling process is determined, and the change state of the resin flow front during the molding process is obtained in real time; after the resin filling is completed, cross-linking molding is performed, and the molding process of the composite material is monitored in real time based on the response voltage of each sensor to determine the resin cross-linking state at different positions.

[0010] As a preferred embodiment of the present invention, cobalt-based alloy fibers are used, with a diameter of 20-150 μm. The beneficial effect is that the magnetic fibers of this composition have moderate electrical conductivity and excellent interfacial stress sensing performance.

[0011] As a preferred embodiment of the present invention, the fiber grating sensor prepared by the steps of the present invention is flexible and can be bent at large angles. Its beneficial effect is that the sensor can deform in coordination with the preform during compaction, enabling local monitoring of curved surfaces or special-shaped structures.

[0012] As a preferred embodiment of the present invention, each amorphous fiber in the grid sensor is spaced 5mm-50mm apart, and the two electrode ports are cold-welded to conductive copper wires with an inner diameter of 40-200μm. During sensor placement, the grid sensor leads are extended from the mold edge. This advantageously ensures stable sensor signal transmission and is unaffected by the resin. This effectively reduces the disturbance caused by liquid resin injection on the sensor, ensuring the continuity and stability of the sensor response signal during resin flow.

[0013] As a preferred embodiment of the present invention, the grid-type sensor is embedded so that its length aligns with the direction of resin flow during the molding process. This advantageously allows for monitoring the resin filling and crosslinking state within a localized region of the fiber preform plane using a single grid-type fiber sensor. Furthermore, grid-type sensors at different locations and layers can be used to three-dimensionally reconstruct the resin flow front and curing crosslinking state within the preform.

[0014] As a preferred embodiment of the present invention, the optimal length of the grid-type fibers placed in the reinforcement interlayer is 10-280 mm on a single side, and the excitation source frequency is 5-200 MHz, with an amplitude of 1-7 V. This advantageously results in high voltage signal sensitivity and low energy consumption when the sensor fiber length matches the excitation source frequency and voltage.

[0015] In response to the problems of existing composite material liquid molding monitoring technology, the method of the present invention adopts a grid-type magnetic fiber sensor as a sensing unit. The monitoring method is simple to operate and can monitor the entire composite material liquid molding process in real time at low cost without affecting the compaction quality of the preform, resin flow filling, and the performance of the material after molding. It is beneficial to optimize the molding process, improve the quality of composite material products, and reduce manufacturing costs.

[0016] The present invention can monitor the entire process of composite material preform compaction, resin filling, and cross-linking in a sealed environment. Furthermore, the grid-type fiber sensor provided by the present invention is compact and does not damage the material, ensuring the integrity and mechanical properties of the final resin-based composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Response curve of the voltage signal of the fiber grid sensor in Example 1 as the applied pressure changes.

[0018] Figure 2 Schematic diagram of the principle of monitoring composite material liquid forming by the grid-type fiber sensor in Example 1.

[0019] Figure 3This is a curve showing the change of the voltage signal of the grid-type fiber sensor in Example 1 along with the real-time voltage signal during the entire liquid forming process of the liquid composite material.

[0020] Figure 4 This is a real-time voltage signal change diagram of the grid-type fiber sensor in Example 1 during the resin filling process. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific examples and drawings. The following examples are only used to illustrate the present method and do not limit the scope of protection of the present invention.

[0022] Example 1:

[0023] This example utilizes the fiber-optic sensor of the present invention to monitor the liquid molding process of a composite material during a low-viscosity liquid-phase epoxy resin vacuum-assisted resin transfer molding process. This example uses Taylor-spinning Co-Fe-Si-B-based amorphous alloy fibers as the sensing element of the fiber-optic sensor. The epoxy resin crosslinking process involves curing at 100°C. The specific implementation steps of this example are as follows:

[0024] The present invention discloses a method for real-time monitoring of the entire composite material liquid forming process based on a grid-type fiber sensor, which comprises the following steps:

[0025] Step 1: Using a fixture, parallely arrange the amorphous alloy fibers selected in this embodiment of the present invention of the same length. Adjacent fibers are connected end-to-end with copper wires to form a grid, which is fixed into a grid model to obtain a two-dimensional grid-type fiber sensor. The stress sensitivity curve P = f(V) of the grid-type fiber sensor is then calibrated under step loading conditions using an electronic universal testing machine.

[0026] Step 2: Evenly apply a release agent to the aluminum mold for liquid resin molding;

[0027] Step 3: placing the prepared 2D grid-type fiber sensor in the middle layer of the preform;

[0028] Step 4: Place the preform prepared in step 3 into the mold of step 2. Inside the mold, from bottom to top, are the aluminum mold, preform, grid-type fiber sensor, release cloth, guide net, resin inlet and outlet silicone interface, and vacuum bag.

[0029] Step 5: Connect the 2D grid fiber sensor to the sensing system, use AC excitation with a frequency of 5-200 MHz and an amplitude of 1-7 V to collect the voltage response signal of the grid sensor.

[0030] Step 6: Compact the preform in the mold using a vacuum pump and atmospheric pressure while monitoring the voltage signal changes from the fiber optic grid sensor. Once the vacuum is achieved, turn off the vacuum pump and maintain pressure for 15-60 minutes to ensure the mold maintains a constant vacuum level. While the preform is compacting and maintaining pressure, monitor the voltage response signal changes from the grid sensor.

[0031] Step 7: Open the vacuum pump and the resin inlet and outlet valves to allow the liquid resin to fill the compacted preform. Once the preform is completely filled with resin and all internal bubbles are expelled, close the resin inlet and outlet and the vacuum pump. While the resin is flowing, measure the changes in the grid-type fiber sensor voltage signal and the position of the resin flow front.

[0032] Step 8: While waiting for the resin to cross-link, collect the changes in the voltage response signal of the grid fiber sensor during the resin cross-linking process.

[0033] The stress sensitivity curve calibration results of the grid-type fiber sensor used in this embodiment are as follows: Figure 1 As shown in Figure 2, as the loading stress gradually increases, the voltage signal gradually decreases. Figure 2 The diagram shows the principle of monitoring composite material liquid-phase molding. It primarily includes a resin drum 1, a signal generator 2, an aluminum mold 3, glass fiber 4, a release cloth 5, a flow guide 6, a vacuum bag 7, an oscilloscope 8, a data recording computer 9, a resin collection drum 10, and a vacuum pump 11. The dashed box contains a two-dimensional grid-type fiber sensor, with the light-colored portion representing the conductive copper tube connecting the sensor. Figure 3 The figure shows the voltage signal change curve of the whole process of composite material liquid molding monitored in real time by the two-dimensional grid fiber sensor at 100°C. Figure 4 The figure shows the curve of the resin filling process during the composite material liquid molding process monitored in real time by a two-dimensional grid fiber sensor at 100°C.

[0034] This example is formed by heat preservation and curing at 100℃. Figure 1 The relationship between the calibrated voltage signal and the pressure is obtained by fitting P = f (V) = 6.5 × 10 -9 V -27 .exist Figure 3In the figure, the start and end of each stage of preform compaction, resin filling and resin cross-linking can be clearly distinguished, among which 0-10min is the preform compaction process, 10-21min is the pressure holding process, 21-23min is the resin filling process, and 23-170min is the resin cross-linking process. During the preform compaction stage, as the pressure in the vacuum bag increases, the voltage signal of the grid fiber sensor gradually decreases. During the pressure holding process, it can be seen that the voltage signal of the 2-dimensional grid fiber sensor remains unchanged, which shows that the stable pressure in the bag can maintain the pressure required for preform compaction. During the resin filling process, as the contact area between the resin front and the 2-dimensional grid fiber sensor increases, the sensor voltage signal further decreases. During the resin cross-linking process, the stress around the 2-dimensional grid fiber sensor gradually changes from atmospheric pressure to the stress of the resin cross-linking process, and the sensor voltage signal gradually rises. In the Figure 4 In the voltage change diagram during the resin injection stage, it can be seen that the voltage signal of the 2D grid fiber sensor is continuous and stable, indicating that the resin filling process will not affect the 2D grid fiber sensor. Therefore, the voltage signal of the 2D grid fiber sensor can reflect the advancement of the flow front.

[0035] The above-described embodiments merely represent optional implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A real-time monitoring method for the entire process of composite material liquid molding based on a grid-type fiber sensor, characterized in that: The following steps are involved: Step 1: A grid-type fiber sensor is prepared by arranging stress-sensitive amorphous magnetic fibers in parallel and connecting them end to end. An offline pressure test is performed to determine the stress sensitivity curve of the grid-type fiber sensor. Step 2: Layers of fiber cloth are stacked and compacted to form a preform according to the preset molding requirements of the composite material. During the stacking process, the fiber grid sensor obtained in Step 1 is embedded between the two layers of fiber cloth at the location to be monitored and fixed according to the preset monitoring requirements. The preform is then placed in a vacuum bag and the fiber grid sensor is connected to the monitoring system via interface leads. Step 3: During the compaction process of the preform vacuum bag, the response voltage of each grid-type fiber sensor is continuously collected, and the compaction state of the preform near the sensor is calculated based on the stress sensitivity curve of the sensor. After the preform is compacted, vacuum infusion resin is performed, and the response voltage of the sensors at each position is collected in real time. Based on the position information of the sensors and the response time of the corresponding sensors, the time when the flow front reaches each position in the internal space of the preform during the resin flow filling process is determined, and the change state of the resin flow front during the molding process is obtained in real time. After the resin filling is completed, cross-linking molding is performed, and the molding process of the composite material is monitored in real time based on the response voltage of each sensor to determine the resin cross-linking state at different positions. During the compaction process of the preform in step 3, the pressure between the layers of fiber cloth increases, causing the response voltage of the grid-type fiber sensor to decrease. The initial voltage V0 in the uncompacted state is recorded, and the stress sensitivity curve P is calibrated. i =f(V i ) calculating the internal pressure of the fiber preform, thereby determining and adjusting the compaction state of the preform; Among them, V i Represents the response signal of the sensor, P i Indicates the pressure applied to the sensor.

2. The method for real-time monitoring of the entire composite material liquid forming process based on a grid-type fiber sensor according to claim 1, characterized in that: The preparation method of the grid-type fiber sensor is as follows: magnetic fibers of the same length are arranged in parallel, adjacent magnetic fibers are connected end to end via copper wires to form a grid, and one or more grids connected in series form a grid-type sensor. The performance and monitoring area of ​​the sensor are adjusted by the number of grids and the length of the grids.

3. The method for real-time monitoring of the entire composite material liquid forming process based on a grid-type fiber sensor according to claim 1, characterized in that: The method for determining the stress sensitivity curve of the sensor in step 1 is as follows: the formed grid sensor is placed between two layers of fiber cloth with a specific area S, and a step load force F is applied by an electronic universal testing machine. i , record the corresponding sensor response signal V i , by responding to voltage and pressure P i The stress sensitivity curve P is obtained by fitting the functional relationship between the two i =f(V i ), where P i =F i / S.

4. The method for real-time monitoring of the entire composite material liquid forming process based on a grid-type fiber sensor according to claim 1, characterized in that: In the step 2, when the grid fiber sensor is embedded, the length direction of the grid fiber is required to be consistent with the direction of resin flow during the molding process, and when the wire is connected, a high-temperature resistant copper wire with a diameter of 100-500μm is used for connection. When the vacuum bag is taken out, double layers of vacuum glue are used to fix it and ensure the vacuum degree in the vacuum bag.

5. The method for real-time monitoring of the entire composite material liquid forming process based on a grid-type fiber sensor according to claim 1, characterized in that: During the vacuum infusion resin infusion process of step 3, when the resin flow front reaches the sensor grid, the pressure near the sensor increases, causing the sensor response signal to decrease. Specifically, during the vacuum infusion resin infusion process, when the sensor response signal drops by more than 0.5% V0, it is determined that the resin flow front has begun to reach that location. When the sensor response signal stabilizes and changes by less than 0.5% V0, it is determined that the resin has completely infiltrated the sensor at that location. Wherein, V0 is the initial voltage in the uncompacted state. Based on the sensor response signal during the resin filling process, the time when the resin arrives at each location along the length of the grid is sequentially confirmed, and the resin flow front in the preform is reconstructed based on the sensor response conditions at different locations.

6. The method for real-time monitoring of the entire composite material liquid forming process based on a grid-type fiber sensor according to claim 1, characterized in that: During the cross-linking molding process in step 3, the cross-linked resin replaces part of the stress caused by the vacuum, causing the voltage of the grid sensor to gradually increase. Specifically, when the vacuum infusion resin is completed and the sensor response signal begins to rise, the resin cross-linking process is considered to have begun. When the response signal of the sensor at a certain position rises by less than 0.5% V0, it can be determined that the cross-linking molding process at that position is complete, where V0 is the initial voltage in the uncompacted state. The real-time cross-linking molding status of each position of the composite material is calculated based on the response voltage.

Images