Composite material liquid forming whole process real-time monitoring method based on grid type fiber sensor

Abstract

The invention discloses a real-time monitoring method for the whole process of liquid forming of a composite material 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 two electrodes of the sensor with an excitation and acquisition module of a monitoring system; s2, in the preforming process, pressure is applied to compact the prefabricated body in the mold, and the voltage signal change of the sensor is collected in real time to reflect the compaction state; s3, opening the resin filling channel, injecting the resin to impregnate the prefabricated body, collecting the voltage signal change of the sensor in the resin injection process in real time to reconstruct the position change of the flowing front edge during resin filling, and closing the resin inlet and outlet after filling is completed; and S4, monitoring the real-time forming quality of the composite material by collecting the voltage signal change of the sensor in the resin cross-linking process in the resin cross-linking forming process. The grid type fiber sensor is adopted, and the whole process of composite material liquid forming can be monitored under the condition that the performance of the prefabricated body and the resin flowing condition are not affected.

Description

Technical Field

[0001] The invention relates to a real-time monitoring method for the entire composite material liquid forming 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 transit, 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 oriented arrangement and pressurization of fiber preforms before molding to improve the mechanical properties and durability of composite materials. The process of resin filling and cross-linking is 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] Some monitoring methods for composite liquid molding have been disclosed in the prior art, such as using optical fiber to monitor the change of optical fiber refractive index or using reinforcing fiber embedded with carbon nano conductive material to monitor the change of conductivity to monitor the liquid resin molding. Both of the above methods can monitor the liquid molding of composite materials, but optical fiber is easily affected by temperature and is not suitable for continuous monitoring in a variable temperature environment. The synthesis process of reinforcing fiber coated with carbon nano conductive material is complicated and expensive, which is not suitable for industrial production and development.

[0004] With the widespread application of resin-based composite materials in the fields of aviation, automobiles, new energy, etc., the requirements for the performance of the materials involved are increasing. In this context, composite molding technology with simple operation, good quality and fast molding speed has attracted more and more attention. Among them, composite liquid molding technology is conducive to rapid molding and improving production efficiency. Real-time monitoring data of molding has become more important for improving product quality. Summary of the invention

[0005] The purpose of the present invention is to provide a method for real-time monitoring of the entire process of composite liquid molding based on a grid-type fiber sensor. The present invention places a grid-type magnetic fiber sensor in the preform interlayer, so that the sensor grid fiber is parallel to the resin flow direction, and monitors the preset grid-type fiber sensor voltage response changes in real time during the fiber preform compaction, resin filling, and resin cross-linking process to monitor the entire process of liquid phase resin flow and molding. The grid-type fiber sensor and signal output terminal used are small in size and stable and reliable, and can monitor the entire process of composite liquid molding without affecting the compaction quality of the preform and the injection of resin.

[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 through a grid-type 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: Lay and compact multiple layers of fiber cloth according to the preset molding requirements of the composite material to obtain a preform; during the laminating process, bury the grid-type fiber sensor obtained in step 1 between the two layers of fiber cloth at the position to be monitored and fix it according to the preset monitoring requirements; then place the obtained preform in a vacuum bag, and connect the grid-type fiber sensor to the monitoring system through the interface lead;

[0009] 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 according to the stress sensitivity curve of the sensor; after the preform is compacted, vacuum infusion resin is performed, and the response voltage of sensors at each position 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 of the internal space of the preform during the resin flow filling process is determined, and the flow front change state of the resin 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 according to the response voltage of each sensor to determine the cross-linking state of the resin 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 interface stress sensing performance.

[0011] As a preferred embodiment of the present invention, the fiber grid sensor prepared by the steps of the present invention is flexible and can be bent at a large angle. Its beneficial effect is that the sensor can be deformed in coordination with the preform during the compaction process, and local monitoring of curved surfaces or special-shaped structural parts can be achieved.

[0012] As a preferred solution of the present invention, each amorphous fiber of the grid sensor is spaced 5mm-50mm apart and the two electrode ports are connected to the conductive copper wire with an inner diameter of 40-200μm by cold welding. During the sensor arrangement process, the lead wire of the grid sensor is led out from the edge of the mold. The beneficial effect is that the sensor signal transmission is stable and not affected by the resin, which can effectively reduce the disturbance effect of liquid resin injection on the sensor and ensure the continuity and stability of the sensor response signal during the resin flow process.

[0013] As a preferred embodiment of the present invention, when the grid sensor is implanted, the length direction of the grid is consistent with the direction of resin flow during the molding process. The beneficial effect is that the resin filling condition and the resin cross-linking state of the resin on the plane of the fiber preform in the local area can be monitored by a single grid fiber sensor. In addition, the grid sensors at different positions and layers can be used for three-dimensional reconstruction of the resin flow front and the curing cross-linking state in the preform.

[0014] As a preferred embodiment of the present invention, the optimal length of the grid-type fiber placed in the reinforcement interlayer is 10-280 mm on one side, the excitation source frequency is 5-200 MHz, and the amplitude is 1-7 V. The beneficial effect is that when the sensor fiber length matches the excitation source frequency and voltage, the voltage signal has high sensitivity and low energy consumption.

[0015] In view of the problems of existing composite 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 liquid molding process in real time at low cost without affecting the compaction quality of the preform, the resin flow filling, and the performance of the material after molding. It is beneficial to optimize the molding process, improve the quality of composite materials products, and reduce manufacturing costs.

[0016] The present invention can monitor the whole process of composite material preform compaction, resin filling and cross-linking molding in a closed environment. In addition, the grid-type fiber sensor provided by the present invention has the characteristics of small size, and does not cause any damage to the material, and can ensure the integrity and mechanical properties of the final molding of the resin-based composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the response curve of the voltage signal of the grid-type fiber 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 3The voltage signal of the grid-type fiber sensor in Example 1 changes 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] Embodiment 1:

[0023] This embodiment is a process of monitoring the liquid molding of composite materials using the grid-type fiber sensor of the present invention in the vacuum-assisted resin transfer molding process of low-viscosity liquid-phase epoxy resin. This embodiment uses Co-Fe-Si-B-based amorphous alloy fibers prepared by Taylor spinning as the sensitive element of the grid-type fiber sensor, and the epoxy resin cross-linking process is 100°C heat preservation and curing. 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: Arrange the amorphous alloy fibers of the same length in parallel by a fixture, connect the adjacent fibers end to end by copper wires to form a grid, fix them into a grid model, obtain a 2D grid fiber sensor, and then calibrate the stress sensitivity curve P=f(V) of the grid fiber sensor under step loading conditions by 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 interlayer of the preform;

[0028] Step 4: Place the preform prepared in step 3 in the mold of step 2. Inside the mold from bottom to top are the aluminum mold, preform, grid-type fiber sensor, demolding 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 5-200MHz and an amplitude of 1-7V to collect the voltage response signal of the grid sensor.

[0030] Step 6: Compact the preform in the mold through the action of the vacuum pump and atmospheric pressure, and monitor the change of the voltage signal of the grid-type fiber sensor at the same time. After evacuating to vacuum, turn off the vacuum pump and maintain the pressure for 15-60 minutes to ensure that the vacuum degree in the mold remains unchanged. While the preform is compacted and maintained, collect the change of the voltage response signal of the grid-type sensor.

[0031] Step 7: Open the vacuum pump and the resin inlet and outlet valves to allow the liquid phase resin to fill the compacted preform. When the preform is completely filled with resin and the internal bubbles are discharged, close the resin inlet and outlet and the vacuum pump. While the resin is flowing, collect the changes in the grid 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-type fiber sensor during the resin cross-linking process.

[0033] The calibration result of the stress sensitivity curve of the grid-type fiber sensor used in this embodiment is as follows: Figure 1 As shown in Figure 1, as the loading stress gradually increases, the voltage signal gradually decreases. Figure 2 The figure shows the principle diagram of monitoring the composite material liquid phase molding, which mainly includes a resin barrel 1, a signal generator 2, an aluminum plate mold 3, glass fiber 4, a demoulding cloth 5, a flow guide net 6, a vacuum bag 7, an oscilloscope 8, a data recording computer 9, a resin collection barrel 10, and a vacuum pump 11. The dotted frame is a 2D grid fiber sensor, in which the light-colored part is a conductive copper tube connected to the sensor. Figure 3 The figure shows the voltage signal change curve of the two-dimensional grid fiber sensor monitoring the entire process of composite material liquid molding in real time at 100°C. Figure 4 The figure shows the resin filling process curve of the composite material liquid molding process monitored in real time by a two-dimensional grid fiber sensor at 100°C.

[0034] This example is cured at 100°C. 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-type fiber sensor gradually decreases. During the pressure holding process, it can be seen that the voltage signal of the 2D grid-type fiber sensor remains unchanged, which means 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 2D grid-type fiber sensor increases, the sensor voltage signal further decreases. During the resin cross-linking process, the stress around the 2D grid-type fiber sensor gradually changes from atmospheric pressure to the stress of the resin cross-linking process, and the sensor voltage signal gradually rises. Figure 4 From the voltage variation 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, and the voltage signal of the 2D grid fiber sensor can reflect the advancement of the flow front.

[0035] The above-mentioned embodiments only express optional implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached 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 in sequence, and an off-line pressure test is used to determine a stress sensitivity curve of the grid-type fiber sensor; Step 2: Lay and compact multiple layers of fiber cloth according to the preset molding requirements of the composite material to obtain a preform; during the laminating process, bury the grid-type fiber sensor obtained in step 1 between the two layers of fiber cloth at the position to be monitored and fix it according to the preset monitoring requirements; then place the obtained preform in a vacuum bag, and connect the grid-type fiber sensor to the monitoring system through the interface lead; 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 according to the stress sensitivity curve of the sensor; after the preform is compacted, vacuum infusion resin is performed, and the response voltage of sensors at each position 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 of the internal space of the preform during the resin flow filling process is determined, and the flow front change state of the resin 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 according to the response voltage of each sensor to determine the cross-linking state of the resin at different positions.

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 is characterized in that: The preparation method of the grid fiber sensor is as follows: magnetic fibers of the same length are arranged in parallel, adjacent magnetic fibers are connected end to end by copper wires to form a grid, one or more grids connected in series form a grid sensor, and 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 is characterized in that: The method for determining the stress sensitivity curve of the sensor in step 1 is as follows: placing the formed grid-type sensor between two layers of fiber cloth with a specific area S, and applying a step load force F to the sensor using 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 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 is 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 connected, a double layer of vacuum glue is 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 compaction 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 ) Calculate the internal pressure of the fiber preform, and then determine and adjust the compaction state of the preform.

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 vacuum infusion resin infusion process of step 3, when the resin flow front reaches the sensor grid, the pressure near the sensor increases, resulting in a decrease in the sensor response signal; 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 begins to arrive at the position; and when the sensor response signal is stable and the change is less than 0.5% V0, it is determined that the resin has completely infiltrated the sensor at the position; wherein V0 is the initial voltage in the uncompacted state; according to the sensor response signal during the resin filling process, the arrival time of the resin at each position in the length direction of the grid is confirmed in turn, and the resin flow front in the preform is reconstructed by the sensor response conditions at different positions.

7. 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 of step 3, the stress caused by part of the vacuum is replaced by the cross-linking of the resin, so that the voltage of the grid sensor gradually increases; specifically, when the vacuum conduction resin infusion is completed and the response signal of the sensor begins to rise, it is considered that the resin cross-linking process has begun, and 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 completed, wherein V0 is the initial voltage in the uncompacted state; the real-time cross-linking molding state of each position of the composite material is obtained by solving the response voltage.

Images