Method for monitoring internal strain of composite material part in real time based on optical fiber sensor

Abstract

The invention relates to the technical field of stress detection between composite laminates, in particular to a real-time monitoring method for internal strain of a composite material part based on an optical fiber sensor, which comprises the following steps: preprocessing an optical fiber, arranging a polyimide coating outside the optical fiber, and sleeving PI pipes with different sizes; a traditional hot press is modified, and an optical fiber vacuum connector is additionally arranged on a bulkhead outlet tool; preprocessing the optical fiber embedding layer, slotting a thin film material of the optical fiber embedding layer, and cutting a bottom layer aluminum foil; embedding the preprocessed fiber bragg grating into the composite material laminate to be tested; and after data monitored by the optical fiber in real time are processed, a stress-strain result of the measuring point is obtained. The method is suitable for detecting the stress-strain conditions of different layers of the composite material laminated structure in the lamination process, overcomes the defect of stress-strain condition research, accurately calculates the defects in the production process and the warping phenomenon generated in the lamination process, and improves the stability of the product in the service process.

Description

Technical Field

[0001] This invention relates to the field of stress detection technology between composite laminates, and in particular to a method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors. Background Technology

[0002] In the manufacturing process of composite materials, lamination is a crucial step in combining multiple layers of different materials under high temperature and pressure to form a composite structure. However, due to significant differences in the material properties of dissimilar materials (such as mismatched coefficients of thermal expansion and different curing shrinkage rates), residual stress is easily generated at the interface during lamination. This uneven distribution of stress can lead to defects such as warping, delamination, or microcracks in the laminated composite board, seriously affecting the dimensional accuracy, assembly reliability, and long-term service life of the product. For example, statistics show that more than 30% of PCB products need to be reworked or scrapped after lamination, with warping accounting for more than 60% of these issues. Traditional process optimization relies heavily on experience to adjust parameters (such as temperature and pressure curves), but due to the lack of real-time monitoring methods for dynamic changes in interlayer stress, it is difficult to accurately locate stress concentration areas, resulting in long process debugging cycles and high costs.

[0003] In the field of strain testing, existing technologies mainly employ resistance strain gauges, digital image correlation (DIC) technology, or ultrasonic testing. While resistance strain gauges are inexpensive, their adhesive installation is susceptible to environmental temperature and humidity fluctuations, and they can only measure surface strain, unable to penetrate multi-layer structures to obtain interface information. DIC technology relies on optical imaging, requiring a high level of cleanliness in the testing environment, and is difficult to implement in high-temperature, high-pressure, closed lamination equipment. Although ultrasonic testing has a certain penetration capability, its resolution is limited by wavelength, resulting in insufficient ability to capture micron-level interlayer strain, and the equipment is complex and data analysis is time-consuming. Furthermore, all of the above methods are "post-process testing," unable to provide real-time feedback of stress and strain data during lamination, leading to the inability to dynamically optimize process parameters. Residual stress problems often only surface in the finished product stage, resulting in resource waste.

[0004] In recent years, fiber Bragg grating (FBG) sensors have been widely used in structural health monitoring of composite materials due to their advantages such as resistance to electromagnetic interference, high temperature resistance, small size, and distributed embedding capability. The principle is to reflect the strain or temperature change of the measured object through the wavelength shift of the grating, and a single optical fiber can connect multiple grating points to achieve synchronous monitoring at multiple locations. However, existing research mainly focuses on the detection of overall deformation or surface strain of composite materials, and there is still a significant technological gap in monitoring the interfacial behavior of multilayer heterogeneous materials such as composite laminates. Specifically, existing FBG application solutions face two major bottlenecks: first, traditional packaging processes make it difficult to accurately embed FBGs into the micron-level interfaces inside composite material boards, and the high-temperature curing process easily leads to grating failure or signal drift; second, multi-physics coupling (such as temperature gradients and uneven pressure distribution) during lamination introduces complex noise, and existing demodulation algorithms struggle to separate the true interfacial strain signal. Therefore, although FBG technology theoretically has the potential for interlayer monitoring, its practical application in composite material manufacturing has yet to yield mature cases.

[0005] Further analysis revealed that current stress studies on lamination processes are mostly based on finite element simulations or destructive physical tests, lacking in-situ data that directly reflects the dynamic behavior of the interface. Key parameters such as the viscoelastic evolution of the prepreg during the curing stage and changes in the interfacial bonding strength between the copper foil and the resin cannot be quantified using existing testing methods. This technological deficiency has kept the optimization of lamination processes in a "black box" mode for a long time, hindering yield improvements in high-end PCB products such as high-density interconnect boards and high-frequency, high-speed boards. Therefore, developing a method that can monitor interlayer strain in composite materials in real time and with high precision has significant engineering value for promoting process intelligence and reducing warpage defects. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the background technology by proposing a real-time monitoring method for the internal strain of composite material parts based on fiber optic sensors. This method is applicable to fields involving the monitoring and testing of the internal strain of composite laminates, while overcoming the lack of previous research in this area and the problem that fiber optic gratings are difficult to survive under high temperature and high pressure environments.

[0007] The technical solution of the present invention, in its first aspect, provides a method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors, comprising the following specific steps:

[0008] S1. Pre-treat the optical fiber by applying a polyimide coating to the outside of the optical fiber and then covering it with PI tubes of different sizes. The pre-treatment steps include: using high-temperature resistant polymer material polyimide as the coating layer of the optical fiber, and determining the diameter of the external PI tube based on the material properties and thickness of the upper and lower layers at the embedding location.

[0009] Traditional fiber Bragg gratings cannot survive in the environment of printed circuit board lamination, and are extremely prone to breakage, resulting in no test results. Firstly, different cladding fiber and PI tube sizes are selected based on the size of the printed circuit board and the materials of the upper and lower layers. For example, if both upper and lower materials are prepreg materials with a thickness of 0.1mm or more, a 125μm fiber and a 160μm PI tube can be selected; if the upper layer is a thin copper foil and the lower layer is a prepreg, an 80μm fiber and a 110μm PI tube are used; if the upper layer is a thick copper foil and the lower layer is a core board material, an 80μm fiber fitted with a 110μm PI tube and a 160μm PI tube can be used to increase the fiber survival rate.

[0010] Considering the environment of printed circuit board lamination (maximum temperature 230℃, maximum pressure 350psi), ordinary fiber optic coatings, even when fitted with PI tubes, still experience softening and carbonization, affecting data transmission. Polyimide fiber optic coatings, however, have a heat resistance of 300℃, and when combined with the outer PI tube, they can minimize signal drift and loss. Furthermore, a smaller, larger PI tube can be fitted at the point where the fiber exits the edge of the printed circuit board, specifically addressing the issue of excessive shear force at the board edge causing fiber breakage.

[0011] S2. Modify the traditional hot press by adding a fiber optic vacuum connector to the outlet fixture of the chamber wall. The modification method of the traditional hot press is to select a customized high-temperature resistant fiber optic vacuum connector according to the number of test points, tool the interface, and connect the optical cable at both ends inside and outside the cavity wall to complete the real-time data transmission. At the same time, the internal optical cable is fixed to the cavity wall with a wire harness and wrapped around the front end of the hot press.

[0012] Traditional PCB hot presses, which require maintaining a vacuum throughout the lamination process, lack a connector for external communication. To make observations more meaningful, real-time monitoring of internal test points on the printed circuit board is essential. Therefore, the traditional hot press is modified by drilling a circular through-hole at the rear door. A custom-made connector with excellent air isolation and high-temperature resistance is then fixed to it. Epoxy resin is used to fill the gap between the connector and the hole, and a film is placed under the flange to ensure no air leakage. This allows for real-time monitoring of stress and strain at internal points on the printed circuit board during lamination via an external demodulator.

[0013] S3. Pre-process the fiber optic embedded layer by slotting the thin film material of the fiber optic embedded layer and cutting the bottom aluminum foil; use V-shaped slotting to treat the PCB thin film material to reduce stress concentration on the upper fiber, wherein the slotting angle is 60°.

[0014] To improve the survival rate of optical fibers, pretreatment is required before embedding them in the printed circuit board (PCB). Firstly, considering that the aluminum foil on the lower layer of the PCB shrinks when heated, causing the outer optical fiber to stick to the foil and affecting patch cord connection, the aluminum foil under the PCB is trimmed. To avoid excessive shearing force at the edges of the PCB, a groove is created in the layer where the fiber is embedded, forming a V-shaped groove in the prepreg to improve the fiber survival rate.

[0015] S4. Embed the pre-treated fiber Bragg grating into the interior of the composite material layer to be tested; the fiber is arranged in an S-shape in the embedded layer to increase the number of test points and avoid crossover between fibers.

[0016] The prepared optical fibers are embedded into the grooves on the prepreg. The starting section of the fiber is fixed to the bottom steel plate with high-temperature resistant tape to prevent the fiber tail from warping and affecting the results. The placement of the optical fibers on the prepreg is mainly based on the test point. According to the strain direction of the test point, the optical fibers are placed in the same direction along their axes, adopting an overall "S" shape. However, the fibers must not cross each other, otherwise they will be squeezed together and break during the lamination process. After all the optical fibers are fixed on the prepreg, the prepared copper foil or core board is placed on it according to the laminate structure of the printed circuit board. Other layers are tested using the same method. After embedding, it can be placed in a hot press for lamination processing.

[0017] S5. After processing the data monitored in real time by the optical fiber, the stress and strain results at the measuring points are obtained. Based on the axial offset of the optical fiber center, the strain magnitude at the measuring points inside the PCB board is obtained in real time as follows:

[0018]

[0019] Where Δε is the axial strain response, Δλ B λ is the center wavelength offset of the optical fiber. B The fiber center wavelength is given by the fiber grating relative wavelength strain sensitivity coefficient K. ε =0.78.

[0020] Essentially, a fiber optic grating (FOP) is a structure formed within a fiber optic waveguide where the refractive index changes periodically due to variations in the fiber core. This alteration causes mode coupling to occur at specific wavelengths, resulting in singularities in the transmission and reflection spectra of the FOP at those wavelengths. This unique mode coupling occurs within the FOP itself. Utilizing the inherent ultraviolet photosensitivity of optical fibers, periodic strong ultraviolet laser irradiation in space causes doped particles within the fiber core to interact with external incident photons. A spatial phase grating is a structure formed within the fiber core under this interaction, characterized by a periodic or non-periodic refractive index arrangement along the fiber core.

[0021] When light waves pass through a fiber Bragg grating sensor, light of a specific wavelength is reflected back by the fiber Bragg grating, while light of other wavelengths passes through. During the lamination process, axial stress exists at the measuring point, causing a shift in the center wavelength of the fiber Bragg grating. The strain is calculated based on the amount of shift, and then the stress is calculated in conjunction with the material properties.

[0022] A second aspect of the present invention provides an optical fiber sensor, wherein the optical fiber is modified using the method described in steps S1-5.

[0023] A third aspect of the present invention provides a PCB quality monitoring method, which uses the above-described fiber optic sensor and monitors the results of internal stress and strain during the PCB production process according to the above method.

[0024] A fourth aspect of the present invention provides a computer-readable medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors.

[0025] A fifth aspect of the present invention provides an electronic device comprising:

[0026] One or more processors;

[0027] A storage device for storing one or more programs, which, when executed by one or more processors, cause the one or more processors to implement the steps of the above-described method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] This invention utilizes polyimide optical fibers to achieve real-time strain monitoring at internal measurement points of composite material boards during the lamination process, offering several beneficial effects: 1. Filling a technological gap: For the first time, it achieves direct, real-time monitoring of interlayer stress and strain within composite material laminate structures, overcoming the data loss problem caused by the inability of traditional methods to penetrate deep into the interlayer, providing crucial data support for optimizing the lamination process. 2. High precision and reliability: Leveraging the high-temperature resistance and high flexibility of polyimide optical fibers, combined with slotting and copper foil protection design, ensures stable operation of the fiber in high-temperature, high-pressure lamination environments, significantly improving detection accuracy and signal anti-interference capabilities. 3. Defect prediction and quality improvement: By real-time analysis of fiber optic grating displacement signals using a demodulator, the interlayer stress distribution and strain trends can be accurately calculated, allowing for early identification of microcracks, delamination, or warping phenomena generated during lamination, reducing product defects at the source, and improving yield and long-term service stability. 4. Strong process adaptability: The fiber and sleeve diameters can be flexibly selected according to different laminate material thicknesses, compatible with diverse printed circuit board structure designs. The seamless connection between the fusion splice and demodulator simplifies the operation process, making it suitable for large-scale industrial production scenarios. 5. Significant cost-effectiveness: Compared to traditional destructive testing or complex sensor embedding solutions, this method is simple to implement and has a high equipment reuse rate. It reduces testing costs while extending the product process optimization cycle, making it highly valuable for widespread application. 6. Application value: This technology provides an innovative solution for quality control of composite material laminate structures in fields such as electronics manufacturing and aerospace, and has significant engineering implications for improving the reliability of high-precision multilayer printed circuit boards and similar composite materials. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the operation of monitoring the internal strain of a composite material plate using a fiber optic grating, as described in this invention.

[0031] Figure 2 This is a diagram of the optical fiber structure used in this invention;

[0032] Figure 3 This is a schematic diagram of the vacuum connector for connecting optical fibers installed on a hot press according to the present invention;

[0033] Figure 4 This is a side view of the vacuum connector of the present invention;

[0034] Figure 5 This is a schematic diagram of the slotting angle before embedding optical fibers in a composite material plate according to the present invention;

[0035] Figure 6 This is a schematic diagram showing the specific arrangement of optical fibers embedded in the composite material plate in this invention;

[0036] Figure 7 This is a comparison diagram of the offset before and after fiber lamination in this invention;

[0037] Figure 8 This is a schematic diagram illustrating the monitoring of temperature and wavelength drift during the lamination process of composite material plates according to the present invention.

[0038] Reference numerals: 1. PI tube; 2. Coating layer; 3. Optical fiber; 2-1 Threaded hole; 2-2. Fiber core hole; 2-3. Inner connector of the bulkhead; 2-4. Outer connector of the bulkhead; 3-1. Upper material layer; 3-2. Lower material layer. Detailed Implementation

[0039] Example 1

[0040] like Figure 1 As shown, this invention discloses a method for real-time monitoring of internal strain in composite material parts based on fiber optic sensors, comprising the following steps:

[0041] S1. Pre-processing of ordinary optical fiber 3 is necessary. Ordinary optical fiber 3 cannot withstand the high temperature and pressure environment during the lamination process of the printed circuit board, and is prone to breakage inside, resulting in no output. Pre-processing of optical fiber 3 is required, specifically as follows: Figure 2 As shown, the designed optical fiber consists of three layers. The first layer is a PI tube (1): its function is to improve the fiber's pressure and temperature resistance, enhancing its survival rate during lamination, especially at the edges of the printed circuit board, preventing fiber breakage due to excessive shear force. This design uses PI tubes of different diameters depending on the thickness of the materials between different layers, providing high accuracy for subsequent measurements. The second layer is a polyimide coating, which has strong high-temperature resistance and will not soften or carbonize under the high temperatures of lamination, greatly improving the fiber's heat resistance, reducing signal attenuation, and providing feasibility for fiber optic embedded monitoring.

[0042] S2. Modifying a traditional hot press: Considering the greater significance of real-time monitoring of printed circuit boards during the lamination process, it is necessary to perform perforation treatment on the hot press. Traditional hot presses, because they require maintaining a vacuum environment inside the cavity, do not have electrical or optical signal connectors on the cavity walls to connect to the outside. The entire machine uses a barometer on top to determine whether the internal air pressure has reached a vacuum environment. Therefore, to achieve real-time monitoring, perforation treatment must be performed on the machine cavity walls.

[0043] This invention designs an optical fiber vacuum connector, including an inner connector 2-3 and an outer connector 2-4; as follows: Figure 4 The image shows a side view of the connector. This connector is a double-connector design; the central flange can be installed on either the inner or outer wall of the machine, and the two side connectors connect to the optical cables inside and outside the cavity, respectively. Figure 3The inner interface of the connector shown has four corresponding blind holes drilled on a hot press. The connector is then fixed in the corresponding position, and a cover is placed on top. When in use, the cover is opened and the optical cable is inserted. Figure 3 2-2 in the diagram refers to the fiber core hole. The number of internal holes can be determined based on the number of detection points and the number of interfaces of the demodulator. The optical cable outside the cavity is divided into an equal number of APC connectors according to the number of core holes on the connector and connected to the demodulator. The optical cable inside the cavity branches out multiple longer bare fibers at the tail and is fixed to the cavity wall with a wire bundle.

[0044] Considering the strength requirements of the entire hot press, drilling holes in the side walls would be both deep and difficult. Therefore, it was decided to drill holes at the bottom of the rear door of the hot press to install the connectors. Rubber sheets were placed under the flanges to ensure a vacuum environment inside. Furthermore, considering the inconvenience and difficulty of splicing the optical fibers inside the printed circuit board and on the optical cable at the rear door, the internal optical cable was moved along the cavity wall to the front door, greatly improving the ease of wiring.

[0045] S3. Pre-treatment of the fiber embedding layer: Grooving is performed on the material layer below the fiber placement to reserve space for fiber survival. Based on research on fiber breakage, such as... Figure 5 As shown, an equilateral triangular groove is cut into the lower material layer 3-2. This groove allows the optical fiber to be placed smoothly while simultaneously transferring the pressure on the fiber during lamination to the lower material layer in two directions, preventing stress concentration on the fiber body and thus avoiding fiber breakage. The upper material layer 3-1 covers it. To ensure more even heat distribution throughout the material layers, an aluminum foil layer is typically placed at the bottom of the printed circuit board. However, the aluminum foil shrinks when heated, and the outer optical fiber may fuse with it, affecting subsequent splicing processes. Therefore, before placing the sample into the laminator, the outer optical fiber placement area is trimmed to allow space for placement, improving fiber survival rate and the accuracy of fiber testing.

[0046] S4. Embed the fiber Bragg grating inside the composite material plate, such as Figure 6As shown, the overall arrangement adopts an S-shaped pattern. This effectively avoids fiber optic crossings within the same layer while maximizing the testing of stress and strain at different locations. Each black square in the diagram represents a pre-etched grating point, and each grating point can be used to test the axial stress at that point. After the internal fiber optic arrangement is complete, the ends of the fibers must be secured to the printed circuit board with high-temperature resistant tape to prevent them from lifting and causing movement of the fibers within the printed circuit board, which could lead to misalignment with the original test points. When embedding the fibers, care must be taken to ensure that fibers within the same layer do not cross each other. If testing the same point on different layers is required, there should be as many material layers as possible in between to prevent the strength and stress of the fibers from intersecting and causing both fibers to break. After all fibers are properly arranged, the sample can be placed in a hot press for lamination.

[0047] S5. To verify the feasibility of the method of the present invention, the strain of the composite material plate before and after lamination was observed and recorded using a DIC device. The strain at the measuring point before and after lamination was found to be 6.8 × 10⁻⁵ m / m. The wavelength of the embedded optical fiber was 1525–1565 nm. The data collected in the demodulator was processed in real time. According to the fiber grating coupling theory, its Bragg wavelength depends on the fiber grating period Λ and the effective refractive index n. eff Any physical process that can change these two parameters of the optical fiber will lead to a drift in the Bragg wavelength. The fiber grating resonance equation is shown in equation (1).

[0048] λ B =2n eff Λ (1)

[0049] Where: n eff λ is the effective refractive index of the fiber core; Λ is the fiber grating period; λ is the effective refractive index of the fiber core. B The wavelength is the center wavelength of the optical fiber.

[0050] The shift in the center wavelength of the fiber grating is mainly caused by axial stress, which is due to the mechanical stretching or compression of the fiber and the elastic-optical effect. This can be described by the following equation (2):

[0051] Δλ B =2n eff ·ΔΛ+2Δn eff ·Λ (2)

[0052] In the formula: ΔΛ is the elastic deformation of the optical fiber itself under stress; Δn eff Δλ represents the refractive index change caused by the elastic effect of the optical fiber. B This represents the center wavelength offset of the optical fiber.

[0053] Based on the elastic-optical effect of the material,

[0054]

[0055] In the formula: p 11 p 12 ε is the pocket coefficient, v is the Poisson's ratio, and Δε is the axial strain response.

[0056] Without considering the influence of external environmental temperature and other factors, substituting the above equation into equation (2) and dividing by λ at the same time B The relative wavelength shift sensitivity caused by the photoelastic effect can be obtained, as shown in equation (4).

[0057]

[0058] In equation (4), the relative wavelength strain sensitivity coefficient K of the fiber grating is introduced. ε Let K ε for

[0059]

[0060] For pure fused silica, p 11 =0.121, p 12 =0.270, ν=0.17, n eff =1.456, from which we can obtain the constant K. ε =0.78. The longitudinal strain sensitivity coefficient of fiber optic grating wavelength drift caused by the photoelastic effect is shown in equation (6) below.

[0061]

[0062] Depend on Figure 7 We can obtain,

[0063]

[0064] The strain at this measuring point is 7 × 10⁻⁶. -5 The error was 2.9% when compared with the result measured by DIC, which meets the expected error and proves that the method is reliable.

[0065] Meanwhile, the method of the present invention has the feature of real-time monitoring, such as... Figure 8 As shown, any segment on the curve can be used to calculate the strain within a certain temperature range or a certain time range.

[0066] It is evident that fiber optic grating sensors, as strain-sensitive elements, possess excellent linear strain sensing characteristics. They can directly convert the grating center wavelength offset into structural strain, thereby directly obtaining the strain inside the printed circuit board. Then, the stress at that point can be calculated based on the material parameters of the material layer at the measured point.

[0067] In summary, this invention establishes a testing method for real-time detection of internal strain in composite material plates during lamination using polyimide optical fibers. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0068] Example 2

[0069] This embodiment provides an optical fiber sensor. First, the optical fiber is modified using the method described in steps S1-5 of Embodiment 1. After modification, it forms as shown in the figure. Figure 2 The structure shown has an outermost PI layer 1, a middle polyimide coating layer 2, and an innermost optical fiber 3.

[0070] In this embodiment, the PI layer 1 improves the fiber's withstand voltage and temperature, enhancing its survival rate during lamination, especially at the edges of the printed circuit board, preventing fiber breakage due to excessive shear force. Furthermore, this design uses PI tubes 1 of different diameters depending on the thickness of the materials between different layers, providing high accuracy for subsequent measurements. The fiber coating in this design uses a polyimide coating, which has strong high-temperature resistance and will not soften or carbonize under the high temperatures of lamination, significantly improving the fiber's heat resistance, reducing signal attenuation, and providing feasibility for fiber optic embedded monitoring.

[0071] Example 3

[0072] This embodiment provides a PCB quality monitoring method, which uses the improved fiber optic sensor in Embodiment 2 and monitors the results of internal stress and strain during the PCB production process according to the method in Embodiment 1.

[0073] In this embodiment, the fiber optic grating sensor, as a strain-sensitive element, has excellent linear strain sensing characteristics. It can directly convert the grating center wavelength offset into structural strain, thereby directly obtaining the strain inside the printed circuit board. Then, the stress at that point is calculated based on the material parameters of the material layer at the measured point. The measured results are compared, and the error is found to be 2.9%, which meets the expected error, proving that the method is reliable.

[0074] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for real-time monitoring of internal strain in composite material parts based on fiber optic sensors, characterized in that, The specific steps include the following: S1. Pre-treat the optical fiber by applying a polyimide coating to the outside of the optical fiber and covering it with PI tubes of different sizes. S2. Modify the traditional hot press and install the fiber optic vacuum connector on the bulkhead outlet tooling; S3. Pre-process the optical fiber embedding layer by slotting the thin film material of the optical fiber embedding layer and cutting the bottom aluminum foil. S4. Embed the pretreated fiber grating into the interior of the composite material laminate to be tested; S5. After processing the data monitored in real time by the optical fiber, the stress and strain results of the measuring point are obtained.

2. The method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors according to claim 1, characterized in that, The pretreatment step in step S1 includes: using high-temperature resistant polymer material polyimide as the coating layer of the optical fiber, and determining the diameter of the external PI tube according to the material properties and thickness of the upper and lower layers at the embedding location.

3. The method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors according to claim 1, characterized in that, In step S2, the traditional hot press is modified by selecting a customized high-temperature resistant fiber optic vacuum connector according to the number of test points, tooling the interface, connecting optical cables at both ends inside and outside the cavity wall to complete real-time data transmission, and fixing the internal optical cable to the cavity wall with a wire harness and wrapping it around the front end of the hot press.

4. The method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors according to claim 1, characterized in that, In step S3, the PCB film material is treated with a V-groove to reduce stress concentration on the upper optical fiber, wherein the groove angle is 60°.

5. The method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors according to claim 1, characterized in that, In step S4, the optical fibers are arranged in an S-shape in the embedded layer to increase the number of measurement points and avoid crossover between optical fibers.

6. The method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors according to claim 1, characterized in that, In step S5, the strain magnitude of the measuring point inside the PCB board is obtained in real time based on the axial offset of the fiber center: Where Δε is the axial strain response, Δλ B λ is the center wavelength offset of the optical fiber. B The fiber center wavelength is given by the fiber grating relative wavelength strain sensitivity coefficient K. ε =0.

78.

7. An optical fiber sensor, characterized in that, The optical fiber is modified using the method described in claim 1.

8. A PCB quality monitoring method, characterized in that, Using the fiber optic sensor of claim 7, and the method described in any one of claims 1-6, the results of monitoring internal stress and strain during PCB manufacturing are obtained.

9. A computer-readable medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors as described in any one of claims 1-6.

10. An electronic device, characterized in that, include: One or more processors; A storage device for storing one or more programs, which, when executed by one or more processors, cause the one or more processors to implement the method for real-time monitoring of internal strain of composite material parts based on fiber optic sensors as described in any one of claims 1-6.

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