An in-situ monitoring device for fiber optic gratings in the internal and external multi-field coupling evolution process

Abstract

This invention discloses an in-situ monitoring device for the coupling evolution of internal and external multi-field processes using fiber optic gratings, belonging to the field of propellant curing and testing technology. The invention includes a gas supply and pressurization system, a pressurization and curing monitoring system, and a multi-field data acquisition system. Temperature and strain fiber optic sensors are deployed inside the pressurization and curing chamber, and their leads are sealed through a fiber feedthrough structure. Strain gauges are deployed on the outer wall of the chamber to measure the structural response of the shell. Simultaneously, a pressure sensor is used to achieve synchronous measurement of multiple physical fields, including temperature, strain, and pressure. This invention enables in-situ real-time monitoring of the entire propellant loading and pressurization process, acquiring information on the coupling evolution of internal and external multi-field processes. It provides reliable data support for curing process optimization and structural integrity assessment, and has advantages such as structural safety and reliability, high measurement accuracy, and wide applicability.

Description

Technical Field

[0001] This invention relates to the field of propellant curing and testing technology, specifically to an in-situ monitoring device for fiber optic gratings of the internal and external multi-field coupling evolution process. Background Technology

[0002] With the continuous increase in the solid rocket motor load ratio, the thermal stress level generated by the propellant grain during curing and subsequent cooling processes has increased significantly, which has a significant impact on the engine's structural integrity, interfacial bonding performance, and service safety. To reduce the residual stress of the propellant grain under high load conditions and improve the interfacial bonding quality, pressure curing molding technology has been gradually adopted in engineering. By applying external pressure during the curing process, the composite material shell undergoes controllable expansion, thereby regulating the contraction behavior and stress distribution of the propellant grain.

[0003] A typical pressure curing process includes stages such as propellant slurry casting, pressurized heating and curing, isothermal and pressure holding, and cooling and depressurization. During this process, the composite shell undergoes elastic deformation under internal pressure, while the propellant grain shrinks in volume during the curing reaction and cooling. In the depressurization stage, the shell's rebound can exert secondary constraints on the propellant grain, thus affecting the final residual stress distribution and interface compaction. Therefore, the pressure curing process is essentially a multi-physics coupled evolution process involving temperature field, stress field, structural deformation, and curing reaction; its mechanism is complex and highly sensitive to process parameters.

[0004] However, existing pressure curing processes and testing equipment still have the following shortcomings: (1) Most devices use high-pressure gas to directly contact the drug slurry for pressurization, which poses certain safety risks and may also have an adverse effect on the integrity of the drug column structure. (2) Existing monitoring methods mainly rely on external pressure and temperature measurement, or indirectly infer the state of the drug column through a single physical quantity, making it difficult to obtain the real evolution information of internal temperature and strain of the drug column during the solidification process; (3) There is a lack of effective synchronous measurement methods for the coupling effect between the composite shell and the propellant grain, making it difficult to reveal the intrinsic relationship of "shell expansion - propellant grain contraction - interface stress evolution"; (4) Existing measurement methods are mostly local or single-point measurements, lacking the ability to conduct distributed monitoring at multiple locations along the radial and axial directions, making it difficult to reflect the spatial non-uniformity characteristics during the curing process; (5) There is a lack of high-precision in-situ monitoring technology that can work stably for a long time under pressure, especially under the condition of temperature-strain cross sensitivity, the accuracy of measurement results is difficult to guarantee.

[0005] Furthermore, traditional methods based on strain gauges or external measurements often only reflect the deformation response of the shell or surface structure, and cannot directly obtain the true strain state inside the propellant grain, resulting in significant uncertainties in the study of the curing mechanism and the verification of numerical models.

[0006] Therefore, in order to improve the structural integrity of solid propellant charges, enhance the safety and controllability of the pressurized curing process, and achieve accurate characterization of the multi-physics coupling behavior during curing, it is necessary to design an in-situ monitoring device and method capable of simultaneously monitoring the propellant interior and exterior, possessing multi-point distributed measurement capabilities, and operating stably under pressure. Based on this, this invention proposes an in-situ fiber optic grating monitoring device for the evolution of internal and external multi-field coupling. Summary of the Invention

[0007] 1. The technical problem to be solved by the present invention The purpose of this invention is to provide an in-situ monitoring device for fiber optic gratings in the internal and external multi-field coupling evolution process to solve the problems mentioned in the background art.

[0008] 2. Technical Solution To achieve the above objectives, the present invention provides the following technical solution: This invention addresses the problem of insufficient multi-field coordinated monitoring between the propellant grain's interior and the outer shell during the pressurization and curing process of traditional solid propellants. It proposes an in-situ monitoring device based on fiber optic grating sensing technology, coupling internal and external multi-fields. By constructing a multi-point distributed temperature and strain fiber optic sensing array inside the pressurization and curing cavity, and combining it with strain measurements outside the cavity, the device achieves simultaneous acquisition and coupled analysis of the temperature field, strain field, pressure field, and structural response during the curing process. Compared to traditional methods using indirect thin-film measurement or single-physical-quantity monitoring, this invention can directly acquire the true internal response of the propellant, improving measurement accuracy and safety. Specifically, it includes the following: An in-situ monitoring device for fiber optic gratings in the internal and external multi-field coupling evolution process includes a gas supply and pressurization system, a pressurization and curing monitoring system, and a multi-field data acquisition system; The gas supply and pressurization system includes a high-pressure nitrogen cylinder, a pressure reducing valve, a metal hose, a three-way connector, a manual valve, a solenoid valve, and a pressurized air inlet pipeline; the high-pressure nitrogen cylinder is fixed on a cylinder rack to prevent tipping, and the pressure reducing valve is threaded onto the high-pressure nitrogen cylinder; The pressure curing monitoring system includes an external explosion-proof cavity, an internal pressure curing cavity, an upper flange of the external explosion-proof cavity, a lower flange of the external explosion-proof cavity, an upper flange of the internal pressure cavity, a lower flange of the internal pressure cavity, an upper sealing cover, a pressure sensor, fiber optic feeder A, fiber optic feeder B, a temperature measuring fiber optic sensor, a strain measuring fiber optic sensor, a cross-shaped fixing bracket, a stainless steel fixing disc, a temperature measuring fiber optic pipeline, a strain measuring fiber optic pipeline, an external strain gauge, and an aviation socket. The multi-field data acquisition system includes a fiber optic demodulator, fiber optic transmission line, pressure transmission line, multi-channel data acquisition unit, fiber optic sensing signal transmission pipeline, temperature fiber optic sensor, strain fiber optic sensor, pressure sensor, temperature fiber optic pipeline, strain fiber optic pipeline, fiber optic feeder A, fiber optic feeder B, and aviation socket.

[0009] Preferably, the high-pressure nitrogen cylinder achieves precise control of the output gas pressure by adjusting the pressure reducing valve, so that the high-pressure gas meets the pressure requirements of the pressure curing test; the downstream of the pressure reducing valve is connected to a three-way connector via a metal hose, one end of the three-way connector is installed on a solenoid valve for automatic control of the pressurization process, and the other end of the three-way connector is installed on a manual valve for system depressurization and emergency pressure relief control; the outlet of the solenoid valve is installed on the pressurized gas inlet pipeline.

[0010] Preferably, an insulated box is installed outside the external explosion-proof cavity. The external explosion-proof cavity provides safety protection for the internal structure during the pressure curing process, preventing structural damage and leakage due to abnormal operating conditions. The internal pressure curing cavity is located inside the external explosion-proof cavity, and the end of the pressure inlet pipe away from the solenoid valve is connected to the internal pressure curing cavity. The internal pressure curing cavity is made of composite material and is used to contain the propellant charge and withstand the internal pressure load during the pressure curing process, causing it to produce measurable elastic deformation during pressurization, thereby enhancing the sensitivity of external strain monitoring. The upper flange and lower flange of the internal pressure curing cavity are bolted to the external explosion-proof cavity, and the bottom of the internal pressure curing cavity is bolted to the lower surface of the lower flange. The upper sealing cover is connected to the gas supply system via a pressurized gas inlet pipe, allowing high-pressure gas to stably enter the internal pressurized curing chamber. A pressure sensor is installed at the interface on the side wall of the upper cover of the chamber to measure pressure changes within the chamber in real time during the pressurized curing process. An array of fiber optic sensors is installed inside the internal pressurized curing chamber: the temperature-measuring fiber optic sensor and the strain-measuring fiber optic sensor are arranged axially along the internal pressurized curing chamber and positioned and supported by a cross-shaped fixing bracket. The cross-shaped fixing bracket uses stainless steel fixing discs for upper and lower limit positioning, ensuring the fiber optics remain vertically stable during curing. An isolation sleeve is installed outside the temperature-measuring fiber optic sensor to eliminate the influence of strain on temperature measurement during curing, achieving decoupled measurement of temperature and strain.

[0011] Preferably, the pressure sensor is installed at the pressure interface of the internal pressure curing chamber to measure the pressure change inside the chamber in real time during the pressure curing process, and transmits the measurement signal to the multi-channel data acquisition unit via a pressure transmission line; the temperature-measuring fiber optic sensor is installed at different positions in the pressure curing chamber to measure the temperature change of the propellant charge in real time during the pressure curing process; the temperature-measuring fiber optic sensor is led out through fiber feedthrough A and a temperature-measuring fiber optic tube; and is connected to a fiber optic grating demodulator through the temperature-measuring fiber optic tube; the strain-measuring fiber optic sensor is led out through fiber feedthrough B and a strain-measuring fiber optic tube; The external strain gauge is installed on the outer wall of the internal pressure-curing chamber to measure the expansion and rebound deformation of the outer wall during pressurization and depressurization; it is connected to an external data acquisition system via an aviation socket; the fiber optic demodulator demodulates the wavelength signal output by the temperature-measuring fiber optic sensor, converts it into a corresponding temperature signal, and transmits it to the multi-channel data acquisition unit; the strain-measuring fiber optic sensor is installed at different locations inside the internal pressure-curing chamber to measure the strain evolution information of the propellant charge during the pressure-curing process in real time; the strain-measuring fiber optic sensor is led out through a fiber feedthrough B seal and connected to a strain-measuring fiber optic cable. The fiber optic cable is connected to the fiber optic demodulator. The external strain gauge is connected to the multi-channel data acquisition unit via a strain data transmission line and an aviation socket, enabling stable transmission of the external strain signal to the data acquisition end. Fiber optic feedthroughs A and B are used for the independent lead-out of the temperature-measuring fiber optic sensor and the strain-measuring fiber optic sensor, respectively, under high-pressure sealing conditions, to ensure the sealing and reliability of different types of fiber optic signals during transmission. The temperature-measuring fiber optic cable and the strain-measuring fiber optic cable constitute the fiber optic sensing signal transmission cable, used to stably guide the fiber optic sensing signal from inside the cavity to the external fiber optic demodulator, and to optimize the fiber optic signal transmission. It serves a protective and guiding function, preventing signal quality from being affected by bending, pulling, or localized pressure during device operation; the fiber optic demodulator is used to demodulate the optical signals output by the temperature and strain fiber optic sensors in real time, converting wavelength changes into temperature and strain signals, and transmitting the converted signals to the multi-channel data acquisition unit; the multi-channel data acquisition unit is used to synchronously acquire, store, and process temperature, strain, and pressure signals, realizing unified monitoring and time-synchronized management of the internal temperature field, internal strain field, external wall structure response, and pressure field during propellant loading and solidification.

[0012] Preferably, the upper flange of the external explosion-proof cavity is fixedly installed with an upper sealing cover by bolts. A sealing groove is formed on the outer side of the bolt holes of the upper flange and the upper sealing cover, and an O-ring is installed in the sealing groove. The bolt includes a screw and a nut. The nut is threaded onto the outer surface of one end of the screw. A detection groove is formed on the outer surface of the middle part of the screw, and pressure plates are evenly installed circumferentially in the detection groove. Rotary rings are slidably installed at both ends of the pressure plates, and the rotating rings are rotatably installed at both ends of the sealing groove of the screw. The O-ring is sleeved on the outside of the screw. An auxiliary groove is evenly formed in the detection groove near the inner surface of the pressure plate of the screw, and a pressure column is slidably installed in the auxiliary groove. A buffer spring is fitted on the outer surface of the column, with one end of the buffer spring fixedly installed on the pressure column and the other end fixedly installed in the screw auxiliary groove. A positioning groove is opened in the middle of the screw, and a linkage shaft is slidably installed in the positioning groove. A return spring is fixedly installed at one end of the linkage shaft, and a sealing piston plate is fixedly installed at the other end of the linkage shaft. A hydraulic cylinder is slidably installed on the outer surface of the sealing piston plate. The hydraulic cylinder is fixedly installed in the screw positioning groove. A trapezoidal groove is linearly opened on the linkage shaft, and the pressure column is slidably installed in the trapezoidal groove. The hydraulic cylinder forms a sealed cavity through the sealing piston plate. An indicator is injected into the hydraulic cylinder cavity. The indicator is a liquid with a special color.

[0013] Preferably, the metal hose adopts a high-pressure resistant flexible structure and connects each gas path component through a threaded seal to improve sealing performance and reduce the impact of vibration on the system; the pressurized air inlet pipeline and the internal pressurized curing chamber adopt a sealed connection structure, so that high-pressure gas can enter the internal pressurized curing chamber uniformly and stably, avoiding local impacts from interfering with the internal structure; multiple fiber optic grating sensor array measuring points are axially distributed in the internal pressurized curing chamber to obtain temperature and strain information at different locations inside the propellant charge; the gas supply system is equipped with a pressure monitoring interface for connecting pressure sensors to realize real-time monitoring and feedback adjustment of the pressurization process; the fiber optic grating demodulator adopts a multi-channel demodulation method, which can simultaneously receive signals from multiple fiber optic sensors to achieve distributed multi-point synchronous measurement.

[0014] Preferably, the strain-measuring fiber optic sensor is in direct contact with the propellant charge to obtain the actual strain response during the propellant curing process; the fiber optic sensor is positioned by a cross-shaped fixing frame and a stainless steel fixing disc to keep the fiber optic cable vertical during the pressure curing process and avoid bending or displacement.

[0015] Preferably, the multi-channel data acquisition unit has a time synchronization function, which performs unified time calibration on temperature, strain, and pressure data to achieve synchronous acquisition and alignment of multi-physical field data; fiber optic sensing signals and electrical signals are transmitted in separate channels to reduce signal interference and improve data acquisition accuracy; the multi-channel data acquisition unit packages the acquired data and sends it to the data acquisition system, which can process the acquired temperature, strain, and pressure data in real time to obtain the evolution law of each physical field during the pressure curing process.

[0016] A method for in-situ monitoring of fiber optic gratings during multi-field coupling evolution, comprising the following steps: S1. Device Assembly: Complete the installation and connection of the external explosion-proof cavity, the internal pressure curing cavity, the upper flange of the internal pressure cavity, and the lower flange of the internal pressure cavity, and conduct sealing and airtightness tests. S2. Sensor deployment: Fix the temperature measuring fiber optic sensor and the strain measuring fiber optic sensor on the cross-shaped fixing frame respectively, and limit them with stainless steel fixing discs to keep the fiber optics vertically arranged along the axial direction. S3. System Connection: Lead out the temperature measurement fiber optic sensor and the strain measurement fiber optic sensor through fiber feeder A and fiber feeder B respectively, and connect them to the fiber optic demodulator; at the same time, connect the pressure sensor and the external strain gauge to the multi-channel data acquisition unit to complete signal initialization and detection. S4. Propellant filling and sealing: The propellant slurry is filled into the internal pressurized and solidified cavity by pouring and the cavity is then sealed. S5. Pressurization: Open the high-pressure nitrogen cylinder and adjust the gas pressure through the pressure reducing valve and solenoid valve to bring the pressure curing chamber to the preset pressure.

[0017] As a preferred option, it also includes: S6. Curing process monitoring: During the pressurization and heating, heat preservation and pressure holding and depressurization and cooling processes, the internal temperature, strain and cavity structure response data of the propellant are collected synchronously through fiber optic grating sensors and external strain gauges to fully record the cavity rebound process and the internal strain changes of the propellant. S7. Data Synchronization Processing: Time synchronization processing is performed on the collected temperature, strain and pressure data to obtain the internal and external multi-field coupling evolution characteristics during the pressure curing process. S8. After the test is completed, close the pressure reducing valve and open the manual valve to release the gas through the metal hose.

[0018] Compared with existing technologies, the integrated system for multi-stage crushing, screening, and grading of biomass provided by this invention has the following advantages: (1) High structural safety and strong test reliability: The present invention adopts a double-layer structure design of internal pressure curing cavity and external explosion-proof cavity, which can effectively isolate risk sources during pressure curing process and improve the overall safety and stability of the device; (2) Realize coordinated monitoring of the propellant interior and shell exterior: By deploying a fiber optic grating sensor array inside the propellant and a strain gauge on the outer wall of the composite material cavity, the internal state of the propellant and the response of the shell structure can be measured synchronously, which can fully reflect the internal and external coupling effect during the pressurization and curing process. (3) Strong ability to measure multiple physical fields simultaneously: The present invention integrates a temperature measuring fiber optic sensor, a strain measuring fiber optic sensor and a pressure sensor, which can collect the temperature field, strain field and pressure field in real time during the pressure curing process, and realize multi-physical field coupling monitoring. (4) Distributed multi-point measurement to improve spatial resolution: The fiber optic grating sensor is set with multiple measuring points along the propellant axis, which can obtain temperature and strain distribution information at different locations. Compared with the traditional single-point measurement method, it can more accurately reflect the spatial non-uniformity characteristics of the curing process. (5) High accuracy of temperature and strain decoupling measurement: By setting an isolation sleeve outside the temperature measuring fiber optic sensor, the cross-sensitivity of strain to temperature measurement is effectively reduced, the accuracy of temperature measurement is improved, and thus the reliability of the overall monitoring data is enhanced. (6) Strong in-situ real-time monitoring capability: The fiber optic grating sensor can work stably for a long time under pressure, realizing in-situ real-time monitoring of the entire process of propellant pressurization and solidification, and can obtain complete evolution data without interrupting the test; (7) Good data synchronization, which facilitates multi-field coupling analysis: Through the fiber optic demodulator and multi-channel data acquisition unit, the temperature, strain and pressure data are acquired synchronously in time, providing a reliable data basis for analyzing the multi-field coupling evolution during the pressure curing process; (8) The structure is reusable and the test cost is low: The pressure curing chamber, fiber optic sensor, pressure sensor and data acquisition system in this invention can all be reused, reducing test consumption and improving test efficiency; (9) Applicable to various pressure curing conditions: By adjusting the pressure parameters of the gas supply system, this invention can be applied to the propellant loading monitoring needs under different pressure levels and different curing process conditions, and has good applicability and scalability. Attached Figure Description

[0019] Figure 1 This is a schematic cross-sectional view (front view) of the main structure of the fiber optic grating in-situ monitoring device for the internal and external multi-field coupling evolution process according to the present invention. Figure 2 This is a schematic diagram (top view) of the macroscopic layout of a fiber optic grating in-situ monitoring device for the internal and external multi-field coupling evolution process according to the present invention. Figure 3 This is a schematic diagram of the FBG principle of the present invention; Figure 4 This is a schematic diagram showing the connection relationship of a partial structure of the external explosion-proof cavity of the present invention; Figure 5 This is a schematic diagram of the partial structural connection relationship of the bolts in this invention; Figure 6 This is a schematic diagram of the structural connection relationship of the bolt in a semi-sectioned state in the middle of the present invention; Figure 7 For the present invention Figure 6 Enlarged view of point A in the middle.

[0020] In the diagram: 1. Strain gauge line; 2. Insulation box; 3. Aviation socket; 4. Upper sealing cover; 5. Upper flange of external explosion-proof cavity; 7. External explosion-proof cavity; 8. Upper flange of internal pressurization cavity; 9. Internal pressurization and curing cavity; 10. External strain gauge; 11. Temperature measuring fiber optic sensor sleeve; 12. Temperature measuring fiber optic sensor; 13. Stainless steel fixed disc; 14. Lower flange of external explosion-proof cavity; 15. Fiber optic transmission line; 16. Metal flexible hose; 17. Sealing base; 18. Pressure sensor; 19. T-connector; 20. Pressurized air inlet pipeline; 21. Temperature measuring fiber optic pipeline; 22. Strain measuring fiber optic pipeline; 23. Fiber optic feeder A; 24. 1. Fiber optic feedthrough B; 25. Internal pressure curing chamber cover plate; 26. Cross-shaped fixing bracket; 27. Strain measurement fiber optic sensor; 28. Internal pressure curing chamber bottom plate; 29. ​​Internal pressure chamber lower flange; 30. Lower connecting cover; 31. High-pressure nitrogen cylinder; 32. Pressure reducing valve; 33. Fiber grating demodulator; 34. Pressure transmission line; 35. Solenoid valve; 36. Manual valve; 37. Multi-channel data acquisition unit; 40. O-ring seal; 41. Screw; 42. Nut; 43. Rotary ring; 44. Pressure plate; 45. Pressure column; 46. Linkage shaft; 47. Trapezoidal groove; 48. Sealing piston plate; 49. Hydraulic cylinder; 50. Return spring. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: See Figure 1 , Figure 2The present invention discloses an in-situ monitoring device for fiber optic gratings in the internal and external multi-field coupling evolution process, which mainly consists of three parts: a gas supply and pressurization system, a pressurization and curing monitoring system, and a multi-field data acquisition system. It can realize synchronous, in-situ, and accurate monitoring of multiple physical fields such as pressure, temperature, and strain during the pressurization and curing process of propellant loading.

[0023] I. Gas Supply and Pressurization System The gas supply and pressurization system provides a stable and controllable high-pressure gas source for the propellant loading and curing test. Its core components include a high-pressure nitrogen cylinder 31, a pressure reducing valve 32, a metal hose 16, a three-way connector 19, a manual valve 36, a solenoid valve 35, and a pressurized gas inlet pipeline 20. The high-pressure nitrogen cylinder 31 is fixedly mounted on a cylinder rack to effectively prevent tipping and ensure safe operation. The pressure reducing valve 32 is threadedly installed at the outlet of the high-pressure nitrogen cylinder 31, allowing precise control of the high-pressure gas output pressure to meet the operating pressure requirements of the curing test.

[0024] Downstream of the pressure reducing valve 32, a metal hose 16 is sealed and connected to a three-way connector 19. The three-way connector 19 connects to a solenoid valve 35 and a manual valve 36 at its two ends, respectively. The solenoid valve 35 is used for automated and precise control of the pressurization process, while the manual valve 36 is used for routine system depressurization and emergency pressure relief in emergency situations. The outlet of the solenoid valve 35 is connected to the pressurized air inlet pipeline 20 to ensure stable delivery of high-pressure gas. Meanwhile, the metal hose 16 adopts a high-pressure resistant flexible structure, and all gas path components use threaded sealing connections, which improves the overall gas path sealing and buffers the impact of equipment operating vibration on system stability. The pressurized air inlet pipeline 20 and the internal pressurized curing chamber 9 use a dedicated sealed connection structure, allowing high-pressure gas to be uniformly and smoothly input into the chamber, preventing localized airflow impacts that could interfere with the internal loading and monitoring structures.

[0025] II. Pressure Curing Monitoring System The pressure curing monitoring system is the core carrier for realizing charge curing, working condition protection, and in-situ sensing monitoring. It mainly includes an external explosion-proof cavity 7, an internal pressure curing cavity 9, an external explosion-proof cavity upper flange 5, an external explosion-proof cavity lower flange 14, an internal pressure cavity upper flange 8, an internal pressure cavity lower flange 29, an upper sealing cover 4, a pressure sensor 18, an optical fiber feeder A 23, an optical fiber feeder B 24, a temperature measuring optical fiber sensor 12, a strain measuring optical fiber sensor 27, a cross-shaped fixing bracket 26, a stainless steel fixing disc 13, a temperature measuring optical fiber pipeline 21, a strain measuring optical fiber pipeline 22, an external strain gauge 10, and an aviation socket 3.

[0026] An insulated box 2 is installed on the outside of the external explosion-proof chamber 7 to stabilize the curing environment temperature. Simultaneously, the chamber effectively prevents internal structural damage and media leakage risks under abnormal pressure curing conditions, providing safe explosion-proof protection for the entire internal test structure. An internal pressure curing chamber 9 is nested inside the external explosion-proof chamber 7. The end of the pressurized air inlet pipe 20 is connected to the internal pressure curing chamber 9 to provide a high-pressure air source. This chamber is made of composite materials and is used to carry the propellant charge. It can withstand the internal pressure load during the curing process and produce controllable elastic deformation, significantly improving the sensitivity of external strain monitoring.

[0027] The upper flange 8 and lower flange 29 of the internal pressurized chamber are bolted to the interior of the external explosion-proof chamber 7. The lower surface of the lower flange 29 is also bolted to the bottom plate 28 of the internal pressurized curing chamber, together forming a sealed pressurized curing space. The upper flange 5 of the external explosion-proof chamber is bolted to the upper sealing cover 4, achieving a seal at the top of the chamber. The upper sealing cover 4 is connected to the pressurized gas inlet pipe 20 of the gas supply and pressurization system, ensuring a stable input of high-pressure gas. The pressure sensor 18 is mounted at the interface position on the side wall of the chamber cover, enabling real-time acquisition of dynamic pressure changes inside the chamber during the curing process.

[0028] An array of fiber optic grating sensors is installed inside the internal pressure-curing chamber 9. Both the temperature-measuring fiber optic sensor 12 and the strain-measuring fiber optic sensor 27 are arranged along the chamber's axial direction and precisely positioned and supported by a cross-shaped fixing bracket 26. The cross-shaped fixing bracket 26 is fixed vertically and vertically by a stainless steel fixing disc 13, ensuring the fiber optic sensors remain vertically stable throughout the pressure-curing process and preventing bending, displacement, or pulling, thus guaranteeing monitoring stability. The temperature-measuring fiber optic sensor 12 is fitted with an isolation sleeve to completely isolate the strain from interference with temperature monitoring during curing, achieving decoupled and accurate measurement of temperature and strain. The strain-measuring fiber optic sensor 27 is in direct contact with the propellant charge, accurately acquiring the true strain response throughout the entire curing process. Simultaneously, multiple sets of fiber optic grating sensor measuring points are arranged axially within the chamber to comprehensively collect temperature and strain distribution data at different locations inside the propellant charge. External strain gauges 10 are attached to the outer wall of the internal pressure-curing chamber 9 to monitor the expansion and rebound deformation of the outer wall during pressurization and depressurization.

[0029] 2.1 Adaptive Indication Structure for Flange Sealing and Tightness Sealing grooves are provided on the outer sides of the bolt holes of the upper flange 5 and upper sealing cover 4 of the external explosion-proof cavity. O-rings 40 are embedded in the sealing grooves to achieve end face sealing. The fastening bolts consist of a screw 41 and a nut 42, with the nut 42 threaded onto the end of the screw 41. A detection groove is provided in the middle of the screw 41, and multiple sets of pressure plates 44 are evenly distributed around the circumference of the detection groove. Rotary rings 43 are slidably mounted at both ends of the pressure plates 44. The rotating rings 43 are rotatably fitted into both ends of the detection groove, which can prevent the screw from getting stuck during rotation and ensure structural adaptability.

[0030] O-ring 40 is fitted onto the outside of screw 41 and adheres to the outer surface of pressure plate 44. Auxiliary grooves are evenly spaced inside the detection groove of screw 41. Pressure column 45 is slidably mounted within these auxiliary grooves. A buffer spring is fitted onto the outside of pressure column 45, with both ends fixed to the pressure column 45 and the groove wall of the auxiliary groove, respectively, to achieve pressure column reset buffering. A positioning groove is also provided in the middle of screw 41. A linkage shaft 46 is slidably mounted within this positioning groove. One end of the linkage shaft 46 is connected to a reset spring 50, and the other end is fixed to a sealing piston plate 48. The sealing piston plate 48 is slidably mounted inside a hydraulic cylinder 49, which is fixedly embedded in the positioning groove. The sealing piston plate 48 forms a sealed cavity filled with a colored indicator liquid. A trapezoidal groove 47 is linearly spaced on the side wall of linkage shaft 46. The end of pressure column 45 slidably adheres to the inclined surface of the trapezoidal groove 47, forming a mechanical linkage structure.

[0031] During equipment assembly and tightening, rotating the nut 42 drives the upper sealing cover 4 to fit and press against the upper flange 5 of the external explosion-proof cavity, compressing the O-ring 40 to undergo elastic deformation and achieving end-face sealing. Simultaneously, the deformed O-ring 40 presses inward against the pressure plate 44, driving the pressure plate 44 to slide along the middle of the screw 41, which in turn compresses the pressure column 45 to slide inward along the auxiliary groove. Under the action of the inclined plane transmission, the pressure column 45 compresses the trapezoidal groove 47, driving the linkage shaft 46 to move the sealing piston plate 48 upward, compressing the indicator inside the hydraulic cylinder 49 cavity. Changes in the indicator's state provide direct feedback on the compression deformation of the O-ring 40 and the tightness of the bolts. It also accurately identifies the uniformity of tightening of individual bolts and the failure of the sealing ring, effectively avoiding defects in localized sealing of the flange end face and ensuring overall sealing consistency and reliability.

[0032] III. Multi-field data acquisition system The multi-field data acquisition system is used to synchronously acquire, transmit, and process pressure, temperature, and strain multi-physical field data during the curing process throughout the entire process. The core components include a fiber optic demodulator 33, an optical fiber transmission line 15, a pressure transmission line 34, a multi-channel data acquisition unit 37, an optical fiber sensing signal transmission pipeline, and supporting optical fiber temperature sensor 12, optical fiber strain sensor 27, pressure sensor 18, optical fiber feeder A23, optical fiber feeder B24, and aviation socket 3.

[0033] The cavity pressure signal collected by pressure sensor 18 is transmitted in real time to multi-channel data acquisition unit 37 via pressure transmission line 34; the charge temperature signal collected by temperature measuring fiber optic sensor 12 is sealed and led out through temperature measuring fiber optic tube 21 and fiber feeder A23 and then connected to fiber optic demodulator 33; the internal strain signal of the charge collected by strain measuring fiber optic sensor 27 is sealed and led out through strain measuring fiber optic tube 22 and fiber feeder B24 and then connected to fiber optic demodulator 33; the structural deformation signal collected by external strain gauge 10 on the outer wall of the cavity is connected to multi-channel data acquisition unit 37 via strain data transmission line and aviation socket 3.

[0034] Fiber optic feeders A23 and B24 are independent of each other, corresponding to the sealed outputs of temperature and strain measurement fiber optic signals respectively. This ensures the airtightness and independence of fiber optic signal transmission under high-pressure, sealed conditions, avoiding signal cross-interference. Temperature measurement fiber optic conduit 21 and strain measurement fiber optic conduit 22 form a dedicated fiber optic sensing signal transmission conduit, guiding and protecting the internal fiber optics, preventing signal distortion caused by fiber bending, pulling, or compression, and ensuring the stability of optical signal transmission.

[0035] The fiber optic grating demodulator 33 employs multi-channel synchronous demodulation technology, enabling it to simultaneously receive optical signals from multiple fiber optic sensors. It accurately converts changes in fiber wavelength into corresponding temperature and strain physical signals, which are then transmitted in real-time to the multi-channel data acquisition unit 37. The multi-channel data acquisition unit 37 features high-precision time synchronization calibration, allowing for unified timing calibration, synchronous acquisition, storage, and integration of four types of signals: pressure, temperature, internal strain, and external wall structure strain. This achieves precise alignment of multi-physics data.

[0036] This device employs a separate transmission mode for optical and electrical signals, significantly reducing coupling interference between different types of signals and effectively improving data acquisition accuracy. Finally, the multi-channel data acquisition unit 37 packages and outputs the integrated, standardized data. Through analysis and computation by the backend data processing system, the dynamic evolution of the temperature field, strain field, pressure field, and cavity structure response during the entire propellant loading and curing process can be accurately obtained, providing data support for curing process optimization and operational safety assessment.

[0037] Example 2: Based on Example 1 but with a difference, the following describes the in-situ monitoring method of fiber optic grating for the internal and external multi-field coupling evolution process proposed in this invention, with reference to specific examples and accompanying drawings. The specific content is as follows.

[0038] This embodiment focuses on in-situ monitoring of the isothermal and isobaric curing process of solid propellant column loading. It is suitable for laboratory small-batch loading and pressure curing test scenarios. It is mainly used to solve the industry pain points of traditional curing monitoring, which cannot simultaneously acquire multi-field coupled data such as internal temperature, micro-strain, cavity pressure, and external wall structural deformation of the loading, and the sealing and fastening status is not visible, the data timing is not synchronized, and temperature and strain signals are cross-interfered.

[0039] The test subject in this scenario was a standard cylindrical solid propellant charge sample, 200 mm in length and 50 mm in diameter. A segmented isothermal-pressure curing process was employed, with a curing pressure range of 0.2–1.0 MPa and a curing temperature range of 40–60 °C, for a total curing time of 12 hours. This device enables in-situ, continuous, and synchronous monitoring of multiple physical fields throughout the entire curing cycle, including the pressurization, isothermal-pressure holding, and depressurization / cooling stages. It accurately captures the coupled evolution of temperature, strain, and pressure fields during the propellant curing process, while simultaneously monitoring the sealing and tightening status of the cavity in real time, ensuring experimental safety and data reliability.

[0040] The entire test scenario is conducted in a closed, explosion-proof test environment. The external insulation box enables precise temperature control of the environment, the explosion-proof cavity isolates the risk of high-pressure testing, and the fiber optic grating sensing system enables interference-free in-situ measurement. Electrical and optical signals are acquired through separate channels, making it fully compatible with the flammable, explosive, high-pressure, and constant-temperature harsh conditions of propellant curing.

[0041] The specific steps are as follows: Secure the high-pressure nitrogen cylinder 31 to the dedicated cylinder rack to prevent tipping. Tighten the pressure reducing valve 32 to the outlet of the nitrogen cylinder. Connect the three-way connector 19, solenoid valve 35, manual valve 36, and pressurized air inlet pipe 20 sequentially through the metal hose 16. Check the sealing structure of all gas lines to ensure there is no risk of leakage. Fix the external explosion-proof chamber 7 to the test bench, nest the internal pressurized curing chamber 9, and tighten the seal with upper and lower flanges and bolts. Assemble the sealing cap 4 to complete the construction of the sealed curing chamber.

[0042] Inside the internal pressure curing chamber 9, a temperature-measuring fiber optic sensor 12 and a strain-measuring fiber optic sensor 27 are vertically fixed by a cross-shaped fixing bracket 26 and a stainless steel fixing disc 13, ensuring that the sensors are in close contact with the propellant sample and remain vertical without bending throughout the process. The temperature-measuring fiber optic sensor is externally isolated by a sleeve to decouple the temperature and strain signals. External strain gauges 10 are uniformly attached to the outer wall of the chamber to collect data on the deformation of the chamber structure.

[0043] All optical fibers are sealed and led out through independent optical fiber feeders A23 and B24, respectively, and connected to the temperature measuring optical fiber pipeline 21 and the strain measuring optical fiber pipeline 22, and then connected to the fiber optic demodulator 33; the pressure sensor 18 and the external strain gauge 10 are connected to the multi-channel data acquisition unit 37 through the corresponding transmission lines, completing the hardware connection of the entire monitoring system.

[0044] Furthermore, tighten all the fastening bolts of the upper sealing cover 4 and the upper flange 5 of the external explosion-proof cavity evenly. The bolts compress the O-ring 40, causing elastic deformation, and simultaneously compress the pressure plate 44 and pressure column 45. Through the inclined plane linkage structure, the sealing piston plate 48 is driven to compress the colored indicator inside the hydraulic cylinder 49. Observe the indicator liquid level corresponding to all bolts to ensure that the tightness of each bolt is uniform and that there is no abnormal drop in the indicator liquid. Determine that there is no local sealing failure on the flange end face and that the sealing ring is not damaged, thus completing the sealing self-inspection.

[0045] Then, the fiber optic demodulator 33 and the multi-channel data acquisition unit 37 were turned on to perform equipment zeroing calibration and time synchronization calibration, unifying the timing reference of all acquisition channels. The demodulator sampling frequency was set to 10Hz, and the pressure and strain signal acquisition frequencies were synchronized with the optical signals to ensure real-time alignment of multi-physics field data; the gas supply pressurization system was debugged, the automatic pressurization function of the solenoid valve and the emergency pressure relief function of the manual valve were tested, and the pressure output accuracy of the pressure reducing valve was calibrated to ensure that the pressure regulation error was ≤±0.02MPa.

[0046] Place the pretreated propellant sample stably in the center of the internal pressure curing chamber 9, ensuring full contact between the sample and the fiber optic sensor. Close the chamber and reconfirm the seal. Start the external insulation chamber 2 to preheat the internal environment to 40°C and maintain a stable temperature for 30 minutes to eliminate the interference of ambient temperature fluctuations on the test data.

[0047] To begin the curing test, the automated pressurization program is activated. The nitrogen output pressure is precisely controlled by the pressure reducing valve 32, using a staged pressurization mode: first, pressurize to 0.2MPa and hold for 1 hour; then gradually increase the pressure to 0.5MPa and hold for 6 hours; finally, increase the pressure to 1.0MPa and hold for 4 hours. The entire process is automatically stabilized by the solenoid valve 35, and in case of abnormal pressure, the manual valve 36 can be used for rapid pressure relief.

[0048] During this phase, multiple simultaneous monitoring operations are conducted: pressure sensor 18 collects real-time data on pressure fluctuations inside the cavity; temperature fiber optic sensor 12 collects in-situ data on temperature changes due to heat release during curing of the propellant; strain fiber optic sensor 27 captures the evolution of micro-strain caused by the curing shrinkage and compression of the propellant; and external strain gauge 10 monitors data on the cavity's expansion and deformation under pressure. Simultaneously, the status of the bolt indicator is observed in real-time, ensuring the stability of the cavity's sealing and tightening throughout the process.

[0049] Further monitoring of the pressure relief and cooling phase was conducted. After the curing and pressure holding process was completed, a slow, staged pressure relief method was adopted, successively reducing the pressure from 1.0 MPa to 0.5 MPa, 0.2 MPa, and finally depressurizing to atmospheric pressure. During the pressure relief process, the cavity rebound strain, residual strain of the charge, and temperature drop pattern were monitored simultaneously. After pressure relief, the insulated chamber was kept at a constant temperature and allowed to cool naturally for 2 hours, during which data on the attenuation of multiple parameters during the cooling phase were collected.

[0050] After the entire test is completed, the pressurization system and monitoring equipment are shut down. Once the chamber temperature has dropped to room temperature and the pressure has completely returned to zero, the propellant sample is removed from the disassembly device. The multi-channel data acquisition unit 37 automatically stores the pressure, temperature, internal strain, and external wall strain data synchronized throughout the entire process, completes data packaging, noise reduction, and alignment processing, and generates multi-field coupled evolution data curves of propellant loading pressurization and solidification.

[0051] This solution has the following advantages over existing technologies: 1. Multi-field synchronous monitoring effect: This implementation scenario can achieve millisecond-level synchronous acquisition of data from four fields: pressure, temperature, internal and external strain, completely solving the timing misalignment problem of traditional equipment and accurately restoring the multi-field coupling mechanism of the charge solidification process.

[0052] 2. Temperature and strain decoupling measurement effect: Through the temperature measurement fiber optic isolation sleeve structure, strain cross interference is completely eliminated, the temperature measurement accuracy is improved to ±0.1℃, and there is no noise error in strain measurement.

[0053] 3. Visual monitoring of sealing status: Relying on the bolt indicator linkage structure, the uniformity of sealing and tightening is fed back in real time throughout the process. It can identify potential micro-damage to the sealing ring and local tightening failure in advance, which greatly improves the safety of high-pressure curing test.

[0054] 4. In-situ real response acquisition: The fiber optic sensor is directly attached to the charge, and with the vertical positioning structure, there is no displacement or bending interference. It can accurately acquire the real strain and temperature evolution of the charge during curing, providing real and reliable experimental data support for the optimization of curing process parameters.

[0055] This implementation method is not only suitable for the constant temperature and pressure curing test of conventional column propellant charges, but can also be extended to the monitoring of curing and molding of propellant charges of different sizes and formulations. It can also be adapted to dynamic curing process tests with variable temperature and pressure, and can be used in various engineering and scientific research scenarios such as the research and development of new curing processes, traceability of charge curing quality, and safety assessment of high-pressure curing conditions.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A device for in-situ monitoring of the evolution of a fiber grating under the coupling of multiple fields from the inside and outside, characterized in that, The device includes a gas supply and pressurization system, a pressurization and curing monitoring system, and a multi-field data acquisition system; The gas supply and pressurization system includes a high-pressure nitrogen cylinder (31), a pressure reducing valve (32), a metal hose (16), a three-way connector (19), a hand valve (36), a solenoid valve (35), and a pressurized air inlet pipeline (20); the high-pressure nitrogen cylinder (31) is fixed on the cylinder rack to prevent it from tipping over, and the pressure reducing valve (32) is threaded onto the high-pressure nitrogen cylinder (31); The pressure curing monitoring system includes an external explosion-proof cavity (7), an internal pressure curing cavity (9), an upper flange (5) of the external explosion-proof cavity, a lower flange (14) of the external explosion-proof cavity, an upper flange (8) of the internal pressure cavity, a lower flange (29) of the internal pressure cavity, an upper sealing cover (4), a pressure sensor (18), an optical fiber feedthrough A (23), an optical fiber feedthrough B (24), a temperature measuring optical fiber sensor (12), a strain measuring optical fiber sensor (27), a cross-shaped fixing bracket (26), a stainless steel fixing disc (13), a temperature measuring optical fiber pipeline (21), a strain measuring optical fiber pipeline (22), an external strain gauge (10), and an aviation socket (3). The multi-field data acquisition system includes a fiber optic demodulator (33), an optical fiber transmission line (15), a pressure transmission line (34), a multi-channel data acquisition unit (37), an optical fiber sensing signal transmission pipeline, a temperature measurement optical fiber sensor (12), a strain measurement optical fiber sensor (27), a pressure sensor (18), a temperature measurement optical fiber pipeline (21), a strain measurement optical fiber pipeline (22), an optical fiber feeder A (23), an optical fiber feeder B (24), and an aviation socket (3).

2. The in-situ monitoring device of fiber grating based on internal and external multi-field coupling evolution process according to claim 1, characterized in that: The high-pressure nitrogen cylinder (31) achieves precise control of the output gas pressure by adjusting the pressure reducing valve (32), so that the high-pressure gas meets the pressure requirements of the pressure curing test; the downstream of the pressure reducing valve (32) is connected to the three-way connector (19) through the metal hose (16). One end of the three-way connector (19) is installed on the solenoid valve (35) for automatic control of the pressurization process, and the other end of the three-way connector (19) is installed on the hand valve (36) for system depressurization and emergency pressure relief control; the outlet of the solenoid valve (35) is installed on the pressurization inlet pipeline (20).

3. The in-situ monitoring device of fiber grating based on internal and external multi-field coupling evolution process according to claim 2, characterized in that: The external explosion-proof cavity (7) is equipped with an insulation box (2). The external explosion-proof cavity (7) is used to provide safety protection for the internal structure during the pressure curing process, preventing structural damage and leakage caused by abnormal working conditions. The internal pressure curing cavity (9) is located inside the external explosion-proof cavity (7). The end of the pressure inlet pipe (20) away from the solenoid valve (35) is connected to the internal pressure curing cavity (9). The internal pressure curing cavity (9) is made of composite material and is used to contain the propellant charge and bear the internal pressure load during the pressure curing process, so that it generates measurable elastic deformation during the pressure process, thereby enhancing the sensitivity of external strain monitoring. The upper flange (8) and the lower flange (29) of the internal pressure cavity are bolted to the external explosion-proof cavity (7). The lower surface of the lower flange (29) of the internal pressure cavity is bolted to the bottom plate (28) of the internal pressure curing cavity, thereby... A sealed pressurized space is formed; the upper sealing cover (4) is connected to the gas supply system through a pressurized gas inlet pipe (20) so that high-pressure gas can stably enter the internal pressurized curing cavity (9); the pressure sensor (18) is installed at the interface of the side wall of the cavity cover (13) for real-time measurement of pressure changes in the cavity during the pressurized curing process; the internal pressurized curing cavity (9) is equipped with a fiber optic grating sensor array: the temperature measuring fiber optic sensor (12) and the strain measuring fiber optic sensor (27) are respectively arranged along the axial direction of the internal pressurized curing cavity (9) and positioned and supported by a cross-shaped fixing bracket (26); the cross-shaped fixing bracket (26) is limited up and down by a stainless steel fixing disc (13) so that the fiber optic cable remains vertically stable during the curing process; the temperature measuring fiber optic sensor (12) is equipped with an isolation sleeve to eliminate the influence of strain on temperature measurement during the curing process and realize decoupled measurement of temperature and strain.

4. The in-situ monitoring device of fiber grating based on internal and external multi-field coupling evolution process according to claim 3, characterized in that: The pressure sensor (18) is installed at the pressure interface of the internal pressure curing chamber (9) to measure the pressure change inside the chamber in real time during the pressure curing process, and transmits the measurement signal to the multi-channel data acquisition unit (37) through the pressure transmission line (34); the temperature measuring fiber optic sensor (12) is installed at different positions in the pressure curing chamber (9) to measure the temperature change of the propellant charge during the pressure curing process in real time; the temperature measuring fiber optic sensor (12) is led out through the fiber feedthrough A (23) and the temperature measuring fiber optic tube (21); and is connected to the temperature measuring fiber optic tube (21) and the pressure interface. The fiber optic demodulator (33) is connected, and the strain measurement fiber optic sensor (27) is led out through the fiber feedthrough B (24) and the strain measurement fiber optic pipeline (22); the external strain gauge (10) is installed on the outer wall of the internal pressure curing cavity (9) to measure the expansion and rebound deformation of the outer wall of the cavity during the pressure and depressurization process; and is connected to the external data acquisition system through the aviation socket (3); the fiber optic demodulator (33) demodulates the wavelength signal output by the temperature measurement fiber optic sensor (12), converts it into the corresponding temperature signal, and transmits it to the multi-channel data acquisition unit (37); The strain measurement fiber optic sensor (27) is installed at different positions inside the internal pressure curing chamber (9) to measure the strain evolution information of the propellant charge during the pressure curing process in real time. The strain measurement fiber optic sensor (27) is sealed and led out through fiber feedthrough B (24) and connected to the fiber optic demodulator (33) through the strain measurement fiber optic pipeline (22). The external strain gauge (10) is connected to the multi-channel data acquisition unit (37) through the strain data transmission line and aviation socket (3) to ensure that the external strain signal can be stably transmitted to the data acquisition end. The fiber feedthrough A (23) and fiber feedthrough B (24) are used for the independent lead-out of the temperature measurement fiber optic sensor (12) and the strain measurement fiber optic sensor (27) under high pressure sealing conditions to ensure the sealing and reliability of different types of fiber optic signals during transmission. The temperature measurement fiber optic pipeline (21) Together with the strain-measuring fiber optic pipeline (22), it forms a fiber optic sensing signal transmission pipeline, which is used to stably guide the fiber optic sensing signal inside the cavity to the external fiber optic demodulator (33), and to protect and guide the fiber optic cable, so as to avoid the signal quality being affected by bending, pulling or local pressure during the operation of the device; the fiber optic demodulator (33) is used to demodulate the optical signals output by the temperature-measuring fiber optic sensor (12) and the strain-measuring fiber optic sensor (27) in real time, convert the wavelength change into temperature and strain signals, and transmit the converted signals to the multi-channel data acquisition unit (37); the multi-channel data acquisition unit (37) is used to synchronously acquire, store and process temperature, strain and pressure signals, so as to realize unified monitoring and time synchronization management of the internal temperature field, internal strain field, cavity outer wall structure response and pressure field during the propellant loading and solidification process.

5. The in-situ monitoring device for fiber optic gratings in the internal and external multi-field coupling evolution process as described in claim 1, characterized in that: The upper flange (5) of the external explosion-proof cavity is fixedly installed with an upper sealing cover (4) by bolts. A sealing groove is opened on the outside of the bolt holes of the upper flange (5) and the upper sealing cover (4), and an O-ring (40) is installed in the sealing groove. The bolt includes a screw (41) and a nut (42). The nut (42) is threaded on the outer surface of one end of the screw (41). A detection groove is opened on the outer surface of the middle part of the screw (41), and a pressure plate (44) is evenly installed in the detection groove. A rotating ring (43) is slidably installed at both ends of the pressure plate (44). The rotating ring (43) is rotatably installed at both ends of the sealing groove of the screw (41). The O-ring (40) is sleeved on the outside of the screw (41). An auxiliary groove is evenly opened in the detection groove of the inner surface of the screw (41) near the pressure plate (44), and a pressure column (45) is slidably installed in the auxiliary groove. A buffer spring is fitted on the outer surface, and one end of the buffer spring is fixedly installed on the pressure column (45), and the other end is fixedly installed in the auxiliary groove of the screw (41). A positioning groove is opened in the middle of the screw (41), and a linkage shaft (46) is slidably installed in the positioning groove. A reset spring (50) is fixedly installed at one end of the linkage shaft (46), and a sealing piston plate (48) is fixedly installed at the other end of the linkage shaft (46). A hydraulic cylinder (49) is slidably installed on the outer surface of the sealing piston plate (48). The hydraulic cylinder (49) is fixedly installed in the positioning groove of the screw (41). A trapezoidal groove (47) is linearly opened on the linkage shaft (46), and the pressure column (45) is slidably installed in the trapezoidal groove (47). The hydraulic cylinder (49) forms a sealed cavity through the sealing piston plate (48). An indicator is injected into the cavity of the hydraulic cylinder (49), and the indicator is a liquid with a special color.

6. The in-situ monitoring device of fiber grating based on internal and external multi-field coupling evolution process according to claim 5, characterized in that: The metal hose (16) adopts a high-pressure resistant flexible structure and is connected to each gas path component by a threaded seal to improve sealing performance and reduce the impact of vibration on the system; the pressurized air inlet pipe (20) and the internal pressurized curing chamber (9) adopt a sealed connection structure to enable high-pressure gas to enter the internal pressurized curing chamber (9) uniformly and stably, avoiding local impact from interfering with the internal structure; multiple fiber optic grating sensor array measurement points are axially distributed in the internal pressurized curing chamber (9) to obtain temperature and strain information at different locations inside the propellant charge; the gas supply system is equipped with a pressure monitoring interface to connect to the pressure sensor (18) to realize real-time monitoring and feedback adjustment of the pressurization process; the fiber optic grating demodulator (28) adopts a multi-channel demodulation method and can simultaneously receive signals from multiple fiber optic sensors to realize distributed multi-point synchronous measurement.

7. The in-situ monitoring device of an inside-outside multi-field coupling evolution process fiber grating according to claim 6, characterized in that: The strain-measuring fiber optic sensor (27) is in direct contact with the propellant charge and is used to obtain the actual strain response during the propellant curing process. The fiber optic sensor is positioned by a cross-shaped fixing bracket (26) and a stainless steel fixing disc (13) to keep the fiber optic cable vertical during the pressure curing process and avoid bending or displacement.

8. The in-situ monitoring apparatus of claim 7, wherein the optical fiber grating is a long period grating. The multi-channel data acquisition unit (31) has a time synchronization function, performs unified time calibration on temperature, strain and pressure data, and realizes synchronous acquisition and alignment of multi-physical field data; fiber optic sensing signals and electrical signals are transmitted in separate channels to reduce signal interference and improve data acquisition accuracy. The multi-channel data acquisition unit (31) packages the acquired data and sends it to the data acquisition system. The data acquisition system can process the acquired temperature, strain and pressure data in real time to obtain the evolution law of each physical field during the pressure curing process.

9. A method for in-situ monitoring of fiber optic gratings in the process of internal and external multi-field coupling evolution, applicable to the in-situ monitoring device for fiber optic gratings in the process of internal and external multi-field coupling evolution as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Assembly of the device: Complete the installation and connection of the external explosion-proof cavity (7), the internal pressure curing cavity (9), the upper flange (8) of the internal pressure cavity and the lower flange (29) of the internal pressure cavity, and conduct sealing and airtightness tests. S2, Sensor layout: Fix the temperature measuring fiber optic sensor (12) and the strain measuring fiber optic sensor (27) on the cross-shaped fixing frame (26) respectively, and limit them with stainless steel fixing disc (13) so that the fiber optics are arranged vertically along the axis. S3. System connection: The temperature measuring fiber optic sensor (12) and the strain measuring fiber optic sensor (27) are led out through fiber feeder A (23) and fiber feeder B (24) respectively, and connected to the fiber optic demodulator (33); at the same time, the pressure sensor (18) and the external strain gauge (10) are connected to the multi-channel data acquisition unit (37) respectively to complete the signal initialization and detection. S4. Propellant filling and sealing: The propellant slurry is filled into the internal pressure-curing cavity (9) by pouring and the cavity is sealed. S5. Pressurization: Open the high-pressure nitrogen cylinder (31), and adjust the gas pressure through the pressure reducing valve (32) and the solenoid valve (35) to make the pressure curing chamber (9) reach the preset pressure.

10. The in-situ monitoring method of claim 9, wherein, Also includes: S6. Monitoring of the curing process: During the pressurization and heating, heat preservation and pressure holding and pressure release and cooling process, the internal temperature, strain and cavity structure response data of the propellant are collected synchronously through fiber optic grating sensors and external strain gauges (10), and the cavity rebound process and internal strain changes of the propellant are fully recorded. S7. Data Synchronization Processing: Time synchronization processing is performed on the collected temperature, strain and pressure data to obtain the internal and external multi-field coupling evolution characteristics during the pressure curing process. S8. After the test is completed, close the pressure reducing valve (32), open the manual valve (36), and discharge the gas from the metal hose (16).

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