Method for embedded monitoring of solid propellant grain curing residual strain-stress

Abstract

The present application relates to engine structure real-time monitoring technical field, disclose a kind of solid propellant grain curing residual strain-stress embedded monitoring method, comprising the following steps: grain structure curing simulation analysis;Based on the grain structure curing simulation analysis result, determine the curing residual stress, and determine the measuring point position of flexible strain gauge embedding, and then layout online in-situ monitoring network;Flexible strain gauge is implanted in the measuring point position determined, and packaging is completed;Bridge and lead wire of flexible strain gauge test network are handled, and the connecting tooling required for testing is fixed;Test network signal is verified and co-site temperature compensation sensor is set;Grain structure casting and curing are carried out, and the residual strain in-situ online monitoring of grain during synchronous curing process is carried out;Grain structure curing is completed, strain test data is extracted, and corresponding curing residual stress is obtained.Can accurately monitor the local concentrated curing residual stress of solid propellant grain in-situ under the high temperature and high pressure environment of grain curing.

Description

Technical Field

[0001] This invention relates to the field of real-time monitoring technology for engine structures, and in particular, to an embedded monitoring method for residual strain-stress of solid propellant grains after solidification. Background Technology

[0002] Solid propellant engines, widely used in aerospace launch vehicles, are crucial for their performance and reliability. During the production of propellant grains, significant differences in mechanical and thermal properties between solid propellants and structural materials such as the engine casing and liner inevitably lead to residual stress and strain during curing and subsequent cooling. Studies have shown that this residual stress is a key factor affecting the structural integrity of the propellant grain, potentially causing internal cracks and debonding at the interface between the propellant grain and the liner / casing. This poses a potential threat to the long-term storage safety and operational reliability of the engine.

[0003] Currently, the technology for accurate measurement and online monitoring of residual stress in the curing structure of propellant grains still faces many challenges, and the relevant technologies are still in the development stage, mainly with the following technical bottlenecks:

[0004] 1. The solidification process of the propellant grain is accompanied by the physicochemical changes of the propellant from a viscous slurry to a viscoelastic solid. The solidification environment is usually high temperature, closed or even pressurized, which makes it difficult for traditional strain measurement devices to be directly implanted into key parts inside the propellant grain (such as stress concentration areas such as the core mold interface and corners of complex surfaces) in the early stage of solidification. As a result, it is difficult to ensure long-term and stable operation throughout the entire solidification cycle.

[0005] 2. The residual strain generated during the curing process of the propellant cartridge is relatively small, which places extremely high demands on the accuracy of the measurement system. At the same time, temperature changes during the curing process can significantly interfere with the strain measurement signal. How to effectively perform temperature compensation to accurately separate the true strain signal caused by stress is the key to ensuring the accuracy of the measurement results.

[0006] 3. The distribution of residual stress is non-uniform, with the maximum stress point often located inside the propellant grain. If the measuring point layout is unreasonable, the most dangerous stress state cannot be effectively captured. Furthermore, the measuring device embedded in the confined and narrow curing space should not interfere with the curing process of the propellant grain material or the final residual stress and strain field.

[0007] In summary, existing technologies struggle to achieve online, in-situ, and precise monitoring of residual strain-strain throughout the solid propellant grain curing process. This technological bottleneck hinders a deeper understanding and optimization of the grain curing process and restricts the proactive design and manufacturing quality control of high-reliability grain structures. Therefore, developing a novel monitoring method capable of overcoming these problems is particularly urgent. Summary of the Invention

[0008] This invention provides an embedded monitoring method for residual strain and stress during the solid propellant grain curing process. It constructs a multi-field coupled constitutive model to simulate the curing process and predicts the residual stress distribution. Based on the simulation results, a flexible strain sensor network is embedded at key locations within the propellant grain for in-situ online monitoring. This method enables precise in-situ monitoring of locally concentrated residual stress during the high-temperature and high-pressure curing environment of the propellant grain. This meets the structural integrity assessment requirements of solid rocket engine propellant grains during the production stage and solves the technical problem of existing technologies being unable to achieve accurate, online, and in-situ monitoring of residual strain and stress throughout the entire solid propellant grain curing process due to the harsh curing environment, difficulty in sensor implantation, and unreasonable measurement point layout.

[0009] This invention provides an embedded monitoring method for residual strain-stress during the curing of solid propellant grains, comprising the following steps: S100, simulation analysis of propellant grain structure curing; S200, based on the simulation analysis results, determining the residual stress after curing and the measurement point positions for embedding flexible strain gauges, and then deploying an online in-situ monitoring network; S300, implanting flexible strain gauges at the determined measurement point positions and completing encapsulation; S400, processing the bridging and leads of the flexible strain gauge test network and fixing the connection fixtures required for testing; S500, verifying the test network signal and setting up a co-location temperature compensation sensor; S600, casting and curing of the propellant grain structure, and performing in-situ online monitoring of residual strain during the synchronous curing process; S700, after the propellant grain structure curing is completed, extracting strain test data and obtaining the corresponding residual stress after curing.

[0010] Further, step S100 specifically involves: constructing a curing simulation model of the propellant column structure based on a multi-field coupled constitutive model, wherein the multi-field coupled constitutive model is a three-dimensional viscoelastic constitutive model related to time-temperature-degree of curing; performing curing simulation analysis through the curing simulation model to obtain the residual stress and residual strain distribution results of the propellant column structure.

[0011] Further, step S200 specifically involves: based on the residual stress and residual strain distribution results of the propellant grain structure, determining that the location of the maximum residual stress and strain is at the contact interface between the propellant grain and the core mold; for the distribution of residual stress and strain under different propellant grain configurations, setting flexible strain gauges at the corresponding residual strain measurement points on the contact interface, and designing an online in-situ monitoring network.

[0012] Furthermore, the location of residual strain measurement points should take into account the actual arrangement range of flexible strain gauges, avoid adjacent residual strain measurement points being too close, and avoid the location of residual strain measurement points on surfaces with large curvature; the online in-situ monitoring network should consider the configuration and symmetry of the propellant grains, and cover the test path of the location and area of ​​the maximum solidification residual stress-strain of the propellant grain structure.

[0013] Furthermore, the online in-situ monitoring network includes residual strain measurement points and verification measurement points; the verification measurement points are axisymmetric measurement points of any measurement point on the propellant-core mold interface.

[0014] Further, step S300 specifically includes: S301, spraying a polyurethane release agent onto the outer surface of the core mold, and waiting for the polyurethane release agent to cure on the surface of the core mold to form a coating with a thickness of 0.1mm ± 0.05mm; S302, attaching a soft film to the outer surface of the core mold with the polyurethane release agent coating, the soft film being made of polyethylene or latex, and the thickness of the soft film being controlled between 0.04mm and 0.06mm; S303, attaching a resistance triaxial strain gauge at the residual strain measurement point; S304, attaching a polyurethane film with a thickness of 0.05mm ± 0.01mm to the outer interface of the core mold.

[0015] Furthermore, the implantation and encapsulation of the flexible strain gauge are carried out in a dry and dust-free environment; a polyurethane release agent is uniformly sprayed on the entire outer surface of the mandrel; a soft latex film is attached to the entire area covering the online in-situ monitoring network and serves as a modified flexible substrate for the strain gauge; a polyurethane film is pasted on the area covering the flexible strain gauge and serves as a bonding transition coating for the propellant charge.

[0016] Furthermore, the substrate material of the resistive triaxial strain gauge is at least one of phenolic-acetal, polyimide, and polyurethane, with a substrate size of less than or equal to 15mm × 15mm and an overall thickness of less than or equal to 30μm; the typical resistance value is 120Ω, and the strain limit is 2.0% ± 0.1%; the operating temperature covers the propellant grain curing temperature range, with an operating temperature of -80℃ to +150℃.

[0017] Further, step S400 specifically includes: S401, the flexible strain gauge bridging method adopts an independently compensated 1 / 4 bridge connection, or a mixed bridge of half bridge and full bridge sharing the compensation gauge; S402, all leads of the flexible strain gauge at each residual strain measuring point in the online in-situ monitoring network are braided into single-strand leads and led out from the wiring hole on the core mold; S403, after all the single-strand leads are led out, the wiring hole is sealed with sealant.

[0018] Furthermore, in the area of ​​residual stress concentration after curing, which is far from the propellant grain structure and is the test area, wiring holes are drilled. The edges and corners of the wiring holes are rounded to avoid frictional contact that could cut the leads. The diameter of the wiring holes is determined based on the number of leads. The wiring holes are designed according to the configuration of the core mold and the network layout of the residual strain measurement points to avoid redundancy of internal leads, and multiple wiring channels are used. The sealant meets the sealing requirements under propellant grain casting and pressure curing.

[0019] Further, step S500 specifically involves: connecting the leads of the flexible strain gauge to the strain test data receiver, which transmits the test data to the computer for data processing and analysis; turning on the data receiver and checking the signals of each connection channel; for flexible strain gauges using 1 / 4 bridge connections, using additional temperature compensation plates to eliminate temperature drift, or using a shared ambient temperature compensation algorithm to eliminate temperature drift.

[0020] Furthermore, when using an additional temperature compensation plate, the three grid wires of the triaxial strain gauge share one temperature compensation plate, which is then pasted in a stress-free location with the same material, the same packaging, and the same ambient temperature. For the residual stress test of propellant grain curing, the temperature compensation plate is placed outside the engine combustion chamber under the same curing environment, with the same core mold material and the same packaging conditions, and is simultaneously cured and monitored.

[0021] Furthermore, when using a shared ambient temperature compensation algorithm, calibration is performed before the propellant grain curing residual stress test. Sample strain gauges of the same batch and model as the actual implanted flexible strain gauges are attached to a stress-free calibration propellant block with the same coefficient of thermal expansion as the propellant grain material, and placed in the same curing temperature environment. This yields the temperature compensation readings of the flexible strain gauges under the curing temperature history in a state of no curing shrinkage stress. At this point, the flexible strain gauge has no other mechanical stress, and the strain reading is entirely caused by the temperature effect.

[0022] Furthermore, when using a shared ambient temperature compensation algorithm, real-time temperature acquisition and compensation calculation are performed, and the real-time strain values ​​of the flexible strain gauges are simultaneously acquired during the curing process. Simultaneously, miniature thermocouples are used to collect temperature data in real time near the flexible strain gauge. .

[0023] Furthermore, when using a shared ambient temperature compensation algorithm, based on real-time temperature data... Call the corresponding temperature compensation data The actual strain is obtained by performing compensation calculations. The specific formula is as follows: .

[0024] Further, step S600 specifically involves: pouring propellant slurry into the combustion chamber of the engine propellant grain, assembling the tooling, transferring it to the curing environment, starting curing, turning on the strain monitoring device, and starting in-situ online monitoring of the residual strain of the propellant grain during the synchronous curing process.

[0025] Further, step S700 specifically involves: after the propellant grain solidification process is completed, ending the monitoring of residual strain during propellant grain solidification, extracting strain test data, and calculating the corresponding residual stress based on the mechanical property parameters of the propellant material during the solidification process. The specific formula is as follows:

[0026] ;

[0027] in, This refers to the current time or a specific calculation moment, i.e., the point in time when stress is calculated. T For the corresponding time Temperature that affects material properties These are variables that reflect the intrinsic properties of propellant materials and are related to their mechanical properties. This refers to the relaxation modulus or a related material response function. This refers to the strain during the curing process. For the integration variable over past time, In response Regarding past time The partial derivatives of .

[0028] The present invention has the following beneficial effects:

[0029] 1. Realized residual strain monitoring during synchronous curing and propellant physical state transformation: By embedding a modified flexible substrate strain gauge at the core mold-propellant interface where residual stress and strain are concentrated during curing, and utilizing the close adhesion between the flexible thin film layer and the propellant during the curing process, the strain gauge can be synchronously cured and the propellant can shrink accordingly, thereby completing the residual strain test during the curing process of the propellant from viscous slurry to viscoelastic propellant.

[0030] 2. In-situ monitoring of residual stress after solidification of propellant grains inside solid rocket motors was achieved: Based on solidification simulation analysis, it was determined that the residual stress after solidification of the propellant grains was concentrated in areas such as the internal core mold-propellant grain interface / wing groove interface. By embedding flexible strain gauges on the corresponding interfaces to form a network of measuring points, the influence of sensor embedding on the solidification shrinkage deformation of the propellant grains was effectively avoided, thus solving the technical problem of internal health monitoring of engine propellant grains.

[0031] 3. Accurate measurement of residual stress during the curing of micro propellant grains was achieved: Real-time monitoring of curing shrinkage strain of the propellant grains was conducted using a high- and low-temperature triaxial strain rosette on a modified flexible substrate. Temperature sensors were used for synchronous temperature monitoring at the measuring points, and a shared ambient temperature compensation algorithm was employed to eliminate temperature drift in strain measurements. This yielded accurate measurement results of the residual strain during propellant curing shrinkage. Combined with the mechanical property parameters of the propellant material during curing, precise residual stress during propellant curing was obtained. This solved the technical challenge of high-precision measurement of micro-strain within the propellant grain.

[0032] 4. A simple, easy-to-operate monitoring method for residual stress in solid propellant grains of various types of solid rocket motors was established: the strain monitoring sensor is based on a modified substrate of a general-purpose resistive triaxial strain gauge, and the embedding, packaging and bridging methods of the sensor are consistent with those of general-purpose triaxial strain gauges in the industry; the measuring point network is based on the solidification simulation analysis of the corresponding configuration of the engine propellant grain, the network is clear, the layout is reasonable, and the applicability to the solidification process is strong.

[0033] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0035] Figure 1 This is a schematic flowchart of the embedded monitoring method for residual strain-stress after solid propellant grain solidification according to a preferred embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the device structure for an embedded monitoring method for residual strain-stress during solid propellant grain curing (before curing after casting) according to a preferred embodiment of the present invention. Figure 2 (a) is a schematic diagram of the detection system for a solid rocket motor structure. Figure 2 (b) is a schematic diagram of the solid rocket motor structure. Figure 2 (c) is a top view of the sensor measurement point arrangement. Figure 2 (d) is a schematic diagram of the embedded monitoring device;

[0037] Figure 3 This is a schematic diagram of the device structure of the embedded monitoring method for residual strain-stress after solid propellant grain curing (after curing), according to a preferred embodiment of the present invention. Figure 3 (a) is a schematic diagram of the detection system for a solid rocket motor structure. Figure 3 (b) is a schematic diagram of the embedded monitoring device;

[0038] Figure 4 This is a schematic diagram of the embedded flexible sensor packaging for monitoring residual strain during solid propellant grain solidification, according to a preferred embodiment of the present invention.

[0039] Figure 5 This is a simulation result of the solid propellant grain solidification process of the embedded monitoring method for residual strain-stress during solid propellant grain solidification according to a preferred embodiment of the present invention.

[0040] Legend:

[0041] 1. Core mold; 2. Liner; 3. Shell; 4. Connecting fixture; 41. Top cap; 42. Bottom flange; 5. Sealing fixture; 51. Bottom sealing bolt; 52. Top sealing bolt; 53. Sealing ring; 6. Embedded monitoring device; 61. Membrane; 62. Triaxial strain gauge; 63. Thermocouple; 64. Cable; 65. Cable routing hole; 66. Data receiver; 67. Data processing terminal; 7. Temperature chamber; 8. Pressurization fixture; 81. Pressurization port; 82. Pressurization liquid bladder; 9. Propellant grain; 91. Uncured propellant slurry after casting; 92. Cured propellant grain. Detailed Implementation

[0042] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available or can be prepared by known methods.

[0043] like Figure 1As shown, the embedded monitoring method for residual strain-stress in solid propellant grain curing in this embodiment includes the following steps: S100, simulation analysis of propellant grain structure curing; S200, based on the simulation analysis results of propellant grain structure curing, determining the residual stress after curing, and determining the measurement point position where the flexible strain gauge (embedded monitoring device 6) is embedded, and then deploying an online in-situ monitoring network; S300, implanting the flexible strain gauge at the determined measurement point position and completing the encapsulation; S400, processing the bridging and leads of the flexible strain gauge test network, and fixing the connection fixture 4 (top cover 41, bottom flange 42) required for testing; S500, verifying the test network signal and setting up a co-location temperature compensation sensor; S600, casting and curing of the propellant grain structure, and performing in-situ online monitoring of residual strain in the propellant grain during the synchronous curing process; S700, after the propellant grain structure curing is completed, extracting strain test data and obtaining the corresponding residual stress after curing. This invention provides an embedded monitoring method for residual strain and stress during the solid propellant grain curing process. By performing curing simulation analysis of the propellant grain structure, it can accurately simulate the distribution of residual stress and strain during the curing process, and in particular, identify stress concentration areas (such as the contact interface between the propellant grain and the mandrel 1). This transforms subsequent physical monitoring from blindly deploying monitoring points to targeted monitoring, providing a scientific basis for determining the location of key measuring points. It ensures that the deployed online in-situ monitoring network can effectively capture the most representative residual stress and strain data, thereby fundamentally guaranteeing the effectiveness and accuracy of the monitoring. By implanting flexible strain gauges, handling bridging and lead wires, and setting up co-location temperature compensation sensors, an embedded monitoring system capable of stable operation in a high-temperature, high-pressure, and sealed curing environment was constructed. The flexible strain gauges can deform synchronously with the propellant during the curing process and shrink accordingly, avoiding interference from rigid sensors on the propellant material curing process and ensuring signal continuity throughout the entire process from slurry to solid. Co-location temperature compensation can eliminate the interference of temperature changes on minute strain measurement signals in real time, thereby accurately separating the true strain caused by stress. These measures together solve the core bottleneck of the difficulty in implanting sensors in the early stages of curing and ensuring stable and accurate operation throughout the entire cycle. The process of casting and curing engine propellant grains is initiated, and in-situ online monitoring of residual strain during the curing process is conducted simultaneously. This allows for real-time acquisition of residual strain evolution data throughout the entire physicochemical transformation of the propellant grains from a liquid slurry to a viscoelastic solid, rather than a one-time measurement after curing. Based on this, the monitored strain data is inverted into residual stress through constitutive relations, thus obtaining a complete and dynamic database reflecting the true stress state of the propellant grains. This achieves process monitoring rather than result detection, providing data support for a deeper understanding of the generation mechanism and evolution law of residual stress.From simulation prediction, sensor embedding, signal processing to data extraction, the entire technical solution constitutes a closed-loop monitoring process. This method system does not rely on a specific propellant grain configuration or curing process. Based on simulation results and employing embedded flexible sensing, it is applicable to various manufacturing scenarios for solid propellant grains. It provides a standardized technical means for process optimization, quality control, and reliability assessment of solid propellant grains, and has significant engineering application value. This invention's embedded monitoring method for residual strain-stress in solid propellant grain curing combines numerical simulation prediction with embedded in-situ monitoring to construct a complete method for accurate, online, and dynamic monitoring of residual strain-stress in solid propellant grain curing. It effectively solves the long-standing technical problem of difficulty in accurate measurement due to harsh monitoring environments, difficult measurement point layout, and temperature interference, providing solid technical support for improving the structural integrity design and manufacturing process of solid propellant grains.

[0044] like Figure 2 and Figure 3 As shown, the application object of the embodiment method is a scaled-down solid rocket motor structure, mainly including a mandrel 1, a liner 2, a housing 3, a connecting fixture 4, a sealing fixture 5, and a propellant grain 9. The embodiment method is completed by a solidified residual strain-stress embedded monitoring device, which mainly includes a thin film 61, a triaxial strain gauge 62, a thermocouple 63, a cable 64, a wiring hole 65, a data receiver 66, and a data processing terminal 67. The embodiment method is completed in the engine propellant grain curing environment. To match the conventional curing process and the pressure curing process in engineering, the curing load loading fixture includes a temperature chamber 7 and a pressure fixture 8. Optionally, the sealing fixture 5 includes: a bottom sealing bolt 51, a top sealing bolt 52, and a sealing ring 53.

[0045] In this embodiment, step S100 specifically involves: constructing a curing simulation model of the propellant grain structure based on a multi-field coupled constitutive model, where the multi-field coupled constitutive model is a three-dimensional viscoelastic constitutive model related to time-temperature-degree of cure; performing curing simulation analysis through the curing simulation model to obtain the residual stress and residual strain distribution results of the propellant grain structure. More specifically:

[0046] A curing simulation model of the propellant grain structure was constructed based on a multi-field coupled constitutive model, which is a three-dimensional viscoelastic constitutive model related to time, temperature, and degree of cure. The construction process includes:

[0047] Obtain material model parameters: Obtain viscoelastic test data of the entire solid propellant curing process, characterize the degree of solid propellant curing based on the equilibrium modulus in the data, and obtain the curing reaction kinetic model through nonlinear fitting; obtain the heat release of the solid propellant curing reaction to establish a heat flow equation containing an internal heat source; based on the viscoelastic test data and the generalized Maxwell model, obtain the viscoelastic evolution model of the entire solid propellant curing process.

[0048] Establishing a constitutive model: Based on the viscoelastic evolution model, a three-dimensional viscoelastic constitutive model and its incremental equations related to time-temperature-degree of cure are established. The constitutive model is specifically expressed as follows:

[0049] ;

[0050] in, For stress components, For stiffness components, For effective strain components, For the current conversion time, For historical time conversion, Integral time; effective strain components It is obtained by subtracting thermal expansion strain and chemical contraction strain from the total strain.

[0051] Simulation analysis was conducted: User material subroutines (including UMAT, UMATHT, UEXPAN, and FILM) were developed based on the heat flow equation, the three-dimensional viscoelastic constitutive model, and its incremental equations. A multi-field coupled finite element analysis model of the solid propellant grain was established using Abaqus software. The solidification simulation model was used to conduct solidification simulation analysis to obtain the residual stress and residual strain distribution results of the propellant grain.

[0052] Step 100 constructed a fully coupled three-dimensional viscoelastic constitutive model that comprehensively considers the exothermic curing reaction (thermal field), the evolution of curing degree (chemical field), and the evolution of the material's mechanical properties from a viscous flow state to a viscoelastic solid (force field). By developing a series of user material subroutines and embedding them into commercial finite element software, a realistic physical simulation of the complex physicochemical process of solid propellant grain curing was achieved. This overcomes the distortion of residual stress prediction results caused by existing sequential coupling methods or simplified models, providing a reliable theoretical basis for the precise layout of subsequent monitoring points. Through multi-field coupled finite element analysis, the spatiotemporal distribution cloud map of residual stress and residual strain of the propellant grain during the entire curing process can be obtained in advance and visualized. This allows technicians to accurately identify key areas where the maximum residual stress / strain occurs (such as the interface between the propellant grain and the core mold 1, stress concentration points such as the tip of the wing groove), thereby enabling the targeted determination of the optimal measurement point location for embedding flexible strain gauges. This avoids blind monitoring and ensures that the deployed online in-situ monitoring network can effectively capture the most representative and dangerous stress-strain states, improving the effectiveness and accuracy of subsequent physical monitoring. Step S100 constructs and solves a highly simulated "thermal-chemical-mechanical" multi-field coupling model, which not only accurately predicts the solidification residual stress / strain field of the propellant column, but also provides prior knowledge and scientific guidance for the entire monitoring method.

[0053] In this embodiment, step S100 specifically involves: the solidification simulation results of the propellant column structure as follows: Figure 5 As shown, based on the axisymmetric configuration of the propellant grain in the embodiment, the solidification residual stress and strain are concentrated at the propellant grain-core mold interface, with the maximum solidification residual stress point located at the top arc segment of core mold 1. Measurement points are arranged at three axial heights (A / B / C) on the propellant grain structure of the embodiment. A is located at the edge of the top arc segment of core mold 1, which is the point of maximum residual stress in the simulation results. Heights B and C are the axial heights of the measurement points equidistant from height A. In this embodiment, the heights of the measurement points are 45mm apart. Measurement points are also arranged at two circumferential angles on the propellant grain structure of the embodiment. A top view of the sensor measurement point arrangement is shown below. Figure 2 As shown in (c), three test points (#1, #2, #3) are arranged at heights A / B / C on the circumferential angle I, and one verification test point (#4) is arranged at height A on the angle III.

[0054] In this embodiment, step S200 specifically involves: based on the residual stress and residual strain distribution results of the propellant grain structure, determining the location of the maximum residual stress and strain at the contact interface between the propellant grain 9 and the core mold 1; for the residual stress and strain distribution under different propellant grain configurations, setting flexible strain gauges at the corresponding residual strain measurement points on the contact interface, and designing an online in-situ monitoring network. Based on the residual stress and residual strain distribution results obtained through the multi-field coupled finite element analysis model in step S100, the location of the maximum stress and strain is determined. Solidification simulation can reveal the distribution law of the internal stress field of the propellant grain in advance and visually, accurately identifying stress concentration areas such as the contact interface between the propellant grain and the core mold 1. This ensures that the placement of flexible strain gauges is no longer based on empirical guesswork or uniform distribution, but rather directly and purposefully locates the most dangerous and representative key areas. This overcomes the problem of blind measurement point layout caused by the complex structure and unclear internal stress distribution of the propellant grain, ensuring that the constructed online in-situ monitoring network can effectively capture the true and most dangerous stress and strain state of the propellant grain, thereby guaranteeing the representativeness and engineering value of subsequent monitoring data. To address the residual stress and strain distribution under different propellant grain configurations, measuring points are set at corresponding locations. The layout of the monitoring network is not static but dynamically depends on the simulation analysis results of specific propellant grain configurations, making this monitoring method widely applicable. Whether it's a simple star-shaped propellant grain or a complex wing-groove propellant grain, the specific curing simulation results can guide the optimized layout of the sensor network, forming a universal monitoring network design paradigm, rather than a customized solution for a specific model, significantly improving the application scope and value of the technology. Step S200 ultimately outputs the specific measuring point locations and the resulting online in-situ monitoring network design scheme, transforming virtual simulation data into a physical monitoring system. This directly guides specific operations in steps S300 (strain gauge implantation) and S400 (lead wire processing), ensuring that the entire monitoring system can be constructed in-situ at key locations inside the propellant grain according to the predetermined scheme. It also provides an implementation plan for online monitoring in step S600, thereby enabling real-time acquisition of internal stress and strain data during the curing process. This not only ensures the validity and representativeness of the monitoring data, but also makes the method adaptable to different propellant grain configurations and reconfigurable, providing technical support for the final realization of accurate, in-situ, and online monitoring of residual stress-strain in solid propellant grains.

[0055] In this embodiment, the location of residual strain measurement points should consider the actual arrangement range of flexible strain gauges to avoid adjacent residual strain measurement points being too close, and the location of residual strain measurement points should avoid being on surfaces with large curvature. The online in-situ monitoring network should consider the configuration and symmetry of the propellant grains and cover the test path of the location and region of the maximum solidified residual stress-strain of the propellant grain structure. When the measurement points are too dense, the size of each flexible strain gauge and its encapsulation structure will have a certain reinforcing effect on the local propellant grain material, thereby changing the local stress-strain field of that small area. This sensor implantation effect will interfere with the measurement results of neighboring measurement points, leading to data distortion. By setting a reasonable spacing between the measurement points, adjacent residual strain measurement points are avoided from being too close, ensuring that each measurement point captures the true strain signal at that location, unaffected by interference from other sensors, thereby significantly improving the accuracy and reliability of the data acquired by the entire monitoring network. Although flexible strain gauges have good flexibility, they may still experience problems such as poor adhesion, wrinkles, or stress concentration on curved surfaces with excessive curvature (such as sharp corners), leading to reduced strain transfer efficiency or even sensor damage. The residual strain measurement points are placed on surfaces with moderate curvature to avoid large curvature surfaces. This ensures that the flexible strain gauges can achieve complete and reliable adhesion and follow-up deformation with the surface of the drug column during the solidification and shrinkage process, thus ensuring the continuity and integrity of strain signal transmission throughout the entire transformation process from drug slurry to solid. Online in-situ monitoring networks should consider the configuration and symmetry of the propellant grains and cover the test paths of the locations and regions of maximum solidification residual stress-strain in the propellant grain structure. This elevates the layout of the monitoring network from point measurements to a field approach. Point placement based on the configuration and symmetry of the propellant grains utilizes the geometric characteristics of the structure to reduce unnecessary measurement points, achieving efficient network deployment. Covering the locations of maximum stress-strain and critical paths allows for targeted deployment directly targeting the monitoring objective (residual stress). This makes the monitoring network an optimized, intelligent information acquisition system, no longer a simple accumulation of sensors. Instead, it achieves effective monitoring of the overall stress state of the propellant grains, especially the most dangerous stress areas, with minimal hardware cost and wiring complexity, greatly improving the efficiency and economy of the monitoring scheme.

[0056] In this embodiment, the online in-situ monitoring network includes residual strain measurement points and verification measurement points; the verification measurement points are axisymmetric measurement points of any measurement point on the propellant-core mold 1 interface. For propellant columns with axisymmetric structures, under ideal, interference-free curing conditions, the stress-strain response at their axisymmetric positions exhibits high consistency. During monitoring, by comparing the data from the residual strain measurement points with their symmetrical verification measurement points in real time, it is possible to quickly determine whether the measurement results are abnormal. If the data from the two measurement points deviate significantly, it indicates possible abnormalities such as sensor installation problems, local material defects, or signal transmission failures. This enables the monitoring system to possess self-diagnostic capabilities, promptly identifying and warning of unreliable data risks, thereby avoiding the use of erroneous measurement data for subsequent stress inversion and structural evaluation, greatly improving the reliability of the overall monitoring results and the safety of engineering decisions. The verification of the measurement points allows the monitoring network to not only focus on the absolute value of stress but also acquire information about the symmetry of the stress field distribution. By analyzing the differences in the data at symmetrical points, the symmetry accuracy of the propellant column geometry and the uniformity of the temperature and reaction fields during curing can be indirectly assessed. If there is a systematic deviation in the strain values ​​at symmetrical points, it may reflect an asymmetry in the propellant column structure or non-uniformity in the curing process (such as temperature control). This provides valuable feedback information for optimizing mold design and improving curing process parameters, elevating the monitoring method beyond simple stress measurement to a process quality diagnostic tool. Ideally, the high degree of agreement between the symmetrical measurement point data can serve as strong evidence that the residual stress distribution conforms to theoretical predictions (such as simulation results), providing important experimental support for the scientific validity and accuracy of the entire monitoring method (from simulation to measurement). This built-in verification mechanism powerfully demonstrates that the method of this invention can obtain reliable and consistent data, rather than accidental or unrepeatable results.

[0057] In this embodiment, in step S300, a flexible strain gauge of a modified substrate is implanted at the determined measuring point location. The modified flexible substrate strain gauge has a multi-layer encapsulated "sandwich" structure, such as... Figure 4 As shown.

[0058] In this embodiment, step S300 specifically includes: S301, spraying polyurethane release agent onto the outer surface of the core mold 1, and waiting for the polyurethane release agent to cure on the surface of the core mold 1 to form a coating with a thickness of 0.1mm ± 0.05mm; S302, attaching a soft film to the outer surface of the core mold 1 with the polyurethane release agent coating, the soft film being made of polyethylene or latex, and the thickness of the soft film being controlled between 0.04mm and 0.06mm; S303, attaching a resistance triaxial strain gauge 62 at the residual strain measurement point; S304, attaching a polyurethane film with a thickness of 0.05mm ± 0.01mm to the outer interface of the core mold 1. A multilayer flexible interface layer (film 61) consisting of a polyurethane release agent coating, a polyethylene / latex soft film, and a polyurethane film was constructed. This layer ensures smooth separation of the propellant grain from the core mold 1 after curing via the polyurethane release agent. Its overall flexibility allows the strain gauges adhered to it to deform synchronously and unconstrainedly with the propellant grain during curing shrinkage, accurately sensing and transmitting the strain of the propellant grain, rather than receiving distorted signals constrained by the rigid core mold 1. This solves the problem of measurement distortion caused by incoordination between the sensor and the substrate deformation. The multilayer structure, especially the polyurethane film of a specified thickness, forms a protective encapsulation layer around the strain gauge. This encapsulation layer effectively isolates the precision strain gauge from the high-temperature, high-pressure curing environment and the direct impact, corrosion, and short-circuit risks from the chemically active propellant slurry. Simultaneously, precise thickness control ensures that the encapsulation layer possesses sufficient protective strength without compromising strain transmission efficiency due to excessive rigidity, thus improving the reliability and durability of the sensor throughout the long and harsh curing cycle. The entire process, from spraying the release agent to finally attaching the protective film, is completed on the surface of the core mold 1. All material layers are extremely thin and flexible, and their total thickness and rigidity are negligible compared to the massive propellant column. This "embedded" layout minimizes the "reinforcing" or constraint effect of the monitoring system itself on the curing and shrinkage behavior of the propellant column material. It avoids artificially altering the residual stress field of the propellant column under test due to the introduction of monitoring methods, thereby ensuring that the measured data can truly reflect the natural state of the propellant column under the given process. The polyurethane release agent coating has a thickness of 0.1mm ± 0.05mm, serving as the release layer to ensure smooth separation of the propellant cartridge from the core mold 1 after curing. A thickness of at least 0.05mm ensures the continuity and integrity of the coating, effectively preventing adhesion between the propellant cartridge and the core mold 1. As the first layer in direct contact with the propellant cartridge, its thickness is limited to within 0.15mm to avoid excessively thick rigid coatings significantly restricting the curing shrinkage of the propellant cartridge. Within this thickness range, the coating itself possesses a certain degree of flexibility, forming a flexible interface system together with the subsequent soft film, which is the basis for achieving dynamic deformation.The flexible thin film layer, made of polyethylene or latex and with a thickness of 0.04 mm to 0.06 mm, is the core functional layer for strain transmission and initial sensor isolation. The film is extremely thin, with a maximum thickness of 0.06 mm, and is made of flexible material (polyethylene or latex). Its own stiffness is very low, allowing the strain gauge attached to it to sense and transmit the micro-strain of the propellant column with almost no loss, avoiding signal attenuation or distortion caused by excessively thick or rigid transmission layers. This flexible layer allows the entire sensor carrier to shrink and deform synchronously with the propellant column during the curing process, accurately reflecting the strain history of the propellant column, rather than a distorted state due to constraint. This thickness is sufficient to isolate the propellant slurry from the strain gauge in the early stages of casting, preventing short circuits or contamination, while its extreme thinness does not significantly affect the behavior of the propellant column material. The outer polyurethane film, with a thickness of 0.05mm ± 0.01mm, serves as the outermost protective encapsulation layer, ensuring the sensor's survivability and long-term stability under high-temperature and high-pressure curing conditions. Its thickness is controlled between 0.04mm and 0.06mm, ensuring sufficient mechanical strength to effectively resist the pressure, temperature, and chemical environment of the propellant slurry during curing, providing final protection for the internal precision strain gauges and leads. Although the polyurethane film possesses a certain strength, its thickness is strictly limited to a very thin range, ensuring that the overall flexibility of the entire "release agent-soft film-protective film" multi-layer interface system remains intact. Excessive thickness would introduce unnecessary rigidity, while insufficient thickness would fail to provide protection. The three-layer structure and their thickness parameters together define an optimized interface with appropriate rigidity and flexibility. The release layer addresses process feasibility, enabling smooth demolding; the soft film layer ensures measurement accuracy, achieving high-fidelity strain transfer and dynamic deformation; and the protective film layer guarantees system reliability. As a whole, the three-layer structure minimizes the total thickness and stiffness of the interface system, thereby reducing the "implantation effect" or "interference effect" on the curing stress field and shrinkage behavior of the propellant column itself, so that the monitoring results can truly reflect the inherent characteristics of the propellant column in an undisturbed state.

[0059] In this embodiment, the implantation and encapsulation of the flexible strain gauge are carried out in a dry and dust-free environment. A polyurethane release agent is uniformly sprayed onto the entire outer surface of the core mold 1. A soft latex film is attached to the entire area covering the online in-situ monitoring network, serving as the modified flexible substrate for the strain gauge. A polyurethane film is pasted onto the area covering the flexible strain gauge, serving as a curing and bonding transition coating for the propellant charge 9. Dust, moisture, and other contaminants can severely affect the adhesion of the strain gauge (leading to debonding) and the insulation performance of the leads (leading to short circuits). Maintaining the implantation and encapsulation of the flexible strain gauge in a dry and dust-free environment eliminates the risk of early sensor failure due to environmental factors from the outset. This ensures that each implanted sensor has consistent and excellent initial performance, laying a solid foundation for the stable operation of the entire monitoring system during the subsequent high-temperature and high-pressure curing cycle lasting tens of hours. The uniform spraying of polyurethane release agent onto the entire outer surface of the core mold 1 is a crucial step in constructing the release layer. Uniform spraying ensures the continuity and integrity of the coating. The release layer effectively prevents chemical adhesion or mechanical interlocking between the propellant grain 9 and the surface of the core mold 1 after curing. This allows the core mold 1, equipped with the sensor, to be smoothly extracted from the propellant grain after curing, a prerequisite for embedded monitoring and ultimately, the removal of the sensor to acquire data. A latex soft film is attached to the monitoring network area as a flexible substrate modified with strain gauges, creating a flexible sensor carrier that deforms synchronously with the propellant grain. The latex material is extremely thin and soft, with a stiffness far less than that of the propellant grain material. This allows the strain gauges attached to it to sense and transmit the micro-strain of the propellant grain during its transformation from slurry to solid almost without constraint or loss. This accurately reflects the contraction behavior of the propellant grain, rather than being distorted by the constraint effect of the rigid substrate, which is the foundation for achieving high-precision strain measurement. A polyurethane film is adhered to the outermost layer to form a robust protective shell, preventing the high-temperature, high-pressure propellant slurry from directly impacting, abrading, or corroding the internal precision strain gauges and leads during casting and curing. This ensures complete isolation of the sensor circuitry from the potentially conductive propellant slurry, preventing short circuits. As a transitional coating for the curing and bonding of the propellant grain 9, its material properties allow it to form a good bond with both the inner latex film and the outer propellant, ensuring interface stability. This protective layer greatly improves the survivability and long-term operational stability of the sensor system under harsh process environments, ensuring the continuity of the monitoring signal from start to finish.

[0060] In this embodiment, the substrate material of the resistive triaxial strain gauge is at least one of phenolic-acetal, polyimide, and polyurethane, with a substrate size less than or equal to 15mm × 15mm and an overall thickness less than or equal to 30μm. The typical resistance value is 120Ω, and the strain limit is 2.0% ± 0.1%. The operating temperature covers the curing temperature range of the propellant grain 9 (20℃ to 70℃), and the operating temperature is -80℃ to +150℃. The triaxial design allows for simultaneous measurement of strain in multiple directions at the measuring point, thereby calculating the magnitude and direction of the principal strain at that point. Combined with the high-precision resistance value of 120Ω and the strain limit of 2.0% ± 0.1%, this ensures that the sensor maintains sufficient measurement sensitivity and has a certain overload margin when measuring the minute curing shrinkage strain of the propellant grain (residual strain level of 0.1% to 10.0%), preventing damage due to accidental local deformation. This solves the technical challenge of high-precision measurement of micro-strain inside the propellant grain. The substrate material is limited to at least one of phenolic acetal, polyimide, and polyurethane. These materials are all proven polymers with excellent insulation, flexibility, and high-temperature resistance. Polyimide, in particular, is known for its excellent high and low temperature resistance and chemical stability. This material selection enables the strain gauge to withstand the high-temperature environment (20°C to 70°C) of the propellant curing process and resist the chemical erosion that may be caused by the propellant slurry. The ultra-thin design with an overall thickness of ≤30μm reduces the stiffness of the sensor itself, allowing it to deform in tandem with the flexible encapsulation layer and minimize the implantation effect on the propellant stress field. The miniaturized design with a substrate size of ≤15mm×15mm allows the sensor to be precisely positioned in key stress areas (such as the interface of mandrel 1) with limited dimensions determined by simulation, without "averaging" local strain peaks due to its physical size covering an excessively large area. The small, ultra-thin sensor combined with flexible packaging technology minimizes the stiffness and volume of the entire monitoring module, effectively avoiding significant changes in the local curing shrinkage behavior of the propellant grain due to embedding the monitoring device. This ensures that the measured strain data accurately reflects the inherent characteristics of the propellant grain under undisturbed conditions, improving the fidelity of the monitoring results. The temperature range covers the curing temperature range of propellant grain 9 (20℃ to 70℃) and can be extended to -80℃ to +150℃. This not only covers conventional curing processes but also reserves space for possible low-temperature storage tests or special high-temperature processes. This makes the monitoring method based on this sensor universal for various curing processes (such as conventional curing and pressure curing), rather than only applicable to a specific temperature profile. The broadened temperature range enhances the potential of this technical solution as a general and standardized monitoring method.

[0061] In this embodiment, step S400 specifically includes: S401, the flexible strain gauge bridging method adopts an independently compensated 1 / 4 bridge connection, or a hybrid bridge of half bridge and full bridge sharing the compensation gauge; S402, all leads of the flexible strain gauge at each residual strain measuring point in the online in-situ monitoring network are braided into a single-strand lead, and cables 64 are led out from the wiring hole 65 on the core mold 1; S403, after all cables 64 are led out, the wiring hole 65 is sealed with sealant. In step S401, the bridging method adopts either an independently compensated 1 / 4 bridge connection or a half-bridge / full-bridge hybrid bridge with a shared compensation plate. Both methods have a built-in temperature compensation mechanism. By connecting the working strain gauge to an adjacent arm of the measuring bridge with a compensation plate that is in the same temperature environment but does not bear mechanical strain, the resistance change caused by temperature change, i.e., temperature drift, can be automatically canceled. This design effectively eliminates the interference of temperature fluctuations on the weak strain signal (micro-strain level) during the curing process from the circuit principle level, so that the measurement system can accurately separate the real mechanical strain caused by the shrinkage of the propellant grain. This solves the technical problem of accurate measurement of the residual stress of the curing of the micro propellant grain 9, and ensures the high signal-to-noise ratio and accuracy of the original data on which the subsequent stress inversion is based. In step S402, the multiple leads of the strain gauge at each measuring point are braided into a single lead and led out from the wiring hole 65 on the core mold 1, integrating the scattered and easily tangled fine leads into a robust wire bundle. The integrated wire bundle avoids the risk of multiple fine leads breaking, short-circuiting or interfering with each other due to fluid impact or material flow during the slurry pouring and curing process, and improves the physical robustness of the signal transmission link. The centralized lead-out through the preset wiring hole 65 makes the wiring clear and orderly, minimizes the space occupied by the leads inside the slurry, reduces interference with the slurry flow and curing field, and meets the requirements of minimal invasiveness for embedded monitoring. In step S403, after all the single-strand leads are led out, the wiring hole 65 is sealed with sealant. This is a sealing step after all internal wiring is completed. Sealing the wiring hole 65 completely prevents propellant slurry from leaking out of the hole during pouring and pressurized curing. The sealing treatment ensures the airtightness of the curing tank or mold, and is particularly suitable for curing processes that require maintaining a specific pressure or atmosphere, preventing the process conditions from being disrupted by the introduction of a monitoring system. The sealant also fixes and buffers the stress on the roots of the leads leading out of the core mold 1, preventing them from being accidentally pulled and damaged in subsequent operations. Optionally, the wiring hole 65 is located at the bottom of the core mold 1, with the lowest C measuring point height spacing being more than 90mm, and the diameter of the wiring hole 65 is 6mm. In addition, the wiring channels (wiring holes 65) of the core mold are all rounded. After wiring, the wiring hole 65 is sealed with waterproof sealant, and the air pressure test verifies that the sealing requirements are met.

[0062] In this embodiment, in the test area, a wiring hole 65 is drilled in the region of residual stress concentration after curing, away from the propellant grain structure of the core mold 1. The edges and corners of the wiring hole 65 are rounded to prevent frictional contact that could cut the lead wire. The diameter of the wiring hole 65 is determined based on the number of leads. The wiring hole 65 is designed according to the configuration of the core mold 1 and the network layout of residual strain measurement points to avoid internal lead wire redundancy, employing a multi-channel design. The sealant meets the sealing requirements under the pouring and pressurized curing of the propellant grain 9. Sharp edges and corners can cause stress concentration during lead wire exit and subsequent propellant grain curing and shrinkage. The rounded edges and corners of the wiring hole 65 disperse the concentrated local stress, smooth the contact interface between the lead wire and the hole wall, eliminate the risk of lead wire breakage due to mechanical friction and stress concentration, and ensure the long-term physical connection reliability of the entire signal path from the sensor to the data acquisition instrument under harsh process conditions. The diameter of the wiring hole 65 is determined according to the number of wirings, and a multi-channel wiring hole is adopted to avoid internal lead redundancy, based on the structured and modular wiring concept of actual needs. The hole diameter is matched with the number of wire bundles to avoid weakening the structural strength of the core mold 1 due to excessively large holes, or causing difficulties in wire threading and compression damage due to excessively small holes. The design is combined with the configuration of the core mold 1 and the network layout of residual strain measurement points to make the wiring path the shortest and most direct, reducing the crossing, entanglement and redundancy of leads inside the core mold 1. This not only reduces the wiring complexity, but also minimizes the potential interference of the leads themselves to the flow of propellant material and the curing field, reflecting the high-order requirement of minimal invasiveness for embedded monitoring. The sealing of the cable routing hole 65 is achieved by sealing the propellant grain 9 with sealant, which meets the sealing requirements during the pouring and pressurized curing of the propellant grain. The sealant plays a dynamic sealing role here. During the pouring stage, it can prevent liquid propellant slurry from leaking out of the hole and ensure the integrity of the propellant grain geometry. During the pressurized curing stage, it can withstand the internal pressure, maintain the sealed environment of the curing tank or mold, and ensure that the process conditions meet the design requirements. Reliable sealing is a prerequisite for preventing production safety accidents and ensuring the curing quality of the propellant grain, enabling online monitoring to be carried out safely without disrupting the original process flow.

[0063] In this embodiment, step S500 specifically involves: connecting the cable 64 of the extended flexible strain gauge to the strain test data receiver 66; the data receiver 66 transmitting the test data to the computer (data processing terminal 67) for data processing and analysis; turning on the data receiver 66 and checking the signals of each connection channel; for flexible strain gauges using a 1 / 4 bridge connection, using an additional temperature compensation plate to eliminate temperature drift, or using a shared ambient temperature compensation algorithm to eliminate temperature drift. By connecting the leads of the extended flexible strain gauge to the strain test data receiver, a physical connection is established from the sensor to the data acquisition hardware. The test data is then transmitted to the computer via the data receiver, completing the conversion and transmission from analog electrical signals to digital data. This enables real-time, continuous acquisition and recording of residual strain data throughout the entire curing process of the propellant column, truly realizing online in-situ monitoring. This ensures that the key mechanical state information inside the propellant column during the curing process can be completely and continuously captured and preserved, providing an indispensable raw data source for subsequent analysis. Before the formal monitoring begins, turning on the data receiver and checking the signals of each connection channel is an initial state diagnosis of the entire signal link (from the strain gauge to the data receiver). By checking the signals of each channel (such as initial resistance value, zero-point drift, etc.), faults caused by broken leads, poor contact, or damaged sensors can be detected and eliminated in time before the curing begins. This ensures that all deployed measuring points are in an effective working state at the start of monitoring, avoids data loss due to hardware problems, and guarantees the integrity and reliability of monitoring data from the source. For flexible strain gauges using a 1 / 4 bridge connection, two paths are provided to eliminate temperature drift: one is hardware compensation using additional temperature compensation gauges, and the other is software compensation using a shared ambient temperature compensation algorithm. Temperature changes cause changes in the resistance value of the strain gauge, generating false signals unrelated to the actual mechanical strain. The compensation gauge method automatically cancels this error by using compensation gauges in adjacent arms of the bridge (which are in the same temperature environment but do not bear strain). The algorithm compensation method measures the ambient temperature and uses a preset model to subtract the error component caused by temperature during the data processing stage. This design accurately solves the problem of accurate measurement of the residual stress of the solidified micro propellant grain 9. Since the residual strain of the solidified propellant grain itself is very small, ranging from 0.1% to 10.0%, the noise introduced by temperature fluctuations can seriously interfere with or even drown out the true signal. Through effective temperature compensation, the mechanical strain caused purely by the contraction of the propellant grain can be extracted with high fidelity, thus providing the most critical and reliable input data for the high-precision inversion of residual stress based on constitutive relations in step S700.

[0064] In this embodiment, when an additional temperature compensation plate is used, the three grid wires of the triaxial strain gauge share a single temperature compensation plate. The temperature compensation plate is attached to a stress-free location with the same material, the same packaging, and the same ambient temperature. For the residual stress test of the propellant grain 9 after curing, the temperature compensation plate is placed outside the engine combustion chamber under the same curing environment, with the same core mold 1 material and the same packaging conditions, and is simultaneously cured and monitored. The design of using a single temperature compensation plate for the three grid wires of the triaxial strain gauge ensures that temperature changes cause synchronous changes in the resistance values ​​of all strain gauges (including the three working grid wires and the compensation plate). Since the compensation plate and the working grid wires are in the same temperature field, connecting them to adjacent arms of the measuring bridge can automatically cancel out the resistance changes caused by temperature. This one-to-many compensation method, compared to configuring a separate compensation plate for each grid wire, significantly simplifies circuit layout, reduces the number of hardware components, and improves system integration and reliability. It ensures that strain measurements in all three directions are compensated based on the same temperature reference, avoiding compensation errors introduced by minor differences in the performance of multiple compensation plates, and guaranteeing the consistency and comparability of measurement data in different directions. The temperature compensation plate is attached to a stress-free location with the same material, the same packaging, and the same ambient temperature. The temperature compensation plate must only sense temperature changes and not bear any mechanical stress caused by the contraction of the propellant or external loads, ensuring that the change in the resistance of the compensation plate is entirely caused by temperature fluctuations. When the working strain gauge (sensing both temperature and stress) and the compensation plate (sensing only temperature) are connected to a Wheatstone bridge, the output signal of the bridge can accurately filter out the temperature component and retain only the true strain signal caused by mechanical stress. For the curing environment of the propellant grain, which is sealed, high-pressure, and encapsulated in propellant slurry, a temperature compensation plate is placed outside the engine combustion chamber under the same curing environment. However, it is also required to be under the same material and encapsulation conditions as the core mold 1, and to be simultaneously cured and monitored. This simulates a twin compensation plate with the exact same thermal history and encapsulation state as the working strain gauge on the core mold 1. This external deployment strategy cleverly solves the problem that the compensation plate cannot find a truly stress-free position inside the propellant grain. By ensuring that the compensation plate and the working strain gauge experience the exact same temperature history and encapsulation conditions, their temperature response characteristics are highly consistent. In this way, even if the compensation plate is outside the combustion chamber, it can accurately simulate and offset the temperature effect experienced by the working strain gauge on the core mold 1, thereby achieving effective compensation and solving the technical bottleneck of implementing high-precision temperature compensation in harsh embedded monitoring scenarios.

[0065] In this embodiment, when using the shared ambient temperature compensation algorithm, calibration is performed before the residual stress test of the propellant grain 9 after curing. Sample strain gauges of the same batch and model as the actually implanted flexible strain gauges are pasted onto a stress-free calibration propellant block with the same coefficient of thermal expansion as the propellant grain 9 material, and placed in the same curing temperature environment. The temperature compensation readings of the flexible strain gauges under the curing temperature history in a state of no curing shrinkage stress are then obtained. At this point, the flexible strain gauge has no other mechanical stress, and the strain reading is entirely caused by temperature effects. Before testing, it is required that strain gauges of the same batch and model be used, adhered to a stress-free calibration propellant block with the same thermal expansion coefficient as the propellant grain 9 material, and calibrated under the same curing temperature environment. This calibration process accurately reproduces the temperature history and most of the physical environment experienced by the strain gauge in actual monitoring (same sensor, same thermal expansion characteristics of the substrate material, same temperature field). However, the only key difference is that the calibration block is in a stress-free state, making the strain readings collected during calibration purely caused by temperature changes. This allows for the direct establishment of an accurate mathematical model (i.e., compensation algorithm) of the "temperature-strain response" for this specific sensor and environment. This model can predict with high fidelity the strain reading generated solely by thermal effects at any temperature. During formal monitoring, by monitoring the ambient temperature in real time and calling the compensation algorithm obtained from the aforementioned calibration, the pure temperature effect reading calculated by the algorithm can be subtracted from the total reading of the working strain gauge in real time. This software compensation method can overcome the residual compensation error that hardware compensation (such as shared compensation gauges) may cause due to slight performance differences or positional temperature differences between the compensation gauge and the working gauge. It is especially suitable for complex structures where it is impossible to arrange hardware compensation gauges in ideal locations near the measuring point. The soft compensation performed by the algorithm achieves near-ideal elimination of temperature interference signals, thereby enabling high-fidelity extraction of mechanical strain caused purely by the solidification and shrinkage of the propellant from complex mixed signals. The method does not rely on finding and deploying additional hardware compensation gauges inside the core mold 1 or the engine. Instead, it achieves compensation through prior calibration experiments and software algorithms, simplifying the complexity and cost of hardware deployment at the monitoring site and avoiding the technical and reliability challenges brought about by additional leads and encapsulated compensation gauges inside the space-constrained propellant. As long as accurate calibration can be performed, this method can be flexibly applied to various complex propellant configurations and sensor layout scenarios, enhancing the versatility and scalability of the entire monitoring method. Based on a pre-calibrated shared environmental temperature compensation algorithm, a software compensation benchmark with clear physical meaning and high environmental matching degree is constructed. This achieves accurate modeling and real-time subtraction of temperature interference signals in a "soft" manner. It not only has potential advantages in compensation accuracy, but also reduces the hardware complexity and implementation difficulty of the monitoring system. It provides another effective and powerful technical path for achieving high-precision and high-reliability measurement of micro residual strain in the complex and harsh environment of solid propellant grain solidification, ensuring the accuracy of the final data of the entire monitoring method.

[0066] In this embodiment, when using a shared ambient temperature compensation algorithm, real-time temperature acquisition and compensation calculation are performed, and the real-time strain values ​​of the flexible strain gauge are simultaneously acquired during the curing process. Simultaneously, a miniature thermocouple (thermocouple 63) is used to collect temperature data in real time near the flexible strain gauge. The effect of temperature on strain gauges is dynamic, and the temperature field during the curing process is not constant. By acquiring temperature data in real time near the flexible strain gauge using miniature thermocouples, the precise temperature history over time at the measurement point can be obtained. The real-time strain value of the strain gauge is acquired simultaneously, and the real-time temperature data is input into a pre-calibrated shared ambient temperature compensation algorithm for real-time calculation, ensuring that the compensation behavior is completely synchronized with the measurement process. The system can instantly deduct the spurious strain component caused by temperature at each moment from the mixed measurement signal, effectively overcoming the lag and inaccuracy of compensation based on fixed temperature values ​​or average temperatures. It achieves dynamic tracking and filtering of temperature interference, thereby ensuring that every data point throughout the long curing cycle represents the true mechanical strain after precise compensation. Inside the propellant column, especially in large propellant columns or complex molds, there may be a slight temperature gradient. If the temperature measurement point and the strain gauge measurement point are too far apart, the temperatures sensed by the two will differ. By placing the temperature acquisition point close to the flexible strain gauge and using a miniature thermocouple for near-field measurement, the temperature sensor and strain gauge are ensured to be in the same local thermal environment. This allows the temperature data used by the compensation algorithm to accurately reflect the actual temperature of the strain gauge, significantly improving the accuracy and reliability of temperature compensation and avoiding residual compensation errors introduced by inaccurate temperature measurement locations. The real-time acquired temperature and raw strain signals are processed in real-time using an embedded algorithm, directly outputting the compensated, true mechanical strain result. This enables the monitoring system to reflect the stress-strain state of the propellant column online and instantly, without waiting for complex post-processing after curing. This not only provides researchers with a real-time window to observe the curing process, allowing them to dynamically understand the impact of process parameters on stress development, but also provides a data foundation and technical possibility for future active intelligent control of the curing process (such as adjusting the temperature control curve based on real-time stress data).

[0067] In this embodiment, when using the shared ambient temperature compensation algorithm, it is based on real-time temperature data. Call the corresponding temperature compensation data The actual strain is obtained by performing compensation calculations. The specific formula is as follows: A clear input-output relationship model was established: True strain = Total measured strain - Pure temperature effect strain; where, It was established through prior calibration and real-time temperature data. A one-to-one correspondence function or database, this mathematical expression eliminates the technical goal of temperature drift, transforming it into a deterministic, programmable subtraction operation. This allows the entire compensation process to be executed automatically and accurately by computer, no longer relying on the operator's experience and judgment. This ensures the objectivity, consistency, and repeatability of the compensation results, providing an algorithmic foundation for building standardized monitoring procedures. Based on real-time temperature data... The corresponding temperature compensation data is retrieved; the effect of temperature on strain is both transient and continuous. This is achieved through real-time data acquisition. And synchronously call the corresponding The compensation calculation is performed synchronously with the measurement process, enabling dynamic tracking and real-time filtering. The system can instantly adjust the temperature fluctuations at any point during the curing process based on the measured values ​​at that moment. Subtract the spurious strain component caused by the temperature at that moment. This effectively overcomes the errors caused by relying on fixed compensation coefficients or post-processing averaging, ensuring that the data collected at each time point during the entire phase transition process from slurry to solid are consistent. These are strain values ​​that have undergone precise and timely compensation and reflect actual mechanical deformation. The output results are... This refers to mechanical strain caused purely by chemical shrinkage and mechanical constraints, stripped of temperature effects. This is the high-quality input data necessary for stress inversion in step S700 using a three-dimensional viscoelastic constitutive model based on the time-temperature-degree-of-curing correlation; by providing high-fidelity... The data stream compensation algorithm fundamentally solves the technical bottleneck of unreliable stress inversion results caused by the low signal-to-noise ratio of the original measurement signal (subjected to temperature noise). It enables the precise calculation of complex constitutive models to be based on reliable data, thereby ultimately achieving the core invention objective of "accurately obtaining the corresponding solidification residual stress".

[0068] In this embodiment, step S600 specifically involves: pouring uncured propellant slurry 91 into the combustion chamber of the engine propellant grain, assembling the fixture, and transferring it to the curing environment, i.e., placing it in the temperature chamber 7 and connecting it to the pressure fixture 8 (including the pressure port 81 and the pressure bladder 82). For pressure curing, the temperature chamber 7 needs to be preheated to the curing environment temperature of 50°C. A hydraulic pump is connected to the pressure port 81 via a sealed pipeline, and the pressure is pumped into the pressure bladder 82 to 1.2 MPa; propellant grain curing begins, and simultaneously, the embedded monitoring device 6 (flexible strain gauge, data receiver 66, data processing terminal 67) is activated to begin in-situ online monitoring of residual strain in the propellant grain during the curing process. After 7 days of curing, the temperature of the temperature chamber is reduced to room temperature at a rate of 1.25°C / h, and the pressure is unloaded to zero at a rate of 0.05 MPa / h. The curing load is then maintained for 6 days to end the curing process. The accumulation of residual stress is a dynamic process that runs through the entire process of chemical cross-linking reaction, volume shrinkage, and cooling of the slurry. By strictly synchronizing the start-up of the monitoring device with the start of the curing process, the monitoring system can continuously and in real time record strain data throughout the entire time series from the start of slurry pouring, through gelation, curing reaction, to final cooling and shaping. This avoids the information loss caused by a one-time measurement after curing. It allows researchers to observe and analyze the accumulation rate and variation law of residual stress in different curing stages (such as the peak of the reaction exothermic period and the main shrinkage period), providing the most direct experimental evidence for a deep understanding of the generation mechanism and evolution dynamics of residual stress. The execution of step S600 is the final verification of steps S100 (solidification simulation analysis) and S200 (deploying the monitoring network based on simulation results). Whether the stress concentration area predicted by the simulation actually exists and whether the deployed sensor network can work effectively must be verified through actual solidification monitoring. The strain data acquired in real time can be dynamically compared and verified with the finite element simulation results in step S100. If the measured data matches the trend and magnitude of the simulation prediction, it strongly proves the accuracy and reliability of the multi-field coupled constitutive model and simulation method. At the same time, this also verifies that the sensor deployment scheme based on simulation guidance (step S200) is scientific and effective, successfully capturing the mechanical response of key parts, thus completing the technical closed loop from virtual prediction to physical verification. By embedding monitoring into standard production processes (pouring, tooling assembly, and transfer to the curing environment), the monitoring data is strictly correlated with specific curing temperature profiles, pressure conditions, and other process parameters over time. This transforms the monitored data from isolated mechanical signals into information with clear engineering significance, bound to specific process conditions. By analyzing the real-time strain response under different process parameters (such as changing the curing temperature profile), the impact of process parameters on the magnitude and distribution of the final residual stress can be quantitatively assessed. This provides a scientific basis and precise data support for optimizing the curing process and actively controlling residual stress to improve propellant quality.

[0069] In this embodiment, the propellant column 9 undergoes shrinkage strain after solidification. At this point, the propellant has completed the solidification process from the slurry (the uncured propellant slurry 91 after casting) to the column (i.e., the solidified propellant column 92). The schematic diagram of the monitoring device after solidification is shown below. Figure 3 As shown. At this time, the flexible strain gauge contracts synchronously with the solidified propellant column 92.

[0070] In this embodiment, step S700 specifically involves: after the propellant grain solidification process is completed, ending the monitoring of residual strain during propellant grain solidification, extracting strain test data, and calculating the corresponding residual stress based on the mechanical property parameters of the propellant material during the solidification process. The specific formula is as follows:

[0071] ;

[0072] in, t This refers to the current time or a specific calculation moment, i.e., the point in time when stress is calculated. T For the corresponding time t Temperature that affects material properties These are variables that reflect the intrinsic properties of propellant materials and are related to their mechanical properties. C (...) represents the relaxation modulus or a related material response function. This refers to the strain during the curing process. For the integration variable over past time, In response Regarding past time The partial derivatives. Step S600, by starting curing and opening the strain monitoring device, begins in-situ online monitoring of residual strain in the propellant column during the synchronous curing process. This ensures strict synchronization between monitoring and process progress. Utilizing the flexible strain sensor network embedded in previous steps, the monitoring system can continuously and in real-time capture the dynamic evolution data of residual strain at key locations inside the propellant column (such as the interface of core mold 1) throughout the entire phase transition process from liquid slurry pouring to viscoelastic propellant column curing. This provides time-series information that traditional destructive testing after curing cannot obtain, providing direct experimental data for understanding the accumulation dynamics of residual stress and verifying the curing simulation model. The integral formula provided in step S700 is an integral constitutive relation describing the stress relaxation behavior of viscoelastic materials. The residual stress σ at the current time t is the cumulative result of the material's memory effect of the entire historical strain rate of change, and it considers the evolution of material properties during the curing process (through...). (Reflection), through this formula, the strain history data obtained from online monitoring in step S600 can be represented. By accurately inverting material parameters into the final engineering parameter of interest, "curing residual stress," the core technical challenge of obtaining accurate residual stress from measured strain data is solved, elevating monitoring from qualitative perception to quantitative assessment. Steps S600 and S700 are the final stages of the entire monitoring process. The real-time monitoring data acquired in S600 can be compared and verified with the prediction results of step S100 (curing simulation based on a multi-field coupled constitutive model). S700 uses the monitoring data and material model to output the final stress assessment result, making the entire technical solution a self-verifying and self-improving closed-loop system. Simulation guides monitoring (point placement in step S200), monitoring data is used to verify and correct the simulation model, and finally, stress information is extracted from the monitoring data through a rigorous constitutive model (formula in step S700). This closed loop greatly enhances the scientific rigor, reliability, and engineering practicality of the monitoring method, making it not only a measurement tool but also a research and development platform for deepening the understanding of the curing process. By closely combining two pillars—in-situ online monitoring to obtain strain history and constitutive model inversion of stress based on viscoelastic theory—a complete technical chain has been realized for capturing the residual stress of solid propellant grains from the dynamic process to static quantitative assessment. This effectively solves the key bottlenecks of traditional methods, such as the difficulty in online measurement under harsh curing environments and the difficulty in accurately deriving stress values ​​from strain data. It provides direct, accurate, and physically meaningful data support and analysis methods for assessing the structural integrity of solid propellant grains, optimizing processes, and improving reliability.

[0073] Matters not covered in this invention are common knowledge.

[0074] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0075] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

[0076] The above description is merely a preferred embodiment of the present invention and is 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. An embedded monitoring method for residual strain-stress after solid propellant grain solidification, characterized in that, Includes the following steps: S100, simulation analysis of solidification of propellant column structure; Step S100 specifically involves: constructing a curing simulation model of the propellant column structure based on a multi-field coupled constitutive model, wherein the multi-field coupled constitutive model is a three-dimensional viscoelastic constitutive model related to time-temperature-degree of curing. The residual stress and residual strain distribution of the propellant grain structure were obtained by performing a solidification simulation analysis using a solidification simulation model. S200. Based on the simulation analysis results of the curing of the propellant column structure, the residual stress of curing is determined, and the measurement point position of the flexible strain gauge is determined, so as to deploy an online in-situ monitoring network. Step S200 specifically involves: based on the residual stress and residual strain distribution results of the propellant grain structure, determining that the location of the maximum residual stress and strain is at the contact interface between the propellant grain and the mandrel; for the distribution of residual stress and strain under different propellant grain configurations, setting flexible strain gauges at the corresponding residual strain measurement points on the contact interface, and designing an online in-situ monitoring network. S300. Insert flexible strain gauges at the determined measuring points and complete the encapsulation. Step S300 specifically includes: S301. Spray polyurethane release agent onto the outer surface of the core mold and wait for the polyurethane release agent to cure on the surface of the core mold to form a coating with a thickness of 0.1mm ± 0.05mm. S302. A soft film is attached to the outer surface of the core mold coated with a polyurethane release agent. The soft film is made of polyethylene or latex and its thickness is controlled between 0.04 mm and 0.06 mm. S303. Adhesive triaxial strain gauges are attached to the residual strain measurement points. S304. A polyurethane film with a thickness of 0.05mm ± 0.01mm is pasted onto the outer interface of the core mold; The implantation and encapsulation of the flexible strain gauge are carried out in a dry and dust-free environment; a polyurethane release agent is uniformly sprayed on the entire outer surface of the core mold; a soft latex film is attached to the entire area covering the online in-situ monitoring network and serves as a modified flexible substrate for the strain gauge; a polyurethane film is pasted on the area covering the flexible strain gauge and serves as a bonding transition coating for the propellant charge. The substrate material of the resistive triaxial strain gauge is at least one of phenolic-acetal, polyimide, and polyurethane, with a substrate size of less than or equal to 15mm × 15mm and an overall thickness of less than or equal to 30μm; the typical resistance value is 120Ω, and the strain limit is 2.0% ± 0.1%; the operating temperature covers the propellant grain curing temperature range, and the operating temperature is -80℃ to +150℃. S400: Handles bridging and lead-in of flexible strain gauge test networks and fixes the connection fixtures required for testing. S500, test the network signal and set the co-position temperature compensation sensor; S600, casting and curing of the propellant column structure, and in-situ online monitoring of residual strain of the propellant column during the synchronous curing process; S700: Once the propellant column structure has cured, strain test data is extracted, and the corresponding residual stress after curing is obtained.

2. The solid propellant grain cure residual strain-stress embedded monitoring method of claim 1, wherein, The online in-situ monitoring network includes residual strain measurement points and verification measurement points; The verification measurement point is an axisymmetric measurement point of any measurement point on the drug-core mold interface.

3. The method of claim 1, wherein the solid propellant grain cure residual strain-stress embedded monitoring method is characterized by, Step S400 is as follows: S401. The flexible strain gauge bridging method adopts an independently compensated 1 / 4 bridge connection, or a hybrid bridge consisting of half bridges and full bridges sharing the compensation gauges. S402. In the online in-situ monitoring network, all leads of the flexible strain gauges at each residual strain measurement point are braided into a single-strand lead and led out from the wiring hole on the mandrel. S403. After all the single-strand leads are led out, seal the cable routing hole with sealant.

4. The solid propellant grain cure residual strain-stress embedded monitoring method of claim 3, wherein, In the area of ​​residual stress concentration after curing, which is far from the propellant charge structure, i.e. the test area, a wiring hole is drilled. The edges of the wiring hole and the corners are rounded to avoid frictional contact that could cut the lead wire. The diameter of the cable routing hole is determined according to the number of cables. The wiring holes are designed based on the core mold configuration and the residual strain measurement point network layout to avoid internal lead redundancy, and multiple wiring channel holes are used. The sealant meets the sealing requirements under propellant grain casting and pressurized curing.

5. The method of claim 1, wherein, Step S500 is as follows: The leads of the flexible strain gauge are connected to the strain test data receiver, which transmits the test data to the computer for data processing and analysis. Turn on the data receiver and check the signal strength of each connection channel; For flexible strain gauges with 1 / 4 bridge connections, additional temperature compensation gauges are used to eliminate temperature drift, or a shared ambient temperature compensation algorithm is used to eliminate temperature drift.

6. The solid propellant grain cure residual strain-stress embedded monitoring method of claim 5, wherein, When using an additional temperature compensation plate, the three grid wires of the triaxial strain gauge share one temperature compensation plate, and the temperature compensation plate is attached to a stress-free position with the same material, the same packaging, and the same ambient temperature. For the residual stress test of propellant grain curing, the temperature compensation sheet was placed outside the engine combustion chamber under the same curing environment, with the same core mold material and the same packaging conditions, and the curing was monitored synchronously.

7. The solid propellant grain cure residual strain-stress embedded monitoring method of claim 5 wherein, When using a shared ambient temperature compensation algorithm, calibration is performed before the propellant grain curing residual stress test. Sample strain gauges of the same batch and model as the actual implanted flexible strain gauges are attached to a stress-free calibration propellant block with the same coefficient of thermal expansion as the propellant grain material, and placed in the same curing temperature environment. The temperature compensation readings of the flexible strain gauges under the curing temperature history under the state of no curing shrinkage stress are then obtained. ; At this point, the flexible strain gauge is not subjected to any other mechanical stress, and the strain reading is entirely caused by the temperature effect.

8. The solid propellant grain cure residual strain-stress embedded monitoring method of claim 7, wherein, When using a shared ambient temperature compensation algorithm, real-time temperature acquisition and compensation calculation are performed, and the real-time strain values ​​of the flexible strain gauges are simultaneously acquired during the curing process. ; Simultaneously, miniature thermocouples are used to collect temperature data in real time near the flexible strain gauge. .

9. The solid propellant grain cure residual strain-stress embedded monitoring method of claim 8, wherein, When the common ambient temperature compensation algorithm is adopted, real-time temperature data is used to calculate the real strain corresponding temperature compensation data is called , and compensation calculation is performed to obtain the real strain The specific formula is as follows: 。 10. The method of claim 1, wherein, Step S600 is as follows: Propellant slurry is poured into the combustion chamber of the engine propellant grain, and after assembling the tooling, it is transferred to the curing environment to begin curing. The strain monitoring device is turned on to start in-situ online monitoring of the residual strain of the propellant grain during the synchronous curing process.

11. The method of claim 1, wherein, Step S700 is as follows: After the propellant grain curing process is completed, residual strain monitoring is stopped, strain test data is extracted, and the corresponding residual stress is calculated based on the mechanical property parameters of the propellant material during the curing process. The specific formula is as follows: in, t This refers to the current time or a specific calculation moment, i.e., the point in time when stress is calculated. T For the corresponding time t Temperature that affects material properties β These are variables that reflect the intrinsic properties of propellant materials and are related to their mechanical properties. C (...) represents the relaxation modulus or related material response function, ε represents the strain during the curing process, and τ represents the integral variable over past time. In response ε Regarding past time τ The partial derivatives of .

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