Strain testing method for ultra-low temperature internal pressure burst test

Abstract

This invention discloses a strain testing method for cryogenic internal pressure burst tests, belonging to the field of ground testing of solid rocket engines. The method includes: placing a pressure vessel in a sealed cryogenic cavity, suspending a reference strain gauge inside the cavity, and arranging a working strain gauge on the surface of the pressure vessel, with all strain gauges operating in the same temperature field; calibrating the inherent deviation coefficients of each channel under ambient temperature and no-load conditions; collecting temperature drift signals from the reference and working strain gauges during cavity cooling and at multiple temperature levels, and fitting a globally shared temperature drift proportionality coefficient using the linear correlation between their temperature drifts; throughout the burst test, uniformly correcting the original strain signals based on the global temperature drift proportionality coefficient and the inherent deviation coefficients of each channel to obtain the true strain. This invention requires only one reference gauge to achieve unified temperature drift compensation across multiple channels, simplifying the cavity layout, unifying the temperature compensation benchmark for all channels, shortening the calibration cycle, and adapting to the entire process of dynamic cooling, steady-state pressure holding, and instantaneous burst testing.

Description

Technical Field

[0001] This invention belongs to the field of ground test technology for solid rocket engines, specifically relating to a strain testing method for cryogenic internal pressure burst tests. It is used to test the strain of pressure vessels in cryogenic internal pressure burst tests, and is particularly suitable for full-range multi-channel strain testing of engine casing structures in a cryogenic environment of 77K in the liquid nitrogen temperature range. Background Technology

[0002] Cryogenic internal pressure burst testing is a core testing method for verifying the structural strength and ultimate load-bearing capacity of engine casings. This test involves continuously applying increasing internal pressure to the casing within a sealed cryogenic chamber, simultaneously collecting strain data at multiple measurement points on the casing surface to accurately determine the ultimate burst failure state of the casing. Because the test conditions involve cryogenic environments ranging from room temperature to liquid nitrogen (77K), accompanied by gradual loading and instantaneous bursting of internal pressure, extremely high requirements are placed on the strain testing system's ability to suppress temperature drift, signal fidelity, and consistency of multi-channel data.

[0003] The resistance strain gauge method is the most widely used technique in structural strain testing. In cryogenic environments, the resistivity of the strain gauge wires and the mechanical properties of the adhesive layer change significantly with temperature. To eliminate spurious strain outputs caused by temperature variations, existing technologies generally employ a Wheatstone bridge compensation architecture. This involves placing a working strain gauge and a compensating strain gauge (also called a reference gauge or dummy gauge) on the measuring bridge, connecting them to adjacent arms of the bridge, and using the differential principle of the bridge to offset the temperature effect. In this approach, each working strain gauge requires a reference gauge of the same specifications. The reference gauge is mounted on a compensation block made of the same material as the specimen or suspended near the specimen, so that it only senses changes in ambient temperature and does not experience mechanical strain.

[0004] In conventional single-point or few-point strain testing scenarios, the aforementioned compensation mode of "one working piece corresponding to one reference piece" can meet basic testing requirements. However, when directly applied to multi-point full-domain strain testing in cryogenic internal pressure burst tests, the following technical drawbacks exist:

[0005] First, the hardware redundancy is large, encroaching on the test space. Cryogenic internal pressure burst tests require high-density strain gauges to be laid out on the shell surface within a sealed cryogenic chamber to obtain information on the stress distribution across the entire range. If a reference plate is configured for each working piece according to the traditional approach, the number of plates on the shell surface and inside the chamber will increase exponentially. The dense wiring and numerous plates not only encroach on the already limited test space within the cryogenic chamber but also easily cause interference during operations such as specimen hoisting and sealing assembly.

[0006] Secondly, the multi-channel temperature compensation reference is inconsistent, resulting in large data dispersion. Cryogenic internal pressure burst testing requires multi-channel synchronous strain data to analyze the overall stress distribution and failure mechanism, placing extremely high demands on the consistency and comparability of data from each channel. In traditional methods, each channel is equipped with an independent reference plate. However, different reference plates exhibit individual differences in production batches, adhesive layer thickness, patching processes, and local micro-temperature fields, leading to inconsistent temperature compensation references for each channel. This increased dispersion in multi-channel data results in a lack of synchronicity in strain data at different measuring points under the same internal pressure load, making it difficult to accurately reflect the overall stress and deformation characteristics of the shell.

[0007] Third, the calibration process is cumbersome and the testing cycle is lengthy. When using the independent reference piece compensation mode, gradient low-temperature calibration needs to be carried out on each set of working pieces and reference pieces to determine the temperature drift characteristics of each channel. For blast tests with dozens of strain measurement points, the workload of independent calibration for each channel increases exponentially, the calibration time is greatly extended, and the testing cost increases significantly, making it difficult to meet the engineering efficiency requirements of batch component blast testing.

[0008] Fourth, it is difficult to adapt to the complex temperature change conditions throughout the entire test process. The complete process of the cryogenic internal pressure burst test includes multiple stages such as uniform cooling, constant temperature and pressure holding, gradual internal pressure loading, and instantaneous burst. Among them, the cooling process is a continuous dynamic temperature change process, rather than a simple steady-state cryogenic condition. Existing test schemes based on fixed temperature compensation parameters are only applicable to steady-state cryogenic test scenarios, and do not consider the cumulative effect of temperature drift caused by continuous temperature changes during the dynamic cooling process. They cannot simultaneously meet the multiple requirements of dynamic temperature drift correction in the cooling stage, high-precision acquisition in the steady-state loading stage, and high-frequency signal fidelity in the instantaneous burst stage.

[0009] In summary, how to achieve high-precision multi-channel strain testing of the entire process of cryogenic internal pressure burst testing (including dynamic cooling and steady-state loading) without increasing the burden of cryogenic cavity layout or sacrificing the consistency of multi-channel data is a technical problem that urgently needs to be solved in this field.

[0010] In view of this, the present invention is hereby proposed. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of the prior art and provide a strain testing method for cryogenic internal pressure burst tests. This method addresses several technical problems in existing cryogenic internal pressure burst tests, such as large hardware redundancy that occupies test space, inconsistent temperature compensation benchmarks leading to large data dispersion, cumbersome calibration procedures and long test cycles, and inability to adapt to the combined working conditions of dynamic temperature changes, steady-state loading, and instantaneous burst.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] This invention provides a strain testing method for cryogenic internal pressure burst tests. The method is used to perform strain testing on a pressure vessel under test during a cryogenic internal pressure burst test, and includes the following steps:

[0014] Step 1: Arrange strain gauges: Place the pressure vessel to be tested in a sealed cryogenic chamber, suspend a reference strain gauge in the sealed cryogenic chamber, and arrange several working strain gauges at preset strain monitoring positions on the surface of the pressure vessel to be tested. The reference strain gauge and all working strain gauges are from the same batch and of the same specifications, and all strain gauges are in the same temperature field environment.

[0015] Step 2, Calibration of inherent deviation under ambient temperature and no-load conditions: Under ambient temperature and no-load conditions, collect the output signals of the corresponding channels of each working strain gauge and determine the inherent fixed deviation coefficient of each channel;

[0016] Step 3, Gradient Low Temperature Global Proportion Coefficient Calibration: Control the sealed low temperature cavity to cool from room temperature to the target ultra-low temperature. During the cooling process and at multiple preset temperature nodes, collect the temperature drift output signal of the reference strain gauge and the temperature drift output signal of each working strain gauge after deducting the corresponding inherent fixed deviation coefficient. Utilize the linear correlation between the temperature drift output of each working strain gauge and the reference strain gauge to fit and solve the global temperature drift proportion coefficient shared by all working channels.

[0017] Step 4: Global unified temperature drift correction throughout the entire process: During the entire cryogenic internal pressure burst test, the original strain signals of each working channel and the real-time temperature drift signals of the reference strain gauge are collected. Based on the global temperature drift ratio coefficient and the inherent fixed deviation coefficient of each channel, the original strain signals of each working channel are uniformly corrected for temperature drift to obtain the true mechanical strain of each channel.

[0018] Furthermore, in step 1, the reference strain gauge is suspended in the center of the uniform temperature field region of the sealed low-temperature cavity, and the maximum temperature difference of the entire temperature field inside the sealed low-temperature cavity is less than 0.5℃.

[0019] Furthermore, in step 1, each working strain gauge is attached to the stress concentration area of ​​the cylinder on the surface of the pressure vessel to be tested, and each working strain gauge is attached to the surface of the pressure vessel to be tested using a uniform curing process and with the same adhesive layer thickness.

[0020] Furthermore, in step 2, under normal temperature, no internal pressure load, and no-load steady-state conditions, all strain test channels are zeroed and left to stand for a preset time. After stabilization, multiple sets of no-load strain data for each working strain gauge's corresponding channel are continuously collected, and the average of multiple sets of data is taken as the inherent fixed deviation coefficient of that channel. ,in Represents the channel number.

[0021] Furthermore, in step 3, the cavity temperature, the real-time temperature drift strain of the reference strain gauge, and the original unloaded strain of each working channel are continuously collected at each moment during the cooling process. After the temperature stabilizes at each preset temperature node, steady-state data is collected, and dynamic continuous data and steady-state fixed-point data are fused to construct a global temperature-strain correlation dataset.

[0022] Furthermore, in step 3, the linear correlation is a univariate linear fitting model without intercept, and its expression is:

[0023]

[0024] In the formula, For reference strain gauges, the strain is determined by the pure temperature drift at each data point. The strain is the pure temperature drift strain of the working strain gauge after deducting the inherent fixed deviation coefficient at the same data point. This is the global temperature drift ratio coefficient.

[0025] Furthermore, the global temperature drift ratio coefficient Solve according to the following formula:

[0026]

[0027] In the formula, The pure temperature drift strain of the reference strain gauge corresponding to each data point. The strain is the pure temperature drift strain of the working strain gauge after deducting the inherent fixed deviation coefficient at the same data point. This represents the total number of data points.

[0028] Further, in step 4, the actual mechanical strain is calculated using the following formula:

[0029]

[0030] In the formula, For the first The actual mechanical strain of the channel, For the first The original measured strain of the channel, This is the global temperature drift ratio factor. To reference the real-time temperature drift strain of the strain gauge, For the first The inherent fixed deviation coefficient of the channel.

[0031] Furthermore, in step 4, the entire process of the cryogenic internal pressure burst test includes a cooling stage, a constant temperature and pressure holding stage, a gradual internal pressure loading stage, and an instantaneous burst stage.

[0032] Furthermore, the test method is applicable to the full-range multi-channel strain test of the internal pressure burst test of solid rocket motor casing in the liquid nitrogen temperature range of 77K cryogenic environment.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention deploys only one global suspended reference plate within a sealed cryogenic cavity, replacing the traditional approach of configuring one reference plate for each working piece. This significantly reduces the number of reference plates, saves internal space within the cryogenic cavity, and avoids interference during specimen hoisting and sealing fixture assembly caused by multiple plates occupying space. It effectively solves the problem of large hardware redundancy occupying test space in the prior art.

[0035] 2. This invention uses a single suspended reference gauge as the sole temperature reference for the entire cavity. Combined with the selection requirements of strain gauges of the same batch and specifications and the control conditions of the same temperature field environment, it eliminates the problem of compensation reference offset of each channel caused by differences in production batches, adhesive thickness, curing process and local micro-area temperature difference in traditional multi-reference gauges. It achieves the unification of temperature compensation reference for all channels, and significantly improves the synchronization and comparability of multi-channel strain data. It can truly reflect the overall stress deformation law of the shell under the stress distribution of the whole domain, and effectively overcome the defects of large data dispersion caused by the lack of unified temperature compensation reference for multiple channels in the prior art.

[0036] 3. This invention adopts a global calibration mode, which only requires a single global calibration to solve the global temperature drift ratio coefficient λ shared by all channels, eliminating the need to perform gradient low temperature calibration for each channel independently, thus significantly reducing calibration time; and the calibration results in inherent fixed deviation coefficients for each channel. The global temperature drift proportionality coefficient λ can be directly reused in subsequent burst tests of pressure vessels of the same specifications and batch without repeated cooling calibration, significantly shortening the batch test cycle and reducing labor costs, effectively overcoming the shortcomings of cumbersome calibration process and long test cycle in the existing technology.

[0037] 4. In the global scaling factor calibration stage, this invention integrates continuous temperature-changing data from the entire dynamic process of uniform cooling with multi-level isothermal steady-state fixed-point data. The constructed global temperature-strain correlation dataset completely covers the entire temperature change history of the cryogenic internal pressure burst test, and the global temperature drift scaling factor obtained is calculated from this dataset. It is compatible with continuous dynamic cooling, constant temperature and pressure holding, gradual pressure increase and instantaneous burst stages. This technical solution fully considers the cumulative effect of temperature drift caused by continuous temperature changes during the dynamic cooling process, making up for the shortcomings of existing technologies that can only perform steady-state calibration and ignore dynamic temperature drift correction. It realizes high-precision strain testing throughout the entire test process and effectively overcomes the shortcomings of existing technologies that cannot adapt to the complex temperature change conditions throughout the entire process. Attached Figure Description

[0038] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 The flowchart shows the strain testing method for cryogenic internal pressure bursting test provided by the present invention. Detailed Implementation

[0041] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples consistent with some aspects of the invention as detailed in the appended claims.

[0042] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0043] Example

[0044] This embodiment uses the internal pressure burst test of a certain type of engine casing under an ultra-low temperature environment of 77K liquid nitrogen as the test scenario to provide a detailed description of the strain test method for ultra-low temperature internal pressure burst test provided by the present invention.

[0045] The experimental equipment used in this embodiment is as follows: The strain acquisition equipment adopts the EX1629 high-precision strain testing system, with a sampling frequency set to 10Hz. It can simultaneously acquire multi-channel strain signals, supporting long-term steady-state acquisition and transient high-frequency acquisition, meeting the data acquisition requirements of the entire process of cryogenic internal pressure burst testing. The cryogenic environment equipment adopts a liquid nitrogen spray-type cryogenic test chamber. The chamber has a sealed cavity structure, and the temperature inside the cavity can be precisely adjusted by controlling the liquid nitrogen spray flow rate, meeting the process requirement of uniform cooling at 0.5℃ / min. All strain gauges are selected from the same production batch, with the same resistance rating, substrate material, and sensitivity coefficient, to ensure that the temperature drift characteristics of each strain gauge are consistent.

[0046] Step 1: Arrange strain gauges

[0047] The engine casing specimen to be tested was hoisted and fixed inside a sealed cryogenic chamber, ensuring no additional mechanical contact between the specimen and the chamber. In the central, uniformly heated area of ​​the chamber, a reference strain gauge was suspended and fixed to a dedicated bracket. This reference gauge did not contact the specimen or any components within the chamber, and bore no mechanical load throughout the process, only sensing changes in ambient temperature. Multiple working strain gauges were placed in stress concentration areas of the engine casing, including key circumferential and axial locations in the middle of the casing, covering all critical failure monitoring locations. All working strain gauges were mounted on the casing surface using a uniform curing process and with the same adhesive layer thickness to eliminate additional errors caused by differences in the mounting process. After deployment, the cryogenic test chamber was started and maintained at 20°C to confirm that all strain gauges were in the same temperature environment, and the maximum temperature difference throughout the chamber was controlled within 0.5°C.

[0048] Step 2: Calibration of inherent deviation under no-load conditions at room temperature

[0049] Under normal temperature (20℃), no internal pressure load, and no-load steady-state conditions, all strain test channels were zeroed and allowed to stand for 30 minutes. After the equipment and operating conditions stabilized, multiple sets of no-load strain data for each working strain gauge's corresponding channel were continuously collected. The average of the multiple sets of data was taken as the inherent fixed deviation coefficient of that channel. (unit: Taking four typical channels as examples, the parameters obtained from calibration are as follows: Channel 1: Channel 2: Channel 3: Channel 4: This set of parameters serves as the fixed baseline parameters for the experiment and will be reused throughout all subsequent test conditions.

[0050] Step 3: Global scaling factor calibration for gradient low temperature

[0051] The low-temperature test chamber was set to cool from 20℃ to the target low temperature of -196℃ at a constant rate of 0.5℃ / min. During the cooling process, the chamber temperature was continuously collected at a sampling frequency of 1Hz at every moment. Real-time temperature drift strain of reference strain gauge and the original no-load strain of each working channel This creates a dynamic dataset of continuous temperature changes. Simultaneously, isothermal steady-state data were collected at six characteristic temperature levels: 20℃, -20℃, -60℃, -100℃, -150℃, and -196℃, with each temperature level remaining stable for at least 30 minutes.

[0052] This invention's global temperature drift correction is based on a linear homology mechanism: under no-load conditions and without mechanical load, after deducting the inherent zero bias of the channel, the temperature drift of the global working strain gauge and the temperature drift of the single reference strain gauge satisfy a unique linear correlation. The optimal global scaling factor is solved by global least squares fitting. The actual mechanical strain under no-load conditions is 0, and the linear fitting model is... In the formula Pure temperature drift strain for reference films at various temperature levels , To subtract the inherent zero bias of the working channel at the corresponding temperature level The actual temperature drift strain afterwards It is a unique global temperature drift ratio coefficient across the entire domain.

[0053] The above-mentioned uniform cooling dynamic continuous data and multi-level steady-state fixed-point data were fused to construct a global temperature-strain correlation dataset. The standard fitting data for characteristic steady-state temperature levels are shown in Table 1 below (all data are the experimental unloaded steady-state mean values, unit: ...). ):

[0054] Table 1. Measured dataset for global fitting

[0055]

[0056] Using a non-intercept univariate linear least squares fitting method, the optimal coefficients are calculated using the following formula:

[0057]

[0058] Calculate the following for each of the above data items: global product sum =0×0+23×16+46×39+119×108+121×112+130×115=0+368+1794+12852+13552+14950=43516; Total Sum of Squares =0 2 +23 2 +46 2 +119 2 +121 2 +130 2 =0+529+2116+14161+14641+16900=48347.

[0059] Substituting into the least squares formula, we obtain λ = 43516 / 48347 = 0.9001. Therefore, the globally unique and universal temperature drift ratio coefficient λ = 0.9001 is determined for this embodiment. This coefficient is compatible with both the uniform cooling dynamic temperature change process and the isothermal steady-state loading stage, allowing for unified reuse of parameters across all channels.

[0060] Step 4: Global unified temperature drift correction throughout the entire process

[0061] During the formal cryogenic internal pressure burst test, the internal pressure loading program is initiated, continuously applying increasing internal pressure to the shell until burst failure occurs. Throughout the entire test, including the cooling phase, the isothermal pressure holding phase, the gradual internal pressure loading phase, and the instantaneous burst phase, the data acquisition system continuously collects the raw strain signals from each working channel. and the real-time temperature drift signal of the reference strain gauge Based on the calibrated global temperature drift ratio coefficient and the inherent fixed deviation coefficient of each channel A uniform temperature drift correction is applied to the original strain signals of each channel. The correction formula is:

[0062]

[0063] Correction calculations were performed using measured data at a certain moment during the steady-state phase of cryogenic and progressive internal pressure loading: real-time cryogenic temperature drift strain of the global reference image. The original acquisition strain and correction calculations for four typical channels are as follows:

[0064] Channel 1, Raw Strain Acquisition Inherent fixed deviation coefficient Substitute into the corrected formula to calculate:

[0065]

[0066] Channel 2, Original Acquisition Strain Inherent fixed deviation coefficient Substitute into the corrected formula to calculate:

[0067]

[0068] Channel 3, Original Acquisition Strain Inherent fixed deviation coefficient Substitute into the corrected formula to calculate:

[0069]

[0070] Channel 4, Raw Strain Acquisition Inherent fixed deviation coefficient Substitute into the corrected formula to calculate:

[0071]

[0072] After correction, the data completely eliminated the ultra-low temperature drift error and the system zero-point error, retaining only the real mechanical strain generated by the pressure loading inside the pressure vessel. The data accuracy meets the requirements for burst test analysis.

[0073] Comparative verification test

[0074] To verify the technical effectiveness of this invention compared to the traditional one-channel-one-reference-chip independent compensation mode, two methods were used to correct and compare the measured data of the above four channels under the same experimental conditions. The traditional method uses... Temperature drift correction is performed by directly subtracting the original strain of each channel from the temperature drift value of the reference film; the method of this invention employs... A global, unified correction was performed. The comparison results are shown in Table 2 below:

[0075] Table 2 Comparison of Correction Values ​​of the Invention and the Prior Art

[0076]

[0077] Among them, the theoretical true value 900με is the theoretical mechanical strain value under this load calculated based on the internal pressure load and the elastic modulus of the shell, and is used as a reference benchmark for comparing the correction effect.

[0078] The standard deviation of multi-channel samples and the global mean residual error were calculated for the two corrected datasets, and the results are shown in Table 3 below:

[0079] Table 3. Quantitative Comparison of the Corrective Effects of the Invention and Existing Technologies

[0080]

[0081] Multi-channel data dispersion characterizes the consistency of output data from each test channel under the same load condition; the smaller the value, the better the consistency of test results across channels. Global average residual error characterizes the degree of deviation of measured results from theoretical mechanical truth; the smaller the value, the higher the measurement accuracy. An ideal testing method should simultaneously possess both small dispersion and small global average residual error.

[0082] As shown in Table 2, regarding the single-channel correction accuracy, the method of this invention reduces the correction deviations of channels 1, 2, and 4 by approximately 78.3%, 57.1%, and 33.3%, respectively. The correction deviation of channel 3 is slightly higher than that of the traditional method. This is because the present invention uses a single reference chip and a single global scaling factor for unified correction, pursuing global overall optimization rather than point-by-point optimization for each channel. Therefore, the slightly lower correction accuracy of individual channels compared to the traditional method is a normal phenomenon under a global optimal strategy. As shown in Table 3, regarding the overall statistical characteristics, the multi-channel dispersion of the method of this invention is... Compared with traditional methods The results are essentially equivalent, indicating that the present invention maintains at least the same level of consistency across multiple channels as traditional methods; the global average residual error of the method of the present invention is... Compared to traditional methods The accuracy was reduced by approximately 8%. Both sets of evaluation index values ​​were better than those of traditional methods, indicating that the method of this invention effectively improved the overall accuracy of the global measurement while ensuring the consistency of multi-channel data, and the compensation effect was optimized and improved compared with traditional methods.

[0083] Based on the above comparison results, the technical solution of "single reference piece global compensation + dual-layer parameter calibration + dynamic steady-state data fusion" adopted in this invention, under the premise of using only one reference piece, replaces "point-by-point optimization" with "global optimization", which significantly improves the overall accuracy of global measurement while ensuring the consistency of multi-channel data, and verifies the effectiveness and superiority of the method of this invention in multi-channel strain testing of cryogenic internal pressure burst test.

[0084] In this embodiment, the calibrated inherent fixed deviation coefficients of each channel are obtained. Global temperature drift ratio factor All parameters are stored in the data processing system. In subsequent cryogenic internal pressure burst tests of pressure vessels of the same specifications and batch, the above parameters can be directly reused without repeating the calibration of inherent deviations under ambient temperature and gradient cryogenic global proportional coefficients, thereby significantly shortening the calibration cycle of batch tests and reducing test time and costs.

[0085] The above embodiments are merely illustrative of specific implementations of the present invention and are not intended to limit the invention. Those skilled in the art can make various modifications and variations to the present invention without departing from its principles, and all such modifications and variations should fall within the protection scope of the appended claims.

Claims

1. A method for strain testing in cryogenic internal pressure burst tests, characterized in that, The test method is used to perform strain testing on the internal pressure burst test of the pressure vessel under test in an ultra-low temperature environment, and includes the following steps: Step 1: Arrange strain gauges: Place the pressure vessel to be tested in a sealed cryogenic chamber, suspend a reference strain gauge in the sealed cryogenic chamber, and arrange several working strain gauges at preset strain monitoring positions on the surface of the pressure vessel to be tested. The reference strain gauge and all working strain gauges are from the same batch and of the same specifications, and all strain gauges are in the same temperature field environment. Step 2, Calibration of inherent deviation under ambient temperature and no-load conditions: Under ambient temperature and no-load conditions, collect the output signals of the corresponding channels of each working strain gauge and determine the inherent fixed deviation coefficient of each channel; Step 3, Gradient Low Temperature Global Proportion Coefficient Calibration: Control the sealed low temperature cavity to cool from room temperature to the target ultra-low temperature. During the cooling process and at multiple preset temperature nodes, collect the temperature drift output signal of the reference strain gauge and the temperature drift output signal of each working strain gauge after deducting the corresponding inherent fixed deviation coefficient. Utilize the linear correlation between the temperature drift output of each working strain gauge and the reference strain gauge to fit and solve the global temperature drift proportion coefficient shared by all working channels. Step 4: Global unified temperature drift correction throughout the entire process: During the entire cryogenic internal pressure burst test, the original strain signals of each working channel and the real-time temperature drift signals of the reference strain gauge are collected. Based on the global temperature drift ratio coefficient and the inherent fixed deviation coefficient of each channel, the original strain signals of each working channel are uniformly corrected for temperature drift to obtain the true mechanical strain of each channel.

2. The strain testing method for cryogenic internal pressure bursting test according to claim 1, characterized in that, In step 1, the reference strain gauge is suspended in the center of the uniform temperature field region of the sealed low-temperature cavity, and the maximum temperature difference of the entire temperature field inside the sealed low-temperature cavity is less than 0.5℃.

3. The strain testing method for cryogenic internal pressure bursting test according to claim 1, characterized in that, In step 1, each working strain gauge is attached to the stress concentration area of ​​the cylinder on the surface of the pressure vessel to be tested, and each working strain gauge is attached to the surface of the pressure vessel to be tested using a uniform curing process and with the same adhesive layer thickness.

4. The strain testing method for cryogenic internal pressure bursting test according to claim 1, characterized in that, In step 2, under normal temperature, no internal pressure load, and no-load steady-state conditions, all strain test channels are zeroed and left to stand for a preset time. After stabilization, multiple sets of no-load strain data for each working strain gauge's corresponding channel are continuously collected. The average of multiple sets of data is taken as the inherent fixed deviation coefficient of that channel. ,in Represents the channel number.

5. The method for strain testing in cryogenic internal pressure burst tests according to claim 1, characterized in that, In step 3, the cavity temperature, real-time temperature drift strain of the reference strain gauge, and original unloaded strain of each working channel are continuously collected at each moment during the cooling process. After the temperature stabilizes at each preset temperature node, steady-state data is collected. The dynamic continuous data and steady-state fixed-point data are fused to construct a global temperature-strain correlation dataset.

6. The strain testing method for cryogenic internal pressure bursting test according to claim 1, characterized in that, In step 3, the linear correlation is a univariate linear fitting model without intercept, and its expression is: In the formula, For reference strain gauges, the strain is determined by the pure temperature drift at each data point. The strain is the pure temperature drift strain of the working strain gauge after deducting the inherent fixed deviation coefficient at the same data point. This is the global temperature drift ratio coefficient.

7. The strain testing method for cryogenic internal pressure bursting test according to claim 6, characterized in that, The global temperature drift ratio coefficient Solve according to the following formula: In the formula, The pure temperature drift strain of the reference strain gauge corresponding to each data point. The strain is the pure temperature drift strain of the working strain gauge after deducting the inherent fixed deviation coefficient at the same data point. This represents the total number of data points.

8. The method for strain testing in cryogenic internal pressure burst tests according to claim 1, characterized in that, In step 4, the actual mechanical strain is calculated using the following formula: In the formula, For the first The actual mechanical strain of the channel, For the first The original measured strain of the channel, This is the global temperature drift ratio factor. To reference the real-time temperature drift strain of the strain gauge, For the first The inherent fixed deviation coefficient of the channel.

9. The method for strain testing in cryogenic internal pressure burst tests according to claim 1, characterized in that, In step 4, the entire process of the cryogenic internal pressure burst test includes a cooling stage, a constant temperature and pressure holding stage, a gradual internal pressure loading stage, and an instantaneous burst stage.

10. The method for strain testing in cryogenic internal pressure burst tests according to any one of claims 1 to 9, characterized in that, The test method described herein is applicable to the full-range multi-channel strain test of the internal pressure burst test of solid rocket motor casing in the liquid nitrogen temperature range of 77K cryogenic environment.

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