Equivalent Accelerated Testing Method for Plexiglass Based on Creep Constitutive Equation

Abstract

This invention relates to an equivalent accelerated testing method for plexiglass based on creep constitutive equations, belonging to the technical field of accelerated testing of polymer structures. Addressing the testing requirements for the creep performance of plexiglass structures, this invention shortens the testing cycle and saves testing costs through the design of testing temperature and pressure. Simultaneously, the reduced testing time indirectly saves manpower and material resources, and also reduces the frequency of random risks such as power outages and equipment failures. Therefore, the testing method of this invention has significant timeliness and economic efficiency, and can effectively improve the accuracy of quantitative analysis, possessing important value for engineering practice.

Description

Technical Field

[0001] This invention relates to the field of accelerated testing technology for polymer structures, and in particular to an equivalent accelerated testing method for plexiglass based on creep constitutive equations. Background Technology

[0002] Acrylic glass is a transparent material with good pressure resistance. Currently, it has good application examples and application prospects in underwater pressure-resistant structures such as observation windows of deep-sea submersibles and fully transparent submersibles, as well as in-situ observation windows of pressure vessels such as room temperature ultra-high pressure cylinders.

[0003] To meet usage requirements, acrylic glass structures should be able to withstand high water pressure for medium to long periods or even continuously within a range of 0°C to room temperature. However, acrylic glass is also a typical viscoelastic material, exhibiting creep behavior under high pressure. This means that strain increases over time under constant stress, and this behavior is significantly correlated with time, stress level, and ambient temperature. To ensure structural safety, pressure-holding deformation tests at design pressure and design temperature are generally required, with a test duration no less than the design service life. However, since the design service life of these structures is generally several years or even decades, conducting creep tests on acrylic glass structures under design conditions typically faces the challenges of being time-consuming and costly.

[0004] Considering the time-temperature equivalence of creep in polymers such as plexiglass (i.e., increasing the temperature and extending the observation time are equivalent for creep in plexiglass), creep test data at one temperature can be converted to time-temperature data to describe creep behavior at another temperature. The traditional time-temperature equivalence accelerated testing method is as follows: First, conduct uniaxial creep tests on the sample at the same stress level but different temperature levels to obtain the corresponding double logarithmic coordinate creep compliance-time curves. The temperature levels should include the operating temperature Td and multiple heating temperatures Ti. Second, using the creep compliance curve segment at the operating temperature as a reference, perform image translation operations along the horizontal or vertical axis on the creep compliance curve segments at the heating temperatures, superimposing and stitching them into a complete creep compliance-time curve. The translation amounts aTx and aTy in the horizontal and vertical directions can be converted into equivalent creep compliance between different temperatures using coordinate readings. The relationship is as follows: The third step is to read the creep compliance Ct of the plexiglass material corresponding to the design service life td based on the complete creep compliance-time curve, and calculate the creep deformation amount of the structure's service design life at the working temperature through mechanical formulas or numerical simulation methods; The fourth step is to select a heating temperature Ti as the test temperature, and read the creep time ti corresponding to the creep compliance Ct based on the creep compliance curve segment at the heating temperature. This creep time can be used as the test time at the test temperature, and it is considered that the creep deformation amount of the structure during the pressure holding test at this test temperature can be equivalent to the creep deformation amount of the design service life at the design temperature.

[0005] However, the above-mentioned accelerated testing methods still have shortcomings: 1. When using the method of plotting curve segments to obtain a complete creep compliance-time curve, the amount of translation of the curve segment is affected by the operator's visual perception and subjective judgment, and there is no unified standard, resulting in a certain degree of dispersion in the plotting results; 2. At different temperature levels, the sensitivity of plexiglass to stress during creep is different. Using only creep compliance as an evaluation parameter for time-temperature equivalence does not consider the influence of stress level on the creep law of plexiglass, and the resulting quantitative equivalence relationship is not accurate enough; 3. The specimen test is a single stress level, while the stress level inside the structure is a range distribution. Directly applying the acceleration ratio of material-level specimen tests to structural-level tests lacks supporting evidence. Summary of the Invention

[0006] To address the shortcomings of existing production technologies, the applicant provides an equivalent accelerated testing method for plexiglass based on creep constitutive equations. This method shortens the testing cycle and saves testing costs by designing the testing temperature and pressure to meet the testing and evaluation requirements of the creep performance of plexiglass structures.

[0007] The technical solution adopted in this invention is as follows: an equivalent accelerated testing method for plexiglass based on creep constitutive equations, comprising the following steps:

[0008] Step 1: Obtain the range of single-pass stress of the plexiglass structure under design pressure and design temperature;

[0009] Step 2: Obtain the creep strain-time curves of the plexiglass material under multiple stress and temperature levels;

[0010] Step 3: Obtain the fitted values ​​of time, stress, and temperature parameters in the constitutive equation for creep of plexiglass;

[0011] Step 4: Calculate the creep deformation of the plexiglass structure after its designed service life under design temperature and pressure;

[0012] Step 5: Calculate the creep behavior of the plexiglass structure at the test temperature;

[0013] Step Six: Determine the accelerated creep test duration for the plexiglass structure;

[0014] Step 7: Conduct accelerated creep test on the acrylic glass structure. The accelerated creep test on the acrylic glass structure under test temperature and test pressure is carried out in a constant temperature structure creep hydrostatic pressure test system.

[0015] As a further improvement to the above technical solution:

[0016] Preferably, the specific method for obtaining the single-bearing stress range of the plexiglass structure under design pressure and design temperature in step one is as follows: the stress-strain measurement method or numerical simulation method is used to obtain the single-bearing stress distribution characteristics of the plexiglass structure under design pressure and design temperature; the stress-strain measurement method includes digital speckle (DIC) non-contact measurement, strain sensor measurement, and photoelastic method; the numerical simulation method includes the finite element method.

[0017] Preferably, the specific method for obtaining the creep strain-time curve of the plexiglass material under multiple stress and temperature levels in step two is as follows: based on the design temperature and single-bearing stress range of the plexiglass structure, a creep test of the plexiglass sample at multiple stress and temperature levels is planned and carried out to obtain the creep strain-time curve of the plexiglass material under multiple stress and temperature levels.

[0018] Preferably, the specific method for obtaining the fitted values ​​of time, stress, and temperature parameters in the creep constitutive equation of plexiglass in step three is to fit the creep curve of the plexiglass sample with the creep constitutive equation, use the fitting analysis results as the evaluation standard for the fitting effect, obtain the corresponding fitted values ​​of time, stress, and temperature parameters, and establish the creep constitutive relationship of plexiglass accordingly; the fitting method includes the least squares method, and the fitting evaluation standard includes the fitting correlation R-square.

[0019] Preferably, the specific method for calculating the creep deformation of the plexiglass structure after its designed service life under design temperature and design pressure in step four is as follows: using the creep constitutive relation of plexiglass as the material parameter input, the creep deformation of the plexiglass structure after its designed service life under design temperature and design pressure is calculated by numerical simulation; the numerical simulation method includes creep nonlinear finite element analysis.

[0020] Preferably, the specific method for calculating the creep behavior of the plexiglass structure at the test temperature in step five is as follows: based on the time-temperature equivalence relationship of plexiglass under a single stress level and the test conditions, the test temperature and test pressure are set as the standard, the creep constitutive relationship of plexiglass is used as the material parameter input, and the creep deformation of the plexiglass structure after holding time at the test temperature and test pressure is calculated by numerical simulation; the maximum creep deformation calculated by numerical simulation is greater than the simulation result in step four.

[0021] Preferably, the specific method for determining the accelerated creep test assessment time of the plexiglass structure in step six is ​​as follows: extract the creep deformation amount and corresponding creep time equivalent to the calculated value in step four from the simulation results obtained by numerical simulation in step five. The creep time is the accelerated creep test assessment duration under test temperature and test pressure.

[0022] Preferably, the specific method for conducting accelerated creep assessment tests on plexiglass structures under test temperature and test pressure in the constant temperature structural creep hydrostatic pressure test system in step seven is as follows: when the structural deformation does not exceed the design verification standard when the pressure holding time exceeds the accelerated creep test assessment time, the tested structure meets the bearing capacity of the design service life under the design temperature and design pressure; the measurement methods for structural deformation during the test include digital speckle (DIC) non-contact measurement, strain sensor measurement, and photoelastic method.

[0023] The beneficial effects of this invention are as follows:

[0024] The method of this invention is reasonable and easy to operate. It involves conducting material-level creep tests at multiple temperatures and stress levels on plexiglass structures exhibiting viscoelastic characteristics. By fitting the data, a creep constitutive relationship incorporating time, stress, and temperature parameters is obtained. This relationship is then applied to numerical simulations to obtain a quantitative equivalent relationship between time, temperature, and stress in the plexiglass structure. Finally, an accelerated creep testing method for plexiglass structures is proposed. This method is applicable to other viscoelastic materials and other types of structures.

[0025] The present invention also has the following advantages:

[0026] (1) The present invention uses the creep constitutive equation to fit the experimental results and uses the fitting analysis results as a unified evaluation standard. This eliminates the interference of subjective judgment in the traditional plotting method, reduces operational errors, and helps to ensure the objectivity and repeatability of experimental data processing.

[0027] (2) The present invention selects a creep constitutive equation that includes time, temperature and stress parameters for fitting analysis, and considers the influence of time, temperature and stress on the creep law of plexiglass, so that the obtained quantitative equivalent relationship is more accurate.

[0028] (3) The creep constitutive relation obtained by fitting the present invention can be used as a material parameter input to participate in the numerical simulation analysis of plexiglass structure, that is, the creep law at the material level is extended to the creep of structure, which can effectively improve the accuracy of the equivalent relation analysis of plexiglass structure and also help improve the reliability of accelerated creep test design. Attached Figure Description

[0029] Figure 1 This is a cloud diagram for stress analysis of the acrylic glass structure of the present invention.

[0030] Figure 2 This is a cloud diagram of the strain analysis of the plexiglass structure of the present invention.

[0031] Figure 3 This is the creep-time curve obtained from the creep test of plexiglass in an embodiment of the present invention.

[0032] Figure 4 This is a comparison chart of the experimental and fitted values ​​of the creep curve in an embodiment of the present invention.

[0033] Figure 5 This is an equivalent relationship diagram of the creep curves of plexiglass at different temperatures under a single stress level in an embodiment of the present invention.

[0034] Figure 6 This is an equivalent relationship diagram of the creep curves of the plexiglass structure at different temperatures and stress levels in the embodiments of the present invention. Detailed Implementation

[0035] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0036] This embodiment takes a long-term pressure-holding test of an acrylic observation window simulating a seawater pressure vessel as an example. The design temperature of this observation window is 3℃, the design pressure is 20MPa, and the design continuous pressure-holding service time is 1 year. Therefore, the duration of the test under the design temperature and design pressure should not be less than 1 year.

[0037] like Figures 1-6 As shown, the equivalent accelerated testing method for plexiglass based on the creep constitutive equation in this embodiment includes the following steps:

[0038] Step 1: Obtain the range of single-bearing stress of the plexiglass structure under design pressure and design temperature. Use experimental measurement or numerical simulation methods to obtain the distribution characteristics of single-bearing stress of the plexiglass structure under design pressure Pd and design temperature Td, especially the range of the main stress levels. Stress and strain measurement methods include, but are not limited to, digital speckle (DIC) non-contact measurement, strain sensor measurement and photoelasticity, etc. Numerical simulation methods include, but are not limited to, the finite element method.

[0039] Specifically, such as Figures 1-2 As shown, material parameters such as the elastic modulus and Poisson's ratio of plexiglass were obtained by consulting the specification manual. A finite element model of the pressure vessel observation window structure was established, and the stress distribution characteristics of the structure under a single load at a design pressure of 20 MPa and a design temperature of 3℃ were obtained. The maximum equivalent stress was 42.18 MPa, and the stress level in the main deformation area was between 20 MPa and 40 MPa. The overall structure was dominated by compressive stress.

[0040] Step 2: Obtain creep strain-time curves of plexiglass material under multiple stress and temperature levels. Based on the design temperature and single-bearing stress range of the plexiglass structure, plan and carry out creep tests of plexiglass samples under multiple stress and temperature levels to obtain creep strain-time curves of plexiglass material under multiple stress and temperature levels.

[0041] Specifically, such as Figure 3 As shown, combining the stress level range obtained from the finite element analysis in step one and the temperature control range of the isothermal structural creep hydrostatic pressure test system, compression creep tests were planned and carried out on plexiglass samples at three stress levels (20 MPa, 30 MPa, and 40 MPa) and four temperature levels (3℃, 15℃, 25℃, and 40℃). A total of 12 sets of tests were conducted, with each set lasting 24 hours. After processing the test data, creep strain-time curves of plexiglass materials under multiple stress and temperature levels were obtained. Figure 3 The creep strain-time curves are shown for 20, 30, and 40 MPa at a temperature of 15℃.

[0042] Step 3: Obtain the fitted values ​​of time, stress, and temperature parameters in the creep constitutive equation of plexiglass. Fit the creep curve of the plexiglass sample using the creep constitutive equation, and use the fitting analysis results as the evaluation criterion for the fitting effect to obtain the corresponding fitted values ​​of time, stress, and temperature parameters. Establish the creep constitutive relationship of plexiglass based on this. The fitting method includes, but is not limited to, the least squares method, and the fitting evaluation criterion includes, but is not limited to, the fitting correlation R-square. Based on this creep constitutive relationship, the time-temperature equivalent relationship of plexiglass under a single stress level can be directly derived.

[0043] Specifically, such as Figures 4-5 As shown, the creep constitutive equation used to fit the creep curve of the plexiglass sample should include functions of stress, temperature, and time, as well as their influencing parameters. In this embodiment, the creep constitutive equation derived from creep aging theory and the WLF time-temperature equivalent equation is used:

[0044]

[0045] Where: ε c Let σ be the creep strain, t be the time, T be the temperature, and e be the natural base; B, a, b, m, p, and q are all material constants obtained from creep tests.

[0046] Nonlinear fitting was performed using the cftool fitting toolbox in MATLAB software to obtain the corresponding fitted values ​​of time, stress, and temperature parameters, and the creep constitutive relation of plexiglass was established based on these values. Figure 4 The graph shows a comparison between the experimental and fitted values ​​of the creep curve at 15℃. Based on this creep constitutive relationship, the time-temperature equivalence relationship of plexiglass under a single stress level can be directly derived. For example, when the stress level is 30MPa, the creep rate of plexiglass at 40℃ is approximately 11.3 times that at 3℃. Figure 5 The equivalent relationship between the creep curves of plexiglass at 30 MPa and 3℃ and 40℃ is shown.

[0047] Step 4: Calculate the creep deformation of the acrylic glass structure after its designed service life under design temperature and design pressure. Using the creep constitutive relation of acrylic glass as the material parameter input, a numerical simulation method is used to calculate the creep deformation of the acrylic glass structure at the design temperature T. d Design pressure P d Lower pressure holding design service life t d The creep deformation ε d Numerical simulation methods include, but are not limited to, creep nonlinear finite element analysis.

[0048] Specifically, using the constitutive relation of organic glass obtained in step three as the material parameter input, the creep nonlinear finite element analysis method was used to calculate that the axial creep displacement of the observation window after 1 year of pressure holding design service life at a design temperature of 3℃ and a design pressure of 20MPa is 0.547mm.

[0049] Step 5: Calculate the creep behavior of the acrylic glass structure at the test temperature. Refer to the time-temperature equivalence relationship of acrylic glass under a single stress level and the test conditions to set the test temperature T. t and test pressure P t Using the creep constitutive relation of plexiglass as the material parameter input, a numerical simulation method is employed to calculate the creep deformation of a plexiglass structure under test temperature and pressure for a certain time t. The calculation time should be sufficiently long to ensure that the maximum creep deformation ε obtained from the numerical simulation is achieved. max The simulation results are greater than those in step four;

[0050] Specifically, based on the creep constitutive relation obtained in step four, the time-temperature equivalence relationship of plexiglass under a single stress level can be derived. For example, the uniaxial compression creep rate of plexiglass at 25℃ and 27MPa is equivalent to 20 times the uniaxial compression creep rate at 3℃ and 20MPa. Based on this, the test temperature of the hydrostatic pressure test of the observation window is set to 25℃ and the test pressure to 27MPa. Similarly, the creep deformation of the observation window under test temperature of 25℃ and test pressure of 27MPa is calculated using the creep nonlinear finite element analysis method. The holding time is set to 1 month. The maximum axial creep displacement obtained is 0.573mm, which exceeds the simulation result of step four.

[0051] Step Six: Determine the accelerated creep test time for the plexiglass structure, and extract the ε value calculated in Step Four from the simulation results of Step Five. d The equivalent creep deformation ε j and the corresponding creep time t j , t j This refers to the duration of the accelerated creep test under the specified test temperature and pressure.

[0052] Specifically, such as Figure 6As shown, the axial creep displacement equivalent to the calculated value of 0.547 mm in step four is extracted from the simulation results in step five. These values ​​are 0.543 mm after 576 hours of creep and 0.549 mm after 600 hours of creep. After linear interpolation, the creep time corresponding to 0.547 mm is 592 hours. That is, the creep deformation of the observation window structure under pressure of 25℃ and 27MPa for 592 hours is equivalent to the creep deformation under pressure of 3℃ and 20MPa for 1 year. In other words, the creep rate of the former is about 14.8 times that of the latter.

[0053] Step 7: Conduct accelerated creep testing of the plexiglass structure, using a constant-temperature structural creep hydrostatic pressure testing system at a test temperature T. t and test pressure P t In the accelerated creep test of the plexiglass structure, if the holding time exceeds the accelerated creep test duration t... j If the structural deformation at temperature T does not exceed the design verification standard, the tested structure can be considered to meet the design temperature T standard. d Design pressure P d Lower pressure holding design service life t d The load-bearing capacity; if a safety margin is required, a safety factor can be set according to the actual situation, multiplied by t. j The actual accelerated creep test duration was then determined. Methods for measuring structural deformation during the test included, but were not limited to, digital speckle (DIC) non-contact measurement, strain sensor measurement, and photoelastic methods.

[0054] Specifically, based on the theoretical calculations and finite element analysis results from steps one through six, an accelerated creep test of the plexiglass structure was conducted in a constant-temperature structural creep hydrostatic pressure test system at a test temperature of 25℃ and a test pressure of 27MPa. If the structural deformation does not exceed the design verification standard when the pressure holding time exceeds 592 hours, the tested observation window structure can be considered to meet the load-bearing capacity of the design service life of 1 year at a design temperature of 3℃ and a design pressure of 20MPa. Considering the need to provide a certain safety margin for engineering applications, a safety factor of 1.5 can be set, and multiplied by 592 hours to determine the actual accelerated creep test duration as 37 days.

[0055] In this embodiment, steps four and five employ creep nonlinear finite element analysis. This involves defining element types, real constants, linear material properties, and creep material properties in the finite element software. The creep material properties are the creep constitutive relations obtained in step three. An observation window model is created and meshed. Environmental temperature and displacement constraints are set for the observation window, and loads are applied. The open-rate related calculation command is used, and analysis options are set to complete the rate-related nonlinear solution. The results are viewed through time history post-processing. Since creep nonlinear finite element analysis is a built-in function in the finite element software, and the specific calculation process is essentially existing technology, it will not be elaborated upon in this embodiment.

[0056] In this embodiment, the design temperature of the plexiglass structure should be between 0°C and 60°C. For other viscoelastic materials, it should also be within their glassy temperature range.

[0057] In this embodiment, the creep constitutive equation used in step three is derived from the creep aging theory and the WLF time-temperature equivalent equation. When other creep constitutive equations are selected, creep constitutive equations that include time, temperature and stress parameters should also be selected.

[0058] In this embodiment, due to the step size setting of the finite element analysis, the load step results saved in step five cannot completely correspond to the calculation results in step four. Therefore, the accelerated creep test assessment time tj in step six can be calculated by linear interpolation of adjacent load step results.

[0059] In this embodiment, the assessment time required using the method of the present invention is 592 hours, which is 37 days after considering a safety factor of 1.5. Based on a unit price of 10,000 yuan / day for a certain constant temperature hydrostatic pressure testing system, the testing cost can be reduced from 3.65 million yuan to 370,000 yuan, representing a saving of nearly 90% in both time and testing costs. Furthermore, the shortened testing time can indirectly save manpower and material resources, and also reduce the frequency of random risks such as power outages and equipment failures. In this embodiment, the equivalent relationship of plexiglass under uniaxial stress is 20 times, while the equivalent relationship under complex structural stress is 15 times. This indicates that directly applying the creep equivalence law at the material level to the structural level will lead to certain errors. The technical solution of the present invention can effectively improve the accuracy of the structural equivalence relationship analysis of plexiglass. Therefore, the testing method of the present invention has significant timeliness and economy, and can also effectively improve the accuracy of quantitative analysis, which is of great value for engineering practice.

[0060] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims. Within the scope of protection of the present invention, any form of modification may be made.

Claims

1. An equivalent accelerated testing method for plexiglass based on creep constitutive equations, characterized in that: Includes the following steps: Step 1: Obtain the range of single-pass stress of the plexiglass structure under design pressure and design temperature; Step 2: Obtain the creep strain-time curves of the plexiglass material under multiple stress and temperature levels; Step 3: Obtain the fitted values ​​of time, stress, and temperature parameters in the constitutive equation for creep of plexiglass; The specific method for obtaining the fitted values ​​of time, stress, and temperature parameters in the creep constitutive equation of plexiglass in step three is to fit the creep curve of the plexiglass sample to the creep constitutive equation, use the fitting analysis results as the evaluation standard for the fitting effect, obtain the corresponding fitted values ​​of time, stress, and temperature parameters, and establish the creep constitutive relationship of plexiglass accordingly. in: ε c For creep strain, σ For stress, t For time, T Here, e represents temperature, and e is the natural base. B, a, b, m, p, q All of these are material constants, obtained from creep tests; Step 4: Calculate the creep deformation of the plexiglass structure after its designed service life under design temperature and pressure; Step 5: Calculate the creep behavior of the plexiglass structure at the test temperature; Step Six: Determine the accelerated creep test duration for the plexiglass structure; Step 7: Conduct accelerated creep test on the acrylic glass structure. The accelerated creep test on the acrylic glass structure under test temperature and test pressure is carried out in a constant temperature structure creep hydrostatic pressure test system.

2. The method for equivalent accelerated testing of plexiglass based on creep constitutive equations as described in claim 1, characterized in that: The specific method for obtaining the single-bearing stress range of the plexiglass structure under design pressure and design temperature in step one is to use stress-strain measurement methods or numerical simulation methods to obtain the single-bearing stress distribution characteristics of the plexiglass structure under design pressure and design temperature.

3. The method for equivalent accelerated testing of plexiglass based on creep constitutive equations as described in claim 2, characterized in that: The stress-strain measurement methods include digital speckle (DIC) non-contact measurement, strain sensor measurement, and photoelasticity; the numerical simulation methods include the finite element method.

4. The method for equivalent accelerated testing of plexiglass based on creep constitutive equations as described in claim 1, characterized in that: The specific method for obtaining the creep strain-time curve of the plexiglass material under multiple stress and temperature levels in step two is as follows: based on the design temperature and single-bearing stress range of the plexiglass structure, plan and carry out creep tests of plexiglass samples at multiple stress and temperature levels to obtain the creep strain-time curve of the plexiglass material under multiple stress and temperature levels.

5. The method for equivalent accelerated testing of plexiglass based on creep constitutive equations as described in claim 1, characterized in that: The fitting method includes the least squares method, and the fitting evaluation criterion includes the fitting correlation R-squared.

6. The method for equivalent accelerated testing of plexiglass based on creep constitutive equations as described in claim 1, characterized in that: The specific method for calculating the creep deformation of the plexiglass structure after its designed service life under design temperature and design pressure in step four is as follows: using the creep constitutive relation of plexiglass as the material parameter input, the creep deformation of the plexiglass structure after its designed service life under design temperature and design pressure is calculated by numerical simulation. The numerical simulation methods include creep nonlinear finite element analysis.

7. The method for equivalent accelerated testing of plexiglass based on creep constitutive equations as described in claim 1, characterized in that: The specific method for calculating the creep behavior of the plexiglass structure at the test temperature in step five is as follows: the test temperature and test pressure are set based on the time-temperature equivalence relationship of plexiglass under a single stress level and the test conditions. The creep constitutive relationship of plexiglass is used as the material parameter input, and the creep deformation of the plexiglass structure after holding time at the test temperature and test pressure is calculated by numerical simulation. The maximum creep deformation calculated using numerical simulation is greater than the simulation result in step four.

8. The method for equivalent accelerated testing of plexiglass based on creep constitutive equations as described in claim 1, characterized in that: The specific method for determining the accelerated creep test assessment time of the plexiglass structure in step six is ​​as follows: extract the creep deformation amount and corresponding creep time equivalent to the calculated value in step four from the simulation results obtained by numerical simulation in step five. The creep time is the accelerated creep test assessment duration under test temperature and test pressure.

9. The method for equivalent accelerated testing of plexiglass based on creep constitutive equations as described in claim 1, characterized in that: The specific method for conducting accelerated creep assessment tests on plexiglass structures under test temperature and test pressure in the constant temperature structural creep hydrostatic pressure test system in step seven is as follows: when the structural deformation does not exceed the design verification standard when the pressure holding time exceeds the accelerated creep test assessment time, the tested structure meets the bearing capacity of the design service life under the design temperature and design pressure. The methods for measuring structural deformation during the experiment include digital speckle (DIC) non-contact measurement, strain sensor measurement, and photoelasticity.

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