A thin-walled pipe structure creep-fatigue test device and a test parameter determination method

Abstract

This invention relates to the technical field of materials mechanics testing, and provides a creep-fatigue testing device and method for determining test parameters for thin-walled tube structures. The device includes: a clamping assembly, a rigid inner plug, a split outer clamp, and a positioning pin; the rigid inner plug is connected to an external loading system via a connecting structure; a temperature control assembly, including a heating mechanism and a cooling mechanism; the heating and cooling mechanisms are arranged along the axial direction of the thin-walled tube structure to form a gauge-length heating zone and a clamping cooling zone; and a measurement assembly for acquiring the axial deformation parameters and temperature parameters of the thin-walled tube structure during the test. This invention balances clamping stability and specimen integrity, allowing direct creep-fatigue testing of thin-walled tube structures while fully preserving the inherent shape, size, and stress distribution characteristics of the thin-walled tube structure; it achieves precise zonal control of damage modes, constructing a differentiated damage system on a single thin-walled tube structure, and accurately controlling the damage evolution rate in each region.

Description

Technical Field

[0001] This invention relates to the technical field of materials mechanics testing, and in particular to a creep-fatigue testing device for thin-walled tube structures and a method for determining test parameters. Background Technology

[0002] Aerospace, nuclear power, and other fields commonly face the critical engineering problem of creep-fatigue failure under high-temperature environments, particularly prominent in thin-walled metal components. These components operate under coupled high-temperature and cyclic loading conditions for extended periods, and the interaction between creep and fatigue damage significantly accelerates the failure process. Therefore, systematically studying the creep-fatigue behavior of thin-walled structures and obtaining reliable experimental data has become an urgent need to support equipment safety design and life assessment.

[0003] Traditionally, due to standardization considerations and technical limitations, creep-fatigue performance has primarily been obtained through standard specimen tests. It is important to clarify that standard tests not only consume a large amount of materials but also fail to reflect the actual damage evolution characteristics of thin-walled tube structures under service conditions, resulting in a long-standing scarcity of test data for relevant structures. Therefore, shifting the testing philosophy from the "material level" to the "structural level," and directly conducting creep-fatigue tests on thin-walled tube structures, has become an inevitable choice for accurately obtaining their performance data. This is irreplaceable for ensuring the safe service of related equipment and verifying the reliability of material performance.

[0004] However, existing technologies still have significant limitations. Due to the low stiffness of thin-walled tube structures, slippage during high-temperature clamping, and the increased stress concentration in the clamping section leading to premature sample failure, reliable and effective data is difficult to obtain. Therefore, existing technologies generally require structural modifications to the thin-walled tubes. While this improves experimental feasibility to some extent, it inevitably alters the original geometry, dimensional distribution, and stress state of the thin-walled tube, making it difficult for test results to accurately reflect its actual service performance. Furthermore, existing thin-walled tube structure testing devices have relatively limited testing modes, failing to cover the complex conditions of creep and fatigue coupling, and neglecting the impact of creep-fatigue interaction on damage evolution and failure mechanisms. This results in discrepancies between test results and actual operating conditions, making it difficult to provide effective support for the life assessment of thin-walled tube structures.

[0005] Therefore, it is urgent to develop a creep-fatigue testing device that can maintain the original shape and size characteristics of thin-walled tube structures, and to establish a reliable test design method. The two should work together to solve the creep-fatigue testing problem of thin-walled tube structures. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a creep-fatigue testing device for a thin-walled tube structure. The thin-walled tube structure is a uniform cross-section thin-walled tube, comprising a clamping section at one end and a gauge section located between the clamping sections. The testing device includes: The clamping assembly includes a rigid inner plug inserted into the inner cavity of the clamping section at the end of the thin-walled tube structure, a split outer clamp covering the outer side of the end of the thin-walled tube structure, and a positioning pin passing through the clamping section at the end of the thin-walled tube structure. The outer clamp is closed and clamped by a locking member. The rigid inner plug is connected to an external loading system through a connecting structure to realize the transmission of axial load. A temperature control assembly includes a heating mechanism and a cooling mechanism; the heating mechanism is disposed in the gauge section of the thin-walled tube structure, and the cooling mechanism is disposed in the clamping section of the thin-walled tube structure; the heating mechanism and the cooling mechanism are arranged along the axial direction of the thin-walled tube structure to form a gauge heating zone and a clamping cooling zone. The measurement components, including a temperature measurement mechanism and a deformation measurement mechanism, are used to obtain the axial deformation parameters and temperature parameters of the thin-walled tube structure during the test.

[0007] Furthermore, the temperature measuring mechanism includes multiple temperature sensors disposed at different axial positions on the gauge length segment, which achieve temperature measurement by closely fitting the upper, middle, and lower axial positions of the gauge length segment.

[0008] Furthermore, the deformation measuring mechanism includes an extensometer for measuring the axial deformation of the gauge length section, and obtains the axial deformation parameters of the thin-walled tube structure by closely fitting the gauge length section.

[0009] On the other hand, the present invention provides a method for determining test parameters of a creep-fatigue testing device for thin-walled tube structures, the method comprising: S1, Parametrically driven modeling of thin-walled tube structure and clamping components is performed to construct a three-dimensional parametric model for correlating experimental design parameters with structural response; S2 assigns material properties to the three-dimensional parametric model, meshes the three-dimensional parametric model, and applies corresponding loads and boundary conditions in combination with the test conditions. S3, damage analysis is performed on the gauge section and clamping section of the thin-walled tube structure respectively to obtain the cumulative damage value of each region; S4. Based on the damage value, establish a parametric response relationship model between the test design parameters and the cumulative damage of the gauge length segment and clamping segment; S5 aims to make the failure of the thin-walled tube structure occur preferentially in the gauge length segment. Based on the parameter response relationship model, damage constraints are introduced, and the test design parameters of the clamping component are solved in reverse to determine the parameter combination used for creep-fatigue testing.

[0010] Furthermore, the specific steps of step S1 are as follows: A three-dimensional parametric model is constructed using the three-dimensional modeling module of finite element calculation software / modeling software. Experimental design parameters are defined, including geometric parameters and experimental loading parameters. A mapping relationship between geometric parameters, experimental loading parameters, and the three-dimensional parametric model is established in the finite element calculation software / modeling software. Among them, the geometric parameters include the position coordinates and diameter of the clamping pin hole; the experimental loading parameters include the creep-fatigue holding time and the amplitude of the axial cyclic load.

[0011] Furthermore, the specific steps of step S2 are as follows: A three-dimensional parametric model was constructed using finite element method (FEM) software / modeling software. Material parameters were defined in the three-dimensional parametric model. The gauge length section, clamping section, and pin hole stress area of ​​the clamping component of the thin-walled tube structure in the three-dimensional parametric model were meshed. The corresponding loads were applied in combination with the test conditions, and the clamping components were subjected to constraints to simulate the real clamping state. The material parameters include material mechanical property parameters and material creep / fatigue property parameters; The loads include axial cyclic fatigue loads and temperature loads applied to the axial heating and cooling zones of the thin-walled tube structure.

[0012] Furthermore, the specific steps of step S3 are as follows: Fatigue damage calculation and creep damage calculation are performed on the gauge length section in the high temperature heating zone, and fatigue damage calculation is performed on the clamping section in the low temperature cooling zone. The process of performing fatigue damage calculation and creep damage calculation on the gauge length segment is as follows: The stress and strain field distribution of thin-walled tubes under thermal and mechanical loads was solved using finite element calculation software / modeling software to determine the stress and temperature distribution characteristics of the gauge length section. Based on the material's SN fatigue curve, a preset axial cyclic load spectrum is imported, and fatigue simulation is carried out in conjunction with fatigue simulation software. Critical nodes in the gauge length segment are identified, and calculations are performed. Fatigue damage value under the next cycle ; Retrieve basic data on creep rupture time under corresponding temperature and stress conditions for the material, and calculate the creep damage value of the gauge length segment using the time-fraction method. ; Following the linear damage accumulation criterion, fatigue damage and creep damage are superimposed to obtain the total damage value of the gauge length segment. ; The specific steps for performing fatigue damage calculations on the clamping section in the low-temperature cooling zone are as follows: The stress and strain distribution of the clamping section of the thin-walled tube under thermal and mechanical loads was solved by finite element calculation software / modeling software to clarify the force constraint characteristics of the clamping section. By combining the material SN curve and axial cyclic load spectrum, fatigue life analysis of the clamping section was completed through joint simulation using finite element calculation software / modeling software and fatigue simulation software, and the fatigue critical area and node life of the clamping section were located. The clamping section is calculated based on fatigue life. fatigue damage value in the second cycle .

[0013] Furthermore, the specific steps of step S4 are as follows: A response surface surrogate model was constructed using simulation software to establish a quantitative correspondence between geometric parameters, experimental loading parameters, and damage indicators in each region. Multiple parameter sample points were generated through Latin hypercube sampling design, and numerical analysis was performed on each parameter sample point. Finally, a parameter response relationship model was constructed through genetic aggregation.

[0014] Furthermore, the specific steps of step S5 are as follows: A multi-objective optimization mathematical relationship is established with the geometric design variables of the clamping component, the experimental loading parameter design variables, and the regional damage as constraints. This relationship is described in the following mathematical form:

[0015] In the formula: This represents the total damage value of the gauge length segment. This indicates pure fatigue damage in the clamping segment. , These are the upper and lower limits of total damage in the gauge length segment. The maximum diameter of the pin hole. The design diameter of the pin hole, This indicates the maximum equivalent strain in the clamping segment. This indicates the strain limit of the clamping section to prevent static strength fracture. Indicates the holding time during test loading. , These are the upper and lower limits of the load-bearing time, respectively. A multi-objective genetic algorithm is used to solve for the optimal solution set. The optimized structure is then verified by detailed finite element analysis to ensure that the results meet the design requirements and output the optimization parameters.

[0016] The present invention has the following beneficial effects: (1) This invention takes into account both clamping stability and sample integrity, and can directly carry out creep-fatigue tests on thin-walled tube structures, fully preserving the inherent shape, size and stress distribution characteristics of thin-walled tube structures; it achieves precise zonal control of damage modes, constructs a differentiated damage system on a single thin-walled tube structure, can accurately control the damage evolution rate of each region, ensures that the total creep-fatigue damage of the gauge length section occurs first, and effectively avoids test failure caused by premature failure of the clamping section.

[0017] (2) This invention realizes the precise quantitative design of test parameters, completes the precise quantitative calculation of multi-region damage of thin-walled tube structure through coupled finite element technology, and reverses the optimal solution of geometric parameters and test loading parameters, replacing the traditional experience trial and error method, and effectively controls the damage evolution process of thin-walled tube structure; and focuses on checking key areas such as pin holes in the parameter design process, which greatly improves the scientificity, rationality and accuracy of the test design. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the device in Embodiment 1.

[0019] Figure 2 This is a top view of the clamping component in Embodiment 1.

[0020] Figure 3 This is a flowchart of the parameter determination method in Example 2.

[0021] Figure 4 This is the response proxy model diagram established in Example 2. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. However, these embodiments are not intended to limit the present invention. Any similar structures and similar variations of the present invention should be included in the protection scope of the present invention. The commas in the present invention all indicate the relationship between and. The English letters in the present invention are case-sensitive.

[0023] Example 1 like Figures 1-2 As shown, this embodiment provides a creep-fatigue testing device for a thin-walled tube structure. The thin-walled tube is a steel pipe product manufactured by cutting steel ingots or solid tube blanks into approximately 1-meter billets, heating them in a furnace, piercing them to form a rough tube, and then hot-rolling, cold-rolling, or cold-drawing processes. The outer diameter to wall thickness ratio is greater than 10. The thin-walled tube structure is a uniform cross-section thin-walled tube, including a clamping section at the end and a gauge section located between the clamping sections. The testing device includes: The clamping assembly 1 includes a rigid inner plug 101 inserted into the inner cavity of the clamping section at the end of the thin-walled tube structure, a split outer clamp 102 covering the outer side of the end of the thin-walled tube structure, and a positioning pin 104 passing through the clamping section at the end of the thin-walled tube structure. The outer clamp is closed and clamped by a locking member 103. The rigid inner plug 101 is connected to the external loading system 4 by a connecting rod and bolts to realize the transmission of axial load. The rigid inner plug 101, the split outer clamp 102 and the positioning pin 104 cooperate with each other so that the axial load applied by the external loading system 4 is mainly transmitted by friction and supplemented by the transmission by the positioning pin 104 to act on the thin-walled tube structure. This reduces the risk of end stress concentration while ensuring the stability of load transmission and improves the anti-slip and anti-torsion ability during the test.

[0024] Temperature control component 2 includes a heating mechanism and a cooling mechanism. The heating mechanism can be a high-temperature furnace 201, which is located on the outside of the intermediate gauge section of the thin-walled tube structure. The cooling mechanism includes a cooling pipe 202 located inside the split outer clamp and in the transition area between the clamping section and the gauge section, and a circulating cooling pipe 203 connected to the cooling pipe. The cooling mechanism is located in the clamping section of the thin-walled tube structure and is used to provide directional cooling to the clamping section. The heating mechanism and the cooling mechanism are arranged along the axial direction of the thin-walled tube structure to form a gauge heating zone and a clamping cooling zone. The gauge heating zone is used to provide the high-temperature environment required for the test gauge section, while the clamping cooling zone is controlled at a lower temperature to avoid overheating of the clamping section of the thin-walled tube structure. The thin-walled tube structure regions corresponding to the heating zone and the cooling zone have different damage evolution characteristics during the test, causing the failure of the thin-walled tube structure to preferentially occur in the high-temperature heating zone.

[0025] Measurement component 3 includes a temperature measurement mechanism and a deformation measurement mechanism, used to acquire the axial deformation parameters and temperature parameters of the thin-walled tube structure during the test. The temperature measurement mechanism includes multiple temperature sensors 301 set at different axial positions of the gauge length, which can be thermocouples, and temperature measurement is achieved by closely fitting them to different axial positions at the top, middle, and bottom of the gauge length. The deformation measurement mechanism includes an extensometer 302 for measuring the axial deformation of the gauge length, and the axial deformation parameters of the thin-walled tube structure are acquired by closely fitting it to the gauge length.

[0026] Example 2 like Figure 3 As shown, this embodiment provides a method for determining the test parameters of a creep-fatigue testing device for thin-walled tube structures. Taking a thin-walled tube structure with an outer diameter of 40 mm, a wall thickness of 1.5 mm, a high-temperature gauge length of 200 mm, a transition section length of 80 mm, a clamping section length of 70 mm, and a total length of 500 mm as an example, the test parameters are determined using the testing device in Embodiment 1. The parameter determination method includes: S1. Parametrically driven modeling of the thin-walled tube structure and clamping components is performed to construct a three-dimensional parametric model for correlating experimental design parameters with structural response. The specific steps are as follows: A three-dimensional parametric model is constructed using the 3D modeling module integrated into the ANSYS Workbench platform. Experimental design parameters are defined, including geometric parameters and experimental loading parameters. A mapping relationship between the geometric design parameters, experimental loading parameters, and the three-dimensional parametric model is established in the platform. The geometric parameters include the position coordinates and diameter of the clamping pin hole. The experimental loading parameters include the creep-fatigue holding time and the amplitude of the axial cyclic load.

[0027] S2, Assign material properties to the 3D parametric model, mesh the 3D parametric model, and apply corresponding loads and boundary conditions based on the experimental conditions. The specific steps are as follows: A three-dimensional parametric model was constructed using ANSYS. Material parameters were defined in the three-dimensional parametric model. The key stress areas such as the gauge section, clamping section, and pin holes of the clamping components of the thin-walled tube structure in the three-dimensional parametric model were refined into meshes. The corresponding loads were applied in combination with the test conditions, and the clamping components were subjected to constraints to simulate the real clamping state. The material parameters include material mechanical property parameters and material creep / fatigue property parameters; The loads include axial cyclic fatigue loads and temperature loads applied to the axial heating and cooling zones of the thin-walled tube structure.

[0028] To simplify calculations, a high temperature of 650°C is applied to the high-temperature gauge length section, and a normal temperature of 20°C is applied to the clamping section. The axial tensile load is applied to the thin-walled tube through a rigid internal plug and a positioning pin. In this embodiment, the failure of the thin-walled tube under service conditions is mainly dominated by creep damage. Therefore, when the pin hole position in the low-temperature clamping section does not meet the fatigue failure condition, it can bear a large load.

[0029] S3. Damage analysis is performed on the gauge length and clamping section of the thin-walled tube structure to obtain the cumulative damage value for each region. The specific steps are as follows: Fatigue damage calculation and creep damage calculation are performed on the gauge length section in the high temperature heating zone, and fatigue damage calculation is performed on the clamping section in the low temperature cooling zone. The process of performing fatigue damage calculation and creep damage calculation on the gauge length segment is as follows: The stress and strain field distribution of thin-walled tubes under thermal and mechanical loads was solved using ANSYS Workbench, and the stress and temperature distribution characteristics of the gauge length section were determined. Based on the material's SN fatigue curve, a preset axial cyclic load spectrum is imported, and fatigue simulation is carried out in conjunction with nCode. Critical nodes in the gauge length segment are identified, and calculations are performed. Fatigue damage value under the next cycle ; Retrieve basic data on creep rupture time under corresponding temperature and stress conditions for the material, and calculate the creep damage value of the gauge length segment using the time-fraction method. ; Following the linear damage accumulation criterion, fatigue damage and creep damage are superimposed to obtain the total damage value of the gauge length segment. ; The specific steps for performing fatigue damage calculations on the clamping section in the low-temperature cooling zone are as follows: The stress and strain distribution of the clamping section of the thin-walled tube under thermal and mechanical loads was solved by ANSYS Workbench to clarify the force constraint characteristics of the clamping section. By combining the material SN curve and axial cyclic load spectrum, fatigue life analysis of the clamping section was completed through joint simulation of ANSYS and nCode, and the fatigue critical area and node life of the clamping section were located. The clamping section is calculated based on fatigue life. fatigue damage value in the second cycle .

[0030] The specific calculation formula is as follows:

[0031] In the formula, For the number of cycles of creep-fatigue, The fatigue life of the clamping segment under the current load. This represents the fatigue life of the gauge length segment under the current load. For the first The load time of each cycle, The creep failure time at the current stress level. For pin hole experience Fatigue damage after one cycle For the gauge length segment experience Fatigue damage after one cycle For the gauge length segment experience Creep damage after one cycle This represents the total creep-fatigue damage of the gauge length segment.

[0032] S4. Based on the damage values, establish a parametric response relationship model between the experimental design parameters and the cumulative damage of the gauge length and clamping section. The specific steps are as follows: A response surface surrogate model was constructed using simulation software to establish quantitative correspondences between geometric parameters, experimental loading parameters, and damage indices in various regions. Multiple parameter sample points were generated using Latin hypercube sampling design, and numerical analysis was performed on each sample point. Furthermore, a parameter response relationship model was constructed through genetic aggregation, such as... Figure 4 As shown, the accuracy of the model is verified.

[0033] S5, aiming to preferentially cause failure of the thin-walled tube structure within the gauge length, introduces damage constraints based on the parametric response relationship model. The geometric parameters and test loading parameters of the clamping assembly are then solved in reverse to determine the parameter combination used for the creep-fatigue test. The specific steps are as follows: A multi-objective optimization mathematical relationship is established with the geometric parameters of the clamping component, the experimental loading parameters, and the regional damage as constraints. This relationship is described in the following mathematical form:

[0034] In the formula: This represents the total damage value of the gauge length segment. This indicates pure fatigue damage in the clamping segment. , These are the upper and lower limits of total damage in the gauge length segment, taken as 0.9 and 1.1 respectively. The maximum diameter of the pin hole. The maximum permissible diameter without causing premature failure of the clamping section is determined based on the wall thickness of the thin-walled tube structure, the length of the clamping section, the strain concentration of the pin hole, and the axial load. Simultaneously, to avoid reducing the axial load-bearing capacity of the thin-walled tube... The radius of the thin-walled tube is used as the upper limit of the constraint; Design the diameter for the pin hole. This indicates the maximum equivalent strain in the clamping segment. This represents the strain limit of the clamping section, taken as 0.05, to avoid static strength fracture according to the definition of uniaxial tensile properties. Indicates the holding time during test loading. , These are the upper and lower limits of the load-bearing time, respectively set to 1 hour and 3 hours; A multi-objective genetic algorithm is used to solve for the optimal solution set. The optimized structure is then verified by detailed finite element analysis. The stress distribution, strain distribution and damage evolution characteristics under working load conditions are checked to ensure that the results meet the design requirements and the optimized parameters are output.

[0035] The algorithm is configured as follows: initially generate 2000 samples, generate 400 samples in each iteration, complete the optimization within a maximum of 20 iterations, converge after 4346 evaluations, and obtain 3 Pareto optimal solutions. The key parameters are shown in Table 1. Table 1

[0036] As shown in Table 1, all three candidate solutions satisfy all constraints, and the equivalent total strain of the clamping segment is approximately 0.0325 mm. mm - ¹, which is much smaller than the upper limit of the constraint of 0.05, and the differences between the three groups are very small, indicating that the strain target has met the constraint requirements; the total damage of the gauge length section is close to the target value of 1, which can ensure that the gauge length section just reaches the design life; there are differences in the fatigue damage of the clamping section, among which the hole position damage of candidate point 1 is 0.66569, which is the lowest among the three groups and has the highest safety margin. At the same time, the gauge length section damage (0.99997) is closest to the target value, which is the preferred solution.

[0037] By utilizing the test apparatus in Example 1, the gauge length region and clamping region of the thin-walled tube structure exhibit different damage evolution characteristics during the test, thereby guiding the failure of the thin-walled tube structure to preferentially occur in the gauge length region. Creep-fatigue tests can be directly conducted on the thin-walled tube structure, fully preserving its inherent shape, size, and stress distribution characteristics. Precise zonal control of damage modes is achieved, constructing a differentiated damage system on a single thin-walled tube structure. This allows for precise control of the damage evolution rate in each region, ensuring that creep-fatigue total damage occurs preferentially in the gauge length section, effectively avoiding test failure due to premature failure of the clamping section.

[0038] Meanwhile, this invention also achieves precise quantitative design of test parameters. By using coupled finite element technology, it completes precise quantitative calculation of multi-region damage in thin-walled tube structures, as well as reverse solving of the optimal solutions for fixture geometric parameters and test loading parameters. This replaces the traditional trial-and-error method and enables effective control over the damage evolution process of thin-walled tube structures. Furthermore, the parameter design process focuses on verifying key areas such as pin holes, significantly improving the scientific rigor, rationality, and accuracy of the test design. This provides reliable technical support for the creep-fatigue design and life assessment of thin-walled tube structures in aerospace, nuclear power, and other fields.

[0039] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

Claims

1. A creep-fatigue test apparatus for a thin-walled tubular structure, the thin-walled tubular structure being a thin-walled tube of constant cross section comprising clamping sections provided at end portions and a gauge section between the clamping sections, characterised in that, The test apparatus includes: The clamping assembly includes a rigid inner plug inserted into the inner cavity of the clamping section at the end of the thin-walled tube structure, a split outer clamp covering the outer side of the end of the thin-walled tube structure, and a positioning pin passing through the clamping section at the end of the thin-walled tube structure. The outer clamp is closed and clamped by a locking member. The rigid inner plug is connected to an external loading system through a connecting structure to realize the transmission of axial load. A temperature control assembly includes a heating mechanism and a cooling mechanism; the heating mechanism is disposed in the gauge section of the thin-walled tube structure, and the cooling mechanism is disposed in the clamping section of the thin-walled tube structure; the heating mechanism and the cooling mechanism are arranged along the axial direction of the thin-walled tube structure to form a gauge heating zone and a clamping cooling zone. The measurement components, including a temperature measurement mechanism and a deformation measurement mechanism, are used to obtain the axial deformation parameters and temperature parameters of the thin-walled tube structure during the test.

2. The apparatus for creep-fatigue testing of thin-walled tubular structures according to claim 1, characterized in that The temperature measuring mechanism includes multiple temperature sensors located at different axial positions on the gauge length, which achieve temperature measurement by closely fitting the upper, middle, and lower axial positions of the gauge length.

3. The apparatus for creep-fatigue testing of thin-walled tubular structures according to claim 1, characterized in that The deformation measuring mechanism includes an extensometer for measuring the axial deformation of the gauge length section, and obtains the axial deformation parameters of the thin-walled tube structure by closely fitting the gauge length section.

4. A method of determining test parameters for a thin-walled tube structure creep-fatigue test apparatus, characterized by, The method for determining test parameters is applicable to any of the test apparatuses described in claims 1-3, and the method for determining test parameters includes: S1, Parametrically driven modeling of thin-walled tube structure and clamping components is performed to construct a three-dimensional parametric model for correlating experimental design parameters with structural response; S2 assigns material properties to the three-dimensional parametric model, meshes the three-dimensional parametric model, and applies corresponding loads and boundary conditions in combination with the test conditions. S3, damage analysis is performed on the gauge section and clamping section of the thin-walled tube structure respectively to obtain the cumulative damage value of each region; S4. Based on the damage value, establish a parametric response relationship model between the test design parameters and the cumulative damage of the gauge length segment and clamping segment; S5 aims to make the failure of the thin-walled tube structure occur preferentially in the gauge length segment. Based on the parameter response relationship model, damage constraints are introduced, and the test design parameters of the clamping component are solved in reverse to determine the parameter combination used for creep-fatigue testing.

5. The method of claim 4, wherein the method is characterized by: The specific steps of step S1 are as follows: A three-dimensional parametric model is constructed using the three-dimensional modeling module of finite element analysis software / modeling software. Experimental design parameters are defined, including geometric parameters and experimental loading parameters. A mapping relationship between geometric parameters, experimental loading parameters, and the three-dimensional parametric model is established in the finite element analysis software / modeling software. Among them, the geometric parameters include the position coordinates and diameter of the clamping pin hole; the experimental loading parameters include the creep-fatigue holding time and the amplitude of the axial cyclic load.

6. The method for determining test parameters of a creep-fatigue testing device for thin-walled tube structures according to claim 5, characterized in that, The specific steps of step S2 are as follows: A three-dimensional parametric model was constructed using finite element method (FEM) software / modeling software. Material parameters were defined in the three-dimensional parametric model. The gauge length section, clamping section, and pin hole stress area of ​​the clamping component of the thin-walled tube structure in the three-dimensional parametric model were meshed. The corresponding loads were applied in combination with the test conditions, and the clamping components were subjected to constraints to simulate the real clamping state. The material parameters include material mechanical property parameters and material creep / fatigue property parameters; The loads include axial cyclic fatigue loads and temperature loads applied to the axial heating and cooling zones of the thin-walled tube structure.

7. The method for determining test parameters of a creep-fatigue testing device for thin-walled tube structures according to claim 4, characterized in that, The specific steps of step S3 are as follows: Fatigue damage calculation and creep damage calculation are performed on the gauge length section in the high temperature heating zone, and fatigue damage calculation is performed on the clamping section in the low temperature cooling zone. The process of performing fatigue damage calculation and creep damage calculation on the gauge length segment is as follows: The stress and strain field distribution of thin-walled tubes under thermal and mechanical loads was solved using finite element calculation software / modeling software to determine the stress and temperature distribution characteristics of the gauge length section. Based on the material's SN fatigue curve, a preset axial cyclic load spectrum is imported, and fatigue simulation is carried out in conjunction with fatigue simulation software. Critical nodes in the gauge length segment are identified, and calculations are performed. Fatigue damage value under the next cycle ; Retrieve basic data on creep rupture time under corresponding temperature and stress conditions for the material, and calculate the creep damage value of the gauge length segment using the time-fraction method. ; Following the linear damage accumulation criterion, fatigue damage and creep damage are superimposed to obtain the total damage value of the gauge length segment. ; The specific steps for performing fatigue damage calculations on the clamping section in the low-temperature cooling zone are as follows: The stress and strain distribution of the clamping section of the thin-walled tube under thermal and mechanical loads was solved by finite element calculation software / modeling software to clarify the force constraint characteristics of the clamping section. By combining the material SN curve and axial cyclic load spectrum, fatigue life analysis of the clamping section was completed through joint simulation using finite element calculation software / modeling software and fatigue simulation software, and the fatigue critical area and node life of the clamping section were located. The clamping section is calculated based on fatigue life. fatigue damage value in the second cycle .

8. The method for determining test parameters of a creep-fatigue testing device for thin-walled tube structures according to claim 5, characterized in that, The specific steps of step S4 are as follows: A response surface surrogate model was constructed using simulation software to establish a quantitative correspondence between geometric parameters, experimental loading parameters, and damage indicators in each region. Multiple parameter sample points were generated through Latin hypercube sampling design, and numerical analysis was performed on each parameter sample point. Finally, a parameter response relationship model was constructed through genetic aggregation.

9. The method for determining test parameters of a creep-fatigue testing device for thin-walled tube structures according to claim 7, characterized in that, The specific steps of step S5 are as follows: A multi-objective optimization mathematical relationship is established with the geometric parameters of the clamping component, the experimental loading parameters, and the regional damage as constraints. This relationship is described in the following mathematical form: In the formula: This represents the total damage value of the gauge length segment. This indicates pure fatigue damage in the clamping segment. , These represent the upper and lower limits of total damage in the gauge length segment. The maximum diameter of the pin hole. The design diameter of the pin hole, This indicates the maximum equivalent strain in the clamping segment. This indicates the strain limit of the clamping section to prevent static strength fracture. Indicates the holding time during test loading. , These are the upper and lower limits of the load-bearing time, respectively. A multi-objective genetic algorithm is used to solve for the optimal solution set. The optimized structure is then verified by detailed finite element analysis to ensure that the results meet the design requirements and to output the optimized parameters.

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