Sample temperature indirect control device and method for thermal mechanical fatigue test

Abstract

The invention relates to the technical field of temperature control in a high-temperature mechanical property test, in particular to a sample temperature indirect control device and method for a thermal mechanical fatigue test. A first thermocouple is used as a main control thermocouple to realize stable tracking of a target temperature waveform; recording a follow-up temperature track measured and fed back by the second thermocouple; the second thermocouple is changed into a main control thermocouple, the follow-up temperature track is mapped into an instruction signal input into the temperature control module, and the follow-up temperature track is corrected through multi-round iteration of a track correction algorithm according to the deviation between the first feedback temperature track and the target temperature track; obtaining a final follow-up temperature track until the first feedback temperature track converges to the target temperature track; only a second thermocouple is welded at the same position of the fatigue specimen for the formal test, and the final follow-up temperature track is mapped into an instruction signal input into the temperature control module, so that indirect control that the temperature track of the gauge length section of the thermal mechanical fatigue specimen meets the target temperature track can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature control in high-temperature mechanical property tests, and particularly to a device and method for indirectly controlling the temperature of a specimen in a thermo-mechanical fatigue test. Background Art

[0002] Under modern high-temperature industrial service conditions such as aero-engine turbine components, piston-engine cylinder heads, and nuclear industry pressure pipelines, materials often bear the superimposed action of alternating mechanical loads and alternating temperature loads, and their fatigue behavior belongs to the category of thermo-mechanical fatigue. Materials subjected to thermo-mechanical fatigue loads often have a shorter fatigue life than those subjected to mechanical loads or thermal loads alone. Therefore, for industrial applications, the thermo-mechanical fatigue load environment is more dangerous than isothermal fatigue and requires more attention and experimental research.

[0003] When conducting a thermo-mechanical fatigue test, the temperature measurement on the surface of the specimen is often carried out by a thermocouple. For metal specimens, the thermocouple can often be fixed to the specimen surface in three forms: welded, strip-wrapped, and bundled. Among them, in the welded form, the temperature measurement part of the thermocouple is directly welded to the specimen surface as a whole; in the strip-wrapped form, the thermocouple wires are respectively led out from both sides of the specimen axially, and the thermocouple wires are tightened by an external force away from the specimen direction so that the thermocouple measurement point is in close contact with the specimen surface; while in the bundled form, the thermocouple measurement point is tied tightly to the specimen surface by a high-temperature-resistant wire. Since metal materials react with oxygen at high temperatures to form an increasingly thick oxide film, the contact state between the strip-wrapped thermocouple and the bundled thermocouple and the specimen surface will be interfered by the thickening of the oxide film on the specimen surface and the thermocouple measurement point, thus affecting the accuracy and stability of the long-term temperature measurement of the specimen surface by the thermocouple. Although the welded thermocouple is integrated with the specimen surface to avoid the influence of high-temperature oxidation on long-term temperature measurement, the welding process itself causes thermal shock damage to the material surface, and thermo-mechanical fatigue belongs to the category of low-cycle fatigue, and the vast majority of its crack initiation originates from the specimen surface. Therefore, directly welding a thermocouple within the gauge section of the fatigue specimen often affects the fatigue life of the specimen. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a device and method for indirectly controlling the temperature of a specimen in a thermo-mechanical fatigue test, which can not only avoid the influence of oxidation on the accuracy and stability of long-term temperature measurement in a high-temperature environment but also avoid the interference of welding a thermocouple within the gauge section on the fatigue life of the thermo-mechanical fatigue specimen.

[0005] The present invention is implemented as follows. There is provided a device for indirectly controlling the temperature of a specimen in a thermo-mechanical fatigue test, including: The first thermocouple is arranged within the gauge length range of the fatigue specimen for temperature adjustment, and is used to collect and output in real time the first feedback temperature trajectory characterizing the surface temperature at the location where it is located; The second thermocouple is arranged outside the gauge length range of the fatigue specimen for temperature adjustment or the fatigue specimen for the formal test, and is used to collect and output in real time the second feedback temperature trajectory characterizing the surface temperature at the location where it is located; The thermo-mechanical fatigue temperature loading module is arranged around the fatigue specimen for temperature adjustment or the fatigue specimen for the formal test, and is used to realize the temperature change of the fatigue specimen for temperature adjustment or the fatigue specimen for the formal test by heating and cooling; The temperature control module and the instruction module. The instruction module is respectively connected to the first thermocouple, the second thermocouple and the temperature control module. The temperature control module is connected to the first thermocouple or the second thermocouple and is also connected to the thermo-mechanical fatigue temperature loading module; The instruction module maps the instruction temperature trajectory generated according to the user setting, or the second feedback temperature trajectory, or the instruction temperature trajectory obtained by real-time operation and optimization using the trajectory correction algorithm based on the first feedback temperature trajectories received multiple times into an instruction signal for output. The temperature control module receives the first feedback temperature trajectory or the second feedback temperature trajectory and analyzes the instruction signal input by the instruction module, and outputs a control quantity to the thermo-mechanical fatigue temperature loading device after calculation by the built-in closed-loop control algorithm.

[0006] Preferably, the first thermocouple is arranged at the exact center position of the gauge length of the fatigue specimen for temperature adjustment along each axial direction of the specimen.

[0007] Preferably, the second thermocouple is arranged at the 2 / 3 position along any axial direction of the transition section of the fatigue specimen for temperature adjustment or the fatigue specimen for the formal test and close to the gauge length direction.

[0008] Preferably, the arrangement method of the first thermocouple and the second thermocouple is welding.

[0009] Preferably, the closed-loop control algorithm in the temperature control module has user-adjustable parameters.

[0010] The present invention also provides an indirect control method for the specimen temperature in a thermo-mechanical fatigue test. Based on the above device, the indirect control method includes the following steps: Step 1) Arrange the first thermocouple inside the gauge length of the fatigue specimen for temperature adjustment, arrange the second thermocouple outside the gauge length of the fatigue specimen for temperature adjustment, and arrange the fatigue specimen for temperature adjustment in the thermo-mechanical fatigue temperature loading module; Step 2) Connect the first thermocouple as the main temperature-measuring thermocouple to the temperature control module, map the target temperature trajectory set by the user into an instruction signal input to the temperature control module, enable the temperature control module to control the thermo-mechanical fatigue temperature loading module to adjust the temperature of the fatigue specimen for temperature adjustment, adjust the parameters of the temperature control module so that the first feedback temperature trajectory measured by the first thermocouple approaches the target temperature trajectory, and record the second feedback temperature trajectory when the first feedback temperature trajectory conforms to the target temperature trajectory as the initial follow-up temperature trajectory; Step 3) Reconnect the second thermocouple as the main temperature-measuring thermocouple to the temperature control module and connect the first thermocouple as the monitoring temperature-measuring thermocouple. Map the initial follow-up temperature trajectory recorded in Step 2 into an instruction signal and output it to the temperature control module. Enable the temperature control module to drive the thermo-mechanical fatigue temperature loading module to adjust the temperature outside the gauge section of the fatigue specimen for temperature adjustment. According to the deviation between the first feedback temperature trajectory and the target temperature trajectory, use the trajectory correction algorithm to iteratively update the follow-up temperature trajectory in real time. After multiple rounds of iteration, the deviation converges to a minimum value, thereby obtaining the final follow-up temperature trajectory; Step 4) Only arrange the second thermocouple outside the gauge section of the fatigue specimen for the formal test. Map the final follow-up temperature trajectory generated in Step 3 into an instruction signal and output it to the temperature control module. Enable the temperature control module to drive the thermo-mechanical fatigue temperature loading module to adjust the temperature outside the gauge section of the fatigue specimen for the formal test, and then the indirect control of the temperature inside the gauge section of the fatigue specimen for the formal test to conform to the target temperature trajectory can be realized.

[0011] Preferably, the fatigue specimen for temperature adjustment and the fatigue specimen for the formal test are exactly the same.

[0012] Preferably, in Step 3), for the temperature trajectory with periodicity, the corresponding trajectory correction algorithm conforms to the following input correction formula:

[0013] where, represents the temperature trajectory of the previous cycle, represents the temperature trajectory corrected in the current cycle, is the deviation between the first feedback temperature trajectory and the target temperature trajectory at any time t, is the differential of, is the control deviation the proportional factor of the direct correction weight of, is the differential factor of the weight for correcting the deviation change trend, is the time correction term for adjusting the error sampling.

[0014] Preferably, in Step 3), for the temperature trajectory without periodicity, the corresponding trajectory correction algorithm conforms to the following input correction formula:

[0015] Among them, represents the temperature trajectory of the previous temperature change process, represents the temperature trajectory after correction of the current temperature change process, is the deviation between the first feedback temperature trajectory and the target temperature trajectory at any time t, is the differential of is the control deviation the proportionality factor of the direct correction weight, is the differential factor of the weight for correcting the change trend of the deviation, is the time correction term for adjusting the error sampling.

[0016] Compared with the prior art, the advantages of the present invention are as follows: Based on the first feedback temperature trajectory measured by the first thermocouple welded inside the gauge section of the fatigue specimen, the present invention takes it as the initial control object and obtains the initial follow-up temperature trajectory measured by the second thermocouple outside the gauge section. Through the trajectory correction algorithm, the control accuracy of the temperature inside the gauge section based on the follow-up temperature trajectory when the second thermocouple is used as the main control thermocouple is improved. In the formal thermo-mechanical fatigue test, only the second thermocouple is welded outside the gauge section of the specimen for the formal test. The accurate control of the temperature inside the gauge section of the specimen is realized through the final follow-up temperature trajectory generated after optimization by the trajectory correction algorithm. It can not only utilize the advantage of the welded thermocouple's oxidation resistance to ensure the accuracy of long-term temperature measurement, but also avoid the interference caused by the welding inside the gauge section to the fatigue damage of the specimen. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0018] Figure 1 is a schematic diagram showing the arrangement positions of the first thermocouple and the second thermocouple on the uniaxial fatigue specimen provided by the present invention; Figure 2 is a schematic diagram showing the arrangement positions of the first thermocouple and the second thermocouple on the biaxial cruciform fatigue specimen provided by the present invention; Figure 3 is a schematic diagram showing the connection relationship between the modules of the specimen temperature indirect control device for the thermo-mechanical fatigue test provided by the present invention; Figure 4A schematic diagram provided by the present invention for preferably characterizing the arrangement positions of the first thermocouple and the second thermocouple on a uniaxial fatigue specimen a) and on a biaxial cruciform fatigue specimen b); Figure 5 A schematic diagram provided by the present invention for preferably characterizing three welding forms of thermocouples on the surface of a fatigue specimen; Figure 6 A schematic diagram of the process for the method of indirectly controlling the specimen temperature in a thermomechanical fatigue test provided by the present invention; Figure 7 A schematic diagram of the correction effect of the trajectory correction algorithm provided by the present invention; Explanation of reference numerals: 1, the first thermocouple; 2, the second thermocouple; 3, the fatigue specimen for temperature adjustment; 4, the thermomechanical fatigue temperature loading module; 5, the temperature control module; 6, the instruction module. Detailed implementation manners

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0020] The purpose of the present invention is to provide a device and method for indirectly controlling the specimen temperature in a thermomechanical fatigue test. By indirectly controlling the temperature change inside the gauge section through the thermocouple welded outside the gauge section of the fatigue specimen, the temperature inside the gauge section conforms to the commanded temperature trajectory, which can not only avoid the influence of oxidation on the long-term temperature measurement accuracy in a high-temperature environment, but also avoid the interference of welding inside the gauge section on the fatigue life of the thermomechanical fatigue specimen.

[0021] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0022] As Figures 1 to 3 shown, a device for indirectly controlling the specimen temperature in a thermomechanical fatigue test provided by the present invention includes: The first thermocouple 1 is arranged within the gauge section of the fatigue specimen 3 for temperature adjustment, and is used to collect and output in real time a first feedback temperature trajectory characterizing the surface temperature of the point where it is located; Specifically, the first thermocouple 1 should be arranged at the point with the highest cyclic peak temperature inside the specimen gauge section, so as to more accurately characterize the representative temperature of the high-temperature part where fatigue crack initiation is most likely to occur.

[0023] The second thermocouple 2 is arranged outside the gauge length section of the fatigue specimen 3 for temperature adjustment or the fatigue specimen for formal test, and is used to collect and output in real time the second feedback temperature trajectory characterizing the surface temperature of the point where it is located. Specifically, the second thermocouple 2 should be arranged at a point as close as possible to the gauge length section of the specimen, and will not cause the crack initiation at the welding point of the second thermocouple 2 first during the thermo-mechanical fatigue process due to the thermal shock damage caused by the thermocouple welding, so as to characterize as much as possible the representative temperature with obvious cyclic temperature fluctuation characteristics outside the gauge length section of the specimen.

[0024] The thermo-mechanical fatigue temperature loading module 4 is arranged around the fatigue specimen 3 for temperature adjustment or the fatigue specimen for formal test, and is used to realize the temperature change of the fatigue specimen 3 or the fatigue specimen for formal test by heating and cooling. Specifically, the heating sub-module in the thermo-mechanical fatigue temperature loading module 4 can adopt heating means such as infrared radiation heating, high-temperature gas convection heating, direct electric heating, and electromagnetic induction heating, and the cooling sub-module in the thermo-mechanical fatigue temperature loading module can adopt cooling means such as gas convection cooling, phase change evaporation cooling, and radiation cooling.

[0025] The temperature control module 5 and the instruction module 6, the instruction module 6 is respectively connected to the first thermocouple 1, the second thermocouple 2 and the temperature control module 5, the temperature control module 5 is connected to the first thermocouple 1 or the second thermocouple 2, and is connected to the thermo-mechanical fatigue temperature loading module 4; the instruction module 6 maps the instruction temperature trajectory generated following the user settings or the second feedback temperature trajectory or the instruction temperature trajectory obtained by real-time operation and optimization using the trajectory correction algorithm based on the first feedback temperature trajectory received multiple times into an instruction signal for output, the temperature control module 5 receives the first feedback temperature trajectory or the second feedback temperature trajectory and analyzes the instruction signal input by the instruction module 6, and outputs a control quantity to the thermo-mechanical fatigue temperature loading device 4 after operation by the built-in closed-loop control algorithm.

[0026] Specifically, the instruction module 6 has the ability to receive, monitor and process temperature signals and the ability to output temperature trajectories in an instruction form, can calculate the deviation between the temperature value fed back by the current thermocouple and the ideal temperature trajectory, and input the deviation into the trajectory correction algorithm in the instruction module 6 to optimize and adjust the instruction temperature trajectory in real time, and finally convert the generated instruction temperature trajectory into an instruction electric signal acceptable to the downstream temperature control module 5 for output.

[0027] Specifically, the temperature control module 5 has the ability to receive and process temperature signals, and the ability to receive and process instruction electric signals. By receiving the instruction electric signal as an input quantity, it calculates in real time the deviation between the input quantity and the temperature fed back by the thermocouple, and inputs the deviation to the built-in control algorithm to calculate the control quantity output to the thermo-mechanical fatigue temperature loading module 4.

[0028] Furthermore, as Figure 4 shown, the first thermocouple 1 is arranged at the exact center position of the gauge section of the temperature-adjusting fatigue specimen 3 along each axial direction of the specimen. The second thermocouple 2 is arranged at the 2 / 3 position along any axial direction of the specimen in the transition section of the temperature-adjusting fatigue specimen 3 or the fatigue specimen for formal test, close to the gauge section.

[0029] Furthermore, as Figure 5 shown, the arrangement method of the first thermocouple 1 and the second thermocouple 2 is welding.

[0030] Specifically, the welding methods include but are not limited to: fusing the two thermocouple wires into a measuring point and then welding the measuring point to the surface of the fatigue specimen; independently welding the two thermocouple wires of the thermocouple relatively closely to the surface of the fatigue specimen; successively stacking and welding the two thermocouple wires of the thermocouple at the same point on the surface of the fatigue specimen.

[0031] Furthermore, the closed-loop control algorithm in the temperature control module 5 has user-adjustable parameters.

[0032] Specifically, the closed-loop control algorithms built in the temperature control module include but are not limited to: PID control, model predictive control, sliding mode control, fuzzy control, adaptive control, etc. By adjusting the user-adjustable parameters, the tracking error of the surface temperature of the feedback fatigue specimen to the commanded temperature trajectory can be reduced, and the tracking accuracy can be improved.

[0033] The present invention also provides a method for indirectly controlling the specimen temperature in a thermo-mechanical fatigue test. As Figure 6 shown, it includes the following steps: Step 1) Arrange the first thermocouple 1 inside the gauge section of the temperature-adjusting fatigue specimen 3, arrange the second thermocouple 1 outside the gauge section of the temperature-adjusting fatigue specimen 3, and arrange the temperature-adjusting fatigue specimen 3 in the thermo-mechanical fatigue temperature loading module 4; Specifically, the arrangement state of the temperature-adjusting fatigue specimen 3 in the thermo-mechanical fatigue temperature loading module 4 should be exactly the same as that in the formal thermo-mechanical fatigue test, so that the temperature trajectory response behavior of the temperature-adjusting fatigue specimen 3 can be used to characterize the temperature trajectory response behavior of all formal test fatigue specimens.

[0034] Step 2) Connect the first thermocouple 1 as the main control temperature-measuring thermocouple to the temperature control module 5, map the target temperature trajectory set by the user into the command signal input to the temperature control module 5, make the temperature control module 5 control the thermo-mechanical fatigue temperature loading module 4 to adjust the temperature of the temperature-adjusting fatigue specimen 3, adjust the parameters of the temperature control module 5 to make the first feedback temperature trajectory measured by the first thermocouple 1 approach the target temperature trajectory, and record the second feedback temperature trajectory when the first feedback temperature trajectory conforms to the target temperature trajectory as the initial follow-up temperature trajectory; Step 3) Use the second thermocouple 2 as the main control temperature measuring thermocouple and connect it to the temperature control module 5, and use the first thermocouple 1 as the monitoring temperature measuring thermocouple. Map the initial follow-up temperature trajectory recorded in Step 2 into an instruction signal and output it to the temperature control module 5. Let the temperature control module 5 drive the thermo-mechanical fatigue temperature loading module to adjust the temperature outside the gauge section of the fatigue specimen 3 for temperature adjustment. According to the deviation between the first feedback temperature trajectory and the target temperature trajectory, use the trajectory correction algorithm to iteratively update the follow-up temperature trajectory in real time. After multiple rounds of iteration, the deviation converges to a minimum value, thereby obtaining the final follow-up temperature trajectory; Specifically, as Figure 7 shown, by repeatedly executing and iteratively updating the follow-up temperature trajectory in multiple rounds, the final follow-up temperature trajectory will converge to a stable trajectory under the continuous correction of the trajectory correction algorithm, and the first feedback temperature trajectory corresponding to this stable trajectory conforms to the target temperature trajectory.

[0035] Step 4) Only arrange the second thermocouple 2 outside the gauge section of the fatigue specimen for the formal test. Map the final follow-up temperature trajectory generated in Step 3 into an instruction signal and output it to the temperature control module 5. Let the temperature control module 5 drive the thermo-mechanical fatigue temperature loading module 4 to adjust the temperature outside the gauge section of the fatigue specimen for the formal test, so as to indirectly control the temperature inside the gauge section of the fatigue specimen for the formal test to conform to the target temperature trajectory.

[0036] Furthermore, the fatigue specimen 3 for temperature adjustment and the fatigue specimen for the formal test are exactly the same. For example, in terms of materials, processing techniques, and geometric dimensions, etc.

[0037] Specifically, the fatigue specimen 3 for temperature adjustment should be randomly selected from the fatigue specimens for the formal test produced in the same batch.

[0038] Furthermore, in Step 3), for the temperature trajectory with periodicity, the corresponding trajectory correction algorithm conforms to the following input correction formula:

[0039] where, represents the temperature trajectory of the previous cycle, represents the temperature trajectory corrected in the current cycle, is the deviation between the first feedback temperature trajectory and the target temperature trajectory at any time t, is the differential of, is the control deviation the proportional factor of the direct correction weight of, is the differential factor of the weight for correcting the change trend of the deviation, is the time correction term for adjusting the error sampling.

[0040] Specifically, the proportionality factor 𝑝 can quickly respond to the tracking deviation of the temperature trajectory by amplifying the amplitude of the deviation. However, relying solely on the action of the proportionality coefficient, the temperature trajectory cannot converge and stabilize well. Especially when the proportionality coefficient is large, although the trajectory correction algorithm can effectively overcome the influence of deviation disturbances, it is also prone to large overshoot and trajectory oscillation, resulting in the inability to converge to produce a stable trajectory. Therefore, by additionally introducing a differential factor , the trajectory correction algorithm can respond to the trajectory oscillation trend caused by the correction of the proportionality factor, eliminate the instability caused by trajectory oscillation, and finally obtain a stable and corrected convergent follow-up temperature trajectory.

[0041] Furthermore, in step 3), for the temperature trajectory without periodicity, the corresponding trajectory correction algorithm conforms to the following input correction formula:

[0042] where represents the temperature trajectory of the previous temperature change process, represents the corrected temperature trajectory of the current temperature change process, is the deviation between the first feedback temperature trajectory and the target temperature trajectory at any time t, is the differential of, is the control deviation the proportionality factor of the direct correction weight of, is the differential factor of the weight for correcting the deviation change trend, is the time correction term for adjusting error sampling.

[0043] In this specification, specific examples are used to elaborate on the principles and implementation methods of the present invention. The descriptions of the above embodiments are only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An indirect control device for the specimen temperature in thermo-mechanical fatigue tests, characterized in that, Including: A first thermocouple (1) arranged within the gauge length range of the fatigue specimen for temperature adjustment (3), used to collect and output in real time a first feedback temperature trajectory characterizing the surface temperature at the location where it is located; A second thermocouple (2) arranged outside the gauge length range of the fatigue specimen for temperature adjustment (3) or the fatigue specimen for the formal test, used to collect and output in real time a second feedback temperature trajectory characterizing the surface temperature at the location where it is located; A thermo-mechanical fatigue temperature loading module (4) arranged around the fatigue specimen for temperature adjustment (3) or the fatigue specimen for the formal test, used to achieve temperature changes of the fatigue specimen for temperature adjustment (3) or the fatigue specimen for the formal test by heating and cooling; A temperature control module (5) and an instruction module (6), the instruction module (6) is respectively connected to the first thermocouple (1), the second thermocouple (2) and the temperature control module (5), the temperature control module (5) is connected to the first thermocouple (1) or the second thermocouple (2), and is connected to the thermo-mechanical fatigue temperature loading module (4); the instruction module (6) maps the instruction temperature trajectory generated following the user's setting, or the second feedback temperature trajectory, or the instruction temperature trajectory obtained by real-time operation and optimization using the trajectory correction algorithm based on the first feedback temperature trajectories received multiple times into an instruction signal for output, the temperature control module (5) receives the first feedback temperature trajectory or the second feedback temperature trajectory and analyzes the instruction signal input by the instruction module (6), and outputs a control quantity to the thermo-mechanical fatigue temperature loading device (4) after calculation by the built-in closed-loop control algorithm.

2. The specimen temperature indirect control device for thermo-mechanical fatigue test according to claim 1, wherein The first thermocouple (1) is arranged at the exact center position of the gauge length of the fatigue specimen for temperature adjustment (3) along each axial direction of the specimen.

3. The specimen temperature indirect control device for thermo-mechanical fatigue test according to claim 1, characterized in that, The second thermocouple (2) is arranged at the 2 / 3 position along any axial direction of the fatigue specimen for temperature adjustment (3) or the transition section of the fatigue specimen for the formal test and close to the gauge length direction.

4. The indirect control device for the specimen temperature in the thermo-mechanical fatigue test according to claim 1, characterized in that, The arrangement method of the first thermocouple (1) and the second thermocouple (2) is welding.

5. The indirect control device for the specimen temperature in the thermo-mechanical fatigue test according to claim 1, wherein, The closed-loop control algorithm in the temperature control module (5) has user-adjustable parameters.

6. An indirect control method for the specimen temperature in a thermo-mechanical fatigue test, characterized in that, Based on the device according to any one of claims 1-5, the indirect control method includes the following steps: Step 1) Arrange the first thermocouple (1) inside the gauge length of the fatigue specimen for temperature adjustment (3), arrange the second thermocouple (1) outside the gauge length of the fatigue specimen for temperature adjustment (3), and arrange the fatigue specimen for temperature adjustment (3) in the thermo-mechanical fatigue temperature loading module (4); Step 2) Connect the first thermocouple (1) as the main control temperature-measuring thermocouple to the temperature control module (5), map the target temperature trajectory set by the user into an instruction signal input to the temperature control module (5), enable the temperature control module (5) to control the thermo-mechanical fatigue temperature loading module (4) to adjust the temperature of the fatigue specimen for temperature adjustment (3), adjust the parameters of the temperature control module (5) to make the first feedback temperature trajectory measured by the first thermocouple (1) approach the target temperature trajectory, and record the second feedback temperature trajectory when the first feedback temperature trajectory conforms to the target temperature trajectory as the initial follow-up temperature trajectory; Step 3) Use the second thermocouple (2) as the main control temperature measuring thermocouple and connect it to the temperature control module (5), and use the first thermocouple (1) as the monitoring temperature measuring thermocouple. Map the initial follow-up temperature trajectory recorded in Step 2) as an instruction signal and output it to the temperature control module (5), so that the temperature control module (5) drives the thermo-mechanical fatigue temperature loading module to adjust the temperature outside the gauge section of the fatigue specimen (3) for temperature adjustment. According to the deviation between the first feedback temperature trajectory and the target temperature trajectory, use the trajectory correction algorithm to iteratively update the follow-up temperature trajectory in real time. After multiple rounds of iteration, the deviation converges to a minimum value, thereby obtaining the final follow-up temperature trajectory; Step 4) Only arrange the second thermocouple (2) outside the gauge section of the fatigue specimen for the formal test. Map the final follow-up temperature trajectory generated in Step 3) as an instruction signal and output it to the temperature control module (5), so that the temperature control module (5) drives the thermo-mechanical fatigue temperature loading module (4) to adjust the temperature outside the gauge section of the fatigue specimen for the formal test, and indirect control of the temperature inside the gauge section of the fatigue specimen for the formal test to conform to the target temperature trajectory can be achieved.

7. The method for indirectly controlling the specimen temperature in a thermo-mechanical fatigue test according to claim 6, characterized in that, The fatigue specimen (3) for temperature adjustment and the fatigue specimen for the formal test are exactly the same.

8. The method for indirectly controlling the specimen temperature in a thermo-mechanical fatigue test according to claim 6, wherein, In Step 3), for a temperature trajectory with periodicity, the corresponding trajectory correction algorithm conforms to the following input correction formula: ； Among them, represents the temperature trajectory of the previous cycle, represents the temperature trajectory after correction in the current cycle, is the deviation between the first feedback temperature trajectory and the target temperature trajectory at any time t, is the differential of, is the control deviation the proportional factor of the direct correction weight, is the differential factor of the weight for correcting the change trend of the deviation, is the time correction term for adjusting the error sampling.

9. The method for indirectly controlling the specimen temperature in a thermo-mechanical fatigue test according to claim 6, wherein, In Step 3), for a temperature trajectory without periodicity, the corresponding trajectory correction algorithm conforms to the following input correction formula: ； Among them, represents the temperature trajectory of the previous temperature change process, represents the temperature trajectory after correction of the current temperature change process, is the deviation between the first feedback temperature trajectory and the target temperature trajectory at any time t, is the differential of, is the control deviation the proportionality factor of the direct correction weight, is the differential factor of the weight for correcting the change trend of the deviation, is the time correction term for adjusting the error sampling.

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