Strain equivalent based proof test method

Abstract

The application provides a load-maintaining test method based on strain equivalence, which comprises the following steps: S1, a first strain gauge is attached to a sample, and the sample to be tested is fixed on a clamping mechanism; S2, a fatigue stretching instrument is used to apply a stretching force to the clamping mechanism, and the stretching force is kept unchanged, and the strain value of the sample is recorded as a; S3, the stretching force of the fatigue stretching instrument is unloaded, and the stretching force of the fatigue stretching instrument is replaced by a coarse adjustment jacking mechanism in the process of unloading, and meanwhile, the strain value is kept below a during the process until the stretching force is completely unloaded; S4, an action force is applied to the clamping mechanism by a fine adjustment jacking mechanism, the stretching force of the replaced fatigue stretching instrument is adjusted, and the strain value is kept stable as a; and S5, the clamping mechanism is detached from the fatigue stretching instrument, and the sample is observed under a microscope. The method can ensure that the sample is always in a load-maintaining state during the process of detaching and crack observation, avoids the influence of crack closure effect, and improves the life prediction accuracy.

Description

Technical Field

[0001] This invention relates to the technical field of vehicle component life prediction, and in particular to a strain-equivalent load-bearing test method. Background Technology

[0002] Because traditional vehicle durability design and testing requirements do not favor life prediction experiments, users are often unaware of the accurate remaining lifespan of components during vehicle service. When faced with components exhibiting a clear tendency to fail, to prevent these components from becoming unusable during service, usable components with acceptable remaining lifespans are often directly replaced, resulting in significant unnecessary waste and increased manufacturing costs. Therefore, accurately predicting the remaining lifespan of vehicle components has high theoretical and practical value.

[0003] The key to accurate lifespan measurement lies in the accurate determination of the threshold value. Currently, there are three main methods for determining the threshold value:

[0004] 1. The first method is to use an in-situ machine independently developed by the Tonglu High Temperature Alloy Laboratory of Zhejiang University for observation. This machine can observe and record the evolution of the microstructure and failure fracture process of the sample in real time. This method can improve the accuracy of crack testing and make the test threshold value closer to the true value. However, since this in-situ machine places the tensile device under a scanning electron microscope for experimentation and observation, this method has the following drawbacks: First, to protect the electron microscope, the in-situ machine can only conduct fatigue tests at lower loading frequencies, and the tensile waveform that this in-situ tensile machine can currently load is only an approximate sine wave, which cannot simulate actual working conditions and cannot meet the testing requirements of actual working conditions; Second, due to the spatial limitations of the device design, the in-situ machine has high requirements for sample size, that is, it can only test the threshold value of small-sized samples and cannot realize the performance testing of engineering structural components; Third, since the in-situ machine requires the entire test to be conducted in an absolute vacuum environment, the test cannot simulate actual engineering environments such as corrosion, vibration, and swaying, and cannot be truly integrated into engineering application scenarios; Fourth, because the in-situ machine design is relatively complex, the experimental requirements during testing are relatively high, and the electron microscope needs to be repaired and maintained regularly, the human and material costs of developing and using the in-situ machine are relatively high.

[0005] 2. The second method involves measuring the crack length of the sample directly on the tensile instrument using a low-power microscope while the instrument is under load (i.e., the sample is clamped). (The high-power microscope cannot adjust the eyepiece to align with the tensile instrument for observation.) However, due to the low accuracy of the low-power microscope, it is difficult to capture points with closely spaced crack length differences (i.e., threshold values) when the number of experiments is small. Generally, it takes many cycles of experiments to see the change in crack length. This directly leads to a large difference between the threshold value obtained from the test and the actual threshold value, resulting in inaccurate life prediction results. Furthermore, conducting experiments in this way increases the number of experimental cycles and raises the time cost.

[0006] 3. The third method involves disassembling the test specimen under unloaded force (i.e., without clamping the specimen) and observing the crack length under an electron microscope. However, the stress state of the specimen changes before and after disassembly. The crack tip is unsupported by external forces after unloading. At this time, the elastic zone near the crack tip will constrain the plastic deformation of the plastic zone, causing the upper and lower surfaces of the crack to tend to close. At the same time, the shape of the crack tip undergoes irreversible changes, and the specimen cannot be used in the next crack test. To ensure the accuracy of crack length measurement, the tester usually discards the specimen after disassembling and measuring its crack length and selects a new specimen to reload the test. Although this slightly improves the accuracy of the measurement results, it consumes a lot of specimens, manpower, and time, which does not meet the requirements of sustainable development and violates the concept of green manufacturing.

[0007] In summary, existing experimental methods all involve directly clamping both ends of the sample in a tensile testing machine. If the sample is to be in a state of load retention, i.e., crack not closing, it must be clamped on the tensile testing machine. However, this method cannot simultaneously solve the problems of low measurement accuracy, severe sample wear, and inability to simulate real experimental conditions. In other words, the existing methods of conducting fatigue tests cannot meet the needs of actual engineering applications and cannot achieve the goal of accurately replacing failed parts during vehicle service. Summary of the Invention

[0008] The purpose of this invention is to solve the problems existing in the prior art and propose a strain equivalent load-holding test method, which can realize the equivalent replacement of the clamping force in the fatigue tensile instrument, ensure that the sample is always in a load-holding state during disassembly and crack observation, avoid the influence of crack closure effect, and improve the accuracy of life prediction.

[0009] To achieve the above objectives, this invention proposes a strain equivalence-based load-bearing test method, comprising the following steps:

[0010] S1. Attach the first strain gauge to the sample and fix the sample to be tested on the clamping mechanism;

[0011] S2. When it is necessary to observe the crack length, a tensile force is applied to the sample on the clamping mechanism using a fatigue tensile instrument, and the tensile force of the fatigue tensile instrument is kept constant. The strain value of the sample detected by the first strain gauge is recorded as a.

[0012] S3. Start unloading the tensile force of the fatigue tensile instrument, and apply a force to the clamping mechanism through the coarse adjustment lifting mechanism during the unloading process to equivalently replace the tensile force of the fatigue tensile instrument. During the equivalent process, keep the strain value of the first strain gauge always lower than a until the fatigue tensile instrument completely unloads the tensile force.

[0013] S4. Apply force to the clamping mechanism by fine-tuning the lifting mechanism, adjust the tensile force of the replacement fatigue tensile instrument until the strain value of the first strain gauge stabilizes at a;

[0014] S5. Remove the clamping mechanism from the fatigue tensile instrument and observe the sample under a microscope.

[0015] Preferably, in step S1, the sample to be tested is fixed at the center of the clamping mechanism.

[0016] Preferably, in step S1, the first strain gauge is placed against the center of the side of the sample.

[0017] Preferably, in step S3, the strain value of the first strain gauge is kept within the range of (a-10μm) to (a-5μm) during the equivalent process.

[0018] Preferably, when the coarse adjustment lifting mechanism and the fine adjustment lifting mechanism are not raised, no force is applied to the clamping mechanism to stretch it.

[0019] Preferably, when the coarse adjustment lifting mechanism and the fine adjustment lifting mechanism are not raised, a gap of 1 to 3 mm is maintained between the lifting end of the two mechanisms and the clamping mechanism, and more preferably a gap of 1 mm is maintained.

[0020] Preferably, the above test method is implemented using a load-holding device including a clamping mechanism, a coarse adjustment lifting mechanism, a first strain gauge, and the fine adjustment lifting mechanism, wherein both the coarse adjustment lifting mechanism and the fine adjustment lifting mechanism are mounted on the clamping mechanism.

[0021] Preferably, the coarse adjustment lifting mechanism includes two first adjustment mechanisms symmetrically arranged on both sides of the sample, and the two first adjustment mechanisms lift and lower by the same amount each time.

[0022] Preferably, the first adjustment mechanism is a hydraulic jack, and the two hydraulic jacks are controlled simultaneously by a hydraulic pump so that the two hydraulic jacks lift and lower the same amount each time.

[0023] Preferably, the fine-tuning lifting mechanism includes two second adjustment mechanisms symmetrically arranged on both sides of the sample, and the two second adjustment mechanisms lift and lower by the same amount each time.

[0024] Preferably, the second adjustment mechanism is equipped with a second strain gauge, so that when the tensile force of the fatigue tensile instrument is adjusted by the fine-tuning lifting mechanism, the changes of the second strain gauges attached to the two second adjustment mechanisms are kept the same.

[0025] The beneficial effects of this invention are as follows: The method of this invention ensures that the sample remains under load throughout the disassembly and crack observation process, thereby maintaining the shape and length of the crack tip. Furthermore, the load-holding device used in this method eliminates the crack closure effect caused by the sample being unloaded after disassembly, reducing experimental costs while improving the accuracy of lifespan prediction. This allows users to accurately determine whether parts need replacement based on their remaining lifespan during vehicle operation, significantly reducing manufacturing costs and aligning with the concept of sustainable development.

[0026] First, the load-bearing device used in this method can keep the sample under constant force before and after the fatigue tensile instrument is disassembled, so that the shape and length of the crack tip remain unchanged. This eliminates the crack closure effect caused by the sample being disassembled and no longer subjected to external force. Therefore, using this device will make the threshold value measurement results more accurate, reduce the experimental cost and improve the accuracy of life prediction, so that users can make a judgment on whether the parts need to be replaced based on the accurate remaining life value of the parts during the operation of the vehicle.

[0027] Secondly, during operation, the tester can remove the support device containing the sample at any time to observe the failure propagation process of the microstructure in real time, obtain high-resolution, high-magnification real-time sequential SEM images, clarify the crack initiation and propagation laws, which is of great significance for studying the micro-mechanism of fatigue failure of various structural materials, and provides an important and novel experimental method for the study of fatigue crack initiation and propagation.

[0028] Third, this method breaks away from the traditional mindset that samples can only be tested using tensile testing machines. It cleverly uses a mechanical device to achieve an equivalent replacement of the clamping force in fatigue tensile testing instruments, thereby achieving a load-bearing function for the sample. This ensures that the sample remains under load throughout disassembly and crack observation, and it has lower requirements for experimental space and sample size. The mechanical structure of the device used in this method is ingenious and simplified, and the device is easy to operate, greatly reducing equipment and experimental costs. Furthermore, the entire experiment can be completed using only one sample, avoiding sample waste and aligning with the requirements of sustainable development and the concept of green manufacturing.

[0029] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the load-carrying device used in the method of implementing the present invention;

[0031] Figure 2 yes Figure 1 Front view diagram. Detailed Implementation

[0032] The present invention provides a strain equivalence-based load-bearing test method, comprising the following steps:

[0033] S1. Attach the first strain gauge 3 to the center of the side of the sample 4, and then fix the sample 4 to be tested at the center of the clamping mechanism 1.

[0034] S2. When it is necessary to observe the crack length, a fatigue tensile instrument is used to apply a tensile force to the sample 4 on the clamping mechanism 1, and the tensile force of the fatigue tensile instrument is kept constant. The strain value of the sample 4 detected by the first strain gauge 3 is recorded as a.

[0035] S3. Start unloading the tensile force of the fatigue tensile instrument, and apply force to the clamping mechanism 1 through the coarse adjustment lifting mechanism 2 during the unloading process, which greatly replaces the tensile force of the fatigue tensile instrument. During the equivalent process, the strain value of the first strain gauge 3 is always kept at (a-10μm)~(a-5μm) until the fatigue tensile instrument completely unloads the tensile force.

[0036] S4. Apply force to the clamping mechanism 1 by fine-tuning the lifting mechanism 5, and adjust the tensile force of the replacement fatigue tensile instrument by a small amount until the strain value of the first strain gauge 3 stabilizes at a;

[0037] S5. Remove the clamping mechanism 1 from the fatigue tensile instrument and observe the sample 4 under a microscope.

[0038] Furthermore, when the coarse adjustment lifting mechanism 2 and the fine adjustment lifting mechanism 5 are not raised, a gap of 1 to 3 mm is maintained between the lifting ends of the two and the clamping mechanism 1, and no force is applied to the clamping mechanism 1 to stretch it.

[0039] The above testing method is implemented using a load-holding device including a clamping mechanism 1, a coarse adjustment lifting mechanism 2, a first strain gauge 3, and a fine adjustment lifting mechanism 5. Both the coarse adjustment lifting mechanism 2 and the fine adjustment lifting mechanism 5 are mounted on the clamping mechanism 1. In this embodiment, the clamping mechanism 1 includes an upper clamping member 11 and a lower clamping member 12. Both the coarse adjustment lifting mechanism 2 and the fine adjustment lifting mechanism 5 are mounted on the lower clamping member 12. The ends of the upper clamping member 11 and the lower clamping member 12 facing away from the loaded sample 4 are respectively connected to a fatigue tensile testing instrument.

[0040] Furthermore, the coarse adjustment lifting mechanism 2 includes two first adjustment mechanisms symmetrically arranged on both sides of the sample 4, with the two first adjustment mechanisms having the same lifting and lowering range each time. Even further, the first adjustment mechanisms are hydraulic jacks, and the two hydraulic jacks are simultaneously controlled by a single hydraulic pump, ensuring that the lifting and lowering range of the two hydraulic jacks is the same each time, thus guaranteeing that the sample 4 being tested is not affected by eccentric force.

[0041] Furthermore, the fine-tuning lifting mechanism 5 includes two second adjustment mechanisms symmetrically arranged on both sides of the sample 4, with the two second adjustment mechanisms raising and lowering by the same amount each time. In this embodiment, the second adjustment mechanism is a nut lifting assembly, including a screw and a lifting nut. By adjusting the position of the lifting nut, a small-amplitude replacement of the tensile force of the fatigue tensile tester can be achieved. Further still, a second strain gauge 50 is provided on the upper part of the second adjustment mechanism. When adjusting and replacing the tensile force of the fatigue tensile tester through the fine-tuning lifting mechanism 5, the changes of the second strain gauges 50 attached to the two second adjustment mechanisms are kept the same, so that both provide the same amount of lifting force to the upper clamping member 11, ensuring that the sample 4 being tested is not affected by eccentric force. The lifting action of the lifting nut can be adjusted and controlled using a digitally adjustable high-precision wrench.

[0042] Furthermore, each of the upper clamping member 11 and the lower clamping member 12 has a mounting base 10 at one of its opposite ends, and both ends of the sample 4 are fixed to the mounting base 10. In this embodiment, the mounting base 10 is provided at the middle position of the opposite ends of the upper clamping member 11 and the lower clamping member 12. A fixing end for connecting a fatigue tensile testing instrument is provided at the middle position of the opposite ends of the upper clamping member 11 and the lower clamping member 12.

[0043] Furthermore, the mounting base 10 is provided with a plurality of mounting holes, and the sample 4 is connected to the mounting base 10 by a plurality of bolts.

[0044] During the experiment, the upper clamp 11 and the lower clamp 12 are first fixed using a fatigue tensile apparatus (not shown in the figure). The sample 4 is then bolted onto the mounting base 10 of the two clamps. The first strain gauge 3 is then attached to the center of the side of the sample 4, and the second strain gauge 50 is attached to the center of the side of the screw. When it is necessary to observe the crack length, the tensile force of the fatigue tensile apparatus is kept constant at this crack length, and the strain value 'a' is recorded. Then, the tensile force of the fatigue tensile apparatus is unloaded, and the hydraulic pump is pressed repeatedly during the unloading process. When the lifting height exceeds the reserved height between the hydraulic jack and the upper clamp 11, both hydraulic jacks will provide a pushing force to the upper clamp 11. At this time, the sample 4 under test is subjected to the combined action of the tensile force of the fatigue tensile apparatus and the pushing force added to the upper clamp 11 by the hydraulic jack. The change in the value of the second strain gauge 50 is constantly observed to ensure that the strain value of the sample is always... The strain value is adjusted by about 5 μm below the value of a until the tensile force of the fatigue tensile instrument is completely unloaded, thus achieving a significant equivalent replacement of the tensile force of the fatigue tensile instrument. Then, the lifting nut on the fine-tuning lifting mechanism 5 is used to apply a lifting force to the upper clamping part 11 to finely adjust the strain value. When the adjusted value is exactly the same as the initial strain value a and remains stable, the load-bearing device is removed from the fatigue tensile instrument and placed under an electron microscope for observation. The crack length of the sample 4 is observed and recorded. After the value is recorded, the device is placed back on the fatigue testing instrument. This operation is repeated when the crack length needs to be observed again.

[0045] This invention uses strain equivalence to keep the tested sample under load throughout the tensile testing and crack observation process, avoiding the crack closure effect that occurs after the sample is removed from the fatigue tensile instrument and no longer subjected to external force. This ensures that the crack condition of the sample remains unchanged before and after removal. In other words, a sample used in one experiment can be used for the next experiment; all tensile tests can be completed using a single sample. This enables real-time and accurate determination of the threshold value, improving the accuracy of lifetime prediction. Furthermore, it allows for the analysis of the microscopic mechanisms of crack initiation and propagation, significantly reducing experimental costs and providing a reference for subsequent lifetime prediction experiments.

[0046] Implementation Case 1

[0047] Experiments have verified that the load-holding device used in this invention is feasible under various experimental conditions such as 1kN, 2kN, and 3kN. The following is an implementation case of the load-holding device used in this invention when the maximum value is 1000N, the waveform is a square wave, the stress ratio is 0, and the load application frequency is 20Hz.

[0048] Using a universal tensile testing machine to clamp the holding device of the present invention, the strain value was recorded as 0 μm without any applied force. A constant tensile force of 1000 N was applied, and after the strain value detected by the first strain gauge 3 attached to the sample tended to stabilize, the strain value was recorded as 40 μm. At this time, the force of the universal tensile testing machine was unloaded, and the hydraulic pump was pressed repeatedly to keep the strain value as stable as possible. During this process, the strain value of the first strain gauge 3 was kept within the range of (a-10 μm) to (a-5 μm). After the force of the tensile testing machine was unloaded, the change in the strain gauge value was observed. The pressing was stopped when the strain value stabilized at 35 μm. At this time, the position of the lifting nut on the fine-tuning lifting mechanism 5 was adjusted to provide a lifting force to the upper clamping member 11. After the strain value stabilized at 40 μm, the holding device was removed from the tensile testing machine and placed flat on the table. It was found that the value of the first strain gauge did not change significantly.

[0049] Table 1. Variation of strain values ​​of the sample during the experiment.

[0050]

[0051] This invention compares with three existing methods for determining threshold values:

[0052] The existing first method for determining the threshold value (i.e., using the in-situ machine independently developed by the Tonglu High-Temperature Alloy Laboratory of Zhejiang University) has the following problems when measured under the conditions of the above implementation case: (1) a load of this frequency cannot be applied; (2) a sample of this size cannot be clamped; and (3) a load of this waveform cannot be applied. Therefore, it can be seen that this method for determining the threshold value will not be feasible under the same experimental conditions. Compared with the first method of determining the threshold value, the present invention has the following advantages: Since the load-holding device of the present invention is used to conduct tests on a standard universal testing machine, and then the load-holding device with the sample is disassembled and placed under an electron microscope for observation of crack length and microstructure evolution, the device has lower requirements for experimental space and sample size. It can achieve the same testing accuracy as an in-situ tensile testing machine, and can arbitrarily select the applied load frequency and waveform. It can use real-world samples to simulate the actual test conditions. Furthermore, the operation of the device is simple, and the device cost and experimental testing cost are low. It can fundamentally solve the problems that in-situ machines cannot simulate actual working conditions and that the machine equipment and experimental operation costs are high.

[0053] The existing second method for determining the threshold value (i.e., directly observing the crack using a low-magnification microscope while the tensile test is under load) has the following problems when measured under the conditions of the above implementation case: Measuring crack length using a low-magnification microscope results in low accuracy, the threshold value cannot be accurately determined, and the lifespan cannot be accurately predicted. Furthermore, this method for determining the threshold value, tested under the same experimental conditions, yielded results with low accuracy. Compared with the second method of determining the threshold value, this invention has the following advantages: First, the tester can immediately remove the support device containing the sample at any time and measure the crack propagation length under an electron microscope, improving the accuracy of crack length observation. This allows for the observation of minute changes in crack length within a shorter cycle, significantly reducing the number of cycles and making the measured threshold value closer to the true threshold value. Second, since the device can be disassembled, the crack length on both sides of the sample can be observed under an electron microscope and averaged, greatly improving the accuracy of the crack length measurement data. Third, because the device can be disassembled and observed under an electron microscope in real time, changes in the crack tip structure can be observed at a microscopic level, allowing for further research into the mechanism of crack initiation and propagation.

[0054] The existing third method for determining the threshold value (i.e., directly observing the cracks of the disassembled sample using an electron microscope) has the following problems when measured under the conditions of the above-mentioned implementation case: after testing the crack size of the sample once, since the sample is no longer under stress, it will be discarded, and a new sample needs to be used to test the crack length again. This method of determining the threshold value wastes a large number of samples under the same experimental conditions, greatly increasing the experimental cost. Compared with the third method of determining the threshold value, the present invention has the following advantages: it ensures that the sample is always under load during disassembly and crack observation, avoiding the crack closure effect caused by the sample being unloaded after disassembly, thus keeping the crack condition of the sample unchanged before and after disassembly. The sample used in one experiment can still be used in the next experiment, and only one sample is needed throughout the entire process, eliminating the need to repeatedly replace samples, saving the time and cost of sample replacement. It also avoids the experimental cost of starting fatigue testing on a new sample from zero load, greatly reducing the manpower and material resources required for the experiment.

[0055] In summary, this invention breaks away from the traditional mindset that testing can only be done by stretching samples using a tensile machine. It cleverly utilizes a streamlined mechanical structure to achieve precise determination of threshold values ​​with extremely low device and experimental operation costs and a simple experimental procedure. This improves the accuracy of lifespan prediction while enabling real-time observation of crack initiation and propagation, thereby facilitating the analysis of microscopic crack failure mechanisms. With accurate lifespan prediction values, users can accurately determine whether to replace components in scenarios with obvious failure tendencies. This reduces service costs and fundamentally lowers component manufacturing costs, truly achieving resource and energy conservation, improving resource utilization, and reducing energy consumption.

[0056] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A load-bearing test method based on strain equivalence, characterized in that: Includes the following steps: S1. Attach the first strain gauge (3) to the sample (4) and fix the sample (4) to be tested on the clamping mechanism (1); S2. When it is necessary to observe the crack length, a fatigue tensile instrument is used to apply a tensile force to the sample (4) on the clamping mechanism (1), and the tensile force of the fatigue tensile instrument is kept constant. The strain value of the sample (4) detected by the first strain gauge (3) is recorded as a. S3. Start unloading the tensile force of the fatigue tensile instrument, and apply force to the clamping mechanism (1) through the coarse adjustment lifting mechanism (2) during the unloading process, equivalently replacing the tensile force of the fatigue tensile instrument, and keep the strain value of the first strain gauge (3) always lower than a during the equivalent process until the fatigue tensile instrument completely unloads the tensile force. S4. Apply force to the clamping mechanism (1) by fine-tuning the lifting mechanism (5) to adjust the tensile force of the replacement fatigue tensile instrument until the strain value of the first strain gauge (3) stabilizes at a; S5. Remove the clamping mechanism (1) from the fatigue tensile instrument and observe the sample (4) under a microscope.

2. The load-bearing test method based on strain equivalence as described in claim 1, characterized in that: In step S1, the sample (4) to be tested is fixed at the center of the clamping mechanism (1).

3. The strain equivalence-based load-bearing test method as described in claim 1, characterized in that: In step S1, the first strain gauge (3) is placed against the center of the side of the sample (4).

4. The strain equivalence-based load-bearing test method as described in claim 1, characterized in that: In step S3, the strain value of the first strain gauge (3) is kept within the range of (a-10μm) to (a-5μm) during the equivalent process.

5. The load-bearing test method based on strain equivalence as described in claim 1, characterized in that: When the coarse adjustment lifting mechanism (2) and the fine adjustment lifting mechanism (5) are not raised, no force is applied to the clamping mechanism (1) to stretch it.

6. The strain equivalence-based load-bearing test method as described in claim 1, characterized in that: When the coarse adjustment lifting mechanism (2) and the fine adjustment lifting mechanism (5) are not raised, a gap of 1~3mm is maintained between the lifting ends of the two and the clamping mechanism (1).

7. The strain equivalence-based load-bearing test method as described in claim 1, characterized in that: Both the coarse adjustment lifting mechanism (2) and the fine adjustment lifting mechanism (5) are mounted on the clamping mechanism (1).

8. A strain equivalence-based load-bearing test method as described in claim 1 or 7, characterized in that: The coarse adjustment lifting mechanism (2) includes two first adjustment mechanisms symmetrically arranged on both sides of the sample (4), and the two first adjustment mechanisms have the same lifting range each time.

9. The load-bearing test method based on strain equivalence as described in claim 8, characterized in that: The first adjustment mechanism is a hydraulic jack. Two hydraulic jacks are controlled simultaneously by a hydraulic pump, so that the two hydraulic jacks lift and lower the same amount each time.

10. A strain equivalence-based load-bearing test method as described in claim 1 or 7, characterized in that: The fine-tuning lifting mechanism (5) includes two second adjustment mechanisms symmetrically arranged on both sides of the sample (4), and the two second adjustment mechanisms have the same lifting range each time.

11. The strain equivalence-based load-bearing test method as described in claim 10, characterized in that: The second adjustment mechanism is equipped with a second strain gauge (50). When the tensile force of the fatigue tensile instrument is adjusted by the fine adjustment lifting mechanism (5), the changes of the second strain gauges (50) attached to the two second adjustment mechanisms are kept the same.

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