Fatigue crack initiation life test method, system, device, and medium

Abstract

This invention belongs to the field of fatigue mechanical property research technology, and provides a method, system, equipment, and medium for testing fatigue crack initiation life. The method includes: constructing a monitoring parameter-cycle count curve; acquiring surface crack state data of the target sample; estimating the fatigue crack initiation life range based on the surface crack state data, recording the current percentage change of the monitoring parameters as a control threshold; conducting several sets of approximation tests based on the control threshold to obtain the shortest crack length of the target sample; determining the target number of cycles corresponding to the shortest crack length on the monitoring parameter-cycle count curve, and defining the target number of cycles as the fatigue crack initiation life. This invention overcomes the difficulty of directly observing crack initiation by correlating abrupt changes in macroscopic mechanical parameters with the microscopic crack initiation state and employing an iterative approximation control scheme, thus achieving accurate testing of fatigue crack initiation life.

Description

Technical Field

[0001] This invention belongs to the field of fatigue mechanical property research technology, and specifically relates to fatigue crack initiation life testing methods, systems, equipment and media. Background Technology

[0002] Engineering structures and components often operate under fatigue loads, and the initiation of fatigue cracks can lead to overall failure and serious consequences. Therefore, researching methods to predict fatigue crack initiation life is of great significance for design, material selection, and application. Currently, the methods for predicting fatigue crack initiation life mainly employ data modeling or finite element simulation, with almost no methods for predicting fatigue crack initiation life through experiments.

[0003] Patent CN119272562A discloses a method and device for predicting the entire lifespan of fatigue crack initiation and propagation in welded rail joints. This method calculates the location of fatigue crack initiation and the corresponding stress component time history by establishing a finite element model, and then calculates the ratio of shear stress amplitude to normal stress amplitude to predict the fatigue crack initiation lifespan. However, predictions of fatigue crack initiation life using data models or finite element simulations rely on theoretical models or simulations and cannot provide information about crack initiation in real materials under actual fatigue loads.

[0004] Because fatigue crack initiation is instantaneous and minute in length, direct observation is difficult and the crack initiation stage is easily missed, resulting in an overly wide range of predicted crack initiation life and low accuracy. Currently, obtaining fatigue crack initiation life through experimental testing is technically challenging, and there is an urgent need for an accurate and reliable testing method and system to obtain fatigue crack initiation life. Summary of the Invention

[0005] To address the problems mentioned in the background, this invention proposes a method, system, equipment, and medium for testing fatigue crack initiation life.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for testing fatigue crack initiation life includes the following steps: The mechanical response data of the target sample is collected in real time and the number of test cycles is recorded. The target monitoring parameters are determined based on the mechanical response data. Based on the target monitoring parameters and the number of cycles, construct a monitoring parameter-cycle number curve; When the monitoring parameter-cycle number curve meets the preset abrupt change condition, pause the current test and obtain the surface crack state data of the target sample; Based on surface crack state data, the fatigue crack initiation life range is estimated, and the current percentage change of monitoring parameters is recorded and used as a control threshold. Several sets of approximation tests were conducted based on the control threshold to obtain the shortest crack length of the target sample. Determine the target number of cycles corresponding to the shortest crack length on the monitoring parameter-cycle number curve, and define the target number of cycles as the fatigue crack initiation life.

[0007] Furthermore, the preset mutation conditions include: the rate of change of the slope of the monitoring parameter-cycle number curve exceeds a preset threshold, or the difference between the peak and trough of the monitoring parameter-cycle number curve exceeds a preset difference within a time period; Recording the percentage change of the current monitoring parameters includes calculating the relative rate of change of the target monitoring parameters in the current cycle relative to the initial target monitoring parameters.

[0008] Furthermore, based on a control threshold, several sets of approximation tests are conducted to approximate the shortest crack length of the target specimen, including the following steps: In several approximation tests, the test was paused when the percentage change of the monitored parameters reached the control threshold, so that the fatigue crack length of the target sample gradually approached the shortest crack length.

[0009] Furthermore, when conducting approximation tests between adjacent groups, the following steps are also included: If the fatigue crack length of the target specimen is greater than the shortest crack length in the previous set of approximation tests, the control threshold will be reduced by a preset step size in the current set of approximation tests; or, if the fatigue crack length of the target specimen does not reach the shortest crack length in the previous set of approximation tests, the control threshold will be increased by a preset step size in the current set of approximation tests.

[0010] Furthermore, the target specimen is a specimen with a uniform cross-section and a uniform straight section, and the roughness is... R a≤0.2 micrometers.

[0011] Furthermore, when the target monitoring parameter is the elastic modulus, the mechanical response data includes load data and strain data; determining the target monitoring parameter based on the mechanical response data includes: The elastic modulus of the current cycle is calculated based on load and strain data; Based on the initial elastic modulus and the elastic modulus of the current cycle, the percentage decrease in elastic modulus is calculated and used as the percentage change of the monitoring parameter.

[0012] Furthermore, the formula for calculating the elastic modulus is: ; in For the load data of the i-th cycle, The cross-sectional area of ​​the sample. For strain data; The elastic modulus of the current cycle; Percentage decrease in elastic modulus The calculation formula is: ; in, This is the initial elastic modulus.

[0013] Furthermore, when the target monitoring parameter is displacement, the mechanical response data includes the displacement of the clamps at both ends of the testing machine, which are used to hold the target specimen; the target monitoring parameter is determined based on the mechanical response data, including: Obtain the relative displacement of the clamps at both ends of the testing machine during the initial and current cycles; Based on the initial relative displacement and the relative displacement of the current cycle, the percentage increase in displacement is calculated and used as the percentage change of the monitoring parameter.

[0014] Furthermore, the percentage increase in displacement The calculation formula is: ; in This represents the initial relative displacement. This represents the relative displacement in the current cycle.

[0015] Further, obtaining surface crack state data of the target sample includes the following steps: Crack length information is obtained by acquiring and identifying crack images on the surface of the target sample using a microscope.

[0016] A fatigue crack initiation life testing system includes: The acquisition unit is used to acquire the mechanical response data of the target sample in real time and determine the target monitoring parameters based on the mechanical response data; The building unit is used to construct a monitoring parameter-cycle number curve based on the target monitoring parameters and the number of cycles. The acquisition unit is used to pause the current test when the monitoring parameter-cycle number curve meets the preset abrupt change condition, and to acquire the surface crack state data of the target sample; Define a unit to predict the fatigue crack initiation life range based on surface crack state data, record the current percentage change of monitoring parameters and use it as a control threshold; The test unit is used to perform several sets of approximation tests based on a control threshold to obtain the shortest crack length of the target specimen. The output unit is used to determine the target number of cycles corresponding to the shortest crack length on the monitoring parameter-cycle number curve, and the target number of cycles is determined as the fatigue crack initiation life.

[0017] An electronic device includes a memory and a processor, wherein a computer program is stored in the memory, and the processor executes the computer program to implement the above-described method.

[0018] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described method.

[0019] The beneficial effects of this invention are: 1. This invention constructs a monitoring parameter-cycle count curve and pauses the experiment when the curve changes abruptly to obtain the crack state on the sample surface, thereby initially estimating the crack initiation life range and recording the corresponding percentage change in monitoring parameters. Subsequently, using this percentage change as a control threshold, the crack length is gradually made to approach the shortest observable length in subsequent sets of approximation experiments. Finally, the precise number of cycles corresponding to the shortest crack length is determined as the fatigue crack initiation life. This method effectively overcomes the difficulty of directly observing crack initiation by associating abrupt changes in macroscopic mechanical parameters with the microscopic crack initiation state and adopting an iterative approximation control scheme, thus achieving accurate testing of fatigue crack initiation life. 2. The method of the present invention can dynamically adjust the control threshold to achieve controllable approximation of crack length, thereby reducing the number of test groups and the overall time required to determine the initiation life.

[0020] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A flowchart of the fatigue crack initiation life test method of the present invention is shown; Figure 2 A schematic diagram of the fatigue test elastic modulus-cycle number curve of the present invention is shown; Figure 3 A schematic diagram of the displacement-cycle number curve of the fatigue test is shown; Figure 4 A framework diagram of the fatigue crack initiation life testing system of the present invention is shown. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] like Figure 1 As shown, this invention proposes a method for testing fatigue crack initiation life, which includes the following steps: S1: Real-time acquisition of mechanical response data of the target sample and recording of the number of test cycles, and determination of target monitoring parameters based on the mechanical response data.

[0025] S2: Construct a monitoring parameter-cycle number curve based on the target monitoring parameters and the number of cycles.

[0026] S3: When the monitoring parameter-cycle number curve meets the preset sudden change condition, generate a pause control command to pause the current test and obtain the surface crack state data of the target sample.

[0027] S4: Based on surface crack state data, estimate the fatigue crack initiation life range, record the current percentage change of monitoring parameters and use it as a control threshold; the percentage change of monitoring parameters can be obtained by calculating the relative change rate of the target monitoring parameters in the current cycle with respect to the target monitoring parameters in the initial cycle.

[0028] S5: Based on the control threshold, conduct several sets of approximation tests to obtain the shortest crack length of the target sample.

[0029] S6: Determine the target number of cycles corresponding to the shortest crack length on the monitoring parameter-cycle number curve, and determine the target number of cycles as the fatigue crack initiation life.

[0030] Furthermore, the target monitoring parameters can be elastic modulus and displacement, and the two cases will be explained below.

[0031] Scenario 1: When the target monitoring parameter is the elastic modulus, the mechanical response data includes load data and strain data. S1 includes the following steps: S101: Calculate the elastic modulus of the current cycle based on load and strain data; S102: Based on the initial elastic modulus and the elastic modulus of the current cycle, calculate the percentage decrease in elastic modulus and use it as the percentage change of the monitoring parameter.

[0032] In addition, the formula for calculating the elastic modulus is: (1) in For the load data of the i-th cycle, The cross-sectional area of ​​the sample. For strain data; This is the elastic modulus of the current cycle.

[0033] Percentage decrease in elastic modulus The calculation formula is: (2) in, This is the initial elastic modulus.

[0034] It should be noted that when using the elastic modulus as a monitoring parameter, its decrease directly reflects the stiffness reduction caused by the initiation and propagation of microcracks in the material. Calculating the current cyclic elastic modulus requires the magnitude of the load change and the corresponding strain change within that cycle. The percentage decrease in elastic modulus is a quantitative indicator obtained by comparing the current stiffness with the initial (undamaged) stiffness. Furthermore, using the elastic modulus as a monitoring parameter can very sensitively reflect the accumulation of damage within the material, making it particularly suitable for metals or composite materials whose elastic modulus is sensitive to microcracks. This makes it easier to trigger preset abrupt change conditions, thereby effectively identifying the crack initiation stage.

[0035] Optionally, when the target monitoring data is the elastic modulus, S1 requires the use of a room temperature extensometer. Using a selected smooth specimen with a uniform cross-section, the test frequency is set. After loading both ends of the specimen into the testing machine clamping device, the room temperature extensometer is clamped in the working section of the specimen. After completing the pre-test preparations, a load is applied to begin the test. During the test, strain data is collected, and the computer automatically calculates the elastic modulus based on the applied load data, outputting an elastic modulus-cycle count curve. The change in the elastic modulus-cycle count curve during loading is observed. The test is paused when the curve meets a preset abrupt change condition. Based on the crack initiation situation on the specimen surface, the fatigue crack initiation stage is predicted, and the fatigue crack initiation life range is estimated, such as... Figure 2 As shown in the schematic diagram of the elastic modulus-cycle number curve of the axial loading stress fatigue test, the percentage decrease in elastic modulus is recorded for cycles from 40,000 to 50,000.

[0036] The second scenario: When the target monitoring parameter is displacement, the mechanical response data includes the relative displacement of the target specimen clamping ends (the upper and lower clamps of the testing machine). In this case, S1 includes the following steps: S101: Obtain the relative displacement of the clamps at both ends of the testing machine during the initial and current cycles.

[0037] S102: Calculate the percentage increase in displacement based on the initial relative displacement and the relative displacement of the current cycle, and use it as the percentage change of the monitoring parameter.

[0038] In addition, the percentage increase in displacement The calculation formula is: (3) in This represents the initial relative displacement. This represents the relative displacement in the current cycle.

[0039] It should be noted that when displacement is used as a monitoring parameter in stress-controlled fatigue testing, a decrease in specimen stiffness can lead to a larger displacement amplitude under the same load data. Therefore, the increase in displacement is directly related to the increase in the overall compliance of the specimen, and the increase in compliance is also a manifestation of microcrack initiation and propagation. Calculating the percentage increase in displacement provides another equivalent quantitative method for monitoring material damage, but with a different data source. Using displacement as a monitoring parameter, the data is usually obtained directly from the sensor built into the testing machine, eliminating the need for an extensometer, simplifying test preparation, and is particularly suitable for materials or test scenarios where the elastic modulus does not change significantly or where it is inconvenient to install an extensometer. In addition, the displacement here refers to the distance from the peak to the trough of the movement of the testing machine's actuating cylinder (causing the chuck to move) during a complete loading cycle.

[0040] Optionally, for materials whose elastic modulus does not change significantly with the number of cycles, or for materials or test scenarios where it is inconvenient to install an extensometer, a displacement monitoring method is used. A selected smooth specimen with a uniform cross-section is used, and the test frequency is set. Both ends of the specimen are inserted into the testing machine; there is no need to clamp a room temperature extensometer in the working section of the specimen. After completing the pre-test preparations, a load is applied and the test begins. The displacement-cycle count curve is monitored on the software system built into the testing machine. The test is paused when a preset abrupt change condition is met. Based on the crack initiation status on the specimen surface, the fatigue crack initiation stage is predicted, and the fatigue crack initiation life range is estimated. Figure 3 As shown in the diagram, the displacement-cycle number curve of the fatigue test is recorded from 50,000 to 60,000 cycles, and the percentage increase in displacement is recorded.

[0041] Furthermore, in S3, the preset abrupt change condition can be that the rate of change of the slope of the monitoring parameter-cycle number curve exceeds a preset threshold. This is because when the monitoring parameter-cycle number curve undergoes a significant change, such as a sudden shift from a relatively flat curve to a rapid decline or rise, and its rate of change exceeds a certain preset threshold, it can be determined that the material properties have entered a rapid degradation stage caused by crack initiation. This judgment method based on the rate of change of slope is more sensitive and earlier. Using this method, early signals of crack initiation can be captured earlier, providing a time window for timely suspension of the experiment and observation of the microscopic state, thus improving the accuracy of the preliminary estimated life range.

[0042] It should be noted that the slope change rate refers to the change in the slope of the curve relative to the current slope when there is no sudden change; it can also be the change in the slope of the current slope relative to a certain time point. The specific choice can be made according to the situation.

[0043] Furthermore, the preset mutation condition can also be set as follows: within a time period, the difference between the peak and trough of the monitoring parameter-cycle number curve exceeds a preset difference. This is because when a material is subjected to cyclic loading, causing crack initiation and propagation, the monitoring parameters will exhibit significant fluctuations along with the damage evolution, with the curve showing alternating peaks and troughs. When cracks begin to initiate, the internal damage of the material intensifies, and the fluctuation amplitude of the parameters will increase significantly. If, within a certain period, the difference between the peak and trough of the curve is greater than the preset difference threshold, it can be determined that the material has experienced a performance mutation related to crack initiation and has entered a rapid degradation stage.

[0044] Furthermore, the time period here can be set according to the actual situation. For example, a fixed physical time length (such as 5ms) can be directly set as the period; on the other hand, the number of cycles can also be used as the period measurement unit, and a fixed number of cycles (such as 100 times) interval can be selected as the judgment period. In practical applications, the selection can be made in combination with the test conditions, material type, loading method, and data sampling characteristics. If time is used as the period, it is suitable for test scenarios with stable loading frequency; if the number of cycles is used as the period, it is suitable for fatigue tests that are not affected by fluctuations in loading frequency.

[0045] In addition, S3 specifically acquires surface crack state data of the target sample, including: Crack images on the surface of the target sample are acquired and identified using a microscope to obtain crack length information. After the experiment is paused, the sample surface is observed using observation equipment such as microscopes. Through image acquisition and recognition technology, micron-level cracks can be detected and their lengths measured.

[0046] Furthermore, S5 includes the following steps: S501: In several approximation tests, when the percentage change of the monitored parameters reaches the control threshold, the test is paused (the test equipment can be paused), so that the fatigue crack length of the target sample gradually approaches the preset minimum crack length.

[0047] Furthermore, during the experiment, due to the influence of factors such as the target sample material and environment, the control threshold can be updated as needed. Therefore, when conducting adjacent groups of tests, the following steps can also be included: if the fatigue crack length of the target sample is greater than the shortest crack length in the previous group of approximation tests, the control threshold is decreased by a preset step size in the current group of approximation tests; and if the fatigue crack length of the target sample does not reach the shortest crack length in the previous group of approximation tests, the control threshold is increased by a preset step size in the current group of approximation tests. The shortest crack length is the judgment benchmark threshold for the fatigue crack approximation test, which includes two determination methods, each corresponding to a different judgment logic, as detailed below: The first method involves directly acquiring the measured value of the shortest crack length using real-time observation equipment, which serves as the benchmark for test judgment. During the test, if the crack length of the sample in any set of approximation tests does not reach the measured shortest crack length, it indicates that the sample has not produced observable crack initiation. In the next set of approximation tests, a preset step size needs to be added.

[0048] The second method involves manually setting a fixed minimum crack length as the judgment benchmark based on actual needs. During the test, if the measured crack length does not reach the manually preset minimum crack length standard, it is still judged as a substandard state, and the control threshold will still be increased by a preset step size in the next set of approximation tests.

[0049] It should be noted that if the crack length observed after a test pause is still greater than the target minimum crack length, it indicates that the pause timing is still too late, and the crack has already overgrown. Therefore, in the next set of tests, by reducing the control threshold (e.g., by 0.2%), the test equipment is paused earlier when the monitored parameters change less, the macroscopic damage is less severe, and the crack is shorter, thus gradually approaching the target crack length. Conversely, if no crack initiation is observed in the target sample (corresponding to the first method) or the minimum crack length is not reached (corresponding to the second method), it indicates that the pause timing is too early, and the control threshold needs to be increased. This method can achieve controllable approximation of the crack length, reducing the number of test sets and the overall time required to determine the initiation life. Optionally, the preset step size can be set according to material properties, test accuracy, and operational experience, for example, 0.1%, 0.2%, or 0.5%.

[0050] Furthermore, the target specimen is a smooth specimen with a long, straight section and uniform cross-section, and its roughness is... R a is preferably less than or equal to 0.2 micrometers; in addition, the test frequency of the fatigue test of the target sample is set in the range of 5~15Hz.

[0051] It should be noted that using a smooth specimen with a long, straight section provides ample space for observing crack initiation and mounting room temperature extensometers for strain measurement. Setting the test frequency in the lower range of 5–15 Hz balances testing efficiency with observation requirements; this range can be modified as needed and is not limited to this specific range.

[0052] Based on the aforementioned embodiments, taking a specific application scenario as an example, the crack initiation life of a certain metal alloy material under axial tensile and compressive fatigue loads is tested.

[0053] First, the testing machine starts running, calculating and plotting the elastic modulus-cycle count curve in real time. When the curve reaches a certain stage, the operator observes abnormal fluctuations and a sharp decline (meeting a preset abrupt change condition), and the testing machine immediately pauses. The operator removes the sample and observes it under a microscope, discovering micron-sized cracks on the surface. Based on this, it is estimated that crack initiation may have occurred within the last few thousand cycles, and the elastic modulus decreases by, for example, 2.5%. Next, a new sample is replaced, and then the control threshold is set to 2.3% (slightly lower than the initial recorded 2.5%), and the test is restarted. When the real-time calculated percentage decrease in elastic modulus reaches 2.3%, the testing machine automatically pauses. Microscopic examination reveals that the crack length is slightly shorter than in the first test. A third set of approximation tests is then performed, further adjusting the control threshold to 2.1%, and this process is iterated until, after a certain test pause, the crack length observed under the microscope is exactly the shortest length that the equipment can clearly identify and measure, or reaches the manually specified shortest crack length. At this point, the number of cycles corresponding to the pause time (i.e., the time when the control threshold is reached) is found from the monitoring parameter-cycle count curve of this experiment, for example, 45,500 cycles. Finally, the fatigue crack initiation life of this material is determined to be 45,500 cycles.

[0054] like Figure 4As shown, this invention also proposes a fatigue crack initiation life testing system, including a data acquisition unit, a construction unit, an acquisition unit, a definition unit, a testing unit, and an output unit. The data acquisition unit is used to acquire mechanical response data of the target sample in real time and determine target monitoring parameters based on the mechanical response data. The construction unit is used to construct a monitoring parameter-cycle number curve based on the target monitoring parameters and the number of cycles. The acquisition unit is used to pause the current test when the monitoring parameter-cycle number curve meets a preset abrupt change condition and acquire surface crack state data of the target sample. The definition unit is used to estimate the fatigue crack initiation life range based on the surface crack state data, record the current percentage change of monitoring parameters, and use it as a control threshold. The testing unit is used to perform several sets of approximation tests based on the control threshold to obtain the shortest crack length of the target sample. The output unit is used to determine the target number of cycles corresponding to the shortest crack length on the monitoring parameter-cycle number curve, and defines the target number of cycles as the fatigue crack initiation life.

[0055] It should be noted that, for the system embodiment, since it basically corresponds to the method embodiment, the relevant parts can be referred to in the description of the method embodiment. The various units and modules of the fatigue crack initiation life test system are divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of each unit are only for easy distinction and are not used to limit the scope of protection of this invention.

[0056] The present invention also proposes an electronic device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the above-mentioned fatigue crack initiation life test method.

[0057] It should be noted that the memory can include random access memory (RAM) or non-volatile memory, such as at least one disk storage device. The processor mentioned above can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0058] The present invention also proposes a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the above-described fatigue crack initiation life test method.

[0059] It should be noted that the computer-readable storage medium may be included in the device / apparatus described in the above embodiments; or it may exist independently and not assembled into the device / apparatus. The computer-readable storage medium carries one or more programs, which, when executed, implement a fatigue crack initiation life test method according to an embodiment of the present invention.

[0060] According to embodiments of the present invention, the computer-readable storage medium may be a non-volatile computer-readable storage medium, such as: a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In the present invention, the computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0061] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing fatigue crack initiation life, characterized in that, Includes the following steps: The mechanical response data of the target sample is collected in real time and the number of test cycles is recorded. The target monitoring parameters are determined based on the mechanical response data. Based on the target monitoring parameters and the number of cycles, a monitoring parameter-cycle number curve is constructed; When the monitoring parameter-cycle number curve meets the preset abrupt change condition, the current test is paused, and the surface crack state data of the target sample is acquired; Based on the surface crack state data, the fatigue crack initiation lifetime range is estimated, and the current percentage change of the monitoring parameters is recorded and used as a control threshold. Several sets of approximation tests were conducted based on the control threshold to obtain the shortest crack length of the target sample. The target number of cycles corresponding to the shortest crack length on the monitoring parameter-cycle number curve is determined, and the target number of cycles is determined as the fatigue crack initiation life.

2. The fatigue crack initiation life test method according to claim 1, characterized in that, The preset mutation conditions include: the rate of change of the slope of the monitoring parameter-cycle number curve exceeds a preset threshold, or the difference between the peak and trough of the monitoring parameter-cycle number curve exceeds a preset difference within a time period. The recorded percentage change of the current monitoring parameters includes calculating the relative rate of change of the target monitoring parameters in the current cycle relative to the initial target monitoring parameters.

3. The fatigue crack initiation life test method according to claim 1, characterized in that, Several sets of approximation tests are conducted based on a control threshold to approximate the shortest crack length of the target specimen, including the following steps: In several approximation tests, the test was paused when the percentage change of the monitored parameters reached the control threshold, so that the fatigue crack length of the target sample gradually approached the shortest crack length.

4. The fatigue crack initiation life test method according to claim 1, when conducting approximation tests of adjacent groups, further includes the following steps: If the fatigue crack length of the target specimen is greater than the shortest crack length in the previous set of approximation tests, the control threshold will be reduced by a preset step size in the current set of approximation tests; or, if the fatigue crack length of the target specimen does not reach the shortest crack length in the previous set of approximation tests, the control threshold will be increased by a preset step size in the current set of approximation tests.

5. The fatigue crack initiation life test method according to claim 1, characterized in that, The target specimen is a specimen with a uniform cross-section and a uniform straight section, and its roughness is... R a≤0.2 micrometers.

6. The fatigue crack initiation life test method according to claim 1, characterized in that, When the target monitoring parameter is the elastic modulus, the mechanical response data includes load data and strain data; determining the target monitoring parameter based on the mechanical response data includes: The elastic modulus of the current cycle is calculated based on the load data and strain data. Based on the initial elastic modulus and the elastic modulus of the current cycle, the percentage decrease in elastic modulus is calculated and used as the percentage change of the monitored parameter.

7. The fatigue crack initiation life test method according to claim 6, characterized in that, The formula for calculating the elastic modulus is: ； in For the load data of the i-th cycle, The cross-sectional area of ​​the sample. For strain data; The elastic modulus of the current cycle; The percentage decrease in elastic modulus The calculation formula is: ； in, This is the initial elastic modulus.

8. The fatigue crack initiation life test method according to claim 1, characterized in that, When the target monitoring parameter is displacement, the mechanical response data includes the displacement of the clamps at both ends of the testing machine, which are used to clamp the target specimen; determining the target monitoring parameter based on the mechanical response data includes: Obtain the relative displacement of the clamps at both ends of the testing machine during the initial and current cycles; Based on the initial relative displacement and the relative displacement of the current cycle, the percentage increase in displacement is calculated and used as the percentage change in the monitored parameter.

9. The fatigue crack initiation life test method according to claim 8, characterized in that, The percentage increase in displacement The calculation formula is: ； in This represents the initial relative displacement. This represents the relative displacement in the current cycle.

10. The fatigue crack initiation life test method according to claim 1, characterized in that, Obtaining the surface crack state data of the target sample includes the following steps: Crack images on the surface of the target sample are acquired and identified using a microscope to obtain crack length information.

11. A fatigue crack initiation life testing system, characterized in that, include: The acquisition unit is used to acquire the mechanical response data of the target sample in real time and determine the target monitoring parameters based on the mechanical response data. The construction unit is used to construct a monitoring parameter-cycle number curve based on the target monitoring parameters and the number of cycles. The acquisition unit is used to pause the current test when the monitoring parameter-cycle number curve meets the preset abrupt change condition, and to acquire the surface crack state data of the target sample; A definition unit is used to estimate the fatigue crack initiation life range based on the surface crack state data, record the current percentage change of monitoring parameters and use it as a control threshold. The test unit is used to perform several sets of approximation tests based on a control threshold to obtain the shortest crack length of the target specimen. The output unit is used to determine the target number of cycles corresponding to the shortest crack length on the monitoring parameter-cycle number curve, and to determine the target number of cycles as the fatigue crack initiation life.

12. An electronic device comprising a memory and a processor, characterized in that, The memory stores a computer program, and when the processor executes the computer program, it implements the fatigue crack initiation life test method according to any one of claims 1 to 10.

13. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the fatigue crack initiation life test method according to any one of claims 1 to 10.

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