Method for rapidly measuring fatigue limit of composite material by infrared thermography

Abstract

The invention discloses a method for rapidly measuring the fatigue limit of a composite material through an infrared thermography method, and belongs to the technical field of composite material inspection. According to the method, the problems that an existing method lacks definite physical significance and obvious temperature rise is difficult to detect are solved, the temperature change of the surface of the composite material is captured through the thermal infrared imager, the relation between the temperature change and the stress level is analyzed, and the dissipation mechanism of the composite material in the elastic stage and the plastic stage can be effectively distinguished; the fatigue limit of the material can be quantitatively determined through linear fitting and intersection calculation by taking the elastic limit as a boundary and combining an inherent dissipation theory and a fatigue damage mechanism, so that inflection point determination has clear physical significance, and the fatigue limit can be accurately determined in a short time; in addition, by means of the non-contact characteristic of the method, physical damage to the samples is reduced, the repeatability and reliability of the experiment are improved, meanwhile, the number of the samples is reduced, the experiment time is shortened, and the experiment cost and time are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of composite material inspection, in particular to a method for quickly determining fatigue limit of composite materials using infrared thermal imaging. Background Art

[0002] Composite materials have been widely used in aerospace, automotive manufacturing and other fields due to their excellent performance. However, accurate and rapid determination of the fatigue limit of composite materials is crucial for their safe application. Traditional fatigue limit determination methods, such as the lift method, are accurate but time-consuming and still have the following drawbacks:

[0003] 1. Relying on experience or simple data fitting, lacking clear physical meaning;

[0004] 2. It has poor applicability to materials with high thermal conductivity and small plastic deformation (such as aluminum alloy), and it is difficult to detect obvious temperature rise;

[0005] 3. Mainly focus on the macroscopic temperature rise phenomenon, and rarely combine it with the microscopic structural evolution.

[0006] Therefore, it does not meet the existing needs. We propose a method for rapid determination of fatigue limit of composite materials using infrared thermography. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for quickly determining the fatigue limit of composite materials using infrared thermal imaging. By capturing the temperature changes on the surface of the composite material with an infrared thermal imager and analyzing the relationship between the temperature changes and the stress levels, the dissipation mechanisms of the composite material in the elastic and plastic stages can be effectively distinguished. By linear fitting and intersection calculation, with the elastic limit as the dividing line, combined with the inherent dissipation theory and fatigue damage mechanism, the fatigue limit of the material can be quantitatively determined, so that the determination of the inflection point has a clear physical meaning, and the fatigue limit can be accurately determined in a short time. In addition, the non-contact characteristics of this method reduce physical damage to the sample, improve the repeatability and reliability of the experiment, and at the same time reduce the number of samples and experimental time, reduce the experimental cost and time, and solve the problems raised in the above-mentioned background technology.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A method for rapidly determining fatigue limit of composite materials using infrared thermography, the method comprising the following steps:

[0010] Select target composite materials with different mechanical properties and microstructures, and process them into standard plate or cylindrical specimens according to experimental requirements;

[0011] The elastic limit, yield strength, and tensile strength of the specimens were obtained through tensile testing. The elastic limit was introduced as the dividing line of the thermal imaging data. The temperature change when the stress was lower than the elastic limit was caused by the anelastic mechanism, while the temperature change when the stress was higher than the elastic limit was caused by the plastic mechanism.

[0012] Perform lifting fatigue tests on the specimen using a fatigue testing machine to obtain the specimen's fatigue limit, which is used to verify the results of infrared thermography.

[0013] Conduct infrared thermal imaging fatigue tests on the specimens using an infrared thermal imager, and record temperature rise data, data below the elastic limit, and data above the elastic limit;

[0014] For each stress level, calculate the temperature rise data of the specimen surface temperature;

[0015] The temperature rise data are divided into two parts, including data below the elastic limit and data above the elastic limit;

[0016] Perform linear fitting on the data below the elastic limit and the data above the elastic limit respectively to obtain two fitting straight lines;

[0017] The intersection of the two fitting straight lines is calculated to obtain the fatigue limit of the specimen measured by the infrared thermal imager.

[0018] Furthermore, for each stress level, the stable temperature rise of the sample surface temperature is calculated using the following formula:

[0019] ΔT=T h -T a

[0020] Among them, T h Expressed as the sample surface temperature; T a Indicated as ambient temperature.

[0021] Based on the stable temperature rise value of each stress level, a curve of the relationship between temperature rise and loading stress is drawn.

[0022] Furthermore, linear fitting is performed on the data below the elastic limit and the data above the elastic limit, respectively, including:

[0023] The relationship curves between temperature rise and loading stress corresponding to the data below the elastic limit and the data above the elastic limit are divided into two parts, and linear fitting is performed on the two parts respectively to obtain fitting lines y1 and y2;

[0024] Elastic region where stress is less than the elastic limit: Fitted straight line

[0025] y1=k1x+b1

[0026] Where k1 represents the slope of the fitted line; b1 represents the intercept of the line on the y-axis;

[0027] Plastic region where stress is greater than the elastic limit: Fitted straight line

[0028] y2=k2x+b2

[0029] Where k2 is the slope of the fitted line, and b2 is the intercept of the line on the y-axis.

[0030] Furthermore, the intersection of the two fitted straight lines is calculated to obtain the fatigue limit of the sample measured by the infrared thermal imager, including:

[0031] Obtain the intersection of the fitted lines y1 and y2, calculate the intersection of the two fitted lines, and obtain the fatigue limit; the calculation formula is as follows:

[0032] k1x+b1=k2x+b2

[0033] Solving the above equation, we get:

[0034]

[0035] The x value is the fatigue limit σ of the target composite material. f .

[0036] Furthermore, after calculating the intersection of the two fitted straight lines and obtaining the fatigue limit of the sample measured by the infrared thermal imager, the following steps are also included:

[0037] The fatigue limit data measured by the lifting method fatigue test and the infrared thermography fatigue test are organized into a table form;

[0038] Directly compare the fatigue limit values ​​measured by the two methods. If the fatigue limit values ​​measured by the two methods are close, it is preliminarily considered that the measurement results of the infrared thermography method are more reliable.

[0039] If there is a large difference between the fatigue limit values ​​measured by the two methods, the relative error of the fatigue limit values ​​measured by the two methods is calculated to quantify the degree of difference in the comparison results;

[0040] A relative error threshold is preset to analyze whether the relative error is within the relative error threshold. If so, the infrared thermal imaging measurement result is determined to be accurate.

[0041] If it exceeds this range, improvements and optimization will be carried out based on the error factors.

[0042] Furthermore, if the error exceeds this range, improvements and optimizations are made to the error factors, including:

[0043] Based on error factors, regular calibration and training of experimental equipment and experimental operations should be carried out;

[0044] Optimize linear fitting methods, as well as optimize data segmentation and data processing methods;

[0045] Repeat the experiment on the improved determination method to verify whether the improvement measures are effective;

[0046] The improved measurement results were compared with those of the lifting method to evaluate the improvement effect.

[0047] Furthermore, the infrared thermal imaging fatigue test is performed on the sample based on the infrared thermal imager, which also includes:

[0048] Check that there are no scratches or damage on the surface of the sample, and perform blackening treatment on the surface of the sample by spraying black matte paint with a thickness of 0.51mm;

[0049] Select a high-precision infrared thermal imager, aim the infrared thermal imager lens at the sample to ensure high consistency, and build an experimental platform;

[0050] Set the experimental parameters, including loading waveform, stress ratio, and loading frequency;

[0051] A step-by-step loading method was used, and each stress cycle was stopped until the surface temperature of the sample stabilized.

[0052] Furthermore, a lifting method fatigue test is performed on the sample using a fatigue testing machine to obtain the fatigue limit of the sample, which also includes:

[0053] Identify the model of the fatigue testing machine and set the parameters of the fatigue testing machine, including: setting the frame rate and viewing angle range parameters;

[0054] Collect temperature data, process and analyze it;

[0055] Combine industrial cameras with infrared thermal imagers to collect deformation information on the sample surface in real time;

[0056] Based on the Vickers hardness tester, positioning indentations are made on the sample surface for positioning tracking observation of the microstructure;

[0057] The microstructural changes on the sample surface were observed using a metallographic microscope.

[0058] Furthermore, the method further comprises:

[0059] Analyze the variation trend of fatigue limit with composite material type, microstructure, and loading conditions;

[0060] The factors affecting the accuracy of fatigue limit determination by infrared thermography are analyzed, including equipment accuracy, environmental conditions and sample preparation.

[0061] Furthermore, the method further comprises:

[0062] Write an experimental report based on the experimental results and analysis, including: experimental purpose, methods, process, results and discussion;

[0063] Use charts or images to visually display experimental results;

[0064] Based on the experimental results presented, the main conclusions are extracted, including the effectiveness and limitations of infrared thermography in determining fatigue limits.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] In the present invention, the temperature change on the surface of the composite material is captured by an infrared thermal imager, and the relationship between the temperature change and the stress level is analyzed, so that the dissipation mechanism of the composite material in the elastic and plastic stages can be effectively distinguished; through linear fitting and intersection calculation, with the elastic limit as the dividing line, combined with the inherent dissipation theory and fatigue damage mechanism, the fatigue limit of the material can be quantitatively determined, so that the determination of the inflection point has a clear physical meaning; at the same time, the fatigue limit can be accurately determined in a short time, and the deviation from the result of the traditional lifting method is within ±6.5%; in addition, the non-contact characteristics of the method reduce physical damage to the sample, improve the repeatability and reliability of the experiment, and at the same time reduce the number of samples and experimental time, reducing the experimental cost and time, which is of great significance for promoting the development of materials science and engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is a flow chart of the method for rapidly determining fatigue limit of composite materials using infrared thermography of the present invention;

[0068] Figure 2 Schematic diagram of the stress and temperature rise curve of the sample of the present invention;

[0069] Figure 3 This is a schematic diagram of the fatigue limit of a sample measured by the infrared thermal imaging method of the present invention;

[0070] Figure 4 Schematic diagram of the temperature rise curve of the sample of the present invention under different stress loadings versus time. DETAILED DESCRIPTION

[0071] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0072] To address the technical issues in existing technologies, such as reliance on experience or simple data fitting, lack of clear physical meaning, poor applicability to materials with high thermal conductivity and small plastic deformation (such as aluminum alloys), and difficulty in detecting significant temperature rises, and focusing mainly on macroscopic temperature rise phenomena and rarely combining microstructural evolution, please refer to Figure 1-Figure 4 , this embodiment provides the following technical solutions:

[0073] A method for rapidly determining fatigue limit of composite materials using infrared thermography comprises the following steps:

[0074] Target composite materials with different mechanical properties and microstructures are selected and processed into standard plate or cylindrical specimens according to experimental requirements so as to be suitable for studying the applicable scope of infrared thermography.

[0075] The elastic limit, yield strength, and tensile strength of the specimens were obtained through tensile testing. The elastic limit was introduced as the demarcation line for the thermal imaging data. Temperature changes below the elastic limit are caused by an anelastic mechanism, while those above the elastic limit are caused by a plastic mechanism. The elastic limit is the critical stress at which a composite material transitions from elastic to plastic deformation. During fatigue loading, the temperature change of the composite material is primarily caused by inherent dissipation, and the inherent dissipation mechanism changes before and after the elastic limit. When the stress is below the elastic limit, the temperature change is primarily caused by an anelastic mechanism; when the stress is above the elastic limit, the temperature change is primarily caused by the plastic mechanism. Therefore, using the elastic limit as the demarcation line for the thermal imaging data is crucial for accurately analyzing temperature changes in infrared thermography fatigue tests. Furthermore, based on the inherent dissipation theory and fatigue damage mechanism, the temperature rise inflection point is accurately determined, allowing for a rapid and accurate prediction of the material's fatigue limit.

[0076] A lifting fatigue test is performed on the specimen using a fatigue testing machine to obtain the specimen's fatigue limit, which is used to verify the results of infrared thermal imaging. The process also includes:

[0077] Identify the model of the fatigue testing machine, such as low-cycle fatigue testing machine (such as Shimadzu EHF-EV101K20200A) and high-cycle fatigue testing machine (such as Changchun Qianbang QBG100), and set the parameters of the fatigue testing machine, including: setting the frame rate (such as 50Hz / 60Hz) and viewing angle range parameters (such as 30°×23°); use dedicated software, such as IRBIS3Puls, to collect temperature data, process and analyze it; combine industrial cameras with infrared thermal imagers to collect deformation information of the sample surface in real time, so as to It can accurately capture the microstructural changes of materials under fatigue loading; based on the Vickers hardness tester, positioning indentations are prepared on the sample surface for positioning tracking observation of the microstructure; based on the metallographic microscope, the microstructural changes on the sample surface are observed, which further enhances the ability to observe the microstructural changes on the surface of composite materials. It not only improves the accuracy and reliability of fatigue limit determination, but also provides rich data support for in-depth understanding of the fatigue behavior and damage mechanism of composite materials through multi-angle and multi-means monitoring, which is conducive to the comprehensive evaluation and optimization of material performance.

[0078] Conduct infrared thermal imaging fatigue tests on the specimens using an infrared thermal imager, and record temperature rise data, data below the elastic limit, and data above the elastic limit for subsequent data processing. The process also includes:

[0079] Check that there are no scratches or damage on the surface of the sample. Blacken the surface of the sample by spraying black matte paint with a thickness of 0.51mm to improve the temperature acquisition accuracy of the infrared thermal imager.

[0080] like Figure 2-Figure 4 As shown: Select a high-precision infrared thermal imager, such as the Infratec YH680, which has high thermal sensitivity (e.g. 0.03°C in optimized mode) and a wide temperature measurement range (e.g. -40°C to 1200°C). Aim the infrared thermal imager lens at the sample to ensure high consistency and set up the experimental platform.

[0081] Set the experimental parameters, including the loading waveform (e.g., sine wave), stress ratio (e.g., R = 0.1), and loading frequency (e.g., 10 Hz or 100 Hz).

[0082] A step-by-step loading method was used, and each stress cycle was stopped until the surface temperature of the sample stabilized.

[0083] For each stress level, calculate the temperature rise data of the sample surface temperature. The calculation formula is as follows:

[0084] ΔT=T h -T a

[0085] Among them, T h Expressed as the sample surface temperature; Ta Indicated as ambient temperature.

[0086] Based on the stable temperature rise value of each stress level, a curve of temperature rise versus loading stress is drawn.

[0087] The temperature rise data is divided into two parts, including data below the elastic limit and data above the elastic limit. Linear fitting is performed on the data below the elastic limit and the data above the elastic limit respectively to obtain two fitting lines, including:

[0088] The relationship curves between temperature rise and loading stress corresponding to the data below the elastic limit and the data above the elastic limit are divided into two parts, and linear fitting is performed on the two parts respectively to obtain fitting lines y1 and y2;

[0089] Elastic region where stress is less than the elastic limit: Fitted straight line

[0090] y1=k1x+b1

[0091] Where k1 represents the slope of the fitted line; b1 represents the intercept of the line on the y-axis;

[0092] Plastic region where stress is greater than the elastic limit: Fitted straight line

[0093] y2=k2x+b2

[0094] Where k2 is the slope of the fitted line, and b2 is the intercept of the line on the y-axis.

[0095] Calculate the intersection of the two fitted straight lines to obtain the fatigue limit of the specimen measured by the infrared thermal imager, including:

[0096] Obtain the intersection of the fitted lines y1 and y2, calculate the intersection of the two fitted lines, and obtain the fatigue limit. Since the intersection of the two fitted lines represents the transition point from elastic behavior to plastic behavior of the target composite material, it can be used as a reference indicator of the fatigue limit. The calculation formula is as follows:

[0097] k1x+b1=k2x+b2

[0098] Solving the above equation, we get:

[0099]

[0100] The x value is the fatigue limit σ of the target composite material. f .

[0101] After obtaining the fatigue limit of the sample measured by infrared thermal imager, it also includes:

[0102] The fatigue limit data measured by the lifting method fatigue test and the infrared thermal imaging fatigue test are organized into a table format to facilitate subsequent comparative analysis;

[0103] Directly compare the fatigue limit values ​​measured by the two methods. If the fatigue limit values ​​measured by the two methods are close, it is preliminarily considered that the measurement results of the infrared thermography method are more reliable.

[0104] If there is a large difference between the fatigue limit values ​​measured by the two methods, the relative error of the fatigue limit values ​​measured by the two methods is calculated to quantify the degree of difference in the comparison results;

[0105] A relative error threshold is preset to analyze whether the relative error is within the relative error threshold. If so, the infrared thermal imaging measurement result is determined to be accurate.

[0106] If it exceeds this range, the error factors should be improved and optimized, including:

[0107] Based on error factors, the experimental equipment and experimental operations are calibrated and trained regularly; the linear fitting method is optimized, as well as the data segmentation and data processing methods are optimized; the improved measurement method is repeated to verify whether the improvement measures are effective; the improved measurement results are compared and analyzed with the results of the lifting method to evaluate the improvement effect; among them, the error factors include experimental equipment: check the accuracy and calibration of the infrared thermal imager, the loading accuracy of the fatigue testing machine, etc.; experimental operation: review whether there are any irregularities in the experimental operation process, such as: whether the specimen is installed correctly, whether the loading frequency is stable, etc.; data processing: check whether the linear fitting in the infrared thermal imaging method is reasonable, whether the data segmentation is accurate, etc.

[0108] In one embodiment, assuming that aluminum alloy 2024 is selected as the target composite material, a standard cylindrical specimen is processed with a diameter of 10 mm and a length of 50 mm. The fatigue limit of aluminum alloy 2024 is measured to be 150 MPa based on the lifting method.

[0109] The sample surface was inspected to ensure there were no scratches or damage. A black matte paint coating with a thickness of 0.51 mm was applied to the sample surface. An Infratec YH680 infrared thermal imager was selected, with the optimized mode set to a thermal sensitivity of 0.03°C and a temperature measurement range of -40°C to 1200°C. The infrared thermal imager lens was focused on the sample, and the experimental parameters were set as follows: a sinusoidal loading waveform, a stress ratio R = 0.1, and a loading frequency of 10 Hz.

[0110] Following the above steps, the fatigue limit of aluminum alloy 2024 was determined to be 152 MPa based on infrared thermography. When compared with the result obtained by the lifting method, the deviation between the two was small, indicating that the current infrared thermography result is more reliable.

[0111] The beneficial effects achieved by the above content are: by capturing the temperature changes on the surface of the composite material with an infrared thermal imager and analyzing the relationship between the temperature changes and the stress level, the dissipation mechanism of the composite material in the elastic and plastic stages can be effectively distinguished; by linear fitting and intersection calculation, with the elastic limit as the dividing line, combined with the inherent dissipation theory and fatigue damage mechanism, the fatigue limit of the material can be quantitatively determined, so that the determination of the inflection point has a clear physical meaning; at the same time, the fatigue limit can be accurately determined in a short time, and the deviation from the result of the traditional lifting method is within ±6.5%; in addition, the non-contact characteristics of this method reduce the physical damage to the sample, improve the repeatability and reliability of the experiment, while reducing the number of samples and experimental time, reducing the experimental cost and time, which is of great significance for promoting the development of materials science and engineering applications.

[0112] The method also includes:

[0113] Analyze the variation trend of fatigue limit with composite material type, microstructure, and loading conditions; analyze the relevant factors affecting the accuracy of fatigue limit determination by infrared thermography, including equipment accuracy, environmental conditions, and specimen preparation; write an experimental report based on the experimental results and analysis, including the experimental purpose, methods, process, results, and discussion; use charts or images to visualize the experimental results for easy understanding and comparison; based on the experimental results presented, extract the main conclusions, including the effectiveness and limitations of infrared thermography in determining fatigue limit.

[0114] Working principle: Based on the heat generated by the intrinsic dissipation of composite materials during fatigue loading, the temperature changes on the sample surface are recorded by an infrared thermal imager. Utilizing the principle that the temperature changes below and above the elastic limit of composite materials are caused by the anelastic mechanism and the plastic mechanism respectively, the elastic limit is determined as the dividing point through tensile testing. The temperature rise data is divided into two parts according to the stress level and linear fitting is performed to obtain two straight lines representing the temperature changes under different mechanisms. The stress level corresponding to the intersection of the two straight lines is the fatigue limit of the material, thereby accurately determining the temperature rise inflection point and realizing rapid and non-destructive determination of the fatigue limit of the composite material.

[0115] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "including," "having," or any other variations thereof are intended to cover non-exclusive possessors, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or includes elements that are inherent to such process, method, article, or apparatus.

[0116] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions, and alterations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for rapidly determining fatigue limit of composite materials using infrared thermography, characterized in that: The method comprises the following steps: Select target composite materials with different mechanical properties and microstructures, and process them into standard plate or cylindrical specimens according to experimental requirements; The elastic limit, yield strength, and tensile strength of the specimens were obtained through tensile testing. The elastic limit was introduced as the dividing line of the thermal imaging data. The temperature change when the stress was lower than the elastic limit was caused by the anelastic mechanism, while the temperature change when the stress was higher than the elastic limit was caused by the plastic mechanism. Perform lifting fatigue tests on the specimen using a fatigue testing machine to obtain the specimen's fatigue limit, which is used to verify the results of infrared thermography. Conduct infrared thermal imaging fatigue tests on the specimens using an infrared thermal imager, and record temperature rise data, data below the elastic limit, and data above the elastic limit; For each stress level, calculate the temperature rise data of the specimen surface temperature; The temperature rise data are divided into two parts, including data below the elastic limit and data above the elastic limit; Perform linear fitting on the data below the elastic limit and the data above the elastic limit respectively to obtain two fitting straight lines; The intersection of the two fitting straight lines is calculated to obtain the fatigue limit of the specimen measured by the infrared thermal imager.

2. The method for rapid determination of fatigue limit of composite materials by infrared thermography according to claim 1, characterized in that: For each stress level, calculate the stable temperature rise of the sample surface temperature using the following formula: ΔT=T h -T a Among them, T h Expressed as the sample surface temperature; T a Indicated as ambient temperature. Based on the stable temperature rise value of each stress level, a curve of the relationship between temperature rise and loading stress is drawn.

3. The method for rapid determination of fatigue limit of composite materials by infrared thermography according to claim 2, characterized in that: Perform linear fitting on data below the elastic limit and data above the elastic limit, including: The relationship curves between temperature rise and loading stress corresponding to the data below the elastic limit and the data above the elastic limit are divided into two parts, and linear fitting is performed on the two parts respectively to obtain fitting lines y1 and y2; Elastic region where stress is less than the elastic limit: Fitted straight line y1=k1x+b1 Where k1 represents the slope of the fitted line; b1 represents the intercept of the line on the y-axis; Plastic region where stress is greater than the elastic limit: Fitted straight line y2=k2x+b2 Where k2 is the slope of the fitted line, and b2 is the intercept of the line on the y-axis.

4. The method for rapidly determining fatigue limit of composite materials using infrared thermography according to claim 3, characterized in that: Calculate the intersection of the two fitted straight lines to obtain the fatigue limit of the specimen measured by the infrared thermal imager, including: Obtain the intersection of the fitted lines y1 and y2, calculate the intersection of the two fitted lines, and obtain the fatigue limit; the calculation formula is as follows: k1x+b1=k2x+b2 Solving the above equation, we get: The x value is the fatigue limit σ of the target composite material. f .

5. The method for rapidly determining fatigue limit of composite materials using infrared thermography according to claim 4, characterized in that: After calculating the intersection of the two fitted straight lines and obtaining the fatigue limit of the specimen measured by the infrared thermal imager, it also includes: The fatigue limit data measured by the lifting method fatigue test and the infrared thermography fatigue test are organized into a table form; Directly compare the fatigue limit values ​​measured by the two methods. If the fatigue limit values ​​measured by the two methods are close, it is preliminarily considered that the measurement results of the infrared thermography method are more reliable. If there is a large difference between the fatigue limit values ​​measured by the two methods, the relative error of the fatigue limit values ​​measured by the two methods is calculated to quantify the degree of difference in the comparison results; A relative error threshold is preset to analyze whether the relative error is within the relative error threshold. If so, the infrared thermal imaging measurement result is determined to be accurate. If it exceeds this range, improvements and optimization will be carried out based on the error factors.

6. The method for rapidly determining fatigue limit of composite materials using infrared thermography according to claim 5, characterized in that: If it exceeds this range, the error factors should be improved and optimized, including: Based on error factors, regular calibration and training of experimental equipment and experimental operations should be carried out; Optimize linear fitting methods, as well as optimize data segmentation and data processing methods; Repeat the experiment on the improved determination method to verify whether the improvement measures are effective; The improved measurement results were compared with those of the lifting method to evaluate the improvement effect.

7. The method for rapidly determining fatigue limit of composite materials using infrared thermography according to claim 1, characterized in that: Infrared thermal imaging fatigue test of the sample is carried out based on the infrared thermal imager, which also includes: Check that there are no scratches or damage on the surface of the sample, and perform blackening treatment on the surface of the sample by spraying black matte paint with a thickness of 0.51mm; Select a high-precision infrared thermal imager, aim the infrared thermal imager lens at the sample to ensure high consistency, and build an experimental platform; Set the experimental parameters, including loading waveform, stress ratio, and loading frequency; A step-by-step loading method was used, and each stress cycle was stopped until the surface temperature of the sample stabilized.

8. The method for rapidly determining fatigue limit of composite materials using infrared thermography according to claim 1, characterized in that: The fatigue limit of the specimen is obtained by performing a lifting fatigue test on the specimen using a fatigue testing machine, which also includes: Identify the model of the fatigue testing machine and set the parameters of the fatigue testing machine, including: setting the frame rate and viewing angle range parameters; Collect temperature data, process and analyze it; Combine industrial cameras with infrared thermal imagers to collect deformation information on the sample surface in real time; Based on the Vickers hardness tester, positioning indentations are made on the sample surface for positioning tracking observation of the microstructure; The microstructural changes on the sample surface were observed using a metallographic microscope.

9. The method for rapidly determining fatigue limit of composite materials using infrared thermography according to claim 8, characterized in that: The method further comprises: Analyze the variation trend of fatigue limit with composite material type, microstructure, and loading conditions; The factors affecting the accuracy of fatigue limit determination by infrared thermography are analyzed, including equipment accuracy, environmental conditions and sample preparation.

10. The method for rapidly determining fatigue limit of composite materials using infrared thermography according to claim 9, characterized in that: The method further comprises: Write an experimental report based on the experimental results and analysis, including: experimental purpose, methods, process, results and discussion; Use charts or images to visually display experimental results; Based on the experimental results presented, the main conclusions are extracted, including the validity and limitations of infrared thermography for fatigue limit determination.

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