Test system, test method and application of indentation radial crack length based on acoustic emission
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XIDIAN UNIV
- Filing Date
- 2023-12-14
- Publication Date
- 2026-05-26
Smart Images
Figure CN117686323B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of wireless communication technology, and specifically to a test system, test method and application for measuring the radial crack length of indentation based on acoustic emission. Background Technology
[0002] Researchers often use fracture toughness to characterize a material's ability to prevent crack propagation, serving as a quantitative indicator of material toughness. Under constant external conditions such as applied force, loading speed, and temperature, fracture toughness is a constant, an inherent property of the material. Currently, fracture toughness testing often employs the indentation method, which involves applying a load to the sample using an indenter to create an indentation, then obtaining the radial crack length of the indentation using scanning electron microscopy or similar methods, and calculating the fracture toughness value (KIC) using empirical formulas. This testing process is cumbersome and inefficient. Many other methods exist for detecting crack length. For example, patent application CN201820366450.6 discloses a crack length detection device that uses two laser emitters to measure the advance distance of a micrometer screw to detect crack length; patent application CN202111043061.2 discloses a method and device for detecting crack length in train components, which uses two current probes on the component surface to carry a constant current, determining the crack length based on the voltage difference between the probes. However, these methods for measuring crack length all require the addition of too many other devices at the sample to assist in the detection of crack length, resulting in low detection efficiency and difficulty in achieving the desired results for small samples where the radial crack length of the indentation needs to be measured. How to efficiently measure the radial crack length of the indentation has been a long-standing concern for researchers. Summary of the Invention
[0003] To overcome the shortcomings of the existing technology, the present invention aims to provide a testing system, method, and application for indentation radial crack length based on acoustic emission. The system connects an acoustic emission sensor to the sample to be tested, applies a load to the sample, and transmits the indentation signal through the sensor to a preamplifier. After amplification and processing, the signal is sent to a computer system to extract acoustic emission characteristic signals. Using a scanning electron microscope, a mathematical model is established to simulate the quantitative relationship between acoustic emission signal characteristic parameters and indentation radial crack length. This quantitative relationship can be directly used in subsequent indentation tests. Based on the specific acoustic emission signal characteristic parameters extracted from the acquired signal, the indentation radial crack length of the tested sample is obtained, and the fracture toughness of the tested sample is calculated efficiently. The system can detect crack propagation state in real time and efficiently obtain the indentation radial crack length, offering advantages such as simple operation and high detection efficiency.
[0004] To achieve the above objectives, the present invention adopts the following technical solution:
[0005] A testing system for indentation radial crack length based on acoustic emission includes a signal acquisition module, a signal storage and display module, and a signal processing and analysis module. The acoustic emission sensor in the signal acquisition module transmits the indentation signal applied to the sample to the preamplifier of the signal acquisition module. The preamplifier amplifies and processes the signal before transmitting it to the signal storage and display module. The data acquisition card in the signal storage and display module converts the received electrical signal into a digital signal, and then transmits the received signal to the computer memory via a computer interface for storage and display. The signal processing and analysis module then extracts the duration of the indentation radial crack length from the acoustic emission signal in the signal storage and display module through cluster analysis and wavelet packet transform. Simulation is used to establish a quantitative relationship between the extracted duration and the radial crack length of the indentation measured by scanning electron microscopy.
[0006] The signal acquisition module includes an acoustic emission sensor. The signal output terminal of the acoustic emission sensor is connected to the signal input terminal of a preamplifier. The signal is amplified by the output terminal of the preamplifier and input to the computer. The acoustic emission sensor converts the weak acoustic signal into an electrical signal to obtain the generation and morphological characteristics of the acoustic emission signal. The preamplifier of the signal acquisition module improves the signal-to-noise ratio, enhances the frequency response, and amplifies the weak electrical signal before transmitting it to the signal storage and display module.
[0007] The signal storage and display module includes a data acquisition card and a computer. The signal receiving end of the data acquisition card is connected to the signal output end of the preamplifier, and then the received electrical signal is converted into a digital signal and transmitted to the computer memory through the computer interface. The acoustic emission signal acquired by the signal acquisition module is stored and displayed.
[0008] The signal processing and analysis module processes the acoustic emission signals in the signal storage and display module: extracts specified acoustic emission characteristic signal parameters, including amplitude, peak frequency, and duration; uses cluster analysis to classify the signals into different categories; performs wavelet packet transformation, decomposition, reconstruction, and time-domain analysis on the signals of different categories to obtain the duration of the indentation radial crack length signal; and establishes a quantitative relationship between the acoustic emission signal characteristic parameters and the measured indentation radial crack length by combining the indentation radial crack length measured by scanning electron microscopy.
[0009] The quantitative relationship between the acoustic emission signal characteristic parameters and the radial crack length of the indentation is as follows: c(x) = Ax B +C, where c is the length from the indentation center to the crack tip, x is the duration characteristic parameter, and A, B, and C are constants of the physical properties of the sample, with B ranging from (-1, 1).
[0010] A testing method for an indentation radial crack length testing system based on acoustic emission, the specific steps of which are as follows:
[0011] Step 1: Before the experiment begins, a lead-breaking test is conducted. HB mechanical pencils with diameters of 0.3 / 0.5 / 0.7 mm and lead elongation of 2-3 mm are used. Each time a lead breaks, the angle between the lead and the surface of the specimen is 30-40°. The acoustic emission sensor is fixed in place using a clamp. The pencil tip is gradually rotated until the lead breaks. The emitted acoustic emission signal is collected, and the sensitivity of the acoustic emission sensor is detected by the obtained waveform.
[0012] Step 2, Sample preparation: Polish the sample to be tested to 0.05-1μm; fix the sample to be tested on the sample stage of the indenter using a clamping device; apply coupling agent between the acoustic emission sensor and the sample to be tested; and apply mechanical force to make the two tightly bonded.
[0013] Step 3: Set the parameters of the indenter. The indentation load range is 4.903-49.03N, the holding time is 5-20s, start the indenter to start the indentation test, and the distance between indentations should be at least 4mm. Each sample should be tested at least 10 times.
[0014] Step 4: Set acoustic emission instrument parameters: Set a sampling threshold value to reduce the influence of ambient noise. The sampling threshold value is ambient noise +5 to +8dB. Select a preamplifier of 20 / 40 / 60dB, a sampling frequency of 1 to 4MHz, a Hit length of 1 to 2k, and a frequency range of 0.1 to 1MHz. Collect and store the acoustic emission signal characteristic parameters.
[0015] Step 5: Extract acoustic emission feature parameters from the received acoustic emission signal, including amplitude, peak frequency, and duration; then classify the acoustic emission signal into different categories; perform wavelet packet transformation, decomposition, reconstruction, and time-domain analysis on the acoustic emission signals of different categories to obtain the duration of the indentation radial crack length signal;
[0016] Step 6: Perform scanning electron microscopy on the sample after the indentation test in Step 3 to measure the radial crack length of the indentation;
[0017] Step 7: Based on the results of Steps 5 and 6, establish a quantitative relationship between the acoustic emission signal characteristic parameters (x, duration) and the indentation radial crack length (c) through data fitting, where c(x) = Ax B +C;
[0018] Step 8: After obtaining the quantitative relationship between the acoustic emission signal characteristic parameters and the radial crack length of the indentation in Step 7, when performing indentation measurement, simply substitute the acoustic emission signal characteristic parameters obtained in Step 5 directly into c(x) = Ax obtained in Step 7.B The radial crack length of the indentation can be obtained by using formula +C.
[0019] The coupling agent mentioned in step 2 includes vacuum grease, petroleum jelly, or butter.
[0020] In step 5, the signals are divided into different categories using cluster analysis methods, including k-means clustering.
[0021] An application of a test system for radial crack length indentation based on acoustic emission is presented, which integrates the hardness H, indentation load P parameter, and c(x) = Ax obtained directly from the indenter. B By substituting the radial crack length c of the indentation in +C and the material elastic modulus E obtained by the nanoindenter into the empirical formula, the fracture toughness value of the material can be calculated.
[0022] The empirical formula is:
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] 1. This invention presents an efficient characterization technique for radial crack length in indentation based on acoustic emission. It involves in-depth research, system construction, and testing of methods for testing radial crack length in indentation. Through cluster analysis and wavelet function analysis, characteristic parameters of the acoustic emission signal characterizing the radial crack length are extracted. Combined with scanning electron microscopy, a quantitative relationship is established between the acoustic emission signal characteristic parameters and the radial crack length. This quantitative relationship can be directly used in subsequent indentation tests to efficiently obtain the radial crack length of the tested sample based on specific acoustic emission signal characteristic parameters extracted from the acquired signal. This method overcomes the cumbersome nature of traditional testing methods and improves efficiency. Calculating the radial crack length of the tested sample from the perspective of acoustic emission signals is a relatively new approach. Within the allowable error range, the radial crack length of the indentation can be represented by the characteristic parameters of the acoustic emission signal.
[0025] 2. The acoustic emission-based indentation radial crack length testing system and method of the present invention provides a brand-new solution for efficiently characterizing the fracture toughness of materials. It is not only a supplement to the traditional fracture toughness testing method, but also has broad application prospects. Attached Figure Description
[0026] Figure 1 This is a diagram of the test system of the present invention.
[0027] Figure 2 The figure shows the fitting curves of acoustic emission signal characteristic parameters and radial crack length of indentation in Al2O3 ceramic block for the example.
[0028] Figure 3The figure shows the fitting curves of acoustic emission signal characteristic parameters and radial crack length of indentation in SiC ceramic bulk for the example.
[0029] Figure 4 The figure shows the fitting curves of acoustic emission signal characteristic parameters and radial crack length of indentation in Si3N4 ceramic block as an example. Detailed Implementation
[0030] The present invention will now be described in further detail with reference to the accompanying drawings.
[0031] Example 1
[0032] Embodiment 1 of the present invention provides a system and method for testing the radial crack length of Al2O3 ceramic bulk indentation based on acoustic emission. The testing system is as follows: Figure 1 As shown.
[0033] A testing system for radial crack length indentation based on acoustic emission includes a signal acquisition module, a signal storage and display module, and a signal processing and analysis module. In the signal acquisition module, a coupling agent is applied between the acoustic emission sensor and the sample to be tested, and then mechanical force is applied to ensure a tight bond. A load is applied to the sample using an indenter, and the acoustic emission sensor transmits the indentation signal applied to the sample to a preamplifier in the signal acquisition module. The preamplifier amplifies and processes the signal before transmitting it to the signal storage and display module. The data acquisition card in the signal storage and display module converts the received electrical signal into a digital signal, and then transmits the received signal to computer memory via a computer interface for storage and display. The signal processing and analysis module then extracts the duration of the radial crack length indentation from the acoustic emission signal in the signal storage and display module through cluster analysis and wavelet packet transform. Simulation is used to establish a quantitative relationship between the extracted duration and the radial crack length of the indentation in the sample measured by scanning electron microscopy.
[0034] A method for testing the radial crack length of indentation based on acoustic emission, the specific steps of which are as follows:
[0035] Step 1: Before the experiment begins, a lead-breaking test is conducted using a 0.5mm HB pencil with a lead elongation of 2.5mm. Each time the lead is broken, ensure that the angle between the lead and the surface of the specimen is 30°. Fix the acoustic emission sensor with a clamp, collect the emitted acoustic emission signal, and test the sensitivity of the acoustic emission sensor.
[0036] Step 2, Sample preparation: Polish the Al2O3 ceramic block to 0.05μm; fix the sample to be tested on the sample stage of the indenter using a clamping device, apply coupling agent between the acoustic emission sensor and the sample, and apply mechanical force to make the two tightly bonded;
[0037] Step 3: Based on the physical properties of the Al2O3 ceramic block, set the parameters of the indentation instrument. The indentation load range is 9.807-49.03N, and the holding time is 15s. Start the indentation instrument to begin the indentation test. To avoid the stress fields generated between indentations from affecting each other, the distance between two indentations should be at least 4mm. To ensure the accuracy and reliability of the test results, each sample should be subjected to 10 indentation tests.
[0038] Step 4: Set the acoustic emission instrument parameters: Determine the sampling threshold value according to the environment to reduce the influence of ambient noise. The sampling threshold value is ambient noise + 5dB. Select a preamplifier of 60dB, a sampling frequency of 2MHz, a Hit length of 1k, and a frequency range of 0.1~1MHz. Collect and store the acoustic emission signal characteristic parameters.
[0039] Step 5: Extract acoustic emission characteristic parameters from the received signal, including amplitude, peak frequency, and duration; then, use cluster analysis to classify the signal into different categories; perform wavelet packet transformation, decomposition, reconstruction, and time-domain analysis on the signals of different categories to obtain the duration of the radial crack length signal of the indentation; the specific wavelet transform principle is referred to in patent application CN200810031180.4.
[0040] Step 6: Perform scanning electron microscopy on the Al2O3 ceramic block after the indentation test in Step 3 to measure the radial crack length of the indentation;
[0041] Step 7: Based on the results of Steps 5 and 6, a quantitative relationship is established between the acoustic emission signal characteristic parameters and the radial crack length of the Al2O3 ceramic block indentation through data fitting, which is c = 1.755x. 0.6336 -5.271;
[0042] Step 8: After obtaining the quantitative relationship between the acoustic emission signal characteristic parameters and the radial crack length of the indentation in Step 7, when performing indentation measurement, simply substitute the acoustic emission signal characteristic parameters of the Al2O3 ceramic block obtained in Step 5 directly into the quantitative relationship obtained in Step 7 to obtain the radial crack length of the indentation.
[0043] See Figure 2The above work establishes a quantitative relationship between the radial crack length of Al2O3 ceramic block indentation and the characteristic parameters of acoustic emission signals. This quantitative relationship can be directly used in subsequent Al2O3 ceramic block indentation tests. By extracting the characteristic parameters of acoustic emission signals from specified Al2O3 ceramic block indentation tests, the radial crack length of the Al2O3 ceramic block indentation can be directly obtained, thereby efficiently calculating the fracture toughness of the tested sample. When the load is 49.03 N, the radial crack length of Al2O3 ceramic block indentation obtained by the proposed method based on acoustic emission indentation radial crack length and the traditional method scanning electron microscopy technique, along with the error value, are shown in Table 1. The error is 2.73%.
[0044] Example 2
[0045] Embodiment 2 of the present invention provides a system and method for testing the radial crack length of SiC ceramic bulk indentation based on acoustic emission. The testing system is as follows: Figure 1 As shown.
[0046] A method for testing the radial crack length of indentation based on acoustic emission, the specific steps of which are as follows:
[0047] Step 1: Before the experiment begins, a lead-breaking test is conducted using a 0.3mm HB pencil with a lead elongation of 2mm. Each time the lead is broken, the angle between the lead and the surface of the specimen is 35°. The acoustic emission sensor is fixed with a clamp, and the emitted acoustic emission signal is collected to test the sensitivity of the acoustic emission sensor.
[0048] Step 2, Sample preparation: Polish the SiC ceramic block to 0.5μm; fix the sample to be tested on the indenter sample stage using a clamping device, apply coupling agent between the acoustic emission sensor and the sample, and apply mechanical force to make the two tightly bonded.
[0049] Step 3: Based on the physical properties of the SiC ceramic block, set the parameters of the indentation instrument. The indentation load range is 4.903-24.52N, the holding time is 5s, and the indentation instrument is started to begin the indentation test. In order to avoid the stress fields generated between the indentations from affecting each other, the distance between the two indentations should be at least 5mm apart. In order to ensure the accuracy and reliability of the test results, each sample should be subjected to 10 indentation tests.
[0050] Step 4: Set the acoustic emission instrument parameters: Determine the sampling threshold value according to the environment to reduce the influence of ambient noise. The sampling threshold value is ambient noise + 8dB. Select a preamplifier of 40dB, a sampling frequency of 1MHz, a Hit length of 1k, and a frequency range of 0.1~1MHz. Collect and store the acoustic emission signal characteristic parameters.
[0051] Step 5: Extract acoustic emission feature parameters from the received signal, including amplitude, peak frequency, and duration; then, use cluster analysis to classify the signal into different categories; perform wavelet packet transformation, decomposition, reconstruction, and time-domain analysis on the signals of different categories to obtain the duration of the indentation radial crack length signal;
[0052] Step 6: Perform scanning electron microscopy on the SiC ceramic block after the indentation test in Step 3 to measure the radial crack length of the indentation;
[0053] Step 7: Based on the results of Steps 5 and 6, establish a quantitative relationship between the acoustic emission signal characteristic parameters and the radial crack length of the indentation in the SiC ceramic bulk through data fitting, where c = 11.33x 0.3887 +1.204;
[0054] Step 8: After obtaining the quantitative relationship between the acoustic emission signal characteristic parameters and the radial crack length of the indentation in Step 7, when performing indentation measurement, simply substitute the acoustic emission signal characteristic parameters of the SiC ceramic block obtained in Step 5 directly into the quantitative relationship obtained in Step 7 to obtain the radial crack length of the indentation.
[0055] See Figure 3 The above work establishes a quantitative relationship between the radial crack length of the indentation in SiC ceramic bulk and the characteristic parameters of the acoustic emission signal. This quantitative relationship can be directly used in subsequent indentation tests of SiC ceramic bulk. By extracting the characteristic parameters of the acoustic emission signal from the indentation test of a specified SiC ceramic bulk, the radial crack length of the indentation in SiC ceramic bulk can be directly obtained, thereby efficiently calculating the fracture toughness of the tested sample. When the load is 49.03 N, the radial crack length of the indentation in SiC ceramic bulk obtained by the proposed method based on the acoustic emission indentation radial crack length and the traditional method scanning electron microscopy, along with the error value, are shown in Table 1. The error is 0.93%.
[0056] Example 3
[0057] Embodiment 3 of the present invention is a system and method for testing the radial crack length of Si3N4 ceramic bulk indentation based on acoustic emission. The testing system is as follows: Figure 1 As shown.
[0058] A method for testing the radial crack length of indentation based on acoustic emission, the specific steps of which are as follows:
[0059] Step 1: Before the experiment begins, a lead-breaking test is conducted using a 0.7mm HB pencil with a lead elongation of 3mm. Each time the lead is broken, ensure that the angle between the lead and the surface of the specimen is 40°. Fix the acoustic emission sensor with a clamp, collect the emitted acoustic emission signal, and test the sensitivity of the acoustic emission sensor.
[0060] Step 2, Sample preparation: Polish the Si3N4 ceramic block to 1μm; fix the sample to be tested on the sample stage of the indenter using a clamping device; apply coupling agent between the acoustic emission sensor and the sample to ensure a tight bond between the two.
[0061] Step 3: Based on the physical properties of the Si3N4 ceramic block, set the parameters of the indentation instrument. The indentation load range is 4.903-49.03N, the holding time is 20s, and the indentation instrument is started to begin the indentation test. To avoid the stress fields generated between the indentations from affecting each other, the distance between the two indentations should be at least 4mm. To ensure the accuracy and reliability of the test results, each sample should be subjected to 10 indentation tests.
[0062] Step 4: Set the acoustic emission instrument parameters: Determine the sampling threshold value according to the environment to reduce the influence of ambient noise. The sampling threshold value is ambient noise + 7dB. Select a preamplifier of 40dB, a sampling frequency of 2MHz, a Hit length of 2k, and a frequency range of 0.1~1MHz. Collect and store the acoustic emission signal characteristic parameters.
[0063] Step 5: Extract acoustic emission feature parameters from the received signal, including amplitude, peak frequency, and duration; then, use cluster analysis to classify the signal into different categories; perform wavelet packet transformation, decomposition, reconstruction, and time-domain analysis on the signals of different categories to obtain the duration of the indentation radial crack length signal;
[0064] Step 6: Perform scanning electron microscopy on the Si3N4 ceramic block after the indentation test in Step 3 to measure the radial crack length of the indentation;
[0065] Step 7: Based on the results of Steps 5 and 6, establish a quantitative relationship between the acoustic emission signal characteristic parameters and the radial crack length of the indentation in the Si3N4 ceramic block through data fitting, c = -2904x -0.7651 +118.5;
[0066] Step 8: After obtaining the quantitative relationship between the acoustic emission signal characteristic parameters and the radial crack length of the indentation in Step 7, when performing indentation measurement, simply substitute the acoustic emission signal characteristic parameters of the Si3N4 ceramic block obtained in Step 5 directly into the quantitative relationship obtained in Step 7 to obtain the radial crack length of the indentation.
[0067] See Figure 4The above work establishes a quantitative relationship between the radial crack length of the indentation in Si3N4 ceramic bulk and the characteristic parameters of the acoustic emission signal. This quantitative relationship can be directly used in subsequent indentation tests of Si3N4 ceramic bulk. By extracting the characteristic parameters of the acoustic emission signal from the specified Si3N4 ceramic bulk indentation test, the radial crack length of the Si3N4 ceramic bulk indentation can be directly obtained, thereby efficiently calculating the fracture toughness of the tested sample. When the load is 49.03 N, the radial crack length of the Si3N4 ceramic bulk indentation obtained by the proposed method based on the acoustic emission indentation radial crack length and the traditional method scanning electron microscopy technique, along with the error value, are shown in Table 1. The error is 1.93%.
[0068] Table 1: Radial crack length of sample indentation measured by different methods when P = 49.03 N.
[0069]
[0070]
[0071] Table 1 compares the radial crack length of the indentation measured by acoustic emission method with that measured by traditional scanning electron microscopy. The test results show that the radial crack length characterization technique based on acoustic emission characteristic parameters has a low error compared to the radial crack length measured by traditional scanning electron microscopy, indicating that within the allowable error range, the radial crack length of the indentation in the tested sample can be calculated based on the characteristic parameters of the acoustic emission signal.
[0072] This invention relates to an indentation radial crack length testing system and method based on acoustic emission, which overcomes the limitations of traditional methods, such as cumbersome steps and low efficiency. It provides a new solution for the efficient calculation of fracture toughness, has broad and promising development prospects, and has high practical value.
[0073] The above are preferred embodiments of the present invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention, and shall not be limited by the above embodiments.
Claims
1. A testing system for radial crack length indentation based on acoustic emission, comprising a signal acquisition module, a signal storage and display module, and a signal processing and analysis module; characterized in that, The acoustic emission sensor of the signal acquisition module transmits the indentation signal applied to the sample to the preamplifier of the signal acquisition module. The preamplifier amplifies and processes the signal before transmitting it to the signal storage and display module. The data acquisition card of the signal storage and display module converts the received electrical signal into a digital signal, and then transmits the received signal to the computer memory through the computer interface for storage and display. Then, the signal processing and analysis module extracts the duration of the radial crack length of the indentation from the acoustic emission signal in the signal storage and display module through cluster analysis and wavelet packet transform. The extracted duration is then used to establish a quantitative relationship between the extracted duration and the radial crack length of the indentation measured by scanning electron microscopy. The quantitative relationship between the acoustic emission signal characteristic parameters and the indentation radial crack length is as follows: Where c is the length from the indentation center to the crack tip, x is the duration characteristic parameter, and A, B, and C are constants of the physical properties of the sample, with B ranging from (-1, 1).
2. The test system for radial crack length of indentation based on acoustic emission according to claim 1, characterized in that, The signal acquisition module includes an acoustic emission sensor. The signal output terminal of the acoustic emission sensor is connected to the signal input terminal of a preamplifier. The signal is amplified by the output terminal of the preamplifier and input to the computer. The acoustic emission sensor converts the weak acoustic signal into an electrical signal to obtain the generation and morphological characteristics of the acoustic emission signal. The preamplifier of the signal acquisition module improves the signal-to-noise ratio, enhances the frequency response, and amplifies the weak electrical signal before transmitting it to the signal storage and display module. The signal storage and display module includes a data acquisition card and a computer. The signal receiving end of the data acquisition card is connected to the signal output end of the preamplifier, and then the received electrical signal is converted into a digital signal and transmitted to the computer memory through the computer interface. The acoustic emission signal acquired by the signal acquisition module is stored and displayed. The signal processing and analysis module processes the acoustic emission signals in the signal storage and display module: extracts specified acoustic emission characteristic signal parameters, including amplitude, peak frequency, and duration; uses cluster analysis to classify the signals into different categories; performs wavelet packet transformation, decomposition, reconstruction, and time-domain analysis on the signals of different categories to obtain the duration of the indentation radial crack length signal; and establishes a quantitative relationship between the acoustic emission signal characteristic parameters and the measured indentation radial crack length by combining the indentation radial crack length measured by scanning electron microscopy.
3. A test method for a test system based on acoustic emission to measure radial crack length indentation, as described in claim 1 or 2, characterized in that, The specific steps are as follows: Step 1: Before the experiment begins, a lead-breaking test is conducted. HB mechanical pencils with diameters of 0.3 / 0.5 / 0.7 mm and lead elongation of 2-3 mm are used. Each time a lead breaks, the angle between the lead and the surface of the specimen is 30-40°. The acoustic emission sensor is fixed in place using a clamp. The pencil tip is gradually rotated until the lead breaks. The emitted acoustic emission signal is collected, and the sensitivity of the acoustic emission sensor is detected by the obtained waveform. Step 2, Sample preparation: Polish the sample to be tested to 0.05~1μm; fix the sample to be tested on the sample stage of the indenter using the clamping device; apply coupling agent between the acoustic emission sensor and the sample to be tested; and apply mechanical force to make the two tightly bonded. Step 3: Set the parameters of the indenter. The indentation load range is 4.903-49.03N, the holding time is 5-20s, start the indenter to start the indentation test, and the distance between indentations should be at least 4mm. Each sample should be tested at least 10 times. Step 4: Set the acoustic emission instrument parameters: Set the sampling threshold value to reduce the influence of ambient noise. The sampling threshold value is ambient noise +5~+8dB; select preamplifier 20 / 40 / 60dB, sampling frequency 1~4MHz, Hit length 1~2k, frequency range 0.1~1MHz, and collect and store the acoustic emission signal characteristic parameters. Step 5: Extract acoustic emission feature parameters from the received acoustic emission signal, including amplitude, peak frequency, and duration; then classify the acoustic emission signal into different categories; perform wavelet packet transformation, decomposition, reconstruction, and time-domain analysis on the acoustic emission signals of different categories to obtain the duration of the indentation radial crack length signal; Step 6: Perform scanning electron microscopy on the sample after the indentation test in Step 3 to measure the radial crack length of the indentation; Step 7: Based on the results of Steps 5 and 6, establish a quantitative relationship between the acoustic emission signal characteristic parameter x, duration, and indentation radial crack length c through data fitting. ; Step 8: After obtaining the quantitative relationship between the acoustic emission signal characteristic parameters and the radial crack length of the indentation in Step 7, when performing indentation measurement, simply substitute the acoustic emission signal characteristic parameters obtained in Step 5 directly into the formula obtained in Step 7. The radial crack length of the indentation can be obtained by using the formula.
4. The testing method for the indentation radial crack length testing system based on acoustic emission according to claim 3, characterized in that, The coupling agent mentioned in step 2 includes vacuum grease, petroleum jelly, or butter.
5. The testing method for the indentation radial crack length testing system based on acoustic emission according to claim 3, characterized in that, In step 5, the acoustic emission signals are classified into different categories using cluster analysis methods, including k-means clustering.
6. The application of the acoustic emission-based indentation radial crack length testing system according to claim 1 or 2, characterized in that, The hardness H and indentation load P parameters obtained directly from the indenter and the indentation instrument By substituting the radial crack length c of the indentation and the material elastic modulus E obtained by the nanoindenter into the empirical formula, the fracture toughness of the material can be calculated.
7. The application of the acoustic emission-based indentation radial crack length testing system according to claim 6, characterized in that, The empirical formula is: .