Integrated fatigue small crack initiation in-situ monitoring device and detection method

Abstract

The invention discloses an integrated fatigue small crack initiation in-situ monitoring device and a detection method, and belongs to the technical field of material mechanical property testing. Comprising a fatigue test system, a digital image correlation test system and an acoustic emission test system, the fatigue test system is used for detecting the fatigue performance of a sample under loading force in situ and comprises a console and an in-situ fatigue testing machine, and two tensile fixtures are symmetrically arranged on the in-situ fatigue testing machine; the digital image correlation test system is used for in-situ detection of time and space trajectories of crack initiation and expansion under fatigue of a sample, and comprises a camera, a bracket and an image acquisition card; the acoustic emission test system is used for in-situ detection of an accumulation process of internal damage of a sample under fatigue, and comprises an acoustic emission sensor, a preamplifier and an acoustic emission acquisition card. By simultaneously capturing and recording the mechanical response, the optical image and the acoustic emission signal of the sample in the fatigue test period, real-time in-situ monitoring of multi-source information such as mechanical, optical and acoustic emission is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of material mechanical property testing, and in particular relates to an integrated in-situ monitoring device and a detection method for small fatigue crack initiation. Background Art

[0002] Fatigue refers to the phenomenon that materials gradually accumulate damage until they are finally destroyed under the action of alternating stress. Fatigue failure under cyclic load is one of the common damages faced by pressure vessels and other pressure-bearing equipment. It poses a great hidden danger to the safe service of pressure vessels and is a problem that has attracted much attention in the petroleum, chemical, electric power and other industries. The fatigue failure process of engineering materials includes different stages such as fatigue crack initiation, steady-state crack expansion, rapid expansion and fracture. Fatigue cracks usually refer to cracks with a physical size of less than 1 mm. According to statistics, the initiation and expansion process of fatigue cracks often accounts for 70% to 80% of the total fatigue life, or even more. Therefore, the development of accurate monitoring technology for the initiation of fatigue cracks will not only help to deeply understand the physical laws of the initiation and expansion of fatigue cracks, but also help to prevent the occurrence of fatigue crack expansion and fracture failure in a timely manner.

[0003] At present, the observation of small fatigue cracks is mainly to observe the initiation and expansion process of small fatigue cracks in materials and measure the size of small cracks through image observation methods such as scanning electron microscopes, optical microscopes or cameras. However, due to the small size of small cracks and the limitation of measurement accuracy of measurement methods, there are large errors in the observation and measurement of small cracks. As a structural health monitoring technology, acoustic emission technology has the advantages of real-time, continuous and high sensitivity in monitoring the expansion of microscopic dynamic defects. By analyzing the characteristics of acoustic emission signals obtained from fatigue experiments, such as amplitude, frequency, energy, etc., the deformation and damage degree of materials can be accurately identified, including the initiation and expansion of small fatigue cracks. However, a single acoustic emission technology cannot accurately and quantitatively describe the starting point of small cracks on the sample surface, the expansion path of small cracks, and other information, and it is difficult to explain the quantitative expansion behavior and mechanism of small fatigue cracks in different metal materials. Summary of the invention

[0004] In order to solve the problem that the existing single acoustic emission technology cannot accurately and quantitatively describe the starting point of small cracks on the sample surface, the expansion path of small cracks and other information, and it is difficult to explain the quantitative expansion behavior and mechanism of fatigue small cracks in different metal materials, the present invention provides an in-situ monitoring device and detection method for the initiation of fatigue small cracks that integrates images, mechanics, and acoustic emission. It can simultaneously capture and record the mechanical response, optical images, and acoustic emission signals of the material during fatigue testing, and realize real-time in-situ monitoring of multi-source information such as mechanics, optics, and acoustic emission.

[0005] The present invention solves the above technical problems through the following technical solutions.

[0006] In one aspect, the present invention provides an integrated in-situ monitoring device for small fatigue crack initiation, comprising:

[0007] Fatigue test system: used for in-situ monitoring of the mechanical fatigue properties of the sample under loading force, including: a control console and an in-situ fatigue tester, the control console and the in-situ fatigue tester are signal connected, two tensile clamps are symmetrically arranged on the in-situ fatigue tester, the two tensile clamps are used to clamp the sample, each tensile clamp is provided with a force sensor, and the two force sensors are axially symmetrically arranged.

[0008] Acoustic emission test system: used for in-situ monitoring of the accumulation process of internal damage of the sample under fatigue, including an acoustic emission sensor and an acoustic emission acquisition card. The acoustic emission sensor is arranged at the clamping section of the sample, and the acoustic emission sensor and the acoustic emission acquisition card are signal-connected.

[0009] Digital image correlation test system: used for in-situ monitoring of the time and space trajectory of crack initiation and expansion of a specimen under fatigue, including a camera and an image acquisition card. The camera is slidably set on the in-situ fatigue testing machine and is located directly in front of the specimen, and the image acquisition card is set on the camera.

[0010] Through the fatigue test system, digital image correlation test system and acoustic emission test system, the mechanical response, optical image and acoustic emission signal of the specimen during the fatigue test are captured and recorded simultaneously, realizing real-time in-situ monitoring of multi-source information such as mechanics, optics and acoustic emission.

[0011] Furthermore, in the above-mentioned integrated small fatigue crack initiation monitoring device, each of the stretching fixtures is provided with a guide rail, one end of the guide rail is connected to the inner wall of the in-situ fatigue testing machine, and the two guide rails are centrally symmetrically arranged to control the displacement position direction of the stretching fixture.

[0012] Furthermore, in the above-mentioned integrated small fatigue crack initiation monitoring device, a bracket is slidably provided on the in-situ fatigue testing machine, and the camera is slidably set on the bracket.

[0013] Furthermore, in the above-mentioned integrated small fatigue crack initiation monitoring device, the acoustic emission sensor signal is connected to a preamplifier, and the preamplifier is connected to the acoustic emission acquisition card signal; the gain of the preamplifier is 40dB.

[0014] Furthermore, in the above-mentioned integrated in-situ monitoring device for the initiation of small fatigue cracks, the diameter of the acoustic emission sensor is smaller than the width of the clamping section of the sample, the sensor resonant frequency is 300kHz, and the bandwidth range is 125kHz to 750kHz; the optical magnification of the camera 11 is 95X to 614X, the resolution is 3840×2160, and the measurement accuracy is 0.001mm to 0.002mm.

[0015] Furthermore, in the above-mentioned integrated small fatigue crack initiation in-situ monitoring device, the control console signal is connected to the first control system, the acoustic emission acquisition card signal is connected to the second control system, and the image acquisition card signal is connected to the third control system.

[0016] On the other hand, the present invention provides an integrated in-situ monitoring method for small fatigue crack initiation, which uses the above-mentioned in-situ monitoring device to perform integrated in-situ monitoring of small fatigue crack initiation, including the following steps:

[0017] After the sample is pre-treated, the two ends of the sample are clamped by the tensile fixture;

[0018] The acoustic emission sensor is fixed to the clamping section of the sample by using a coupling agent, and then the position of the camera is adjusted by sliding so that the camera is located directly in front of the sample to collect an image at the notch of the sample;

[0019] The in-situ fatigue testing machine is turned on, and after the loading force, loading waveform and loading frequency are adjusted by the console, the two stretching fixtures move in opposite directions to stretch the sample in-situ, and the signal of the loading force is collected by the force sensor, and the signal of the strain is collected by the guide rail, so as to monitor the fatigue performance of the sample under the loading force in real time;

[0020] The acoustic emission sensor and camera are turned on at the same time. The acoustic emission sensor obtains the acoustic emission signal generated by the initiation and expansion process of small fatigue cracks, which is then amplified by the preamplifier and transmitted to the acoustic emission acquisition card for signal storage, so as to monitor the accumulation process of internal damage of the in-situ test sample under fatigue in real time; the camera continuously collects surface images at the notch of the sample, which are then transmitted to the image acquisition card to detect the time and space trajectory of crack initiation and expansion of the sample under fatigue, so as to realize real-time in-situ monitoring of the sample in multi-source information such as mechanics, optics and acoustic emission.

[0021] Furthermore, the sample is a dumbbell-shaped plate structure, and there is a notch with a depth of 0.5 mm and a radius R of 0.2 mm on one side of the center of the gauge section of the sample, which serves as a crack initiation point.

[0022] Furthermore, the loading force of the in-situ fatigue testing machine is greater than 0 kN and less than or equal to 2 kN, the loading waveform includes a sine wave, a triangle wave and a rectangular wave, and the loading frequency ranges from 0.2 kN to 2 Hz.

[0023] Furthermore, the coupling agent is vacuum silicone grease or vaseline.

[0024] Furthermore, the sample was pretreated under the following conditions: sanded to 2000# with sandpaper and then polished.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The integrated in-situ monitoring device for the initiation of small fatigue cracks provided by the present invention comprises a fatigue test system, an acoustic emission test system and a digital image correlation test system. The clamping sections of the sample in the fatigue test system are respectively clamped on two stretching fixtures. When the stretching fixture is stretched, the in-situ fatigue tester is used to detect the fatigue performance of the sample under the loading force in-situ, the camera observes the small cracks on the surface of the sample, and the image acquisition card is set on the camera. The image acquisition card is used to collect the data observed by the camera, so that the macroscopic mechanical behavior of the material can be displayed through the mechanical system, the time and space trajectory of the initiation and expansion of small cracks on the surface can be described through the optical system, and the accumulation process of the internal damage of the material can be revealed through the acoustic emission system. The mechanical response, optical image and acoustic emission signal of the material during the fatigue test can be captured and recorded at the same time, so as to realize the real-time in-situ monitoring of multi-source information such as mechanics, optics and acoustic emission. And then through the comprehensive analysis of multi-source data, it is helpful to systematically analyze the inherent laws of the initiation and expansion process of small fatigue cracks in the material. The device has a simple structure and is easy to operate. It can adapt to a variety of loading conditions and provide high-definition and sharp images, as well as high-fidelity acoustic emission signals. It can be widely used in the initiation and propagation behaviors and mechanisms of small fatigue cracks in different metal materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of the integrated in-situ monitoring device for initiation of small fatigue cracks of the present invention.

[0028] Figure 2 It is a schematic diagram of the structure of the sample in the integrated in-situ monitoring device for small fatigue crack initiation of the present invention.

[0029] Figure 3 The structural schematic diagram of the tensile fixture of the present invention is 。

[0030] Description of reference numerals:

[0031] 1. Control console, 2. In-situ fatigue testing machine, 3. Force sensor, 4. Tensile fixture, 5. Specimen, 6. Dual-axis slide rail, 7. Acoustic emission sensor, 8. Preamplifier, 9. Acoustic emission acquisition card, 10. Second computer, 11. First computer, 12. Camera, 13. Bracket, 14. Image acquisition card.

[0032] Figure 4 This is a graph showing the variation of the loading force of the steel sample 316 with time in the application example of the present invention.

[0033] Figure 5 This is a graph showing the strain variation of steel sample 316 in the application example of the present invention over time.

[0034] Figure 6This is a graph showing the time variation of the acoustic emission amplitude of the 316 steel sample in the application example of the present invention.

[0035] Figure 7 This is a diagram of crack initiation and growth under fatigue of 316 steel specimen in the application example of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0037] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The existing single acoustic emission technology cannot accurately and quantitatively describe the starting point of small cracks on the sample surface, the development trend of small cracks and other information. Therefore, the acoustic emission monitoring technology and image observation technology are combined to simultaneously monitor the initiation and propagation of small fatigue cracks, and synchronously obtain multi-source information such as optical (image), mechanical and acoustic signals to achieve complementary advantages. Through comprehensive analysis of these multi-source data, it is useful to study the initiation and propagation mechanism of small fatigue cracks in materials and prevent the occurrence of fatigue fracture failure of materials.

[0039] Based on this, the present invention provides an integrated in-situ monitoring device for the initiation of small fatigue cracks, including: a fatigue test system: used for in-situ detection of fatigue performance of a sample under a loading force, including: a control console 1 and an in-situ fatigue tester 2, wherein the control console 1 and the in-situ fatigue tester 2 are signal-connected, and two tensile clamps 4 are symmetrically arranged on the in-situ fatigue tester 2, and the two tensile clamps 4 are used to clamp a sample 5, wherein each of the tensile clamps 4 is provided with a force sensor 3, and the two force sensors 3 are axially symmetrically arranged; an acoustic emission test system: used for in-situ detection of internal damage of a sample under fatigue The accumulation process includes an acoustic emission sensor 7 and an acoustic emission acquisition card 9, wherein the acoustic emission sensor 7 is arranged at the clamping section of the sample 5, and the acoustic emission sensor 7 and the acoustic emission acquisition card 9 are connected by signal, and the acoustic emission acquisition card 9 is used to collect the acoustic emission signal transmitted after amplification; a digital image correlation test system: used for in-situ detection of the time and space trajectory of crack initiation and expansion of the sample under fatigue, including a camera 12 and an image acquisition card 14, wherein the camera 12 is slidably arranged on the in-situ fatigue testing machine 2 and directly in front of the sample 5, and the image acquisition card 14 is arranged on one end of the camera 12 away from the sample 5. Through the fatigue test system, the digital image correlation test system and the acoustic emission test system, the real-time in-situ monitoring of the mechanical response, optical image and acoustic emission information of the sample 5 during the fatigue test is realized.

[0040] The integrated in-situ monitoring device for the initiation of small fatigue cracks provided by the present invention comprises a fatigue test system, an acoustic emission test system and a digital image correlation test system. The clamping sections of the sample 5 are respectively clamped on two stretching clamps 4. When the stretching clamps 4 are stretched, the in-situ fatigue testing machine 2 is used to in-situ detect the fatigue performance of the sample under loading force. The camera 12 observes small cracks on the surface of the sample 5. The image acquisition card 14 is arranged on the camera 12. The image acquisition card 14 is used to collect data observed by the camera 12. Through the fatigue test system, the digital image correlation test system and the acoustic emission test system, the mechanical response, optical image and acoustic emission signal of the sample 5 during the fatigue test are captured and recorded at the same time, so as to realize real-time in-situ monitoring of multi-source information such as mechanics, optics and acoustic emission.

[0041] The present invention can display the macroscopic mechanical behavior of the material through the mechanical system, describe the time and space trajectory of the initiation and expansion of small cracks on the surface through the optical system, and reveal the accumulation process of internal damage of the material through the acoustic emission system, so as to obtain the macroscopic mechanical behavior of the material, the time and space trajectory of the initiation and expansion of small cracks on the surface, and the acoustic emission information of the development process of small fatigue cracks in the material, thereby realizing the in-situ coordinated monitoring of multi-source information such as optical (image), mechanical and acoustic signals. Through the comprehensive analysis of multi-source data, it is helpful to systematically analyze the inherent laws of the initiation and expansion process of small fatigue cracks in the material. The device has a simple structure and is easy to operate. It can adapt to various loading conditions, and provides high-definition and sharp images, and provides high-fidelity acoustic emission signals. It can be widely used in the initiation and expansion behavior and mechanism of small fatigue cracks in different metal materials.

[0042] The invention is further described below through specific examples.

[0043] An integrated in-situ monitoring device for the initiation of small fatigue cracks, comprising a fatigue test system, a digital image correlation test system and an acoustic emission test system; the fatigue test system is used for in-situ detection of fatigue performance of a sample under loading force, and the fatigue test system comprises: a control console 1 and an in-situ fatigue test machine 2, the control console 1 and the in-situ fatigue test machine 2 are signal-connected, two tensile clamps 4 are symmetrically arranged on the in-situ fatigue test machine 2, the two tensile clamps 4 are used to clamp a sample 5, each of the tensile clamps 4 is provided with a force sensor 3, the two force sensors 3 are axially symmetrically arranged, and the force sensor 3 collects the signal of the corresponding tensile clamp 4 loading force; the acoustic emission test system is used for in-situ detection of the accumulation process of internal damage of the sample under fatigue, and the acoustic emission test system comprises an acoustic emission sensor 7 and an acoustic emission acquisition card 9, the The acoustic emission sensor 7 is arranged at the clamping section of the sample 5, and the acoustic emission sensor 7 is signal-connected to the acoustic emission acquisition card 9; the digital image correlation test system is used for in-situ detection of the time and space trajectory of crack initiation and expansion of the sample under fatigue, and the digital image correlation test system includes a camera 12, a bracket 13 and an image acquisition card 14, the camera 12 is slidably arranged on the in-situ fatigue testing machine 2 and is located directly in front of the sample 5, the camera 12 is fixed in front of the sample 5 through the bracket 13, and the image acquisition card 14 is arranged on the camera 12; through the fatigue test system, the digital image correlation test system and the acoustic emission test system, the mechanical response, optical image and acoustic emission signal of the sample 5 during the fatigue test are captured and recorded at the same time, so as to realize the real-time in-situ monitoring of multi-source information such as mechanics, optics and acoustic emission.

[0044] In the present invention, the console 1 is a GTC650 fully digital closed-loop console, which drives the ball screw to operate through a fully digital AC servo motor and driver, thereby controlling the movement of the tensile fixture on the beam, the in-situ fatigue testing machine 2 is a WD2 in-situ fatigue testing machine, the force sensor 3 is a Shiquan 2000N load sensor, the guide rail 6 is a BRH15B guide rail, and the acoustic emission sensor 7 is a Nano 30 miniature broadband sensor, preamplifier 8 is 2 / 4 / 6 preamplifier, acoustic emission acquisition card 9 is PCI-8 acquisition card, camera 12 is GP-300 high-definition CCD camera, in the present invention, the console 1 and the in-situ fatigue testing machine 2 are connected by wire signals, the console 1 is connected to the first control system by wire signals, the acoustic emission acquisition card 9 is connected to the second control system by wire signals, the image acquisition card 14 is connected to the third control system by wire signals, the first control system and the third control system are both arranged in the first computer 11, the first computer 11 records the data of the loading force changing with time and analyzes it, and monitors the fatigue performance of the sample under the loading force in real time; and the first computer 11 analyzes and processes the information collected by the image acquisition card 14, so as to detect cracks under fatigue of the sample. The time and space trajectory of initiation and expansion; the second control system is arranged in the second computer 10, and the information collected by the acoustic emission acquisition card 9 is analyzed and processed by the second computer 10, so as to monitor the accumulation process of internal damage of the in-situ test sample under fatigue in real time; the clamping sections of the sample 5 are clamped on the two stretching clamps 4 respectively, when the stretching clamps 4 are stretched, the in-situ fatigue testing machine 2 is used to in-situ detect the fatigue performance of the sample under loading force, the camera 12 observes the small cracks on the surface of the specimen 5, and the image acquisition card 14 is arranged on the camera 12, and the image acquisition card 14 is used to collect the data observed by the camera 12, and the mechanical response, optical image and acoustic emission signal of the material during the fatigue test can be captured and recorded by the second computer 10 and the first computer 11, so as to realize the real-time in-situ monitoring of multi-source information such as mechanics, optics and acoustic emission.

[0045] Two tensile fixtures 4 are symmetrically arranged on the upper part of the in-situ fatigue testing machine 2. Figure 3 As shown, each stretching fixture 4 is provided with a U-shaped groove, and the sample 5 is divided into two clamping sections and a gauge section. The gauge section is located between the two clamping sections, and both ends of the sample 5 are clamped in a corresponding U-shaped groove respectively. The gauge section of the sample 5 is left between the two stretching fixtures 4. When the in-situ fatigue testing machine 2 controls the stretching fixture 4 to perform reverse stretching, a fatigue fracture test is performed on the crack initiation point in the center of the gauge section of the sample 5. The mechanical response, optical image and acoustic emission signal of the sample 5 during the fatigue test are captured and recorded by the fatigue test system, the digital image correlation test system and the acoustic emission test system, so as to realize real-time in-situ monitoring of multi-source information such as mechanics, optics and acoustic emission.

[0046] In a specific embodiment, each of the stretching fixtures 4 is provided with a guide rail 6, one end of which is connected to the inner wall of the in-situ fatigue testing machine 2, and the two guide rails 6 are centrally symmetrically arranged to control the displacement position direction of the stretching fixture 4. Each stretching fixture 4 moves with the position of the guide rail 6, and the guide rail 6 can accurately control the displacement, increase the test efficiency, and accurately collect strain data.

[0047] In a specific embodiment, the in-situ fatigue test machine 2 is slidably provided with a bracket 13, and the camera 12 is slidably provided on the bracket 13. The bracket 13 is slidably provided on the in-situ fatigue test machine 2, and can be moved left and right, and after sliding to a corresponding position, it can be fixed by a fixer, and the camera 12 is fixed to the bracket 13 by a connecting rod and a sliding sleeve rod, the sliding sleeve rod is slidably provided on the bracket 13, and the two ends of the connecting rod are respectively fixed to the sliding sleeve rod and the camera 12, and the position of the camera 12 can be moved up and down by the sliding sleeve rod, and the sliding sleeve rod is fixed to the bracket 13 by rotating bolts.

[0048] In a specific embodiment, the acoustic emission sensor 7 is connected to a preamplifier 8, and the preamplifier 8 is connected to an acoustic emission acquisition card 9. After being amplified by the preamplifier 8, the signal is transmitted to the acoustic emission acquisition card 8 for signal storage, and the gain of the preamplifier 8 is 40dB. The acoustic emission sensor 7 is connected to the preamplifier 8 through a wire signal; the gain of the preamplifier 8 is set to 40dB, the purpose of which is to significantly improve the strength of the acoustic emission signal while ensuring that the signal has a high quality.

[0049] The acoustic emission sensor 7 is a miniature broadband sensor, the diameter of which is smaller than the width of the clamping section of the sample 5, the sensor resonant frequency is 300kHz, and the bandwidth range is 125kHz to 750kHz. The diameter of the acoustic emission sensor 7 is smaller than the width of the sample clamping section, in order to enable the sensor surface to be fully coupled with the sample to ensure the transmission effect of the acoustic emission signal. The type of acoustic emission sensor is required to be a broadband sensor, which has a higher sensitivity over a wider frequency range. The sensor parameters adopted in the embodiment are a resonant frequency of 300kHz and a bandwidth range of 125kHz to 750kHz. The advantage of this sensor is that it has a higher sensitivity over a bandwidth range of 125kHz to 750kHz, and can ensure the authenticity of the signal as much as possible.

[0050] In a specific embodiment, the camera 12 is a high-definition measuring tool microscope with an optical magnification of 95X to 614X, a resolution of 3840×2160, and a measurement accuracy of 0.001 mm to 0.002 mm, which can ensure high-precision observation of small fatigue cracks.

[0051] In a specific embodiment, the sample 5 is a dumbbell-shaped plate structure, and a notch with a depth of 0.5 mm and a radius R of 0.2 mm is provided on one side of the center of the gauge section of the sample 5, which serves as a crack initiation point.

[0052] The integrated in-situ monitoring method for small fatigue crack initiation using the above device comprises the following steps:

[0053] Step 1, grinding the sample 5 to 2000# with sandpaper and performing polishing treatment, then clamping the two ends of the sample 5 with the tensile fixture 4, and recording and analyzing the data of the loading force changing with time with the first computer 11;

[0054] Step 2, using a coupling agent such as vacuum silicone grease or vaseline to fix the acoustic emission sensor 7 to the clamping section of the sample 5, and then adjusting the position of the camera 12 through the bracket 13 so that the camera 12 is located directly in front of the sample 5 to collect an image of the notch of the sample 5;

[0055] Step 3, start the in-situ fatigue testing machine 2, adjust the loading force, loading waveform and loading frequency by using the control console 1, collect the signal of the loading force by the force sensor 3, collect the signal of the strain by the guide rail 6, and the first computer 10 records and analyzes the data of the loading force and strain changing with time, so as to monitor the fatigue performance of the sample under the loading force in real time;

[0056] Step 4, turn on the acoustic emission sensor 7 and the camera 12 at the same time, the acoustic emission sensor 7 obtains the acoustic emission signal generated by the initiation and expansion process of the fatigue small crack, and then transmits it to the acoustic emission acquisition card 9 for signal storage after amplification by the preamplifier 8, and analyzes and processes the information collected by the acoustic emission acquisition card 9 through the second computer 10, and monitors the accumulation process of internal damage of the in-situ detection sample under fatigue in real time; the camera 12 continuously collects the surface image of the notch of the sample 5, and then transmits it to the image acquisition card 14, and analyzes and processes the information collected by the image acquisition card 14 through the first computer 11, which is used to detect the time and space trajectory of crack initiation and expansion under fatigue of the sample, and realizes the real-time in-situ monitoring of the sample 5 in multi-source information such as mechanics, optics and acoustic emission. Through the above method, the macroscopic mechanical behavior of the material, the time and space trajectory of the initiation and expansion of small cracks on the surface, and the acoustic emission information of the development process of the fatigue small crack of the material are obtained, thereby realizing the in-situ coordinated monitoring of multi-source information such as optical (image), mechanics and acoustic signals.

[0057] The present invention takes 316 steel specimens as the object, and tests the mechanical response, optical image and acoustic emission signal during the fatigue test through the above-mentioned integrated fatigue small crack initiation in-situ monitoring, thereby realizing real-time in-situ monitoring of multi-source information such as mechanics, optics and acoustic emission.

[0058] Application Example 1

[0059] The integrated fatigue small crack initiation in-situ monitoring experiment of 316 steel specimens was carried out at room temperature. A load of 400-800N was applied, and a sinusoidal loading method was used. At the same time, an acoustic emission broadband sensor was used to record the acoustic emission signals during the crack initiation and expansion process of the specimen under fatigue. The acquired acoustic emission signal data was imported into the computer and the acoustic emission characteristic parameters were extracted. At the same time, the surface image of the specimen notch was continuously collected by the camera to realize the real-time in-situ monitoring of the specimen in multi-source information such as mechanics, optics and acoustic emission.

[0060] The specific steps are as follows:

[0061] Step 1: The sample 5 is sanded to 2000# with sandpaper and polished, and then the two ends of the sample 5 are clamped by the tensile fixture 4, and the data of the loading force changing with time is recorded and analyzed by the first computer 11.

[0062] Step 2: Use a coupling agent such as vacuum silicone grease or vaseline to fix the acoustic emission sensor 7 to the clamping section of the sample 5, and then adjust the position of the camera 12 through the bracket 13 so that the camera 12 is located directly in front of the sample 5 to collect images of the notch of the sample 5.

[0063] Step 3: Turn on the in-situ fatigue testing machine 2, set the loading force to 400-800N, the loading waveform to a sine wave, and the loading frequency to 0.5Hz by using the console 1, collect the loading force signal through the force sensor 3, collect the strain signal through the guide rail 6, and the first computer 10 records and analyzes the data of the loading force and strain changes over time. The data of the loading force and strain changes over time are respectively as follows: Figure 4 and Figure 5 As shown, the fatigue performance of the specimen under loading force is monitored in real time.

[0064] Step 4: Turn on the acoustic emission sensor 7 and the camera 12 at the same time. The acoustic emission sensor 7 obtains the acoustic emission signal generated by the initiation and expansion process of the fatigue small crack, and then transmits it to the acoustic emission acquisition card 9 for signal storage after amplification by the preamplifier 8. The information collected by the acoustic emission acquisition card 9 is analyzed and processed by the second computer 10. The data of the acoustic emission amplitude changing with the test piece is as follows: Figure 6 As shown, the accumulation process of internal damage of the in-situ detection sample under fatigue is monitored in real time; the camera 12 continuously collects the surface image acquisition card 14 at the notch of the sample 5, and the information collected by the image acquisition card 14 is analyzed and processed by the first computer 11. The image of crack initiation and expansion under fatigue of the sample is as shown in FIG. Figure 7 As shown, it is used to detect the time and space trajectory of crack initiation and propagation of the sample under fatigue, and realize real-time in-situ monitoring of sample 5 in multiple sources such as mechanics, optics and acoustic emission.

[0065] The above method is used to obtain the macroscopic mechanical behavior of 316 steel, the temporal and spatial trajectories of the initiation and expansion of small cracks on the surface, and the acoustic emission information of the development process of small fatigue cracks in the material, thereby realizing in-situ coordinated monitoring of multi-source information such as optical (image), mechanical and acoustic signals.

[0066] It should be noted that the component connection relationships not specifically mentioned in the present invention are assumed to adopt the existing technology. Since they do not involve the invention point and are widely used in the existing technology, the structural connection relationships are not described in detail.

[0067] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0068] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. An integrated in-situ monitoring device for small fatigue crack initiation, characterized in that: include: A fatigue test system: used for in-situ monitoring of the mechanical fatigue properties of a sample, comprising: a control console (1) and an in-situ fatigue test machine (2), wherein the control console (1) and the in-situ fatigue test machine (2) are signal-connected, and two tensile clamps (4) are symmetrically arranged on the in-situ fatigue test machine (2), wherein the two tensile clamps (4) are used for clamping a sample (5), and each of the tensile clamps (4) is provided with a force sensor (3); An acoustic emission test system: used for in-situ monitoring of the accumulation process of internal damage of a specimen under fatigue, comprising an acoustic emission sensor (7) and an acoustic emission acquisition card (9), wherein the acoustic emission sensor (7) is arranged at the clamping section of the specimen (5), and the acoustic emission sensor (7) and the acoustic emission acquisition card (9) are signal-connected; A digital image correlation test system: used for in-situ monitoring of the time-space trajectory of crack initiation and expansion of a specimen under fatigue, comprising a camera (12) and an image acquisition card (14), wherein the camera (12) is slidably arranged on an in-situ fatigue testing machine (2) and is located directly in front of the specimen (5), and the image acquisition card (14) is arranged on an end of the camera (12) away from the specimen (5); The fatigue test system, the digital image correlation test system and the acoustic emission test system are used to achieve real-time in-situ monitoring of the mechanical response, optical image and acoustic emission information of the sample (5) during the fatigue test.

2. The integrated in-situ monitoring device for small fatigue crack initiation according to claim 1 is characterized in that: Each of the stretching clamps (4) is provided with a guide rail (6), one end of which is connected to the inner wall of the in-situ fatigue testing machine (2), and the two guide rails (6) are arranged in a centrally symmetrical manner and are used to control the stretching clamp (4) to obtain a displacement position direction.

3. The integrated in-situ monitoring device for small fatigue crack initiation according to claim 1 is characterized in that: A bracket (13) is slidably provided on the in-situ fatigue testing machine (2), and the camera (12) is slidably arranged on the bracket (13).

4. The integrated in-situ monitoring device for small fatigue crack initiation according to claim 1 is characterized in that: The acoustic emission sensor (7) is signal-connected to a preamplifier (8), and the preamplifier (8) is signal-connected to an acoustic emission acquisition card (9); the gain of the preamplifier (8) is 40 dB.

5. The integrated in-situ monitoring device for small fatigue crack initiation according to claim 1 is characterized in that: The diameter of the acoustic emission sensor (7) is smaller than the width of the clamping section of the sample (5), the sensor resonant frequency is 300kHz, and the bandwidth range is 125kHz to 750kHz; the optical magnification of the camera (12) is 95X to 614X, the resolution is 3840×2160, and the measurement accuracy is 0.001mm to 0.002mm.

6. The integrated in-situ monitoring device for small fatigue crack initiation according to claim 1 is characterized in that: The console (1) is signal-connected to a first control system, the acoustic emission acquisition card (9) is signal-connected to a second control system, and the image acquisition card (14) is signal-connected to a third control system.

7. An integrated in-situ monitoring method for small fatigue crack initiation, characterized in that: Using the in-situ monitoring device according to any one of claims 1 to 6 to perform integrated in-situ monitoring of small fatigue crack initiation comprises the following steps: After pre-treating the sample (5), clamping the two ends of the sample (5) by two stretching clamps (4); The acoustic emission sensor (7) is fixed to the clamping section of the sample (5) by using a coupling agent, and then the position of the camera (12) is adjusted by sliding so that the camera (12) is located directly in front of the sample (5) to collect an image of the notch of the sample (5); The in-situ fatigue testing machine (2) is turned on, and after the loading force, loading waveform and loading frequency are adjusted using the control console (1), the two stretching clamps (4) move in opposite directions to stretch the sample (5) in-situ, and the signal of the loading force is collected by the force sensor (3), so as to monitor the fatigue performance of the sample (5) under the loading force in real time; The acoustic emission sensor (7) and the camera (12) are turned on at the same time. The acoustic emission sensor (7) obtains the acoustic emission signal generated by the initiation and expansion process of the fatigue small crack, and then transmits it to the acoustic emission acquisition card (9) for signal storage after amplification, so as to monitor the accumulation process of internal damage of the in-situ test sample under fatigue in real time; the camera (12) continuously collects the surface image of the notch of the sample (5), and then transmits it to the image acquisition card (14) for detecting the time and space trajectory of the crack initiation and expansion of the sample under fatigue, so as to realize the real-time in-situ monitoring of the sample (5) in terms of multiple sources of information such as mechanics, optics and acoustic emission.

8. The integrated in-situ monitoring method for small fatigue crack initiation according to claim 7, characterized in that: The sample (5) is a dumbbell-shaped plate structure, and a notch with a depth of 0.5 mm and a radius R of 0.2 mm is provided on one side of the center of the gauge section of the sample (5), serving as a crack initiation point.

9. The integrated in-situ monitoring method for small fatigue crack initiation according to claim 7, characterized in that: The loading force of the in-situ fatigue testing machine (2) is greater than 0 kN and less than or equal to 2 kN, the loading waveform includes a sine wave, a triangle wave and a rectangular wave, and the loading frequency ranges from 0.2 Hz to 2 Hz.

10. The integrated in-situ monitoring method for small fatigue crack initiation according to claim 7, characterized in that: The coupling agent is vacuum silicone grease or vaseline.

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