Multi-scale in-situ monitoring device for material crack propagation and test method thereof

Abstract

The application relates to the technical field of mechanical testing devices, and particularly discloses a multi-scale in-situ monitoring device applied to material crack propagation and a testing method thereof. The device comprises a DCPD testing part, a DIC testing part and an electric control cabinet; the DCPD testing part comprises a fixed frame, a room temperature clamping device, a force loading system and a data acquisition system; and the DIC testing part comprises a DIC camera. Through the cooperation of the DCPD and the DIC, real-time monitoring of a macroscopic crack propagation rate and in-situ analysis of a microscopic crack tip stress and strain field distribution are realized, so that cross-scale material damage evolution information is obtained. The device has the advantages of computer full-digital control, high measurement precision, multi-dimensional synchronous data acquisition and the like, and is particularly suitable for high-precision, multi-scale material damage detection and failure mechanism research in an air environment.

Description

Technical Field

[0001] This invention relates to the field of mechanical testing equipment, and in particular to a multi-scale in-situ monitoring device and testing method for material crack propagation. Background Technology

[0002] Effective detection of crack damage in materials is of paramount engineering and scientific significance. Cracks are one of the main forms of material and structural failure. In aerospace, energy, and power industries, structural components often operate under complex loads and harsh environments for extended periods. Therefore, developing high-precision crack detection technology is a core element in achieving structural health diagnosis, preventing sudden damage, and ensuring the safety of life and property. From a materials research and development perspective, a deep understanding of the microscopic mechanisms of crack propagation is inseparable from in-situ, precise experimental data. Microscopic information such as the strain field distribution at the crack tip and the evolution of the plastic zone is crucial for revealing material fracture mechanisms, evaluating material properties, and guiding the design of novel fatigue-resistant and high-toughness materials.

[0003] DC voltage drop (DCPD) is an advanced detection technique that reflects crack propagation behavior in materials by monitoring voltage changes. This technique is based on applying a constant direct current to a sample and accurately measuring the voltage drop between preset locations to invert the crack length and calculate the crack growth rate (CGR) in real time. Compared to other damage detection methods, DCPD technology possesses excellent accuracy and repeatability, and exhibits good stability even under complex environments such as high temperatures and corrosion. Therefore, it is widely considered one of the mainstream techniques for quantitative characterization and life assessment of material damage in the future.

[0004] Digital image correlation (DIC) is a non-contact optical measurement method based on high-resolution image processing and digital algorithms. It achieves precise quantification of the deformation and strain fields on a material surface at the microscale (from millimeters to nanometers) by tracking changes in the speckle field before and after deformation. This technique has been widely applied to the study of the microscopic mechanisms of material surface damage behavior, revealing the local strain concentration and evolution during crack initiation, propagation, and fracture, providing crucial experimental evidence for understanding material failure mechanisms.

[0005] By combining DCPD and DIC technologies, real-time monitoring of crack propagation rate on a macroscopic scale can be achieved, while capturing strain distribution and evolution behavior in the crack tip region on a microscopic scale. This establishes a cross-scale correlation of material damage evolution, providing a powerful experimental means for in-depth research on the damage mechanism of materials under complex loading environments.

[0006] There are some limitations in the existing technology. For example, Chinese patent publication number CN115046872A discloses a real-time fatigue crack measurement method based on DCPD, but the obtained data is concentrated on the macroscopic crack propagation rate and lacks the capture of microscopic mechanical information such as the microscopic plastic zone at the crack tip and the strain field distribution. Chinese patent application publication number CN105842062A discloses a real-time crack propagation monitoring device and method, but relying solely on the strain information of the micro-region where the local crack is located cannot represent the failure trend of the main crack, and therefore cannot assess and predict its macroscopic crack propagation rate.

[0007] Therefore, there is a need for a monitoring device and its testing method that can simultaneously acquire macroscopic and microscopic crack propagation information. Summary of the Invention

[0008] The purpose of this invention is to provide a multi-scale in-situ monitoring device and its testing method for material crack propagation, so as to solve the problems existing in the prior art.

[0009] To achieve the above objectives, the present invention provides a multi-scale in-situ monitoring device for material crack propagation, comprising:

[0010] DCPD test section, the DCPD test section includes a fixed frame, a room temperature clamping device, a force loading system and a data acquisition system;

[0011] DIC testing unit, the DIC testing unit including DIC camera;

[0012] An electrical control cabinet, which is electrically connected to the force loading system, the data acquisition system and the DIC camera respectively;

[0013] The fixed frame has an observation window on its side, through which the DIC camera collects the strain of the sample held by the room temperature clamping device.

[0014] The room temperature clamping device includes a sample clamp, an insulating ceramic gasket, and an insulating ceramic tube. The sample clamp is mounted on the fixed frame, and the insulating ceramic gasket and the insulating ceramic tube are used to isolate the current between the sample and the sample clamp.

[0015] The force loading system includes a tensile machine and a tensile machine controller. The tensile machine is electrically connected to the tensile machine controller and is drivenly connected to the room temperature clamping device.

[0016] The data acquisition system includes a current line, a main voltage drop line, a reference voltage drop line, a constant current source, and a nanovoltmeter. The sample is connected to the constant current source through the current line, and the sample is connected to different nanovoltmeters through the main voltage drop line and the reference voltage drop line, respectively. The main voltage drop line is distributed on both sides of the crack in the sample.

[0017] Preferably, the fixed frame includes an upper surface, a lower surface, and four fixed support columns disposed between the upper surface and the lower surface. A fixing bolt extends from the center of the lower surface, and the sample clamp is connected to the stretching machine through the fixing bolt.

[0018] Preferably, the room temperature clamping device includes a detachable room temperature upper clamp and a room temperature lower clamp. Both the room temperature upper clamp and the room temperature lower clamp are provided with a first fastening bolt and nut and a second fastening bolt and nut. The room temperature upper clamp and the room temperature lower clamp adjust the verticality and tightness of the sample by means of the first fastening bolt and nut and the second fastening bolt and nut.

[0019] Preferably, the upper surface of the fixed frame is provided with bolts and nuts, the room temperature upper clamp is connected to the upper surface of the fixed frame through the bolts and nuts, and the room temperature lower clamp is connected to the tensioning machine through the fixing bolts, so that the room temperature lower clamp can move up and down to apply load.

[0020] Preferably, the current line, the main voltage drop line, and the reference voltage drop line in the data acquisition system all include platinum wire and an insulating PTFE heat shrink tubing wrapped around the platinum wire.

[0021] Preferably, the constant current source is used to provide a stable current output, the nanovoltmeter is used to measure the current and voltage drop in each wire, and the reference voltage drop line is used to correct the main voltage drop to improve test accuracy.

[0022] Preferably, the force loading system is connected to a computer via the electrical control cabinet, and the computer's control program controls the parameters of the force loading system, including constant stress intensity factor, load ratio, wave frequency, and waveform.

[0023] This invention provides a test method for a multi-scale in-situ monitoring device for material crack propagation, employing the aforementioned multi-scale in-situ monitoring device for material crack propagation, comprising the following steps:

[0024] Step 1: Place the DIC camera to the side of the DCPD test section and collect the strain of the sample through the observation window;

[0025] Step 2, prepare the sample, including sanding the sample surface with sandpaper and mechanically polishing it until there are no obvious scratches, then performing electrolytic polishing or vibratory polishing to eliminate the stress layer, and spraying speckle on the side of the sample.

[0026] Step 3: Clamp the sample with the room temperature upper clamp and the room temperature lower clamp. Use the first and second fastening bolts and nuts to adjust the verticality of the sample. Use an insulating ceramic tube to isolate the sample from the clamp. Adjust the length and verticality of the sample clamp. Then use bolts and nuts to connect the room temperature upper clamp to the upper surface of the fixed frame. Use fixing bolts to connect the room temperature lower clamp to the tensile machine.

[0027] Step 4: Weld a pair of current lines, a pair of main voltage drop lines, and a pair of reference voltage drop lines to the sample. The current lines are connected to the upper and lower surfaces of the sample, the main voltage drop lines are connected to both sides of the sample opening, and the reference voltage drop lines are connected to the opposite surfaces of the sample opening.

[0028] Step 5: Turn on the force holding function of the electrical control cabinet and set it to ON, then fully tighten the room temperature upper clamp and the room temperature lower clamp.

[0029] Step 6: Set the required constant stress intensity factor, load ratio, wave frequency and waveform in the control program. Set the protection parameters to avoid damage to the equipment and sample due to excessive load or displacement. Then, apply current and determine whether the voltage drop error is within the allowable range. If it is within the allowable range, the test can begin. Otherwise, the insulation condition and welding quality need to be re-evaluated.

[0030] Step 7: Adjust the brightness and focal length of the DIC camera to achieve the clearest speckle pattern. Set the pixels for DIC acquisition and calculation. The camera first captures the speckle morphology of the ROI on the sample surface as a reference image. Then, a load is applied, the fatigue crack propagation rate is collected, and speckle images at the same location are captured again at intervals. By measuring the displacement changes of the speckle on the sample surface before and after applying the load, the stress and strain field distribution data of the sample surface are calculated using a computer program.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] 1. This invention combines DCPD and DIC technologies, dividing the host into a DCPD test section and a DIC test section. In actual operation, it can obtain both macroscopic crack propagation rate and microscopic stress-strain field distribution at the crack tip, thus obtaining richer multi-scale sample cracking information. This helps researchers to study and analyze the failure mechanism of the sample and is more suitable for scenarios in air environment where high precision of material damage detection and acquisition of multi-scale information are required.

[0033] 2. The DCPD technology used in this invention enables the control of parameters such as the magnitude of the load and the rate of load change using computer software. The sample is fixedly connected to the room temperature clamping device using bolts and nuts, and then both are connected to the fixed frame using bolts and nuts. Next, the current line, main voltage drop line, and reference voltage line are welded to the sample. Finally, the sample's length, width, thickness, the magnitude of the load required for the test, waveform frequency, and other parameters are input into the software to start the test. This computer control reduces the difficulty of operation and improves the accuracy of the test.

[0034] 3. This invention uses a DIC camera to measure the strain of the sample instead of using displacement change to calculate the strain. It is not affected by fixtures and frames, and DIC can obtain more accurate strain, thereby greatly improving the accuracy of the test. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the overall structure of the testing machine of the present invention;

[0037] Figure 2 This is a schematic diagram of the internal structure of the fixed frame of the present invention;

[0038] Figure 3 This is an exploded schematic diagram of the room temperature clamping device of the present invention;

[0039] In the diagram: 1. Fixed frame; 2. Room temperature clamping device; 3. Tensile machine; 4. Tensile machine controller; 5. DIC camera; 6. Electrical control cabinet; 7. Insulating ceramic gasket; 8. Insulating ceramic tube; 9. Sample; 10. Current line; 11. Main voltage drop line; 12. Reference voltage drop line; 13. Nanovoltmeter; 14. Bolt and nut; 15. Fixing bolt; 16. Room temperature upper clamp; 17. Room temperature lower clamp; 18. First fastening bolt and nut; 19. Second fastening bolt and nut; 20. Constant current source. Detailed Implementation

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] Example 1

[0042] like Figures 1 to 3 As shown, this invention provides a multi-scale in-situ monitoring device for material crack propagation, comprising a DCPD testing unit, a DIC testing unit, and an electrical control cabinet 6. The DCPD testing unit includes a fixed frame 1, a room temperature clamping device 2, a force loading system, and a data acquisition system. The DIC testing unit includes a DIC camera 5. The electrical control cabinet 6 is electrically connected to the force loading system, the data acquisition system, and the DIC camera 5.

[0043] The fixed frame 1 includes an upper surface, four fixed support columns, and a metal frame that fixes the lower surface. A fixing bolt 15, connected to the tensile machine 3, extends from the center of the lower surface. An observation window is provided on the side of the fixed frame 1, through which the DIC camera 5 collects the strain of the sample 9 held by the room temperature clamping device 2.

[0044] The room temperature clamping device 2 includes a detachably mounted room temperature upper clamp 16 and a room temperature lower clamp 17. The room temperature upper clamp 16 and the room temperature lower clamp 17 cooperate to clamp the vertical sample 9. The room temperature upper clamp 16 is connected to the upper surface of the fixed frame 1 by bolts and nuts 14, and the room temperature lower clamp 17 is connected to the tensile machine 3 by fixing bolts 15, allowing the room temperature lower clamp 17 to move up and down to apply load. Both the room temperature upper clamp 16 and the room temperature lower clamp 17 include a first fastening bolt and nut 18 and a second fastening bolt and nut 19, used to adjust the verticality and tightness of the sample 9. An insulating ceramic gasket 7 is used to isolate the sample 9 from the clamps and from the insulating ceramic tube 8 to improve the accuracy of voltage drop measurement. The insulating ceramic gasket 7 is made of zirconia insulating ceramic.

[0045] The force loading system includes a tensile machine 3 and a tensile machine controller 4, which are driven and connected to a room temperature clamping device 2.

[0046] The data acquisition system includes a current line 10, a main voltage drop line 11, a reference voltage drop line 12, a constant current source 20, and a nanovoltmeter 13. The current line 10 is used to input current through the sample 9. The main voltage drop line 11 is used to measure the main voltage drop, reflecting the crack propagation rate. The reference voltage drop line 12 is used to correct the main voltage drop and improve the accuracy of the test. The constant current source 20 provides a stable current output, and the nanovoltmeter 13 measures the current and voltage drop in each wire. The current line 10, main voltage drop line 11, and reference voltage drop line 12 all include platinum wire and an external insulating PTFE heat-shrink tubing to ensure insulation and improve the accuracy of the voltage drop measurement.

[0047] The electrical control cabinet 6 integrates all control systems and controls the parameters of the force loading system through a computer control program. These parameters include constant stress intensity factor, load ratio, wave frequency and waveform, etc.

[0048] During operation, first connect sample 9 to room temperature clamping device 2, isolating the contact points between sample 9 and room temperature clamping device 2 using insulating ceramic gasket 7 and insulating ceramic tube 8. Then, connect both to the fixing frame 1 using threads. Next, use a spot welder to weld current line 10, reference voltage drop line 12, and main voltage drop line 11 onto the surface of sample 9. After opening the testing software and inputting the corresponding parameters required for the test, the test can begin.

[0049] This application adopts a combined DCPD and DIC design, which conducts DCPD and DIC tests simultaneously. In actual operation, it can obtain the crack propagation rate online and simultaneously obtain the strain field distribution on the sample surface, thus realizing multi-scale acquisition of cracking information.

[0050] Example 2

[0051] Based on Example 1, the present invention provides a test method for a multi-scale in-situ monitoring device for material crack propagation, including a room temperature test method.

[0052] When conducting a room temperature test, the room temperature test method includes the following steps:

[0053] Step 1: Place the DIC camera 5 on the side of the DCPD test section and collect the strain of the sample 9 through the observation window;

[0054] Step 2: The surface of sample 9 is polished with 400-grit, 800-grit, 1200-grit, and 2000-grit sandpaper respectively, and mechanically polished until there are no obvious scratches. Then, electrolytic polishing or vibratory polishing is performed to eliminate the stress layer. Speckle coating is sprayed on the side of sample 9 for subsequent measurement by DIC camera 5.

[0055] Step 3: Clamp sample 9 with room temperature upper clamp 16 and room temperature lower clamp 17. Adjust the verticality of sample 9 with first fastening bolt nut 18 and second fastening bolt nut 19. Use insulating ceramic gasket 7 and insulating ceramic tube 8 to isolate sample 9 from clamp. Adjust the clamping length and verticality of sample 9. Then connect room temperature upper clamp 16 to the upper surface of fixed frame 1 with bolt nut 14. Connect room temperature lower clamp 17 to tensile machine 3 with fixing bolt 15.

[0056] Step 4: Weld a pair of current lines 10, a pair of main voltage drop lines 11, and a pair of reference voltage drop lines 12 to the sample 9. The current lines 10 are connected to the upper and lower surfaces of the sample 9, the main voltage drop lines 11 are connected to both sides of the opening of the sample 9, and the reference voltage drop lines 12 are connected to the opposite surfaces of the opening of the sample 9.

[0057] Step 5: Turn on the force holding function of the electrical control cabinet 6 and set it to ON, then fully tighten the room temperature upper clamp 16 and the room temperature lower clamp 17.

[0058] Step 6: Set the required constant stress intensity factor, load ratio, wave frequency and waveform in the control program. Set the protection parameters to avoid damage to the equipment and sample due to excessive load or displacement. Then, apply current and determine whether the voltage drop error is within the allowable range. If it is within the allowable range, the test can begin. Otherwise, the insulation condition and welding quality need to be re-evaluated.

[0059] Step 7: Adjust the brightness and focal length of the DIC camera 5 to make the speckle clearest, set the pixels for DIC acquisition and calculation, and first take a picture of the speckle morphology of the ROI on the sample surface as a reference image. Then apply a load, collect the fatigue crack propagation rate, and take another picture of the speckle at the same location at intervals. By measuring the displacement change of the speckle on the sample surface before and after applying the load, the computer program calculates the stress and strain field distribution data on the sample 9 surface.

[0060] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-scale in-situ monitoring device for material crack propagation, characterized in that, include: DCPD test section, the DCPD test section includes a fixed frame, a room temperature clamping device, a force loading system and a data acquisition system; DIC testing unit, the DIC testing unit including DIC camera; An electrical control cabinet, which is electrically connected to the force loading system, the data acquisition system and the DIC camera respectively; The fixed frame has an observation window on its side, through which the DIC camera collects the strain of the sample held by the room temperature clamping device. The room temperature clamping device includes a sample clamp, an insulating ceramic gasket, and an insulating ceramic tube. The sample clamp is mounted on the fixed frame, and the insulating ceramic gasket and the insulating ceramic tube are used to isolate the current between the sample and the sample clamp. The force loading system includes a tensile machine and a tensile machine controller. The tensile machine is electrically connected to the tensile machine controller and is drivenly connected to the room temperature clamping device. The data acquisition system includes a current line, a main voltage drop line, a reference voltage drop line, a constant current source, and a nanovoltmeter. The sample is connected to the constant current source through the current line, and the sample is connected to different nanovoltmeters through the main voltage drop line and the reference voltage drop line, respectively, with the main voltage drop line distributed on both sides of the crack in the sample; The fixed frame includes an upper surface, a lower surface, and four fixed support columns disposed between the upper surface and the lower surface. A fixing bolt extends from the center of the lower surface, and the sample clamp is connected to the stretching machine through the fixing bolt. The room temperature clamping device includes a detachable room temperature upper clamp and a room temperature lower clamp. Both the room temperature upper clamp and the room temperature lower clamp are provided with a first fastening bolt and nut and a second fastening bolt and nut. The room temperature upper clamp and the room temperature lower clamp adjust the verticality and tightness of the sample by means of the first fastening bolt and nut and the second fastening bolt and nut. The current line, the main voltage drop line, and the reference voltage drop line in the data acquisition system all include platinum wire and an insulating PTFE heat shrink tubing wrapped around the platinum wire. The constant current source is used to provide a stable current output, the nanovoltmeter is used to measure the current and voltage drop in each wire, and the reference voltage drop line is used to correct the main voltage drop to improve test accuracy.

2. The multi-scale in-situ monitoring device for material crack propagation according to claim 1, characterized in that, The upper surface of the fixed frame is provided with bolts and nuts. The room temperature upper clamp is connected to the upper surface of the fixed frame through the bolts and nuts. The room temperature lower clamp is connected to the tensioning machine through the fixing bolts, so that the room temperature lower clamp can move up and down to apply load.

3. The multi-scale in-situ monitoring device for material crack propagation according to claim 1, characterized in that, The force loading system is connected to a computer via the electrical control cabinet. The computer's control program controls the parameters of the force loading system, including constant stress intensity factor, load ratio, wave frequency, and waveform.

4. A test method for a multi-scale in-situ monitoring device for material crack propagation, characterized in that, The multi-scale in-situ monitoring device for material crack propagation, as described in any one of claims 1-3, comprises the following steps: Step 1: Place the DIC camera to the side of the DCPD test section and collect the strain of the sample through the observation window; Step 2, prepare the sample, including grinding, polishing and spraying speckle on the side; Step 3: Clamp the sample with the room temperature upper clamp and the room temperature lower clamp, and use an insulating ceramic tube to isolate the current between the sample and the room temperature upper clamp and the room temperature lower clamp; Step 4: Weld the current line, main voltage drop line, and reference voltage drop line to the sample. Step 5: Activate the force holding function of the electrical control cabinet and tighten the clamps; Step 6: Set parameters in the control program, apply current, and check voltage drop error; Step 7: Adjust the DIC camera and take a reference image. After applying the load, take a speckle image and calculate the stress-strain field distribution.

5. The test method for a multi-scale in-situ monitoring device for material crack propagation according to claim 4, characterized in that, The steps for preparing the sample include: sanding the sample surface with sandpaper and mechanically polishing it until there are no obvious scratches, and then performing electropolishing or vibratory polishing to eliminate the stress layer.

6. The test method for a multi-scale in-situ monitoring device for material crack propagation according to claim 4, characterized in that, The parameters set in the control program include constant stress intensity factor, load ratio, wave frequency and waveform, and protection parameters are set to avoid damage to the equipment and sample due to excessive load or displacement.

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