Fatigue test device for small in-situ hydrogen filling punch

Abstract

The invention provides an in-situ hydrogen charging small punch fatigue experiment device. An upper clamp and a lower clamp which are arranged in a cylinder body up and down are used for clamping a small punch sample; a pressing block is arranged above the upper clamp; a plurality of vertical through holes of the upper clamp, the lower clamp and the pressing block form a stamping path; the pressing rod is connected with the cathode of the power supply, and the upper part is provided with a tray contacted with the high-precision displacement sensor; when an experiment is carried out, a metal ball is placed on the top surface of a sample, electrolyte is injected, a pressing rod is driven by an upper compression clamp to pass through a stamping path, the metal ball applies stamping force and power supply voltage to the small stamping rod sample, so that the sample deforms, hydrogen is generated on the surface of the sample when the electrolyte is electrolyzed, and a hydrogen environment is formed; the high-precision displacement sensor measures the displacement of the pressing rod, and the force sensor at the compression clamp measures the load of the pressing rod; according to the invention, the problem of carrying out fatigue test on the small punch sample under the in-situ hydrogen charging condition is solved, and meanwhile, the device is suitable for testing operation of various fatigue loading waveforms.

Description

Technical Field

[0001] The invention relates to the technical field of experimental equipment, in particular to an in-situ hydrogen-filled small punch fatigue experimental device. Background Art

[0002] Hydrogen will lead to a decrease in fracture toughness and fatigue life for almost all metal materials, so studying the effect of hydrogen on materials is the key to ensuring the safety and economic use of materials. In order to further explore the effect of hydrogen on material properties, mechanical tests must be performed on hydrogen-containing specimens. Commonly used hydrogenation methods include aqueous solution electrolysis hydrogenation, molten salt electrolysis hydrogenation, and gas phase hydrogenation. Among them, aqueous solution electrolysis hydrogenation is widely used due to its safety and ease of operation.

[0003] At present, the basic mechanical properties tests of metal materials mainly include uniaxial tensile tests, fracture toughness tests and fatigue tests. However, these tests usually require the use of large-sized samples, which may cause inevitable damage to structures and equipment, especially for in-service equipment. In addition, large-sized samples inevitably prolong the test time and cost. Therefore, the use of small-sized sample test methods, such as small punch tests, will help overcome these shortcomings and improve the efficiency and economy of the test.

[0004] Conventional hydrogen-induced fatigue testing usually adopts the method of pre-charging hydrogen before conducting fatigue experiments. However, hydrogen will escape from the sample after pre-charging hydrogen when exposed to the air, and fatigue experiments usually last for a long time, which will lead to a significant reduction in hydrogen inside the sample, thus adversely affecting the study of the effect of hydrogen on the fatigue properties of the material. In addition, the stress state has an important influence on the diffusion of hydrogen in the material, and the diffused hydrogen will in turn affect the redistribution of stress. A simple pre-charging hydrogen experiment can only reflect the effect of hydrogen on the stress state, but cannot show the effect of the stress state on the diffusion of hydrogen. Therefore, in order to explore the coupling effect between the stress field and the hydrogen concentration, an in-situ hydrogen charging device is indispensable in fatigue experiments. In addition, this in-situ hydrogen charging fatigue test device can better simulate the operating conditions of the equipment in the actual hydrogen environment, so that the experimental results are more instructive and provide a more effective reference for industrial production.

[0005] In summary, there is no device that can simultaneously perform hydrogen charging and fatigue testing on small punch specimens, which cannot meet the needs of fatigue performance testing of micro specimens in a hydrogen environment. Therefore, the design and development of an in-situ hydrogen charging small punch fatigue test device system has important research and application value. Summary of the invention

[0006] The present invention proposes an in-situ hydrogen-filled small punch fatigue test device, which solves the problem of performing fatigue tests on small punch specimens under in-situ hydrogen-filled conditions. The device is also suitable for testing operations of various fatigue loading waveforms and can evaluate the fatigue performance of materials in a hydrogen environment through fracture morphology, fatigue life, fatigue strength limit and interruption experiments.

[0007] The present invention adopts the following technical solutions.

[0008] An in-situ hydrogen-filled small punch fatigue test device is used for fatigue testing of small punch specimens. The device clamps the small punch specimen (7) with an upper clamp (12) and a lower clamp (13) arranged up and down in a cylinder (15); a clamping block (11) is arranged above the upper clamp; the upper clamp, the lower clamp and the clamping block are all provided with vertical through holes, and a plurality of vertical through holes are coaxially arranged to form a punching path for penetrating a punch rod (4); the punch rod is connected to a power source, and a probe end of a high-precision displacement sensor (2) is provided on its upper portion. tray; when conducting an experiment, a metal ball is placed on the top surface of the small punch rod sample through the vertical through hole of the upper fixture, a neutral hydrogen-filled electrolyte is injected into the cylinder to immerse the small punch rod sample, and after the pressure rod is energized, a punching force and a power supply voltage are applied to the small punch rod sample through the punching path and the metal ball under the drive of the upper compression fixture to deform the sample, and hydrogen is generated on the surface of the sample when the electrolyte is electrolyzed to form a hydrogen environment, a high-precision displacement sensor measures the displacement of the pressure rod, and a force sensor (17) at the compression fixture measures the load of the pressure rod.

[0009] The metal ball is a steel ball (6); and the small punch sample is a metal sample of microscopic size.

[0010] The tray is a circular tray (3), the edge of which contacts the detection end of a high-precision displacement sensor (2); the high-precision displacement sensor is placed on a sensor fixing bracket (1).

[0011] The lower clamp and the upper clamp are both placed in a mold support (14), and a liquid inlet (5) for a neutral hydrogen-charging electrolyte to enter is provided on a side wall of the mold support; The bottom end of the upper compression fixture is adjacent to the top end of the pressure rod, and the top end of the upper compression fixture is connected to a force sensor provided at a crossbeam (16). The crossbeam drives the upper compression fixture so that when the bottom end of the upper compression fixture applies a punching force to the pressure rod, the force sensor measures the load force applied to the upper compression fixture.

[0012] A nut connected to the clamping block for clamping the clamping block is provided on the top of the mold support. The pressure rod enters the punching path through the through hole in the center of the nut. When the nut is tightened, the small punch rod sample is clamped and fixed by the upper clamp and the lower clamp.

[0013] The nut is a hexagonal nut (10).

[0014] The mold support is fixed to the cylinder body via fixing bolts (8).

[0015] The power source is a constant current power source (21), and a platinum electrode (20) is provided in the cylinder. When conducting an experiment, the platinum electrode is connected to the anode of the constant current power source, and the pressure rod is connected to the cathode of the constant current power source.

[0016] The assembly of the experimental device includes the following steps: Step S1, fixing the cylinder body of the small punch fatigue test device to the lower fixture joint (22) by means of fasteners; fixing the upper compression fixture to the force sensor by means of a locking nut (18); Step S2: During the experiment, first place the sample in the groove of the lower fixture, and fix the upper fixture and the lower fixture together to form a fixture as a whole to ensure the stability of the sample; then, place the fixed fixture as a whole into the mold support, and then place the steel ball into the upper fixture to make it contact with the top surface of the sample; Step S3, placing a clamping block on the upper clamp, and tightening the clamping hexagonal nut so that the clamping block clamps the upper clamp, and then inserting the pressure rod into the corresponding hole of the clamping hexagonal nut, passing through the clamping block and the upper clamp to contact the steel ball; Step S4, fix the assembled small punch test fixture to the cylinder body through the fixing bolts, and place the detection end of the high-precision displacement sensor on the round tray. Then, connect the anode of the constant current power supply to the platinum electrode, and the cathode to the pressure rod. To prevent the fixture from corrosion, pour the pre-configured neutral hydrogen-filled electrolyte into the cylinder body until the liquid level is flush with the upper liquid inlet hole of the mold support to ensure that the small punch sample is completely immersed in the electrolyte.

[0017] The use of the experimental device includes the following steps: Step A1, input the pre-written fatigue loading curve code into the computer, and ensure that the set fatigue load ratio R>0; then, use the driving beam to perform up and down loading movement, thereby driving the upper compression fixture to perform cyclic loading on the compression rod to perform stamping force; Step A2, after setting the hydrogen charging current density, turn on the constant current power supply, at this time the platinum electrode acts as an anode to generate oxygen, and the pressure rod connected to the cathode contacts the small punch rod sample through the steel ball, prompting the sample surface to generate hydrogen to form a hydrogen environment, thereby achieving the simultaneous in-situ hydrogen charging treatment and fatigue test at the sample; Step A3, after the fatigue test is completed, the experimental result data of the load-displacement curve and the number of cycles are saved on the computer; Step A4, turn off the constant current power supply, open the liquid drain valve to discharge the electrolyte, loosen the fixing bolts, remove the mold support, and remove the small punch sample from between the upper and lower clamps; finally, clean and dry the small punch sample so that the fracture morphology formed at the sample during the experiment can be observed by scanning electron microscopy later.

[0018] The present invention relates to a small punch fatigue testing device suitable for various conditions, which can test samples under different hydrogen charging current densities and fatigue loading curves. The device is equipped with high-precision displacement and force sensors, which can monitor and record the deformation and fatigue behavior of the small punch sample in real time, thereby improving the accuracy of the test data.

[0019] The present invention realizes in-situ hydrogen charging of the sample by electrolysis of the electrolyte. The device can simulate the influence of hydrogen on the material in the actual working environment, making the test results more realistic and repeatable. In addition, the device not only supports in-situ hydrogen charging fatigue test, but also can carry out corrosion fatigue test of small punches, providing more abundant experimental data.

[0020] The experimental device proposed by the present invention has a simple structure, convenient assembly, wide application range and high stability. The surface of the fixture is coated with anti-corrosion paint to ensure the corrosion resistance of the device; the outer layer of the cylinder body is coated with waterproof sealant to effectively prevent leakage of hydrogen-filled electrolyte.

[0021] In the present invention, by programming the fatigue loading curve, the device can realize various forms of cyclic loading, providing important technical support for the hydrogen charging fatigue coupling test of metal materials.

[0022] The present invention proposes an in-situ hydrogen-filled small punch fatigue test device based on a simple mechanical structure, which mainly solves the problem of fatigue testing of small punch specimens under in-situ hydrogen-filled conditions, and is also suitable for testing operations of various fatigue loading waveforms. Through fracture morphology, fatigue life, fatigue strength limit and interruption experiments, the fatigue performance of materials in a hydrogen environment is evaluated to solve the problems raised in the above background technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: Attached Figure 1 is a schematic diagram of the clamp of the present invention when it is placed on a cylinder body; Attached Figure 2 It is a schematic diagram of the present invention when conducting a test; In the figure: 1: sensor fixing bracket; 2: high-precision displacement sensor; 3: round tray; 4: pressure rod; 5: liquid inlet hole (four in total); 6: steel ball; 7: small punch specimen; 8: fixing bolt (four in total); 9: drain valve; 10: hexagonal nut; 11: clamping block; 12: upper fixture; 13: lower fixture; 14: mold support; 15: cylinder body; 16: crossbeam; 17: force sensor; 18: locking nut (two in total); 19: upper compression fixture; 20: platinum electrode; 21: constant current power supply; 22: lower fixture connector. DETAILED DESCRIPTION

[0024] As shown in the figure, an in-situ hydrogen-filled small punch fatigue test device is used for fatigue test of small punch specimens. The device clamps the small punch specimen 7 with an upper clamp 12 and a lower clamp 13 arranged up and down in a cylinder body 15; a clamping block 11 is arranged above the upper clamp; the upper clamp, the lower clamp, and the clamping block are all provided with vertical through holes, and a plurality of vertical through holes are coaxially arranged to form a punching path for passing the pressure rod 4; the pressure rod is connected to the cathode of the power supply, and a tray is provided on the upper part thereof to contact the detection end of the high-precision displacement sensor 2 When conducting the experiment, the metal ball is placed on the top surface of the small punch rod sample through the vertical through hole of the upper fixture, and the cylinder is injected with neutral hydrogen-filled electrolyte to immerse the small punch rod sample. After the pressure rod is energized, the upper compression fixture drives the small punch rod sample through the punching path and the metal ball to apply punching force and power supply voltage to deform the sample, and hydrogen is generated on the surface of the sample to form a hydrogen environment when the electrolyte is electrolyzed. The high-precision displacement sensor measures the displacement of the pressure rod, and the force sensor 17 at the compression fixture measures the load of the pressure rod.

[0025] The metal ball is a steel ball 6; the small punch sample is a metal sample of micro size.

[0026] The tray is a circular tray 3 , the edge of which contacts the detection end of the high-precision displacement sensor 2 ; the high-precision displacement sensor is placed on the sensor fixing bracket 1 .

[0027] The lower clamp and the upper clamp are both placed in the mold support 14, and the side wall of the mold support is provided with a liquid inlet 5 for the neutral hydrogen-filled electrolyte to enter; The bottom end of the upper compression fixture is adjacent to the top end of the pressure rod, and the top end of the upper compression fixture is connected to a force sensor arranged at the crossbeam 16. The crossbeam drives the upper compression fixture so that when the bottom end of the upper compression fixture presses the pressure rod, the force sensor measures the load force on the upper compression fixture.

[0028] A nut connected to the clamping block for clamping the clamping block is provided on the top of the mold support. The pressure rod enters the punching path through the through hole in the center of the nut. When the nut is tightened, the small punch rod sample is clamped and fixed by the upper clamp and the lower clamp.

[0029] The nut is a hexagonal nut 10 .

[0030] The mold support is fixed to the cylinder body via fixing bolts 8.

[0031] The power source is a constant current power source 21, and a platinum electrode 20 is arranged in the cylinder. When conducting an experiment, the platinum electrode is connected to the anode of the constant current power source, and the pressure rod is connected to the cathode of the constant current power source.

[0032] The assembly of the experimental device includes the following steps: Step S1, fix the cylinder body of the small punch fatigue test device to the lower fixture joint 22 through fasteners; fix the upper compression fixture to the force sensor through the locking nut 18; Step S2: During the experiment, first place the sample in the groove of the lower fixture, and fix the upper fixture and the lower fixture together to form a fixture as a whole to ensure the stability of the sample; then, place the fixed fixture as a whole into the mold support, and then place the steel ball into the upper fixture to make it contact with the top surface of the sample; Step S3, placing a clamping block on the upper clamp, and tightening the clamping hexagonal nut so that the clamping block clamps the upper clamp, and then inserting the pressure rod into the corresponding hole of the clamping hexagonal nut, passing through the clamping block and the upper clamp to contact the steel ball; Step S4, fix the assembled small punch test fixture to the cylinder body through the fixing bolts, and place the detection end of the high-precision displacement sensor on the round tray. Then, connect the anode of the constant current power supply to the platinum electrode, and the cathode to the pressure rod. To prevent the fixture from corrosion, pour the pre-configured neutral hydrogen-filled electrolyte into the cylinder body until the liquid level is flush with the upper liquid inlet hole of the mold support to ensure that the small punch sample is completely immersed in the electrolyte.

[0033] The use of the experimental device includes the following steps: Step A1, input the pre-written fatigue loading curve code into the computer, and ensure that the set fatigue load ratio R>0; then, use the driving beam to perform up and down loading movement, thereby driving the upper compression fixture to perform cyclic loading on the compression rod to perform stamping force; Step A2, after setting the hydrogen charging current density, turn on the constant current power supply, at this time the platinum electrode acts as an anode to generate oxygen, and the pressure rod connected to the cathode contacts the small punch rod sample through the steel ball, prompting the sample surface to generate hydrogen to form a hydrogen environment, thereby achieving the simultaneous in-situ hydrogen charging treatment and fatigue test at the sample; Step A3, after the fatigue test is completed, the experimental result data of the load-displacement curve and the number of cycles are saved on the computer; Step A4, turn off the constant current power supply, open the liquid drain valve to discharge the electrolyte, loosen the fixing bolts, remove the mold support, and remove the small punch sample from between the upper and lower clamps; finally, clean and dry the small punch sample so that the fracture morphology formed at the sample during the experiment can be observed by scanning electron microscopy later.

[0034] Example: See also Figure 1In this example, an in-situ hydrogen filling small punch test fixture for the experiment is proposed, which mainly includes: a sensor fixing bracket 1, a high-precision displacement sensor 2, a round tray 3, a pressure rod 4, a liquid inlet 5, a steel ball 6, a small punch specimen 7, a fixing bolt 8, a clamping hexagonal nut 10, a clamping block 11, an upper fixture 12, a lower fixture 13, a mold support 14, and a cylinder body 15.

[0035] The mold support 14 is fixed to the cylinder body 15 by the fixing bolts 8. Next, the lower clamp 13 is placed into the mold support 14, and then the small punch sample 7 is placed on the lower clamp 13. Subsequently, the upper clamp 12 is placed on the top of the small punch sample 7, and the steel ball 6 is placed into the upper clamp 12, and then the clamping block 11 is placed on the upper clamp 12. Then, tighten the clamping hexagonal nut 10 to ensure that the small punch sample 7 is firmly fixed between the upper and lower clamps. Next, the pressure rod 4 is inserted into the clamping hexagonal nut 10 so that the pressure rod 4 applies pressure through the steel ball 6, thereby punching the small punch sample 7. Finally, the detection end of the high-precision displacement sensor 2 is placed on the circular tray 3 to record the displacement changes in real time.

[0036] See also Figure 2 The experimental device in this example needs to be assembled as follows when used for the first time: First, fix the small punch test fixture to the lower fixture joint through the locking nut. Then, fix the upper compression fixture to the force sensor through the locking nut to complete the basic assembly of the device.

[0037] In the subsequent use process, first place the sample in the groove of the lower clamp, and fix the upper and lower clamps to ensure the stability of the sample. Then, put the fixed clamp as a whole into the mold support, and then put the steel ball into the upper clamp. On this basis, place a clamping block on the upper clamp, and tighten the clamping hexagonal nut to make the clamping block clamp the upper clamp, and then insert the pressure rod into the hole of the corresponding clamping hexagonal nut, pass through the clamping block and the upper clamp to contact the steel ball.

[0038] Next, fix the assembled small punch test fixture to the cylinder body with fixing bolts, and place the detection end of the high-precision displacement sensor on the round tray. Then, connect the anode of the constant current power supply to the platinum electrode, and the cathode to the pressure rod. To prevent corrosion of the fixture, pour the pre-configured neutral hydrogen-filled electrolyte into the cylinder body until the liquid level is flush with the upper liquid inlet hole of the mold support to ensure that the small punch specimen is completely immersed in the electrolyte.

[0039] After that, input the pre-written fatigue loading curve code into the computer and ensure that the set fatigue load ratio R>0. Then, use the driving beam to load up and down, and then drive the upper compression fixture to perform cyclic loading on the pressure rod. After setting the hydrogen charging current density, turn on the constant current power supply. At this time, the platinum electrode acts as the anode to produce oxygen, and the pressure rod connected to the cathode contacts the small punch rod sample through the steel ball, prompting the generation of hydrogen on the sample surface, thereby realizing the simultaneous in-situ hydrogen charging and fatigue testing.

[0040] After the fatigue test is completed, the load-displacement curve and the number of cycles and other experimental results are saved on the computer. Then, turn off the constant current power supply, open the drain valve to drain the electrolyte, loosen the fixing bolts, remove the mold support, and remove the small punch sample from the upper and lower clamps. Finally, the small punch sample is cleaned and blown dry so that the fracture morphology can be observed later by scanning electron microscopy.

Claims

1. An in-situ hydrogen-filled small punch fatigue test device, used for fatigue test of small punch specimens, characterized by: The device clamps a small punch rod sample (7) with an upper clamp (12) and a lower clamp (13) arranged in a cylinder body (15); a clamping block (11) is arranged above the upper clamp; the upper clamp, the lower clamp and the clamping block are all provided with vertical through holes, and a plurality of vertical through holes are coaxially arranged to form a punching path for inserting a punch rod (4); the punch rod is connected to the cathode of a power source, and a tray is provided on its upper part to contact the detection end of a high-precision displacement sensor (2); when conducting an experiment, the metal The ball is placed on the top surface of the small punch sample through the vertical through hole of the upper fixture, and the cylinder is injected with neutral hydrogen-filled electrolyte to immerse the small punch sample. After the pressure rod is energized, the upper compression fixture drives the small punch sample through the punching path and the metal ball to apply punching force and power supply voltage to the small punch sample to deform the sample, and hydrogen is generated on the sample surface during electrolysis of the electrolyte to form a hydrogen environment. The high-precision displacement sensor measures the displacement of the pressure rod, and the force sensor (17) at the compression fixture measures the load of the pressure rod.

2. The in-situ hydrogen charging small punch fatigue test device according to claim 1, characterized in that: The metal ball is a steel ball (6); and the small punch sample is a metal sample of microscopic size.

3. The in-situ hydrogen charging small punch fatigue test device according to claim 1, characterized in that: The tray is a circular tray (3), the edge of which contacts the detection end of a high-precision displacement sensor (2); the high-precision displacement sensor is placed on a sensor fixing bracket (1).

4. The in-situ hydrogen charging small punch fatigue test device according to claim 1, characterized in that: The lower clamp and the upper clamp are both placed in a mold support (14), and a liquid inlet (5) for a neutral hydrogen-charging electrolyte to enter is provided on a side wall of the mold support; The bottom end of the upper compression fixture is adjacent to the top end of the pressure rod, and the top end of the upper compression fixture is connected to a force sensor provided at a crossbeam (16). The crossbeam drives the upper compression fixture so that when the bottom end of the upper compression fixture applies a punching force to the pressure rod, the force sensor measures the load force applied to the upper compression fixture.

5. The in-situ hydrogen-filled small punch fatigue test device according to claim 4, characterized in that: A nut connected to the clamping block for clamping the clamping block is provided on the top of the mold support. The pressure rod enters the punching path through the through hole in the center of the nut. When the nut is tightened, the small punch rod sample is clamped and fixed by the upper clamp and the lower clamp.

6. The in-situ hydrogen-filled small punch fatigue test device according to claim 5, characterized in that: The nut is a hexagonal nut (10).

7. The in-situ hydrogen charging small punch fatigue test device according to claim 1, characterized in that: The mold support is fixed to the cylinder body via fixing bolts (8).

8. The in-situ hydrogen charging small punch fatigue test device according to claim 1, characterized in that: The power source is a constant current power source (21), and a platinum electrode (20) is provided in the cylinder. When conducting an experiment, the platinum electrode is connected to the anode of the constant current power source, and the pressure rod is connected to the cathode of the constant current power source.

9. The in-situ hydrogen-filled small punch fatigue test device according to claim 8, characterized in that: The assembly of the experimental device includes the following steps: Step S1, fixing the cylinder body of the small punch fatigue test device to the lower fixture joint (22) by means of fasteners; fixing the upper compression fixture to the force sensor by means of a locking nut (18); Step S2: During the experiment, first place the sample in the groove of the lower fixture, and fix the upper fixture and the lower fixture together to form a fixture as a whole to ensure the stability of the sample; then, place the fixed fixture as a whole into the mold support, and then place the steel ball into the upper fixture to make it contact with the top surface of the sample; Step S3, placing a clamping block on the upper clamp, and tightening the clamping hexagonal nut so that the clamping block clamps the upper clamp, and then inserting the pressure rod into the corresponding hole of the clamping hexagonal nut, passing through the clamping block and the upper clamp to contact the steel ball; Step S4, fixing the assembled small punch test fixture to the cylinder body through fixing bolts, and placing the detection end of the high-precision displacement sensor on the circular tray; Then, the anode of the constant current power supply is connected to the platinum electrode, and the cathode is connected to the pressure rod; To prevent corrosion of the fixture, pour the pre-prepared neutral hydrogen-filled electrolyte into the cylinder until the liquid level is flush with the liquid inlet hole above the mold support to ensure that the small punch specimen is completely immersed in the electrolyte.

10. The in-situ hydrogen-filled small punch fatigue test device according to claim 9, characterized in that: The use of the experimental device includes the following steps: Step A1, input the pre-written fatigue loading curve code into the computer, and ensure that the set fatigue load ratio R>0; then, use the driving beam to perform up and down loading movement, thereby driving the upper compression fixture to perform cyclic loading on the compression rod to perform stamping force; Step A2, after setting the hydrogen charging current density, turn on the constant current power supply, at this time the platinum electrode acts as an anode to generate oxygen, and the pressure rod connected to the cathode contacts the small punch rod sample through the steel ball, prompting the sample surface to generate hydrogen to form a hydrogen environment, thereby achieving the simultaneous in-situ hydrogen charging treatment and fatigue test at the sample; Step A3, after the fatigue test is completed, the experimental result data of the load-displacement curve and the number of cycles are saved on the computer; Step A4, turn off the constant current power supply, open the liquid drain valve to discharge the electrolyte, loosen the fixing bolts, remove the mold support, and remove the small punch sample from between the upper and lower clamps; finally, clean and dry the small punch sample so that the fracture morphology formed at the sample during the experiment can be observed by scanning electron microscopy later.

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