Hydrogen-doped natural gas environment fatigue test device based on vacuum multi-arc ion plating

Abstract

The application discloses a hydrogen-doped natural gas environment fatigue test device based on vacuum multi-arc ion plating, which comprises a fatigue testing machine, a high-pressure gas environment box filled with high-pressure hydrogen-doped natural gas and a pressure detection mechanism arranged in the high-pressure gas environment box; the upper end and the lower end of the high-pressure gas environment box are respectively in sealing connection with the upper stretching rod and the lower stretching rod of the fatigue testing machine, and the upper part and the lower part of a sample are respectively in fixed connection with the upper stretching rod and the lower stretching rod; a sealable rotating door is arranged on one side of the high-pressure gas environment box; the pressure detection mechanism comprises a horizontal supporting plate, a vertical baffle arranged on the left side of the horizontal supporting plate, a vertical rod arranged on the lower surface of the horizontal supporting plate on the right side of the vertical baffle, an L-shaped rod in rotation connection with the lower end of the vertical rod and a strain gauge arranged on the side surface of the vertical baffle on the lower left of the L-shaped rod. The application has the characteristics that the fatigue crack propagation rate of a sample in a hydrogen-doped natural gas environment can be stably detected.

Description

Technical Field

[0001] This invention relates to the field of specimen fatigue testing technology, and in particular to a fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating. Background Technology

[0002] The key to fatigue crack propagation rate testing lies in the measurement of crack length. Two common methods are: DC voltage drop (DCPD) and strain gauge extensometer. DCPD involves analyzing the potential field of the CT sample to establish a calibration curve, ultimately obtaining the relationship between crack length and voltage drop. The limitation of this technique lies in the complexity of the calibration curve and the reliability of the test results. The other method uses a strain gauge extensometer with a strain-sensitive element attached. During measurement, the extensometer is clamped onto the CT sample. As the crack propagates, strain is transmitted to the sensitive element, generating a change in electrical signal. The computer terminal records the changes in the electrical signal data, and the corresponding crack length change value can be obtained from the change in the electrical signal. This technique is currently the most widely used method for fatigue crack propagation rate testing.

[0003] In hydrogen-blended natural gas environments, conventional strain gauge extensometers have two major limitations. First, traditional strain-sensitive element materials, such as pure copper and copper-nickel alloys, exhibit significant zero-point drift in hydrogen-rich environments, affecting the accuracy of test results. Second, the sensitive element is attached to an elastic substrate via adhesives, with commonly used adhesives including epoxy resin and phenolic resin. Hydrogen can easily penetrate the adhesive, causing bubbling and cracking, leading to increased drift and strain transmission lag. Furthermore, hydrogen-blended natural gas contains reducing gases such as CH4, CO2, and CO, which can easily cause aging and failure of the adhesive. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing pure copper and copper-nickel alloy sensing elements in hydrogen-containing environments, which exhibit significant zero-point drift. Furthermore, the sensing elements are attached to an elastic substrate with adhesive, which allows hydrogen to easily penetrate the adhesive, causing bubbling and cracking, resulting in increased drift and delayed strain transmission. This invention provides a fatigue testing device for hydrogen-doped natural gas environments based on vacuum multi-arc ion plating.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating includes a fatigue testing machine, a high-pressure gas environment chamber filled with high-pressure hydrogen-doped natural gas, and a pressure detection mechanism located within the high-pressure gas environment chamber. The upper and lower openings of the high-pressure gas environment chamber are respectively sealed to the upper and lower tension rods of the fatigue testing machine, and the upper and lower parts of the sample are fixedly connected to the upper and lower tension rods, respectively. A sealable rotating door is provided on one side of the high-pressure gas environment chamber. The pressure detection mechanism includes a horizontal support plate, a vertical baffle on the left side of the horizontal support plate, and a vertical baffle on the right side. The vertical rod on the lower surface of the horizontal support plate on the right side of the baffle, the L-shaped rod rotatably connected to the lower end of the vertical rod, and the strain gauge on the side of the vertical baffle located to the lower left of the L-shaped rod; the vertical baffle is fixedly connected to the strain gauge, the right end of the transverse extension plate is fixedly connected to the upper left side of the sample, the lower end of the vertical rod is connected to the upper left end of the L-shaped rod through a longitudinal rotating shaft, an arc-shaped buffer pad is provided on the outer side of the corner of the L-shaped rod, the strain gauge is electrically connected to the strain tester, the L-shaped rod to the right of the arc-shaped buffer pad includes a sleeve and a telescopic rod that extends into the sleeve and is slidably connected to the sleeve, and the right end of the L-shaped rod is rotatably connected to the lower left side of the sample.

[0007] The fatigue testing machine is equipped with a hydraulic cylinder at the bottom to drive the lower tension rod to move up and down reciprocally; the specimen is machined with a notch, and an alternating load is used to pre-create cracks extending along the notch. The rotating door is opened to place the upper part of the specimen into the U-shaped opening groove of the upper tension rod. A cylindrical pin is passed through the specimen fixing hole above the notch and the holes on both sides of the U-shaped opening groove of the upper tension rod to connect the specimen and the upper tension rod.

[0008] Place the lower part of the sample into the U-shaped opening groove of the lower tension rod, and use a cylindrical pin to pass through the sample fixing hole below the notch and the holes on both sides of the U-shaped opening groove of the lower tension rod to connect the sample and the lower tension rod; make the horizontal support plate horizontal and the telescopic rod horizontal.

[0009] As the hydraulic cylinder repeatedly pulls the sample downwards, the crack at the notch of the sample continues to extend, the notch gradually opens, the telescopic rod gradually tilts and extends to the lower right, and the arc-shaped buffer pad gradually approaches the strain gauge. The pressure signal detected by the strain gauge is transmitted to the strain testing instrument.

[0010] To determine the correlation between the pressure signal detected by the strain gauge and the crack length, tensile tests on the specimens were repeatedly performed in a hydrogen-blended natural gas environment. The pressure value detected by the strain gauge and the corresponding crack length were recorded. Points were plotted in a two-dimensional coordinate system with the pressure value as the abscissa and the crack length as the ordinate. Adjacent points were connected to form a curve. The curve was then fitted to obtain the fitting function corresponding to the curve.

[0011] The strain gauge obtains the pressure value corresponding to the pressure signal detected by the strain gauge. The pressure value is used as the independent variable and substituted into the fitting function to obtain the crack length a corresponding to the pressure value. Furthermore, based on the stress cycle number N of the current fatigue testing machine, the relationship between the stress cycle number N and the crack length a is obtained. The fatigue crack propagation rate of the sample in the hydrogen-doped natural gas environment is calculated using the formula da / dN. The fatigue crack propagation rate is used to estimate the fatigue life of the cracked body (sample).

[0012] Preferably, the strain gauge includes a substrate, a transition buffer layer disposed on the substrate, an insulating layer disposed on the transition buffer layer, a functional layer disposed on the upper surface of the insulating layer, and a protective layer disposed on the functional layer; the substrate is made of X52MS pipeline steel, the transition buffer layer is a metal CrAl film, and the insulating layer is a TGA / Al2O3 film.

[0013] This invention employs vacuum atmosphere thermal growth and vacuum multi-arc ion plating technology for deposition; the functional layer is an FeMoW alloy film, prepared using vacuum multi-arc ion plating deposition technology; the protective layer is an epoxy resin coating.

[0014] Preferably, the functional layer is an FeMoW alloy film, and the protective layer is an epoxy resin coating.

[0015] As a preferred option, the fabrication process of the strain gauge is as follows:

[0016] (4-1) Preparation of FeMoW alloy target material for vacuum multi-arc ion plating;

[0017] (4-2) After physical grinding and polishing the substrate, the substrate is placed in a mixed solution of anhydrous ethanol and acetone for ultrasonic cleaning, and then dried with a hair dryer.

[0018] (4-3) Place the substrate on the workpiece rack in the coating chamber, and symmetrically place 99.99% Cr target and 99.99% Al target on the cathode arc source, so that the distance between the Cr target, Al target and the substrate is 75mm-85mm; evacuate the coating chamber to below 0.003Pa, and introduce argon gas at a flow rate of 15sccm-25sccm into the coating chamber, and control the working pressure of the coating chamber to 0.09Pa; start the cathode arc source, set the negative bias voltage of the substrate to 750V-850V, and bombard the substrate with arc light for 15min-20min;

[0019] (4-4) A transition buffer layer of metal CrAl film is deposited on the upper surface of the substrate.

[0020] (4-5) Preparation of insulating layer by vacuum atmosphere thermal growth and vacuum multi-arc ion plating: First, the substrate is placed in a vacuum tube furnace, the vacuum tube furnace is evacuated, and O2 is continuously introduced to carry out thermal growth, and a thermally grown TGA film is obtained on the upper surface of the metal CrAl film.

[0021] The substrate is placed in the coating chamber, and an Al target is placed on the cathode arc source. The distance between the Al target and the substrate is set to 75mm-85mm. After evacuating the coating chamber, argon and oxygen are introduced. The cathode arc source is started, and the negative bias voltage, working pressure and magnetic field frequency of the substrate are adjusted. The current and coating time of the Al target are adjusted to perform coating. An Al2O3 film is obtained on the upper surface of the TGA film on the substrate, and an insulating layer of TGA / Al2O3 film is obtained.

[0022] (4-6) Preparation of the functional layer of FeMoW alloy film by vacuum multi-arc ion plating: The substrate is placed in the coating chamber, and the patterned grid mask is tightly attached to the upper surface of the substrate using a fixture. The FeMoW target is placed on the cathode arc source, and the distance between the FeMoW target and the substrate is set to 75mm-85mm. After evacuating the coating chamber, argon gas is introduced, the cathode arc source is started, and the negative bias voltage, working pressure and magnetic field frequency of the substrate are adjusted. The current and coating time of the FeMoW target are adjusted to perform coating. The functional layer of FeMoW alloy film is obtained on the upper surface of the Al2O3 thin film of the substrate.

[0023] (4-7) Preparation of protective layer: Stir the mixture of epoxy resin, dibutyl phthalate and ethylenediamine evenly, coat the mixture on the outer surface of the substrate, and after the mixture cures, a cured protective layer is formed, and the strain gauge is completed.

[0024] Preferably, step (4-4) includes the following specific steps:

[0025] The coating chamber is evacuated to 0.001Pa-0.003Pa, and argon gas with a flow rate of 25sccm-30sccm is introduced to make the working gas pressure of the coating chamber 0.1Pa-0.5Pa, the negative bias voltage of the substrate 100V-150V, the magnetic field frequency of the substrate 100Hz-170Hz, the current of both the Cr and Al targets 30A-60A, and the coating time 40min-60min. The coating is then performed to obtain a 300nm-500nm metal CrAl film transition buffer layer on the upper surface of the substrate.

[0026] Preferably, step (4-5) includes the following specific steps:

[0027] First, place the substrate in a vacuum tube furnace, evacuate the vacuum tube furnace to 0.1 Pa, and continuously introduce O2 at 0.1 Pa-0.5 Pa. Oxidize the substrate at 600℃ for 1-3 hours. Turn off the heating power of the vacuum tube furnace and allow the vacuum tube furnace to cool to room temperature. Open the vacuum vent valve of the vacuum tube furnace, remove the substrate, and obtain a 100 nm-200 nm thermally grown TGA film on the upper surface of the metal CrAl film.

[0028] The substrate is then placed in the coating chamber, and an Al target is placed on the cathode arc source. The distance between the Al target and the substrate is set to 75mm-85mm. The coating chamber is evacuated to 0.001Pa-0.003Pa. Argon and oxygen in a ratio of (1-3):1 are introduced into the coating chamber. The cathode arc source is started, and the negative bias voltage of the substrate is set to 100V-150V, the working pressure of the substrate is set to 0.5Pa-0.8Pa, the magnetic field frequency of the substrate is set to 100Hz-150Hz, the current of the Al target is set to 50A-60A, and the coating time is set to 2h-3h. The coating is then carried out, and an Al2O3 film with a thickness of 300nm-500nm is obtained on the upper surface of the TGA film on the substrate.

[0029] Preferably, the FeMoW alloy target has an elemental composition of 5%-10% Mo, 3%-7% W, and the balance being Fe; the FeMoW alloy target has an impurity content of less than 0.02%, void defects of less than 0.1 mm, and grain size of less than 50 μm.

[0030] Preferably, steps (4-6) include the following specific steps:

[0031] The substrate is placed on the workpiece stage of the coating chamber. A patterned grid mask is fixed to the upper surface of the substrate using a fixture, ensuring a tight fit between the mask and the substrate. An FeMoW target is placed on the cathode arc source, with the distance between the FeMoW target and the substrate set to 75mm-80mm. The coating chamber is evacuated to 0.001Pa-0.003Pa, and argon gas is introduced at a flow rate of 20sccm-30sccm. The cathode arc source is activated, and the negative bias voltage of the substrate is set to 100V-150V, the working pressure of the substrate to 0.1Pa-0.6Pa, the magnetic field frequency of the substrate to 120Hz-150Hz, the current of the FeMoW target to 40A-60A, and the coating time to 0.5h-1h. The coating process is carried out, resulting in a 600nm-1000nm thick FeMoW alloy film with a patterned grid shape on the upper surface of the Al2O3 thin film on the substrate.

[0032] Preferably, step (4-7) includes the following specific steps:

[0033] Epoxy resin, dibutyl phthalate, and ethylenediamine are weighed in a mass ratio of 100:(4-7):(4-7). The weighed epoxy resin and dibutyl phthalate are mixed and stirred evenly within a temperature range of 55℃-65℃. After cooling to 30℃-40℃, the weighed ethylenediamine is added and stirred evenly to obtain a mixture. The mixture is then coated on the outer surface of the substrate taken out of the coating chamber. Air bubbles and excess mixture on the substrate are removed by rolling with cellophane. After the mixture cures, a cured protective layer is formed.

[0034] Therefore, the present invention has the following beneficial effects:

[0035] 1) The ion-plated thin film sensing element is grown directly on the substrate in the form of a thin film, which reduces contact with the hydrogen-doped natural gas medium containing CH4, CO2, CO, H2, H2O and H2S, while avoiding the strain transmission error and pressure influence caused by adhesives.

[0036] 2) The CrAl metal film, as a transition buffer layer, exhibits good adhesion to the substrate interface, resolving the issue of poor bonding between the substrate and the insulating layer. Furthermore, due to Al's strong affinity for oxygen, under vacuum O2 atmosphere heat treatment conditions, Al atoms readily precipitate on the CrAl film surface and react with O2 to form a dense TGA film. The TGA / Al2O3 film, as an insulating layer, yields a continuous, uniform, high-quality film with high and stable resistivity and excellent insulation performance through process parameter control. The FeMoW alloy film has a resistivity approximately twice that of constantan, improving the sensitivity of the sensing element. Simultaneously, the FeMoW alloy film lacks Cr and Al elements, which readily form oxide films, resulting in good surface weldability, reduced contact resistance, and improved stability of test data. The cured epoxy resin, as a protective layer, is relatively thin, negligible in its effect on interlayer adhesion caused by differences in thermal expansion coefficients. It also provides protection for the FeMoW alloy film, contributing to the long-term stable operation of ion-plated thin-film sensing elements.

[0037] 3) In a hydrogen-doped natural gas environment, the ion-plated thin film sensing element composed of CrAl / (TGA / Al2O3) / FeMoW / epoxy resin multilayer film has inorganic interconnections between the functional film layers, eliminating zero-point drift and creep caused by hydrogen-doped natural gas media containing CH4, CO2, CO, H2, H2O, and H2S, thereby improving the sensitivity of the ion-plated thin film sensing element and the accuracy of the measurement results.

[0038] 4) It realizes a direct correspondence between the number of tensile cycles (number of cycles) of the tension rod and the crack change value, effectively reducing the calculation error of crack propagation rate. At the same time, the drift and strain hysteresis of the strain gauge itself are also greatly reduced, and the sensitivity is improved. Due to the reduction of the extensometer electrode interface, the overall airtightness of the environmental chamber is increased, which can realize fatigue testing of materials in high-pressure (0MPa-25MPa) hydrogen-doped natural gas environment or other hydrogen-containing environments. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the present invention;

[0040] Figure 2 This is a schematic diagram of the structure of a sample of the present invention;

[0041] Figure 3 This is a side view of the strain gauge of the present invention;

[0042] Figure 4 This is a top view of the strain gauge of the present invention. Detailed Implementation

[0043] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0044] Example 1

[0045] like Figure 1 The embodiment shown in Figure 2 is a fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating. It includes a fatigue testing machine, a high-pressure gas environment chamber filled with high-pressure hydrogen-doped natural gas, and a pressure detection mechanism located within the high-pressure gas environment chamber. The upper and lower openings of the high-pressure gas environment chamber are respectively sealed to the upper and lower tension rods of the fatigue testing machine. The upper and lower parts of the sample 7 are fixedly connected to the upper and lower tension rods, respectively. A sealable rotating door is provided on one side of the high-pressure gas environment chamber. The pressure detection mechanism includes a horizontal support plate 1, a vertical baffle 2 located on the left side of the horizontal support plate, and a vertical baffle 2 located on the right side of the sample 7. The vertical rod 3 on the lower surface of the horizontal support plate on the right side of the baffle, the L-shaped rod 4 rotatably connected to the lower end of the vertical rod, and the strain gauge 5 on the side of the vertical baffle located to the lower left of the L-shaped rod; the vertical baffle and the strain gauge are fixedly connected, the right end of the transverse extension plate is fixedly connected to the upper part of the left side of the sample, the lower end of the vertical rod and the upper left end of the L-shaped rod are connected by a longitudinal rotating shaft 31, an arc-shaped buffer pad 6 is provided on the outer side of the corner of the L-shaped rod, the strain gauge is electrically connected to the strain tester, the L-shaped rod to the right of the arc-shaped buffer pad includes a sleeve 41 and a telescopic rod 42 that extends into the sleeve and is slidably connected to the sleeve, and the right end of the L-shaped rod is rotatably connected to the lower part of the left side of the sample.

[0046] The L-shaped bar is made of 18Ni(200) martensitic aging steel, which is an ultra-high strength steel with a micro-carbon martensite matrix that undergoes precipitation hardening of intermetallic compounds during aging. Unlike traditional high-strength steel, 18Ni(200) martensitic aging steel does not use carbon but relies on the dispersed precipitation of intermetallic compounds for strengthening. It possesses some unique properties: high strength and toughness, low hardening index, and good formability.

[0047] like Figure 3 , Figure 4 As shown, the strain gauge includes a substrate 101, a transition buffer layer 102 disposed on the substrate, an insulating layer 103 disposed on the transition buffer layer, a functional layer 104 disposed on the upper surface of the insulating layer, and a protective layer 105 disposed on the functional layer. The substrate is made of X52MS steel, the transition buffer layer is a CrAl film, the insulating layer is a TGA / Al2O3 film, the functional layer is an FeMoW alloy film, and the protective layer is an epoxy resin coating.

[0048] The manufacturing process of strain gauges is as follows:

[0049] (4-1) Preparation of FeMoW alloy target material for vacuum multi-arc ion plating;

[0050] (4-2) After physical grinding and polishing the substrate, the substrate is placed in a mixed solution of anhydrous ethanol and acetone for ultrasonic cleaning, and then dried with a hair dryer.

[0051] (4-3) Place the substrate on the workpiece rack in the coating chamber, and symmetrically place 99.99% Cr target and 99.99% Al target on the cathode arc source, so that the distance between the Cr target, Al target and the substrate is 80mm; evacuate the coating chamber to below 0.003Pa, and introduce argon gas at a flow rate of 20sccm into the coating chamber, and control the working pressure of the coating chamber to 0.09Pa; start the cathode arc source, set the negative bias voltage of the substrate to 800V, and bombard the substrate with arc light for 18min;

[0052] (4-4) A transition buffer layer of metal CrAl film is deposited on the upper surface of the substrate:

[0053] The coating chamber was evacuated to 0.002 Pa, and argon gas with a flow rate of 28 sccm was introduced to make the working gas pressure of the coating chamber 0.3 Pa, the negative bias voltage of the substrate 130 V, the magnetic field frequency of the substrate 150 Hz, the current of both the Cr and Al targets 50 A, and the coating time 50 min. The coating was carried out to obtain a 400 nm metal CrAl film transition buffer layer on the upper surface of the substrate.

[0054] (4-5) Preparation of insulating layers by vacuum atmosphere thermal growth and vacuum multi-arc ion plating:

[0055] First, place the substrate in a vacuum tube furnace, evacuate the vacuum tube furnace to 0.1 Pa, and continuously introduce 0.4 Pa of O2. Oxidize the substrate at 600°C for 2 hours. Then, turn off the heating power of the vacuum tube furnace and allow the vacuum tube furnace to cool to room temperature. Open the vacuum vent valve of the vacuum tube furnace, remove the substrate, and obtain a 150 nm thermally grown TGA film on the upper surface of the metal CrAl film.

[0056] The substrate is then placed in the coating chamber, and an Al target is placed on the cathode arc source. The distance between the Al target and the substrate is set to 80 mm. The coating chamber is evacuated to 0.002 Pa. Argon and oxygen in a ratio of 2:1 are introduced into the coating chamber. The cathode arc source is started, and the negative bias voltage of the substrate is set to 130 V, the working pressure of the substrate is set to 0.6 Pa, the magnetic field frequency of the substrate is set to 130 Hz, the current of the Al target is set to 55 A, and the coating time is set to 2.5 h. The coating is then carried out, and an Al2O3 film with a thickness of 400 nm is obtained on the upper surface of the TGA film on the substrate.

[0057] (4-6) Functional layer preparation of FeMoW alloy film by vacuum multi-arc ion plating:

[0058] The substrate is placed on the worktable of the coating chamber. A patterned grid mask is fixed to the upper surface of the substrate using a fixture, ensuring a tight fit between the mask and the substrate. An FeMoW target is placed on the cathode arc source, with a distance of 80 mm between the FeMoW target and the substrate. The coating chamber is evacuated to 0.002 Pa, and argon gas is introduced at a flow rate of 25 sccm. The cathode arc source is started, setting the substrate's negative bias voltage to 130 V, its working pressure to 0.5 Pa, its magnetic field frequency to 140 Hz, and the FeMoW target current to 50 A. The coating time is 0.8 h. Coating is then performed, resulting in a thin film of Al₂O₃ on the substrate. Figure 4 The functional layer shown is an 800nm ​​thick FeMoW alloy film with a patterned grid shape.

[0059] (4-7) Preparation of the protective layer:

[0060] Epoxy resin, dibutyl phthalate, and ethylenediamine were weighed in a mass ratio of 100:6:7. The weighed epoxy resin and dibutyl phthalate were mixed and stirred evenly within a temperature range of 60°C. After cooling to 35°C, the weighed ethylenediamine was added and stirred evenly to obtain a mixture. The mixture was then coated onto the outer surface of the substrate taken out of the coating chamber. Air bubbles and excess mixture on the substrate were removed by rolling with cellophane. After the mixture cured, a cured protective layer was formed, and the strain gauge was completed.

[0061] The FeMoW alloy target has an elemental composition of 5% Mo, 3% W, and the balance being Fe; the impurity content of the FeMoW alloy target is less than 0.02%, the void defect is less than 0.1 mm, and the grain size is less than 50 μm.

[0062] The working process of this invention is as follows:

[0063] The fatigue testing machine is equipped with a hydraulic cylinder at the bottom to drive the lower tension rod to reciprocate up and down; for example Figure 2 As shown, a notch is machined on the sample. An alternating load is used to pre-create a crack 72 extending along the notch. The rotating door is opened and the upper part of the sample is placed in the U-shaped opening groove of the upper tension rod. A cylindrical pin is passed through the sample fixing hole 71 above the notch and the holes on both sides of the U-shaped opening groove of the upper tension rod to connect the sample and the upper tension rod.

[0064] Place the lower part of the sample into the U-shaped opening groove of the lower tension rod, and use a cylindrical pin to pass through the sample fixing hole below the notch and the holes on both sides of the U-shaped opening groove of the lower tension rod to connect the sample and the lower tension rod.

[0065] like Figure 1 As shown, the right end of the horizontal support plate is provided with an upper vertical connecting plate 11, which is connected to the two screw holes reserved on the upper left side of the sample by two screws.

[0066] The right end of the telescopic rod is provided with a rotating seat 421. The rotating seat includes a lower vertical connecting plate, a front side plate 4211 and a rear side plate on the left side of the lower vertical connecting plate. The right end of the telescopic rod is rotatably connected to the front side plate and the rear side plate through a longitudinal rotating shaft 4212. The lower vertical connecting plate is connected to the two screw holes reserved on the lower left side of the sample with two screws.

[0067] Make the horizontal support plate and the telescopic rod horizontal. Close the rotating door to seal the high-pressure gas environment box. Open the valve of the gas cylinder to allow the hydrogen-blended natural gas to enter the high-pressure gas environment box. When the pressure of the gas in the high-pressure gas environment box reaches 12 MPa, close the valve of the gas cylinder.

[0068] As the hydraulic cylinder repeatedly pulls the sample downwards, the crack at the notch of the sample continues to extend, the notch gradually opens, the telescopic rod gradually tilts and extends to the lower right, and the arc-shaped buffer pad gradually approaches the strain gauge. The pressure signal detected by the strain gauge is transmitted to the strain testing instrument.

[0069] The strain gauge obtains the pressure value corresponding to the pressure signal detected by the strain gauge. The pressure value is used as the independent variable and substituted into the fitting function to obtain the crack length a corresponding to the pressure value. Furthermore, based on the stress cycle number N of the current fatigue testing machine, the relationship between the stress cycle number N and the crack length a is obtained. The fatigue crack propagation rate of the sample in the hydrogen-doped natural gas environment is calculated using the formula da / dN. The fatigue crack propagation rate is used to estimate the fatigue life of the cracked body (sample).

[0070] Example 2

[0071] The thickness of the metallic CrAl film is 300 nm, the thickness of the TGA / Al2O3 film is 450 nm, the thickness of the FeMoW alloy film is 600 nm, and the Ar:O2 ratio of the Al2O3 film is 2:1.

[0072] The FeMoW alloy target material has an elemental composition of 10% Mo, 7% W, and the balance being Fe; the impurity content of the FeMoW alloy target material is less than 0.02%, the void defect is less than 0.1 mm, and the grain size is less than 50 μm. The preparation process of the epoxy resin cured protective layer is as follows:

[0073] Epoxy resin, dibutyl phthalate, and ethylenediamine were weighed in a mass ratio of 100:4:4. The weighed epoxy resin and dibutyl phthalate were mixed and stirred evenly at 65°C. After cooling to 35°C, the weighed ethylenediamine was added and stirred evenly to obtain a mixture. The mixture was then coated onto the outer surface of a substrate removed from the coating chamber. Air bubbles and excess mixture were removed from the substrate by rolling with cellophane. After the mixture cured, a cured protective layer was formed. The other contents of Example 2 are the same as in Example 1.

[0074] Example 3

[0075] The thickness of the metallic CrAl film is 300 nm, the thickness of the TGA / Al2O3 film is 450 nm, the thickness of the FeMoW alloy film is 600 nm, and the Ar:O2 ratio of the Al2O3 film is 2:1.

[0076] The FeMoW alloy target has an elemental composition of 5% Mo, 7% W, and the balance being Fe; the impurity content of the FeMoW alloy target is less than 0.02%, the void defect is less than 0.1 mm, and the grain size is less than 50 μm.

[0077] The preparation process of the epoxy resin cured protective layer is as follows:

[0078] Epoxy resin, dibutyl phthalate, and ethylenediamine were weighed in a mass ratio of 100:4:7. The weighed epoxy resin and dibutyl phthalate were mixed and stirred evenly at 60°C. After cooling to 40°C, the weighed ethylenediamine was added and stirred evenly to obtain a mixture. The mixture was then coated onto the outer surface of a substrate removed from the coating chamber. Air bubbles and excess mixture were removed from the substrate by rolling with cellophane. After the mixture cured, a cured protective layer was formed. The other contents of Example 3 are the same as in Example 1.

[0079] Example 4

[0080] The thickness of the metallic CrAl film is 350 nm, the thickness of the TGA / Al2O3 film is 500 nm, the thickness of the FeMoW alloy film is 800 nm, and the Ar:O2 ratio of the Al2O3 film is 2.2:1.

[0081] The elemental composition of the FeMoW alloy target is 10% Mo, 3% W, and the balance is Fe; the impurity content of the FeMoW alloy target is less than 0.02%, the void defect is less than 0.1 mm, and the grain size is less than 50 μm.

[0082] The preparation process of the epoxy resin cured protective layer is as follows:

[0083] Epoxy resin, dibutyl phthalate, and ethylenediamine were weighed in a mass ratio of 100:7:4. The weighed epoxy resin and dibutyl phthalate were mixed and stirred evenly at 55°C. After cooling to 30°C, the weighed ethylenediamine was added and stirred evenly to obtain a mixture. The mixture was then coated onto the outer surface of a substrate removed from the coating chamber. Air bubbles and excess mixture were removed from the substrate by rolling with cellophane. After the mixture cured, a cured protective layer was formed. The other contents of Example 4 are the same as in Example 1.

[0084] Example 5

[0085] The thickness of the metallic CrAl film is 500 nm, the thickness of the TGA / Al2O3 film is 600 nm, the thickness of the FeMoW alloy film is 1000 nm, and the Ar:O2 ratio of the Al2O3 film is 2.5:1.

[0086] The FeMoW alloy target has an elemental composition of 8% Mo, 5% W, and the balance being Fe; the impurity content of the FeMoW alloy target is less than 0.02%, the void defect is less than 0.1 mm, and the grain size is less than 50 μm.

[0087] The preparation process of the epoxy resin cured protective layer is as follows:

[0088] Epoxy resin, dibutyl phthalate, and ethylenediamine were weighed in a mass ratio of 100:5:5. The weighed epoxy resin and dibutyl phthalate were mixed and stirred evenly at 60°C. After cooling to 40°C, the weighed ethylenediamine was added and stirred evenly to obtain a mixture. The mixture was then coated onto the outer surface of a substrate removed from the coating chamber. Air bubbles and excess mixture were removed from the substrate by rolling with cellophane. After the mixture cured, a cured protective layer was formed. The other contents of Example 5 are the same as in Example 1.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating, characterized in that, The system includes a fatigue testing machine, a high-pressure gas environment chamber filled with high-pressure hydrogen-doped natural gas, and a pressure detection mechanism located in the high-pressure gas environment chamber; the upper and lower openings of the high-pressure gas environment chamber are respectively sealed to the upper and lower tension rods of the fatigue testing machine, and the upper and lower parts of the sample (7) are respectively fixedly connected to the upper and lower tension rods; a sealable rotating door is provided on one side of the high-pressure gas environment chamber; the pressure detection mechanism includes a horizontal support plate (1), a vertical baffle (2) located on the left side of the horizontal support plate, a vertical rod (3) located on the lower surface of the horizontal support plate on the right side of the vertical baffle, an L-shaped rod (4) rotatably connected to the lower end of the vertical rod, and a strain gauge (5) located on the side of the vertical baffle located to the lower left of the L-shaped rod; the vertical baffle is fixedly connected to the strain gauge, the right end of the transverse extension plate is fixedly connected to the upper part of the left side of the sample, and the lower end of the vertical rod is fixedly connected to the upper part of the sample. The upper left ends of the L-shaped rods are connected by a longitudinal rotating shaft (31). An arc-shaped buffer pad (6) is provided on the outer side of the corner of the L-shaped rod. The strain gauge is electrically connected to the strain tester. The L-shaped rod on the right side of the arc-shaped buffer pad includes a sleeve (41) and a telescopic rod (42) that extends into the sleeve and is slidably connected to the sleeve. The right end of the L-shaped rod is rotatably connected to the lower left side of the sample. The strain gauge includes a substrate (101), a transition buffer layer (102) on the substrate, an insulating layer (103) on the transition buffer layer, a functional layer (104) on the upper surface of the insulating layer, and a protective layer (105) on the functional layer. The substrate is made of X52MS pipeline steel. The transition buffer layer is a metal CrAl film. The insulating layer is a TGA / Al2O3 film. The functional layer is a FeMoW alloy film. The protective layer is an epoxy resin coating.

2. The fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating according to claim 1, characterized in that, The manufacturing process of strain gauges is as follows: (2-1) Preparation of FeMoW alloy target material for vacuum multi-arc ion plating; (2-2) After physical grinding and polishing the substrate, the substrate is placed in a mixed solution of anhydrous ethanol and acetone for ultrasonic cleaning, and then dried using a hair dryer. (2-3) Place the substrate on the workpiece rack in the coating chamber, and symmetrically place 99.99% Cr target and 99.99% Al target on the cathode arc source, so that the distance between the Cr target, Al target and the substrate is 75mm-85mm; evacuate the coating chamber to below 0.003Pa, and introduce argon gas at a flow rate of 15sccm-25sccm into the coating chamber, and control the working pressure of the coating chamber to 0.09Pa; start the cathode arc source, set the negative bias voltage of the substrate to 750V-850V, and bombard the substrate with arc light for 15min-20min; (2-4) A transition buffer layer of metal CrAl film is deposited on the upper surface of the substrate; (2-5) Preparation of insulating layer by vacuum atmosphere thermal growth and vacuum multi-arc ion plating: First, the substrate is placed in a vacuum tube furnace, the vacuum tube furnace is evacuated, and O2 is continuously introduced to carry out thermal growth, and a thermally grown TGA film is obtained on the upper surface of the metal CrAl film. The substrate is placed in the coating chamber, and an Al target is placed on the cathode arc source. The distance between the Al target and the substrate is set to 75mm-85mm. After evacuating the coating chamber, argon and oxygen are introduced. The cathode arc source is started, and the negative bias voltage, working pressure and magnetic field frequency of the substrate are adjusted. The current and coating time of the Al target are adjusted to perform coating. An Al2O3 film is obtained on the upper surface of the TGA film on the substrate, and an insulating layer of TGA / Al2O3 film is obtained. (2-6) Preparation of the functional layer of FeMoW alloy film by vacuum multi-arc ion plating: The substrate is placed in the coating chamber, and the patterned grid mask is tightly attached to the upper surface of the substrate using a fixture. The FeMoW target is placed on the cathode arc source, and the distance between the FeMoW target and the substrate is set to 75 mm-85 mm. After evacuating the coating chamber, argon gas is introduced, the cathode arc source is started, and the negative bias voltage, working pressure and magnetic field frequency of the substrate are adjusted. The current and coating time of the FeMoW target are adjusted to perform coating. The functional layer of FeMoW alloy film is obtained on the upper surface of the Al2O3 thin film of the substrate. (2-7) Preparation of protective layer: Stir the mixture of epoxy resin, dibutyl phthalate and ethylenediamine evenly, coat the mixture on the outer surface of the substrate, and after the mixture is cured, a cured protective layer is formed, and the strain gauge is completed.

3. The fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating according to claim 2, characterized in that, Steps (2-4) include the following specific steps: The coating chamber is evacuated to 0.001Pa-0.003Pa, and argon gas with a flow rate of 25sccm-30sccm is introduced to make the working gas pressure of the coating chamber 0.1Pa-0.5Pa, the negative bias voltage of the substrate 100V-150V, the magnetic field frequency of the substrate 100Hz-170Hz, the current of both the Cr and Al targets 30A-60A, and the coating time 40min-60min. The coating is then performed to obtain a 300nm-500nm metal CrAl film transition buffer layer on the upper surface of the substrate.

4. The fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating according to claim 2, characterized in that, Steps (2-5) include the following specific steps: First, place the substrate in a vacuum tube furnace, evacuate the vacuum tube furnace to 0.1 Pa, and continuously introduce O2 at 0.1 Pa-0.5 Pa. Oxidize the substrate at 600℃ for 1-3 hours. Turn off the heating power of the vacuum tube furnace and allow the vacuum tube furnace to cool to room temperature. Open the vacuum vent valve of the vacuum tube furnace, remove the substrate, and obtain a 100 nm-200 nm thermally grown TGA film on the upper surface of the metal CrAl film. The substrate is then placed in the coating chamber, and an Al target is placed on the cathode arc source. The distance between the Al target and the substrate is set to 75mm-85mm. The coating chamber is evacuated to 0.001Pa-0.003Pa. Argon and oxygen in a ratio of (1-3):1 are introduced into the coating chamber. The cathode arc source is started, and the negative bias voltage of the substrate is set to 100V-150V, the working pressure of the substrate is set to 0.5Pa-0.8Pa, the magnetic field frequency of the substrate is set to 100Hz-150Hz, the current of the Al target is set to 50A-60A, and the coating time is set to 2h-3h. The coating is then carried out, and an Al2O3 film with a thickness of 300nm-500nm is obtained on the upper surface of the TGA film on the substrate.

5. The fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating according to claim 2, characterized in that, The FeMoW alloy target has an elemental composition of 5%-10% Mo, 3%-7% W, and the balance being Fe; the FeMoW alloy target has an impurity content of less than 0.02%, void defects of less than 0.1 mm, and grain size of less than 50 μm.

6. The fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating according to claim 2, characterized in that, Steps (2-6) include the following specific steps: The substrate is placed on the workpiece stage of the coating chamber. A patterned grid mask is fixed to the upper surface of the substrate using a fixture, ensuring a tight fit between the mask and the substrate. An FeMoW target is placed on the cathode arc source, with the distance between the FeMoW target and the substrate set to 75mm-80mm. The coating chamber is evacuated to 0.001Pa-0.003Pa, and argon gas is introduced at a flow rate of 20sccm-30sccm. The cathode arc source is activated, and the negative bias voltage of the substrate is set to 100V-150V, the working pressure of the substrate to 0.1Pa-0.6Pa, the magnetic field frequency of the substrate to 120Hz-150Hz, the current of the FeMoW target to 40A-60A, and the coating time to 0.5h-1h. The coating process is carried out, resulting in a 600nm-1000nm thick FeMoW alloy film with a patterned grid shape on the upper surface of the Al2O3 thin film on the substrate.

7. The fatigue testing device for hydrogen-doped natural gas environment based on vacuum multi-arc ion plating according to claim 2, 3, 4, 5, or 6, characterized in that, Steps (2-7) include the following specific steps: Epoxy resin, dibutyl phthalate, and ethylenediamine are weighed in a mass ratio of 100:(4-7):(4-7). The weighed epoxy resin and dibutyl phthalate are mixed and stirred evenly within a temperature range of 55℃-65℃. After cooling to 30℃-40℃, the weighed ethylenediamine is added and stirred evenly to obtain a mixture. The mixture is then coated on the outer surface of the substrate taken out of the coating chamber. Air bubbles and excess mixture on the substrate are removed by rolling with cellophane. After the mixture cures, a cured protective layer is formed.

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