A method for testing hydrogen-induced cracking of a material under a high-pressure hydrogen environment

Abstract

The application relates to the technical field of material testing, and discloses a material hydrogen-induced cracking test method under a high-pressure hydrogen environment, wherein first, an extended compact tension specimen is prepared based on size data of a standard wedge-opening loading specimen and a standard compact tension specimen; then, the extended compact tension specimen is subjected to fatigue crack pre-preparation by a fatigue testing machine, and shape conversion is carried out, so that a standard wedge-opening loading specimen with a fatigue crack is obtained, which is used as a target wedge-opening loading specimen; next, a load is applied to the fatigue crack end on the target wedge-opening loading specimen, and the target wedge-opening loading specimen is placed in a high-pressure hydrogen environment, so that a current hydrogen-induced crack length is determined; finally, according to an initial applied stress intensity factor, the current hydrogen-induced crack length and a standard value of the hydrogen-induced crack length, a stress intensity factor threshold value of a material to be tested is determined. The method can not only obtain a more accurate hydrogen-induced lagging cracking stress intensity factor threshold value, but also effectively reduce the test cost.

Description

Technical Field

[0001] This application relates to the field of materials testing technology, and in particular to a method for testing hydrogen-induced cracking of materials under high-pressure hydrogen conditions. Background Technology

[0002] Hydrogen-induced cracking is a brittle fracture phenomenon in metallic materials caused by the adsorption, diffusion, and local enrichment of hydrogen atoms in a hydrogen environment. Essentially, hydrogen reduces the fracture toughness of the material and promotes crack nucleation and propagation. In high-pressure hydrogen environments (such as hydrogen storage containers and hydrogen pipelines), hydrogen-induced cracking has become one of the key risk factors leading to material failure during service.

[0003] The hydrogen-induced hysteresis cracking stress intensity factor threshold is an important fracture mechanics parameter for hydrogen-exposed materials. This parameter characterizes the material's resistance to hydrogen-induced cracking under high-pressure hydrogen conditions. It can serve as a basis for screening hydrogen-exposed materials and as fundamental data for calculating the fatigue life of hydrogen-exposed components based on fracture mechanics methods. In related technologies, a pre-cracked sample is subjected to a certain initial load and then tested under high-pressure hydrogen conditions. The hydrogen-induced hysteresis cracking stress intensity factor threshold is obtained based on the test results. However, the accuracy of the hydrogen-induced hysteresis cracking stress intensity factor threshold measured in related technologies needs improvement. Therefore, a new testing method is urgently needed. Summary of the Invention

[0004] This application provides a method for testing hydrogen-induced cracking of materials under high-pressure hydrogen environment, which solves the technical problem that the accuracy of the stress intensity factor threshold value for hydrogen-induced hysteresis cracking needs to be improved in related technologies, and achieves the technical effect of obtaining a more accurate stress intensity factor threshold value.

[0005] To achieve the above objectives, the main technical solutions adopted in this application include:

[0006] This application provides a method for testing hydrogen-induced cracking of materials under high-pressure hydrogen conditions, the method comprising:

[0007] Based on the dimensional data of the standard wedge-shaped open loading specimen and the dimensional data of the standard compact tensile specimen, the extended dimensions that meet the installation requirements of the fatigue testing machine are determined. Based on the extended dimensions, an extended compact tensile specimen of the material to be tested is prepared. The material to be tested is a certain material intended for use in hydrogen storage containers or structural components of hydrogen energy equipment in high-pressure hydrogen environments.

[0008] The fatigue cracks of the extended compact tensile specimen are pre-formed using the fatigue testing machine to obtain an extended compact tensile specimen with fatigue cracks.

[0009] The shape of the extended compact tensile specimen with fatigue cracks is transformed to obtain a standard wedge-shaped opening loading specimen with fatigue cracks, which is used as the target wedge-shaped opening loading specimen.

[0010] A load is applied to the fatigue crack tip on the target wedge-shaped opening loading specimen, and the loaded target wedge-shaped opening loading specimen is placed in a high-pressure hydrogen environment to determine the current hydrogen-induced crack length; wherein, the load is the initial applied stress intensity factor, which is determined based on the stress intensity factor threshold estimate;

[0011] Based on the initial applied stress intensity factor corresponding to the target wedge-shaped opening loaded specimen, the current hydrogen-induced crack length, and the standard value of the hydrogen-induced crack length, the stress intensity factor threshold value of the material to be tested is determined.

[0012] Optionally, the initial applied stress intensity factor corresponding to the target wedge-shaped opening loading specimen adopts the initial applied stress intensity factor of the target specimen group to which the target wedge-shaped opening loading specimen belongs; determining the stress intensity factor threshold value of the material to be tested based on the initial applied stress intensity factor corresponding to the target wedge-shaped opening loading specimen, the current hydrogen-induced crack length, and the standard value of the hydrogen-induced crack length includes:

[0013] If the target sample group is determined to meet the preset requirements based on the current hydrogen-induced crack length and the standard value of the hydrogen-induced crack length, then the stress intensity factor threshold value of the test material is determined based on the initial applied stress intensity factor corresponding to the target sample group.

[0014] Optionally, the target sample set includes multiple target wedge-shaped opening loading samples; the target sample set is determined to meet the preset requirements by the following method:

[0015] The current hydrogen-induced crack length of the target sample group is determined based on the hydrogen-induced crack length of each target wedge-shaped opening loaded sample.

[0016] The current hydrogen-induced crack length of the target sample group is compared with the standard value of the hydrogen-induced crack length, and the target sample group is determined to meet the preset requirements based on the comparison result.

[0017] Optionally, determining that the target sample group meets the preset requirements based on the comparison results includes:

[0018] If the current hydrogen-induced crack length is less than or equal to the standard value and the difference data between the current hydrogen-induced crack length and the standard value meets the preset difference requirement, the target sample group is determined to meet the preset requirement.

[0019] Optionally, the target wedge-shaped opening loading specimen belongs to a target specimen group, and the target specimen group corresponds to an initial applied stress intensity factor; the step of applying a load to the fatigue crack tip on the target wedge-shaped opening loading specimen and placing the loaded target wedge-shaped opening loading specimen into a high-pressure hydrogen environment includes:

[0020] Based on the initial applied stress intensity factor corresponding to the target sample group, a load is applied to the fatigue crack end of each target wedge-shaped opening loaded sample in the target sample group, and each target wedge-shaped opening loaded sample with applied load is placed in a high-pressure hydrogen environment to determine the current hydrogen-induced crack length corresponding to the target sample group.

[0021] Optionally, the initial applied stress intensity factor corresponding to the target wedge-shaped opening loading specimen is adopted as the initial applied stress intensity factor of the target specimen group to which the target wedge-shaped opening loading specimen belongs; the target specimen group is determined in the following way:

[0022] Multiple initial specimen sets are provided; wherein each initial specimen set includes multiple target wedge-shaped opening-loaded specimens with fatigue cracks;

[0023] The initial applied stress intensity factor for any initial sample group is determined between the first stress intensity factor threshold and the second stress intensity factor threshold.

[0024] Based on the initial applied stress intensity factor of any initial sample group, hydrogen-induced cracking test is performed on each target wedge opening loading sample in any initial sample group to obtain the current hydrogen-induced crack length corresponding to any initial sample group.

[0025] The target sample group is determined from the plurality of initial sample groups based on the current hydrogen-induced crack length and the standard value of the hydrogen-induced crack length corresponding to any initial sample group.

[0026] Optionally, applying a load to the fatigue crack tip on the target wedge-shaped opening loading specimen includes:

[0027] Obtain the estimated value of the stress intensity factor threshold for the material under test; wherein the estimated value of the stress intensity factor threshold is used to characterize the estimation of the stress intensity factor threshold value for hydrogen-induced hysteresis cracking.

[0028] Determine the initial applied stress intensity factor of the material to be tested;

[0029] The constant displacement method was used to apply a load to the fatigue crack end of the target wedge-shaped opening loading specimen.

[0030] Optionally, obtaining the estimated stress intensity factor threshold of the material under test includes:

[0031] Based on the relationship between the yield strength of the material and the stress intensity factor threshold value, the stress intensity factor threshold value of the material to be tested is estimated to obtain the estimated value of the stress intensity factor threshold.

[0032] Optionally, the fatigue testing machine has a matching U-shaped clamp. The process of pre-forming fatigue cracks in the extended compact tensile specimen using the fatigue testing machine to obtain an extended compact tensile specimen with fatigue cracks includes:

[0033] The extended compact tensile specimen is clamped using the U-shaped clamp;

[0034] Adjust the Young's modulus in the fatigue testing machine; wherein, the fatigue testing machine before adjustment was used to pre-incubate fatigue cracks in standard compact tensile specimens;

[0035] Fatigue crack pre-induction was performed on the extended compact tensile specimen using the adjusted fatigue testing machine.

[0036] Optionally, the step of converting the fatigue-cracked extended compact tensile specimen into a standard wedge-shaped opening loading specimen, as the target wedge-shaped opening loading specimen, includes:

[0037] The extended compact tensile specimen with fatigue cracks is machined to adjust its length to the target length required by the standard wedge-shaped opening loading specimen, and the flat pin hole and threaded hole required by the standard wedge-shaped opening loading specimen are machined; wherein, during the machining of the threaded hole, a shock-absorbing component needs to be added at the machined crack.

[0038] In this embodiment, firstly, the extended dimensions that meet the installation requirements of the fatigue testing machine are determined based on the dimensional data of the standard wedge-shaped opening loading specimen and the standard compact tensile specimen. Then, an extended compact tensile specimen of the material to be tested is prepared based on the extended dimensions. This allows for fatigue crack pre-forming using an existing fatigue testing machine for pre-forming fatigue cracks in compact tensile specimens. After pre-forming, the specimen is then processed into the target wedge-shaped opening loading specimen. There is no need to introduce new equipment for pre-forming fatigue cracks in wedge-shaped opening loading specimens. Compared with the use of three-point bending specimens in related technologies, the extended compact tensile specimen can significantly reduce the material requirements of the test material. Furthermore, fatigue crack pre-induction can be performed using existing fatigue testing machines, thus effectively saving testing costs in two aspects. Then, the load is determined based on the estimated stress intensity factor threshold, and a load is applied to the end of the fatigue crack on the target wedge-shaped open loading specimen to conduct hydrogen-induced crack testing. Based on the initial applied stress intensity factor, the current hydrogen-induced crack length, and the standard value of the hydrogen-induced crack length corresponding to the target wedge-shaped open loading specimen, the stress intensity factor threshold value of the material to be tested is determined. Compared with related technologies, determining the initial applied stress intensity factor based on the estimated stress intensity factor threshold can obtain a more accurate stress intensity factor threshold value. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1a A flowchart of the hydrogen-induced cracking test method for materials under high-pressure hydrogen environment provided in the embodiments of this specification;

[0041] Figure 1b This is a schematic diagram of the structure of a standard wedge-shaped opening loading specimen provided in the embodiments of this specification;

[0042] Figure 1c This is a schematic diagram of the structure of the extended compact tensile specimen provided in the embodiments of this specification;

[0043] Figure 2 A flowchart of the hydrogen-induced cracking test method for materials under high-pressure hydrogen environment provided in the embodiments of this specification;

[0044] Figure 3 A flowchart of the hydrogen-induced cracking test method for materials under high-pressure hydrogen environment provided in the embodiments of this specification;

[0045] Figure 4A flowchart of the hydrogen-induced cracking test method for materials under high-pressure hydrogen environment provided in the embodiments of this specification;

[0046] Figure 5 This is a flowchart of a test method for hydrogen-induced cracking of materials under high-pressure hydrogen conditions, provided in the embodiments of this specification. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] Hydrogen-induced cracking is a key risk factor leading to material failure during service. Therefore, when designing hydrogen-contaminated containers, it is necessary to test the material's resistance to hydrogen embrittlement under high-pressure hydrogen environments. The ASME BPVC KD10 standard specifies that the suitability of a material for a hydrogen environment is determined by testing its hydrogen-induced hysteresis cracking stress intensity factor threshold value. The common testing procedure involves applying an initial load to a wedge-opening load (WOL) specimen, then placing it in a high-pressure hydrogen environment for a specified period. After the specified test time, the specimen is removed, and the crack propagation is measured. The crack propagation value is used to determine the material's hydrogen-induced hysteresis cracking stress intensity factor threshold value K. IH In related technologies, fatigue crack pre-induction is first performed using a three-point bending specimen, which is then machined into a wedge-shaped open-load specimen. However, the initial machining of the three-point bending specimen requires several times the amount of test material compared to the target specimen, resulting in high material consumption and testing costs. Furthermore, the ASME BPVCKD10 standard only specifies the initial applied stress intensity factor (K). IAPP The configurable range means that any K selected within the defined range... IAPP All values ​​can be considered reasonable experimental conditions. For the same material and testing environment, different people may obtain different K values ​​by setting different initial applied stress intensity factors. IH The values ​​are different, and the differences are significant. However, K IH This refers to a material's ability to resist hydrogen-induced cracking under high-pressure hydrogen conditions. It is an inherent property of the material and should not be altered by loading conditions. Such artificially imposed dependence seriously violates the theoretical framework of fracture mechanics and may mislead engineering material selection. For example, overestimating the suitability of high-strength steel in a hydrogen environment may lead to potential structural failure risks.

[0049] Based on this, this application provides a method for testing hydrogen-induced cracking of materials under high-pressure hydrogen conditions. The method includes: first, determining the expansion dimensions that meet the installation requirements of a fatigue testing machine based on the dimensional data of a standard wedge-shaped opening loading specimen and a standard compact tensile specimen; then, preparing an expanded compact tensile specimen of the material to be tested based on the expansion dimensions; next, pre-fabricating fatigue cracks in the expanded compact tensile specimen using a fatigue testing machine to obtain an expanded compact tensile specimen with fatigue cracks; finally, transforming the expanded compact tensile specimen with fatigue cracks into a standard wedge-shaped opening loading specimen with fatigue cracks, which serves as the target wedge-shaped opening loading specimen. Compared with related technologies, this method can significantly reduce the consumption of the material to be tested, thereby reducing testing costs.

[0050] Furthermore, during hydrogen-induced cracking testing, firstly, multiple initial sample groups are provided; each initial sample group includes multiple target wedge-shaped opening-loaded specimens with fatigue cracks. Then, an initial applied stress intensity factor for any initial sample group is determined between a first stress intensity factor threshold and a second stress intensity factor threshold. Next, hydrogen-induced cracking testing is performed on each target wedge-shaped opening-loaded specimen in any initial sample group based on the initial applied stress intensity factor, obtaining the current hydrogen-induced crack length corresponding to any initial sample group. Finally, a target sample group is determined from the multiple initial sample groups based on the current hydrogen-induced crack length and the standard value of the hydrogen-induced crack length corresponding to any initial sample group. The threshold value of the hydrogen-induced hysteresis cracking stress intensity factor for the tested material is determined based on the test data of the target sample group. Through this method, the target sample group whose current hydrogen-induced crack length is closest to the standard value can be obtained. Based on the initial applied stress intensity factor corresponding to this group, an accurate threshold value of the hydrogen-induced hysteresis cracking stress intensity factor can be determined, effectively solving the problem of the potential need to improve the accuracy of the hydrogen-induced hysteresis cracking stress intensity factor threshold value in the ASME BPVC KD10 standard.

[0051] According to an embodiment of this application, a method for testing hydrogen-induced cracking of materials under high-pressure hydrogen environment is provided. It should be noted that although the logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than that shown here.

[0052] This embodiment provides a method for testing hydrogen-induced cracking of materials under high-pressure hydrogen conditions. Please refer to [link to relevant documentation]. Figure 1a The method includes:

[0053] S110. Based on the dimensional data of the standard wedge-shaped open loading specimen and the dimensional data of the standard compact tensile specimen, determine the extended dimensions that meet the installation requirements of the fatigue testing machine, and prepare an extended compact tensile specimen of the material to be tested based on the extended dimensions.

[0054] The dimensions of the standard wedge-shaped open-loaded specimen can be those specified in ASTM E1681. The dimensions of the standard compact tensile specimen can be those specified in ASTM E399. The extended dimensions refer to the dimensions adjusted based on the standard compact tensile specimen dimensions. The fatigue testing machine can be an MTS fatigue testing machine suitable for testing standard compact tensile specimens, capable of fatigue crack pre-induction according to ASTM E399. It is a commonly used and widely available device for fatigue crack pre-induction. This application utilizes this device to achieve fatigue crack pre-induction of wedge-shaped open-loaded specimens, thus eliminating the need to introduce new equipment for fatigue crack pre-induction of wedge-shaped open-loaded specimens. The material to be tested is a material intended for use in high-pressure hydrogen storage containers or structural components of hydrogen energy equipment.

[0055] In some implementations, please refer to Figure 1b , Figure 1b The figure shows a standard wedge-shaped opening loading specimen. The first direction in the figure is parallel to the machining crack, and the second direction is perpendicular to the first direction. The dimensional data of the standard wedge-shaped opening loading specimen are as follows:

[0056] The width (from the center line of the screw hole to the back of the sample) is W, along the first direction, with an error of ±0.005W;

[0057] The distance from the centerline of the screw hole to the end of the machining crack is 'a', along the first direction;

[0058] The total width of the sample is 1.255W, and the error along the first direction is ±0.005W;

[0059] Thickness B is 0.5W, along the first direction, with an error of ±0.01W;

[0060] The distance from the crack center plane to the bottom of the specimen is 0.486W, with an error of ±0.005W along the second direction;

[0061] The distance from the center plane of the flat pin to the center plane of the crack is 0.1W, and the error is ±0.005W along the second direction;

[0062] The diameter of the flat pin hole is 0.25W, with an error of ±0.005W;

[0063] The screw hole diameter is 0.25W;

[0064] The side groove has a V-shaped groove structure with an opening angle of 53±2°, and the groove depth is precisely controlled within 10±0.5% of the sample thickness.

[0065] It should be noted that the dimensions of the extended compact tensile specimen are based on the aforementioned dimensions of the standard wedge-shaped open-load specimen, but do not include the screw hole and flat pin hole dimensions, as these two holes do not need to be machined in this case. It should also be noted that the extension dimension is the dimension extended in the second direction, i.e., the length direction of the standard wedge-shaped open-load specimen. Its purpose is to allow space on the specimen to machine the two symmetrical loading holes of the standard compact tensile specimen, so that fatigue crack pre-induction can be performed on the extended compact tensile specimen using a fatigue testing machine. The dimensions of the loading holes are consistent with the dimensions of the standard compact tensile specimen, and the distance from the centerline of the loading hole to the machined crack tip is 'a'. For an example, please refer to [link to example]. Figure 1c , Figure 1c For extended compact tensile specimens, the first direction in the figure is parallel to the machining crack, and the second direction is perpendicular to the first direction. The dimensional data are as follows:

[0066] The width (from the center line of the screw hole to the back of the sample) is W, along the first direction, with an error of ±0.005W;

[0067] The total width of the sample is 1.255W, and the error along the first direction is ±0.005W;

[0068] Thickness B is 0.5W, along the first direction, with an error of ±0.01W;

[0069] The distance from the centerline of the loading hole to the end of the machining crack is 'a', along the first direction;

[0070] The distance from the centerline of the loading hole to the crack center plane is 0.714W, along the second direction, with an error of ±0.005W.

[0071] The distance from the center plane of the extended crack to the bottom of the specimen is 0.942W, with an error of ±0.005W along the second direction;

[0072] The loading hole diameter is 0.25W.

[0073] It should be noted that, based on the above dimensional data, the thickness and width of the test material used in the extended compact tensile specimen are the same as those of the standard wedge-shaped open loading specimen, and the length is less than twice that of the standard wedge-shaped open loading specimen. In other words, the material consumption is less than twice that of the standard wedge-shaped open loading specimen. Compared with the three-point bending specimen used in related technologies, which requires several times the test material of the standard wedge-shaped open loading specimen, the consumption of test material is significantly reduced.

[0074] In some implementations, when sampling from the material to be tested, the specimen should be oriented in the TL direction, i.e., the normal direction of the specimen fracture surface is transverse to the plate or circumferential to the tubular product, and the expected crack propagation direction is the direction of maximum grain flow, or longitudinal to the plate or tubular product. For weld metal and the heat-affected zone of weld joints, if TL specimens cannot be obtained from the material to be tested, LT specimens can also be used.

[0075] S120. Fatigue cracks are pre-formed on the extended compact tensile specimen using a fatigue testing machine to obtain an extended compact tensile specimen with fatigue cracks.

[0076] In some embodiments, the surface of the extended compact tensile specimen is first degreased and derusted, and the crack surface and side grooves are cleaned. Then, it is clamped onto the fatigue testing machine with a U-clamp and fatigue crack pre-formed with a sinusoidal loading waveform with a stress ratio of 0.1 and a frequency of 20Hz. The ratio of the pre-formed initial crack length a0 (the distance from the fatigue crack terminal to the loading center line) to the specimen width W, a0 / W, is controlled between 0.45 and 0.55.

[0077] Specifically, firstly, the stress intensity factor threshold value of the material to be tested is estimated to obtain the estimated stress intensity factor threshold value. During the fatigue crack pre-crack process, the maximum stress intensity factor (Kmax) should be controlled to not exceed 80% of the estimated stress intensity factor threshold value, and in the last 1 mm stage of fatigue pre-crack, the maximum stress intensity factor (Kmax) should not exceed 60% of the estimated stress intensity factor threshold value. Then, since the MTS fatigue testing machine uses a force control method, the maximum stress intensity factor (Kmax) needs to be converted into the force that the fatigue testing machine should apply, according to the formula for CT specimens in ASTM E399:

[0078]

[0079]

[0080] Where B is the thickness of the extended compact tensile specimen, B N denoted as , where is the net thickness of the specimen with side grooves (the distance between the lowest points of the two grooves), W is the width of the specimen, a is the distance from the centerline of the loading hole to the end of the machined crack (also known as the machined crack length), K is the stress intensity factor, and P is the force to be applied by the fatigue testing machine. The crack length can be measured using the compliance method during the prefabrication process.

[0081] It should be noted that before fatigue crack pre-forming, the length of the machining crack needs to be checked using an MTS fatigue testing machine, and the Young's modulus of the material to be tested needs to be adjusted to offset the effect of the increased specimen length. Specifically, a small force can be applied to the extended compact tensile specimen for elastic tensile testing, and the Young's modulus can be adjusted based on the length of the machining crack measured by the MTS fatigue testing machine, so that the deviation between the manually measured value and the value measured by the MTS fatigue testing machine is less than 0.02 mm.

[0082] It should also be noted that the MTS fatigue testing machine is a commonly used and readily available device for pre-inducing fatigue cracks in CT specimens; there are also new devices specifically designed for pre-inducing fatigue cracks in WOL specimens in related technologies. Obviously, through the method of the embodiments of this application, those skilled in the art can use existing equipment to pre-induce fatigue cracks in WOL specimens without purchasing new specialized equipment, which greatly reduces testing costs.

[0083] S130. The shape of the extended compact tensile specimen with fatigue cracks is transformed to obtain a standard wedge-shaped opening loading specimen with fatigue cracks, which is used as the target wedge-shaped opening loading specimen.

[0084] Among them, the form conversion can be to convert an extended compact tensile specimen with fatigue cracks into a standard wedge-shaped open loading specimen with fatigue cracks through physical processing.

[0085] In some implementations, the extended compact tensile specimen with fatigue cracks is machined according to the drawings of the standard wedge-shaped open loading specimen in ASTM E1681. First, the extended portion is removed, then a flat pin hole is machined, and finally a threaded hole is machined.

[0086] S140. Apply a load to the end of the fatigue crack on the target wedge-shaped opening loading specimen, and place the loaded target wedge-shaped opening loading specimen in a high-pressure hydrogen environment to determine the current hydrogen-induced crack length.

[0087] Here, the load is the initial applied stress intensity factor, which is determined based on the estimated stress intensity factor threshold. The target wedge-shaped opening loading specimen can be a standard wedge-shaped opening loading specimen that has completed fatigue crack pre-fabrication. The current hydrogen-induced crack length can be the length of crack propagation when the target wedge-shaped opening loading specimen is tested in a high-pressure hydrogen environment.

[0088] In some implementations, firstly, the stress intensity factor threshold value K of the material to be tested is determined. IHA preliminary stress intensity factor threshold is obtained. Then, twice the preliminary stress intensity factor threshold is used as the initial applied stress intensity factor, and a constant displacement method is used to apply a load to the fatigue crack tip on the target wedge-shaped opening loading specimen.

[0089] Specifically, firstly, the initial applied stress intensity factor can be converted into the initial applied displacement using the following formula:

[0090]

[0091]

[0092] Where Vm is the displacement, E is the Young's modulus of the material under test, a is the sum of the lengths of the machining crack and the fatigue pre-crack, W is the width of the specimen, and K is the stress intensity factor. Then, in an air environment, a flat pin is inserted into the flat pin hole of the target wedge-shaped opening loading specimen, with the flat pin plane facing upwards and forming an angle of 90±2° with the loading axis. The extensometer is embedded into the knife edge of the target wedge-shaped opening loading specimen, and the bolt is screwed into the bolt hole for constant displacement loading. During loading, the extensometer reading is monitored, and loading is stopped once the initial applied displacement is reached. Next, the extensometer is removed, and the loaded target wedge-shaped opening loading specimen is placed in a high-pressure hydrogen environment for 1000 hours.

[0093] In some implementations, after the test duration reaches 1000 hours, the unloaded target wedge-shaped loading specimen is subjected to heat-colored treatment to distinguish between hydrogen-induced cracks and cracks caused by artificial brittle fracture. Specifically, this can be achieved by heating the specimen to 300°C in a high-temperature furnace and holding it for 30 minutes. Subsequently, the specimen is broken, and the fracture surface crack is measured using an electron microscope with a nine-point method. The initial crack length a0 (distance from the fatigue crack terminal to the loading center line) before the test and the final crack length a1 (distance from the hydrogen-induced crack terminal to the loading center line) after the test are calculated. The current hydrogen-induced crack length Δl = a1 - a0.

[0094] S150. Determine the stress intensity factor threshold value of the material to be tested based on the initial applied stress intensity factor, the current hydrogen-induced crack length, and the standard value of the hydrogen-induced crack length corresponding to the target wedge-shaped opening loading specimen.

[0095] The standard value for hydrogen-induced crack length can be the maximum permissible hydrogen-induced crack length of a standard wedge-shaped open-loaded specimen, 0.25 mm, as specified in the ASME BPVC KD10 standard. The stress intensity factor threshold value is used to characterize the stress intensity factor threshold for hydrogen-induced cracking.

[0096] In some implementations, if the current hydrogen-induced crack length does not exceed the standard value of 0.25 mm for hydrogen-induced crack length, the stress intensity factor threshold value K of the material under test is determined. IH This is half of the initially applied stress intensity factor. It should be noted that this stress intensity factor threshold value also needs to be verified for the effectiveness of the basic plane strain: 2.5 (K IH / R p0.2 ) 2 It must be less than B, a o and Wa o , where R p0.2 The stress intensity factor threshold is the yield strength of the material under test. If the test passes, it indicates that the stress intensity factor threshold value is independent of the thickness of the material under test and can be used as the stress intensity factor threshold value; otherwise, it indicates that the stress intensity factor threshold value is related to the thickness of the material under test and cannot be used as the stress intensity factor threshold value. It is understandable that if the current hydrogen-induced crack length exceeds the standard value for hydrogen-induced crack length, a slightly smaller initial applied stress intensity factor can be tested to obtain an accurate stress intensity factor threshold value. This method effectively solves the problem that in the ASMEBPVC KD10 standard, the initial applied stress intensity factor is selected from a settable range. For the same material and test environment, different people may obtain different K values ​​due to setting different initial applied stress intensity factors. IH The value is different, and the difference is significant.

[0097] In the above embodiments, firstly, the extended dimensions that meet the installation requirements of the fatigue testing machine are determined based on the dimensional data of the standard wedge-shaped opening loading specimen and the standard compact tensile specimen. Then, an extended compact tensile specimen of the material to be tested is prepared based on the extended dimensions. This allows for fatigue crack pre-forming using an existing fatigue testing machine for pre-forming fatigue cracks in compact tensile specimens. After pre-forming, the specimen is then processed into the target wedge-shaped opening loading specimen. There is no need to introduce new equipment for pre-forming fatigue cracks in wedge-shaped opening loading specimens. Compared with the use of three-point bending specimens in related technologies, the extended compact tensile specimen can significantly reduce the material requirements of the test material. In addition to reducing energy consumption, existing fatigue testing machines can be used for fatigue crack pre-induction, effectively saving testing costs in two ways. Then, the load is determined based on the estimated stress intensity factor threshold, and a load is applied to the end of the fatigue crack on the target wedge-shaped open loading specimen to conduct hydrogen-induced crack testing. Based on the initial applied stress intensity factor, the current hydrogen-induced crack length, and the standard value of the hydrogen-induced crack length corresponding to the target wedge-shaped open loading specimen, the stress intensity factor threshold value of the material to be tested is determined. Compared with related technologies, determining the initial applied stress intensity factor based on the estimated stress intensity factor threshold can obtain a more accurate stress intensity factor threshold value.

[0098] In some embodiments, the initial applied stress intensity factor corresponding to the target wedge-shaped opening loading specimen adopts the initial applied stress intensity factor of the target specimen group to which the target wedge-shaped opening loading specimen belongs; the stress intensity factor threshold value of the material to be tested is determined based on the initial applied stress intensity factor corresponding to the target wedge-shaped opening loading specimen, the current hydrogen-induced crack length, and the standard value of the hydrogen-induced crack length, including:

[0099] If the target sample group is determined to meet the preset requirements based on the current hydrogen-induced crack length and the standard value of the hydrogen-induced crack length, then the stress intensity factor threshold value of the test material is determined based on the initial applied stress intensity factor corresponding to the target sample group.

[0100] The preset requirement can be that the current hydrogen-induced crack length does not exceed the standard value of the hydrogen-induced crack length. The target specimen group can be a specimen group composed of multiple target wedge-shaped opening loading specimens.

[0101] In some embodiments, if the maximum value of the hydrogen-induced crack length of the target wedge-shaped open-loaded specimen in the target specimen group does not exceed the standard value of the hydrogen-induced crack length, the target specimen group is determined to meet the preset requirements, and the initial applied stress intensity factor K corresponding to the target specimen group is set. IAPP Half of the value is determined as the stress intensity factor threshold value K of the material to be tested. IH Understandably, this stress intensity factor threshold value still needs to undergo a basic plane strain validity test before it can be definitively determined whether it can be used as the stress intensity factor threshold value for the material under test.

[0102] In the above embodiments, by conducting hydrogen-induced cracking tests on the target sample group, the randomness of individual sample test data can be avoided, the stability of test data can be increased, and the accuracy of the stress intensity factor threshold value can be improved.

[0103] In some embodiments, the target specimen set includes multiple target wedge-shaped opening loading specimens; the target specimen set is determined to meet preset requirements by the following method:

[0104] S310. Determine the current hydrogen-induced crack length of the target sample group based on the hydrogen-induced crack length of each target wedge-shaped opening loaded sample.

[0105] S320. Compare the current hydrogen-induced crack length of the target sample group with the standard value of the hydrogen-induced crack length, and determine that the target sample group meets the preset requirements based on the comparison results.

[0106] The current hydrogen-induced crack length of the target sample group can be the average of the hydrogen-induced crack lengths of all target wedge-opening loaded samples in the target sample group.

[0107] In some embodiments, the average value of the hydrogen-induced crack lengths of all target wedge-opening loaded specimens in the target specimen group is determined as the current hydrogen-induced crack length of the target specimen group. If the current hydrogen-induced crack length of the target specimen group does not exceed the standard value of the hydrogen-induced crack length, the target specimen group is determined to meet the preset requirements.

[0108] In the above embodiments, the current hydrogen-induced crack length of the target sample group is first determined based on the hydrogen-induced crack length of each target wedge-shaped opening loading sample. Then, the current hydrogen-induced crack length of the target sample group is compared with the standard value of the hydrogen-induced crack length. Based on the comparison result, it is determined that the target sample group meets the preset requirements. Compared with testing with a single sample, the sample group can reduce the influence of random errors, thereby improving the accuracy of the stress intensity factor threshold value.

[0109] In some embodiments, determining that the target sample group meets the preset requirements based on the comparison results includes: determining that the target sample group meets the preset requirements when the current hydrogen-induced crack length is less than or equal to the standard value and the difference data between the current hydrogen-induced crack length and the standard value meets the preset difference requirements.

[0110] The preset difference requirement can be that, when there are multiple initial sample groups, the difference between the current hydrogen-induced crack length of the target sample group and the standard value is the smallest among all initial sample groups.

[0111] In some implementations, multiple initial sample groups are present. After the hydrogen-induced cracking test is completed, firstly, based on the nine-point method, the hydrogen-induced crack length of all samples is measured and calculated using an electron microscope. Then, the average value of the hydrogen-induced crack length of the initial sample groups is calculated as their current hydrogen-induced crack length. Next, the relationship between the current hydrogen-induced crack length of each initial sample group and the standard value is determined, and several initial sample groups whose current hydrogen-induced crack length is less than or equal to the standard value are selected. Furthermore, the group with the smallest difference between the current hydrogen-induced crack length and the standard value is selected as the target sample group.

[0112] In the above embodiments, firstly, based on the fact that the current hydrogen-induced crack length is less than or equal to the standard value, a sample group that meets the ASMEBPVC KD10 standard is determined. Then, based on the fact that the difference data between the standard value and the standard value meets the preset difference requirements, it is determined whether the target sample group meets the preset requirements, and the target sample group that can test the most accurate threshold value of hydrogen-induced hysteresis cracking stress intensity factor is determined.

[0113] In some embodiments, the target wedge-shaped opening loading specimen belongs to a target specimen group, and the target specimen group corresponds to an initial applied stress intensity factor; applying a load to the fatigue crack terminus on the target wedge-shaped opening loading specimen, and placing the loaded target wedge-shaped opening loading specimen in a high-pressure hydrogen environment, includes:

[0114] Based on the initial applied stress intensity factor corresponding to the target sample group, a load is applied to the fatigue crack end of each target wedge-shaped open loading sample in the target sample group, and each target wedge-shaped open loading sample with applied load is placed in a high-pressure hydrogen environment to determine the current hydrogen-induced crack length corresponding to the target sample group.

[0115] In some implementations, a target specimen group includes multiple target wedge-shaped opening-loaded specimens, which require the same load, i.e., the same initial applied stress intensity factor, to be applied to the fatigue crack terminus. Exemplarily, the constant displacement method is used to apply the load to the fatigue crack terminus on each target wedge-shaped opening-loaded specimen. First, the initial applied stress intensity factor can be converted into an initial applied displacement using the following formula:

[0116]

[0117]

[0118] Where Vm is the displacement, E is the Young's modulus of the material under test, a is the sum of the lengths of the machining crack and the fatigue pre-crack, W is the width of the specimen, and K is the stress intensity factor. Then, in an air environment, a flat pin is inserted into the flat pin hole of the target wedge-shaped opening loading specimen, with the flat pin plane facing upwards and forming an angle of 90°±2° with the loading axis. The extensometer is embedded into the knife edge of the target wedge-shaped opening loading specimen, and the bolt is screwed into the bolt hole for constant displacement loading. During loading, the extensometer reading is monitored, and loading is stopped once the initial applied displacement is reached. Next, the extensometer is removed, and the loaded target wedge-shaped opening loading specimen is placed in a high-pressure hydrogen environment for 1000 hours.

[0119] Further, after the testing time is reached, each target wedge-shaped loading specimen in the target specimen group is unloaded and subjected to heat-colored treatment to distinguish between hydrogen-induced cracks and cracks caused by artificial brittle fracture. Specifically, this can be achieved by heating the specimen to 300°C in a high-temperature furnace and holding it for 30 minutes. The specimen is then broken, and the fracture surface crack is measured using an electron microscope employing the nine-point method. The initial crack length a0 (distance from the fatigue crack terminus to the loading centerline) before the test and the final crack length a1 (distance from the hydrogen-induced crack terminus to the loading centerline) after the test are measured and calculated. The hydrogen-induced crack length Δl = a1 - a0. Finally, the average hydrogen-induced crack length of the target specimen group is calculated as its current hydrogen-induced crack length.

[0120] In some embodiments, the initial applied stress intensity factor corresponding to the target wedge-shaped opening loading specimen is adopted as the initial applied stress intensity factor of the target specimen group to which the target wedge-shaped opening loading specimen belongs; the target specimen group is determined in the following manner:

[0121] S610 provides multiple initial sample sets.

[0122] S620, Determine the initial applied stress intensity factor for any initial sample group between the first stress intensity factor threshold and the second stress intensity factor threshold.

[0123] S630. Based on the initial applied stress intensity factor of any initial sample group, perform hydrogen-induced cracking test on each target wedge-shaped opening loading sample in any initial sample group to obtain the current hydrogen-induced crack length corresponding to any initial sample group.

[0124] S640. Determine the target sample group from multiple initial sample groups based on the current hydrogen-induced crack length and the standard value of the hydrogen-induced crack length corresponding to any initial sample group.

[0125] Each initial specimen set comprises multiple target wedge-shaped open-loaded specimens with fatigue cracks. The first stress intensity factor threshold can be the minimum initially applied stress intensity factor. The second stress intensity factor threshold can be the maximum initially applied stress intensity factor.

[0126] In some implementations, the estimated value of the stress intensity factor threshold K0 is first obtained, then the first stress intensity factor threshold is determined to be 1.6K0 and the second stress intensity factor threshold is determined to be 2.2K0. Then, the initial applied stress intensity factor is set between the first stress intensity factor threshold and the second stress intensity factor threshold at an interval of 10-15%K0. For example, there are 7 initial sample groups, and 1.6K0, 1.7K0, 1.8K0, 1.9K0, 2.0K0, 2.1K0 and 2.2K0 are set as the initial applied stress intensity factors respectively.

[0127] Furthermore, in air, the constant displacement method was used to apply the corresponding initial applied stress intensity factor to multiple target wedge-shaped opening loaded specimens of each initial specimen group. Then, all the initial specimen groups with applied overload were placed in the same high-pressure hydrogen environment for hydrogen-induced cracking test for a duration of 1000h.

[0128] Furthermore, after the hydrogen-induced cracking test, firstly, based on the nine-point method, the length of hydrogen-induced cracks in all samples was measured and calculated using an electron microscope; then, the average length of hydrogen-induced cracks in each initial sample group was calculated as its current hydrogen-induced crack length; next, the relationship between the current hydrogen-induced crack length of each initial sample group and the standard value was determined, and several initial sample groups with current hydrogen-induced crack lengths less than or equal to the standard value were selected; finally, the group with the smallest difference between the current hydrogen-induced crack length and the standard value was selected as the target sample group.

[0129] It should be noted that in this embodiment, if the current hydrogen-induced crack length is less than the standard value of 0.25 mm, the stress intensity factor threshold value is equal to half of the initially applied stress intensity factor. The stress intensity factor threshold value can be estimated based on the performance parameters of the material under test, such as the mapping relationship between yield strength and stress intensity factor threshold value. Therefore, this embodiment determines a first stress intensity factor threshold and a second stress intensity factor threshold on both sides based on twice the estimated stress intensity factor threshold value, and determines multiple initial applied stress intensity factors between the two thresholds for hydrogen-induced crack testing. By using a squeeze method, the current hydrogen-induced crack length closest to the standard value is obtained, thus yielding an accurate stress intensity factor threshold value. This effectively solves the problem in the ASME BPVC KD10 standard where the initial applied stress intensity factor is selected from a settable range. For the same material and testing environment, different people may obtain different K values ​​due to setting different initial applied stress intensity factors. IH The issue of values ​​differing significantly is of paramount importance for the design of hydrogen storage containers or pipelines.

[0130] In the above embodiments, using the squeeze method, multiple initial applied stress intensity factors corresponding to multiple initial sample groups are first determined based on a first stress intensity factor threshold and a second stress intensity factor threshold. Then, by performing hydrogen-induced cracking tests on multiple initial sample groups, a target sample group of the material to be tested is obtained based on the current hydrogen-induced crack length and standard value of each group. Subsequently, an accurate stress intensity factor threshold value can be obtained based on the initial applied stress intensity factor corresponding to the target sample group.

[0131] In some embodiments, applying a load to the fatigue crack terminus of a target wedge-shaped opening loaded specimen includes:

[0132] S710. Obtain the estimated threshold value of the stress intensity factor of the material to be tested.

[0133] S720. Determine the initial applied stress intensity factor of the material to be tested.

[0134] S730. Apply a load to the fatigue crack end on the target wedge-shaped opening loading specimen using the constant displacement method.

[0135] Among them, the estimated value of the stress intensity factor threshold is used to characterize the estimation of the stress intensity factor threshold value for hydrogen-induced hysteresis cracking.

[0136] In some implementations, the estimated stress intensity factor threshold is obtained based on the tensile strength of the material, as shown in the following formula:

[0137] K IH =60×(R m / 950)

[0138] Among them, Rm It represents the tensile strength of the material, measured in MPa, and can be determined through a tensile test in air. This is the stress intensity factor threshold value, in MPa·m. 1 / 2 When the tensile strength of the material to be tested is known, the above formula can be used to obtain the estimated value of its stress intensity factor threshold.

[0139] Furthermore, several values ​​of the initial applied stress intensity factor of the test material were determined, each approximately twice the estimated threshold value. Then, the initial applied stress intensity factor was converted into displacement using the following formula. The constant displacement method was then used to apply loads to the fatigue crack ends of multiple target wedge-shaped open-loaded specimens to conduct hydrogen-induced crack testing.

[0140]

[0141]

[0142] Where Vm is the displacement, E is the Young's modulus of the material under test, a is the sum of the lengths of the machining crack and the fatigue pre-crack, W is the width of the specimen, and K is the stress intensity factor.

[0143] Furthermore, after the testing time is reached, the sample is unloaded and subjected to heat-colored treatment to distinguish between hydrogen-induced cracks and man-made brittle fractures. Finally, based on the initial applied stress intensity factor corresponding to the target wedge-shaped opening loaded sample whose current hydrogen-induced crack length is closest to the standard value, the stress intensity factor threshold value of the material under test is determined. This stress intensity factor threshold value is half of the initial applied stress intensity factor.

[0144] In some embodiments, obtaining the estimated value of the stress intensity factor threshold of the material to be tested includes: estimating the stress intensity factor threshold value of the material to be tested based on the relationship between the yield strength of the material and the stress intensity factor threshold value, thereby obtaining the estimated value of the stress intensity factor threshold.

[0145] In some implementations, the stress intensity factor threshold value of the material to be tested is estimated according to the following formula:

[0146]

[0147] Among them, R p0.2 The yield strength of the material, expressed in MPa. This is the stress intensity factor threshold value, in MPa·m. 1 / 2 Once the yield strength of the material under test is obtained through tensile testing, the above formula can be used to obtain the estimated value of its stress intensity factor threshold.

[0148] It should be noted that the formula and Both are used to calculate the estimated threshold value of the stress intensity factor for the tested material. Based on experiments, the inventors discovered the formula... Effective prediction within a specific intensity range The formula relates to the tensile strength of materials; however, when the tensile strength exceeds a certain range, the predicted results deviate significantly from experimental observations. Based on this, the inventors proposed a new formula... The formula has demonstrated wider applicability and higher predictive accuracy in experiments.

[0149] In some embodiments, the fatigue testing machine has a matching U-shaped clamp. The fatigue testing machine is used to pre-invent fatigue cracks in extended compact tensile specimens to obtain extended compact tensile specimens with fatigue cracks, including:

[0150] S910. Use a U-shaped clamp to clamp the extended compact tensile specimen.

[0151] S920. Adjust the Young's modulus in the fatigue testing machine. The fatigue testing machine before adjustment was used to pre-incubate fatigue cracks in standard compact tensile specimens.

[0152] S930. Fatigue crack pre-forming of extended compact tensile specimens is performed using an adjusted fatigue testing machine.

[0153] The U-shaped clamp is a specially designed clamping tool used to fix standard compact tensile specimens for fatigue crack pre-induction on a fatigue testing machine, but it cannot be used to fix standard wedge-shaped open-load specimens. It should be noted that since the loading hole of the extended compact tensile specimen is designed based on the standard compact tensile specimen, the U-shaped clamp in this application can be used to fix the extended compact tensile specimen, thereby enabling fatigue crack pre-induction using a fatigue testing machine.

[0154] In some embodiments, the extended compact tensile specimen is pre-fatigue-cracked using an MTS fatigue testing machine, which is used for pre-fatigue cracking of standard compact tensile specimens. First, the extended compact tensile specimen is clamped using a U-clamp. Then, the length of the machining crack is checked using the MTS fatigue testing machine, and the Young's modulus of the material is adjusted to offset the effect of the specimen elongation. Specifically, a small force can be applied to the extended compact tensile specimen for tensile testing, and the Young's modulus is adjusted based on the machining crack length measured by the MTS fatigue testing machine, ensuring that the deviation between the manually measured value and the MTS fatigue testing machine value is less than 0.02 mm.

[0155] Furthermore, fatigue crack pre-induction was performed on the extended compact tensile specimen using a sinusoidal loading waveform with a stress ratio of 0.1 and a frequency of 20Hz on an adjusted fatigue testing machine. The ratio of the initial crack length a0 to the specimen width W, a0 / W, was controlled between 0.45 and 0.55. Specifically, the stress intensity factor threshold value of the test material was estimated, and a stress intensity factor threshold estimate was obtained. During the fatigue crack pre-induction process, the maximum stress intensity factor (Kmax) should be controlled to not exceed 80% of the stress intensity factor threshold estimate, and in the last 1 mm stage of the fatigue pre-crack, the maximum stress intensity factor (Kmax) should not exceed 60% of the stress intensity factor threshold estimate. Then, since the MTS fatigue testing machine uses a force control method, the maximum stress intensity factor (Kmax) needs to be converted into the force that the fatigue testing machine should apply, according to the formula for CT specimens in ASTM E399:

[0156]

[0157]

[0158] Where B is the thickness of the extended compact tensile specimen, B N Where is the net thickness of the specimen including the side groove, W is the width of the specimen, a is the distance from the center line of the loading hole to the end of the machined crack (also known as the machined crack length), K is the stress intensity factor, and P is the force to be applied by the fatigue testing machine. The crack length can be measured using the compliance method during the prefabrication process.

[0159] In some embodiments, the extended compact tensile specimen with fatigue cracks is transformed into a standard wedge-shaped opening loading specimen with fatigue cracks, which serves as the target wedge-shaped opening loading specimen. This includes: machining the extended compact tensile specimen with fatigue cracks, adjusting its length to a target length that meets the requirements of the standard wedge-shaped opening loading specimen, and machining the flat pin hole and threaded hole required by the standard wedge-shaped opening loading specimen; wherein, during the machining of the threaded hole, a shock-absorbing component needs to be added at the machined crack.

[0160] In some implementations, the extended compact tensile specimen with fatigue cracks is machined according to the standard wedge-shaped open loading specimen drawings in ASTM E1681. First, the extended portion is removed, then a flat pin hole is machined, and finally a threaded hole is machined. It should be noted that when machining the threaded hole, a 3mm thick carbide shim should be installed in the intermediate groove to isolate the influence of machining vibration on the pre-existing crack tip.

[0161] In some embodiments, the method for testing hydrogen-induced cracking of materials under high-pressure hydrogen conditions includes:

[0162] S1001 provides multiple initial sample sets.

[0163] Each initial sample group includes multiple target wedge-shaped opening loading samples with fatigue cracks.

[0164] S1002. For any initial sample group, according to the initial applied stress intensity factor corresponding to any initial sample group, apply a load to the fatigue crack end of each target wedge-shaped opening loading sample in any initial sample group, and place each target wedge-shaped opening loading sample with applied load into a high-pressure hydrogen environment to determine the current hydrogen-induced crack length corresponding to any initial sample group.

[0165] In some implementations, the estimated threshold value K0 of the stress intensity factor is first obtained, and then several values ​​are determined on and around 2K0 as the initial set of applied stress intensity factors. For example, the initial set of applied stress intensity factors consists of 1.6K0, 1.8K0, 2K0, 2.2K0, and 2.4K0, and each initial applied stress intensity factor in the set corresponds to an initial sample group.

[0166] Furthermore, in air, the constant displacement method was used to apply the corresponding initial applied stress intensity factor to multiple target wedge-shaped opening loaded specimens of each initial specimen group. Then, all the initial specimen groups with applied overload were placed in the same high-pressure hydrogen environment for hydrogen-induced cracking test for a duration of 1000h.

[0167] Furthermore, after the hydrogen-induced cracking test is completed, firstly, based on the nine-point method, the hydrogen-induced crack length of all samples is measured and calculated using an electron microscope; then, the average value of the hydrogen-induced crack length of multiple samples in each initial sample group is calculated as its current hydrogen-induced crack length.

[0168] S1003. Compare the current hydrogen-induced crack length and the standard value of the hydrogen-induced crack length corresponding to each initial sample group to determine the target sample group among multiple initial sample groups whose current hydrogen-induced crack length is less than or equal to the standard value and whose difference data between the current hydrogen-induced crack length and the standard value meets the preset requirements.

[0169] The preset requirement is that the difference between the current hydrogen-induced crack length and the standard value of the target sample group is the smallest among all groups.

[0170] In some implementations, the relationship between the current hydrogen-induced crack length and the standard value of each initial sample group is determined, and several initial sample groups whose current hydrogen-induced crack length is less than or equal to the standard value are selected. Finally, the group with the smallest difference between the current hydrogen-induced crack length and the standard value is selected as the target sample group.

[0171] S1004. Determine the stress intensity factor threshold value of the material to be tested based on the initial applied stress intensity factor corresponding to the target sample group.

[0172] In some implementations, half the initial applied stress intensity factor corresponding to the target sample group is used as the stress intensity factor threshold value of the material to be tested.

[0173] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0174] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0175] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

[0176] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for testing hydrogen-induced cracking of materials under high-pressure hydrogen conditions, characterized in that, The method includes: Based on the dimensional data of the standard wedge-shaped open loading specimen and the dimensional data of the standard compact tensile specimen, the extended dimensions that meet the installation requirements of the fatigue testing machine are determined. Based on the extended dimensions, an extended compact tensile specimen of the material to be tested is prepared. The material to be tested is a certain material intended for use in hydrogen storage containers or structural components of hydrogen energy equipment in high-pressure hydrogen environments. The fatigue cracks of the extended compact tensile specimen are pre-formed using the fatigue testing machine to obtain an extended compact tensile specimen with fatigue cracks. The shape of the extended compact tensile specimen with fatigue cracks is transformed to obtain a standard wedge-shaped opening loading specimen with fatigue cracks, which is used as the target wedge-shaped opening loading specimen. A load is applied to the fatigue crack tip on the target wedge-shaped opening loading specimen, and the loaded target wedge-shaped opening loading specimen is placed in a high-pressure hydrogen environment to determine the current hydrogen-induced crack length; wherein, the load is the initial applied stress intensity factor, which is determined based on the stress intensity factor threshold estimate; Based on the initial applied stress intensity factor corresponding to the target wedge-shaped opening loaded specimen, the current hydrogen-induced crack length, and the standard value of the hydrogen-induced crack length, the stress intensity factor threshold value of the material to be tested is determined.

2. The method according to claim 1, characterized in that, The initial applied stress intensity factor corresponding to the target wedge-shaped opening loading specimen adopts the initial applied stress intensity factor of the target specimen group to which the target wedge-shaped opening loading specimen belongs; the step of determining the stress intensity factor threshold value of the test material based on the initial applied stress intensity factor corresponding to the target wedge-shaped opening loading specimen, the current hydrogen-induced crack length, and the standard value of the hydrogen-induced crack length includes: If the target sample group is determined to meet the preset requirements based on the current hydrogen-induced crack length and the standard value of the hydrogen-induced crack length, then the stress intensity factor threshold value of the test material is determined based on the initial applied stress intensity factor corresponding to the target sample group.

3. The method according to claim 2, characterized in that, The target sample set includes multiple target wedge-shaped opening loading samples; the target sample set is determined to meet the preset requirements by the following method: The current hydrogen-induced crack length of the target sample group is determined based on the hydrogen-induced crack length of each target wedge-shaped opening loaded sample. The current hydrogen-induced crack length of the target sample group is compared with the standard value of the hydrogen-induced crack length, and the target sample group is determined to meet the preset requirements based on the comparison result.

4. The method according to claim 3, characterized in that, The step of determining whether the target sample group meets the preset requirements based on the comparison results includes: If the current hydrogen-induced crack length is less than or equal to the standard value and the difference data between the current hydrogen-induced crack length and the standard value meets the preset difference requirement, the target sample group is determined to meet the preset requirement.

5. The method according to claim 1, characterized in that, The target wedge-shaped opening loading specimen belongs to a target specimen group, and the target specimen group corresponds to an initial applied stress intensity factor; applying a load to the fatigue crack terminus on the target wedge-shaped opening loading specimen and placing the loaded target wedge-shaped opening loading specimen in a high-pressure hydrogen environment includes: Based on the initial applied stress intensity factor corresponding to the target sample group, a load is applied to the fatigue crack end of each target wedge-shaped opening loaded sample in the target sample group, and each target wedge-shaped opening loaded sample with applied load is placed in a high-pressure hydrogen environment to determine the current hydrogen-induced crack length corresponding to the target sample group.

6. The method according to claim 1, characterized in that, The initial applied stress intensity factor corresponding to the target wedge-shaped opening loading specimen is the initial applied stress intensity factor of the target specimen group to which the target wedge-shaped opening loading specimen belongs; The target sample group was determined in the following manner: Multiple initial specimen sets are provided; wherein each initial specimen set includes multiple target wedge-shaped opening-loaded specimens with fatigue cracks; The initial applied stress intensity factor for any initial sample group is determined between the first stress intensity factor threshold and the second stress intensity factor threshold. Based on the initial applied stress intensity factor of any initial sample group, hydrogen-induced cracking test is performed on each target wedge opening loading sample in any initial sample group to obtain the current hydrogen-induced crack length corresponding to any initial sample group. The target sample group is determined from the plurality of initial sample groups based on the current hydrogen-induced crack length and the standard value of the hydrogen-induced crack length corresponding to any initial sample group.

7. The method according to claim 1, characterized in that, Applying a load to the fatigue crack tip on the target wedge-shaped opening loaded specimen includes: Obtain the estimated value of the stress intensity factor threshold for the material under test; wherein the estimated value of the stress intensity factor threshold is used to characterize the estimation of the stress intensity factor threshold value for hydrogen-induced hysteresis cracking. Determine the initial applied stress intensity factor of the material to be tested; The constant displacement method was used to apply a load to the fatigue crack end of the target wedge-shaped opening loading specimen.

8. The method according to claim 7, characterized in that, The process of obtaining the estimated threshold value of the stress intensity factor for the material under test includes: Based on the relationship between the yield strength of the material and the stress intensity factor threshold value, the stress intensity factor threshold value of the material to be tested is estimated to obtain the estimated value of the stress intensity factor threshold.

9. The method according to claim 1, characterized in that, The fatigue testing machine has a matching U-shaped clamp. The process of pre-forming fatigue cracks in the extended compact tensile specimen using the fatigue testing machine to obtain an extended compact tensile specimen with fatigue cracks includes: The extended compact tensile specimen is clamped using the U-shaped clamp; Adjust the Young's modulus in the fatigue testing machine; wherein, the fatigue testing machine before adjustment was used to pre-incubate fatigue cracks in standard compact tensile specimens; Fatigue crack pre-induction was performed on the extended compact tensile specimen using the adjusted fatigue testing machine.

10. The method according to claim 1, characterized in that, The step of transforming the fatigue-cracked extended compact tensile specimen into a standard wedge-shaped opening loading specimen, which serves as the target wedge-shaped opening loading specimen, includes: The extended compact tensile specimen with fatigue cracks is machined to adjust its length to the target length required by the standard wedge-shaped opening loading specimen, and the flat pin hole and threaded hole required by the standard wedge-shaped opening loading specimen are machined; wherein, during the machining of the threaded hole, a shock-absorbing component needs to be added at the machined crack.

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