Crack length measuring system
By sealing CT samples in a reaction vessel and using a gas extraction device and a DC potential drop system (DCPD system), the problem of measuring crack length under specific conditions was solved, enabling accurate crack length measurement under different conditions and improving the reliability of material fracture toughness assessment.
Patent Information
- Application Number
- CN202510956004.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-11
- Publication Date
- 2025-10-17
AI Technical Summary
Existing technologies cannot measure crack length under specific conditions, especially outside of air, which limits the assessment of material fracture toughness and defect detection.
The CT sample was sealed in a reaction vessel. The gas in the reaction vessel was evacuated to a vacuum using a gas extraction device and then filled with the target experimental environment gas. The crack length was measured using a DC potential drop system (DCPD system), and the crack length was determined by measuring the resistance change in the crack region using the DCPD system.
It enables accurate measurement of crack length under specific conditions, improving the reliability of material fracture toughness assessment and detection capability under different environments.
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Figure CN120800995A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the technical field of fatigue crack, and in particular to a crack length measurement system. BACKGROUND
[0002] Fracture toughness refers to the ability of a material to resist crack unstable expansion, and is a key index parameter for material safety evaluation and defect evaluation. When the crack size is constant, the greater the fracture toughness value of the material, the greater the critical stress required for crack unstable expansion; when the external force is given, if the fracture toughness value of the material is higher, the critical size of the crack when reaching unstable expansion is greater.
[0003] At present, most laboratories still use a microscope visual inspection method to measure the crack length, and this method must be measured when the test is interrupted. However, the above scheme needs to be tested in an air environment, and the crack length in a specific environment cannot be measured. SUMMARY
[0004] The application provides a crack length measurement system, which can measure the crack length in a specific environment.
[0005] To achieve the above object, the application adopts the following technical scheme:
[0006] In a first aspect, the application provides a crack length measurement system. The system comprises:
[0007] A reaction kettle is used to seal a compact tension CT specimen, the CT specimen is clamped on a fatigue testing machine, and the CT specimen comprises a crack region. A gas exhaust device is used to exhaust the gas in the reaction kettle to a vacuum state and to fill the target experimental environment gas into the reaction kettle. A direct current potential drop system DCPD system is used to measure the crack length of the crack region in the CT specimen at multiple time points.
[0008] Based on the above technical scheme, the reaction kettle is used to seal the compact tension CT specimen, the CT specimen is clamped on the fatigue testing machine, and the CT specimen comprises the crack region. The gas exhaust device is used to exhaust the gas in the reaction kettle to the vacuum state and to fill the target experimental environment gas into the reaction kettle. In this way, the CT specimen can be placed in the target experimental environment gas, and the direct current potential drop system DCPD system can be used to measure the crack length of the crack region in the CT specimen at multiple time points under the target experimental environment gas.
[0009] In a possible implementation manner, after the gas exhaust device is used to exhaust the gas in the reaction kettle to the vacuum state, the gas exhaust device is used to fill and discharge the target value of nitrogen gas, and the number of times of filling and discharging the nitrogen gas is a preset value. After the filling and discharging of the nitrogen gas is completed, the gas exhaust device is used to fill the target experimental environment gas into the reaction kettle.
[0010] In another possible implementation, the gas extraction device is specifically configured to, in the process of releasing nitrogen, re-fill the reaction kettle with nitrogen of the target value when it is detected that the vacuum degree in the reaction kettle is less than a preset vacuum degree threshold.
[0011] In another possible implementation, the loading system is configured to apply an external force to the CT sample, and includes a loading pin, a clamp, a tensile rod, and a loading frame. The CT sample is insulated from the loading pin by a ceramic insulation sleeve, the CT sample is insulated from the clamp by a ceramic insulation gasket, and the tensile rod is insulated from the loading frame by a polytetrafluoroethylene gasket.
[0012] In another possible implementation, the DCPD system includes a voltmeter configured to collect DCPD signals, a multi-channel collection system configured to collect various required output signals and store them in a computing device, and a DC power supply system configured to provide reversible steady DC. The DCPD system is specifically configured to, when the steady DC passes through a crack region of the CT sample, a change in the crack length changes the resistance of the crack region, thereby changing the potential difference between the multiple probes, and by measuring the potential difference on both sides of the crack region, the crack length is determined.
[0013] In another possible implementation, the system further includes a computing device. The DCPD system is further configured to obtain multiple initial potentials of the CT sample under different environments, one initial potential corresponding to one environment. The different environments include: the CT sample is in air, the CT sample is in the reaction kettle and the reaction kettle is in a normal air state, and the CT sample is in the reaction kettle and the reaction kettle is in a pressurized state. The computing device is configured to, when the multiple initial potentials all meet a preset potential condition, determine the multiple crack lengths obtained by the DCPD system.
[0014] In another possible implementation, the computing device is further configured to obtain an initial crack length of the crack region and a sample width of the CT sample, and determine a first ratio based on the initial crack length and the sample width. The preset potential condition is determined based on the first ratio and the initial potential. The initial potential includes at least two of the following: a first potential when the first ratio is a first value, a second potential when the first ratio is a second value, a third potential when the first ratio is a third value, and a fourth potential when the first ratio is a fourth value.
[0015] In another possible implementation, the computing device is further configured to determine a fracture elongation and a J integral of the CT sample based on the applied external force, a sample thickness of the CT sample, the sample width, a net thickness between the slots on both sides of the sample, and the initial crack length. The fracture elongation and the J integral are both used to represent a fracture toughness value.
[0016] In another possible implementation, Wherein, F is the external force applied during the test, B is the thickness of the sample, B N is the net thickness between the grooves on both sides of the sample, W is the width of the sample, a is the initial crack length, v is the Poisson's ratio, R P0.2 is the 0.2% yield strength of the material, E is the elastic modulus, V P is the plastic displacement component corresponding to the applied external force.
[0017]
[0018] Wherein, J is the J integral, U P is the integral area of the plastic displacement corresponding to the applied load.
[0019] In another possible implementation manner, the target experimental environment gas is hydrogen. BRIEF DESCRIPTION OF DRAWINGS
[0020] Figure 1 is an example schematic diagram of a CT sample provided by an embodiment of the present application;
[0021] Figure 2 is a schematic diagram of a force-potential curve relationship provided by an embodiment of the present application. DETAILED DESCRIPTION
[0022] The technical solutions in the embodiments of the present application will be apparently and completely described in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without any creative effort fall within the protection scope of the present application.
[0023] In addition, the terms “comprising” and “having” and any variations thereof mentioned in the description of the present application are intended to cover the inclusions without exclusivity. For example, a process, method, system, product or device that includes a series of steps or modules is not limited to the listed steps or modules, but can optionally include other steps or modules not listed, or can optionally include other steps or modules inherent to the process, method, product or device.
[0024] In addition, in the embodiments of the present application, the words “exemplary” or “for example” are used to mean serving as an example, instance, or illustration. Any embodiment or design described as “exemplary” or “for example” in the present application should not be construed as being more preferred or advantageous than other embodiments or designs. In fact, the use of the words “exemplary” or “for example” is intended to present concepts in a concrete manner.
[0025] In some embodiments, the crack length measurement system may include: a reactor, a gas extraction device, and a direct current potential drop (DCPD) system.
[0026] The reactor is used to seal a compact tension (CT) specimen, which is clamped in a fatigue testing machine and includes a crack area.
[0027] In the embodiment of the present application, the CT specimen is made of a variety of metal materials, the specimen is pre-cracked, both sides of the CT specimen are machined, and guide grooves with a depth of 10% of the thickness are opened on both sides of the CT specimen.
[0028] In addition, wires can be welded to the CT specimen, and measurements can be made using one pair of current measuring wires and two pairs of potential measuring wires.
[0029] For example, Figure 1 As shown, V+ and V-, as well as V R + and V R - is 2 pairs of potential measurement wires, CC+ is 1 pair of current wires.
[0030] It should be understood that the measuring wire should be made of an inert metal. If the temperature is room temperature, copper wire can be used as the measuring wire, but it must be treated with corrosion protection. Typically, the current measuring wire diameter is 0.75mm, and the potential measuring wire diameter is 0.5mm. Before welding the wires, the specimen is positioned and a small spot is punched at the location with a sample punch, forming a small dimple. A double-pulse spot welder is used for welding, and the specimen is welded in an upright position.
[0031] The gas extraction device is used to extract the gas in the reactor to a vacuum state and fill the reactor with the target experimental environment gas.
[0032] It should be noted that the target experimental environment gas is not limited in the embodiments of the present application. For example, the target experimental environment gas may be hydrogen.
[0033] In the embodiments of the present application, the gas extraction device is specifically configured to, after extracting the gas from the reactor to a vacuum state, charge or discharge a target amount of nitrogen gas, the number of times the nitrogen is charged or discharged being a preset value. The gas extraction device is also configured to, after completing the nitrogen charging or discharging process, fill the reactor with the target experimental environment gas.
[0034] It should be noted that the present embodiment does not limit the preset value and the target value. For example, the target value may be 1 MPa and the preset value may be 5 times.
[0035] Optionally, the gas extraction device is specifically used to refill a target value of nitrogen into the reactor when it is detected that the vacuum degree in the reactor is less than a preset vacuum degree threshold during the process of releasing nitrogen.
[0036] For example, the CT sample is sealed in a reaction kettle, the reaction kettle is vacuumized by a vacuum pump (i.e. a gas exhaust device), then 1 MPa nitrogen is filled into the kettle, then the nitrogen is discharged, and the filling and discharging of nitrogen is repeated for multiple times. Preferably, the vacuum degree in the reaction kettle is reduced to 20 Pa before the nitrogen is filled and discharged again; preferably, the nitrogen is filled and discharged for five times. After the last time of filling and discharging of nitrogen is completed, the reaction kettle is filled with an experimental environment gas at a specified pressure,
[0037] The direct current potential drop system (DCPD system) is used to measure the crack length of the crack region in the CT sample at multiple time points, and determine the crack propagation rate of the crack region based on the multiple crack lengths.
[0038] In the embodiments of the present application, the DCPD system includes a voltmeter for collecting DCPD signals, a multi-channel collection system for collecting various required output signals and storing the output signals in a computing device, and a direct current power supply system for providing reversible steady direct current. The DCPD system is particularly used for when the steady direct current passes through the crack region of the CT sample, the change of the crack length changes the resistance of the crack region, thereby changing the potential difference between the multiple probes, and the crack length is determined by measuring the potential difference on both sides of the crack region.
[0039] It should be understood that the wires welded to the CT sample can be connected to the constant current output unit and the micro-voltage measurement unit of the DCPD system.
[0040] In the embodiments of the present application, the computing device can obtain multiple external forces applied and obtain the potential corresponding to each external force. Then, the relationship between the external force and the potential can be established.
[0041] For example, as shown in Figure 2 A curve diagram between force and potential can be established. Moreover, a reference straight line can be fitted on the linear segment of the force-potential curve, the DCPD signal under any given load is processed by regression through the line, so as to calculate the reference potential difference φ0 and the relative change amount Δφ. These values are substituted into the conversion formula of the potential difference and the crack length (usually the a-Φ relationship established by calibration or finite element method), so as to obtain the real-time crack length a and the propagation rate thereof. Wherein, the measured potential difference satisfies the following formula:
[0042] φ = φ0 + Δφ.
[0043] Wherein, φ is the measured potential difference, φ0 is the reference potential difference, and Δφ is the relative change amount. φ0 and Δφ are key voltage parameters for crack length calculation, which are derived from the linear feature in the stable stage of the load-voltage curve.
[0044] φ0 represents the initial value of the potential difference (i.e. the DCPD signal) of the crack region under a certain known load (usually selected at the initial stage of linear loading or a reference state), which is a reference voltage. Δφ is the voltage increment relative to φ0 under the application of external force, i.e. Δφ = φ - φ0, which reflects the potential difference change corresponding to the resistance change caused by crack propagation.
[0045] In a possible implementation, the crack length satisfies formula one.
[0046]
[0047] wherein a is the measured crack length, y is half of the distance of the voltage probe, W is the width of the sample, and a0 is the initial crack length.
[0048] Further, the DCPD system can determine the crack propagation amount based on the crack length and the initial crack length.
[0049] For example, the crack propagation amount satisfies formula two.
[0050] Δa = a - a0 formula two.
[0051] wherein Δa is the measured crack propagation amount.
[0052] In some embodiments, the crack length measurement system further comprises a computing device configured to determine, based on the applied external force, the sample thickness of the CT sample, the sample width, the net thickness between the grooves on both sides of the sample, and the initial crack length, an elongation at break of the CT sample, the elongation at break being used to represent the fracture toughness value.
[0053] In a possible implementation, the elongation at break satisfies formula three.
[0054]
[0055] wherein F is the applied external force during the test, B is the sample thickness, B N is the net thickness between the grooves on both sides of the sample, W is the sample width, a is the initial crack length, v is the Poisson's ratio, which can be 0.3, R P0.2 is the 0.2% yield strength of the material, E is the elastic modulus, which is 2.06 x 10 5 MPa, and V P is the plastic displacement component corresponding to the applied external force.
[0056] In some embodiments, based on the applied external force, the sample thickness of the CT sample, the sample width, the net thickness between the grooves on both sides of the sample, and the initial crack length, a J integral of the CT sample can be determined, the J integral being used to represent the fracture toughness value.
[0057]
[0058] wherein J is the J integral, U P is the integrated area of plastic displacement corresponding to the applied load, η P = 3.667 - 2.199(a / W) + 0.437(a / w)2.
[0059] Optionally, the computing device is a device in the DCPD.
[0060] Based on the above technical solution, the reaction kettle is used for sealing and compactly stretching the CT sample, the CT sample is clamped on the fatigue testing machine, and the CT sample includes a crack area. The gas exhaust device is used for exhausting the gas in the reaction kettle to a vacuum state and filling the target experimental environment gas into the reaction kettle. In this way, the direct current potential drop system DCPD system can measure the crack length of the crack area in the CT sample at multiple moments, and the CT sample is in the target experimental environment gas.
[0061] In some embodiments, the crack length measurement system can further include a loading system for applying an external force to the CT sample; the loading system includes a loading pin, a clamp, a stretching rod, and a loading frame. The CT sample is insulated from the loading pin through a ceramic insulating sleeve, the CT sample is insulated from the clamp through a ceramic insulating gasket, and the stretching rod is insulated from the loading frame through a polytetrafluoroethylene gasket.
[0062] In this way, since the DCPD itself adopts the direct current voltage drop method, the pin of the CT sample and the CT sample should be insulated to avoid electrical signal interference, and the gasket is used to ensure the insulation of the sample pre-clamp.
[0063] In some embodiments, the DCPD system is further configured to obtain multiple initial potentials of the CT sample under different environments, one initial potential corresponding to one environment; the different environments include: the CT sample is in air, the CT sample is in the reaction kettle and the reaction kettle is in normal air state, and the CT sample is in the reaction kettle and the reaction kettle is in a pressurized state. The computing device is configured to determine the multiple crack lengths obtained by the DCPD system when the multiple initial potentials all meet a preset potential condition.
[0064] For example, the initial potential can be measured once under normal temperature and pressure air. The CT sample can be placed in the reaction kettle, and the initial potential can be measured once when the reaction kettle is in normal temperature and pressure air. The initial potential can be measured once when the CT sample is in the reaction kettle and the reaction kettle is in a pressurized state.
[0065] It should be understood that the normal temperature mentioned in the above embodiments can refer to 20℃ or 25℃, the normal pressure can refer to 1 standard atmosphere (atm), and the specific numerical value is 1 atm = 101.325 kilopascal (kPa). The pressurized state can be increased by 0.1-10 MPa.
[0066] In a possible implementation, the standard deviation can be determined based on the initial potential and a potential reference value corresponding to the environment. In a case where the standard deviation is within a preset range, it is determined that the initial potential meets a preset potential condition.
[0067] Optionally, the computing device is further configured to acquire an initial crack length of the crack region and a specimen width of the CT specimen, and determine a first ratio based on the initial crack length and the specimen width. The preset potential condition is determined based on the first ratio and the initial potential. The initial potential includes at least two of a first potential in a case where the first ratio is a first value, a second potential in a case where the first ratio is a second value, a third potential in a case where the first ratio is a third value, and a fourth potential in a case where the first ratio is a fourth value.
[0068] For example, the first ratio is 1.1, and the first potential is a potential V 1.1 when the first ratio is 1.1. The second potential is a potential V 1.0 when the first ratio is 1.0. The third potential is a potential V 0.6 when the first ratio is 0.6. The fourth potential is a potential V 0.4 when the first ratio is 0.4.
[0069] In the embodiments of the present application, different first ratios and initial potentials correspond to different preset potential conditions, and the preset potential condition includes a preset ratio threshold.
[0070] For example, Table 1 shows the preset ratio threshold corresponding to different first ratios and initial potentials. Wherein a0 is used to represent the initial crack length, and W is used to represent the specimen width of the CT specimen.
[0071] Table 1: Initial potential effectiveness reference table
[0072]
[0073]
[0074] For example, V 1.1 vs V 0.4 , the voltage V 1.1 is the voltage when the first ratio is 1.1, and the voltage V 0.4is the voltage when the first ratio is 0.4. When the first ratio of the CT sample is 0.2, the preset ratio threshold is 0.4729, and the measured potential ratio V 1.1 / 0.4 The measured potential ratio V
[0075] That is, the preset potential condition includes that the difference between the ratio between the two potentials in the initial potential and the corresponding preset ratio threshold is less than the preset difference.
[0076] It can be understood that the ratio between the two potentials in the initial potential is mainly used for calibration, effectiveness verification, and inverse calculation of the crack length of the DCPD measurement system. By ratio calculation with the voltage when the standard reference crack length ratio (such as the first ratio is 0.4 or 0.6), the influence of non-ideal factors such as contact resistance, wire position deviation, and temperature drift can be effectively eliminated, and the accuracy and stability of the measurement are improved. The potential ratio in Table 1 corresponds to different initial crack lengths a0 / W, which provides a reliable reference for crack length calculation during the experiment, and ensures the repeatability and reliability of the crack propagation monitoring results.
[0077] It should be understood that in several embodiments provided in the present application, the disclosed system can be implemented in other ways. For example, the system embodiments described above are only illustrative, for example, the division of modules or units is only a logical function division, and actual implementation can have another division manner, for example, a plurality of units or components can be combined or integrated into another device, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the displayed or discussed units can be indirect coupling or communication connection through some interfaces, devices or units, and can be electrical, mechanical or other forms.
[0078] The units described as separate components can or can not be physically separated, and the components displayed as units can be one physical unit or multiple physical units, that is, can be located in one place, or can be distributed to multiple different places. Part or all of the classified units can be selected according to actual needs to achieve the purpose of the embodiment scheme.
[0079] In addition, each functional unit in each embodiment of the present application can be integrated in one processing unit, or each unit can be physically present alone, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.
[0080] The integrated unit, if implemented in the form of a software function unit and sold or used as an independent product, can be stored in a readable storage medium. Based on such understanding, the technical solutions of the embodiments of the present application essentially or say the part that contributes to the prior art or the entire classification or part of the technical solutions can be embodied in the form of a software product. The software product is stored in a storage medium, including a plurality of instructions to make a device (which can be a single-chip microcomputer, a chip, etc.) or a processor execute all or part of the steps of the system of various embodiments of the present application. The aforementioned storage medium includes a U disk, a mobile hard disk, a ROM, a RAM, a magnetic disk or an optical disk, and various media that can store program codes.
[0081] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any change or replacement within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.
Claims
1. A crack length measurement system, characterized in that: The system comprises: A reactor for sealing a compact tensile CT specimen, wherein the CT specimen is clamped in a fatigue testing machine, and wherein the CT specimen includes a crack region; A gas extraction device, used to extract the gas in the reactor to a vacuum state and fill the reactor with the target experimental environment gas; The DCPD system is used to measure the crack length of the crack area in the CT sample at multiple times.
2. The system according to claim 1, wherein: The gas extraction device is specifically used to extract the gas in the reactor to a vacuum state, and then fill or release a target amount of nitrogen, and the number of times of filling and releasing the nitrogen is a preset value; The gas extraction device is further used to fill the target experimental environment gas into the reactor after completing the filling and discharge of the nitrogen.
3. The system according to claim 2, characterized in that The gas extraction device is specifically used to refill the target value of nitrogen into the reactor when it is detected that the vacuum degree in the reactor is less than a preset vacuum degree threshold during the process of releasing the nitrogen.
4. The system according to claim 1, wherein: The system also includes a loading system; The loading system is used to apply external force to the CT specimen; the loading system includes: a loading pin, a clamp, a stretching rod, and a loading frame; The CT specimen is insulated from the loading pin by a ceramic insulating sleeve, the CT specimen is insulated from the fixture by a ceramic insulating gasket, and the stretching rod is insulated from the loading frame by a polytetrafluoroethylene gasket.
5. The system according to claim 1, wherein: The DCPD system includes: a voltmeter for collecting DCPD signals, a multi-channel acquisition system for collecting various required output signals and connecting them to a computing device for storage, and a DC power supply system for providing reversible steady DC power; The DCPD system is specifically used to determine the crack length by measuring the potential difference between the two sides of the crack area when a steady direct current passes through the crack area of the CT specimen. The change in the crack length changes the resistance of this crack area, thereby changing the potential difference between multiple probes.
6. The system according to claim 1, wherein: The system also includes a computing device; The DCPD system is further configured to obtain a plurality of initial potentials of the CT sample under different environments, each initial potential corresponding to one environment; the different environments include: the CT sample being in air, the CT sample being in the reactor and the reactor being in a normal air state, and the CT sample being in the reactor and the reactor being in a pressurized state; The computing device is configured to determine, when the multiple initial potentials all meet a preset potential condition, the multiple crack lengths obtained through the DCPD system.
7. The system according to claim 6, characterized in that The computing device is further configured to obtain an initial crack length of the crack region and a specimen width of the CT specimen, and determine a first ratio based on the initial crack length and the specimen width; determining the preset potential condition based on the first ratio and the initial potential; The initial potential includes at least two of the following: a first potential when the first ratio is a first value, a second potential when the first ratio is a second value, a third potential when the first ratio is a third value, and a fourth potential when the first ratio is a fourth value.
8. The system according to claim 6, wherein: The calculation device is further configured to determine the fracture elongation and J-integral of the CT specimen based on the applied external force, the specimen thickness, the specimen width, the net thickness between the grooves on both sides of the specimen, and the initial crack length. The fracture elongation and the J-integral are both used to represent the fracture toughness value.
9. The system according to claim 8, characterized in that Where F is the external force applied during the test, B is the thickness of the sample, and B N is the net thickness between the slots on both sides of the specimen, W is the specimen width, a is the initial crack length, v is the Poisson's ratio, R P0.2 is the 0.2% yield strength of the material, E is the elastic modulus, V P is the plastic displacement component corresponding to the applied external force; Among them, J is the J integral, U P is the integrated area of the plastic displacement corresponding to the applied load.
10. The system according to claim 1, wherein: The target experimental environment gas is hydrogen.