A method for evaluating the creep damage state of metals based on conductivity measurement

Abstract

This invention discloses a method for evaluating the creep damage state of metals based on conductivity measurement, belonging to the field of metal testing technology. The method includes taking n sets of standard experimental samples with different creep degrees and plotting an evaluation curve to characterize the mapping relationship between electromagnetic properties and creep degree. The evaluation curve is divided into multiple intervals with peaks and troughs as boundaries. Within any interval, the creep degree and electromagnetic properties exhibit a monotonic relationship. Starting from the start of service of the in-service workpiece, the electromagnetic property value at the same location on the in-service workpiece is measured at time intervals t'. This invention, through a technical chain of constructing evaluation curves using standard sample experiments → dividing intervals with peaks and troughs to ensure monotonicity → dynamic monitoring of the in-service workpiece → deriving the creep degree of the in-service workpiece based on the creep calculation formula, not only solves the problem of difficult online non-destructive evaluation of metal creep but also enables the evaluation of in-service workpieces with nonlinear and non-monotonic electromagnetic properties.

Description

Technical Field

[0001] This invention relates to the field of metal testing technology, and specifically to a method for evaluating the creep damage state of metals based on conductivity measurement. Background Technology

[0002] When metallic materials are subjected to stress below their yield strength and at high temperatures, they will develop creep damage (a gradual change in the microstructure caused by sustained stress). Creep damage can easily lead to the initiation and propagation of microcracks, which greatly increases the risk of fracture failure of metallic materials. Therefore, the evaluation of creep damage status of critical metallic components is very important.

[0003] Currently, commonly used creep detection methods include metallographic analysis and scanning tunneling microscopy. These methods require complex processes such as slicing and preparation, and can damage the parts, making them unsuitable for testing in-service metal parts.

[0004] A search revealed that patent application number 202310945652.1 discloses a multi-frequency eddy current method and apparatus for evaluating the creep damage state of high-temperature alloys. This method uses multi-frequency eddy currents for non-destructive testing of creep damage in high-temperature alloys. However, multi-frequency eddy current testing can only reflect the linear change in creep damage and electromagnetic properties. Since the electromagnetic properties of creep damage in most metallic materials are typically non-linear and non-monotonic, the technical solution in the aforementioned patent can only detect a limited range of in-service workpiece types and cannot evaluate the creep degree of many types of in-service workpieces. Therefore, there is an urgent need to develop a new method for evaluating the creep damage state of metals based on electromagnetic property measurement. Summary of the Invention

[0005] The purpose of this invention is to address the problems in the prior art by proposing a method for evaluating the creep damage state of metals based on conductivity measurement. This evaluation method, by constructing an evaluation curve, can continuously reflect the creep degree of in-service workpieces whose electromagnetic properties are nonlinear and non-monotonic, thus providing an accurate assessment of the overall working condition of in-service workpieces.

[0006] To address the above problems, the present invention provides the following technical solution:

[0007] A method for evaluating the creep damage state of metals based on conductivity measurement includes the following steps:

[0008] S1: Construct the evaluation curve;

[0009] S10: Take n sets of standard test samples, randomly select one set to conduct a creep test on it until it breaks, and record the creep test time as T;

[0010] S11: Take n-1 experimental points between 0 and T, and conduct creep tests on the remaining n-1 sets of standard experimental samples according to the n-1 experimental points respectively, so as to obtain creep samples of different degrees at the corresponding n-1 experimental points.

[0011] S12: Measure the electromagnetic properties of the above n groups of creep samples with different degrees of creep respectively, and plot the evaluation curve to characterize the mapping relationship between electromagnetic properties and creep degree;

[0012] S13: The evaluation curve is divided into multiple intervals with peaks and troughs as boundaries. Within any interval, the degree of creep and electromagnetic properties show a monotonic relationship.

[0013] S2: Evaluation and verification;

[0014] S20: Starting from the beginning of service of the in-service workpiece, measure the electromagnetic characteristic value at the same location of the in-service workpiece at time intervals t'.

[0015] S21: Substitute the measured electromagnetic characteristic value into the evaluation curve to obtain the creep degree value corresponding to the corresponding electromagnetic characteristic value. Determine the interval in which the creep degree value falls according to the measurement time sequence, and record this interval as the reference interval.

[0016] S22: After the reference range is determined, the creep degree at that position and time of the in-service workpiece is obtained according to the creep calculation formula.

[0017] As a further aspect of the present invention: the evaluation curve used to characterize the mapping relationship between electromagnetic property Q and creep degree value p is expressed as Q= f (p), the creep calculation formula in S22 is:

[0018] ;

[0019] in: This is expressed as a creep degree value. This is represented by the electromagnetic characteristic values ​​measured for each in-service workpiece. Represented as one endpoint value of the reference interval. Represented as the value at the other endpoint of the reference interval. Represented as The corresponding creep degree value, Represented as The corresponding creep degree value.

[0020] As a further aspect of the present invention: In S12, a single-point eddy current detection sensor is used to measure the electromagnetic properties of n groups of creep samples with different degrees of creep. During the test, the eddy current coil in the single-point eddy current detection sensor and the creep sample mutually induct to form a transformer circuit. The eddy current coil is then regarded as an excitation coil, and its number of turns is... The resistance is Excitation voltage is The inductance is L1 and the current is The creep sample is considered as an equivalent coil, with the same number of turns (H) and resistance (H). The inductance is L2 and the current is The electromagnetic property Q is represented as follows:

[0021] ;

[0022] ;

[0023] in: Indicated as motivation Impedance mode Indicated as motivation The real part of the impedance. Indicated as motivation The imaginary part of impedance, This is expressed as the voltage of the excitation coil. This is expressed as the current in the excitation coil. Represented as the resistance of the excitation coil, Expressed as a resistance-conductivity scaling factor, f (p) represents the degree of creep, and σ represents the conductivity. Expressed as angular frequency, L1 represents the mutual inductance coefficient, L2 represents the inductance of the excitation coil, and L3 represents the inductance of the equivalent coil.

[0024] As a further aspect of the present invention: the loop equations in the excitation coil and the equivalent coil are as follows:

[0025] ;

[0026] ;

[0027] in: This is expressed as the current in the excitation coil. Represented as the resistance of the excitation coil, Represented as the resistance of the equivalent coil. Let L1 represent the inductance of the excitation coil, and L2 represent the inductance of the equivalent coil. Represented as mutual inductance coefficient, It is expressed as the voltage of the excitation coil.

[0028] As a further aspect of the present invention: the resistor It is directly proportional to conductivity, and the relationship between conductivity σ and creep value p is set as σ = f (p), then:

[0029] ;

[0030] in: Represented as the resistance of the equivalent coil. The resistance-conductivity proportionality factor is expressed as σ, where σ represents conductivity. f (p) indicates the degree of creep.

[0031] As a further aspect of the present invention: in S20, an array-type electromagnetic detection sensor is used to measure the electromagnetic characteristics at the same location of the in-service workpiece, wherein the array-type electromagnetic detection sensor has i rows × j columns of identical electromagnetic detection units.

[0032] As a further aspect of the present invention: the electromagnetic property is any one of conductivity, permeability, resistance, capacitance, dielectric strength, inductance, hysteresis loop and coercivity.

[0033] A readable storage medium having a computer program stored thereon, which, when executed, implements the above-described method for evaluating the state of metal creep damage based on conductivity measurement.

[0034] An electronic device includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the aforementioned method for evaluating the state of metal creep damage based on conductivity measurement.

[0035] A computer program product comprising a computer program / instructions that, when executed by a processor, implement the aforementioned method for evaluating the state of metal creep damage based on conductivity measurement.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The technical chain of constructing an evaluation curve through standard sample experiments → dividing the interval with peaks and troughs as boundaries to ensure monotonicity → dynamic monitoring of in-service workpieces → deriving the degree of creep of in-service workpieces based on creep calculation formulas, compared with the existing technology which can only reflect the linear changes in creep damage and electromagnetic properties, not only solves the problem of difficult online non-destructive evaluation of metal creep, but also provides guidance for the evaluation of in-service workpieces with nonlinear and non-monotonic electromagnetic properties.

[0038] 2. When obtaining the creep degree value based on the electromagnetic characteristic value mapping, the reference range in which the creep degree value falls is determined. The creep degree value falling within this range is calculated according to the designed creep calculation formula, so that the creep degree of the in-service workpiece under this state is better evaluated, rather than directly using the creep degree value corresponding to the electromagnetic characteristics as the evaluation.

[0039] 3. When multiple creep degree values ​​are obtained based on electromagnetic characteristic mapping, in order to accurately determine the current creep degree value corresponding to the in-service workpiece, these multiple creep degree values ​​are recorded. When a single or multiple creep degree values ​​are obtained in the next electromagnetic characteristic mapping, these creep degree values ​​are connected with the aforementioned multiple creep degree values ​​on the evaluation curve to draw multiple change curves. The change curve with the same trend as the evaluation curve is selected as the creep curve of the in-service workpiece. The beginning and end values ​​of the change curve are the first and second creep degree values.

[0040] 4. By selecting electromagnetic properties as conductivity, the conductivity of in-service workpieces can be directly obtained through a conductivity meter, eliminating the need for complex tests and simplifying the entire evaluation process. Attached Figure Description

[0041] The invention will now be further described with reference to the accompanying drawings.

[0042] Figure 1 This is a flowchart of the present invention;

[0043] Figure 2 This is a graph showing the conductivity of the experimental sample of the present invention under different degrees of creep. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] like Figures 1-2 As shown, a method for evaluating the creep damage state of metals based on conductivity measurement includes the following two main steps:

[0046] S1: Construct the evaluation curve.

[0047] S2: Verify and evaluate in-service workpieces based on the evaluation curve.

[0048] (a) The construction of the evaluation curve includes the following steps:

[0049] S10: Take n sets of standard test specimens. These test specimens belong to the same type and batch as the in-service workpieces (both have the same material properties and geometric dimensions). Randomly select one set to conduct a creep test on it until it breaks. Record the creep test time as T.

[0050] S11: Take n-1 experimental points between 0 and T (preferably, the n-1 experimental points are divided equally according to the time interval), and conduct creep tests on the remaining n-1 sets of standard experimental samples according to the n-1 experimental points respectively, so as to obtain creep samples of different degrees under the corresponding experimental points of n-1 sets.

[0051] S12: Measure the electromagnetic properties of the above n groups of creep samples with different degrees of creep, and plot the evaluation curve characterizing the mapping relationship between electromagnetic property Q and creep degree value p, denoted as Q= f (p), where the horizontal axis is p and the vertical axis is Q;

[0052] S13: The evaluation curve is divided into multiple intervals with peaks and troughs as boundaries. Within any interval, the creep degree p and the electromagnetic property Q show a monotonically changing relationship.

[0053] It should be noted that the electromagnetic properties in this application are a broad generalization, and can specifically be any one of conductivity, permeability, resistance, capacitance, dielectric strength, inductance, hysteresis loop and coercivity. This paper preferably selects conductivity as the electromagnetic property for description.

[0054] In step S12 above, a single-point eddy current sensor is used to measure the electromagnetic properties of n groups of creep samples with different degrees of creep. During the test, the eddy current coil in the single-point eddy current sensor and the creep sample form a transformer circuit through mutual inductance. The eddy current coil is considered as the excitation coil, and its number of turns is... The resistance is Excitation voltage is The inductance is L1 and the current is The creep sample is considered as an equivalent coil, with the same number of turns (H) and resistance (H). The inductance is L2 and the current is .

[0055] At this point, the loop equations in the excitation coil and the equivalent coil are:

[0056] ;

[0057] ;

[0058] in: This is expressed as the current in the excitation coil. Represented as the resistance of the excitation coil, Represented as the resistance of the equivalent coil. Let L1 represent the inductance of the excitation coil, and L2 represent the inductance of the equivalent coil. Represented as mutual inductance coefficient, It is expressed as the voltage of the excitation coil.

[0059] Due to resistance The conductivity σ is directly proportional to the creep value p. Let the relationship between conductivity σ and creep value p be σ = ... f (p), then:

[0060] ;

[0061] in: It is a resistance-conductivity proportionality factor, which is independent of the electromagnetic properties of the workpiece under test and only related to its geometric dimensions.

[0062] Combining the above three equations, we can obtain the relationship between the coil impedance and the creep degree of the in-service workpiece under test as follows:

[0063] ;

[0064] in: Indicated as motivation Impedance mode Indicated as motivation The real part of the impedance. Indicated as motivation The imaginary part of impedance, This is expressed as the voltage of the excitation coil. This is expressed as the current in the excitation coil. Represented as the resistance of the excitation coil, Expressed as a resistance-conductivity scaling factor, f (p) represents the degree of creep, and σ represents the conductivity. Expressed as angular frequency, L1 represents the mutual inductance coefficient, L2 represents the inductance of the excitation coil, and L3 represents the inductance of the equivalent coil.

[0065] The impedance is divided into real part. and the virtual part ,make This is used as a characteristic parameter for assessing the degree of creep.

[0066] (ii) Evaluation and verification include the following steps:

[0067] S20: Starting from the start of service of the in-service workpiece, the electromagnetic characteristic value at the same location of the in-service workpiece is measured at intervals t'. It should be noted that since different in-service workpieces are in different environments, their creep degree changes in different ways. t' can be set according to the corresponding usage scenario and other conditions, such as seven days.

[0068] S21: Substitute the measured electromagnetic characteristic values ​​into the evaluation curve Q= fIn (p), the creep degree value corresponding to the corresponding electromagnetic characteristic value is obtained. Based on the measurement time sequence, the interval in which the creep degree value falls is determined, and this interval is recorded as the reference interval. For example, the first electromagnetic characteristic value measurement is performed on the seventh day after the in-service workpiece begins service, based on the evaluation curve Q= f (p) Obtain the creep degree value. Based on the creep degree value, the creep status of the in-service workpiece can be obtained. If there are multiple creep degree values ​​corresponding to the first electromagnetic characteristic value, these multiple values ​​can be recorded in advance. After seven days, the second electromagnetic characteristic value is measured to obtain a single creep degree value. The creep degree value obtained this time is compared with the aforementioned multiple values. The second creep degree value is connected with the multiple creep degree values ​​of the first time in the evaluation curve to obtain multiple change curves. Select the change curve with the same trend as the evaluation curve. This change curve is the desired curve. The beginning and end values ​​of this change curve are the first and second creep degree values ​​corresponding to the in-service workpiece. At this time, the first creep degree value and the second creep degree value will both fall into the corresponding interval.

[0069] It should be noted that if the second electromagnetic characteristic measurement still corresponds to multiple creep degree values, the above-mentioned connection processing and evaluation can be performed. Alternatively, a third electromagnetic characteristic measurement can be conducted to obtain a single creep degree value. The three values ​​can then be connected to find the trend and plotted as a curve that matches the evaluation curve, which is the desired curve. If the third electromagnetic characteristic measurement also corresponds to multiple creep degree values, this process can be repeated for a fourth, fifth, and subsequent measurements until a curve matching the trend of the evaluation curve is found.

[0070] S22: After the reference range is determined, the degree of creep at that location and time of the in-service workpiece is obtained according to the creep calculation formula. The creep calculation formula is as follows:

[0071] ;

[0072] in: This is expressed as a creep degree value. This is represented by the electromagnetic characteristic values ​​measured for each in-service workpiece. Represented as one endpoint value of the reference interval. Represented as the value at the other endpoint of the reference interval. Represented as The corresponding creep degree value, Represented as The corresponding creep degree value.

[0073] Since there are many types of in-service workpieces, when they have irregular three-dimensional structures and multiple locations need to be measured, an array-type electromagnetic detection sensor can be fabricated. It can be made using FPCB and has flexible characteristics. The array-type electromagnetic detection sensor has i rows × j columns of identical electromagnetic detection units. This design can not only adapt to in-service workpieces with different structures, but also measure the electromagnetic characteristics of multiple locations on the in-service workpiece simultaneously.

[0074] The following example illustrates the creep damage evaluation of the nickel-based superalloy GH4169:

[0075] (1) First, seven GH4169 creep samples of the same type and batch were prepared. The sample shapes and sizes were exactly the same. One GH4169 creep sample was randomly selected and numbered as 1#. Then, the 1# sample was continuously subjected to creep test at 700℃ and 353MPa using a high-temperature creep testing machine until the sample broke. The time was recorded as 1100h. This state was taken as 100% creep degree.

[0076] (2) The remaining six GH4169 creep samples were numbered as 2#, 3#, 4#, 5#, 6# and 7# respectively. Six sets of experiments were conducted to make their creep degrees 0, 20%, 30%, 40%, 50%, 60% and 80% respectively. The corresponding test times in the high temperature creep tester were 0h, 220h, 330h, 440h, 550h, 660h and 880h. The creep tester was also set to 700℃ and 353Mpa.

[0077] (3) Based on the use of conductivity to evaluate electromagnetic properties in this application, the conductivity of samples 2#, 3#, 4#, 5#, 6#, and 7# after creep experiments was measured using a conductivity meter, and the results were recorded to plot the evaluation curves, as shown below. Figure 2 As shown, the horizontal axis represents the degree of creep, and the vertical axis represents electrical conductivity.

[0078] (4) Starting from the start of service of the workpiece, its conductivity is measured at regular intervals. The interval can be determined based on human experience and the environment of the workpiece. When the conductivity value measured for the first time is 0.90, it corresponds to three horizontal axes, namely the creep degree values ​​of three situations. Record the three creep degree values, and then perform a second measurement to obtain the creep degree value corresponding to this measurement. Connect the creep degree value with the multiple creep degree values ​​of the first measurement on the evaluation curve to obtain multiple sets of change curves. Find the change curve with the same trend as the evaluation curve among the multiple sets of change curves. That is, the first and second creep degree values ​​on the change curve are the values ​​corresponding to the first and second conductivity values, respectively. Observe the intervals on the evaluation curve where the first and second creep degree values ​​are located, and determine the corresponding reference intervals. After the reference intervals are determined, the creep degree of the workpiece in service can be obtained by using the creep calculation formula.

[0079] Based on the measurement sequence and the positive correlation between the creep degree of in-service workpieces and their service life, the creep degree value obtained by the next measurement and calculation is used to cover the creep degree value obtained by the previous measurement and calculation. The creep degree value obtained by the last measurement and calculation is the most reliable indicator of the creep degree of in-service workpieces.

[0080] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for evaluating a metal creep damage state based on a conductivity measurement, characterized by, Includes the following steps: S1: Constructing the evaluation curve: The experiment takes n groups of standard experimental samples with different degrees of creep and obtains the evaluation curve used to characterize the mapping relationship between electromagnetic properties and creep degree. S2: Using peaks and troughs as boundaries, and taking the condition that the degree of creep and electromagnetic properties change monotonically within any interval, the evaluation curve is divided into multiple intervals. S3: Starting from the beginning of service of the in-service workpiece, measure the electromagnetic characteristic value at the same location of the in-service workpiece at time intervals t'. S4: Substitute the measured electromagnetic characteristic value into the evaluation curve to obtain the creep degree value corresponding to the corresponding electromagnetic characteristic value. Determine the interval in which the creep degree value falls according to the measurement sequence and record this interval as the reference interval. When multiple creep degree values ​​are obtained based on electromagnetic characteristic mapping, record these multiple creep degree values ​​in order to obtain the current creep degree value corresponding to the in-service workpiece. When the next electromagnetic characteristic mapping obtains one or more creep degree values, connect the creep degree value with the aforementioned multiple creep degree values ​​on the evaluation curve to draw multiple change curves. Select the change curve with the same change trend as the evaluation curve as the creep curve of the in-service workpiece. The beginning and end values ​​of the change curve are the first and second creep degree values. S5: After determining the reference interval, the creep degree at that location and time of the in-service workpiece is obtained according to the creep calculation formula; the evaluation curve used to characterize the mapping relationship between electromagnetic property Q and creep degree value p is expressed as Q= f (p), the creep calculation formula in S5 is: ； in: This is expressed as a creep degree value. This is represented by the electromagnetic characteristic values ​​measured for each in-service workpiece. Represented as one endpoint value of the reference interval. Represented as the value at the other endpoint of the reference interval. Represented as The corresponding creep degree value, Represented as The corresponding creep degree value.

2. The method for evaluating the creep damage state of metals based on conductivity measurement according to claim 1, characterized in that, In step S1, a single-point eddy current sensor is used to measure the electromagnetic properties of n groups of creep samples with different degrees of creep. During the test, the eddy current coil in the single-point eddy current sensor and the creep sample form a transformer circuit through mutual inductance. The eddy current coil is considered as the excitation coil, and its number of turns is... The resistance is Excitation voltage is The inductance is L1 and the current is The creep sample is considered as an equivalent coil, with the same number of turns (H) and resistance (H). The inductance is L2 and the current is The electromagnetic property Q is represented as follows: ； ； Where Z represents the excitation coil impedance, and |Z| represents the magnitude of the excitation coil impedance. This is represented by the real part of the excitation coil impedance. This is represented as the imaginary part of the excitation coil impedance. This is expressed as the voltage of the excitation coil. This is expressed as the current in the excitation coil. Represented as the resistance of the excitation coil, Expressed as a resistance-conductivity scaling factor, f (p) represents the degree of creep, and σ represents the conductivity. Expressed as angular frequency, L1 represents the mutual inductance coefficient, L2 represents the inductance of the excitation coil, and L3 represents the inductance of the equivalent coil.

3. The method for evaluating the creep damage state of metals based on conductivity measurement according to claim 2, characterized in that, The loop equations in the excitation coil and the equivalent coil are as follows: ； ； in: This is expressed as the current in the excitation coil. Represented as the resistance of the excitation coil, Represented as the resistance of the equivalent coil. Let L1 represent the inductance of the excitation coil, and L2 represent the inductance of the equivalent coil. Represented as mutual inductance coefficient, It is expressed as the voltage of the excitation coil.

4. The method for evaluating the creep damage state of metals based on conductivity measurement according to claim 3, characterized in that, The resistor It is directly proportional to conductivity, and the relationship between conductivity σ and creep value p is set as σ = f (p), then: ； in: Represented as the resistance of the equivalent coil. The resistance-conductivity proportionality factor is expressed as σ, where σ represents conductivity. f (p) indicates the degree of creep.

5. A method for evaluating the creep damage state of metals based on conductivity measurement according to any one of claims 1-4, characterized in that, In S3, an array-type electromagnetic detection sensor is used to measure the electromagnetic characteristics of the same location on the in-service workpiece. The array-type electromagnetic detection sensor has i rows × j columns of identical electromagnetic detection units.

6. A method for evaluating the creep damage state of metals based on conductivity measurement according to any one of claims 1-4, characterized in that, The S1 mentioned above specifically includes the following steps: S10: Take n sets of standard test samples, randomly select one set to conduct a creep test on it until it breaks, and record the creep test time as T; S11: Take n-1 experimental points between 0 and T, and conduct creep tests on the remaining n-1 sets of standard experimental samples according to the n-1 experimental points respectively, so as to obtain creep samples of different degrees at the corresponding n-1 experimental points. S12: Measure the electromagnetic properties of the above n groups of creep samples with different degrees of creep respectively, and plot the evaluation curve to characterize the mapping relationship between electromagnetic properties and creep degree.

7. An electronic device, characterized in that, It includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the method for evaluating the state of metal creep damage based on conductivity measurement as described in any one of claims 1 to 6.

8. A computer program product, characterized in that, It includes a computer program / instruction that, when executed by a processor, implements the method for evaluating the state of metal creep damage based on conductivity measurement as described in any one of claims 1 to 6.

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