Fatigue damage detection method for good conductor bar based on current skin effect

Abstract

The invention discloses a good conductor bar fatigue damage detection method based on a current skin effect. The method comprises the following steps: firstly, calculating to obtain an imposable minimum current frequency through the diameter of a to-be-detected bar and the mark of a material; the current frequency value applied to the to-be-detected bar by the power supply is gradually increased from the minimum current frequency which can be applied, and meanwhile, the change condition of the resistance value of the detected bar along with the current current frequency is calculated; when the resistance value of the detected bar does not change along with the increase of the current current frequency, recording the resistance value at the moment and the corresponding frequency; the sum h of the maximum contour peak height absolute value and the maximum contour valley depth absolute value of the surface of the bar to be detected is calculated, and h serves as the surface roughness value of the detected bar; and calling a calibration database according to the diameter, the mark and the h of the detected bar to obtain the severity of the fatigue damage. The method eliminates the influence of the surface roughness on the fatigue damage detection result, can directly detect the to-be-detected bar, and has low requirements on the detection environment.

Description

Technical Field

[0001] The invention belongs to the technical field of testing or analyzing materials using electricity, and specifically is a method for detecting fatigue damage of a good conductor bar based on the current skin effect. Background Art

[0002] Currently, the methods used to detect fatigue damage of metal or metal alloy bars mainly include visual inspection, ultrasonic inspection, X-ray or CT scanning inspection, vibration analysis inspection, etc.

[0003] Visual inspection depends on the experience of the operator and cannot quantitatively analyze fatigue damage. The present invention can quantitatively analyze the degree of fatigue damage of the bar through high-frequency resistance changes.

[0004] Ultrasonic testing requires that the surface of the bar be smooth and the surface roughness of the bar should not exceed Ra0.2.

[0005] X-ray or CT scanning equipment is expensive, operators are required to take radiation protection measures when the equipment is working, and it takes an average of 1.5 hours to complete one test.

[0006] Vibration analysis testing is not sensitive enough to detect small-scale or initial fatigue damage, is easily affected by environmental noise, and requires a testing environment temperature of 10 to 35°C.

[0007] However, when using these methods to detect fatigue damage on the entire bar, it is necessary to detect point by point and area by area, and the fatigue damage status of the entire bar can be obtained based on the results of each detection point and detection area; therefore, the above methods are difficult to directly detect the fatigue damage status of the entire bar, and there are problems such as limited detection range, low efficiency, complex operation, and high requirements for the detection environment. Summary of the invention

[0008] In view of the problems of limited detection range, low efficiency, complex operation, and high requirements on the detection environment of the traditional detection method mentioned in the background technology, the present invention provides a fatigue damage detection method for good conductor bars based on the current skin effect, and the technical solution includes:

[0009] Step 1: Input the diameter of the bar to be tested and the grade of the material, and calculate the minimum current frequency f that can be applied;

[0010] The calculation formula of the minimum current frequency that can be applied is:

[0011]

[0012] f is the minimum current frequency that can be applied, in Hz,

[0013] ρ is the resistivity of the bar to be tested, in Ω·m.

[0014] d is the diameter of the bar to be tested, in meters.

[0015] μ is the magnetic permeability of the bar to be tested, in H / m;

[0016] Step 2: Install two probes at both ends of the bar to be tested;

[0017] Step 3: The power supply applies a high-frequency current to the bar to be inspected through two probes, and the applied current frequency value gradually increases from the minimum current frequency f that can be applied;

[0018] Step 4: Calculate the resistance value R of the tested bar through the voltage value U at both ends of the bar and the current I applied to the bar. 测 With the current frequency f 当前 changes in

[0019] Step 5: When the resistance value of the tested bar is R 测 No longer follows the current frequency f 当前 When the resistance value R 测 and the corresponding frequency f 测 ;

[0020] Step 6: Calculate the sum h of the absolute value of the maximum profile peak height and the absolute value of the maximum profile valley depth on the surface of the bar to be tested, and use h as the surface roughness Rz value of the bar to be tested, where:

[0021]

[0022] f 测 is the resistance value R 测 No longer with the current frequency f 当前 The frequency when it changes with the increase of, the unit is Hz;

[0023] ρ is the resistivity of the bar to be tested, in Ω·m;

[0024] μ is the magnetic permeability of the bar to be tested, in H / m;

[0025] Step 7: According to the diameter of the bar being tested, the grade of the material and h, retrieve the corresponding original resistance value R in the calibration database to obtain the resistance difference ΔR=R 测 -R, compare ΔR with the data in the calibration database to obtain the severity of fatigue damage.

[0026] In step 1, the control system searches the database for the resistivity and magnetic permeability corresponding to the national standard according to the grade of the material.

[0027] The calibration database is a database of fatigue damage degrees corresponding to resistance differences of bars of various grades at corresponding diameters, roughnesses, and current frequencies during the previous calibration process.

[0028] The material of the bar to be inspected is a good conductor of electricity.

[0029] The beneficial effects of the present invention are:

[0030] 1. The present invention first measures the surface roughness of the material to be tested and corrects the fatigue damage detection result, which can eliminate the influence of the surface roughness on the fatigue damage detection result and improve the accuracy of the detection result; it can be used to detect fatigue damage under the working condition that the surface roughness of the material changes with the service time.

[0031] 2. The present invention does not require the preparation of undamaged original samples in advance, and can directly detect the material to be tested, saving time and having high detection efficiency.

[0032] 3. Compared with X-ray or CT scanning detection equipment, the equipment of the present invention has a simple structure, low cost, no need to take radiation protection measures, and only takes 1 to 2 minutes on average to complete one detection.

[0033] 4. The detection range of the present invention reaches the roughness detection range of Rz0.2~206, and the versatility is extremely high. Compared with ultrasonic detection, since it can detect solid electrical good conductor rods with a surface roughness of Rz0.2~206, the scope of application is greatly increased.

[0034] 5. Compared with vibration analysis detection, the present invention can detect small-scale or initial fatigue damage of good conductor bars of solid-state electricity, is not affected by environmental noise, and can work normally in an environment with a temperature of 0 to 40°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a schematic flow chart of an embodiment of a method for detecting fatigue damage of a good conductor bar based on the current skin effect.

[0036] Figure 2 Schematic diagram of the clamping of the bar to be inspected in an embodiment of the present invention.

[0037] Among them, 1. Wire; 2. Probe 1; 3. Rod to be tested; 4. Probe 2. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0039] like Figure 1 The application device of the embodiment of the present invention shown includes: a wire 1, a probe 2, a rod 3 to be detected and a probe 4, wherein the probe 2 and the probe 4 are clamped at both ends of the rod 3 to be detected, and the probe 2 and the probe 4 are respectively connected to the power supply through a signal amplifier, and the signal amplifier is connected to the control system through a filtering system.

[0040] The power supply is used to release high-frequency current, and the frequency of the high-frequency current is 100kHz~100GHz;

[0041] The signal amplifier can amplify the signal of the high-frequency resistance detection probe and pass the amplified signal to the filtering system.

[0042] The filtering system is used to filter out the noise in the amplifier circuit; specifically, it can filter the signal amplified by the amplifier circuit and filter out the noise that interferes with the detection result.

[0043] In this embodiment, probe 1 2 and probe 2 4 use clips;

[0044] The rod material 3 to be detected needs to be a solid rod material that is a good electrical conductor. In this embodiment, the rod material 3 to be detected is specifically made of copper alloy.

[0045] The method of the embodiment comprises:

[0046] Step 1. Enter the diameter and material grade of the bar to be tested. Specifically:

[0047] The diameter of the bar to be inspected and the grade of the material are input into the control system;

[0048] The grade of the material of the bar to be inspected is a type of copper alloy in this embodiment, and the control system searches the database for the parameters (resistivity, magnetic permeability) corresponding to the national standard according to the grade of the material;

[0049] The control system calculates the minimum current frequency that can be applied according to formula (1):

[0050]

[0051] f is the minimum current frequency that can be applied, in Hz

[0052] ρ is the resistivity of the bar to be tested, in Ω·m

[0053] d is the diameter of the bar to be tested, in m

[0054] μ is the magnetic permeability of the bar to be tested, in units of H / m

[0055] Step 2: Clamp the two clamps to the two ends of the bar to be inspected and turn on the control system;

[0056] Step 3: The power supply applies a high-frequency current to the bar to be inspected through the clamp, and the current frequency value gradually increases from the result f calculated in step 1, and the voltage change at both ends of the bar is collected, and the signal is transmitted to the amplifier through the wire;

[0057] Step 4: The signal is collected by the control system through the amplifier; the control system calculates the resistance value R of the detected bar through the voltage value U at both ends of the bar and the current I applied to the bar. 测 With the current frequency f 当前 changes in

[0058] Step 5: When the resistance value of the tested bar is R 测 With the current frequency f 当前 When the resistance value R 测 and the corresponding frequency f 测 ;

[0059] Step 6: Calculate h according to formula (2):

[0060]

[0061] f 测 is the resistance value R 测 No longer with the current frequency f 当前 The frequency when it changes with the increase of, the unit is Hz;

[0062] ρ is the resistivity of the bar to be tested, in Ω·m;

[0063] μ is the magnetic permeability of the bar to be tested, in H / m;

[0064] h is the sum of the absolute value of the maximum profile peak height and the absolute value of the maximum profile valley depth on the surface of the bar to be inspected;

[0065] h is taken as the surface roughness Rz value of the tested rod.

[0066] Step 7: According to the diameter of the bar being tested, the grade of the material and the surface roughness value obtained in step 6, retrieve the corresponding original resistance value R in the calibration database to obtain the resistance difference ΔR=R 测 -R, compare ΔR with the data in the calibration database to obtain the severity of fatigue damage; the calibration database is a database of fatigue damage degrees corresponding to resistance differences of copper alloy bars of various brands at a certain diameter, roughness, and current frequency during the calibration process. The roughness detection range of this method is Rz0.2~206.

Claims

1. A method for detecting fatigue damage of good conductor bars based on current skin effect, characterized in that: include: Step 1: Input the diameter of the bar to be tested and the grade of the material, and calculate the minimum current frequency f that can be applied; The calculation formula of the minimum current frequency that can be applied is: f is the minimum current frequency that can be applied, in Hz, ρ is the resistivity of the bar to be tested, in Ω·m. d is the diameter of the bar to be tested, in meters. μ is the magnetic permeability of the bar to be tested, in H / m; Step 2: Install two probes at both ends of the bar to be tested; Step 3: The power supply applies high-frequency current to the bar to be inspected through two probes. The current frequency value f 当前 Starting from the minimum current frequency f that can be applied, it gradually increases; Step 4: Calculate the resistance value R of the tested bar through the voltage value U at both ends of the bar and the current I applied to the bar. 测 With the current frequency f 当前 changes in Step 5: When the resistance value of the tested bar is R 测 No longer follows the current frequency f 当前 When the resistance value R 测 and the corresponding frequency f 测 ; Step 6: Calculate the sum h of the absolute value of the maximum profile peak height and the absolute value of the maximum profile valley depth on the surface of the bar to be tested, and use h as the surface roughness Rz value of the bar to be tested, where: f 测 is the resistance value R 测 No longer with the current frequency f 当前 The frequency when it changes with the increase of, the unit is Hz, ρ is the resistivity of the bar to be tested, in Ω·m. μ is the magnetic permeability of the bar to be tested, in H / m; Step 7: According to the diameter of the bar being tested, the grade of the material and h, retrieve the corresponding original resistance value R in the calibration database to obtain the resistance difference ΔR=R 测 -R, compare ΔR with the data in the calibration database to obtain the severity of fatigue damage.

2. The method for detecting fatigue damage of a good conductor bar based on the current skin effect according to claim 1 is characterized in that: In step 1, the control system searches the database for the resistivity and magnetic permeability corresponding to the national standard according to the grade of the material.

3. The method for detecting fatigue damage of a good conductor bar based on the current skin effect according to claim 1 is characterized in that: The calibration database is a database of fatigue damage degrees corresponding to resistance differences of bars of various grades at corresponding diameters, roughnesses, and current frequencies during the previous calibration process.

4. A method for detecting fatigue damage of a good conductor bar based on current skin effect according to any one of claims 1 to 3, characterized in that: The material of the bar to be inspected is a good conductor of electricity.

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