A fatigue damage detection method for good conductor rods based on the current skin effect

Abstract

This invention discloses a fatigue damage detection method for good conductor rods based on the skin effect of current. First, the minimum applicable current frequency is calculated using the diameter and material grade of the rod under test. The current frequency applied to the rod is gradually increased from the minimum applicable current frequency, while simultaneously calculating the change in the resistance of the rod with the current frequency. When the resistance no longer changes with the current frequency, the resistance value and corresponding frequency are recorded. The sum of the absolute values ​​of the maximum profile peak height and the maximum profile valley depth, h, is calculated and used as the surface roughness value of the rod. Based on the diameter, material grade, and h, a calibration database is retrieved to determine the severity of fatigue damage. This invention eliminates the influence of surface roughness on fatigue damage detection results, allows direct detection of the rod under test, and has low requirements for the testing environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material testing or analysis by electrical method, and particularly relates to a good conductor bar fatigue damage detection method based on current skin effect. BACKGROUND

[0002] At present, methods for detecting fatigue damage of metal or metal alloy bars mainly include visual detection, ultrasonic detection, X-ray or CT scanning detection, vibration analysis detection and the like.

[0003] Visual detection depends on the experience of operators and cannot quantitatively analyze fatigue damage. The application can quantitatively analyze the fatigue damage degree of the bar through high-frequency resistance change.

[0004] Ultrasonic detection needs to ensure that the bar surface is smooth material, and requires that the bar surface roughness is not greater than Ra0.2.

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

[0006] Vibration analysis detection is not sensitive to small-scale or initial fatigue damage, is easily affected by environmental noise, and requires that the detection environment temperature is 10-35 DEG C.

[0007] However, when these methods are used to detect fatigue damage of the whole bar, it is necessary to detect point by point and zone by zone, and the fatigue damage of the whole bar is obtained according to the results of each detection point and detection zone. Therefore, the above-mentioned methods are difficult to directly detect the fatigue damage of the whole bar, and have problems of limited detection range, low efficiency, complex operation, high requirement for detection environment and the like. SUMMARY

[0008] In view of the problems of limited detection range, low efficiency, complex operation and high requirement for detection environment of the traditional detection methods proposed in the background, the application provides a good conductor bar fatigue damage detection method based on current skin effect, and the technical scheme comprises the following steps:

[0009] Step 1, inputting the diameter of the bar to be detected and the grade of the material, and calculating the minimum applicable current frequency f;

[0010] The calculation formula of the minimum applicable current frequency is as follows:

[0011]

[0012] f is the minimum applicable current frequency, the unit is Hz,

[0013] ρ is the resistivity of the bar to be detected, the unit is Ω·m,

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

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

[0016] Step 2, install two probes at both ends of the bar to be detected;

[0017] Step 3, the power supply applies a high-frequency current to the bar to be detected through the two probes, and the frequency value of the applied current is gradually increased from the minimum current frequency f that can be applied;

[0018] Step 4, calculate the resistance value R of the bar to be detected through the voltage value U at both ends of the bar and the current I applied to the bar 测 with the change of the current frequency f 当前 ;

[0019] Step 5, when the resistance value R of the bar to be detected 测 no longer changes with the increase of the current frequency f 当前 , record the resistance value R 测 and the corresponding frequency f 测 at this time;

[0020] Step 6, calculate the sum h of the maximum profile peak absolute value and the maximum profile valley absolute value of the surface of the bar to be detected, and take h as the surface roughness Rz value of the bar to be detected, wherein:

[0021]

[0022] f 测 is the frequency at which the resistance value R 测 no longer changes with the increase of the current frequency f 当前 , in Hz;

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

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

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

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

[0027] The calibration database is a database in which the resistance difference of each grade of bar under the corresponding diameter, roughness and current frequency corresponds to the degree of fatigue damage in the calibration process.

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

[0029] The beneficial effects of this invention are as follows:

[0030] 1. This invention first measures the surface roughness of the material under test and then corrects the fatigue damage detection results, which can eliminate the influence of surface roughness on the fatigue damage detection results and improve the accuracy of the detection results; it can be used to detect fatigue damage under working conditions where the surface roughness of the material changes with the service time.

[0031] 2. This invention does not require the preparation of non-destructive original samples in advance, and can directly test the material being tested, saving time and having high testing efficiency.

[0032] 3. Compared with X-ray or CT scanning equipment, the device of this invention has a simple structure, low cost, does not require radiation protection measures, and takes only 1 to 2 minutes on average to complete one detection.

[0033] 4. The detection range of this invention reaches the roughness detection range Rz0.2~206, which is extremely versatile. Compared with ultrasonic testing, it can detect solid-state electrical good conductor rods with surface roughness Rz0.2~206, which greatly increases the scope of application.

[0034] 5. Compared with vibration analysis and detection, this invention can detect small-scale or early fatigue damage in solid-state electrical good conductor rods, is not affected by environmental noise, and can work normally in environments with temperatures ranging from 0 to 40°C. Attached Figure Description

[0035] Figure 1 This is a schematic flowchart of an embodiment of the fatigue damage detection method for good conductor rods based on the current skin effect of the present invention.

[0036] Figure 2 This is a 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 one; 3. rod to be tested; 4. probe two. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings.

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

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

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

[0042] The filtering system is used to filter the noise of the amplification circuit; specifically, the signal amplified by the amplification circuit is filtered to filter out the noise that interferes with the detection result.

[0043] In the embodiment, the probe one 2 and the probe two 4 use clamps;

[0044] The rod to be detected 3 needs to be a solid-state electrically good conductor rod, and in the embodiment, the rod to be detected 3 specifically selects copper alloy as the material.

[0045] The method of the embodiment comprises:

[0046] Step 1, input the diameter and material grade of the rod to be detected, specifically:

[0047] The diameter and material grade of the rod to be detected are input to the control system;

[0048] The material grade of the rod to be detected is the type of copper alloy in the embodiment, and the control system finds the corresponding parameters (resistivity, magnetic permeability) of the national standard from the database according to the material grade;

[0049] The control system calculates the minimum applicable current frequency f according to formula (1)

[0050]

[0051] f is the minimum applicable current frequency, and the unit is Hz

[0052] ρ is the resistivity of the rod to be detected, and the unit is Ω·m

[0053] d is the diameter of the rod to be detected, and the unit is m

[0054] μ is the magnetic permeability of the rod to be detected, and the unit is H / m

[0055] Step 2, clamp the two clamps to the two ends of the rod to be detected, and turn on the control system;

[0056] Step 3, the power supply applies high-frequency current to the rod to be detected through the clamps, the current frequency value is gradually increased from the calculation result f of step 1, and the voltage change of the rod 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 rod through the voltage value U of both ends of the rod and the current I applied to the rod 测 with the change of the current frequency f 当前 ;

[0058] Step 5, when the resistance value R of the detected rod 测 no longer changes with the increase of the current frequency f 当前 , record the resistance value R 测 and the corresponding frequency f 测 ;

[0059] Step 6, calculate h

[0060]

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

[0062] ρ is the resistivity of the rod to be detected, unit: Ω·m;

[0063] μ is the permeability of the rod to be detected, unit: 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 of the surface of the rod to be detected;

[0065] Take h as the surface roughness Rz value of the detected rod.

[0066] Step 7, according to the diameter of the detected rod, 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, 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 in which the resistance difference of each grade of copper alloy rod at a certain diameter, roughness and current frequency corresponds to the degree of fatigue damage in the calibration process before. The detection range of the roughness of the present method is Rz0.2~206.

Claims

1. A method for detecting fatigue damage in a good conductor rod based on current skin effect, characterized in that, The application relates to a method for detecting the surface roughness of a rod material, and a device thereof. Step 1, inputting the diameter and the material grade of the rod material to be detected, and calculating the minimum applicable current frequency f; The calculation formula of the minimum applicable current frequency is as follows: f is the minimum applicable current frequency, and the unit is Hz, rho is the resistivity of the rod material to be detected, and the unit is omega*m, d is the diameter of the rod material to be detected, and the unit is m, mu is the magnetic permeability of the rod material to be detected, and the unit is H / m; Step 2, installing two probes at two ends of the rod material to be detected; Step 3, the power supply applies a high-frequency current to the bar to be inspected through two probes, and the current frequency value f applied at present 当前 gradually increases from the minimum current frequency f that can be applied; Step 4, calculate the resistance value R of the detected rod by the voltage value U of both ends of the rod and the current I applied to the rod 测 with the current frequency f 当前 ​ Step 5, when the resistance value R of the detected bar is increased 测 no longer changes with the increase of the current frequency f 当前 , record the resistance value R 测 at this time and the corresponding frequency f 测 ; Step 6, calculating the sum h of the maximum profile peak absolute value and the maximum profile valley absolute value of the surface of the rod material to be detected, and taking h as the surface roughness Rz value of the detected rod material, wherein: f 测 for the resistance value R 测 no longer changes with the increase in the current frequency f 当前 of the frequency, in Hz, rho is the resistivity of the rod material to be detected, and the unit is omega*m, mu is the magnetic permeability of the rod material to be detected, and the unit is H / m; Step 7, according to the diameter of the detected bar, the grade of the material and h, the corresponding original resistance value R in the calibration database is called to obtain the resistance difference value ΔR = R 测 R, compare ΔR with the data in the calibration database to obtain the severity of fatigue damage.

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

3. The method for fatigue damage detection of a good conductor rod based on current skin effect according to claim 1, characterized in that, The calibration database is a database of the fatigue damage degree corresponding to the resistance difference of each grade of rod material under the corresponding diameter, roughness and current frequency in the calibration process.

4. A method for fatigue damage detection of a good conductor rod based on current skin effect according to one of claims 1 to 3, characterized in that The material of the rod material to be detected is an electric good conductor.

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