Zero stress calibration method of stress magnetic measurement method

Abstract

The invention provides a zero stress calibration method of a stress magnetic measurement method, and relates to the technical field of stress detection. The method comprises the following steps: obtaining a vertical voltage value of a measurement point; obtaining a zero stress calibration value according to the voltage value in the vertical direction of the measurement point; according to the zero stress calibration value, a voltage value generated only under the influence of stress is obtained; and obtaining a stress difference and a principal stress direction angle according to a voltage value generated only under the influence of the stress. The measurement accuracy and efficiency of a quadrupole magnetic method are improved, the stress measurement difficulty and cost are reduced, and the problem that a zero-stress sample needs to be manufactured in an existing method can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of stress detection, and in particular, to a zero-stress calibration method for stress magnetic measurement method. Background Art

[0002] The magnetic measurement method is used to evaluate the internal stress according to the change of magnetism after the ferromagnetic material is stressed. Its basic principle is that stress or defects will cause the change of the magnetic characteristic field of the material, and the stress or defects are measured and evaluated by detecting the change of the magnetic response caused by the change of the magnetic characteristic field. The commonly used magnetic measurement methods include the magnetic Barkhausen method, the magnetic method (inverse magnetostrictive effect method, magnetic strain method), the magnetic memory method, etc.

[0003] The magnetic Barkhausen method is a non-destructive testing technology based on the Magnetic Barkhausen Noise Signal (MBNS). In an external magnetic field, the magnetic domains in the ferromagnetic material move discontinuously or approximately jump at the pinning points, causing a large number of micro-perturbations during the magnetization process of the material, that is, the Barkhausen noise. There is a correlation between the MBNS characteristics and the stress. By establishing a standard calibration curve between the MBNS and the stress, the stress of the sample to be measured can be evaluated. The magnetic Barkhausen detection technology is sensitive to surface stress and has a fast detection speed, but the MBNS is affected by the surface microstructure, and it is difficult to perform quantitative detection.

[0004] The magnetic memory testing technology (MMT) is a new technology for detecting residual stress using the magnetic memory characteristics of materials proposed by Russian scholar Dubov in the 1990s. MMT uses the geomagnetic field as the external magnetic field without applying excitation, and has the characteristics of fast detection speed, convenience, support for on-line detection, non-contact, small equipment volume, etc. However, the detection signal of MMT is weak, the anti-interference ability is poor, it is easily affected by the external magnetic field, the repeatability of the detection results is poor, and the requirements for the detection environment are relatively high.

[0005] The development history of the magnetic method for stress measurement can be traced back to the last century. Early research mainly focused on the magnetic change law of ferromagnetic materials under stress. With the deepening of the understanding of the magnetostrictive effect, researchers began to explore the connection between magnetic changes and stress states, and gradually developed the magnetic method for stress measurement technology. The magnetic method has the characteristics of non-destructiveness, high efficiency and accuracy, small temperature influence, good repeatability and high sensitivity.

[0006] Before various measurement methods are used, zero-stress specimens made of the same material and with the same texture as the measured specimens need to be prepared to ensure the accuracy of the measurement data. The preparation of zero-stress specimens places high requirements on aspects such as the machining, heat treatment, surface quality, and preparation process of the material, and the manufacturing error has an impact on the entire measurement result. The four-pole magnetic method also requires zero-stress calibration specimens due to the influence of probe manufacturing errors, which restricts the application of this method. Summary of the Invention

[0007] In view of the technical problem of the need to prepare zero-stress specimens in the existing methods proposed above, a zero-stress calibration method for stress magnetic measurement is provided.

[0008] The technical means adopted in the present invention are as follows:

[0009] A zero-stress calibration method for stress magnetic measurement includes the following steps:

[0010] Obtain the voltage value in the vertical direction of the measurement point of the specimen;

[0011] Obtain the zero-stress calibration value according to the voltage value in the vertical direction of the measurement point;

[0012] Obtain the voltage value generated only under the influence of stress according to the zero-stress calibration value;

[0013] Obtain the stress difference and the principal stress direction angle according to the voltage value generated only under the influence of stress.

[0014] Further, obtaining the voltage value in the vertical direction of the measurement point of the specimen includes:

[0015] Use a four-pole magnetic measurement instrument to measure, and set the excitation frequency and excitation current of the four-pole magnetic measurement instrument to be the same as the stress measurement state. Place the probe of the four-pole magnetic measurement instrument in any direction of the measurement area of the specimen to measure, and obtain the output voltage value U 测0 ; then rotate the probe by 90° to measure, and obtain the output voltage value U 测90 .

[0016] Further, obtaining the zero-stress calibration value according to the voltage value in the vertical direction of the measurement point includes: calculating according to the zero-stress determination principle, and taking the average of the output voltage value U 测0 and the output voltage value U 测90 to obtain the zero-stress calibration value U'.

[0017] Further, the zero-stress calibration value U' satisfies the following formula:

[0018]

[0019] Where: U′ is the zero-stress calibration value / μV; U0 is the output voltage value measured in any direction of the measurement area of the specimen by the probe / μV; U 90 is the output voltage value measured when the probe rotates 90° / μV.

[0020] Furthermore, according to the zero-stress calibration value, the voltage value generated only under the influence of stress includes:

[0021] Denote the measurement direction as the 0° direction, and subtract the zero-stress calibration value U′ of this measurement point from the original measurement voltage value U0 in the 0° direction measured within the measurement range, to obtain the voltage value U affected by stress in the 0° direction within this measurement range. 测 Subtract the zero-stress calibration value U′ of this measurement point from the original measurement voltage value U0 in the 0° direction measured within the measurement range, to obtain the voltage value U affected by stress in the 0° direction within this measurement range.

[0022] Furthermore, the voltage value U generated only under the influence of stress satisfies the following formula:

[0023]

[0024] Where: U is the voltage value affected by stress in the 0° direction within the measurement range / μV; U0 测 is the original measurement voltage value in the 0° direction measured within the measurement range / μV; U 测0 is the output voltage value measured in any direction of the measurement area of the specimen by the probe / μV; U 测90 is the output voltage value measured when the probe rotates 90° / μV.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The zero-stress calibration method of the stress magnetic measurement method provided by the present invention does not require the production of zero-stress specimens, reducing the measurement difficulty and cost.

[0027] 2. The zero-stress calibration method of the stress magnetic measurement method provided by the present invention does not require the production of zero-stress specimens and zero-stress calibration, improving the measurement efficiency.

[0028] 3. The zero-stress calibration method of the stress magnetic measurement method provided by the present invention can accurately obtain the zero-stress calibration value of any measurement point of the measurement piece, improving the measurement accuracy.

[0029] Based on the above reasons, the present invention can be widely promoted in the fields of non-destructive testing of stress of ferromagnetic materials, etc. Description of the Drawings

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0031] Figure 1 Schematic diagram of the measurement in the 0° direction of the magnetic method four-pole magnetic core vertical probe of the present invention. Detailed implementation manners

[0032] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The following will detail the present invention with reference to the drawings and in combination with the embodiments.

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. The description of at least one exemplary embodiment is actually only illustrative and in no way restricts the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0034] It should be noted that the terms used herein are only for describing the specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless otherwise clearly specified in the context, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of the features, steps, operations, devices, components, and / or their combinations.

[0035] Unless otherwise specifically stated, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationships. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the specification. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0036] Embodiment 1

[0037] The present invention provides a zero-stress calibration method for stress magnetic measurement, which is a zero-stress calibration method for non-destructive stress detection by the four-pole magnetic method based on the unique principle characteristics of the four-pole magnetic method. It has the characteristics of high efficiency, precision for the texture of specific measurement points, and does not require the production of zero-stress specimens, overcoming the problem of the existing method that requires the production of zero-stress specimens, and greatly improving the measurement accuracy and efficiency.

[0038] The four-pole magnetic method for stress detection of ferromagnetic materials has the characteristics of non-destructive, low influence on the surface of the test specimen, high efficiency, and high precision. And various stress detection methods require zero-stress specimens for zero-stress calibration to ensure the accuracy of measurement data. The preparation of zero-stress specimens poses high requirements on aspects such as machining, heat treatment, surface quality, and preparation process of materials, and its manufacturing errors affect the entire measurement result. The present invention proposes a zero-stress calibration method that does not require zero-stress specimens based on the principle characteristics of the four-pole magnetic method, improving the accuracy and efficiency of the four-pole magnetic method measurement, reducing the difficulty and cost of stress measurement, and having broad application prospects in the field of non-destructive stress detection of ferromagnetic materials.

[0039] A zero-stress calibration method for stress magnetic measurement of the present invention is a method for calibrating zero-stress values without relying on zero-stress specimens in a four-pole non-destructive stress detection magnetic method, that is, a method for zero-stress calibration that does not require zero-stress specimens, and includes the following steps:

[0040] Step 1: Obtain the voltage value in the vertical direction of the measurement point of the test piece:

[0041] Use a four-pole magnetic measurement instrument for measurement, and set the excitation frequency and excitation current of the four-pole magnetic measurement instrument to be the same as the state during stress measurement. Place the probe of the four-pole magnetic measurement instrument in any direction within the measurement range of the test piece for measurement, and record the measured output voltage value as U测0 ; then rotate the probe by 90° for measurement, and record the output voltage value obtained from the measurement as U 测90 , that is, the voltage value in the vertical direction of the measurement point.

[0042] Step 2: Obtain the zero-stress calibration value:

[0043] Calculate according to the zero-stress determination principle, take the average of the above two output voltage values to obtain the zero-stress calibration value U' for this measurement range. The calculation formula is shown as follows:

[0044]

[0045] In the formula: U' is the zero-stress calibration value / μV; U 测0 is the output voltage value obtained from the measurement in any direction of the measurement area of the specimen by the probe / μV; U 测90 is the output voltage value obtained from the measurement when the probe is rotated by 90° / μV.

[0046] Step 3: Obtain the voltage value generated only under the influence of stress:

[0047] Subtract the zero-stress calibration value U' of this measurement point from the original measurement voltage value U0 in the 0° direction obtained from the measurement in this measurement range to obtain the voltage value U affected by stress in the 0° direction within this measurement range. The 0° direction is the measurement direction. The calculation formula for the voltage value U generated only under the influence of stress is as follows: 测

[0048]

[0049] In the formula: U is the voltage value generated under the influence of stress in the 0° direction within the measurement range / μV; U0 测 is the original measurement voltage value in the 0° direction obtained from the measurement within the measurement range / μV; U 测0 is the output voltage value obtained from the measurement in any direction of the measurement area of the specimen by the probe / μV; U 测90 is the output voltage value obtained from the measurement when the probe is rotated by 90° / μV.

[0050]

[0051] Step 4: Combine the sensitivity coefficient k obtained from the calibration to solve for the stress difference and the principal stress direction angle, which can be obtained by existing methods. The stress difference is the principal stress difference between the maximum principal stress and the minimum principal stress.

[0051] The stress difference and the principal stress direction angle respectively satisfy the following formulas:

[0052]

[0053] Where: σ1 is the maximum principal stress / Mpa; σ2 is the minimum principal stress / Mpa; U0 is the voltage value affected by stress in the 0° direction obtained by subtracting the zero-stress calibration value from the output voltage value measured when the probe is placed in the measurement area of the specimen / μV; U 45 is the voltage value affected by stress in the 45° direction obtained by subtracting the zero-stress calibration value from the output voltage value measured when the probe rotates 45° / μV; k is the sensitivity coefficient / mA·Mpa -1 ; θ is the principal stress direction angle / degree.

[0054] Principle description of the present invention:

[0055] The voltage value U generated only by the influence of stress obtained during the measurement by the four-pole magnetic method probe is equal to the difference between the measured output voltage value U 测 and the voltage value U′ (zero-stress calibration voltage value) caused by the probe error, that is:

[0056] U = U 测 - U′;

[0057] At a certain excitation frequency and excitation current, the voltage value U0 generated only by the influence of stress in a certain direction measured by the four-pole magnetic method probe at a certain point is proportional to the normal stress difference between this measurement direction and its perpendicular measurement direction at this measurement point. Let the measurement direction be the 0° direction and the perpendicular measurement direction be the 90° direction, that is:

[0058] U0 = k(σ0 - σ 90 );

[0059] Then,

[0060]

[0061] Where: U′ is the zero-stress calibration value / μV; U 测0 is the output voltage value measured in any direction within the measurement range / μV; U 测90 is the output voltage value measured in the direction rotated 90° within the measurement range / μV; k is the sensitivity coefficient obtained by calibration through a tensile test / mA·Mpa -1 ; σ0 is the normal stress in the 0° direction / Mpa; σ 90 is the normal stress in the 90° direction / Mpa.

[0062] Then, the sum of the voltage values measured in the 0° direction and the 90° direction is:

[0063] U 和 = U 测0 + U 测90 = 2U′;

[0064] Then,

[0065]

[0066] From the above reasoning, it can be known that the zero-stress calibration voltage value U′ can be obtained by taking the average of the measured voltage values in two perpendicular directions within the measurement point.

[0067] The conventional calibration method is to use the zero-stress voltage value corresponding to the zero-stress specimen with the same texture as the measured specimen as the zero-stress calibration value for the entire plate to be measured. However, the texture of different points on the same plate to be measured is slightly different, so the zero-stress calibration values at different measurement points are slightly different. The method of the present invention can give targeted zero-stress calibration values for different points, so as to finally obtain a more accurate zero-stress calibration voltage value at the measurement point that is not affected by texture but only by stress. The zero-stress calibration value of the measurement point can be obtained by taking the average of the measured voltage values in any two perpendicular directions at the measurement point. Moreover, both theory and experiments show that the sum of the measured voltage values in any two perpendicular directions at the same point is the same.

[0068] Example 2

[0069] The conditions of this example are set as follows: The measured specimen is a 45# steel flat plate with dimensions of 360mm×360mm×10mm, and the measuring probe is a magnetic four-pole magnetic core vertical probe.

[0070] The specific implementation steps are as follows:

[0071] (1) Obtain the voltage value in the vertical direction of the measurement point:

[0072] Set the excitation frequency and excitation current of the four-pole magnetic measurement instrument to be the same as those in the stress measurement state. Place the probe in any direction in the measurement area of the 45# steel flat plate for measurement, and record the measured output voltage value as U0; then rotate the probe by 90° for measurement, and record the measured output voltage value as U 90 .

[0073] (2) Obtain the zero-stress calibration value:

[0074] Calculate according to the zero-stress determination principle. Take the average of the above two output voltage values to obtain the zero-stress calibration value U′ of the measurement range. The calculation formula is shown as follows:

[0075]

[0076] (3) Obtain the voltage value generated only under the influence of stress:

[0077] Subtract the zero-stress calibration value U′ of the measurement point from the original measured voltage value U0 in the 0° direction obtained within the measurement range 测 to obtain the voltage value U affected by stress in the 0° direction within the measurement range:

[0078]

[0079] (4) Solve for the stress difference and the principal stress direction angle by using the sensitivity coefficient k obtained from the calibration as follows:

[0080]

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A zero stress calibration method for stress magnetic measurement, characterized in that: The steps include: Obtain the voltage value in the vertical direction of the test piece’s measuring point; According to the voltage value in the vertical direction of the measuring point, the zero stress calibration value is obtained; According to the zero stress calibration value, the voltage value only affected by stress is obtained; According to the voltage value generated only by the stress, the stress difference and the principal stress direction angle are obtained.

2. The zero stress calibration method of stress magnetic measurement according to claim 1, characterized in that: Obtaining the vertical voltage value of the test piece measurement point includes: A quadrupole magnetic measuring instrument is used for measurement, and the excitation frequency and excitation current of the quadrupole magnetic measuring instrument are set to be the same as the stress measurement state. The probe of the quadrupole magnetic measuring instrument is placed in any direction of the test piece measurement area for measurement, and the output voltage value U is measured. 测0 Then rotate the probe 90° to measure the output voltage U 测90 .

3. The zero stress calibration method of stress magnetic measurement according to claim 2, characterized in that: According to the voltage value in the vertical direction of the measuring point, the zero stress calibration value is obtained, including: calculating according to the zero stress determination principle, and converting the output voltage value U 测0 And the output voltage value U 测90 Take the average and obtain the zero stress calibration value U′.

4. The zero stress calibration method of stress magnetic measurement according to claim 3, characterized in that: The zero stress calibration value U′ satisfies the following formula: Where: U′ is the zero stress calibration value / μV; U 测0 The output voltage value measured by placing the probe in any direction of the test piece measurement area / μV; U 测90 This is the output voltage value / μV measured when the probe is rotated 90°.

5. The zero stress calibration method of stress magnetic measurement according to claim 1, characterized in that: According to the zero stress calibration value, the voltage value affected only by stress is obtained, including: The measurement direction is recorded as 0° direction, and the original measured voltage value of 0° direction measured within the measurement range is Subtract the zero stress calibration value U′ of the measuring point to obtain the voltage value U affected by stress in the 0° direction within the measuring range.

6. The zero stress calibration method of stress magnetic measurement according to claim 5, characterized in that: The voltage value U generated only by stress satisfies the following formula: Where: U is the voltage value generated by stress in the 0° direction within the measurement range / μV; U is the original measured voltage value in the 0° direction measured within the measurement range / μV; 测0 The output voltage value measured by placing the probe in any direction of the test piece measurement area / μV; U 测90 This is the output voltage value / μV measured when the probe is rotated 90°.

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