Magnetic measurement method for plane vector stress

Abstract

The invention provides a magnetic measurement method for plane vector stress, and relates to the technical field of iron-based material stress testing. The method comprises the following steps: acquiring a principal stress difference between the maximum principal stress and the minimum principal stress of an iron-based test piece; obtaining the principal stress sum of the maximum principal stress and the minimum principal stress of the iron-based test piece; and combining the principal stress difference with the principal stress sum to obtain the maximum principal stress and the minimum principal stress. According to the method, the accurate numerical values of the maximum principal stress and the minimum principal stress and the principal stress direction can be directly obtained, subsequent calculation errors and accumulative errors are avoided, and the problem that only the principal stress direction angle and the principal stress difference can be determined through an existing calculation method can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of stress testing of iron-based materials, and more particularly, to a magnetic measurement method for planar vector stress. Background Art

[0002] In order to minimize the energy during the spontaneous magnetization equilibrium distribution process, magnetic domains are generated in iron-based materials. A magnetic domain is defined as a small region in an iron-based material, in which the spontaneous magnetization orientation of each atom is the same. Under the action of a magnetic field, the magnetization difficulty of magnetic domains with different orientations is different, which is called the magnetocrystalline anisotropy. When an iron-based material is under the action of an external magnetic field, the process of changing from a magnetically neutral state to a magnetic saturation state where all magnetic moments are in the direction of the external magnetic field is called the magnetization process of the material. Applying stress to the iron matrix causes deformation, and through the magnetoelastic effect, the magnetic moments are preferentially oriented, which will cause stress anisotropy. Similar to magnetic anisotropy, stress anisotropy also hinders magnetization. For iron-based materials with a magnetostrictive coefficient greater than zero, the magnetic permeability in the tensile stress direction increases, and the magnetic permeability in the compressive stress direction decreases. This leads to the generation of magnetic anisotropy. The magnitude of the magnetic permeability changes with the magnitude of the stress, and the principal magnetic permeability is consistent with the principal stress direction. The magnetic permeability μ changes with the angle θ due to the stress anisotropy. Therefore, the magnitude and direction of the principal stress can be obtained by measuring the changes in the magnetic permeability values in different directions at a certain point of the material.

[0003] The magnetic measurement method of stress for a two-pole probe stress detector utilizes the mutual relationship among the circuit, magnetic field, and stress. The influence of stress on the magnetic field is expressed by circuit parameters. Stress changes the total magnetic resistance in the magnetic circuit, the magnetic flux of the entire magnetic circuit changes, and the voltage across the coil ends changes. By detecting the current at both ends of the measuring resistor in the bridge, the stress change value can be deduced inversely. Wang Zhenshan et al. from Xi'an Jiaotong University studied the relationship between the output of a two-pole magnetic measurement sensor and the principal stress and the measurement angle, and proposed the difference I 2 -I 1 between the magnetic measurement signal currents in two directions and the principal stress difference (σ 1 -σ 2 ) approximately has a single-valued linear relationship; Li Siyuan deduced the relationship expressions between the sum of the principal stresses, the principal stress difference, and the output in the principal stress direction, and established a calculation formula for the residual stress. R. Langman improved a new type of sensor by using a two-pole excitation source and placing two orthogonal induction coils on the surface of the material to be measured between the two poles. When the material is in a stressed state, due to magnetic anisotropy, under the action of an externally applied excitation magnetic field, the direction of the magnetization intensity of the material deflects, and the output signals of the two induction coils change. The principal stress difference can be evaluated by the ratio of these two output signals.

[0004] Existing calculation methods can only solve the principal stress difference and the principal stress direction angle. If one wants to obtain the absolute values of the maximum principal stress and the minimum principal stress, more complex derivation formulas need to be used, which brings non-negligible cumulative errors and relatively large errors in the obtained stress values. Summary of the Invention

[0005] In view of the technical problem that the existing calculation methods can only determine the principal stress direction angle and the principal stress difference, a magnetic measurement method for planar vector stress is provided.

[0006] The technical means adopted by the present invention are as follows:

[0007] A magnetic measurement method for planar vector stress includes the following steps:

[0008] Obtain the principal stress difference between the maximum principal stress and the minimum principal stress of the iron-based specimen;

[0009] Obtain the principal stress sum between the maximum principal stress and the minimum principal stress of the iron-based specimen;

[0010] Combine the principal stress difference and the principal stress sum to obtain the maximum principal stress and the minimum principal stress.

[0011] Further, obtaining the principal stress difference between the maximum principal stress and the minimum principal stress of the iron-based specimen includes:

[0012] Obtain the principal stress direction angle of the iron-based specimen;

[0013] Obtain the non-equilibrium current value of the 0° bridge circuit and the non-equilibrium current value of the 90° bridge circuit;

[0014] According to the principal stress direction angle, the non-equilibrium current value of the 0° bridge circuit, and the non-equilibrium current value of the 90° bridge circuit, obtain the difference between the current output values in the directions of the maximum principal stress and the minimum principal stress;

[0015] According to the difference between the current output values in the directions of the maximum principal stress and the minimum principal stress, obtain the principal stress difference between the maximum principal stress and the minimum principal stress.

[0016] Further, the principal stress difference between the maximum principal stress and the minimum principal stress satisfies the following formula:

[0017]

[0018] Wherein,

[0019] (I 2 -I 1 )=K 1 (σ 1 -σ 2 );

[0020]

[0021] In the formula: σ 1 is the maximum principal stress / Mpa; σ 2 is the minimum principal stress / Mpa; I 1 is the current output value in the direction of the maximum principal stress / mA; I 2 is the current output value in the direction of the minimum principal stress / mA; K 1 is the sensitivity coefficient / mA·Mpa -1 ; I 0° is the unbalanced current value of the 0° bridge circuit / mA; I 90° is the unbalanced current value of the 90° bridge circuit / mA; θ is the angle between the direction of the maximum principal stress and the X-axis / degree.

[0022] Furthermore, when the direction of the principal stress is unknown, the principal stress direction angle satisfies the following formula:

[0023]

[0024] In the formula: θ is the angle between the direction of the maximum principal stress and the X-axis / degree; I 0° 、I 45° 、I 90° are the unbalanced current values of the bridge circuits in the three directions of 0°, 45°, and 90° respectively / mA.

[0025] Furthermore, the sensitivity coefficient K 1 is determined by a unidirectional tensile calibration test and satisfies the following formula:

[0026]

[0027] In the formula: K 1i is the stress difference sensitivity coefficient; n is the number of loading times.

[0028] Furthermore, obtaining the sum of the principal stresses of the maximum principal stress and the minimum principal stress of the iron-based specimen includes:

[0029] Obtain the unbalanced current value of the 0° bridge circuit and the unbalanced current value of the 90° bridge circuit, and obtain the sum of the currents of the unbalanced current value of the 0° bridge circuit and the unbalanced current value of the 90° bridge circuit;

[0030] According to the sum of the currents of the unbalanced current value of the 0° bridge circuit and the unbalanced current value of the 90° bridge circuit, obtain the sum of the principal stresses of the maximum principal stress and the minimum principal stress.

[0031] Furthermore, the sum of the principal stresses satisfies the following formula:

[0032]

[0033] In the formula: σ 1 is the maximum principal stress / Mpa; σ 2is the minimum principal stress / Mpa; K 2 is the sensitivity coefficient / mA·Mpa -1 ;I 0° ,I 90° They are the unbalanced current values / mA of the bridge circuit in the 0° and 90° directions respectively.

[0034] Furthermore, the sensitivity coefficient K 2 Determined by uniaxial tensile calibration test, it satisfies the following formula:

[0035]

[0036] Where: K 2i are stress and sensitivity coefficient; n is the number of loading times.

[0037] Furthermore, the maximum principal stress and the minimum principal stress satisfy the following formula:

[0038]

[0039] Where: 1 is the maximum principal stress / Mpa; σ 2 is the minimum principal stress / Mpa; K 1 is the sensitivity coefficient / mA·Mpa -1 ; K 2 is the sensitivity coefficient / mA·Mpa -1 ;I 0° is the 0° bridge unbalanced current value / mA; I 90° is the unbalanced current value of the 90° bridge circuit / mA; θ is the angle between the maximum principal stress direction and the X-axis / degree.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] The present invention provides a magnetic measurement method for plane vector stress, and proposes an improved method for a stress algorithm of a secondary stress meter based on a magnetic anisotropy method for measuring stress. The improved method is combined with the original calculation method, so that the accurate values ​​of the maximum principal stress, the minimum principal stress and the principal stress direction can be directly obtained without going through tedious and lengthy subsequent calculation steps, thereby avoiding subsequent calculation errors and cumulative errors, and solving the problem that the existing calculation method can only determine the principal stress direction angle and the principal stress difference.

[0042] Based on the above reasons, the present invention can be widely promoted in fields such as stress testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] 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 also be obtained based on these drawings.

[0044] Figure 1 This is a sensor device diagram of the secondary measuring instrument for measuring stress based on the magnetic anisotropy method of the present invention.

[0045] Figure 2 This is the calibration curve of the sensor (probe) of the two-pole stress measuring instrument of the present invention. Detailed implementation manners

[0046] 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 describe the present invention in detail with reference to the drawings and in combination with the embodiments.

[0047] 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 the embodiments. The description of at least one exemplary embodiment below is actually only illustrative and in no way restrictive of 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.

[0048] It should be noted that the terms used here are only for describing the specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used here, unless the context clearly indicates otherwise, 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 features, steps, operations, devices, components and / or their combinations.

[0049] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps set forth in these embodiments do not limit the scope of the present invention. Meanwhile, it should be clear that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0050] Example 1

[0051] The original calculation method can only solve the principal stress difference and the principal stress direction angle. If you want to obtain the absolute value of the maximum principal stress and the minimum principal stress, you need to use other more complex derivation formulas, and it will bring about a non-negligible cumulative error, and the error of the obtained stress value is large. The present invention provides a magnetic measurement method for plane vector stress, which is a new relationship between the principal stress and the current. It can be further combined with the original calculation method in this field to solve the plane vector stress. The new algorithm does not require complex subsequent calculations and additional stress measurement steps, and has the advantages of being simple and accurate. The present invention can quickly solve the maximum principal stress, the minimum principal stress and the principal stress direction angle, and is particularly suitable for measuring stress secondary sensor probes based on the magnetic anisotropy method. The measurement data obtained can be directly brought into the calculation, which is suitable for rapid evaluation and calculation of stress distribution.

[0052] The magnetic measurement method of a plane vector stress of the present invention proposes a new calculation method, which makes it possible to solve the situation where only the stress difference and the direction of the principal stress can be obtained by using the original calculation method, and then the accurate values ​​of the maximum principal stress, the minimum principal stress and the principal stress direction angle can be obtained by combining the new calculation method with the original calculation method.

[0053] There is an established theoretical connection between the calculation method of the present invention and the original calculation method. That is, in the original calculation method, the principal stress difference and the current difference in two directions approximately have a single-valued linear relationship; in the newly proposed calculation method, the principal stress sum and the current sum in two directions also approximately have a single-valued linear relationship.

[0054] The coefficient K in the single-valued linear relationship in the original calculation method and the single-valued linear relationship in the new calculation method proposed in the present invention 1 , K 2 Both can be calibrated through the same calibration test.

[0055] Coefficient K 1 , K 2 After simultaneous tensile calibration, when stress measurement is carried out, it can still be carried out according to the original measurement steps without adding new measurement steps. When measuring the stress data after calibration, similar to the original calculation method, the original calculation method and the newly proposed calculation method can be combined and simplified. Then, only by substituting the data into the simplified formula, the accurate values of the maximum principal stress, the minimum principal stress, and the principal stress direction angle can be solved.

[0056] I. Analysis and induction of the original calculation method

[0057] As shown in the appendix Figure 1 is the sensor device diagram of the stress secondary measuring instrument based on the magnetic anisotropy method. A closed loop is composed of magnetic core I, coil II, and iron-based specimen III. The exciting current generates an alternating magnetic field after passing through the exciting coil, and the magnetic field is emitted into the iron-based specimen for stress detection of the specimen. Then, the feedback magnetic signal will be recovered by the detection coil and converted into a detection current through the electromagnetic induction phenomenon. According to the relationship between stress, magnetic signal, and electrical signal, the internal stress distribution of the specimen is deduced, so as to achieve the purpose of stress detection of the iron-based specimen. For the measurement of surface stress by a two-probe device, a large number of theoretical analyses and experimental studies have proved that there is approximately a single-valued linear relationship between the principal stress difference and the current difference in two directions, and its expression is:

[0058] (I 2 -I 1 ) = K 1 (σ 1 -σ 2 ) (1)

[0059] In the formula: I 1 is the current output value in the direction of the maximum principal stress / mA; I 2 is the current output value in the direction of the minimum principal stress / mA; K 1 is the sensitivity coefficient / mA·Mpa -1 ; σ 1 is the maximum principal stress / Mpa; σ 2 is the minimum principal stress / Mpa.

[0060] When the principal stress direction is unknown, the following formula can be used to determine the principal stress direction angle:

[0061]

[0062] In the formula: θ is the angle between the direction of the maximum principal stress and the X-axis / degree; I 0° , I 45° , I 90° are the unbalanced bridge current values in the three directions of 0°, 45°, and 90° respectively / mA.

[0063] Current output value I in the direction of maximum principal stress 1 , the current output value I in the direction of minimum principal stress 2 The unbalanced current value I 0° 、90° bridge unbalanced current value I 90° The following relationship exists:

[0064]

[0065] Therefore, by combining formula (1) and formula (3), we can get:

[0066]

[0067] The original calculation method ends here. It can be seen that the original calculation formula only obtains the stress difference value, which cannot intuitively reflect the maximum principal stress value and the minimum principal stress value. If you want to continue to solve, you need to use the shear stress difference method. The shear stress difference method formula is cumbersome and has a cumulative error that cannot be ignored, which undoubtedly affects the calculation accuracy and difficulty.

[0068] 2. Proposal of a new calculation method

[0069] The existing calculation method cannot directly obtain the magnitude of the maximum principal stress and the lowest principal stress of the plane, but can only obtain the difference between the principal stresses and the direction of the principal stresses. On this basis, the present invention explores the relationship formula between the sum of principal stresses and the sum of currents, and then combines it with the original calculation method to complete the transformation from formula to formula, and then obtain the values ​​of the maximum principal stress and the minimum principal stress.

[0070] According to the stress Mohr circle, at the same point in a plane, the sum of the normal stresses in any two mutually perpendicular directions is equal. That is:

[0071] σ 1 +σ 2 =σ 0° +σ 90° (5)

[0072] After single-point stress measurement, it can be obtained that the test result data of the relationship between the principal stress and the current and approximately satisfies the following relationship:

[0073] I 90° +I 0° =K 2 (σ 1 +σ 2 ) (6)

[0074] Where: K 2 is the sensitivity coefficient / mA·Mpa -1 ;I 0° ,I 90°The unbalanced current value of the bridge circuit in the two directions of 0° and 90° / mA; σ 1 is the maximum principal stress / Mpa; σ 2 is the minimum principal stress / Mpa.

[0075] The sensitivity coefficient K 2 Through the same K 1 Calibration is performed in the same way as the tensile calibration experiment.

[0076] ① Transform formula (6) to obtain:

[0077]

[0078] ② Combining formula (4) with formula (7), we can get:

[0079]

[0080] ③Simplify the above formula to get:

[0081]

[0082] When the principal stress direction is unknown, formula (2) can still be used to determine the principal stress direction angle:

[0083]

[0084] At this point, the new calculation method of this invention has been obtained through the induction and summary of step one and the simplification of step two. Using this calculation method, the final result can be directly obtained from the test data without the need for subsequent calculations, thus avoiding cumulative errors.

[0085] The newly proposed calculation method can solve the defect that the original calculation method cannot directly obtain the magnitude of the maximum principal stress and the lowest principal stress of the plane. By combining the newly proposed calculation method with the original calculation method, the specific values ​​of the maximum principal stress and the lowest principal stress of the plane can be obtained.

[0086] 3. Sensitivity coefficient K 1 and K 2 Calibration

[0087] Sensitivity coefficient K 1 , K 2 Determined by uniaxial tension and compression test. Because the sensitivity coefficients of the calculation method proposed by the present invention and the original calculation method both use the axial and vertical axial data during the uniaxial tensile test, they can be calibrated at the same time, which is also one of the advantages of the present invention. There is no need to add the step of tensile calibration, and the tensile calibration test can be carried out simultaneously.

[0088] Define the stress difference as ΔI 1 =I 90° -I0° ; The sum of stresses is ΔI 2 = I 90° + I 0° . When performing unidirectional loading, the loading stress σ and ΔI 1 and ΔI 2 should show a linear relationship, which appears as two approximate straight lines passing through the origin in the coordinate system. These two lines are called calibration curves, and the slopes of the two lines are the sensitivity coefficients K 1 、K 2 . When the loading stress is different, the relationship between stress and ΔI 1 and ΔI 2 is:

[0089]

[0090] In the formula: K 1i is the stress difference sensitivity coefficient, K 2i is the stress sum sensitivity coefficient, σ i is the axial normal stress. Thus, the expressions of the sensitivity coefficients K 1 and K 2 are determined.

[0091]

[0092] In the formula: n is the number of loading times.

[0093] Example 2

[0094] I. Summarize the relationship between the sum of principal stresses and the sum of currents

[0095] As can be seen from Example 1, at the same point in the plane, the sum of the normal stresses in any two mutually perpendicular directions is equal. That is:

[0096] σ 1 + σ 2 = σ 0° + σ 90° (5)

[0097] According to the relationship mentioned in formula (5), it can be known that the σ 1 + σ 2 in the unknown direction is equal to the σ 0° + σ 90° in the known direction. Therefore, I 0° + I 90° can be used for subsequent calculations to facilitate the confirmation of the measurement angle.

[0098] Therefore, a square steel plate with a size of 360mm × 360mm and a thickness of 10mm is used, and the material of the steel plate is quenched 45 steel. The current values in the 0°, 45°, 90°, and 135° directions at a single point on the quenched steel plate are measured.

[0099] From the measured data, the experimental result data of the relationship between the principal stress and the current can be fitted, and approximately satisfy the following relationship:

[0100] I 90° +I 0° =K 2 (σ 1 +σ 2 ) (6)

[0101] Where: K 2 is the sensitivity coefficient / mA·Mpa -1 ; I 0° 、I 90° are the unbalanced bridge current values in the two directions of 0° and 90° respectively / mA; σ 1 is the maximum principal stress / Mpa; σ 2 is the minimum principal stress / Mpa.

[0102] The sensitivity coefficient K in the formula 2 can be calibrated by the same tensile calibration experiment as K 1 .

[0103] II. Proposal of a new calculation method

[0104] The specific process is as follows:

[0105] ① Deform formula (6) to obtain:

[0106]

[0107] ② Combine formula (4) and formula (7) to obtain:

[0108]

[0109] ③ Simplify the above formula to obtain:

[0110]

[0111] When the principal stress direction is unknown, formula (2) can still be used to determine the principal stress direction angle:

[0112]

[0113] So far, the new calculation method of this invention has been obtained through the induction and summary in step one and the simultaneous simplification in step two. Using this calculation method, the final result can be directly obtained from the test data without further subsequent calculations, avoiding cumulative errors.

[0114] III. Calibrating the sensitivity coefficients K 1 、K 2

[0115] Define the stress difference as ΔI 1 = I 90° - I 0° ; The stress sum is ΔI 2 = I 90° + I 0° . When performing unidirectional loading, the loading stress σ and ΔI 1 and ΔI 2 should show a linear relationship, which appears as two approximate straight lines passing through the origin in the coordinate system. These two straight lines are called calibration curves, and the slopes of the two straight lines are the sensitivity coefficients K 1 、K 2 . When the loading stress is different, the relationship between the stress and ΔI 1 and ΔI 2 is:

[0116]

[0117] In the formula, K 1i is the stress difference sensitivity coefficient, K 2i is the stress sum sensitivity coefficient, and σ i is the axial normal stress. Thus, the expressions of the sensitivity coefficients K 1 and K 2 are determined.

[0118]

[0119] In the formula: n is the number of loading times.

[0120] For the uniaxial tensile calibration test, a microcomputer-controlled hydraulic universal tensile testing machine is used to conduct a tensile calibration test on the tensile specimen. The measuring instrument is a two-pole probe stress magnetic measuring instrument, and the material of the tensile specimen is 45# steel annealed. The sensitivity coefficients K 1 、K 2 are 0.00105 mA / Mpa and 0.00276 mA / Mpa respectively through the experiment calibration.

[0121] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; 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 recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A magnetic measurement method for plane vector stress, characterized in that: The steps include: Obtain the principal stress difference between the maximum principal stress and the minimum principal stress of the iron-based specimen; Obtain the principal stress sum of the maximum principal stress and the minimum principal stress of the iron-based specimen; Combining the principal stress difference with the principal stress sum gives the maximum and minimum principal stresses.

2. The magnetic measurement method of plane vector stress according to claim 1, characterized in that: The principal stress difference between the maximum principal stress and the minimum principal stress of the iron-based specimen is obtained by: Obtain the principal stress direction angle of the iron-based specimen; Obtain the 0° bridge unbalanced current value and the 90° bridge unbalanced current value; According to the principal stress direction angle, the 0° bridge unbalanced current value and the 90° bridge unbalanced current value, the difference between the maximum principal stress direction current output value and the minimum principal stress direction current output value is obtained; The principal stress difference between the maximum principal stress and the minimum principal stress is obtained according to the difference between the current output value in the direction of the maximum principal stress and the current output value in the direction of the minimum principal stress.

3. The magnetic measurement method of plane vector stress according to claim 2, characterized in that: The principal stress difference between the maximum principal stress and the minimum principal stress satisfies the following formula: in, (I2-I1)=K1(σ1-σ2); Where: σ1 is the maximum principal stress / Mpa; σ2 is the minimum principal stress / Mpa; I1 is the current output value in the direction of the maximum principal stress / mA; I2 is the current output value in the direction of the minimum principal stress / mA; K1 is the sensitivity coefficient / mA·Mpa -1 ;I 0° is the 0° bridge unbalanced current value / mA; I 90° is the unbalanced current value of the 90° bridge circuit / mA; θ is the angle between the maximum principal stress direction and the X-axis / degree.

4. The magnetic measurement method of plane vector stress according to claim 2 or 3, characterized in that: When the principal stress direction is unknown, the principal stress direction angle satisfies the following formula: Where: θ is the angle between the maximum principal stress direction and the X-axis (degrees); I 0° ,I 45° ,I 90° They are the unbalanced current values / mA of the bridge circuit in the three directions of 0°, 45° and 90° respectively.

5. The magnetic measurement method of plane vector stress according to claim 3, characterized in that: The sensitivity coefficient K1 is determined by the uniaxial tensile calibration test and satisfies the following formula: Where: K 1i is the stress difference sensitivity coefficient; n is the number of loading times.

6. The magnetic measurement method of plane vector stress according to claim 1, characterized in that: The principal stress sum of the maximum principal stress and the minimum principal stress of the iron-based specimen includes: Obtaining a 0° bridge unbalanced current value and a 90° bridge unbalanced current value, and obtaining a current sum of the 0° bridge unbalanced current value and the 90° bridge unbalanced current value; According to the current sum of the 0° bridge unbalanced current value and the 90° bridge unbalanced current value, the principal stress sum of the maximum principal stress and the minimum principal stress is obtained.

7. The magnetic measurement method of plane vector stress according to claim 6, characterized in that: The principal stresses and satisfy the following formula: Where: σ1 is the maximum principal stress / Mpa; σ2 is the minimum principal stress / Mpa; K2 is the sensitivity coefficient / mA·Mpa -1 ; I 0° ,I 90° They are the unbalanced current values / mA of the bridge circuit in the 0° and 90° directions respectively.

8. The magnetic measurement method of plane vector stress according to claim 7, characterized in that: The sensitivity coefficient K2 is determined by the uniaxial tensile calibration test and satisfies the following formula: Where: K 2i are stress and sensitivity coefficient; n is the number of loading times.

9. The magnetic measurement method of plane vector stress according to claim 1, characterized in that: The maximum principal stress and the minimum principal stress satisfy the following formula: Where: σ1 is the maximum principal stress / Mpa; σ2 is the minimum principal stress / Mpa; K1 is the sensitivity coefficient / mA·Mpa -1 ; K2 is the sensitivity coefficient / mA·Mpa -1 ; I 0° is the 0° bridge unbalanced current value / mA; I 90° is the unbalanced current value of the 90° bridge circuit / mA; θ is the angle between the maximum principal stress direction and the X-axis / degree.

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