Residual stress measuring method

Abstract

The invention provides a residual stress measurement method, which comprises the following steps of: obtaining a stress calibration elastic interval of a test block through elastic limit stretching operation; acquiring the reference resistivity of the zero-stress test block; obtaining a relation curve between the tensile stress value and the resistivity of the test block; performing multi-frequency current access and voltage detection on the test block to obtain the resistivity of the test block on different thicknesses; and obtaining the residual stress values of the test block on different thicknesses based on the resistivity of the test block on different thicknesses, the relation curve between the tensile stress value and the resistivity of the test block and the reference resistivity. According to the method, the residual stress distribution data of the equipment part such as an aero-engine part in each machining part manufacturing stage, test stage and operation stage can be quickly and nondestructively acquired, in addition, the cost for detecting the residual stress of the part can be greatly reduced, and the detection efficiency of the residual stress of the part can be improved. And the manufacturing and processing technology of aero-engine parts can be optimized.

Description

Technical Field

[0001] The invention mainly relates to the field of material performance analysis, and in particular to a residual stress measurement method. Background Art

[0002] Residual stress has an important impact on the service life of equipment components, such as key components of aircraft engines. More and more studies have shown that if the existence of residual stress is not taken into account, the remaining service life of aircraft engine components cannot be reliably and accurately predicted.

[0003] The SN curves (stress-life curves) of most materials become quite flat at high cycle numbers, so residual stress levels equivalent to about 10%-20% of the yield strength superimposed on the applied principal stress will significantly affect their remaining service life. However, both the absolute level and spatial distribution of residual stress have large uncertainties, one of the reasons being that residual stress is easily affected by changes in manufacturing processes. In addition, residual stresses tend to evolve continuously due to thermomechanical relaxation when the components are in working condition. Therefore, reliable periodic measurements are required to establish the actual level and spatial distribution of residual stress, which requires reliable and economical nondestructive testing methods. Therefore, providing a nondestructive characterization method for residual stress gradients that is both economical and reliable is of great significance for the life assessment of aircraft engines. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a residual stress measurement method to achieve non-destructive, efficient and convenient measurement operation of the residual stress of equipment components.

[0005] In order to solve the above technical problems, the present invention provides a residual stress measurement method, comprising: obtaining the stress calibration elastic range of the test block through an elastic limit stretching operation; obtaining the reference resistivity of the zero stress test block; obtaining the relationship curve between the tensile stress value and the resistivity of the test block; performing current access and voltage detection at multiple frequencies on the test block to obtain the resistivity of the test block at different thicknesses; based on the resistivity of the test block at the different thicknesses, the relationship curve between the tensile stress value and the resistivity of the test block and the reference resistivity, obtaining the residual stress value of the test block at different thicknesses.

[0006] In one embodiment of the present invention, the zero stress test block is obtained by performing vibration aging treatment on the test block.

[0007] In one embodiment of the present invention, the test block is a flat test block, and obtaining a relationship curve between the tensile stress value and the resistivity of the test block includes: forming four endpoints of a square shape with the detection end of the first probe, the detection end of the second probe, the detection end of the third probe and the detection end of the fourth probe; loading a first excitation current on the same side surface of the flat test block through the detection end of the first probe and the detection end of the second probe; obtaining a corresponding first sensing voltage on the same side surface of the flat test block through the detection end of the third probe and the detection end of the fourth probe; loading a second excitation current on the same side surface of the flat test block through the detection end of the first probe and the detection end of the third probe; obtaining a corresponding second sensing voltage on the same side surface of the flat test block through the detection end of the second probe and the detection end of the fourth probe; obtaining a tensile stress value-resistivity curve of the test block in a first direction according to the first excitation current and the first sensing voltage obtained by multiple measurements; and obtaining a tensile stress value-resistivity curve of the test block in a second direction according to the second excitation current and the second sensing voltage obtained by multiple measurements.

[0008] In one embodiment of the present invention, the length l and the width w of the flat test block and the side length a of the square shape satisfy l≥k*a, w≥k*a; k≥3 and is a rational number.

[0009] In one embodiment of the present invention, according to the measured first excitation current V x and the first sensing voltage I x , the first direction resistivity ρ is obtained based on the following formula x :

[0010]

[0011]

[0012] Wherein, t is the thickness of the flat test block, and a is the side length of the square shape.

[0013] In one embodiment of the present invention, according to the measured second excitation current V y and the second sensing voltage I y , the second direction resistivity ρ is obtained based on the following formula y :

[0014]

[0015]

[0016] Wherein, t is the thickness of the flat test block, and a is the side length of the square shape.

[0017] In one embodiment of the present invention, current connection and voltage detection at multiple frequencies are performed on the test block to obtain the resistivity at different thicknesses, including: at a first current frequency f n Under, according to the input current I n and the detected voltage V n , and the first resistivity ρ is obtained n (f n ); at the second current frequency f n-1 Under, according to the input current I n-1 and the detected voltage V n-1 , and the second resistivity ρ is obtained n-1 (f n-1 );According to the first resistivity ρ n (f n ) and the second resistivity ρ n-1 (f n-1 ), and the skin depth d of the test block is obtained. n The corresponding resistivity ρ(f).

[0018] In one embodiment of the present invention, according to the first resistivity ρ n (f n ) and the second resistivity ρ n-1 (f n-1 ), and the skin depth d of the test block is obtained. n The corresponding resistivity ρ(f) includes:

[0019]

[0020] Among them, T n and T n-1 is related to the first current frequency f n and the second current frequency f n-1 The corresponding eddy current distribution volume in the test piece material.

[0021] In one embodiment of the present invention, based on the resistivity of the test block at different thicknesses, the relationship curve between the tensile stress value and the resistivity of the test block, and the reference resistivity, obtaining the residual stress value of the test block at different thicknesses includes:

[0022]

[0023] Among them, τ n is the residual stress value of the test block at different thicknesses, ρ(f) is the resistivity of the test block at different thicknesses, K c It is the slope corresponding to the relationship curve between the tensile stress value and resistivity of the test block.

[0024] In one embodiment of the present invention, the multiple measurements include stretching the flat test block multiple times in the stress calibration elastic range of the test block, and each stretching is loaded with N levels of stress values ​​step by step, where N≥3 and is a positive integer.

[0025] In one embodiment of the present invention, the signal connection end of the first probe, the signal connection end of the second probe, the signal connection end of the third probe and the signal connection end of the fourth probe are connected to a current generating device or a voltage sensing device.

[0026] In one embodiment of the present invention, the signal connection end of the first probe, the signal connection end of the second probe, the signal connection end of the third probe and the signal connection end of the fourth probe are connected to a current generating device or a voltage sensing device through a multi-way signal selector.

[0027] In one embodiment of the present invention, the current generating device and the voltage sensing device are located in a phase-locked analyzer.

[0028] In one embodiment of the present invention, the multi-way signal selector includes a first multi-way signal selector and a second multi-way signal selector; a low-noise current amplifier is connected between the first multi-way signal selector and the current generating device; and a low-noise voltage amplifier is connected between the second multi-way signal selector and the voltage sensing device.

[0029] In one embodiment of the present invention, the first multiplexer, the second multiplexer, the current generating device and the voltage sensing device are connected to a main control module; the main control module is configured to: run a main control program to issue control instructions to the first multiplexer, the second multiplexer, the current generating device and the voltage sensing device.

[0030] In one embodiment of the present invention, the main control module is further connected to a display module to display the measurement process data and measurement result data of the residual stress value.

[0031] Compared with the prior art, the present invention has the following advantages: The technical solution of the present application can quickly and non-destructively obtain residual stress distribution data of equipment components, such as aircraft engine components, at various manufacturing and processing stages, test stages, and operation stages. The present application solution can greatly reduce the cost of residual stress detection of components and help optimize the manufacturing and processing technology of aircraft engine components. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are provided to provide a further understanding of the present application. They are included in and constitute a part of the present application. The accompanying drawings illustrate embodiments of the present application and together with the description serve to explain the principles of the present application.

[0033] In the attached figure:

[0034] Figure 1 4 is a flow chart of a residual stress measurement method according to an embodiment of the present application.

[0035] Figure 2 It is a process flow chart of obtaining a relationship curve between the tensile stress value and the resistivity of a test block according to an embodiment of the present application.

[0036] Figure 3 Schematic diagram of a flat test block according to an embodiment of the present application.

[0037] Figure 4 It is a schematic diagram of a tensile stress value-resistivity curve of a test block according to an embodiment of the present application.

[0038] Figure 5 This is a process flow chart of obtaining the resistivity of a test block at different thicknesses according to an embodiment of the present application.

[0039] Figure 6 It is a schematic diagram of the residual stress gradient distribution of a test block in a test area according to an embodiment of the present application.

[0040] Figure 7 Schematic diagram of the application environment of the residual stress measurement method according to an embodiment of the present application. DETAILED DESCRIPTION

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0042] As shown in this application and claims, unless the context clearly indicates an exception, the words "a", "an", "an" and / or "the" do not refer to the singular and may also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements.

[0043] 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 application. At the same time, it should be understood 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 field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the authorization 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, so that once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0044] Flowcharts are used in the present application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed accurately in order. On the contrary, various steps may be processed in reverse order or simultaneously. At the same time, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0045] The embodiments of the present application describe a residual stress measurement method.

[0046] Figure 1 FIG. 1 is a flow chart of a residual stress measurement method according to an embodiment of the present application. Figure 1 As shown, the residual stress measurement method includes step 101, obtaining the stress calibration elastic range of the test block through elastic limit stretching operation; step 102, obtaining the reference resistivity of the zero stress test block; step 103, obtaining the relationship curve between the tensile stress value and the resistivity of the test block; step 104, connecting the test block to current (actually alternating current) of multiple frequencies and performing voltage detection to obtain the resistivity of the test block at different thicknesses; step 105, based on the resistivity of the test block at the different thicknesses, the relationship curve between the tensile stress value and the resistivity of the test block and the reference resistivity, obtaining the residual stress value of the test block at different thicknesses.

[0047] In some embodiments, the elastic limit stretching operation is performed on the test block in step 101, for example, by a stretching machine (or a universal testing machine). The zero stress test block in step 102 is obtained by performing vibration aging treatment on the test block.

[0048] In some embodiments, the test block is, for example, a flat test block having corresponding length, width and thickness. In some cases, it is, for example, a rectangular test block, or a shape formed on the basis of a rectangular test block to facilitate stretching operation.

[0049] Figure 2 It is a process flow chart of obtaining a relationship curve between the tensile stress value and the resistivity of a test block according to an embodiment of the present application. Figure 3 Schematic diagram of a flat test block according to an embodiment of the present application.

[0050] refer to Figure 2 and Figure 3 , the step 103 of obtaining the relationship curve between the tensile stress value and the resistivity of the test block includes: step 201, forming four endpoints of a square shape with the detection end of the first probe 311, the detection end of the second probe 312, the detection end of the third probe 313 and the detection end of the fourth probe 314; step 202, loading a first excitation current on the same side surface of the flat test block through the detection end of the first probe 311 and the detection end of the second probe 312; step 203, obtaining a corresponding first sensing voltage on the same side surface of the flat test block through the detection end of the third probe 313 and the detection end of the fourth probe 314; step 204, A second excitation current is loaded on the same side surface of the flat test block through the detection end of the first probe 311 and the detection end of the third probe 313; step 205, a corresponding second sensing voltage is obtained on the same side surface of the flat test block through the detection end of the second probe 312 and the detection end of the fourth probe 314; step 206, a tensile stress value-resistivity curve of the test block in the first direction is obtained according to the first excitation current and the first sensing voltage obtained by multiple measurements; step 207, a tensile stress value-resistivity curve of the test block in the second direction is obtained according to the second excitation current and the second sensing voltage obtained by multiple measurements. In some embodiments, multiple measurements include multiple stretching of the flat test block in the stress calibration elastic range of the test block, and each stretching loads N levels of stress values ​​step by step, N ≥ 3 and is a positive integer. N is, for example, 5, 8 or 10. Multiple measurements are, for example, 3, 5 or 8 times.

[0051] In some embodiments, according to the measured first excitation current V x and the first sensing voltage I x , the first direction resistivity ρ is obtained based on the following formula x :

[0052]

[0053]

[0054] According to the measured second excitation current V y and the second sensing voltage I y , the second direction resistivity ρ is obtained based on the following formula y :

[0055]

[0056]

[0057] Wherein, t is the thickness of the flat test block, and a is the side length of the square shape. The side length a of the square shape is the distance between the detection end of the first probe 311 and the detection end of the second probe 312, or the distance between the detection end of the first probe 311 and the detection end of the third probe 312, or the distance between the detection end of the second probe 312 and the detection end of the fourth probe 314. The first direction x and the second direction y are, for example, Figure 3 The first direction x is, for example, parallel to the length direction of the test block. The second direction y is, for example, parallel to the width direction of the test block.

[0058] The probe arrangement in the present application can improve the sensitivity to the electrical anisotropy of the material when measuring the resistivity of the test block, and facilitate residual stress detection in two orthogonal directions, thereby improving the residual stress detection efficiency.

[0059] Figure 4 Schematic diagram of the tensile stress value-resistivity curve of a test block in one embodiment of the present application. Figure 4 The curve 401 in the figure represents the relationship between the tensile stress value σ and the first direction resistivity ρ x The relationship curve between K x is the first direction slope. Figure 4 The curve 402 in FIG. 4 represents the relationship between the tensile stress value σ and the second direction resistivity ρ y The relationship curve between K y is the second direction slope.

[0060] In some embodiments, reference Figure 3 , the length l and width w of the flat test block 301, and the side length a of the square shape satisfy l≥k*a, w≥k*a; k≥3 and is a rational number. To facilitate the stretching operation, a first stretching portion 302 and a second stretching portion 303 are also formed at both ends of the flat test block. F1 and F2 are, for example, the first side stretching force and the second side stretching force applied. The flat test block 301 also has a thickness h in the direction z, for example. The first stretching portion 302 and the second stretching portion 303 have the same thickness as the flat test block 301. By setting the length l and width w of the flat test block 301, the influence of the edge effect of the material on the residual stress measurement during the stretching operation can be avoided.

[0061] In some embodiments, a temperature sensor is also installed on the surface of the test block. When the test block is subjected to a stretching operation corresponding to stress measurement, the temperature rise value on the surface of the test block is made less than a set temperature change threshold, such as 0.3 degrees Celsius (°C), 0.5 degrees Celsius or 0.8 degrees Celsius, thereby avoiding the influence of temperature changes on the resistivity value.

[0062] Figure 5 This is a process flow chart of obtaining the resistivity of a test block at different thicknesses according to an embodiment of the present application.

[0063] In some embodiments, reference Figure 5 In step 104, current is connected to the test block at multiple frequencies and voltage is detected to obtain the resistivity at different thicknesses, which includes: step 501, at a first current frequency f n Under, according to the input current I n and the detected voltage V n , and the first resistivity ρ is obtained n (f n ); Step 502, at the second current frequency f n-1 Under, according to the input current I n-1 and the detected voltage V n-1 , and the second resistivity ρ is obtained n-1 (f n-1 ); Step 503, according to the first resistivity ρ n (f n ) and the second resistivity ρ n-1 (f n-1 ), and the skin depth d of the test block is obtained. n The corresponding resistivity ρ(f). n is a marking number, n≥1 and is a positive integer.

[0064] In some embodiments, according to the first resistivity p n (f n ) and the second resistivity ρ n-1 (f n-1 ), and the skin depth d of the test block is obtained. n (or thickness d n ) The corresponding resistivity ρ(f) includes:

[0065]

[0066] Among them, T n and T n-1 is related to the first current frequency f n and the second current frequency f n-1 The distribution volume of the eddy currents in the test block material respectively corresponds to the distribution volume of the eddy currents in the test block material. The distribution volume of the eddy currents in the test block material is calculated, for example, by the finite element method.

[0067] In some embodiments, obtaining the residual stress value of the test block at different thicknesses based on the resistivity of the test block at different thicknesses, the relationship curve between the tensile stress value and the resistivity of the test block, and the reference resistivity in step 105 includes:

[0068]

[0069] Among them, τ n is the residual stress value of the test block at different thicknesses, ρ(f) is the resistivity of the test block at different thicknesses, K c K is the slope of the relationship curve between the tensile stress value and resistivity of the test block. c For example, the first direction slope K corresponding to the relationship curve between the tensile stress value of the test block and the resistivity in the first direction is x The second direction slope K corresponding to the relationship curve between the tensile stress value of the test block and the resistivity in the second direction y .

[0070] In some embodiments, a plurality of residual stress values ​​of different thicknesses are obtained by calculation, and on this basis, the data are filtered and fitted to obtain the residual stress gradient distribution of the test area of ​​the test block. Figure 6 It is a schematic diagram of the residual stress gradient distribution of a test block in a test area according to an embodiment of the present application. Figure 6 In the figure, the horizontal axis is the thickness d of the test block on the test area, in millimeters (mm), and the vertical axis is the residual stress σ, in megapascals (MPa). Figure 6 The schematic diagram of residual stress gradient distribution of the test block in the test area can be a schematic diagram of residual stress gradient distribution corresponding to the first direction x, or a schematic diagram of residual stress gradient distribution corresponding to the second direction y. The first direction x and the second direction y are, for example, Figure 3 Indicated in .

[0071] Figure 7 Schematic diagram of the application environment of the residual stress measurement method according to an embodiment of the present application. Figure 7 In some embodiments, the signal connection end of the first probe 311, the signal connection end of the second probe 312, the signal connection end of the third probe 313, and the signal connection end of the fourth probe 314 are connected to the current generating device 601 or the voltage sensing device 602. The current generating device 601 and the voltage sensing device 602 are located in the phase-locked analyzer 603, and the measurement accuracy of the resistivity of the test block is improved by adjusting the signal sampling rate of the phase-locked analyzer.

[0072] In some embodiments, the signal connection end of the first probe 311, the signal connection end of the second probe 312, the signal connection end of the third probe 313, and the signal connection end of the fourth probe 314 are connected to a current generating device or a voltage sensing device through a multiplexer. The multiplexer includes a first multiplexer 611 and a second multiplexer 612. A low-noise current amplifier 621 is connected between the first multiplexer and the current generating device. A low-noise voltage amplifier 622 is connected between the second multiplexer and the voltage sensing device.

[0073] In some embodiments, the first multiplexer 611, the second multiplexer 612, the current generator 601, and the voltage sensing device 602 are connected to a main control module 631. The main control module 631 is configured to run a main control program to issue control instructions to the first multiplexer 611, the second multiplexer 612, the current generator 601, and the voltage sensing device 602. The main control module is also connected to a display module 632 to display the measurement process data and measurement result data of the residual stress value.

[0074] The non-destructive residual stress measurement method of the present application can quickly obtain residual stress distribution data of equipment parts, such as aircraft engine parts, in various manufacturing and processing stages, test stages, and operation stages. The present application scheme can greatly reduce the cost of residual stress detection of parts, and help guide the optimization of aircraft engine component manufacturing and processing technology, and provide an effective reference for failure mode analysis of material-level and component-level test pieces. In addition, the residual stress measurement values ​​obtained by the residual stress measurement method of the present application can also provide important reference data for the life assessment of key engine components, which is of great significance for the service life assessment and lightweight design of key aircraft engine components.

[0075] The basic concepts have been described above. Obviously, for those skilled in the art, the above invention disclosure is only used as an example and does not constitute a limitation of the present application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and amendments to the present application. Such modifications, improvements and amendments are suggested in the present application, so such modifications, improvements and amendments still belong to the spirit and scope of the exemplary embodiments of the present application.

[0076] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0077] It should be noted that in order to simplify the description of the disclosure of this application and thus help understand one or more embodiments of the invention, in the above description of the embodiments of this application, multiple features are sometimes combined into one embodiment, figure or description thereof. However, this disclosure method does not mean that the features required by the object of this application are more than the features mentioned in the claims. In fact, the features of the embodiments are less than all the features of the single embodiment disclosed above.

[0078] In some embodiments, numbers describing the number of components and attributes are used. It should be understood that such numbers used in the description of the embodiments are modified by the modifiers "about", "approximately" or "substantially" in some examples. Unless otherwise specified, "about", "approximately" or "substantially" indicate that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may change according to the required features of individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and adopt the general method of retaining digits. Although the numerical domains and parameters used to confirm the breadth of their range in some embodiments of the present application are approximate values, in specific embodiments, the setting of such numerical values ​​is as accurate as possible within the feasible range.

[0079] Although the present application has been described with reference to the current specific embodiments, ordinary technicians in this technical field should recognize that the above embodiments are only used to illustrate the present application, and various equivalent changes or substitutions may be made without departing from the spirit of the present application. Therefore, as long as the changes and modifications to the above embodiments are within the essential spirit of the present application, they will fall within the scope of the claims of the present application.

Claims

1. A residual stress measurement method, comprising: Through elastic limit stretching operation, the stress calibration elastic range of the test block is obtained; Obtain the baseline resistivity of the zero stress test block; Obtaining a relationship curve between the tensile stress value and the resistivity of the test block; Conduct current access and voltage detection at multiple frequencies on the test block to obtain the resistivity of the test block at different thicknesses; Based on the resistivity of the test block at the different thicknesses, the relationship curve between the tensile stress value and the resistivity of the test block, and the reference resistivity, the residual stress values ​​of the test block at the different thicknesses are obtained.

2. The residual stress measurement method according to claim 1, characterized in that: The zero stress test block is obtained by performing vibration aging treatment on the test block.

3. The residual stress measurement method according to claim 1, characterized in that: The test block is a flat test block, and the relationship curve between the tensile stress value and the resistivity of the test block is obtained by: The detection end of the first probe, the detection end of the second probe, the detection end of the third probe and the detection end of the fourth probe form four end points of a square shape; A first excitation current is applied to the same side surface of the flat test block through the detection end of the first probe and the detection end of the second probe; Acquiring a corresponding first sensing voltage on the same side surface of the flat test block through the detection end of the third probe and the detection end of the fourth probe; A second excitation current is applied to the same side surface of the flat test block through the detection end of the first probe and the detection end of the third probe; Acquiring a corresponding second sensing voltage on the same side surface of the flat test block through the detection end of the second probe and the detection end of the fourth probe; Obtaining a tensile stress value-resistivity curve of the test block in a first direction according to a first excitation current and a first sensing voltage obtained by multiple measurements; A tensile stress value-resistivity curve of the test block in the second direction is obtained according to the second excitation current and the second sensing voltage obtained by multiple measurements.

4. The residual stress measurement method according to claim 3, characterized in that: The length l and width w of the flat test block satisfy l≥k*a, w≥k*a with the side length a of the square shape; k≥3 and is a rational number.

5. The residual stress measurement method according to claim 3, characterized in that: According to the measured first excitation current V x and the first sensing voltage I x , the first direction resistivity ρ is obtained based on the following formula x : Wherein, t is the thickness of the flat test block, and a is the side length of the square shape.

6. The residual stress measurement method according to claim 3, characterized in that: According to the measured second excitation current V y and the second sensing voltage I y , the second direction resistivity ρ is obtained based on the following formula y : Wherein, t is the thickness of the flat test block, and a is the side length of the square shape.

7. The residual stress measurement method according to claim 1, characterized in that: The test block is subjected to current access and voltage detection at multiple frequencies to obtain the resistivity at different thicknesses, including: At the first current frequency f n Under, according to the input current I n and the detected voltage V n , and the first resistivity ρ is obtained n (f n ); At the second current frequency f n-1 Under, according to the input current I n-1 and the detected voltage V n-1 , and the second resistivity ρ is obtained n-1 (f n-1 ); According to the first resistivity ρ n (f n ) and the second resistivity ρ n-1 (f n-1 ), and the skin depth d of the test block is obtained. n The corresponding resistivity ρ(f).

8. The residual stress measurement method according to claim 7, characterized in that: According to the first resistivity ρ n (f n ) and the second resistivity ρ n-1 (f n-1 ), and the skin depth d of the test block is obtained. n The corresponding resistivity ρ(f) includes: Among them, T n and T n-1 is related to the first current frequency f n and the second current frequency f n-1 The corresponding eddy current distribution volume in the test piece material.

9. The residual stress measurement method according to claim 1, characterized in that: Based on the resistivity of the test block at different thicknesses, the relationship curve between the tensile stress value and the resistivity of the test block, and the reference resistivity, the residual stress values ​​of the test block at different thicknesses are obtained, including: Among them, τ n is the residual stress value of the test block at different thicknesses, ρ(f) is the resistivity of the test block at different thicknesses, K c It is the slope corresponding to the relationship curve between the tensile stress value and resistivity of the test block.

10. The residual stress measurement method according to claim 3, characterized in that: The multiple measurements include multiple stretching of the flat test block in the stress calibration elastic range of the test block, and each stretching is loaded with N levels of stress values ​​step by step, where N is ≥ 3 and is a positive integer.

11. The residual stress measurement method according to claim 3, characterized in that: The signal connection end of the first probe, the signal connection end of the second probe, the signal connection end of the third probe and the signal connection end of the fourth probe are connected to a current generating device or a voltage sensing device.

12. The residual stress measurement method according to claim 11, characterized in that: The signal connection end of the first probe, the signal connection end of the second probe, the signal connection end of the third probe and the signal connection end of the fourth probe are connected to a current generating device or a voltage sensing device through a multi-way signal selector.

13. The residual stress measurement method according to claim 11, characterized in that: The current generating device and the voltage sensing device are located in a phase-locked analyzer.

14. The residual stress measurement method according to claim 12, characterized in that: The multiplexer includes a first multiplexer and a second multiplexer; a low-noise current amplifier is connected between the first multiplexer and the current generating device; A low-noise voltage amplifier is connected between the second multiplexer and the voltage sensing device.

15. The residual stress measurement method according to claim 14, characterized in that: The first multiplexer, the second multiplexer, the current generating device and the voltage sensing device are connected to a main control module; The main control module is configured to run a main control program to issue control instructions to the first multiplexer, the second multiplexer, the current generating device and the voltage sensing device.

16. The residual stress measurement method according to claim 15, characterized in that: The main control module is also connected to a display module to display the measurement process data and measurement result data of the residual stress value.

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