Method for measuring average residual stress in work-hardened layer of metal surface

Abstract

The application provides a method for measuring average residual stress in a work-hardened layer of a metal surface, which comprises the following steps: firstly, linearly cutting two narrow strips from a plate after surface strengthening, measuring the curvature radius R0 of the surface of the hardened layer of the two narrow strips, and clamping opposite surfaces of the hardened layer of the narrow strips; the two narrow strips have different t values, each of the two narrow strips is cut into a thin strip with a thickness of t at a distance of t from the surface of the hardened layer with a curvature radius of R0-t, then the curvature radius R of the two thin strips is measured, and the average residual stress σ0 in the work-hardened layer and the acting thickness t0 thereof are calculated according to the different t and R values of the two thin strips and a formula. The detection equipment used in the application is easy to obtain, the detection process is simple, the detection speed is fast, the detection efficiency is high, the average residual stress and the acting thickness thereof can be obtained at the same time, and the application has the characteristics of directness, reliability and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of residual stress detection, and particularly relates to a method for measuring average residual stress in a hardening layer on a metal surface. BACKGROUND

[0002] Residual stress refers to stress remaining in a workpiece after the workpiece is unloaded after some machining processes. Common mechanical strengthening processes, such as shot blasting and roll pressing, can cause the generation of residual stress in a surface layer. The residual stress in the surface layer is closely related to the performance of the workpiece. Therefore, it is of great significance to effectively detect and control the residual stress of the workpiece during the machining process.

[0003] Common methods for measuring residual stress in a surface hardening layer include neutron diffraction, layer stripping X-ray method, crack compliance method, blind hole method, and curvature method. The neutron diffraction method can detect a relatively large depth, but the spatial resolution of neutron diffraction is relatively low, and the neutron diffraction method requires a high device and is not easy to implement. The layer stripping X-ray method requires layer-by-layer electrolytic corrosion and measurement, which is time-consuming and inefficient. The crack compliance method and the blind hole method require precise machining, pasting strain gauges, and other processes, which are relatively complex and also have the problems of long time consumption and low efficiency.

[0004] The curvature method is mainly used for measuring residual stress in a thin film and a coating on a relatively thin substrate. In the document "Comparative Study on Different Measurement Methods of Shot Blasting Residual Stress" (Master's Thesis of Henan University of Science and Technology, 2014), the curvature method is used for measuring residual stress in a surface hardening layer (shot blasting layer). The curvature method is combined with the layer stripping X-ray method to measure the average residual stress and thickness of the hardening layer of a 45 steel shot blasting sample. In the document, the curvature method is used to calculate the average residual stress in the hardening layer based on the stress acting thickness measured by the layer stripping X-ray method. The curvature method in the document does not provide the average residual stress and thickness in the hardening layer, and the stress calculation formula needs to be improved.

[0005] In view of the problems in the prior art, a method for measuring average residual stress in a hardening layer on a metal surface is provided. SUMMARY

[0006] The technical problem to be solved by the application is to provide a method for measuring average residual stress in a hardening layer on a metal surface to solve the problems in the background art.

[0007] To solve the above technical problems, the application adopts the following technical solution: a method for measuring average residual stress in a hardening layer on a metal surface, comprising the following steps:

[0008] S1, cut two narrow strips in the metal plate after surface strengthening, and measure the curvature radius R0 of the two narrow strips;

[0009] S2, clamp the opposite surface of the narrow strip hardened layer, and take different t values for the two narrow strips. At the distance t from the surface of the hardened layer, cut a thin strip with the curvature radius R0-t and the thickness t;

[0010] S3, measure the curvature radius R of the two thin strips, and calculate the average residual stress σ0 in the work-hardened layer and the acting thickness t0 according to the different t and R values of the two thin strips.

[0011] Further, in S1, the cutting is performed by wire cutting. The line perpendicular to the length direction of the narrow strip in the upper and lower surfaces of the narrow strip cut by wire cutting, i.e. the Y direction line in the two surfaces, is approximately a straight line, and the curvature radius R0 of each part along the thickness direction of the narrow strip, i.e. the Y direction, is considered to be the same. The height difference of multiple points is measured at the half position of the width of the strengthened surface along the length direction, i.e. the X direction, by using a profile measuring instrument or a micrometer. The curvature radius R0 of the strengthened surface is fitted according to the height difference along the length direction.

[0012] Further, in S2, the clamping position must not be on the thin strip to be cut in the narrow strip. Different t values are taken for the two narrow strips. At the distance t from the surface of the hardened layer, the thin strip is cut with the curvature radius R0-t. Before cutting, the acting thickness t0 value of the average residual stress in the work-hardened layer is estimated in advance, and the t value should be selected within the range of 2t0-10t0.

[0013] Further, in S3, the method for measuring the curvature radius R of the two thin strips is the same as R0. The thickness t of the thin strip is measured by using a vernier caliper at multiple points and the average value is taken.

[0014] Further, in S3, the t and R of the two thin strips are different, and the equation used for calculation is as follows:

[0015]

[0016] Wherein, E is the elastic modulus, and T0 is the thickness of the metal plate;

[0017] Substitute the t and R values of the two thin strips into the equation respectively to obtain two equations, which form an equation set. The average residual stress σ0 in the work-hardened layer and the acting thickness t0 value can be obtained by solving the equation set.

[0018] Further, the finally obtained t0 value is used to detect the original t value taken. If t is less than 2t0 or greater than 10t0, the thin strip needs to be cut again for measurement;

[0019] If the hardened surface of the metal plate is convex, σ0 is a compressive stress;

[0020] If the metal plate is hardened and the surface is concave, σ0 is the tensile stress.

[0021] Compared with the prior art, the present application has the following advantages:

[0022] The device used in the present application is easy to obtain; the detection process is simple, fast, and efficient; and the average residual stress and its acting thickness can be obtained simultaneously by using simple wire cutting without layer-by-layer peeling. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a cutting and measuring schematic diagram in the embodiment of the present application;

[0024] Figure 2 is a deformation equivalent transformation and stress analysis diagram in the embodiment of the present application;

[0025] Figure 3 is a stress distribution analysis diagram in the thin strip in the embodiment of the present application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0027] As shown in Figures 1-3 , the present application provides a technical solution: a measurement method for average residual stress in a work-hardened layer of a metal surface, comprising the following steps:

[0028] S1, line cutting two narrow strips in the metal plate after surface strengthening, and measuring the curvature radius R0 of the two narrow strips;

[0029] The metal plate is a plate after surface work hardening by rolling, shot blasting or cutting, the plate thickness is T0, the cutting is wire cutting, specifically, electric spark wire cutting processing, and the influence of electric spark wire cutting processing on the residual stress of the surface strengthening layer is negligible.

[0030] Specifically, the dotted line shown in Figure 1 (a) is the path of electric spark wire cutting, and the two narrow strips to be cut are shown as the first strip and the second strip in the figure, the upper and lower surfaces of the narrow strip are perpendicular to the length direction of the strip and are considered to have no flexure, that is, the two surfaces in the Y direction are straight lines, as shown in Figure 1 (b); Figure 1 (b) at the same time

[0031] The height difference of several points is measured along the length direction, i.e. X direction, at the half position of the width of the two narrow strip reinforced surfaces, i.e. at Figure 1 The radius measuring line in (b) is measured at several points, and a profile measuring instrument or a micrometer is used to measure the height difference along the length direction, and the curvature radius R0 of the reinforced surface is fitted according to the height difference along the length direction.

[0032] S2, the opposite side of the clamped narrow strip hardened layer is clamped, and the two narrow strips take different t values, and each narrow strip is cut at a distance of t from the surface of the hardened layer to have a curvature radius of R0-t, and a thin strip with a thickness of t is cut;

[0033] The clamping position must not be on the thin strip to be cut by the narrow strip, and the two narrow strips take different thickness t values along Figure 1 (b) The line cutting position is marked, and a thin strip is cut by a line with a curvature radius of R0-t, and the action thickness t0 value of the average residual stress in the hardened layer is estimated before cutting, and the t value is selected in the range of 2t0-10t0;

[0034] If the t value is too small, the error of the average residual stress in the hardened layer will be too large;

[0035] If the t value is too large, the deformation of the cut thin strip will be too small, and the measurement error of the deformation will be larger.

[0036] S3, the curvature radii R of the two thin strips are measured, and the average residual stress σ0 in the work hardened layer and the action thickness t0 are calculated according to the different t and R values of the two thin strips.

[0037] The method for measuring the curvature radii R of the two thin strips is the same as R0. The thickness t of the thin strip is measured by a vernier caliper at several points and the average value is taken;

[0038] In S3, the t and R of the two thin strips are different.

[0039] In Figure 1 , the narrow strip cut in Figure 2 (a) has a width of b, an average residual stress in the hardened layer of σ0 and an action thickness of t0, a thickness of T0, and a curvature radius of R0, and the average stress in the lower substrate is σ m .

[0040] First, it is assumed that the narrow strip is not bent, as shown in Figure 2 (b), and the cutting line is cut in Figure 2 (b), and the thin strip with the hardened layer is bent, as shown in Figure 2 (c), and the curvature radius of the bent surface of the hardened layer is R. In Figure 2 (d), there is a flat thin strip without stress, and the height is t and the width is b, i.e. the same as Figure 2 (c).

[0041] There is an action force F1 in the middle of the t0 thickness, and

[0042] F1 = σ0t0b;

[0043] In the following t-t0 thickness there is a force F2, and

[0044] F2 = σ m (t-t0)b

[0045] Under the action of F1 and F2, the flat strip will bend, and the surface bending radius will also be R, that is, the same as in 2(c).

[0046] For Figure 2 (d) strip force analysis. F1 and F2 are moved to the height of the strip, that is, to the height of t / 2. According to the force translation theorem, F1 generates a bending moment M1; F2 generates a bending moment M2, as shown in Figure 2 (e).

[0047] Again for the strip in Figure 2 (e) deformation analysis:

[0048] According to the force balance principle and the force translation theorem, then:

[0049] F1 = σ0t0b = σ m (T0-t0)b

[0050]

[0051]

[0052]

[0053]

[0054] For the cross section of Figure 3 (e), stress distribution analysis, the stress can be seen as the stress σ1 generated by F1 and the stress σ 1m generated by M1, and the stress σ2 generated by F2 and the stress σ 2m generated by M2, as shown in Figure 1 .

[0055] σ1, σ2, σ 1m , σ 2m After stress superposition, the upper surface stress σ us is:

[0056]

[0057] The lower surface stress σ ls is:

[0058]

[0059] The distance z2 of the neutral plane from the upper surface is

[0060]

[0061] Generally, R is much larger than z2, E is the modulus of elasticity, the strain of the upper surface is ε us Then

[0062]

[0063] From equations (1), (3) and (4), we have

[0064]

[0065] If the original deformation R0 is considered, σ0 is approximately

[0066]

[0067] Substitute the t and R values of the two strips into equation (6) respectively to obtain two equations, which form an equation group. Solving the equation group can obtain the average residual stress σ0 in the hardened layer and the acting thickness t0 value.

[0068] The finally obtained t0 value is used to detect the originally taken t value. If t is less than 2t0 or greater than 10t0, the strip needs to be cut and measured again.

[0069] If the hardened surface of the metal plate is convex, σ0 is a compressive stress.

[0070] If the hardened surface of the metal plate is concave, σ0 is a tensile stress.

[0071] Experimental Example 1

[0072] A 45 steel quenched and tempered square plate sample with a size of 120mm×120mm×15mm is used. The two surfaces of 120mm×120mm are ground on a surface grinder to remove the oxide skin, and one of the two surfaces is shot blasted. The shot blasting equipment is a Q765 type trolley shot blasting machine. The cast steel shot has a diameter of 1.5-2.0mm, the shot blasting speed is 18.20m / s, and the shot blasting time is 30min.

[0073] I. The residual stress is measured by using the present application.

[0074] The used equipment and instruments are: linear cutting on the fast wire CNC linear cutting machine, model DK7732, wire speed is 6 m / s, molybdenum wire diameter is 0.18 mm. Thickness measurement is vernier caliper, accuracy 0.02 mm. Curvature radius measurement is hommel etamic profile measurement instrument, model hommel etamic nanoscan 855, test accuracy 0.1 μm.

[0075] 1. The quenched and tempered square plate of 45 steel after grinding is placed on the platform of the shot blasting machine, and the shot blasting is performed according to the above process, and one 120 mm x 120 mm surface contacts the platform and is not blasted. After shot blasting, about 1.5 mm is cut off from each side, and the square plate becomes about 117 mm in length and width. The thickness of the plate is measured by a vernier caliper, and T0=14.80 mm.

[0076] 2. The square plate is clamped on the linear cutting machine, and the linear cutting is performed along the Figure 1 (a) dashed line to cut out two narrow strips, and the width of the narrow strips is 10 mm.

[0077] 3. The profile measurement instrument is used to measure the height difference of multiple points at the position of about 5 mm in the middle of the width of the two cut-out narrow strips along the length direction X, and about 100 points are measured in the range of 0-110 mm in length.

[0078] That is, in the Figure 1 (b) point line radius measurement line, multiple points are measured, and the curvature radius R0 value is fitted based on the measured value by the profile measurement instrument self-provided program.

[0079] The R0 values of the two narrow strips are very large, the first one is 40084.50 mm and the second one is 40317.62 mm, the relative deviation is 0.6%, the deviation is small, and the average value is R0=40201.06 mm.

[0080] 4. The first narrow strip and the second narrow strip are respectively clamped on the linear cutting machine, and thin strips with different thicknesses are cut. The clamping position is not on the thin strip to be cut out, so as to avoid interfering with the free deformation of the thin strip with the hardening layer. The cutting path is as shown in the dashed line position in Figure 1 (b). The first narrow strip is cut to have a thin strip with a thickness t of about 1.50 mm, and the second narrow strip is cut to have a thin strip with a thickness t of about 3.00 mm, and the curvature radii R0-t of the two narrow strips cutting paths dashed lines are 40199.56 mm and 40198.06 mm respectively.

[0081] 5. The profile measurement instrument is used to measure the curvature radii R of the two thin strips, and the curvature radius R is measured in the same way as R0. The R of the first thin strip cut out from the first narrow strip is measured to be 919.84 mm, and the R of the second thin strip cut out from the second narrow strip is measured to be 3205.00 mm.

[0082] The thickness t of the thin strip was measured again accurately, 10 points were measured along the length direction of the thin strip by using a vernier caliper, and then the average value was taken, and the average value of the measurement was taken in the following formula. The average values of the thickness t of the first narrow strip and the second narrow strip were 1.46 mm and 3.04 mm respectively.

[0083] 6. The measured values of each parameter and the modulus of elasticity E were checked according to the manual values as shown in Table 1. The values of t and R of the two thin strips were respectively substituted into the following equation to obtain two equations, the two equations formed an equation group, and the average residual stress σ0 in the hardened layer and the acting thickness t0 thereof were obtained by solving the equation group.

[0084] 7. The σ0 obtained by solving the equation group was 273 MPa (compressive stress), and t0 was 0.36 mm. The t of the two thin strips was greater than 2t0 and less than 10t0, and the measurement was effective.

[0085] Table 1 Parameters of 45 steel samples

[0086]

[0087]

[0088] II. The measurement results of the present application were verified by using the layer stripping X-ray diffraction method.

[0089] Although the layer stripping X-ray diffraction method for measuring the surface residual stress has the problems of long time consumption and low efficiency, people have a high recognition degree for the method. The residual stress of the same 45 steel shot blasting plate was measured by using the layer stripping X-ray diffraction method, so as to verify the effectiveness of the method of the present application.

[0090] The equipment used was XSTRESS3000 portable X-ray stress analyzer and Struers Movipol-3 portable metallographic electrolytic polishing instrument. The layer stripping polishing voltage was 10 V, the current was 1.5 A, and the corrosion liquid was NaCl saturated aqueous solution. The layer stripping thickness was controlled by the electrolytic polishing time, and was measured and corrected by using a depth micrometer, and the accuracy of the depth micrometer was 0.01 mm.

[0091] The layer stripping X-ray measurement results are shown in Table 2. According to Table 2, the average residual stress measured by the layer stripping X-ray is 240 MPa (compressive stress). The stress acting layer thickness is 0.35 mm.

[0092] Table 2 45 steel layer stripping X-ray residual stress measurement results (- is compressive stress, + is tensile stress)

[0093]

[0094]

[0095] The average residual stress of the measuring method of the application only differs 33MPa from the result of the X-ray measurement, and the thickness of the stress layer only differs 0.01mm. The average residual stress and the thickness of the stress layer measured by the two methods are basically consistent, which proves the feasibility of the method of the application.

[0096] Example 2

[0097] A 16Mn normalizing square plate sample with a size of 120mmx120mmx15mm is used. The two surfaces of 120mmx120mm are ground to remove the oxide skin on the plane grinder, and one of the two surfaces is shot blasted. The shot blasting equipment is a Q765 type trolley shot blasting machine. The cast steel shot has a diameter of 1.5-2.0mm, the shot blasting speed is 18.20m / s, and the shot blasting time is 30min.

[0098] I. The residual stress is measured by using the application.

[0099] The used equipment and instruments are as follows: wire cutting is carried out on a fast wire speed numerical control wire cutting machine bed, the model is DK7732, the wire speed is 8m / s, and the molybdenum wire diameter is 0.18mm. The thickness measurement is a vernier caliper with an accuracy of 0.02mm. The curvature radius measurement is a hommel etamic profile measurement instrument, the model is hommel etamic nanoscan 855, and the test accuracy is 0.1μm.

[0100] 1. The ground 16Mn normalizing square plate is placed on the platform of the shot blasting machine, and is shot blasted according to the above process. One 120mmx120mm surface is not shot blasted because it contacts the platform. After shot blasting, about 1.5mm is cut from each side, and the square plate becomes about 117mm in length and width. The thickness of the plate is measured by a vernier caliper, and T0=14.80mm.

[0101] 2. The square plate is clamped on the wire cutting machine bed, and is cut along Figure 1 (a) the dashed line to form two narrow strips. The width of the narrow strips is 10mm.

[0102] 3. The height difference of multiple points is measured by the profile measurement instrument at the position of about 5mm in the middle of the width of the two cut narrow strips along the length direction X in the range of 0-110mm, that is, about 100 points are measured in the range of 0-110mm. Figure 1 (b) multiple points are measured on the radius measurement line, and the curvature radius R0 value is fitted based on the measured values by the program of the profile measurement instrument. The R0 values of the two narrow strips are very large, the first one is 38972.45mm, the second one is 38290.19mm, the relative deviation is 1.8%, and the average value is R0=38631.32mm.

[0103] 4. Mount the first and second narrow strips separately on the wire cutting machine and cut thin strips of different thicknesses. The mounting positions should not be on the thin strips to be cut to avoid interfering with the free deformation of the hardened layer. The cutting path is as follows: ​ The position of the dashed line in (b). A thin strip with a thickness of about 1.50 mm is cut from the first narrow strip, and a thin strip with a thickness of about 4.00 mm is cut from the second narrow strip. The radius of curvature R0-t of the dashed lines of the cutting paths of the two narrow strips are 38629.82 mm and 38627.32 mm, respectively.

[0104] 5. Measure the radius of curvature R of the two thin strips using a profile measuring instrument. The method for measuring the radius of curvature R is the same as for R0. The measured R for the first thin strip cut from the first narrow strip is 926.46 mm, and the measured R for the second thin strip cut from the second narrow strip is 4595.87 mm. The thickness t of the thin strip is then precisely measured again using 10 evenly spaced measurements along the length of the thin strip with vernier calipers. The average value is then taken, and the average value is used in the calculations below.

[0105] The average thicknesses t of the first and second thin strips are 1.50 and 4.00 mm, respectively.

[0106] 6. The measured values ​​of each parameter and the elastic modulus E (from the handbook) are shown in Table 3. Substituting the t and R values ​​of the two thin strips into the equations below, we obtain two equations. These two equations form a system of equations. Solving this system of equations yields the average residual stress σ0 in the hardened layer and its effective thickness t0. Solving the system of equations yields σ0 = 237 MPa (compressive stress) and t0 = 0.60 mm. The t values ​​for both thin strips are greater than 2t0 and less than 10t0, indicating the measurement is valid.

[0107] Table 3 Parameters of 16Mn Samples

[0108]

[0109]

[0110] 2. The measurement results of this invention were verified by the peeling X-ray diffraction method.

[0111] Although the exfoliation X-ray diffraction method for measuring surface residual stress has the problems of being time-consuming and inefficient, it is widely accepted. The residual stress of the same 16Mn steel shot-peened plate was measured using the exfoliation X-ray diffraction method to verify the effectiveness of the method of the present invention.

[0112] The used equipment is XSTRESS3000 portable X-ray stress analyzer and Struers Movipol-3 portable metallographic electrolytic polishing instrument. The stripping polishing voltage is 10V, the current is 1.5A, and the etching solution is saturated aqueous solution of NaCl. The stripping thickness is controlled by the electrolytic polishing time, and is measured and corrected by the depth micrometer, and the accuracy of the depth micrometer is 0.01mm.

[0113] The stripping X-ray measurement results are shown in Table 4. By integrating the stress along the depth from Table 4, the average residual stress of the stripping X-ray measurement is 224MPa (compressive stress). The stress acting layer thickness is 0.45mm.

[0114] Table 4 16Mn stripping X-ray residual stress measurement results (- is compressive stress, + is tensile stress)

[0115]

[0116]

[0117] The measurement method results of the present application compared with the stripping X-ray measurement results, the average residual stress only differs by 13MPa, and the acting layer thickness differs slightly by 0.15mm. The residual stress measurement accuracy of the commonly recognized stripping X-ray method is ±25MPa. The average residual stress and stress acting layer thickness measured by the two methods are basically consistent, which proves the feasibility of the method of the present application.

[0118] It should be noted that the relational terms herein such as first and second, are used only to differentiate one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations exist in any actual relationship or order. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, methods, articles or equipment including a series of elements not only include those elements, but also include other elements not explicitly listed or inherent to such processes, methods, articles or equipment.

[0119] Although the embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for measuring the average residual stress within a work-hardened layer on a metal surface, characterized in that: Includes the following steps: S1. Cut two narrow strips along the centerline of the surface-strengthened metal plate and measure the radii of curvature of the two narrow strips. R 0; S2, opposite to the narrow strip hardened layer, the two narrow strips take different... t The value is the distance between each narrow strip and the surface of the hardened layer. t At this point, the radius of curvature is... R 0- t Wire cutting to a thickness of t The thin strip must not be clamped on the thin strip to be cut from within the narrow strip. Before cutting, the thickness of the average residual stress in the hardened layer should be estimated in advance. t 0 value, select t The value should be in the range of 2. t 0~10 t Within the range of 0; S3. Measure the radius of curvature of the two thin strips. R According to the different two thin strips t and R The average residual stress within the work-hardened layer was calculated. σ 0 and its effective thickness t 0, Two thin strips t and R They are all different; the equations used for the calculation are as follows: ； in, E For elastic modulus, T 0 represents the thickness of the metal plate; Separately place the two thin strips t and R Substituting the values ​​into the equations yields two equations, which together form a system of equations. Solving this system of equations gives the average residual stress within the hardened layer. σ 0 and its effective thickness t 0 value.

2. The method for measuring the average residual stress within a work-hardened layer on a metal surface according to claim 1, characterized in that, In S1, the cutting is done using wire cutting. The wire-cut strip has lines perpendicular to the length of the strip on both its upper and lower surfaces, i.e., lines on both surfaces. Y The direction of the line is approximately a straight line, and it is also along the thickness direction of the narrow strip. Y radius of curvature at all directions R 0 is considered the same, and the two narrow strips are cut out along the length direction at half the width of the reinforced surface. X The height difference at multiple points along the direction is measured using a profile measuring instrument or dial indicator. The radius of curvature of the reinforced surface is then fitted based on the height difference along the length direction. R 0.

3. The method for measuring the average residual stress within a work-hardened layer on a metal surface according to claim 2, characterized in that, In S3, the radii of curvature of the two thin strips are measured. R The method is the same R 0, for thin strip thickness t Use vernier calipers to measure at multiple points and take the average value.

4. The method for measuring the average residual stress within a work-hardened layer on a metal surface according to claim 1, characterized in that, The final result t A value of 0, in turn, is used to check the previously selected value. t Value, if t Less than 2 t 0 or greater than 10 t 0, requires recutting into thin strips and measuring; If the hardened surface of the metal plate is raised. σ 0 represents compressive stress; If the hardened surface of the metal plate is concave. σ 0 represents tensile stress.

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