Measurement method for three-dimensional internal residual stress distribution

Abstract

To provide a more efficient and convenient measuring method of three-dimensional internal residual stress.SOLUTION: The measuring method of three-dimensional internal residual stress distribution is a method of measuring three-dimensional internal residual stress distribution in a member as a measurement object, and includes: a cutting step of cutting the member into two cut pieces; a surface condition measurement step of measuring the state of a surface where a deformation occurs on the cut surface of the cut piece; a released internal residual stress calculation step of calculating three-dimensionally the internal residual stress released in the cut surface based on the measured surface condition; an unreleased internal residual stress calculation step of calculating an unreleased internal residual stress remaining in the cut surface that is not completely released at the cut surface; and a three-dimensional internal residual stress calculation step of calculating a three-dimensional internal residual stress distribution by summing the calculated released internal residual stress and unreleased internal residual stress in the released internal residual stress calculation step and the unreleased internal residual stress calculation step.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for measuring a three-dimensional internal residual stress distribution. [Background technology]

[0002] Metal components used in various industries undergo various processing processes during their manufacturing process, including machining, plastic processing, casting, welding, and heat treatment. It is well known that these processes generate three-dimensional tensile and compressive residual stresses inside the components (three-dimensional internal residual stress).

[0003] For example, in steel parts such as gears, shafts, and bearings, steel is used that has been carburized and quenched to improve the hardness of the surface matrix in order to meet requirements such as load-bearing strength and long-term wear resistance.However, this heat treatment creates a gradient in carbon concentration, which generates three-dimensional internal residual stress from the surface to the interior of the part.

[0004] The distribution and magnitude of this three-dimensional internal residual stress have a significant impact on the stress-strain behavior and fatigue life of components and structures that use them, and in some cases may even lead to destruction. For this reason, measuring and evaluating the distribution and magnitude of the three-dimensional internal residual stress generated near the construction site is extremely important for the accuracy control of components and products.

[0005] Currently, various methods have been proposed for measuring three-dimensional internal residual stress distribution, including X-ray diffraction (e.g., Patent Document 1), neutron diffraction (e.g., Patent Document 2), inherent strain method (e.g., Patent Document 3), and deep hole method (e.g., Patent Documents 4 and 5). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-187352 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-336993 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-162381 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-184118 [Patent Document 5] Japanese Patent Application Publication No. 2019-109099 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the above-mentioned measurement methods have various problems in terms of efficiency and simplicity as a method for measuring three-dimensional internal residual stress distribution.

[0008] First, X-ray diffraction is a measurement method that determines internal residual stress by measuring X-rays diffracted by the crystal grains of a component. Because it is a non-destructive method that does not require cutting the component, it can be said to be a relatively easy measurement method. However, it can only measure to a depth of the order of μm, less than 1 mm from the surface, and is essentially limited to two-dimensional measurement of internal residual stress distribution.

[0009] Next, neutron diffraction is a measurement method that determines internal residual stress by measuring diffracted neutrons, and is a non-destructive method that can measure to a depth of up to several tens of millimeters, but because the measurement is performed using special equipment that requires prior application and review, it takes time to start measurement and the measurement costs are high. There are also restrictions on the size of the test specimen.

[0010] The inherent strain method is a measurement technique that determines internal residual stress based on the unique correspondence between inherent strain and residual stress. Specifically, a component is finely cut in an area larger than the inherent strain region, and the residual stress is completely released. The elastic strain is recorded using strain gauges, and the inherent strain is identified using inverse calculations using the elastic finite element method. This destructive method can measure to depths of over 100 mm. However, preparation and measurement are time-consuming, and measurements using cutting and strain gauges are particularly labor-intensive and time-consuming, making it an inefficient and convenient measurement method.

[0011] Next, the deep hole method is a semi-non-destructive method in which a hole is drilled at the measurement location, a hole with a diameter slightly larger than the drilled hole is then bored out, and the released residual stress is calculated based on the change in the size of the hole as it is measured.This method can measure depths of more than several tens of mm.However, it takes time to prepare for the measurement and requires very precise measurements, making it not an efficient or simple measurement method.In addition, as a natural result, it can only measure the residual stress at the drilled location.

[0012] As described above, all of the current methods for measuring three-dimensional internal residual stress distribution have problems in terms of efficiency and simplicity, and there is a demand for a more efficient and simpler method for measuring three-dimensional internal residual stress.

[0013] Therefore, an object of the present invention is to provide a method for measuring three-dimensional internal residual stress that is more efficient and simpler than current methods for measuring three-dimensional internal residual stress. [Means for solving the problem]

[0014] The present inventors have conducted extensive research into solving the above problems and have found that the above problems can be solved by the invention described below, thereby completing the present invention.

[0015] The invention described in claim 1 is A method for measuring a three-dimensional internal residual stress distribution in a member to be measured, comprising: a cutting step of cutting the member into two cut pieces; As a planar state of the deformation occurring on the cut surface of the cut piece, Cut plane normal direction a planar state measuring step of measuring the displacement of the a released internal residual stress calculation step of three-dimensionally calculating the released internal residual stress at the cut surface by finite element analysis using a contour method based on the measured planar state; an unreleased internal residual stress calculation step of calculating, by elastic analysis, unreleased internal residual stress that is not completely released at the cut surface and remains within the cut surface; a three-dimensional internal residual stress calculation step of adding up the released internal residual stress and the unreleased internal residual stress calculated in the released internal residual stress calculation step and the unreleased internal residual stress calculation step to calculate a three-dimensional internal residual stress distribution, This is a method for measuring three-dimensional internal residual stress distribution, characterized in that the released internal residual stress calculation process is a process of calculating the released internal residual stress by applying a forced displacement in the opposite direction corresponding to the deformation occurring on the cut surface to a finite element model forming the cut surface of the cut piece.

[0017] Claim 2 The invention described in 4. The method of claim 3, wherein the calculation step includes filtering the calculation results to remove errors. 1 to This is a method for measuring the three-dimensional internal residual stress distribution described above.

[0018] Claim 3 The invention described in The filtering process is a polynomial approximation filtering process or a Gaussian filtering process. 2 This is a method for measuring three-dimensional internal residual stress distribution described in

[0019] Claim 4 The invention described in 2. The method according to claim 1, wherein the unreleased internal residual stress calculation step is a step of calculating the unreleased internal residual stress using a non-destructive surface residual stress measurement method.3 1. A method for measuring a three-dimensional internal residual stress distribution according to any one of claims 1 to 9.

[0020] Claim 5 The invention described in 3. The non-destructive surface residual stress measurement method is an X-ray diffraction method. 4 This is a method for measuring three-dimensional internal residual stress distribution described in

[0021] Claim 6 The invention described in 10. The method of claim 1, wherein a filtering process is performed to remove errors from the calculation results in the unreleased internal residual stress calculation step. 5 1. A method for measuring a three-dimensional internal residual stress distribution according to any one of claims 1 to 9.

[0022] Claim 7 The invention described in The filtering process is a polynomial approximation filtering process or a Gaussian filtering process. 6 This is a method for measuring three-dimensional internal residual stress distribution described in

[0023] Claim 8 The invention described in 3. The method according to claim 1, further comprising, after the three-dimensional internal residual stress calculation step, a mapping step of mapping the calculation results in the three-dimensional internal residual stress calculation step. 7 1. A method for measuring a three-dimensional internal residual stress distribution according to any one of claims 1 to 9. [Effects of the Invention]

[0024] According to the present invention, a more efficient and simple method for measuring three-dimensional internal residual stress can be provided. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram illustrating measurement of internal residual stress distribution by a conventional contour method. [Figure 2] FIG. 10 is a diagram illustrating a thermal load history for a model used in a simulation. [Figure 3] FIG. 10 is a diagram illustrating the correlation between stress values calculated based on Case A (horizontal axis) and stress values calculated based on Case D (vertical axis) in a simulation. [Figure 4] This is a diagram comparing ΔσXX+σXX', ΔσYY+σYY', ΔσZZ+σZZ', and ΔτXY+τXY' obtained in the simulation with σXX, σXX, σXX, and τXY. [Figure 5] FIG. 10 is a diagram showing the internal residual stress distribution obtained in the simulation. [Figure 6] FIG. 2 is a diagram illustrating measurement points according to an embodiment of the present invention. [Figure 7] FIG. 10 is a diagram showing a stress distribution obtained in one embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing a mapping result obtained in one embodiment of the present invention. [Figure 9] FIG. 1 is a diagram illustrating a processing flow according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described below based on the embodiments. However, the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope of the present invention.

[0027] [1] About the present invention The present inventors have been conducting extensive research into solving the problem of the present invention, which is to provide a more efficient and simple method for measuring three-dimensional internal residual stress, and have focused on the contour method, which has not previously been considered for application to measuring three-dimensional internal residual stress distribution.

[0028] 1. Contour method The contour method is a measurement method that has attracted attention in recent years. It involves cutting a component and measuring the residual stress perpendicular to the cut surface. It has been proposed in publications such as US6470756B1 and JP2020-41918A as a measurement method that requires little preparation time and, due to its clear theory, allows measurements to be performed in a short time.

[0029] Figure 1 is a schematic diagram explaining the measurement of internal residual stress distribution using the conventional contour method, showing how the analysis progresses from (a) to (d). In Figure 1, the direction perpendicular to the cut surface is the Z axis, and the directions parallel to the cut surface are the X and Y axes.

[0030] First, as shown in Figure 1(a), a cylindrical member is cut at the center in the height direction, and then divided into two parts as shown in Figure 1(b). As a result, residual internal stress is released at the cut surface, and deformation occurs in the direction perpendicular to the cut surface (Z-axis direction), as shown in Figure 1(c). The force required to restore this deformation corresponds to the released internal stress, so the reverse displacement corresponding to the displacement of the component perpendicular to the cut surface that occurs with this stress release is applied to the cut surface of the finite element analysis mesh that forms the cut surface, and the stress component perpendicular to the cut surface is calculated. This calculation is carried out over the entire cut surface, and the internal residual stress distribution (σ) in the Z-axis direction over the entire cut surface is obtained, as shown in Figure 1(d). ZZ ) can be obtained.

[0031] As such, the contour method requires only one cutting operation and has a clear theory for determining the internal residual stress distribution, allowing for highly accurate measurements without requiring much time for preparation and measurement.

[0032] However, this contour method has traditionally been considered to be basically only capable of measuring residual stress in the direction perpendicular to the cut surface (Z-axis direction), and is not a method for measuring three-dimensional internal residual stress distribution.

[0033] For this reason, if one were to apply this method to measuring three-dimensional internal residual stress distribution, it would be necessary to cut the specimen so as to obtain cross sections perpendicular to the X, Y, and Z axes, and then perform measurements on the results in three dimensions. Considering the need to prepare many test specimens, this method cannot be applied to measurements that can be made in a short time.

[0034] 2. Application to the present invention However, the inventor noticed that the deformation occurring in the direction perpendicular to the cut surface (Z-axis direction) was not uniform, and suspected that this deformation was due not only to residual stress in the direction perpendicular to the cut surface (Z-axis direction), but also to residual stress in the direction parallel to the cut surface (X-axis-Y-axis direction).Instead of the conventional finite element analysis that targeted only the Z-axis, the inventor performed finite element analysis targeting the X-axis, Y-axis, and Z-axis.As a result, it was confirmed that residual stress was also released in the direction parallel to the cut surface (X-axis-Y-axis direction).

[0035] However, the residual stress released in the direction parallel to the cut surface (X-axis-Y-axis direction) did not match the known residual stress generated by the pre-existing thermal history.

[0036] The inventors suspected that the discrepancy in stress in the direction parallel to the cut surface (X-axis-Y-axis direction) was caused by a portion of the residual stress before cutting remaining on the cut surface without being released, and so they measured the stress on the cut surface. When the results were combined with the results measured by the contour method, they found that there was good agreement with the "known residual stress" mentioned above, which led to the completion of the present invention.

[0037] [2] Embodiments of the present invention The present invention will be described in detail below based on specific embodiments.

[0038] As described above, the present invention is a method for measuring three-dimensional internal residual stress distribution, which determines the three-dimensional internal residual stress distribution by adding up the released residual stresses in the direction perpendicular to the cut surface (Z-axis direction) and the direction parallel to the cut surface (X-axis-Y-axis direction) obtained using the contour method, and the unreleased residual stress remaining on the cut surface.

[0039] 1. Usefulness of the present invention First, the usefulness of the method for measuring three-dimensional internal residual stress distribution according to the present invention will be explained based on the results of simulations.

[0040] (1) Test specimen First, a cylindrical member with dimensions of 80 mm (diameter) x 240 mm (height) and the physical properties shown in Table 1 was assumed as the test specimen (hereinafter also referred to as the "model"). Note that this model is divided into two regions, the central part (Part 1) and the peripheral part (Part 2), according to the magnitude of the internal residual stress to be released, i.e., the thermal expansion coefficient.

[0041] [Table 1]

[0042] Next, this model was subjected to heat treatment to apply a thermal load history, as shown in Figure 2, and this was used as the measurement object. That is, a thermal elastic-plastic analysis was performed on the model using a temperature load that involved heating the model from 0°C to 800°C in 60 seconds, and then cooling it from 800°C to 0°C in 60 seconds, thereby generating residual stress inside the model in advance.

[0043] (2) Measurement of three-dimensional internal residual stress distribution Next, the measurement of the three-dimensional internal residual stress distribution in the test specimen was simulated by numerical experiments, following the steps shown below.

[0044] (a)STEP1 First, the three-dimensional internal residual stress distribution in the model before cutting, specifically, the internal residual stress distribution (σ XX , σYY , σ ZZ , τ XY ) was calculated by a known thermo-elastic-plastic analysis. At this time, it was considered that the model was in a state before cutting. The obtained results correspond to the "pre-generated residual stress" mentioned above.

[0045] (b) STEP 2 Next, the model was cut at the center in the height direction, and the residual stress on the surface (cut surface) of the model after cutting, that is, the residual stress that remained after cutting (unreleased internal residual stress), was calculated as the internal residual stress distribution (σ XX ', σ YY ', σ ZZ ', τ XY ') was calculated by known elastic analysis.

[0046] The cross-sectional deformation at this time is brought about by the release of residual stress in the STEP 1 state.

[0047] (c)STEP3 Next, the residual stress released by cutting (released internal residual stress) was calculated using the contour method. Specifically, the residual stress distribution (Δσ ZZ , Δσ XX , Δσ YY , Δτ XY ) was calculated based on finite element analysis. Specifically, the final deformation state in STEP 2 was given as shape data (mesh data in finite element analysis), and a reverse displacement corresponding to the displacement calculated in STEP 2 in a stress-free state was forcibly given. This allows the stress state before cutting to be reproduced.

[0048] In this case, the following four cases can be set as methods for applying reverse displacement: Case A applies the reverse displacement of the X, Y, and Z displacements that occurred in STEP 2 to all nodes of the mesh data; Case B applies the reverse displacement of the X, Y, and Z displacements that occurred in STEP 2 to surface nodes; Case C applies the reverse displacement of the X, Y, and Z displacements that occurred in STEP 2 to cutting plane nodes; and Case D applies the reverse displacement of the cutting plane normal direction (Z direction displacement) that occurred in STEP 2 to cutting plane nodes.

[0049] However, when the inventors conducted experiments by applying reverse displacement according to each of these four cases, they found that there was almost no difference in the calculation results (stress values) regardless of the way the case was applied.

[0050] Figure 3 illustrates the correlation between stress values calculated based on Case A and stress values calculated based on Case D. It shows the results of a correlation analysis after plotting stress values for the same element. In Figure 3, the horizontal axis represents the stress value (MPa) calculated based on Case A, and the vertical axis represents the stress value (MPa) calculated based on Case D. Circles are placed at coordinate positions corresponding to the stress values for Case A and Case D calculated for the same element. An approximate equation is calculated for all the results indicated by the circles using the least squares method, and the result is plotted as an approximate straight line.

[0051] As shown in Figure 3(a) to (d), the slope of the approximation line is Δσ ZZ , Δσ XX , Δσ YY , Δτ XY In both cases, the value is nearly 1.00, and it can be seen that there is almost no difference in the stress values obtained based on either Case A or Case D.

[0052] And this result is Δσ XX , Δσ YY , Δτ XYIn the calculation of Δσ, instead of giving inverse displacements in all directions as in Case A, the inverse displacement of the displacement normal to the cutting plane (Z-direction displacement) generated in STEP 2 was given at the cutting plane nodes as in the conventional contour method (Case 4). XX , Δσ YY , Δτ XY This shows that it is possible to calculate Δσ ZZ , Δσ XX , Δσ YY , Δτ XY It turns out that it is possible to find

[0053] (d) STEP 4 Next, add the results from STEP 2 and STEP 3 together to obtain Δσ XX +σ XX ', Δσ YY +σ YY ', Δσ ZZ +σ ZZ ', Δτ XY +τ XY ', and the result in STEP 1 (σ XX , σ XX , σ XX , τ XY ) compared with

[0054] Figure 4 shows the results of this comparison in the X-axis direction (the area enclosed in a box in Figure 5), where (a) is the σ XX , (b) is σ YY , (c) is σ ZZ , (d) is τ XY In each figure, the horizontal axis represents the distance from the center (mm), the vertical axis represents the stress value (MPa), the square plots represent the stress value (MPa) obtained in STEP 1, and the circle plots represent the stress value (MPa) obtained by adding together the results obtained in STEP 2 and STEP 3.

[0055] From FIG. 4, it can be seen that the stress value obtained in STEP 1 and the stress value obtained by adding together the results obtained in STEP 2 and STEP 3 are in good agreement, confirming the usefulness of the present invention.

[0056] Then, by performing the processes in STEP 2 and STEP 3 and adding up the obtained values over the entire cut surface, the three-dimensional internal residual stress distribution of the model shown in FIG. 5 can be obtained.

[0057] In the above, the (X, Y, Z) coordinate system has been used as the coordinate system for explanation. However, in the case of a cylindrical member, the (r, θ, z) coordinate system may also be used. Based on the relationship of X=r cosθ and Y=r sinθ, the results obtained in the (r, θ, z) coordinate system can be easily converted into results in the (X, Y, Z) coordinate system.

[0058] 2. Specific Embodiments The usefulness of the present invention has been confirmed by simulation, and a specific embodiment will now be described.

[0059] The method for measuring a three-dimensional internal residual stress distribution according to the present embodiment includes the steps of: (1) A cutting process in which a component is cut into two pieces. (2) A flatness measurement process for measuring the flatness of the cut surface of the cut piece. (3) A released internal residual stress calculation step for three-dimensionally calculating the released internal residual stress at the cut surface based on the measured planar state. (4) A process for calculating unreleased internal residual stresses that are not completely released at the cut surface and remain within the cut surface. (5) a three-dimensional internal residual stress calculation process in which the released internal residual stress and the unreleased internal residual stress calculated in the released internal residual stress calculation process and the unreleased internal residual stress calculation process are summed up to calculate a three-dimensional internal residual stress distribution. Each step will be explained below.

[0060] (1) Cutting process First, the member to be measured is cut using, for example, laser discharge. For cutting, it is preferable to use, for example, a wire with a diameter of 0.2 to 0.5 mm.

[0061] As a result, the internal residual stress that had been generated is released at the cut surface, and irregularities occur at the cut surface due to elastic deformation.

[0062] (2) Planar condition measurement process Next, the planar state of the cut surface is measured. Specifically, a three-dimensional measuring machine such as a laser displacement meter, a three-dimensional coordinate measuring machine, or a non-contact optical scanner (specifically, for example, a Keyence VL-350 / VL-370 / VL360) is used to measure the degree of unevenness of the cut surface in the direction normal to the cut surface, i.e., the displacement in the Z-axis direction. Note that the measurement is performed, for example, at intersections (nodes) formed when the cut surface is divided at predetermined intervals in the X and Y directions, as shown in FIG. 6.

[0063] This allows the measured data to be output in large quantities (hundreds of thousands to millions of points) as digital data that combines the coordinates of the cross section and the height of the unevenness, and the shape of the measurement object can be approximated using a finite element model.

[0064] Since the measurement values contain measurement errors, it is preferable to apply a filtering process to the height data to eliminate the measurement errors. The specific filtering process is not particularly limited and may be selected appropriately taking into consideration the reliability of the measurement values at the end points, but a polynomial approximation filter or a Gaussian filter is preferably used.

[0065] (3) Released internal residual stress calculation process Next, based on the measured flat state, the height data obtained at the nodes of the cut surface of the finite element model is returned to 0. In other words, a forced displacement is applied to return the unevenness that occurred due to stress release on the cut surface to a flat surface, and finite element analysis is performed to calculate the released internal residual stress (Δσ ZZ , Δσ XX , Δσ YY , Δτ XY ) is found.

[0066] (4) Unrelieved internal residual stress calculation process In the above process, all residual stress in the direction perpendicular to the cut surface (Z-axis direction) is released, but as mentioned above, all residual stress in the direction parallel to the cut surface (X-axis-Y-axis direction) is not released.

[0067] Next, we will determine the unreleased internal residual stress remaining in the cut surface. Here, we will calculate the internal residual stress (σ XX ', σ YY ', τ XY Since the residual stress in the Z-axis direction is all released, it is preferable to measure and calculate it using a conventional X-ray diffraction method (for example, a measuring device such as "μ-X360" manufactured by Pulstec Industrial Co., Ltd.). ZZ ' is 0.

[0068] In this case, it is preferable to perform electrolytic polishing on the cut surface prior to measurement to remove the influence of cutting. Also in this step, it is preferable to perform filtering using a polynomial approximation filter or a Gaussian filter to eliminate measurement errors.

[0069] (5) Three-dimensional internal residual stress calculation process Next, the released internal residual stress and the unreleased internal residual stress calculated in the released internal residual stress calculation process and the unreleased internal residual stress calculation process are added together as shown in the following formula to obtain the three-dimensional internal residual stress distribution (σ XX , σ YY , σ ZZ , τ XY ) is calculated as σ XX =Δσ XX +σ XX ' σ YY =Δσ YY +σ YY ' σ ZZ =Δσ ZZ +σ ZZ '(However, σ ZZ '=0) τ XY = ΔτXY +τ XY '

[0070] Figure 7 shows the results of this summation on the X axis, where (a) is σ XX , (b) is σ YY , (c) is σ ZZ , (d) is τ XY The horizontal axis represents the distance from the origin (mm), and the vertical axis represents stress (MPa). By adding these values up over the entire cross section, the overall three-dimensional internal residual stress distribution can be determined.

[0071] At this time, the data is aligned so that the released internal residual stress and the unreleased internal residual stress at the same measurement position are added together. Specifically, as mentioned above, the three-dimensional shape measurement data (released internal residual stress) on the cut surface of the measurement object is composed of digital data of positions and heights at hundreds of thousands to millions of points. When the height data is statistically processed, assuming that the distribution is approximately normal, there will be a group of data that is quite far from the median (more than three times the standard deviation from the median). This group of data is located on the periphery of the cut surface, so this is used to align the cut surface of the finite element model with the three-dimensional measurement data.

[0072] (6) Mapping process In this embodiment, it is preferable to further include a mapping step of mapping the results obtained in the three-dimensional internal residual stress calculation step. Figure 8 shows mapping based on the results obtained over the entire cut surface, where (a) shows mapping in the XX direction, (b) in the YY direction, (c) in the ZZ direction, and (d) in the XY direction. XX , Δσ YY , Δσ ZZ , Δτ XY Centered on σ XX ', σ YY ', τ XY By adding ', the right side σ XX , σ YY , σ ZZ , τ XYWe are looking for...

[0073] As shown in Figure 8, by performing this type of mapping, the integrated data can be visualized, making it easy to understand the three-dimensional internal residual stress distribution.

[0074] 3. Systematization of calculation processing In this embodiment, it is preferable that the calculation processes for the above steps (3) to (6) be systematized in accordance with the content of each process.

[0075] Figure 9 is a diagram explaining the flow of the systemized calculation process, with the upper left side showing the process flow for (3) the released internal residual stress calculation process, and the upper right side showing the process flow for (4) the unreleased internal residual stress calculation process. The results of each process are then combined to calculate and map three-dimensional internal residual stress, as shown in the lower part.

[0076] Specifically, as shown in the upper left, the displacement in the Z-axis direction measured in the flatness measurement process is input, filtered as necessary, and then converted into stress analysis data (Δσ ZZ , Δσ XX , Δσ YY , Δτ XY ) is created.

[0077] On the other hand, as shown in the upper right, the unreleased internal residual stress (σ XX ', σ YY ', τ XY ') is input, filtered if necessary, and then created as an unrelieved residual stress file.

[0078] Next, the stress analysis data (Δσ ZZ , Δσ XX , Δσ YY , Δτ XY ) and the unreleased residual stress file (σ XX ', σ YY ', τ XY') are summed up, and as shown in the center of the bottom row, stress analysis is performed. Based on the results, mapping is performed, and the result is the three-dimensional internal residual stress distribution (σ XX , σ YY , σ ZZ , τ XY ) is output. The figure on the right side of the bottom row shows the output σ XX and similarly, σ YY , σ ZZ , τ XY can also be output.

[0079] 4. Effects of this embodiment As described above, according to this embodiment, σ XX , σ YY , σ ZZ , τ XY Therefore, it is possible to measure three-dimensional internal residual stress efficiently and easily.

Claims

1. A method for measuring a three-dimensional internal residual stress distribution in a measurement target member, comprising: a cutting step of cutting the member into two cut pieces; a planar state measuring step of measuring a displacement of the cut surface in a direction normal to the cut surface as a planar state of the deformation occurring on the cut surface of the cut piece; a released internal residual stress calculation step of three-dimensionally calculating the released internal residual stress at the cut surface by finite element analysis using a contour method based on the measured planar state; an unreleased internal residual stress calculation step of calculating, by elastic analysis, unreleased internal residual stress that is not completely released at the cut surface and remains within the cut surface; a three-dimensional internal residual stress calculation step of adding up the released internal residual stress and the unreleased internal residual stress calculated in the released internal residual stress calculation step and the unreleased internal residual stress calculation step to calculate a three-dimensional internal residual stress distribution, A method for measuring three-dimensional internal residual stress distribution, characterized in that the released internal residual stress calculation step is a step of calculating the released internal residual stress by applying a forced displacement in the opposite direction corresponding to the deformation occurring on the cut surface to a finite element model forming the cut surface of the cut piece.

2. 2. The method for measuring a three-dimensional internal residual stress distribution according to claim 1, wherein a filtering process is performed to remove errors from the calculation results in the released internal residual stress calculation step.

3. 3. The method for measuring a three-dimensional internal residual stress distribution according to claim 2, wherein the filtering process is a polynomial approximation filtering process or a Gaussian filtering process.

4. 4. The method for measuring a three-dimensional internal residual stress distribution according to claim 1, wherein the unreleased internal residual stress calculation step is a step of calculating the unreleased internal residual stress using a non-destructive surface residual stress measurement method.

5. 5. The method for measuring a three-dimensional internal residual stress distribution according to claim 4, wherein the non-destructive surface residual stress measurement method is an X-ray diffraction method.

6. 6. The method for measuring a three-dimensional internal residual stress distribution according to claim 1, wherein a filtering process is performed to remove errors from the calculation results in the unreleased internal residual stress calculation step.

7. 7. The method for measuring a three-dimensional internal residual stress distribution according to claim 6, wherein the filtering process is a polynomial approximation filtering process or a Gaussian filtering process.

8. 8. The method for measuring a three-dimensional internal residual stress distribution according to claim 1, further comprising, after the three-dimensional internal residual stress calculation step, a mapping step of mapping the calculation results in the three-dimensional internal residual stress calculation step.

Images