Strain amount measuring device, strain amount measuring method, and program

Abstract

A strain amount measuring device 1 comprises: a total strain amount determining unit 11 that determines a distribution [Expression 1] of each component of a total strain amount during loading or after unloading of a material; and an elastic strain amount calculating unit 12 that calculates an eigen strain amount [Expression 2] after unloading of the material. The elastic strain amount calculating unit 12 subjects the total strain amount to an inverse Fourier transform [Expression 5] using a 6×6 matrix [Expression 4] defined by an elastic constant Cijkl and a wave number k [Expression 3], to thereby calculate an eigen strain amount, and then calculates an elastic strain amount [Expression 6].

Description

Strain measurement device, strain measurement method, and program

[0001] The present invention relates to a strain amount measuring device, a strain amount measuring method, and a program.

[0002] One technique for displaying the stress distribution on a sample surface involves calculating the stress at each pixel position from images of the sample surface before loading, during loading, and after unloading, and displaying the calculated stress distribution at each pixel position (see, for example, Patent Document 1).

[0003] A method for measuring the distribution of strain due to deformation of a material surface is the Digital Image Correlation Method (hereinafter referred to as the "DIC method") (see, for example, Patent Document 2).

[0004] International Publication No. WO2020 / 262087 International Publication No. WO2015 / 008404

[0005] The DIC method is a technique for analyzing the deformation behavior of material surfaces. It calculates the displacement and strain at each location of the material by tracing the location of a pattern that is similar to the image of the material before deformation from the image of the material after deformation. This makes it possible to obtain the strain distribution on the material surface. This is particularly effective for analyzing non-uniform deformation.

[0006] The strain measured by applying the DIC method when a material such as metal is deformed by applying an external force (load) is called total strain. Total strain is classified into two types: elastic strain, which contributes to stress, and strain that does not contribute to stress (hereinafter referred to as "eigen strain" or "eigenstrain"). Eigen strain is strain that does not contribute to stress no matter how large it is, and is typified by plastic strain. Other examples of eigen strain include thermal expansion strain, transformation strain, and misfit strain. If it is possible to measure only the value of elastic strain out of total strain, excluding eigen strain, it can, in principle, be applied to stress distribution calculations.

[0007] If the deformation load is sufficiently small, the metallic material can be considered to return to its original state by reducing the load to zero (i.e., by unloading). At this point, the material is considered to be in the elastic region, where total strain is approximately equal to elastic strain. On the other hand, when deformation exceeds the elastic region and enters the plastic region, localized plastic deformation occurs within the material in addition to elastic deformation. When plastic deformation occurs, plastic strain, a type of eigenstrain, is introduced. Furthermore, the introduction of non-uniform plastic strain also leads to non-uniformity in the distribution of elastic strain. Therefore, in the plastic region, even if total strain is measured using the DIC method, the results cannot be used to consider the magnitude and distribution of elastic strain.

[0008] The technology described in Patent Document 1 captures images of the sample surface before loading, during loading, and after unloading, measures a first strain amount for each pixel position based on the correlation between the image before loading and the image after unloading, and a second strain amount for each pixel position based on the correlation between the image before loading and the image during loading, calculates stress for each pixel position based on the difference between the first strain amount and the second strain amount, and displays the calculated stress distribution at each pixel position. This technology is based on the idea that the difference between the strain during loading and after unloading corresponds to elastic strain, and that stress can, in principle, be calculated if elastic strain can be measured.

[0009] Since no external force is applied to the material after unloading, the average elastic strain and average stress of the material as a whole are zero. However, in actual materials, even after unloading, non-uniform elastic strain is thought to exist due to constraints from the internal structure in the microstructure. The stress resulting from such elastic strain accumulated in the material is called residual stress (internal stress after unloading). Measuring residual stress is essential for accurate stress evaluation of materials. However, the technology described in Patent Document 1 has the problem of being unable to measure residual stress because it measures the difference from the state after unloading (i.e., it assumes that the elastic strain distribution after unloading is uniformly zero).

[0010] In order to solve the above problems, a strain measuring device according to one embodiment of the present invention is provided for measuring the distribution of each component of the total strain of a material during loading or after unloading. The total strain determination part determines the elastic strain of the material. The elastic strain calculation unit calculates the elastic constant C ｉｊｋｌ and the wave number k A 6x6 matrix defined by Using the Fourier transform, the total strain is By executing Calculate.

[0011] In one embodiment, the strain measuring device may further include a stress calculation unit that calculates the stress occurring inside the material. By calculating the stress Calculate.

[0012] In one embodiment, the total strain amount determining unit may determine the total strain amount by measuring the strain amount in the depth direction using a three-dimensional DIC method.

[0013] In one embodiment, the total strain amount determining unit may determine the total strain amount by measuring the strain amount in the depth direction using a nanoindentation method.

[0014] Another aspect of the present invention is a method for measuring strain, which involves measuring the distribution of each component of the total strain of a material during loading or after unloading. The total strain determination step determines the elastic strain of the material. The elastic strain calculation step includes calculating the elastic constant C ｉｊｋｌ and the wave number k A 6x6 matrix defined by Using the Fourier transform, the total strain is By executing Calculate.

[0015] In an embodiment, the strain measurement method may further include a stress calculation step of calculating a stress occurring inside the material. By calculating the stress Calculate.

[0016] Another aspect of the present invention is a program that calculates each component of the total strain of a material after unloading. The total strain determination step determines the elastic strain of the material. The elastic strain calculation step calculates the elastic constant C ｉｊｋｌ and the wave number k A 6x6 matrix defined by Using the Fourier transform, the total strain is By executing Calculate.

[0017] In an embodiment, the program may further cause the computer to execute a stress calculation step of calculating stress occurring inside the material. By doing this, stress Calculate.

[0018] Any combination of the above components, and any transformation of the present invention into an apparatus, method, system, recording medium, computer program, etc., are also valid aspects of the present invention.

[0019] According to the present invention, it is possible to measure the residual stress and elastic strain after a load applied to a material is removed.

[0020] FIG. 1 is a graph showing the relationship between strain and stress when stress is applied to a material. FIG. 2 is a functional block diagram of a strain measurement device according to a first embodiment. FIG. 3 is a schematic diagram showing how the total strain amount of a material is measured using a three-dimensional DIC method. FIG. 4 is a schematic diagram showing how the total strain amount of a material is measured using a nanoindenter. FIG. 5 is a functional block diagram of a strain measurement device according to a second embodiment. FIG. 6 is a flowchart showing the processing steps of a strain measurement method according to a third embodiment. FIG. 7 is a flowchart showing the processing steps of a strain measurement method according to a fourth embodiment. FIG. 8 is a diagram showing the results of a verification experiment.

[0021] The present invention will be described below based on preferred embodiments with reference to the drawings. In the embodiments and modified examples, identical or equivalent components, steps, and members are designated by the same reference numerals, and redundant descriptions will be omitted where appropriate. The dimensions of the components in the drawings are enlarged or reduced as appropriate for ease of understanding. Some components that are not important for explaining the embodiments are omitted from the drawings. Terms including ordinal numbers such as "first" and "second" are used to describe various components, but these terms are used only to distinguish one component from another and do not limit the components.

[0022] Before describing specific embodiments, we will explain basic knowledge. Figure 1 shows the relationship between strain and stress when stress is applied to a material such as a metal. The horizontal and vertical axes represent strain (ε) and stress (σ), respectively.

[0023] When stress σ is applied to the material from the initial state A, σ≦σ Ｙ，Ｓ． The material undergoes elastic deformation in the range of stress σ Ｙ，Ｓ． is called the elastic limit. State A to state B is called the elastic region. The strain that occurs in the elastic region is called elastic strain. In the elastic region, the relationship between strain ε and stress σ is linear. In other words, the material changes along a straight line AB (load line) from state A to state B. The slope of the load line is equal to Young's modulus E.

[0024] After passing state B, σ>σ Ｙ，Ｓ．When this occurs, the material undergoes plastic deformation and enters the plastic region (state B to state C). At this time, the relationship between strain ε and stress σ is generally nonlinear. In other words, the material changes from state B to C along curve BC. Point B, where the state of the material changes from the elastic region to the plastic region, is called the yield point. Since strain in the plastic region is the addition of plastic strain to elastic strain, the slope of stress σ relative to strain ε in the plastic region is gentler than in the elastic region.

[0025] When the stress is reduced to zero (unloaded) at state C, the material state changes, on average, along the unloading line indicated by the dotted line CD, returning to state D. The slope of this unloading line is equal to the slope of the loading line in the elastic region (i.e., Young's modulus E). When unloading is complete, the elastic strain ε Ｅｌ is elastically recovered, and the plastic strain ε Ｐ On the other hand, the strain ε occurring in the plastic region is the elastic strain ε Ｅｌ and plastic strain ε Ｐ It is the sum of.

[0026] In state D, the average total strain is plastic strain ε Ｐ However, it is believed that locally, non-uniform elastic strain exists due to constraints from the internal structure of the material on the non-uniformly introduced plastic strain. The stress resulting from the elastic strain stored in such a material is called residual stress (internal stress after unloading). The effect of residual stress is thought to become more significant as the amount of plastic deformation and its non-uniformity increase.

[0027] Unless otherwise specified, the subscripts i, j, k, l, m, and n are natural numbers from 1 to 3 (i, j, k, l, m, n = 1, 2, 3). In addition, according to Einstein's contraction notation, when the subscripts overlap in the same term, the sum of the subscripts is taken. For example, σ ｉｊ The subscript is sometimes omitted and written as σ. is the total strain average and total strain variation It is expressed as the sum of the following: Total strain variation and displacement u ｉ , uｊ The following relationship holds between Total strain average In the stress-applied state (state C in FIG. 1), When the stress is released (state D in Figure 1), It coincides with the eigen strain is the total strain from elastic strain is defined as follows:

[0028] The relationship between stress (σ) and elastic strain (ε) is given by Hooke's law: Here, C ｉｊｋｌ are the elastic constants. For a material at rest, the following equation of mechanical equilibrium holds:

[0029] In the case of metallic materials, the elastic constants are uniquely determined for each crystal grain (i.e., each region with a common crystal structure and crystal orientation). The elastic constants for each crystal structure are determined mainly through experiments and calculations on single crystals, and are stored as literature values ​​in large databases such as the following: MatNavi (https: / / mits.nims.go.jp / index.html)

[0030] Assuming an isotropic elastic body, the elastic constants do not vary with crystal orientation. However, when defining the elastic constants of individual crystal grains, it is necessary to consider the crystal orientation. In this case, it is better to perform an appropriate coordinate transformation on the literature values.

[0031] Total strain ε after unloading (state D in Figure 1) Ｃ is expressed as follows: ＊ and the local elastic strain ε Ｅｌ It is expressed as the sum of and. In this case, Hook's law is as follows: In this case, Hooke's law alone does not provide the local elastic strain ε Ｅｌ Since the distribution of is not available, it cannot be solved, but the equation of mechanical equilibrium to total strain ε Ｃ and eigen strain ε ＊The relationship between By incorporating the above-mentioned micromechanics approach, the present inventors have discovered that if information on total strain can be obtained using, for example, a DIC method, it is possible to measure elastic strain and stress from the information.

[0032] Total strain variation is the eigen strain from where is the elastic constant C ｉｊｋｌ and the wave number k, which is a 6×6 matrix defined as follows:

[0033] Micromechanical formula for total strain variation By inverse Fourier transform of of Furthermore, after using this result to obtain the elastic strain, the stress can be obtained.

[0034] The above calculation will be explained in detail below. The following conditional expression is assumed: Hooke's law Partial differential relationship between displacement and total strain Equation of mechanical equilibrium using stress derivatives Fourier representation of displacement (k is the wave vector)

[0035] formula From this, the following relationship is obtained: formula to Applying the Fourier representation of and comparing the absolute values ​​of both, we get Therefore, This becomes:

[0036] formula to Applying the relationship, we get: Here is the formula Applying the Fourier representation of where is the elastic constant C ｉｊｋｌ and the wave number k, which is a 6×6 matrix defined as follows:

[0037] formula By performing an inverse Fourier transform of and eigen strain The relationship can be obtained as follows: At this time, the stress is obtained by Hooke's law as follows:

[0038] 2 is a functional block diagram of a strain measuring device 1 according to a first embodiment. The strain measuring device 1 includes a total strain determining unit 11 and an elastic strain calculating unit 12.

[0039] The total strain amount determining unit 11 determines the distribution of each component of the total strain amount during loading or after unloading of the material. Determine where: Among them, the one with i = j is the normal strain component, and the one with i ≠ j is the shear strain component. is a symmetric tensor, so Therefore, the total distortion amount determining unit 11 determines the six total distortion amount components as unknowns. It is sufficient to determine the following.

[0040] The total strain amount determining unit 11 may determine the total strain amount including the depth direction based on, for example, a plurality of images of the material.

[0041] The total strain determination unit 11 transmits each component of the determined total strain to the elastic strain calculation unit 12. The elastic strain calculation unit 12 calculates the elastic strain of the material based on each component of the received total strain. Specifically, the elastic strain calculation unit 12 calculates the total strain as follows: After obtaining the total strain variation, the elastic constant C ｉｊｋｌ and the wave number k A 6x6 matrix defined by The total strain amount is subjected to an inverse Fourier transform using By executing Calculate.

[0042] The average value of all strains in Eq. is ε Ｃ ｉｊ In this case, the average value of total strain is calculated as the average value of (x) when stress is applied (state C in Figure 1). and in the unloaded state (state D in Figure 1), matches. The average stress in the table is the value output from a tensile testing machine or the like during deformation. gives the average value of the eigen strain.

[0043] Although FIG. 2 shows an imaging device (camera) for observing the total strain amount of the material and a display device (display) for displaying the calculated elastic strain amount, these are not essential to this embodiment.

[0044] [Determination of Total Strain Amount by Three-Dimensional DIC Method] As an example, the total strain amount determiner 11 may determine the total strain amount by measuring the strain amount in the depth direction by three-dimensional DIC method. Figure 3 shows a schematic diagram of how the total strain amount of the material M is measured by three-dimensional DIC method.

[0045] The 3D DIC method uses two cameras C1 and C2 to photograph the material M, and calculates the correlation between the images taken simultaneously from two different directions to measure the displacement in the depth direction based on the principle of triangulation. By using the 3D DIC method to observe the deformation process, the strain component in the depth direction can be calculated. and the plane strain components can be obtained simultaneously.

[0046] In the example of Fig. 3, two cameras C1 and C2 are used to photograph the material M from two directions, but the photographing method is not limited to this. For example, one camera may be used to obtain images from different directions while tilting the material to be observed.

[0047] When analyzing images using the 3D DIC method, it is even more advantageous to obtain a flat surface of the material by polishing, to apply a pattern to the surface by coating it with colloidal particles, or to create a grid pattern on the material surface using an FIB or the like.

[0048] [Determination of Total Strain Amount by Nanoindentation Method] As another example, the total strain amount determination unit 11 may determine the total strain amount by measuring the strain amount in the depth direction by nanoindentation method. Figure 4 shows a schematic diagram of how the total strain amount of the material M is measured using the nanoindenter NI.

[0049] Nanoindentation is a technique for measuring the composite elastic modulus and hardness by simultaneously measuring the load (force) and displacement (push distance) when a sharp indenter is pressed into a material, thereby obtaining a load-displacement curve. By using this technique, the three-dimensional shape of the surface can be obtained from the coordinates of the indenter tip by scanning the indenter over the material surface. The strain component in the depth direction obtained by nanoindentation in this way and, for example, the plane strain component obtained by the 2D DIC method By integrating these, each component of the desired total strain can be obtained.

[0050] According to this embodiment, it is possible to measure the residual stress and elastic strain after the load applied to the material is removed.

[0051] [Second embodiment] Figure 5 is a functional block diagram of a strain amount measuring device 2 according to a second embodiment. The strain amount measuring device 2 includes a total strain amount determining unit 11, an elastic strain amount calculating unit 12, and a stress calculating unit 13. That is, the strain amount measuring device 2 includes the stress calculating unit 13 in addition to the configuration of the strain amount measuring device 1 in Figure 2. The stress calculating unit 13 calculates the stress occurring inside the material. The other configurations and operations of the strain amount measuring device 2 are common to the strain amount measuring device 1.

[0052] The stress calculation unit 13 By calculating the stress Calculate.

[0053] According to this embodiment, in addition to elastic strain, stress including residual stress after a load applied to a material is released can be measured.

[0054] 6 is a flowchart showing the procedure of a strain measurement method according to a third embodiment of the present invention, which includes step S1 of determining the distribution of each component of the total strain of a material during loading or after unloading, and step S2 of calculating the elastic strain of the material.

[0055] In step S1, the method calculates the distribution of each component of the total strain of the material during loading or after unloading. The total strain amount may be determined using the three-dimensional DIC method or the nanoindentation method, as described above.

[0056] In step S2, the method calculates the elastic strain of the material. Specifically, in step S2, the total strain is calculated as follows: After obtaining the total strain variation, the elastic constant C ｉｊｋｌ and the wave number k A 6x6 matrix defined by Using the Fourier transform, the total strain variation is By executing Calculate.

[0057] The average value of all strains in Eq. is ε Ｃ ｉｊ In this case, the average value of total strain is calculated as the average value of (x) when stress is applied (state C in Figure 1). and in the unloaded state (state D in Figure 1), matches. The average stress in the table is the value output from a tensile testing machine or the like during deformation. gives the average value of the eigen strain.

[0058] Although FIG. 5 shows an imaging device (camera) for observing the total strain of the material and a display device (display) for displaying the calculated elastic strain and stress, these are not essential to this embodiment.

[0059] According to this embodiment, it is possible to measure the residual stress and elastic strain after the load applied to the material is removed.

[0060] [Fourth Embodiment] Figure 7 is a flowchart showing the processing steps of a strain measurement method according to a fourth embodiment. This method includes step S1 of determining the distribution of each component of the total strain of a material during loading or after unloading, step S2 of calculating the elastic strain of the material after unloading, and step S3 of calculating stress. That is, this strain measurement method includes step S3 of calculating stress in addition to the processing of the strain measurement method of Figure 6. Step S3 of calculating stress calculates the stress generated inside the material. The other processing steps of this method are common to the strain measurement method of Figure 6.

[0061] In step S3 of calculating the stress, By calculating the stress Calculate.

[0062] According to this embodiment, in addition to elastic strain, stress including residual stress after a load applied to a material is released can be measured.

[0063] [Fifth Embodiment] The fifth embodiment is a program. Fig. 6 is a flowchart showing the procedure of processing executed by this program. This program causes a computer to execute step S1 of determining the distribution of each component of the total strain amount of a material during loading or after unloading, and step S2 of calculating the elastic strain amount of the material.

[0064] In step S1, the distribution of each component of the total strain amount during loading or after unloading of the material is calculated. The total strain amount may be determined using the three-dimensional DIC method or the nanoindentation method, as described above.

[0065] In step S2, the elastic strain of the material is calculated. Specifically, in step S2, the total strain is calculated as follows: After obtaining the total strain variation, the elastic constant C ｉｊｋｌ and the wave number k A 6x6 matrix defined by The total strain amount is subjected to an inverse Fourier transform using By executing Calculate.

[0066] The average value of all strains in Eq. is ε Ｃ ｉｊ In this case, the average value of total strain is calculated as the average value of (x) when stress is applied (state C in Figure 1). and in the unloaded state (state D in Figure 1), matches. The average stress in the table is the value output from a tensile testing machine or the like during deformation. gives the average value of the eigen strain.

[0067] According to this embodiment, the process of measuring the residual stress and elastic strain after the load applied to the material is removed can be implemented as a computer program.

[0068] [Sixth embodiment] Figure 7 is a flowchart showing the processing steps executed by this program. This program causes a computer to execute step S1 of determining the distribution of each component of the total strain of a material during loading or after unloading, step S2 of calculating the elastic strain of the material, and step S3 of calculating stress. That is, this program causes the computer to further execute step S3 of calculating stress in addition to the processing of the program in Figure 6. Step S3 of calculating stress calculates the stress occurring inside the material. The other processing steps of this method are common to the strain measurement method in Figure 6.

[0069] In step S3 of calculating the stress, By calculating the stress Calculate.

[0070] According to this embodiment, in addition to the elastic strain, a process for measuring the residual stress and elastic strain after the load applied to the material is released can be implemented as a computer program.

[0071] (Verification Experiment) The present inventors conducted an experiment to verify the usefulness of this embodiment, and the results are shown in FIG.

[0072] Figure 8(a) shows the results of a single-field observation of the metal structure. In the microstructure at e = 0.03 after unloading, the formation of band-like deformation-induced martensite, which is not observed at e = 0 before deformation, is observed. This region has a different (transformation) strain from the parent phase.

[0073] From the results in Figure 8(a), the total strain can be obtained using the DIC method, with the e = 0 point as the reference point. Figure 8(b) shows the xx components of total strain, elastic strain, and stress (residual stress) in a color map corresponding to a portion of Figure 8(a). The total strain distribution here was modeled by applying image processing to the experimental results obtained using the DIC method. The elastic strain and stress were calculated based on each component of total strain, assuming periodic boundary conditions (a state in which the same structure is infinitely continuous in the Z direction). Furthermore, the line profile along the line A-B-C in Figure 8(b) is shown in Figure 8(c).

[0074] In this case, when treating elastic strain and stress separately for components such as xx and xy, it is important to note that components other than xx (yy, zz, etc.) also have an effect. An actual calculation example is shown below.

[0075] In this experiment, μ = 31 GPa and λ = 138 GPa. ｉｊｋｌ The values ​​of are as follows (units are GPa): Elastic strain ε at point B in Figures 8(b) and 8(c) ｋｌ The value of is as follows: (ε １１ ,ε ２２ ,ε ３３ ,ε ２３ ,ε ３１ ,ε １２) = (-0.0021, 0.0089, -0.0071, -0.0024, -0.0011, 0.0124) From this, the stress σ at point B is ｉｊ is calculated as follows: Of these, σ １１ As shown in the right diagram of Figure 8(c), σ １１ = -0.17 GPa, which is a negative value.

[0076] On the other hand, the elastic strain ε between points A and B (on the deformation band) in Figures 8(b) and 8(c) ｋｌ The value of is as follows: (ε １１ ,ε ２２ ,ε ３３ ,ε ２３ ,ε ３１ ,ε １２ ) = (-0.0421, 0.0172, 0.0469, -0.0083, 0.0018, -0.0141) From this, the stress σij between points A and B is calculated as follows: Of these, σ １１ As shown in the right diagram of Figure 8(c), σ １１ = 0.43 GPa, which is a positive value.

[0077] Thus, for example, at point B, the strain ε １１ Although the stress σ (=-0.0021) is almost zero, １１ = (-0.17) takes a relatively large negative value. On the other hand, for example, between points A and B, the strain ε １１ (=-0.0421) takes a negative value, while ε ２２ (=0.0172) and ε ３３ (=0.0469) takes a positive value. At this time, the stress σ １１ = (0.43) is a positive value. １１ and σ １１ In this way, since there are cases that seem counterintuitive at first glance, it is thought that it is useful to obtain not only the strain distribution but also the stress distribution.

[0078] As described above, Figure 8(c) shows that the distribution patterns of total strain, elastic strain, and stress are different. In particular, stress has a negative value between the deformation bands (point B), suggesting that the stress of the parent phase acts in a direction that suppresses the tensile stress in the bilateral transformation bands. This has been difficult to confirm experimentally using conventional methods.

[0079] The present invention has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and treatment processes, and that such modifications are also within the scope of the present invention.

[0080] In the above embodiment, an example has been described in which the 3D DIC method is used to determine the total strain amount. In addition to the 3D DIC method, there are other methods that can similarly reconstruct the surface shape of a material based on the results of observation from different angles. For example, some commercially available software can perform calibration from three SEM (scanning electron microscope) images to construct a highly accurate surface shape. Since the surface shape corresponds to the displacement in the depth direction of the material, the strain based on the displacement can be calculated. can be obtained.

[0081] Such a modification provides the same functions and effects as the embodiment.

[0082] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present invention. A new embodiment resulting from the combination has the combined effects of each of the combined embodiments and modifications.

[0083] The method according to the present invention can be applied to a variety of materials including metals, and is useful for evaluating, selecting, and improving the performance of materials.

[0084] 1...Strain amount measuring device, 2...Strain amount measuring device, 11...Total strain amount determining unit, 12...Elastic strain amount calculating unit, 13...Stress calculating unit, S1...Step of determining the distribution of each component of the total strain amount during loading or after unloading of a material, S2...Step of calculating the elastic strain amount of a material, S3...Step of calculating stress, M...Material, NI...Nanoindenter, C1...Camera, C2...Camera.

Claims

1. Distribution of each component of the total strain during or after loading of the material a total strain determining unit for determining the elastic strain of the material; and an elastic strain amount calculation unit that calculates an elastic constant C ｉｊｋｌ and the wave number k A 6x6 matrix defined by The total strain amount is subjected to an inverse Fourier transform using By executing A strain measurement device characterized by calculating the following.

2. The material further includes a stress calculation unit that calculates stress occurring inside the material, and the stress calculation unit By calculating the stress 2. The strain measuring device according to claim 1, wherein the strain measuring device calculates the following:

3. A strain measurement device according to claim 1 or 2, characterized in that the total strain determination unit determines the total strain by measuring the strain in the depth direction using a three-dimensional DIC method.

4. Distribution of each component of the total strain during or after loading of the material a total strain determination step for determining the eigen strain of the material after unloading; and an eigen strain calculation step of calculating an elastic constant C ｉｊｋｌ and the wave number k A 6x6 matrix defined by The total strain amount is subjected to an inverse Fourier transform using By executing A strain measurement method comprising the steps of:

5. The method further includes a stress calculation step of calculating stress occurring inside the material, wherein the stress calculation step includes: By calculating the stress 5. The strain measurement method according to claim 4, further comprising the step of calculating the strain.

6. Distribution of each component of total strain during or after loading of the material a total strain determination step for determining the eigen strain of the material after unloading; and an eigen strain amount calculation step of calculating an elastic constant C ｉｊｋｌ and the wave number k A 6x6 matrix defined by The total strain amount is subjected to an inverse Fourier transform using By executing A program for calculating 7. The computer is further caused to execute a stress calculation step of calculating stress occurring inside the material, wherein the stress calculation step By calculating the stress 7. The program according to claim 6, wherein the program calculates:

Images