Stress and strain amount distribution display method, device, and program product

Abstract

The method for displaying the stress distribution on the surface of the sample includes: a step of taking images of the sample surface before loading, during loading, and after unloading (S4); a step of measuring a first strain at each pixel location based on the correlation between the image before loading and the image after unloading (S5); a step of measuring a second strain at each pixel location based on the correlation between the image before loading and the image during loading (S6); a step of calculating the stress at each pixel location based on the difference between the first strain and the second strain (S7); and a step of displaying the calculated stress distribution at each pixel location (S8).

Description

Technical Field

[0001] This invention relates to methods, apparatus, and procedures for displaying the distribution of stress and strain. Background Technology

[0002] As a method for determining the distribution of strain caused by deformation on the surface of a material, there is the digital image correlation (DIC) method (for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: International Publication No. WO2015 / 008404 Summary of the Invention

[0006] Summary of the invention

[0007] The problem that the invention aims to solve

[0008] Previously, it was believed that even if an external force (load) was applied to materials such as metals, causing them to deform, the material would return to its original state if the load was reduced to zero (unloading), provided the load was sufficiently small. That is, the deformation in this case was reversible, and the material remained within its elastic range overall. However, even within the elastic range of small loads, repeated loading and unloading can sometimes induce localized plastic deformation within the material. This localized plastic deformation can lead to dislocations in the metal lattice or localized microcracks, and it was thought that their accumulation would eventually cause fatigue failure. Therefore, measuring localized plastic deformation is crucial to understanding the causes of fatigue failure. However, it is difficult to measure such localized plastic deformation using conventional methods such as DIC.

[0009] The present invention was made in view of such a problem, and its object is to provide a method for displaying the distribution of local stress and strain caused by repeated loading and unloading of a material.

[0010] Solution for solving the problem

[0011] To address the aforementioned issues, one aspect of the present invention provides a method for repeatedly loading and unloading a sample and displaying the distribution of strain on the sample surface, comprising: taking images of the sample surface before loading and after unloading; measuring the strain at each pixel location based on the correlation between the images before loading and after unloading; and displaying the measured distribution of strain at each pixel location.

[0012] Another aspect of the present invention is also a method. This method involves repeatedly loading and unloading a sample and displaying the stress distribution on the sample surface, comprising: taking images of the sample surface before loading, during loading, and after unloading; measuring a first strain at each pixel location based on the correlation between the images before loading and after unloading; measuring a second strain at each pixel location based on the correlation between the images before loading and during loading; calculating the stress at each pixel location based on the difference between the first strain and the second strain; and displaying the calculated stress distribution at each pixel location.

[0013] Another aspect of the present invention is an apparatus. This apparatus is used to repeatedly load and unload a sample and display the stress distribution on the sample surface. It comprises: a photographic unit that captures images of the sample surface before loading, during loading, and after unloading; a strain measurement unit that measures a first strain at each pixel location based on the correlation between the images before loading and after unloading, and measures a second strain at each pixel location based on the correlation between the images before loading and during loading; a stress calculation unit that calculates the stress at each pixel location based on the difference between the first strain and the second strain; and a display unit that displays the calculated stress distribution at each pixel location.

[0014] Another aspect of the invention is a program. This program repeatedly loads and unloads a sample and displays the stress distribution on the sample surface. It causes a computer to perform the following steps: capturing images of the sample surface before loading, during loading, and after unloading; measuring a first strain at each pixel location based on the correlation between the images before loading and after unloading; measuring a second strain at each pixel location based on the correlation between the images before loading and during loading; calculating the stress at each pixel location based on the difference between the first and second strains; and displaying the calculated stress distribution at each pixel location.

[0015] It should be noted that any combination of the above-mentioned constituent elements, or any scheme that transforms the description of the present invention among devices, methods, systems, recording media, computer programs, etc., is also valid as a scheme of the present invention.

[0016] Invention Effects

[0017] According to the present invention, it is possible to display the distribution of local stress and strain caused by repeated loading and unloading of materials. Attached Figure Description

[0018] Figure 1 It is a coordinate graph that shows the relationship between strain and stress when stress is applied to a material.

[0019] Figure 2It is a coordinate graph showing the relationship between strain and stress when the stress is calculated based on total strain using the stress measurement method of the first embodiment.

[0020] Figure 3 This is a flowchart of the method of the first embodiment.

[0021] Figure 4 This is a flowchart of the method of the second embodiment.

[0022] Figure 5 This is a flowchart of the method of the third embodiment.

[0023] Figure 6 This is a flowchart of the method of the fourth embodiment.

[0024] Figure 7 This is a flowchart of the method of the fifth embodiment.

[0025] Figure 8 This is a flowchart of the method of the sixth embodiment.

[0026] Figure 9 This is a block diagram of the apparatus according to the seventh embodiment.

[0027] Figure 10 The frequency distribution of stress difference is displayed based on the method of the fourth embodiment. Detailed Implementation

[0028] Hereinafter, the present invention will be described based on preferred embodiments and with reference to the accompanying drawings. In the embodiments and modifications, the same or equivalent constituent elements, steps, and components are labeled with the same symbols, and repeated descriptions are appropriately omitted. Furthermore, the dimensions of the components in the drawings are appropriately enlarged or reduced for ease of understanding. Moreover, in the drawings, parts of components that are not important in explaining the embodiments are omitted. Furthermore, terms including ordinal numbers such as "first," "second," etc., are used to describe various constituent elements, but such terms are used only for the purpose of distinguishing one constituent element from other constituent elements, and the constituent elements are not limited by such terms.

[0029] Approximately 90% of mechanical component failures can be attributed to metal fatigue. Fatigue tests are conducted to study material fatigue failure; this involves repeatedly applying stress and displacement to test specimens, measuring the presence and number of repetitions until fracture occurs. The mechanism of metal fatigue failure is that repeated loading and unloading within the elastic region causes localized plastic deformation within the material. It is believed that this localized plastic deformation leads to dislocations in the metal lattice and localized microcracks, which, through their accumulation, eventually result in material fracture.

[0030] The primary cause of the localized plastic deformation described above can be considered as localized stress concentration associated with the complexity of the material's shape or the material's inherent inhomogeneity. Therefore, in order to observe or predict the occurrence of localized plastic deformation, it is desirable to be able to measure and display the localized stress distribution. However, while conventional DIC (Distributed Intensity Concentration) methods can measure the distribution of strain caused by deformation, they cannot directly measure the distribution of stress generated on the material. In particular, since the strain observed in the plastic region of the material includes both elastic and plastic strain, it is difficult to directly calculate the stress from the strain. Therefore, the inventors have considered a method for determining the stress by extracting only the elastic strain from the total strain observed in the plastic region. Before describing specific embodiments, firstly, refer to... Figure 1 and Figure 2 This explains the method of determining stress by taking only the elastic strain when the total strain includes both elastic and plastic strain.

[0031] Figure 1 This illustrates the relationship between strain and stress when stress is applied to materials such as metals. The horizontal and vertical axes represent strain and stress, respectively.

[0032] If σ is applied to the material Y Under the following stress, the material undergoes elastic deformation. In this case, the strain is proportional to the stress. That is, the material's state changes along the straight line OA (load line) from point O to point D. If the stress is reduced to zero (unload) from this state, the material returns to point O, and the strain also becomes zero. The region from point O to point A is usually called the elastic region, and the strain generated in the elastic region is called elastic strain. Furthermore, the maximum stress σ in the elastic region... Y This is called the elastic limit.

[0033] On the other hand, if an elastic limit σ is applied to the material... Y When the stress reaches the elastic region, the material enters the plastic region (the region from point A to point B). The point A where the material's state changes from the elastic region to the plastic region is called the yield point. As will be explained later, the strain in the plastic region is the sum of the elastic strain and the plastic strain; therefore, the slope of the stress relative to the strain in the plastic region is gentler than that in the elastic region. Moreover, if the stress is removed in the plastic region, the material's state returns to point C along the unloading line indicated by arrow BC. The slope of this unloading line is equal to the slope of the load line in the elastic region (i.e., Young's modulus E). When unloading is complete, the elastic strain e elastically recovers, and the plastic strain... Residual. The strain ε generated in the plastic region is the sum of elastic strain and plastic strain.

[0034] Hereinafter, the material is assumed to be an isotropic and homogeneous elastic body. (1) represents the one-dimensional relationship between elastic strain and stress, and (2) and (3) represent the two-dimensional relationship between elastic strain and stress.

[0035] [Formula 1]

[0036]

[0037] [Equation 2]

[0038]

[0039] [Formula 3]

[0040]

[0041] Here, E represents Young's modulus, ν represents Poisson's ratio, σ represents stress along the length, and e represents elastic strain along the length. 11 e represents the stress in the first direction. 11 σ represents the elastic strain in the first direction. 22 e represents the stress in the second direction. 22 This represents the elastic strain in the second direction.

[0042] As mentioned above, equations (1) to (3) all represent the relationship between stress and elastic strain. Therefore, in order to determine the stress based on the strain in the plastic region using these equations, it is necessary to remove the plastic strain from the observed total strain and only take out the elastic strain.

[0043] Figure 2 This is a coordinate graph showing the relationship between strain and stress when stress is measured based on total strain. The dashed line represents the theoretical straight line based on Young's modulus determined by mechanics of materials, and the solid line represents the measured value.

[0044] First, a stress greater than the elastic limit is applied to the material in its state of zero strain, causing it to enter state B (hereinafter referred to as the first state) in the plastic region. As shown in the figure, if the stress applied to the material is increased, the material's state changes from point o through the yield point A to the first state B. In this example, the elastic limit is σ. Y =496MPa (megapascals), and the stress under the first state B is σ=1000MPa.

[0045] Next, the strain ε under the first state B is measured at multiple measurement points determined on the material. In this example, the strain ε is found to be 0.0083. As mentioned earlier, the strain ε measured here is the sum of elastic strain and plastic strain.

[0046] Next, the stress applied to the material in state B is gradually reduced until it is unloaded to 0. The state of the material changes along line BC, from point B to point C (hereinafter referred to as state B). As shown in the figure, the unloading line indicated by the solid arrow BC is completely consistent with the theoretical straight line indicated by the dashed line.

[0047] Next, at the aforementioned multiple measurement points, the strain under the second state C was measured. In this example, the dependent variable is obtained. =0.0033. As mentioned earlier, the strain measured here... Plastic strain .

[0048] Finally, based on the strain ε under the first state B and the plastic strain under the second state C... The difference is used to calculate the elastic strain e at the aforementioned multiple measurement points. In this example, the elastic strain e = ε - =0.0083-0.0033=0.0050.

[0049] In this way, the plastic strain can be removed from the total strain observed in the plastic region at each measurement point, and only the elastic strain can be obtained. Thus, if the strain distribution can be obtained by, for example, DIC, the stress distribution can be obtained by applying the known Young's modulus or Poisson's ratio to Equation (1) (one-dimensional case) or Equations (2) and (3) (two-dimensional case).

[0050] To verify the accuracy of the measurements obtained in this embodiment, the inventors conducted an experiment in which stress was applied again to bring the material to state point E after it had reached state C. As a result, as shown in the figure, the load line from point C to point E coincides with the unload line from point B to point C with high precision, indicating that the material in state C exhibits normal elastic properties.

[0051] As mentioned earlier, it is believed that even regions previously designated as elastic zones will experience localized plastic deformation due to repeated loading and unloading, which may sometimes be contained within the material. Therefore, in this specification, the strain region below the yield point is collectively referred to as the "elastic domain." That is, the elastic domain is the general term for (1) the strain region when the material undergoes elastic deformation as a whole and (2) the strain region when the elastically deformed portion and the locally plastically deformed portion coexist within the material. It should be noted that some metallic materials, such as mild steel, exhibit a definite yield point, but in other metals, the yield point is sometimes not clearly observable. Therefore, in cases where the yield point is not clearly defined, the point exhibiting 0.2% permanent strain (0.2% endurance) in the stress-strain curve is considered the yield point.

[0052] [First Implementation Method]

[0053] Figure 3 This is a flowchart of the method of the first embodiment. The method involves repeatedly loading and unloading a sample and displaying the distribution of strain on the sample surface, including steps S1, S2, and S3.

[0054] In step S1, this method captures images of the sample surface before loading and after unloading. The equipment and methods used for capturing these images are not particularly limited; for example, a general digital camera, a microscope camera, or a high-speed camera can be used. Furthermore, a single camera can be used to capture images from one direction, or multiple cameras can be used to capture images from different directions. The captured images are stored according to pixel positions.

[0055] In step S2, this method measures the strain at each pixel location based on the correlation between the image before loading and the image after unloading captured in step S1. The specific method for measuring the strain is not particularly limited; for example, the images before loading and after unloading can be compared, and the displacement can be determined by finding the location where a point on the sample surface before loading moved to after unloading. The strain can be measured for all images before loading and after unloading, or several sets of images before loading and after unloading can be selected for measurement. By executing step S2, the strain generated on the sample surface during repeated loading and unloading can be calculated sequentially by pixel location.

[0056] In step S3, this method displays the distribution of strain measured in step S2 at each pixel location. The display method is not particularly limited, but the magnitude of the strain can be displayed according to each pixel location using color, shade, contour lines, three-dimensional display, etc. By executing step S3, the strain generated on the sample surface during repeated loading and unloading can be visualized sequentially according to pixel location.

[0057] According to this embodiment, since the distribution of strain of a sample that has undergone repeated loading and unloading can be displayed at each pixel position, it is possible to measure the local plastic deformation generated inside the material and visualize it as the distribution of strain.

[0058] [Second Implementation]

[0059] Figure 4 This is a flowchart of the method according to the second embodiment. The method is a method of displaying the stress distribution on the surface of the sample while repeatedly loading and unloading the sample, including steps S4, S5, S6, S7, and S8.

[0060] In step S4, this method captures images of the sample surface before loading, during loading, and after unloading.

[0061] That is, in step S4, in addition to step S1 of the first embodiment, an image of the sample surface under load (when the load is applied) is also captured.

[0062] In step S5, this method measures the first strain at each pixel location based on the correlation between the image before loading and the image after unloading captured in step S4. The first strain is the plastic strain (when plastic strain is present).

[0063] In step S6, this method measures the second strain at each pixel location based on the correlation between the image before loading and the image under loading captured in step S4. The second strain is the sum of elastic strain and plastic strain (when plastic strain is present) (total strain).

[0064] In step S7, this method calculates the stress at each pixel location based on the difference between the first strain measured in step S5 and the second strain measured in step S6. By executing step S7, following the aforementioned method, the difference between the second strain (total strain) and the first strain (plastic strain) is calculated at each pixel location, thereby enabling the calculation of the stress at each pixel location by taking only the elastic strain at each pixel location.

[0065] In step S8, this method displays the stress distribution calculated in step S7 at each pixel location. By executing step S8, the distribution of stress acting on the sample surface during repeated loading and unloading can be visualized sequentially by pixel location.

[0066] According to this embodiment, since the stress distribution of a sample that has undergone repeated loading and unloading can be displayed at each pixel position, it is possible to measure the local stress that is caused by local plastic deformation or the like inside the material and visualize it as a stress distribution.

[0067] In particular, during the execution of this method, the sample is preferably located in the elastic region. According to this method, loading and unloading of the sample are typically performed repeatedly within a range defined as the elastic region. At this time, the material as a whole is within the elastic region, and if the deformation of the material is reversible, there should be no difference between the images taken in step S4 before and after the loading. On the other hand, if localized plastic deformation occurs within the material due to repeated loading and unloading, there should be pixel locations with differences between any of the images taken in step S4 before and after the loading. That is, according to this embodiment, it is possible to determine the localized plastic deformation caused by small loads (loads applied within a range typically defined as the elastic region) and visualize it as a stress distribution. This provides insights related to the local structure of the sample that cannot be obtained in conventional fatigue tests of this type, which involve repeated loading and unloading until fracture.

[0068] [Third Implementation Method]

[0069] Figure 5This is a flowchart of the method of the third embodiment. The third embodiment further includes steps S9 and S10 compared to the second embodiment.

[0070] In step S9, this method calculates the difference between the stress distribution obtained by the previous (n-1) load and unload and the stress distribution obtained by the current (n) load and unload, at the same pixel position.

[0071] In step S10, this method displays the positions of pixels where the difference calculated in step S9 is above a predetermined threshold. That is, the stress distribution after the (n-1)th unloading is compared with the stress distribution after the nth unloading, and if a pixel exists where the stress difference is above the predetermined threshold, that pixel position is displayed. Since the stress at that pixel position changes significantly, it is considered that there is a high probability that localized plastic deformation, etc., will occur in the portion corresponding to that pixel position during the nth loading and unloading process. In other words, it can be estimated that the timing of localized plastic deformation, etc., occurring at that pixel position is during the nth loading and unloading process when the sample has been repeatedly loaded and unloaded.

[0072] As described above, according to this embodiment, it is possible to estimate and display the timing and location of localized plastic deformation occurring inside the sample when the sample is repeatedly loaded and unloaded.

[0073] [Fourth Implementation Method]

[0074] Figure 6 This is a flowchart of the method according to the fourth embodiment. The fourth embodiment, compared to the third embodiment, replaces step S10 with step S110.

[0075] In step S9, this method calculates the difference between the stress distribution obtained by the previous (n-1) load and unload and the stress distribution obtained by the current (n) load and unload, and the stress displayed at the same pixel position.

[0076] In step S110, this method displays the difference calculated in step S9 according to the frequency distribution of the pixel position based on the specified stress value range. The specified stress value range can be arbitrarily determined. The following describes 12 specific examples: -200MPa~-100MPa, -100MPa~0MPa, 0MPa~100MPa, 100MPa~200MPa, 200MPa~300MPa, 300MPa~400MPa, 400MPa~500MPa, 500MPa~600MPa, 600MPa~700MPa, 700MPa~800MPa, 800MPa~900MPa, and 900MPa~1000MPa.

[0077] Figure 10 This refers to the frequency distribution of the stress difference at a certain pixel location displayed in step S110. In this example, the frequency distribution of the stress difference at four different times is displayed: (a) T=t0, (b) T=t0+t1, (c) T=t0+t1+Δt, and (d) T=t0+t1+2Δt. Here, T represents the time.

[0078] It can be seen that at T=t0 in (a), the larger the stress value, the larger the stress difference. The residual stress at this time point is generated by... Figure 10 The performance of (a) is shown. Then, if loading and unloading are repeatedly performed, the stress difference within each stress range becomes 0, and the frequency distribution becomes flat. This flat state continues until T = t0 + t1 in (b). At the next moment in (b) (i.e., after (b), when one loading and unloading is performed) T = t0 + t1 + Δt, the frequency distribution changes and is no longer flat. Here, the time required for one loading and unloading is represented by Δt. It is believed that this frequency distribution suggests the discovery of new deformation structures in the material. Thus, it shows that the state of residual stress generation has changed significantly up to that point. Furthermore, at the next moment T = t0 + t1 + 2Δt, the frequency distribution changes again to another form ((d)). That is, at this stage, the deformation structure of the material develops rapidly over time, suggesting a significant change in residual stress.

[0079] In this way, by displaying the obtained stress difference according to the frequency distribution of the pixel position within a specified range of stress values, information equivalent to the temporal derivative of the stress is obtained. This allows for the tracking of the generation of residual stress at various points in the material over time.

[0080] As described above, according to this embodiment, it is possible to estimate and display the timing and location of localized plastic deformation occurring inside the sample when the sample is repeatedly loaded and unloaded.

[0081] In one embodiment, instead of calculating the stress difference between points displayed at the same pixel location and displaying the frequency distribution of the stress difference by pixel location, the overall stress difference of the material can be calculated and displayed as a frequency distribution after unloading. According to this embodiment, it is not necessary to repeatedly apply multiple loads and unloads at pixel locations to display the frequency distribution of the stress difference; instead, the changes in the overall deformation structure of the material can be evaluated by unloading.

[0082] [Fifth Implementation Method]

[0083] Figure 7 This is a flowchart of the method according to the fifth embodiment. Compared with the second embodiment, the fifth embodiment replaces step S6 with step S11 and also includes step S12.

[0084] In step S11, this method measures the second strain at each pixel location based on the correlation between the image before loading and the image during loading, and detects pixels where the maximum value of the correlation between the image before loading and the image during loading is below a predetermined threshold. If the sample does not break during repeated loading and unloading, it is considered that there is a certain correlation between the image before loading and the image after loading. That is, if a load is applied to the sample, each position of the sample will shift, but as long as no breakage occurs, the displacement at each position is considered to be within a certain range. In this case, it is considered that there is a correlation between the image before loading and the image during loading. However, if a part of the sample breaks after loading, the area around that part shifts significantly compared to before loading, resulting in the loss of the correlation between the image before loading and the image during loading. Thus, by executing step S11 to detect pixels where the maximum value of the correlation between the image before loading and the image during loading is below a predetermined threshold, it can be inferred that a local breakage or similar event has occurred in the area corresponding to that pixel.

[0085] In step S12, this method displays the locations of pixels where the maximum correlation between the image before and during loading, detected in step S11, falls below a predetermined threshold. By executing step S12, the locations where localized fractures or similar defects are presumed to have occurred are visualized.

[0086] According to this embodiment, it is possible to estimate and display the location of local fractures when the sample is repeatedly loaded and unloaded.

[0087] [Sixth Implementation Method]

[0088] Figure 8This is a flowchart of the method according to the sixth embodiment. Compared with the second embodiment, the sixth embodiment replaces step S4 with step S13, and also includes steps S14 and S15.

[0089] In step S13, this method uses a microscope camera to capture images of the surface of the polycrystalline metal material sample before loading, during loading, and after unloading. The microscope used is not particularly limited, but can be an optical microscope, scanning electron microscope, transmission electron microscope, etc. By capturing images of the polycrystalline metal material sample surface using a microscope camera, information related to the crystal structure, such as grains, grain boundaries, and linear structures, can be obtained.

[0090] In step S14, this method detects the orientation of the metal crystals in the sample photographed in step S13.

[0091] In step S15, this method displays the orientation of the metal crystals detected in step S14 according to the metal crystal structure. By performing steps S8 and S15, the stress distribution of the sample and the orientation of the metal crystals can be visualized together. This allows observation of situations, such as stress concentration at grain boundaries. Furthermore, it enables comparison of the stress distribution differences at the boundaries between crystals with small orientation differences and between crystals with large orientation differences.

[0092] According to this embodiment, the relationship between grain boundaries and locally generated plastic deformation can be obtained.

[0093] [Seventh Implementation Method]

[0094] Figure 9 This is a block diagram of the stress display device 1 according to the seventh embodiment. The stress display device 1 is a device that repeatedly loads and unloads a sample and displays the stress distribution on the surface of the sample, and includes a photographic unit 10, a strain measuring unit 20, a stress calculation unit 30, and a display unit 40.

[0095] The imaging unit 10 captures images of the sample surface before loading, during loading, and after unloading, and sends these images to the strain measurement unit 20. Based on the correlation between the images received from the imaging unit 10 before and after loading, the strain measurement unit 20 measures a first strain at each pixel location. The strain measurement unit 20 also measures a second strain at each pixel location based on the correlation between the images received from the imaging unit 10 before and during loading. The strain measurement unit 20 sends the measured first and second strains to the stress calculation unit 30. The stress calculation unit 30 calculates the stress at each pixel location based on the difference between the first and second strains received from the strain measurement unit 20. The stress calculation unit 30 sends the calculated stress at each pixel location to the display unit 40. The display unit 40 displays the stress distribution received from the stress calculation unit 30 at each pixel location.

[0096] According to this embodiment, an apparatus is available for measuring local stresses that are the cause of localized plastic deformation or the like within a material and for visualizing them as stress distributions.

[0097] [Eighth Implementation Method]

[0098] The program of the eighth embodiment is a program that displays the stress distribution on the surface of the sample while repeatedly loading and unloading the sample. This program causes a computer to perform the following steps: capturing images of the sample surface before loading, during loading, and after unloading; measuring a first strain at each pixel location based on the correlation between the images before loading and after unloading; measuring a second strain at each pixel location based on the correlation between the images before loading and during loading; calculating the stress at each pixel location based on the difference between the first and second strains; and displaying the calculated stress distribution at each pixel location.

[0099] According to this embodiment, it is possible to use a computer to measure the local stress that is caused by local plastic deformation or other phenomena that occur within a material and to visualize it as a stress distribution.

[0100] The present invention has been described above based on embodiments. These embodiments are illustrative, and those skilled in the art should understand that the combinations of the above-described constituent elements or processes can include various modifications, and such modifications are also included within the scope of the present invention.

[0101] For example, the distribution of strain and stress can be obtained by taking tomographic images at different depths. According to this modified example, the distribution of strain and stress within a three-dimensional material can be obtained.

[0102] The above-described variations serve the same function and effect as the implementation method.

[0103] Any combination of the above-described embodiments and variations is also useful as an embodiment of the present invention. New embodiments resulting from combinations simultaneously possess the effects of each of the combined embodiments and variations.

[0104] The method of this invention can be applied to a variety of materials at low cost, and can help with material evaluation, manufacturing method selection, and material performance improvement, thus having extremely high industrial applicability.

[0105] Industrial availability

[0106] The present invention enables the use of methods, apparatus and procedures for displaying the distribution of stress and strain.

[0107] Symbol explanation:

[0108] S1...The steps for taking images of the sample surface before loading and after unloading.

[0109] S2... is a step to measure the strain at each pixel location based on the correlation between the image before loading and the image after unloading.

[0110] S3... is the step of displaying the distribution of the measured strain at each pixel location.

[0111] S4...The steps for taking images of the sample surface before loading, during loading, and after unloading.

[0112] S5 is a step that measures the first strain at each pixel location based on the correlation between the image before loading and the image after unloading.

[0113] S6...The step of measuring the second strain at each pixel location based on the correlation between the image before and during loading.

[0114] S7... The step of calculating the stress at each pixel location based on the difference between the first strain and the second strain.

[0115] S8... is the step that displays the calculated stress distribution at each pixel location.

[0116] S9... is the step of calculating the difference between the stress distribution obtained through the previous load and unload and the stress distribution obtained through the current load and unload, displayed at the same pixel location.

[0117] S10...The step of displaying the positions of pixels whose difference is above a specified threshold.

[0118] S110... This step involves displaying the frequency distribution of the difference based on pixel position within a specified range of stress values.

[0119] S11...A step to measure the second strain at each pixel location based on the correlation between the image before and during loading, and to detect pixels whose maximum correlation between the image before and during loading is below a predetermined threshold.

[0120] S12...The step of displaying the position of pixels whose maximum correlation between the image before and during loading is below a specified threshold.

[0121] S13···The procedure of taking images of the surface of a polycrystalline metal material sample before loading, during loading, and after unloading using a microscope camera.

[0122] S14...The procedure for detecting the orientation of metal crystals in the test sample.

[0123] S15... The step of displaying the orientation of the detected metal crystals according to the metal crystal structure.

[0124] 1. Stress display device

[0125] 10. Photography Department

[0126] 20. Strain Measurement Department

[0127] 30. Stress Calculation Section

[0128] 40··· Display Department.

Claims

1. A method for repeatedly loading and unloading a sample and displaying the stress distribution on the sample surface, comprising: The steps for taking images of the sample surface before loading, during loading, and after unloading; The steps for measuring the first strain at each pixel location based on the correlation between the image before loading and the image after unloading; The step of measuring the second strain at each pixel location based on the correlation between the image before loading and the image under loading; The step of calculating the stress at each pixel position based on the difference between the first strain and the second strain; The step of calculating the difference between the stress distribution obtained by the previous load and unload and the stress distribution obtained by the current load and unload, displayed at the same pixel position. The step of displaying the calculated stress distribution at each pixel location; as well as The step of displaying the pixel positions where the difference is above a specified threshold.

2. The method according to claim 1, wherein, The method, in the step of measuring the second strain, further includes the step of detecting pixels whose maximum correlation between the image before loading and the image under loading is below a predetermined threshold and displaying the location of the detected pixels.

3. The method according to claim 1, wherein, The sample is in the elastic region.

4. A method for repeatedly loading and unloading a sample and displaying the stress distribution on the sample surface, comprising: The steps for taking images of the sample surface before loading, during loading, and after unloading; The steps for measuring the first strain at each pixel location based on the correlation between the image before loading and the image after unloading; The step of measuring the second strain at each pixel location based on the correlation between the image before loading and the image under loading; The step of calculating the stress at each pixel position based on the difference between the first strain and the second strain; The step of calculating the difference between the stress distribution obtained by the previous load and unload and the stress distribution obtained by the current load and unload, displayed at the same pixel position. The step of displaying the calculated stress distribution at each pixel location; as well as The step of displaying the frequency distribution of the stress differences between each other according to the pixel position and the range of stress values ​​is as follows.

5. A method for repeatedly loading and unloading a sample and displaying the stress distribution on the sample surface, comprising: The steps for taking images of the sample surface before loading, during loading, and after unloading; The steps for measuring the first strain at each pixel location based on the correlation between the image before loading and the image after unloading; The step of measuring the second strain at each pixel location based on the correlation between the image before loading and the image under loading; The step of calculating the stress at each pixel position based on the difference between the first strain and the second strain; The step of calculating the difference between the stress distribution obtained through the previous loading and unloading and the stress distribution obtained through the current loading and unloading. The step of displaying the calculated stress distribution at each pixel location; as well as The step of displaying the frequency distribution of the stress difference between the entire material according to the unload.

6. The method according to any one of claims 1, 2, 4, and 5, wherein, The sample was a polycrystalline metal material, and the imaging step was performed using a microscope camera. The method further includes the steps of detecting the orientation of the metal crystals in the sample and displaying the orientation of the detected metal crystals according to the metal crystals.

7. An apparatus for repeatedly loading and unloading a sample and displaying the stress distribution on the sample surface, comprising: The photography department takes images of the sample surface before loading, during loading, and after unloading. The strain measurement unit measures a first strain at each pixel location based on the correlation between images before and after loading, and measures a second strain at each pixel location based on the correlation between images before and during loading; the stress calculation unit calculates the stress at each pixel location based on the difference between the first strain and the second strain; and The display unit shows the calculated stress distribution at each pixel location and displays the pixel locations where the difference is above a predetermined threshold. The difference between the stress distribution obtained through the previous load and unload and the stress distribution obtained through the current load and unload is calculated, and the stress displayed at the same pixel position is calculated.

8. A program product for repeatedly loading and unloading a sample and displaying the stress distribution on the sample surface, said program product causing a computer to execute: The steps for taking images of the sample surface before loading, during loading, and after unloading; The steps for measuring the first strain at each pixel location based on the correlation between the image before loading and the image after unloading; The step of measuring the second strain at each pixel location based on the correlation between the image before loading and the image under loading; The step of calculating the stress at each pixel position based on the difference between the first strain and the second strain; The step of calculating the difference between the stress distribution obtained by the previous load and unload and the stress distribution obtained by the current load and unload, displayed at the same pixel position. The step of displaying the calculated stress distribution at each pixel location; as well as The step of displaying the pixel positions where the difference is above a specified threshold.

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