Test piece analysis device and test piece analysis method

Abstract

To analyze a test piece on the basis of a result of analysis from an initial crack generated in a surface of the test piece to a crack immediately before the test piece ruptures in high-temperature fatigue testing.SOLUTION: In one of picked-up images created at the timing when tensile stress becomes maximum in a predetermined cycle, a test piece analysis device specifies a crack in the picked-up image on the basis of the difference in luminance occurring according to the difference in temperature between a surface of a test piece heated by a heating unit and the inside of the crack, extracts the picked-up images capturing the specified crack as crack observation images, pays attention to, of the extracted crack observation images, a crack observation image immediately before rupture capturing a crack that can be considered as a crack immediately before the test piece ruptures, goes back to find a past crack observation image obtained by picking up an image of a position corresponding to a position on the surface of the test piece captured in the crack observation image immediately before rupture, from the crack observation image immediately before rupture to an initial crack observation image capturing an initial crack that is the starting point from which the crack is generated, and thereby analyzes the crack generated in the surface of the test piece.SELECTED DRAWING: Figure 14

Description

[Technical Field]

[0001] The present invention relates to a test specimen analysis device and a test specimen analysis method for analyzing a test specimen based on cracks that occur on the surface of the test specimen during a high-temperature fatigue test in which the surface temperature of the test specimen is maintained within a set temperature range of 700°C or higher. [Background technology]

[0002] Cracks that develop on the surface of a specimen during high-temperature fatigue testing are observed by stopping the testing machine after each cycle, allowing it to cool to room temperature, and then visually inspecting the specimen and by microscopic observation using the replica method. However, cracks that develop immediately after initiation are typically only a few tens of micrometers in size, making them difficult to detect even with a microscope. In the early stages of high-temperature fatigue testing, it is difficult to determine the location and presence of cracks. When replicas of the specimen surface are taken after each cycle, cracks that become visible under a microscope using the replica method only grow to a size of several hundred micrometers to a few millimeters, making it possible to identify their location. By reexamining the initial replicas taken from the position of visible cracks, the initial crack and its subsequent growth rate can be investigated. However, microcracks such as initial cracks are difficult to transfer to the replica, making their identification impossible. Furthermore, air bubbles may appear in the replica, making observation of the specimen surface itself difficult.

[0003] The replica method requires advanced technology to accurately transfer initial cracks to the replica, and replica fabrication is time-consuming. Furthermore, the process requires careful checking for air bubbles in the replica, which can take more than an hour in some cases. Furthermore, replica fabrication is a part of the high-temperature fatigue test process, and replica fabrication is performed after the specimen has cooled down. After replica fabrication, the specimen is reheated and fatigue tested until the next specified cycle. This process, which involves repeated heating, cooling, replica fabrication, and reheating, requires an enormous amount of time for fatigue testing of a single specimen. Furthermore, even if large cracks are identified in the later stages of high-temperature fatigue testing, failure to transfer the initial cracks often renders the high-temperature fatigue test itself useless. While the replica method is extremely difficult, identifying cracks on the surface of the specimen at each specified cycle and evaluating their propagation is crucial for accurately determining the lifespan and strength of the product corresponding to the specimen. Therefore, underestimating crack size or overlooking cracks is essential.

[0004] The following methods have been proposed as techniques for observing cracks in a test specimen. Patent Document 1 discloses a method in which a dot pattern or grid pattern is applied to the surface of a test specimen in advance, and the strain on the surface of the test specimen is measured using a moire method and an image correlation method based on changes in the pattern during a fatigue test. Patent Document 2 discloses a method in which a one-dimensional or two-dimensional pattern (grating) is applied to the surface of a test specimen in advance, and the strain on the surface of the test specimen is measured using a Fourier transform and phase change based on changes in the pattern during a fatigue test.

[0005] Furthermore, the following method has been proposed as a method for measuring the length of a crack: Patent Document 3 proposes a method in which the tip of a crack is detected based on an image captured by an imaging device, at least one of the imaging device and the test piece support device is moved relative to the other by a moving device so that the field of view of the imaging device moves relative to the test piece in the direction of crack growth, and the growth dimension of the crack is calculated based on the amount of relative movement of the imaging device and the test piece support device. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-27526 [Patent Document 2] Japanese Patent Application Publication No. 2019-66369 [Patent Document 3] Japanese Patent Application Publication No. 5-223717 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the methods described in Patent Documents 1 and 2 have a problem in that the pattern peels off from the surface of the test specimen during the high-temperature fatigue test. Furthermore, the method described in Patent Document 3 is premised on detecting the tip of a crack, and therefore has a problem in that the tip of a crack cannot be detected in the case of an initial crack. Therefore, there is room for improvement in order to be able to analyze a test specimen based on the results of analyzing the crack from the initial crack that appears on the surface of the test specimen during the high-temperature fatigue test to the crack that occurs immediately before the test specimen breaks.

[0008] The present invention aims to provide a test specimen analysis device and a test specimen analysis method that can analyze a test specimen based on the results of analyzing the initial crack that appears on the surface of the test specimen during high-temperature fatigue testing, from the crack that appears just before the test specimen breaks. [Means for solving the problem]

[0009] A first aspect of the present invention is a test piece analyzing device that analyzes a test piece based on cracks that occur on the surface of the test piece during a high-temperature fatigue test performed by maintaining the temperature of the surface of the test piece within a set temperature range of 700°C or higher, the device comprising: a heating unit that heats the surface of the test piece to the temperature range as a load in the high-temperature fatigue test; a stress applying unit that repeatedly applies tensile stress and compressive stress in a predetermined cycle in the axial direction of the test piece as a load in the high-temperature fatigue test; an imaging unit that images the surface of the test piece and generates the images; and a calculation processing unit that uses the images generated by the imaging unit to analyze cracks that occur on the surface of the test piece and analyzes the test piece based on the analysis results, and the calculation processing unit selects cracks that occur on the surface of the test piece within the predetermined cycle from the images generated by the imaging unit. This test specimen analysis device has: a crack observation image extraction unit that identifies a crack in an image generated when the tensile stress is at its maximum based on the difference in brightness that occurs depending on the temperature difference between the surface of the test specimen heated by the heating unit and the inside of the crack, and extracts the image containing the identified crack as a crack observation image; and a crack analysis unit that focuses on a crack observation image just before fracture that captures a crack that can be considered to be a crack that occurs just before the test specimen fractures, among the crack observation images extracted by the crack observation image extraction unit, and analyzes cracks that occur on the surface of the test specimen by tracing back from the crack observation image just before fracture to an initial crack observation image that captures an initial crack that is the starting point for crack generation.

[0010] A second aspect of the present invention is a test specimen analysis method for analyzing a test specimen based on cracks that occur on the surface of the test specimen during a high-temperature fatigue test performed while maintaining the temperature of the surface of the test specimen within a set temperature range of 700°C or higher, the method using a test specimen analysis device having: a heating unit that heats the surface of the test specimen to the temperature range as a load in the high-temperature fatigue test; a stress application unit that repeatedly applies tensile stress and compressive stress in a predetermined cycle in the axial direction of the test specimen as a load in the high-temperature fatigue test; an imaging unit that images the surface of the test specimen and generates the images; and a calculation processing unit that analyzes cracks that occur on the surface of the test specimen using the images generated by the imaging unit and analyzes the test specimen based on the analysis results, and a crack observation image extraction step of identifying a crack in the captured image based on a difference in brightness that occurs in accordance with a temperature difference between the surface of the test piece heated by the heating unit and the inside of the crack in the captured image generated at a timing when the temperature difference is maximum, and extracting the captured image showing the identified crack as a crack observation image; and a crack analysis step of focusing on a crack observation image just before fracture that shows a crack that can be considered to be a crack that occurs just before the test piece fractures, among the crack observation images extracted in the crack observation image extraction step, and analyzing a crack that occurs on the surface of the test piece by tracing back from the crack observation image just before fracture to an initial crack observation image that shows an initial crack that is the starting point for crack generation. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a test specimen analysis device and a test specimen analysis method that can analyze a test specimen based on the results of analyzing the initial crack that appears on the surface of the test specimen during high-temperature fatigue testing, from the crack that appears just before the test specimen breaks. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a block diagram showing an example of the configuration of a test piece analyzing device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a front view showing an example of the configuration of a heating unit and a stress applying unit. [Figure 3] FIG. 2 is a perspective view showing an example of the configuration of an imaging unit. [Figure 4] FIG. 2 is a plan view showing an example of the configuration of an imaging unit. [Figure 5] FIG. 2 is a block diagram showing an example of the configuration of a calculation processing unit. [Figure 6] FIG. 10 is an explanatory diagram showing an example of the relationship between a tensile load, time, and a captured image. [Figure 7] Examples of images taken during each cycle of a high-temperature fatigue test are shown below. [Figure 8] FIG. 10 is a block diagram showing an example of a processing flow from a multi-resolution processing unit to a crack analysis unit. [Figure 9] 10A and 10B are explanatory diagrams showing an example of multi-resolution processing by a multi-resolution processing unit and enhancement processing by an enhancement processing unit; [Figure 10] FIG. 10 is an explanatory diagram showing an example of an enhanced image generated immediately before the test specimen breaks. [Figure 11] 10 is an explanatory diagram showing an example of processing by the crack analysis unit to trace back past crack observation images. FIG. [Figure 12] FIG. 10 is an explanatory diagram showing an example of a manner in which the crack extraction region is updated in sequence. [Figure 13] FIG. 10 is an explanatory diagram showing an example of an enhanced image generated at the beginning of a high-temperature fatigue test. [Figure 14] 1 is a flowchart showing an example of the flow of a test piece analysis method according to an embodiment of the present invention. [Figure 15] 10 is a graph showing an example of the results of detecting the length of a main crack using a test specimen analysis method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] FIG. 1 shows an example of the configuration of a test specimen analyzing apparatus 10 according to one embodiment of the present invention. The test specimen analyzing apparatus 10 is an apparatus that analyzes a test specimen 80 based on cracks that appear on the surface of the test specimen 80 during a high-temperature fatigue test in which the surface temperature of the test specimen 80 is maintained within a temperature range set, for example, above 700°C (i.e., a temperature range corresponding to hot treatment). The test specimen 80 is made of a metal such as steel or an aluminum alloy and is formed in a cylindrical shape. However, the test specimen 80 may be formed in a shape other than a cylindrical shape, such as a square pillar. In the following description, the surface of the test specimen 80 refers to the surface around the axial direction of the test specimen 80 (i.e., the outer circumferential surface).

[0014] More specifically, the high-temperature fatigue test is a test in which one cycle consists of a tension process in which the tensile stress acting in the axial direction of the test specimen 80 is gradually increased, and a compression process in which the compressive stress acting in the axial direction of the test specimen 80 is gradually increased, and this cycle is repeated multiple times. The time for the tension process, the time for the compression process, the tensile load, and the compressive load are predetermined to be the same for each cycle. The high-temperature fatigue test may be terminated when the number of cycles reaches a predetermined number, or may be terminated when the test specimen 80 breaks due to the tensile stress or buckles due to the compressive stress.

[0015] The test specimen analysis device 10 includes a heating unit 12, a stress applying unit 14, an imaging unit 16, a control unit 18, and an arithmetic processing unit 20. The heating unit 12 heats the surface of the test specimen 80 to the above-mentioned temperature range as a load in the high-temperature fatigue test. The stress applying unit 14 repeatedly applies tensile stress and compressive stress in the axial direction of the test specimen 80 in the above-mentioned predetermined cycle as a load in the high-temperature fatigue test. The imaging unit 16 continuously captures images of the entire circumference and entire length of the surface of the test specimen 80 during the high-temperature fatigue test and generates the captured images. The arithmetic processing unit 20 uses the captured images generated by the imaging unit 16 to analyze cracks that occur on the surface of the test specimen 80 and analyzes the test specimen 80 based on the analysis results.

[0016] 2 shows an example of the configuration of the heating unit 12 and the stress applying unit 14. The heating unit 12 has an induction coil 22 and an AC power supply 24. The induction coil 22 is formed in a spiral shape. A test piece 80 is placed inside the induction coil 22. The AC power supply 24 is connected to the induction coil 22. When an AC current is supplied from the AC power supply 24 to the induction coil 22, a magnetic flux is generated by the induction coil 22, which generates an eddy current in the test piece 80, and the test piece 80 is heated by Joule heat.

[0017] The stress applying unit 14 has a first gripping unit 26, a second gripping unit 28, and a driving unit 30. The first gripping unit 26 and the second gripping unit 28 are configured with a chuck mechanism. The first gripping unit 26 grips one axial end of the test specimen 80, and the second gripping unit 28 grips the other axial end of the test specimen 80. The first gripping unit 26 is connected to the driving unit 30, and the second gripping unit 28 is fixed to a test table 32. The driving unit 30 moves the first gripping unit 26 in the axial direction of the test specimen 80, thereby repeatedly applying tensile stress and compressive stress in the axial direction of the test specimen 80. The driving unit 30 is configured with, for example, a reduction mechanism, a motor, etc.

[0018] 3 and 4 show an example of the configuration of the imaging unit 16. The imaging unit 16 has multiple cameras 34. Each camera 34 is an area camera (e.g., a monochrome area camera). Each camera 34 is installed, for example, so that the horizontal direction of the camera 34 is parallel to the axial direction of the test piece 80. The number of multiple cameras 34 is, for example, four. The four cameras 34 are provided facing the surface of the test piece 80 and are arranged at 90° intervals around the periphery of the test piece 80. The four cameras 34 capture images of the surface of the test piece 80 from the normal direction of the surface of the test piece 80, and each generate a captured image. The field of view of each camera 34 is set so that the four cameras 34 can capture images of the entire circumference and entire length of the outer periphery of the test piece 80.

[0019] As long as the four cameras 34 can capture images of the entire circumference and entire length of the surface of the test piece 80, the four cameras 34 may be arranged around the test piece 80 at angular intervals other than 90°. Any number of cameras 34 may be used. Each camera 34 may be installed, for example, so that the horizontal direction of the camera 34 and the axial direction of the test piece 80 are perpendicular to each other.

[0020] The control unit 18 (see FIG. 1) is a device that controls the heating unit 12, the stress applying unit 14, and the imaging unit 16, and is configured by a computer. The control unit 18 has a function of controlling the heating unit 12 and the stress applying unit 14 to perform a high-temperature fatigue test, and a function of controlling the imaging unit 16 so that an image of the surface of the test piece 80 is taken during the high-temperature fatigue test.

[0021] Specifically, the control unit 18 controls the drive unit 30 of the stress application unit 14 so that the first gripping unit 26 gradually moves away from the second gripping unit 28 during the tension process of the high-temperature fatigue test, and controls the drive unit 30 of the stress application unit 14 so that the first gripping unit 26 gradually moves closer to the second gripping unit 28 during the compression process of the high-temperature fatigue test. The control unit 18 also controls the AC power supply 24 of the heating unit 12 so that the surface temperature of the test piece 80 is maintained within a set temperature range of 700°C or higher from the start to the end of the high-temperature fatigue test. Furthermore, the control unit 18 controls the multiple cameras 34 constituting the imaging unit 16 so that the entire circumference and entire length of the surface of the test piece 80 are continuously imaged by the multiple cameras 34 from the start to the end of the high-temperature fatigue test.

[0022] 5 shows an example of the configuration of the arithmetic processing unit 20. The arithmetic processing unit 20 is configured by a computer having a CPU (Central Processing Unit) 40, a memory 42, and a storage device 44. The CPU 40, the memory 42, and the storage device 44 are connected to each other so as to be able to communicate with each other via a bus 46 or the like. The computer that constitutes the arithmetic processing unit 20 and the computer that constitutes the above-mentioned control unit 18 may be the same computer or may be separate computers.

[0023] The CPU 40 is a central processing unit that reads programs from the storage device 44 and executes the programs using the memory 42 as a work area. The memory 42 is composed of RAM (Random Access Memory) or the like, and temporarily stores programs and data as a work area. The storage device 44 is composed of ROM (Read Only Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), or the like, and stores various programs including the operating system and various data.

[0024] The storage device 44 stores a program for analyzing the test specimen 80. The CPU 40 reads the program for analyzing the test specimen 80 from the storage device 44, and loads and executes the read program in the memory 42, thereby functioning as each functional unit of the arithmetic processing unit 20. Specifically, the CPU 40 functions as a captured image storage control unit 50, a crack observation image extraction unit 52, a multi-resolution processing unit 54, an enhancement processing unit 56, and a crack analysis unit 58.

[0025] The captured image storage control unit 50 acquires a captured image 100 generated by each of the multiple cameras 34 constituting the imaging unit 16 each time the entire circumference and entire length of the surface of the test specimen 80 are captured by the multiple cameras 34 during the high-temperature fatigue test. The captured image storage control unit 50 may combine the acquired captured images 100 in a direction corresponding to the circumferential direction of the test specimen 80. As a result, a single captured image 100 capturing the entire circumference and entire length of the surface of the test specimen 80 is obtained each time an image is captured by the multiple cameras 34. The captured image storage control unit 50 then stores the captured image 100 in the storage device 44. As a result, a plurality of captured images 100 obtained by continuously capturing images from the start to the end of the high-temperature fatigue test are stored in the storage device 44.

[0026] The crack observation image extraction unit 52 identifies a crack in the captured image 100 generated by the imaging unit 16 at the timing when the tensile stress is maximized in a predetermined cycle based on the difference in brightness that occurs depending on the temperature difference between the surface of the test piece 80 heated by the heating unit 12 and the interior of the crack, and extracts the captured image 100 containing the identified crack as the crack observation image 102. That is, after the high-temperature fatigue test, the crack observation image extraction unit 52 selects and acquires the captured image 100 corresponding to the timing when the tensile stress is maximized from the multiple captured images 100 stored in the storage device 44. At this time, the crack observation image extraction unit 52 may identify the timing when the tensile stress is maximized based on the elapsed time from the start of the high-temperature fatigue test. The crack observation image extraction unit 52 may then identify the captured image 100 corresponding to the timing when the tensile stress is maximized based on the elapsed time from the start of the high-temperature fatigue test and time information attached to the captured image 100.

[0027] Furthermore, if a synchronization signal is obtained from the control unit 18 in accordance with the timing at which the tensile stress becomes maximum during the high-temperature fatigue test, the crack observation image extraction unit 52 may identify the timing at which the tensile stress becomes maximum based on the synchronization signal from the control unit 18. Then, the crack observation image extraction unit 52 may identify the captured image 100 corresponding to the timing at which the tensile stress becomes maximum based on the time at which the synchronization signal was obtained after the start of the high-temperature fatigue test and the time information attached to the captured image 100.

[0028] Depending on the period during which the multiple cameras 34 take images, strictly speaking, there may be a discrepancy between the timing at which the tensile stress reaches its maximum and the timing at which the multiple cameras 34 take images. In this case, of the multiple captured images 100 obtained by continuously capturing images from the start to the end of the high-temperature fatigue test, the captured image 100 that is closest in time to the timing at which the tensile stress reaches its maximum can be considered to be the captured image 100 that corresponds to the timing at which the tensile stress reaches its maximum.

[0029] FIG. 6 shows an example of the relationship between the tensile load, time, and captured images 100. The tensile load gradually increases from the start to the end of the tensile process. The tensile stress applied to the test piece 80 is minimum at the start of the tensile process and maximum at the end of the tensile process. Each captured image 100 is stored in the storage device 44 at each timing from when the tensile stress is minimum to when it is maximum. If a crack 82 occurs on the surface of the test piece 80, the captured images 100 obtained at each timing include the crack 82 as well as the surface of the test piece 80. The crack 82 extends, for example, in a direction intersecting the axial direction of the test piece 80. In FIG. 6, the crack 82 is shown as a straight line as a schematic example.

[0030] The high-temperature fatigue test is performed by maintaining the surface temperature of the specimen 80 within a set temperature range of 700°C or higher, so the specimen 80 is in a red-hot state accompanied by thermal radiation. The interior of the specimen 80 is in a higher temperature state than the surface, which is cooled in air. If a crack 82 occurs on the surface of the specimen 80 during the high-temperature fatigue test, the crack 82 opens due to the application of tensile stress to the specimen 80, and opens largest when the tensile stress is at its maximum. The interior of the opening of the crack 82 is hotter than the surface of the specimen 80 and emits more heat than the surface of the specimen 80, so it is imaged brighter than the surface of the specimen 80 (see FIG. 7, described below). The image 100 corresponding to the time when the tensile stress is at its maximum includes a crack 82 with a larger opening as an image compared to the image 100 corresponding to the time when the tensile stress is at its minimum, making it suitable for observing the crack 82. That is, the captured image 100 generated at the timing when the tensile stress is at its maximum shows the difference in brightness between the surface of the test piece 80 and the inside of the opening of the crack 82, and is suitable for observing the crack 82. The crack observation image extraction unit 52 designates the captured image 100 that shows the crack 82 with a large difference in brightness from the surface of the test piece 80 as the crack observation image 102, as described above.

[0031] As described above, the captured image storage control unit 50 stores the captured image 100 in the storage device 44 each time an image is captured by the multiple cameras 34. The captured image storage control unit 50 may combine the captured images 100 generated by each camera 34 and store the combined captured image 100 in the storage device 44, but may also identify the timing at which the tensile stress becomes maximum during the high-temperature fatigue test, acquire and combine the captured images 100 generated by each camera 34 only at the identified timing, and store the combined captured image 100 in the storage device 44.

[0032] Furthermore, as described above, the control unit 18 may control the multiple cameras 34 constituting the imaging unit 16 so that the entire circumference and entire length of the surface of the test specimen 80 are continuously imaged by the multiple cameras 34. Alternatively, the control unit 18 may identify the timing at which the tensile stress is at its maximum during the high-temperature fatigue test, and control the multiple cameras 34 so that the entire circumference and entire length of the surface of the test specimen 80 are imaged by the multiple cameras 34 only at the identified timing.

[0033] Furthermore, the crack observation image extraction unit 52 may acquire the captured image 100 corresponding to the timing when the tensile stress is at its maximum only in a predetermined number of cycles (for example, odd-numbered cycles) among the multiple cycles.

[0034] FIG. 7 shows an example of the captured images 100 acquired by the imaging unit 16 in each cycle of the high-temperature fatigue test (i.e., the captured images 100 corresponding to the timing at which the tensile stress reaches its maximum in each cycle). The presence, location, and size of a crack 82 can be easily confirmed in the captured image 100 acquired immediately before the fracture of the test specimen 80, but it is difficult to confirm the presence, location, and size of the crack 82 in the captured image 100 acquired in the early stage of the high-temperature fatigue test. However, identifying the crack 82 that appears on the surface of the test specimen 80 for each cycle and evaluating the growth rate of the crack 82 are extremely important for accurately determining the life and strength of the product corresponding to the test specimen 80. Therefore, underestimating the size of the crack 82 or overlooking the crack 82 must be avoided.

[0035] Therefore, in the calculation processing unit 20, the multi-resolution processing unit 54, the emphasis processing unit 56, and the crack analysis unit 58 perform the respective processes described below so that the initial cracks 82 that appear on the surface of the test piece 80 during the high-temperature fatigue test can be analyzed, from the cracks 82 that appear just before the test piece 80 breaks.

[0036] 8 shows an example of the processing flow from the multi-resolution processing unit 54 to the crack analysis unit 58. In the arithmetic processing unit 20, for each crack observation image 102 extracted by the crack observation image extraction unit 52, multi-resolution processing by the multi-resolution processing unit 54, emphasis processing by the emphasis processing unit 56, and crack analysis processing by the crack analysis unit 58 are performed in this order. At this time, in the arithmetic processing unit 20, for each crack observation image 102 extracted by the crack observation image extraction unit 52, the processing from the multi-resolution processing unit 54 to the crack analysis unit 58 is repeatedly performed by tracing back the crack observation images 102 one by one, starting from the crack observation image 102 acquired immediately before the fracture of the test piece 80 to the crack observation image 102 acquired at the beginning of the high-temperature fatigue test. The processing flow will be specifically described below.

[0037] The crack analysis unit 58 focuses on the crack observation image 102 extracted by the crack observation image extraction unit 52, which is a crack 82 that can be considered to be a crack that occurred just before the test piece 80 broke, and analyzes the crack that occurs on the surface of the test piece by tracing back past crack observation images 102 that were taken at positions corresponding to the position of the surface of the test piece 80 that was captured in the crack observation image 102 just before the break, from the crack observation image 102 just before the break to the initial crack observation image 102 that captured the starting point of the crack. Specifically, first, the crack analysis unit 58 focuses on the crack observation image 102 immediately before fracture, among the crack observation images 102 extracted by the crack observation image extraction unit 52, which captures a crack 82 that can be considered to be the crack that occurred immediately before fracture of the test specimen 80. That is, among the captured images 100 captured immediately before the end of the high-temperature fatigue test, the crack analysis unit 58 focuses on the crack observation image 102 that captures the crack 82 that can be considered to be the crack that caused the fracture of the test specimen 80. Next, the crack analysis unit 58 identifies a past captured image 102 that was captured after the start of the high-temperature fatigue test by the imaging unit 16 that captured the focused crack observation image 102 immediately before fracture at the same position as the focused crack observation image 102 immediately before fracture. The crack analysis unit 58 traces the multiple past crack observation images 102 acquired in chronological order, from the crack observation image 102 immediately before fracture to the initial crack observation image 102. By performing the above process, even a minute initial crack immediately after its occurrence can be identified. Details of the process of tracing back past crack observation images 102 will be described later.

[0038] FIG. 9 shows an example of multi-resolution processing by the multi-resolution processor 54 and enhancement processing by the enhancement processor 56. It is preferable to perform multi-resolution processing by the multi-resolution processor 54 and enhancement processing by the enhancement processor 56 because this makes it easier to observe cracks. The multi-resolution processor 54 performs multi-resolution processing to convert the acquired crack observation image 102 into captured images 100A with multiple different resolutions. For example, the number of resolution levels is set to 20. The number of resolution levels may be any number. The high-resolution captured image 100A is an image for observing minute cracks, and the low-resolution captured image 100A is an image for observing extremely large cracks. By generating the captured images 100A with multiple different resolutions, it is possible to observe everything from small initial cracks immediately after their occurrence to extremely large cracks immediately before the fracture of the test piece 80.

[0039] The enhancement processing unit 56 performs enhancement processing on the captured images 100A at multiple resolutions generated by the multi-resolution processing unit to generate enhanced images. The enhancement processing includes first, second, and third processes. The first process includes Gabor filtering and binarization. The Gabor filtering process applies a first Gabor filter corresponding to the axial direction of the test object 80 and a second Gabor filter corresponding to a direction perpendicular to the axial direction of the test object 80 to the captured images 100A at each resolution to enhance the crack 82 in the captured images 100A. By applying the first and second Gabor filters corresponding to the horizontal and vertical directions of the captured images 100A, it is possible to enhance the boundary portion with a difference in brightness corresponding to the opening edge of the crack 82 in both the horizontal and vertical directions of the captured images 100A. The binarization process binarizes the captured images 100A at each resolution after the Gabor filtering process. As a result, a new captured image 100B is generated for each resolution, on which Gabor filtering and binarization have been performed. The Gabor filtering process is not limited to the horizontal and vertical directions, and emphasis processes can also be added in other directions.

[0040] The second process is an averaging process that adds together the new captured images 100B generated for each resolution in the first process. This generates an averaged captured image 100C. The third process is a process that further binarizes the captured image 100C averaged in the second process. This generates an enhanced image 100D in which the cracks 82 are enhanced. The enhanced image 100D in which the cracks 82 are enhanced is an example of the "enhanced image" of the present invention.

[0041] Fig. 10 shows an example of an enhanced image 100D generated immediately before the fracture of the test piece 80. The enhanced image 100D shown in Fig. 10 is a captured image generated from a crack observation image 102 acquired immediately before the fracture of the test piece 80. By performing multi-resolution processing and enhancement processing on the crack observation image 102 acquired immediately before the fracture of the test piece 80, the brightness difference in the enhanced image 100D becomes clearer depending on the temperature difference between the surface of the test piece 80 heated by the heating unit 12 and the inside of the crack 82, and therefore the crack 82 can be imaged more clearly.

[0042] The crack analysis unit 58 chronologically traces past crack observation images 102, starting with the crack observation image 102 immediately before fracture as the first image, from the crack observation image 102 immediately before fracture to the initial crack observation image 102. FIG. 11 shows an example of the process of tracing past crack observation images 102 by the crack analysis unit 58. FIG. 11 shows an enhanced image 100D obtained by performing multi-resolution processing and enhancement processing on the ith (variable i is an integer equal to or greater than 1) and (i+1)th crack observation images 102, where the crack observation image 102 immediately before fracture is the first image. That is, the enhanced image 100D1 shown in FIG. 11 is an image generated from the ith crack observation image 102. The enhanced image 100D2 shown in FIG. 11 is a captured image generated from the (i+1)th crack observation image 102.

[0043] The crack analysis unit 58 sets a rectangular area having approximately the same height and width as the height of a crack portion that has occurred due to an initial crack among the cracks captured in the ith crack observation image 102 as a first crack extraction area 104 in the ith crack observation image 102. That is, the crack analysis unit 58 sets the first crack extraction area 104 that surrounds the crack 82 in the ith enhancement-processed image 100D1 shown in FIG. Next, the crack analysis unit 58 sets, in the (i+1)th crack observation image 102, a region representing the same position as the first crack extraction region 104 in the i-th crack observation image 102 as the second crack extraction region 106, and for a portion of the crack included in the second crack extraction region 106 that has occurred due to an initial crack, sets a rectangular region having approximately the same height and width as the height of the crack portion as the first crack extraction region 104 in the (i+1)th crack observation image 102. That is, in the (i+1)th enhancement-processed image 100D2 shown in FIG. 11 , the crack analysis unit 60 sets, as the second crack extraction region 106, a region representing the same position as the first crack extraction region 104 in the i-th enhancement-processed image 100D1, and identifies, among the cracks included in the second crack extraction region 106, a portion of the crack 82 that has occurred due to an initial crack. Then, a rectangular area having approximately the same height as the height of the identified crack 82 portion and approximately the same width as the width of the crack portion is set as the first crack extraction area 104 in the (i+1)th enhanced processed image 100D2. In this way, by identifying cracks that have arisen due to an initial crack within the second crack extraction region 106 in the (i+1)th enhanced processed image 100D2 and setting the first crack extraction region 104, it is possible to avoid erroneously extracting noise (such as cracks that have not arisen due to an initial crack). Here, the crack that has occurred due to the initial crack can be the largest crack in the second crack extraction region 106. By detecting the length, depth, etc. of the crack, it is possible to identify the crack that has occurred due to the initial crack. The crack analysis unit 58 repeats the above process to chronologically trace past crack observation images 102, from the crack observation image 102 immediately before fracture to the initial crack observation image 102. If the second crack extraction region 106 can be set in the (i+1)th crack observation image 102 but the first crack extraction region 104 cannot be set, the (i+1)th crack observation image 102 is determined to be an initial crack observation image, and a starting point for crack generation is present within the second crack extraction region 106 of the initial crack observation image. Specifically, FIG. 12 shows an example of how the first crack extraction region 104 is sequentially set when tracing back past crack observation images in chronological order. As shown in FIG. 12, in the (n+1)th enhanced image 100D(n+1), the region representing the same position as the first crack extraction region 104 in the (n)th enhanced image 100D(n) can be set as the second crack extraction region 106. However, a minute initial crack cannot be detected, and the first crack extraction region 104 cannot be set. Therefore, the (n+1)th enhanced image 100D(n+1) is determined to be an initial crack observation image, and it is determined that the starting point of a crack is present within the second crack extraction region 106 of the initial crack observation image. Through the above process, the crack analysis unit 58 can analyze the progression (progression amount and propagation speed) of the crack that caused the fracture from the starting point of the crack.

[0044] The crack analysis unit 58 sets a first crack extraction region 104 for the ith enhanced image 100D1 generated using the multi-resolution processing unit 54 and the enhancement processing unit 56. That is, the multi-resolution processing by the multi-resolution processing unit 54 and the enhancement processing by the enhancement processing unit 56 described above are performed when tracing back past crack observation images 102 in chronological order, starting with the crack observation image 102 immediately before fracture as the first image, from the crack observation image 102 immediately before fracture to the initial crack observation image 102.

[0045] FIG. 13 shows an example of an enhanced image 100D generated at the beginning of a high-temperature fatigue test. The enhanced image 100D shown in FIG. 13 is a captured image generated from a crack observation image 102 acquired at the beginning of a high-temperature fatigue test. It is difficult to confirm the presence, position, and size of a crack 82 from the crack observation image 102 acquired at the beginning of a high-temperature fatigue test. However, in this embodiment, multi-resolution processing and enhancement processing are performed on the crack observation image 102 acquired at the beginning of a high-temperature fatigue test to generate the enhanced image 100D. As a result, the difference in brightness corresponding to the temperature difference between the surface of the test piece 80 heated by the heating unit 12 and the interior of the crack 82 becomes clear in the enhanced image 100D, making it possible to confirm the presence, position, and size of the crack 82.

[0046] Furthermore, because an initial crack is small, it is difficult to detect the initial crack from the beginning based on a crack observation image 102 acquired at the beginning of a high-temperature fatigue test. However, in this embodiment, first, attention is focused on a crack observation image 102 for observing a crack that can be considered to be a crack immediately before the test piece 80 breaks, and then past crack observation images 102 captured at a position corresponding to the position on the surface of the test piece 80 captured in the focused crack observation image 102 are traced back to the initial crack observation image 102 in which the initial crack that is the starting point for the crack 82 to occur was captured. This makes it possible to predict the position of the initial crack, thereby making it possible to detect the initial crack.

[0047] An example of the flow of the test piece analyzing method according to this embodiment is shown in Figure 14. The test piece analyzing method according to this embodiment is executed using a test piece analyzing device 10.

[0048] When the test specimen analysis method is started, first, in step S10, the captured image storage control unit 50 acquires captured images 100 generated by each of the multiple cameras 34 constituting the imaging unit 16 each time the entire circumference and entire length of the surface of the test specimen 80 are captured by the multiple cameras 34 during the high-temperature fatigue test. Then, the captured image storage control unit 50 stores the acquired captured images 100 in the storage device 44. In this way, the multiple captured images 100 obtained by continuously capturing images from the start to the end of the high-temperature fatigue test are stored in the storage device 44.

[0049] In step S12, the crack observation image extraction unit 54 identifies a crack in the captured image 100, which is generated by the imaging unit 16 at the timing when the tensile stress is at its maximum in a predetermined cycle, based on the difference in brightness that occurs in accordance with the temperature difference between the surface of the test piece 80 heated by the heating unit 12 and the inside of the crack, and extracts the captured image 100 in which the identified crack appears as the crack observation image 102. Step S12 is an example of the "crack observation image extraction step" in the present invention.

[0050] In step S14, the crack analysis unit 60 focuses on the crack observation image 102 immediately before fracture that captures a crack 82 that can be considered to be a crack immediately before fracture of the test piece 80, among the crack observation images 102 extracted by the crack observation image extraction unit 54. That is, the crack analysis unit 60 performs processing using the crack observation image immediately before fracture as the first image.

[0051] In step S16, the multi-resolution processing unit 54 performs multi-resolution processing and the enhancement processing unit 56 performs enhancement processing on the crack observation image 102 immediately before fracture, thereby generating an enhanced image 100D. Specifically, the multi-resolution processing unit 54 converts the crack observation image 102 immediately before the fracture into captured images 100A at a plurality of different resolutions. Next, the enhancement processing unit 56 performs Gabor filtering on the captured image 100A at each resolution, and performs binarization on the captured image 100A at each resolution that has been subjected to the Gabor filtering process, thereby generating a new captured image 100B for each resolution that has been subjected to the Gabor filtering process and binarization process. Furthermore, the enhancement processing unit 56 performs averaging processing to add together the new captured images 100B for each resolution that have been binarized, thereby generating an averaged captured image 100C. Finally, the enhancement processing unit 56 performs binarization processing to further binarize the averaged captured image 100C, thereby generating an enhancement-processed image 100D in which the cracks 82 are enhanced.

[0052] In step S18, the crack analysis unit 58 sets a rectangular area in the enhanced processed image 100D, which is generated in step S16 by processing the crack observation image 102 just before fracture, having a height approximately equal to the height of the crack just before fracture and a width approximately equal to the width of the crack just before fracture as the first crack extraction area 104 in the crack observation image 102 just before fracture.

[0053] In step S20, the crack analysis unit 58 performs multi-resolution processing by the multi-resolution processing unit 54 and enhancement processing by the enhancement processing unit 56 on the next (i+1th) crack observation image 102 when tracing back past crack observation images 102 in chronological order, from the crack observation image 102 just before fracture to the initial crack observation image 102, to generate an enhanced processed image 100D.

[0054] In step S22, the crack analysis unit 58 sets, in the (i+1)th enhanced image 100D, an area that represents the same position as the first crack extraction area 104 in the i-th crack observation image 102 as the second crack extraction area 106. That is, when the crack observation image 102 immediately before fracture is set as the i-th crack observation image (i=1), in the (i+1)th enhanced image 100D, an area that represents the same position as the first crack extraction area 104 in the crack observation image 102 immediately before fracture set in step S18 is set as the second crack extraction area 106.

[0055] In step S24, the crack analysis unit 58 sets a rectangular area having approximately the same height and width as the height of the crack portion that was caused by an initial crack among the cracks contained in the second crack extraction area 106 in the (i+1)th enhanced processed image 100D as the first crack extraction area 104 in the (i+1)th crack observation image 102.

[0056] In step S26, the crack analysis unit 58 determines whether the first crack extraction region 104 was set in the (i+1)th enhancement-processed image 100D. If the second crack extraction region 106 was set in the (i+1)th enhancement-processed image 100D but the first crack extraction region 104 was not set, the process proceeds to step S28. If the first crack extraction region 104 was set in the (i+1)th enhancement-processed image 100D, the process proceeds to step S32. Specifically, i is updated. That is, past crack observation images 102 are traced back in time series, and the process proceeds to step S20 to generate an enhancement-processed image 100D for the next crack observation image 102.

[0057] In step S28, the crack analysis unit 60 determines that the (i+1)th crack observation image 102 is an initial crack observation image, and determines that the starting point of a crack is present within the second crack extraction region 106 of the initial crack observation image.

[0058] In step S30, the crack analysis unit 60 analyzes the progress (amount of progress and progress rate) of the crack from the crack initiation point determined in step S28. Then, the test specimen analysis method ends. Steps S26, S30, and S32 are an example of a "crack analysis step" in the present invention.

[0059] As described above in detail, in this embodiment, first, attention is paid to the crack observation image 102 for observing a crack that can be considered to be a crack immediately before the test piece 80 breaks, and then past crack observation images 102 that captured a position corresponding to the position of the surface of the test piece 80 captured in the focused crack observation image 102 are traced back to the initial crack observation image 102 that captured an initial crack that is the starting point for the crack 82 to occur. Therefore, the position of the initial crack can be predicted, and therefore the initial crack can be detected.

[0060] In this embodiment, multi-resolution processing and enhancement processing are performed on the crack observation image 102 acquired during the high-temperature fatigue test to generate an enhanced image 100D. Therefore, in the enhanced image 100D, the difference in brightness becomes clear depending on the temperature difference between the surface of the test piece 80 heated by the heating unit 12 and the inside of the crack 82, so that the presence, position, and size of the crack 82 can be confirmed from the captured image acquired at the beginning of the high-temperature fatigue test to the captured image 100 acquired immediately before the fracture of the test piece 80.

[0061] In addition, in this embodiment, when tracing back past crack observation images 102 in chronological order from the crack observation image 102 immediately before fracture to the initial crack observation image 102, with the crack observation image 102 immediately before fracture as the first image, in the (i+1)th crack observation image 102, a region representing the same position as the first crack extraction region 104 in the i-th crack observation image 102 is set as a second crack extraction region 106, and among the cracks included in the second crack extraction region 106, a crack portion caused by the initial crack is extracted. A rectangular area having approximately the same height as the height of the crack portion and approximately the same width as the width of the crack portion is set as the first crack extraction area 104 in the (i+1)th crack observation image 102, and if the second crack extraction area 106 can be set in the (i+1)th crack observation image 102 but the first crack extraction area 104 cannot be set, the (i+1)th crack observation image 102 is determined to be an initial crack observation image, and it is determined that the starting point of a crack is present in the second crack extraction area 106 of the initial crack observation image. Therefore, it is possible to prevent noise from being included around the crack 82 in the crack observation image 102, and it is possible to prevent the maximum length of the crack 82 in the crack observation image 104 from being erroneously detected as being too long.

[0062] Furthermore, in this embodiment, the crack 82 is analyzed based on the captured image 100. Therefore, the time required to analyze the crack 82 can be shortened compared to the replica method.

[0063] FIG. 15 shows an example of the results of detecting the length of a main crack using the test specimen analysis method according to this embodiment. In the graph of FIG. 15, the horizontal axis represents the test time [sec], which is the time elapsed since the start of the high-temperature fatigue test, and the vertical axis represents the length of the main crack. As shown in FIG. 15, the test specimen analysis method according to this embodiment makes it possible to detect the length of a main crack immediately after its occurrence. This makes it possible to evaluate the amount and rate of growth of the main crack, which change with each cycle, and therefore makes it possible to accurately determine the lifespan, strength, etc. of the product corresponding to test specimen 80.

[0064] The above describes one embodiment of the present invention, but the present invention is not limited to the above, and it goes without saying that the present invention can be implemented in various modified forms within the scope of the gist of the present invention. [Explanation of symbols]

[0065] 10. Test specimen analysis equipment 12 Heating section 14 Stress applying section 16 Imaging unit 18 Control Unit 20 Processing unit 22 induction coil 24 AC power supply 26 1st grip part 28 Second grip part 30 Drive unit 32 Test bench 34 Camera 40 CPU 42 memory 44 Storage device 46 Bus 50 Captured image storage control unit 52 Crack observation image extraction unit 54 Multi-resolution processing unit 56 Emphasis processing unit 58 Crack Analysis Department 80 test specimens 82 Crack 100 captured images 102 Crack observation image 104 First crack extraction area 106 Second crack extraction area

Claims

1. 1. A test specimen analyzing apparatus for analyzing a test specimen based on cracks that occur on the surface of the test specimen during a high-temperature fatigue test in which the surface temperature of the test specimen is maintained within a set temperature range of 700°C or higher, a heating unit that heats the surface of the test specimen to the temperature range as a load in the high-temperature fatigue test; a stress applying unit that repeatedly applies tensile stress and compressive stress in a predetermined cycle in the axial direction of the test specimen as a load in the high-temperature fatigue test; an imaging unit that captures an image of the surface of the test piece and generates a captured image; a calculation processing unit that analyzes cracks occurring on the surface of the test specimen using the captured image generated by the imaging unit and analyzes the test specimen based on the analysis results; and The arithmetic processing unit a crack observation image extraction unit that identifies a crack in the captured image, which is generated at the timing when the tensile stress is maximized in the predetermined cycle, based on a difference in brightness that occurs according to a temperature difference between the surface of the test piece heated by the heating unit and the inside of the crack, among the captured images generated by the imaging unit, and extracts the captured image showing the identified crack as a crack observation image; and a crack analysis unit that focuses on a crack observation image immediately before fracture, which captures a crack that can be considered to be a crack that occurs immediately before fracture of the test piece, among the crack observation images extracted by the crack observation image extraction unit, and analyzes cracks that occur on the surface of the test piece by tracing back past crack observation images that were taken at positions corresponding to the positions on the surface of the test piece captured in the crack observation image immediately before fracture from the crack observation image immediately before fracture to an initial crack observation image that captures an initial crack that is the starting point for crack generation; A test specimen analysis device having the above.

2. The crack analysis unit When tracing back the past crack observation images in chronological order from the crack observation image immediately before the fracture to the initial crack observation image, with the crack observation image immediately before the fracture being the first image, In an i-th crack observation image (variable i is an integer of 1 or more), for a portion of a crack that has occurred due to the initial crack among the cracks captured in the i-th crack observation image, a rectangular area having approximately the same height as the height of the portion of the crack and approximately the same width as the width of the portion of the crack is set as a first crack extraction area in the i-th crack observation image; In the (i+1)th crack observation image, a region representing the same position as the first crack extraction region in the i-th crack observation image is set as a second crack extraction region, and for a portion of a crack included in the second crack extraction region that has occurred due to the initial crack, a rectangular region having approximately the same height as the height of the portion of the crack and approximately the same width as the width of the portion of the crack is set as the first crack extraction region in the (i+1)th crack observation image; In the (i+1)th crack observation image, when the second crack extraction region can be set and the first crack extraction region cannot be set, A test specimen analysis device as described in claim 1, which determines that the (i+1)th crack observation image is the initial crack observation image and determines that the starting point of a crack exists within the second crack extraction area of ​​the initial crack observation image.

3. The arithmetic processing unit a multi-resolution processing unit that converts the captured image generated by the imaging unit into captured images with a plurality of different resolutions; an enhancement processing unit that applies a first Gabor filter corresponding to a first direction and a second Gabor filter corresponding to a second direction different from the first direction to the captured images of the plurality of resolutions generated by the multi-resolution processing unit to generate new captured images, and adds and averages the new captured images to generate an enhancement-processed image; and When tracing back the past crack observation images in chronological order from the crack observation image immediately before the fracture to the initial crack observation image, with the crack observation image immediately before the fracture being the first image, A test specimen analysis device as described in claim 2, wherein the i+1th enhanced processed image is generated for the i+1th crack observation image using the multi-resolution processing unit and the enhancement processing unit, and a first crack extraction region is set in the i+1th enhanced processed image.

4. 1. A test specimen analysis method for analyzing a test specimen based on cracks that occur on the surface of a test specimen during a high-temperature fatigue test in which the surface temperature of the test specimen is maintained within a set temperature range of 700°C or higher, comprising: a heating unit that heats the surface of the test specimen to the temperature range as a load in the high-temperature fatigue test; a stress applying unit that repeatedly applies tensile stress and compressive stress in a predetermined cycle in the axial direction of the test specimen as a load in the high-temperature fatigue test; an imaging unit that captures an image of the surface of the test piece and generates a captured image; a calculation processing unit that analyzes cracks occurring on the surface of the test specimen using the captured image generated by the imaging unit and analyzes the test specimen based on the analysis results; Using a test specimen analysis device having a crack observation image extraction step of identifying a crack in the captured image, which is generated at a timing when the tensile stress is maximized in the predetermined cycle among the captured images generated by the imaging unit, based on a difference in brightness that occurs according to a temperature difference between the surface of the test body heated by the heating unit and the inside of the crack, and extracting the captured image showing the identified crack as a crack observation image; a crack analysis step of analyzing cracks occurring on the surface of the test piece by focusing on a crack observation image immediately before fracture that captures a crack that can be considered to be a crack that occurs immediately before fracture of the test piece among the crack observation images extracted in the crack observation image extraction step, and tracing back past crack observation images captured at positions corresponding to the positions on the surface of the test piece captured in the crack observation image immediately before fracture from the crack observation image immediately before fracture to an initial crack observation image that captures an initial crack that is the starting point for crack generation; A test specimen analysis method comprising:

Images