Crack detection method and crack detection device

Abstract

To provide a crack detection method and a crack detection device capable of detecting cracks that are difficult to see with naked eyes on a surface layer part of an object, and arbitrarily selecting a region where cracks are detected.SOLUTION: A crack detection method comprises: a thermal load application step in which a thermal load is applied to an arbitrary position on a surface of an object by a thermal load application unit, thereby generating a temperature gradient along the surface of a front surface layer including the surface of the object; an infrared image acquisition step in which an infrared image is acquired by imaging a temperature gradient region, which is a region of the front surface layer of the object where a temperature gradient occurs, using an infrared camera, to generate an infrared image for detecting cracks that have occurred in the front surface layer; and an infrared image display step in which the infrared image is displayed on a display.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a crack detection method and a crack detection device for detecting a crack occurring in an object. [Background technology]

[0002] The following technology is known as a crack detection method for detecting cracks, particularly fatigue cracks, that have occurred in an object: Patent Document 1 discloses a crack detection method for detecting cracks in a welded portion where a rib is welded to a deck plate in the bridge axis direction in a steel deck having a deck plate and a rib arranged on the underside of the deck plate.

[0003] This crack detection method includes a temperature distribution acquisition step of moving a device that acquires a temperature distribution by detecting infrared radiation energy emitted from an object along the direction of the weld while sequentially acquiring a temperature distribution in a direction intersecting the weld along the direction of movement of the device by detecting infrared radiation energy emitted from the object, a temperature gradient calculation step of calculating a temperature gradient in the weld from the acquired temperature distribution, and a detection step of detecting cracks in the weld based on the calculated temperature gradient. This crack detection method is said to make it possible to easily and quickly determine the presence or absence of cracks in the weld of a steel deck. It is also said that the temperature distribution acquisition step is preferably performed when the deck plate is heated by sunlight. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-141114 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a temperature gradient is generated along the surface of an object, including the surface, and cracks occurring in the surface of the object are detected based on the temperature gradient, using sunlight as a heat source to generate the temperature gradient results in a wide area of ​​the object's surface being uniformly heated from above, making it impossible to detect vertically extending cracks that are difficult to detect due to a temperature gradient gap, or short horizontal cracks that are difficult to see. Here, "hard-to-see cracks" refers to, for example, cracks that are too fine to be detected visually or with a camera (e.g., cracks with an opening of tens of micrometers or less), or cracks that are formed under a coating such as a paint film or protective film and are difficult to see visually from outside the object. Furthermore, when sunlight is used as a heat source, a wide area of ​​the object's surface is uniformly heated, making it impossible to arbitrarily select the area in which cracks are to be detected.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a crack detection method and crack detection device that can detect cracks that are difficult to see with the naked eye that have occurred on the surface of an object, and that can arbitrarily select the area in which to detect the cracks. [Means for solving the problem]

[0007] A first aspect of the present invention is a crack detection method comprising a thermal load application step of applying a local thermal load to an arbitrary position on the surface of an object using a thermal load application unit, thereby generating a temperature gradient along the surface in a surface layer portion including the surface of the object; an infrared image acquisition step of acquiring an infrared image for detecting cracks that have occurred in the surface layer portion by imaging a temperature gradient region, which is the region of the surface layer where the temperature gradient is generated, using an infrared camera; and an infrared image display step of displaying the infrared image on a display.

[0008] A second aspect of the present invention is the crack detection method according to the first aspect, wherein the thermal load applying step includes using a heating device as the thermal load applying unit.

[0009] A third aspect of the present invention is the crack detection method according to the first aspect, wherein the thermal load applying step includes using a cooling device as the thermal load applying unit.

[0010] A fourth aspect of the present invention is a crack detection method according to the first aspect, wherein the thermal load application step includes selecting either a heating device or a cooling device as the thermal load application unit depending on the properties of the object.

[0011] A fifth aspect of the present invention is a crack detection method according to any one of the first to fourth aspects, wherein the infrared image acquisition step includes acquiring a plurality of still images or videos as the infrared image by imaging the temperature gradient area with the infrared camera when the temperature gradient of the temperature gradient area is changing.

[0012] A sixth aspect of the present invention is a crack detection method according to any one of the first to fifth aspects, wherein the thermal load application step includes applying local thermal loads to a plurality of arbitrary positions on the surface by the thermal load application unit.

[0013] A seventh aspect of the present invention is a crack detection method according to any one of the first to sixth aspects, wherein the thermal load application step includes moving a position along the surface where a local thermal load is applied by the thermal load application unit, and the infrared image acquisition step includes imaging the temperature gradient region with the infrared camera each time the position where the thermal load is applied is moved.

[0014] An eighth aspect of the present invention is a crack detection method according to any one of the first to seventh aspects, comprising an image processing step of performing image processing on the infrared image, in which, for each of a plurality of image pixels constituting the infrared image, the difference between the temperature corresponding to the image pixel and the temperature corresponding to an adjacent image pixel adjacent to the image pixel is calculated, and the maximum value of the differences is set as the temperature corresponding to the image pixel, and the infrared image display step includes displaying the infrared image after the image processing has been performed on the display.

[0015] A ninth aspect of the present invention is a crack detection method according to any one of the first to eighth aspects, comprising a crack detection step of detecting the crack based on a temperature gradient in the infrared image displayed on the display.

[0016] A tenth aspect of the present invention is a crack detection device comprising: a thermal load applying unit that applies a local thermal load to any position on the surface of an object, thereby generating a temperature gradient along the surface of a surface layer including the surface of the object; an infrared image acquisition unit that acquires an infrared image for detecting cracks that have occurred in the surface layer by imaging a temperature gradient region, which is an area of ​​the surface layer where the temperature gradient occurs, using an infrared camera; an infrared image output unit that outputs the infrared image; and a display that displays the infrared image. [Effects of the Invention]

[0017] According to the present invention, a crack detection method and a crack detection device are provided that can detect cracks that are difficult to see with the naked eye and that occur on the surface of an object, and that can arbitrarily select the area in which to detect the crack. [Brief explanation of the drawings]

[0018] [Figure 1] 3 is a flowchart showing an example of the flow of a crack detection method according to the first embodiment. [Figure 2]FIG. 4 is a perspective view showing an example of a heat load applying step according to the first embodiment. [Figure 3] FIG. 4 is a perspective view showing an example of an infrared image acquisition step according to the first embodiment. [Figure 4] FIG. 10 is a perspective view showing an example in which an infrared ray anti-reflection material is attached to the surface of an object. [Figure 5] 1 is a block diagram showing an example of a crack detection device according to a first embodiment. [Figure 6] FIG. 10 is a diagram showing an example of an infrared image obtained by capturing an image of an object having a crack. [Figure 7] FIG. 10 is a diagram showing an example of an infrared image of an object without cracks. [Figure 8] FIG. 1 is a diagram showing an example of a comparison of temperature distributions in a cracked portion and a healthy portion of an object. [Figure 9] FIG. 10 is a diagram showing an example of a comparison between temperature distribution and deviation temperature. [Figure 10] FIG. 10 is a diagram showing an example of an infrared image on which image processing has been performed. [Figure 11] FIG. 10 is a perspective view showing an example of a heat load applying step according to the second embodiment. [Figure 12] FIG. 10 is a block diagram showing an example of a crack detection device according to a third embodiment. [Figure 13] 10 is a flowchart showing an example of the flow of a crack detection method according to a third embodiment. [Figure 14] FIG. 10 is a plan view showing an example of a heat load applying step according to the fourth embodiment. [Figure 15] FIG. 10 is a side view showing a heating device according to a first example of the fourth embodiment. [Figure 16] FIG. 13 is a side view showing a heating device according to a second example of the fourth embodiment. [Figure 17] FIG. 13 is a side view showing a cooling device according to a third example of the fourth embodiment. [Figure 18] FIG. 10 is a perspective view showing a cooling device according to a fourth example of the fourth embodiment. [Figure 19] FIG. 10 is a perspective view showing a cooling device according to a fifth example of the fourth embodiment. [Figure 20] FIG. 10 is a block diagram showing an example of a crack detection device according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] [First embodiment] First, a first embodiment of the present invention will be described.

[0020] (Outline of crack detection method) The crack detection method according to the first embodiment applies a local thermal load to the surface of an object, generating a temperature gradient along the surface of the object in a surface layer including the surface of the object, and detects cracks that have occurred in the surface layer of the object based on the temperature gradient. The local thermal load is applied by heating or cooling. The object may be made of any material as long as a temperature gradient is generated along the surface of the object in the surface layer of the object when a local thermal load is applied to the surface of the object. For example, the object may be made of metal or resin, but metal is preferable from the viewpoint of thermal conduction. When the object is made of metal, the metal may be iron, steel, titanium, aluminum, a copper alloy, stainless steel, or the like.

[0021] Furthermore, the object may be any object, and there are no limitations on size, shape, or use. For example, the object may be a steel plate, a steel bar, a wire rod, a building material, or a steel pipe. When the object is a steel plate, the steel plate may be a thick plate or a thin plate. The object may also be a transportation or industrial machinery part such as a railway wheel or a vehicle crankshaft. Furthermore, the object may be a structure. For example, the structure may be a steel manufacturing facility, social infrastructure, or a building. The structure may also be a ship, a bridge, a tank, a pipeline, a piping, an aircraft, or an automobile. The building may be a steel architectural structure.

[0022] FIG. 1 shows an example of the flow of the crack detection method according to the first embodiment. The crack detection method according to the first embodiment includes a thermal load application step S1, an infrared image acquisition step S2, an image processing step S3, an infrared image display step S4, and a crack detection step S5. In the crack detection method according to the first embodiment, each step is executed in the following order: thermal load application step S1, infrared image acquisition step S2, image processing step S3, infrared image display step S4, and crack detection step S5. An overview of each step will be described below.

[0023] The thermal load application step S1 is a step of generating a temperature gradient along the surface of the object in a surface layer portion including the surface of the object by applying a local thermal load to an arbitrary position on the surface of the object by a thermal load application unit. The infrared image acquisition step S2 is a step of generating an infrared image for detecting cracks that have occurred in the surface layer portion of the object by capturing an image of a temperature gradient region, which is a region in the surface layer portion of the object where a temperature gradient occurs, with an infrared camera, and acquiring the infrared image.

[0024] The image processing step S3 is a step of performing image processing on the infrared image acquired in the infrared image acquisition step S2 to clarify cracks that appear in the infrared image. The infrared image display step S4 is a step of displaying the infrared image after image processing on a display. The crack detection step S5 is a step of detecting cracks that have occurred in the surface layer of the object based on the temperature gradient in the infrared image displayed on the display. The crack detection method according to the first embodiment ends after the crack detection step S5. Each step will be described in detail below.

[0025] (Specific Description of Heat Load Application Step S1) FIG. 2 shows an example of the thermal load application step S1 according to the first embodiment. The object 10 is, for example, a metal test material formed into a plate shape. Below, an example will be described in which the test material is used as an example of the object 10. A crack 12 has occurred in a part of the surface layer including the surface of the object 10. In the example of FIG. 2, the crack 12 reaches the end face of the object 10. For example, the crack 12 is a very fine crack (for example, a crack with an opening of about several tens of μm or less) that cannot be seen with the naked eye or a camera. In FIG. 2, the size of the crack 12 is exaggerated.

[0026] In the thermal load application step S1 according to the first embodiment, a heating device 20 is used as an example of a thermal load application unit. The heating device 20 is operated, for example, by an operator (not shown). The heating device 20 may be any device that can apply a local thermal load (i.e., a heating load) to any position on the surface of the object 10. One example of the heating device 20 is a heat gun. A heat gun is a device that blows hot air from its tip.

[0027] The center of thermal load C indicates the center point of the thermal load applied by the heating device 20. In FIG. 2, the dotted areas indicate the areas to which the thermal load is applied by the heating device 20, with dark dots indicating high thermal loads and light dots indicating low thermal loads. As an example, the diameter of the area to which the thermal load is directly applied by the heating device 20 (i.e., the area exposed to hot air) may be approximately 10 to 100 mm. Furthermore, the temperature raised by the heating device 20 to the area to which the thermal load is directly applied may be 30°C or higher. When applying a thermal load to a wide area, if a large amount of energy and time are required, the temperature gradient becomes small, making it difficult to detect fine cracks. Therefore, it is advisable to narrow the area to which the thermal load is applied.

[0028] The heating device 20 may be a heat gun or various other heaters, such as a halogen heater. A halogen heater is a device that emits heat and light from a halogen lamp. A heat gun can heat a wide area, so it is suitable for use when relatively large (long, deep) cracks are expected, even among fine cracks. On the other hand, a halogen heater can heat locally, so it is suitable for use when particularly small (short, shallow) cracks are expected, even among fine cracks. A heat gun or a halogen heater may be selected when appropriately setting the size of the heating area depending on the expected size of the crack.

[0029] Because the crack 12 is a very small crack, the worker cannot visually confirm where the crack 12 has occurred on the surface layer of the object 10. Therefore, the worker estimates the location of the crack 12 and applies a local heat load using the heating device 20 to a position away from the direction intersecting the crack 12 so that a temperature gradient is generated in the direction intersecting the crack 12. The location of the crack 12 can be estimated based on the history of stress acting on the object 10, etc. The worker can arbitrarily select the location to apply the heat load based on the estimated location of the crack 12.

[0030] In the example shown in FIG. 2, crack 12 occurs at the location estimated by the operator. A localized thermal load is applied by heating device 20 to a position away from crack 12, resulting in a temperature gradient in the direction intersecting crack 12. When a temperature gradient occurs in the direction intersecting crack 12, crack 12 impedes heat transfer, causing the temperature gradient to become discontinuous. Therefore, crack 12 can be detected by detecting the discontinuity of the temperature gradient. When no temperature gradient occurs in the direction intersecting crack 12 (e.g., when a temperature gradient occurs in a direction parallel to crack 12) or when a thermal load is applied to crack 12, it can be difficult to detect the discontinuity of the temperature gradient. Therefore, when the temperature gradient is not discontinuous, it is advisable to change the position where the thermal load is applied (thermal load center C).

[0031] Furthermore, the size of the detectable crack 12 varies depending on the range and temperature of the temperature gradient region 14, which is the region of the surface layer of the object 10 where a temperature gradient occurs. Therefore, it is advisable to set the range and temperature of the temperature gradient region 14, and therefore the conditions of the local heat load applied by the heating device 20, according to the estimated size of the crack 12. Furthermore, if a sudden change in the temperature gradient (i.e., a large temperature difference) occurs due to the crack 12, the detection accuracy of the crack 12 improves. Therefore, it is advisable to apply a local heat load to the surface of the object 10 in a short period of time so as to create a steep temperature gradient. As an example, it is advisable to set the temperature rise rate as fast as possible, at 10°C / sec or higher. For example, since it is difficult to control the heat capacity of components, refrigerants, etc., and the thermal conductivity to the components, it is advisable to devise a method for heating and cooling as quickly as possible.

[0032] (Specific example of infrared image acquisition step S2) FIG. 3 shows an example of the infrared image acquisition step S2 according to the first embodiment. In the infrared image acquisition step S2, an infrared camera 42 is used. The infrared camera 42 is a camera that detects infrared rays emitted from the object 10 and generates an infrared image 70 that shows a temperature distribution according to the energy of the detected infrared rays. In the infrared image acquisition step S2, the temperature gradient region 14 is imaged by the infrared camera 42. As a result, the infrared camera 42 generates an infrared image 70 for detecting cracks 12 that have occurred in the surface layer of the object 10. The infrared camera 42 is operated, for example, by an operator (not shown). The infrared camera 42 preferably has a resolution that allows it to detect cracks 12 based on the temperature gradient. As an example, the infrared camera 42 preferably has a resolution higher than 0.1°C (for example, 0.02°C or 0.07°C).

[0033] FIG. 4 shows an example in which an infrared anti-reflection material 16 is attached to the surface of the object 10. If the surface of the object 10 has high infrared reflectivity, infrared rays emitted by a worker or the like may be reflected by the surface of the object 10, and the reflected infrared rays may be erroneously detected by the infrared camera 42. In this case, the infrared rays reflected by the surface of the object 10 may become a disturbance, and due to the influence of the disturbance, the temperature gradient in the temperature gradient region 14 may not be accurately detected by the infrared camera 42. Therefore, to suppress the influence of the disturbance, an infrared anti-reflection material 16 that prevents the reflection of infrared rays emitted from outside the object 10 may be attached to the surface of the object 10. For example, a matte black tape may be used as the infrared anti-reflection material 16.

[0034] 5 shows an example of a crack detection device 40 according to the first embodiment. The crack detection device 40 according to the first embodiment includes an infrared camera 42, a processing unit 44, and a display 46. The infrared camera 42 and the display 46 are connected to the processing unit 44 so as to be able to communicate with each other. The processing unit 44 is configured by a computer having a CPU (Central Processing Unit) 50, a memory 52, and a storage device 54. The CPU 50, the memory 52, and the storage device 54 are connected to each other so as to be able to communicate with each other via a bus 56 or the like.

[0035] The CPU 50 is a central processing unit that reads programs from the storage device 54 and executes the programs using the memory 52 as a work area. The memory 52 is composed of RAM (Random Access Memory) or the like, and temporarily stores programs and data as a work area. The storage device 54 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.

[0036] The storage device 54 stores a program 58 for detecting cracks 12. The CPU 50 reads out the program 58, expands the read program 58 into the memory 52, and executes it, thereby functioning as each functional unit of the arithmetic processing device 44. Specifically, the CPU 50 functions as an infrared image acquisition unit 62, an image processing unit 64, and an infrared image output unit 66.

[0037] The infrared image acquisition unit 62 acquires the infrared image 70 generated by the infrared camera 42. The infrared image acquisition step S2 according to the first embodiment includes capturing an image of the temperature gradient region 14 (see FIG. 3) by the infrared camera 42, and acquiring the infrared image 70 generated by the infrared camera 42 by the infrared image acquisition unit 62.

[0038] FIG. 6 shows an example of an infrared image 70 obtained when an object 10 having a crack 12 is imaged. The infrared image 70 is composed of a plurality of image pixels arranged in the horizontal and vertical directions of the infrared image 70. The plurality of image pixels respectively correspond to a plurality of physical pixels that make up a light receiving element (not shown) mounted on the infrared camera 42. The plurality of physical pixels output pixel values ​​proportional to the energy of the infrared light received by the light receiving element. The plurality of image pixels are represented by colors corresponding to the pixel values ​​of the respective physical pixels.

[0039] FIG. 7 shows an example of an infrared image 70 of an object 10 without a crack 12. In FIGS. 6 and 7, dotted areas indicate areas to which a thermal load is applied by the heating device 20, with darker dots indicating higher thermal loads and lighter dots indicating lower thermal loads. As can be seen by comparing FIGS. 6 and 7, when a crack 12 occurs on the surface of the object 10 and a temperature gradient occurs in a direction intersecting the crack 12, the crack 12 impedes heat transfer, resulting in a lower temperature in region A on the opposite side of the thermal load center C relative to the crack 12 than when no crack 12 occurs on the surface of the object 10. This results in a discontinuity in the temperature gradient across the crack 12. When the occurrence of a crack 12 can be detected by the discontinuity in the temperature gradient, as in FIG. 6, image processing step S3 may be omitted, as in a modified example described below.

[0040] Figure 8 shows an example comparing the temperature distribution in a cracked portion and a healthy portion of object 10. The cracked portion is the portion that crosses crack 12 along the temperature gradient, while the healthy portion is the portion that follows the temperature gradient and passes through areas other than crack 12. As shown in the graph in Figure 8, in the healthy portion, heat transfer is smooth, so the temperature gradient is continuous, whereas in the cracked portion, heat transfer is blocked at the location where crack 12 occurs, resulting in a temperature difference ΔT, which causes the temperature gradient to change suddenly and become discontinuous.

[0041] In this way, it is possible to detect cracks 12 by detecting that the temperature gradient is discontinuous. However, when the temperature difference ΔT is small, it may be difficult to read from the infrared image 70 that the temperature gradient in the infrared image 70 is discontinuous. In such cases, the crack detection method according to the first embodiment can perform image processing on the infrared image 70 acquired in the infrared image acquisition step S2 to clarify the cracks 12 that appear in the infrared image 70.

[0042] (Specific example of image processing step S3) The image processing step S3 is performed using the image processing unit 64 (see FIG. 5). For each of the multiple image pixels constituting the infrared image 70 acquired by the infrared image acquisition unit 62, the image processing unit 64 calculates the difference between the temperature corresponding to the image pixel and the temperature corresponding to the adjacent image pixel adjacent to that image pixel, and performs image processing on the infrared image 70 to set the maximum value of the calculated differences as the temperature corresponding to that image pixel. This image processing corresponds to a differentiation process in which the temperature difference between adjacent image pixels is differentiated by the distance between the adjacent image pixels.

[0043] Specifically, the image processing unit 64 executes image processing as follows: First, the image processing unit 64 determines, among the multiple image pixels constituting the infrared image 70, the image pixel that is the xth pixel counting from the first image pixel in the horizontal direction of the infrared image 70 and the yth pixel counting from the first image pixel in the vertical direction of the infrared image 70 as the (i, j) image pixel.

[0044] Next, the image processing unit 64 calculates the temperature corresponding to the (i, j) image pixel based on the pixel value corresponding to the (i, j) image pixel, and calculates the temperatures corresponding to each of the eight adjacent image pixels adjacent to the (i, j) image pixel, i.e., the (i+1, j) image pixel, the (i+1, i+1) image pixel, the (i+1, j-1) image pixel, the (i, j+1) image pixel, the (i, j-1) image pixel, the (i-1, j+1) image pixel, the (i-1, j-1) image pixel, and the (i-1, j) image pixel, based on the pixel values ​​corresponding to each adjacent image pixel.

[0045] Next, the image processing unit 64 calculates the difference between the temperature corresponding to the (i,j) image pixel and the temperatures corresponding to each of the eight adjacent image pixels, and sets the maximum of the calculated differences as the temperature corresponding to the (i,j) image pixel. The image processing unit 64 performs the above calculation for each of the multiple image pixels. The image processing unit 64 then generates an infrared image 70 that shows the calculated temperatures for each of the multiple image pixels as the processed infrared image 70.

[0046] Figure 9 shows an example of a comparison between temperature distribution and deviation temperature. Figure 9(A) is a graph showing an example of temperature distribution, and Figure 9(B) is a graph showing an example of deviation temperature. When determining the location of a crack from temperature change data of a line crossing a crack in an infrared image (e.g., the dashed line in the right diagram of Figure 8), the temperature of the object also changes significantly depending on the environment, as shown in Figure 9(A). For this reason, it is necessary to view temperature contours over a wide range. On the other hand, as shown in Figure 9(B), when displaying only the temperature gradient using the temperature derivative, it is sufficient to extract the portion where the temperature gradient is large due to the crack compared to the stable portion of the temperature derivative of the heat conduction area as a peak; the peak of the change amount itself does not need to be identified. When the derivative value is displayed as a contour by software, the values ​​before and after the crack crossing are small, and only the values ​​near the crack are large, making it possible to detect cracks by setting a narrow display temperature range. In other words, the image processing step S3 can increase the resolution of the contour display, making it easier to find the tip of the crack where the temperature gradient becomes small on the screen.

[0047] The image processing unit 64 may calculate temperatures corresponding to four adjacent image pixels adjacent to the (i,j) image pixel, i.e., the (i+1,j) image pixel, the (i,j+1) image pixel, the (i,j-1) image pixel, and the (i-1,j) image pixel, based on pixel values ​​corresponding to each adjacent image pixel, calculate the differences between the temperature corresponding to the (i,j) image pixel and the temperatures corresponding to each of the four adjacent image pixels, and set the maximum of the calculated differences as the temperature corresponding to the (i,j) image pixel. The image processing unit 64 may then generate an infrared image 70 indicating the temperatures obtained by the calculation for each of the multiple image pixels as the processed infrared image 70. The number of multiple adjacent image pixels adjacent to the (i,j) image pixel may be any number or any number.

[0048] FIG. 10 shows an example of an infrared image 70 after image processing. In the infrared image 70 after image processing, the temperature difference ΔT shown in FIG. 8 is converted into the differential value shown in FIG. 9(B). Therefore, in FIG. 10, dots indicate the amount of temperature change, with darker dots indicating a larger amount of temperature change and lighter dots indicating a smaller amount of temperature change. FIG. 10 also shows an enlarged schematic view of the vicinity of the crack, with each small square corresponding to a pixel. As shown in FIG. 10, the temperature difference between the pixel where the crack exists and the adjacent pixels on either side of it is significantly larger than the temperature difference between adjacent pixels in other areas. The width of the crack is represented by three pixels, and the dots are lighter as they approach the tip of the crack, making it easy to detect the position, path, and dimensions of the crack 12.

[0049] (Specific example of infrared image display step S4) The infrared image display step S4 is performed using the infrared image output unit 66 and the display 46 (see FIG. 5 for both). The infrared image output unit 66 acquires the infrared image 70 generated by the image processing unit 64 and outputs the acquired infrared image 70 (i.e., image data) to the display 46. The display 46 acquires the infrared image 70 input from the arithmetic processing unit 44 and displays the infrared image 70. The display 46 is, for example, a liquid crystal display capable of displaying color images. The display 46 may be installed in the same location as the work site where the thermal load application step S1 is performed, or in a different location.

[0050] (Specific example of crack detection step S5) In the crack detection step S5, the worker checks the infrared image 70 displayed on the display 46 and detects the position, size, shape, etc. of the crack 12 that has occurred in the surface layer based on the temperature gradient in the infrared image 70. In other words, the position, size, shape, etc. of the crack 12 can be detected based on the manner in which the temperature gradient in the infrared image 70 changes suddenly. The worker in the crack detection step S5 and the worker in the thermal load application step S1 may be the same person or different people.

[0051] (effect) As described above in detail, the crack detection method according to the first embodiment uses a heating device 20 that applies a localized heat load to any position on the surface of the object 10. Therefore, a temperature gradient can be generated along the surface of the object 10 in a surface layer including the surface of the object 10, and therefore, for example, cracks 12 that are too fine to be seen with the naked eye or a camera, etc. (for example, cracks with an opening of about several tens of μm or less) can be detected based on the temperature gradient. Moreover, because the heating device 20 can apply a localized heat load to any position on the surface of the object 10, the area in which the crack 12 is to be detected can be selected arbitrarily.

[0052] Incidentally, another example of a heat load applying unit for generating a temperature gradient is a cooling device, which will be described later. However, depending on the properties of the object 10, cooling may not be permitted (for example, corrosion may occur due to condensation). In this regard, the crack detection method according to the first embodiment uses a heating device 20, so that cracks 12 can be detected based on the temperature gradient even in an object 10 that cannot be cooled.

[0053] Furthermore, in the crack detection method according to the first embodiment, image processing can be performed on the infrared image 70 generated by the infrared camera 42. As described above, the image processing is performed by calculating, for each of the multiple image pixels constituting the infrared image 70, the difference between the temperature corresponding to the image pixel and the temperature corresponding to the adjacent image pixel adjacent to that image pixel (the temperature difference between adjacent image pixels), and setting the maximum value of the calculated differences as the temperature corresponding to that image pixel. As a result, changes in the temperature gradient are converted into the temperature difference between adjacent image pixels, and the crack 12 from its start point to its end point can be represented, for example, as the shade of a dot. Therefore, in the infrared image 70 on which image processing has been performed, the position, path, dimensions, etc. of the crack 12 can be easily detected based on the temperature difference between adjacent image pixels.

[0054] Furthermore, in the crack detection method according to the first embodiment, an infrared image 70 is displayed on the display 46, and a crack 12 occurring in the surface layer is detected based on the temperature gradient or the temperature difference between adjacent image pixels in the infrared image 70 displayed on the display 46. As a result, when a crack 12 is detected, it is possible to take measures such as identifying the position of the crack 12 or repairing the crack 12 while checking the infrared image 70 displayed on the display 46.

[0055] (Variation) In the above description, the crack 12 occurs on the surface of the object 10, but it may be formed under a coating such as a paint film or a protective film. A crack 12 formed under a coating such as a paint film or a protective film is a crack that cannot be seen with the naked eye from the outside of the object 10, and is therefore difficult to see. However, if there is peeling between the paint film or protective film and the specific target component, it becomes difficult to measure, so it is preferable that the paint film or protective film is in close contact.

[0056] In this way, even if the crack 12 is formed under a coating such as a paint film or a protective film on the object 10, as long as the coating is formed of a heat-conducting material and has a thickness that allows heat to be transmitted, a temperature gradient can be generated along the surface (specifically, along the surface of the surface layer) of the surface layer portion including the surface of the object 10 (i.e., the surface layer portion including the layer below the coating) by using the heating device 20. This makes it possible to detect cracks 12 formed under a coating such as a paint film or a protective film on the object 10 based on the temperature gradient or the temperature difference between adjacent image pixels. In other words, cracks 12 formed under the coating can be detected without peeling off the coating.

[0057] Furthermore, in the crack detection method according to the first embodiment, image processing is performed on the infrared image 70. However, for example, if a crack 12 occurring in the surface layer of the object 10 can be detected based on the temperature gradient in the infrared image 70 displayed on the display 46 without performing image processing on the infrared image 70, image processing may be omitted. In addition, if image processing is omitted, the infrared image 70 (see FIG. 6 ) generated by capturing an image with the infrared camera 42 may be displayed on the display 46. In this case, the operator can detect the position, path, dimensions, etc. of the crack 12 occurring in the surface layer based on the temperature gradient in the infrared image 70 displayed on the display 46.

[0058] [Second embodiment] Next, a second embodiment of the present invention will be described.

[0059] In the crack detection method according to the second embodiment, the thermal load application step S1 is changed as follows compared to the crack detection method according to the first embodiment. Below, the differences between the crack detection method according to the second embodiment and the crack detection method according to the first embodiment will be described.

[0060] FIG. 11 shows an example of the thermal load application step S1 according to the second embodiment. In the thermal load application step S1 according to the second embodiment, a cooling device 30 is used as an example of a thermal load application unit. The cooling device 30 is operated by an operator (not shown). The cooling device 30 may be any device that can apply a local thermal load (i.e., a cooling load) to an arbitrary position on the surface of the object 10. One example of the cooling device 30 is a cooling spray. The cooling spray sprays a refrigerant from a tubular container to cool the object 10. The temperature of the refrigerant immediately after being sprayed from the cooling spray is, for example, −85° C. The cooling spray may be a type commonly used for household use.

[0061] The center of thermal load C indicates the center point of the thermal load applied by the cooling device 30. In FIG. 11, the dotted areas indicate the areas to which the thermal load is applied by the cooling device 30, with dark dots indicating high thermal loads and light dots indicating low thermal loads. As an example, the diameter of the area to which the thermal load is directly applied by the cooling device 30 (i.e., the area to which the refrigerant hits) may be approximately 10 to 100 mm. Furthermore, the temperature reduced by the cooling device 30 in the area to which the thermal load is directly applied by the cooling device 30 may be 20°C or more.

[0062] The cooling device 30 may be, other than a cooling spray, a cooling gel foam spray, a cooling mist spray, an air cooler, etc. A cooling gel foam spray sprays a foam gel as a refrigerant, a cooling mist spray sprays a mist as a refrigerant, and an air cooler (ultra-low temperature air generator) sprays cold air as a refrigerant.

[0063] The cooling device 30 to be used may be selected depending on the estimated size of the crack 12 or the range that can be cooled by the cooling device 30. The worker estimates the location of the crack 12, and applies a local heat load by the cooling device 30 to a position away from the direction intersecting the crack 12 so that a temperature gradient occurs in the direction intersecting the crack 12. The position to which the heat load is applied can be arbitrarily selected by the worker based on the estimated location of the crack 12.

[0064] In the example shown in FIG. 11 , a crack 12 has occurred at the position estimated by the operator, and a temperature gradient has occurred in the direction intersecting the crack 12 due to the application of a local heat load by the cooling device 30 to a position away from the crack 12 in the direction intersecting the crack 12. When a temperature gradient has occurred in the direction intersecting the crack 12, the crack 12 prevents heat transfer, causing the temperature gradient to become discontinuous. Therefore, the crack 12 can be detected by detecting that the temperature gradient is discontinuous. As in the first embodiment, if the temperature gradient is not discontinuous, it is advisable to change the position at which the heat load is applied (heat load center C).

[0065] Furthermore, the size of the detectable crack 12 varies depending on the range and temperature of the temperature gradient region 14, which is the region of the surface layer of the object 10 where a temperature gradient occurs. Therefore, it is advisable to set the range and temperature of the temperature gradient region 14, and ultimately the conditions of the local heat load applied by the cooling device 30, according to the estimated size of the crack 12. Furthermore, if a sudden change in the temperature gradient (i.e., a large temperature difference) occurs due to the crack 12, the detection accuracy of the crack 12 improves, so it is advisable to apply a local heat load to the surface of the object 10 in a short period of time so as to make the temperature gradient steep.

[0066] Incidentally, another example of a heat load applying unit for generating a temperature gradient is the above-mentioned heating device 20 (see FIG. 2), but depending on the properties of the object 10, heating may not be permitted (for example, damage to a paint film or protective film may occur). In this regard, the crack detection method according to the second embodiment uses a cooling device 30, so that cracks 12 can be detected based on the temperature gradient even in an object 10 that cannot be heated.

[0067] Note that either the heating device 20 or the cooling device 30 may be selected as the heat load applying unit depending on the properties of the object 10 (for example, whether it is heat-resistant or not). In this way, a temperature gradient can be generated depending on the properties of the object 10.

[0068] In addition, if the refrigerant sprayed from the cooling device 30 liquefies on the surface of the object 10, the refrigerant may be guided away from the crack 12 using, for example, a guide member, etc., to prevent the refrigerant from penetrating into the crack 12.

[0069] [Third embodiment] Next, a third embodiment of the present invention will be described.

[0070] In the crack detection method according to the third embodiment, the thermal load application step S1 is changed as follows compared to the crack detection method according to the first embodiment. Below, the differences between the crack detection method according to the third embodiment and the crack detection method according to the first embodiment will be described.

[0071] 12 shows an example of a crack detection device 140 according to the third embodiment. The crack detection device 140 according to the third embodiment further includes an end determination unit 68. That is, in the crack detection device 140 according to the third embodiment, the CPU 50 functions as the end determination unit 68 in addition to the infrared image acquisition unit 62, the image processing unit 64, and the infrared image output unit 66.

[0072] FIG. 13 shows an example of the flow of the crack detection method according to the third embodiment. The crack detection method according to the third embodiment includes an additional termination determination step S6. The termination determination step S6 is executed using a termination determination unit 68. The termination determination unit 68 determines whether a termination condition for terminating the crack detection method is met. Examples of the termination condition include a condition that the elapsed time since the thermal load application step S1 was executed exceeds a predetermined elapsed time, and a condition that an operator issues an instruction to the arithmetic processing device 44 to terminate the crack detection method. The predetermined elapsed time is set, for example, to the time from the application of the thermal load until the temperature gradient becomes small enough that crack 12 cannot be detected based on the temperature gradient due to heat diffusion.

[0073] If it is determined in the termination determination step S6 that the termination condition is satisfied, the crack detection method is terminated. On the other hand, if it is determined in the termination determination step S6 that the termination condition is not satisfied, the crack detection method continues and proceeds to the infrared image acquisition step S2. If it is determined in the termination determination step S6 that the termination condition is not satisfied, the infrared image acquisition step S2 to the crack detection step S5 are repeatedly executed until it is determined that the termination condition is satisfied.

[0074] When the steps from the infrared image acquisition step S2 to the crack detection step S5 are repeatedly executed, the temperature gradient of the temperature gradient region 14 changes over time. That is, the temperature gradient gradually decreases due to heat diffusion. Furthermore, each time the steps from the infrared image acquisition step S2 to the crack detection step S5 are repeatedly executed, the infrared image acquisition step S2 is executed, thereby generating a plurality of infrared images 70.

[0075] The multiple infrared images 70 may be generated as multiple still images or as a moving image (more specifically, frames of a moving image). The multiple still images or moving images generated are displayed on the display 46. That is, the multiple still images or moving images are sequentially updated for each infrared image display step S4 and displayed on the display 46. The frame rate of the moving image is set to, for example, 30 fps (frames per second). The time interval at which the multiple still images are sequentially updated is set to, for example, longer than the time interval between frames of the moving image.

[0076] As described above, in the crack detection method according to the third embodiment, when the temperature gradient of the temperature gradient region 14 is changing, the temperature gradient region 14 is imaged by the infrared camera 42, whereby a plurality of still images or videos are generated as the infrared image 70, and the generated still images or videos are displayed on the display 46. Therefore, the worker can confirm how the temperature gradient around the crack 12 changes over time through the infrared image 70 displayed on the display 46. This allows the crack 12 to be detected based on how the temperature gradient around the crack 12 changes over time, thereby improving the detection accuracy of the crack 12.

[0077] In the crack detection method according to the third embodiment, similarly to the crack detection method according to the second embodiment, a cooling device 30 (see FIG. 11) may be used as an example of the thermal load applying section.

[0078] In addition, by repeating steps S2 to S4, data for determining cracks can be obtained as a video, and the resulting video can be viewed later to determine cracks in a separate task in step S5.

[0079] Alternatively, the operation of step S2 may be repeated to obtain a video of the temperature distribution, and steps S3 and S4 may be performed using software as post-processing, after which cracks may be determined in step S5 as a separate operation.

[0080] [Fourth embodiment] Next, a fourth embodiment of the present invention will be described.

[0081] In the crack detection method according to the fourth embodiment, the thermal load application step S1 is changed as follows compared to the crack detection method according to the first embodiment. Below, the differences between the crack detection method according to the fourth embodiment and the crack detection method according to the first embodiment will be described.

[0082] Fig. 14 shows an example of the thermal load application step S1 according to the fourth embodiment. In the thermal load application step S1 according to the fourth embodiment, local thermal loads are applied to a plurality of arbitrary positions on the surface of the object 10. Each thermal load center C indicates the center point of the thermal load. In Fig. 14, dotted areas indicate areas to which a thermal load is applied, with dark dots indicating a high thermal load and light dots indicating a low thermal load.

[0083] 14, when a temperature gradient occurs in a direction intersecting with the crack 12, the crack 12 hinders heat transfer, and the temperature of the region A on the opposite side of the thermal load center C relative to the crack 12 becomes lower than when no crack 12 occurs in the surface layer of the object 10. As a result, the temperature gradient becomes discontinuous at the boundary of the crack 12.

[0084] FIG. 15 shows a heating device 120 according to a first example of the fourth embodiment. The heating device 120 includes a metal member 122 and a plurality of heat transfer members 124. The metal member 122 is formed, for example, in a block shape. The plurality of heat transfer members 124 are formed, for example, from a thermally conductive gel or the like, and are connected to the metal member 122. The metal member 122 is placed on the surface of the object 10 via the plurality of heat transfer members 124, and is heated by a heater or the like (not shown). When the metal member 122 is heated, the heat of the metal member 122 is transferred to the surface of the object 10 via the plurality of heat transfer members 124. As a result, local thermal loads are simultaneously applied to a plurality of arbitrary positions on the surface of the object 10.

[0085] In this way, in the crack detection method according to the fourth embodiment, local thermal loads are applied to a plurality of arbitrary positions on the surface of the object 10. This allows cracks 12 to be detected over a wider range than when a local thermal load is applied to one location.

[0086] Furthermore, in the crack detection method according to the fourth embodiment, a heating device 120 is used to simultaneously apply local heat loads to multiple arbitrary positions on the surface of the object 10. This makes it possible to detect cracks 12 (especially long cracks) over a wide range in a short period of time.

[0087] 15 may be used as a cooling device. That is, the metal member 122 may be cooled by a refrigerant or the like. In this way, local heat loads (i.e., cooling loads) can be simultaneously applied to a plurality of arbitrary positions on the surface of the target object 10.

[0088] In addition, in the heating device 120 shown in FIG. 15, a metal member 122 may be used to apply a thermal load to a plurality of heat transfer members 124 in sequence.

[0089] FIG. 16 shows a heating device 220 according to a second example of the fourth embodiment. The heating device 220 includes a plurality of heat source members 222, a plurality of heat transfer members 224, and a plurality of magnets 226. Each heat source member 222 is formed, for example, from a heat-conductive gel or the like. Each heat source member 222 is formed in a block shape. Each magnet 226 is built into the heat source member 222. The plurality of heat transfer members 224 are formed, for example, from a metal plate or the like, and are placed on the surface of the object 10. Each heat source member 222 is placed on the surface of the object 10 via the heat transfer member 224 due to an attraction force acting between the magnet 226 and the heat transfer member 224. The plurality of heat source members 222 are heated by a heater or the like (not shown). For example, the temperature of the heat source member 222 may be 60° C. or more higher than the temperature of the surface of the object 10. Each heat source member 222 is attached to the surface of the object 10 using a magnet 226, so that the heat source member 222 can be prevented from coming off.

[0090] When the plurality of heat source members 222 placed on the surface of the object 10 are heated in sequence, or when the heated heat source members 222 are placed in sequence on the surface of the object 10, the heat of each heat source member 222 is transferred in sequence to the surface of the object 10 via the heat transfer member 224. This allows localized heat loads to be applied in sequence to a plurality of arbitrary positions on the surface of the object 10.

[0091] In this way, by sequentially applying localized thermal loads to multiple arbitrary positions on the surface of the object 10, it is possible to detect cracks 12 over a wide area while preventing the temperature from rising all at once over a wide area.

[0092] 16, a plurality of heat source members 222 placed on the surface of the object 10 may be heated simultaneously, or heated heat source members 222 may be placed simultaneously on the surface of the object 10. In this way, local heat loads can be applied simultaneously to a plurality of arbitrary positions on the surface of the object 10.

[0093] 16, the heat transfer member 224 on which the heat source member 222 is to be installed may be selected from a plurality of heat transfer members 224 previously installed on the surface of the object 10, and the heat source member 222 may be installed on the selected heat transfer member 224. In this way, the position to which the heat load is to be applied can be selected from a plurality of positions on the surface of the object 10.

[0094] 16 may be used as a cooling device. That is, each heat source member 222 may be cooled by a refrigerant or the like. In this way, local heat loads (i.e., cooling loads) can be applied sequentially or simultaneously to a plurality of arbitrary positions on the surface of the target object 10.

[0095] FIG. 17 shows a cooling device 130 according to a third example of the fourth embodiment. The cooling device 130 has multiple nozzles 132. The multiple nozzles 132 simultaneously spray mist as a refrigerant. The temperature of the mist should be at least 40° C. lower than the temperature of the surface of the object 10. Using a cooling device 130 configured in this way makes it possible to simultaneously apply local heat loads (i.e., cooling loads) to multiple arbitrary positions on the surface of the object 10.

[0096] 17, mist may be sprayed sequentially from multiple nozzles 132. In this way, localized heat loads can be applied sequentially to multiple arbitrary positions on the surface of the object 10. The refrigerant (mist) may be selected according to the temperature of the surface of the object 10, such as alcohol, organic solvent, or gas liquefied under pressure. Gas liquefied under pressure is an ideal refrigerant because it is sprayed as a mist and then rapidly vaporizes and its temperature drops due to reduced pressure.

[0097] FIG. 18 shows a cooling device 230 according to a fourth example of the fourth embodiment. The cooling device 230 has a plurality of cylindrical members 232. The plurality of cylindrical members 232 are formed, for example, from urethane resin or the like, and are installed on the surface of the object 10. Inside each cylindrical member 232, for example, a highly volatile refrigerant that immediately turns into gas upon contact with the object to be measured and escapes through holes, an aerosol-type refrigerant that easily evaporates, or dehumidified cooling air (hereinafter referred to as "refrigerant, etc.") is poured. Inside each cylindrical member 232, the refrigerants, etc. may be accommodated sequentially or simultaneously. In this manner, local heat loads (i.e., cooling loads) can be applied sequentially or simultaneously to a plurality of arbitrary positions on the surface of the object 10.

[0098] Furthermore, even when a refrigerant or the like is sequentially injected into the inside of each cylindrical member 232, for example, by previously installing a plurality of cylindrical members 232 on the surface of the target object 10, it is possible to prevent the refrigerants or the like injected into each cylindrical member 232 (i.e., refrigerants or the like having different temperatures due to injection time differences) from mixing together. This makes it possible to generate a temperature gradient around each cylindrical member 232.

[0099] 18, a cylindrical member 232 into which the refrigerant or the like is to be injected may be selected from a plurality of cylindrical members 232 previously installed on the surface of the target object 10, and the refrigerant or the like may be injected into the selected cylindrical member 232. In this way, a position to which a heat load is to be applied can be selected from a plurality of positions on the surface of the target object 10.

[0100] FIG. 19 shows a cooling device 330 according to a fifth example of the fourth embodiment. The cooling device 330 has a plurality of cylindrical members 332. The plurality of cylindrical members 332 are formed, for example, from urethane tubes or the like, and are placed on the surface of the target object 10 while being bundled together by a restraining member 334. A refrigerant or the like is poured into the inside of each cylindrical member 332. An overflow exhaust hole 336 is formed in each cylindrical member 332. The restraining member 334 is formed, for example, from urethane foam, sponge, or the like, and absorbs the refrigerant or the like that overflows from the cylindrical members 332. The refrigerant or the like may be poured into the inside of each cylindrical member 332 sequentially or simultaneously. In this manner, local heat loads (i.e., cooling loads) can be applied sequentially or simultaneously to a plurality of arbitrary positions on the surface of the target object 10.

[0101] Furthermore, even when a refrigerant or the like is sequentially injected into the inside of each cylindrical member 332, for example, by previously installing a plurality of cylindrical members 332 on the surface of the target object 10, it is possible to prevent the refrigerants or the like injected into each cylindrical member 332 (i.e., refrigerants or the like having different temperatures due to injection time differences) from mixing together. This makes it possible to generate a temperature gradient around each cylindrical member 332.

[0102] 19, a cylindrical member 332 into which the refrigerant or the like is to be injected may be selected from a plurality of cylindrical members 332 previously installed on the surface of the target object 10, and the refrigerant or the like may be injected into the selected cylindrical member 332. In this way, a position to which a heat load is to be applied can be selected from a plurality of positions on the surface of the target object 10.

[0103] Furthermore, in the crack detection method according to the fourth embodiment, local thermal loads may be sequentially applied to a plurality of arbitrary positions on the surface of the object 10, thereby moving the positions where the local thermal loads are applied along the surface of the object 10. Then, each time the positions where the thermal loads are applied are moved, an image of the temperature gradient region 14 may be taken by the infrared camera 42 (see FIG. 4). In this way, the region where cracks 12 are detected can be moved, and therefore cracks 12 can be detected over a wider range than when a local thermal load is applied to one location.

[0104] Furthermore, in the crack detection method according to the fourth embodiment, the position where a local thermal load is applied may be moved along the surface of the object 10, for example, by moving the heating device 20 shown in FIG. 2 or the cooling device 330 shown in FIG. 11. Then, each time the position where the thermal load is applied is moved, an image of the temperature gradient region 14 may be taken by the infrared camera 42 (see FIG. 4). Even in this way, the region where cracks 12 are detected can be moved, and therefore cracks 12 can be detected over a wider range than when a local thermal load is applied to one location.

[0105] Furthermore, when the temperature gradient region 14 is imaged by the infrared camera 42 each time the position where the thermal load is applied is moved, multiple infrared images 70 may be stitched together. In this way, the position, size, shape, etc. of the long crack 12 that appears across multiple infrared images 70 can be detected.

[0106] [Fifth embodiment] Next, a fifth embodiment of the present invention will be described.

[0107] The crack detection method according to the fifth embodiment is modified as follows from the crack detection method according to the first embodiment: Below, the differences between the crack detection method according to the fifth embodiment and the crack detection method according to the first embodiment will be described.

[0108] FIG. 20 shows an example of a crack detection device 240 according to the fifth embodiment. The crack detection method according to the fifth embodiment is executed using the crack detection device 240 according to the fifth embodiment. The crack detection device 240 according to the fifth embodiment includes a thermal load applying unit 242 and a thermal load driving unit 244. The above-mentioned heating device or cooling device may be applied to the thermal load applying unit 242. The thermal load driving unit 244 is a device that moves the thermal load applying unit 242, and is configured by a robot arm, a motor driving device, or the like.

[0109] The crack detection device 240 according to the fifth embodiment further includes a control unit 60. That is, in the crack detection device 240 according to the fifth embodiment, the CPU 50 functions as the control unit 60 in addition to the infrared image acquisition unit 62, the image processing unit 64, and the infrared image output unit 66.

[0110] The control unit 60 controls the heat load applying unit 242 so that a local heat load is applied by the heat load applying unit 242 to any position on the surface of the object 10. The control unit 60 also controls the heat load driving unit 244 so that the heat load applying unit 242 moves to any position on the surface of the object 10. The control unit 60 also controls the infrared camera 42 so that the temperature gradient region 14 is imaged by the infrared camera 42. Note that the control unit 60 may also control the heat load applying unit 242 and the heat load driving unit 244 so that local heat loads are applied to a plurality of any positions on the surface of the object 10.

[0111] In this way, when the crack detection device 140 is equipped with a heat load application unit 242, a heat load driving unit 244, and a control unit 60, the heat load application step S1 and the infrared image acquisition step S2, and ultimately the heat load application step S1 to the infrared image display step S4, can be automated.

[0112] The first to fifth embodiments of the present invention have been described above, but the present invention is not limited to the above, and it goes without saying that various modifications can be made within the scope of the gist of the present invention.

[0113] Furthermore, among the multiple techniques described in the first to fifth embodiments, techniques that can be combined may be appropriately combined and implemented. [Explanation of symbols]

[0114] 10 Object 12 Crack 14 Temperature gradient region 16 Infrared anti-reflection material 20 Heating device 30 Cooling device 40 Crack detection device 42 Infrared Camera 44 Processing Unit 46 Display 50 CPU 52 memory 54 Storage device 56 Bus 58 Programs 60 Control Unit 62 Infrared image acquisition unit 64 Image processing section 65 Crack detection unit 66 Infrared image output unit 68 End Determination Section 70 Infrared Images 120 Heating device 122 Metallic parts 124 Heat transfer material 130 Cooling device 132 nozzles 140 Crack detection device 220 Heating device 222 Heat Source Materials 224 Heat Transfer Materials 226 Magnet 230 Cooling device 232 Tube material 240 Crack detection device 242 Heat load applying section 244 Heat Load Drive Unit 330 Cooling device 332 Tube material 334 Restraining member 336 Exhaust Vent

Claims

1. a heat load applying step of applying a local heat load to an arbitrary position on a surface of the object by a heat load applying unit, thereby generating a temperature gradient along the surface in a surface layer portion including the surface of the object; an infrared image acquisition step of acquiring an infrared image for detecting cracks generated in the surface layer portion by capturing an image of a temperature gradient region, which is a region of the surface layer portion where the temperature gradient occurs, using an infrared camera; an infrared image display step of displaying the infrared image on a display; A crack detection method comprising:

2. The thermal load applying step includes using a heating device as the thermal load applying unit. The crack detection method of claim 1 .

3. The thermal load applying step includes using a cooling device as the thermal load applying unit. The crack detection method of claim 1 .

4. the thermal load applying step includes selecting either a heating device or a cooling device as the thermal load applying unit depending on the properties of the object. The crack detection method of claim 1 .

5. the infrared image acquisition step includes acquiring a plurality of still images or moving images as the infrared image by capturing an image of the temperature gradient region with the infrared camera when the temperature gradient of the temperature gradient region is changing. The crack detection method of claim 1 .

6. the thermal load applying step includes applying local thermal loads to a plurality of arbitrary positions on the surface by the thermal load applying unit; The crack detection method of claim 1 .

7. the thermal load applying step includes moving a position where a local thermal load is applied by the thermal load applying unit along the surface; the infrared image acquisition step includes capturing an image of the temperature gradient region with the infrared camera every time the position to which the thermal load is applied is moved. The crack detection method of claim 1 .

8. an image processing step of calculating, for each of a plurality of image pixels constituting the infrared image, a difference between a temperature corresponding to the image pixel and a temperature corresponding to an adjacent image pixel adjacent to the image pixel, and performing image processing on the infrared image such that the maximum value of the differences is the temperature corresponding to the image pixel; the infrared image display step includes displaying the infrared image on the display device after the image processing has been performed. The crack detection method of claim 1 .

9. a crack detection step of detecting the crack based on a temperature gradient in the infrared image displayed on the display. The crack detection method of claim 1 .

10. a thermal load applying unit that applies a local thermal load to an arbitrary position on a surface of an object, thereby generating a temperature gradient along the surface in a surface layer portion including the surface of the object; an infrared image acquisition unit that acquires an infrared image generated by capturing an image of a temperature gradient region, which is a region of the surface layer where the temperature gradient occurs, using an infrared camera, for detecting cracks that have occurred in the surface layer; and an infrared image output unit that outputs the infrared image; a display that displays the infrared image; A crack detection device comprising:

Images