Stress light emission measurement device and stress light emission measurement method

Abstract

A stress light emission measurement device (100) comprises an excitation light source (50), an imaging device (60), optical filters (F1, F2), and a processing device (70). The excitation light source (50) is configured to irradiate a stress light-emitting body (90) with excitation light before and during application of external force to the stress light-emitting body. The imaging device (60) images light emitted by the stress light-emitting body (90). The optical filters (F1, F2) remove an excitation light component from the captured image. The processing device (70) calculates, on the basis of the captured image produced by the imaging device (60), a stress light emission image that indicates stress light emission when external force is applied to the stress light-emitting body (90).

Description

Mechanoluminescence measurement device and mechanoluminescence measurement method

[0001] The present disclosure relates to a mechanoluminescence measurement device and a mechanoluminescence measurement method.

[0002] There is known a technique for analyzing strain in a sample, structure, or the like to which a mechanoluminescent material is applied or mixed, by measuring the stress generated in the mechanoluminescent material based on the luminescence phenomenon of the mechanoluminescent material.

[0003] For example, Japanese Patent Application Laid-Open No. 2020-112514 (Patent Document 1) discloses a stress-luminescence measuring device configured to measure stress-luminescence corresponding to stress generated in a stress-luminescent material by irradiating the stress-luminescent material with excitation light to put the material into an excited state, and then imaging the light emitted from the stress-luminescent material with the excitation light turned off.

[0004] Japanese Patent Application Laid-Open No. 2020-112514

[0005] As described in Patent Document 1, in order to accurately visualize the mechanoluminescence phenomenon, it is necessary to irradiate the mechanoluminescent material with excitation light in advance to provide the material with excitation energy. After the irradiation of excitation light is completed, the mechanoluminescent material emits light and releases energy. Furthermore, the mechanoluminescent material emits light when stress is generated by the application of an external force. Therefore, the amount of light emitted by the mechanoluminescent material attenuates with the passage of time and the application of an external force after the irradiation of excitation light is completed. Since the amount of light emitted when an external force is applied to the mechanoluminescent material varies depending on the excited state of the mechanoluminescent material, when an external force is repeatedly applied to the mechanoluminescent material over a long period of time, it is necessary to irradiate the mechanoluminescent material with excitation light each time in order to excite the mechanoluminescent material to a constant state.

[0006] However, when an external force is applied to a stress-stimulated luminescent material while irradiating it with excitation light and capturing an image of the luminescence of the stress-stimulated luminescent material, an optical image of the sample is captured by the excitation light simultaneously with the emission of the stress-stimulated luminescent material. Therefore, there is a concern that the desired image of the stress-stimulated luminescent material may be buried in the optical image of the sample in the captured image. In particular, when the luminescence intensity of the stress-stimulated luminescent material is sufficiently smaller than the intensity of the excitation light, this may hinder accurate visualization of the stress-stimulated luminescence phenomenon.

[0007] Furthermore, the light emitted by an excited mechanoluminescent material contains a light component that is emitted even without the application of an external force. This light component has the same wavelength band as the mechanoluminescence. After the irradiation of the excitation light is terminated, this light component decays over time. Therefore, conventionally, a method has been adopted in which the mechanoluminescence is imaged by waiting for this light component to decay before applying an external force to the mechanoluminescent material. However, when the above-mentioned configuration of imaging a mechanoluminescent material while irradiating it with excitation light is adopted, this light component becomes background light without decay, which may reduce the contrast of the mechanoluminescence that occurs above it. As a result, there is a concern that it may be difficult to accurately visualize the progression of mechanoluminescence accompanying the application of an external force.

[0008] The present disclosure has been made to solve such problems, and its purpose is to provide a technology for accurately visualizing the progression of mechanoluminescence occurring in a mechanoluminescent material during the application of an external force in a mechanoluminescence measurement device and a mechanoluminescence measurement method that measure the stress occurring in a mechanoluminescent material based on the luminescence phenomenon of the mechanoluminescent material.

[0009] A stress-luminescence measurement device according to one aspect of the present disclosure measures stress generated in a stress-luminescent material based on the luminescence phenomenon of the stress-luminescent material. The stress-luminescence measurement device includes an excitation light source, an imaging device, an optical filter, and a processing device. The excitation light source is configured to irradiate the stress-luminescent material with excitation light before and during application of an external force to the stress-luminescent material. The imaging device images the light emitted by the stress-luminescent material. The optical filter removes the excitation light component from the image captured by the imaging device. The processing device calculates a stress-luminescence image showing stress-luminescence when an external force is applied to the stress-luminescent material based on the image captured.

[0010] According to the present disclosure, in a stress-stimulated luminescence measurement device and a stress-stimulated luminescence measurement method that measure stress generated in a stress-stimulated luminescent material based on the luminescence phenomenon of the stress-stimulated luminescent material, it is possible to accurately visualize the progression of stress-stimulated luminescence generated in the stress-stimulated luminescent material during the application of an external force.

[0011] 9 is a diagram showing an example of the configuration of a stress-luminescence measurement device according to the present embodiment; FIG. 10 is a diagram showing an example of the configuration of a sample; FIG. 11 is a diagram showing an example of the transition of the luminous intensity of a stress-luminescent material; FIG. 12 is a diagram showing a schematic diagram of the spectrum of excitation light and the spectrum of stress-luminescence; FIG. 13 is a diagram showing an example of the characteristics of an optical filter F1; FIG. 14 is a diagram showing an example of the characteristics of an optical filter F2; FIG. 15 is a diagram showing experimental results regarding the filtering effect of an optical filter; FIG. 16 is a flowchart showing the procedure of stress-luminescence measurement processing executed in a stress-luminescence measurement device; FIG. 17 is a flowchart showing a first example of the procedure of the calculation processing of a stress-luminescence image; FIG. 18 is a diagram showing experimental results regarding the calculation processing of the stress-luminescence image shown in FIG. 9; FIG. 19 is a flowchart showing a second example of the procedure of the calculation processing of a stress-luminescence image; FIG. 19 is a diagram showing the configuration of a sample used in an experimental example; FIG. 19 is a diagram showing a background image; FIG. 19 is a diagram showing a captured image of a stress-luminescent material to which an external force is applied; and FIG. 19 is a diagram showing a difference image.

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0013] <Configuration of Stress-Luminescence Measurement Apparatus> Fig. 1 is a diagram showing a configuration example of a stress-luminescence measurement apparatus according to the present embodiment. As shown in Fig. 1, a stress-luminescent material 90 is attached to a sample 1. The stress-luminescence measurement apparatus 100 is configured to measure the luminescence of the stress-luminescent material 90 when a tensile load is applied to the sample 1.

[0014] The stress-luminescence measurement device 100 includes a holder 40, an excitation light source 50, a camera 60, a first driver 45, a second driver 62, a third driver 52, and a processing device 70.

[0015] The holder 40 is configured to support the sample 1 by contacting at least two points on the sample 1. In the example of Fig. 1, the holder 40 is configured to support two opposing ends 1c and 1d of the sample 1. Specifically, the holder 40 has a fixing member 42, a moving member 41, and connecting members 43 and 44. In Fig. 1, when the holder 40 is placed, the width direction is the X direction, the depth direction is the Y direction, and the vertical direction is the Z direction.

[0016] The fixed member 42 and the moving member 41 are installed facing each other in the Z direction. The fixed member 42 is fixed to the bottom surface of the holder 40. The moving member 41 is configured to be able to move in the Z direction when it receives an external force from a first driver 45.

[0017] A first end 1c of the sample 1 is connected to a fixed member 42 by a connecting member 44. A second end 1d of the sample 1 is connected to a moving member 41 by a connecting member 43. A first driver 45 is connected to the holder 40 via an actuator 46. The first driver 45 drives the actuator 46 to move the moving member 41 upward in the Z direction (upward in the plane of the drawing), thereby applying a tensile force to the sample 1. The holder 40 and the first driver 45 correspond to an example of a "test device" for applying an external force to the stress-luminescent body 90.

[0018] A stress-stimulated luminescent material 90 is formed on the surface of the sample 1. FIG. 2 is a diagram showing an example of the configuration of the sample 1. The sample 1 is made of a metallic material. In the example shown in FIG. 2, a test piece specified in Japanese Industrial Standards (JIS) Z-2201 "Tensile test piece for metallic materials" is used as the sample 1. In this embodiment, the mechanical properties of the metallic material are measured by applying a tensile force to the sample 1 until it breaks.

[0019] Sample 1 is a plate-shaped test piece conforming to JIS No. 13B. The metal material constituting Sample 1 is aluminum, and it has a total length L of 220 mm, a width W of 25 mm, and a plate thickness t of 1 mm. A stress-stimulated luminescent body 90 is formed in a predetermined region on the surface of Sample 1. This predetermined region has a rectangular shape and is positioned so as to cover the parallel portion of Sample 1. The stress-stimulated luminescent body 90 can be formed, for example, by printing a stress-stimulated luminescent material in the predetermined region or by attaching a sheet containing a stress-stimulated luminescent material to the predetermined region.

[0020] The stress-stimulated luminescent material 90 is a member that emits light when subjected to an external force, and may be a conventionally known material. The stress-stimulated luminescent material 90 has the property of emitting light in response to mechanical energy applied from the outside, and the luminous intensity thereof changes depending on the mechanical energy.

[0021] The stress-stimulated luminescent material 90 is a material in which an element serving as a luminescence center is dissolved in a crystal skeleton, and by selecting an inorganic base material and an element serving as a luminescence center, it is possible to emit light at various wavelengths from ultraviolet to visible to infrared. A typical composition is strontium aluminate (SrAl ２ O ４ :Eu, emitting green light), zinc sulfide doped with manganese as the luminescent center (ZnS:Mn, emitting yellow-orange light), barium calcium titanate doped with praseodymium as the luminescent center ((Ba,Ca)TiO ３ :Pr, which emits red light).

[0022] 1 , the excitation light source 50 is configured to irradiate the sample 1 with excitation light. The stress-luminescent material 90 on the sample 1 is excited by the excitation light from the excitation light source 50 and transitions to a light-emitting state. The excitation light source 50 is, for example, an LED (Light Emitting Diode) light source that emits blue light. The number of excitation light sources 50 may be one or more.

[0023] The third driver 52 supplies power for driving the excitation light source 50. The third driver 52 controls the power supplied to the excitation light source 50 in response to a command received from the processing device 70, thereby controlling conditions such as the intensity of the excitation light and the irradiation time of the excitation light. As will be described later, the excitation light source 50 is driven to irradiate the sample 1 with excitation light at least while an external force is being applied by the holder 40 and the first driver 45.

[0024] The camera 60 is positioned so that at least a part of the stress-luminescent material 90 on the sample 1 is included in the imaging field of view. Specifically, the camera 60 is positioned so that the focus position is located at at least one point on the stress-luminescent material 90.

[0025] The camera 60 includes an optical system such as a lens and an imaging element. The imaging element is realized by, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor. The imaging element generates a captured image by converting light incident from an object to be imaged via the optical system into an electrical signal. Data of the captured image is transmitted to the processing device 70. The camera 60 corresponds to one embodiment of an "imaging device."

[0026] The second driver 62 changes the focus position of the camera 60 in response to a command received from the processing device 70. In one aspect, the second driver 62 adjusts the focus position of the camera 60 so that the camera 60 is positioned at at least one point on the stress-luminescent body 90 by moving the camera 60 along the Z direction in synchronization with the first driver 45.

[0027] The processing device 70 controls the entire stress-luminescence measurement device 100. The processing device 70 includes, as main components, a processor 701, a memory 702, an input / output interface (I / F) 703, and a communication I / F 704. These components are connected to each other via a bus (not shown) so as to be able to communicate with each other.

[0028] The processor 701 may be realized by one or more arithmetic processing devices such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The processor 701 controls the operation of each part of the stress-stimulated luminescence measurement device 100 by reading and executing a program stored in the memory 702. Specifically, the processor 701 realizes a stress-stimulated luminescence measurement process, which will be described later, by executing the program.

[0029] The memory 702 is realized by a non-volatile memory such as a random access memory (RAM), a read only memory (ROM), or a flash memory. The memory 702 stores programs executed by the processor 701, data used by the processor 701, and the like.

[0030] The input / output I / F 703 is an interface through which the processor 701 exchanges various data with the first driver 45 , the third driver 52 , the camera 60 , and the second driver 62 .

[0031] The communication I / F 704 is a communication interface for exchanging various data between the stress-luminescence measurement device 100 and other devices, and is realized by an adapter, a connector, etc. The communication method may be a wireless communication method using a wireless LAN (Local Area Network) or the like, or a wired communication method using a USB (Universal Serial Bus) or the like.

[0032] A display 71 and an operation unit 72 are connected to the processing device 70. The display 71 is configured with a liquid crystal panel or the like. The operation unit 72 accepts operation inputs from a user to the stress-luminescence measurement device 100. The operation unit 72 is typically configured with a touch panel, a keyboard, a mouse, or the like.

[0033] The processing device 70 is communicatively connected to the first driver 45, the third driver 52, the camera 60, and the second driver 62. The communication between the processing device 70 and the first driver 45, the third driver 52, the camera 60, and the second driver 62 may be realized by wireless communication or by wired communication.

[0034] <Excitation Light Source> As described above, the stress-luminescent material 90 is excited by receiving excitation light from the excitation light source 50 and transitions to a light-emitting state. As described in Patent Document 1, a conventional stress-luminescent measurement method is configured to irradiate the stress-luminescent material 90 with excitation light for a predetermined time to put the stress-luminescent material 90 into an excited state, and then apply an external force (mechanical energy) to the stress-luminescent material 90 with the excitation light turned off, and capture an image of the light emitted by the stress-luminescent material 90.

[0035] 3 is a diagram showing an example of the transition of the luminous intensity of the stress-stimulated luminescent material 90 captured by the camera 60. In FIG. 3, it is assumed that the irradiation of the excitation light from the excitation light source is completed at time t0. A solid line k1 in FIG. 3 indicates the transition of the luminous intensity of the stress-stimulated luminescent material 90.

[0036] When the irradiation of the excitation light is finished, the stress-stimulated luminescent material 90 emits light and releases energy. Therefore, the luminous intensity of the light emitted (afterglow) from the stress-stimulated luminescent material 90 after the irradiation of the excitation light is finished decreases with the passage of time.

[0037] At time t1, a tensile force is applied to the sample 1, thereby applying an external force to the stress-stimulated luminescent material 90. The sample 1 is elastically deformed by the tensile force. Therefore, when the tensile force is removed, the sample 1 returns to the state before the tensile force was applied.

[0038] When an external force is applied to the stress-stimulated luminescent material 90, its luminous intensity increases. Hereinafter, the luminescence caused by stress due to the application of an external force will be referred to as "stress-stimulated luminescence," and the increase in luminous intensity due to stress-stimulated luminescence will be referred to as "stress-stimulated luminescence amount." Note that the afterglow of the stress-stimulated luminescent material 90 and the stress-stimulated luminescence of the stress-stimulated luminescent material 90 have the same wavelength band.

[0039] Then, when the external force is removed at time t2, the luminous intensity decreases again with the passage of time. The dotted line k2 in Fig. 3 shows the change in luminous intensity when no tensile force is applied to the sample 1, i.e., when no external force is applied to the stress-stimulated luminescent material 90. This dotted line k2 represents the amount of afterglow of the stress-stimulated luminescent material 90.

[0040] The amount of mechanoluminescence, which is the increment in the luminous intensity due to mechanoluminescence, is obtained by subtracting the amount of afterglow from the total amount of luminescence when an external force is applied to the mechanoluminescent material 90. This amount of mechanoluminescence corresponds to the transition of the solid line k1 when the dotted line k2 is used as the base.

[0041] As shown in Fig. 3, the light emission amount of the stress-stimulated luminescent material 90 attenuates with the passage of time and application of external force after the end of irradiation with excitation light. The light emission amount when an external force is applied to the stress-stimulated luminescent material 90 varies depending on the excited state of the stress-stimulated luminescent material 90. Therefore, when an external force is repeatedly applied to the stress-stimulated luminescent material 90 for a long period of time, it is necessary to irradiate the stress-stimulated luminescent material 90 with excitation light each time in order to raise the energy level of the stress-stimulated luminescent material 90 to a predetermined energy state.

[0042] Therefore, in this embodiment, the excitation light source 50 is configured to irradiate the sample 1 with excitation light before and during application of a tensile force. That is, this embodiment differs from the conventional stress-luminescence measurement method in that excitation light is irradiated onto the stress-luminescent material 90 to which an external force is applied. This allows the stress-luminescent material 90 to be kept in a constant excited state, thereby suppressing attenuation of the light emission of the stress-luminescent material 90 over time and due to application of an external force.

[0043] However, on the other hand, since the image of the stress-luminescent material 90 is captured by applying an external force to the stress-luminescent material 90 while irradiating it with excitation light from the excitation light source 50, the light emitted by the stress-luminescent material 90 and the reflected light of the excitation light irradiated from the excitation light source 50 are simultaneously incident on the camera 60 capturing the image of the stress-luminescent material 90. Note that the light emitted by the stress-luminescent material 90 includes light emitted by excitation and light emitted by external force. Hereinafter, the light emitted by excitation may be referred to as "background light."

[0044] That is, the camera 60 captures an optical image of the sample 1 by the excitation light simultaneously with the luminescence image of the stress-luminescent material 90. This raises a concern that the desired stress-luminescent image may be buried in the optical image of the sample 1 in the captured image. In particular, when the luminescence intensity of the stress-luminescent material 90 is sufficiently smaller than the intensity of the excitation light, the above-mentioned concern becomes significant and may become an obstacle to accurately visualizing the stress-luminescent image.

[0045] <Optical Filter> The stress-luminescence measurement device 100 further includes an optical filter as a configuration for removing the influence of excitation light from the captured image. The optical filter is configured to remove excitation light components from the captured image. In the example of FIG. 1, the stress-luminescence measurement device 100 includes optical filters F1 and F2. The optical filter F1 corresponds to an example of a "first filter," and the optical filter F2 corresponds to an example of a "second filter." The characteristics of the optical filters F1 and F2 will be described below.

[0046] (Optical Filter F1) Fig. 4 is a diagram showing the spectrum of excitation light and the spectrum of stress-stimulated luminescence, in which the vertical axis represents luminous intensity and the horizontal axis represents wavelength.

[0047] 4, the solid line k3 schematically shows the spectrum of the excitation light. When the excitation light source 50 is a blue LED light source, the excitation light has a wavelength band of 430 to 500 nm. The peak wavelength of the excitation light is approximately 520 nm.

[0048] 4. The solid line k4 in FIG. 4 shows a schematic spectrum of mechanoluminescence. ２ O ４ :Eu), the mechanoluminescence is green light and has a wavelength band of 420 to 600 nm. The peak wavelength of the mechanoluminescence is about 520 nm. As shown in FIG. 4, the peak wavelengths of the excitation light and the mechanoluminescence are close to each other and have overlapping wavelength bands.

[0049] In a configuration in which excitation light is actually irradiated onto the stress-luminescent material 90, the intensity of the reflected light of the excitation light emitted from the sample 1, among the light incident on the camera 60, is far greater than the intensity of the stress-luminescent light from the stress-luminescent material 90. In other words, the peak intensity of the stress-luminescence incident on the camera 60 is far smaller than the peak intensity of the excitation light. Therefore, even if an attempt is made to capture with the camera 60 the weak stress-luminescence output from the stress-luminescent material 90 in response to the application of an external force, the image is obstructed by the background light of the excitation light.

[0050] 1, the optical filter F1 is disposed between the stress-luminescent body 90 and the camera 60. The optical filter F1 is provided to remove an excitation light component from the light incident on the camera 60 from the stress-luminescent body 90.

[0051] FIG. 5 is a diagram illustrating an example of the characteristics of the optical filter F1, and is a diagram to be compared with FIG. 4 . The solid line k5 in FIG. 5 represents the transmittance spectrum of the optical filter F1. As shown in FIG. 5 , the optical filter F1 blocks the entire wavelength band of the spectrum of the excitation light and transmits wavelength bands longer than the entire wavelength band. The wavelength band transmitted by the optical filter F1 includes the wavelength band of mechanoluminescence. That is, the optical filter F1 is configured to block the wavelength band of the excitation light and transmit the wavelength band of mechanoluminescence. In the example of FIG. 5 , the optical filter F1 has a cutoff wavelength of approximately 500 nm and cuts off light with a cutoff wavelength shorter than 500 nm.

[0052] 5, the spectrum blocked by the optical filter F1 is represented by a dotted line. The characteristics (cutoff wavelength) of the optical filter F1 can be appropriately set according to the wavelength band of the excitation light, from the viewpoint of suppressing transmission of the excitation light.

[0053] 5 is placed between the stress-luminescent body 90 and the camera 60, it is possible to block most of the excitation light that is the source of the background light. Note that the optical filter F1 also blocks the stress-luminescence, which has a wavelength band overlapping with that of the excitation light, and therefore the amount of light of the stress-luminescence is somewhat reduced. However, since the excitation light that is the background light has been removed, the amount of light of the stress-luminescence is sufficient to be captured by the camera 60.

[0054] 1, the optical filter F2 is disposed between the excitation light source 50 and the stress-luminescent body 90. The optical filter F2 is provided to remove, from the excitation light output from the excitation light source 50, light components whose wavelength band overlaps with that of the stress-luminescent body.

[0055] FIG. 6 is a diagram illustrating an example of the characteristics of the optical filter F2, and is a diagram to be compared with FIG. 4 . The solid line k6 in FIG. 6 represents the transmittance spectrum of the optical filter F2. As shown in FIG. 6 , the optical filter F2 blocks a portion of the wavelength band of the excitation light spectrum that overlaps with the spectrum of mechanoluminescence and a wavelength band longer than that portion, and transmits a wavelength band shorter than that portion. The wavelength band blocked by the optical filter F2 includes the wavelength band of mechanoluminescence. That is, the optical filter F2 is configured to transmit the wavelength band of the excitation light and block the wavelength band of mechanoluminescence. In the example of FIG. 6 , the optical filter F2 has a cutoff wavelength of approximately 480 nm and blocks light with a cutoff wavelength of 480 nm or more.

[0056] In Fig. 6, the spectrum blocked by the optical filter F2 is indicated by a dotted line. The characteristics (cutoff wavelength) of the optical filter F2 can be appropriately set according to the wavelength bands of the mechanoluminescence and the excitation light, from the viewpoint of suppressing transmission of the excitation light that overlaps with the wavelength band of the mechanoluminescence. Note that, when the spectrum of the mechanoluminescence is broad and the wavelength band that overlaps with the excitation light is wide, as in Fig. 6, the influence of the excitation light on the mechanoluminescence can be reduced by setting the characteristics of the optical filter F2 so as to block at least a part of the excitation light in that wavelength band.

[0057] 7 shows the experimental results of the filtering effects of the optical filters F1 and F2, in which the camera 60 captures an image of the stress-luminescent material 90 while irradiating it with excitation light in the stress-luminescent measurement device 100 shown in FIG.

[0058] In the experiment, a rectangular stress-luminescent material 90 was formed in a predetermined region of the sample 1, and a rectangular white piece of paper was attached outside the predetermined region. Then, in the experiment, without applying a tensile force to the sample 1, i.e., without applying an external force to the stress-luminescent material 90, an optical image of the light emitted by the stress-luminescent material 90 upon receiving excitation light was captured by the camera 60.

[0059] 7A shows the result of capturing an image of Sample 1 with a camera 60 while irradiating Sample 1 with white light from a white LED light source. This white light has intensities in both the wavelength band of the excitation light and the wavelength band of the stress-luminescence shown in FIG. 4. Region A in FIG. 7A shows an image of the piece of paper, and region B shows an image of the stress-luminescent material 90. Under the white light, both the piece of paper and the stress-luminescent material 90 are observed as images.

[0060] 7(B) shows the result of irradiating sample 1 with excitation light (blue light) from a blue LED light source (excitation light source 50) instead of a white LED light source, and capturing an image of sample 1 with camera 60. Unlike in FIG. 7(A), the piece of paper only emits reflected light of the excitation light. Due to the action of optical filter F1, which blocks the excitation light, area A corresponding to the piece of paper is not captured in the image.

[0061] On the other hand, the background light emitted by the excited stress-luminescent material 90 is not blocked by the optical filter F1 and is incident on the camera 60. Therefore, the area B corresponding to the stress-luminescent material 90 is captured as an image.

[0062] The experimental results suggest that the action of the optical filters F1 and F2 makes it possible to capture an image of the light emitted from the stress-luminescent material 90 without being disturbed by the reflected light image of the high-intensity excitation light.

[0063] <Stimulated-stimulated luminescence measurement processing> Next, a stimulated-stimulated luminescence measurement processing executed in the stimulated-stimulated luminescence measurement device 100 according to the present embodiment will be described.

[0064] FIG. 8 is a flowchart illustrating the procedure of the stress-stimulated luminescence measurement process executed by the stress-stimulated luminescence measurement device 100.

[0065] 8, first, in step S10, the sample 1 is set in the holder 40. The sample 1 is set so that the surface on which the stress-luminescent body 90 is formed faces the camera 60.

[0066] Next, in step S20, the excitation light source 50 is activated. In S20, the third driver 52 supplies power to the excitation light source 50 in response to the activation command received from the processing device 70, thereby activating the excitation light source 50. The third driver 52 controls the power supplied to the excitation light source 50 so that the excitation light source 50 emits a predetermined amount of excitation light. The excitation light from the excitation light source 50 is irradiated onto the stress-luminescent material 90 via the optical filter F2. As a result, the stress-luminescent material 90 is excited to a constant state.

[0067] Next, in step S30, the camera 60 starts capturing images. The second driver 62 starts the camera 60 in response to a start command received from the processing device 70, and adjusts the focus position of the camera 60 so that the camera 60 is positioned at at least one point on the stress-luminescent body 90.

[0068] Light emitted from the stress-luminescent material 90 is incident on the camera 60 via the optical filter F1. The camera 60 captures the light emitted from the stress-luminescent material 90 at a predetermined frame rate. The frame rate is the number of frames processed per unit time in video processing. At the start of imaging, since no tensile force is applied to the sample 1, light emitted from the stress-luminescent material 90 to which no external force is applied (background light) is captured.

[0069] Next, in step S40, a tensile force is applied to the sample 1. In S40, the first driver 45 applies a tensile force to the sample 1 by driving the actuator 46 in response to a command from the processing device 70 to move the moving member 41 of the holder 40. The application of the tensile force starts when a predetermined time has elapsed since the start of irradiation with the excitation light. This predetermined time is the time required for the excitation light to raise the stress-luminescent material 90 to a predetermined energy state, and is determined, for example, by the intensity of the excitation light output from the excitation light source 50 and the type of the stress-luminescent material 90.

[0070] When a tensile force is applied to the sample 1 in S40, the stress generated by the external force causes the stress-luminescent material 90 to emit light. The background light and the stress-luminescent material 90 are photographed by the camera 60 via the optical filter F1.

[0071] After the tensile force is removed from the sample 1, image capture by the camera 60 is stopped in step S50. In S50, the second driver 62 stops the camera 60 in response to a stop command received from the processing device 70. During the image capture time of the camera 60, a number of still images are generated according to the frame rate of the camera 60. The captured image data including the generated still images is stored in chronological order in the memory 702 in the processing device 70 together with the frame numbers.

[0072] Next, in step S60, the excitation light source 50 is stopped. In S60, the third driver 52 stops the power supply to the excitation light source 50 in response to the stop command received from the processing device 70, thereby stopping the emission of excitation light from the excitation light source 50.

[0073] Next, in step S70, a stress-luminescence image capturing the stress-luminescence of the stress-luminescent material 90 is calculated based on the captured image data stored in the memory 702 in the processing device 70. Details of the stress-luminescence image calculation process (S70) are described below.

[0074] (Calculation process of stress-luminescence image) In this embodiment, since the excitation light is irradiated onto the stress-luminescent material 90 even during application of an external force, the background light of the stress-luminescent material 90 does not attenuate, in contrast to the afterglow after the end of irradiation shown in Fig. 3. Therefore, there is a concern that the background light becomes bright background light for stress-luminescence, reducing the contrast of stress-luminescence in the captured image.

[0075] Therefore, in the calculation process of the stress-luminescence image (S70 in FIG. 8), a process is performed to remove the influence of background light from the captured image, thereby extracting a stress-luminescence image with high contrast.

[0076] 9 is a flowchart showing a first example of the procedure of the calculation process of the stress-luminescence image executed in S70 of FIG.

[0077] 9 , the processing device 70 first acquires, in step S701, an image (background image) of the background light of the stress-luminescent body 90 from the captured image data stored in the memory 702. In S701, an image captured after a predetermined time has elapsed since the start of irradiation with excitation light and before the start of application of tensile force is acquired as the background image.

[0078] Next, in step S702, the processing device 70 acquires images captured during the time when the tensile force is being applied to the sample 1 from the captured image data stored in the memory 702. The captured images include a plurality of still images arranged in chronological order according to frame number.

[0079] Next, in step S703, the processing device 70 calculates a difference image by subtracting the background image acquired in S701 from the captured image (still image) of each frame included in the captured image. The amount of mechanoluminescence is obtained by subtracting the amount of background light from the total amount of light emitted when an external force is applied to the mechanoluminescent material 90. In other words, the difference image represents a mechanoluminescent image.

[0080] 10A and 10B are diagrams showing experimental results relating to the calculation process of the stress-luminescence image shown in Fig. 9. Fig. 10A shows an image captured by the camera 60 when a tensile force is applied to the sample 1. The rectangular area C in Fig. 10A shows an image of the entire stress-luminescent material 90, capturing the background light of the stress-luminescent material 90.

[0081] Region D in Figure 10(A) is located within region C and shows a mechanoluminescent image of the part where stress is occurring. However, because the background light is bright, the mechanoluminescent image is buried in the background light image, reducing the contrast of the mechanoluminescent image.

[0082] Fig. 10(B) shows a mechanoluminescence image obtained by subtracting the background image from the captured image shown in Fig. 10(A). Compared to Fig. 10(A), it can be seen that the contrast of the mechanoluminescence image is improved due to the reduced brightness of the background light image.

[0083] Fig. 11 is a flowchart showing a second example of the procedure of the stress-luminescence image calculation process executed in S70 of Fig. 8. The flowchart shown in Fig. 11 is executed by the processing device 70.

[0084] 11 , first, in step S711, the processing device 70 acquires the kth frame of the image captured during the time when the tensile force is applied to the sample 1 from the captured image data stored in the memory 702. k is an integer of 2 or greater.

[0085] Next, in step S712, the processing device 70 acquires the captured image of the (k-1)th frame captured during the time when the tensile force is applied to the sample 1 from the captured image data stored in the memory 702.

[0086] Next, in step S713, the processing device 70 calculates a difference image by subtracting the captured image of the (k-1)th frame from the captured image of the kth frame. The difference image does not contain a background light image and represents only the increase in the amount of mechanoluminescence in the kth frame relative to the (k-1)th frame. In other words, the difference image represents a mechanoluminescence image.

[0087] It is possible to measure the transition of the amount of mechanoluminescence due to the application of an external force by performing the process of step S713 on all images captured while the tensile force is being applied to the sample 1. The second example is an effective method when there is a fluctuation in the amount of background light.

[0088] <Experimental Example> Next, an experimental example of a stress-stimulated luminescence measurement process using the stress-stimulated luminescence measurement device 100 according to the present embodiment will be described.

[0089] (Sample 1) Fig. 12 is a diagram showing the configuration of Sample 1 used in this experiment. Sample 1 is a plate-shaped test piece conforming to JIS No. 13B. The metal material constituting Sample 1 is aluminum, and it has a total length L of 220 mm, a width W of 25 mm, and a plate thickness t of 1 mm.

[0090] A stress-stimulated luminescent body 90 was formed on the parallel portion of Sample 1. The parallel portion had a rectangular shape with a width of 80 mm and a length of 12.5 mm. The stress-stimulated luminescent body 90 was formed by applying (by screen printing) a coating material containing a stress-stimulated luminescent material to the surface of the parallel portion. The stress-stimulated luminescent material was strontium aluminate (SrAl) doped with europium. ２ O ４ :Eu).

[0091] A notch 20 is provided in a part of the parallel portion of the sample 1, and is shaped to induce stress concentration and fracture in that part.

[0092] (Stimulated Luminescence Measurement Process) In the stimulated luminescence measurement process, the stimulated luminescence measurement device 100 was used to apply a tensile force to the sample 1 shown in FIG. 12, and the light emitted from the stimulated luminescent material 90 was captured by the camera 60.

[0093] First, the sample 1 was set in the holder 40, and the excitation light from the excitation light source 50 was irradiated onto the sample 1 through the optical filter F2, while the image of the stress-luminescent material 90 was captured by the camera 60 through the optical filter F1. A blue LED light source was used as the excitation light source 50.

[0094] As an imaging condition, the exposure time of the camera 60 was set to 250 milliseconds. To capture the weak light emitted by the stress-luminescent body 90, this exposure time is necessary even if a bright lens with an aperture value of 1.4 is used. When imaging was performed while irradiating the excitation light without using the optical filters F1 and F2, the image was overexposed, resulting in only a saturated white image.

[0095] 13 is an image (background image) of light (background light) emitted by the stress-stimulated luminescent material 90 to which no external force is applied. As shown in FIG. 13, the captured image shows that the excitation light component is removed by the filtering effect of the optical filters F1 and F2, and the entire stress-stimulated luminescent material 90 is emitting light.

[0096] Next, a tensile force was applied to the sample 1 while irradiating it with excitation light, and the stress-stimulated luminescent material 90 was imaged by the camera 60. Figure 14 shows images of the stress-stimulated luminescent material 90 to which an external force was applied. The images shown in Figures 14(A), 14(B), and 14(C) show the state change of the stress-stimulated luminescent material 90 in chronological order as an external force was applied.

[0097] 14(A) and 14(B), two linear stress-stimulated luminescence lines appear, originating from the notch 20 provided in the sample 1, as an external force is applied. This shows that two linear stress lines originate from the notch 20. Furthermore, in FIG. 14(C), the intensity of these two linear stress-stimulated luminescence lines increases and they appear to merge. However, because a background image is superimposed on both captured images, the contrast is low.

[0098] Next, the processing device 70 performed a calculation process for mechanoluminescence images based on the images captured during the application of tensile force. In this calculation process, difference images were calculated by subtracting the background image shown in FIG. 13 from each captured image shown in FIG. 14. The calculated difference images are shown in FIG. 15. The difference images shown in FIGS. 15(A), 15(B), and 15(C) are images calculated from the captured images shown in FIGS. 14(A), 14(B), and 14(C), respectively.

[0099] 15(A) and 14(A), it can be seen that the subtraction image captures the weak mechanoluminescence occurring in the area of ​​the notch 20 because the background light has been removed. In addition, in FIGS. 15(B) and 15(C), it can be seen that the reduction in contrast due to the background light has been eliminated, thereby emphasizing the mechanoluminescence and improving its visibility.

[0100] <Effects of the Present Embodiment> As described above, according to the stress-stimulated luminescence measuring device of the present embodiment, the stress-stimulated luminescent material can be kept in an excited state by irradiating the material with excitation light before and during application of an external force, and therefore the attenuation of the light emission amount of the stress-stimulated luminescent material due to the passage of time and the application of an external force can be suppressed. As a result, in a situation where an external force is applied to the stress-stimulated luminescent material for a long period of time, it is possible to suppress a decrease in the stress-stimulated luminescence amount of the stress-stimulated luminescent material depending on the excited state of the stress-stimulated luminescent material.

[0101] Furthermore, by providing an optical filter for removing excitation light components from the captured image, it is possible to prevent the mechanoluminescence image to be captured from being buried in the reflected light image of high-intensity excitation light in the captured image. Furthermore, by performing image processing on the captured image to remove background images, it is possible to obtain a mechanoluminescence image with high contrast. As a result, the mechanoluminescence measurement device according to this embodiment makes it possible to accurately visualize the transition of mechanoluminescence generated in the mechanoluminescent material during the application of an external force.

[0102] The mechanoluminescence measuring device according to the present embodiment is effective for capturing mechanoluminescence images when an external force is continuously applied to a mechanoluminescent material over a long period of time. For example, when the mechanoluminescence measuring device according to the present embodiment is applied to a fatigue test of a metallic material, it becomes possible to accurately visualize the process of fracture progression in the metallic material and the state of the material at the time of fracture.

[0103] Aspects It will be understood by those skilled in the art that the above-described embodiments are specific examples of the following aspects.

[0104] (Item 1) A stress-luminescence measuring device according to one embodiment measures stress generated in a stress-luminescent material based on the luminescence phenomenon of the stress-luminescent material. The stress-luminescence measuring device includes an excitation light source configured to irradiate the stress-luminescent material with excitation light before and during application of an external force to the stress-luminescent material, an imaging device that captures an image of the light emitted by the stress-luminescent material, an optical filter that removes the excitation light component from the image captured by the imaging device, and a processing device that calculates a stress-luminescence image that shows stress-luminescence when an external force is applied to the stress-luminescent material based on the captured image.

[0105] According to the stress-luminescence measurement device described in paragraph 1, by irradiating the stress-luminescent material with excitation light before and during application of an external force, the stress-luminescent material can be kept in an excited state, thereby suppressing attenuation of the light emission amount of the stress-luminescent material over time and due to application of an external force. This makes it possible to suppress a decrease in the stress-luminescent amount of the stress-luminescent material depending on the excited state of the stress-luminescent material when an external force is applied to the stress-luminescent material for a long period of time. Furthermore, by providing an optical filter for removing excitation light components from the captured image, it is possible to prevent the desired stress-luminescent image from being buried in the reflected light image of the excitation light, which has a high intensity, in the captured image.

[0106] (2) In the stress-luminescence measurement device described in (1), the optical filter includes a first filter disposed between the imaging device and the stress-luminescent material for removing an excitation light component from light incident on the imaging device from the stress-luminescent material. The first filter is configured to transmit a wavelength band of stress-luminescence and block a wavelength band of excitation light.

[0107] According to the stress-luminescence measurement device described in paragraph 2, the first filter suppresses transmission of the excitation light, thereby making it possible to reduce the excitation light that becomes background light in the captured image.

[0108] (3) In the stress-luminescence measurement device described in (2), the optical filter further includes a second filter disposed between the excitation light source and the stress-luminescent material for removing, from the excitation light output from the excitation light source, a light component whose wavelength band overlaps with that of the stress-luminescence. The second filter is configured to transmit the wavelength band of the excitation light and to block the wavelength band of the stress-luminescence.

[0109] According to the stress-luminescence measurement device described in paragraph 3, the second filter suppresses transmission of excitation light that overlaps with the wavelength band of stress-luminescence, thereby blocking excitation light that becomes background light in the captured image.

[0110] (4) In the mechanoluminescence measurement device according to the second or third aspect, the excitation light has a first wavelength band, and the mechanoluminescence has a second wavelength band. The second wavelength band partially overlaps with the first wavelength band on the short wavelength side. The first filter is configured to block the first wavelength band and transmit the second wavelength band except for the portion overlapping with the first wavelength band.

[0111] According to the stress-luminescence measurement device described in paragraph 4, when a part of the short wavelength side of the stress-luminescence wavelength band overlaps with the wavelength band of the excitation light, the first filter can block most of the excitation light that is the source of background light.

[0112] (5) In the stress-luminescence measurement device described in the 4th paragraph, the second filter is configured to block the second wavelength band and block the first wavelength band except for a portion overlapping with the second wavelength band.

[0113] According to the stress-luminescence measurement device described in paragraph 5, the second filter can block at least a part of the excitation light that overlaps with the wavelength band of stress-luminescence.

[0114] (6) In the mechanoluminescence measurement device described in any one of the preceding paragraphs 1 to 5, the processing device acquires a background image captured before the application of an external force, and calculates a mechanoluminescence image by subtracting the background image from the image captured during the application of the external force.

[0115] According to the mechanoluminescence measurement device described in paragraph 6, a mechanoluminescence image with high contrast can be obtained by performing image processing to remove background images from the captured image, which makes it possible to accurately visualize the transition of mechanoluminescence generated in the mechanoluminescent material during application of an external force.

[0116] (7) In the stress-luminescence measurement device described in any one of the first to fifth paragraphs, the imaging device is configured to capture images of the stress-luminescent material at a predetermined frame rate. The processing device acquires a captured image of a first frame during application of an external force and a captured image of a second frame subsequent to the first frame during application of the external force. The processing device calculates a stress-luminescence image by subtracting the captured image of the first frame from the captured image of the second frame.

[0117] According to the stress-luminescence measurement device described in paragraph 7, a high-contrast stress-luminescence image can be obtained by performing image processing on the captured image to remove a background image.

[0118] (Item 8) One embodiment of a stress-luminescence measurement method is a stress-luminescence measurement method for measuring stress generated in a stress-luminescent body based on the luminescence phenomenon of the stress-luminescent body, and includes the steps of irradiating the stress-luminescent body with excitation light from an excitation light source before and during the application of an external force to the stress-luminescent body, capturing an image of the light emitted by the stress-luminescent body using an imaging device, and calculating, by a processing device, a stress-luminescence image showing the stress-luminescence when an external force is applied to the stress-luminescent body based on the image captured by the imaging device.

[0119] According to the stress-luminescence measurement method described in paragraph 8, the stress-luminescent material can be kept in an excited state by irradiating the material with excitation light before and during application of an external force, thereby suppressing attenuation of the light emission amount of the stress-luminescent material due to the passage of time and application of an external force. Therefore, in a situation where an external force is applied to the stress-luminescent material for a long period of time, it is possible to suppress a decrease in the stress-luminescent amount of the stress-luminescent material depending on the excited state of the stress-luminescent material.

[0120] (Item 9) In the stress-luminescence measurement method described in Item 8, the imaging step includes a step of imaging light that is transmitted through a first filter disposed between the imaging device and the stress-luminescent material and is incident on the imaging device, the first filter being configured to remove an excitation light component from the light that is incident on the imaging device from the stress-luminescent material.

[0121] According to the mechanoluminescence measurement method described in paragraph 9, the excitation light that becomes background light in a captured image can be reduced by suppressing transmission of the excitation light with the first filter.

[0122] (Item 10) In the stress-luminescence measurement method described in Item 8, the step of irradiating the stress-luminescent material with excitation light includes a step of irradiating the stress-luminescent material with excitation light that has passed through a second filter disposed between the excitation light source and the stress-luminescent material. The second filter is configured to remove, from the excitation light output from the excitation light source, a light component whose wavelength band overlaps with that of the stress-luminescent material.

[0123] According to the mechanoluminescence measurement method described in paragraph 10, the second filter can block the excitation light that becomes background light in the captured image by suppressing transmission of the excitation light that overlaps with the wavelength band of mechanoluminescence, thereby preventing the mechanoluminescence image to be captured from being buried in the reflected light image of the excitation light having a high intensity in the captured image.

[0124] (Item 11) In the stress-stimulated luminescence measurement method described in items 8 to 10, the step of calculating a stress-stimulated luminescence image includes a step of acquiring an image captured before the application of an external force as a background image, and a step of calculating a stress-stimulated luminescence image by subtracting the background image from the image captured during the application of the external force.

[0125] According to the mechanoluminescence measurement method described in paragraph 11, a mechanoluminescence image with high contrast can be obtained by performing image processing on the captured image to remove background images, and as a result, it becomes possible to accurately visualize the transition of mechanoluminescence generated in the mechanoluminescent material during application of an external force.

[0126] (Item 12) In the mechanoluminescence measurement method described in items 8 to 10, the imaging step includes a step of imaging the mechanoluminescent material at a predetermined frame rate by an imaging device. The calculating step includes a step of acquiring a first frame image captured during application of an external force and a second frame image captured during application of the external force and preceding the first frame, and a step of calculating the mechanoluminescence image by subtracting the second frame image from the first frame image.

[0127] According to the mechanoluminescence measurement method described in paragraph 12, a mechanoluminescence image with high contrast can be obtained by performing image processing to remove background images from the captured image, which makes it possible to accurately visualize the transition of mechanoluminescence generated in the mechanoluminescent material during application of an external force.

[0128] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. Furthermore, it is intended that each technique in the embodiments can be implemented alone or, if necessary, in combination with other techniques in the embodiments to the extent possible.

[0129] REFERENCE SIGNS LIST 1 sample, 40 holder, 41 moving member, 42 fixing member, 43, 44 connecting member, 45 first driver, 46 actuator, 50 excitation light source, 52 third driver, 60 camera, 62 second driver, 70 processing device, 71 display, 72 operation unit, 90 stress-luminescent body, 100 stress-luminescent measuring device, 701 processor, 702 memory, 703 input / output I / F, 704 communication I / F, F1, F2 optical filter.

Claims

1. A stress-luminescence measuring device for measuring stress generated in a stress-luminescent body based on the luminescence phenomenon of the stress-luminescent body, comprising: an excitation light source configured to irradiate the stress-luminescent body with excitation light before and during the application of an external force to the stress-luminescent body; an imaging device for imaging the light emitted by the stress-luminescent body; an optical filter for removing excitation light components from an image captured by the imaging device; and a processing device for calculating a stress-luminescence image showing the stress-luminescence when an external force is applied to the stress-luminescent body based on the captured image.

2. The stress-luminescence measuring device of claim 1, wherein the optical filter includes a first filter disposed between the imaging device and the stress-luminescent material for removing the excitation light component from the light incident from the stress-luminescent material to the imaging device, and the first filter is configured to transmit the wavelength band of the stress-luminescence and block the wavelength band of the excitation light.

3. The stress-luminescence measuring device according to claim 2, wherein the optical filter further includes a second filter disposed between the excitation light source and the stress-luminescent material for removing from the excitation light output from the excitation light source a light component whose wavelength band overlaps with that of the stress-luminescence, the second filter being configured to transmit the wavelength band of the excitation light and to block the wavelength band of the stress-luminescence.

4. The stress-luminescence measuring device according to claim 3, wherein the excitation light has a first wavelength band, the stress-luminescence has a second wavelength band, a part of the second wavelength band on the short wavelength side overlaps with the first wavelength band, and the first filter is configured to block the first wavelength band and transmit the second wavelength band excluding the part overlapping with the first wavelength band.

5. The stress-luminescence measurement device of claim 4, wherein the second filter is configured to block the second wavelength band and block the first wavelength band except for a portion that overlaps with the second wavelength band.

6. The stress-luminescence measuring device of claim 1, wherein the processing device acquires the captured image before the application of the external force as a background image, and calculates the stress-luminescence image by subtracting the background image from the captured image during the application of the external force.

7. The stress-luminescence measuring device of claim 1, wherein the imaging device is configured to image the stress-luminescent material at a predetermined frame rate, and the processing device acquires an image of a first frame during application of the external force and an image of a second frame subsequent to the first frame during application of the external force, and calculates a stress-luminescence image by subtracting the image of the first frame from the image of the second frame.

8. A method for measuring stress generated in a stress-luminescent material based on the luminescence phenomenon of the stress-luminescent material, comprising the steps of: irradiating the stress-luminescent material with excitation light from an excitation light source before and during the application of an external force to the stress-luminescent material; capturing an image of the light emitted by the stress-luminescent material by an imaging device; and calculating, by a processing device, a stress-luminescence image showing the stress-luminescence when an external force is applied to the stress-luminescent material based on the image captured by the imaging device.

9. The stress-luminescence measurement method of claim 8, wherein the imaging step includes a step of imaging light that is transmitted through a first filter arranged between the imaging device and the stress-luminescent material and is incident on the imaging device, and the first filter is configured to remove excitation light components from the light that is incident from the stress-luminescent material to the imaging device.

10. A method for measuring stress-induced luminescence according to claim 9, wherein the step of irradiating the excitation light includes a step of irradiating the stress-induced luminescence body with the excitation light that has passed through a second filter arranged between the excitation light source and the stress-induced luminescence body, and the second filter is configured to remove light components having a wavelength band overlapping with that of the stress-induced luminescence from the excitation light output from the excitation light source.

11. A method for measuring stress-induced luminescence as described in claim 8, wherein the step of calculating the stress-induced luminescence image includes the steps of: acquiring the captured image before the application of the external force as a background image; and calculating the stress-induced luminescence image by subtracting the background image from the captured image during the application of the external force.

12. A method for measuring stress-luminescence as described in claim 8, wherein the imaging step includes a step of the imaging device imaging the stress-luminescent material at a predetermined frame rate, and the calculating step of the stress-luminescence image includes a step of acquiring an image of a first frame during the application of the external force and an image of a second frame prior to the first frame during the application of the external force, and a step of calculating a stress-luminescence image by subtracting the image of the second frame from the image of the first frame.

Images