Method for measuring the elastocaloric effect

Abstract

To provide a method for measuring an elastic heat quantity effect that is suitable when used for a search for a material with a large elastic heat quantity effect per unit input stress.SOLUTION: A method for measuring an elastic heat quantity effect includes the steps of: applying tensile stress or tensile strain to a measurement test piece 10 in an aspect where the measurement test piece is in a thermally unsteady state (S102); measuring a thermal image of a surface of the measurement test piece 10 (S104); reading the thermal image of the measurement test piece 10 (S106); extracting, from the read thermal image of the measurement test piece 10, a temperature change derived from stress or strain applied to the measurement test piece 10 (S108); and according to a temperature change signal derived from stress or strain occurring in the measurement test piece 10, extracting an amplitude component and a phase component from the temperature change occurring in synchronization with the stress or strain and converting the extracted components into images (S110, S112).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention The present invention relates to a method for measuring an elastocaloric effect, which is suitable for use in searching for materials that exhibit an elastocaloric effect. [Background technology]

[0002] The elastocaloric effect is the effect in which heat is generated or absorbed in response to the application or removal of stress, corresponding to the difference in entropy. The elastocaloric effect is a universal effect possessed by all solid materials, and is attracting attention as a temperature modulation technology to replace vapor compression systems that use gaseous refrigerants such as chlorofluorocarbons, which have a large environmental impact. Therefore, by using temperature modulation components that utilize the elastocaloric effect, it is possible to freely design the temperature distribution, intensity, and sign generated by the elastocaloric effect.

[0003] Non-Patent Document 1 discloses a copper alloy that can expand and contract by approximately 7% down to extremely low temperatures (4.2 K) by using a Cu-Al-Mn alloy and utilizing the "property (superelasticity) of shape memory alloys to return to their original shape when a large deforming force is removed."The article also claims that by using the Cu-Al-Mn alloy as a low-temperature solid cooling element, it is expected to be applied to superconducting devices, refrigerators for liquefied gases, etc.

[0004] However, when measuring the elastocaloric effect, for example, in the case of the Cu-Al-Mn alloy mentioned above, a thermocouple is required to measure the temperature over a wide range from high to extremely low temperatures. However, when measuring the temperature of a sample using a contact thermometer such as a thermocouple, the heat flows into the thermocouple, making it impossible to accurately measure the temperature of the sample, which hinders the measurement of the elastocaloric effect. Furthermore, since the measurement of the elastocaloric effect involves deformation (displacement) of the element, the stability of the thermometer fixation also affects the temperature measurement.

[0005] On the other hand, as proposed in Patent Documents 1 to 3, for example, it has been proposed to detect defects in an object to be inspected by non-destructive testing by searching for a thermal image of the object to be inspected using a lock-in thermography (LIT) device that uses an infrared camera and a processor. The use of a lock-in thermography device, which is a non-contact temperature measurement method, reduces the invasiveness of temperature measurement and enables accurate temperature measurement of a sample without the need to fix the thermometer, allowing for relatively accurate and smooth measurement of the elastocaloric effect. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 5,201,582 [Patent Document 2] U.S. Patent No. 5,376,793 [Patent Document 3] U.S. Patent No. 5,582,485 [Non-patent literature]

[0007] [Non-Patent Document 1] Cryogenic superelasticity with large elastocaloric effect, Kodai Niitsu, et.al., NPG Asia Materials (2018) 10, e457, doi:10.1038 / am.2017.213 Summary of the Invention [Problem to be solved by the invention]

[0008] When searching for a material with a large elastocaloric effect per unit input stress that is suitable for use in a temperature modulation element, there is a problem in that the magnitude of the elastocaloric effect of a general linear elastic material is limited by the thermoelastic coefficient inherent to the material, and the output is smaller than that of a superelastic material. Furthermore, the small output means that when applying the fluctuating load required for LIT measurement, the proportion of error due to positional displacement relative to the temperature change caused by the elastocaloric effect increases, which has an adverse effect on accurate measurement of the elastocaloric effect. Furthermore, research into the elastocaloric effect has focused primarily on material exploration, and the optimal shape of the temperature modulation member has not yet been clarified.

[0009] Therefore, the present invention aims to provide a temperature modulation element that allows for the flexible design of the temperature distribution, intensity, sign, and elasticity of materials generated by the elastocaloric effect, not only for hyperelastic materials but also for general linear elastic materials. Another object of the present invention is to provide a test piece for measuring the elastocaloric effect and a method for measuring the elastocaloric effect that are suitable for use in searching for materials with a large elastocaloric effect per unit input stress. [Means for solving the problem]

[0012] [ 1 ) The method for measuring the elastocaloric effect of the present invention includes, for example, as shown in Figure 5, a step (S102) of applying tensile stress or tensile strain to a measurement specimen 10 in a manner that puts the measurement specimen 10 in a thermally non-steady state; a step (S104) of measuring a thermal image of the surface of the measurement specimen 10; a step (S106) of reading the thermal image of the measurement specimen 10; a step (S108) of extracting, from the read thermal image of the measurement specimen 10, a temperature change resulting from the stress or strain applied to the measurement specimen 10; a step (S110) of extracting and imaging an amplitude component of the temperature change that changes in synchronization with the stress or strain from a temperature change signal resulting from the stress or strain generated in the measurement specimen 10; and a step (S112) of extracting and imaging a phase component of the temperature change that changes in synchronization with the stress or strain from a temperature change signal resulting from the stress or strain generated in the measurement specimen 10. [ 2) The method for measuring the elastocaloric effect [9] of the present invention preferably further includes a step (S114) of determining a temperature change profile using temperature changes of the amplitude component and phase component in a certain region of the measurement test piece 10, and a step (S116) of calculating the elastocaloric effect coefficient of the composition of the measurement test piece 10 using the temperature change profile. [Effects of the Invention]

[0013] The present invention According to the measurement method of the elastocaloric effect, the LIT measurement is used, so the cut Even if stress concentration occurs near the turn and temperature fluctuations occur locally due to the elastocaloric effect, stress Large temperature variations can be detected accurately near concentrated areas. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a structural diagram showing an example of the shape of a temperature modulation member according to one embodiment of the present invention, and also shows a temperature fluctuation distribution diagram that visualizes the elastic caloric effect due to low-frequency strain deformation. [Figure 2] 1 is a structural view showing an example of the shape of a measurement test piece according to an embodiment of the present invention. [Figure 3] FIG. 1 is a conceptual diagram of an experimental setup for lock-in thermography measurements of the elastocaloric effect. [Figure 4] FIG. 4 is a functional block diagram of the analysis computer shown in FIG. 3. [Figure 5] 1 is a flowchart showing an embodiment of a method for measuring an elastocaloric effect according to the present invention. [Figure 6] FIG. 1 is an explanatory diagram illustrating a comparative example of the present invention, visualizing the elastocaloric effect due to low-frequency strain deformation of a flat-plate type test piece. [Figure 7] FIG. 1 is an explanatory diagram illustrating an embodiment of the present invention, visualizing the elastocaloric effect due to low-frequency strain deformation of a Kirigami-type test piece. [Figure 8] FIG. 1 is an explanatory diagram of stress distribution due to tensile stress in a kirigami-type test piece. [Figure 9] FIG. 10 is an explanatory diagram illustrating a modified embodiment of the present invention, visualizing the heat distribution due to low-frequency strain deformation of a kirigami-type test piece, showing the cases of plate thicknesses of 0.2 mm and 0.3 mm. [Figure 10] FIG. 1 is an explanatory diagram of stress-strain curves of a paper-shaped test piece as an example of the present invention and a flat-plate test piece as a comparative example. [Figure 11] FIG. 10 is a comparative explanatory diagram of the elastocaloric effect per unit input stress of a paper-shaped test piece as an embodiment of the present invention and a flat-plate test piece as a comparative example. [Figure 12] FIG. 1 is an explanatory diagram comparing the elastocaloric effects of various plastic materials. [Figure 13] This is an explanatory diagram comparing the elastocaloric effect of various plastic materials, comparing the elastocaloric effect per unit input stress. [Figure 14] FIG. 10 is an explanatory diagram of a temperature modulation member in which dot holes are formed in a lattice pattern. [Figure 15] 10 is an explanatory diagram of a temperature modulation member in which dot holes are formed in a staggered pattern. FIG. [Figure 16] 10 is an explanatory diagram of a temperature modulation member in which dot holes having an inner diameter of about half the total width are formed. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. [Temperature modulation material] Figure 1 is a structural diagram showing an example of the shape of a temperature modulation member according to one embodiment of the present invention, along with a temperature fluctuation distribution diagram that visualizes the elastocaloric effect caused by low-frequency strain deformation. In Figure 1, (A) is an outline drawing of a kirigami-type temperature modulation member 60, (B) is a temperature fluctuation distribution diagram using an amplitude image, (B2) is a grayscale of the temperature fluctuation distribution, (C) is a temperature fluctuation distribution diagram using a phase image, and (C2) is a grayscale of the phase difference. In the figure, the kirigami-shaped temperature modulating element 60 is a flat slab with an outer shape of 7 mm wide, 20 mm long, and 0.3 mm thick. It has edge cutouts 62a, 62b on the left and right edges and a central cutout 62c in the widthwise center. The edge cutouts 62a, 62b are, for example, 2 mm long, and are arranged in parallel, four on each side, at equal intervals of 4 mm. The central cutouts 62c are, for example, 3 mm long, and are arranged in parallel, five on each side, at equal intervals of 4 mm. In the kirigami-shaped temperature modulating element 10b, the edge cutouts 62a, 62b and the central cutout 62c are arranged alternately in the longitudinal direction, so the distance between the edge cutouts 62a, 62b and the central cutout 62c is 2 mm.

[0016] According to the Kirigami-type temperature modulation member configured in this manner, by applying a tensile stress that is a combination of a static offset tensile stress and a dynamic modulated tensile stress, a temperature fluctuation occurs locally due to the elastocaloric effect. Specifically, a tensile tester was used to apply an initial strain of 1.5% to the kirigami-type temperature modulation element 60 (ε0), and a reciprocating tensile test was performed with a drive frequency of 1 Hz and a strain amplitude of 1.0%. Noise was reduced by integrating the thermal image signals over a one-minute period. Because stress concentrations occur in the kirigami-type temperature modulation element 60 adjacent to the edge cuts 62a and 62b and the central cut 62c, bright spots with a central intensity of approximately 400 mK appear in the temperature fluctuation amplitude distribution. These bright spots are located at the vertices of a hexagon centered on the central cut 62c. On the other hand, the phase component is 180° at the area corresponding to the sides of the hexagon centered around the central notch 62c, while the phase is 0° at the center of the central notch 62c and the edge including the edge notches 62a and 62b, resulting in a phase difference of 180°. In other words, phase inversion is observed depending on the local location of the kirigami-type temperature modulation member 60. This indicates that both heat absorption and heat release exist in a single kirigami-type temperature modulation member 60.

[0017] [Test piece for measuring elastocaloric effect] FIG. 2 is a structural diagram showing an example of the shape of a measurement test piece according to one embodiment of the present invention, in which (A) shows a flat-plate type measurement test piece, and (B) shows a flat plate with cutouts in a paper cutting pattern. In the figure, the flat test piece 10a is a flat slab made of, for example, polystyrene, an example of plastic, with a width of 7 mm, a length of 20 mm, and a thickness of 0.3 mm. The shape of the test piece is not limited to this, but for the purpose of searching for materials with a high elastocaloric effect, it is preferable to standardize the shape of the test piece. The paper-cut test specimen 10b has the same external shape as the flat test specimen 10a, but has edge notches 12a and 12b on the left and right edges and a central notch 12c in the widthwise center. The edge notches 12a and 12b are, for example, 2 mm long, with four of them on each side, equally spaced 4 mm apart and parallel to each other. The central notches 12c are, for example, 3 mm long, with five of them equally spaced 4 mm apart and parallel to each other along the length. In the paper-cut test specimen 10b, the edge notches 12a and 12b and the central notch 12c are alternately spaced along the length, so the distance between the edge notches 12a and 12b and the central notch 12c is 2 mm. The test specimen may be provided with a mounting section for applying tensile stress along the length of the rectangular shape to facilitate installation in the tensile tester 20.

[0018] [Elastocaloric effect measurement device] FIG. 3 is a conceptual diagram of an experimental setup for lock-in thermography measurement of the elastocaloric effect, used for a test piece for measuring the elastocaloric effect. As shown in FIG. 3, the elastocaloric effect measuring device includes a tensile testing machine 20 for performing a tensile test on a measurement specimen 10, an infrared camera 30, an analysis computer 40, a Fourier analysis unit 50, an amplitude image unit 52, and a phase image unit 54.

[0019] 3, the tensile tester 20 clamps both longitudinal ends of the flat test piece 10 and increases the tensile stress at a constant rate. In this case, the constant rate refers to the strain rate, which is the deformation rate of the test piece 10, and the rate of stress applied to the test piece 10. In addition, in the method for measuring the elastocaloric effect of the present invention, it is assumed that heat conduction from the measurement test piece 10 to the tensile tester 20 is negligible. Therefore, when the measurement test piece 10 is in direct contact with the upper surface of the tensile tester 20, it is preferable that the contact part be made of a material with appropriate thermal insulation properties or have a connection structure with high thermal resistance.

[0020] The tensile tester 20 is capable of applying stress or strain at a predetermined stress or strain rate and a predetermined frequency to the test piece 10. The predetermined stress or strain rate is a stress or strain rate that is adjusted so that the tensile stress and elongation can be measured in a static equilibrium state and the measurement time is not excessively long. Note that the tensile tester 20 may be configured to apply a linear stress or strain at a predetermined stress or strain rate to the test piece 10, as in a normal tensile tester, and measure the breaking stress and breaking elongation.

[0021] In addition, the tensile testing machine 20 is electrically connected to the analysis computer 40 and is configured to be able to transmit a reference signal (a signal corresponding to the period of the stress or strain applied to the measurement test piece 10) from the tensile testing machine 20 to the analysis computer 40.

[0022] In the elastocaloric effect measurement device, a stress or strain is applied to a test specimen 10 at a predetermined frequency from a tensile tester 20, causing a temperature change in the test specimen 10 in response to the applied stress or strain. This temperature change is photographed by an infrared camera 30. More specifically, the tensile tester 20 applies stress or strain to the test specimen 10 at a frequency that causes the material to be measured to enter a thermally unsteady state, while measuring the temperature distribution on the surface of the test specimen 10 using the infrared camera 30. The measured temperature distribution is then transmitted as a thermal image signal to an analysis computer 40 electrically connected to the infrared camera 30.

[0023] The analytical computer 40 uses the thermal image signal transmitted from the infrared camera 30 and the reference signal transmitted from the tensile tester 20 to generate a thermal image showing the temperature change caused by the stress or strain. The Fourier analysis unit 50 selectively extracts a temperature change signal that changes over time at the same frequency as the stress or strain applied to the measurement test piece 10, and displays the analysis image in the amplitude image unit 52 and the phase image unit 54. Specifically, a technique called lock-in thermography is used, and Fourier analysis is performed by a Fourier analysis unit 50 via an analysis computer 40 on the thermal image signal transmitted from the infrared camera 30. By setting the stress or strain application conditions so that the temperature change signal derived from the stress or strain generated in the measurement test piece 10 periodically changes in synchronization with the stress or strain, the temperature change signal component derived from the elastocaloric effect generated in the measurement test piece 10 is extracted from the thermal image signal transmitted from the infrared camera 30, and an amplitude image and a phase image are generated.

[0024] The analytical computer 40 then calculates the elastocaloric effect coefficient of the material being measured using a temperature change profile based on the temperature changes in the amplitude and phase components of the amplitude and phase components within a certain range of the test piece 10 for the amplitude and phase images obtained in this manner. Here, the temperature change profile is, for example, an estimate of temperature change by taking the average value within a certain area of ​​the thermal image. If the signal is large, averaging is not necessary. A one-dimensional profile or a two-dimensional profile of a specified width may be used as long as it can estimate the magnitude of the temperature change. The temperature change profile may be an arbitrary line profile defined to avoid the processing pattern, or the temperature change may be estimated directly from the thermal image without producing a line profile.

[0025] Furthermore, in the elastocaloric effect measurement device, the tensile testing machine 20 is also capable of steadily applying stress or strain at a predetermined stress or strain value to the measurement test piece 10, so the analytical computer 40 can calculate the elastocaloric effect in the measurement test piece 10 using the temperature change signal obtained by steadily applying stress or strain in one direction to the measurement test piece 10 and the temperature change signal obtained by steadily applying stress or strain in the opposite direction.

[0026] The lock-in frequency may be set to, for example, 1 Hz, taking into account the mechanically stable and thermally unsteady state. However, it is not limited to this and may be in the range of 0.1 Hz to 100 Hz, and more preferably in the range of 0.1 Hz to 10 Hz. Here, the tensile tester 20 and the analysis computer 40 that executes lock-in thermography must be perfectly matched in terms of lock-in frequency. Although phase synchronization is possible, synchronization is desirable. If the two are synchronized, the phase image will have a fixed phase, and the heat source will exhibit a phase near 0 or 180°, resulting in a phase image that includes the time delay due to thermal diffusion. On the other hand, if the two are not synchronized, the phase is not necessarily limited to 0 or 180°. The elastocaloric effect is essentially an adiabatic temperature change or an isothermal entropy change due to a change in an external driving field, and can be visualized on a patterned measurement specimen 10 using lock-in thermography.

[0027] FIG. 4 is a block diagram showing an example of the configuration of an analytical computer 40 for the evaluation system for the elastocaloric effect of this embodiment. As shown in Figure 4, the analysis computer 40 includes an input section 41 to which a thermal image signal transmitted from the infrared camera 30 (i.e., a thermal image signal measuring the temperature distribution on the surface of the measurement sample due to the stress or strain applied to the measurement test piece 10) is input, a calculation section 42 that generates a thermal image using the thermal image signal and calculates the elastic caloric effect of the measurement test piece 10 using the thermal image, a memory section 43 that stores a program executed by the calculation section 42, and an output section 44 that outputs the calculation results including the thermal image and the calculation results of the elastic caloric effect of the measurement test piece 10.

[0028] The calculation unit 42 stores the thermal image signal input to the input unit 41 in the memory unit 43. 3 is a computer program (elastic caloric effect) for carrying out the evaluation method of the elastocaloric effect described later. The memory area for various analysis data stored and referenced during program execution is also secured. The analysis data memory area includes, for example, an amplitude image 43a, a phase image 43b (including temperature change profiles relating to temperature changes in amplitude and phase components obtained from these amplitude and phase images, and their feature quantities), an elastic caloric effect coefficient 43c, and the like.

[0029] The calculation unit 42 executes predetermined processing based on a computer program (a program for analyzing the elastocaloric effect), and outputs the execution results to the output unit 44. The output unit 44 may be, for example, a liquid crystal display device, a printer, or the like. The output unit 44 may also be a recording device that records the execution results on a recording medium such as a floppy disk or USB memory.

[0030] [Method for measuring the elastocaloric effect] Measurement of the elastocaloric effect The elastocaloric effect measurement method used for the test piece for measuring the elastocaloric effect is carried out as follows using the elastocaloric effect measurement device shown in FIG. FIG. 5 is a flowchart showing an embodiment of the method for measuring the elastocaloric effect of the present invention, and shows an example of the contents of an elastocaloric effect analysis program executed by the calculation unit 42 of the analysis computer 40.

[0031] First, the test piece 10 is set in the tensile tester 20 (S102). Next, the tensile tester 20 applies a tensile stress or a tensile strain to the test piece 10 in such a manner that the test piece 10 is in a thermally unsteady state (S102). The thermally unsteady state means that the tensile stress or the tensile strain is applied at a rate faster than the response time required to reach a thermally steady state. A thermal image of the measurement specimen 10 is acquired using the infrared camera 30 (S104). Next, the thermal image of the measurement specimen 10 transmitted from the infrared camera 30 is input to the input unit 41 of the analysis computer 40, and a thermal image signal measuring the temperature distribution on the surface of the measurement sample caused by the stress or strain applied to the measurement specimen 10 is read (S106).

[0032] Next, the temperature change resulting from the stress or strain applied to the measurement test piece 10 is extracted from the read thermal image of the measurement test piece 10 (S108). Specifically, a technique called lock-in thermography is used to selectively extract a temperature change signal that changes over time at the same frequency as the stress or strain applied to the measurement test piece 10 from the thermal image signal transmitted from the infrared camera 30 by Fourier analysis by the Fourier analysis unit 50.

[0033] The analysis computer 40 then extracts and images an amplitude component of the temperature change that occurs in synchronization with the stress or strain from the temperature change signal resulting from the stress or strain generated in the measurement test piece 10 (S110), and extracts and images a phase component of the temperature change that occurs in synchronization with the stress or strain from the temperature change signal resulting from the stress or strain generated in the measurement test piece 10 (S112). Note that lock-in thermography can be performed in two ways: one is to perform Fourier analysis on each pixel in real time while the thermal image is being measured, and the other is to take a video of the thermal image and perform Fourier analysis after the measurement is completed; either method may be used.

[0034] Next, the calculation unit 42 obtains a temperature change profile using temperature changes of the amplitude component and phase component in a certain region of the measurement specimen 10 (S114), and then calculates the elastocaloric effect coefficient of the composition of the measurement specimen 10 using the temperature change profile (S116). The range for acquiring the temperature change profile can be set to any value, taking into consideration the size (number of pixels) and pixel size (particle diameter) of the thermal image. In the examples described below, an example will be described in which a temperature modulation profile is acquired by setting the region of interest (ROI) to 7 × 7 pixels or 300 × 240 pixels in a 640 × 512 pixel thermal image (pixel size: 11 μm × 11 μm). [Example]

[0035] Fig. 6 is an explanatory diagram showing a comparative example of the present invention, visualizing the elastocaloric effect due to low-frequency strain deformation of a flat-type test piece. Fig. 6(A) is an outline drawing of a flat-type test piece 10a, (B) is a temperature fluctuation distribution map based on an amplitude image, (B2) is the temperature fluctuation distribution grayscale, (C) is a temperature fluctuation distribution map based on a phase image, and (C2) is the phase difference grayscale. In the figure, the flat-plate test specimen 10a is a 0.3 mm thick polystyrene slab. The tensile testing machine 20 applies a 1.0% tensile strain to the flat-plate test specimen 10a as an initial strain ε0, performs a reciprocating tensile test with a drive frequency of 1 Hz and an amplitude of 0.5%, and accumulates thermal image signals for one minute. The flat-plate test specimen 10a exhibits an isotropic temperature fluctuation amplitude distribution of approximately 50 to 70 mK. Meanwhile, the phase component is uniform at 180°.

[0036] In contrast, when no strain is applied to the flat test specimen 10a, even when the tensile tester 20 moves at 1 Hz, the temperature fluctuation distribution map remains uniform (not shown), and no temperature fluctuation distribution signal is observed in the amplitude image visualizing the elastocaloric effect. In other words, this thermal image signal corresponds to the thermal response of elastic deformation, and the elastocaloric effect is visualized. Furthermore, this thermal image signal shows no change over time, even after at least 10 minutes have passed.

[0037] Figure 7 is an explanatory diagram visualizing the elastocaloric effect due to low-frequency strain deformation of a kirigami-shaped polystyrene plate, showing one embodiment of the present invention. Figure 7(A) is an outline drawing of a kirigami-shaped test piece 10b, (B) is a temperature fluctuation distribution map based on an amplitude image, (B2) is the temperature fluctuation distribution grayscale, (C) is a temperature fluctuation distribution map based on a phase image, and (C2) is the phase difference grayscale. In the figure, the kirigami-type test specimen 10b is a 0.3 mm thick polystyrene flat slab, with a 2 mm longitudinal distance between the edge notches 12a, 12b and the central notch 12c. The tensile testing machine 20 applies an initial strain of 1.5% to the kirigami-type test specimen 10b, and performs a reciprocating tensile test at a driving frequency of 1 Hz and a strain amplitude of 1.0%. Noise is reduced by integrating thermal image signals over one minute. Because stress concentrations occur in the kirigami-type test specimen 10b adjacent to the edge notches 12a, 12b and the central notch 12c, bright spots with a central intensity of approximately 400 mK appear in the temperature fluctuation amplitude distribution. These bright spots are located at the vertices of a hexagon centered on the central notch 12c. On the other hand, the phase component of the region corresponding to the sides of the hexagon centered on the central notch 12c is 180°, while the phase of the center of the central notch 12c and the edge including the edge notches 12a and 12b is 0°, resulting in a phase difference of 180°. In other words, phase inversion is observed depending on the local location of the kirigami-type test piece 10b. This indicates that both heat absorption and heat dissipation exist in one kirigami-type test piece 10b.

[0038] Figure 8 is an explanatory diagram of the stress distribution due to tensile stress in the kirigami-type test piece 10b. An initial strain ε0 was applied to the kirigami-type test piece 10b, and a reciprocating tensile strain with an amplitude smaller than the initial strain ε0 was applied. Under these stress conditions, compressive stress acts at the opening of the central notch 12c, while tensile stress acts in the region at the boundary between adjacent central notches 12c. The region at the boundary between adjacent central notches 12c is also the region sandwiched between the left and right edge notches 12a and 12b. The region where phase inversion is observed in the phase diagram of Figure 7(C) is interpreted as corresponding to the direction of the stress acting in the area corresponding to the sides of the hexagon centered on the central notch 12c, and in the edge region including the center of the central notch 12c and the edge notches 12a and 12b.

[0039] 9 is an explanatory diagram visualizing the heat generation distribution due to low-frequency strain deformation of kirigami-type test pieces 10c and 10d, which show a modified embodiment of the present invention. Fig. 9(A) is an outline drawing of the kirigami-type test pieces 10c and 10d, (B) is a temperature fluctuation distribution map of the amplitude image of the 0.2 mm thick polystyrene kirigami-type test piece 10c, (B2) is the temperature fluctuation distribution grayscale, (C) is a temperature fluctuation distribution map of the amplitude image of the 0.3 mm thick polystyrene kirigami-type test piece 10d, and (C2) is the temperature fluctuation distribution grayscale.

[0040] In Figure 9(A), the paper-cut test specimen 10c is a 0.2 mm thick polystyrene flat slab. The edge notches 12d, 12e are, for example, 3 mm long, with eight of them on each side, evenly spaced 2 mm apart and parallel to each other. The central notches 12f are, for example, 5 mm long, with nine of them evenly spaced 2 mm apart and parallel to each other in the longitudinal direction. In the paper-cut test specimen 10c, the edge notches 12d, 12e and the central notch 12c are alternately arranged in the longitudinal direction, so the distance between the edge notches 12d, 12e and the central notch 12f is 1 mm. The paper-cut test piece 10d is a flat slab made of polystyrene and has a thickness of 0.3 mm. The positional relationship between the edge cuts 12d and 12e and the center cut 12f is the same as that of the paper-cut test piece 10c.

[0041] In Figure 9(B), the tensile testing machine 20 applies a tensile strain of 1.5% to the paper-cut test piece 10c as an initial strain ε0, and performs a reciprocating tensile test with a drive frequency of 1 Hz and an amplitude Δε of 1.0% strain, and accumulates thermal image signals for one minute. In the Kirigami-type test piece 10c, the temperature fluctuation amplitude A at an amplitude Δε of 1.0% strain is lower than the temperature fluctuation amplitude A at an amplitude Δε of 1.0% strain in the Kirigami-type test piece 10b. However, the required stress is lower. In other words, the tensile stress required to produce a strain ε = 1% is as follows: (i) 13 MPa for the flat-plate type test piece 10a without a cut pattern, (ii) 4 MPa for the paper-cut test piece 10b in which the spacing between the edge notches 12a, 12b and the central notch 12c is 2 mm. (iii) 0.8 MPa for the paper-cut test piece 10c in which the spacing between the edge notches 12d, 12e and the central notch 12f is 1 mm.

[0042] In Figure 9(C), the tensile testing machine 20 applies a 6% tensile strain to the paper-cut test piece 10d as an initial strain ε0, and performs a reciprocating tensile test with a drive frequency of 1 Hz and an amplitude Δε of 5.0% strain, accumulating thermal image signals for one minute.

[0043] Next, the stress σ-strain ε curve will be explained. As shown in the following formula, the stress σ is obtained by dividing the load value F of the load cell of the tensile tester 20 by the cross-sectional area obtained by multiplying the width w and thickness t of the test piece 10.

[0044]

number

[0045] Fig. 10 is an explanatory diagram of the stress-strain curves of a kirigami-type test piece according to an embodiment of the present invention and a flat-type test piece 10a as a comparative example. Fig. 10(A) shows the stress-strain curves of a 0.2 mm thick polystyrene kirigami-type test piece and a flat-type test piece 10a, (B) shows the stress-strain curves of a 0.3 mm thick polystyrene kirigami-type test piece and a flat-type test piece 10a, and (C) shows the hysteresis curves resulting from repeated loading and unloading. The stress σ increases monotonically with the strain ε, which corresponds to Hooke's law, i.e., elastic deformation. If a pigment is applied to the paper-type test piece 10b, the pigment may affect the elasticity. The shapes of the edge notches 12a, 12b and the central notch 12c in the kirigami-type test specimen 10b contribute to a decrease in the effective Young's modulus of the test specimen 10, but this is not a completely linear correlation. Also, the hysteresis generated by the application of cyclic strain is small.

[0046] In Figure 11, (A) is a comparative explanatory diagram of the elastocaloric effect per unit input stress of kirigami-type test specimens 10b, 10c, and 10d as examples of the present invention, compared with the comparative flat-plate test specimen 10a and a Ni-Ti alloy, and (B) is a temperature fluctuation distribution diagram using an amplitude image. The elastocaloric effect per unit input stress is expressed as the temperature fluctuation amplitude A (=A / Δσ) per unit stress deviation Δσ. Here, A / Δσ was calculated using a strain amplitude Δε of 0.5%. The temperature fluctuation amplitude A of the kirigami sample of the kirigami-type test specimen 10b was measured at the edges of the edge-side notches 12a and 12b. Here, the region of interest (ROI) for acquiring the temperature fluctuation amplitude A was set to 7 × 7 pixels. The elastocaloric effect per unit input stress, A / Δσ [K / MPa], for the flat-plate test specimen 10a is 0.02 [K / MPa] for both the 0.2 mm and 0.3 mm thicknesses. In contrast, for the kirigami-type test specimen 10b, it is 0.10 [K / MPa] for the 0.2 mm thickness and 0.18 [K / MPa] for the 0.3 mm thickness. The kirigami-type test specimen 10c is 0.14 [K / MPa] for the 0.2 mm thickness, and the kirigami-type test specimen 10d is 0.28 [K / MPa] for the 0.3 mm thickness. The superelastic Ni-Ti alloy is 0.07 [K / MPa].

[0047] Compared to the flat-type test specimen 10a, the kirigami-type test specimens 10b, 10c, and 10d have a better elastocaloric effect per unit input stress near the stress concentration point. Furthermore, optimizing the shape of the edge and center notches in the kirigami-type test specimens increases the temperature change due to the elastocaloric effect that occurs locally per unit input stress. For example, it is recommended to use elastoplastic mechanical analysis using the finite element method to accurately determine the acting stress at the stress concentration point and the optimal structure of the test specimen. In terms of the elastocaloric effect per unit input stress, a very rough comparison between the superelastic Ni-Ti alloy (approximately 10 K / 250 MPa: Δε=3%) and the kirigami-type measurement test piece 10b shows that the performance of the kirigami-type measurement test piece 10b is superior.

[0048] Figure 12 is an explanatory diagram comparing the elastocaloric effects of various plastic materials, showing the chemical formula, Young's modulus [GPa], specific heat [J / g K], density [g / cm ], and specific heat capacity [J / g K] for polypropylene (PP), polyvinyl chloride (PVC), high-density polyethylene (HDPE), polyethylene terephthalate (PET), polystyrene (PS), and polyvinylidene fluoride (PVDF). 3 ], thermal expansion coefficient [10 -5 / K] is shown.

[0049] Figure 13 is an explanatory diagram comparing the elastocaloric effect of various plastic materials, comparing the elastocaloric effect per unit input stress. Here, the ROI for obtaining the temperature modulation due to the elastocaloric effect is set to 240 x 300 pixels. The stress amplitude Δσ in the amplitude image was set to ±0.5%. The thickness of the flat test specimens for the various plastic materials was 1 mm, and the width was 6 mm. However, for PVDF, the thickness was set to 50 μm and the width to 6 mm. The temperature fluctuation amplitude A (=A / Δσ) per unit stress deviation Δσ was 0.08 [K / MPa] for PP, 0.09 [K / MPa] for PVC, 0.20 [K / MPa] for HDPE, 0.14 [K / MPa] for PET, 0.15 [K / MPa] for PS, and 0.12 [K / MPa] for PVDF. In other words, the order of elastocaloric effect per unit input stress was HDPE > PS > PET, PVDF, PVC, and PP. From the above, it was found that polystyrene (PS) is relatively suitable as a plastic material for evaluating elastocaloric effect measurement devices.

[0050] [Comparative example of temperature modulation material] Next, a comparative example of the temperature modulation member will be described. Figure 14 is an explanatory diagram of a temperature modulation element with dot holes formed in a grid pattern, where (A) is an outline drawing of the temperature modulation element, (B) is a temperature fluctuation distribution diagram based on an amplitude image of the main part, and (B2) is a grayscale of the temperature fluctuation distribution. Figure 15 is an explanatory diagram of a temperature modulation element with dot holes formed in a staggered pattern, where (A) is an outline drawing of the temperature modulation element, (B) is a temperature fluctuation distribution diagram based on an amplitude image of the main part, and (B2) is a shading scale of the temperature fluctuation distribution. Figure 16 is an explanatory diagram of a temperature modulation element in which dot holes with an inner diameter of approximately half the total width are formed, where (A) is an outline drawing of the temperature modulation element, (B) is a temperature fluctuation distribution diagram based on an amplitude image of the main part, and (B2) is a shading scale of the temperature fluctuation distribution.

[0051] Temperature modulation elements with dot holes formed in a grid or staggered pattern have lower stress concentrations than kirigami-style temperature modulation elements with edge or center notches. The same is true for temperature modulation elements with dot holes formed with an inner diameter of about half the total width. Therefore, in the temperature modulation elements disclosed in Figures 14 to 16, an isotropic temperature fluctuation amplitude component of about 50 to 70 mK was observed as the temperature fluctuation amplitude distribution, which is not significantly different from the flat-plate type test piece 10a.

[0052] Next, a further explanation will be given of the temperature modulation member using the elastocaloric effect of the present invention. The temperature modulation element using the elastocaloric effect of the present invention may have a shape similar to that of the test piece for measuring the elastocaloric effect of the present invention, but the outer shape is not limited to a substantially rectangular shape and may be round, oval, or any other shape. While a plastic material was used in the examples of the present invention, similar effects can be expected from any material that exhibits the elastocaloric effect, not limited to plastic materials. In particular, in the case of superelastic materials, the entropy change associated with the martensitic phase change can be superimposed on the entropy change associated with normal elastic deformation, allowing for a large adiabatic temperature change due to the elastocaloric effect. Kirigami processing can improve the elasticity of the entire element, making it highly compatible with wearable devices and flexible electronics devices. Kirigami processing allows the material to be pulled with a weak force, which is expected to expand the applications of the elastocaloric effect in superelastic metals, which are difficult to tensile and compress when in their plate form. Note that the range of tensile stress is preferably within the range of elastic deformation, but in applications where some plastic deformation is acceptable, it may be acceptable to slightly exceed the tensile strength.

[0053] According to the temperature modulation element of the present invention using the elastocaloric effect, a cut pattern is formed, which causes stress concentration near the cut pattern, resulting in localized temperature fluctuations due to the elastocaloric effect.This temperature fluctuation is several to several tens of times larger than the temperature fluctuations that occur throughout the entire test piece, so large temperature modulation can be achieved near the stress concentration area. [Industrial Applicability]

[0054] The temperature modulation element of the present invention, which utilizes the elastocaloric effect, can locally heat and cool the temperature modulation element while providing flexibility and stretchability, and the temperature distribution can be designed in a variety of ways, making it suitable for use in cooling wearable devices and flexible electronics. The test piece for measuring the elastocaloric effect and the method for measuring the elastocaloric effect of the present invention use LIT measurement, so even if stress concentration occurs near the cut pattern and temperature fluctuations due to the elastocaloric effect occur locally, large temperature modulations can be accurately detected near the stress concentration area, making them suitable for use in searching for materials with a large elastocaloric effect per unit input stress. [Explanation of symbols]

[0055] 10. Measurement specimen 10a Flat test piece 10b, 10c, 10d Paper-shaped test piece 12a, 12b, 12d, 12e Edge notch 12c, 12f central notch 20 Tensile testing machine 30 Infrared Camera 40 Measurement computer 41 Input section 42 Arithmetic section 43 Storage section 44 Output section 50 Elastic caloric effect extraction section (Fourier analysis section) 52 Amplitude image section 54 Phase Imaging Section 56 Elastic-caloric effect coefficient calculation section 60 Temperature modulation member 62a, 62b Edge notch 62c central notch

Claims

1. applying a tensile stress or a tensile strain to a measurement test piece in such a manner that the measurement test piece is in a thermally non-steady state; measuring a thermal image of the surface of the measurement test piece; reading a thermal image of the measurement specimen; extracting a temperature change resulting from a stress or strain applied to the measurement test piece from the thermal image of the measurement test piece that has been read; extracting an amplitude component of a temperature change that changes in synchronization with the stress or strain generated in the test piece from a temperature change signal derived from the stress or strain generated in the test piece, and imaging the amplitude component; extracting a phase component of a temperature change that changes in synchronization with the stress or strain generated in the measurement test piece from the temperature change signal resulting from the stress or strain generated in the measurement test piece, and imaging the phase component; A method for measuring an elastocaloric effect comprising:

2. The method for measuring the elastocaloric effect according to claim 1, further comprising a step of calculating the elastocaloric effect coefficient of the composition of the test piece using a temperature change profile obtained by using temperature changes in the amplitude component and phase component in a certain region of the test piece.

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