Fatigue information acquisition device, fatigue information acquisition method, program, fatigue evaluation system, and life evaluation method

Abstract

To acquire information on fatigue of an object in a non-contact manner.SOLUTION: A fatigue information acquisition device comprises: an irradiation unit that emits light that heats a surface of an object; a detection unit that detects temperature distribution of a back surface of the object heated by the irradiation from the irradiation unit; and an acquisition unit that acquires information on fatigue of the object based on the temperature distribution detected by the detection unit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fatigue information acquisition device, a fatigue information acquisition method, a program, a fatigue state evaluation system, and a lifespan evaluation method. [Background technology]

[0002] Patent document 1 discloses a content information acquisition device that includes a heating unit that irradiates light onto a composite material containing fibers to heat the composite material, a detection unit that detects the temperature distribution in the area of ​​the composite material heated by the heating unit, and an acquisition unit that acquires information about the fiber content in the composite material based on the temperature distribution detected by the detection unit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-178970 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a sample such as a composite material is subjected to repeated loads, fatigue occurs in the sample. Information about this fatigue may be required to be obtained in a non-contact manner, for example, without cutting out the sample.

[0005] The technology disclosed in this specification aims to obtain information about fatigue of an object in a non-contact manner. [Means for solving the problem]

[0006] With this objective in mind, the technology disclosed in this specification is a fatigue information acquisition device that includes an irradiation unit that irradiates light to heat the surface of an object, a detection unit that detects the temperature distribution on the back surface of the object heated by irradiation from the irradiation unit, and an acquisition unit that acquires information regarding fatigue of the object based on the temperature distribution detected by the detection unit. Here, the acquisition unit may calculate information about the thermal diffusivity of the object based on the temperature distribution, and acquire the information about fatigue. The acquisition unit may also calculate, as the information on the thermal diffusivity of the object, information on the in-plane thermal diffusivity of the object and information on the thermal diffusivity of the object through a thickness direction. The heating unit may also heat the object by irradiating light onto an area extending in one direction on the surface of the object. The heating section may include a light source and a deformation section that transmits light emitted from the light source and transforms the light into sheet light. The image forming apparatus may further comprise a moving body that moves the deformation unit and the object relative to each other and moves the position of the region on the object in a direction intersecting the one direction. The apparatus may also include a tensile testing unit that performs a tensile test on the object, and a decision unit that decides to continue the tensile test on the object based on information about fatigue of the object. The information regarding fatigue of the object may include information regarding a location in the object where fatigue failure is predicted to occur.

[0007] From another perspective, the technology disclosed in this specification is a fatigue information acquisition method comprising the steps of irradiating a surface of an object with light to heat it, detecting the temperature distribution on the back surface of the object heated by the irradiation, and acquiring information regarding fatigue of the object based on the detected temperature distribution.

[0008] From another perspective, the technology disclosed in this specification is a program that causes a computer to perform the functions of detecting the temperature distribution on the back surface of an object that has been heated by irradiating the surface of the object with light, and obtaining information regarding fatigue of the object based on the detected temperature distribution.

[0009] From another perspective, the technology disclosed in this specification is a fatigue evaluation system that includes a load unit that holds an object using a holder and applies a load to the object, an irradiation unit that irradiates light to heat the surface of the object while the object is being loaded by the load unit and held by the holder, a detection unit that detects the temperature distribution on the back surface of the object heated by irradiation by the irradiation unit, and an acquisition unit that acquires information regarding the fatigue of the object based on the temperature distribution detected by the detection unit.

[0010] From another perspective, the technology disclosed in this specification is a lifetime evaluation method comprising the steps of irradiating a surface of an object with light to heat it, detecting the temperature distribution on the back surface of the object heated by the irradiation, and calculating the thermal diffusivity of the object based on the detected temperature distribution, thereby calculating information regarding the lifetime of the object. [Effects of the Invention]

[0011] According to the technology disclosed in this specification, information regarding fatigue of an object can be obtained in a non-contact manner. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram showing a fatigue state evaluation device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a functional configuration diagram of a computer. [Figure 3] FIG. 1 illustrates an example of a hardware configuration of a computer. [Figure 4] FIG. 2 is a diagram showing the configuration of a measurement sample and its surroundings in the fatigue state evaluation device. [Figure 5]FIG. 1 is a diagram illustrating microcracks and micro-delamination. [Figure 6] FIG. 10 is a diagram showing a distribution of phase delays occurring in a measurement sample. [Figure 7] 10 is a flowchart illustrating a fatigue life determination operation performed by the fatigue state evaluation device. [Figure 8] 10 is a flowchart illustrating a fatigue assessment process performed by the fatigue state assessment device. [Figure 9] This is an expected diagram of the change in the in-plane and thickness direction thermal diffusivity distribution with respect to the number of loading cycles. [Figure 10] FIG. 10 is a graph showing changes in fatigue evaluation with respect to the number of loads. [Figure 11] FIG. 10 is a diagram illustrating prediction of damage occurrence. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings. <Configuration of fatigue state assessment device 100> FIG. 1 is a schematic diagram showing the configuration of a fatigue state assessment device 100 according to the present embodiment. First, with reference to FIG. 1, the configuration of a fatigue state assessment device 100 to which this embodiment is applied will be described.

[0014] As shown in Figure 1, the fatigue state evaluation device 100 to which this embodiment is applied comprises a diode laser 10 that functions as a light source for heating the measurement sample 1, a light guiding section 20 that guides the laser light from the diode laser 10 to the measurement sample 1, an infrared thermograph (lock-in thermograph) 30 that is arranged opposite the measurement sample 1, a computer 50 that receives signals from the infrared thermograph 30, a periodic signal generator 70 that generates periodic signals and outputs them to the diode laser 10 and the computer 50, and a tensile testing machine 80 that performs a tensile test on the measurement sample 1.

[0015] Here, the light guide section 20 has a mirror 21 that reflects the laser light emitted from the diode laser 10, a beam expander 23 that expands the beam diameter of the laser light from the mirror 21, a cylindrical lens 25 that converts the laser light from the beam expander 23 into sheet light, a holder 27 that holds the measurement sample 1, and a positioning device 29 that determines the position of the cylindrical lens 25 relative to the measurement sample 1.

[0016] In the fatigue state evaluation device 100, laser light emitted from a diode laser 10 passes through a mirror 21, a beam expander 23, and a cylindrical lens 25 and is irradiated onto a measurement sample 1. In the measurement sample 1, the area irradiated with the laser light is periodically heated. That is, a specific area on the surface of the measurement sample 1 is periodically spot heated.

[0017] The temperature of the measurement sample 1, which has been periodically heated by the laser light from the diode laser 10, is measured from the rear surface of the measurement sample 1 by an infrared thermograph 30. The infrared thermograph 30 captures (measures) an infrared image of a predetermined range including the area periodically spot heated by the diode laser 10. That is, the infrared thermograph 30 measures the temperature response of the rear surface of the measurement sample 1 in two dimensions. A periodic signal is input to the infrared thermograph 30 from a periodic signal generator 70. Temperature distribution data, which is data on the temperature measured by the infrared thermograph 30, is output to a computer 50.

[0018] The computer 50, in conjunction with the infrared thermograph 30, continuously captures and calculates infrared images at a predetermined frame rate, creating an averaged image from the temperature change over time (lock-in method). More specifically, the data obtained by the infrared thermograph 30 is processed by the computer 50 to evaluate fatigue in the measurement sample 1. The computer 50 also executes a tensile test via the tensile tester 80 at predetermined timings, repeatedly evaluating fatigue in the measurement sample 1.

[0019] The tensile tester 80 receives instructions from the computer 50 and drives the holder 27 to perform a tensile test on the measurement sample 1. The tensile tester 80 receives a condition signal (described later) from the computer 50 and performs a tensile test on the measurement sample 1 based on the condition signal.

[0020] In the following description, the direction along the surface of the measurement sample 1 in Fig. 1, i.e., the left-right direction in the figure, may be referred to as the x-direction. The up-down direction in Fig. 1 may be referred to as the z-direction. The direction into the paper in Fig. 1 may be referred to as the y-direction.

[0021] <Functional configuration of computer 50> FIG. 2 is a functional block diagram of the computer 50. Next, the functional configuration of a computer 50 to which this embodiment is applied will be described with reference to FIGS.

[0022] As shown in Figure 2, a computer 50 to which this embodiment is applied includes a data acquisition unit 51 that acquires temperature distribution data and periodic signals input from the infrared thermography 30 (see Figure 1), a phase lag distribution calculation unit 52 that calculates a phase lag distribution based on the temperature distribution data and periodic signals acquired by the data acquisition unit 51, a thermal diffusivity calculation unit 53 that calculates a thermal diffusivity distribution based on the calculated phase lag, a fatigue evaluation calculation unit 54 that calculates a fatigue evaluation (described below) that is an evaluation of the fatigue of the measurement sample 1 (see Figure 1) based on the calculated thermal diffusivity distribution, a calculation result display unit 55 that displays the calculated fatigue evaluation, etc. on a liquid crystal display (not shown), and a tensile test execution unit 56 that executes a tensile test using a tensile tester 80.

[0023] The thermal diffusivity calculation unit 53 calculates the thermal diffusivity based on equation (3) described later. The fatigue evaluation calculation unit 54 calculates the fatigue evaluation based on equation (5) described later. The tensile test execution unit 56 outputs a condition signal to the tensile testing machine 80, specifying test conditions such as the tensile load and number of loads for the tensile test. The tensile test execution unit 56 also receives a signal indicating the end of the tensile test from the tensile testing machine 80.

[0024] In this embodiment, the computer 50 evaluates the measurement sample 1 (see FIG. 1 ) based on the temperature distribution of the measurement sample 1 detected by the infrared thermography 30, and more specifically, evaluates the fatigue state of the measurement sample 1. Here, the fatigue state refers to the degree of material deterioration that occurs when the measurement sample 1 is continuously or repeatedly subjected to repeated stress. Furthermore, evaluating the fatigue state refers to evaluating the degree of fatigue. Here, as fatigue progresses, cracks due to fatigue damage occur in the measurement sample 1, the fatigue cracks propagate, and fractures occur.

[0025] <Hardware configuration of computer 50> FIG. 3 is a diagram showing an example of the hardware configuration of the computer 50. As shown in FIG. As shown in FIG. 3, computer 50 includes a CPU (Central Processing Unit) 501, which is a computing means, and a main memory 503 and an HDD (Hard Disk Drive) 505, which are storage means. Here, CPU 501 executes various programs such as an OS (Operating System) and application software. Main memory 503 is a storage area that stores various programs and data used for executing the programs. HDD 505 is a storage area that stores input data for the various programs and output data from the various programs. These components included in computer 50 execute the various functions described above in FIG. 2 and elsewhere.

[0026] The computer 50 is equipped with a communication interface (communication I / F) 507 for communicating with external devices such as the infrared thermography 30. The program executed by the CPU 501 (for example, the program for calculating the fatigue evaluation) can be stored in advance in the main memory 503, or can be stored on a storage medium such as a CD-ROM and provided to the CPU 501, or can be provided to the CPU 501 via a network (not shown).

[0027] <Configuration of measurement sample 1 and its surroundings> FIG. 4 is a diagram showing the configuration of the measurement sample 1 and its surroundings in the fatigue state evaluation device 100. As shown in FIG. Next, the configuration of the measurement sample 1 and the peripheral configuration of the measurement sample 1 in the fatigue state evaluation device 100 will be described with reference to FIG.

[0028] <Measurement sample 1> First, the structure of the measurement sample 1 will be described. As shown in FIG. 4, the measurement sample 1 is a flat plate-shaped member. The material of the measurement sample 1 is not particularly limited, but it may be made of a composite material such as carbon fiber reinforced plastics (CFRP). As shown in FIG. 4, the measurement sample 1 has an upper surface 11, which is the side irradiated with laser light from the diode laser 10 (see FIG. 1), i.e., the upper surface in the figure, and a lower surface 13, which is the side opposite to the side irradiated with laser light from the diode laser 10, i.e., the lower surface in the figure. The lower surface 13 is the surface facing the infrared thermograph 30. Additionally, the infrared thermograph 30 measures the heat distribution on the lower surface 13 of the measurement sample 1.

[0029] <Peripheral configuration of measurement sample 1> Next, the peripheral configuration of the measurement sample 1 in the fatigue state evaluation device 100 will be described. First, the cylindrical lens 25 is provided at a position facing the upper surface 11 of the measurement sample 1. The cylindrical lens 25 is an optical element that deforms the laser light from the diode laser 10. To explain further, the cylindrical lens 25 diffuses the laser light in one direction (x direction in the figure) on an imaginary plane perpendicular to the laser light from the diode laser 10, while maintaining the dimensions of the laser light in a direction intersecting the one direction (y direction in the figure). In this way, the cylindrical lens 25 deforms the optical path of the laser light into a sheet shape (planar shape).

[0030] This cylindrical lens 25 forms a light irradiation area HA on the upper surface 11 of the measurement sample 1. This light irradiation area HA has a light intensity (for example, 1 / e of the heating center HP) that has a predetermined relationship with the heating center HP where the light intensity is maximum. 2 ) The light irradiation area HA shown in the figure has a substantially elliptical or rectangular shape with its major axis along the x-direction. In addition, the light irradiation area HA has a shape that is elongated in one direction on the upper surface 11 of the measurement sample 1. This light irradiation area HA enables line heating on the upper surface 11 of the measurement sample 1. The light irradiation area HA can be regarded as a linear heat source.

[0031] The holder 27 has a first holder 271 and a second holder 273 that hold both ends of the measurement specimen 1. Here, the first holder 271 and the second holder 273 are driven by the tensile tester 80 to apply a tensile load to the measurement specimen 1. The first holder 271 and the second holder 273 repeatedly apply a tensile load to the measurement specimen 1 for a specified number of loads in accordance with a condition signal received by the tensile tester 80 from the tensile test execution unit 56. In the illustrated example, the first holder 271 and the second holder 273 apply a tensile force to the measurement specimen 1 in a direction along the x-direction. More specifically, the first holder 271 and the second holder 273 apply a tensile force in a direction along the longitudinal direction of the light irradiation area HA.

[0032] The positioning device 29 determines the positional relationship between the cylindrical lens 25 and the infrared thermography 30 and the measurement sample 1. The positioning device 29 holds the cylindrical lens 25 and the infrared thermography 30 so that they are positioned facing each other with the measurement sample 1 in between.

[0033] Here, the positioning device 29 can change the position of the cylindrical lens 25 in a direction intersecting the longitudinal direction of the light irradiation area HA. ​​In the illustrated example, the positioning device 29 can move the cylindrical lens 25 in the y direction (see arrow D1 in the figure). This movement of the cylindrical lens 25 changes the position of the light irradiation area HA on the measurement sample 1. In other words, by moving the cylindrical lens 25 with the positioning device 29, different areas on the measurement sample 1 can be measured.

[0034] The laser light emitted from the diode laser 10 has a substantially circular cross section, with a diameter of, for example, 0.1 μm to 1 mm. The length of the light irradiation area HA in the x direction is, for example, 10 mm to 1000 mm. The length of the light irradiation area HA in the y direction may be shorter than the length in the x direction, and may be, for example, 0.1 μm to 100 mm. The size (one side) of the (substantially rectangular) area imaged by the infrared thermography 30 is 10 mm to 1000 mm. This imaged area may have dimensions that include the entire light irradiation area HA, i.e., larger than the light irradiation area HA, or may have dimensions that include a portion of the light irradiation area HA, i.e., smaller than the light irradiation area HA.

[0035] Furthermore, for example, if the upper surface 11 of the measurement sample 1 has irregularities, when the light of the diode laser 10 is irradiated obliquely onto the upper surface 11, some of the laser light may be blocked by the convex portions, and the laser light may not be irradiated onto the concave portions. Therefore, in the illustrated example, the laser light from the diode laser 10 directed toward the cylindrical lens 25 is oriented perpendicular to the upper surface 11 of the measurement sample 1. Additionally, the above configuration can reduce variations in light intensity in the light irradiation area HA.

[0036] Here, the fatigue state evaluation device 100 can measure the fatigue state of the measurement sample 1 in a non-contact and non-destructive manner. More specifically, the fatigue state evaluation device 100 can perform a fatigue test while the measurement sample 1 continues to be held by the first holding unit 271 and the second holding unit 273 (see FIG. 4). In other words, when a tensile load is repeatedly applied, it is possible to measure the fatigue state of the measurement sample 1 without releasing the holding of the measurement sample 1. This can make it easier to measure the fatigue state of the measurement sample 1.

[0037] <Measurement principle> Fig. 5 is a diagram illustrating microcracks CR and microdelaminations DL, where Fig. 5(a) is a diagram showing microcracks CR occurring in the measurement specimen 1, and Fig. 5(b) is a diagram showing microdelaminations DL occurring in the measurement specimen 1. Fig. 6 is a diagram showing the distribution of phase delays occurring in the measurement sample 1. Here, the horizontal axis of the graph shown in Fig. 6 represents the distance from the heating center HP in the x direction, and the vertical axis represents the distance from the heating center HP in the y direction.

[0038] Next, the fatigue characteristics of a carbon fiber reinforced composite material, which is an example of the measurement sample 1, will be described, and then the principle of the measurement method in this embodiment will be described. Carbon fiber reinforced composite materials, an example of measurement sample 1, are expected to be used in fields such as the transportation and aerospace industries due to their advantages, such as high specific strength, corrosion resistance, and fatigue resistance. However, the fatigue properties of carbon fiber reinforced composite materials vary greatly depending on the manufacturing quality and operating environment. Therefore, there is a need to understand the fatigue properties of carbon fiber reinforced composite materials. Understanding these fatigue properties is expected to extend the design life of products, for example.

[0039] Repeated loading of carbon fiber-reinforced composite materials can cause cracks (fatigue cracks) to form in the material. As these fatigue cracks grow, they can develop into delamination or fiber breakage within the carbon fiber-reinforced composite, ultimately resulting in fatigue failure of the entire material. Micro-delamination (micro-delamination) can also develop and propagate, leading to larger delaminations. These originate from microvoids (tiny voids) within the material during manufacturing, areas where the fibers are close together and the resin layer is thin, and stress concentrations between laminated layers. Microcracks and micro-delamination then initiate and grow from these stress concentrations, eventually leading to macroscopic fatigue cracks and delamination. Quantifying this process can potentially enable the diagnosis of a material's fatigue properties or state.

[0040] Image analysis and X-ray CT are known methods for detecting the origin of fatigue cracks in carbon fiber reinforced composite materials and their propagation patterns after initiation. However, image analysis can only extract information on the surface layer of the sample and is unable to evaluate the interior. Furthermore, X-ray CT requires a very small observation area, making it extremely time-consuming to evaluate the entire sample. Furthermore, X-ray CT requires cutting out the sample, making it difficult to observe large components. Therefore, in this embodiment, the fatigue state of the measurement sample 1 is calculated by measuring the thermal diffusivity distribution in the plane and thickness directions on a macroscale scale using non-contact heating with a laser.

[0041] To explain further, the microcracks CR in the test specimen 1 shown in FIG. 5(a) and the microdelaminations DL shown in FIG. 5(b) are accompanied by the occurrence of crack interfaces within the test specimen 1. These interfaces then act as thermal resistance, locally reducing the effective thermal diffusivity within the test specimen 1. To further explain, for example, the presence of the microcracks CR shown in FIG. 5(a) can be detected by measuring the thermal diffusivity in the in-plane direction of the test specimen 1 (see arrows IP in the figure). Furthermore, the presence of the microdelaminations DL shown in FIG. 5(b) can be detected by measuring the thermal diffusivity in the thickness direction of the test specimen 1 (see arrows OP in the figure). In this embodiment, these changes in thermal diffusivity are utilized to quantify the increasing tendency of the microcracks CR and microdelaminations DL using a laser, enabling the fatigue state of the test specimen 1 to be diagnosed. This allows the fatigue state of the test specimen 1 to be quantified nondestructively and over a wider range.

[0042] In this embodiment, it is possible to detect the initial deterioration of the measurement specimen 1 by detecting, for example, an increasing tendency of microcracks CR and microdelasing DL, which are not visible to the naked eye. Although the above description has been given using microcracks CR and microdelasing DL as examples, the material deterioration that occurs inside the measurement specimen 1 is not limited to this. Examples of material deterioration include lattice defects and bond breakage that occur inside the measurement specimen 1. In this embodiment, these material deteriorations can also be quantified by utilizing changes in thermal diffusivity, which is an example of a thermophysical property.

[0043] Next, an outline of thermal diffusivity measurement in this embodiment will be described. As described above, a linear heat source is generated in the measurement sample 1 using the diode laser 10 and cylindrical lens 25. Here, by varying the laser output at a constant heating frequency, periodic temperature fluctuations occur inside the measurement sample 1. Furthermore, the fluctuation amplitude decreases and the temperature fluctuation delay increases with increasing distance from the linear heat source. The infrared thermograph 30 then measures the temperature response of the rear surface of the sample and transmits it to the computer 50. The computer 50 performs lock-in processing on the reference signal sent to modulate the output of the diode laser 10 and the two-dimensional temperature response sent from the infrared thermograph 30, and outputs a phase image (phase delay distribution diagram) representing the delay in the temperature fluctuation.

[0044] In the phase lag distribution diagram shown in Figure 6, the in-plane thermal diffusivity in the horizontal direction (y direction) is calculated from the linear gradient of the phase lag in the analysis section defined as shown. On the other hand, the thickness direction thermal diffusivity is calculated from the frequency dependence of the phase lag at the center of the horizontal direction in the diagram, i.e., directly below the line heating source in the phase lag distribution diagram.

[0045] Here, ρce on the surface of the continuous medium i(2πft) When there is a periodic line heat source, the temperature response T at a distance r ac (r, t) is expressed by equation (1), where ρ is density, c is specific heat capacity, and f is heating frequency.

[0046]

number

[0047] Here, Q is a constant and D is the thermal diffusivity. The phase lag θ is given by

[0048]

number

[0049] Here, when the phase delay θ is differentiated with respect to the distance r, the in-plane thermal diffusivity D Lis expressed by equation (3).

[0050]

number

[0051] On the other hand, when the phase delay θ at r=d directly below the heating point is differentiated with respect to the heating frequency √f, the thermal diffusivity in the thickness direction D d is expressed by equation (4).

[0052]

number

[0053] For the above principle equation to hold, it is necessary to select a frequency that satisfies the heating frequency restrictions. As described above, by measuring the phase delay θ of the temperature response between the periodic line heat source and the back surface of the sample, it is possible to determine the in-plane thermal diffusivity from the distance dependence of the phase delay, and the thickness thermal diffusivity from the frequency dependence of the phase delay directly below the heat source (r = d).

[0054] In this embodiment, multiple points on the measurement sample 1 are cyclically heated simultaneously by line heating, and the in-plane thermal diffusivity and thickness thermal diffusivity at each point are calculated to calculate the in-plane thermal diffusivity distribution and thickness thermal diffusivity distribution. In other words, a long region in one direction on the measurement sample 1 is cyclically heated, and the in-plane thermal diffusivity and thickness thermal diffusivity according to the position in one direction are calculated to evaluate the fatigue state of the measurement sample 1. Note that simultaneous measurement of multiple points on the measurement sample 1 shortens the measurement time and enables simplification of the equipment.

[0055] <Fatigue life determination operation> FIG. 7 is a flowchart illustrating the fatigue life determination operation performed by the fatigue state evaluation device 100 (see FIG. 1). Next, the fatigue life determination operation of the fatigue state evaluation device 100 in this embodiment will be described with reference to Figures 1 and 7. It is assumed that the measurement specimen 1 is held at both ends by holders 27. It is also assumed that the fatigue state of the measurement specimen 1 is measured in a state before a load is applied, i.e., in an undamaged state.

[0056] First, the tensile test execution unit 56 executes a tensile test (step 701). Then, after a predetermined number of tensile tests have been executed, the fatigue evaluation calculation unit 54 executes a fatigue evaluation (step 702).

[0057] Next, the fatigue evaluation calculation unit 54 determines whether the fatigue evaluation is less than the threshold value (S703). If the fatigue evaluation is less than the threshold value (YES in S703), the tensile test execution unit 56 executes the tensile test (step 701). On the other hand, if the fatigue evaluation is equal to or greater than the threshold value (NO in S703), the calculation result display unit 55 displays the calculation result of the measurement specimen 1 in a display area (not shown) such as a liquid crystal display (step 704). The calculation result includes an image indicating that the measurement specimen 1 has reached its fatigue life.

[0058] Although it has been described above that the calculation result of the measurement sample 1 is displayed when the fatigue evaluation is compared with the threshold value, more specifically, when the fatigue evaluation is equal to or greater than the threshold value, the present invention is not limited to this. For example, the calculation result of the fatigue evaluation may be displayed regardless of the comparison result between the fatigue evaluation and the threshold value.

[0059] <Fatigue level evaluation processing> FIG. 8 is a flowchart illustrating the fatigue assessment process performed by the fatigue state assessment device 100 (see FIG. 1). Next, the fatigue assessment process of the fatigue state assessment device 100 according to the present embodiment will be described with reference to FIGS.

[0060] First, the surface of the measurement sample 1 is periodically line-heated by laser light emitted from the diode laser 10 in the fatigue state evaluation device 100 (step 801). Then, the phase lag distribution measurement unit 53 calculates the phase lag distribution based on the temperature distribution measured by the infrared thermography 30 (step 802).

[0061] Then, based on the phase lag distribution, the thermal diffusivity calculation unit 53 calculates the thickness direction thermal diffusivity distribution and the in-plane direction thermal diffusivity distribution (step 803). Then, based on the calculated thickness direction thermal diffusivity distribution and the in-plane direction thermal diffusivity distribution, the fatigue evaluation calculation unit 54 calculates the fatigue evaluation of the measurement sample 1 (step 804).

[0062] <Change in thermal diffusivity> Figure 9 shows the expected change in the in-plane and thickness thermal diffusivity distributions with respect to the number of loads. Figure 9(a) shows the widthwise distribution of in-plane thermal diffusivity. The horizontal axis of the graph in Figure 9(a) indicates the position in the widthwise direction (x direction), and the vertical axis indicates the in-plane thermal diffusivity. Figure 9(b) shows the relationship between the widthwise average in-plane thermal diffusivity and the number of loads. The horizontal axis of the graph in Figure 9(b) indicates the number of loads, and the vertical axis indicates the in-plane thermal diffusivity. Figure 9(c) shows the widthwise distribution of thickness thermal diffusivity. The horizontal axis of the graph in Figure 9(c) indicates the position in the widthwise direction (x direction), and the vertical axis indicates the thickness thermal diffusivity. Figure 9(d) shows the relationship between the widthwise average thickness thermal diffusivity and the number of loads. The horizontal axis of the graph in Figure 9(d) indicates the number of loads, and the vertical axis indicates the thickness thermal diffusivity. Note that the error bars in Figures 9(b) and 9(d) represent the standard deviation of the widthwise distribution.

[0063] Next, we will explain the change in the in-plane and thickness direction thermal diffusivity distribution with respect to the number of loading cycles, with reference to Figure 9. As shown in Figures 9(a) and (b), as the number of loading cycles increases, microcracks increase, fatigue progresses, and the in-plane thermal diffusivity decreases. Similarly, as shown in Figures 9(c) and (d), the thickness direction thermal diffusivity decreases with an increase in the number of loading cycles.

[0064] In this embodiment, it is possible to identify areas where fatigue has progressed compared to other areas based on the decrease in the in-plane / thickness thermal diffusivity width-direction distribution at a specific number of load cycles compared to the undamaged state (N=0). Furthermore, by taking the average value in the width direction as shown in Figures 9(b) and (d), the fatigue state around the heated area can be represented by the average value, and the fatigue state can be diagnosed based on the decrease from the undamaged state. More specifically, the greater the decrease in thermal diffusivity, the more advanced the fatigue is judged to be.

[0065] <Evaluation function> FIG. 10 shows the change in fatigue evaluation with respect to the number of load cycles. Here, FIG. 10(a) shows the relationship between thermal diffusivity and the number of load cycles. The horizontal axis of the graph shown in FIG. 10(a) shows the number of load cycles, and the vertical axis shows thermal diffusivity. FIG. 10(b) shows the relationship between the evaluation function and the number of load cycles. The horizontal axis of the graph shown in FIG. 10(b) shows the number of load cycles, and the vertical axis shows the evaluation function.

[0066] Next, the evaluation function will be described with reference to FIG. As described above, the fatigue evaluation calculation unit 54 calculates the fatigue evaluation of the measurement specimen 1 (see step 804 in FIG. 8 above). Here, the fatigue evaluation of the measurement specimen 1 is performed using a value (fatigue evaluation value) calculated based on the evaluation function F(N) shown in equation (5), for example. F(N)=D(0)-D(N) (5)

[0067] D(N) is the thermal diffusivity as a function of the number of loads (N), and D(0) is the thermal diffusivity in an undamaged state. In other words, this evaluation function F(N) evaluates the difference in thermal diffusivity, or more specifically, the decrease in thermal diffusivity, as a function of the number of loads. The larger this evaluation function, the more advanced the fatigue is, i.e., the more significant the fatigue is. By monitoring this evaluation function, it is possible to diagnose the fatigue state. Furthermore, if the fatigue evaluation value exceeds the set value at fatigue damage, it is determined that the fatigue life has been reached.

[0068] As shown in Figure 10(a) as measurement data, thermal diffusivity is measured at a predetermined number of load cycles, and the difference from the thermal diffusivity in an undamaged state is obtained as an evaluation function. Furthermore, as shown in Figure 10(b), the evaluation function F(N) is plotted. The maximum value of the evaluation function is then taken as the thermal diffusivity difference when delamination or transverse cracking occurs, and the state where the maximum value (threshold TH1) is reached is diagnosed as the fatigue life. Note that by obtaining a data plot of the change in thermal diffusivity from the start of fatigue in advance, as shown in Figure 10(a), it is possible to evaluate the magnitude of the fatigue progression rate at the time of measurement relative to the preliminary evaluation.

[0069] Furthermore, by measuring the thermal diffusivity in situ during fatigue testing, it is possible to quantify the continuous changes in the fatigue state. Furthermore, if pre-examined evaluation data is available, the fatigue state and its progression rate can be evaluated by comparing it with the actual measurement data. If pre-examined evaluation data is unavailable, the fatigue state can be quantified by comparing it with the undamaged state. In either case, it is possible to provide guidelines for predicting the occurrence of fatigue cracks.

[0070] Furthermore, the above evaluation functions are set for the in-plane thermal diffusivity and the thickness direction thermal diffusivity, respectively. That is, an evaluation function for the in-plane direction and an evaluation function for the thickness direction are set separately. Then, a threshold value is set for each of the evaluation function for the in-plane direction and the evaluation function for the thickness direction. Note that the evaluation function may be set based on either the in-plane thermal diffusivity or the thickness direction thermal diffusivity. Alternatively, the sum or average value of the in-plane thermal diffusivity and the thickness direction thermal diffusivity may be combined and set as a single evaluation function.

[0071] <Damage occurrence prediction> FIG. 11 is a diagram illustrating damage occurrence prediction. Here, FIG. 11(a) shows the widthwise distribution of thermal diffusivity. The horizontal axis of the graph shown in FIG. 11(a) indicates the position in the widthwise direction (x direction), and the vertical axis indicates the in-plane thermal diffusivity. FIG. 11(b) shows a damage occurrence prediction image 551 displayed in a display area 550.

[0072] Next, an example of damage occurrence prediction performed by the fatigue state assessment device 100 will be described with reference to FIG. First, the fatigue state evaluation device 100 detects the occurrence of microcracks CR, microdelaminations DL, and the like inside the measurement specimen 1 from changes in the in-plane and thickness thermal diffusivities as described above. Here, the microcracks CR, microdelaminations DL, and the like are the origins of fatigue cracks, for example. Therefore, the locations where the microcracks CR and microdelaminations DL occur can be locations in the measurement specimen 1 where damage such as fatigue cracks is likely to occur.

[0073] Therefore, as shown in FIG. 11(a), for example, the thermal diffusivity calculation unit 53 detects whether there is a location where the thermal diffusivity is low, for example, a location below the threshold value TH2 (see point EP), in the width direction distribution of the thermal diffusivity. 11(b), the calculation result display unit 55 displays a damage occurrence prediction image 551 in a display area 550 configured by a display or the like. This damage occurrence prediction image 551 includes a possibility image 553 indicating the degree of possibility of damage occurrence, and a position image 555 indicating the location where the value is below the threshold, i.e., the location where damage is predicted to occur. This damage occurrence prediction image 551 makes it possible to grasp the locations in the measurement specimen 1 where there is a high possibility of damage, such as cracks, occurring.

[0074] <Modification> In the above description, it has been explained that different regions on the measurement sample 1 can be measured by the positioning device 29 moving the cylindrical lens 25 in the y direction, but this is not limiting. For example, the positioning device 29 may rotate the angle of the cylindrical lens 25 to change the orientation of the light irradiation area HA formed on the measurement sample 1. To explain further, as shown in FIG. 4, by rotating the cylindrical lens 25 by 90 degrees, the longitudinal direction of the light irradiation area HA is switched from the direction along the x direction to the direction along the y direction. This makes it possible to measure different regions on the measurement sample 1.

[0075] Furthermore, in the above embodiment, it has been described that the positioning device 29 moves the cylindrical lens 25, but for example, other members of the light guide section 20 (mirror 21, beam expander 23) or the infrared thermography 30 may be moved together with the cylindrical lens 25. Furthermore, if the position of the light irradiation area HA on the measurement sample 1 is movable, the position of the measurement sample 1 may be moved instead of or in addition to the positioning device 29 moving the cylindrical lens 25 or the infrared thermography 30.

[0076] In the above embodiment, the laser light from the diode laser 10 directed toward the cylindrical lens 25 is perpendicular to the upper surface 11 of the measurement sample 1, but this is not limiting. That is, as long as the light irradiation area HA on the upper surface 11 of the measurement sample 1 is elongated in one direction, the laser light from the diode laser 10 may be irradiated obliquely onto the upper surface 11 of the measurement sample 1.

[0077] In the above embodiment, the cylindrical lens 25 is used to form the light irradiation area HA in a shape elongated in one direction, but this is not limiting. For example, instead of the cylindrical lens 25, a masking member may be provided to block part of the laser light, thereby forming the light irradiation area HA in a shape elongated in one direction. Furthermore, instead of the diode laser 10, a sheet laser that emits sheet light may be used as the light source. Furthermore, the light irradiation area HA may be formed in a shape elongated in one direction by irradiating the upper surface 11 of the measurement sample 1 in an oblique direction without using the cylindrical lens 25 or the like.

[0078] In the above embodiment, the light irradiation area HA is formed to be long in one direction, but this is not limiting. Laser light may be used for so-called point heating, and the positioning device 29 may move the cylindrical lens 25 and the infrared thermograph 30 to move the light irradiation area HA on the measurement sample 1.

[0079] Furthermore, in the above embodiment, fatigue evaluation is performed by measuring the thermal diffusivity of the measurement sample 1. However, the present invention is not limited to this, as long as fatigue evaluation is performed based on the temperature distribution formed in the measurement sample 1. For example, fatigue evaluation of the measurement sample 1 may be performed by measuring the distribution of temperature rise in the measurement sample 1 as the measurement sample 1 is heated for a predetermined time, or the distribution of absolute temperature after heating. Note that as deterioration such as fatigue cracks occurs inside the measurement sample 1, the thermal properties (thermophysical properties) of the measurement sample 1, such as the thermal diffusivity, change. Therefore, fatigue evaluation of the measurement sample 1 becomes possible by observing the temperature distribution formed in the measurement sample 1.

[0080] Furthermore, the heating of the measurement sample 1 performed by the diode laser 10 is not limited to laser heating. Other heating methods such as induction heating and resistance heating may be used as long as they are capable of locally heating the measurement sample 1.

[0081] Furthermore, in the above embodiment, the measurement sample 1 is described using a carbon fiber reinforced resin, but is not limited to this. For example, the measurement sample 1 may be an uncured carbon fiber reinforced resin before it is molded (cured) by heating / pressurizing, i.e., an intermediate substrate. The measurement sample 1 may also be a sample made up of multiple types of materials with different thermal conductivities. The measurement sample 1 may also be a material other than a composite material. For example, the measurement sample 1 may be glass, a semiconductor, a polymer film, a liquid crystal, or the like.

[0082] Furthermore, products currently in operation (such as automobiles and aircraft) may also be used as the measurement sample 1. For example, in the case of aircraft structural components, many of which are made of composite materials, fatigue testing and thermal diffusivity evaluation are performed on parts during the manufacturing process where fatigue damage could have a significant impact on airworthiness. Then, during heavy maintenance during operation, the above-described thermal diffusivity measurements can be performed on the aircraft as part of the maintenance task to assess the fatigue state of the relevant parts. This is possible because the present embodiment is a portable, non-contact, non-destructive testing method using thermography and laser heating. Furthermore, the ability to evaluate and diagnose fatigue states makes it possible to determine whether the design life specified in the flight cycle needs to be extended or shortened, thereby extending the life and improving the reliability of aircraft. Furthermore, incorporating this data into the design process can lead to accurate estimation of the design life taking into account the effects of actual operation, contributing to life extension.

[0083] Although the fatigue evaluation was described using the difference in thermal diffusivity from a reference undamaged state, this is not limiting. For example, the ratio of thermal diffusivities or the absolute value of thermal diffusivity may also be used for fatigue evaluation. Instead of or in addition to using the undamaged state as the reference, fatigue evaluation may be performed using a state where the fatigue life has been reached, pre-assessment data, or theoretical values ​​as a reference. Furthermore, fatigue information includes not only the value calculated as the fatigue evaluation of the measurement specimen 1, but also information such as a relative evaluation of fatigue (e.g., the degree of fatigue progression), whether the fatigue life has been reached, the estimated time and number of times that the specimen can be used before reaching the fatigue life, and the presence or absence of microcracks CR and microdelaminations DL within the measurement specimen 1.

[0084] Alternatively, information about thermal diffusivity obtained in the process of calculating information about fatigue of the measurement sample 1 may be output and stored together with or instead of information about fatigue. Here, information about thermal diffusivity includes the value of thermal diffusivity, a relative evaluation of thermal diffusivity (for example, the magnitude of thermal diffusivity), and a comparison result with pre-evaluation data or theoretical values.

[0085] Furthermore, information about the lifespan of the measurement specimen 1 may be output and stored together with or instead of fatigue information about the measurement specimen 1. Here, information about the lifespan includes whether or not the fatigue lifespan has been reached, the estimated time or number of times that the specimen can be used before reaching the fatigue lifespan, the degree of progression of fatigue (for example, a percentage) based on the fatigue lifespan, and the like.

[0086] Furthermore, although the above description has been given of acquiring fatigue information of the measurement specimen 1 in association with a tensile test using the tensile tester 80, the present invention is not limited to this. Fatigue information of the measurement specimen 1 may also be acquired in other load tests, such as a plane bending fatigue test, a rotating bending fatigue test, or an ultrasonic fatigue test, as long as the test applies a load to the measurement specimen 1. Note that the fatigue state evaluation device 100 may be configured without including the tensile tester 80, as long as it is capable of supporting the measurement specimen 1.

[0087] Furthermore, in the above embodiment, it has been described that fatigue information of the measurement sample 1 is acquired by the fatigue state evaluation device 100, but information regarding the density of the measurement sample 1 can also be acquired as a sample evaluation of the measurement sample 1. Note that the information regarding density is information that makes it possible to ascertain the density of the measurement sample 1. This information regarding density includes not only the density value of the measurement sample 1, but also a relative evaluation of the density (for example, whether dense or loose) and the presence or absence of voids inside the measurement sample 1.

[0088] The measurement sample 1 is an example of an object. The diode laser 10 is an example of an irradiation unit and a light source. The infrared thermography 30 is an example of a detection unit. The fatigue evaluation calculation unit 54 is an example of an acquisition unit and a determination unit. The fatigue state evaluation device 100 is an example of a fatigue information acquisition device and a fatigue evaluation system. The cylindrical lens 25 is an example of a deformation unit. The positioning device 29 is an example of a moving body. The tensile test execution unit 56 is an example of a tensile test unit. The tensile testing machine 80 is an example of a load unit.

[0089] Although various embodiments and modifications have been described above, it is of course possible to combine these embodiments and modifications. Furthermore, the present disclosure is not limited to the above-described embodiments, and can be implemented in various forms without departing from the gist of the present disclosure. [Explanation of symbols]

[0090] 1... measurement sample, 10... diode laser, 25... cylindrical lens, 30... infrared thermography, 50... computer, 53... thermal diffusivity calculation unit, 54... fatigue evaluation calculation unit, 80... tensile testing machine, 100... fatigue state evaluation device

Claims

1. an irradiation unit that irradiates light to heat the surface of the object; a detection unit that detects a temperature distribution on a back surface of the object heated by irradiation from the irradiation unit; an acquisition unit that continuously calculates information about the thermal diffusivity of the object based on the temperature distribution detected by the detection unit, compares the calculated information with a predetermined reference value, and acquires information about the progress of fatigue of the object; A fatigue information acquisition device comprising:

2. The acquisition unit calculates information about the in-plane thermal diffusivity of the object and information about the thickness direction thermal diffusivity of the object as the information about the thermal diffusivity of the object. The fatigue information acquisition device according to claim 1.

3. The irradiation unit irradiates a region extending in one direction on the surface of the object with light to heat the object.

3. The fatigue information acquisition device according to claim 1 or 2.

4. The irradiation unit is A light source and a deformation section that transmits light emitted from the light source and transforms the light into sheet light; The fatigue information acquisition device according to any one of claims 1 to 3, further comprising:

5. a moving body that moves the deformation unit and the object relative to each other and moves the position of the region in the object in a direction intersecting the one direction; The fatigue information acquisition device according to claim 4.

6. a tensile test unit that performs a tensile test on the object; a decision unit that decides to continue the tensile test of the object based on information about fatigue of the object; The fatigue information acquisition device according to claim 1 , further comprising:

7. The information about the fatigue of the object includes information about a location in the object where fatigue failure is predicted to occur. The fatigue information acquisition device according to any one of claims 1 to 6.

8. irradiating a surface of the object with light to heat the surface; detecting a temperature distribution on a rear surface of the object heated by the irradiation; continuously calculating information about the thermal diffusivity of the object based on the detected temperature distribution and comparing it with a predetermined reference value to obtain information about the progress of fatigue of the object; A fatigue information acquisition method comprising:

9. On the computer, A function of detecting the temperature distribution on the back surface of an object heated by irradiating the surface of the object with light; and a program that executes a function of continuously calculating information regarding the thermal diffusivity of the object based on the detected temperature distribution, comparing it with a predetermined reference value, and obtaining information regarding the progression of fatigue of the object.

10. a load unit that holds an object using a holder and applies a load to the object; an irradiation unit that irradiates light to heat the surface of the object in a state where the object is loaded by the loading unit and held by the holder; a detection unit that detects a temperature distribution on a back surface of the object heated by irradiation from the irradiation unit; an acquisition unit that continuously calculates information about the thermal diffusivity of the object based on the temperature distribution detected by the detection unit, compares the calculated information with a predetermined reference value, and acquires information about the progress of fatigue of the object; A fatigue assessment system comprising:

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