Fatigue limit load specifying system, fatigue limit load specifying device, and fatigue limit load specifying method

Abstract

To specify a fatigue limit load of a measurement object with higher accuracy than before.SOLUTION: An information processing device 4 vibrates a measurement object 1 at a predetermined frequency and with a gradually increasing load amplitude. The information processing device 4 acquires a fundamental wave component and a second harmonic component of a mechanical fluctuation of the measurement object 1 generated by vibrating the measurement object 1. The information processing device 4 calculates a first ratio indicating a ratio of an amplitude of the second harmonic component of the mechanical fluctuation to an amplitude of the fundamental wave component of the mechanical fluctuation. The information processing device 4 acquires a fundamental wave component and a second harmonic component of a temperature fluctuation of the measurement object 1 generated by vibrating the measurement object 1. The information processing device 4 calculates a second ratio indicating a ratio of an amplitude of the second harmonic component of the temperature fluctuation to an amplitude of the fundamental wave component of the temperature fluctuation. The information processing device 4 specifies the load amplitude at which a gradient of a difference between the first and second ratios relating to the load amplitude increases discontinuously as a fatigue limit load of the measurement object 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a fatigue limit load specifying system, a fatigue limit load specifying device, and a fatigue limit load specifying method. [Background technology]

[0002] There is a technique for measuring the temperature rise behavior of a test object subjected to repeated loads using an infrared camera, and estimating the fatigue limit based on the change in the temperature rise behavior relative to the amplitude of the repeated load.

[0003] For example, Patent Document 1 discloses a fatigue limit stress identification system that measures the fatigue limit stress of an object to be measured based on the temperature fluctuations that occur when the object to be measured is vibrated while the load is increased stepwise. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7122670 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional fatigue limit stress determination systems can produce errors in the estimated fatigue limit due to the nonlinearity of the system. Therefore, there is a need to determine the fatigue limit of the object to be measured with higher accuracy than conventional systems.

[0006] An object of the present disclosure is to provide a fatigue limit load specifying system, a fatigue limit load specifying device, and a fatigue limit load specifying method that can specify the fatigue limit load of a measurement object with higher accuracy than conventional methods. [Means for solving the problem]

[0007] A fatigue limit load specifying system according to one aspect of the present disclosure includes: an actuator that vibrates the measurement object; an infrared camera for measuring the temperature of the measurement object; an information processing device that identifies a fatigue limit load of the measurement object based on a temperature of the measurement object, The information processing device includes: controlling the actuator to vibrate the measurement object at a predetermined frequency and with a gradually increasing load amplitude; Acquire a fundamental wave component and a second harmonic component of a mechanical fluctuation of the object to be measured that is generated by vibrating the object to be measured, calculating a first ratio indicating a ratio of an amplitude of a second harmonic component of the mechanical variation to an amplitude of a fundamental component of the mechanical variation; acquiring a fundamental wave component and a second harmonic component of a temperature fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a second ratio indicating a ratio of an amplitude of a second harmonic component of the temperature fluctuation to an amplitude of a fundamental component of the temperature fluctuation; The load amplitude at which the gradient of the difference between the first and second ratios with respect to the load amplitude increases discontinuously is identified as the fatigue limit load of the object to be measured. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, the fatigue limit load of a measurement object can be determined with higher accuracy than conventional methods. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of a fatigue limit load specifying system 10 according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing the configuration of an information processing device 4 in FIG. [Figure 3] 2 is a diagram showing the shape and dimensions of the measurement object 1 in FIG. [Figure 4] 2 is a flowchart showing a measurement process executed by the information processing device 4 of FIG. 1. [Figure 5]2 is a flowchart showing a calculation process executed by the information processing device 4 of FIG. [Figure 6] 1 is a graph showing the simulation results for a first example of an embodiment, which shows the amplitude ratio M2 / M1 of the mechanical fluctuation of the object to be measured 1 and the amplitude ratio T2 / T1 of the temperature fluctuation of the object to be measured 1 when the thermal conduction of the object to be measured 1 in FIG. 1 is taken into consideration and the object to be measured 1 is vibrated at 1 Hz. [Figure 7] 1 is a graph showing the simulation results for a first example of an embodiment, which shows the amplitude ratio M2 / M1 of the mechanical fluctuation of the object to be measured 1 and the amplitude ratio T2 / T1 of the temperature fluctuation of the object to be measured 1 when the thermal conduction of the object to be measured 1 in FIG. 1 is taken into consideration and the object to be measured 1 is vibrated at 5 Hz. [Figure 8] 1 is a graph showing the simulation results for a first example of an embodiment, which shows the amplitude ratio M2 / M1 of the mechanical fluctuation of the object to be measured 1 and the amplitude ratio T2 / T1 of the temperature fluctuation of the object to be measured 1 when the thermal conduction of the object to be measured 1 in FIG. 1 is taken into consideration and the object to be measured 1 is vibrated at 25 Hz. [Figure 9] 1 is a graph showing the simulation results for a first example of an embodiment, illustrating the amplitude ratio M2 / M1 of the mechanical fluctuation of the object to be measured 1 and the amplitude ratio T2 / T1 of the temperature fluctuation of the object to be measured 1 when the object to be measured 1 of FIG. 1 is vibrated under adiabatic conditions. [Figure 10] 10 is a graph showing fatigue characteristics calculated based on the simulation results of FIGS. 6 to 9. [Figure 11] 6 is a diagram for explaining boundary points of the range of load amplitude determined in steps S11 to S15 of the calculation process in FIG. 5. FIG. [Figure 12] FIG. 6 is a diagram for explaining the upper limit of the load amplitude determined in steps S16 to S20 of the calculation process in FIG. [Figure 13] 10 is a graph showing the simulation results for the first comparative example, illustrating the characteristics of temperature fluctuations of a measurement object relative to load amplitude. [Figure 14] 14 is a table showing errors in fatigue limit loads calculated based on the simulation results of FIGS. 10 and 13. [Figure 15] 10 is a fatigue characteristic graph showing a simulation result according to a second example of the embodiment, in which heat conduction of the measurement object 1 in FIG. 1 is taken into consideration and the measurement object 1 is vibrated at 1 Hz. [Figure 16] 10 is a fatigue characteristic graph showing a simulation result according to a second example of the embodiment, in which heat conduction of the measurement object 1 in FIG. 1 is taken into consideration and the measurement object 1 is vibrated at 5 Hz. [Figure 17] 10 is a fatigue characteristic graph showing a simulation result according to a second example of the embodiment, in which heat conduction of the measurement object 1 in FIG. 1 is taken into consideration and the measurement object 1 is vibrated at 25 Hz. [Figure 18] 10 is a fatigue characteristic graph showing a simulation result according to a second example of the embodiment, in which the measurement object 1 of FIG. 1 is vibrated under adiabatic conditions. [Figure 19] 10 is a graph showing the results of a simulation according to a second comparative example, in which the thermal conduction of the object to be measured is taken into consideration and the object to be measured is vibrated at 1 Hz, showing the characteristics of temperature fluctuations of the object to be measured relative to the load amplitude. [Figure 20] 10 is a graph showing the simulation results for the second comparative example, illustrating the characteristics of the temperature fluctuation of the object to be measured relative to the load amplitude when the thermal conduction of the object to be measured is taken into consideration and the object to be measured is vibrated at 5 Hz. [Figure 21] 10 is a graph showing the simulation results for the second comparative example, illustrating the characteristics of the temperature fluctuation of the object to be measured relative to the load amplitude when the thermal conduction of the object to be measured is taken into consideration and the object to be measured is vibrated at 25 Hz. [Figure 22] 10 is a graph showing the simulation results for the second comparative example, illustrating the characteristics of temperature fluctuations of a measurement object relative to load amplitude when the measurement object is vibrated under adiabatic conditions. [Figure 23] 23 is a table showing errors in fatigue limit loads calculated based on the simulation results of FIGS. 15 to 22. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, more detailed description than necessary may be omitted. For example, detailed description of well-known matters and / or redundant description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art.

[0011] The inventors provide the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and do not intend for them to limit the subject matter described in the claims.

[0012] [Configuration of the embodiment] A fatigue limit load specifying system according to an embodiment will be described below with reference to the accompanying drawings. The fatigue limit load specifying system described below specifies the fatigue limit load of a measurement object.

[0013] 1 is a diagram showing the configuration of a fatigue limit load specifying system 10 according to an embodiment. The fatigue limit load specifying system 10 includes a measuring device 2, an infrared camera 3, and an information processing device 4, and calculates the fatigue limit load of a measurement object 1.

[0014] The object to be measured 1 is attached to the measuring device 2. The measuring device 2 includes an actuator 21, a load cell 22, a displacement sensor 23, and a strain gauge 24. The actuator 21 vibrates the object to be measured 1 at a predetermined frequency and a predetermined load amplitude under the control of an information processing device. The load cell 22 detects the load applied to the object to be measured 1 by the actuator 21. The displacement sensor 23 detects the displacement of the object to be measured 1 generated by the actuator 21. The strain gauge 24 detects the strain of the object to be measured 1 generated by the actuator 21. The detected load, displacement, and strain are transmitted to the information processing device 4.

[0015] The infrared camera 3 measures the temperature of the measurement object 1 by capturing a temperature image, for example, an infrared image, of the measurement object 1. The temperature image is transmitted to the information processing device 4. The infrared camera 3 has a frame rate that is sufficiently higher than the frequency at which the actuator 21 vibrates the measurement object 1. For example, if the actuator 21 vibrates the measurement object 1 at 25 Hz, the infrared camera 3 may have a frame rate of 250 Hz.

[0016] The information processing device 4 transmits a control signal to the measuring device 2 to control the actuator 21 so as to vibrate the object to be measured 1 at a predetermined frequency and a predetermined load amplitude. The information processing device 4 receives the detected load, displacement, and strain from the measuring device 2. The information processing device 4 receives a temperature image from the infrared camera 3. The information processing device 4 identifies the fatigue limit load of the object to be measured 1 based on the temperature of the object to be measured 1.

[0017] Fig. 2 is a block diagram showing the configuration of the information processing device 4 in Fig. 1. The information processing device 4 includes a bus 40, a processor 41, a memory 42, a storage device 43, a device interface (I / F) 44, an input device 45, a display device 46, and a communication interface (I / F) 47.

[0018] The processor 41 controls the overall operation of the information processing device 4. The processor 41 executes a program (described later) stored in the storage device 43 to identify the fatigue limit load of the measurement object 1 based on the temperature of the measurement object 1. The processor 41 may be, for example, a CPU (Central Processing Unit) or an MPU (Microprocessing Unit).

[0019] The memory 42 temporarily stores programs and data necessary for the operation of the information processing device 4. The memory 42 functions as a work area for the processor 41.

[0020] The storage device 43 is a non-volatile storage medium that stores programs and data necessary for the operation of the information processing device 4. The programs include instructions for controlling the overall operation of the information processing device 4, and also include instructions for executing measurement processing and calculation processing, which will be described later with reference to FIGS. 4 and 5. The storage device 43 may be, for example, a hard disk drive (HDD), a solid state drive (SSD), or an optical disk. The storage device 43 also functions as a work area for the processor 41.

[0021] The device interface 44 is connected to the measurement device 2 (i.e., the actuator 21, the load cell 22, the displacement sensor 23, and the strain gauge 24) and also to the infrared camera 3. The device interface 44 may be configured to operate in accordance with standards such as USB, HDMI (registered trademark), and IEEE1394.

[0022] The input device 45 receives user input that controls the operation of the information processing device 4. The input device 45 includes, for example, a keyboard and a pointing device.

[0023] Display device 46 displays the calculated value of the fatigue limit load of measurement object 1 and related information (such as the setting value of measurement device 2). Display device 46 may be, for example, a liquid crystal display or an organic EL display.

[0024] The communication interface 47 may be communicatively connected to another information processing device via a communication line such as a local area network or the Internet, etc. The communication interface 47 may be configured to operate in compliance with standards such as IEEE802.11, Wi-Fi (registered trademark), and Bluetooth (registered trademark).

[0025] The processor 41 , memory 42 , storage device 43 , device interface 44 , input device 45 , display device 46 , and communication interface 47 are connected to one another via a bus 40 .

[0026] The program stored in the storage device 43 may be provided from another information processing device via a communication line and the communication interface 47, or may be provided via the device interface 44 using a USB memory or the like.

[0027] The information processing device 4 may be a general-purpose computer, or may be a dedicated device for calculating the fatigue limit load of the measurement object 1.

[0028] The information processing device 4 is an example of a fatigue limit load specifying device.

[0029] FIG. 3 is a diagram showing the shape and dimensions of the measurement object 1 of FIG. 1. In the example of the present disclosure, the measurement object 1 is a strip-shaped test piece. In this case, the measurement object 1 is stainless steel having a width B and a thickness t. The measurement object 1 has a notch 1n with a depth d and a curvature radius rh on both sides at the center in the longitudinal direction. The length b from the bottom of the notch 1n to the center in the width direction of the measurement object 1 is equal to the depth d of the notch 1n.

[0030] [Operation of the embodiment] When a periodically fluctuating load is applied to the measurement object 1, the temperature of the measurement object 1 rises due to the thermoelastic effect. Furthermore, when the amplitude of the load applied to the measurement object 1 exceeds the fatigue limit load, the temperature of the measurement object 1 rises further due to the energy dissipation of plastic deformation inside the measurement object 1. Therefore, it is thought that the fatigue limit load of the measurement object 1 can be determined based on the temperature fluctuations of the measurement object 1.

[0031] First, the information processing device 4 performs the measurement process of Fig. 4 to measure the temperature fluctuation of the object 1 while vibrating the object 1 at a predetermined frequency with a gradually increasing load amplitude, and generates a fatigue characteristic graph showing the relationship between the fundamental wave and harmonic components of the temperature fluctuation and the load amplitude. Next, the information processing device 4 performs the calculation process of Fig. 5 to identify the fatigue limit load of the object 1 based on the fatigue characteristic graph.

[0032] FIG. 4 is a flowchart showing the measurement process executed by the information processing device 4 of FIG.

[0033] In step S1, the information processing device 4 sets the frequency at which the measurement object 1 is vibrated, i.e., the frequency at which the load applied to the measurement object 1 is changed, to a predetermined fixed value, for example, 1 Hz, 5 Hz, or 25 Hz. The information processing device 4 also sets the vibration amplitude, i.e., the load amplitude indicating the amplitude of the load applied to the measurement object 1, to an initial value, for example, 0 kN.

[0034] In step S2, the information processing device 4 controls the actuator 21 so as to vibrate the measurement object 1 at the set frequency and load amplitude.

[0035] In step S3, the information processing device 4 acquires the mechanical fluctuation of the measurement object 1 that occurs by vibrating the measurement object 1. The mechanical fluctuation of the measurement object 1 indicates a temporal fluctuation of any one of the load applied to the measurement object 1, the displacement of the measurement object 1, and the strain of the measurement object 1.

[0036] In step S4, the information processing device 4 performs a Fourier transform on the mechanical fluctuation of the measurement object 1 to obtain the amplitude M1 of the fundamental wave component of the mechanical fluctuation and the amplitude M2 of the second harmonic component, and calculates the amplitude ratio M2 / M1. The fundamental wave component of the mechanical fluctuation has a frequency equal to the frequency that vibrates the measurement object 1. The harmonic components of the mechanical fluctuation are caused by distortion of the waveform of the fluctuating load applied to the measurement object 1 (i.e., deviation from a sine wave).

[0037] In step S5, the information processing device 4 acquires the temperature fluctuation of the measurement object 1 caused by vibrating the measurement object 1 based on the temperature image captured by the infrared camera 3. The temperature fluctuation of the measurement object 1 is the temporal fluctuation of the temperature of the target pixel in the temperature image.

[0038] In step S6, the information processing device 4 performs a Fourier transform on the temperature fluctuation of the measurement object 1 to obtain the amplitude T1 of the fundamental wave component of the temperature fluctuation and the amplitude T2 of the second harmonic component, and calculates the amplitude ratio T2 / T1. The fundamental wave component of the temperature fluctuation is caused by the fundamental wave component of the mechanical fluctuation and has a frequency equal to the frequency that vibrates the measurement object 1. Furthermore, the harmonic component of the temperature fluctuation is caused by the harmonic component of the mechanical fluctuation.

[0039] In step S7, the information processing device 4 determines whether the load amplitude has reached the upper limit, and if YES, proceeds to step S9, and if NO, proceeds to step S8. The upper limit of the load amplitude is set to, for example, 4.5 kN.

[0040] In step S8, the information processing device 4 increases the load amplitude by a predetermined step width, for example, 0.05 kN.

[0041] The information processing device 4 repeats steps S1 to S8 to vibrate the measurement object 1 at a predetermined frequency with a gradually increasing load amplitude, while acquiring mechanical fluctuations and temperature fluctuations of the measurement object 1. In this way, the information processing device 4 acquires the characteristics of the ratio M2 / M1 of mechanical fluctuations related to the load fluctuations and the characteristics of the ratio T2 / T1 of temperature fluctuations related to the load fluctuations.

[0042] When acquiring the characteristics of the ratio T2 / T1 of temperature fluctuations related to load fluctuations, the information processing device 4 may identify a target pixel in a temperature image captured by an infrared camera 3 and use the temperature of the target pixel as the temperature of the measurement object 1, as described in Patent Document 1, for example. The target pixel is determined by finding the relationship between the ratio T2 / T1 of temperature fluctuations and the load amplitude, and fitting the line to this relationship to the pixel with the greatest slope. It is believed that the magnitude of the sum of principal stresses is maximized at the target pixel, causing the greatest stress concentration and resulting in fatigue damage.

[0043] Fig. 6 is a simulation result according to the first example of the embodiment, which is a graph showing the amplitude ratio M2 / M1 of the mechanical fluctuation of the object 1 and the amplitude ratio T2 / T1 of the temperature fluctuation of the object 1 when the thermal conduction of the object 1 in Fig. 1 is taken into consideration and the object 1 is vibrated at 1 Hz. Fig. 7 is a simulation result according to the first example of the embodiment, which is a graph showing the amplitude ratio M2 / M1 of the mechanical fluctuation of the object 1 and the amplitude ratio T2 / T1 of the temperature fluctuation of the object 1 when the thermal conduction of the object 1 in Fig. 1 is taken into consideration and the object 1 is vibrated at 5 Hz. Fig. 8 is a simulation result according to the first example of the embodiment, which is a graph showing the amplitude ratio M2 / M1 of the mechanical fluctuation of the object 1 and the amplitude ratio T2 / T1 of the temperature fluctuation of the object 1 when the thermal conduction of the object 1 in Fig. 1 is taken into consideration and the object 1 is vibrated at 25 Hz. Figure 9 is a graph showing the simulation results for the first example of the embodiment, showing the amplitude ratio M2 / M1 of the mechanical fluctuation of the object to be measured 1 and the amplitude ratio T2 / T1 of the temperature fluctuation of the object to be measured 1 when the object to be measured 1 in Figure 1 is vibrated under adiabatic conditions.

[0044] The simulations shown in Figures 6 to 9 used a test object 1 with a fatigue limit load of 3.2 kN. Figures 6 to 9 show that the amplitude ratio M2 / M1 of the mechanical fluctuations has a nearly constant gradient across the load amplitude range of 2.5 to 4.5 kN. Furthermore, the amplitude ratio T2 / T1 of the temperature fluctuations changes with characteristics similar to the amplitude ratio M2 / M1 of the mechanical fluctuations when the load amplitude is equal to or less than the fatigue limit load. However, once the load amplitude exceeds the fatigue limit load, the gradient of the amplitude ratio T2 / T1 of the temperature fluctuations increases at a greater gradient than that of the amplitude ratio M2 / M1 of the mechanical fluctuations. In other words, the gradient of the amplitude ratio T2 / T1 of the temperature fluctuations increases discontinuously near the fatigue limit load of 3.2 kN. This phenomenon is due to the fact that, when the load amplitude increases beyond the fatigue limit load, the test object 1 undergoes plastic deformation, generating dissipated energy, resulting in a sudden increase in temperature, particularly the amplitude T2 of the second harmonic component of the temperature fluctuations. Therefore, it is believed that the fatigue limit load of the test object 1 can be determined based on the amplitude ratio T2 / T1 of the temperature fluctuations.

[0045] 6 to 9, the amplitude ratio M2 / M1 of the mechanical fluctuations is calculated based on the load applied to the measurement object 1. However, the amplitude ratio M2 / M1 of the mechanical fluctuations calculated based on the displacement or strain of the measurement object 1 also has approximately the same characteristics and approximately the same value as when calculated based on the load.

[0046] 4, the information processing device 4 generates a fatigue characteristic graph of the measurement object 1, i.e., a graph of the difference T2 / T1-M2 / M1 in relation to the load amplitude, based on the ratio M2 / M1 of mechanical fluctuations and the ratio T2 / T1 of temperature fluctuations. Hereinafter, the difference T2 / T1-M2 / M1 will also be referred to as the "fatigue characteristic value."

[0047] Fig. 10 is a fatigue characteristic graph calculated based on the simulation results of Fig. 6 to Fig. 9. Fig. 10 shows that when the load amplitude is in the range of not more than the fatigue limit load of 3.2 kN, the fatigue characteristic value T2 / T1-M2 / M1 is in good agreement with the case where the measurement object 1 is vibrated under adiabatic conditions, regardless of whether the measurement object 1 is vibrated at 1 Hz, 5 Hz, or 25 Hz.

[0048] FIG. 5 is a flowchart showing the calculation process executed by the information processing device 4 of FIG.

[0049] 5, the information processing device 4 identifies the load amplitude at which the gradient of the fatigue characteristic graph increases discontinuously, in other words, the load amplitude at which the fatigue characteristic value begins to increase abruptly, as the fatigue limit load of the measurement object 1. To this end, the information processing device 4 fits approximation lines to the fatigue characteristic graph in two ranges of load amplitude, and identifies the load amplitude corresponding to the intersection of the two approximation lines as the fatigue limit load of the measurement object 1. The information processing device 4 determines the boundary point between the two ranges of load amplitude so as to properly fit the approximation line to the fatigue characteristic graph (i.e., so as to reduce the residual sum of squares), and also determines the upper limit of the load amplitude.

[0050] In step S11, the information processing device 4 sets the boundary point between the two ranges of the load amplitude to an initial value. The initial value of the boundary point may be set to, for example, the minimum value of a predetermined search range.

[0051] In step S12, the information processing device 4 fits a first approximation line to a plurality of data points of the fatigue characteristic graph (i.e., a plurality of calculated values respectively indicating the fatigue characteristic value T2 / T1-M2 / M1) in a first range of load amplitude, and fits a second approximation line to a plurality of data points of the fatigue characteristic graph in a second range of load amplitude higher than the first range. The information processing device 4 also calculates the residual sum of squares for the two approximation lines.

[0052] The first and second approximation lines may be either straight lines or curved lines. The first and second approximation lines are expressed by, for example, the following polynomial functions f1 and f2.

[0053] y=f1(x)=a1·x 2 +b2·x+c1 (1) y=f2(x)=a2·x 2 +b2·x+c2 (2)

[0054] Here, x represents the load amplitude, y represents the fatigue characteristic value T2 / T1-M2 / M1, and a1 to c2 are coefficients.

[0055] In step S13, the information processing device 4 determines whether the boundary point has reached the final value of the search range, for example, the maximum value, and if YES, proceeds to step S15, and if NO, proceeds to step S14.

[0056] In step S14, the information processing device 4 shifts the boundary point by a predetermined step size.

[0057] In step S15, the information processing device 4 determines the boundary point corresponding to the minimum residual sum of squares.

[0058] Fig. 11 is a diagram for explaining the boundary points of the range of weight amplitudes determined in steps S11 to S15 of the calculation process in Fig. 5. In the example of Fig. 11, when the boundary point of the range of weight amplitudes is at q3, the residual sum of squares for the first and second approximation lines is smaller than when the boundary point is at q2 or q4. The information processing device 4 determines the weight amplitude q3 corresponding to the smallest residual sum of squares as the boundary point, and sets ranges I1 and I2 for boundary point q3.

[0059] When the load amplitude is large, the fatigue characteristic graph may include data points that are inappropriate for identifying the fatigue limit load. For this reason, the information processing device 4 sets an upper limit for the load amplitude range to remove data points that are inappropriate for identifying the fatigue limit load.

[0060] 5, the information processing device 4 sets the upper limit of the load amplitude to an initial value. The initial value of the upper limit of the load amplitude may be set to, for example, the maximum value in a predetermined search range.

[0061] In step S17, the information processing device 4 fits an approximation line to the fatigue characteristic graph in each of the first and second ranges, and calculates the coefficient of determination adjusted for the degrees of freedom for the approximation line.

[0062] The coefficient of determination in a regression analysis indicates how well the approximation line fits to multiple data points. Generally, the higher the number of variables in the approximation line or the order of the approximation line, the larger the coefficient of determination. Therefore, in this embodiment, to compensate for the increase in the coefficient of determination due to the order of the approximation line, an adjusted coefficient of determination is used, which is defined as follows:

[0063]

number

[0064] where R a 2indicates the coefficient of determination adjusted for the degrees of freedom. N indicates the number of data points included in the first or second range. K indicates the order of the first or second approximation line. y(i) indicates the value of the fatigue characteristic value T2 / T1-M2 / M1 calculated by actually performing the measurement process, where 1≦i≦N. y a (i) is the average value of y(i) in the first or second range. y b (i) is the fatigue characteristic value calculated using the first or second approximation line.

[0065] In step S18, the information processing device 4 determines whether the upper limit of the load amplitude has reached the final value of the search range, for example, the minimum value, and if YES, proceeds to step S20, and if NO, proceeds to step S19.

[0066] In step S19, the information processing device 4 reduces the upper limit of the load amplitude by a predetermined step size.

[0067] In step S20, the information processing device 4 determines the upper limit of the load amplitude corresponding to the maximum degree-of-freedom adjusted coefficient of determination, and sets a new second range for this upper limit.

[0068] FIG. 12 is a diagram illustrating the upper limit of the load amplitude determined in steps S16 to S20 of the calculation process in FIG. 5. According to the example in FIG. 11, in range I2, the behavior of the fatigue characteristic value at large load amplitudes differs significantly from the behavior of the fatigue characteristic value at small load amplitudes. This is thought to be due to the initiation and propagation of microcracks, the occurrence of strain-induced martensitic transformation, and other factors. To accurately determine the fatigue limit load, it is desirable to fit an approximation line to the data points at small load amplitudes among the data points included in range I2. However, according to the example in FIG. 11, if the approximation line f2 is fitted to all data points included in range I2, the residual sum of squares for the approximation line f2 will be large due to the data points at large load amplitudes. Therefore, in the example in FIG. 12, the information processing device 4 reduces the upper limit of range I2 from load amplitude q5 to load amplitude q6 and removes data points that are inappropriate for determining the fatigue limit load. The information processing device 4 fits an approximation line f2a to data points included in the range I2a of the load amplitudes q3 to q6, instead of the range I2.

[0069] The information processing device 4 reduces at least one of the first and second ranges so that the coefficients of determination after adjustment for the degrees of freedom for each of the first and second approximation lines approach 1. The information processing device 4 may also reduce at least one of the first and second ranges so as to maximize the coefficients of determination after adjustment for the degrees of freedom for each of the first and second approximation lines.

[0070] In step S21 of FIG. 5, the information processing device 4 determines approximation lines in each of the first and second ranges.

[0071] In step S22, the information processing device 4 identifies the load amplitude corresponding to the intersection of the two approximation lines as the fatigue limit load of the measurement object 1. Referring to FIG. 12, the load amplitude q7 corresponding to the intersection P0 of the approximation lines f1 and f2a is identified as the fatigue limit load of the measurement object 1. The gradient of the fatigue characteristic value T2 / T1-M2 / M1 related to the load amplitude increases discontinuously at the intersection P0 of the approximation lines f1 and f2a. Therefore, at the load amplitude q7 corresponding to the intersection P0, the measurement object 1 is considered to be at its fatigue limit.

[0072] FIG. 13 is a graph showing the temperature fluctuation characteristics of the object to be measured versus load amplitude, illustrating the results of a simulation performed in the first comparative example. The vertical axis of the graph represents the amplitude T2 of the second harmonic component of the temperature fluctuation. The graph in FIG. 13 shows simulation results for a case where the thermal conduction of the object to be measured is taken into account and the object to be measured is vibrated at 1 Hz, 5 Hz, or 25 Hz, and a case where the object to be measured is vibrated under adiabatic conditions. The simulation in FIG. 13 was performed substantially according to the method described in Patent Document 1. Patent Document 1 discloses generating a graph showing the amplitude of the second harmonic component of the temperature fluctuation versus the amplitude of the fundamental component of the temperature fluctuation, and then fitting two approximation lines to this graph to determine the fatigue limit stress. However, for ease of explanation, the graph in FIG. 13 shows the amplitude T2 of the second harmonic component of the temperature fluctuation versus the load amplitude.

[0073] 10 and 13, although the units of the vertical axis are different, the graphs change with similar characteristics. However, in the case of the first example, it can be seen that the variation for each frequency is smaller than in the case of the first comparative example at a load amplitude equal to or less than the fatigue limit load of 3.2 kN. Furthermore, in the case of the first example, it can be seen that at a load amplitude exceeding the fatigue limit load of 3.2 kN, the characteristics when the test object 1 is vibrated at 25 Hz are closer to the characteristics when the test object 1 is vibrated under adiabatic conditions than in the case of the first comparative example.

[0074] FIG. 14 is a table showing the error of the fatigue limit load calculated based on the simulation results of FIGS. 10 and 13. The table in FIG. 14 shows the error relative to the true value of the fatigue limit load of the measurement object 1, i.e., 3.2 kN. The table in FIG. 14 indicates that the error of the simulation results for the first example is smaller than the error of the simulation results for the first comparative example, regardless of whether the thermal conduction of the measurement object 1 is taken into consideration and the measurement object 1 is vibrated at 1 Hz, 5 Hz, or 25 Hz. This indicates that the influence of thermal conduction within the measurement object 1 on the determination of the fatigue limit load is reduced in the first example compared to the first comparative example. Furthermore, even when the measurement object 1 is vibrated under adiabatic conditions, the error of the simulation results for the first example is smaller than the error of the simulation results for the first comparative example. As the frequency at which the measurement object 1 is vibrated increases, thermal conduction becomes less likely to occur, approaching adiabatic conditions. Therefore, the fatigue limit load can be determined more accurately as the frequency at which the measurement object 1 is vibrated increases.

[0075] In the measurement object 1, not only mechanical fluctuations occur when the actuator 21 vibrates the measurement object 1, but also extraneous mechanical fluctuations may occur due to some other cause within the measurement device 2. These extraneous mechanical fluctuations cause extraneous temperature fluctuations in the measurement object 1, which may introduce errors into the fatigue limit load that is determined. According to this embodiment, by calculating the difference between the mechanical fluctuation ratio M2 / M1 and the temperature fluctuation ratio T2 / T1, the influence of the measurement device 2 itself, which is included in the temperature fluctuation ratio T2 / T1, can be reduced, and the fatigue limit load of the measurement object 1 can be determined with high accuracy.

[0076] Furthermore, according to this embodiment, the influence of heat conduction within the measurement object 1 on the determination of the fatigue limit load can be reduced more than in the first comparative example, thereby making it possible to determine the fatigue limit load of the measurement object 1 with higher accuracy than in the first comparative example.

[0077] As described above, the fatigue limit load specifying system 10 according to this embodiment can specify the fatigue limit load of the measurement object 1 with higher accuracy than conventional systems.

[0078] [Variations] In the examples of equations (1) and (2) above, the approximation lines are expressed by second-order polynomial functions f1 and f2. Because the energy dissipation of plastic deformation increases nonlinearly with increasing load amplitude, the approximation lines may be expressed by higher-order polynomial functions. Generally, the higher the order of the polynomial function used as the approximation line, the smaller the error. However, determining the order of the approximation line is a difficult problem, as it requires consideration of the fracture mechanism of the object 1 to be measured. Furthermore, the higher the order of the polynomial function used as the approximation line, the more complex the calculations for fitting the approximation line to the fatigue characteristic graph become. Therefore, it is desirable to simplify the fitting calculations.

[0079] For this reason, the information processing device 4 may generate a fatigue characteristic graph expressed in double logarithms in step S9 of Fig. 4. In this case, in step S12 of Fig. 5, the information processing device 4 fits a first approximation line to a plurality of calculated values each indicating the logarithm of the fatigue characteristic value T2 / T1-M2 / M1 in a first range of the logarithm of the load amplitude, and fits a second approximation line to a plurality of calculated values each indicating the logarithm of the fatigue characteristic value T2 / T1-M2 / M1 in a second range higher than the first range of the logarithm of the load amplitude.

[0080] The first and second approximation lines are expressed by, for example, the following linear functions f11 and f12.

[0081] Y=f11(X)=a11·X+b11 (4) Y=f12(X)=a12·X+b12 (5)

[0082] where X is the logarithm of the load amplitude x, Y is the logarithm of the fatigue characteristic value y = T2 / T1-M2 / M1, and a11 to b12 are coefficients. When the logarithm is base 10, the following equations are obtained by expressing Equations (4) and (5) as exponential functions.

[0083] y=10 b11 x a11 (6) y=10 b12 x a12 (7)

[0084] The information processing device 4 executes the other steps of FIGS. 4 and 5 in the same manner as described above.

[0085] FIG. 15 is a fatigue characteristic graph showing the results of a simulation according to a second example of the embodiment, where the thermal conduction of the object 1 shown in FIG. 1 is taken into consideration and the object 1 is vibrated at 1 Hz. FIG. 16 is a fatigue characteristic graph showing the results of a simulation according to a second example of the embodiment, where the thermal conduction of the object 1 shown in FIG. 1 is taken into consideration and the object 1 is vibrated at 5 Hz. FIG. 17 is a fatigue characteristic graph showing the results of a simulation according to a second example of the embodiment, where the thermal conduction of the object 1 shown in FIG. 1 is taken into consideration and the object 1 is vibrated at 25 Hz. FIG. 18 is a fatigue characteristic graph showing the results of a simulation according to a second example of the embodiment, where the object 1 shown in FIG. 1 is vibrated under adiabatic conditions. As described above, by reducing the upper limit of the load amplitude, inappropriate data points for determining the fatigue limit load are eliminated.

[0086] FIG. 19 is a graph showing the temperature fluctuation characteristics of the object to be measured versus load amplitude when the thermal conduction of the object to be measured is taken into account and the object to be measured is vibrated at 1 Hz, which is a simulation result of the second comparative example. FIG. 20 is a graph showing the temperature fluctuation characteristics of the object to be measured versus load amplitude when the thermal conduction of the object to be measured is taken into account and the object to be measured is vibrated at 5 Hz, which is a simulation result of the second comparative example. FIG. 21 is a graph showing the temperature fluctuation characteristics of the object to be measured versus load amplitude when the thermal conduction of the object to be measured is taken into account and the object to be measured is vibrated at 25 Hz, which is a simulation result of the second comparative example. FIG. 22 is a graph showing the temperature fluctuation characteristics of the object to be measured versus load amplitude when the object to be measured is vibrated under adiabatic conditions, which is a simulation result of the second comparative example. The simulations of FIGS. 19 to 22 were performed substantially according to the method described in Patent Document 1.

[0087] FIG. 23 is a table showing the error of the fatigue limit load calculated based on the simulation results of FIGS. 15 to 22. The table in FIG. 23 shows the error relative to the true value of the fatigue limit load of the measurement object 1, i.e., 3.2 kN. The table in FIG. 23 shows that the error of the simulation result of the second example is smaller than the error of the simulation result of the second comparative example, regardless of whether the thermal conduction of the measurement object 1 is taken into consideration and the measurement object 1 is vibrated at 1 Hz, 5 Hz, or 25 Hz. It can also be seen that the error of the simulation result of the second example is smaller than the error of the simulation result of the second comparative example, even when the measurement object 1 is vibrated under adiabatic conditions. Furthermore, the fatigue limit load can be determined more accurately as the frequency at which the measurement object 1 is vibrated increases.

[0088] Comparing FIG. 14 and FIG. 23, it is clear that in the second embodiment, the fatigue limit load of the measurement object 1 can be determined with higher accuracy than in the first embodiment.

[0089] According to this modification, similarly to the first embodiment described with reference to FIG. 14 etc., the fatigue limit load of the measurement object 1 can be determined with higher accuracy than conventionally.

[0090] Furthermore, according to this modified example, by using an approximation line that is a linear function, the calculation for fitting the approximation line to the fatigue characteristic graph can be simplified compared to when using an approximation line that is a polynomial function of second degree or higher.

[0091] [Effects of the embodiment] A fatigue limit load specifying system 10 according to the embodiment includes an actuator 21 that vibrates a measurement object 1, an infrared camera 3 that measures the temperature of the measurement object 1, and an information processing device 4 that specifies the fatigue limit load of the measurement object 1 based on the temperature of the measurement object 1. The information processing device 4 controls the actuator 21 to vibrate the measurement object 1 at a predetermined frequency with a gradually increasing load amplitude. The information processing device 4 acquires a fundamental wave component and a second harmonic component of a mechanical fluctuation of the measurement object 1 that is generated by vibrating the measurement object 1. The information processing device 4 calculates a first ratio M2 / M1 that indicates the ratio of an amplitude M2 of the second harmonic component of the mechanical fluctuation to an amplitude M1 of the fundamental wave component of the mechanical fluctuation. The information processing device 4 acquires a fundamental wave component and a second harmonic component of a temperature fluctuation of the measurement object 1 that is generated by vibrating the measurement object 1. The information processing device 4 calculates a second ratio T2 / T1 that indicates the ratio of an amplitude T2 of the second harmonic component of the temperature fluctuation to an amplitude T1 of the fundamental wave component of the temperature fluctuation. The information processing device 4 identifies the load amplitude at which the gradient of the difference T2 / T1-M2 / M1 between the first and second ratios relating to the load amplitude increases discontinuously as the fatigue limit load of the measurement object 1.

[0092] This configuration makes it possible to determine the fatigue limit load of the measurement object 1 with higher accuracy than conventionally possible.

[0093] According to the fatigue limit load identification system 10 according to the embodiment, the information processing device 4 may fit a first approximation line f1 to a plurality of calculated values each representing the difference between the first and second ratios T2 / T1-M2 / M1 within a first range of load amplitude. The information processing device 4 may fit a second approximation line f2 to a plurality of calculated values each representing the difference between the first and second ratios T2 / T1-M2 / M1 within a second range of load amplitude that is higher than the first range. In this case, the information processing device 4 identifies the load amplitude corresponding to the intersection of the first approximation line f1 and the second approximation line f2 as the fatigue limit load of the measurement object 1. The first approximation line f1 and the second approximation line f2 are expressed by polynomial functions.

[0094] With this configuration, the load amplitude corresponding to the intersection of the two approximation lines can be identified as the load amplitude at which the gradient of the difference between the first and second ratios T2 / T1-M2 / M1 with respect to the load amplitude increases discontinuously.

[0095] According to the fatigue limit load identification system 10 according to the embodiment, the information processing device 4 may fit a first approximation line f1 to a plurality of calculated values each representing the logarithm of the difference between the first and second ratios T2 / T1-M2 / M1 within a first range of the logarithm of the load amplitude. The information processing device 4 may fit a second approximation line f2 to a plurality of calculated values each representing the logarithm of the difference between the first and second ratios T2 / T1-M2 / M1 within a second range higher than the first range of the logarithm of the load amplitude. In this case, the information processing device 4 identifies the load amplitude corresponding to the intersection of the first approximation line f1 and the second approximation line f2 as the fatigue limit load of the measurement object 1. The first approximation line f1 and the second approximation line f2 are expressed as linear functions.

[0096] With this configuration, the load amplitude corresponding to the intersection of the two approximation lines can be identified as the load amplitude at which the gradient of the difference between the first and second ratios T2 / T1-M2 / M1 with respect to the load amplitude increases discontinuously.

[0097] According to the fatigue limit load identification system 10 of the embodiment, the information processing device 4 may narrow at least one of the first and second ranges so as to bring the degree of freedom-adjusted coefficient of determination for each of the first approximation line f1 and the second approximation line f2 closer to 1.

[0098] This configuration allows for the elimination of data points that are inappropriate for determining the fatigue limit load.

[0099] According to the fatigue limit load specifying system 10 according to the embodiment, the fatigue limit load specifying system 10 may further include a load cell 22 that detects the load applied to the measurement object 1 by the actuator 21. In this case, the mechanical fluctuation of the measurement object 1 indicates the fluctuation of the load applied to the measurement object 1.

[0100] With this configuration, the mechanical fluctuation of the measurement object 1 can be acquired based on the load applied to the measurement object 1.

[0101] According to the fatigue limit load specifying system 10 according to the embodiment, the fatigue limit load specifying system 10 may further include a displacement sensor 23 that detects the displacement of the measurement object 1 generated by the actuator 21. In this case, the mechanical fluctuation of the measurement object 1 indicates a fluctuation in the displacement of the measurement object 1.

[0102] With this configuration, the mechanical fluctuation of the measurement object 1 can be acquired based on the displacement of the measurement object 1.

[0103] According to the fatigue limit load specifying system 10 according to the embodiment, the fatigue limit load specifying system 10 may further include a strain gauge 24 that detects strain in the measurement object 1 generated by the actuator 21. In this case, the mechanical fluctuation of the measurement object 1 indicates a fluctuation in strain in the measurement object 1.

[0104] With this configuration, the mechanical fluctuation of the measurement object 1 can be acquired based on the strain of the measurement object 1.

[0105] The fatigue limit load identifying device according to the embodiment includes a first interface 44 connected to an actuator 21 that vibrates a measurement object 1, a second interface 44 connected to an infrared camera 3 that measures the temperature of the measurement object 1, and a processor 41 that identifies the fatigue limit load of the measurement object 1 based on the temperature of the measurement object 1. The processor 41 controls the actuator 21 to vibrate the measurement object 1 at a predetermined frequency with a gradually increasing load amplitude. The processor 41 acquires a fundamental component and a second harmonic component of a mechanical fluctuation of the measurement object 1 that occurs when the measurement object 1 is vibrated. The processor 41 calculates a first ratio M2 / M1 that indicates the ratio of an amplitude M2 of the second harmonic component of the mechanical fluctuation to an amplitude M1 of the fundamental component of the mechanical fluctuation. The processor 41 acquires a fundamental component and a second harmonic component of a temperature fluctuation of the measurement object 1 that occurs when the measurement object 1 is vibrated. The processor 41 calculates a second ratio T2 / T1 that indicates the ratio of an amplitude T2 of the second harmonic component of the temperature fluctuation to an amplitude T1 of the fundamental component of the temperature fluctuation. The processor 41 identifies the load amplitude at which the gradient of the difference T2 / T1-M2 / M1 between the first and second ratios with respect to the load amplitude increases discontinuously as the fatigue limit load of the measurement object 1.

[0106] This configuration makes it possible to determine the fatigue limit load of the measurement object 1 with higher accuracy than conventionally possible.

[0107] A method for determining a fatigue limit load according to an embodiment includes vibrating a measurement object (1) at a predetermined frequency and with a gradually increasing load amplitude using an actuator (21). The method includes acquiring a fundamental component and a second harmonic component of a mechanical fluctuation of the measurement object (1) generated by vibrating the measurement object (1). The method includes calculating a first ratio (M2 / M1) indicating a ratio of an amplitude (M2) of a second harmonic component of the mechanical fluctuation to an amplitude (M1) of the fundamental component of the mechanical fluctuation. The method includes measuring the temperature of the measurement object (1) using an infrared camera (3). The method includes acquiring a fundamental component and a second harmonic component of a temperature fluctuation of the measurement object (1) generated by vibrating the measurement object (1). The method includes calculating a second ratio (T2 / T1) indicating a ratio of an amplitude (T2) of a second harmonic component of the temperature fluctuation to an amplitude (T1) of the fundamental component of the temperature fluctuation. The method includes identifying a load amplitude at which a gradient of a difference (T2 / T1-M2 / M1) between the first and second ratios with respect to the load amplitude increases discontinuously as the fatigue limit load of the measurement object (1).

[0108] This configuration makes it possible to determine the fatigue limit load of the measurement object 1 with higher accuracy than conventionally possible.

[0109] (Other embodiments) As described above, the embodiments have been described as examples of the technology disclosed in this application. For this purpose, the accompanying drawings and detailed description have been provided. However, the technology in this disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. Furthermore, the components described in the above embodiments can be combined to create new embodiments.

[0110] Therefore, the components shown in the accompanying drawings and detailed description may include not only components essential for solving the problem, but also components that are not essential for solving the problem in order to illustrate the above technology. Therefore, the fact that these non-essential components are shown in the accompanying drawings and / or detailed description should not be interpreted as immediately being essential.

[0111] Furthermore, since the above-described embodiments are intended to illustrate the technology of the present disclosure, various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0112] In the example of FIG. 3, the case where the measurement object 1 is a strip-shaped test piece has been described, but the measurement object 1 may be a part of any shape.

[0113] If the displacement and / or strain of the measurement object 1 is not used, the displacement sensor 23 and / or the strain gauge 24 may be omitted.

[0114] In step S20 of Fig. 5, the information processing device 4 may determine an upper limit of a weight amplitude that exceeds a predetermined threshold value, instead of determining an upper limit of a weight amplitude that corresponds to the maximum degree-of-freedom-adjusted coefficient of determination. In this case, the information processing device 4 may determine an upper limit of a weight amplitude that first exceeds the threshold value while repeating steps S16 to S19. Alternatively, the information processing device 4 may determine an upper limit of a weight amplitude when an increase amount or an increase rate of the degree-of-freedom-adjusted coefficient of determination exceeds a threshold value while repeating steps S16 to S19. In either case, the information processing device 4 narrows at least one of the first and second ranges so that the degree-of-freedom-adjusted coefficients of determination for the first and second approximation lines approach 1, respectively.

[0115] [Summary of the embodiment] A fatigue limit load specifying system according to a first aspect of the present disclosure includes: an actuator that vibrates the measurement object; an infrared camera for measuring the temperature of the measurement object; an information processing device that identifies a fatigue limit load of the measurement object based on a temperature of the measurement object, The information processing device includes: controlling the actuator to vibrate the measurement object at a predetermined frequency and with a gradually increasing load amplitude; Acquire a fundamental wave component and a second harmonic component of a mechanical fluctuation of the object to be measured that is generated by vibrating the object to be measured, calculating a first ratio indicating a ratio of an amplitude of a second harmonic component of the mechanical variation to an amplitude of a fundamental component of the mechanical variation; acquiring a fundamental wave component and a second harmonic component of a temperature fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a second ratio indicating a ratio of an amplitude of a second harmonic component of the temperature fluctuation to an amplitude of a fundamental component of the temperature fluctuation; a load amplitude at which a gradient of the difference between the first and second ratios with respect to the load amplitude increases discontinuously is identified as a fatigue limit load of the object to be measured; Fatigue limit load determination system.

[0116] According to the fatigue limit load specifying system according to the second aspect of the present disclosure, in the fatigue limit load specifying system according to the first aspect, The information processing device includes: fitting a first approximation line to a plurality of calculated values each representing a difference between the first and second ratios within a first range of the load amplitude; fitting a second approximation line to a plurality of calculated values each representing a difference between the first and second ratios in a second range of the load amplitude that is higher than the first range; Identifying the load amplitude corresponding to the intersection of the first and second approximation lines as a fatigue limit load of the measurement object; The first and second approximation lines are expressed by polynomial functions.

[0117] According to the fatigue limit load specifying system according to the third aspect of the present disclosure, in the fatigue limit load specifying system according to the first aspect, The information processing device includes: fitting a first approximation line to a plurality of calculated values each representing a logarithm of a difference between the first and second ratios within a first range of the logarithm of the load amplitude; fitting a second approximation line to a plurality of calculated values each representing a logarithm of a difference between the first and second ratios in a second range higher than the first range of the logarithm of the load amplitude; Identifying the load amplitude corresponding to the intersection of the first and second approximation lines as a fatigue limit load of the measurement object; The first and second approximation lines are expressed by linear functions.

[0118] According to the fatigue limit load specifying system according to the fourth aspect of the present disclosure, in the fatigue limit load specifying system according to the second or third aspect, The information processing device reduces at least one of the first and second ranges so that a coefficient of determination adjusted for the degrees of freedom for each of the first and second approximation lines approaches one.

[0119] According to the fatigue limit load specifying system according to the fifth aspect of the present disclosure, in the fatigue limit load specifying system according to one of the first to fourth aspects, the fatigue limit load specifying system further includes a load cell that detects a load applied to the measurement object by the actuator, The mechanical fluctuation of the measurement object indicates a fluctuation of the load applied to the measurement object.

[0120] According to the fatigue limit load specifying system according to the sixth aspect of the present disclosure, in the fatigue limit load specifying system according to one of the first to fourth aspects, the fatigue limit load specifying system further includes a displacement sensor that detects a displacement of the measurement object generated by the actuator, The mechanical fluctuation of the measurement object indicates a fluctuation in the displacement of the measurement object.

[0121] According to the fatigue limit load specifying system according to the seventh aspect of the present disclosure, in the fatigue limit load specifying system according to one of the first to fourth aspects, the fatigue limit load specifying system further includes a strain gauge that detects strain of the measurement object generated by the actuator, The mechanical fluctuation of the measurement object indicates a fluctuation in strain of the measurement object.

[0122] A fatigue limit load specifying device according to an eighth aspect of the present disclosure includes: a first interface connected to an actuator that vibrates the measurement object; a second interface connected to an infrared camera that measures the temperature of the measurement object; a processor for determining a fatigue limit load of the measurement object based on a temperature of the measurement object; The processor: controlling the actuator to vibrate the measurement object at a predetermined frequency and with a gradually increasing load amplitude; Acquire a fundamental wave component and a second harmonic component of a mechanical fluctuation of the object to be measured that is generated by vibrating the object to be measured, calculating a first ratio indicating a ratio of an amplitude of a second harmonic component of the mechanical variation to an amplitude of a fundamental component of the mechanical variation; acquiring a fundamental wave component and a second harmonic component of a temperature fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a second ratio indicating a ratio of an amplitude of a second harmonic component of the temperature fluctuation to an amplitude of a fundamental component of the temperature fluctuation; The load amplitude at which the gradient of the difference between the first and second ratios with respect to the load amplitude increases discontinuously is identified as the fatigue limit load of the object to be measured.

[0123] A fatigue limit load specifying method according to a ninth aspect of the present disclosure includes: vibrating the measurement object at a predetermined frequency and with a gradually increasing load amplitude using an actuator; acquiring a fundamental wave component and a second harmonic component of a mechanical fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a first ratio indicative of a ratio of an amplitude of a second harmonic component of the mechanical variation to an amplitude of a fundamental component of the mechanical variation; Measuring the temperature of the measurement object using an infrared camera; acquiring a fundamental wave component and a second harmonic component of a temperature fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a second ratio indicative of the ratio of the amplitude of the second harmonic component of the temperature fluctuation to the amplitude of the fundamental component of the temperature fluctuation; and identifying the load amplitude at which the gradient of the difference between the first and second ratios with respect to the load amplitude increases discontinuously as the fatigue limit load of the object to be measured. [Industrial Applicability]

[0124] The present disclosure is useful for an apparatus for measuring a fatigue limit load of an object to be measured. [Explanation of symbols]

[0125] 1. Measurement object 2. Measuring equipment 3. Infrared camera 4. Information processing equipment 10. Fatigue limit load identification system 21 Actuator 22 load cells 23 Displacement Sensor 24 Strain gauge 40 Bus 41 processors 42 memory 43 Storage device 44 Device Interface (I / F) 45 Input Devices 46 Display device 47 Communication Interface (I / F)

Claims

1. an actuator that vibrates the measurement object; an infrared camera for measuring the temperature of the measurement object; an information processing device that identifies a fatigue limit load of the measurement object based on a temperature of the measurement object, The information processing device includes: controlling the actuator to vibrate the measurement object at a predetermined frequency and with a gradually increasing load amplitude; acquiring a fundamental wave component and a second harmonic component of a mechanical fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a first ratio indicating a ratio of an amplitude of a second harmonic component of the mechanical variation to an amplitude of a fundamental component of the mechanical variation; acquiring a fundamental wave component and a second harmonic component of a temperature fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a second ratio indicating a ratio of an amplitude of a second harmonic component of the temperature fluctuation to an amplitude of a fundamental component of the temperature fluctuation; a load amplitude at which a gradient of the difference between the first and second ratios with respect to the load amplitude increases discontinuously is identified as a fatigue limit load of the measurement object; Fatigue limit load determination system.

2. The information processing device includes: fitting a first approximation line to a plurality of calculated values each representing a difference between the first and second ratios within a first range of the load amplitude; fitting a second approximation line to a plurality of calculated values each representing a difference between the first and second ratios in a second range of the load amplitude that is higher than the first range; Identifying the load amplitude corresponding to the intersection of the first and second approximation lines as a fatigue limit load of the measurement object; the first and second approximation lines are expressed by polynomial functions; The fatigue limit load specifying system according to claim 1.

3. The information processing device includes: fitting a first approximation line to a plurality of calculated values each representing a logarithm of a difference between the first and second ratios within a first range of the logarithm of the load amplitude; fitting a second approximation line to a plurality of calculated values each representing a logarithm of a difference between the first and second ratios in a second range higher than the first range of the logarithm of the load amplitude; Identifying the load amplitude corresponding to the intersection of the first and second approximation lines as a fatigue limit load of the measurement object; the first and second approximation lines are expressed by linear functions, The fatigue limit load specifying system according to claim 1.

4. the information processing device reduces at least one of the first and second ranges so that a coefficient of determination after adjusting the degrees of freedom for each of the first and second approximation lines approaches 1; The fatigue limit load specifying system according to claim 2 or 3.

5. the fatigue limit load specifying system further includes a load cell that detects a load applied to the measurement object by the actuator, The mechanical fluctuation of the measurement object indicates a fluctuation of a load applied to the measurement object. The fatigue limit load specifying system according to claim 1.

6. the fatigue limit load specifying system further includes a displacement sensor that detects a displacement of the measurement object generated by the actuator, The mechanical fluctuation of the measurement object indicates a fluctuation in the displacement of the measurement object. The fatigue limit load specifying system according to claim 1.

7. the fatigue limit load specifying system further includes a strain gauge that detects strain of the measurement object generated by the actuator, The mechanical fluctuation of the measurement object indicates a fluctuation of strain of the measurement object. The fatigue limit load specifying system according to claim 1.

8. a first interface connected to an actuator that vibrates the measurement object; a second interface connected to an infrared camera for measuring the temperature of the measurement object; a processor for determining a fatigue limit load of the measurement object based on a temperature of the measurement object; The processor: controlling the actuator to vibrate the measurement object at a predetermined frequency and with a gradually increasing load amplitude; acquiring a fundamental wave component and a second harmonic component of a mechanical fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a first ratio indicating a ratio of an amplitude of a second harmonic component of the mechanical variation to an amplitude of a fundamental component of the mechanical variation; acquiring a fundamental wave component and a second harmonic component of a temperature fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a second ratio indicating a ratio of an amplitude of a second harmonic component of the temperature fluctuation to an amplitude of a fundamental component of the temperature fluctuation; a load amplitude at which a gradient of the difference between the first and second ratios with respect to the load amplitude increases discontinuously is identified as a fatigue limit load of the measurement object; Fatigue limit load determination device.

9. vibrating the measurement object at a predetermined frequency and with a gradually increasing load amplitude using an actuator; acquiring a fundamental wave component and a second harmonic component of a mechanical fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a first ratio indicative of a ratio of an amplitude of a second harmonic component of the mechanical variation to an amplitude of a fundamental component of the mechanical variation; Measuring the temperature of the measurement object using an infrared camera; acquiring a fundamental wave component and a second harmonic component of a temperature fluctuation of the object to be measured that is generated by vibrating the object to be measured; calculating a second ratio indicative of the ratio of the amplitude of the second harmonic component of the temperature fluctuation to the amplitude of the fundamental component of the temperature fluctuation; and identifying a load amplitude at which a gradient of a difference between the first and second ratios with respect to the load amplitude increases discontinuously as a fatigue limit load of the measurement object. Method for determining fatigue limit load.

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