Torsional fatigue evaluation method

Abstract

To provide a torsional fatigue evaluation method that can evaluate the torsional fatigue of a metal using an electromagnetic acoustic wave.SOLUTION: A torsional fatigue evaluation method according to the present invention is a method for evaluating the torsional fatigue of a metal to be evaluated, and comprises: measurement steps S1 and S3 for measuring a sound velocity (or a resonance frequency) of an ultrasonic wave of an axisymmetric SH wave propagating in the evaluation target; and evaluation steps S4, S5 for evaluating the torsional fatigue of the evaluation target based on the sound velocity (or the resonance frequency) measured in the measurement steps S1 and S3.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] This invention relates to a method for evaluating torsional fatigue in metals. [Background technology]

[0002] Metal fatigue involves changes in dislocation structure, as well as the initiation and propagation of cracks. Ultrasound is sensitive to these changes in material structure, and in the MHz frequency range, the attenuation coefficient α, sound velocity v, and dislocation structure can be described by the model equation: α∝ΛL, where Λ is the dislocation density, L is the length of the dislocation loop, and v0 is the sound velocity when there are no dislocations. 4 、(v0-v) / v0∝ΛL 2 It is known that these are related by [the following factors]. For this reason, measuring the damping coefficient α and the speed of sound v is considered effective for evaluating metal fatigue. Various methods for evaluating metal fatigue using ultrasound are known, one of which is the electromagnetic ultrasonic resonance method (for example, Patent Documents 1 and 2).

[0003] This method for evaluating metal fatigue using electromagnetic ultrasonic resonance involves generating burst wave ultrasound on the object to be evaluated using an electromagnetic ultrasonic transducer with a burst wave current, receiving the ultrasound propagating through the object, and setting the frequency of the burst wave so that the phases of each ultrasound wave, which travel back and forth through the object and interfere with each other, are aligned, thereby generating ultrasonic resonance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 3397574 [Patent Document 2] International Publication No. 2014 / 155612 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, Patent Document 1 and Patent Document 2 do not disclose or suggest torsional fatigue. Therefore, this proposal newly presents a method for evaluating the torsional fatigue of metals.

[0006] The present invention was made in view of the above circumstances, and an object thereof is to provide a torsional fatigue evaluation method capable of evaluating the torsional fatigue of a metal by electromagnetic ultrasonic waves.

Means for Solving the Problems

[0007] As a result of various studies, the present inventor has found that the above object can be achieved by the following present invention. That is, a torsional fatigue evaluation method according to one aspect of the present invention is a method for evaluating the torsional fatigue of a metal as an evaluation object, and includes a measurement step of measuring the sound velocity or resonance frequency in ultrasonic waves of an axisymmetric SH wave propagating through the evaluation object, and an evaluation step of evaluating the torsional fatigue of the evaluation object based on the sound velocity or resonance frequency measured in the measurement step.

[0008] Such a torsional fatigue evaluation method can evaluate the torsional fatigue of the evaluation object by measuring the sound velocity or resonance frequency (resonance frequency) in ultrasonic waves of an axisymmetric SH wave propagating through the evaluation object.

[0009] andIn the torsional fatigue evaluation method described above, the measurement step measures the change over time in the sound velocity or resonant frequency, and the evaluation step evaluates the torsional fatigue of the object to be evaluated based on the presence or absence of a peak in the change over time. Preferably, in the torsional fatigue evaluation method described above, the measurement step measures the change over time by measuring the sound velocity or resonant frequency multiple times, either periodically or irregularly. Preferably, in the torsional fatigue evaluation method described above, the evaluation step rephrases the determination of the presence of a peak in relation to the fatigue index representing the degree of torsional fatigue in the object to be evaluated, and expresses the evaluation using the rephrased fatigue index. Preferably, the fatigue index is a damage rate (degree of damage) representing the degree of damage in the object to be evaluated. Preferably, in the torsional fatigue evaluation method described above, the object to be evaluated is cylindrical (round bar) carbon steel, and the determination of the presence of a peak is rephrased as a damage rate of 40% or more.

[0010] This method of evaluating torsional fatigue monitors changes over time and determines the fatigue index based on the presence or absence of peaks, thus allowing for a more accurate determination of the fatigue index.

[0013] In another embodiment, in the torsional fatigue evaluation method described above, the axially symmetric SH wave ultrasound is an ultrasound of the first-order resonance mode by electromagnetic ultrasonic resonance.

[0014] Since this torsional fatigue evaluation method uses electromagnetic ultrasonic resonance, the signal-to-noise ratio can be improved and the conversion efficiency of the electromagnetic ultrasonic transducer can be enhanced, so that the ultrasonic waves propagating through the object to be evaluated can be received more reliably by the electromagnetic ultrasonic transducer.

[0015] In another embodiment, the torsional fatigue evaluation method described above further includes a remaining life prediction step that predicts the remaining life of the object to be evaluated when the evaluation step determines that the peak is present. Preferably, in the torsional fatigue evaluation method described above, the object to be evaluated is a cylindrical (round bar) carbon steel, and the remaining life processing step replaces the determination that the peak is present with the remaining life of the object to be evaluated based on the correspondence between the determination that the peak is present and the remaining life of the object to be evaluated.

[0016] This type of torsional fatigue evaluation method predicts the remaining lifespan, allowing for the identification of maintenance or replacement timings for the equipment being evaluated. [Effects of the Invention]

[0019] The torsional fatigue evaluation method according to the present invention can evaluate the torsional fatigue of metals using electromagnetic ultrasound. [Brief explanation of the drawing]

[0020] [Figure 1] This is a block diagram showing the configuration of a torsional fatigue evaluation device in an embodiment. [Figure 2] This is a diagram illustrating the electromagnetic ultrasonic transducer in the torsional fatigue evaluation device. [Figure 3] This is a schematic diagram illustrating how to determine the resonant frequency. [Figure 4] This is a schematic diagram illustrating how to determine the damping coefficient in the first embodiment. [Figure 5] This is a schematic diagram illustrating how to determine the damping coefficient in the second embodiment. [Figure 6] As an example, this is a diagram illustrating a test specimen for torsional fatigue. [Figure 7] As an example, this is a diagram illustrating the relationship between fatigue damage rate and rate of change in sound velocity. [Figure 8] This is a flowchart showing the operation of the torsional fatigue evaluation device. [Figure 9] This is a flowchart showing the operation of the torsional fatigue evaluation device in the first modified form. [Figure 10] As an example, this diagram illustrates the relationship between fatigue damage rate and resonant frequency change rate. [Modes for carrying out the invention]

[0021] Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. In each figure, components denoted by the same reference numerals are identified as identical components, and their descriptions are omitted where appropriate. In this specification, general reference numerals are used without subscripts, while individual components are indicated by subscripts.

[0022] The torsional fatigue evaluation method in this embodiment is a torsional method for evaluating the torsional fatigue of a metal to be evaluated, comprising: a measurement step of measuring the sound velocity or resonant frequency in an axially symmetric SH wave ultrasonic wave propagating through the metal to be evaluated; and an evaluation step of evaluating the torsional fatigue of the metal to be evaluated based on the sound velocity or resonant frequency measured in the measurement step. The torsional fatigue evaluation method described below will be explained in more detail using a torsional fatigue evaluation device that implements this method as an example.

[0023] Figure 1 is a block diagram showing the configuration of a torsional fatigue evaluation device in an embodiment. Figure 2 is a diagram illustrating the electromagnetic ultrasonic transducer in the torsional fatigue evaluation device. Figure 2A is a schematic diagram showing the configuration of the electromagnetic ultrasonic transducer, and Figure 2B is a schematic diagram illustrating the operation of the electromagnetic ultrasonic transducer. Figure 3 is a schematic diagram illustrating how to determine the resonant frequency. In Figure 3, the horizontal axis is frequency, and the vertical axis is amplitude. Figure 4 is a schematic diagram illustrating how to determine the damping coefficient in the first embodiment. In Figure 4, the horizontal axis is time (elapsed time), and the vertical axis is amplitude. Figure 5 is a schematic diagram illustrating how to determine the damping coefficient in the second embodiment. In Figure 5, the horizontal axis is frequency, and the vertical axis is amplitude. Figure 6 is a diagram illustrating a torsional fatigue test specimen as an example. Figure 6A is a front view (viewed from the radial direction perpendicular to the axial direction), and Figure 6B is a side view (viewed from the axial direction). Figure 7 is a diagram illustrating the relationship between fatigue injury rate and rate of change in sound velocity, as an example. The horizontal axis of Figure 7 represents the fatigue injury rate, and the vertical axis represents the rate of change in sound velocity.

[0024] The torsional fatigue evaluation device 1000 is a device for evaluating the torsional fatigue of a metal to be evaluated, and for example, as shown in Figures 1 and 2, it comprises an electromagnetic ultrasonic transducer 1, a control processing unit 2, an input unit 3, an output unit 4, an interface unit (IF unit) 5, and a storage unit 6. The object to be evaluated can be any axially symmetric metal (including alloys), such as a solid cylindrical member (e.g., a round bar) or a hollow cylindrical member (e.g., a circular tube).

[0025] An electromagnetic acoustic transducer (EMAT) 1 is a probe that generates a sound source directly within a sample through electromagnetic action and transmits and receives ultrasonic waves. It does not require an acoustic coupling agent for transmitting and receiving ultrasonic waves, and non-contact measurement is possible. There are two types of EMATs: Lorentz type and magnetostrictive type, both of which consist of a magnet and a coil. A Lorentz type EMAT comprises a magnet that forms a static magnetic field in a metal and a coil that generates eddy currents in the metal using a high-frequency current. The interaction between the static magnetic field and the eddy currents generates a Lorentz force in the metal, thereby generating ultrasonic waves, and the reverse action receives the ultrasonic waves propagating through the metal. On the other hand, a magnetostrictive type EMAT is applicable only to magnetic materials and transmits and receives ultrasonic waves by utilizing the magnetostrictive effect of the magnetic material. A magnetostrictive type EMAT is preferably used when the object to be evaluated is a magnetic material, while a Lorentz type EMAT is preferably used when the object to be evaluated is a non-magnetic material.

[0026] There are various types of EMAT1, but in this embodiment, since it deals with axially symmetric SH wave ultrasound, for example, the EMAT1 shown in Figure 2 is used. As shown in Figure 2A, this EMAT1 is a so-called magnetostrictive type EMAT, comprising a solenoid coil 11 that forms a static magnetic field along the axial direction of the cylindrical (round bar) object to be evaluated Ob, and a meandering coil 12 that forms a fluctuating magnetic field in the circumferential direction of the object to be evaluated Ob. The solenoid coil 11 is an electromagnet formed by winding a conductor wire around an air core. The meandering coil 12 is a coil in which a straight portion of the conductor wire extending in the axial direction is wound in a zigzag pattern around the outer circumference of the object to be evaluated Ob. The meandering coils 12 wound around the object to be evaluated Ob are arranged inside the solenoid coil 11 so that they are concentric with each other and their axes coincide.

[0027] In such an EMAT1, when a DC current is passed through the solenoid coil 11, a static magnetic field H0 is formed along the axial direction, as shown in Figure 2B, for example. That is, a static magnetic field H0 is formed along the axial direction within the object Ob under evaluation. When a high-frequency current is passed through the meandering coil 12, a fluctuating magnetic field H0 is formed directly below the meandering coil 12 in a direction perpendicular to the static magnetic field.ω is excited. The surface of the evaluation object Ob is affected by the combined magnetic field H ω of these static magnetic fields H0 and the fluctuating magnetic field H t (=H0 + H ω ) and is magnetized. The direction of the combined magnetic field H t is obliquely inclined from the axial direction toward the radial direction. In the zigzag meandering coil 12, since the current flows in opposite directions in each conductor wire of the straight portions adjacent in the circumferential direction as indicated by ⇒ in Fig. 2B, the combined magnetic field H t in each conductor wire of the straight portions adjacent in the circumferential direction inclines in opposite directions to each other, so that reverse magnetostriction occurs and shear deformation occurs. As a result, a surface wave (ultrasonic wave of axially symmetric SH wave) that deflects in the axial direction and propagates in the circumferential direction is excited. Generally, changes in the dislocation structure accompanying the progress of fatigue occur near the material surface. Since the ultrasonic wave of the axially symmetric SH wave is sensitive to the tissue transformation near the surface, it is suitable for evaluating torsional fatigue.

[0028] And in the present embodiment, for example, the electromagnetic ultrasonic resonance method disclosed in Patent Document 1, Patent Document 2, etc. is used. In this electromagnetic ultrasonic resonance method, the resonance condition; nJ n (kr) - krJ n+1 (kr) = 0 holds, and axially symmetric SH waves can be obtained in a plurality of resonance modes (resonance modes) that satisfy this resonance condition. Here, n is the number of turns of the meandering coil 12, J n is the nth-order first-kind Bessel function, r is the radius in the cylindrical evaluation object Ob, and k is the wave number. Axially symmetric SH waves have the characteristic that the vibration region moves from the surface to the inside as the resonance mode becomes higher order. The first-order mode vibrates only near the surface, and as the order of the mode increases, the maximum value of the vibration amplitude penetrates into the inside. Generally, since metal fatigue progresses from the surface, it is preferable to use the first-order resonance mode that is most sensitive to the surface. On the other hand, when evaluating internal fatigue, it is preferable to use a higher-order mode that has sensitivity to the internal region. If the distance between each conductor wire of the straight portions adjacent in the circumferential direction is d, the period of the meandering coil 12 is 2d (one turn for a pair of two), and the number of turns n is determined as an integer close to 2πr / 2d. Therefore, the sound velocity C is the mth-order resonance frequency fn m In that case, C = 2πf n m It is represented by / k.

[0029] Returning to Figure 1, the input unit 3 is connected to the control processing unit 2 and is a device that inputs various commands, such as a command to instruct the start of the evaluation, and various data necessary for operating the torsional fatigue evaluation device 1000, such as the radius r of the object to be evaluated Ob and the period 2d of the meandering coil 12, to the torsional fatigue evaluation device 1000. For example, it is a keyboard, mouse, and multiple input switches to which predetermined functions are assigned. The output unit 4 is connected to the control processing unit 2 and is a device that outputs commands and data input from the input unit 3, as well as evaluation results, etc., according to the control of the control processing unit 2. For example, it is a display device such as a CRT display, LCD (liquid crystal display device), and organic EL display, or a printing device such as a printer.

[0030] The input unit 3 and output unit 4 may be configured as touch panels. In this configuration, the input unit 3 is a position input device that detects and inputs the operating position, such as a resistive or capacitive touchscreen, and the output unit 4 is a display device. In this touch panel, a position input device is provided on the display surface of the display device, and one or more candidate input contents that can be input to the display device are displayed. When the user touches the display position that displays the input content they want to input, the position input device detects that position, and the display content displayed at the detected position is input to the torsional fatigue evaluation device 1000 as the user's operation input. With such a touch panel, the user can easily understand the input operation intuitively, thus providing a torsional fatigue evaluation device 1000 that is easy for the user to use.

[0031] The IF unit 5 is connected to the control processing unit 2 and, in accordance with the control of the control processing unit 2, is a circuit that inputs and outputs data to and from external devices, for example. Examples include an RS-232C serial communication interface circuit, an interface circuit using the Bluetooth® standard, and an interface circuit using the USB standard. Alternatively, the IF unit 5 may be a communication interface circuit that sends and receives communication signals to and from external devices, such as a data communication card or a communication interface circuit conforming to the IEEE 802.11 standard.

[0032] The memory unit 6 is connected to the control processing unit 2 and is a circuit that stores various predetermined programs and various predetermined data in accordance with the control of the control processing unit 2. The various predetermined programs include, for example, a control processing program, which includes, for example, a control program, a resonance frequency detection program, an attenuation coefficient processing program, a sound velocity processing program, and a fatigue evaluation processing program. The control program is a program that controls each part 1, 3 to 6 of the torsional fatigue evaluation device 1000 according to the function of each part. The resonance frequency detection program is a program that detects the resonance frequency of the object to be evaluated Ob. The attenuation coefficient processing program is a program that determines the attenuation coefficient at the resonance frequency detected by the resonance frequency detection program. The sound velocity processing program is a program that determines the sound velocity in an axially symmetric SH wave ultrasound. The fatigue evaluation program is a program that evaluates the torsional fatigue of the object to be evaluated based on the sound velocity determined by the sound velocity processing program. The various predetermined data include, for example, the radius r of the object to be evaluated Ob, the period 2d of the meandering coil 12, and damage rate correspondence information, which are data necessary for executing each of these programs.

[0033] Such a storage unit 6 may include, for example, a non-volatile memory element such as ROM (Read Only Memory) or a rewritable non-volatile memory element such as EEPROM (Electrically Erasable Programmable Read Only Memory). Furthermore, the storage unit 6 includes RAM (Random Access Memory) which serves as the working memory of the control processing unit 2, storing data generated during the execution of the predetermined program. The storage unit 6 may also be configured to include a hard disk drive with a relatively large storage capacity.

[0034] The memory unit 6 functionally includes a damage rate correspondence information storage unit 61 that stores damage rate correspondence information. The damage rate correspondence information is information that represents the correspondence between the determination of whether there is a peak in the change of sound speed over time and the damage rate which represents the degree of damage in the object under evaluation. The damage rate corresponds to an example of a fatigue index which represents the degree of torsional fatigue in the object under evaluation. The damage rate correspondence information will be described further later.

[0035] The control processing unit 2 is a circuit for evaluating the torsional fatigue of the object to be evaluated Ob by controlling each part 1, 3 to 6 of the torsional fatigue evaluation device 1000 according to the function of each part. The control processing unit 2 is configured, for example, with a CPU (Central Processing Unit) and its peripheral circuits. When the control processing program is executed, the control unit 21, the resonance frequency detection unit 22, the damping coefficient processing unit 23, the sound velocity processing unit 24, and the fatigue evaluation processing unit 25 are functionally configured in the control processing unit 2.

[0036] The control unit 21 controls each of the parts 1, 3 to 6 of the torsional fatigue evaluation device 1000 according to the function of each part, and is in charge of controlling the entire torsional fatigue evaluation device 1000.

[0037] The resonance frequency detection unit 22 detects the resonance frequency in the Ob under evaluation. More specifically, the resonance frequency detection unit 22 measures the amplitude of the received signal by sweeping (scanning) the frequency (excitation frequency) of the burst wave current supplied to EMAT1 to excite ultrasound using electromagnetic ultrasonic resonance. As a result, multiple peaks, such as those shown in Figure 3, can be measured according to multiple resonance modes. Note that Figure 3 illustrates one of the multiple peaks. The frequency corresponding to the amplitude peak is the resonance frequency. From the low frequency side to the high frequency side, the resonance frequency f in the first resonance mode... n Resonant frequency f in the 1st and 2nd resonant modes n Resonant frequency f in the 2nd and 3rd resonant modes n 3. ...as shown, the resonant frequency f in the low-order resonant mode. n m From the resonant frequency f in the higher-order resonant mode n m In order, each resonant mode and its resonant frequency f n m The peaks are aligned. In this embodiment, the ultrasound of the first-order resonance mode by electromagnetic ultrasonic resonance is used as an axially symmetric SH wave ultrasound for evaluating the torsional fatigue of the object Ob to be evaluated. Therefore, the resonance frequency detection unit 22 determines the lowest frequency resonance frequency f from the measurement results. n m The resonance frequency f in ultrasound of the first resonance mode n It is detected as 1. In Figure 3, the amplitude graph with respect to frequency is represented by a continuous curve, but in reality, each amplitude is measured at each sampling frequency within a predetermined frequency interval (sampling interval), so the measurement results are discrete. For this reason, in this embodiment, the resonance frequency detection unit 22 finds an upward-convex function curve (for example, a Gaussian function curve or a Lorentz function curve) that best fits the measurement results, and the frequency corresponding to the peak in this found function curve is the resonance frequency f n m The degree of fitting is evaluated, as described later, for example, by least squares error. This allows for a higher resolution than the predetermined frequency interval and more accurately determines the resonant frequency f.n m This is required.

[0038] The damping coefficient processing unit 23 determines the damping coefficient at the resonant frequency detected by the resonant frequency detection unit 22. More specifically, the damping coefficient processing unit 23 determines the damping coefficient at the resonant frequency f detected by the resonant frequency detection unit 22. n m By exciting the device for a predetermined time, a resonant state is formed, and the damped free vibration after excitation is measured. This allows for the measurement of a damped free vibration, such as that shown in Figure 4. The damping coefficient processing unit 23 then determines the damping coefficient α by finding the envelope of the damped free vibration from the measurement results. For example, the damping coefficient processing unit 23 finds the exponential function e that best fits the envelope of the damped free vibration from the measurement results. -αt The damping coefficient α is determined by calculating (t is time (elapsed time after the start of damped free vibration)). The predetermined time in the excitation is set appropriately in advance so that a resonance state can be formed.

[0039] Alternatively, for example, as shown in Figure 5, the damping coefficient processing unit 23 obtains the resonance spectrum, and when the peak value of the resonance spectrum is Amax, it calculates Amax / 2 in the obtained resonance spectrum. 0.5 The frequency range △f is determined, and the value π△f obtained by multiplying the determined frequency range △f by π is used as the attenuation coefficient α (approximate attenuation coefficient α) (α = π△f).

[0040] The sound velocity processing unit 24 determines the sound velocity in axially symmetric SH wave ultrasound. More specifically, it determines the resonance condition (resonance condition); nJ n (kr)-krJ n+1 By solving (kr)=0 in advance, the wavenumbers in each resonant mode are determined and stored in the memory unit 6, and the sound velocity processing unit 24 determines the resonant frequency f in each resonant mode detected by the resonant frequency detection unit 22. n m and each wavenumber k in each next resonance mode stored in the memory unit 6 m The above-mentioned speed of sound C m =2πf nm / k m By using this, each sound velocity C in each resonant mode m To determine this, since the first-order resonance mode is used, the sound velocity C1 in the first-order resonance mode is determined.

[0041] The fatigue evaluation processing unit 25 evaluates the torsional fatigue of the object to be evaluated based on the sound velocity obtained by the sound velocity processing unit 24. More specifically, the change in sound velocity over time is measured by measuring the sound velocity multiple times, either periodically or irregularly, and the fatigue evaluation processing unit 25 evaluates the torsional fatigue of the object to be evaluated based on the presence or absence of a peak in the change over time. More specifically, the fatigue evaluation processing unit 25 translates the determination of the presence of a peak into the fatigue index, based on the correspondence between the determination of the presence of a peak and the fatigue index that represents the degree of torsional fatigue in the object to be evaluated, and expresses the evaluation using the translated fatigue index. In this embodiment, the fatigue index is the damage rate (degree of damage) described above, which represents the degree of damage in the object to be evaluated.

[0042] Here, we will explain the torsional fatigue test and its results. The test specimen (subject to evaluation) Ob is, for example, a square prism-shaped carbon steel (S45C) with a chamfered edge, which is then processed into a cylindrical shape (round bar shape) of φ20 [mm] in the axial direction, as shown in Figure 6. This cylindrical processed portion is the part to be evaluated in the torsional test. When this test specimen Ob was subjected to a torsional test at a torque of 350 [Nm] under limit conditions; ±1 [degree] after angle stabilization, the torsional test was stopped at 75,400 cycles. As a result, with 75,400 cycles representing a damage rate of 100 [%], test specimens Ob with damage rates of 10 [%], 20 [%], 30 [%], ..., and 90 [%] were created, and the sound velocity C and damping coefficient α in each test specimen Ob were measured using axially symmetric SH wave ultrasound by electromagnetic ultrasonic resonance. For this measurement, a serpentine coil 12 with a period d=1[mm] was used, and the first-order resonance mode was employed. The results are shown in Figure 7. As can be seen from Figure 7, the damping coefficient α showed a peak at around 80% damage rate (degree of damage), exhibiting behavior similar to that of ultrasound for general torsional fatigue. On the other hand, the sound velocity C increased from the initial stages of fatigue as fatigue progressed, peaking at around 40% damage rate (degree of damage), and then decreasing as fatigue progressed. Generally, it has been reported that the sound velocity decreases monotonically with the progression of fatigue, and this behavior is considered to be unique to torsional fatigue. When torsional fatigue is evaluated based on the presence or absence of a peak in the damping coefficient α, the damage rate is approximately 80% at the point where the presence of the peak is determined. However, when torsional fatigue is evaluated based on the presence or absence of a peak in the sound velocity C, the damage rate is approximately 40% at the point where the presence of the peak is determined. Therefore, evaluating torsional fatigue using the sound velocity C allows for earlier evaluation of torsional fatigue.

[0043] Therefore, in this embodiment, the damage rate correspondence information is information representing the correspondence between the determination that there is a peak in the change of sound speed C over time and the damage rate of 40% or more, which represents the degree of damage in the object Ob to be evaluated. In this embodiment, the fatigue evaluation processing unit 25 rephrases the determination that there is a peak in the change of sound speed C over time as the damage rate of 40% or more, based on the correspondence represented by the damage rate correspondence information, and represents the evaluation with the rephrased damage rate of 40% or more.

[0044] The control processing unit 2, input unit 3, output unit 4, IF unit 5, and storage unit 6 in such a torsional fatigue evaluation device 1000 can be configured by a computer, such as a desktop or notebook computer.

[0045] Next, the operation of this embodiment will be described. Figure 8 is a flowchart showing the operation of the torsional fatigue evaluation device.

[0046] When the torsional fatigue evaluation device 1000 with this configuration is powered on, it performs the initialization of each necessary part and starts operating. The control processing unit 2 is functionally configured with a control unit 21, a resonance frequency detection unit 22, a damping coefficient processing unit 23, a sound velocity processing unit 24, and a fatigue evaluation processing unit 25 through the execution of its control processing program.

[0047] The torsional fatigue evaluation device 1000 repeatedly performs each of the processes S1 to S6 shown in Figure 8, either periodically or irregularly, until at least a peak is detected, in order to measure the change in sound velocity C over time.

[0048] In Figure 8, the torsional fatigue evaluation device 1000 uses the EMAT1 and the resonance frequency detection unit 22 of the control processing unit 2 to determine the resonance frequency f at the target Ob for evaluation. n m The resonant frequency f is detected and stored in the storage unit 6 in association with the detection date and time (S1, resonance frequency measurement step of the measurement step). In this embodiment, as described above, the first resonance mode is used, and its resonance frequency f n 1 is detected and stored.

[0049] Next, the torsional fatigue evaluation device 1000 uses the EMAT1 and the damping coefficient processing unit 23 of the control processing unit 2 to determine the damping coefficient α of the object to be evaluated Ob, and stores this coefficient in the storage unit 6 in association with the detection date and time (S2).

[0050] Next, the torsional fatigue evaluation device 1000, using the sound velocity processing unit 24 of the control processing unit 2, determines the resonant frequency f of each next resonant mode detected by the resonant frequency detection unit 22 in the process S1. n m In this embodiment, each resonant frequency f in the first resonant mode n Based on step 1, the sound velocity C of the object to be evaluated, Ob, is determined and stored in the memory unit 6 in association with the detection date and time (S3, sound velocity measurement step of the measurement process).

[0051] Next, the torsional fatigue evaluation device 1000 uses the fatigue evaluation processing unit 25 of the control processing unit 2 to determine the change in sound velocity C over time using the sound velocity C measured in the past and the sound velocity C measured in the current measurement and stored in the storage unit 6 in the above process S3, and determines whether or not there is a peak in this determined change over time (S4, peak determination process of the evaluation process). If the determination results in the presence of a peak, the torsional fatigue evaluation device 1000 then executes process S5. On the other hand, if the determination results in the absence of a peak, the torsional fatigue evaluation device 1000 then executes process S6.

[0052] In the process S5 described above, the torsional fatigue evaluation device 1000, using the fatigue evaluation processing unit 25, uses the damage rate correspondence information to rephrase the determination that there is a peak in the change of sound velocity C over time as a damage rate of 40% or more for the object Ob to be evaluated (damage rate conversion process of the evaluation process).

[0053] In the process S6 described above, the torsional fatigue evaluation device 1000 outputs the evaluation result to the output unit 4 via the fatigue evaluation processing unit 25, and terminates the current process. For example, if the fatigue evaluation processing unit 25 determines that a peak is present, it outputs to the output unit 4 that the damage rate of the evaluation target Ob is 40% or higher. If the fatigue evaluation processing unit 25 determines that there is no peak, it outputs to the output unit 4 a message indicating that no peak was detected (for example, "No peak was detected in this evaluation"). The fatigue evaluation processing unit 25 may also output the evaluation result to an external device via the IF unit 5 as needed.

[0054] As described above, the torsional fatigue evaluation method implemented in the torsional fatigue evaluation device 1000 in the embodiment can evaluate the torsional fatigue of the object to be evaluated Ob by measuring the sound velocity C in the ultrasonic waves of the axially symmetric SH wave propagating through the object to be evaluated Ob.

[0055] The torsional fatigue evaluation method described above monitors changes over time and determines the fatigue index based on the presence or absence of peaks; in the example above, it calculates the damage rate, allowing for a more accurate determination of the fatigue index.

[0056] Since the above torsional fatigue evaluation method uses electromagnetic ultrasonic resonance, the signal-to-noise ratio can be improved and the conversion efficiency of EMAT1 can be increased, so that ultrasonic waves propagating through the object to be evaluated Ob can be received more reliably by EMAT1.

[0057] In the above embodiment, the determination of whether there is a peak in the change of sound velocity C over time was converted into a damage rate of 40% or more for the object Ob to be evaluated. However, the damage rate may also be determined by converting the measured sound velocity C to a corresponding damage rate using the correspondence between each damage rate and each sound velocity C at each damage rate (first modified form). In this case, the correspondence between each damage rate and each sound velocity C at each damage rate is determined in advance from, for example, multiple samples, and information representing this correspondence is stored in the damage rate correspondence information storage unit 61 as damage rate correspondence information. In the example shown in Figure 7, the same sound velocity can occur at different damage rates before and after the peak. Therefore, damage rate correspondence information to be used before determining the presence of a peak (pre-peak damage rate correspondence information) and damage rate correspondence information to be used after determining the presence of a peak (post-peak damage rate correspondence information) are prepared in advance and stored in the damage rate correspondence information storage unit 61. The fatigue evaluation processing unit 25 then converts the speed of sound C into the fatigue index (in this example, the damage rate) based on the correspondence between the speed of sound C and a fatigue index representing the degree of torsional fatigue in the object Ob to be evaluated, which in the above example is an example of the damage rate. The evaluation is then expressed using the converted fatigue index. In the example shown in Figure 7, before the conversion, the fatigue evaluation processing unit 25 determines whether the presence or absence of the peak has been determined or not, and uses the correspondence relationship represented by the damage rate correspondence relationship information corresponding to this determination result. This torsional fatigue evaluation method obtains the fatigue index (in this example, an example of the damage rate) from the correspondence relationship, so the fatigue index can be determined without measuring changes over time.

[0058] In this case, the torsional fatigue evaluation device 1000 operates as follows. Figure 9 is a flowchart showing the operation of the torsional fatigue evaluation device in the first deformation form.

[0059] In Figure 9, the torsional fatigue evaluation device 1000 performs the same process as described in S1 above, at the resonant frequency f of the object Ob to be evaluated. n mThe system detects and stores the sound (S11), calculates and stores the damping coefficient α of the object to be evaluated Ob, similar to the process S2 described above (S12), and calculates and stores the sound velocity C of the object to be evaluated Ob, similar to the process S3 described above (S13). Subsequently, the torsional fatigue evaluation device 1000, using the fatigue evaluation processing unit 25 of the control processing unit 2, converts the sound velocity C obtained in process S13 into a damage rate from the correspondence relationship represented by the damage rate correspondence relationship information stored in the damage rate correspondence relationship information storage unit 61 (S14). If it is necessary to determine the presence or absence of a peak during the conversion, the fatigue evaluation processing unit 25 also determines the presence or absence of a peak in the change of sound velocity C over time. Then, the torsional fatigue evaluation device 1000, using the fatigue evaluation processing unit 25, outputs the damage rate of the evaluation result to the output unit 4 (S15), and terminates this process.

[0060] Furthermore, in the above embodiment, the torsional fatigue of the object Ob was evaluated based on the speed of sound C, but instead of the speed of sound C, the resonant frequency f n m This may also be used (second variant).

[0061] Figure 10 is a diagram illustrating the relationship between fatigue damage rate and the rate of change of resonance frequency as an example. The horizontal axis of Figure 10 represents the damage rate (degree of damage), and its vertical axis represents the rate of change of resonance frequency. Figure 10 shows the results of the torsional fatigue test described above, expressed in terms of resonance frequency. As can be seen from Figure 10, the resonance frequency f n m Similar to the speed of sound C, f increases from the initial stages of fatigue as fatigue progresses, peaking around a damage rate (degree of damage) of 40%, and then decreasing as fatigue progresses. For this reason, the torsional fatigue evaluation device 1000 uses the resonant frequency f instead of the speed of sound C. n m This can be used and produces the same effects as in the case of sound speed C.

[0062] Furthermore, in the above-described embodiment, the torsional fatigue evaluation device 1000 may be configured to predict the remaining life of the object to be evaluated Ob (third modified form). In such a torsional fatigue evaluation device 1000, the control processing program further includes a remaining life prediction program that predicts the remaining life of the object to be evaluated Ob, and by executing this control processing program, the control processing unit 2 is functionally further configured with a remaining life prediction unit 26 that predicts the remaining life of the object to be evaluated, as shown by the dashed line in Figure 1. The storage unit 6 is further functionally equipped with a remaining life correspondence information storage unit 62 that stores the remaining life correspondence information used by the remaining life prediction unit 26, as shown by the dashed line in Figure 1.

[0063] More specifically, the remaining life prediction unit 26 predicts the remaining life of the object to be evaluated when the fatigue evaluation processing unit 25 determines that there is a peak (first aspect of the third modified form). As described above, at the time of the peak, the damage rate is 40%, and there is remaining life. This remaining life is the time from the time of torsional fatigue evaluation until the torsional fatigue progresses and the object to be evaluated needs to be repaired or replaced. For this reason, the period TW from the time of determination that there is a peak to the time when the damage rate of the object to be evaluated reaches a level where repair or replacement is necessary (e.g., 100%, 95%, or 90%) is determined in advance from multiple samples, and this is called the remaining life TW. In this remaining life TW, the damage rate at the time of determination that there is a peak is assumed to be 40%. Then, the determination of whether there is a peak in the change of sound speed C over time is associated with this remaining life TW, and information representing the correspondence between this determination of whether there is a peak and the remaining life of the evaluation target Ob is stored in the remaining life correspondence information storage unit 62 as the remaining life correspondence information. Then, the remaining life prediction unit 26 translates the determination of whether there is a peak into the remaining life of the evaluation target from the correspondence represented by the remaining life correspondence information stored in the remaining life correspondence information storage unit 62.

[0064] Alternatively, for example, the remaining life prediction unit 26 predicts the remaining life of the object to be evaluated by determining the remaining life corresponding to the converted fatigue index from the correspondence between the evaluation index and the remaining life (second aspect of the third modified form). More specifically, the correspondence between each damage rate and each remaining life at each damage rate is determined in advance from, for example, multiple samples, and information representing this correspondence is stored in the remaining life correspondence information storage unit 62 as remaining life correspondence information. The remaining life prediction unit 26 predicts the remaining life of the object to be evaluated by determining the remaining life corresponding to the damage rate converted by the fatigue evaluation processing unit 25 from the correspondence represented by the remaining life correspondence information stored in the remaining life correspondence information storage unit 62.

[0065] In this third modified form, the torsional fatigue evaluation device 1000 further predicts the remaining life of the object to be evaluated Ob by the remaining life prediction unit 26 of the control processing unit 2 during process S5 shown in Figure 8 and process S14 shown in Figure 9 (remaining life prediction process), and further outputs this predicted remaining life to the output unit 4 during process S6 shown in Figure 8 and process S15 shown in Figure 9. As a result, the remaining life is predicted, so for example, the maintenance time or replacement time of the object to be evaluated can be recognized.

[0066] To illustrate the present invention, the embodiments have been adequately and fully described above with reference to the drawings. However, those skilled in the art should recognize that it is easy to modify and / or improve upon the embodiments described above. Therefore, unless such modifications or improvements implemented by those skilled in the art fall outside the scope of the claims, such modifications or improvements shall be considered to be included within the scope of the claims. [Explanation of Symbols]

[0067] 1000 Torsional Fatigue Evaluation Device 1. Electromagnetic ultrasonic transducer 2 Control Processing Unit 6 Memory section 61 Damage Rate Correspondence Information Storage Unit 62 Remaining Life Corresponding Information Storage Unit

Claims

1. A torsional fatigue evaluation method for evaluating the torsional fatigue of a metal that is the subject of evaluation, A measurement step of measuring the sound velocity or resonant frequency in an ultrasonic wave of an axisymmetric SH wave propagating through the object to be evaluated, The system comprises an evaluation step in which the torsional fatigue of the object to be evaluated is evaluated based on the sound velocity or resonant frequency measured in the measurement step, The measurement step involves measuring the change over time in the sound velocity or resonant frequency, The evaluation step evaluates the torsional fatigue of the object to be evaluated based on the presence or absence of a peak in the change over time. Torsional fatigue evaluation method.

2. The aforementioned axially symmetric SH wave ultrasound is an ultrasound of the first-order resonance mode by electromagnetic ultrasonic resonance. The method for evaluating torsional fatigue according to claim 1.

3. If the evaluation step determines that there is a peak, the system further includes a remaining life prediction step for predicting the remaining life of the object to be evaluated. The method for evaluating torsional fatigue according to claim 1.

Images