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] The present invention relates to a torsional fatigue evaluation method for evaluating torsional fatigue of metals. [Background technology]

[0002] Metal fatigue is accompanied by changes in dislocation structures and the occurrence and progression of cracks. Ultrasonic waves are sensitive to such changes in material structures, and at frequencies in the MHz range, the attenuation coefficient α, sound speed v, and dislocation structure are expressed as follows: dislocation density is Λ, dislocation loop length is L, and sound speed without dislocations is v. 0 In this case, the model formula is: α ∝ ΛL 4 , (v 0 -v) / v 0 ∝ΛL 2 It is known that the relationship between the attenuation coefficient α and the sound velocity v is given by: For this reason, it is believed that measuring the attenuation coefficient α and the sound velocity v is effective for evaluating metal fatigue. Various methods for evaluating metal fatigue using ultrasonic waves are known, one of which is a method using electromagnetic ultrasonic resonance (for example, Patent Document 1 and Patent Document 2).

[0003] This method of evaluating metal fatigue using electromagnetic ultrasonic resonance involves using an electromagnetic ultrasonic transducer to generate ultrasonic burst waves in a non-contact manner in the object to be evaluated using a burst wave current, receiving the ultrasonic waves propagating through the object to be evaluated, and setting the frequency of the burst waves so that the phases of the ultrasonic waves that interfere with each other as they travel back and forth through the object to be evaluated are aligned (matched), thereby causing ultrasonic resonance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3397574 [Patent Document 2] International Publication No. 2014 / 155612 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, since Patent Document 1 and Patent Document 2 do not disclose or suggest anything about torsional fatigue, the present invention proposes a new method for evaluating the torsional fatigue of metals.

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a torsional fatigue evaluation method capable of evaluating the torsional fatigue of metals by using electromagnetic ultrasonic waves. [Means for solving the problem]

[0007] As a result of various investigations, the present inventors have found that the above object can be achieved by the present invention described below. That is, a torsional fatigue evaluation method according to one aspect of the present invention is a method for evaluating torsional fatigue of a metal to be evaluated, comprising a measurement step of measuring the sound velocity or resonant frequency of an ultrasonic wave of an axially symmetric 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 resonant frequency measured in the measurement step.

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

[0009] In another aspect, in the above-mentioned torsional fatigue evaluation method, the measurement step measures the change over time in the sound velocity or the resonance frequency, and the evaluation step evaluates the torsional fatigue of the evaluation object based on the presence or absence of a peak in the change over time. Preferably, in the above-mentioned torsional fatigue evaluation method, the measurement step measures the change over time by periodically or irregularly measuring the sound velocity or the resonance frequency a plurality of times. Preferably, in the above-mentioned torsional fatigue evaluation method, the evaluation step rephrases the determination of the presence of a peak as the fatigue index based on a correspondence relationship between the determination of the presence of a peak and a fatigue index representing the degree of torsional fatigue in the evaluation object, and expresses the evaluation with the rephrased fatigue index. Preferably, the fatigue index is a damage rate (damage degree) representing the degree of damage in the evaluation object. Preferably, in the above-mentioned torsional fatigue evaluation method, the evaluation object is a 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] Such a torsional fatigue evaluation method monitors the change over time and determines the fatigue index based on the presence or absence of a peak, so that the fatigue index can be determined more accurately.

[0011] In another aspect, in the above-mentioned torsional fatigue evaluation method, the evaluation step converts the sound velocity or the resonance frequency into a fatigue index representing the degree of torsional fatigue in the evaluation object based on a correspondence relationship between the sound velocity or the resonance frequency and the fatigue index representing the degree of torsional fatigue in the evaluation object, and expresses the evaluation by the converted fatigue index. Preferably, the fatigue index is a damage rate (damage degree) representing the degree of damage in the evaluation object.

[0012] In such a torsional fatigue evaluation method, the fatigue index is determined from the correspondence between the sound velocity or resonance frequency and the fatigue index, and therefore the fatigue index can be determined without measuring changes over time.

[0013] In another aspect, in the above-described torsional fatigue evaluation method, the axially symmetric SH wave ultrasonic waves are ultrasonic waves in a first resonance mode by an electromagnetic ultrasonic resonance method.

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

[0015] In another aspect, the above-mentioned torsional fatigue evaluation method further includes a remaining life prediction step of predicting a remaining life of the evaluation object when the evaluation step determines that the peak has been present. Preferably, in the above-mentioned torsional fatigue evaluation method, the evaluation object is a cylindrical (round bar) carbon steel, and the remaining life processing step translates the determination that the peak has been present into the remaining life of the evaluation object based on a correspondence relationship between the determination that the peak has been present and the remaining life of the evaluation object.

[0016] Such a torsional fatigue evaluation method predicts the remaining life, and therefore makes it possible to recognize, for example, the timing of maintenance or replacement of the evaluation target.

[0017] In another aspect, the above-mentioned torsional fatigue evaluation method further includes a remaining life prediction step of predicting the remaining life of the evaluation object by determining the remaining life corresponding to the converted fatigue index from the correspondence relationship between the evaluation index and the remaining life.

[0018] Such a torsional fatigue evaluation method predicts the remaining life, and therefore makes it possible to recognize, for example, the timing of maintenance or replacement of the evaluation target. Effect of the Invention

[0019] The torsional fatigue evaluation method according to the present invention can evaluate the torsional fatigue of metals by using electromagnetic ultrasonic waves. [Brief description of the drawings]

[0020] [Figure 1] 1 is a block diagram showing a configuration of a torsional fatigue evaluation device in an embodiment. [Diagram 2] 3 is a diagram for explaining an electromagnetic ultrasonic transducer in the torsional fatigue evaluation device. FIG. [Diagram 3] FIG. 4 is a schematic diagram for explaining how to obtain a resonance frequency. [Figure 4] FIG. 4 is a schematic diagram for explaining how to obtain a damping coefficient in the first embodiment. [Diagram 5] FIG. 11 is a schematic diagram for explaining how to obtain a damping coefficient in a second embodiment. [Figure 6] FIG. 1 is a diagram for explaining a test piece for torsional fatigue as an example. [Figure 7] FIG. 13 is a diagram for explaining the relationship between the fatigue damage rate and the rate of change of sound velocity, as an example. [Figure 8] 4 is a flowchart showing an operation of the torsional fatigue evaluation device. [Figure 9] 5 is a flowchart showing an operation of the torsional fatigue evaluation device in the first modified embodiment. [Figure 10] FIG. 11 is a diagram for explaining the relationship between the fatigue damage rate and the resonant frequency change rate, as an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 addition, configurations with the same reference numerals in each drawing indicate that they are the same configurations, and their description will be omitted as appropriate. In this specification, when referring to a general term, a reference numeral without a subscript is used, and when referring to an individual configuration, a reference numeral with a subscript is used.

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

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

[0024] This 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, includes 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 evaluation object may 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 pipe).

[0025] An electromagnetic acoustic transducer (EMAT) 1 is a probe that generates a sound source directly in a sample by electromagnetic action and transmits and receives ultrasonic waves. No acoustic coupling agent is required for transmitting and receiving ultrasonic waves, and non-contact measurement is possible. There are Lorentz type and magnetostrictive type EMATs, both of which are composed of a magnet and a coil. A Lorentz type EMAT has a magnet that forms a static magnetic field in a metal and a coil that generates eddy currents in the metal by high-frequency current, and generates ultrasonic waves by generating a Lorentz force in the metal through the interaction between the static magnetic field and the eddy current, and receives ultrasonic waves propagating through the metal by the reverse action. On the other hand, a magnetostrictive EMAT is applicable only to magnetic materials, and transmits and receives ultrasonic waves by utilizing the magnetostrictive effect of a magnetic material. A magnetostrictive EMAT is preferably used when the evaluation target is a magnetic material, and a Lorentz type EMAT is preferably used when the evaluation target is a non-magnetic material.

[0026] There are various types of EMAT1, but in this embodiment, since ultrasonic waves of axially symmetric SH waves are handled, for example, the EMAT1 shown in FIG. 2 is used. As shown in FIG. 2A, this EMAT1 is a so-called magnetostrictive EMAT, which includes a solenoid coil 11 that forms a static magnetic field along the axial direction of a cylindrical (round bar) evaluation object Ob, and a meandering coil 12 that forms a variable magnetic field in the circumferential direction of the evaluation object 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 zigzag around the outer periphery of the evaluation object Ob in the circumferential direction. The meandering coils 12 wound around the evaluation object Ob are arranged in the solenoid coil 11 so as to be concentric with each other and have the same axis.

[0027] In such an EMAT1, when a direct current is applied to the solenoid coil 11, a static magnetic field H 0 That is, a static magnetic field H along the axial direction is formed within the evaluation object Ob. 0When a high-frequency current is applied to the meandering coil 12, a variable magnetic field H ω The surface of the evaluation object Ob is subjected to these static magnetic fields H 0 and the varying magnetic field H ω The combined magnetic field H t (=H 0 +H ω ) is magnetized by the resultant magnetic field H t In the meandering coil 12, currents flow in the opposite directions in the conductor wires of the straight portions adjacent to each other in the circumferential direction, as shown by the arrows in FIG. 2B. Therefore, the resultant magnetic field H t are inclined in opposite directions, causing magnetostriction in opposite directions, resulting in shear deformation. This excites a surface wave (axially symmetric SH wave ultrasonic wave) that deflects in the axial direction and propagates in the circumferential direction. In general, changes in the dislocation structure that accompany the progression of fatigue occur near the material surface. Axisymmetric SH wave ultrasonic waves are sensitive to structure transformations near the surface, making them suitable for evaluating torsional fatigue.

[0028] In this embodiment, the electromagnetic ultrasonic resonance method disclosed in, for example, the above-mentioned Patent Document 1 and Patent Document 2 is used. In this electromagnetic ultrasonic resonance method, the resonance condition (resonance condition); nJ n (kr)-krJ n+1 (kr)=0 holds, and axially symmetric SH waves are obtained in multiple resonance modes that satisfy this resonance condition. Here, n is the number of turns of the meandering coil 12, and J nis the n-th order Bessel function of the first kind, r is the radius of the cylindrical evaluation object Ob, and k is the wave number. The axially symmetric SH wave has the characteristic that the higher the order of the resonance mode, the more the vibration region moves from the surface to the inside. The first order mode vibrates only near the surface, and the maximum value of the vibration amplitude increases with increasing order of the mode. It penetrates into the inside. In general, metal fatigue develops from the surface, so 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 is sensitive to the inner area. If the distance between each conductor wire of the straight parts adjacent in the circumferential direction is d, the period of the meandering coil 12 is 2d (one turn for a pair of two wires), and the number of turns n is determined as an integer close to 2πr / 2d. Therefore, the sound speed C is calculated by dividing the m-th order resonance frequency by f n m Then, C=2πf n m It is expressed as / k.

[0029] 1, the input unit 3 is connected to the control processing unit 2 and is a device for inputting various commands, such as a command to start evaluation, and various data required for operating the torsional fatigue evaluation device 1000, such as the radius r of the evaluation object Ob and the period 2d of the meandering coil 12, to the torsional fatigue evaluation device 1000, and is, for example, a keyboard, a mouse, and a plurality of input switches to which predetermined functions are assigned. The output unit 4 is connected to the control processing unit 2 and is a device for outputting the commands and data input from the input unit 3 and the evaluation results under the control of the control processing unit 2, and is, for example, a display device such as a CRT display, an LCD (liquid crystal display device), or an organic EL display, or a printing device such as a printer.

[0030] The input unit 3 and the output unit 4 may be configured with a touch panel. In the case of configuring this touch panel, the input unit 3 is a position input device that detects and inputs an operation position, for example, a resistive film type or a capacitive type, 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 input content candidates that can be input to the display device are displayed. When a user touches a display position that displays the input content that the user wants to input, the position is detected by the position input device, and the display content displayed at the detected position is input to the torsional fatigue evaluation device 1000 as the user's operation input content. In such a touch panel, the user can easily intuitively understand the input operation, so that a torsional fatigue evaluation device 1000 that is easy for the user to handle is provided.

[0031] The IF unit 5 is connected to the control processing unit 2 and is a circuit that inputs and outputs data to and from, for example, an external device under the control of the control processing unit 2, and is, for example, an interface circuit of RS-232C, which is a serial communication method, an interface circuit using the Bluetooth (registered trademark) standard, an interface circuit using the USB standard, etc. The IF unit 5 may also be, for example, a communication interface circuit that transmits and receives communication signals to and from an external device, such as a data communication card or a communication interface circuit conforming to the IEEE802.11 standard, etc.

[0032] The storage unit 6 is connected to the control processing unit 2 and is a circuit that stores various predetermined programs and various predetermined data according to the control of the control processing unit 2. The various predetermined programs include, for example, a control processing program, and the control processing program includes, for example, a control program, a resonance frequency detection program, a damping coefficient processing program, a sound speed processing program, and a fatigue evaluation processing program. The control program is a program that controls each unit 1, 3 to 6 of the torsional fatigue evaluation device 1000 according to the function of each unit. The resonance frequency detection program is a program that detects a resonance frequency in the evaluation object Ob. The damping coefficient processing program is a program that calculates a damping coefficient at a resonance frequency detected by the resonance frequency detection program. The sound speed processing program is a program that calculates the sound speed of an ultrasonic wave of an axisymmetric SH wave. The fatigue evaluation program is a program that evaluates the torsional fatigue of the evaluation object Ob based on the sound speed calculated by the sound speed processing program. The various predetermined data include, for example, data necessary for executing each of these programs, such as the radius r of the evaluation object Ob, the period 2d of the meandering coil 12, and damage rate correspondence information.

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

[0034] The storage 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 a correspondence between a determination of the presence of a peak in the change in sound speed over time and a damage rate that represents the degree of damage in the evaluation object Ob. The damage rate corresponds to an example of a fatigue index that represents the degree of torsional fatigue in the evaluation object Ob. The damage rate correspondence information will be described further below.

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

[0036] The control unit 21 controls each of the units 1, 3 to 6 of the torsional fatigue evaluation device 1000 in accordance with the function of each unit, and is responsible for controlling the entire torsional fatigue evaluation device 1000.

[0037] The resonance frequency detection unit 22 detects the resonance frequency of the evaluation object Ob. More specifically, the resonance frequency detection unit 22 sweeps (scans) the frequency (excitation frequency) of the current of the burst wave supplied to the EMAT1 to excite ultrasonic waves by the electromagnetic ultrasonic resonance method, and measures the amplitude of the received signal. This makes it possible to measure a plurality of peaks, for example as shown in FIG. 3, according to a plurality of resonance modes. Note that FIG. 3 illustrates one of the plurality of 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 n 1 , the resonant frequency f of the second resonant mode n 2 , the resonant frequency f in the third resonant mode n 3, ... n m Resonant frequency f in higher resonance modes n m In order, each resonant frequency f n m In this embodiment, the ultrasonic waves of the first resonance mode by the electromagnetic ultrasonic resonance method are used as the ultrasonic waves of the axisymmetric SH wave for evaluating the torsional fatigue of the evaluation object Ob, so the resonance frequency detection unit 22 detects the lowest resonance frequency f n m The resonant frequency f of the first resonant mode ultrasound is n 1 In FIG. 3, the graph of amplitude versus frequency is shown as a continuous curve, but in reality, the measurement results are discrete because each amplitude is measured at each sampling frequency at a predetermined frequency interval (sampling interval). For this reason, in this embodiment, the resonance frequency detection unit 22 determines an upwardly convex function curve (such as a Gaussian function curve or a Lorentz function curve) that best fits the measurement results, and determines the frequency corresponding to the peak in this determined function curve as the resonance frequency f n m The degree of fitting is evaluated by, for example, the least square error, as in the case described later. This makes it possible to obtain the resonance frequency f with a higher resolution than the predetermined frequency interval and with a higher accuracy. n m is required.

[0038] The attenuation coefficient processing unit 23 calculates a damping coefficient at the resonance frequency detected by the resonance frequency detection unit 22. More specifically, the attenuation coefficient processing unit 23 calculates a damping coefficient at the resonance frequency f n mA resonant state is formed by exciting the vibration source for a predetermined time, and the damped free vibration after the excitation is measured. As a result, the damped free vibration as shown in FIG. 4 is measured. The damping coefficient processing unit 23 then obtains the damping coefficient α by obtaining the envelope of the damped free vibration of the measurement result. For example, the damping coefficient processing unit 23 obtains the exponential function e that best fits the envelope of the damped free vibration of the measurement result. -αt (t is time (time elapsed after the start of damped free vibration)). The predetermined time in the excitation is appropriately set in advance so that a resonant state can be formed.

[0039] Alternatively, for example, the attenuation coefficient processing unit 23 obtains a resonance spectrum as shown in FIG. 5, and when the peak value of the resonance spectrum is Amax, the attenuation coefficient processing unit 23 obtains Amax / 2 0.5 A frequency range Δf in which this is equal to or greater than this is obtained, and the frequency range Δf thus obtained is multiplied by π to obtain the value πΔf as the attenuation coefficient α (approximate attenuation coefficient α) (α=πΔf).

[0040] The sound velocity processing unit 24 calculates the sound velocity of the axially symmetric SH wave in ultrasonic waves. More specifically, the above-mentioned resonance condition (resonance condition); nJ n (kr)-krJ n+1 By solving (kr)=0 in advance, each wave number in each resonance mode is obtained and stored in the memory unit 6, and the sound speed processing unit 24 calculates each resonance frequency f in each resonance mode detected by the resonance frequency detection unit 22. n m and each wave number k in each resonance mode stored in the memory unit 6 m The above-mentioned sound speed C m =2πf n m / k m By using the above, the sound velocity C in each resonant mode m In this embodiment, the first resonance mode is used, so the sound velocity C 1 is required.

[0041] The fatigue evaluation processing unit 25 evaluates the torsional fatigue of the evaluation object Ob based on the sound velocity calculated by the sound velocity processing unit 24. More specifically, the sound velocity is measured multiple times, either periodically or irregularly, to measure the change in sound velocity over time, and the fatigue evaluation processing unit 25 evaluates the torsional fatigue of the evaluation object Ob based on the presence or absence of a peak in the change over time. More specifically, the fatigue evaluation processing unit 25 paraphrases 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 a fatigue index representing the degree of torsional fatigue in the evaluation object, and expresses the evaluation with the paraphrased fatigue index. In this embodiment, the fatigue index is the above-mentioned damage rate (damage level) representing the degree of damage in the evaluation object.

[0042] Here, the torsional fatigue test and its results will be described. The test piece (evaluation target) Ob is a member in which a C-chamfered square columnar carbon steel (S45C) is processed into a cylindrical (round bar) shape of φ20 [mm] at the center of the axial direction, as shown in FIG. 6. This cylindrical processed part is the evaluation target part of the torsion test. When this test piece Ob was subjected to a torsion test at a torque of 350 [Nm] and limit conditions; ±1 [degree] after the angle stabilized, the torsion test was stopped at 75,400 times. As a result, test pieces Ob with damage rates of 10 [%], 20 [%], 30 [%], ..., and 90 [%] were created, with 75,400 times being considered as a damage rate of 100 [%], and the sound velocity C and attenuation coefficient α of each test piece Ob were measured with ultrasonic waves of axially symmetric SH waves by the electromagnetic ultrasonic resonance method. For this measurement, a meandering coil 12 with a period d=1 [mm] was used, and the first-order resonance mode was used. The results are shown in FIG. 7. As can be seen from FIG. 7, the attenuation coefficient α peaked at a damage rate (damage degree) of about 80 [%], and the behavior was similar to that of ultrasonic waves for general torsional fatigue. On the other hand, the sound velocity C increased from the early stage of fatigue as fatigue progressed, peaked at a damage rate (damage degree) of about 40 [%], and then decreased as fatigue progressed. In general, it has been reported that the sound velocity decreases almost monotonically as fatigue progresses, and such behavior is considered to be specific to torsional fatigue. When torsional fatigue is evaluated based on the presence or absence of a peak in the attenuation coefficient α, the damage rate is about 80 [%] at the time of judging whether the peak exists, but when torsional fatigue is evaluated based on the presence or absence of a peak in the sound velocity C, the damage rate is about 40 [%] at the time of judging whether the peak exists, and by evaluating torsional fatigue with the sound velocity C, torsional fatigue can be evaluated earlier.

[0043] For this reason, in this embodiment, the damage rate correspondence information is information that represents a correspondence relationship between a determination that there is a peak in the change over time of the sound speed C and a damage rate of 40[%] or more that indicates the degree of damage in the evaluation object Ob. In this embodiment, the fatigue evaluation processing unit 25 rephrases the determination that there is a peak in the change over time of the sound speed C to the damage rate of 40[%] or more from the above-mentioned correspondence relationship represented by the damage rate correspondence information, and represents the evaluation by 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, for example, a desktop or notebook computer.

[0045] Next, the operation of this embodiment will be described with reference to a flowchart shown in Fig. 8.

[0046] When the power is turned on, the torsional fatigue evaluation device 1000 having such a configuration initializes each required section and starts its operation. In the control processing section 2, a control section 21, a resonance frequency detection section 22, a damping coefficient processing section 23, a sound speed processing section 24, and a fatigue evaluation processing section 25 are functionally configured by executing the control processing program.

[0047] In order to measure the change over time in the sound speed C, the torsional fatigue evaluation device 1000 repeatedly executes the steps S1 to S6 shown in FIG. 8 periodically or irregularly, at least until a peak is detected.

[0048] In FIG. 8, the torsional fatigue evaluation device 1000 detects the resonance frequency f of the evaluation object Ob by the EMAT 1 and the resonance frequency detection unit 22 of the control processing unit 2. n m 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 determines the damping coefficient α of the evaluation object Ob by the EMAT 1 and the damping coefficient processing unit 23 of the control processing unit 2, and stores this in the storage unit 6 in association with the detection date and time (S2).

[0050] Next, the torsional fatigue evaluation device 1000 calculates, by the sound velocity processing unit 24 of the control processing unit 2, each resonance frequency f n m In this embodiment, each resonance frequency f n 1 The sound speed C of the evaluation object Ob is calculated based on the above, and is stored in the storage unit 6 in association with the detection date and time (S3, sound speed measurement step of the measurement step).

[0051] Next, the torsional fatigue evaluation device 1000, by means of the fatigue evaluation processing unit 25 of the control processing unit 2, obtains a change in the sound speed C over time using the previously measured sound speed C stored in the memory unit 6 and the sound speed C from the current measurement stored in the memory unit 6 in the process S3, and judges whether or not a peak exists in the obtained change over time (S4, peak judgment process of the evaluation process). If it is determined that a peak exists as a result of this judgment, the torsional fatigue evaluation device 1000 next executes process S5, whereas if it is determined that no peak exists as a result of the judgment, the torsional fatigue evaluation device 1000 next executes process S6.

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

[0053] In the process S6, the torsional fatigue evaluation device 1000 outputs the evaluation result to the output unit 4 by the fatigue evaluation processing unit 25, and ends this process. For example, if the fatigue evaluation processing unit 25 determines that there is a peak, it outputs a damage rate of 40% or more for the evaluation object Ob to the output unit 4. If the fatigue evaluation processing unit 25 determines that there is no peak, it outputs a message to the output unit 4 indicating that the peak was not detected (for example, "No peak was detected in this evaluation"). Note that the fatigue evaluation processing unit 25 may output the evaluation result to an external device via the IF unit 5 as necessary.

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

[0055] The above torsional fatigue evaluation method monitors the change over time and determines the fatigue index based on the presence or absence of a peak, and in the above example, the damage rate is one example of the fatigue index, so that the fatigue index can be determined more accurately.

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

[0057] In the above embodiment, the determination of the presence of a peak in the time-dependent change in the sound speed C is converted to a damage rate of 40[%] or more for the evaluation object Ob, but the damage rate may be obtained by converting the measured sound speed C into a corresponding damage rate using the correspondence between each damage rate and each sound speed C at each damage rate (first modified embodiment). In this case, the correspondence between each damage rate and each sound speed C at each damage rate is obtained in advance from, for example, a plurality of 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 FIG. 7, the same sound speed can be obtained at different damage rates before and after the peak, so damage rate correspondence information (pre-peak damage rate correspondence information) used before (before) determining the presence of a peak and damage rate correspondence information (post-peak damage rate correspondence information) used after (after) determining the presence of a peak are prepared in advance and stored in the damage rate correspondence information storage unit 61. Then, the fatigue evaluation processing unit 25 converts the sound speed C into the fatigue index (damage rate in this example) based on a correspondence relationship between the sound speed C and a fatigue index that indicates the degree of torsional fatigue in the evaluation object Ob (the damage rate in the above example), and expresses the evaluation with the converted fatigue index. In the example shown in FIG. 7, the fatigue evaluation processing unit 25 judges whether the peak is present before (before) or after (after) the peak is present before the conversion, and uses the correspondence relationship represented by the damage rate correspondence information that corresponds to this judgment result. Such a torsional fatigue evaluation method obtains a fatigue index from the correspondence relationship, the damage rate being an example of the above example, and therefore can obtain the fatigue index 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 modified embodiment.

[0059] In FIG. 9, the torsional fatigue evaluation device 1000 performs the process similar to the above-mentioned process S1 to obtain the resonance frequency f n m(S11), and similarly to the above-mentioned process S2, the attenuation coefficient α of the evaluation object Ob is calculated and stored (S12), and similarly to the above-mentioned process S3, the sound speed C of the evaluation object Ob is calculated and stored (S13). Next, the torsional fatigue evaluation device 1000 converts the sound speed C calculated in the above-mentioned process S13 into a damage rate from the correspondence represented by the damage rate correspondence information stored in the damage rate correspondence information storage unit 61 by the fatigue evaluation processing unit 25 of the control processing unit 2 (S14). Note that, when 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 over time of the sound speed C. Then, the torsional fatigue evaluation device 1000 outputs the damage rate of the evaluation result to the output unit 4 by the fatigue evaluation processing unit 25 (S15), and ends this process.

[0060] In the above embodiment, the torsional fatigue of the evaluation object Ob is evaluated based on the sound speed C. However, instead of the sound speed C, the resonant frequency f n m may be used (second variant).

[0061] FIG. 10 is a diagram for explaining the relationship between the fatigue damage rate and the rate of change of the resonant frequency, as an example. The horizontal axis of FIG. 10 is the damage rate (damage level), and the vertical axis is the rate of change of the resonant frequency (resonant frequency). FIG. 10 shows the results of the above-mentioned torsional fatigue test in terms of the resonant frequency. As can be seen from FIG. 10, the resonant frequency f n m Similar to the sound speed C, the resonance frequency f increases from the early stage of fatigue as the fatigue progresses, peaks at a damage rate (damage level) of about 40% and then decreases as the fatigue progresses. For this reason, the torsional fatigue evaluation device 1000 uses the resonance frequency f instead of the sound speed C. n m can be used, and the same effects as in the case of the sound speed C can be obtained.

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

[0063] More specifically, the remaining life prediction unit 26 predicts the remaining life of the evaluation object Ob when, for example, the fatigue evaluation processing unit 25 judges that the peak exists (first aspect of the third modified embodiment). As described above, at the time of the peak, the damage rate is 40[%] and there is a remaining life. This remaining life is the time from the time of evaluation of the torsional fatigue to the time when the torsional fatigue progresses and the evaluation object Ob becomes necessary, for example, for repair or replacement. For this reason, the period TW from the time of judgment that the peak exists to the time when the damage rate of the evaluation object Ob becomes necessary, for example, for repair or replacement (for example, 100[%], 95[%], 90[%], etc.) is obtained in advance from, for example, a plurality of samples, and is set as the remaining life TW. In this remaining life TW, the damage rate at the time of judgment that the peak exists is considered to be 40[%]. The determination that a peak has occurred in the change over time in the sound speed C is then associated with this remaining life TW, and information expressing the correspondence between this determination that a peak has occurred and the remaining life of the evaluation object Ob is stored as the remaining life correspondence information in the remaining life correspondence information storage unit 62. The remaining life prediction unit 26 then translates the determination that a peak has occurred into the remaining life of the evaluation object, based on 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 evaluation object Ob by determining the remaining life corresponding to the converted fatigue index from the correspondence relationship between the evaluation index and the remaining life (second aspect of the third modified embodiment). More specifically, the correspondence relationship between each damage rate and each remaining life at each damage rate is determined in advance, for example, from a plurality of samples, and information representing this correspondence relationship 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 evaluation object Ob by determining the remaining life corresponding to the damage rate converted by the fatigue evaluation processing unit 25 from the correspondence relationship represented by the remaining life correspondence information stored in the remaining life correspondence information storage unit 62.

[0065] In the torsional fatigue evaluation device 1000 in the third modified embodiment, in step S5 shown in Fig. 8 and step S14 shown in Fig. 9, the remaining life prediction unit 26 of the control processing unit 2 further predicts the remaining life of the evaluation object Ob (remaining life prediction step), and in step S6 shown in Fig. 8 and step S15 shown in Fig. 9, further outputs this predicted remaining life to the output unit 4. Since the remaining life is predicted, it is possible to recognize, for example, the timing of maintenance or replacement of the evaluation object.

[0066] In order to express the present invention, the present invention has been described adequately and sufficiently through the embodiments with reference to the drawings in the above description, but it should be recognized that those skilled in the art can easily change and / or improve the above-mentioned embodiments. Therefore, unless the changes or improvements made by those skilled in the art are at a level that departs from the scope of the claims described in the claims, the changes or improvements are interpreted as being included in the scope of the claims. [Explanation of symbols]

[0067] 1000 Torsional fatigue evaluation device 1. Electromagnetic ultrasonic transducer 2. Control processing section 6 Memory section 61 Damage rate correspondence information storage unit 62 Remaining life correspondence information storage unit

Claims

1. A torsional fatigue evaluation method for evaluating torsional fatigue of a metal to be evaluated, comprising the steps of: a measuring step of measuring a sound velocity or a resonant frequency of an ultrasonic wave of an axially symmetric 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. Torsional fatigue evaluation method.

2. The measuring step measures a change over time in the sound velocity or the resonant frequency, The evaluation step evaluates the torsional fatigue of the evaluation object based on the presence or absence of a peak in the change over time. The torsional fatigue evaluation method according to claim 1 .

3. The evaluation step converts the sound velocity or the resonance frequency into a fatigue index based on a correspondence relationship between the sound velocity or the resonance frequency and a fatigue index indicating a degree of torsional fatigue in the evaluation object, and expresses the evaluation using the converted fatigue index. The torsional fatigue evaluation method according to claim 1 .

4. The axially symmetric SH wave ultrasonic wave is a first-order resonant mode ultrasonic wave by an electromagnetic ultrasonic resonance method. The torsional fatigue evaluation method according to claim 1 .

5. a remaining life prediction step of predicting a remaining life of the evaluation object when it is determined that the peak is present in the evaluation step, The torsional fatigue evaluation method according to claim 2.

6. a remaining life prediction step of predicting a remaining life of the evaluation object by obtaining a remaining life corresponding to the converted fatigue index from a correspondence relationship between the evaluation index and a remaining life. The torsional fatigue evaluation method according to claim 3.

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