JP2010038696A - Non-destructive evaluation method of degree of metal fatigue damage and ultrasonic metal fatigue damage degree measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-destructive evaluation method of a degree of metal fatigue damage capable of measuring an accurate degree of metal fatigue in a short time, and an ultrasonic metal fatigue damage degree measuring instrument having a simple structure and a small size and also excellent in portability. <P>SOLUTION: The ultrasonic metal fatigue damage degree measuring instrument is equipped with a transmitter 14 brought into contact with the surface of a metal material 12 to transmit an ultrasonic wave, a receiver 16 for receiving the ultrasonic wave propagated along the surface of the metal material 12 and a body part 20 for separating the transmitter 14 and the receiver 16 at a definite interval to integrally hold them. The sound pressure attenuation ratio or propagation time of the ultrasonic wave propagated in the vicinity of the surface of the metal material 12 is measured, and the metal fatigue degree of the metal material 12 is calculated from the relation of the sound pressure attenuation ratio or propagation data of the ultrasonic wave to a known metal fatigue degree. An SH wave used as the ultrasonic wave and a metal member is intended for the metal material having a hexagonal crystal structure such as a magnesium alloy. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-destructive evaluation method of a metal fatigue damage degree and an ultrasonic metal fatigue damage degree measuring apparatus for measuring a fatigue degree without destroying a measurement object that is a metal material using ultrasonic waves.

  Conventional non-destructive inspection methods for metal fatigue include an X-ray diffraction method, a positron annihilation method, and an electron back-scattering diffraction method. However, these methods are advanced in order to follow extremely small changes such as distortion of crystals due to metal fatigue, increase in atomic vacancies, and disturbance of diffraction images due to the introduction of crystal rotation and dislocations. It becomes a complicated configuration. For this reason, except for some expensive equipment such as nuclear reactors, it was not a practical measuring device in terms of cost.

  Furthermore, the metal fatigue evaluation is a non-destructive inspection, which is a major requirement for practical use. However, in general, these devices cannot cope with it and cannot be a measuring device that can be easily used in various fields.

On the other hand, as a non-destructive inspection method for metal fatigue, as disclosed in Patent Documents 1 and 2, an inspection method using ultrasonic waves has been proposed. In the inspection method disclosed in Patent Document 1, the ultrasonic wave is propagated to the object to be inspected, and the attenuation coefficient, frequency, waveform, propagation time, reception sensitivity, etc. of the ultrasonic wave are measured, and the measured values are the same as those in the standard sample. In comparison with the above data, the surface deterioration of the material, fatigue, and the like are relatively diagnosed by comparison with the determination threshold value. Moreover, the measurement method disclosed in Patent Document 2 is to propagate ultrasonic waves on the surface of a metal material and measure fatigue of the metal material based on the propagation speed of the ultrasonic waves. In particular, surface-hardened metal materials measure fatigue of surface-hardened metal materials by utilizing the fact that residual compressive stress increases due to fatigue and the propagation speed of ultrasonic waves propagating on the surface of metal materials decreases. Is.
Japanese Patent Laid-Open No. 9-5309 JP 2003-329657 A

  The metal fatigue measurement methods disclosed in Patent Documents 1 and 2 above detect the measured state at that time. However, in the case of metallic materials that are severely limited in deformation due to slip, such as magnesium with a hexagonal crystal structure, the accumulation of residual stress is intermittently released due to the occurrence of microcracks during the fatigue process. May have a general fatigue behavior. For this reason, in the metal fatigue measurement methods disclosed in Patent Documents 1 and 2, even if information on ultrasonic propagation at a certain point in time is obtained, the value obtained from the ultrasonic propagation state depends on the state of residual stress. Even if the fatigue states are substantially the same, there may be cases where accurate fatigue information cannot be obtained.

  The present invention has been made in view of the above-described background art, and has a simple structure, a small size, excellent portability, and a metal fatigue damage degree that allows accurate measurement of metal fatigue in a short time. An object is to provide a fracture evaluation method and an ultrasonic metal fatigue damage degree measuring apparatus.

  The present invention relates to a transmitter that contacts the surface of a metal material and transmits ultrasonic waves, a receiver that receives the ultrasonic waves propagated in the vicinity of the surface of the metal material, and the transmitter and receiver are separated from each other by a certain distance. A body part integrally held, and the sound pressure attenuation rate or propagation time when the ultrasonic wave propagates near the surface of the metal material is measured, and the sound pressure attenuation rate or propagation with respect to a known degree of metal fatigue damage This is a non-destructive evaluation method for the degree of metal fatigue damage in which the metal fatigue damage degree of the metal material is calculated by comparing the time with the sound pressure decay rate or propagation time obtained by the measurement.

  In addition, the metal fatigue level measurement unit on the surface of the metal material is coated with a liquid medium that ensures close contact with the surface of the metal material and improves the propagation of ultrasonic waves on the surface of the metal material. A pair of probe parts, which are respectively attached to a machine and a receiver and are in contact with the solid surface, are brought into contact with the metal fatigue level measuring part via the medium.

  The ultrasonic waves use SH waves, and the metal member is a metal material having a hexagonal crystal structure such as a magnesium alloy.

  The present invention also provides a transmitter that contacts the surface of the metal material and transmits ultrasonic waves, a receiver that receives the ultrasonic waves propagated in the vicinity of the surface of the metal material, and the transmitter and the receiver that are spaced at regular intervals. A body part that is integrally held apart, a measuring means for measuring the sound pressure attenuation rate or propagation time when the ultrasonic wave propagates near the surface of the metal material, and the measured sound pressure attenuation rate or propagation time. It is an ultrasonic metal fatigue damage degree measuring apparatus provided with a calculation means for analyzing and calculating a metal fatigue damage degree of the metal material based on a change amount of history data.

  The main body is formed in a U-shape, the transmitter is provided at one end of the U-shaped main body, and the ultrasonic output unit of the transmitter faces the metal material surface side and receives the signal. The receiver is provided at the other end of the U-shaped main body, and the ultrasonic receiver of the receiver faces the metal material surface side and the transmitter side. The ultrasonic output section of the transmitter and the ultrasonic reception section of the receiver are each provided with a probe section that contacts the surface of the metal material.

  According to the metal fatigue damage degree nondestructive evaluation method and ultrasonic metal fatigue damage degree measuring apparatus of the present invention, the structure is small with a simple structure and can be easily transported to and attached to a measurement object. It is. As a result, the metal fatigue degree can be measured more frequently with respect to the measurement object that is a metal material, and the safety and durability of the product can be easily evaluated.

  Embodiments of the present invention will be described below. As shown in FIG. 1, the ultrasonic metal fatigue damage degree measuring apparatus 10 of the present invention is in contact with the surface of a metal material 12 that is an object to be measured and transmits an ultrasonic wave, and the vicinity of the surface of the metal material 12. Is provided with a receiver 16 for receiving the ultrasonic wave propagated through. The transmitter 14 and the receiver 16 are located apart from each other by a certain distance, and are provided in a main body 20 that integrally holds them. The transmitter 14 includes an oscillation circuit unit 15 that is a transmission circuit that transmits a frequency in the ultrasonic region, and the receiver 16 also includes a reception circuit unit 17 that includes a reception circuit that receives the frequency in the ultrasonic region.

  The main body 20 is provided with a weight 22 for pressing the transmitter 14 and the probe parts 14a and 16a of the receiver 16 against the metal material 12, and a pressing jig 24 that reliably presses the weight 22 against the metal material 12. Yes. The pressing pressure can be set as appropriate, but is preferably about 3 MPa, for example, in order to improve the propagation of ultrasonic waves. In measurement, grease is applied to the surface of the metal material 12 as an acoustic coupling agent and comes into contact with the probe portions 14a and 16a. The grease is preferably oily to avoid the effects of moisture absorption.

  The main body 20 is formed, for example, in a substantially U shape so as to separate the transmitter 14 and the receiver 16 from each other for a certain distance. The transmitter 14 is located at one end of the U shape, and includes a piezoelectric element or the like inside. An ultrasonic output unit 14b is provided in connection with the probe unit 14a. The ultrasonic output unit 14 b is disposed so as to face the surface side of the metal material 12, and is provided obliquely toward the receiver 16. The receiver 16 is located at the other end of the U-shape, and an ultrasonic receiving unit 16b such as a piezoelectric element is connected to the probe unit 16a. The ultrasonic receiver 16b is also arranged so as to face the surface side of the metal material 12, and is provided obliquely toward the transmitter 14. Note that the angles of the ultrasonic input / output portions (14b and 16b) with respect to the surface of the test piece are adjusted to be close to the critical angle according to the solid sound velocity of the test piece in order to efficiently propagate the ultrasonic wave to the vicinity of the surface layer of the test piece. The For example, when the evaluation material is a magnesium alloy, the angle of the ultrasonic output unit 14b and the ultrasonic receiving unit 16b with respect to the magnesium alloy surface is preferably about 21 °.

  The output of the receiving circuit unit 17 is connected to an A / D converter 26 that converts an analog electrical signal generated by ultrasonic waves into a digital signal, and the output of the A / D converter 26 is a waveform memory that stores received waveform data. 28. The output of the waveform memory 28 is connected to a peak detector 30 and is connected to an arithmetic processing device 32 such as a microcomputer having a CPU or memory for performing arithmetic processing described later. A monitor, an input / output device, a storage device, etc. (not shown) are connected to the arithmetic processing device 32. The ultrasonic wave to be used is a shear horizontal wave (referred to as SH wave (Horizontally Polarized Shear Wave in the present invention)).

  As shown in FIGS. 2 to 4, the measurement principle of the ultrasonic metal fatigue measuring apparatus 10 of this embodiment is that ultrasonic waves are generated by a transmitter 14 and a receiver 16 that are provided in the main body 20 and are spaced apart from each other by a predetermined distance. It measures the propagation time of s, and utilizes the fact that the propagation time of the ultrasonic wave s varies depending on the state of internal stress of the metal material 12. In the measurement, an ultrasonic output unit 14b that oscillates an ultrasonic wave (SH wave) and probes 14a and 16a of the ultrasonic wave receiving unit 16b are arranged to face each other, and an ultrasonic wave is propagated near the surface layer of the metal material 12, and a received waveform thereof. By calculating the amount of change, the metal fatigue state of the material is evaluated.

  The ultrasonic wave is an elastic wave, and its energy flow is shifted by the strain (stress state) of the crystal structure. In the case of the SH wave, if the stress field is shifted to the tension side between the probes having fixed transmission and reception angles, the sonic energy is further refracted to the surface layer side of the material (dashed line s1 in FIG. 2). On the other hand, in the case of compression, it acts in reverse (two-dot chain line s2 in FIG. 2). This is called the acoustoelastic effect. Due to this effect, the propagation time of the SH wave and the attenuation rate of the sound pressure change according to the stress state of the material (FIG. 3). That is, the propagation time and sound pressure decay rate decrease when the stress state of the material changes to the tension side, and conversely increases when the stress state of the material changes to the compression side (FIG. 4).

  The evaluation method of the present invention is a non-destructive inspection method using a transmission method using SH waves, and accurate information on residual stress fluctuations in metallic materials is obtained from the increase or decrease in sound pressure attenuation rate or propagation time based on the above-mentioned acoustoelastic effect. In particular, the metal fatigue nondestructive evaluation of a magnesium alloy is performed by performing extraction / calculation processing.

  Magnesium alloys have a hexagonal crystal structure and are less likely to slip at room temperature. In addition, the magnesium alloy generates microcracks starting from inclusions and the like against repeated stress. For this reason, in the fatigue process, destruction and repetitive accumulation and release of residual stress occur. In a slippery crystal structure material such as an aluminum alloy, the residual stress changes in almost one direction as the fatigue level increases, but in a magnesium alloy, microcracks occur due to fatigue accumulation, so the residual stress temporarily Open to some extent. This behavior is repeated, and eventually the fracture is caused while narrowing the fluctuation range of the residual stress (while converging the fluctuation range of the stress). For this reason, in a magnesium alloy, it becomes possible to evaluate a metal fatigue damage degree by calculating the sound pressure attenuation rate of ultrasonic vibration or the convergence amount of propagation time.

  As shown in FIG. 3, the propagation time T1 of the ultrasonic wave s is obtained by detecting the first peak A1 of the received ultrasonic waveform with the peak detector 30, and the period from the time of transmission to the peak A1 is the propagation time T1. Become. These timings are synchronized with a clock in the arithmetic processing unit 32, and a transmission time, a peak detection time, and the like are obtained.

  The evaluation of the sound pressure attenuation rate is performed by the arithmetic processing unit 32 based on the peak detected by the peak detector 30. This is because the sound pressure peak earlier in time is slower than the sound pressure later in time. Divide by the peak of. For example, A1 / A2 which is the ratio of the positive peak in FIG. 3 is an evaluation index, but it is not always necessary to evaluate by the sound pressure peak having the same sign. For example, in FIG. You may evaluate the relationship with the negative peak between A1 and A2 which adjoin. When the attenuation rate is evaluated with the sound pressures having such different signs, the relationship with respect to the residual stress in FIG. 4 can be similarly expressed by treating the ratio of the sound pressures as an absolute value. Note that the sound pressure attenuation rate may be organized by natural logarithm or the like based on the rate of change.

  The relationship between the propagation time or sound pressure decay rate and the metal fatigue damage level is determined in advance by measuring the metal fatigue damage level for the same material as the object to be measured using a precise metal fatigue level measuring machine. Measurement and recording are performed, and a predetermined table or arithmetic expression is created and stored in the memory of the arithmetic processing unit 32. When measuring a member whose degree of metal fatigue damage is unknown, the degree of metal fatigue damage is evaluated from this table or formula and the measured propagation time or sound pressure decay rate and displayed on a monitor or the like.

  As a specific evaluation method in the apparatus, the history of ultrasonic data is accumulated by performing a periodic inspection or implanting the metal fatigue damage degree measuring machine in equipment. Logarithmic decay rate of sound pressure, or measurement data of propagation time is recorded, a graph like the example of FIG. 5 described later is obtained, and the upper and lower envelope width ratios, or the decreasing ratio of the differential coefficient of the envelope, The fatigue soundness of the metal material of the apparatus is judged by comparing with a preset threshold value of the database.

  Note that dislocation growth and change in elastic modulus accompanying fatigue strongly affect the sound velocity of the solid and greatly change the propagation time. Therefore, the propagation time does not accurately reflect the variation in residual stress compared to the sound pressure decay rate. Therefore, when it is necessary to more accurately evaluate the fluctuation of the residual stress, it is desirable to use the sound pressure attenuation rate as an evaluation term.

  According to the ultrasonic metal fatigue degree measuring apparatus 10 of this embodiment, an extremely small metal fatigue damage degree measuring apparatus can be configured by, for example, integrating the arithmetic processing unit 32 that performs calculation into one chip, and the portability is high. Yes, the fatigue damage degree of any metal material can be measured at any place. In addition, by predicting the degree of metal fatigue, the safety and predicted life of the material can be easily obtained, which can be used for a wide range of product inspections.

  In addition, the non-destructive evaluation method and the ultrasonic metal fatigue damage degree measuring apparatus of the metal fatigue damage degree of the present invention are not limited to the above-described embodiment, and the shape of the main body portion other than the U-shape, the curvature surface, etc. It is sufficient that the transmitter and the receiver are integrally provided with a predetermined interval in a shape that matches the shape of the evaluation surface. In addition to magnesium, applicable materials are applicable to hexagonal metals and alloys thereof, and for example, alloy materials such as Ti, Co, Zn, Zr, Be, and Bi can also be used. In addition, a cubic metal can be applied as long as the residual stress is converged in the process of fatigue fracture. The frequency of the ultrasonic wave can be selected as appropriate, and the liquid applied to the surface may be an ultrasonic gel or other oil in addition to grease.

  Hereinafter, as one embodiment of the present invention, measurement data of a fatigue test of a magnesium alloy AZ31 rolled material is shown (measurement conditions: uniaxial tension, stress ratio 0, stress amplitude 64 MPa, excitation frequency 30 Hz, test temperature: room temperature). . The shape and dimensions (mm) of the test piece are shown in FIG. The measurement area 42 at the center of the test piece 40 was measured by the ultrasonic metal fatigue damage degree measuring apparatus of this example. FIG. 5 shows the relationship between the ultrasonic wave propagation time and the sound pressure attenuation rate with respect to the fatigue level N / Nf (N: the number of repetitions of weight applied to the metal material, Nf: the number of repetitions leading to the fracture).

  According to this result, as shown in FIGS. 5 (a) and 5 (b), it was confirmed that the propagation time and the sound pressure decay rate both lead to fatigue failure while repeatedly increasing and decreasing, and the upper and lower envelopes of the measurement data from the new product The degree of fatigue damage of the metal material could be judged by comparing the ratio of the upper and lower envelope widths of the line or the reduction ratio of the differential coefficient of the envelope with a preset database. It was also possible to predict the number of weighted repetitions leading to fatigue failure from the tendency of the upper and lower envelopes, the expiration date of the metal material, and the like.

  FIG. 7 shows the result of measuring the residual stress by X-ray diffraction with the same load applied to the test piece of the same lot as that used in the above test. This graph shows that, due to repeated loading on the test piece, the residual stress shifts to the compression side with the accumulation of fatigue, causing release in the middle, and repeating the cycle toward the compression side again.

  According to the measurement results shown in FIG. 7, the residual stress of the test piece converges while fluctuating, leading to fracture. The trend of fluctuation in this graph shows the same tendency as the sound pressure attenuation rate shown in FIG. 5 (b). Since the accumulation and release of stress is repeated, the fluctuation range is gradually narrowed, leading to destruction. It was confirmed that fatigue failure due to repeated loading can be predicted by measuring the pressure decay rate.

It is a schematic block diagram which shows the ultrasonic metal fatigue damage degree measuring apparatus of one Embodiment of this invention. It is the schematic diagram explaining propagation in the metal material of the ultrasonic wave by the ultrasonic metal fatigue damage degree measuring apparatus of this embodiment. It is a graph which shows the waveform of the ultrasonic wave received by the ultrasonic metal fatigue damage degree measuring apparatus of this embodiment. It is a graph which shows the relationship between the propagation time of an ultrasonic wave and the sound pressure attenuation factor with respect to the residual stress of a metal material in the ultrasonic metal fatigue damage degree measurement of this invention. In the measurement of the ultrasonic metal fatigue damage degree according to one embodiment of the present invention, the propagation time (a) and the sound pressure decay rate with respect to the fatigue level N / Nf (N: number of repeated weights, Nf: number of repeated loads leading to fracture) ( It is a graph which shows the relationship of b). It is a front view which shows the test piece shape of the magnesium alloy used for the ultrasonic metal fatigue damage degree measurement of the said Example. It is a graph which shows the result of having applied the same load in the test piece of the same lot as what was used for the test of the said Example, and measuring the residual stress by X-ray diffraction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ultrasonic metal fatigue damage measuring apparatus 12 Metal material 14 Transmitters 14a and 16a Probe part 14b Ultrasonic output part 15 Oscillation circuit part 16 Receiver 16b Ultrasonic reception part 17 Reception circuit part 20 Main body part 32 Arithmetic processing device

Claims (6)

  A transmitter that contacts the surface of the metal material and transmits ultrasonic waves, a receiver that receives the ultrasonic waves propagated in the vicinity of the surface of the metal material, and the transmitter and receiver are separated from each other and held together. And measuring the sound pressure attenuation rate or propagation time when the ultrasonic wave propagates in the vicinity of the surface of the metal material, the sound pressure attenuation rate or propagation time with respect to a known degree of metal fatigue damage, A non-destructive evaluation method for the degree of metal fatigue damage, characterized in that the metal fatigue damage degree of the metal material is calculated by comparing the sound pressure attenuation rate or propagation time obtained by the measurement.   The metal fatigue level measurement unit on the surface of the metal material is coated with a liquid medium that ensures close contact with the surface of the metal material and improves the propagation of ultrasonic waves on the surface of the metal material, and the transmitter. The non-destructive evaluation of the degree of metal fatigue damage according to claim 1, wherein a pair of probe parts each attached to a receiver and in contact with the solid surface are brought into contact with the metal fatigue degree measurement part via the medium. Method.   The non-destructive evaluation method for metal fatigue damage degree according to claim 1, wherein an SH wave is used as the ultrasonic wave.   The method for nondestructive evaluation of the degree of metal fatigue damage according to claim 1, wherein the metal member is a metal material having a hexagonal crystal structure.   A transmitter that contacts the surface of the metal material and transmits ultrasonic waves, a receiver that receives the ultrasonic waves propagated in the vicinity of the surface of the metal material, and the transmitter and the receiver are separated from each other by a certain distance. Main body held, measuring means for measuring the sound pressure attenuation rate or propagation time when the ultrasonic wave propagates near the surface of the metal material, and the amount of change in the history data of the measured sound pressure attenuation rate or propagation time An ultrasonic metal fatigue damage degree measuring apparatus comprising: a calculation means for analyzing and calculating the metal fatigue damage degree of the metal material based on the above. The main body is formed in a U-shape, the transmitter is provided at one end of the U-shaped main body, and the ultrasonic output unit of the transmitter faces the metal material surface side and receives the signal. The receiver is provided at the other end of the U-shaped main body, and the ultrasonic receiver of the receiver faces the metal material surface side and the transmitter side. 6. A probe unit that is positioned facing the transmitter and that is in contact with the surface of the metal material is provided on each of the ultrasonic output unit of the transmitter and the ultrasonic receiver unit of the receiver. Ultrasonic metal fatigue damage measuring device.

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