JP4243702B2 - Measurement method of sound velocity distribution inside material - Google Patents

Description

The present invention relates to a method for measuring sound velocity distribution in a plate-like material and a tubular material in an ultrasonic resonance method for measuring the material of a plate-like material and a tubular material and measuring internal stress.

It is well known that the ultrasonic resonance method is effective for measuring the thickness of metal materials, measuring materials, and measuring internal stress.
Japanese Patent Laid-Open No. 6-118064 discloses a method for measuring the material of a metal plate by an electromagnetic ultrasonic resonance method capable of transmitting and receiving ultrasonic waves without contact with a material to be tested. Japanese Patent Laid-Open No. 10-48068 discloses a method for measuring internal stress of metal using electromagnetic ultrasonic waves. Japanese Patent Laid-Open No. 9-280969 discloses a method for measuring internal stress of a metal tube using electromagnetic ultrasonic waves. Supervised by Junichi Miyoshi, Yoshimitsu Kikuchi, Otohiko Kumamoto, “Ultrasonic Technology Handbook, New Edition”, Nikkan Kogyo Shimbun, published May 25, 1989, p737-738 describes the principle of ultrasonic resonance method Yes. Takao Omoguchi, Toshio Akagi, Yasuhiro Kawashima et al., “Development of on-line r-value measurement technology for cold-rolled steel sheets by resonant electromagnetic ultrasonic method”, Iron and Steel, Vol. 79 (1993) p139-144 describes the principle and experimental results of an electromagnetic ultrasonic resonance method capable of transmitting and receiving ultrasonic waves without contact with the material under test. Hiroyuki Tsuji, Masahiko Hirao, Hidekazu Fukuoka, “Acoustoelastic Stress Measurement of Thin Metal Sheets by Electromagnetic Ultrasonic Resonance”, The Japan Society of Mechanical Engineers (A), Volume 60, No. 569 (1994-1) Describes the principle and experimental results of the electromagnetic ultrasonic resonance method that can transmit and receive ultrasonic waves without contact.

式（１）においてｄは板状材料の厚さ、λは超音波の波長、ｎは正の整数である。すなわち板状材料の厚さが超音波の波長の半分の整数倍のときに超音波の共振がおこるといえる。ｎが１，２，３．．．のときの共振をそれぞれ１次、２次、３次．．．の共振という。
一方、超音波の速度Ｖ、波長λ、周波数ｆの間に次の（２）式が成り立つことは一般的によく知られている。

式（１）、（２）より次の式（３）を導くことができる。

式（３）のｆはｎ次の共振のときの周波数であるのでこれを明確に示すためにｆ_ｎと書き直すと次の式（４）ができる。

式（４）より、板状材料の厚さｄを測定し、ｎ次共振周波数ｆ_ｎを測定することにより板状材料内部の超音波の速度Ｖを知ることができる。板状材料内部の超音波の速度Ｖが板状材料の内部応力や材質に関連していることはよく知られている。上記の特許文献１、非特許文献２、非特許文献３はこのことを利用したものであり、金属板内部の超音波の速度Ｖを測定し、それより金属板の内部応力や材質を判定している。FIG. 2 is a schematic diagram of the ultrasonic resonance method. An ultrasonic transducer 1 is used for both transmission and reception of ultrasonic waves. Reference numeral 2 denotes a plate-like material, which is a material to be tested. Its thickness is d. When an AC voltage is applied to the ultrasonic vibrator 1 and the frequency of the AC voltage is continuously changed, according to the non-patent document 1, a super Resonance of sound waves occurs.

In formula (1), d is the thickness of the plate-like material, λ is the wavelength of the ultrasonic wave, and n is a positive integer. That is, it can be said that ultrasonic resonance occurs when the thickness of the plate-like material is an integral multiple of half the wavelength of the ultrasonic wave. n is 1, 2, 3,. . . Resonance at first, second, third,. . . This is called resonance.
On the other hand, it is generally well known that the following equation (2) holds between the ultrasonic velocity V, wavelength λ, and frequency f.

The following equation (3) can be derived from equations (1) and (2).

F is this rewritten as f _n to clearly show it is the following equation (4) because the frequency in the case of n-order resonance of the formula (3).

From equation (4), the thickness d of the plate-like material is measured, and the ultrasonic velocity V inside the plate-like material can be known by measuring the _n- th resonance frequency f _n . It is well known that the ultrasonic velocity V inside the plate-like material is related to the internal stress or material of the plate-like material. The above-mentioned Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3 make use of this fact, and measure the ultrasonic velocity V inside the metal plate to determine the internal stress and material of the metal plate. ing.

The inventions disclosed in Patent Literature 1, Non-Patent Literature 2, and Non-Patent Literature 3 basically use Equation (4), and the ultrasonic velocity V inside the metal plate is the test object. It is assumed that the inside of the metal plate is constant regardless of the depth from the surface. Therefore, it can be said that it can be measured only when the material and internal stress are constant inside the metal plate regardless of the depth from the surface. However, it is well known that in an actual metal plate, the material and internal stress are often not constant depending on the depth from the surface due to rolling or heat treatment. Therefore, the invention disclosed in Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3 cannot be applied when the material and internal stress are not constant depending on the depth from the surface inside the metal plate.

In order to solve the above problems, the present invention provides an ultrasonic resonance method that can be applied even when the velocity V of the ultrasonic wave inside the material is not constant depending on the depth from the surface.
The invention according to claim 1 is characterized in that a plurality of resonance frequencies are measured in the ultrasonic resonance method, and the distribution of ultrasonic velocity inside the material is determined from the result of calculating these values. Conventionally, the resonance frequencies f ₁ , f ₂ , f ₃ ,... Were considered to be directly proportional to the order of resonance. Therefore, it has been considered from equation (4) that the ultrasonic velocity V having the same value can be obtained using any resonance frequency among f ₁ , f ₂ , f ₃ ,. The inventor of the present invention has incomplete the conventional idea, and when the velocity V of the ultrasonic wave inside the plate-like material is not constant depending on the depth from the surface, the resonance frequencies f ₁ , f ₂ , f ₃ ,. They discovered that it was not directly proportional to the order of resonance, but slightly deviated from direct proportionality, and invented a method for determining the distribution of ultrasonic velocities inside the material from the result of calculating those values.

The invention according to claim 2 is the ultrasonic resonance method in which a plurality of resonance frequencies are measured, a sum of values obtained by multiplying each of the plurality of resonance frequencies of the first order and the fifth order by a numerical value, a second order and more and It is characterized in that the ultrasonic velocity distribution inside the plate-like material and the tubular material is determined from the sum of the values obtained by multiplying each of a plurality of resonance frequencies of the 20th order or lower by a numerical value.

According to a third aspect of the present invention, in the ultrasonic resonance method according to the first and second aspects, the material quality and internal stress of the material are determined from the distribution of ultrasonic velocity inside the material.

The best mode for carrying out the invention is the invention according to claim 3, and from the distribution of ultrasonic velocity inside the material measured by the ultrasonic resonance method according to claim 1 and claim 2, the material The ultrasonic resonance method is characterized in that the material and the internal stress are determined. The ultrasonic resonance method may be an electromagnetic ultrasonic resonance method or an ultrasonic resonance method using a piezoelectric vibrator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on examples with reference to the drawings. FIG. 1 is a schematic diagram showing an outline of a resonant electromagnetic ultrasonic inspection apparatus as an example of an embodiment of the invention. Since Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3 disclose resonant electromagnetic ultrasonic inspection apparatuses, only a schematic diagram is shown. In FIG. 1, 3 is a resonant electromagnetic ultrasonic transmitter / receiver, 4 is an electromagnetic ultrasonic transducer, and 5 is a steel plate having a thickness of 15 mm, which is an object to be inspected. 6 shows the amplitude distribution of the standing wave of the transverse ultrasonic wave generated by the resonance in the steel plate. The electromagnetic ultrasonic transducer 4 transmits and receives transverse wave ultrasonic waves. It is well known that ultrasonic waves propagating in solids such as metals include longitudinal wave ultrasonic waves whose traveling direction and vibration direction are parallel, and transverse wave ultrasonic waves whose traveling direction and vibration direction are perpendicular. Detailed description is omitted. The measurement is performed by sweeping the frequency of the resonant electromagnetic ultrasonic transceiver 3.

FIG. 3 shows digital measurement data obtained by the resonant electromagnetic ultrasonic inspection apparatus of FIG. The horizontal axis represents the frequency swept by the resonant electromagnetic ultrasonic transmitter / receiver 3, and the vertical axis represents the amplitude of the transverse ultrasonic wave obtained by the measurement. Resonance of the ultrasound at the amplitude of the transverse ultrasonic waves are represented by particularly large S _{n (n} = 1~20) is occurring in FIG. n represents the order of resonance. The resonance frequency at which ultrasonic resonance occurs is f _n (n = 1 to 20). The subscript n represents the order of resonance. f ₁ was measured as 1.007 MHz. Conventionally, these resonance frequencies f _n are directly proportional to the resonance order n, and the ultrasonic sound velocity V obtained by substituting the resonance frequency f _n and the resonance order n into the equation (4) is a value of n. Regardless, they have all been equal.
However, as a result of careful examination of the digital measurement data shown in FIG. 3, the present inventor has found that these resonance frequencies f _n are not directly proportional to the resonance order n, and therefore, the sound speed of the ultrasonic wave obtained by the equation (4) is all. I found it slightly different.

FIG. 4 shows the relationship between the resonance frequency f _n and the resonance order n obtained by carefully examining the measurement data of FIG. In FIG. 4, the horizontal axis represents the order of resonance, and the vertical axis represents the resonance frequency. FIG. 4 shows that the resonance frequency f _n is not directly proportional to the resonance order n. The straight line 7 is a straight line representing the relationship when it is assumed that the resonance frequency is directly proportional to the order of resonance. In order to emphasize that the resonance frequency f _n is not directly proportional to the resonance order n, the deviation from the straight line 7 is drawn larger than actual.

In order to show this more clearly, (f _n / n), which is a value obtained by dividing each resonance frequency f _n by n, is further divided by (f _n / n) / f ₁ by the primary resonance frequency f _1. FIG. 5 shows the relationship between the calculation and the resonance order n. In FIG. 5, the horizontal axis represents the order of resonance, and the vertical axis represents (f _n / n) / f ₁ . Referring to FIG. _{5 (f 1/1) /} f 1 = 1, (f 2/2) / f 1 = 1.0076, (f 3/3) / f 1 = 1.0090, (f 4/4 _{) / f 1 = 1.0095, (} f 5/5) / f 1 = 1.0097, a, thereafter is slightly increases with increasing _(f n / n) / value of _{f 1} is n, When n is 2 or more, the rate of increase is small and is almost constant 1.01. That is, the value of (f _n / n) / f ₁ where n is 2 or more and 20 or less is substantially equal to 1.01. Therefore, if n is 2 or more, it can be said that the error is small even if (f _n / n) = f ₁ × 1.01 = 1.0171 MHz. Thus, when (f _n / n) where n is 10, that is, (f ₁₀ /10)=1.0171 MHz is used, the ultrasonic sound velocity is calculated from Equation (4) to be 3051 m / s.

After such measurement, the steel plate 5 with a thickness of 15 mm in FIG. The results are shown in FIG. The horizontal axis in FIG. 6 represents the depth from the surface, and the vertical axis represents the ultrasonic velocity at that depth. As a result, the sound velocity of the ultrasonic wave inside the original steel plate 5 varies depending on the depth from the surface, the ultrasonic sound velocity is 3150 m / s at the maximum near the surface, and the ultrasonic sound velocity is minimum at the center, 3000 m / s. I found out that The ratio is 3150/3000 = 1.05. Further, it was found that the ultrasonic sound velocity distribution is a quadratic curve with respect to the depth from the surface and the center, and the average ultrasonic sound velocity is 3050 m / s.

For the other five different steel plates (thickness is 15 mm), the measurement of the resonance frequency and the ultrasonic speed of sound after slicing were performed in the same manner as described above. 7 and 8 show the measurement results of the steel plate 5 and other five different steel plates, that is, a total of six steel plates. 7, the horizontal axis is the value of the resonance was measured by an electromagnetic ultrasonic inspection apparatus _{(f 10/10) / f} 1. The vertical axis in FIG. 7 is the ratio between the ultrasonic sound velocity V _S near the surface and the central ultrasonic sound velocity V _C measured after slicing the steel sheet. From the value of (f _10/10 ) / f ₁ measured by the resonance electromagnetic ultrasonic inspection apparatus from FIG. 7, the ratio between the ultrasonic velocity V _S near the surface and the ultrasonic velocity V _C at the center is expressed by the following equation. Can be sought.
_{V S / V C = 5 (} f 10/10) / f 1 -4 (5)
If n is 2 or more because _(f n / n) / value of _{f 1} is approximately _equal, in place of _{(f 10/10) / f} 1, n is other than 2 _(f n / n) Needless to say, the same result can be obtained by using / f ₁ . It goes without saying that substantially the same result can be obtained even if an average value of a plurality of (f _n / n) / f ₁ having an arbitrary n of 2 or more is used.

ることができる。ここでｄは鋼板の厚さである。

ｎが２以上であれば（ｆ_ｎ／ｎ）の値はほぼ等しいので、（ｆ_１０／１０）のかわりに、ｎが２以上である他の（ｆ_ｎ／ｎ）を使ってもほぼ同じ結果が得られることはいうまでもない。
超音波の音速分布が表面からの深さに関して２次曲線状で且つ中心に関して対象である場合は、平均の超音波音速と、鋼板の表面近くの超音波音速と中心の超音波音速との比の両方がわかれば超音波の音速分布を完全に知ることができることは数学的にも自明である。このようにして共振電磁超音波検査装置による測定結果より鋼板内部の定量的超音波音速の分布を判定することができることがわかった。The horizontal axis of FIG. 8 is an ultrasonic sound velocity of calculating the value of which is determined by the resonant electromagnetic ultrasonic inspection apparatus (f _10/10) into Equation (4). The vertical axis | shaft of FIG. 8 is the average ultrasonic sound speed measured after slicing the steel plate.
From FIG. 8, the ultrasonic sound velocity calculated by substituting the value of (f _10/10 ) measured by the resonance electromagnetic ultrasonic inspection apparatus into the equation (4) and the average ultrasonic sound measured after slicing the steel sheet.

Can. Here, d is the thickness of the steel plate.

If n is 2 or more, the value of (f _n / n) is almost equal. Therefore, instead of (f _10/10 ), it is almost the same if another (f _n / n) _where n is 2 or more is used. It goes without saying that results are obtained.
When the ultrasonic sound velocity distribution is a quadratic curve with respect to the depth from the surface and the object is the center, the ratio of the average ultrasonic sound velocity to the ultrasonic sound velocity near the surface of the steel sheet and the ultrasonic sound velocity at the center. It is also mathematically obvious that if both of these are known, the ultrasonic velocity distribution can be completely known. In this way, it was found that the distribution of quantitative ultrasonic sound velocity inside the steel sheet can be determined from the measurement result by the resonance electromagnetic ultrasonic inspection apparatus.

ｐ_ｎは０より大きく１より小さい正の数である。
次に式（８）により鋼板の表面近くの超音波音速Ｖ_Ｓと中心の超音波音速Ｖ_Ｃとの比をもとめる。

ｑ_ｎは０より大きく１より小さい正の数である。
ｐ_ｎとｑ_ｎの値としては次のような値を選ぶとよいことがわかった。
ｐ_２＝１．００２４，ｐ_３＝１．００１，ｐ_４＝１．０００５，ｐ_５＝１．０００３，ｐ_６〜ｐ_２０＝１．００ｑ_１＝１．０００、ｑ_２＝０．９９２５、ｑ_３＝０．９９１１、ｑ_４＝０．９９０６，ｑ_５＝０．９９０４そしてこうしてもとめられた平均の超音波音速と、鋼板の表面近くの超音波音速と中心の超音波音速との比の両方より鋼板内部の超音波の音速分布を判定したところ鋼板をスライスして測定した超音波の音速分布とほぼ等しいことがわかった。このほかにもさまざまなｐ_ｎ、ｑ_ｎの値の組み合わせが可能であることもわかった。共振の次数ｎが２１以上のｆ_ｎは測定の誤差の範囲内で全く同じ値であることが実験によりわかった。したがって次数ｎが２１以上のｆ_ｎを利用する価値がないこともわかった。It was found that the quantitative distribution of the ultrasonic sound velocity inside the steel sheet can also be determined from the measurement result obtained by the resonance electromagnetic ultrasonic inspection apparatus by the following method different from the calculation method used in Example 1.

_pn is a positive number greater than 0 and less than 1.
Next, the ratio between the ultrasonic sound velocity V _S near the surface of the steel sheet and the central ultrasonic sound velocity V _C is obtained by equation (8).

q _n is a positive number greater than 0 and less than 1.
The value of p _n and q _n was found to be a good choice values as follows.
_{p 2 = 1.0024, p 3 =} 1.001, p 4 = 1.0005, p 5 = 1.0003, p 6 ~p 20 = 1.00q 1 = 1.000, q 2 = 0.9925, q ₃ = 0.9911, q ₄ = 0.9906, q ₅ = 0.9904 and the ratio of the average ultrasonic velocity thus determined to the ultrasonic velocity near the surface of the steel sheet and the ultrasonic velocity at the center The ultrasonic velocity distribution inside the steel plate was judged from both, and it was found that it was almost equal to the ultrasonic velocity distribution measured by slicing the steel plate. In addition to various well of p _n, also it has been found that it is possible combination of values of q _n. Order n 21 or more f _n of the resonance that is exactly the same value in the range of measurement error was found by experiments. Therefore, it was also found that it is not worth using f _n of order n of 21 or more.

The present invention can be applied not only to transverse wave ultrasound but also to longitudinal wave ultrasound. The present invention can be applied not only to plate-like materials but also to tubular materials, as long as the tube wall is not extremely curved and has a relatively large diameter. The present invention can be applied by a combination of appropriate p _n and q _n even if the sound velocity distribution in the ultrasonic wave is not a quadratic curve shape with respect to depth from the surface. Further, the present invention can be applied by appropriately selecting and calculating not only an expression including only f _n such as Expressions (7) and (8) but also an expression including a term _equal to or larger than the square of f _n . Alternatively applicable by appropriately Pick computing functions including f _n.

The invention's effect

As described above, according to the present invention, the following excellent effects can be obtained. With any one of the ultrasonic resonance methods described in claims 1 and 2, sound velocity distribution measurement along the thickness direction inside the plate-like material or tubular material can be realized. On the other hand, the relationship between the acoustic velocity of the ultrasonic wave propagating through the plate-like material or the tubular material and the residual stress or the material property is [Patent Document 1], [Patent Document 2] [Patent Document 3], [Non-Patent Document 1], [ It has been clarified in many documents such as Non-Patent Document 2] and [Non-Patent Document 3]. That is, the ultrasonic resonance method described in claim 3 is used to measure the distribution of residual stress along the thickness direction inside the plate-like or tubular material, which has been impossible until now, Measurement can be realized with high reliability.

The present invention can be applied not only to a plate-like material but also to a tubular material as long as the tube wall is not extremely curved and has a relatively large diameter. In the steel industry and the aluminum industry, it can be used for measuring the distribution of residual stress inside the plate-like material and tubular material and measuring the distribution of material properties.

It is a schematic diagram which shows the outline | summary of a resonance electromagnetic ultrasonic inspection apparatus. It is the schematic of an ultrasonic resonance method. FIG. 2 shows digital measurement data obtained by a resonance electromagnetic ultrasonic inspection apparatus (FIG. 1). The horizontal axis represents the frequency swept by the resonant electromagnetic ultrasonic wave transmitter / receiver 3 in FIG. 1, and the vertical axis represents the amplitude of the transverse wave ultrasonic wave obtained by the measurement. It shows the relationship between the order n of the resonance and the resonance frequency f _n. The horizontal axis is the order of resonance, and the vertical axis is the resonance frequency. The relationship between (f _n / n) / f ₁ and the resonance order n is shown. The horizontal axis is the resonance order n, and the vertical axis is (f _n / n) / f ₁ . 1 shows a result of slicing the steel plate 5 of FIG. 1 into 11 thin steel plates along a plane parallel to the surface and measuring the speed of sound thereof. The horizontal axis represents the depth from the surface, and the vertical axis represents the ultrasonic sound velocity at that depth. The ratio between (f _10/10 ) / f ₁ measured by the resonance electromagnetic ultrasonic inspection apparatus (FIG. 1) and the ultrasonic sound velocity V _S near the surface measured after slicing the steel sheet and the ultrasonic sound velocity V _C at the center Shows the relationship. The horizontal axis is the value of (f _10/10 ) / f ₁ , and the vertical axis is the ratio between V _S and V _C. The relationship between the ultrasonic sound speed calculated from the value of (f _10/10 ) measured by the resonance electromagnetic ultrasonic inspection apparatus (FIG. 1) and the average value of the ultrasonic sound speed measured after slicing the steel sheet is shown. The horizontal axis represents the ultrasonic sound velocity calculated from the value of (f _10/10 ), and the vertical axis represents the average value of the ultrasonic sound velocity measured after slicing the steel sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic transducer 2 Plate-shaped material 3 Resonance electromagnetic ultrasonic transmitter / receiver 4 Electromagnetic ultrasonic transducer 5 15 mm-thick steel plate 6 Amplitude distribution of standing wave of transverse wave generated by resonance in the steel plate 7 Resonance frequency is A straight line representing the relationship when it is assumed to be directly proportional to the order of resonance

Claims (3)

In the ultrasonic resonance method, the primary resonance frequency and the resonance frequency of the second order to the twentieth order are measured, and the value of the ratio between the resonance frequency of the second order and the twentieth order and the primary resonance frequency is obtained. The ultrasonic wave characterized by determining the change in the thickness direction of the velocity of the ultrasonic wave propagating while changing the velocity as it propagates in the direction of the thickness in the plate material and the tubular material from the value of the ratio Resonance method. In the ultrasonic resonance method, a primary resonance frequency and a resonance frequency from the second order to the twentieth order are measured, and an average of the plurality of resonance frequencies of the resonance frequencies from the second order to the twentieth order and the first order is calculated. Find the value of the ratio to the resonance frequency, and the change in the thickness direction of the velocity of the ultrasonic wave propagating while the velocity changes as the value propagates through the plate and tubular materials in the thickness direction. An ultrasonic resonance method characterized by determining. 3. The ultrasonic resonance method according to claim 1, wherein the change in the thickness direction of the plate material and the tubular material and the thickness direction of the internal stress is determined from the change in the thickness direction of the ultrasonic velocity. The ultrasonic resonance method.

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