JP3644628B2 - Stress measuring method and apparatus using magnetic anisotropy sensor - Google Patents

Description

ここでは、上磁芯５による出力を消磁方向θ＝０としてＶ（０，σ）と表し、下磁芯６による出力を消磁方向θ＝π／２としてＶ（π／２，σ）と表している。
【００２６】
ところが、実際のＭＡＳの出力Ｖ（θ，σ）は、本来の応力による出力Ｖｓに、被測定物の形状に依存する見掛けの出力Ｖｃが加えられている。したがって、Ｖは次式で与えられる。
【数２】

さらに、本来の応力による出力Ｖｓは、リフトオフの距離δにも依存するため、ある測定方向における応力をＡ（σ）とすると、次式で表される。
【数３】

ここに、Δは無視できる程度の定数（δの１／１０以下）を表す。
【００２７】
ここで、被測定物１０の測定部位がＭＡＳの寸法に比べて十分広い（約３倍以上）平面でない場合は、ＭＡＳの出力Ｖには、測定部位の曲率や測定部位近傍の端部の形状等により、見掛けの出力Ｖｃが含まれる。ところが、この見掛けの出力Ｖｃはリフトオフの距離δには鈍感であり、逆に本来の応力による出力Ｖｓはリフトオフの距離δに極めて敏感である。そこで、実際の測定の際にリフトオフの距離δを大きくとると（ＭＡＳを被測定物１０から少し離すようにする）、本来の応力による出力Ｖｓは無視できるほど小さくなり、図７に示すように、見掛けの出力Ｖｃのみが測定できる。したがって、ＭＡＳの出力Ｖから見掛けの出力Ｖｃを差し引くと、本来の応力による出力Ｖｓが得られる。
【００２８】
したがって、上述した消磁方向θ、応力σ及びリフトオフの距離δを考慮すると、一般的なＭＡＳの出力は、これらθ、σ及びδの関数として次式で表される。
【数４】

なお、この式において、見掛けの出力ＶｃはＶ（θ，σ，∞）を意味する。
【００２９】
そこで、演算器１８では、リフトオフの距離δの影響をなくすために、第１の測定値Ｖ（０，σ，δ）と第２の測定値Ｖ（π／２，σ，δ）との平均値から見掛けの出力Ｖｃ＝Ｖ（θ，σ，∞）を引き算して、その結果を第１の測定値と第２の測定値との差｛Ｖ（０，σ，δ）−Ｖ（π／２，σ，δ）｝で割ることにより、被測定物における応力に対応する出力Ｕを演算する。
【数５】

【００３０】
上式からわかるように、出力Ｕはリフトオフの距離δには依存しないことがわかる。これにより、ＭＡＳの出力は、図８に示すような直線化されたものとなる。すなわち、図４（Ａ）における消磁方向θ＝０とθ＝π／２に注目すると、これら両曲線の出力差は、図４（Ｂ）に示すように応力の小さいところでは大きく、大きいところでは小さい。そこで、これら両曲線の平均、すなわち中央の曲線で表される出力を各応力において出力差で割ることにより、図８に示すような広い範囲で直線化された関係を得ることができる。このため、応力感度χが一定になり、残留応力の存在にかかわらず外力による応力σ_apを求めることができる。
【００３１】
このＭＡＳの演算結果は、図６に示すステップ（ｆ）において表示器１９で表示する。なお、測定器１を当てて電源をＯＮにしてから、ステップ（ａ）〜（ｆ）を終了するまでのトータルの所要時間は、約２秒程度である。
【００３２】
【発明の効果】
以上の説明から明らかなように、本発明によれば、第１の測定値と第２の測定値との平均値から、上記センサを上記被測定物から離して磁化の強さを測定することにより得られた値を引き算して、その結果を第１の測定値と第２の測定値との差で割ることにより、被測定物における応力に対応する出力値が広い範囲で直線になって、応力感度χが一定になるので、残留応力や、被測定物表面の塗料や被覆物、錆等の存在とは無関係に、より正確な応力測定を行うことができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る応力測定装置の測定器を示す図であり、（Ａ）は斜視図、（Ｂ）は下側から見た図である。
【図２】ＭＡＳを用いた応力測定の原理を説明するための図である。
【図３】同応力測定装置の全体構成を示すブロック図である。
【図４】図４（Ａ）は、ＭＡＳ出力と応力の関係を表す図であり、図４（Ｂ）は、消磁方向によるＭＡＳ出力の差を表す図である。
【図５】図５（Ａ）は、二軸圧縮の場合のＭＡＳ出力と応力の関係を表す図であり、図５（Ｂ）は、一軸圧縮の場合のＭＡＳ出力と応力の関係を表す図である。
【図６】本実施形態に係る応力測定方法の測定手順を説明するための説明図である。
【図７】ＭＡＳ出力とリフトオフの関係を表す図である。
【図８】本発明を適用した場合のＭＡＳ出力と応力の関係を表す図である。
【符号の説明】
１ 測定器 ２ 消磁器
３ 磁気異方性センサ（ＭＡＳ） ４Ａ、４Ｂ 磁芯
５、６ 磁芯 ５Ａ、６Ａ 消磁用コイル
１０ 被測定物
１２、１３ 発振器 １５ 制御回路
１６ 増幅器 １７ 同期整流器
１８ 演算器 １９ 表示器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for non-destructively measuring stress in steel structures such as railroad rails or steel machine parts. In particular, stress using a magnetic anisotropy sensor that can perform more accurate stress measurement regardless of the residual stress in the object to be measured and the presence of paint, coating, rust, etc. on the surface of the object to be measured. The present invention relates to a measurement method and apparatus.
[0002]
[Prior art and problems to be solved by the invention]
In the stress measurement of steel products, a method using a magnetic anisotropy sensor (abbreviated as MAS) has been conventionally known. This method has many advantages such as being able to measure in a short time, measuring apparatus being small and inexpensive, and having a high degree of freedom in measurement. However, on the other hand, if the surface of the object to be measured has paint, coating, rust, etc., there is a disadvantage that the measured value is easily influenced by lift-off. In addition, the lift-off here means the distance from the magnetic core of the sensor to the object to be measured.
[0003]
As a conventional example of this type of stress measuring apparatus, for example, Japanese Patent Publication No. 6-95052 by the present inventor can be cited. The stress measuring device disclosed in this publication can measure stress irrespective of lift-off regardless of the presence or absence of paint, coating, rust, and the like.
[0004]
The stress measuring device of the above publication includes a magnetic anisotropy sensor having two U-shaped magnetic cores orthogonal to each other. An excitation coil and a lift-off detection coil are wound around one magnetic core of the sensor, and a magnetic potential difference detection coil is wound around the other magnetic core. The exciting coil is connected to an oscillator. From this oscillator, a steady current is supplied to the exciting coil. The lift-off detection coil is connected to the rectifier through an amplifier. On the other hand, the magnetic potential difference detection coil is connected to a synchronous rectifier through an amplifier. In this synchronous rectifier, the output voltage of the magnetic potential difference detection coil is rectified in synchronization with the signal of the oscillator. The synchronous rectifier and the rectifier are connected to the arithmetic unit. In this computing unit, the output ratio V ₁ (δ, σ) of the synchronous rectifier, the output voltage V ₂ (δ) of the rectifier, and the output voltage V ₂ (∞) of the rectifier when there is no measurement object are output ratios. V ₁ (δ, σ) / {V ₂ (δ) −V ₂ (∞)} is calculated. Here, δ represents lift-off, and σ represents stress. The output of the computing unit is displayed on the display unit connected to the computing unit.
[0005]
According to the magnetic anisotropy sensor of this stress measuring apparatus, the lift-off between the tip of the magnetic core wound with the excitation coil and the lift-off detection coil and the tip of the magnetic core wound with the magnetic potential difference detection coil is detected. The difference can be adjusted. Thereby, the lift-off characteristics can be matched between the output of the lift-off detection coil and the output of the magnetic potential difference detection coil. That is, by adjusting the difference in lift-off, the value of the output ratio V ₁ (δ, σ) / {V ₂ (δ) −V ₂ (∞)} calculated by the calculator is made independent of lift-off. can do.
[0006]
The relationship between the measured value (sensor output value) V and the stress σ of the object to be measured is generally non-linear and becomes a curve when drawn on a graph. If the relationship between V and σ is a curve, the stress sensitivity χ (= dV / dσ) differs at each part of the curve. When an external force is acting on an object having unknown residual stress, the stress sensitivity χ _ap is not determined, so the stress σ _ap due to the external force cannot be measured accurately.
The present invention has been made in view of the above, and in stress measurement using a magnetic anisotropy sensor, stress measurement capable of performing more accurate stress measurement by eliminating the effects of residual stress and lift-off It is an object to provide a method and apparatus.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, a stress measurement method according to the present invention includes (a) a step of demagnetizing an object to be measured by applying a damped alternating magnetic field in a first direction, and (b) the object to be measured using a sensor. Obtaining a first measurement value by applying a predetermined alternating magnetic field to the object and measuring the magnetization intensity in the first direction; and (c) orthogonal to the first direction with respect to the object to be measured. Demagnetizing by applying a damped alternating magnetic field in the second direction; and (d) measuring a magnetization intensity in the first direction by applying a predetermined alternating magnetic field to the object to be measured using the sensor. And (e) measuring the strength of magnetization by separating the sensor from the object to be measured from the average value of the first measurement value and the second measurement value. by subtracting the obtained value, the resulting first measurement and the second By dividing the difference between the value comprises a step of obtaining a value corresponding to the stress in the measurement object.
[0008]
According to the present invention, the value obtained by measuring the magnetization intensity by separating the sensor from the object to be measured is subtracted from the average value of the first measurement value and the second measurement value. By dividing the result by the difference between the first measurement value and the second measurement value, the output value corresponding to the stress in the object to be measured becomes a straight line in a wide range. Therefore, the stress sensitivity χ becomes constant, and the stress σ _ap due to the external force can be obtained regardless of the presence of the residual stress. Further, since the lift-off δ term is eliminated, the influence of lift-off can be eliminated.
[0009]
In the stress measurement method, in the step (b), an alternating magnetic field is applied to the object to be measured in a third direction different from the first and second directions, and the intensity of magnetization in the first direction is determined. Preferably, the step (d) includes a step of applying a predetermined alternating magnetic field to the device under test in a third direction to measure the strength of magnetization in the first direction.
[0010]
The stress measuring device according to the present invention includes a demagnetizer for demagnetizing the device under test by applying a decaying AC magnetic field in a first direction and a second direction orthogonal to each other, and a predetermined amount for the device under test. A sensor for measuring the strength of magnetization by applying an alternating magnetic field, a current to the demagnetizer to generate a damped alternating magnetic field, and a current to the sensor to generate a predetermined alternating magnetic field 1 and one or more Oscillator, after degauss the measuring object in a first direction, measuring the intensity of magnetization in a first direction by applying a predetermined AC magnetic field to the measurement object To obtain a first measurement value, and after demagnetizing the object to be measured in the second direction, a predetermined alternating magnetic field is applied to the object to be measured to measure the strength of magnetization . so as to obtain a second measurement in the direction, control at least the Oscillator A control circuit for, from the average value of the first measurement value and second measurement value, the sensor by subtracting a value obtained by measuring the intensity of magnetization away from the measurement object, An arithmetic unit for obtaining a value corresponding to the stress in the measured object by dividing the result by the difference between the first measured value and the second measured value.
[0011]
The stress measuring device preferably further includes means for amplifying the output of the sensor and synchronously rectifying the current that generates a predetermined alternating magnetic field. With this means for synchronous rectification, it is possible to determine whether the uniaxial stress is positive or negative (tensile / compressed).
[0012]
Further, in the stress measuring apparatus, the sensor applies a predetermined alternating magnetic field to the object to be measured in a third direction different from the first and second directions, and obtains the strength of magnetization in the first direction. Can be measured.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A and 1B are diagrams showing a measuring instrument of a stress measuring device according to an embodiment of the present invention, in which FIG. 1A is a perspective view and FIG.
As shown in FIG. 1A, the measuring instrument 1 includes a demagnetizer 2 and a magnetic anisotropy sensor (MAS) 3. The demagnetizer 2 includes two upper and lower U-shaped magnetic cores 5 and 6 made of, for example, a laminated silicon steel plate or ferrite. The upper magnetic core 5 and the lower magnetic core 6 are orthogonal to each other in the first and second directions. Demagnetizing coils 5A and 6A are wound around the magnetic cores 5 and 6, respectively. The MAS 3 is disposed at the center position of the demagnetizer 2. As shown in FIG. 1B, the MAS 3 includes an exciting magnetic core 4A provided in the X direction that forms an angle of 45 ° with the first direction, and a detecting magnetic core provided in the Y direction. 4B is embedded. An excitation coil and a detection coil are wound around each of the magnetic cores 4A and 4B. The demagnetizer 2 and the MAS 3 are integrally molded in a casing (not shown) of the measuring instrument 1.
[0014]
Here, the measurement principle of MAS will be described with reference to FIG. As shown in FIG. 2, when a quadruped MAS is placed on a measurement object on which main stresses σ ₁ and σ ₂ are applied, the magnetic flux emitted from E _{1 of the} exciting core 4A is measured. toward the E ₂ spreads the surface. A part of it goes to E ₂ through a path (indicated by a solid line and a broken line arrow) passing through the detection magnetic core 4B having a high magnetic permeability. When σ ₁ > σ ₂ , the magnetic permeability in the σ ₁ direction is larger than the magnetic permeability in the σ ₂ direction, and the magnetic flux indicated by the solid line is larger than the magnetic flux indicated by the broken line. The magnetic flux passing through the detection core is the difference between the two magnetic fluxes. Based on the output of the MAS, the main stress difference σ ₁ −σ ₂ can be measured.
[0015]
Next, the overall configuration of the stress measuring device will be described with reference to FIG.
FIG. 3 is a block diagram showing the overall configuration of the stress measuring apparatus.
This stress measuring device is roughly divided into the following components.
(1) Oscillator 12 connected to demagnetizer 2
The oscillator 12 supplies predetermined currents I ₁ and I ₂ to the two coils 5A and 6A of the demagnetizer 2, respectively. By supplying the current from the oscillator 12, the demagnetizer 2 makes a first direction (direction of a magnetic field generated by the upper magnetic core 5) and a second direction (lower magnetic core) orthogonal to each other with respect to the DUT 10. The direction of the magnetic field generated by 6) is sequentially demagnetized by applying a decaying AC magnetic field.
[0016]
(2) Oscillator 13 connected to MAS 3
The oscillator 13 supplies a predetermined current to the exciting coil of the MAS 3. By supplying the current from the oscillator 13, the MAS 3 causes the device under test 10 to be demagnetized in each direction and then the third direction different from the first and second directions with respect to the device under test 10 (FIG. 1 ( A predetermined alternating magnetic field is applied to B) and the X direction in FIG. 2, and the strength of magnetization in the first direction is measured by the detection coil.
[0017]
(3) Control circuit 15 connected to oscillators 12 and 13
The control circuit 15 controls the current supplied from the oscillator 12 to the demagnetizer 2 to demagnetize the device under test 10 in the first direction (the direction of the magnetic field generated by the upper magnetic core 5). A predetermined alternating magnetic field is applied to the DUT 10 to measure the strength of magnetization to obtain a first measurement value. Further, after demagnetizing the device under test 10 in the second direction (the direction of the magnetic field generated by the lower magnetic core 6), a predetermined alternating magnetic field is applied to the device under test 10 to measure the strength of magnetization. A second measurement is obtained. The control circuit 15 controls the current supplied from the oscillator 13 to the MAS 3. The MAS 3 applies an AC magnetic field to the device under test 10 in a third direction (X direction in FIGS. 1B and 2) different from the first and second directions, and the magnetization in the first direction is measured. Measure strength. Then, these measured values are output to the calculator 18.
[0018]
(4) Synchronous rectifier 17 connected to MAS 3 via amplifier 16
The output of the MAS 3 is amplified by the amplifier 16 and then synchronously rectified in the synchronous rectifier 17 with the excitation current supplied from the oscillator 13 to the MAS 3 as a reference. By performing synchronous rectification, it is possible to determine whether the uniaxial stress is positive or negative (tensile / compressed).
[0019]
(5) An arithmetic unit 18 and a display 19 connected to the synchronous rectifier 17
The computing unit 18 subtracts a predetermined value from the average value of these values based on the first measurement value and the second measurement value obtained in the control circuit 15, and obtains the result as the first measurement value and the first measurement value. By dividing by the difference from the measured value of 2, a value corresponding to the stress in the measured object is obtained. The calculation result of the calculator 18 is displayed on the display 19.
[0020]
Next, a stress measurement method using the stress measurement apparatus having the above configuration will be described.
FIG. 4A is a diagram illustrating the relationship between the MAS output and stress, and FIG. 4B is a diagram illustrating the difference in the MAS output depending on the demagnetization direction.
First, for a steel specimen having no residual stress, the relationship between the output V of the MAS and the uniaxial stress σ _ap due to the load is a curve as shown in FIG. . Moreover, focusing on the output V ₂ in the case of FIG. 4 outputs V ₁ and θ = π / 2 in the case of theta = 0 in (A), these output difference between the two curves, where small absolute value of the stress Big and small at large places. This is a distribution curve as shown in FIG. If such a V-σ _ap curve is obtained from a steel specimen having no residual stress, the total stress σ = σ _ap + σ _r including the unknown residual stress σ _r in the same steel material can be measured by MAS.
[0021]
By the way, an actual railway rail is subjected to repeated loads such as wheel load and lateral pressure, and has a stress history effect. If such measures the uniaxial stress railway rails is carried out by applying a MAS in the web (abdomen) of the rail, the residual stress sigma _r at each location in the longitudinal direction of the rail are different uniaxial stresses of rail sigma _ap It is difficult to accurately determine
[0022]
This will be explained in more detail. When a stress σ _ap due to an external force is applied to an object having a residual stress σ _r such as a railroad rail, the origin of the curve in FIG. Become. A graph of biaxial compression in this case is shown in FIG. 5A, and a graph of uniaxial compression is shown in FIG. 5B. Comparing FIG. 4A and FIG. 5, when the same amount of stress σ _ap is applied, the output V of FIGS. 5A and 5B is more than the output V of FIG. 4A. Becomes smaller. This is because since the relationship between V and σ _ap is a curve, the stress sensitivity χ (= dV / dσ; that is, the slope of the tangent line) is different in each part of the curve. Since both the stress σ _ap due to the external force and the residual stress σ _r are stresses, the MAS 3 cannot distinguish between them and measure the total stress σ = σ _ap + σ _r which is the sum of them. Therefore, when the stress σ _ap due to the external force is obtained, if the residual stress σ _r is different, an accurate measurement value cannot be obtained.
[0023]
Therefore, in the stress measurement according to the present invention, the MAS output value corresponding to the stress is linearized over a wide range, thereby making the stress sensitivity χ constant and more accurately obtaining the stress due to external force regardless of the presence of residual stress. Is realized.
This will be described with reference to FIGS. First, the measuring instrument 1 is applied to the object to be measured 10, and a power switch (not shown) is turned ON. Then, as shown in FIG. 6, in the first step (a), a current is supplied from the oscillator 12 to the upper magnetic core 5, and the direction of the magnetic field generated by the upper magnetic core 5 with respect to the object to be measured 10 (first direction). ) Is demagnetized by applying a damped alternating magnetic field. Next, in step (b), current is supplied from the oscillator 13 to the exciting coil of the MAS, and an AC magnetic field is applied to the device under test 10 in the X direction (third direction) of FIG. The intensity of magnetization in the first direction is measured. The time required for these steps (a) and (b) is about 1 second.
[0024]
Next, in step (c), a current is supplied from the oscillator 12 to the lower magnetic core 6, and a demagnetizing magnetic field is applied to the device under test 10 in the direction of the magnetic field generated by the lower magnetic core 6 (second direction). To do. Next, in step (d), a current is supplied from the oscillator 13 to the exciting coil of the MAS, an AC magnetic field is applied to the device under test 10 in the X direction of FIG. Measure the strength of
Then, the magnetization strength obtained in steps (b) and (d) is output to the synchronous rectifier 17 via the amplifier 16 and further output to the calculator 18. Here, the synchronous rectifier 17 synchronously rectifies the output from the MAS with respect to the current supplied from the oscillator 13 to the MAS (current that generates an AC magnetic field in the MAS). Thereby, the positive / negative (tensile / compressed) of uniaxial stress can be distinguished.
[0025]
Next, in step (e), the arithmetic unit 18 performs the following arithmetic processing.
First, assuming that the demagnetization direction is θ, the stress is σ, and the output of MAS is V (θ, σ), the average value V of the output V ₁ when θ = 0 and the output V ₂ when θ = π / 2. (= (V ₁ + V ₂ ) / 2) is given by the following equation.
[Expression 1]

Here, the output from the upper magnetic core 5 is expressed as V (0, σ) when the demagnetization direction θ = 0, and the output from the lower magnetic core 6 is expressed as V (π / 2, σ) when the demagnetization direction θ = π / 2. ing.
[0026]
However, the actual output V (θ, σ) of the MAS is obtained by adding the apparent output Vc depending on the shape of the object to be measured to the output Vs due to the original stress. Therefore, V is given by
[Expression 2]

Furthermore, since the output Vs due to the original stress also depends on the lift-off distance δ, when the stress in a certain measurement direction is A (σ), it is expressed by the following equation.
[Equation 3]

Here, Δ represents a constant that can be ignored (1/10 or less of δ).
[0027]
Here, when the measurement site of the DUT 10 is not a plane that is sufficiently wide (about 3 times or more) compared to the size of the MAS, the output V of the MAS includes the curvature of the measurement site and the shape of the end near the measurement site. Etc., the apparent output Vc is included. However, the apparent output Vc is insensitive to the lift-off distance δ, and conversely, the output Vs due to the original stress is extremely sensitive to the lift-off distance δ. Therefore, if the lift-off distance δ is increased during actual measurement (MAS is slightly separated from the object to be measured 10), the output Vs due to the original stress becomes negligibly small, as shown in FIG. Only the apparent output Vc can be measured. Therefore, when the apparent output Vc is subtracted from the output V of the MAS, the output Vs due to the original stress is obtained.
[0028]
Therefore, in consideration of the demagnetization direction θ, stress σ, and lift-off distance δ described above, a general MAS output is expressed by the following equation as a function of θ, σ, and δ.
[Expression 4]

In this equation, the apparent output Vc means V (θ, σ , ∞).
[0029]
Therefore, the calculator 18 averages the first measurement value V (0, σ, δ) and the second measurement value V (π / 2, σ, δ) in order to eliminate the influence of the lift-off distance δ. The apparent output Vc = V (θ, σ , ∞) is subtracted from the value, and the result is the difference between the first measured value and the second measured value {V (0, σ, δ) −V (π By dividing by / 2, σ, δ)}, an output U corresponding to the stress in the object to be measured is calculated.
[Equation 5]

[0030]
As can be seen from the above equation, the output U does not depend on the lift-off distance δ. As a result, the output of the MAS is linearized as shown in FIG. That is, paying attention to the demagnetization directions θ = 0 and θ = π / 2 in FIG. 4A, the output difference between these two curves is large when the stress is small as shown in FIG. small. Therefore, by dividing the average of these two curves, that is, the output represented by the central curve by the output difference at each stress, a linearized relationship as shown in FIG. 8 can be obtained. Therefore, the stress sensitivity χ is constant, and the stress σ _ap due to the external force can be obtained regardless of the presence of the residual stress.
[0031]
The calculation result of MAS is displayed on the display 19 in step (f) shown in FIG. It should be noted that the total required time from turning on the power supply by applying the measuring instrument 1 to ending steps (a) to (f) is about 2 seconds.
[0032]
【The invention's effect】
As is apparent from the above description, according to the present invention, from the average value of the first measurement value and the second measurement value, the strength of the magnetization is measured by separating the sensor from the object to be measured. By subtracting the value obtained from the above and dividing the result by the difference between the first measurement value and the second measurement value, the output value corresponding to the stress in the object to be measured becomes a straight line in a wide range. Since the stress sensitivity χ becomes constant , more accurate stress measurement can be performed regardless of the residual stress, the presence of paint, coating, rust, etc. on the surface of the object to be measured.
[Brief description of the drawings]
1A and 1B are diagrams showing a measuring instrument of a stress measuring device according to an embodiment of the present invention, in which FIG. 1A is a perspective view and FIG.
FIG. 2 is a diagram for explaining the principle of stress measurement using MAS.
FIG. 3 is a block diagram showing an overall configuration of the stress measuring apparatus.
FIG. 4A is a diagram showing the relationship between MAS output and stress, and FIG. 4B is a diagram showing the difference in MAS output depending on the demagnetization direction.
FIG. 5A is a diagram showing the relationship between MAS output and stress in the case of biaxial compression, and FIG. 5B is a diagram showing the relationship between MAS output and stress in the case of uniaxial compression. It is.
FIG. 6 is an explanatory diagram for explaining a measurement procedure of the stress measurement method according to the embodiment.
FIG. 7 is a diagram illustrating a relationship between MAS output and lift-off.
FIG. 8 is a diagram illustrating a relationship between MAS output and stress when the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Measuring device 2 Demagnetizer 3 Magnetic anisotropy sensor (MAS) 4A, 4B Magnetic core 5, 6 Magnetic core 5A, 6A Degaussing coil 10 Measured object 12, 13 Oscillator 15 Control circuit 16 Amplifier 17 Synchronous rectifier 18 Calculator 19 Display

Claims (5)

(A) demagnetizing the device under test by applying a damped alternating magnetic field in the first direction;
(B) applying a predetermined alternating magnetic field to the object to be measured using a sensor to measure the magnetization intensity in the first direction, and obtaining a first measurement value;
(C) demagnetizing the device under test by applying a damped alternating magnetic field in a second direction orthogonal to the first direction;
(D) obtaining a second measurement value by applying a predetermined alternating magnetic field to the object to be measured using the sensor and measuring the magnetization intensity in the first direction ;
(E) The result obtained by subtracting the value obtained by measuring the strength of magnetization by separating the sensor from the object to be measured from the average value of the first measured value and the second measured value. Dividing the value by the difference between the first measured value and the second measured value to obtain a value corresponding to the stress in the measured object;
A stress measurement method comprising: The step (b) includes the step of measuring the strength of magnetization in the first direction by applying an AC magnetic field to the device under test in a third direction different from the first and second directions,
The step (d) includes a step of applying a predetermined alternating magnetic field in a third direction to the object to be measured to measure the strength of magnetization in the first direction. Stress measurement method. A demagnetizer for demagnetizing the device under test by applying a damped AC magnetic field in a first direction and a second direction orthogonal to each other;
A sensor for measuring a magnetization intensity by applying a predetermined alternating magnetic field to the object to be measured;
The degaussing circuit current to generate a damping AC magnetic field by supplying to, one or more of an oscillator to generate a predetermined alternating magnetic field by supplying a current to the sensor,
After demagnetizing the object to be measured in the first direction, a predetermined AC magnetic field is applied to the object to be measured to measure the strength of magnetization in the first direction, thereby obtaining a first measured value. Then, after demagnetizing the object to be measured in the second direction, a predetermined AC magnetic field is applied to the object to be measured to measure the strength of magnetization in the first direction, thereby obtaining a second measured value. as a control circuit for controlling at least the oscillation unit,
A value obtained by measuring the strength of magnetization by separating the sensor from the object to be measured is subtracted from the average value of the first measurement value and the second measurement value, and the result is calculated as the first value. An arithmetic unit for obtaining a value corresponding to the stress in the measured object by dividing by the difference between the measured value and the second measured value;
A stress measuring device comprising:   4. The stress measuring apparatus according to claim 3, further comprising means for amplifying the output of the sensor and synchronously rectifying a current that generates a predetermined alternating magnetic field.   The sensor measures the strength of magnetization in the first direction by applying a predetermined alternating magnetic field to the object to be measured in a third direction different from the first and second directions. The stress measuring device according to 3 or 4.

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