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Estimation of fatigue level by rotational Barkhausen noise
Journal of Magnetism and Magnetic Materials 160 (1996) 43-44
Journal of magnetism and magnetic materials
ELSEVIER
Estimation of fatigue level by rotational Barkhausen noise M. Enokizono a,*, A. Nishimizu a, M. Oka b Faculty of Engineering, Oita Unit'ersity, 700 Dannoharu, Oita 870-11, Japan b Department of Computer and Control Engineering, Oita National Collega of Technology, 1666 Maki, Oita 870-01, Japan
Abstract We have measured the Barkhausen noise (BHN) of Inconel-600 sheet material in a rotating magnetic field. We have found that the limit stress amplitude of each life fraction can be estimated using the power of the BHN. The limit stress amplitude is the minimum bending cyclic stress of each life fraction. In this paper we present a new method for the estimation of fatigue which utilizes the change of BHN in a rotating magnetic field. Keywords." Barkhausen noise; Fatigue level; Inconel-600; NDT; Rotational magnetic field
Exciting coil
1. Introduction The estimation of fatigue in the materials used in nuclear power generation systems is a serious problem. If we know the internal state of the materials before destruction, we can determine the life time of the materials. Moreover, we can prolong the life time by keeping the internal energy state constant. To determine the progress of fatigue and to understand the internal state in the materials, we investigated the change of the BHN in a rotating magnetic field with bending fatigue as a way of non-destructive testing [1,2].
Speci
- Yoke ~
Excitin
Y Fig. 1. Apparatus for excitation of the rotational magnetic field and arrangement of the specimen.
2. Experimental method 2.2. Measurement conditions 2.1. Measurement o f BHN using a magnetic" sensor Inconel-600 is a weakly ferromagnetic substance with a relative permeability of about 10. Hence we can observe BHN of an lnconel-600 sheet in a rotating magnetic field. The advantage of a rotational magnetic field is that we can obtain the BHN unaffected by the anisotropy of the specimen. Fig. l shows the apparatus used for excitation of the rotational magnetic field and the arrangement of the specimen. Exciting currents are controlled to generate a rotating magnetic field with constant amplitude. Fig. 2 shows the shape of the BHN sensor, which is placed in the center of the specimen. Fig. 3 shows a block diagram of the BHN measurement system.
We applied a bending cyclic load to three sample sheets until the samples were destroyed. The bending cyclic load was stopped while the BHN was measured. The bending frequency was 30 Hz. In order to determine the dependence on bending fatigue, each sample was subjected to a different stress amplitude. The applied stress for
_ _ ~ _ M a g n e t i e head
5.Smm * Corresponding author. Fax: + 81-975-695949. 0304-8853/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 8 8 5 3 ( 9 6 ) 0 0 103-5
Fig. 2. Shape of the BHN sensor.
44
M. E oki=ono et c I / 1o "m I q/'Mc ,q,tetism and Magnelic Materials 160 (1996) 43 44
1
iI I
Wave Synthesizer
1.8 1.7
Computer
/
1.6
-
/4
<
• /
1.5
//"
/
BtpolarIX3Wer [ Bipolarpower supplyt supplyI ]amplifier.,[ amplifier
1.3
IA
/
1
Z71 Fig. 3. Block diagram of the BHN measurement system.
each sample was: 480 MPa (P3-4), 372 MPa (P3-5) and 284 MPa (P3-6).
3. Results and discussion Fig. 4 shows the relation between P / P o and life fraction, where Po is the power of the BHN before adding the bending cyclic load and P is the power of the BHN at each life fraction. The power of the BHN was measured under the condition that the magnetic flux density was 0.009 T and the exciting frequency 60 Hz. The change of power of the BHN is large at an early stage of progress of the bending fatigue. Consequently, it is possible to esti-
/
/ /,e* v//
1.2
Wavumemo~
,-
100
- - ~ ' ~ .f...w 200
300
400
Stress [MPa]
500
[
600
Fig. 5. P / P o vs. stress. mate the limit stress amplitude which is dependent on the bending fatigue. Fig. 5 shows the relationship between P / P o and stress. The new method for estimating the limit stress amplitude using this figure is as follows: firstly, we plot P / P o for each life fraction (0.01, 0.1 and 0.5 n / N f ) in Fig. 5. The P / P o value is obtained from Fig. 4. For P3-5 and P3-6 we estimated the P / P o value by extrapolation assuming that the life fraction is 0.5 n / N f . The line in Fig. 5 was determined using the least squares method for each life fraction. In order to estimate the dispersion of the measured data, we drew a line parallel to the x-axis which shows the limit of the dispersion of Po- Po~,,~ is the average value of Po for three samples. Hence the limit of dispersion is the mid point between (Po/Po~,.~) ..... and (Po/Po~vo)mm. Then we obtain three crossing points in Fig. 5. The stresses at these crossing points give the limit stress amplitude. In these cases, the limit stress amplitudes are 513 MPa (0.01 n/Nf), 263 MPa (0.1 n / N f ) and 223 MPa (0.5 n/Nf).
4. Conclusion
1.8 1.7
We have measured the BHN of Inconel-600 sheet material in a rotating magnetic field. We show that it is possible to estimate the limit stress amplitude at various life fractions using the change in BHN.
1.6 1.5
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~1,4
I~
1.3
J Jf
t
.......
•
/, "f
References
1.2
V
1.1
! 0
0,1
0,2
0~3 0.4 0,5 0,6 Life fraction In/Nil
0.7
Fig. 4. Life fraction (n/N0 vs. P / P o .
0.8
[I] M. Enokizono and A. Nishimizu, J. Magn. Magn. Mater. 133 (1994) 599. [2] M. Enokizono, M. Akita and A. Nishimizu, ESAEM 6 (1995) 121.
Journal of magnetism and magnetic materials
ELSEVIER
Estimation of fatigue level by rotational Barkhausen noise M. Enokizono a,*, A. Nishimizu a, M. Oka b Faculty of Engineering, Oita Unit'ersity, 700 Dannoharu, Oita 870-11, Japan b Department of Computer and Control Engineering, Oita National Collega of Technology, 1666 Maki, Oita 870-01, Japan
Abstract We have measured the Barkhausen noise (BHN) of Inconel-600 sheet material in a rotating magnetic field. We have found that the limit stress amplitude of each life fraction can be estimated using the power of the BHN. The limit stress amplitude is the minimum bending cyclic stress of each life fraction. In this paper we present a new method for the estimation of fatigue which utilizes the change of BHN in a rotating magnetic field. Keywords." Barkhausen noise; Fatigue level; Inconel-600; NDT; Rotational magnetic field
Exciting coil
1. Introduction The estimation of fatigue in the materials used in nuclear power generation systems is a serious problem. If we know the internal state of the materials before destruction, we can determine the life time of the materials. Moreover, we can prolong the life time by keeping the internal energy state constant. To determine the progress of fatigue and to understand the internal state in the materials, we investigated the change of the BHN in a rotating magnetic field with bending fatigue as a way of non-destructive testing [1,2].
Speci
- Yoke ~
Excitin
Y Fig. 1. Apparatus for excitation of the rotational magnetic field and arrangement of the specimen.
2. Experimental method 2.2. Measurement conditions 2.1. Measurement o f BHN using a magnetic" sensor Inconel-600 is a weakly ferromagnetic substance with a relative permeability of about 10. Hence we can observe BHN of an lnconel-600 sheet in a rotating magnetic field. The advantage of a rotational magnetic field is that we can obtain the BHN unaffected by the anisotropy of the specimen. Fig. l shows the apparatus used for excitation of the rotational magnetic field and the arrangement of the specimen. Exciting currents are controlled to generate a rotating magnetic field with constant amplitude. Fig. 2 shows the shape of the BHN sensor, which is placed in the center of the specimen. Fig. 3 shows a block diagram of the BHN measurement system.
We applied a bending cyclic load to three sample sheets until the samples were destroyed. The bending cyclic load was stopped while the BHN was measured. The bending frequency was 30 Hz. In order to determine the dependence on bending fatigue, each sample was subjected to a different stress amplitude. The applied stress for
_ _ ~ _ M a g n e t i e head
5.Smm * Corresponding author. Fax: + 81-975-695949. 0304-8853/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PII S 0 3 0 4 - 8 8 5 3 ( 9 6 ) 0 0 103-5
Fig. 2. Shape of the BHN sensor.
44
M. E oki=ono et c I / 1o "m I q/'Mc ,q,tetism and Magnelic Materials 160 (1996) 43 44
1
iI I
Wave Synthesizer
1.8 1.7
Computer
/
1.6
-
/4
<
• /
1.5
//"
/
BtpolarIX3Wer [ Bipolarpower supplyt supplyI ]amplifier.,[ amplifier
1.3
IA
/
1
Z71 Fig. 3. Block diagram of the BHN measurement system.
each sample was: 480 MPa (P3-4), 372 MPa (P3-5) and 284 MPa (P3-6).
3. Results and discussion Fig. 4 shows the relation between P / P o and life fraction, where Po is the power of the BHN before adding the bending cyclic load and P is the power of the BHN at each life fraction. The power of the BHN was measured under the condition that the magnetic flux density was 0.009 T and the exciting frequency 60 Hz. The change of power of the BHN is large at an early stage of progress of the bending fatigue. Consequently, it is possible to esti-
/
/ /,e* v//
1.2
Wavumemo~
,-
100
- - ~ ' ~ .f...w 200
300
400
Stress [MPa]
500
[
600
Fig. 5. P / P o vs. stress. mate the limit stress amplitude which is dependent on the bending fatigue. Fig. 5 shows the relationship between P / P o and stress. The new method for estimating the limit stress amplitude using this figure is as follows: firstly, we plot P / P o for each life fraction (0.01, 0.1 and 0.5 n / N f ) in Fig. 5. The P / P o value is obtained from Fig. 4. For P3-5 and P3-6 we estimated the P / P o value by extrapolation assuming that the life fraction is 0.5 n / N f . The line in Fig. 5 was determined using the least squares method for each life fraction. In order to estimate the dispersion of the measured data, we drew a line parallel to the x-axis which shows the limit of the dispersion of Po- Po~,,~ is the average value of Po for three samples. Hence the limit of dispersion is the mid point between (Po/Po~,.~) ..... and (Po/Po~vo)mm. Then we obtain three crossing points in Fig. 5. The stresses at these crossing points give the limit stress amplitude. In these cases, the limit stress amplitudes are 513 MPa (0.01 n/Nf), 263 MPa (0.1 n / N f ) and 223 MPa (0.5 n/Nf).
4. Conclusion
1.8 1.7
We have measured the BHN of Inconel-600 sheet material in a rotating magnetic field. We show that it is possible to estimate the limit stress amplitude at various life fractions using the change in BHN.
1.6 1.5
-~l["
~1,4
I~
1.3
J Jf
t
.......
•
/, "f
References
1.2
V
1.1
! 0
0,1
0,2
0~3 0.4 0,5 0,6 Life fraction In/Nil
0.7
Fig. 4. Life fraction (n/N0 vs. P / P o .
0.8
[I] M. Enokizono and A. Nishimizu, J. Magn. Magn. Mater. 133 (1994) 599. [2] M. Enokizono, M. Akita and A. Nishimizu, ESAEM 6 (1995) 121.