RELATION BETWEEN MECHANICAL BARKHAUSEN NOISE AND MAGNETOMECHANICAL INTERNAL FRICTION

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RELATION BETWEEN MECHANICAL BARKHAUSEN NOISE AND

MAGNETOMECHANICAL INTERNAL FRICTION

B. Augustyniak, A. Vannes

To cite this version:

B. Augustyniak, A. Vannes. RELATION BETWEEN MECHANICAL BARKHAUSEN NOISE AND

MAGNETOMECHANICAL INTERNAL FRICTION. Journal de Physique Colloques, 1987, 48 (C8),

pp.C8-407-C8-412. �10.1051/jphyscol:1987861�. �jpa-00227165�

RELATION BETWEEN MECHANICAL BARKHAUSEN NOISE AND MAGNETOMECHANICAL INTERNAL FRICTION

B. AUGUSTYNIAK and A. VANNES'

Institute of Physics, Technical University of ~dan/sk, PL-80-952 ~ d a g s k , Poland

' ~ r o u p e d'studes de MBtallurgie Physique et de Physique des MatBriaux, LA 341, INSA d e Lyon, Bdt. 502,

F-69621 Villeurbanne Cedex, France

Abstract. T h e mechanical Barkhausen n o i s e ( M B N ) induced by torsional vibration ( 8 0 Hz) was measured for Copt alloy.The shear s t r a i n hysteresis loop and the frequency spectrum were analyzed. T h e a m p l i t u d e dependence of MEN was discussed and compared with the a m p l i t u d e dependence of magnetomechanical damping. T h e maximal intensity of the M E N was found a t the shear s t r a i n value equal to vibration a m p l i t u d e s a t which the internal f r i c t i o n maximum appears.

At the high s t r a i n v a l u e s additionally the s t r e s s induced magnetical Barkhausen n o i s e w a s detected.

INTRODUCTION

Ferromagnetic materials under c y c l i c vibration manifest magnetomecha- nical internal friction ( M I F ) d u e to the magnetomechanical hysteresis

I l l . T h e importance of MIF depends o n the magnetic d o m a i n configuration

and in particular o n the 90° d o m a i n wall (DW) s u r f a c e C21. A c l o s e relation w a s round between MIF and classical Barkhausen n o i s e ( B N ) a s measured for cold worked s o f t magnetic s a m p l e C31. T h e discussed f e s t u r r s or B N and MIF were consistent with magnetical and magnetome- chanical loop theories. It w a s concluded that both phenomena depend o n t h e internal s t r e s s value. External mechanical stress involves irrever- s i b l e displacement of 90° DW. T h e s e movements c r e a t e the Barkhausen n o i s e called mechanical Barkhausen noise ( M B N ) . MIF and MBN a r e d u e to the s a m e process and s o they should be strongly correlated. T h e aim of this paper is to present the results of preliminary s t u d i e s of MBN of Copt alloy. T h e a m p l i t u d e d e p e n d e n c e of MBN was compared with the s n a l o g o u z dependence or MIF. T h e Copt alloy was c h o s e n because or its high magnetostriction and elastic limit values.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987861

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EXPER1 MENTAL RESULTS

The Copt s a m p l e was maae in torm of the wire 1 mm in diameter and 5 0 mm length.The a l l o y w a s in the disordered state a s quenched [4j.The s a m p i e surrounded by thc sensor coil was tired in a n invert pendulum. T h e frequency of vibration was about 80 Hz. Electronic s e t for MBN mkasurements was like for BN measurements C3,Sl.The input signal from sensor coil U(t) w a s amplified (20 dB to 60 dB) and filtered in high pass t i lter t f requency from f,, u p to 200 KHz, where t o was from 0.1 KHz u p t o 40 KHz). In the next s t e p the signal U(t) was rectified and integrated. T h e D C output signal Us is proportional t o the mean a m p l i t u d e of U(t). T h e measurements of MBN were made for a given a m p l i t u d e of shear strain y (from 10-" u p to 10-s).lnternal friction ( 1 F ) w a s calculated from logarithmic decrement, then the a m p l i t u d e dependence of MIF was deduced from IF results C 4 1 . Fig.1 s h o w s schema- tically the oscillograph r e c o r d s of the amplified input signal U(t) a s observed for s o m e vibration amplitudes. T h e MBN high frequency signal is shown by solid l i n e - D a s h e d line presents the shear s t r a i n versus time dependence where time c h a n g e s from t = O u p to tf0.75 T tT is the oscillation period).The time scale of oscillograph records is constant (1 ms/div) but the tension s c a l e a r e different for each graph. T h e distinct MBN signal a p p e a r s when shear strain c h a n g e s s i g n ( t = O and t=0.5 T ) and disappears w h e n shear s t r a i n takes its maximal value ( t = 0 . 2 5 TI.When the vibration a m p l i t u d e increases the MBN intensity increases progressively. It must be pointed out that the MBN signal is modulated by the low frequency signal and this e f f e c t is a m p l i t u d e dependent tsee picture c a n d d in fig.1). T h e hysteresis loop of M B N c a n be deduced a l s o from the oscillograph records. T h e a m p l i t u d e of MBN Uct) signal w a s estimated and plotted versus s t r a i n for a given vibration amplitude. Four e x a m p l e s of s u c h MBN loops a r e s h o w n in fig.2 by solid lines. T h e dashed lines in fig.2 present the corrected MBN loops w h e n a constant shear s t r a i n rate was assumed. T h e MBN intensity reveals distinct hysteresis. T h i s intensity and s h a p e of the MBN loop depend o n the vibration amplitude. Increase of the a m p l i t u d e involves a n increase of MBN intensity and a s h i f t of its maximal value position to the higher values of s t r a i n tcurves a a n d b in fig.21. T h e MBN hysteresis loop saturates progressively w h e n vibration a m p l i t u d e exceeds the s t r a i n of a b o u t litlo-. but the maximum position remains s t a b l e tcurves c.d in fig.2). T h e frequency a n a l y s i s of M B N s p e c t r u m was a l s o performed. For a given vibration a m p l i t u d e the value o f U s tension w a s measured a s a f u n c t i o n of the threshold frequency f o . T h e results of these measurements a r e s h o w n in fig.3. T h e Us(fo) functions reveal similar slopes. T h e MBN intensity decreases monotonously. It is due to t h e progressive elimination o f low frequency c o m p o n e n t s in MBN frequency spectrum. T h e s l o p e of this c u r v e is proportional to the frequency spectrum intensity. Relatively low value of this parameter s e e n a t the first part o f the tested f u n c t i o n indicates that MBN spectrum is composed mainly of high frequency components ( f > 1 0 K H z ) . T h i s remark is not true generally because w h e n the high vibration a m p l i t u d e s w e r e applied

.

the distinct deflection a p p e a r s o n the c u r v e s 6 a n d 7 (fig.3) for the low f a values.

T h e f o l l o w i n g t h r e e a s p e c t s of t h e MBN p h e n o m e n o n s h o u l d be discussed:

1- t h e MBN loop s h a p e , 2- t h e MBN f r e q u e n c y s p e c t r u m and 3 - r e l a t i o n b e t w e e n MBN and MIF.

1.The MBN loop shape. S u p p o s i n g t h e m a g n e t o m e c h a n i c a l h y s t e r e s i s loop d o e s not d e p e n d on v i b r a t i o n f r e q u e n c y ( f t 3 0 0 K H z ) o n e c a n w r i t e t h e f o l l o w i n g b a s i c e x p r e s s i o n for t h e signal d e l i v e r e d by s e n s o r coil:

U ( t ) = - d @ / d t = ( d $ / d v ) * ( . d u / d t ) . T h e MBN signal d e p e n d s o n the m a g n e t i c s t r u c t u r e ( t h e first f a c t o r ) and o n the external s t r e s s r a t e ( t h e next f a c t o r ) . When t h e external s t r e s s is a s i n u o u s t y p e f u n c t i o n , t h e MBN intensity is proportional t o t h e s t r e s s a m p l i t u d e and o s c i l l a t i o n f r e q u e n c y . T h e f e a t u r e s of t h e MBN loop d e d u c e d from fig.1 and fig.2 a r e c o n s i s t e n t w i t h t h e s e predictions. T h e MBN v a n i s h e s w h e n s t r e s s r a t e d o / d t = O , ( f i g . 2 ) and its intensity i n c r e a s e s w i t h v i b r a t i o n a m p l i t u d e , a s s h o w n in fig.3. T h e s i n u s like v i b r a t i o n m a k e s that MBN intensity d e c r e a s e s w h e n s h e a r s t r e s s a p p r o a c h e s its maximum value.

T o e l i m i n a t e t h i s effect, the MBN loop should be measured u s i n g a c o n s t a n t s t r e s s rate. In our c a s e t h e MBN i n t e n s i t y v a l u e s w e r e d i v i d e d by t h e s t r e s s r a t e v a l u e and s u c h c o r r e c t e d loops a r e p r e s e n t e d in fig.2 by d a s h e d lines. T h e s e lines s h o w t h a t t h e MBN m a x i m u m a p p e a r s a t c o n s t a n t v a l u e o f a p p l i e d s t r e s s ( s h e a r s t r a i n equal /1.5?0.5/*10-• 1 , c u r v e s 3 and 4 in fig.2. T h e MBN loop s a t u r a t e s w h e n s h e a r s t r a i n e x c e e d s t h i s t h r e s h o l d value. T h e mean v a l u e of MBN i n t e n s i t y ' i n c r e a s e s m o n o t o n o u s l y with v i b r a t i o n a m p l i t u d e a s s h o w s fig.3.

2.The MBN f r e q u e n c y spectrum. F r o m t h e f r e q u e n c y d e p e n d e n c i e s a s presented in fig.3 it w a s d e d u c e d that t h e MBN f r e q u e n c y s p e c t r u m is f o r m e d mainly of high f r e q u e n c y components. T h a t is b e c a u s e o n l y 90° DW c a n move and that leads t o d e m a g n e t i z a t i o n of r e l a t i v e l y small regions.

For the higher s t r e s s a m p l i t u d e s a low f r e q u e n c y c o m p o n e n t a p p e a r s ( c u r v e s 6.7 in fig.3). W e a s s u m e that t h i s B a r k h a u s e n n o i s e c a n be d u e t o t h e m a g n e t i c field induced by t h e external s t r e s s ( m a g n e t o e l a s t i c effect). M a g n e t i c field i n v o l v e s 180° DW j u m p s w h i c h a r e c o a r s e and tend to f o r m c l u s t e r s C6.71. T h e m a g n e t i c BN (HBN) has a s p e c t r u m w i t h r e l a t i v e l y low f r e q u e n c y c o m p o n e n t s , C71. T h e HBN i n t e n s i t y w a s measured for C o p t a l l o y too, 131. T h e f r e q u e n c y d e p e n d e n c i e s of t h e H B N and MBN a r e presented in fig.4. It c a n b e s e e n that H B N s p e c t r u m of a s quenched s a m p l e has the low f r e q u e n c y c o m p o n e n t s ( c u r v e i.fig.4).

P l a s t i c d e f o r m a t i o n r e d u c e s t h e H B N i n t e n s i t y and c h a n g e s t h e f r e q u e n c y s p e c t r u m ( c u r v e 2, fig.4). In this s p e c t r u m t h e high f r e q u e n c y c o m p o n e n t s dominate. T h e i n c r e a s e of internal s t r e s s e s leads t o the d o m a i n d i m e n s i o n s d i m i n u t i o n and to c l u s t e r n u m b e r reduction. T h e s l o p e of MBN f r e q u e n c y d e p e n d e n c e ( c u r v e 3.fig.4) is like t h a t of H E N of c o l d w o r k e d sample. It c a n be a s s u m e d that t h e low f r e q u e n c y c o m p o n e n t of MBN is d u e t o t h e HBN p h e n o m e n o n but the H B N c a n o c c u r w h e n s t r e s s induced m a g n e t i c field e x c e e d s c o e r c i v e f o r c e of t h e s a m p l e

.

T h e value of t h i s m a g n e t i c field w a s e s t i m a t e d using t h e low f r e q u e n c y c o m p o n e n t of t h e input MEN signal s h o w n in fig.l. I n t e g r a t i o n of t h i s c o m p o n e n t g i v e s o n l y the a m p l i t u d e of m a g n e t i c i n d u c t i o n B change. Fig.5 s h o w s t h e h y s t e r e s i s loop of B c a l c u l a t e d from the r e s u l t s presented in fig.1 by record d.

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Because of the negative magnetostriction of Copt alloy, the induced magnetic field B is parallel to the sample axis. The B value increases strongly when the applied strain is higher then 1 * 1 0 - * . The amplitude of B changes is higher than 0.001 T so the induced magnetic field exceeds the coercive force of Copt alloy. This confirms our assumption that HBN is created during mechanical vibration.

3.Tho MBN and MIF relation. Magnetomechanical internal friction (MIF) reveals a characteristic maximum in the amplitude dependence C1,21. The amplitude dependence of MIF for Copt alloy is presented in fig.6 by curve 1.The distinct maximum appears at shear strain /1.8+0.5/*10-'.

The theory of MIF as proposed by Birchac and Smith, tl1,predicts that strain position of MIF maximum corresponds to the strain at which maximal number of DW jumps appears. The MBN measurements lead to the results which can be compared with some predictions of MIF model. It was found that MBN loop maximum position (fig.2, corrected curves) appears at strain value very close to that obtained for MIF maximum position (fig.6,curve 1).The internal friction values can be estimated from the MBN reversals too. Ue assume that energy losses

&

are proportional to the integral of the MBN intensity to the second power.

Because the MBN loops are not precise enough to make such integration we have tried only to estimate

r \ w

from measured Us values.The time constant of the integration set is longer than oscillation period so the Us value is proportional to the maximal value of MEN intensity.

Curve 2 in fig.6 presents the amplitude dependence of Us measured for f 0 = 2 0 0 Hz. Assuming that

AW

is proportional to the ( U s l 2 value one can estimate the MlF by simple expression: Q - ' = ( U S / ~ ) ~ . This function, presented by curve 3 in fig.6, shows that MIF estimated from MBN intensity reveals amplitude dependence which is analogous to that of measured MIF. The maximum positions of these functions are very close to each other. The agreement between the slopes of presented amplitude dependencies is only approximate.lt means that our assumption on A U vs. Us relation is not true.The appropriate MIF estimation can be done by using the results of the precise MBN loops measurements.

CONCLUSIONS

1 ) Using inverted pendulum the mechanical Barkhausen noise was

measured. It was found that the MEN hysteresis loop saturates when shear strain exceeds some critical value.

2 ) Frequency spectrum of MBN is formed by high frequency components.

3) For high strain amplitudes the magnetic Barkhausen noise appears.

4) MBN results are consistent with magnetomechanical IF model but for further discussion the MBN reversals should be measured.

R E F E R F N W

C 1 1 Birchak I.B.,Smith G.W.;J.Appl. Phys. 43.1238 /1972/.

C21 Bozorth R.M.;Ferromagnetism, D.Van Nostrand Comp.,N.York,l961.

C 3 1 Augustyniak B.,Fantozzi G.;Journal de Phys.46,ClO-733/1985/.

( 4 1 Augustyniak B.,Chomka W.;Acta Phys.Pol.A46.515/1983/.

151 Vannes A.,Cousinou E.,Augustyniak B.,Flambard C.;Proc.Journee Nat.

du COFREND, G r e n o b l e , l 9 8 5 ; C O F R E N D , 2 0 9 / 1 9 8 5 / . C61 De Lustrac J . ; T h e s i s , G r e n o b l e , l 9 7 1 .

C71 Beithel H.;IEEE Trans.Magn.,NAG-5,5,355/1968/.

1 0

Fig.1 Oscillograph records of MBN Fig.2 MBN hysteresls loop for the

signal (solid lines) and given strain amplitude (lo-* ) :

shear strain (dashed line) solid line

-

as measured,

for the amp1 itudes (lo-'): dashed line - after correction

a- 0.33,b- 1 . 0 , ~ - 3.3,d- 1 0 ; on strain rate.

abscissa scale :1 ms/div., ordinate scale for MEN tension

( mV/div. :a- 5 , b - 20,c,d- 50.

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Fig.3 M B N i n t e n s i t y ( U s ) v s . t h r e s h o l d f r e q u e n c y f o f o r g i v e n s t r a i n a m p l i t u d e ) :

1- 0.22,2- 0.40.3- 0.60, 4- 1.0,5- 3.3,6- 5.0,7- 10.

to3

lo'

f,,

^[HZ]

fig.4 D e p e n d e n c i e s o n t h r e s h o l d f r e q u e n c y o f H B N i n t e n s i t y ( d a s h e d l i n e s ) end MEN i n t e n s i t y ( s o l i d lines):

1 - a s quenched.2-5% c o l d vorked.3- smel l amp1 l t u d e ⁽ < 1 0 - ~ ) , 4 - h i g h a m p l i t u d e ( l o 3

).

Fig.5 H y s t e r e n l s loop f o r s t r e s s Fig.6 A n p l l t u d e d e p e n d e n c i e s of:

i n d u c e d s a m p l e m a g n e t i z a t i o n . 1- m a g n e t o m e c h a n i c e l IF.

2 - MBN i n t e n s i t y a n d 3- IF d e d u c e d f r o m MBN.