Barkhausen Signal Research Articles

Effect of surface mechanical changes on magnetic Barkhausen emissions

Magnetic Barkhausen emissions are sensitive to changes in the surface mechanical condition in magnetic materials. This sensitivity arises because magnetic properties of the material are closely linked to stress via the magnetoelastic coupling. Barkhausen signals in steels which are typically in the frequency range 20-200 KHz, are detected predominantly from a surface layer up to 0.5 mm in depth. Signals from deeper layers are attenuated by eddy currents in the material. The depth sensitivity can be controlled to analyze material condition at different depths by an adjustment of the frequency bandwidth of the detected signal.

An investigation of various procedures for analysis of micromagnetic Barkhausen signals for nondestructive evaluation of steels : 52761 Sipahi, L.B.; Jiles, D. Nondestructive Testing and Evaluation, Vol. 10, No. 3, pp. 183–199 (1993)

An investigation of various procedures for analysis of micromagnetic Barkhausen signals for nondestructive evaluation of steels : 52761 Sipahi, L.B.; Jiles, D. Nondestructive Testing and Evaluation, Vol. 10, No. 3, pp. 183–199 (1993)

Evaluation of fatigue damage in steel structural components by magnetoelastic Barkhausen signal analysis : 52757 Govindaraju, M.R.; Strom, A.; Jiles, D.C.; Biner, S.B.; Chen, Z.J. Journal of Applied Physics, Vol. 73, No. 10, pp. 6165–6167 (15 May 1993)

Evaluation of fatigue damage in steel structural components by magnetoelastic Barkhausen signal analysis : 52757 Govindaraju, M.R.; Strom, A.; Jiles, D.C.; Biner, S.B.; Chen, Z.J. Journal of Applied Physics, Vol. 73, No. 10, pp. 6165–6167 (15 May 1993)

Nondestructive evaluation of steels using acoustic and magnetic Barkhausen signals—I. Effect of carbide precipitation and hardness : 37267 Kameda, J.; Ranjan, R. Acta Metallurgica, Vol. 35, No. 7, pp. 1515–1526 (Jul. 1987)

Nondestructive evaluation of steels using acoustic and magnetic Barkhausen signals—I. Effect of carbide precipitation and hardness : 37267 Kameda, J.; Ranjan, R. Acta Metallurgica, Vol. 35, No. 7, pp. 1515–1526 (Jul. 1987)

Nondestructive evaluation of steels using acoustic and magnetic Barkhausen signals—II. Effect of intergranular impurity segregation : 37266 Kameda, J.; Rajan, R. Acta Metallurgica, Vol. 35, No. 7, pp. 1527–1531 (Jul. 1987)

Nondestructive evaluation of steels using acoustic and magnetic Barkhausen signals—II. Effect of intergranular impurity segregation : 37266 Kameda, J.; Rajan, R. Acta Metallurgica, Vol. 35, No. 7, pp. 1527–1531 (Jul. 1987)

Characterization of tempered martensite microstructure and embrittlement by acoustic and magnetic Barkhausen signal measurement : 38958 Kameda, J. Scripta Metallurgica, Vol. 22, No. 9, pp. 1487–1492 (Sep. 1988)

Characterization of tempered martensite microstructure and embrittlement by acoustic and magnetic Barkhausen signal measurement : 38958 Kameda, J. Scripta Metallurgica, Vol. 22, No. 9, pp. 1487–1492 (Sep. 1988)

Effects of surface condition on Barkhausen emissions from steel

Temperature changes during mechanical processing such as grinding of steel parts can cause phase changes in the microstructure. Thermal shock during the process can give rise to localized surface residual stress. The net result can be reduced wear resistance and fatigue life leading to early failure during service. Effective methods for the detection of such damage are necessary. Barkhausen emissions, which arise from discontinuous motion of domain walls, are sensitive to microstructual changes that affect domain dynamics. Detected Barkhausen signals are predominantly from a surface layer about 200 μm thick, those from deeper being attenuated due to eddy currents. An analysis of the detected signals can provide an indication of the surface condition of the material. Barkhausen signals from parts ground under controlled conditions were found to be dependent on the grinding process conditions. The signal changes were consistent with residual stress measured by x-ray diffraction and with hardness measurements that are indicative of changes in microstructure.

Barkhausen noise in FeCoB amorphous alloys (abstract)

In recent years, the Barkhausen effect has been indicated as a promising tool to investigate and verify the ideas about the self-organization of physical complex systems displaying power law distributions and 1/f noise. When measured at low magnetization rates, the Barkhausen signal displays 1/fα-type spectra (with α=1.5÷2) and power law distributions of duration and size of the Barkhausen jumps. These experimental data are quite well described by the model of Alessandro et al. which is based on a stochastic description of the domain wall dynamics over a pinning field with brownian properties. Yet, this model always predicts a 1/f 2 spectrum, and, at the moment, it is not clear if it can take into account possible effects of self-organization of the magnetization process. In order to improve the power of the model and clarify this problem, we have performed a thorough investigation of the noise spectra and the amplitude distributions of a wide set of FeCoB amorphous alloys. The stationary amplitude distribution of the signal is very well fitted by the gamma distribution P(ν)=νc−1 exp(−ν)/Γ(c), where ν is proportional to the domain wall velocity, and c is a dimensionless parameter. As predicted in Ref. , this parameter is found to have a parabolic dependence on the magnetization rate. In particular, the linear coefficient is related to the amplitude of the fluctuations of the pinning field, a parameter which can be measured directly from the power spectra. In all measured cases, the power spectra show α exponents less than 2, and thus poorly fitted by the model. Actually, the absolute value of the high frequency spectral density is not consistent with the c parameter determined from the amplitude distribution data. This discrepancy requires to introduce effects not taken into account in the model, as the propagation of the jumps along the domain wall. This highly enhances the fit of the data and indicates effects of propagation on the scale of a few millimeters. These results are analyzed in terms of new descriptions of the statistical properties of the pinning field based on fractional brownian processes.

Effects of tensile stress on magnetic Barkhausen emissions in amorphous FeSiB alloy

Magnetic hysteresis and Barkhausen emissions have been measured for amorphous Fe 82B 10Si 8 samples with positive magnetostriction of λ s = 27 × 10 −6 under tensile stress of up to 35 MPa. The root mean square voltage of the Barkhausen signal and the number of events per cycle increased monotonically with the applied stress. The results are explained in terms of a theory which includes a stress-dependent hysteresis model and a stochastic process model for the Barkhausen emissions.

FRACTALS, SCALING AND THE QUESTION OF SELF-ORGANIZED CRITICALITY IN MAGNETIZATION PROCESSES

The main physical aspects and the theoretical description of stochastic domain wall dynamics in soft magnetic materials are reviewed. The intrinsically random nature of domain wall motion results in the Barkhausen effect, which exibits scaling properties at low magnetization rates and 1/f power spectra. It is shown that the Barkhausen signal ν, as well as the size Δx and the duration Δu of jumps follow distributions of the form ν−α, Δx−β, Δu−γ, with α=1−c, β=3/2−c/2, γ=2–c, where c is a dimensionless parameter proportional to the applied field rate. These results are analytically calculated by means of a stochastic differential equation for the domain wall dynamics in a random perturbed medium with brownian properties and then compared to experiments. The Barkhausen signal is found to be related to a random Cantor dust with fractal dimension D=1−c, from which the scaling exponents are calculated using simple properties of fractal geometry. Fractal dimension Δ of the signal v is also studied using four different methods of calculation, giving Δ≈1.5, independent of the method used and of the parameter c. The stochastic model is analyzed in detail in order to clarify if the shown properties can be interpreted as manifestations of self-organized criticality in magnetic systems.

Fractal properties of the Barkhausen effect

The Barkhausen effect exhibits self-similarity properties at sufficiently low domain wall velocity. The statistical properties of the Barkhausen signal are in fact associated with a random Cantor dust of dimension D = 1 − c, where c < 1 is proportional to the applied field rate. Using general properties of the fractal geometry, we calculate the exponents γ = 2 − c and β = 3/2 − c/2 of the duration and size distribution, respectively. These predictions are well confirmed by experiments performed on a SiFe alloy.

Influence of microstructure on micromagnetic Barkhausen emissions in AISI 4140 steel

The effects of microstructure on the micromagnetic Barkhausen signal emissions in AISI 4140 steel are reported. The Barkhausen signal amplitude is known to be highly sensitive to the type and distribution of microstructural inhomogeneities, such as grain boundaries, precipitates and dislocations. The Barkhausen measurements were taken on samples having pearlitic, spheroidized and bainitic microstructures. The Barkhausen emissions were measured in terms of rms voltage peak-to-peak voltage and number of events per cycle. It is shown that Barkhausen signals can be used to distinguish between pearlitic and bainitic microstructures.

Scaling aspects of domain wall dynamics and Barkhausen effect in ferromagnetic materials

It is shown through theoretical considerations on stochastic domain wall motion in a perturbed medium with quenched-in disorder that the Barkhausen signal v, as well as the size Δx and duration Δu of Barkhausen jumps follow scaling distributions of the form v−α, Δx−β, Δu−γ, where α=1−c, β=3/2−c/2, γ=2−c, and c is proportional to the magnetization rate. In order to test these predictions, Barkhausen effect experiments were performed on polycrystalline SiFe alloys. Preliminary experiments to determine both the absolute value and the c dependence of the measured exponents are in agreement with the theoretical predictions.

Effects of surface stress on Barkhausen effect emissions: model predictions and comparison with X-ray diffraction studies

The detection of surface stress in materials is becoming increasingly important in failure analysis. In the case of ferromagnetic steels, the Barkhausen effect provides a practical tool for surface stress evaluation. However, one of the drawbacks of the method has been the lack of an underlying model theory for use in computer simulations of these effects. In recent work a model theory has been suggested and calculations of the effects of stress on the Barkhausen signal amplitude have been made. In this paper results are presented on Barkhausen measurements taken from surface modified materials and x-ray diffraction data from the same specimens. These results show a decrease in Barkhausen signal envelope amplitude with compressive stress in the surface of the material. >

Imaging surface conditions of ferromagnetic steel using Barkhausen technique

When ferromagnetic materials are magnetized, the resulting hysteresis curve consists of discontinuous changes in magnetization. This Barkhausen effect is produced by discontinuous domain mechanisms such as the domain wall breaking away from pinning sites due to the application of a magnetic field. For this reason, the Barkhausen effect is very useful for analyzing the microstructure of a material, since inhomogeneities in the microstructure act as pinning sites which restrict domain wall motion. It can be shown that Barkhausen data, in the form of an rms Barkhausen signal amplitude, can be used to image flaws on the surface of ferromagnetic steels. The material surface conditions, such as stress, cracking, oxidation, plastic deformation and pitting produce signal changes which ran be visualized through a computer generated image of the related Barkhausen parameters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Micromagnetic surface measurements for evaluation of surface modifications due to cyclic stress

The results of inspection fatigue damage by two magnetic nondestructive methods are presented. The magnetic hysteresis method can detect fatigue damage in the later stages of fatigue life. Magnetic Barkhausen signals, being highly sensitive to the surface condition of a material, show continuous change during the whole fatigue process. The Barkhausen effect measurement, aided by signal processing techniques, is therefore capable of monitoring surface modifications due to cyclic stress.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The retarding field model of Barkhausen noise and permeability in conventional and highly grain-oriented 3% Si-Fe polycrystals

The Barkhausen noise envelope, the permeability and the hysteresis curve in highly grain-oriented HiB-8, and in annealed and cold-worked conventional 3% Si-Fe were measured simultaneously in order to investigate the microstructural dependence of domain wall dynamics. The square and round hysteresis loops in the annealed and cold-worked specimen, respectively, are explained by the retarding field curve H r( x). The Barkhausen signal and the permeability are represented by the sum of the fluctuating Δ H I, i and the instantaneous averaged net field 〈 H I, i 〉. The two peaks of the enve lope observed in the annealed conventional 3%Si-Fe and HiB-8 at the knees of B-H loop and the single peak in the cold-worked specimen at H c are explained in terms of the distribution functions of the processes of domain nucleation f[Δ H I, i (nucl)], annihilation f[Δ H I, i (annih)] and wall displacement f[Δ H I, i (disp)]. T he frequency spectrum of the Barkhausen pulses was measured to investigate the nature of clustering and overlapping.

Evaluation of fatigue damage in steel structural components by magnetoelastic Barkhausen signal analysis

This paper is concerned with using a magnetic technique for the evaluation of fatigue damage in steel structural components. It is shown that Barkhausen effect measurements can be used to indicate impending failure due to fatigue under certain conditions. The Barkhausen signal amplitude is known to be highly sensitive to changes in density and distribution of dislocations in materials. The sensitivity of Barkhausen signal amplitude to fatigue damage has been studied in the low-cycle fatigue regime using smooth tensile specimens of a medium strength steel. The Barkhausen measurements were taken at depths of penetration of 0.02, 0.07, and 0.2 mm. It was found that changes in magnetic properties are sensitive to microstructural changes taking place at the surface of the material throughout the fatigue life. The changes in the Barkhausen signals have been attributed to distribution of dislocations in stage I and stage II of fatigue life and the formation of a macrocrack in the final stage of fatigue.

Comprehensive analysis of Barkhausen emission spectra using pulse height analysis, frequency spectrum, and pulse wave form analysis

The dependence of magnetic Barkhausen emissions (MBE) upon both field excitation and detection frequencies and excitation wave form was studied in order to investigate two of several crucial factors which affect the emissions. Sinusoidal, triangular, and square wave forms were used to generate the MBE and the pulse height spectra, frequency spectra, and pulse wave forms of these signals were analyzed. The frequency spectra of sinusoidal and triangular alternating field excitations showed similar behavior but the spectrum under square wave excitation was different due to the existence of high frequency components during square wave switching. As yet, no common standard has been agreed upon for parameterization and representation of Barkhausen signals. It appears from this work that field excitation wave form and frequency should define the inputs, while detection frequency range, pulse height spectrum, frequency spectrum, and emitted pulse wave form analysis should be used to quantify the output.

Effect of sensor configuration on magnetic Barkhausen observations

A number of characteristics of the magnetic Barkhausen signal, including power density, autocorrelation, jumpsum density, and noise emission rates, are obtained with different sensor types on low-carbon sheet steels and compared. The steel samples used in this study produced single, narrow Barkhausen peaks and the shapes of the rms voltage and jumpsum curves were found to be nearly independent of the sensor type.