Magnetic Barkhausen Noise Profile Research Articles

Barkhausen Noise as A Magnetic Nondestructive Testing Technique

Magnetic Barkhausen Noise (MBN) is a magnetic-based non-destructive electromagnetic testing method. Due to the electromagnetic working principle of MBN, it can be used for ferromagnetic materials, which consist of small magnetic fields discredited by domain walls and oriented in various directions. In an external magnetic field application, the fields turn to the magnetic direction, and the domain walls move and cause magnetic flux jumps. The jumps are named Barkhausen Noise (BN). The domain wall movements are sometimes pushed down by microstructure, composition, and defects. As the magnetic domain walls break away from the pinning sites produce MBN signal. MBN can be used for different material properties such as microstructure, composition, residual stress, and hardness. The paper's purpose is to analyze MBN as an improved NDT, clarify the relationship between material properties and MBN profile, and introduce MBN's applications and test equipment of MBN.

Quantitative Evaluation of the Effect of Temperature on Magnetic Barkhausen Noise.

The effect of temperature on magnetic Barkhausen noise (MBN) can be divided into two types: the direct effect of temperature itself and the indirect effect of thermally induced stress. The theoretical model is proposed in this paper to describe the effects of temperature on the MBN signal. For the case considering the direct effect of temperature only, the analytical model allows the prediction of the effect of temperature on MBN profile, and, based on the model, a simple linear calibration curve is presented to evaluate the effect of temperature on MBN amplitude quantitatively. While for the case where the indirect effect of thermal stress is taken into account in addition to the direct effect, the proposed theoretical model allows the deduction of parabolic function for quantitative evaluation of the combined effect on MBN. Both effects of temperature on MBN, i.e., the direct only and the combined one, have been studied experimentally on 0.5 mm thickness non-oriented (NO) electrical steel and the adhesive structure of NO steel and ceramic glass, respectively. The reciprocal of the measured MBN peak amplitude (1/MBNp) in the first case shows a linear function of temperature, which agrees with the proposed linear calibration curve. While in the experiments considering the combined effects, 1/MBNp shows parabolic dependence on temperature, which is further simplified as a piecewise function for the practical applications.

Non-Destructive Characterization of Subsurface Plastic Deformation in Case Carburized Steel Using Magnetic Barkhausen Noise Technique

The effect of extreme loading in bending was investigated by magnetic Barkhausen Noise (MBN) and X-ray diffraction (XRD) in two types of inhomogeneous steels that widely used in gear industry. EN 36 and H8620 steels in the carburized, tempered and ground condition were investigated after unloading from high stress levels. The inhomogeneity arising from the variation in carbon content showed up clearly by double peaks MBN profiles before loading. The first MBN peak at low field revealed the soft subsurface region and the second peak at higher field revealed the hard surface layer. Residual stresses profiles were produced by XRD before and after loading to probe plasticity in the cross sections of both specimens. Barkhausen noise measurements showed a considerable change in the first peak height in both steels as a response to plastic deformation in tension and compression in the subsurface material. The height of the second peak remained unchanged in EN 36 specimen but increased slightly in the H8620 specimen. The residual stress measurements after unloading indicated that the subsurface materials after a depth of 0.4 mm in both specimens were yielded. The surface layer of the H8620 steel was also affected slightly by bending as revealed by an increase in the second MBN peak height and confirmed by XRD as indication of yielding. The experiment confirmed that the magnetic Barkhausen noise can be used to characterize yielding in inhomogeneous steels non-destructively.

Non-Destructive Characterization of Subsurface Plastic Deformation in Case Carburized Steel Using Magnetic Barkhausen Noise Technique

The effect of extreme loading in bending was investigated by magnetic Barkhausen Noise (MBN) and X-ray diffraction (XRD) in two types of inhomogeneous steels that widely used in gear industry. EN 36 and H8620 steels in the carburized, tempered and ground condition were investigated after unloading from high stress levels. The inhomogeneity arising from the variation in carbon content showed up clearly by double peaks MBN profiles before loading. The first MBN peak at low field revealed the soft subsurface region and the second peak at higher field revealed the hard surface layer. Residual stresses profiles were produced by XRD before and after loading to probe plasticity in the cross sections of both specimens. Barkhausen noise measurements showed a considerable change in the first peak height in both steels as a response to plastic deformation in tension and compression in the subsurface material. The height of the second peak remained unchanged in EN 36 specimen but increased slightly in the H8620 specimen. The residual stress measurements after unloading indicated that the subsurface materials after a depth of 0.4 mm in both specimens were yielded. The surface layer of the H8620 steel was also affected slightly by bending as revealed by an increase in the second MBN peak height and confirmed by XRD as indication of yielding. The experiment confirmed that the magnetic Barkhausen noise can be used to characterize yielding in inhomogeneous steels non-destructively.

Barkhausen noise signal of different steels upon face-turning process

This paper deals with understanding the effects of excitation field parameters on the nature of Barkhausen noise profile in order to improve the validity of Barkhausen noise results for the machining process. The experiment has been performed on total of four samples, two of high carbon steel and two of high carbon chromium steel. First, all samples are subjected to process annealing and later one sample of each steel was subjected to face-turning process. Barkhausen noise measurement was performed in two steps: first, magnetizing frequency varied and magnetic field intensity kept constant, and second, magnetic field intensity varied and magnetizing frequency kept constant. Magnetic Barkhausen noise profile is obtained by fitting Gaussian function to the root-mean-square distribution of the Barkhausen signal. The complicated behaviour of the profiles with frequency suggests optimum frequency determined statistically, which reflects the stochastic behaviour and can be applied to describe and control the face-turning process. The peak value of the profiles with amplitude of the sinusoidal magnetic field intensity has found to resemble exponential decay correlation.

Experimental evaluation of domain wall dynamics by Barkhausen noise analysis in Fe30Co70 magnetostrictive alloy wire

Abstract Magnetic Barkhausen noise (MBN) plays significant roles to describe the dynamic of domain walls (DWs), but an in-depth understanding of the correlation between Barkhausen effect and magnetostrictive effect during magnetization process is still limited. In this study, we investigated MBN signals and the frequency spectra in a high-magnetostrictive Fe30Co70 alloy wire (λs = 102 ppm) by evaluating the stress effects on MBN profiles at the stress range of 0–150 MPa using tensile test machine. The results from MBN profiles revealed that MBN in the high magnetic field region was responsible for the localized changes of magnetic flux density, dB/dt induced by magnetic distortion related to non-180° DWs or the magnetization rotation. In MBN spectra, the peak shift towards lower frequencies with the increase of stress indicates that the rough pulse-like MBN outbreaks increase, and it results mainly from the increase of DW jumping length which is caused by the pinning effect at grain boundaries where DW energy is relatively high. In addition, stress dependence of the root mean square (RMS) value of MBN showed a good sensitivity (0.038 mV/MPa). Overall, these findings indicate that new MBN measurement system utilizing magnetostrictive materials can be helpful for a wide range of applications such as mechanical stress sensors and energy harvester systems.

Important Factors Influencing the Magnetic Barkhausen Noise Profile

The systematic effects of applied current amplitude to the magnetizing coil, distance between the poles of the electromagnetic yoke, magnetic excitation frequency, sensitivity and frequency response of magnetic Barkhausen noise (MBN) pickup coil, and the geometry of the test sample on the applied magnetic field strength, the tangential magnetic field strength, and the MBN signal profile are presented in this paper. The influence of different parameters is discussed with measurement results obtained from harder case-carburized steel and softer spheroidized annealed steel samples. This paper shows the importance of maximizing the shape of the MBN profile for an appropriate evaluation of ferritic steels.

On the shape of the magnetic Barkhausen noise profile for better revelation of the effect of microstructures on the magnetisation process in ferritic steels

The shape of the Magnetic Barkhausen Noise (MBN) profiles has been compared for two different methods of MBN measurements in order to reveal the true extent of the influence of different carbon-content related microstructures on the magnetisation process. The MBN profiles were measured using high frequency and low frequency MBN measurement systems on samples from low carbon 18CrNiMo5 steel and high carbon 42CrMo4 steel heat treated by isothermal annealing, spheroidising annealing and quenching and tempering processes. The high frequency MBN (HFMBN) profile shows only a single peak for all the samples due to insufficient applied magnetic field strength and shallow skin-depth of detection of HFMBN signals. The low frequency MBN (LFMBN) profile shows two peaks for all the samples due to larger magnetisation range revealing the difference in the interaction of domain walls with different microstructural features such as ferrite, pearlite, martensite and carbides. The shape of the LFMBN profile shows systematic and distinct variation in the magnetisation process with respect to carbon content and different microstructures. This study shows that the LFMBN profile reveals distinct changes in shape which could be successfully used for characterisation of different microstructural phases in ferritic steels.

New feature extraction for applied stress detection on ferromagnetic material using magnetic Barkhausen noise

This paper reports on the new feature extraction for the determination of applied stress using magnetic Barkhausen noise (MBN). Low frequency triangular waveform excitation is used to produce alternative magnetic field on case-carburized and tempered En36 steel specimens. Under applied elastic stress, both of the compressive and tensile type, the MBN signal is measured and the profile of MBN signal is obtained. Effective damping in Barkhausen noise for asymmetric shape is studied with compressive and tensile applied stress characterization. Then the skewness of the MBN profile is presented as a new feature for stress detection. Non-linear behavior and sensitivity of the new feature are compared with root mean square (RMS) peak value and peak position. Domain wall energy and eddy current damping are discussed as the reason of the phenomenon.

Magnetic Barkhausen Noise Profile Analysis: Effect of Excitation Field Strength and Detection Coil Sensitivity in Case Carburized Steel

The sensitivity of magnetic Barkhausen noise (MBN) profile to changes in the excitation field strength and the number of turns of the detection coil was investigated in inhomogeneous material. Generally, the 0.5 mm case depth EN 36 steel specimen shows a double peak profile indicative of inhomogeneity through the detected depth the magnetized landscape. Various excitation field amplitudes were applied to the specimen and the induced MBN emission was analyzed for each magnetizing current. Excitation field at the lowest level induced an MBN emission of two peaks of equivalent heights. The first peak occurs at lower field than the second peak in the magnetization period. As the excitation field increased, the height of both peaks increased but the second peak increased in a higher rate than that of the first peak. Beyond certain excitation level, both peaks began to saturate and no increase in the MBN intensity was observed with increased excitation field strength. However, peak position and the number of Barkhausen events, indicated linearly as a function of the applied field strength. The experiment also establishes that the number of turns in the detection coil is important parameter which controls the height of the first peak. Low field peak height increases as the number of turn of the detection coil increases. The results indicate that the potential difference applied to the electromagnet and the sensitivity of the detection coil, determine the MBN profile characteristics.

Influence of applied magnetic field strength and frequency response of pick-up coil on the magnetic barkhausen noise profile

The influence of applied magnetic field strength and frequency response of the pick-up coil on the shape of Magnetic Barkhausen Noise (MBN) profile have been studied. The low frequency MBN measurements have been carried out using 5 different MBN pick-up coils at two different ranges of applied magnetic field strengths on quenched and tempered (QT) and case-carburised and tempered (CT) 18CrNiMo7 steel bar samples. The MBN pick-up coils have been designed to obtain different frequency response such that the peak frequency response varies from ∼4kHz to ∼32kHz and the amplitude of low frequency signals decreases gradually. At lower applied magnetic field strength of ±14,000A/m, all the pick-up coils produced a single peak MBN profile for both QT and CT sample. However, at higher applied magnetic field strength of ±22,000A/m, the MBN profile showed two peaks for both QT and CT samples for pick-up coils with peak frequency response up to ∼17kHz. Also, there is systematic reduction in peak 2 for QT sample and asymmetric reduction in the heights of peak 1 and peak 2 for CT sample with increase in peak frequency response of the pick-up coils. The decreasing sensitivity of pick-up coils with increasing peak frequency response to MBN signal generation is indicated by the gradual reduction in width of MBN profile and height of peak 2 in the QT sample. The drastic reduction in peak 1 as compared to peak 2 in the CT sample shows the effect of decreasing low frequency response of the pick-up coils on lowering skin-depth of MBN signal detection. This study clearly suggests that it is essential to optimise both maximum applied magnetic field strength and frequency response of the MBN pick-up coil for maximising the shape of the MBN profile for appropriate correlation with the magnetisation process and hence the material properties.

The effect of microstructure and applied stress on magnetic Barkhausen emission in induction hardened steel

The influence of elastic deformation on the emission of magnetic Barkhausen noise (MBN) was investigated for induction-hardened low alloy steel with two different treatments: a standard temper (ST) and an over temper (OT) heat treatment. The rectified MBN profiles were found to be reversible with respect to loading and unloading, i.e., a profile that was changed by application of stress was recovered when the stress was removed. Characteristics of the profiles (peak height Vp, peak position Ip and half-width Wp) were recorded as a function of applied stressσ. Plots of Vp versus σ were S-shaped, with Vp reaching a maximum on the tensile side of the graph and a minimum on the compression side. In a more restricted stress range, between −500 and 1,000 MPa, Vp was an approximately a linear function of σ. The OT specimens showed greater sensitivity to stress than the ST specimens. Another difference was that the OT specimens produced an MBN profile with two overlapping peaks when under compression. The other profile characteristics showed a relationship with stress that ran counter to that of Vp, i.e., where Vp increased with increasing stress, Ip and Wp decreased. The observations are discussed in the light of established models of Barkhausen noise.

Effect of hardness and composition gradients on Barkhausen emission in case hardened steel

The effect of gradients in hardness, structure and composition in the surface layers on magnetic Barkhausen noise (MBN) was investigated in two widely used low alloy steels. One material was case hardened by induction hardening. The other was case carburised. Similar hardness profiles were produced by the two treatments. It was found that the variation in structure and hardness through the case in the induction-hardened steel had a minor effect on the MBN profile. In contrast, the inhomogeneity in the case-carburised material showed up clearly. This took the form of a broadened or two-peak MBN profile. When the surface layer containing the case was removed by etching, the broadened profile was replaced by a profile with a single peak. It is concluded that the shape and position of the MBN profile is significantly affected when a gradient in microstructure is induced by a gradient in carbon content. On the other hand, a gradient in microstructure induced by heat treatment with a constant carbon level has much less affect on the MBN profile for the induction-hardened steel.

Surface decarburisation of steel detected by magnetic barkhausen emission

The effect of decarburisation of the surface layer on magnetic Barkhausen noise (MBN) emission was investigated in quenched and tempered steel containing 0.67% carbon. The MBN profile of intensity versus energising current from the un-decarburised material showed a single peak typifying the martensite structure. After decarburisation, a profile with a double peak was obtained. The presence of the decarburised layer produced a second, overlapping peak at a lower field value. The height of the second peak increased with increasing depth of decarburisation and its position moved to increasingly lower field values.

Effect of deformation in bending on magnetic Barkhausen noise in low alloy steel

The influence of bending deformation on magnetic Barkhausen noise (MBN) was studied in low alloy steel. The peak height of the rectified MBN profile was observed to increase systematically with increasing tensile strain until the onset of plastic deformation. Increasing compressive strain initially produced a reduction in peak height, but more complex behaviour was observed at larger values. In particular, broadened profiles were produced under compression, which may indicate the presence of two or more overlapping peaks. As confirmed by X-ray diffraction measurements, one effect of plastic deformation is to leave a residual compressive stress on the tension side of the specimen and a residual tensile stress on the compression side. Measurements of residual stress were correlated with MBN peak height, to the extent that both quantities show functional forms similar to the theoretical relationship between residual stress and the bending moment applied prior to unloading.

Magnetic Barkhausen noise: the influence of microstructure and deformation in bending

The effect of microstructure and bending deformation on the characteristics of magnetic Barkhausen noise profiles were examined in carbon steel of the type used for wear-resistant engineering components. Microstructures associated with magnetic softness produced the largest profile peaks and the lowest peak positions. Multi-peak profiles were observed in compression in spherodised cementite specimens and to a much smaller extent in the martensite tempered at 400 °C. In the spherodised cementite, the change from a sharp, single peak to a broad, three-peak profile, with a greatly reduced height was precipitous and occurred over a small strain increment. Where single-peak profiles were obtained, strain affected emission but did not alter the ranking imposed by microstructure. The most magnetically soft microstructure (spheroidal cementite) seems to confer little scope for a positive increase in emission with increasing strain. The most magnetically hard (martensite) showed the greatest relative strain sensitivity. All the profiles observed were reversible with respect to loading and unloading in the elastic regime. The onset of plasticity did not induce any discontinuous change in the profiles whilst under load but it did induce irreversibility on unloading, due, in part, to the residual stresses induced by the inhomogeneous deformation in bending. The observations are discussed in the light of established models of Barkhausen noise.

Effect of deformation in bending on magnetic Barkhausen noise in low alloy steel

The influence of bending deformation on magnetic Barkhausen noise (MBN) was studied in low alloy steel. The peak height of the rectified MBN profile was observed to increase systematically with increasing tensile strain until the onset of plastic deformation. Increasing compressive strain initially produced a reduction in peak height, but more complex behaviour was observed at larger values. In particular, broadened profiles were produced under compression, which may indicate the presence of two or more overlapping peaks. As confirmed by X-ray diffraction measurements, one effect of plastic deformation is to leave a residual compressive stress on the tension side of the specimen and a residual tensile stress on the compression side. Measurements of residual stress were correlated with MBN peak height, to the extent that both quantities show functional forms similar to the theoretical relationship between residual stress and the bending moment applied prior to unloading.

Evaluation of tempering induced changes in the hardness profile of case-carburised EN36 steel using magnetic Barkhausen noise analysis

The effect of tempering on the magnetic Barkhausen noise (MBN) signal profile was studied in case-carburised EN36 steel using a range of magnetic excitation frequencies and a number of frequency ranges for analysis of the MBN signal. The MBN level generally increases with tempering due to coarsening of the microstructure. With higher values of excitation frequency, f EX, the MBN profile exhibits a single peak, but with low values of f EX, double peaks are observed. The MBN peak obtained with higher f EX was found to correlate well with hardness changes in a region, down to 100 μm below the surface. The analysis of the MBN signal produced with low f EX, in narrow frequency ranges selected by software frequency filtering, showed variations in the extent of changes in the relative height of the two MBN peaks in the profile. After taking into account the skin depth-frequency relation for the MBN signal, variations in the values of the two MBN peaks in different analysing frequency ranges were found to correlate well with hardness variations at different depths down to 425 μm below the surface. An empirical relationship has been established between the hardness-depth profile and the MBN measurements.