Magnetic Barkhausen Emission Research Articles

A Generalized Classification Framework with Simultaneous Feature Weighting and Selection Using Antlion Optimization Algorithm

ABSTRACT The use of machine-learning based algorithms on a large-scale nondestructive evaluation (NDE) data considerably advances the NDE techniques toward complete industrial automation. In this article, simultaneous feature selection and feature weighting are carried out on the magnetic Barkhausen emission (MBE) dataset to demonstrate the significance of optimization in NDE data. Antlion optimization is employed as a searching method to determine the optimum feature set that will maximize the classification performance. The proposed framework is validated for different magnetization frequencies separately and found to be frequency independent. The framework resulted in the selection of four significant features extracted from the MBE response thereby reducing the computational effort and improving the accuracy to 98.4% for AdaBoost classifier. The developed machine learning methodology is a potential strategy for processing industrial sensory data since material testing, property prediction, and categorization are frequent tasks in manufacturing and production engineering industries. Further, this research demonstrated the necessity of embedded intelligence in automation of NDE toward Industrial Revolution 4.0.

A Study of Stress – Induced Subtle Magnetic Changes in a Mild Steel using Barkhausen Emission-Aided Analysis Approaches

In this study magnetic Barkhausen emission – based approaches were used to reveal and characterize some interesting elastic stress - induced quantitative and qualitative subtle changes in the micromagnetic activity of steels. The quantitative changes consist in a multiplication of domain walls whereas the qualitative in the formation of two major modes of domain wall motion. Concerning the first kind of changes, it was shown that the experimentally obtained low limit of elastic stress at which such micromagnetic changes may occur is in reasonable agreement with existing theoretical as well as experimental results. Concerning the second kind of changes, it was shown by means of two types of distribution approach, that these two modes of wall motion may be related to the grain boundaries as well as the grain interior micromagnetic activity. In this context, it was also shown that an increase in the supplied elastic strain leads to a broadening of both distribution modes.

Microstructure- Assisted Changes in the Magnetic Barkhausen Emission of a Mild Steel Under the Influence of Various Mechanical and Environmental Loading Factors; a Semiquantitative Analysis

The aim of the present work is to introduce some novel possible ways for the semiquantitative analytical characterization of ferromagnetic steels. The characterization attempt focuses on microstructural changes occurring under the combined influence of certain mechanical loading as well as physico – chemical degradation factors such as applied stressstrain, tempering processing and salt water – induced electrochemical corrosion. In this direction, various conveniently simple developed functional modelling approaches are used to be able to analyse and estimate related experimental results obtained by means of micromagnetic Barkhausen emission measurements. The approaches are correlated to macroscaling as well as microscaling parameters such as stress-strain, dislocation – controlled cell size and pinning spacing – strength as well as internal cell flow stress. The needed correlations and estimations are made on the basis of an adopted specific micromagnetic activity parameter by which the obtained experimental data are compared and analysed. In this manner the opposite effects of internal flow stress and cell size reduction on the micromagnetic activity can reasonably be demonstrated where the first tends to stimulate an increase while the second a decrease in the specific micromagnetic parameter with progressive plastic deformation. One can further demonstrate that various physico-chemical degradation factors may markedly influence the microstructural as well as micromagnetic behaviour. For instance, hydrogen produced by corrosion of steel in NaCl – water solution and tempering processing lead to appreciable mechanical embrittlement as well as magnetic hardening of steel, expressed by an associated decrease in the specific micromagnetic parameter. With respect to this the tempering processing leads to a higher magnetic hardening compared to the corrosion process of steel.

Classification of process conditions in martensitic stainless steel: A machine learning approach on magnetic Barkhausen emission signals

Sorting of materials at different stages of manufacturing processes is very important to ensure the final product quality. In this paper, the machine learning algorithms are used on the magnetic Barkhausen emission (MBE) signals for the classification of martensitic stainless-steel specimens, which are subjected to different heat treatments. The variation in MBE parameters, such as root mean square, peak height, peak position, and full width at half maximum, was found to be marginal for normalized and quenching and partitioned specimens even though their x-ray diffraction analysis showed distinct microstructural conditions. The conventional MBE parameters are used to train the machine learning models. The performance of decision tree and ensemble learning techniques, such as Bagging, Random Subspace, AdaBoost, RUSBoost, Total Boost, and LP Boost classifiers, is compared and found that the AdaBoost classifier provides the maximum accuracy of 98% in the classification of complex materials. The results showed that the machine learning approach using a limited number of features is sufficiently sensitive toward the classification of specimens that are otherwise indistinguishable in their conventional MBE response.

Impact of Pre-formed Martensite on the Electromagnetic Properties and Martensitic Transformation Kinetics of Uniaxially Tensile Loaded 304 Stainless Steel

The investigation addresses the influence of tensile deformation on the magnetic properties of 304SS samples in their as-received state as well as those with martensite content of 12 and 17%. Non-destructive electromagnetic techniques like magnetic Barkhausen emission (MBE) and magnetic hysteresis loop have been used to measure variation in MBE voltage and coercivity, respectively, during plastic deformation through tensile loading. As both the techniques use surface probe, the present investigation will be useful for in situ evaluation of structural components. With progressive plastic deformation, those measurements revealed different stages of deformation indicated by change in MBE signal and magnetic coercivity. The stages of magnetoelastic response, strain-induced martensitic transformation, dislocation pile-ups and formation of voids reflected different patterns of magnetic Barkhausen emission and magnetic coercivity variation with progressive straining of austenitic stainless steel samples. The changes in true strain with variation in martensite content along gauge length of fractured samples have been analyzed with respect to martensite transformation kinetics. Mathematical fitting methodology has been adopted to distinguish as-received and pre-strained martensitic transformation characteristics. In situ magnetic NDE and associated martensitic transformation parameters may be useful for structural health monitoring of in-service components.

Effect of annealing treatment on magnetic texture of cold rolled ULC steel

Anisotropic behaviors of cold rolled and annealed ULC steels are evaluated by orientation imaging microscopy (OIM) and magnetic Barkhausen emission (MBE) techniques. The MBE voltage is found higher along RD than TD, indicating the presence of favorable magnetic easy axis along RD for both 50 and 80% cold rolled steels. The recovery occurred at low temperature (T < 500 °C) annealing causes a higher anisotropy coefficient (‘k’) for 50% than 80% CR steel, while at high temperature (T > 500 °C) annealing leads to an abrupt drop of ‘k’ value for both cold rolled steels. Furthermore, the kernel average misorientation map, obtained from OIM, decreases with increasing annealing temperatures.

Effect of high strain rate deformation on the properties of SS304L and SS316LN alloys

Effect of high strain rate deformation on the properties of SS304L and SS316LN alloys has been studied using Split Hopkinson Pressure Bar (SHPB) in the strain rate regime of 7 × 102–3 × 103. The results indicate towards a higher rate of increase in flow stress for SS304L steel as compared to SS316LN with increasing the strain rates. The results corroborate well with the extent of strain induced volume fraction of martensite, as measured using Magnetic Barkhausen Emission (MBE) technique. The steep increase in strength of SS304L at low strain e.g., < 5% and strain rate up to ∼1.8 × 103 s−1 is attributed to strain induced martensitic transformation. Whereas, SS316LN remains mostly nonresponsive in the strain induced phase transformation process in the entire strain rate regime. Both the materials have shown a poor strain hardening behaviour. Up to the strain rate 1.8 × 103 s−1 a growth of 23% and 18.5% of hardness value was observed in SS304L and SS316LN materials respectively. As the strain rate is further increased, hardness value in case of SS304L material has shown a decreasing trend, while that of SS316LN material has shown an increasing trend. The experimental observation has been tried to explain in terms of strain induced changes in their lattice structure that occur in the respective materials due to mechanical impact and their respective chemical composition.

Magnetic Evaluation of Tensile Deformation Behaviour of TRIP Assisted Steels

Two grades (690 and 980 MPa) of Transformation Induced Plasticity (TRIP) assisted steels were tensile-deformed to various strain levels to find the effect of tensile deformation on the mechanical properties of the steels. Brinell hardness was measured to find the hardening behaviour of the tensile-deformed steels. Magnetic Barkhausen Emissions (MBE) and magnetic hysteresis loop measurements were carried out on the specimens for the correlation of magnetic properties with the mechanical properties of the steels for their non-destructive magnetic evaluations. Coercivity and hardness were found to increase with the increase in plastic strain indicating work hardening of the steels whereas a continuous decrease in Root Mean Square (RMS) voltage of the MBE was found after an early increase. The early increase in RMS voltage of the MBE is due to the stress relaxation effect on the early stage of plastic deformation. A strong correlation was found between the coercivity and hardness of the steels indicating the potential application of the magnetic technique for the non-destructive evaluation of deformation behaviour of TRIP steels.

Magnetic Non-Destructive Evaluation of Softening of Cold Rolled Low Carbon IF Steel

Electromagnetic techniques such as Magnetic Hysteresis Loop and Barkhausen Emission are applied to determine recovery and recrystallization in low carbon IF steel. Isothermal annealing at 450 and 620°C are carried to promote recovery and recrystallization. In present study, the magnetic non-destructive parameters such as coercivity and magnetic Barkhausen noise signal measurements, recovery and onset of recrystallization are monitored for annealing treatments. Mechanical softening is very small changes than magnetic softening at 450°C, while at 620°C, both the parameters are sensitive. Microstructure analysis examined through Optical microscopy at each annealing temperature in order to determine recovery and recrystallization. Keywords: IF steel, Recrystallization, MHL, MBE, Hardness, Optical microscopy

Comparison Between Different Experimental Set-Ups for Measuring the Magnetic Barkhausen Noise in a Deformed 1050 Steel

The magnetic Barkhausen emission is investigated in deformed ANSI 1050 steel samples using four experimental configurations. These configurations vary according the type of magnetization (solenoid or yoke) and the recording the magnetic signal (bobbin above or around sample).The level of total strain was 0.4, 0.8, 1.0 and 3.0%. In all cases the same monotonous decrease dependence of emission magnetic with strain was obtained, showing that the four configurations give similar results. However, the yoke–pancake configuration was the most sensitive.

Detection and evaluation of embedded mild steel can material into 18 Cr-oxide dispersion strengthened steel tubes by magnetic Barkhausen emission

The paper presents a new methodology for detection and evaluation of mild steel (MS) can material embedded into oxide dispersion strengthened (ODS) steel tubes by magnetic Barkhausen emission (MBE) technique. The high frequency MBE measurements (125Hz sweep frequency and 70–200kHz analyzing frequency) are found to be very sensitive for detection of presence of MS on the surface of the ODS steel tube. However, due to a shallow depth of information from the high frequency MBE measurements, it cannot be used for evaluation of the thickness of the embedded MS. The low frequency MBE measurements (0.5Hz sweep frequency and 2–20kHz analyzing frequency) indicate presence of two MBE RMS voltage peaks corresponding to the MS and the ODS steel. The ratio of the two peaks changes with the thickness of the MS and hence, can be used for measurement of the thickness of the MS layer.

Characterization of High Temperature (873 K) Low Cycle Fatigue Damage in Modified 9Cr–1Mo Steel Using Magnetic Barkhausen Emission Technique

Modified 9Cr–1Mo (P91) ferritic steel is the steam generator structural material for prototype fast breeder reactor. During the start-ups and shutdowns, the material is subjected to conditions leading to low cycle fatigue damage. Detection of initiation of the fatigue damage is required to prevent the catastrophic failure in components of the steam generator. The present study reports the non-destructive characterization of substructural and microstructural changes occurring during low cycle fatigue (LCF) of modified 9Cr–1Mo base metal and weld joint at 873 K, using MBE measurements. MBE studies have been carried out on the samples at various levels of fatigue life by interrupting the fatigue test. MBE RMS voltage has been measured at different locations in the gauge portion of the samples to map the damage profile. The systematic changes in the MBE revealed various stages of progressive LCF damage starting from initial softening to final failure in the ferritic steel.

Non-destructive Magnetic Evaluation of Laser Weld Quality in Hot Rolled Coils

Weld quality evaluation was conducted on laser welded thin sectsions (2 mm) of hot-rolled (HR) low-carbon steel coils during cold rolling process. The analysis revealed that the poor welds consisting of the weld defects like incomplete fusion, cluster of porosity, and large difference in hardness between the weld zone and base metal were responsible for the weld failures. Experiments were conducted by varying the welding parameters; laser power and welding speed to optimize the parameters for minimizing the weld defects. The optimized weld process parameters have helped elimination of weld defects and the results are verified with microscopy and microhardness measurements. As destructive evaluation techniques are time consuming and not always permitted in industrial applications, attempts have been made in the present investigation for the utilization of suitable non-destructive techniques for the evaluation of weld quality. Non-destructive magnetic techniques of magnetic hysteresis loop and magnetic Barkhausen emissions were used in the present investigation to establish possible correlations of magnetic properties across the weld seam with the mechanical property (microhardness) for evaluation of weld quality. It is inferred that the magnetic properties of coercivity and inverse of root mean square voltage can be effectively utilized to determine weld quality in HR steel coils.

Evaluation of post-weld heat treatment behavior in modified 9Cr–1Mo steel weldment by magnetic Barkhausen emission

The butt joint of two sight tubes of modified 9Cr–1Mo steel is welded by TIG technique. Subsequently, the post-weld heat treatment (PWHT) of the tubes has been carried out at 650, 700 and 750 °C temperatures for 3 h. Magnetic Barkhausen emission (MBE) measurements are performed in fusion zone, heat affected zone (HAZ) and base metal region of as-welded and all the post-weld heat treated samples. In each weldment, the variation of the MBE signal emanated from fusion zone, HAZ and base metal has been examined. It is found that the RMS voltage of MBE signal increases with PWHT temperature. The conversion of retained austenite to alpha ferrite during PWHT makes the fusion region as a softer zone in the weldment. The variation of magnetic parameters with different PWHT is correlated with hardness and microstructures. This study can be used as an effective tool in evaluation of PWHT parameters in modified 9Cr–1Mo weld joint.

Damage evaluation of fossil fuelled power plant boiler tubes through magnetic Barkhausen technique

The failure mechanism of two economizer tubes of a fossil fuelled 260MW power plant has been investigated through the magnetic Barkhausen emission (MBE) technique along with the conventional and established materials characterization and evaluation techniques (like microstructures, mechanical properties and X-ray diffraction). The longer service exposer period results in the breaking of ferrite–pearlite structure and spheroidization lamellar cementite in ferrite matrix, associating with high magnetic r.m.s. voltage for former structure. The failure mechanism was governed by the cold end corrosion process with the presence of sulfates, and the subsequent erosion through hard quartz particles leads to a localized thinning of outer surface. Accordingly, the hoop stress was operative in tube walls and failed through fish-mouth opening. The MBE r.m.s. voltage response and pulse height distribution throw light on microstructural changes with duration of service exposure as well as leaked and non-leaked regions of economizer tubes.

Optimization of sensor design for Barkhausen noise measurement using finite element analysis

The effects of design parameters for optimizing the performance of sensors for magnetic Barkhausen emission measurement are presented. This study was performed using finite element analysis. The design parameters investigated include core material, core-tip curvature, core length, and pole spacing. Considering a combination of permeability and saturation magnetization, iron was selected as the core material among other materials investigated. Although a flat core-tip would result in higher magnetic flux concentration in the test specimen, a curved core-tip is preferred. The sensor-to-specimen coupling is thereby improved especially for materials with different surface geometries. Smaller pole spacing resulted in higher flux concentration.

Barkhausen spectroscopy: Non-destructive characterization of magnetic materials as a function of depth

In this study, we conceptually divided a ferromagnetic specimen into layers along its depth. For each layer, we derived a non-linear integral equation that describes the attenuation with frequency and distance of magnetic Barkhausen emissions coming from that layer. We postulate that the Barkhausen spectrum measured at the surface by an induction coil can be expressed as the sum of the individual layer spectra. We show how a non-linear least squares algorithm can be used to recover the properties in individual layers. These are related to stress using an extension to the theory of ferromagnetic hysteresis. We found that the quality of the fit is influenced by the sensitivity of the ferromagnetic material to strain, as well as by the sensor-specimen coupling. The proposed method can be used for the non-destructive characterization of stress as a function of depth in magnetic materials.

Comparison of four NDT methods for indication of reactor steel degradation by high fluences of neutron irradiation

Results of three magnetic nondestructive methods, Magnetic Barkhausen Emission (MBE), magnetic minor loops Power Scaling Laws (PSL) and Magnetic Adaptive Testing (MAT), and of one reference mechanical measurement, Vickers Hardness (HV), applied on the same series of neutron heavily irradiated nuclear reactor pressure vessel steel materials, were normalized and presented here for the purpose of their straightforward quantitative mutual comparison. It is uncommon to carry out different round-robin testing on irradiated materials, and if not answering all open questions, the comparison alone justifies this paper. The assessment methods were all based on ferromagnetism, although each of them used a different aspect of it. The presented comparison yielded a justified recommendation of the most reliable nondestructive method for indication of the reactor steel irradiation hardening and embrittlement effects. The A533 type B Class 1 steel (JRQ), and the base (15Kh2MFA) and welding (10KhMFT) steels for the WWER 440-type Russian reactors were used for the investigations. The samples were irradiated by high-energy neutrons (>1MeV) with up to 11.9×1019n/cm2 fluences. From all the applied measurements, the results of MAT produced the most satisfactory correlation with independently measured ductile-brittle-transition temperature (DBTT) values of the steel. The other two magnetic methods showed a weaker correlation with DBTT, but some other aspects and information could be assessed by them. As MAT and MBE were sensitive to uncontrolled fluctuation of surface quality of the steel, contact-less ways of testing and more conveniently shaped irradiated nuclear pressure vessel steel samples were suggested for future measurements.

Residual Stress Analysis in Surface Mechanical Attrition Treated (SMAT) Iron and Steel Component Materials by Magnetic Barkhausen Emission Technique

Surface plastic deformation processes like shot peening (SP) have been extensively used by engineering industries to introduce compressive stresses at the surface to achieve superior mechanical properties (especially fatigue and wear resistance). A new family of surface severe plastic deformation processes (S <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PD) using high-energy balls, widely known as the Surface Mechanical Attrition Treatment (SMAT), is gaining prominence. The investigation addresses the analysis of residual stresses in SMAT-exposed pure iron and SA 516 Grade 70 pressure vessel steel components by Magnetic Barkhausen emission (MBE) technique which is a potential nondestructive evaluation tool. The stresses corresponding to optimized band filter frequencies in MBE technique exhibit good correlation with the X-ray-diffraction based residual stress measurement data. The stresses correlate at a filter frequency of 100-250 kHz in the case of pure iron and 100-300 kHz in the case of SA 516 Grade 70 pressure vessel steel. Depth profiling by chemical etching showed that the nature of stresses changed from compressive to tensile. Microhardness measurements revealed an exponential decrease of hardness with depth.

Modeling the effects of nanosized precipitates on magnetic hysteresis and Barkhausen effect signal

A model has been developed for describing the effects of randomly distributed precipitates on magnetic hysteresis and Barkhausen emissions based on a hysteretic-stochastic process model of domain wall dynamics. The pinning of magnetic domain walls by spherical precipitates is described in terms of the pinning strength, which is proportional to the number density and cross-sectional area of the precipitates, and of the interaction range, which depends on the particle spacing and grain size. The model was used to simulate hysteresis loops and Barkhausen effect signals of a series of thermally aged FeCu samples with different number densities and sizes of Cu-rich precipitates. The linear dependence of the coercivity on the sample hardness was reproduced in the simulations. The rms values and pulse height distributions of the measured and modeled Barkhausen signals show similar dependence on the aging time, which can be interpreted by considering the effects of varying the precipitate size and spacing on the strength and interaction range of domain wall pinning.