Barkhausen Noise Measurements Research Articles

A data-based modelling scheme for estimating residual stress from Barkhausen noise measurements

A data-based modelling scheme for estimating residual stress from Barkhausen noise measurements

Non‐destructive subsurface damage monitoring in bearings failure mode using fractal dimension analysis

PurposeBearings in field applications with high dynamic loading, e.g. wind energy plants, suffer from sudden failure initiated by subsurface material transformation, known as white etching cracks in a typical scale of μm, preferably around the maximum Hertzian stress zone. Despite many investigations in this field no precise knowledge about the root cause of those failures is available, due to the fact that failure under real service conditions of wind energy plants differs from what is known from test rig results in terms of contact loading, lubrication or dynamics. The purpose of this paper is to apply Barkhausen noise measurement to a full bearing test ring running under conditions of elastohydrodynamic lubrication (EHL) with high radial preload.Design/methodology/approachFull bearing tests are carried out by use of DGBB (Deep Grove Ball Bearings) with 6206 specification, material set constant as 100Cr6, martensitic hardening, 10‐12 percent maximum retained austenite and radial preload of 3500 MPa. Speed is set 9000 rpm, temperature is self setting at 80°C by test conditions. For tests, synthetic hydrocarbon base oil (Poly‐α‐Olefine) with a 1 percent amount of molydenum‐dithiophosphate (organic chain given as 2‐ethylhexyl) was used.FindingsNon‐destructive fractal dimension analyses by use of Barkhausen noise measurements is of versatile value in terms of recording bearing manufacturing processes, but can also be part of non‐destructive condition monitoring of bearings in field applications, where predictive reactive maintenance is crucial for availability of the plant.Research limitations/implicationsBarkhausen noise signal recording may also be valuable for case studies related to microstructure changes of steel under operation conditions. Bearings are exposed in plenty of conditions to phenomena such as straying currents, subsequently straying magnetic fields. Hardly anything is known about how microstructure of bearing steel is susceptible to such conditions. This will be part of further studies.Originality/valueResults given in the paper show that sudden bearing failure, according to formation of subsurface material property changes might be driven by activities of dislocations. Since those activities start with sequences of stress field‐induced formation of domains, later by formation of low‐angle subgrains, and at least phase transformation, recording of the Barkhausen signal would lead to real predictive condition monitoring in applications where a highly dynamic loading of the contact, even with low nominal contact pressure leads to sudden failure induced by white etching.

Effect of Plastic Deformation on the Excess Loss of Electrical Steel

The interpretation of the effect of plastic deformation on the calculated excess loss component (anomalous-loss) supports the concept of loss separation. Magnetic losses and Barkhausen noise of nonoriented electrical steel sheets were measured on Epstein strips taken from a single coil of 0.8% Si nonoriented electrical steel. Sheets were extracted in the annealed condition, without any skin pass and with a grain size of 18 μm. This material was cold rolled in order to obtain sets of samples with true strain from 2% up to 29%. X-ray diffraction was used to estimate the dislocation density. The analysis of magnetic properties was performed by Barkhausen noise measurements and also by analyzing the hysteresis loops obtained from Epstein frame measurements for different inductions and different frequencies (including the quasi-static regime for hysteresis loss measurements). These data allowed us to observe that most of the well known total loss increase with plastic deformation is due to an increase in the hysteresis loss component, while excess loss decreases to become negligible. This behavior can be explained if it is assumed that the plastic deformation lead to an increase in the number of domain walls per unit volume, thereby decreasing the excess loss. Barkhausen peak area increases with plastic deformation, reproducing results taken from samples of different silicon content.

Study of Residual Stress and Vacancy Defects in Oxide Dispersion Strengthened Steels

Abstract This study was focused on commercial oxide-dispersion strengthened (ODS) steels -MA 956 (20%Cr), ODM 751 (16%Cr) and ODS Eurofer (9%Cr), developed for fuel cladding of GEN IV reactors. The ODS steels are described in order to comparison their microstructure features. Vacancy defects were observed by Doppler Broadening Spectroscopy (DBS) and Positron Annihilation Lifetime Spectroscopy (PALS). Residual stress proportional to all kinds of defects was investigated by Magnetic Barkhausen Noise (MBN) measurement. The positron techniques demonstrated the highest defect concentration for ODS Eurofer followed by MA 956. The lowest defect density belongs to ODM 751; although these defects are the largest (three or four vacancy clusters). MA 956 and ODS Eurofer have di-vacancies in predominance. MBN results are in a good accordance with positron techniques. The highest residual stress is for ODS Eurofer, followed by MA 956. Finally, the lowest residual stress proportional to hardness is found for ODM 751.

Quantitative prediction of residual stress and hardness in case-hardened steel based on the Barkhausen noise measurement

The aim of this study is to predict residual stress and hardness of a case-hardened steel samples based on the Barkhausen noise measurements. A data-based approach for building a prediction model proposed in the paper consists of feature generation, feature selection and model identification and validation steps. Features are selected with a simple forward-selection algorithm. A multivariable linear regression models are used in predictions. Throughout the selection and identification procedures a cross-validation is used to guarantee that the results are realistic and hold also for future predictions. The obtained prediction models are validated with an external validation data set. Prediction accuracy of the prediction models is good showing that the proposed modelling scheme can be applied to prediction of material properties.

Physics and Modeling of Magnetic Non Destructive Testing Techniques

Magnetic Non Destructive Testing (MNDT) methods are a tool not limited in the detection of cracks and defects, like traditional NDT methods for ferrous structures, but they have shown a potential for the monitoring of the structure and crack prevention. MNDT techniques include surface Magnetic Barkhausen Noise measurements (MBN) yielding localized information about the surface stresses and magnetization processes in the vicinity of the measurement; the use of Magnetostrictive Delay Lines (MDL) for the measurement of surface stresses; the Magneto Acoustic Emission (MAE), revealing information about the magnetic domain wall propagation and indirectly about the underlying structure’s role in the magnetization process of the material; magnetic major and minor loop (B-H) bulk measurements which yield information on the macroscopic magnetic properties of the material such as, the coercivity, Hc, the remanence, Br, or the permeability, µ. Results show that changes in these properties are definite signs of non-uniformly distributed stresses along the material and reveal a definitive dependence of the various magnetization reversal mechanisms such as domain wall propagation and domain rotation on the microstructure of the material,eg, the domain wall structure, the effect of dislocations, the grain size, built-in stresses. However, the quantitative mapping of the MNDT results to the microstructure and from there to the possibility of crack generation and propagation is still a very attractive but open question. Modeling at the atomic level involving Ising Models, at the microscopic level using micromagnetic calculations and at the macroscopic level employing the Preisach formalism, has so far provided useful insight. The use of modeling in order to not only explain experimental results but in forecasting is expected to greatly enhance the position of the MNDT techniques in industrial NDT.

Non-destructive examination of helium implanted HTRs construction materials

High chromium steels belong to the most prospective materials for reactor pressure vessel of High Temperature Reactors as well as for more components used in GEN IV facilities. Radiation resistance of GEN IV materials is a significant attribute. Therefore the process of microstructure deterioration due to irradiation followed by degradation of mechanical properties must be consistently investigated.This paper is focused on microstructure study of 9% chromium steels (T91, P91) and observation of residual stress as well as open volume defect accumulation after helium ion implantation performed at room temperature. Helium ion implantation should simulate changes of structure due to knocking-out of atoms during neutron irradiation. Investigated materials were studied by non-destructive experimental techniques based on the positron annihilation in the matter (Positron Annihilation Spectroscopy, Doppler Broadening Spectroscopy) and magnetic properties of iron alloys (Magnetic Barkhausen Noise Measurement). Results indicate higher resistance of T91 to defect formation during implantation than P91, although T91 shows higher residual stress in microstructure prior to implantation.

System for controllable magnetic measurement with direct field determination

This work describes a specially designed setup for magnetic hysteresis and Barkhausen noise measurements. The setup combines two main elements: an improved fast algorithm to control the waveform of magnetic induction and simultaneous direct determination of the magnetic field. The digital feedback algorithm uses only the previous measurement cycle to correct the magnetization voltage without any additional correlation parameter; it usually converges after several tens of cycles. The magnetic field is measured at the sample surface using a vertically mounted array of sensitive Hall sensors. Linear extrapolation of the tangential field profile to the sample surface determines the true waveform of the magnetic field. This unique combination of physically based control for both parameters of the magnetization process provides stable and reliable results, which are independent of a specified experimental configuration. This is illustrated for the industrially attractive measurements of non-oriented electrical steels with a 50Hz sinusoidal induction waveform.

Influence of microstructural constituents on the hysteresis curves in 0.2%C and 0.45%C steels

Steels with 0.2% and 0.45%C were submitted to different types of heat treatment, leading to different microstructures, with different amounts of the microstructural constituents: ferrite, pearlite and martensite. Measurements of magnetic hysteresis and Barkhausen noise were performed at different frequencies. A relationship was found between coercive force and the volume fraction of the microstructural constituents. The influence of the microstructural constituents on the shape of hysteresis curve is also discussed. The presence of martensite leads to more magnetization reversal by domain rotation, reducing the relevance of domain wall movement as a reversal mechanism. When domain wall movement predominates, permeability increases and coercivity decreases. As a consequence, when the martensite volume fraction increases, coercivity also increases. The results help clarify the relation between microstructure of steels and Barkhausen noise measurements in non-destructive testing.

New residual stress detector using angle resolved Barkhausen noise

A new possibility of residual stress detector is proposed for iron based materials through measurement of angle resolved Barkhausen noise which is known as phenomena of dynamic magnetic process. It is important for keeping safety of our society to early detect metal fatigue, therefore the convenient residual stress detector will be available especially for machines including any robots given heavy loads

Characterisation of as-cast model steels with parametric variation of Ni, Mn, Si and Cr content

In order to understand the role and influence of Cr, Ni, Si and Mn alloying elements on the mechanical properties of steels a large spectrum of ferritic steels with parametric variation of alloying elements as well as impurities content were prepared in the frame of the SAFELIFE Action of JRC-IE and the AMES Network. The composition of the 12 prepared model steels were inspired by typical base composition of WWER-1000 and PWR materials. The testing results showed the important role of Cr and Ni concentration in model steels composition. The ranges of ductile-to-brittle transition temperature differ between high and low Cr containing steels. An increase of Cr content in model steels leads to an increase of root mean square values of the Barkhausen noise measurements, independently on Mn and Si content. On the contrary, amount of Ni influences mostly the results of Barkhausen noise and relative Seebeck coefficient measurements.

NDT study of oxide dispersion strengthened steels

Various oxide dispersion strengthened (ODS) steels (PM2000, MA956, ODM751 and ODS Eurofer) have been investigated using positron annihilation lifetime spectroscopy. Preliminary characterization of the vacancy type defects and the yttria nanoparticles are reported in this paper. The interpretation of the experimental data considers also the results of magnetic Barkhausen noise (BN) measurements as well as SEM and TEM investigations. Significant differences due to the presence of the yttria oxides (namely Y2O3) were observed in the studied materials in comparison to conventional ferritic/martensitic steels (e.g. Eurofer). Higher positron mean lifetime in ODS steels is, however, not only due to the presence of dispersoids, but also a result of vacancy agglomeration (clusters of 6–8 vacancies) which have been confirmed in recrystallised ODM751 and MA956 materials. On the other hand, positron trapping at dislocations was observed in the as-extruded ODS Eurofer in contrast to the other, recrystallised, materials where the high temperature treatment had led to the static recovery of these defects. It is suggested that some defects which are present (dislocations, vacancy clusters and dispersoids) and affect positron trapping in the materials are also important pinning sites for the magnetic domains. This is reflected by a shift of the signal peak in the BN spectra. The present complementary study provides more comprehensive information about materials microstructure and can support the interpretation of the physical/mechanical testing results (hardness, fracture mechanics etc.) obtained on these materials.

Model Materials for Reactor Pressure Vessel

In this paper we report preliminary results from a study focused on investigation of the role of elements as Cr, Ni, Mn and Si in the radiation stability of reactor pressure vessel steels. Twelve model ferritic steels and eight model welds with basic composition derived from Russian VVER-1000 and Western PWR reactor pressure vessel materials were studied by magnetic Barkhausen noise and Charpy-V impact measurements. Comparison of these two model materials led to the conclusion that the ductile-brittle transition temperatures and Barkhausen noise RMS values of model steels are shifted to the lower values as those of model welds. The VVER-1000 as reference point is shifted to lower RMS values in comparison with model steels and model welds. The next stage of the assessment will involve the investigation of the radiation eect

Monitoring the Microstructural Evolution in Spheroidized Steels by Magnetic Barkhausen Noise Measurements

The aim of this study is to monitor nondestructively the degree of spheroidization in steels by Magnetic Barkhausen Noise (MBN) method. Various series of specimens consisting of either lamellar pearlite or partially/completely spheroidized carbides were produced from AISI 1060 steel by appropriate heat treatments. All specimens were characterized by metallographic examinations, hardness and MBN measurements. The results show that MBN signals are very sensitive to the variations in the microstructure caused by the spheroidizing heat treatment. The change of microstructure, from coarse lamellar carbides to uniformly dispersed spherical carbides in ferrite matrix, is reflected as higher Barkhausen activity due to less effective pinning of domain walls.

Investigation of shot-peened austenitic stainless steel 304L by means of magnetic Barkhausen noise

Different shot peening conditions were applied to an austenitic stainless steel AISI 304L in order to transform austenite to martensite α′ at different depths. Magnetic Barkhausen noise measurements performed on this steel reveal a correlation between the strength of the signal and the depth of the treatment. The combined effect of the volume fraction of martensite and the residual stress in martensite determined using X-ray diffraction analysis were found to be responsible for the evolution of the Barkhausen noise response. Using tensile plastic deformation, the residual stress in martensite was changed, giving rise to a strong increase of the Barkhausen noise activity. This variation was correlated to a modification of the sign and amplitude of the residual stress in the martensite phase. Directional measurements of the Barkhausen noise revealed the anisotropy of the residual stresses induced by the tensile plastic deformation. It is concluded that the Barkhausen noise activity recording could lead to the determination of the residual stresses in martensite induced by shot peening processes.

BARKHAUSEN: A study on laser-processed grinding burn simulation and analysis based on Barkhausen noise measurement

Barkhausen noise (BN) is widely used as a quality control method for grinding burn detection in ferromagnetic materials such as the case-hardened steels used in gears. The study of grinding burns with BN equipment requires, however, a calibration reference sample with a known BN response. The demand for better calibration samples is well recognised. In this study, artificial grinding burns with laser processing were produced in case-hardened steel. The laser was selected because it is a surface-sensitive heating method and it accurately simulates the heat generation during grinding between the grinding wheel and work-piece. A test series was made by changing the laser input power and traverse rate to process the surface of a ground gear wheel sample. The laser-processing parameters were optimised experimentally. The BN measurement data was used in the modelling of selected quality measures: hardness and residual stress (RS). The BN measurement device provided some features from the time-domain analysis of the signal and a new feature, BN entropy, was also used. The modelling was done with Matlab® using linear regression. The results showed that laser processing had a clear effect on the BN features and residual stresses.

The effect of precipitate size on magnetic domain behavior in grain-oriented electrical steels

Precipitates in the form of grain growth inhibitors play an essential role in the production of grain-oriented electrical steels, as they promote the development of Goss texture during secondary recrystallization. However, the presence of precipitates in the final material can have a detrimental effect on loss and permeability, as they impede domain wall motion during the magnetization process. In previous work [K. Jenkins and M. Lindenmo, J. Magn. Magn. Mater. 320, 2423 (2008)], a conventional grain-oriented electrical steel was presented that contained very fine precipitates, which did not damage the bulk magnetic properties. In this article the influence of precipitate size is investigated by comparing local Barkhausen noise measurements and electron backscatter diffraction analysis for a number of grain-oriented electrical steels, which are metallurgically similar except for the size and abundance of precipitates.

Barkhausen Noise and Magnetic Properties of Plastically Deformed Silicon Steels

We present Barkhausen noise and magnetic measurements on two fully processed, nonoriented electrical steels which had been cold-rolled to thickness reductions of up to 60%. Both coercive field H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and hysteresis loss W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> show an almost linear increase with thickness reduction up to the highest deformations. These changes are almost fully reversed after vacuum annealing for 2 h at 760°C. The hysteresis loss can be conveniently subdivided into high and low induction components as suggested by recent modelling. Electron back-scatter diffraction (EBSD) shows no texture change during initial phases of cold-rolling. Barkhausen noise measurements were obtained on both cold-rolled and annealed samples. The undeformed material shows a Barkhausen signature consisting of two small peaks which coalesce into one peak upon plastic deformation and thereafter grow steadily. Annealing the material brings back the two-peaked signature. These results are discussed and hypotheses are presented for the behavior of the Barkhausen noise.

Magnetic Barkhausen Noise for Characterization of Recovery and Recrystallization

The capacity of magnetic Barkhausen noise (MBN) measurements to characterize recovery and the onset and evolution of recrystallization processes occurring during the annealing of cold rolled low carbon steel is analyzed. Cold rolled low carbon steel samples were isothermally annealed at laboratory under different conditions in order to promote various degrees of recovery or recrystallization. The effect of recovery and recrystallization processes on the MBN envelope, the amplitude of the peak of the MBN envelope, the time integral of the MBN envelope and the MBN energy is discussed and related to the microstructural changes produced by these softening processes. The obtained results prove that several parameters derived from the MBN are able to follow the progress of recovery and recrystallization.

A Completely Configurable Digital System for Simultaneous Measurements of Hysteresis Loops and Barkhausen Noise

This paper describes a new accurate completely digital configurable computer-aided system for the simultaneous measurements of magnetic hysteresis loops and Barkhausen noise in a wide range of excitation frequencies (from 0.01 to 80 Hz) for the purposes of inspection of material properties and microstructure characterization. The importance of the correct choice of the data-acquisition (DAQ) card to have enough resolution in both hysteresis loop and magnetic Barkhausen noise (MBN) measurements is emphasized. Both the magnetic induction signal to construct the magnetic hysteresis loop and the Barkhausen noise are computed by the digital processing (numerical integration and digital filtering, respectively) of the induced electromotive force (EMF) signal. The accuracy of the hysteresis loop measurements is improved by using additional digital filters. The resolution of MBN results in simultaneous measurements is tested. Finally, some results of hysteresis loops and root-mean-square (RMS) envelopes of the MBN signal are presented to show the capability of the system to work at different excitation frequencies without changing any hardware.