Boleslaw Augustyniak

Application of Barkhausen effect measurements in piezomagnetic study of metallic glasses

Abstract Annealings can increase the ΔE effect up to 0.8, which is 0.05–0.3 in the as-quenched alloys. The Barkhausen effect gives information about the influence of the annealing conditions on the internal stresses (10–30 MPa in the as-quenched and 1–5 MPa in annealed alloys).

Comparison of Properties of Magnetoacoustic Emission and Mechanical Barkhausen Effects for P91 Steel After Plastic Flow and Creep

The correlation between magnetoacoustic emission intensity and mechanical Barkhausen effect intensity has been tested in the case of P91 steel having different microstructure states due to either plastic flow at room temperature or speeded-up creep, performed under stress 290 MPa at temperature 773 K. The plastic strain range for the first set of samples has been from 2.0% up to 10.5% and for the second one from 0.85% up to 10.0%. Both effects revealed analogous monotonous decrease of their intensities as a function of resulting plastic strain. The decrease was higher for plastic flow than for creep. Those results are well consistent with results of tensile tests of the as damaged samples.

Influence of Plastic Deformation on Stray Magnetic Field Distribution of Soft Magnetic Steel Sample

The effect of various combinations of conditions, i.e., presence of the Earths magnetic field during and after deformation on the distribution of stray magnetic field of S355 steel sample, which is locally deformed, was investigated. Some of the stages of the experiment were carried out in zero magnetic field. Compensation of the Earths magnetic field was obtained by the application of a pair of Helmholtz coils. These coils are able to produce homogeneous field compensating Earths magnetic field over the full length of the sample. Stray magnetic field measurements were carried out along the longest dimension of the sample using the probe consisting of mutually perpendicular sensors allowing the simultaneous measurement of two magnetic field components, i.e., tangential and normal to a surface of the sample. Research has shown that there is a correlation between the level of plastic deformation of the investigated sample and the distribution of stray magnetic field. It was found that the nature of stray magnetic field of the sample depends on presence of external magnetic field during unloading. An attempt was also made, with the finite-element analysis, to verify experimentally obtained stray magnetic field distribution of undeformed sample.

Multiparameter analysis of the Barkhausen noise signal and its application for the assessment of plastic deformation level in 13HMF grade steel

The paper presents the results of multiparameter analysis of Barkhausen noise (BN) signal properties. In addition to the commonly used quantifiers of the BN signal, such as amplitude, integral of the BN envelope or results of pulse count analysis, we propose an additional analysis based on the change in magnetizing current amplitude. As it turns out the character of the change of the BN signal (as a function of the plastic deformation level) measured for various magnetizing currents differs significantly. Being so, a comparison of the results obtained for at least two magnetizing intensities gives a much better description of a plastic deformation level. In addition to that we observe two monotonic changes in the BN signal properties—a systematic shift of the BN signal peak position and the increase in the frequency for which the maximum in the BN FFT spectra occurs.

Barkhausen Noise Properties Measured by Different Methods for Deformed Armco Samples

The main goal of this research is the comparison of Barkhausen effect (BN) properties evaluated by means of two different methods: 1) using a ¿point probe¿ appropriate for industrial application; and 2) using a surrounding coil. The point probe contains ferrite core with searching coil perpendicular to the surface, and the sample is magnetized with a C-core electromagnet. Three quantities have been measured using first method: V1- rms voltage over many periods, Nc-number of BN pulses with amplitude higher than a given threshold, V2-maximal value of the flux derivative in the C-core. In the second method, the sample is magnetized with external solenoid and voltage signal induced in surrounding coil is analyzed providing several quantities: hysteresis loop of magnetic flux density, envelopes of BN rms voltage and pulse count rate over one period of magnetization, In-an integral of the rms envelope, N-total number of pulses, ¿ m-maximal value of differential permeability. The samples made from Armco iron sheet have been plastically deformed by tensile load at room temperature up to ¿ p =20%. The differences in BN properties revealed by these two methods are discussed qualitatively and explained.

An In-Depth Study of the Barkhausen Emission Signal Properties of the Plastically Deformed Fe-2%Si Alloy

This paper presents the results of the in-depth study of the Barkhausen effect signal properties for the plastically deformed Fe-2%Si samples. The investigated samples have been deformed by cold rolling up to plastic strain epsivp = 8%. The first approach consisted of time-domain-resolved pulse and frequency analysis of the Barkhausen noise signals whereas the complementary study consisted of the time-resolved pulse count analysis as well as a total pulse count. The latter included determination of time distribution of pulses for different threshold voltage levels as well as the total pulse count as a function of both the amplitude and the duration time of the pulses. The obtained results suggest that the observed increase in the Barkhausen noise signal intensity as a function of deformation level is mainly due to the increase in the number of bigger pulses.

Modeling of Effect of Plastic Deformation on Barkhausen Noise and Magnetoacoustic Emission in Iron With 2% Silicon

Before one models the effect of plastic deformation on magnetoacoustic emission (MAE), one must first treat non-180 domain wall motion. In this paper, we take the Alessandro‐Beatrice‐Bertotti‐Montorsi (ABBM) model and modify it to treat non-180 wall motion. We then insert a modified stress-dependent Jiles‐Atherton model, which treats plastic deformation, into the modified ABBM model to treat MAE and magnetic Barkhausen noise (HBN). Infitting the dependence of these quantities on plastic deformation, we apply a model for when deformation gets into the stage where dislocation tangles are formed, noting two chief effects, one due to increased density of emission centers owing to increased dislocation density, and the other due to a more gentle increase in the residual stress in the vicinity of the dislocation tangles as deformation is increased. Index Terms—Iron-silicon steel, magnetic Barkhausen noise, magnetoacoustic emission, plastic deformation.

Separation of the Effects of Notch and Macroresidual Stress on the MFL Signal Characteristics

Magnetic flux leakage (MFL) distribution for three configurations of samples has been investigated in order to study the influence of notch and plastic deformation separately as well as together. Samples have been made of S355 steel. The MFL signal measurements were carried out along the longest dimension of the sample over a length of 120 mm. Two components of magnetic field were measured: 1) tangential to the main axis and 2) normal to the largest surface of the sample. Study has shown that geometrical effect, related to the notch presence, as well as plastic deformation with associated compressive macroresidual stresses, together are responsible for the specific MFL distribution above the sample. In order to confirm the assumption that the decrease of the permeability in the central part of the sample and the change of cross section are the main sources of the MFL anomaly, disrupting flux from demagnetization field, a series of simulations has been made. Simulation results coincide with those obtained experimentally and thus confirming the above hypothesis.

A new eddy current method for nondestructive testing of creep damage in austenitic boiler tubing

A new nondestructive eddy current technique is described for testing for incipient creep damage in austenitic steel boiler tubing in power plants. It is used because as incipient creep damage is formed, a magnetic oxide scale forms on the outside of the boiler tube in concentration proportional to the incipient creep damage; simultaneously in the base metal under the scale, a magnetic ferrite phase also forms in the grains and grain boundaries, which is in smaller concentration, but which is also in concentration proportional to the incipient creep damage. The eddy current signal can be processed in such a way that it varies monotonically and nearly linearly with the magnetic phase concentration and monotonically and nearly linearly with the incipient creep damage. Various aspects of the measurement are analysed and discussed—for example, liftoff, wall thickness, and diameter dependence. Using a zero point value to assess oxide layer permeability and dependence on conductivity is also discussed. Comparison is made between measurements and finite element modelling results.

The Finite Element Method Simulation of the Space and Time Distribution and Frequency Dependence of the Magnetic Field, and MAE

The study concerns a flat large construction steel plate of varying thickness magnetized with a C-core magnet. Modeling of the time- and spacefield distribution inside the plate is carried out. The novelty of the approach consists in carrying out a transient solution when a driving saw-tooth voltage is used. Also new is a refined magnetoacoustic emission (MAE) signal modeling, numerically deduced for various frequencies, and compared with experimental data. The distributions of fields are indirectly compared with stray field measurements and a close agreement is found