Oleksiy Perevertov

Correlation Between Hysteresis and Barkhausen Noise Parameters of Electrical Steels

In this work the potential of the Barkhausen noise technique for testing of the magnetic properties of electrical steels was studied. Different grades of nonoriented and grain oriented steels were tested in the quasi-static magnetization regime. A vertical array of three Hall sensors was used to control the sample field. Barkhausen noise was detected locally by a pancake coil with Fe-Si laminated core. A new parameter, Barkhausen noise coercivity, was introduced. Its linear correlation with the important magnetic parameters, the real coercive force and the hysteresis loss, was established. The applicability of the Barkhausen noise method for industrial control of the steel quality was discussed.

A System for Controllable Magnetic Measurements of Hysteresis and Barkhausen Noise

A specially developed setup for precise measurement of magnetic hysteresis and Barkhausen noise is presented in this paper. A novelty of the setup consists in a unique combination of two main features: an accurate local determination of the magnetic field and an improved feedback control of the magnetization process. First, the magnetic field is measured by two Hall sensors at different distances above the sample. The sample field is determined by a linear extrapolation of these measured profiles of the tangential fields to the sample surface. Second, a digital feedback loop for precise control of the ac magnetization process is proposed. The feedback algorithm combines two methods of magnetizing signal adjustment: linear corrections of the magnetizing voltage amplitude and phase. The presented system is able to adjust the waveform of the magnetic induction or field to the prescribed sinusoidal or triangular shape. This provides stable and physically accurate results, which are independent of a specific experimental configuration.

Magnetic response to cyclic fatigue of low carbon Fe-based samples

The Preisach model formalism has been applied to analyse hysteresis measurement results for evaluating fatigue damage in Fe-C alloys caused by cyclic fatigue loading. Hysteresis loops and differential permeability curves were measured at various stages of the fatigue life of the samples. The parameters which were built by means of the PMF and the classical hysteresis magnetic parameters (such as saturation magnetization, coercive field and others) were studied as a function of the fatigue lifetime. The present results show that the Preisach model analysis can be used to improve the sensitivity of magnetic hysteresis measurements for non-destructive evaluation of the accumulation of fatigue damage in steel components.

Investigation of two-phase samples by Preisach modelling

Model samples of iron-based alloys containing two magnetically different phases are used to demonstrate applicability of the Preisach model formalism for non-destructive testing of ferromagnetic materials. The suggested material uniformity parameters show their high sensitivity, provide quantitative relation with the relative volumes of the two phases in the samples and do not require saturation of the samples in the measurement.

Investigation of sensitivity of Preisach analysis for nondestructive testing

We applied the Preisach model formalism as a nondestructive material testing method to theoretical systems described by the Jiles-Atherton model. We investigated 1) the influence of stress in the model with magnetomechanical effects on a Preisach-model-based parameter and 2) the sensitivity of the parameter with respect to variation of all the Jiles-Atherton model constants and of the traditional magnetic hysteresis variables.

Dynamical Properties of Magnetic Barkhausen Noise in a Soft Microalloyed Steel

This paper investigates dynamical behavior of magnetic Barkhausen noise (BN). The measurements were performed for a soft mild steel at controllable magnetizing conditions: 1) the fixed sinusoidal/triangular waveforms of the magnetic induction or 2) the surface magnetic field. Two vertically mounted Hall sensors were used for direct determination of the sample magnetic field. The BN was detected locally by a surface-mounted coil. A typical two-peak shape of the BN envelope was found to reduce to a usual single-peak profile at the constant field rate. These two peaks were shown to correspond to the regions of the magnetic domain reconfiguration preceding and following the rapid magnetization reversal at the coercive field. In ac magnetizing frequency range of 0.2-30 Hz, the BN parameters followed a nearly square root dependence on the frequency. A low-frequency component of the BN signal, approximately up to 25 kHz, was revealed to contain an important part of the micromagnetic information.

3-D Branching of Magnetic Domains on Compressed Si-Fe Steel With Goss Texture

The influence of an applied compressive stress on the hysteresis curve and domain structure in conventional (110) [001] Fe-3%Si steel cut parallel to the rolling direction was studied. Quasi-static hysteresis loops under compressive stress up to 70 MPa were measured. The magnetic domains and magnetization processes were observed by longitudinal Kerr microscopy at different levels of stress. With increasing compressive stress, the domain structure in the demagnetized state evolves from initial simple 180° slab-like domains along the surface-parallel easy axis into stress pattern I, checkerboard pattern, and finally into stress pattern II at high stresses. The checkerboard pattern, observed at the intermediate stress level between 10 and 25 MPa, has not been reported before such thin sheets. The applied magnetic field makes the surface-parallel [001] domains with magnetization in field direction grow into the bulk at the expense of all other domains for all stress levels. The magnetization curves at stress above 10 MPa have a constricted shape with a sudden change of magnetization at a critical fields. The averaged critical field changes linearly with stress with a slope close to theoretical predictions.

Ni–Mn–Ga Single Crystal Exhibiting Multiple Magnetic Shape Memory Effects

Both magnetically induced phase transformation and magnetically induced reorientation (MIR) effects were observed in one Ni50Mn28Ga22 single crystal sample by direct measurement of the magnetic field-induced strain. We investigated various twinning microstructures ranged from single twin interface to fine twinning and crossing twins to evaluate what controls the apparent twinning stress crucial for MIR. The main challenges for the applications of these effects are outlined.

Changes in magnetic domain structure during twin boundary motion in single crystal Ni-Mn-Ga exhibiting magnetic shape memory effect

The complexity of Ni-Mn-Ga single crystal originates from the interplay between ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure in the vicinity of single twin boundary was studied using magneto-optical indicator film and magnetic force microscopy technique. The single twin boundary of Type I was formed mechanically and an initial magnetization state in both variants were restored by local application of magnetic field (≈40 kA/m). The differently oriented variants exhibited either stripe or labyrinth magnetic domain pattern in agreement with the uniaxial magnetocrystalline anisotropy of the martensite. The twin boundary was then moved by compressive or tensile stress. The passage of the boundary resulted in the formation of granular or rake domains, respectively. Additionally, the specific magnetic domains pattern projected by twin boundary gradually vanished during twin boundary motion.

A system for controllable magnetic measurements of hysteresis and Barkhausen noise

A specially developed setup for precise measurement of the magnetic hysteresis and Barkhausen noise is presented in this work. A novelty of the setup consists in a unique combination of two main features: an accurate local determination of the magnetic field and an improved feedback control of the magnetization process. Firstly, the magnetic field is measured by two Hall sensors at different distances above the sample. Linear extrapolation of this measured profile of the tangential fields to the sample surface gives the true local values of the magnetic field. Secondly, a digital feedback loop for precise control of the ac magnetization process is proposed. The system combines two known methods of magnetizing signal adjustment: linear corrections of the magnetizing voltage amplitude and phase. The presented system is able to adjust the waveform of the magnetic induction or field to the prescribed sinusoidal or triangular shape. This provides stable and physically accurate results, which are independent of a specific experimental configuration.