Papers by Keyword: Barkhausen Noise

Abstract: 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, H_c, the remanence, B_r, 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.

Abstract: Results of an experimental study of electrical steel annealed at 500, 600, 700 °C and subsequently cooled via quenching or air, are presented. The samples have been characterized with respect to their magnetic properties using Magnetic Barkhausen Noise (MBN) and major and minor loop (B-H) measurements. MBN increases slightly with the annealing temperature especially in the quenched samples. The B-H loops suggest that the prevalent magnetization reversal mechanism in the air cooled samples is domain wall propagation, while in the quenched samples non 180^o domain rotation seems to be significant approaching the high induction region. Scanning Electron Microscopy studies show a more homogeneous texture after annealing which in the case of the quenched samples is accompanied by not fully formed grain boundaries and orientation along he easy axis

Abstract: The corrosive influence of 3,5% sodium chloride – water solution on tensile mechanical and Barkhausen magnetical noise response of an ARMCO steel was investigated. This response was correlated with the micro-failure behavior gained by SEM – Fractography observations. It was found that the increasing time (degree) of corrosion leads to a dramatic and consistent decrease of the tensile ductility and to a noticeable increase of the Barkhausen noise signal. Especially, it was shown that during the tensile loading of the corroded specimens the magnetic Barkhausen signal is monotonically increasing up to the fracture point. This on load increase of the magnetic signal is enhaced by the time (degree) of corrosion. Fractography analysis shown features concerning ductile-brittle, mixed-mode of failure where the brittle component tends to dominate with increasing time (degree) of corrosion.

Abstract: This research targets to localize the most stressed areas of the iron T-clamps of Epikourios Apollon temple (420 B.C.) during their production. This research aiming to localize their stress uses the method of counting the Barkhausen noise (BHN).

Abstract: The Barkhausen noise in low carbon steel is analyzed in this paper, illustrating a monotonic dependence on the degree of plastic deformation.

Abstract: The Barkhausen noise technique (BHN) has been used as a non destructive tool for the measurement of the hardness in various types of steel, namely low carbon steel, TRIP steel, Duplex steel and welding in low carbon steel. The steel samples have undergone different mechanical treatment, such as plastic deformation, cold rolling or welding. Hardness and microhardness have been determined in terms of Vickers standards. A remarkably linear dependence of the BHN on the Vickers hardness of the corresponding samples with an uncertainty in the order of 3-5% has been achieved, illustrating that the BHN may be used as a non destructive tool for determining the Vickers hardness in steels. Furthermore, BHN measurements have obtained on the welding area, along the thermally affected zone and the weld itself, illustrating the theoretically expected stress field distribution.

Abstract: The surface magnetic properties, namely Barkhausen noise and surface dc B-H loops and the microstructure of low carbon steel, namely electron back scattering diffraction, have been correlated in this paper, showing a good monotonic behavior.

Abstract: Aim of this study was to evaluate the use of the Barkhausen Noise as a mean to detect the residual stresses developed in the heat-affected zone (HAZ) of mild steel welds.

Abstract: The effects of low temperature isothermal treatments on a quenched AISI D2 tool steel was studied using Barkhausen Noise, X-ray diffraction, dilatometry and optical and electronic microscopy. The specimens were austenitized at 1040°C and quenched in oil. The isothermal treatments involved immersion in hot oil baths at 80° or 130°C for 0.1, 0.6, 1, 3, 10 and 30 hours, except for the dilatometry, in which the specimens were submitted to a single thermal cycle for 30 hours. These thermal treatments are industrially known as “stress relief treatments”, and are used to prevent cracks and catastrophic failures during cryogenic treatments. The comparison of global and local (microscopy) measurements allows the discussion of the phenomena involved in the aging process.

Abstract: Different experimental procedures for the location of sources of Acoustic Emission (AE) avalanches during Martensitic Transformations are discussed. A first example corresponds to the 1D location of AE events during stress-induced martensitic transitions in a Cu-Zn-Al shape memory alloy (3.5 cm length). The obtained data allows monitoring of the interface advancement with a spatial resolution of less than 1 mm. Secondly, we discuss two different ideas that have significant potential for improving this resolution in the case of thermally induced transitions in small single crystalline samples (~1 cm): the use of elastodynamic simulations based on finite element methods and the simultaneous detection of AE and Barkhausen noise in ferromagnetic samples.