B. Augustyniak

The effect of mechanical stress on a Barkhausen noise signal integrated across a cycle of ramped magnetic field

Experimental Barkhausen data are presented for XC10 French steel at various stress levels. The experimental data show an apparent almost linear correlation with stress of WH (hysteresis loss) and WBN (Barkhausen noise amplitude integrated over H). A model previously suggested by Sablik for Barkhausen noise stress and field dependence is used for analysis of the experimental data. With slight modifications of the previous model, it has been possible to produce semiquantitative fits to the Barkhausen peaks as a function of H while at the same time obtaining the apparent linear correlation between WH and WBN and stress. The model suggests however that the apparent linear correlation may only apply to certain types of materials. In addition, the fit to experiment suggests that additional refinements to the model may yet be necessary.

Correlation between acoustic emission and magnetic and mechanical Barkhausen effects

The Barkhausen effect and magneto-acoustic emission as well as the mechanical Barkhausen and mechanically induced magneto-acoustic emission were measured for the XC10 steel. Mechanical load was performed for different levels of magnetic field. A close correlation between Barkhausen noise and acoustic emission was observed for mechanical load. It was argued that magneto-acoustic emission is due to non-180° DW irreversible motion.

The effects of biaxial stress on Barkhausen noise signals when the magnetic field is noncoaxial with the stress axes

The Barkhausen noise amplitude was measured under conditions of biaxial stress in steel pipe for the case of a magnetic field noncoaxial with the stress axes. The stress axes for stresses σ1 and σ2 were orthogonal to each other. In particular, σ1 was the axial stress and σ2 was the hoop stress. Various angles were used for the field direction, along with various stress magnitudes, both compressive and tensile. The stress σ2 was always tensile, but σ1 was both compressive and tensile. A model for this biaxial stress situation, based on the Sablik–Jiles magnetomechanical model, was formulated. Using a model for the Barkhausen noise deriving from the Alessandro et al. model, the Barkhausen noise power maximum amplitude was computed for various field angles and stresses σ1 and σ2. The numerical results from this model calculation agreed qualitatively with many features of the experimental results. Thus, one found both numerically and experimentally that with field direction at small angles from the σ1 axis, t...

MODELING BIAXIAL STRESS EFFECTS ON MAGNETIC HYSTERESIS IN STEEL WITH THE FIELD AND STRESS AXES NONCOAXIAL

A model based on the domain wall pinning magnetomechanical hysteresis model of Sablik and Jiles [M. J. Sablik and D. C. Jiles, IEEE Trans. Magn. 29, 2113 (1993)] was formulated to compute changes in magnetic hysteresis under biaxial stress conditions with the magnetic field and stress axes noncoaxial. The model included the Villari effect and other asymmetric stress effects. The magnetic field was taken at various angles relative to the stress axis. The Barkhausen noise, hysteresis loss, and maximum flux density were computed for fields varying between ±1 kA/m. The results compared favorably to experimental data on several steels—Polish St3 steel, Polish St41 steel, and US commercial grade steel pipe.

Designing a magnetoacoustic emission measurement configuration for measurement of creep damage in power plant boiler tubes

We discuss design features that are needed for magnetoacoustic emission (MAE) measurement of creep damage in the outer walls of boiler tubes. MAE is used because it decreases monotonically with increasing creep damage. Features of magnet design for boiler tube inspection are presented. Relationship of total MAE to Barkhausen noise path integrals is discussed. Also, dependence of MAE on frequency and tube wall thickness is delineated. Finally, measurements are discussed which show how azimuthal asymmetry in creep damage is echoed in azimuthal asymmetry in MAE. All tests were performed on 2Cr–1Mo Polish steel tube specimens.

New approach to hysteresis process investigation using mechanical and magnetic Barkhausen effects

Abstract Mechanical Barkhausen Effect and Magnetic Barkhausen Effect intensity have been measured by means of pulse integral and pulse counts rate for pure Fe and Fe-C alloys (80 and 160 ppm wt of C). Using this information, Barkhausen jump volume ν i and internal stress ρ i level have been evaluated for five types of sample.

Relationship between magnetostriction and the magnetostrictive coupling coefficient for magnetostrictive generation of elastic waves

Elastic waves are generated in a ferromagnetic material in a static magnetic field by a time-varying magnetic field which magnetostrictively couples to the material. We present modeling showing that this coupling is proportional not to the magnetostriction, but to the magnetization derivative of the static magnetostriction. We present experimental evidence showing that the elastic wave amplitude is a minimum (zero if no noise were present) at the field for which the magnetostriction derivative is zero and magnetostriction is maximum. No such minimum is found in steel when the field is high enough to make the magnetostriction go through zero and become negative. Thus, experiment also indicates that the coupling is proportional to the derivative of the magnetostriction, and not to the magnetostriction itself.

NDE OF CREEP DAMAGE AT SEAM WELDS VIA MAE

Abstract This paper presents magnetoacoustic emission measurements taken on creep-damaged seamwelded pipe. Measurements were made with portable field-usable equipment on a special pipe that was strongly creep-damaged on one end but essentially undamaged on the other end. The MAE voltage decreased as the C-core magnetizing magnet was moved from the undamaged end to the damaged end of the pipe. The results suggest that magnetoacoustic emission is reduced as a result of the presence of creep damage at and near the seam weld. This agrees with recent modeling predictions,

Finite element modeling of magnetoacoustic emission and of stress-induced magnetic effects at seam welds in steel pipes

Prior finite element modeling (FEM) has shown how creep damage reduces the voltage signal in a secondary coil wrapped around a C-core electromagnet positioned above a seam weld in a steel pipe. Prior hysteresis modeling has also demonstrated the reduction of magnetoacoustic emission (MAE) due to uniform creep damage in a steel specimen. In this article, it is shown how to evaluate the MAE due to a nonuniform distribution of creep damage at a seam weld using FEM. Also, FEM is used to evaluate the C-core secondary emf due to a nonuniform stress distribution, which is developed at a seam weld due to the internal pressure of hot steam passing through the pipe. In this latter case, use is made of the stress distribution computed at the seam weld by Stevick. It is found that nonuniform creep damage also reduces the MAE signal, as is found experimentally. The stresses due to internal pressure in the pipe are shown by FEM to increase the C-core secondary emf, which is opposite to the effect of creep damage. A com...

Investigation of magnetic and magnetomechanical hysteresis properties of Fe–Si alloys with classical and mechanical Barkhausen effects and magnetoacoustic emission

Grain oriented Fe 3.5% Si sheet samples with a Goss (GO) microstructure and Fe 3.5% samples with nonoriented (NO) grains were tested using two Barkhausen effects, the classical Barkhausen effect (HBE) and the mechanical Barkhausen effect (MBE), as well as the magnetoacoustic emission (MAE). The aim of the work was to present further evidence that the B(H) hysteresis with effects like HBE and MAE, and magnetomechanical hysteresis with MBE are correlated via internal stress barriers pinning domain walls (DWs). In the case of a GO alloy, the long axis of the sample was parallel to the [100], [110], and [111] directions with respect to the rolling direction. The HBE and MAE were measured using a C-core electromagnet supplied with a triangular wave form of current intensity. The MBE intensity was recorded during a monotonous increase of shear stress using a torque machine. The maxima of MBE intensity for the “first load” mode for a NO sample and for three GO samples indicate an internal stress distribution pin...