Levent B. Sipahi

Modeling of micromagnetic Barkhausen activity using a stochastic process extension to the theory of hysteresis

Recent work by Bertotti [IEEE Trans. Magn. MAG‐24, 621 (1988)] and others has shown that it is possible to model the micromagnetic Barkhausen discontinuities at the coercive point using a two‐parameter stochastic model. However, the present formulation of the model is restricted to limited regions of the hysteresis curve over which dM/dH is approximately constant and when dH/dt is held at a constant rate. A natural extension of this model is to take the basic result, in which the level of Barkhausen activity in one time period is related to the activity in the previous time period, and increment it by a small amount which is dependent on the differential permeability. The extension of the model proposed here uses the theory of ferromagnetic hysteresis to determine the differential permeability at any point of the hysteresis loop. The Barkhausen activity is then assumed to vary in proportion to the differential permeability. The resulting model allows the Barkhausen sum of discontinuous changes in magnetiz...

Overview of applications of micromagnetic Barkhausen emissions as noninvasive material characterization technique

In this concise overview, the physical principles of magnetic Barkhausen effect will be briefly discussed and its recent applications in material characterization will be considered. There are new trends in micromagnetic Barkhausen effect emissions and its applications in the material characterization area. These emissions take place in magnetic materials subjected to changing applied magnetic field, and can be used, for instance, to study noninvasively surface characterization of materials. Since these emissions are quite sensitive to changes in the microstructure and subsurface stress states in magnetic materials, various applications of these of micromagnetic emissions have been found in areas such as nuclear, aerospace, and automotive technologies which use magnetic materials.

Comprehensive analysis of Barkhausen emission spectra using pulse height analysis, frequency spectrum, and pulse wave form analysis

The dependence of magnetic Barkhausen emissions (MBE) upon both field excitation and detection frequencies and excitation wave form was studied in order to investigate two of several crucial factors which affect the emissions. Sinusoidal, triangular, and square wave forms were used to generate the MBE and the pulse height spectra, frequency spectra, and pulse wave forms of these signals were analyzed. The frequency spectra of sinusoidal and triangular alternating field excitations showed similar behavior but the spectrum under square wave excitation was different due to the existence of high frequency components during square wave switching. As yet, no common standard has been agreed upon for parameterization and representation of Barkhausen signals. It appears from this work that field excitation wave form and frequency should define the inputs, while detection frequency range, pulse height spectrum, frequency spectrum, and emitted pulse wave form analysis should be used to quantify the output.

Monitoring neutron embrittlement in nuclear pressure vessel steels using micromagnetic Barkhausen emissions

In nuclear power plants, neutron embrittlement of pressure vessel steels has been one of the main concerns. The use of micromagnetic Barkhausen emissions is a promising method to monitor the variations in microstructural and subsurface stress states due to their influence on these emissions. Measurements of these emissions can reveal neutron irradiation degradation in nuclear power plant components. Samples which were irradiated at different neutron fluences and annealed at different temperatures were obtained from three reactor surveillance programs. The results of different neutron fluences and annealing procedures showed noticeable fractional changes in the magnetic Barkhausen effect signal parameter, ΔMBE/MBE, and in the mechanical properties of these specimens. For example, increased intensity of neutron fluence decreased the ΔMBE/MBE as well as impact energy and upper‐shelf energy, but increased Rockwell hardness and yield strength. Typical changes in this parameter were in the range from −20% to −4...

Effects of tensile stress on magnetic Barkhausen emissions in amorphous FeSiB alloy

Abstract Magnetic hysteresis and Barkhausen emissions have been measured for amorphous Fe 82 B 10 Si 8 samples with positive magnetostriction of λ s = 27 × 10 −6 under tensile stress of up to 35 MPa. The root mean square voltage of the Barkhausen signal and the number of events per cycle increased monotonically with the applied stress. The results are explained in terms of a theory which includes a stress-dependent hysteresis model and a stochastic process model for the Barkhausen emissions.

Barkhausen Emission Technique for Evaluating Shot Peening Quality in High Strength Steels

In the aerospace industry, there is an continuing need to characterize the stress state in structural materials. This includes structures manufactured using high strength steels, such as landing gear components. Magnetic methods have recently been playing an increasing role in nondestructive evaluation. Of these methods, the magnetic Barkhausen effect has been used with some success due to the dependence of Barkhausen emissions on material stress states and microstructures [1], Magnetic methods have been used previously in investigating compressive overloading in high strength steels [2,3]. Fatigue failures in landing gear components have resulted in an increased awareness of the stress states and corresponding methods for nondestructive evaluation of stress.

AN INVESTIGATION OF VARIOUS PROCEDURES FOR ANALYSIS OF MICROMAGNETIC BARKHAUSEN SIGNALS FOR NONDESTRUCTIVE EVALUATION OF STEELS

Abstract Current research undertaken at Iowa State University has been concerned with both the theoretical and experimental aspects of the Barkhausen effect. Here we discuss mainly the experimental techniques and including new Barkhausen effect instrumentation to detect and measure the emissions from ferromagnetic materials under the action of an alternating magnetic field H [21]. The capability of the system includes measurements of RMS Barkhausen voltage signals induced in a flux coil, pulse height analysis of these signals, frequency spectrum analysis, and Barkhausen pulse count rate analysis.

Effects of creep damage, shot peening, and case hardening on magnetic Barkhausen noise analysis

The micromagnetic emissions, commonly known as Barkhausen noise, are very sensitive to variations in the microstructure and sub-surface stress states of magnetic materials. Steel pipelines at power plants often have creep damage due to microstructural changes in their service life. Early detection of this damage will prevent costly failures. There is also an increasing demand to characterize the sub-surface stress states in structural materials such as high strength materials used in landing gear components in the aerospace industry. Shot peening is used to improve the fatigue strength of these components by the introduction of residual compressive stresses to the surface. Because the magnitude of Barkhausen noise varies with the magnitude of compressive stress, these noise measurements can be used for in-situ evaluation of the effectiveness of the shot peening process. Furthermore, surface modification such as case hardened magnetic samples can be easily observed using micromagnetic Barkhausen noise (MBE) to determine further modification needs. >

Influence of DC bias field, excitation and detection frequencies on magnetic Barkhausen noise analysis

The micromagnetic Barkhausen emissions, widely known as Barkhausen noise, are quite dependent on excitation and detection frequencies. The input variables to generate these emissions are amplitude, wave form and frequency of magnetic excitation field. When DC bias field is coupled with an AC magnetic field, this complex excitation give rises to distortion of the magnetic hysteresis loop. Recent work showed the frequency dependence of hysteresis curves in ferromagnetic materials. Since there is strong correlation between the location on the B/spl Pi/ loop and Barkhausen noise, comprehending the magnetization mechanisms at each location is essential. The current investigation indicated significant changes in voltage waveforms, pulse height spectra, frequency spectra and RMS voltages of magnetic Barkhausen noise in magnetic materials with different DC bias fields, detection and excitation frequencies. >