Measurement Potential of the Barkhausen Effect for Obtaining Additional Information on the Component Condition in Manufacturing

The measurement of Barkhausen noise is one of the non-destructive testing methods which allows the use within the production line and within the cycle time at a high production volume. The aim of the present study was to answer the question, whether it is possible to extract the informations that the Barkhausen noise includes, concerning work-piece conditions, from the signal characteristic and more important assigning these findings. Therefore, soft machined and heat treated shaft components made of the ferromagnetic material Cf53 (1.1213) were analyzed to find characteristics in the Signal that allow to separate clearly an increase in temperature of the tested area from a change in the microstructure. For this purpose the shafts were analyzed at higher temperatures (up to 80 °C) and after an additional annealing process (to change the microstructure specifically). Both investigated situations (higher temperature and modified microstructure) showed different characteristic in the Barkhausen signal, thus an assigning is possible. Metallographic investigation and hardness measurements has been carried out to support the results.

Propagating bands of plastic deformation in a metal alloy as critical avalanches

The plastic deformation of metal alloys localizes in the Portevin–Le Chatelier effect in bands of different types, including propagating, or type “A” bands, usually characterized by their width and a typical propagation velocity. This plastic instability arises from collective dynamics of dislocations interacting with mobile solute atoms, but the resulting sensitivity to the strain rate lacks fundamental understanding. Here, we show, by using high-resolution imaging in tensile deformation experiments of an aluminum alloy, that the band velocities exhibit large fluctuations. Each band produces a velocity signal reminiscent of crackling noise bursts observed in numerous driven avalanching systems from propagating cracks in fracture to the Barkhausen effect in ferromagnets. The statistical features of these velocity bursts including their average shapes and size distributions obey predictions of a simple mean-field model of critical avalanche dynamics. Our results thus reveal a previously unknown paradigm of criticality in the localization of deformation.

Research and Evaluation of the Mechanical Anisotropy of Steel an Alloys by the Magnetic Noise Method

The aim of this work is to experimentally study the relationship between mechanical properties using the example of the normal anisotropy coefficient of sheet metal, mechanical stresses during elastic deformation of electrical steel and anisotropy of the physical and mechanical properties of a set of steels and alloys with magnetic noise parameters. The mechanical anisotropy of the ferromagnetic materials properties predetermines the need for its study and evaluation, since it has a significant impact on the basic physical and mechanical characteristics of components, products and structures. Taking into account the relationship between the physical and mechanical properties of the material with the magnetic characteristics, to study the possibility of non-destructive testing of anisotropy the method of the Barkhausen effect was used, the informative parameters of which are magnetostructural and magnetoanisotropic. To study mechanical anisotropy a device for circular rotation of the Barkhausen transducer over the sample surface and a device for the production of elastic tensile / compressive stresses during static bending were made. Comparison of the results obtained using magnetic noises with the known coefficients of normal anisotropy of thin-sheet steel samples showed their qualitative and quantitative agreement, confirming the presence of a close relationship between them. It was found that elastic deformation in samples of anisotropic electrical steel leads to a sharp change in the level of magnetic noise and the type of circular diagrams, taking into account the sign of stresses. It is shown that as a result of cold rolling according to magnetic noise the samples have a pronounced texture due to the direction of rolling along the longest side of the sheet. The formed elastic deformation under tension and compression during static bending practically does not change the texture - the induced crystallographic anisotropy after rolling. The relationship between the intensity of magnetic noise and the degree of anisotropy is established and the possibility of evaluating the magnetic anisotropy in various steels and alloys using the Barkhausen effect method is investigated and confirmed.

Research on pipeline internal stress detection technology based on the Barkhausen effect

Focusing on the requirements of pipeline in-line testing for stress concentration, mechanical scratches and corrosion discrimination, a numerical calculation and experimental verification study of the internal testing excitation of oil and gas pipelines based on the Barkhausen effect (magnetic Barkhausen noise (MBN)) is carried out. This paper uses finite element calculation to determine the optimal position of the sensor, quantitatively analyses the influence of parameters, such as the excitation structure size and excitation intensity, on the magnetisation field of the pipeline and obtains the optimal exciting parameters for acquiring continuous Barkhausen signals, which can provide references for designing the pipeline in-line inspection gauge for stress concentration. The feasibility of the continuous Barkhausen noise (CBN) method for long-distance pipeline stress detection is verified by simulating the operating conditions of the internal detector in the pipeline using dynamic rotating excitation.

Use of Time-Frequency Representation of Magnetic Barkhausen Noise for Evaluation of Easy Magnetization Axis of Grain-Oriented Steel

The paper presents a new approach to non-destructive evaluation of easy/hard magnetization axis in grain-oriented SiFe electrical steels based on the Barkhausen phenomenon and its time-frequency (TF) characteristics. Anisotropy in steels is influenced by a number of factors that formulate the global relationship and affect the Barkhausen effect. Due to the observed high variability in the dynamics of magnetic Barkhausen noise (MBN) over time, obtained for various directions in grain-oriented steel, it becomes justified to conduct MBN signal analyses in the time-frequency domain. This representation allows not only global information from MBN signal over entire period to be expressed, but also detailed relationships between properties in time and in frequency to be observed as well. This creates the opportunity to supplement the information obtained. The main aspect considered in the work is to present a procedure that allows an assessment of the resultant angular characteristics in steel. For this purpose, a sample of a conventional grain-oriented SiFe sheet was used. Measurements were made for several angular settings towards the rolling and transverse directions. A data transformation procedure based on short-time Fourier transform (STFT) as well as quantitative analysis and synthesis of information contained in the TF space was presented. Angular characteristics of selected TF parameters were shown and discussed. In addition, an analysis of the repeatability of information obtained using the proposed procedure under various measurement conditions was carried out. The relationship between the selection of calculation parameters used during transformation and the repeatability of the obtained TF distributions were demonstrated. Then the selection of the final values of the calculation parameters was commented upon. Finally, the conclusions of the work carried out were discussed.

Waiting-time statistics in magnetic systems

Many complex systems, from earthquakes and financial markets to Barkhausen effect in ferromagnetic materials, respond with a noise consisting of discrete avalanche-like events with broad range of sizes and durations, separated by waiting times. Here we focus on the waiting-time statistics in magnetic systems. By investigating the Barkhausen noise in amorphous and polycrystalline ferromagnetic films having different thicknesses, we uncover the form of the waiting-time distribution in time series recorded from the irregular and irreversible motion of magnetic domain walls. Further, we address the question of if the waiting-time distribution evolves with the threshold level, as well as with the film thickness and structural character of the materials. Our results, besides informing on the temporal avalanche correlations, disclose the waiting-time statistics in magnetic systems also bring fingerprints of the universality classes of Barkhausen avalanches and a dimensional crossover in the domain wall dynamics.

Berührungslose Analyse des Sägebandzustands/Contactless saw blade analysis. Investigation of saw blade conditions using the Barkhausen Effect

Im Bereich der Bandsägeprozesse werden Verschleißzusammenhänge meist aus dem Antriebsstrom und einer Bandspannungsüberwachung prognostiziert. In-Prozess-Messungen zur Identifizierung von Rissen oder Eigenspannungsänderungen finden hier bisher nur unzureichend Anwendung. Für eine prozessbegleitende Zustandsüberwachung bei Sägebändern wird in der vorgestellten Versuchsreihe der Einsatz eines Messsystems zur Aufzeichnung des Barkhausen-Rauschens geprüft und es werden erste Signalzusammenhänge dargestellt.   In the field of band sawing processes, wear relationships are usually predicted from the drive current and band tension monitoring systems. In-process measurements for the identification of cracks or residual stress changes have only been used insufficiently so far. In order to implement an online condition monitoring of saw bands, the use of a measuring system recording the Barkhausen noise is tested in the scope of a test series and first signal correlations are presented.

TO THE QUESTION OF THE STANDARD OF MECHANICAL STRESSES

The results of a study of a biaxial stress-strain state using neutron diffraction, standardized in the field of stress measurement, and the Barkhausen effect method are presented. The possibility of using a device with a biaxial load as a standard of stress is evaluated. The article gives an assessment of an error in measuring voltage using strain gauges in relation to measurements made by the neutron diffraction method. The Barkhausen effect method is used as one of the non-destructive testing methods that are sensitive to the stress-strain state. The studies describe the possibility of adapting this method to the proposed stress standard.