Barkhausen Noise Technique Research Articles

On the mechanism of nondestructive evaluation of cementite content in steels using a combination of magnetic Barkhausen noise and magnetic force microscopy techniques

The influence of carbon content in the form of globular cementite precipitates in unalloyed steels was macroscopically characterized by means of magnetic hysteresis loop and Barkhausen noise techniques. The choice of the frequency of the applied field has a strong influence on the Barkhausen noise profiles. At sufficiently high frequency (0.5Hz) there are two peaks, one at lower field, the amplitude of which corresponds to the amount of ferrite and one at higher field, the amplitude of which corresponds to the amount of the cementite phase, respectively. Magnetic force microscopy and electron backscattered diffraction techniques were used to determine the magnetic and crystallographic microstructures of the steels. Cementite has its own domain structure and stray fields which influence the magnetization process of the steel by its own magnetic contribution. When an external magnetic field is applied, the magnetization process in ferrite occurs mainly at lower fields through the 180° and 90° domain walls. A higher field is required for the observation of 180° domain wall movements in cementite.

Detection of Surface Damage after Grinding of Large Case–Hardened Bearing Rings

This paper deals with detection of surface damage after grinding of bearing rings made of case hardened steel. Micromagnetic technique based on Barkhausen noise is adopted for monitoring of surface integrity during grinding rings of large diameter (1500 mm). Except micromagnetic testing, investigation of surface integrity is also expressed in such parameters as structure alterations, residual stresses measured via X - ray technique and microhardness measurement. It was found that Barkhausen noise technique enables reliable detection of surface integrity and damage induced by dry grinding and insufficient coolant supply can be easily distinguished.

Local Non-contact Evaluation of the ac Magnetic Hysteresis Parameters of Electrical Steels by the Barkhausen Noise Technique

The potential of the magnetic Barkhausen noise method for local repeatable testing of the magnetic hysteresis properties of electrical steels was investigated. Strips of non-oriented and grain-oriented electrical steels were magnetized by a single yoke through 0–10 mm air gaps. The measurements were performed at standard ac conditions: 50 Hz sine induction waveform with different amplitudes. A vertically mounted array of three Hall sensors was used for the direct measurement of the surface magnetic field. The Barkhausen noise was detected locally by a surface-mounted pancake coil. The simultaneous measurement of the actual sample field makes it possible to stabilize a recently introduced parameter, called Barkhausen noise coercivity. This parameter demonstrates strong linear correlations to the hysteresis coercive force and to the hysteresis losses measured by the standard single sheet tester.

Relation Between Magnetic Barkhausen Noise and Hardness for Jominy Quench Tests in SAE 4140 and 6150 Steels

The nondestructive Magnetic Barkhausen Noise (MBN) technique was applied for the evaluation of SAE 4140 and SAE 6150 steels after a Jominy end-quench test. Microstructures were also characterized by SEM (Scanning Electron Microscope) and hardness tests. MBN measurements were performed on the same sample regions at three excitation frequencies. Different parameters of the measured signals (signal peak position and height, and Root mean square) were calculated. A relationship between mechanical hardness and MBN parameters was found for both materials, with the best correlation coefficient being found in low excitation frequency range.

Mapping Stress as a Function of Depth at the Surface of Steel Structures Using a Frequency Dependent Magnetic Barkhausen Noise Technique

Profiling of stress as a function of depth is an important tool for nondestructive evaluation and can be used to prevent catastrophic failures in structures. In this work, the underlying theory of a new model for the depth profiling of stress in ferromagnetic structures based on the magnetic Barkhausen method is investigated and commented upon. In the model, a ferromagnetic structure is divided into layers of different stress states. By analysis of the constituent equations it was found that the measured Barkhausen voltage increases as the frequency span increases, for both the one- and the two layer cases. It was also found that two layers with the same amplitude of Barkhausen emission at the origin can be approximated as one layer, provided that the upper and lower depths, as well as the frequency range are identical.

Magnetic Barkhausen Noise, Metal Magnetic Memory Testing and Estimation of the Ship Plate Welded Structure Stress

Using the Magnetic Barkhausen Noise (MBN) technique in combination with the Metal Magnetic Memory (MMM) technique, the stress in a welded steel ship plate was investigated. As part of this, the three dimensional image of the self-leakage magnetic field was obtained. In addition, MBN measurements were made in the same test area. The stress distribution, as deduced from the MBN measurements was found to correspond well with the MMM self-leakage image. As a consequence of this positive result, a new testing procedure using the combined MBN and MMM technique is proposed. First, the region with high residual stress is located rapidly using the MMM technique. Then, the actual level of residual stress is determined using the MBN technique, based on prior calibration using specimens made from the same material. This method combining with the X-ray testing method, the damage degree of the ship welded structure which suffered the navigation vibration and environment impact and so on is comprehensively estimated. This test method can not only reduce the workload of the non-destructive testing, but also improve the accuracy of the stress testing.

Study of surface integrity of ground bearing steel using Barkhausen noise technique

An experimental study was undertaken to compare the role of process parameters on the grindability of bearing steel (unhardened and hardened) in conventional grinding domain with particular emphasis on surface integrity. Surface residual stress on the ground specimens has been assessed using X-ray diffraction technique and Barkhausen noise analysis. The aim of this article was to compare the applicability of Barkhausen noise analysis technique to assess the state of residual stress with simultaneous change in microstructure along with the formation of white layer, microhardness, the incorporation of plastic deformation, etc. The results indicate a significant effect of downfeed and work speed on surface integrity parameters like residual stress, microstructure, and microhardness. Residual stress varied in the present work over a domain of 50–700 MPa. Despite simultaneous variation in the microhardness, microstructure, and residual stress during grinding, a linear correlation could be established between Barkhausen noise parameters and residual stress.

Steel Hardness Determination Using the Barkhausen Noise Effect

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.

Residual Stress Prediction in Welds via the Barkhausen Noise Technique

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.

Magnetic and spontaneous Barkhausen noise techniques used in investigation of a martensitic transformation

Magnetic Barkhausen noise (MBN) was used to characterize the progress of austenite to martensite phase transformation while cooling steel specimens, using a conventional Barkhausen noise emission setup stimulated by an alternating magnetic field. The phase transformation was also followed by electrical resistivity measurements and by optical and scanning electron microscopy. MBN measurements on a AISI D2 tool steel austenitized at 1473 K and cooled to liquid nitrogen temperature presented a clear change near 225 K during cooling, corresponding to the MS (martensite start) temperature, as confirmed by resistivity measurements. Analysis of the resulting signals suggested a novel experimental technique that measures spontaneous magnetic emission during transformation, in the absence of any external field. Spontaneous magnetic noise emission measurements were registered in situ while cooling an initially austenitic sample in liquid nitrogen, showing that local microstructural changes, corresponding to an avalanche or “burst” phenomena, could be detected. This spontaneous magnetic emission (SME) can thus be considered a new experimental tool for the study of martensite transformations in ferrous alloys, at the same level as acoustic emission.

Magnetic Barkhausen emission in lightly deformed AISI 1070 steel

The Magnetic Barkhausen Noise (MBN) technique can evaluate both micro- and macro-residual stresses, and provides indication about the relevance of contribution of these different stress components. MBN measurements were performed in AISI 1070 steel sheet samples, where different strains were applied. The Barkhausen emission is also analyzed when two different sheets, deformed and non-deformed, are evaluated together. This study is useful to understand the effect of a deformed region near the surface on MBN. The low permeability of the deformed region affects MBN, and if the deformed region is below the surface the magnetic Barkhausen signal increases.

Assessment of Microhardness Profile in Grinding Using Barkhausen Noise Technique at Various Analysis Parameters

An experimental investigation was carried out to study the effect of variation in Barkhausen noise (BN) analysis parameters (magnetizing voltage and excitation frequency) for assessment of microhardness profile upon surface grinding. A varying amount of surface damage was induced in the ground samples by changing the downfeed during grinding. It was observed that variation in microhardness inversely affects root mean square (rms) value of BN signal. The observed BN profile indicated no phase transformation or microstructural changes upon grinding. Metallographic study of ground samples has been undertaken to confirm the results obtained by BN analysis. Barkhausen noise parameter (rms value of BN signal), at elevated magnetizing voltage and excitation frequency, increased with reduction in microhardness along the depth indicating the applicability of BN analysis technique in assessing the microhardness profile of ground steel.

Evaluation of surface decarburization depth by magnetic Barkhausen noise technique

Industrially unfavorable process of steel surface decarburization was induced by annealing in air. Two methods of after-anneal surface treatment were used: an acid pickling and a sand blasting. The obtained decarburized layers were examined by optical microscope, wave dispersive spectrometer, and surface X-ray diffraction method. Magnetic Barkhausen noise technique was tested for applicability of non-destructive characterization of the decarburized layer depth. A newly introduced parameter, Barkhausen noise coercivity, was proposed for practical use due to its sensitivity to decarburization and stability to measurement conditions. Other magnetic parameters, e.g. number of Barkhausen noise counts, were found to be sensitive to the compressive residual stress caused by the sand blasting.

Magnetic anisotropy of plastically deformed low-carbon steel

Macroscopic hysteresis and local Barkhausen noise techniques were used for the comprehensive magnetic investigation of structural low-carbon steel subjected to uniaxial plastic tension. Scattering of the measured magnetic parameters was substantial within the Lüders band region with stabilization at higher strains. Compressive residual stresses in the deformation direction formed a hard magnetization axis with intriguing two-phase remagnetization. The magnetic parameters had the highest sensitivity to strain in this direction. They changed as cos2 with rotation to the perpendicular easy magnetization axis, where the magnetic sensitivity was the lowest. The relation between the deformed steel microstructure (dislocation and residual stress patterns) and the obtained magnetic behaviour is interpreted. The applicability of the examined techniques for the non-destructive characterization of steel degradation is discussed.

Stress measurement using magnetic Barkhausen noise and metal magnetic memory testing

This paper introduces a comparison of the magnetic Barkhausen noise (BN) and metal magnetic memory (MMM) testing techniques for stress measurement. BN has become an important non-destructive technique due to its exceptional material and stress characterization capabilities. MMM is a recently developed technique with special ability for stress detection and stress history. In the applied tensile experiment, BN and MMM signals were acquired via a BN measurement system and EMS-2003 MMM instrument. Relationships between magnetic signals and applied tensile stresses were derived from experiment results. The difference and correlation of the two methods are investigated. Conclusions were derived based on the experiment results.

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.

Non-destructive determination of residual stress state in steel weldments by Magnetic Barkhausen Noise technique

The purpose of this study is non-destructive determination of residual stresses in the welded steel plates by Magnetic Barkhausen Noise (MBN) technique. A MBN-stress calibration set-up and a residual stress measurement system with scanning ability were developed. To control the accuracy and the effectiveness of the developed system and procedure, various MBN measurements were carried out. The MBN results were verified by the hole-drilling method. Microstructural investigation and hardness measurements were also conducted. It was concluded that if the calibration procedure including the effect of microstructure is appropriate then MBN is a very promising method for non-destructive, fast and accurate prediction of residual stresses in the welded plates.

NDT flaw mapping of steel surfaces by continuous magnetic Barkhausen noise: Volumetric flaw detection case

This paper reports the use of a non-destructive, continuous magnetic Barkhausen noise (CMBN) technique to investigate the size and thickness of volumetric defects, in a 1070 steel. The magnetic behavior of the used probe was analyzed by numerical simulation, using the finite element method (FEM). Results indicated that the presence of a ferrite coil core in the probe favors MBN emissions. The samples were scanned with different speeds and probe configurations to determine the effect of the flaw on the CMBN signal amplitude. A moving smooth window, based on a second-order statistical moment, was used for analyzing the time signal. The results show the technique's good repeatability, and high capacity for detection of this type of defect.

Damage assessment of boiler tubes subjected to erosion and corrosion failures by non-invasive technique

Incompatible permanent strains in any engineering component are caused by the formation of residual stresses due to mechanical loading or thermal effect. They get generated or modified at every stage of the service life of the component. The stresses tend to increase due to the type of damage occurring in any engineering component such as fatigue, corrosion, erosion, or a synergistic effect under the influence of environmental conditions. The present investigation highlights about the residual stresses in a typical boiler tube component and the same is characterized by nondestructive methods viz., Magnetic Barkhausen Noise and X-ray Diffraction techniques to identify the type of damage such as corrosion and erosion have been discussed. The correlation of the stress data with respect to the hardness and microstructure of the in-service boiler tubes in comparison with an unused tube has been attempted. The result reveals that there is a considerable variation in the magnitude of the stress level as well as the hardness value in the damaged region compared to the unaffected location. Furthermore, it is seen that the microstructural features support the data. The damage assessment methodology thus serves as a tool to quantify the type and extent of damage of in-service tubes and forms a part of the quality assurance practice.

The characterisation of creep damage using non-destructive Barkhausen noise detection techniques

Industry today sees an ever-increasing demand for power and energy. Due to the environmental, time and financial constraints of building new power generation and petrochemical processing facilities it has become feasible to run existing plant and equipment beyond their original design lives. Considering this and the demand to achieve greater production targets there is an increased requirement for plant and equipment inspection. The causes, identification and consequences of creep damage on equipment within the power and energy industries are examined. The Electricity Supply Boards (ESBs) current approach to Non-Destructive Evaluation (NDE) of creep damage, its advantages and disadvantages are presented. This project concentrates on using Barkhausen noise techniques for the NDE of creep damage in Cr-Mo-V steels, as used in the manufacture of power generation and chemical processing plant and equipment. The two main Barkhausen noise detection methodologies, Magneto-Acoustic Emission (MAE) and Magnetic Barkhausen Noise (MBN), and how they can be applied to creep damage detection will be discussed. Barkhausen noise techniques will be shown to offer an alternative NDE solution.