Non-destructive Magnetic Methods Research Articles

Low-frequency incremental permeability for the evaluation of deep carburization treatments: Theoretical understanding

Precise evaluation of deep carburization treatments is essential to prevent degradation of high-performance mechanical components. A nondestructive magnetic method called low-frequency incremental permeability testing appears to be particularly suitable for this purpose. This method consists of slowly magnetizing the specimen to be controlled and then superimposing a relatively low-frequency eddy current testing process on the specimen (<2 kHz). The sensor’s coil impedance is monitored along with the magnetization cycle. When plotted versus the magnetic excitation, the impedance produced butterfly-shaped curves that were dependent on the carburization depth. Operating at low frequency increases the scanned layer thickness up to the untreated inner part of the specimen and induces characteristic variations in the butterfly-shaped curves. A model to solve for the indirect relationship between the magnetic properties and the carburization treatment properties is presented in this manuscript. This model combines the Dodd and Deeds analytical expression for a flat sensor coil above a two-layer conductor with Jiles-Atherton theory for consideration of the hysteresis. The magnetic and electromagnetic responses are well considered, providing accurate reconstructions of experimental data. The model predictions reveal magnetic indicators that are highly correlated with the carburization depth and provide optimal conditions for nondestructive testing observation.

Investigation of the Influence of Neutron Irradiation on Cladded Nuclear Reactor Pressure Vessel Steel Blocks by Magnetic Adaptive Testing

The influence of neutron irradiation degradation on reactor pressure vessel steel was investigated. Large blocks were irradiated by neutrons in the BR2 reactor at a low irradiation temperature. They were measured by a nondestructive magnetic method, magnetic adaptive testing, before and after the neutron irradiation. It was shown that the modification of the magnetic parameters due to the neutron irradiation was well detectable by this nondestructive method. It was also shown that the influence of neutron irradiation could be detected with a reasonable signal-to-noise ratio through the cladding. The present results are considered as a first step towards the application of magnetic adaptive testing in the nuclear industry.

Interpretation of Nondestructive Magnetic Measurements on Irradiated Reactor Steel Material

Neutron irradiation-generated embrittlement of nuclear pressure vessel steel was inspected by a nondestructive magnetic method, called magnetic adaptive testing (MAT). This method is based on systematic measurement and evaluation of minor magnetic hysteresis loops. Result of MAT measurement was compared with the result of the traditional Charpy measurement. Good correlation was found between these parameters. One of the main findings of the present work is that the considerable part of scatter of points obtained by magnetic measurement can be attributed to local material inhomogeneity. Another important conclusion is that the embrittlement highly depends on the initial local material conditions, i.e., the initial microstructure, which are very different even within the same block of reactor steel material. By taking this into account, the magnetic descriptors obtain more precise determination of the local embrittlement than the traditionally used destructive mechanical parameters from Charpy data.

Application of Artificial Neural Network and Multi-magnetic NDE Methods to Determine Mechanical Properties of Plain Carbon Steels Subjected to Tempering Treatment

The present paper shows the results of applying an artificial neural network to three non-destructive magnetic methods including magnetic hysteresis loop (MHL), eddy current (EC), and magnetic flux leakage (MFL) techniques to determine mechanical features of plain carbon steels with unknown carbon contents subjected to tempering treatment. To simultaneously evaluate the effects of carbon content and microstructure on the magnetic and mechanical properties, four grades of hypoeutectoid steel samples containing 0.30, 0.46, 0.54, and 0.71 wt.% carbon were austenitized in the range of 830-925 °C and then subjected to quench-tempering treatments at 200, 300, 400, 500 and 600 °C. In the next step, mechanical properties including tensile strength, elongation, and hardness were measured using tensile and hardness tests, respectively. Finally, to study the electromagnetic parameters, MHL, MFL and EC non-destructive electromagnetic tests were applied to the heat-treated samples and their outputs were fed to a generalized neural network designed in this work. The results revealed that using a proper combination of electromagnetic parameters as the ANN input for each mechanical parameter enables us to determine the hardness, UTS and elongation of hypoeutectic carbon steel parts after tempering treatment with high accuracy.

Monitoring of S235 steel over-stressing by the use of Barkhausen noise technique

This paper deals with monitoring of the rupture of S235 steel used in ship structures under uniaxial loading by the use of a non-destructive magnetic method based on Barkhausen noise emission. Component failure in constructions of marine or civil engineering can be found during their long-term operation or/and over-stressing. Especially the corrosion process can significantly reduce effective cross-section area of structures, which in turn increases true stresses. This study demonstrates that Barkhausen noise emission and extracted parameters can reliably reveal structure over-stressing. A remarkable decrease of Barkhausen noise near the true yield stress alerts the high risk of incoming breakage. It was found that the evolution of Barkhausen noise is driven by the steel hardening (expressed in terms of hardness and the corresponding dislocation density) and the superimposing stress state.

Nondestructive Magnetic Monitoring of Residual Stresses in a Medical Ti–6Al–4V–ELI Alloy Using a Fluxgate Sensor

Attempts to improve the osteointegration, fixation and stability of Ti-base implants have been focused by producing a significative surface roughness that enhances the surface area available for bone/ implant apposition. In this research study, it shows the experimental data by synchrotron radiation X-ray diffraction (SR-XRD) of the main material surface properties (residual stress and cold work) that changed significantly during the application of different surface treatments such as grit blasting and laser shock peening in a biometallic Ti–6Al–4V alloy. The ratio of residual stress to cold work is primarily determined by the material and the specific surface treatment applied. In order to establish how they alter the recorded magnetic signatures and to validate that the residual stress and cold work effects govern the outcome of the magnetic measurements, we used a nondestructive magnetic method. It was displayed that the magnetic method provides the unique capability of nondestructively sensing the thermomechanical relaxation below the treated surface only calculating the normal and tangential magnetic intensities induced by thermocurrents using a fluxgate magnetometer.

Comparison of magnetic nondestructive methods applied for inspection of steel degradation

A series of low carbon steel specimens is investigated in the frame of a chain of magnetic non-destructive measurements on round robin samples, organized by the Universal Network for Magnetic Non-Destructive Evaluation. The samples have been plastically deformed by cold rolling to five consecutive stages of deformation. They were examined by several different nondestructive magnetic methods and the results were compared with each other and with the destructive mechanical measurements of Vickers hardness and ductile-brittle transition temperature. Very well correlated and qualitatively very similar relations between the magnetic and mechanical parameters were found in all cases, and for all the methods. Difference between the results of different measurements was found only in the sensitivity of the measurement with respect to the independent parameter, which is a promising message for the potential practical applications and possible future standardization of magnetic nondestructive methods.

An accurate method for determining residual stresses with magnetic non-destructive techniques in welded ferromagnetic steels

The scope of the present research work was to investigate the proper selection criteria for developing a suitable methodology for the accurate determination of residual stresses existing in welded parts. Magnetic non-destructive testing took place by the use of two magnetic non-destructive techniques: by the measurement of the magnetic Barkhausen noise and by the evaluation of the magnetic hysteresis loop parameters. The spatial distribution of residual stresses in welded metal parts by both non-destructive magnetic methods and two diffraction methods was determined. The conduction of magnetic measurements required an initial calibration of ferromagnetic steels. Based on the examined volume of the sample, all methods used were divided into two large categories: the first one was related to the determination of surface residual stress, whereas the second one was related to bulk residual stress determination. The first category included the magnetic Barkhausen noise and the X-ray diffraction measurements, while the second one included the magnetic permeability and the neutron diffraction data. The residual stresses determined by the magnetic techniques were in a good agreement with the diffraction ones.

The prediction of bending strengths in SFRSCC using Computational Fluid Dynamics (CFD)

This research establishes a correlation between the predicted fiber orientation in Steel Fiber Reinforced Concrete (SFRC) and the flexural behavior of the composite material. It is well known that the proper alignment of fibers in the direction of tensile force enhances the mechanical properties of concrete. As recent studies have corroborated, the flow induced by self-compacting properties can influence fiber orientation. Thus, both technologies may be combined in the casting of a real-scale Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) wall (3-m high, 6-m long and 0.15-m thick). Computational Fluid Dynamics (CFD) methods are applied, implementing a Bingham plastic model in a homogeneous fluid, in order to predict fiber orientation. The acceptability of the expected orientations is confirmed by analyzing the velocity fields of the fluid throughout successive time-steps of the simulation and by linking those fields to the bending strengths (pre- and post-cracking) of prismatic specimens extracted from the wall. Expected orientations are further supported by non-destructive magnetic methods. Prediction techniques are of paramount importance nowadays, because design rules are only based on the response of preliminary prismatic specimens that are not representative of the final real structural elements. This novel methodology characterizes the material through the analysis of numerical simulations, without the cost of casting real elements, which notably simplifies the assessment of materials for use in new structural elements and geometries.

Nondestructive magnetic characterization of TRIP steels

Different nondestructive magnetic methods – major hysteresis loop measurement, Barkhausen noise measurement and minor hysteresis loop analysis (Magnetic Adaptive Testing) – were applied on a plastically deformed series of transformation induced plasticity (TRIP) steel samples. The results of the different methods were compared with each other. Good correlation was found between magnetic characteristics, measured in different ways. Magnetic Adaptive Testing (MAT) seems to be the most sensitive method. Good correlation was also found between magnetic parameters and with the destructively measured Vickers hardness values. MAT yields a linear correlation between Vickers hardness and magnetic descriptors, without magnetic saturation of the specimen. ► Plastically deformed series of TRIP steel samples were studied. ► Different nondestructive magnetic methods were applied on this sample series. ► The results of different magnetic methods were compared with each other. ► Good correlation was found between magnetic parameters and Vickers hardness values. ► MAT yields linear correlation between Vickers hardness and magnetic descriptors.

Model of the state of stress in a bilayer steel workpiece during uniaxial tension

A model for the state of stress in a planar bilayer workpiece under uniaxial tension conditions is proposed, and a method for the calculation of its stress-strain diagram from the experimentally obtained tensile curves of its components is developed. This method can be used to solve the inverse problem: using the stress-strain diagrams of one of the components and the entire workpiece, one can calculate the tensile curve of the second component. Since stress-strain diagrams can be obtained by nondestructive magnetic methods directly during loading, the results obtained are important for the diagnostics of loaded bilayer steel construction members.

Complex magnetic and microstructural investigation of duplex stainless steel

Heat treatment induced microstructural processes were studied by different non-destructive magnetic methods in the present work. A commercial SAF 2507 type superduplex stainless steel was investigated. This alloy contains about 40% ferrite and 60% austenite phases in its initial condition. The ferrite phase is not stable, therefore it can decompose to sigma phase and secondary austenite due to heat treatment. All the mechanical, corrosion resistance and magnetic properties are strongly influenced by the microstructural changes. This study had two aims: to understand better the kinetics of the ferrite decomposition process and to study the application possibilities of the applied magnetic measurements. The results, which were supported by electronmicroscopic method (electron back scattered diffraction, EBSD), help us to understand better the microstructural changes in duplex stainless steels caused by heat treatment.

Magnetic quantification of urban pollution sources in atmospheric particulate matter

A new method is presented for fast quantification of urban pollution sources in atmospheric particulate matter (PM). The remanent magnetization of PM samples collected in Switzerland at sites with different exposures to pollution sources is analysed. The coercivity distribution of each sample is calculated from detailed demagnetization curves of anhysteretic remanent magnetization (ARM) and is modelled using a linear combination of appropriate functions which represent the contribution of different sources of magnetic minerals to the total magnetization. Two magnetic components, C1 and C2, are identified in all samples. The low-coercivity component C1 predominates in less polluted sites, whereas the concentration of the higher-coercivity component C2 is large in urban areas. The same sites were monitored independently by Hüglin using detailed chemical analysis and a quantitative source attribution of the PM. His results are compared with the magnetic component analysis. The absolute and relative magnetic contributions of component C2 correlate very well with absolute and relative mass contributions of exhaust emissions, respectively. Traffic is the most important PM pollution source in Switzerland: it includes exhaust emissions and abrasion products released by vehicle brakes. Component C2 and traffic-related PM sources correlate well, which is encouraging for the implementation of non-destructive magnetic methods as an economic alternative to chemical analysis when mapping urban dust pollution.

Detection of coarse grains by nondestructive magnetic methods : 40492 Segalini, S.; Dunand, C.; Putignani, M.; Genet, S. Nondestructive Characterisation of Materials 2, Montreal (Canada), 21–23 Jul. 1986. pp. 241–250. Edited by J.F. Bussiere, J.P. Monchalin, C.O. Ruud, R.E. Green Jr. Plenum Press, 1987

Detection of coarse grains by nondestructive magnetic methods : 40492 Segalini, S.; Dunand, C.; Putignani, M.; Genet, S. Nondestructive Characterisation of Materials 2, Montreal (Canada), 21–23 Jul. 1986. pp. 241–250. Edited by J.F. Bussiere, J.P. Monchalin, C.O. Ruud, R.E. Green Jr. Plenum Press, 1987

Detection of coarse grains by nondestructive magnetic methods : Nondestructive Characterisation of Materials 2, Montreal (Canada), 21–23 Jul. 1986. pp. 241–250. Edited by J.F. Bussiere, J.P. Monchain C.O. Ruud, R.E. Green Jr. Plenum Press, 1987

Detection of coarse grains by nondestructive magnetic methods : Nondestructive Characterisation of Materials 2, Montreal (Canada), 21–23 Jul. 1986. pp. 241–250. Edited by J.F. Bussiere, J.P. Monchain C.O. Ruud, R.E. Green Jr. Plenum Press, 1987

Coercive force and properties of corrosion-resisting steels: 39140 Voronenko, B.I. Soviet Journal of Nondestructive Testing, Vol. 23, No. 10, pp. 670–674 (Jun. 1988)

The effects are examined of quenching temperature of corrosion-resisting steels of various structural grade on their magnetic and mechanical properties and on phase composition to clarify the possibilities of using nondestructive magnetic methods for inspecting the structure and properties of high-alloy steels. The results show that the mechanical properties of martensitic and austenitic-ferritic steels correlate with the coercive force and those of austenitic-martensitic steels with the saturation magnetization. The coercimetric method can be used to determine the type of ferromagnetic phase and, in a number of cases, the critical points and temperature ranges of phase transformations.

Nondestructive magnetic method of inspection of the mechanical properties of cast steels. I. Construction of correlation models: 37635 Vais, I.A.; Bashkirov, Yu.P.; Ivanskii, A.E.; Bida, G.V.; Sakovich, E.D.; Strelyanov, V.E. Soviet Journal of Nondestructive Testing, Vol. 23, No. 2, pp. 81–85 (Oct. 1987)

Investigations were conducted into single-factorial dependences of yield strength, relative elongation, and coercive force on the carbon, manganese, vanadium, and titanium content of cast steels in the normalized and quenched and tempered conditions, and also on quenching and tempering temperatures. Multifactorial correlations models were constructed.

Nondestructive magnetic method of inspection of the mechanical properties of cast steels. I. Construction of correlation models 37635 Vais, I.A.; Bashkirov, Yu.P.; Ivanskii, A.E.; Bida, G.V.; Sakovich, E.D.; Strelyanov, V.E. Soviet Journal of Nondestructive Testing, Vol. 23, No. 2, pp. 81–85 (Oct. 1987)

Nondestructive magnetic method of inspection of the mechanical properties of cast steels. I. Construction of correlation models 37635 Vais, I.A.; Bashkirov, Yu.P.; Ivanskii, A.E.; Bida, G.V.; Sakovich, E.D.; Strelyanov, V.E. Soviet Journal of Nondestructive Testing, Vol. 23, No. 2, pp. 81–85 (Oct. 1987)