A review of three magnetic NDT technologies

https://www.physics.queensu.ca/~lynann/references/research8.pdf

Plastic versus elastic deformation effects on magnetic Barkhausen noise in steel

The dependence of Barkhausen noise on elastic and plastic deformations, achieved in tension and in compression, has been investigated both in Armco iron and a low carbon steel These materials exhibit quite different behaviours, especially with regard to the effect of plastic deformation: a tensile plastic deformation (>1%) induces a marked increase in Barkhausen noise for Armco iron while it induces a steep decrease in the low carbon steel The comparison between the tensile and compressive behaviours, as well as between the elastic and plastic regimes of deformation enables us to attribute these effects to two underlying mechanisms, ie effect of residual internal stresses through magneto-elastic coupling and dislocation–domain wall interaction In Armco iron, the latter mechanism seems to have the strongest influence on the Barkhausen noise, while in the low carbon steel the influence of residual internal stresses prevails

On the role of residual internal stresses and dislocations on Barkhausen noise in plastically deformed steel

The aim of this study is to predict residual stress and hardness of a case-hardened steel samples based on the Barkhausen noise measurements. A data-based approach for building a prediction model proposed in the paper consists of feature generation, feature selection and model identification and validation steps. Features are selected with a simple forward-selection algorithm. A multivariable linear regression models are used in predictions. Throughout the selection and identification procedures a cross-validation is used to guarantee that the results are realistic and hold also for future predictions. The obtained prediction models are validated with an external validation data set. Prediction accuracy of the prediction models is good showing that the proposed modelling scheme can be applied to prediction of material properties.

Quantitative prediction of residual stress and hardness in case-hardened steel based on the Barkhausen noise measurement

Measuring spontaneous stray field signals provides a promising tool to analyze the stress in ferromagnetic materials. However, strong initial stray field signals on the surface of ferromagnetic materials originating from various manufacturing processes can disturb stress-induced stray field signals. Consequently, it is necessary to conduct a study that will clarify the stress dependence of spontaneous stray field signals by eliminating initial random signals. In the present work, the focus is placed on sheet specimens that have a clean initial magnetic state by means of vacuum heat treatment. Measurements of the normal component H p ( y ) signals of stray field were performed during the whole tensile test. The results showed that the stress-induced H p ( y ) signal curve had good linearity after loading, i.e., the slope coefficient K s increased continuously in the elastic deformation stage but decreased slightly during the plastic deformation stage. This phenomenon was discussed and explained from both the stress-induced effective magnetic field and residual compressive stress viewpoints.

Stress dependence of the spontaneous stray field signals of ferromagnetic steel

A mild steel specimen was loaded in tension up to ≈0.4% strain, with Magnetic Barkhausen Noise (MBN) measurements made at increasing strain levels. In addition, an MBN investigation was performed on a mild steel specimen bent progressively to ≈0.2% longitudinal surface strain. Overall, the parameter termed ‘MBNenergy’ increased significantly in the elastic, yet remained basically unchanged in the plastic range of deformation. While still in the elastic range, particular strain levels displayed abrupt changes in the MBNenergy. Variations in scatter about the average MBNenergy value, as well as distinct modifications in pulse height distributions, occurred simultaneously with the abrupt changes in MBNenergy. The non-uniform stress distribution among grains in the polycrystalline samples initiated dislocation formation in some grains before extending to other grains. Dislocation strain fields contributed to redistribution of strain within a grain leading to non-uniform changes in magnetic texture. Results indicate that the magnetic Barkhausen noise technique can detect microyielding.

Subtle changes in magnetic Barkhausen noise before the macroscopic elastic limit

Magnetic Barkhausen Noise (MBN) was used to evaluate the magnetic behaviour of nuclear reactor pressure vessel steel specimens cold rolled to reduction ratios between 0% and 60%. Measurements performed at increasing reduction ratios revealed variations in the angular dependence of a parameter termed ‘MBNenergy’, concurrent with modifications in the shape of the pulse height distribution curves. The angular preference of MBNenergy present prior to cold rolling was destroyed at intermediate reduction ratios (≈25%), and restored with further reduction (≈40%). Along the rolling direction, the number of large voltage pulses was reduced at reduction ratios of ≈25%, increasing again at ≈60% reduction ratio. Results were attributed to competing effects between crystallographic texture, microscopic and macroscopic residual stresses.

Analysis of cold rolled steels of different reduction ratio using the magnetic Barkhausen noise technique

Plastically deformed steel specimens were analyzed using surface magnetic Barkhausen noise (MBN) Three types of samples were investigated: mild steel specimens uniaxially deformed up to 40% strain, mild steel specimens deformed in bending to 02% longitudinal strain, cold-rolled nuclear reactor pressure vessel steel specimens from 0% to 60% reduction ratio The angular dependence of an “MBNenergy” term was used to examine magnetic anisotropy changes with increasing deformation, with linear MBN scans used to monitor changes in magnetic properties along the specimen axis Average MBNenergy values were observe to vary significantly with stress within the elastic region, yet only slightly in the plastic range of deformation Changes in the shape of the pulse height distribution curves were evidence of plastic deformation effects on domain wall pinning sites We conclude that a complex interplay between stress and strain mechanisms, residual stresses and crystallographic texture generates variations in MBN si

C.-G. Stefanita

Papers

Plastic versus elastic deformation effects on magnetic Barkhausen noise in steel

Subtle changes in magnetic Barkhausen noise before the macroscopic elastic limit

Analysis of cold rolled steels of different reduction ratio using the magnetic Barkhausen noise technique

Plastic deformation effects on magnetic Barkhausen noise