Paper presents new possibilities of Jiles-Atherton model of magnetic hysteresis parameters determination. The main problem connected with this model is the fact that its parameters have to be determined during the optimization process. However, due to the local minima on the target function, the gradient optimization methods are not effective, whereas evolutionary strategies, such as (µ+λ) strategy, are very time consuming. Results of calculation presented in the paper indicate that differential strategies create possibility of reliable and fast determination of Jiles-Atherton model parameters. Paper also presents guidelines for practical determination of model's parameters, which is very important from practical point of view.

Paper presents the possibility of application of the Jiles-Atherton extended model to describe the magnetic characteristics of construction steel C45 under the inuence of tensile stresses. Experiment was performed on the frame-shaped samples. Then, the inuence of stresses on hysteresis loops was modelled with the Jiles-Atherton extended model. The obtained results of the modelling are consistent with results of the experimental measurements. The results of modelling create new possibilities of explanation of the physical phenomena connected with magnetisation of the magnetic materials under stresses, which is esential for the assessment of the state of the construction steel during its exploitation in industrial conditions.

Abstract. Paper presents the frame-shaped cores based methodology of testing of magnetoelastic characteristics of energetic steels such as X30Cr13 steel, subjected to tensile stresses. In presented method, the magnetic circuit of the sample is closed. For this reason, the results of magnetoelastic investigation are independent of the shape of the sample. To validate the proposed method, the influence of tensile stresses on B(H) hysteresis loop of X30Cr13 martensitic corrosion resistant steel was carried out. On the base of these result, clear criteria for non-destructive assessment of mechanical stresses in the material were determined.Keywords: magnetoelastic effect, corrosion resistant steel, stress assessment. IntroductionUnder the influence of mechanical stresses, the shape of B(H) magnetic hysteresis loop changes significantly for both crystalline [1] and amorphous [2] magnetic materials. This effect is commonly known as magnetoelastic effect [3,16]. In spite of the fact that changes of flux density B under stresses are most significant for high permeability amorphous and nanocrystalline alloys [4,5,6], the magnetoelastic effect is also observed in steels [7,8,9]. As a result, measurements of stress-induced changes of shape of hysteresis loop of steel, creates the possibility of non-destructive assessment of mechanical stresses generated during the use mechanical component. Magnetoelastic-effect based non-destructive testing of corrosion resisting steels can be considered only for the martensitic steels, such as X30Cr13 steel. Austenitic steels are non-magnetic, however, under specified mechanical stresses austenite may be conversed to martensite [10,11,12]. This phenomenon is also very interesting from the non-destructive testing point of view, but its principle is different than magnetoelastic effect in martensitic steels.Martensitic corrosion resisting X30Cr13 steel exhibits good resistance to the corrosive effect of salt water, weather and various corrosion agents. Moreover, this steel

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