Ugur Aydin

Modeling of Hysteresis Losses in Ferromagnetic Laminations Under Mechanical Stress

A novel approach for predicting magnetic hysteresis loops and losses in ferromagnetic laminations under mechanical stress is presented. The model is based on combining a Helmholtz free-energy-based anhysteretic magnetoelastic constitutive law to a vector Jiles-Atherton hysteresis model. This paper focuses only on unidirectional and parallel magnetic fields and stresses, albeit the model is developed in a full 3-D configuration in order to account also for strains perpendicular to the loading direction. The model parameters are fitted to magnetization curve measurements under compressive and tensile stresses. Both the hysteresis loops and the losses are modeled accurately for stresses ranging from -50 to 80 MPa.

Coupled Magneto-Mechanical Analysis of Iron Sheets Under Biaxial Stress

A novel single sheet tester design is proposed and a directly coupled magneto-mechanical model is used to numerically analyze the behavior of iron sheets under biaxial magneto-mechanical loading applied by the tester device. magneto-mechanically coupled constitutive equations of the material derived using an energy-based approach are integrated into a finite element model of the single sheet tester device, and simulations are performed to solve for the displacement field and the magnetic vector potential in the sample. The obtained numerical results of magnetostriction evolution due to uniaxial stress and stress-induced anisotropies due to permeability variation under different magneto-mechanical loadings are presented. The simulation results are compared with the results published in the literature for the purpose of validation.

Analysis of iron losses on the cutting edges of induction motor core laminations

A 37 kW induction motor is modeled numerically taking into account the deterioration of the magnetic material properties at the cut edges of the core laminations. The magnetization properties and specific loss curves of the damaged edge and the intact material have been estimated from measurements published earlier. The deteriorated edges affect the iron losses of the machine in two distinct ways. First of all, the reduced permeability at the edges causes higher local flux densities elsewhere, which increases the losses. On the other hand, the cutting also has a direct effect on the specific loss density at the edges. By numerical simulations we show that the main effect is the latter one, and that the effect of decreased permeability remains low. The iron losses increase up to 37.6 %. The torque and active power of the machine are not much affected by the cutting, although also the current and resistive losses slightly increase due to the decreased permeability at the edges.

Modeling the Effect of Multiaxial Stress on Magnetic Hysteresis of Electrical Steel Sheets: A Comparison

The abilities of a simplified multiscale and a Helmholtz energy HE models models from the literature to predict the multiaxial stress dependent magnetic hysteresis behavior of electrical steel sheets are analyzed. The identification of the models is performed using only uniaxial magneto-mechanical measurements. Reasonable accuracy between the measurements and the modeled results is obtained. With this paper, the applicability of the HE-based model for predicting the multiaxial magneto-mechanical behavior of electrical steel sheets is verified for the first time. The differences between the studied models and possible modifications to increase the accuracy of them are discussed. Some brief guidelines for the applications are given.

Computational and experimental segregation of deformations due to magnetic forces and magnetostriction

This paper presents a novel experimental set up to measure the deformation in an iron sheet under the influence of electromagnetic field, and the results of Finite Element Analysis used for segregating the magnetic forces and magnetostriction induced mechanical deformation. The magnetic forces are calculated using the virtual work principle and the magnetostriction is modeled by means of an energy-based model. The 3D computations are performed in an open source finite element software Elmer. The experimental results and numerical simulations were analyzed and the deformation due to magnetic forces and magnetostriction were identified.

Magneto-mechanical analysis of an axially laminated synchronous reluctance machine

The performance of an axially laminated synchronous reluctance motor is calculated by considering the magneto-mechanical interaction on the electrical steel sheets. The elasticity analysis is performed with 2D finite element method for centrifugal force and shrink-fittings in both the stator frame and the rotor shaft. The 2D magnetostatic analysis is formulated with a mixed formulation involving the magnetic field in edge finite elements. The stress distribution and the components of the magnetic field affect locally the magnetic permeability of the electrical steel sheets. Their constitutive laws account for this magneto-mechanical effect with an equivalent stress approach. With a fixed-point method, this non-linear magneto-static problem is solved and the computation of the torque and the magnetic losses is performed in post-processing. Finally, the effect of the mechanical loads can increase the magnetic losses by 4.1 % mainly due to the stator shrink-fittings, whereas the electromagnetic torque only slightly decreases.

Demagnetization field in a uniformly magnetized ellipsoid embedded in an infinite anisotropic media

In this paper, we determine analytically the demagnetization field within a uniformly magnetized ellipsoid embedded in an infinite anisotropic media. The anisotropic boundary condition consists of decomposing the external magnetization into an isotropic part parallel to the external field and an anisotropic part. The resulting demagnetization field within the ellipsoid is then calculated by superposing the demagnetization fields produced by the ellipsoid magnetization, the isotropic part of the external magnetization and field, and the anisotropic part of the external magnetization. Such computation is needed in developing accurate anisotropic multi-scale models of electrical steel sheets, for example.

Modelling the effect of multiaxial stress on magnetic hysteresis of electrical steel sheets: A comparison

A simplified multiscale approach and a Helmholtz energy based approach for modelling the multiaxial stress dependent magnetic hysteresis behavior of electrical steel sheets are compared. The models are identified from uniaxial magneto-mechanical measurements. Both approaches model the hysteresis losses under multiaxial stresses with reasonable accuracy compared to the measurements.