No. 4, 1998


Vladimir Kreisinger: Analysis of the spatial distribution of magnetic volume forces acting on magnetized bodies in a magnetic field, 325–343

The method for the determination of the distribution of magnetic volume forces acting on a magnetized body in an outer magnetic field based on the work of electromotoric forces needed to increase the flux density in a body without current sources from zero to a given value was generalized to nonlinear anizotropic ferromagnetics. The results acquired by this method in case of a synchronous machine model with permanent magnets and a magnetically izotropic stator were compared with the results acquired if the stator was formed by magnetically anizotropic ferromagnetics.

Jaroslav Kucera, Pavel Broz, Maciej Hajduga, Zbigniew Jurasz: The oxidation of Fe-rollers with different diameters in ambient air at 1100C, 345–359

The influence of diameter size f of Fe-rollers on oxidation course in ambient air at 1000C is reported in this paper. The diameters f of the particular series of Fe-specimens amounted to 3, 5, 7, 9, and 11 mm. The time periods of oxidation anneals varied from 5 up to 100 hr. Weight gain measurement was used as main experimental method and metallography as complementary method. It has been shown that the time dependence of oxidation of Fe-rollers with diameter f = 3 mm obeys the exponential law y(t) = A[1 - e{-Bt}] and that the oxidation run of Fe-rollers with f = 5, 7, 9, 11 mm, can be described more perfectly by common parabola y(t) = ktm. The oxidation rate w(t) of Fe-rollers decreases with increasing rollers diameter.

Jerzy Barglik, Bohus Ulrych: Three-dimensional analysis of induction heating of non-magnetic plate with finite dimensions, 361–373

Mathematical model of an induction heater with a transverse flux magnetic field is used to describe the non-stationary temperature field in a non-ferrous plate. The two three-dimensional fields are considered weakly coupled and processed using the professional software OPERA 3D to calculate the electromagnetic field, and the specially prepared software TEMP 3D to evaluate the temperature field. Examples of calculation are presented.

Vratislav Kafka, David Vokoun: Two-Way Shape Memory: Its nature and modeling, 375–391

An important property of materials with shape memory is two-way shape memory consisting in repeated change of shape undr repeated cooling and heating. To achieve this property the respective specimen of the shape memory material must undergo some kind of `training'. It is generally recognized that this effect is connected with self-equilibrated microstresses in the material. On the basis of previous papers of the authors [8], [9], [15], [16] the two-way shape memory effect and the process of training are explained and modeled using the latent variables concept with tensorial latent variables having dimension of stress. According to our approach the process of training consists in subsequent reduction of randomly orientated microstresses resulting from martensitic transformation, and creation of uniaxially orientated microstresses in the direction of training. The resulting model is able to describe the main features of the two-way shape memory effect and its training.

Josef Cadek, Karel Milicka, Shijie Zhu: Creep behaviour of ODS aluminium reinforced by silicon carbide particulates-an ODS Al-30SiCp composite, 393–411

Results of an investigation of creep behaviour in ODS aluminium reinforced by silicon carbide particulates – an ODS Al-30SiCp composite – are reported. The minimum tensile creep strain rates were measured at temperatures 623, 673 and 723 K and applied stresses ranging from 0.00277 G to 0.00774 G, where G is the shear modulus of aluminium. The creep in the composite is associated with a relatively high true threshold stress which decreases with increasing temperature more strongly than the shear modulus. The true threshold stress is suggested to originate predominantly from an attractive dislocation/fine alumina particle interaction, the presence of SiC particulates does not seem to contribute to it significantly.

The minimum creep strain rate is matrix lattice diffusion controlled and the true stress exponent of this strain rate is close to 5. In this respect, the creep behaviour of the ODS Al-30SiCp composite is similar to that of an Al-30SiCp composite.

Depending on the conditions of applied stress and temperature, the minimum creep strain rate in the ODS Al-30SiCp composite is up to 8 orders of magnitude lower than that in the Al-30SiCp composite. This effect of strengthening of aluminium matrix by fine alumina particles is largely, but not entirely, due to the higher threshold stress in the ODS Al-30SiCp composite. Some other possible contributions to this effect are discussed, but the load transfer is not considered to play any significant role in the heavily alumina particle strengthened Al-30SiCp composite.

Jerzy Barglik: Induction heaters for thin strips, 413–421

Paper presents a review of induction heaters used for continuous heating of thin charges. In case of thin non-ferrous metals strips or plates, induction heaters with a transverse flux magnetic field were commonly used. For heating of steel products induction heaters with a travelling magnetic field are more effective. Exemplary industrial stands are presented.