|ACTA TECHNICA CSAV|
The paper deals with the mathematical and computer modelling of the induction hardening of ferromagnetic bodies. The mathematical description of this non-stationary process consists of two second-order partial differential equations describing the induction heating (time evolution of the electromagnetic and temperature fields) and a theoretically empirical algorithm for mapping the consequent cooling and hardening. The task is solved in the quasi-coupled formulation, with partial respecting the temperature dependencies of all important material parameters. The theoretical analysis is supplemented with several illustrative examples, whose solution was performed by means of combination of professional codes and single-purpose user programs developed by the authors. Important results showing the distribution of hardness as well as particular material components (martensite, ferrite, pearlite) within the hardened body are presented and discussed.
Thermal spraying processes are widely used techniques enabling production of different protective coatings that can be used as thermal-barrier, wear-resistant, and corrosion-resistant surface layers. Industrial application of coated components implicitly demand to ascertain how the coatings affect fatigue behaviour of components.
This paper is concerned with an experimental study of fatigue behaviour and failure processes of flat steel specimens with thermally sprayed coatings. The four different types of coatings under study were: electric arc-sprayed and HVOF-sprayed austenitic steel 316L, plasma sprayed molybdenum and alumina (Al2O3). The results of fatigue bending tests are shown and discussed from the point of view of coating technology influence on fatigue lives. Fractographic analysis of fractured test specimens was carried out and main fractographic features of sprayed coatings were described. In-situ study of coated specimens in the vacuum chamber of SEM was used to specify fracture mechanisms of coatings.
The velocity distribution function of free electrons in a partially ionized gaseous medium is considered as a solution of an initial boundary value problem for the nonlinear Boltzmann equation. External electric field and internal sources are assumed. The solution is constructed as a limit of a sequence of iterations.
The paper presents an algorithm for numerical calculation of mutual- and self-inductances for massive, rotationally symmetric, cylinder-shaped coils without iron. The Monte Carlo method is primarily used for the calculation. The paper contains several numerical examples.
This contribution deals with parametrically excited systems due to periodic variation of a mass. The aim is to determine the instability intervals of the equilibrium position and thus also the possible parametric resonances. Attention is given not only to the instability intervals of the first kind but especially to the instability intervals of the second kind (combination parametric resonances). As for the latter instability intervals the purpose of this study is to find out whether summed or differences combination resonances or both types can occur.
Structure and phase composition are important parameters deciding on properties of thermal spray (TS) deposits-e. g. , . This work points out that the spatial distribution of phases, structural features and chemical elements is not necessarily uniform over the entire TS deposits. Moreover, non-uniform distribution can be found even in individual splats forming a deposit. Therefore two parameters were introduced: 1) macrohomogeneity across a deposit; 2) microhomogeneity across an individual splat. Scanning electron microscopy combined with X-ray microanalysis was used for detail study of several examples of various ceramic (silicates, titanates, oxides) and metal deposits made by thermal spraying. Microhomogeneity was studied on single splats and variation of structure and chemical composition was demonstrated on chromia based ceramics, AlSi metal deposits and others. Non-homogeneity is probably connected to the modes of solidification. Variation of phase composition, degree of porosity, crystallite size and distribution of chemical elements across deposits-macrohomogeneity-is then demonstrated for several materials, like CaTiO3 based powders, zircon, alumina , etc. It is interesting to note, that some materials are more sensitive, while others are practically insensitive (e. g. CaTiO3).