No. 3, 1999


Frantisek Chvala: On linearization of the Boltzmann equation with a source term, 213–223

A linearization of a problem with boundary conditions and initial data for the nonlinear Boltzmann equation with an external force and a source term is studied in the cases when the solution is not close to the Maxwellian distribution. A sequence of linearized problems is constructed such that their solutions converge to the solution of the original nonlinear problem.

Jaroslav Feda: Cataclastic compression of soils, 225–237

Grain crushing is an important structural mechanism affecting deformation and strength of soils. It is studied using a model material-air-dry granulated silica gel. It is shown that the compression curves are, due to crushing, of a garlandlike type. They are generally multilinear in a semilogarithnic plot. The value of the secondary compression coefficient Ca is stress dependent and correlates well with the course of the compression index Cc. The ratio of the secondary compression coefficient Ca and compression index Cc amounts to 0.02.

Viktor Pekarek: Matter waves-the concept underlying electrostatic and gravitational field, 239–244

A hypothetical interaction of two stationary electrons in vacuum is examined to show the congeniality of the electrostatic and gravitational field. The correlating factor turning vacuum into the two fields seems associated with the matter waves that are induced through the electron spin. The theory gives the correct numerical value of the gravitational constant, interpreting the elementary charge on the electron as a specific form of matter.

Martin Skopek, Bohus Ulrych, Ivo Dolezel: Induction Heating and its Utilization for Assembly and Disassembly of Hot-Pressed Joints, 245–259

The paper deals with the solution of the induction heating in common with the corresponding thermoelastic stresses and deformations in axi-symmetric bodies, that is applied to the problem of assembly and disassembly of the hot-pressed joints. The task is formulated as a weakly coupled problem. Its mathematical model that is based on differential equations and boundary conditions describing the distribution of the primary time dependent electromagnetic field, consequent non-stationary temperature field and finally the field of the thermoelastic displacements is then solved by the FEM-based professional programs QuickField and MARC. The methodology is supplemented by an illustrative example demonstrating the possibilities of the presented algorithm.

Josef Cadek, Kveta Kucharova: Creep behaviour of discontinuous aluminium and aluminium alloy matrix composites: An overview. Part II: Solution alloying and combined solution alloying and dispersion strengthening of the matrix. Final discussion, 261–320

Creep behaviour of dilute primary Al-Mg solid solution alloys is briefly reviewed first. Then the e(s,T) creep data for an Al-5Mg-26(Al2O3) and Al-4Mg-10SiC composites are re-analyzed and discussed. Further, it is shown that the discontinuous composites with magnesium concentrations in the matrix lower than ~ 1.6 at. % behave in creep similarly to unreinforced solid solution alloys produced by powder metallurgy route, but rather differently than discontinuous composites with magnesium concentrations in aluminium matrix higher than about 4.5 at. %. The distinguished attention is paid to combined solid solution strengthening and oxide dispersion strengthening in creep of discontinuous aluminium matrix composites, specifically to creep behaviour of an ODS Al-5Mg-30SiCp composite. Load transfer effect in creep of this composite is briefly discussed and the same holds for the threshold effect. Similarly as in Part I, an attention is paid to the strong temperature dependence of the true threshold stress. It is shown that alloying the ODS Al-30SiCp composite matrix with 5 wt. % Mg has almost no effect on the creep strength of this composite. The final discussion comprises all the main topics treated in both Part I and Part II of the present paper. Some needs for further research are outlined.