Journal of Theoretical and Applied Mechanics

Volume 33, Number 3, 2003




V. Abadjiev, D. Petrova


Institute of Mechanics, Bulgarian Academy of Sciences

Acad. G. Bonchev Str., block 4

1113 Sofia, Bulgaria






Abstract. Some aspects of the synthesis and computer design of Spiroid gears taking into account their specific characteristics are treated  (Spiroid and Helicon are trade mark of Illinois Tool Works – Chicago, Illinois, USA). Special accent is put on the applied mathematical models on the basis of which are elaborated the algorithms for synthesis of these skew-axes gears: mathematical model for a pitch contact point synthesis, and mathematical model based on a region of mesh. The principles of an organization of Spiroid gears synthesis and of a design by computer programs are discussed. Computer programs are worked out on the basis of the described mathematical models and the relations between them are shown.


Key words: gearing, synthesis and design pitch contact point, region of mesh, estimation criteria.


Al. B. Kazakoff


Institute of Mechanics, Bulgarian academy of Sciences,

Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria,





Abstract. Shock protection mounts comprising viscous-elastic elements, are widely used in modern warship design to reduce the high accelerations imposed by non-contact underwater explosions. However, predictions of the behaviour of viscous-elastic materials in this severe loading regime present a significant challenge due to the large strains and strain rates imposed in the viscous-elastic elements. The objective of this paper was to investigate the dynamic response of a “benchmark” model and a “back-to-back benchmark” model, which basically is a combination of two “benchmark” models mounted in series are subjected to defined shock input loading and a correlation against the experimental test results was performed. Both ELASTIC and HYPERELASTIC options within the ABAQUS code were used in the Finite Element (FE) analysis to cover the full range of deformation magnitudes. An ELASTIC analysis suffices up to a nominal 50% strain level, above this an HYPERELASTIC analysis is needed to reproduce good correlation with experimental data. Dynamic transient responses of half-sine shock impact in vertical and lateral direction are measured and compared with the FE optimal mesh prediction.


Key words: shock and vibration protection, Finite Element (FE) analysis, viscous-elastic mounts, dynamic transient responses, half-sine shock impact.


Y. D. Nikolova, N. D. Nikolov


University “Prof. Dr. Assen Zlatarov” – Bourgas,

1, Prof. Yakimov Str., 8010 Bourgas, Bulgaria



Application of an Ultrafiltration Module with Screw Mixers


Abstract. An ultrafiltration process in specially designed tubular module having an insert with thread guide mixers is investigated. The experiments were carried out under stationary conditions - Re 2000 and temperature 20°C with 3% aqueous solution of dextrin with molecular weight 40 000 Da. The insert placed in the membrane is cylindrical surface with a certain number of double-start thread guides cut on it, so that they change screwing direction, and the beginning of the next thread is rotated by 90° vs. the end of the former one. The process productivity is found to increase compared to the experiments with flat cylindrical insert and a membrane without an insert.


Key words: ultrafiltration, concentration polarization gel layer.



N. Georgiev, C. Kouyumdjiev


Department of Technical mechanics, “Angel Kanchev”University of Rousse,

8, Studentska Str., 7017 Rousse, Bulgaria,



D. Tatchev, S. Armyanov


Institute of Physical Chemistry, Bulgarian Academy of Sciences,

Acad. G Bonchev Str., Bl. 10, 1113 Sofia, Bulgaria,



Isothermal investigation of stress relaxation

IN metallic glass Co58 Ni10 Fe5 B16 Si11


Abstract. An investigation of stress relaxation in the metallic glass Co58 Ni10 Fe5 B16 Si11 is presented. Isothermal annealing of pre-stressed samples is carried out at five temperatures in the range of 573°?673° K. Using the Luborsky bending method the stress relaxation curves are plotted. They are described satisfactorily by the Kohlrausch equation. Second annealing of the samples is conducted to eliminate the anelastic deformation in the material and the related residual stress. In this way the viscous-elastic deformation is revealed. The activation energy of the relaxation and the time constant in the Kohlrausch equation are determined.


Keywords: stress relaxation, metallic glasses.




Institute of Mechanics and Civil Engineering,

University of Liege, B-4000, Belgium,



A.    Baltov, M. Datcheva


Institute of Mechanics, Bulgarian Academy of Sciences,

 Acad. G. Bontchev Str., bl.4, 1113 Sofia, Bulgaria,





Institute of Mechanics and Civil Engineering,

University of Liege, B-4000, Belgium,



Conditions for ELASTO-PLASTIC strain localization in Unsaturated soils


Abstract. The necessary and sufficient conditions for elasto-plastic strain localization initiation in unsaturated soil massifs are proposed. Unsaturated behaviour is described using net stress and suction as independent stress variables and modifying the basic constitutive surface parameters and hardening rules to consider the role of suction. The process is accepted to be static and isothermal. The conception that the localization band initiates due to the loss of stability of deformation process is assumed. In that case, the rates of process measure bifurcate. A special example is given to illustrate the application of the obtained conditions.


Key words: elasto-plastic localization, conditions for localization initiation, unsaturated soil.


Philip Philipoff


Central Laboratory for Seismic Mechanics and Earthquake Engineering (CLSMEE),

 Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 3, 113 Sofia, Bulgaria,



SH Wave Propagation trough Multilayer Media


Abstract. An investigation of SH wave propagation trough multilayer geological media is presented. An original structural model of the geological column is developed. The layers are isotropic with constant depth and parallel to the skyline. SH rays are with arbitrary angle in regarding to the layers. The main results of the study are illustrated graphically. The comparison between the experimental and the numerical surface signals (direct problem) for the considered geological column is shown.


Key words: structural model, digital seismic signals, power spectral density.