JOURNAL OF THEORETICAL AND APPLIED MECHANICS
Volume 28 Number 3 1998
                                                                    CONTENTS
 

GENERAL

MECHANICS

Vl. Damgov

Chr. Iliev
 

Space Research Institute, Bulg. Ac. Sci., Sofia

Presence of a Smale Horseshoe in the Dynamics of a Particle Under the Action of Two Waves

Here, we consider the motion of a particle under the action of two waves which is a problem that originally comes from plasma physics. By means of the Melnikov technique, we establish sufficient conditions for presence of a Smale horseshoe-like dynamics in a neighbourhood of homoclinic trajectory of the equation of motion. The last implies phenomena deterministic chaos.



L. Angelova

Y. Toshev

B. Filipov

D. Uzunov
 

Institute of Mechanics, Bulg. Acad. Sci., Sofia

Force-Time Criteria for Diagnosis of Human Locomotion
 

Selected dynamic characteristics data of human locomotion investigation are analysed in the work. The basic experimental data are the vertical and horizontal force reaction components (separately for left and right lower extremity) of 20 health male group in 18-25 age and for some cases of SCFE (slipped capital femoral epiphysis) patients.

The proposed dynamic criteria are analysed statistically and some hypothesis concerning their diagnostic application are verified. The results from the health male group investigation are compared with those of a small patients group in the meantime. These results are good basis to continue the work for the criteria precising by experimental data base increasing.



CONTINUUM

MECHANICS

Ch. T. Christov

L. B. Petrova
 

Higher Military School of Transport, Sofia

Static Analysis of Complex Prismatic Orthotropic Shell Structures by the Analytical Finite Strip Method

In this paper is developed the analytical finite strip method for linear static analysis of thin-walled prismatic orthotropic structures simply supported at their transverse ends and subjected to general loads and temperature actions.

The matrix displacement method is used. The three displacements and one rotation are basic unknowns in the linear joints. The particular rectangular finite strip of eight degrees of freedom is solved presenting the unknown quantities by single series the terms of which are products of trigonometric functions in the longitudinal direction and exact hyperbolic functions in the transverse direction. The basic equations and relations of the plane stresses, the folded plate and the general stresses of the strip are obtained. The strip stiffness matrices and load vectors are derived.



A. Dimitrova

G. Zamfirova
 

Higher Institute of Transport Engineering ``T. Kableshkov'', Sofia.

Microhardness Investigations of UHMWPE Obtained on Different Co-catalyst Systems
 

Microhardness characteristics of three type ultrahigh molecular weight polyethylene (UHMWPE) obtained on different supported modified Ziegler - Natta catalyst systems, and with respectively different molecular weights were studied. Samples were obtained by compression moulding. Investigations were curried out on Vickers microhardness device mhp - 160 for light microscope NU - 2.
Definitive for values of Vicker's microhardness (MHV) are rather type of morphology and polymer structure ( in particle), realized at the different polymerization conditions, than the concrete molecular weight. In this case total micrihardness (MHT), which is close connected with both the crystal and amorphous phases is defined generally by the quantity and structure of amorphous ones.



FLIUD

MECHANICS

N. Antonova
 

Institute of Mechanics, Bulg. Ac. Sci., Sofia

Blood Viscoelastic and Thixotropic Properties

The main works studied viscoelastic and thixotropic properties are reviewed. A brief background of viscoelasticity of blood is given and the sinusoidal oscillating rheometry is discussed.The study examines rheological properties of whole blood and RBC's suspensions under steady and dynamic shear conditions. A Couette viscometer LS 30 sinus Contraves with a firmly set amplitude by ±30deg has been used. The shear stress variations as a function of time for rectangular and triangular change of shear rates are determined. The viscoelastic properties are measured at a frequency varied between 0.00022 and 1.63 Hz. From the rheograms of different blood samples information is deduced about the shear thinning, thixotropy and viscoelasticity of blood. The founded results are discussed with respect to the aggregation-disaggregation processes in the whole blood in comparison with those in the suspensions.



D. Dankov
 

Institute of Mechanics, Bulg. Ac. Sci, Sofia

Monte Carlo Simulation of the Benard Instability in a Rarefied Gas Mixture
 
 

The existence of the Benard instability in a rectangular 2D domain of a rarefied gas, heated from below and under the action of a constant external force (gravity), is numerically investigated by using the Direct Simulation Monte Carlo method.



SOLID

MECHANICS

Zs. Gàspàr

K. Mladenov
 

Technical University of Budapest
University of Architecture, Civil Engineering and Geodesy, Sofia

On a Model with Compound Post-Critical Equilibrium

Cantilevered column with suppressed rotation at its movable end is charged by a polar force of constant magnitude. The post-critical behaviour is characterised by an infinite number of equilibrium forms related to one and the same post-critical load. In that event an equilibrium surface comes into light instead of equilibrium paths. The surface in question consists of an infinite number of secondary and tertiary equilibrium paths.



P. Gospodinov

R. Kazandjiev

T. Partalin

M. Mironova
 

Institute of Mechanics, Bulg.Ac.Sci., Sofia

Institute of Mechanics, Bulg.Ac.Sci., Sofia

Faculty of Mathematics and Informatics, University of Sofia ``St. Kl. Ohridski''

Central Laboratory of Physico-Chemical Mechanics, Bulg. Ac. Sci., Sofia

Strength Changes Occurring in Cement Stone Under Sulfate
Attack

The paper studies the strength changes which occur in a cement stone subjected to a sulfate attack. Thin plates are immersed and kept for different periods of time in a water solution of sodium sulfate. They are periodically tested to three point bending and bending strength for each period of time is determined. A relation between the bending strength of the material and the thickness of the external layer, formed within the specimen and affected by the sulfate corrosion, is proposed. The layer thickness is calculated on such a basis and good agreement between theory and experiment is obtained.



D. Dontchev

Kl. Hadjov

Sv. Nenov
 

University of Chemical Technology and Metallurgy - Sofia

Mechanical Behaviour of Multilayered Anisotropic Plates

The behaviour of multilayered anisotropic plates containing different uni-directional laminates under global tensile loading has been investigated. The investigation consists of a structural analysis and calculation of the global response of laminates.We have use a micromechanical model founded on the following basic assumption: stresses in an inclusion can be calculated as the stresses in such one inclusion that is embedded in an infinite matrix under remote matrix average stress loading. We have found the local stress redistribution and predict the local damage in the near fibre/matrix interface and matrix microcracks adjacent to voids.



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