**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.

**Y. Toshev**

**B. Filipov**

**D. Uzuno**v

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.

**MECHANICS**

**Ch. T. Christov**

**L. B. Petrov**a

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.

**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.

**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.

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.

**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.

**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.

**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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