**GENERAL**

**MECHANICS**

**Al. Cheremensky**

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

Meaning of Feedbacks with the Highest Derivatives

Various effects produced
by the feedbacks with the highest derivatives of output have been pointed
out in order to explain why they may not be put in practice. Within the
framework of the concept of negligible small time-delay, this paper makes
clear the meaning that these feedbacks have themselves. It is shown that
the known methods of the model diagonalizing and reducing its inaccuracy
are not robust with respect to a small time-delay.

**S. Grozdev**

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

Examination of a Nonstability

A state equation problem
of parabolic type is considered in the paper under a nonlinear perturbation.
A sufficient condition is given when the state could be determined by the
control in an unique way.

Institute of Theoretical Astronomy, Russ. Ac. Sci. St. Petersburg

Influence of the radiation pressure on the motion of a satellite with large eccentricity

Analytical theory of the
first-order perturbations from the solar radiation pressure is developed
for artificial Earth satellites with large eccentricities using trigonometric
expansions of satellite disturbing function in multiples of the elliptic
anomaly.

Central Laboratory of Mechatronics and Instrumentation, Bulg. Ac. Sci., Sofia

Some Aspects in the Design
of Adaptive Measuring Systems

The development of adaptive measurement systems for geometrical shape recognition of mechanical parts during each stage of production is a design problem which cannot be solved without developing new methods for using conventional and advanced-construction measurement devices and applying sensor technology. A concept for design of adaptive measuring systems, applicable to simultaneous quality control of multiple machine parts in small and medium series production is presented. The general structure of the system and the major characteristics of its subsystems are discussed from the viewpoint of Mechatronics. The results of experiments are summarized.

**MECHANICS**

**V. Vassilev**

Institute of Mechanics, Bulg. Ac. Sci. Sofia

Symmetry Groups and Equivalence
Transformations in the Nonlinear Donnell - Mushtari - Vlasov Theory for
Shallow Shells

In the case of transversely
only loaded shallow shells, the nonlinear Donnell - Mushtari - Vlasov theory
for large deflection of isotropic thin elastic shells leads to a system
of two coupled nonlinear fourth-order partial differential equations known
as Marguerre's equations. This system involves two arbitrary elements -
the curvature tensor of the shell middle-surface and the function of transversal
load per unit surface area. In the present note, the point symmetry groups
of Marguerre's equations are established, the corresponding group classification
problem being solved. It is shown that Marguerre's equations are equivalent
to the von Kármán equations for large deflection of plates
in the time-independent case and in the time-dependent case as well. It
is also observed that the same holds true in respect of the field equations
for anisotropic shallow shells.

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

Elastic Modulus
of Cement Stone Beam Subjected to Sulphate
Attack

The paper presents a theoretical-experimental
method for assessing the elasticity modulus of a cement stone, the latter
affected by sulphate corrosion. The specimen is treated as having a two-layered
srtucture (an external layer affected by corrosion and a pure cement core)
owing to the corrosion effects on the material. The material mechanical
characteristics are determined by performing fractureless experiments on
compression and bending. A relation between the thickness of the external
layer and its specific elasticity modulus is also determined. Good agreement
between the theoretical assumptions and the experimental results is obtained.

**A. Metchkov**

**A. Popov**

**S. Metchkova**

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

Non-destructive Testing of
Iron Base PM Materials

The deformation of sintered
powder metallurgical materials on iron base was studied. The acoustic emission
was monitored during the process of samples bending. It was founded that
acoustic emission activity in the elastic region is successful criterion
for the recognition of the structure and chemical compositions of the sintered
powder metallurgical materials.

**MECHANICS**

**A. Baltov**

**M. Popova**

**V. Iliev**

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

University of Chemical Technology
and Metallurgy, Sofia

Simulation of the Mechanical
Behaviour of Textile Composites

In this paper a method for modelling of the mechanical behaviour of the textile composites is developed. A convenient model is adopted and it takes into account the effects of the structural anisotropy and the loading type sensitivity of the investigated materials. The idea of the model is to introduce a six-dimensional vector space of the stresses which consists of subspaces of the different types of loading and also to construct the hyper-quadratic surfaces in each subspace. The elastic characteristics of the material are identical in every subdomain. The computer simulation method is developed for obtaining of the elastic characteristics. The simulation is carried out on the representative element substituted in a suitable way by a lattice system. The rigidities of the various bars are determined on the basis of test data from comparatively simple experiments. The method suggested is applied for determining the elastic characteristics of a woven composite material on the base of glass fibres and a polyester resin in the case of two dimensional stress state.

**G. Kolarov**

**R. Tenchev**

Technical University of Sofia

Error Estimates for the Finite Prism Method

There are investigated the possibilities to estimate the error in the finite prism solution, that is a semianalytical method for solving elastic problems for 3D prismatic bodies. There is proposed an a-priori error estimator for the analytical part of the solution. For the numerical parts of the solution, performed by finite elements, there are tested with some modifications two well known a-posteriori error estimators - these of Zienkiewicz-Zhu and of Babu ska-Miller. A detailed example for the application of the error estimation is considered.

University of Mining and Geology, Sofia

Influence of the Number of Plies and the Elastic Moduli of the Rubber and the Plies on the Stresses Distribution in a Conveyor Belt

Equations are obtained and an algorithm is worked out for determination of the location of the neutral line of the cross-section of a conveyor belt at pure bending and in the presence of external axial force. The influence of the number of textile plies and the ratio of the elastic moduli of the rubber and the plies on the stresses distribution is examined.

**P. Hovsepyan**

**I. Ivanov**

**R. Tanov**

University of Rousse, Rousse

Determination of
the Stresses in Isotropic Multilayer Thin
Coatings

A new algorithm for determinig the distribution of the initial and residual stress in multilayer coatings by the bending strip method is proposed. The algorithm is applicable for coatings obtained by consecutive deposition by various technological processes of arbitrary number of elastic, homogeneous and isotropic layers of different materials. An example about the determination of the stresses in composite Ti and TiN vacuum coating deposited on a steel substrate is given.

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

Propagation of Transversal Shock Waves in a Rod

In the present paper we consider
the propagation of transversal shock waves in an elastic rod, which is
in ideal contact with a semibounded elastic medium from where the shock
wave in the rod comes from. On the boundary between the rod and the semibounded
medium we have a reflection and a refraction of the shock wave coming from
the semibounded medium. The moving wave then reflects from the other end
of the rod, which is stress free and returns back to the first end of the
rod and etc.The formulas for the stresses, the strains and the velocities
of displacement in the rod during these numerous reflection and refraction
of the shock wave are obtained. Generalized results of the case when the
rod structure is not homogeneous but consist of n sectors with different
mechanical characteristics are obtained.

**MECHANICS**

**V. Baranov**

**G. Kalujny**

**P. Poltev**

**H. Hristov**

**Z. Chiwikov**

**K. Boyadjiev**

Tula State University, Tula,
Russia

GNPP -Splav, Tula, Russia

Military Research Institute,
Sofia, Bulgaria

Dunarit-Ltd., Rousse, Bulgaria

Vazov Engineering Plants-Ltd.,
Sopot, Bulgaria

Experimental - Theoretical Determination of Physical Constants Included in a Phenomenologic Model of Destructions

In this paper has been developed and realized an experimental theoretical method for determination of the numerical values of the physical constants included in the structure of the phenomenologic model for destruction of real material which allows the application of this model for evaluation of strength of structures in case of tensile step loading. The authors present the constant value of aluminum.

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