Issue 3
JTAM, Sofia, vol. 5 Issue 3 (1974)

The Influence of Destruction on the Mechanical Behaviour of Polymers

G. Brankov, N. Petrov
Sofia, Bulgarian Academy of Sciences; 1, Sedmi Noemvri Street; Institute of Mathematics and Mechanics with Computing Centre BAN, IV km


The authors consider a polymer body subjected to radiation or sun-ray irradiation. The ageing of the material, expressed in destruction of the molecular chains, is accounted for by the concentration of the components that are the product of the photochemical reaction.

JTAM, Sofia, vol. 5 Issue 3 pp. 009-016 (1974)

On the Formation and the Initial Stage of Development of a Laminar Boundary Layer Around a Parabolic Cylinder

Z. Zapryanov, G. Simeonov
Sofia, Institute of Mathematics and Mechanics with Computing Centre, BAN, IV km

The investigation covers the formation and the initial stage of development of a non-stationary boundary layer around a parabolic cylinder moving in the direction of the axis of the controlling parabola. The problem has been solved on the basis of the Navier-Stokes equations by the method of matched asymptotic expansions. The asymptotic solution obtained is uniformly valid in the interior and exterior regions.

JTAM, Sofia, vol. 5 Issue 3 pp. 017-028 (1974)
On a Stability Citerion for Visco-Plastic Bodies

A. Baltov
Sofia, Institute of Mathematics and Mechanics with Computing Centre, BAN, IV km

Some energy criterion has been applied for visco-plastic bodies, dynamic ally loaded and in the presence of a temperature field. A thermodynamic approach has been applied, and Lyapunov's definition of stability has been used. As particular cases, stability criteria of the equilibrium form, of the thermal state and of the internal-structural state of viscous-plastic bodies have been obtained.

JTAM, Sofia, vol. 5 Issue 3 pp. 029-035 (1974), [Full Article]

Study of Vibration of Viscoelastic Timoshenko Beam on Viscoelastic Foundation Subjectedt to Axial Force

D.K. Rao, I.S. Rao
Indian Institute of Technology Kharagpur, India

This is an examination of it simply supported viscoelastic beam according to Timoshenko's model and the mechano-mathematical model of a standard viscoelastic body. The beam lies on a viscoelastic foundation and is subjected to axial forces under given initial conditions and time-dependent boundary conditions. The problem is to find the free oscillations of the beam under conditions of established frequency and velocity impulse.

JTAM, Sofia, vol. 5 Issue 3 pp. 037-053 (1974), [Full Article]

On the Yield Condition in Cossert Media with Internal Friction

N. Bogdanova-Bontcheva
Sofia, Institute of Mathematics and Mechanics with Computer Centre, BAN, IV km

The author examines rigid-plastic media of Cosser which are characterized by the presence of internal friction and cohesion. The yield condition has been worked out for such media, and the influence has been examined of the instantaneous stresses on the yield limit in the plane of Moore's circle. A boundary problem of infinite medium with cylindrical hollow has been solved.

JTAM, Sofia, vol. 5 Issue 3 pp. 055-066 (1974)
Certain Equations of the Dynamics of Mechanical Systems of Variable Mass

S. Buchvarov
Sofia, Higher Institute of Mechanical and Electrical Engineering, Department of Mechanics

Tsenov's equations of the first and second order have been worked out in the article, as well as Nielsen's equations for mechanical systems with variable mass in the presence of non-holonomic connections. The assumption is made that the mass of the points from the mechanical systems depends on the time, on the summarized coordinates and on the summarized velocities. Upon working out these equations account has been taken also of the relative movement of the joining and separation particles within the body which has been accepted as material point with variable mass. The corresponding equations for holonomic systems have also been obtained in a particular case.

JTAM, Sofia, vol. 5 Issue 3 pp. 067-076 (1974)
Non-Linear Longitudinal and Transverse Waves in Semi-Space

Y.K. Engelbrecht
U.S.S.R. 200001, Tallin, 10 Lenin Blvd., institute of Cybernetics of the Academy of Sciences of the Estonian S.S.R.

This is a discussion of general problems of the connections between unidimensional longitudinal and transverse waves in a non-linear medium with heat dissipation. The mathematical model of the semi-space has been introduced on the basis of the physical and geometrical non-linear theory of thermoelasticity. General principles have been worked out and model non-linear equations have been analyzed which are true for big times.

JTAM, Sofia, vol. 5 Issue 3 pp. 077-086 (1974)
Numerical Solation of Comperdent Bidimensional Problem of Thernmelasticity

I.K. Naval, V.G. Cheban
Moldavian S.S.R. Kishinev, 5, Akademicheskaya Street, Institute of Mathematics with Computing Centre of Academy of Sciences of the Moldivian S.S.R.

A numerical solution lies been given of the bidimensional cquations the compendent thermoelasticity by means of a method using the lilies intersection of the coordinate and characteristic surfaces with fixed uniform grid.

JTAM, Sofia, vol. 5 Issue 3 pp. 087-094 (1974)
Solution of the Volume Dynamic Problem of the Elasticity Theory by the Method of Terminal Elements

I.Y. Harhurim
U. S. S. R., Leningrad, C-15, 45 Tavricheskaya Street, kv. 54

Numerical results have been obtained for volume bodies subjected to temperature and dynamic loading by means of the method of terminal elements. Elements with curvilinear outlines along a square parabola were also used.

JTAM, Sofia, vol. 5 Issue 3 pp. 095-106 (1974)