Issue 1

JTAM, Sofia, vol. 7 Issue 1 (1976)

Plane Strain State of Perfectly Plastic Cosserat Media under Changing Mechanical Characteristics

N.Ja. Bogdanova-Bontcheva
Sofia 1113, Institute of Mathematics and Mechanics with Computer Center, Bulgarian Academy of Sciences

The plane strain state of perfectly plastic loose granular media is considered with the change of the internal friction angle due to volume changes in the deformation process taken into consideration. A solution of a numerical example is given as the graphical time dependence of the stresses and the velocities.

JTAM, Sofia, vol. 7 Issue 1 pp. 009-017 (1976)

The Determination and Analysis of Links Position Functions of a Spatial Linkage

F.L. Litvin
Leningrad USSR, Leningrad Institute of Precision Mechanics and Optics

Methods for determining: a) the functions of the link positions, b) the special position of the links where the functions of position are ambiguous for local situations, c) the conditions under which for space lever mechanisms there are one or two links with full rotations or there are no such links, are proposed in this paper.

JTAM, Sofia, vol. 7 Issue 1 pp. 018-024 (1976), [Full Article]

The Initial Flow Pasta Circular Cylinder which is Started with Unsteady Velocity

S.G. Slavchev
Sofia 1113, Institute of Mathematics and Mechanics with a Computer Center, Bulgarian Academy of Sciences

The initial flow past a circular cylinder started from rest in a viscous incompressible fluid with unsteady velocity is investigated. The Navier-Stokes equations are solved by the method of matched asymptotic expansions. The second approximation for the flow velocity and the skin friction is calculated. The solution is uniformly valid in the whole flow field and takes into account second order effects as a curvature of body surface and an interaction between the boundary layer and the inviscid outer flow.

JTAM, Sofia, vol. 7 Issue 1 pp. 025-031 (1976), [Full Article]

Computer Aided Determination of the Safety of Elastic Arcs for Symmetric and Inverse Symmetric Forms of Stability Loss

E.M. Milčev
Sofia, Lenin Square 16, Institute of Building Cybernetics

A method of determining the safety with respect to the loss of stability in the Euler sense of elastic arcs for symmetric and inverse symmetric forms of stability loss proposed by the author is applied. An algorithm is obtained as well as a computer program. Numerical illustrations are given.

JTAM, Sofia, vol. 7 Issue 1 pp. 032-038 (1976)

The Influence of the Primary Creep on the Creep Buckling of a Cylindrical Shell

P.T. Kolev
Sofia, boul. H. Smirnenski 1, Higher Institute of Civil Engineering, Department of Theoretical Mechanics

The creep buckling of a thin isotropical cylindrical shell with simple support and under uniformly distributed axial loading is considered in the pre-sent paper. A specification of the expression for the creep rate, taking into account the primary creep is made without application of the known idealizations. A variational approach is used for the solution of the problem. A non-symmetric buckling and linear distribution of stress through the shell thickness is assumed. It is established that the idealization makes the structures "stiffer", leading to an increase in the critical time. When the loading is heavy, it is necessary to apply the specified formula for the influence of the primary creep.

JTAM, Sofia, vol. 7 Issue 1 pp. 039-047 (1976)

Creep Stability of a Polymeric Stick under the Influence of a Linearly Increasing Force of Stress

E.K. Bončev, G.J. Mandičev, K.G. Popov, P. Lazarov
Sofia – Dărvenica, Higher Institute of Mechanical and Electrical Engineering

The stability of a polymeric stick with a constant rectangular cross section, fixed at the joint, loaded with a constantly increasing force is considered. The Maxwell-Gurevič generalized nonlinear equation is used as a starting point for the stress and the strain (deformation). A numerical method for solving the obtained system of differential equations with the respective initial and border conditions is given.

JTAM, Sofia, vol. 7 Issue 1 pp. 048-052 (1976)

Unsteady MHD Flow in Rotating Fluid

V.M. Soundalgekar
Cardiff, Great Britain, UWIST, Department of Mechanical Engineering

An analysis of the flow of an electrically conducting, viscous fluid past an (uniformly accelerated, infinite plate, in a rotating fluid has been carried. Solutions for the velocity are derived in terms of the parabolic cylinder functions. The velocity profiles and the skin-friction are shown on graphs. It is observed that due to an uniformly accelerated plate or owing to an increase in M, the magnetic field parameter, there is a fall in the skin-friction. At small values of M, τx increases with increasing the angular velocity ω, but at large values of M, τx decreases with increasing ω.

JTAM, Sofia, vol. 7 Issue 1 pp. 053-058 (1976), [Full Article]

On the Existence and Unity of the Solution of Integral and Integro-Differential Equations of the Volterra Type in the Theory of Viscosielasticity

M.M. Konstantinov1, D.D. Bajnov2
1Sofia, Higher Institute of Mechanical and Electrical Engineering
2Sofia, The Academy of Medicine

The conditions of existence and unity of the solution of some classes nonlineal integral and integro-differential equations of the Volterra type are treated in the paper.

JTAM, Sofia, vol. 7 Issue 1 pp. 059-062 (1976)

On the Dynamic Criteria for Evaluation of the Machine Units Motion Mode

E.S. Stančev, N.D. Minčev
Varna Higher Military Naval Academy "N. J. Vapcarov", The Department of Engineering Mechanics

It is demonstrated in the paper that the dynamic factor of irregularity and the characteristic criteria of the first and second order do not give a more complete evaluation of the dynamic state of the machine units than the law of angular velocity change, angular acceleration and the first order acceleration respectively.

JTAM, Sofia, vol. 7 Issue 1 pp. 063-068 (1976)