Issue 1

JTAM, Sofia, vol. 23 Issue 1 (1992)

Si licet parva componere magnis

I. Chobanov
Sofia University, Sofia

The paper contains a critical of some view-points of the author of article [1] concerning itself with an would-be scientific and personal rivalry between Euler and D'Alembert. Special attention is paid to D'Alembert's main dynamical treatise [4] and to the so called "principe de d'Alembert" popularized by Lagrange in his fundamental work [7] on analytical dynamics. As it is well-known, the basic idea of D'Alembert-Lagrangean machanical phylosophy consists in the assumption that a rigid body is an "ensemble de corpuscules" supported at constant distances by some kind of internal forces realizing this hypotetical model and it is answered in the negative by a reduction to absurdity.

JTAM, Sofia, vol. 23 Issue 1 pp. 010-025 (1992), [Full Article]

Kinematics of a Three-Degrees of Freedom Manipulator with Parallel Topology

T. Tanev1, N. Shivarov1, M. Constantinov2
1Institute of Engineering Cybernetics and Robotics, Bulg. Acad. Sci, Sofia
2University for Architecture, Civil Eng. and Geod., Sofia

This paper presents a complete kinematic analysis of a mechanism of parallel topology, possesing three degrees of freedom, of the 3RRS type. The possible utilization of this mechanism as a link of manipulation system is examined. Solutions of the direct and inverse kinematic problems for this manipulation system are given. The restrictions on the parallel topology robot motion are analysed.

JTAM, Sofia, vol. 23 Issue 1 pp. 026-039 (1992), [Full Article]

Measurement of the Dynamic Properties of Machine Aggregate with Variable Parameters and Asynchronous Motor

J. Mudric
Institute of Materials and Machine Mechanics SAS, Bratislava

The paper deals with one of the possible methods for measurement of the .dynamic characteristics of a machine aggregate with electric drive. The method is based on the measurement of the electromagnetic moment and the calculation of the absolute slip of an asynchronous motor based on the current and the voltages at the motor terminals.

JTAM, Sofia, vol. 23 Issue 1 pp. 040-051 (1992), [Full Article]

Hydroelasticity in Cases of Waterhammer

N. Nikolov, M. Maradgieva
University for Architecture, Civil Eng. and Geod., Sofia

In this paper the authors give a new solution of the partial differential equations for waterhammer by introducing one characteristic direction. The numerical solution is obtained by Euler's method. This solution takesinto account the influence of the elasticity of the fluid and the pipe material. The boundary condition at the pump is described by Nikolov's method with the four quadrant characteristics of the pump.

JTAM, Sofia, vol. 23 Issue 1 pp. 052-062 (1992), [Full Article]

Mathematical Simulation of Weakly Compressible Fluid in Hydraulic Drives Mechanics

P. Matus, V. Corolkevich, M. Chuiko
Institute of Mathematics, Acad. Sci., Minsk, Byelorussia

Effective, unconditionally stable numerical methods for weakly compressible fluid equations describing process in machine hydraulic drives are constructed. Numerical experiments are discissed.

JTAM, Sofia, vol. 23 Issue 1 pp. 063-073 (1992), [Full Article]

Creep Damage and Ruprure of a Nonproportionally Loaded Solid Circular Tortion Bar

M. Datcheva
Institute of Mechanics and Biomechanics, Bulg. Acad. Sci., Sofia

New damage variables are associated with anisotropic damage processes. It is shown that the material damage in creep can be represented by a combination of vector and scalar damage parameters. The constitutive equations of creep and creep damage are formulated by employing the damage vector and the scalar damage parameters as internal state variables. Anisotropic damage law, Norton type flow law and the extended to the multiaxial state of stress Kachanov-Robotnov's rupture criterion are assumed to specify the resulting constitutive equations. The rupture time and damage .processes of steadily and non-proportionally loaded solid circular tortion bars are compared and the proposed model is shown to represent well the principal views on the creep damage in metals.

JTAM, Sofia, vol. 23 Issue 1 pp. 074-082 (1992), [Full Article]

Approach to Contact Friction Modelling at Hot and Cold Rolling

A. Baltоv, A. Nedev
Institute of Mechanics and Biomechanics, Bulg. Acad. Sci., Sofia

A generalized Zibel friction law is propossed in the pressent paper. The coupling effect between the Coulon friction mechanism and the plastic one is taken into account. The plastic anisotropy at the contact layer is included in the model offered. A resonable linear approximation is made for the friction factor according to the rolling process factors.

JTAM, Sofia, vol. 23 Issue 1 pp. 083-091 (1992), [Full Article]

An Examination of the Status of Stress in Coated Flat Pieces by the Finite Element Method

Ch. Kouyumdjiev, N. Stancheva, M. Todorov
Technical University, Russe

The present paper describes a new field of application of the results, obtained by the strip bending method, namely the determination of stress in real coated pieces on the bases of these results. It is possible to determine the planar state of stress in various coated flat pieces by updating an automated programme system. As an example, the stress in a metal-cutting tool and in a titanium nitrade deposit coated on it are determined.

JTAM, Sofia, vol. 23 Issue 1 pp. 092-107 (1992), [Full Article]

Damage Accumulation During Hot Rolling of a Metal Sheet in a Multi-Cell Rolling Mill

R. Kazandjiev
Institute of Mechanics and Biomechanics, Bulg. Acad. Sci., Sofia

The paper studies the damage accumulation in a metal sheet which undergoes hat rolling. A method to calculate the damage growth at each stage of the process is used, based on the theory of linear. defect nucleation. Sheet rolling in a multi cell 1700 rolling mill is analysed as an example, where the direct occurrence and nucleation is followed and a tecnologically admissible redistribution of the degree of deformation in each cell is determined. The paper is a preliminary step to a further optimization of the rolling regime, aiming at attaining a possible maximum of the mill productivity and minimum material damage, accumulated during the forming process.

JTAM, Sofia, vol. 23 Issue 1 pp. 108-117 (1992), [Full Article]

The Effect of Strain-Rate on Dynamic Characteristics of Structural Steels

K. Minchev
Institute of Metal Science and Technology, Bulg. Acad. Sci., Sofia

Low carbon, low allow structural steels have been evaluated in the present work by means of their characteristics under dynamic load. The possibilities of Charpy instrumented Pendulum and of Hopkinson Pressure Bar Arrangement have been used for determinating dynamic yield strength and dynamic fracture toughness. Experimental data are presented for the change of the dynamic yield strength of the tested steels. Load rate effect on fracture toughness variation has been determined for a temperature interval.

JTAM, Sofia, vol. 23 Issue 1 pp. 118-134 (1992), [Full Article]