Issue 4

JTAM, Sofia, vol. 23 Issue 4 (1992)

Stability of Certain Solutions in a Mechanical Model Generating the Rigid Body Problem

O. Christov
Sofia University, Sofia

A mechanical model which generalizes the classical rigid body problem is considered in this paper. By analogy, the cases of Euler, Lagrange and Kowalewski are introduced and necessary and sufficient conditions for stability of certain solutions, possessed by them, are obtained. The sufficient conditions are obtained by Tchetaev's method (Lyapunov's function is constructed by the help of the first integrals) and the necessary conditions are obtained through linearizing the perturbed equations of motion.

JTAM, Sofia, vol. 23 Issue 4 pp. 009-021 (1992), [Full Article]

Reliability Prognosis of Mechatronic Systems using Analytical Simulation Method

Yu. Krakovsky
Irkutsk Scientific Center, Russia

Analytical-simulation procedure (ASP) for accessing and investigating reliability factors of mechatronic systems (MS) which are formalized as a set of four groups of elements is developed. A random marked point process is chosen as a mathematical model describing the MS behaviour in the course of time. ASP estimates the fault flow parameter, fulfillment task probability and other factors. Using factor analysis the influence of some variables on the MS reliability factors has been reaserched.

JTAM, Sofia, vol. 23 Issue 4 pp. 022-029 (1992), [Full Article]

On the Numerical Solution of a Class of Diffusion and Sorption Problems

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

A numerical approach for solving one class of diffusion and sorption problems is developed on the basis of the finite element method and a time difference scheme. The proposed hybrid scheme is investigated under the physical correctness conditions. The sufficient conditions for its initial stability are derived. A numerical algorithm for two-dimensional problems in various domains and of different types of internal diffusion and sorption is created. It is illustrated with numerical examples for diffusion and first order reaction. The obtained numerical results are in a very good correspondence with the available analytical ones.

JTAM, Sofia, vol. 23 Issue 4 pp. 030-041 (1992), [Full Article]

Investigation of the Deformations due to Wood Swelling in the Process of Water Sorption by Speckle Photography

N. Nedelchev1, V. Kavardjikov2, N. Terziev2
1Higher Institute on Forestry and Technology, Sofia
2Institute of Mechanics and Biomechanics, Bulg. Acad. Sci., Sofia

The present paper describes a new application of the double - exposure speckle-photography. The wood swelling kinetics in the process of water sorption is investigated by this coherent-optical method. Three phases of the sorption development are experimentally differentiated. This result confirms the existing theoretical ideas about the mechanism of wood water sorption. It is shown, that at the second phase the swelling process significantly decelerates and even stops regardless of the continuous water sorption.

JTAM, Sofia, vol. 23 Issue 4 pp. 042-050 (1992), [Full Article]

Analysis of Reinforced Concrete Frames of Seismic Excitations Taking into Account Their Physical and Geometrical Nonlinearity

E. Vasseva
Central Laboratory of Seismic Mechanics, Bulg. Acad. Sci., Sofia

A method for a nonlinear study of reinforced concrete structures under strong ground motions is presented in this paper, at the same time the effect of the physical and geometrical nonlinearity on their behaviour is investigated. The cases when the predominant period of the seismic excitation is close to the one of the structure and when the difference between them is significant are discussed. The numerical results of the study of two-storey frames indicate a change in their rigidity and a reduction of the seismic impact.

JTAM, Sofia, vol. 23 Issue 4 pp. 051-062 (1992), [Full Article]

On tne Constitutive Ilushin's Theory Relations. Part II

P. Trusov, Y. Nyashin
Politechnical Institute, Perm, Russia

This paper seeks to establish the constitutive relations which are the generalization of Ilushin's Elastoplastic Processes Theory for the case of large plastic deformations. Motion decomposition methods, the strain trajectory notion and the loading process image are generalized for the case of large deformations in this connection. The usage of specific constitutive equations for the various path types is suggested. The results of the test problems and extrusion problem solutions are presented.

JTAM, Sofia, vol. 23 Issue 4 pp. 063-086 (1992), [Full Article]

Dynamic Penetration and Perforation of Plates by a Rigid Cylindrical Cone Tip Projectile

L. Parashkevova
Institute of Mechanics and Biomechanics, Bulg. Acad. Sci., Sofia

The penetration of a rigid cylindrical cone tip projectile into ideal-plastic plate at initial impact velocities between 100 - 900 m/s is discussed. The problem is analized on the basis of the upper bound method, including kinetic energy rate of deformed material. Two kinematically admissible schemes and their velocity fields are presented. The ontribution in terms to the energy rate loss, connected with the admissible acceleration jumps on the respective surfaces of velocity discontinuities is taken into account. Appropriate upper bound estimates are calculated for – all subvariants. The computer code implementation of the above mentioned aproach includes numerical solution of the projectile equation of motion, it's right-hand lade depending on the infimum of the upper bound estimates at each moment.

JTAM, Sofia, vol. 23 Issue 4 pp. 087-097 (1992), [Full Article]

Dynamic Loading Behaviour of Nitrogen-Alloyed Structural Steels

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

Some results showing the behavior of nitrogen-alloyed structural steels subjected to dynamic loading are presented in this paper. The substantial sensitivity of the mechanical properties to loading rate and operating temperature determines their application range as much as they strongly influence the steel transient between brittle and ductile behaviour. The tests have been conducted on a dynamic loading, i.e. /Charpy test/ equipped with devices for recording the loadtime diagram. The test temperature range was -100°C to +20°C with an impact speed of 1.5 to 5.5 m/s. The fracture toughness as a function of temperature, the dynamic yield stress and the stress intensity factor at the crack tip have been established.

JTAM, Sofia, vol. 23 Issue 4 pp. 098-108 (1992), [Full Article]