Issue 2
JTAM, Sofia, vol. 2 Issue 2 (1971)

Flutter of Two Co-Axial Ellastically Connected Shells in Supersonic Gas Flow

P. Kyurkchiev


The problem for the flutter of a system of two co-axial infinitely long cylindrical shells is considered. The space between the shells is filled with Winkler’s elastic material. Only the outer shell is flown over. The pressure of the fluid is defined with the “piston” theory. With the Routh-Hurwitz criterion the critical flutter speeds are defined.

JTAM, Sofia, vol. 2 Issue 2 pp. 007-012 (1971)

Strain State of a Circular Cylindric Polymer Shell at One-axial Loading

P. Marin'ov, L. Hadjikov, G. Zahariev

The strain state of a circular cylindric shell of net polymer at one-axial strain according to the law p(t) = Vpt is investigated. The physical relation between stresses and strains is considered according to an equation proposed by A. L. Rabinovich. Expressions defining the translations and the strains are obtained. The results are compared with the elastic and linearized solutions.

JTAM, Sofia, vol. 2 Issue 2 pp. 013-022 (1971)
Pressure and Strength Diagrams of Non-orthogonal Glass Plastic at Pressure

A.A. Nikishin, I.M. Naumov

The limit strength at pressure of glass plastics from glass textolite with normal and fanwise arrangement of the elementary layers is experimentally investigated for loadings at different angle. The experimental results for the limit strength of glass plastics with fanwise structure after testing of cylindric and cone samples are given. Qualitative and qualitative estimations for the effective elasticity modulus, the reduced effective visco-elasticity modulus and the limit strengths are made on the basis of the experimental results.

JTAM, Sofia, vol. 2 Issue 2 pp. 023-030 (1971)
On the Total Stability of Certain Systems of Differential Equations of the Third Order

Z. Zaprianov, P. Kalitzova

The total stability of the zero solution of sertain non-linear systems of differential equations of the third order is studied. Sufficient conditions for total stability of the zero solution of the systems under consideration are obtained by the use of special constructed Liapunoff’s functions. In the linear case these conditions are just the necessary and sufficient conditions of Routh–Hurwitz.

JTAM, Sofia, vol. 2 Issue 2 pp. 031-039 (1971), [Full Article]

Investigation of Slope Shells with Double Curvature on Rectangular Base at Initial Strains, Taking into Account the Creep

A. Popov, R. Rangelov

Homogeneous and reinforced slope shells with double curvature on rectangular base, made of creeping material are investigated. The basic premises of the slope shells technical theory and the premises of the linear theory of creeping are accepted. The integral-differential equations describing the stressed and strained state of the shells when subjected to arbitrary temperature effects, are deduced. A general solution of these equations after the Bubnov-Gal’orkin’s method is shown, the integral differential equations being reduced to integral ones. The system of the integral equations is solved by two methods – the method of the consequent approximations and the numerical method of dividing the interval to equal parts. The expressions for the stresses and strains of the shell are obtained. A numerical example is considered. The values of the strains in the middle oi a square shell are given as a function of time.

JTAM, Sofia, vol. 2 Issue 2 pp. 040-054 (1971)
Study on a Polymer Material with Complex Stressed State

D. Kolarov, R. Dobrev, N. Todorov, A. Baltov, N. Bogdanova, S. Tankova

A theoretical-experimental study of a polymer material – alkaline polyamide, in conditions of complex stress and instantaneous strain state is given. Special experimental method using tube-wise samples, a machine for complex loading and specially designed measuring gauges, are given. The results from the experiments are shown in graphs. An analysis of the results is made and the theoretical conclusions are deduced. The described and applied method can also be used for testing of other polymer materials.

JTAM, Sofia, vol. 2 Issue 2 pp. 055-070 (1971)