Issue 4
JTAM, Sofia, vol. 33 Issue 4 (2003)

Boundary Element Thermoelastic Stress Analysis with Crack Opening

G. Gospodinov
University of Architecture, Civil Engineering and Geodesy, 1, Christo Smirnenski Blvd., 1046, Sofia, Bulgaria


In this paper the boundary element method is developed for thermoelastic stress analysis of plane sheets of arbitrary geometry and boundary conditions. The steady state temperature field is considered to be known or calculated in advance. Although a linear elastic solution is employed, an elevated temperature procedure is applied and at certain stage brittle, traction free cracks may develop, typical for a quasi-brittle type of materials, such as concrete. A special type of displacement discontinuity fundamental solution is used in order to include the crack opening into the boundary element solution. In the appendix a few approaches to reducing domain integrals into boundary ones only are given for the most general cases of the temperature distribution function.

JTAM, Sofia, vol. 33 Issue 4 pp. 01 (2003)

Yield Criterion for Pressure Sensitive Materials

K. Tushtev1, G. B. Stoychev2
1Keramische Werkstoffe und Bauteile, University of Bremen, Am Biologischen Garten 2 / IW3, D-28359 Bremen, Germany
2Technical University Sofia, 8, Kl. Ohridski Blvd., 1756 Sofia, Bulgaria

A new yield criterion for pressure sensitive materials is proposed. The criterion is based on the first invariant of the stress tensor, second and third invariants of the stress deviator tensor and includes three material constants. In the space of the principal stresses the criterion can be represented as a smooth and convex surface, opened in the negative direction of the hydrostatic axis. Convexity conditions are formulated for anelastic solid. Based on experimental data the validity of the criterion in a case of two dimensional stress state is shown for grey cast iron.

JTAM, Sofia, vol. 33 Issue 4 pp. 02 (2003)
On the Effect of the Harmonic Heating of High-Alloy and High-Carbon Steel Ingots on Chromium Homogenization in Them

Alexander Zlatarski, Angel Baltov
1Industrial Heat Engineering Branch, NIPRORUDA JSCo 205, Al. Stamboliyski Str., 1309 Sofia, Bulgaria
2Institute of Mechanics, Bulgarian Academy of Science, Acad. G. Bonchev Str., Bl. 4, 1113 Sofia, Bulgaria

The effect of harmonic heating of high-alloy and high-carbon steel ingots on the homogeneous Chromium distribution in alloying elements is investigated. The effect of the higher temperature of the ingot core due to the harmonic thermal regime is estimated.

JTAM, Sofia, vol. 33 Issue 4 pp. 03 (2003)
On the Relationships between Linear and Angular Strains in Twisting

N. G. Gospodinov
Technical University of Sofia, 8, Kl. Ohridsky Blvd., 1756 Sofia, Bulgaria

Based on an experimental approach, the applicability of two logarithmic expressions for the relationships: "True angular strain – technical angular strain", on the one hand, or "true angular strain – relative angular strain" – on the other hand, is determined for twisting of plastic materials up to the occurrence of fracture. The theoretical relationships "twisting moment (or tangential stress) – angular strain" are compared with curves obtained experimentally.

JTAM, Sofia, vol. 33 Issue 4 pp. 04 (2003)
Modelling Elastoplastic Deformations in Grey Cast Iron

G. Stoychev
Technical University of Sofia, 8, Kl. Ohridski Blvd., 1756 Sofia, Bulgaria

Elasto-plastic deformation of grey cast iron is in consideration. A non-associated constitutive model, based on the phenomenological approach is proposed. The yield condition is established on the second invariant of the stress deviator, on the first invariant of the stress tensor. The plastic potential is based on the same invariants. Modified form of the plastic work is defined as a hardening parameter and tensile test curve is used to calculate it. An algorithm of the computer procedure is given to compute the strains if the principal stresses are known. The verification of the model is realized by bi-axial tests on tubular specimens.

JTAM, Sofia, vol. 33 Issue 4 pp. 05 (2003)