Marko Dunđer

Determination of clad plates residual stresses by x-ray diffraction method

The paper elaborates the influence that clad procedure has on the level and nature of residual stresses in clad plates. There are three clad procedures applied, as follows: hot rolling, submerged arc welding (SAW) with strip electrode in two layers and explosion welding. Theoretical basics on residual stresses measured by x-ray diffraction are reviewed in the paper, with special emphasis put on problems of underclad cracking tendency. In all applied cladding procedures, usage of heat treatment by anealing resulted in the decrease of residual stresses values. However, transformation of commpresed stresses into tensile stresses in some cases was very unfavourable, if referring to the tendency of plating corrosion resistant steel to stress corrosion and to underclad cracking.

The influence of biomass quality on the stability and sustainability of district heating systems of low-accumulation objects

Original scientific paper Research was conducted during the incineration of six different biomass groups, whereat each group was observed for three cases of average initial moisture level for the purpose of quantifying the values of impact parameters and contribution to the correlation between biomass quality and the efficiency of a thermal power system. A hot water plant with the power to heat ratio amounting to Q = 600 kW was used, which included a district heating system of a low-accumulation object with a low thermophysical constant and a low time constant. Research was conducted in 18 equal cycles at low outside air temperatures and a maximum need for useful thermal energy. Quantified values showed the consumption of all groups of all average moisture levels of biomass. By analysing the examined temperature of a heating medium and flue gases during the combustion of each biomass group, a direct influence of its quality and average moisture on the sustainability and stability of the district heating system was shown. The most favourable biomass was proposed. Direct application of research results contributes to correct determination of the type, composition and average moisture of biomass, as well as a higher efficiency of the whole thermal power system.

Analytical heat conduction models at arc fusion welding

It is of high importance to determine the distribution of thermal fields in arc fusion welding processes due to their influence on mechanical properties and quality of welded joints. This paper presents analytical models for 2D and 3D heat conduction based on solutions of the Fourier’s heat conduction differential equation. Furthermore, authors provide simplified equations for the calculation of cooling time and cooling rate for 2D and 3D heat conduction models.