Failure analysis of mechanical elements in steelworks equipment by methods of experimental mechanics

New technological equipment is mostly designed with the goal of increasing the productivity of manufacturing. This aim often results in an increased loading of structural support members. In the paper attention is given to the reasons for crack initiation in the supporting part of the converter torsion system that ensures transfer of the tilting moments from the converter vessel to the converter pedestal. The numerical and experimental analysis of the reasons for crack initiation in the pedestals of the converter torsion systems was carried out over the period of 2 years. In the paper forces and stresses in the structure are analysed both under normal and extraordinary operational conditions of the converter (big steel residues on the converter wall, demolition of the converter lining). Alongside the reasons for crack initiation the ways for solving the problem of further safe operation of the converter are suggested.     

Interactions of polarons in poly(3-dodecythiophene) at low temperature

Zero-field cooled-field-cooled (ZFC-FC) technique was used to investigate the effect of low temperature (4.6 K) on the interactions of polarons in weakly FeCl₃-doped poly(3-dodecylthiophene (PDDT). It was found that the magnetic properties of the system changed with the length of time system spent at low temperature: the Currie–Weiss paramagnetism gradually changed over to “antiferromagnetism” and ultimately to diamagnetism. This effect is connected with the thermochromic properties of self-organized PDDT in primary (10–15 nm) or secondary (30–50 nm) induced aggregates, in which cooling under the glass transition temperature T_g (～240 K) causes extension of the effective conjugation length of coplanar polymer chains. Changes in magnetic properties are related to the inter- and intra-chain interactions of polaron states within both the primary and secondary induced aggregates.     

Mechanochemical reaction in the K2CO3–Nb2O5 system

We studied the mechanochemical synthesis of KNbO₃, starting from a powder mixture of K₂CO₃ and Nb₂O₅. The milling experiments were designed with different ball-impact energies in order to investigate the mechanochemical reactions. X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, Raman spectroscopy and transmission electron microscopy were used to characterize the samples. Based on the results, we propose a mechanism for the mechanochemical reaction between K₂CO₃ and Nb₂O₅. The first stage of the reaction is characterized by the formation of an amorphous carbonato complex, which decomposes after prolonged milling at higher ball-impact energy giving rise to the crystallization of KNbO₃ and other niobate phases with a molar ratio K/Nb < 1. The reaction course is discussed and compared with the Na₂CO₃–Nb₂O₅ system.     

Implementation of Artificial Neural Networks in Modeling the Water-Air Temperature Relationship of the River Drava

Water temperature directly affects the physical, biological and chemical characteristics of the river and determines the fitness and life of all aquatic organisms. It has direct and indirect effects on nearly all aspects of stream ecology. Accurately estimating water temperature is a complex problem. The purpose of this article is to analyze the relationship between the air and water temperature of the River Drava by constructing an artificial neural network (ANN) model and choosing appropriate network architectures for the River Drava’s daily river water temperature as well as demonstrating its application in improving the interpretation of the results. A linear regression model, as well as a stochastic model are also constructed and compared to ANN models consisting of a multilayer perceptron neural network and a radial basis function network. The results indicate that the ANN models are much better models and that ANNs are powerful tools that can be used for the estimation of daily mean river temperature.     

Antifungal activity of lauric acid derivatives against Aspergillus niger

The antifungal effects of lauric acid and four lauric acid derivatives (monolauroylglycerol, D-laurate A, T-laurate A, 6-O-lauroysucrose) were tested on the spore germination and the growth rate of Aspergillus niger DMF 0801. The results showed that the tested substances varied in their antifungal activity and they also confirmed the relation of the structure of tested substances and their antifungal effects. Monolauroylglycerol at concentration level between 0.2 and 1.8 mmol l^-1 caused the highest inhibition of spore outgrowths whereas 6-O-lauroysucrose at concentration between 0.05 and 1.8 mmol l^-1 did not exhibit inhibition of spore germination. The inhibition of colony growth rate was detected mainly at presence of 6-O-lauroysucrose.     

Intensity and effectiveness of sintering of iron powder compacts

Translated from Poroshkovaya Metallurgiya, No. 3(327), pp. 15–20, March, 1990.     

Residual stress state after the laser surface remelting process

Residual stresses are a result of elasto-plastic deformations induced in the workpiece material during the heat treatment process. The extent and magnitude of internal stresses depend on temperature conditions in heating and cooling and physical properties of the workpiece material. This contribution discusses the extent and distribution of residual stresses after laser remelting a thin surface layer on ductile iron 80-55-06 (ASTM specification) or Gr 500-7 according to ISO. Residual stresses are not only induced by temperature differences but also result from stresses due to microstructural changes between the surface and the core of the specimen subsequent to cooling to the ambient temperature. The distribution and extent of residual stresses in the remelted thin surface layer depend mostly on melt composition and cooling conditions. Different rates of solidification and subsequent cooling of the remelted layer are reflected in the volume proportions of the created cementite, residual austenite, and martensite in the microstructure. The rate of heating and cooling of the thin surface layer is a function of laser power, beam diameter on the workpiece surface, and interaction time. In addition, the number of passes of the laser beam over the workpiece surface and different degrees of laser trace overlapping were increased to see how these can affect the thermal conditions in the workpiece. To determine the residual stresses, the relaxation method was used. This is based on measuring the specimen strain during electrochemical material removal.     

A graded-gap detector of ionizing radiation

The current response of Al_xGa_1−x As graded-gap layers to optical and X-ray radiation was studied. A graded-gap electric field in the 15-μm-thick Al_xGa_1−x As layers, with x varying from 0 to 0.4, ensures the complete collection of charges generated by ionizing radiation and makes it possible to attain the value of 0.25 A/W for the current-power sensitivity of Al_xGa_1−x As. In the layers with a lowered doping level of the narrow-gap region of the graded-gap Al_xGa_1−x As layer, the voltage-power sensitivity to X-ray radiation with energy lower than 15 keV is as high as 1.6×10³ V/W in the photovoltaic mode. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 36, No. 1, 2002, pp. 124–128. Original Russian Text Copyright ? 2002 by J. Požela, K. Požela, Šilėnas, Jasutis, Dapkus, Kinduris, Jucienė.     

Andreev and normal reflections at normal metal—Superconductor boundaries: Limitations of the semiclassical approximation

We study the scattering of quasiparticles at a normal metal—superconductor interface using Bogoliubov-de Gennes equations, taking the motion parallel to the interface fully into account. We show that while the Andreev reflection is the dominant scattering process in case of nearly perpendicular impacts (as predicted by the semiclassical theory), the normal reflection becomes increasingly important for quasiparticles with large momenta parallel to the interface, and the semiclassical approximation becomes progressively inadequate. We work out consequence of this feature for spectra of bound states in superconductor—normal metal—superconductor junctions.     

Scattering of electrons in beta-spectroscopy sources

Experimental spectra of the¹⁶⁹Yb conversion lines having kinetic energies of 3.7–18.4 keV and the beta spectrum from the decay of²⁴¹Pu are compared with calculations by the Monte Carlo method which take into account the individual elastic and inelastic scattering processes of the electrons in the source, in the substrate, and in a carbon layer contaminating the source. Good agreement is obtained between the theoretical and experimental results. It is also shown that the scattering of the electrons depends on their emission angle. Translated from Izmeritel'naya Tekhnika, No. 8, pp. 63–65, August. 1997.