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Arsic M.,Serbian Institute for Testing of Materials IMS | Bosnjak S.,University of Belgrade | Zrnic N.,University of Belgrade | Sedmak A.,University of Belgrade | Gnjatovic N.,University of Belgrade
Engineering Failure Analysis

Cracks in the welded joints on the bucket wheel (BW) body of the bucket wheel excavator (BWE) SRs 1300 were discovered after merely 1800 h of operation. Investigations are carried out in order to detect the causes of cracks occurrence and thus prevent possible heavy damages to the machine.Working stresses in the BW body are defined by using FEM. Methods of strain gauges are used for the experimental stress analysis in real working conditions. Measurements of welding residual stresses are carried out by applying the centre hole drilling method. Additionally, experimental investigations defined the chemical composition, tensile properties, hardness, impact toughness, as well as the susceptibility to cracking (measurement of residual hydrogen, FISCO, Tekken and CTS methods).External loads induced by the resistance-to-excavation are determined by following a model that encompasses all relevant structural parameters and also the BWE duty cycle parameters. By using FEM, it was identified that the maximum values of equivalent stress in the zones of cracks occurrence are lower than the allowable values. This conclusion is confirmed by measurements. The measured values of welding residual stresses reach the value of yield strength in critical zones. Non-compliances during grooving (clearance in the root is substantially larger than the prescribed one) caused large filler material deposition and heat input. Such welded joints are susceptible to cold cracking.Based on the results of the numerical-experimental analysis, findings show that in critical zones the combination of working (dynamic) and residual (static) stress can be above the limit lines of modified Goodman's diagrams i.e. that the fatigue safety of the BW body structure was insufficient. © 2010 Elsevier Ltd. Source

Savkovic M.,University of Kragujevac | Gasic M.,University of Kragujevac | Arsic M.,Serbian Institute for Testing of Materials IMS | Petrovic R.,University of Kragujevac
Engineering Failure Analysis

The common design of the bucket wheel drive mechanism in some bucket wheel excavators (BWE) consists of a gearbox and a hollow shaft, while the bucket wheel is supported by the axle passing through the hollow shaft. Improper maintenance and inadequate elimination of axis misalignment of the hollow shaft and the bucket wheel axle are the main causes of excavator failure and axle fracture. The paper examines the causes of bucket wheel axle fractures.Experimental testing of the chemical composition and mechanical properties of the material used to make the bucket wheel axle and metallographic inspections of the fracture surfaces in the bucket wheel axle by means of electronic and light microscope carried out in the first part of the paper have shown that there are no significant inhomogeneities and errors in the material of the axle.The second part of the paper presents the FEM analysis of influences of disturbances on the manner of support of the bucket wheel axle on the fracture. It shows that the negative influences of support of the axle reflected through the increase in the stress concentration and occurence of the initial crack are the main causes of the axle fracture. © 2010 Elsevier Ltd. Source

Arsenovic M.,Serbian Institute for Testing of Materials IMS | Pezo L.,University of Belgrade | Mancic L.,Serbian Academy of Science and Arts | Radojevic Z.,Serbian Institute for Testing of Materials IMS
Thermochimica Acta

This paper describes a study of 11 selected samples of loess soil from Serbia, by using differential scanning calorimetry, simultaneously with thermogravimetry and its differential calculation, known as simultaneous thermal analysis (STA). This survey is supplemented by chemical and mineralogical analysis, particle size distribution, and plasticity and drying susceptibility tests. Correlation analysis of major oxides content and certain technological test results were used for better understanding of the raw material composition and product physical properties. The results indicate that the samples were rich in carbonates, with the highest content of alevrite fraction and variable content of clay-sized particles. Mineralogical analysis confirms significant correlations between major oxides content and reveals that the most common non-clay mineral present is quartz, followed by calcite, dolomite and sodium feldspar. Major clay minerals include illite, chlorite, smectite and, in some cases, low quantities of kaolinite. Although STA method is well-known, this is the first time that it was used for discussion about its practical aspect, for characterization of the loess deposits, in terms of exploitation in brick industry. © 2014 Elsevier B.V. Source

Arsenovic M.,Serbian Institute for Testing of Materials IMS | Radojevic Z.,Serbian Institute for Testing of Materials IMS | Stankovic S.,University of Belgrade
Construction and Building Materials

The aim of this study was to test utilization possibilities of industrial sludge in masonry industry, as well as risk of toxic elements leaching potential. Sludge is generated in a hot-dip galvanizing process after waste water neutralization. This waste is considered to be hazardous due to the presence of toxic elements, which can be fixed within heavy clay matrix after thermal treatment. Relatively large amounts of toxic metals were found in used raw materials, but their leachability reduces to a negligible level after firing at 1020 °C. The results show that sludge can be used to produce eco-friendly bricks. © 2012 Elsevier Ltd. All rights reserved. Source

Pezo L.,University of Belgrade | Arsenovic M.,Serbian Institute for Testing of Materials IMS | Radojevic Z.,Serbian Institute for Testing of Materials IMS
Ceramics International

Mineralogical composition of heavy clays is one of the most important properties when stadying raw materials in brick industry. Within this study, quantitative determination of minerals using LPNORM calculation was performed, using the first algorithm among the so-called norms that allows the introduction of a list of minerals and their configuration. This algorithm is implemented for the first time in practice, in order to calculate the minerals content in brick raw materials. The influence of minerals quantity, along with the firing temperature (800-1100 °C), and several shape formats of laboratory brick samples were investigated, and the acquired data were used to build Artificial Neural Network (ANN) model. ANN model was developed in order to predict the final products parameters, and its results have been afterwards compared to experimental data. ANN model, coupled with sensitivity analysis, was obtained with high prediction accuracy, according to coefficient of determination, r 2: 0.880-0.884 in compressive strength calculation, 0.954-0.960 for water absorption, 0.869 for firing shrinkage, 0.979-0.984 for water loss during firing and 0.907 for volume mass of cubes model. © 2014 Elsevier Ltd and Techna Group S.r.l. Source

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