Kraljice Marije 16

Belgrade, Serbia

Kraljice Marije 16

Belgrade, Serbia
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Grbovic A.,Kraljice Marije 16 | Sedmak A.,Kraljice Marije 16
Frattura ed Integrita Strutturale | Year: 2016

The extended finite element (XFEM) method has been used to simulate fatigue crack growth in casing pipe, made of API J55 steel by high-frequency welding, in order estimate its structural integrity and life. Based on the critical value of stress intensity factor KIc, measured in different regions of welded joint, the crack was located in the base metal as the region with the lowest resistance to crack initiation and propagation. The XFEM was first applied to the 3 point bending specimens to verify numerical results with the experimental ones. After successful verification, the XFEM was used to simulate fatigue crack growth, position axially in the pipe, and estimate its remaining life. © 2016 Gruppo Italiano Frattura. All Rights Reserved.

Simonovic V.,University of Belgrade | Markovic D.,University of Belgrade | Markovic I.,University of Belgrade | Kirin S.,Kraljice Marije 16
Tehnicki Vjesnik | Year: 2016

The paper analyzes the impact of sensor readings of dry grain mass yield of wheat, barley and rapeseed on combine speed during harvesting on three plots. The combine was fitted with site-specific yield monitoring sensors. This paper displays detailed tables of statistical procedure carried out for wheat in the analysis of combine speed, whereas final results for barley and rapeseed are itemized. After harvest, the three plots were divided into three groups each according to yield levels: low, medium and high, respectively. On the rapeseed plot, the Kruskal-Wallis H test did not reveal statistically significant difference in combine speed between the plot zones that belong to different yield-level groups, χ2(2, N = 2187) = 4,570, p = 0,102. On the basis of mean values for group ranks, the highest combine speed on wheat and barley plots has been found in the medium-yield-level group. Therefore, subsequent analysis of differences was conducted between the groups using Mann-Whitney U test. Combine speed during wheat harvest did not differ significantly in the low- and high-yield-level zones of the plot, Z = −1,213 and N = 3453, p = 0,225, while comparison between speeds within the medium-yield-level group to the other two groups exhibited statistically significant difference, effect size being approx. 0,1. During barley harvest, combine speeds differ statistically significantly when all three groups are compared for low and high impact according to Cohen’s criterion based on effect size. © 2016, Strojarski Facultet. All rights reserved.

Slavkovic G.,University of Belgrade | Budimir S.J.,Institut Gosa | Rakonjac I.M.,Project Management College | Jaric M.S.,Kraljice Marije 16 | Budimir N.J.,Kraljice Marije 16
Tehnicki Vjesnik | Year: 2014

The paper deals with the investment and exploitation costs for shell and tube heat exchangers with parallel helical tube coils. The most common correlations for estimating prices of shell and tube heat exchangers found in open literature were tested using the market data for a comparison and they have shown significant deviations. A new correlation for calculating prices of heat exchangers with helical tubes (when the shell is made of carbon steel and the helical tube of copper) was determined. In addition, the costs of electricity needed to drive pumps, as well as the costs of chemical cleaning of the apparatuses with inhibited mineral acids were estimated.

Camagic I.,Kneza Milosa 7 | Vasic N.,Kneza Milosa 7 | Cirkovic B.,Kneza Milosa 7 | Burzic Z.,Military Technical Institute Belgrade | And 2 more authors.
Frattura ed Integrita Strutturale | Year: 2016

The influence of exploitation period and temperature on the fatigue crack growth parameters in different regions of a welded joint is analysed for new and exploited low-alloyed Cr-Mo steel A-387 Gr. B. The parent metal is a part of a reactor mantle which was exploited for over 40 years, and recently replaced with new material. Fatigue crack growth parameters, threshold value ∆Kth, coefficient C and exponent m, have been determined, both at room and exploitation temperature. Based on testing results, fatigue crack growth resistance in different regions of welded joint is analysed in order to justify the selected welding procedure specification. © 2016 Gruppo Italiano Frattura. All Rights Reserved.

Arsic M.,Serbian Institute for Materials Testing | Savic Z.,Serbian Institute for Materials Testing | Sedmak A.,Kraljice Marije 16 | Bosnjak S.,Kraljice Marije 16 | Sedmak S.,Innovation Center
Frattura ed Integrita Strutturale | Year: 2016

This paper presents results of experimental examinations of stress concentration influence to fatigue life of butt welded joints with K-groove, produced from the most frequently used structural steel S355J2+N. One group of experiments comprised examinations carried out on the K-groove specimens with stress concentrators of edged notch type. Specimens with short cracks (limited length of initial crack), defined on the basis of the experience from fracture mechanics by the three points bending examinations, have been examined according to standard for the determination of S-N curve, and aimed to determine fatigue strengths for different lengths of initial crack and Relationship between fatigue strength and crack length. Other group of experiments comprised examinations of specimens with edge notch, prepared in accordance with ASTM E 399 for three points bending, in order to establish regularity between crack growth and range of exerted stress intensity factor aimed to determine resistance of welded joint to initial crack growth, namely fatigue threshold (ΔKth). © 2016 Gruppo Italiano Frattura. All Rights Reserved.

Arsic M.,Serbian Institute for Materials Testing | Bosnjak S.,Kraljice Marije 16 | Grabulov V.,Serbian Institute for Materials Testing | Veljovic A.,Serbian Institute for Materials Testing | Savic Z.,Serbian Institute for Materials Testing
Advanced Materials Research | Year: 2014

Stable supply tank, with volume V = 250 m3 and operating pressure p = 1,5 MPa, of generation unit 6 at thermal power plant 'Nikola Tesla A' in Obrenovac, is designed for water-steam working fluid. It was made of steel Č 1204 as a single-part welded structure with a single wall. Cylindrical tank shell consists of 8 segments, while torispherical deep bottoms consist of 3 segments. The tank is in the horizontal position and it lays on 4 supports. There are five manometers installed at the tank for pressure control, as well as 5 spring-loaded safety valves. In this paper results of non-destructive tests performed on the tank are presented. Mechanical damages on parent material, up to 1.5 mm deep, were detected at the outer surface of the cylindrical section of the right bottom (as seen from the boiler) and on the inner surface of the shell, as well as sporadic pitting corrosion, up to 0.5 mm deep, and 2 mm misalignment of sheet metals in areas where shell segments are joined. Crack type linear indications were detected on the surface of welded joints through the use of magnetic particle testing. Through ultrasonic and radiographic testing it was determined that the homogeneity of welded joints is satisfactory. Hardness testing was performed on all segments of the tank, and obtained values were in the range between 118 and 130 HB. Metallographic examination, performed on specimens of all segments of the tank, showed that microstructure of material is either fine-grained or striped ferrite-pearlite. On the basis of test results the repair technology for shell and bottom segments was made, while on the basis of the analytical calculation of tank strength the integrity evaluation was carried out for the upcoming period of service, depending on the category of the vessel. © (2014) Trans Tech Publications, Switzerland.

Mickovia D.,Kraljice Marije 16 | Jaramaz S.,Kraljice Marije 16
Propellants, Explosives, Pyrotechnics | Year: 2010

Igniters are elements of the ignition system of granular propellant charges, which have to give prescribed energetic impulse to charges. This paper includes theoretical and experimental investigations of ignition of propellant charge by igniter. The theoretical studies comprise modelling of two-phase flow of black powder grains and their combustion products in the igniter. The interaction of igniter efflux generated by two-phase flow of black powder in the igniter with the two-phase flow in propellant chamber with granular propellant charge is considered. The experimental investigations of igniter function in open air and in live propellant charge placed in fibreglass propellant chambers are performed. Influence of igniter characteristics on the ignition of propellant charge is established. Verification of the developed theoretical model by the comparison with experimental data is carried out. The presented theoretical-experimental access enables the choice of optimum igniter for ignition of propellant charge. © 2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.

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