Gordana Bakić

University of Belgrade

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Bratislav Rajičić

University of Belgrade

Milos B. Djukic

University of Belgrade

Vera Sijacki Zeravcic

University of Belgrade

VŠ

Vera Šijački-Žeravčić

University of Belgrade

MĐ

Miloš Đukić

University of Belgrade

Vesna Maksimović

University of Belgrade

Aleksandar Sedmak

University of Belgrade

Aleksandar Maslarević

University of Belgrade

Vladimir Pavkov

University of Belgrade

Branko Matović

University of Belgrade

Cooperative Institutions

University of Belgrade

Institute of Economic Sciences

University of Belgrade - Faculty of Mechanical Engineering

Vinča Institute of Nuclear Sciences

Univerzitetski Klinički Centar Srbije

Vienna Institute for Nature Conservation & Analyses

Military Technical Institute

Institut za filozofiju

Institute for Multidisciplinary Research

Centar za Promociju Nauke

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Determination of Stress Intensity Factors in Low Pressure Turbine Rotor Discs

Mathematical Problems in Engineering (2014)

Ivana Vasović Stevan Maksimović Katarina Maksimović Slobodan Stupar Gordana Bakić

An attention in this paper is focused on the stress analysis and the determination of fracture mechanics parameters in low pressure (LP) turbine rotor discs and on developing analytic expressions for stress intensity factors at the critical location of LP steam turbine disc. Critical locations such as keyway and dovetail area experienced stress concentration leading to crack initiation. Major concerns for the power industry are determining the critical locations with one side and fracture mechanics parameters with the other side. For determination of the critical locations in LP turbine rotor disc conventional finite elements are used here. For this initial crack length and during crack growth it is necessary to determine SIFs. In fatigue crack growth process it is necessary to have analytic formulas for the stress intensity factor. To determine analytic formula for stress intensity factor (SIF) of cracked turbine rotor disc special singular finite elements are used. Using discrete values of SIFs which correspond to various crack lengths analytic formula of SIF in polynomial forms is derived here. For determination of SIF in this paper, combinedJ-integral approach and singular finite elements are used. The interaction of mechanical and thermal effects was correlated in terms of the fracture toughness.

Intensity

10.1155/2014/304638

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Citations (11)

Assessment of hydrogen embrittlement and a model for structural integrity analysis

Milos B. Djukic Gordana Bakić Vera Sijacki Zeravcic Bratislav Rajičić Aleksandar Sedmak

Hydrogen embrittlement (HE) in a specific sense meaning can be defined as the hydrogen-caused deterioration of the mechanical properties of most metallic materials and alloys. The coexistence of different HE mechanisms and their simultaneous effects in metallic materials, including steels, is still not well documented, while recognition of the dominant mechanism, one or more, is an extremely challenging and crucial problem. A special structural integrity model was proposed [1] for analysis, prevention, and prediction of HE based on the HELP + HEDE model [2] for HE in steels. The structural integrity model corresponds with the observed coexistence of HE mechanisms (HELP + HEDE model) in metals and transition from HELP dominance to HEDE dominance at a hydrogen concentration above the critical hydrogen concentration [2,3]. The further implementation of methods for evaluation, control, and prevention of hydrogen-assisted mechanical degradation processes and HE in metals requires that the variables relevant to the application be incorporated into the basic concept that define all necessary successive steps (5-step approach) for the industrial application [2]. The global 5-step approach in assessment and prevention of hydrogen assisted mechanical degradation processes and hydrogen embrittlement in metals for the practical industrial application was proposed and consist of the following steps [3]: (1) phenomenology analysis of hydrogen-related degradation (multiscale modeling and simulation of HE phenomena); (2) hydrogen sources and entry into metal/component; (3) structural integrity (SiM) model and (4) predictive maintenance (PdM) model which should provide the basis for future (5) reliable and accurate HE damage prediction of different industrial components. [1] M.B. Djukic, G.M. Bakic, V. Sijacki Zeravcic, A. Sedmak, B. Rajicic, Hydrogen embrittlement of industrial components: prediction, prevention, and models, Corrosion, 72 (2016), pp. 943-961. [2] M.B. Djukic, V. Sijacki Zeravcic, G.M. Bakic, A. Sedmak, B. Rajicic, Hydrogen damage of steels: A case study and hydrogen embrittlement model, Engineering Failure Analysis, 58 (2015), pp. 485-498. [3] M.B. Djukic, V. Sijacki Zeravcic, G.M. Bakic, A. Sedmak, B. Rajicic, The synergistic action and interplay of hydrogen embrittlement mechanisms in steels and iron: Localized plasticity and decohesion, Engineering Fracture Mechanics 216 (2019), p. 106528.

Structural integrity

10.3390/cmdwc2021-09888

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Corrosion effects on structural integrity and life of oil rig drill pipes

Hemijska industrija (2022)

Aleksandar Sedmak Radzeya Zaidi Borivoje Vujicic Živče Šarkoćević Snežana Kirin

Corrosion effects on structural integrity and life of oil rig welded pipes are analysed by experimental, analytical, and numerical methods. Experiments were performed using standard tensile specimens and CT specimens for static loading, Charpy specimens for impact loading, and 3 Point Bending specimens for fatigue crack growth with amplitude loading. In each case new and old pipes were used to evaluate corrosion effects. Results indicated negligible corrosion effects in the case of tensile properties and impact toughness, and strong effects in the case of fracture toughness and especially fatigue crack growth rates, increasing the risk of static failure and reducing significantly structural life. Analytical expressions are used for oil rig pipe structural integrity and life assessment to quantify these effects. Recently introduced risk-based approach is applied to analyse oil rig drill pipe with a corrosion defect treated as a surface crack.

Charpy impact test

Structural integrity

Drill pipe

10.2298/hemind220222014s

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Citations (7)

Novel basalt-stainless steel composite materials with improved fracture toughness

Science of Sintering (2023)

Vladimir Pavkov Gordana Bakić Vesna Maksimović Ivana Cvijović‐Alagić Dušan Bučevac

This paper presents the technological process for obtaining basalt-stainless steel composite materials and testing their physical and mechanical properties. The phases of the technological process consist of: milling, homogenization, pressing, and sintering to obtain composite materials with improved fracture toughness. Andesite basalt from the deposit site "Donje Jarinje", Serbia, was used as a matrix in the composites, while commercial austenitic stainless steel 316L in the amount of 0-30 wt.% was used as a reinforcement. Although the increase of 316L amount caused a continuous decrease in the relative density of sintered samples, the relative density of sample containing 30 wt.% of 316L was above 94%. The 316L grains, which possess a larger coefficient of thermal expansion than the basalt matrix, shrinking faster during cooling from sintering temperature resulting in the formation of compressive residual stress in the basalt matrix surrounding the spherical steel grains. The presence of this stress activated toughening mechanisms such as crack deflection and toughening due to compressive residual stress. The addition of 20 wt.% of reinforcing 316L particles increased the fracture toughness of basalt by more than 30%. The relative density of these samples was measured to be 97%, whereas macrohardness was found to be 6.2 GPa.

Relative density

Austenitic stainless steel

10.2298/sos220429002p

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Chitosan and pectin-based films and coatings with active components for application in antimicrobial food packaging

Progress in Organic Coatings (2021)

Jelena Jovanović Jovana Ćirković Aleksandar Radojković Dragosav Mutavdžić Gordana Tanasijević

Gelatin

Pectin

Biopolymer

Active packaging

10.1016/j.porgcoat.2021.106349

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Citations (83)

Material Characterization of the Main Steam Gate Valve Made of X20CrMoV 12.1 Steel after Long Term Service

Procedia Materials Science (2014)

Gordana Bakić Vera Sijacki Zeravcic Milos B. Djukic V. Perunicic Ana Prodanović

Martensitic steel X20CrMo12.1 has been extensively used within the last few decades as a material for tubing systems and pipelines in thermal power plants (TPP). Long term behavior of this steel is very well known and understood and because of that was found to be reliable material for prolonged service at elevated temperatures. It is well known that during operation TPP components are subject to microstructural changes that inevitably reflect decrease in their mechanical properties that lead to the loss of structural integrity and serviceability of component. This paper deals with the comprehensive investigation carried out on the main steam gate valve parent material of welded joint, as a part of main steam pipeline, after 170.000 h of service (545 °C and 19 MPa). The obtained results showed that the microstructural degradation caused by long term operation had little effects on the hardness and strength of material, while the changes in impact toughness were observed. Comprehensive microstructural analysis included the examination of the microstructure on the surface and trough the wall thickness.

Serviceability (structure)

10.1016/j.mspro.2014.06.244

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Citations (9)

Life estimation of first stage high pressure gas turbine blades

Scientific Technical Review (2008)

Yasmina Assoul S. Benbelaid Vera Šijački-Žeravčić Gordana Bakić Miloš Đukić

Based on very early occurring ruptures found in the first stage high pressure turbine blades of a turbo reactor in a local aviation company, this study has the aim to determine their safe life. The first stage blades are subjected to simultaneous action of gas pressure coming from the combustion chamber, centrifugal forces in the case of the rotor blades and to important temperatures transients, which progress in a very aggressive environment due to hot gases. These combined parameters cause a high state of stress involving several complex mechanisms of damage, such as: fatigue caused by mechanical stress fluctuations, thermo-mechanical fatigue caused by temperature variations and corrosion caused on the stressed elements. Life cycle determination asks for stress evaluation of blades regarding several variables which are approached deterministically in the study. Heat exchange between combustion gases and metal blades is considered. The total stress on two kinds of blades is calculated by the addition of the thermal effect and the mechanical loading. The stress cycle is then calculated for different steps of the engine function during the operation by considering the variation of the thermal and the mechanical properties of the system. Safe life determination is done by two different approaches: the safe life approach by the initiation model and the damage tolerance approach considering the defect growth mechanics and considering the pitting corrosion effect. The calculation is applied for stator and rotor blades of an aero engine high pressure turbine made of NI 738. Since these parts are high risk components from the point of view of potential failure consequences, the risk is assessed as well. The results obtained are studied to determine the solution to the problem, and to propose a safe decision to be taken about the design or maintenance procedures. .

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Citations (6)

Structure Integrity of Pressure Vesels Repair Welding Joints

Springer eBooks (2008)

Vera Sijacki Zeravcic Gordana Bakić Milos B. Djukic Bratislav Rajičić

Upset welding

10.1007/1-4020-4972-2_537

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Case Study of Supporting Tubes Failure

Springer eBooks (2008)

Vera Sijacki Zeravcic Milos B. Djukic Gordana Bakić Biljana Andjelić Bratislav Rajičić

10.1007/1-4020-4972-2_536

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Citations (3)

Numerical analysis of thermal stresses in welded joint smade of steels X20 and X22

Thermal Science (2013)

Saša Mladenović Vera Šijački-Žeravčić Gordana Bakić Jasmina Lozanović Šajić Marko Rakin

Stress calculation of steam pipeline is presented, focused on the welded joint. Numerical calculation was performed using the finite element method to obtain stress distribution in the welded joint made while replacing the valve chamber. Dissimilar materials were used, namely steel 10CrMoV9-10 according to EN 10216-2 for the valve chamber, the rest of steam pipeline was steel X20, whereas the transition piece material was steel X22. Residual stresses were calculated, in addition to design stresses, indicating critical regions and necessity for post-weld heat treatment.

10.2298/tsci131211178m

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Citations (2)