Zoran Radakovic | University of Belgrade, Faculty of Mechanical Engineering (original) (raw)

Papers by Zoran Radakovic

Materials, Aug 25, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Crack tip fields effects on crack propagation through the heat affected zone in an overmatched welded joint

Fatigue & Fracture of Engineering Materials & Structures

Comparative Study of Pressurized Spherical Shell with Different Materials

Advances in Intelligent Systems and Computing, 2022

Integrity and Life Assessment of Welded Joints Made of Micro-Alloyed High Strength Steels

Advanced Materials Research, 2020

Structural integrity and life of welded joints made of a micro-alloyed low-carbon fine-grained no... more Structural integrity and life of welded joints made of a micro-alloyed low-carbon fine-grained normalised high strength pressure vessel steel, P460NL1 is presented [1]. The researach performed within the scope of this topic involved a large number of experiments, including tensile and bending tests, hardness and toughness, as well as metallography and fractography tests, in order to determine the mechanical properties of the materials and the welded joints in detail, along with their microstructures and their influence on the obtained test results. Specimens cut out of a welded plate with dimensions of 500x500x14 mm were used for the experiments, whereas certain tests required the making of notches in the specimens, inside the heat affected zone, and this welded joint region was the focus of the research. Fatigue experimental tests were based on the assumption that fatigue crack growth rate changes depending on the regions through which the crack passed during its propagation. For t...

Concerning new challenges in structural integrity assessment, the identification of relaxation an... more Concerning new challenges in structural integrity assessment, the identification of relaxation and service life extension of structural steels by qualitative and quantitative determination of dynamic fracture mechanics parameters is highly significant. Problems in experimental research are in connection with precise determination of resistance to fracture in conditions of dynamic loading of structures, where standard procedures in the case of precracked Charpy specimens are yet to be defined. Instrumented Charpy testing is performed by magnetic emission (ME) technique for determining critical crack initiation properties in a steel of dominant ductile properties. The equivalent brittle, ductile, and mixed fracture behaviour is simulated by the choice of test temperature and impact velocity. Analysis of acquired ME and integrated ME signals, both employed in deriving the critical J integral, has been successful in interpreting the results for unstable or stable crack propagation.

Determination of ductile crack initiation by magnetic emission and potential drop techniques using pre-cracked Charpy specimens

From Charpy To Present Impact Testing, 2002

... In: S. Sedmak, A. Sedmak and D. Ruić, Editors, ECF9-Reliability and structural integrity of a... more ... In: S. Sedmak, A. Sedmak and D. Ruić, Editors, ECF9-Reliability and structural integrity of advanced materials, EMAS, Warley West Midlands (1992), pp. 315320. ... PF Thomas, Ductile Fracture of Metals, Pergamon Press, Oxford (1990). ESIS P2-92 (1992). ...

Materials

The search for alternative materials that can be used for parts of aircraft hydraulic systems has... more The search for alternative materials that can be used for parts of aircraft hydraulic systems has led to the idea of applying S32750 duplex steel for this purpose. This steel is mainly used in the oil and gas, chemical, and food industries. The reasons for this lie in this material’s exceptional welding, mechanical, and corrosion resistance properties. In order to verify this material’s suitability for aircraft engineering applications, it is necessary to investigate its behaviour at various temperatures since aircrafts operate at a wide range of temperatures. For this reason, the effect of temperatures in the range from +20 °C to −80 °C on impact toughness was investigated in the case of S32750 duplex steel and its welded joints. Testing was performed using an instrumented pendulum to obtain force–time and energy–time diagrams, which allowed for more detailed assessment of the effect of testing temperature on total impact energy and its components of crack initiation energy and cra...

$Research paper thumbnail of From fracture mechanics to structural integrity assessment : this monograph contains the lectures presented at the eighth international fracture mechanics summer school held in Belgrade, Serbia and Montenegro, 23-27 June 2003$

From fracture mechanics to structural integrity assessment : this monograph contains the lectures presented at the eighth international fracture mechanics summer school held in Belgrade, Serbia and Montenegro, 23-27 June 2003

The Challenge of Materials and Weldments : Structural Integrity and Life Assessments

To avoid unexpected and frequent serious failures of objects and equipment in service, and save t... more To avoid unexpected and frequent serious failures of objects and equipment in service, and save their structural integrity, proper experimental and theoretical analyses are required, that are supported by modelling and numerical analysis. Structural failures in service have been experienced and can not be neglected. The developed procedures, based on fracture mechanics, enable to predict behaviour of a crack in a fracture process and to evaluate the safety and reliability of a structure under the applied loading in an operating environment. Regarding the significance of structural integrity, objects are classified into three groups. In the first group are objects made of stone, not sensitive to cracking, as are the preserved monuments of the ancient era. The second group includes objects prone to fracture from cracks: in this case structural integrity assessment is a requirement in order to prevent failure. In the third group are modern engineering achievements as are very large bui...

Owing to their excellent mechanical and physical characteristics, superalloys are the most suitab... more Owing to their excellent mechanical and physical characteristics, superalloys are the most suitable material for use in hot sections of aircraft engines. Thousands of holes need to be drilled in constructive parts of machines, with laser technique emerging as the most effective. Laser drilling has been used to produce small diameter, accurately positioned holes, with little damage in regions around them, and in various materials. Effective laser employment of drilling of high quality holes for critical applications highly depends on correct selection and optimization of laser drilling parameters. In this work, the holes were drilled by a pulsed Nd3+:YAG laser, with maximum average power of 160 W, in superalloy Nimonic 263 sheets, thickness 0,7 mm and 1,2 mm. The holes were observed by optical and scanning electron microscope. Geometrical characteristics of laser drilled holes that depend on laser parameters were investigated and analysed. The aim of this investigation was to find op...

International Journal of Fracture, 1999

Charpy impact testing of the high strength low-alloyed steel has been performed by simultaneously... more Charpy impact testing of the high strength low-alloyed steel has been performed by simultaneously recording two independent signals. The magnetic emission (ME) and potential drop (PD) techniques were used to determine critical crack initiation properties on standard three-point pre-cracked bending specimens at room temperature. Both signals (ME and PD) were recorded by digital oscilloscope with a high sampling rate and

Thermal Science, 2010

The analytical modelling of the PbSb alloy resistance spot welding process has been developed on ... more The analytical modelling of the PbSb alloy resistance spot welding process has been developed on the basis of mathematical analysis of thermomechanical conservation laws. The numerical solution of partial differential equations, obtained by such modelling, has been achieved by the finite element method. Thermomechanical equilibrium equations are derived, including specific properties, typical for PbSb alloys. The paper utilizes the basic experimentally proven assumption, that the temperature fields govern all processes during welding. Full agreement is evident between the experimental and analytical data.

Innovation Centre of the Faculty of Mechanical Engineer- ing, Belgrade, Serbia Abstract Direct... more 2) Innovation Centre of the Faculty of Mechanical Engineer- ing, Belgrade, Serbia Abstract Direct measurement of J integral has been analysed in respect to the effect of material (heterogeneity and strength- ening) and different boundary conditions, enabling its appli- cation to pressure vessels with a crack in welded joint. It has been shown that modifications of the original expression are needed. The possibility of applying direct measurement of J integral for pressure vessel integrity assessment has been considered. Kljucne reci • direktno merenje J integrala • cilindricna posuda pod pritiskom • heterogenost materijala • granicni uslovi Izvod Direktno merenje J integrala je analizirano u odnosu na uticaj heterogenosti i ojacavanja materijala, kao i razlicitih granicnih uslova, a u cilju primene na posude pod pritis- kom sa prslinom u zavarenom spoju. Pokazano je da su neophodne modifikacije originalnog izraza. Takođe su razmatrane mogucnosti primene direktnog merenja J inte- gra...

Quality Improvement of Steel Pipes Produced by Seam Welding with New Magneto-Dielectric Impeder

The standard technology of steel pipe production is the high frequency (HF) inductive welding. A ... more The standard technology of steel pipe production is the high frequency (HF) inductive welding. A mechanically formed profile is introduced into an inductor. Inside the pipe, in the position of the inductor there is an impeder, whose function is to form a suitable distribution of the electromagnetic and temperature field. In previous paper of the authors, the new magneto-dielectric (MD) material for the impeder is proposed and results of extraordinary energy saving are shown. This paper treats the aspect of the pipe quality, which represent the essential parameter in a production technology. The analyses were made for the widely spread ferrite impeder and for the proposed MD impeder. From this point of view, the MD impeder appeared to be advantageous material also. In addition to the standard mechanical tests of pipes quality, extensive chemical and physical analyses of the material in the weld, as well as in the basic section of the pipe, have been performed. The aim of the investig...

$Research paper thumbnail of Dynamic fracture testing using charpy instrumented pendulum$

Charpy impact testing of a high strength low-alloyed (HSLA) steel has been performed by simultane... more Charpy impact testing of a high strength low-alloyed (HSLA) steel has been performed by simultaneously recording two independent signals. The magnetic emission (ME) and potential drop (PD) techniques were used to determine critical crack initiation properties on standard V-notched and pre-cracked three-point bending specimens at room temperature. Both signals (ME and PD) were recorded and compared, with the purpose of more precise identification of critical fracture mechanics parameters determining the onset of ductile crack growth. Standard Charpy specimens made of HSLA steel, oriented perpendicular to rolling direction were tested by a modified instrumentation of the Charpy machine, which included the original magnetic emission, and the potential drop techniques. The strain gauges and emission probes, located on the hammer tup, measured the force, thus both the magnetic and electric potential drop signals were monitored and recorded as a function of time. The obtained results indi...

Extended FEM analysis of fatigue crack growth in Ti-6Al-4V orthopaedic plates

Procedia Structural Integrity

Fracture Toughness in the Transition Temperature Region

Advanced Materials Research

The steels fracture toughness was measured at two different temperature T= - 60°C and T = -90°C, ... more The steels fracture toughness was measured at two different temperature T= - 60°C and T = -90°C, at v=0.02 mm/min and v=0.5mm/min. The following steels: CrMoV, 20MnMoNi55, A533B and A508 were tested with three different sizes of CT specimens 50 and 100 and 200. Those steels are weldable, although the authors investigated the fracture behaviour of base material. In order to satisfy statistical analyses, a large number of specimens were tested. Fracture behaviour has turned out to be typical, S-shaped curve for transitional fracture at low temperatures. Apart from the other variables, specimen’s width significantly affects measured toughness. Smaller specimens, CT50, might be considered of upper bound reliability while the CT200 specimens were shown to be the most conservative. In this way it has been shown that wider specimens are more reliable in a fracture assessment of the examined steels. In this paper, the fracture probabilities of specimens in function of fracture toughness wer...

Temperature distribution in thermal processes

Welding in the World

This paper investigates the principle and ways for heat and temperature distribution in thermal p... more This paper investigates the principle and ways for heat and temperature distribution in thermal processes. It provides a review of achieved theoretical explanations and contributions while indicating on mismatches, previews, and even mistakes. Mistakes made in equations in this area that are noticed in investigations in the previous years have been corrected. Special focus is aimed at surface and volume heat treatment in electrothermia for which the necessary analytical dependencies should be developed and proved.