A. Sedmak

• Professor Emeritus
• Professor (Full) at University of Belgrade

Existing studies dealing with structural strength of bucket wheel excavators (BWE) include a traditional approach that does not take into account the whole structural response of the object, but only considers the maximum response at the single location. To solve this issue, this paper proposes assessment of the structural response of BWE SchRs 630...

The facture and fatigue behaviour of welded joints made of A516 Gr 60 was analysed, bearing in mind their susceptibility to cracking, especially in the case of components which had been in service for a long time period. With respect to fracture, the fracture toughness was determined for all three zones of a welded joint, the base metal (BM), heat-...

This research aims to provide comprehensive data on PLA polymer tensile properties via conducted tensile tests on 100 % infill density specimens (for 0.3; 0.2; 0.1 mm layer height), and all possible lower infill results (i.e., from 90 to 10 %, with a 10 % increment) obtained by interpolation of previous research findings. Tensile tests are performe...

This conference is intended as a forum for discussion about recent advances in the fields of structural integrity approach on engineering structures: development and recent trends, classic approaches to stuctural integrity assessment, methods for reliability and probabilistic safety assessment, investigation on structural integrity of engineering s...

Numerical simulation of fatigue crack growth in welded joints is not well represented in the literature, especially from the point of view of material heterogeneity in a welded joint. Thus, several case studies are presented here, including some focusing on fracture, presented by two case studies of mismatched high-strength low-alloyed (HSLA) steel...

The role of welding in fracture mechanics development is considered from historical point of view. Starting point was analysis of Schenectady ship failure during the II World War, leading to development of linear elastic, as well as elastic-plastic fracture mechanics, soon afterwards. Two case studies are described to illustrate weldment fracture m...

This paper presents the repair welding technology of a Pelton runner blade, including an analysis of damage caused by cavitation. Extreme exploitation conditions resulted in crack initiation followed by its propagation, with a length 200 mm, detected during regular annual maintenance, compromising Peltron turbine’s structural integrity. The base ma...

Impact fracture behaviour of welded joints made of A516 Gr. 60 is analysed as a commonly used carbon structural steel for welded structures. Impact testing on Charpy instrumented pendulum is performed using specimens with a notch at positions: the base metal (BM), heat-affected-zone (HAZ), and weld metal (WM). The total impact energy is presented a...

This paper describes fatigue crack growth in a friction stir welded T joints made of aluminum alloy A2024-T351 under three-point bending load. For this purpose, three-dimensional homogeneous isotropic model is used to study the mechanical properties of the welded structure. Extended Finite Element Method (XFEM) implemented into ABAQUS and Morfeo/Cr...

The fracture properties of ferritic steels in transition temperature region are usually statistically treated by models that presuppose the existence of various forms of quenched disorder (critical cleavage triggers). In this study, the fracture toughness from the Euro fracture toughness dataset (stress intensity factor used in the master curve KJc...

In this paper, hip implants made of Ti-6Al-4V titanium alloy are analyzed numerically using Extended Finite Element Method XFEM. The combined effect of corrosion and fatigue was considered here since this is a common cause of failure of hip implants. Experimental testing of Ti-6Al-4V alloy was performed to determine its mechanical properties under...

Failure analysis of welded joint with multiple defects was performed taking into account the effect of all defects, not just a dominant one. Four cases of multiple defects in welded joint under the uniaxial tensile loading were investigated using extended Finite Element Method. Two-dimensional Finite Element Models were made according to the tensil...

The paper presents the results of research into the possibility of aluminium alloy lap joint production. The friction stir welding process is used to weld two aluminium alloy 5754-H111 plates into a lap joint. Friction stir welding ensures material joining without melting and use of additional material. By correctly selecting technological paramete...

The paper deals with the application of finite element method in determining the stress state in dental implants with different geometries subjected to various loads. Models that included mini dental implants and the bone used as a support are made in SolidWorks® and exported to Abaqus®. Obtained results show which load case is the most favourable...

Research presented here involves numerical analysis of stresses in partial hip implant subjected to static loads, for two cases of patient weight. The numerical analysis requires the development of 3D models that would accurately represent real partial hip implant geometry, hence a reverse engineering approach via 3D scanning is also included. This...

This paper deals with the tool plunge stage of friction stir welding which precedes the formation of the T-joint. A three-dimensional numerical model, developed in software package Simulia Abaqus® is applied for numerical analysis. The material of the welding plates is high strength aluminium alloy 2024-T3 of 3 mm thickness. The change of thermomec...

Three-parameter optimisation of a wing-fuselage attachment lug was applied to its thickness, rounding radius, and radius of pin hole, using the fatigue life and mass as criteria. Numerical simulation of fatigue crack growth by finite element method (FEM) and Separating Morphing and Adaptive Remeshing Technology (SMART) was used to evaluate the numb...

Considering that additive manufacturing technology, has evolved significantly over the past few decades, understanding of materials mechanical properties became important part of researches with the goal of further improvement of production Among the seven different AM technologies, in this research is used digital light processing (DLP) 3D printin...

Numerical simulation of fatigue crack growth (FCG) is presented, based on the application of the extended finite element method (XFEM). Couple of case studies are presented, as a review of recent experience of the Belgrade school of XFEM simulations, established at the Faculty of Mechanical Engineering. Case studies comprised Charpy specimen with i...

Dear colleagues and friends, We invite you to participate at 12th Annual Conference of Society of Structural Integrity and Life (DIVK12) organized by The Society for Structural Integrity and Life „Prof. dr Stojan Sedmak“ in co-organization with IMS Institute and Innovation Center of Faculty of Mechanical Engineering in Belgrade! This conference wi...

Polylactic Acid (PLA) is a widely used material in Fused Deposition Modeling (FDM) technology. Additive Manufacturing (AM) parameters are known to have an influence on the mechanical properties of final components. In FDM, the layer thickness is an influencing parameter providing overall better mechanical properties with lower layer thickness value...

In recent years, Additive Manufacturing (AM) has become an increasingly popular method in industrial applications for fabricating components with complex geometries, offering several benefits over traditional (subtractive) manufacturing methods. Among all available AM technologies, “vat photopolymerization” is still a reliable approach for manufact...

This paper presents an analysis of train screw coupling used mainly in Europe as mechanical connection of wagons in train. An analysis of train breaks apart incidents revealed that less than 30 % of the cases were caused by elements of the screw coupling, with coupling links accounting for only 5 % of the failures. Therefore, the investigation focu...

Numerous roads and railways network steel bridges exist with more than 100 years in service, often of great historical value. The in-service safety assessment of these structures is a complex problem which requires interdisciplinary approaches – from civil engineering application of Eurocodes or European recommendation for fatigue life estimation,...

Additive manufacturing (AM), also known as 3D printing, represent technologies where the production of physical models with complex shapes is performed in a layer-by-layer manner, directly from the CAD model. With these processes, there is no need for additional tools or fixtures, and there is no excess material. There are seven different AM techno...

Existing studies dealing with structural strength of bucket wheel excavators (BWE), include traditional approach that does not take into account the whole structural response of the object, just maximum response at the single location. On the other side, this paper proposes additional assessment of the structural response of BWE SchRs 630 that sepa...

In the paper, the cavitation resistance of cordierite samples with the addition of 10%, 15% and 20% talc, sintered at 1200?C, was investigated. The ultrasonic vibration method with a stationary sample according to the ASTM G32 standard was applied. The formation and development of damage to the surface of the samples was monitored using a scanning...

Structural integrity assessment of welded joints is presented, based on calculation of fracture mechanics parameters and risk analysis by using risk matrix, with an aim to improve safety of welded structures. As a case study, pressure vessel is presented, with crack-like defects, non-acceptable according to standard. Linear elastic fracture mechani...

Belgrade fair hall 1 is well known for its dome, which is still the world largest self-supported construction made of pre-stressed concrete, with its diameter of 106 m. In this paper the Finite Element Method (FEM) was performed to analyze different loading and supporting conditions. At the same time, crack growth in a support column was simulated...

The structural life of a functional component includes the period when the component has developed some sort of defect (e.g., crack). In such cases, damage-tolerant design utilizes fracture mechanics parameters for the assessment of the component's structural capability to withstand loads expected in the exploitation. One of the most fundamental pa...

A selection of suitable materials is critical for the safety of any hydrogen application. Most engineers know that hydrogen embrittlement and other hydrogen-specific damaging mechanisms of various metallic materials represent serious threats. The deleterious hydrogen effects and provoked degradation of mechanical properties of steel are expressed i...

The phenomenon of ductile-to-brittle transition in ferritic steels has been a ubiquitous research challenge for the last 50 years. The characterization of this problem using the fracture mechanics concept, from the earliest studies based on the linear-elastic fracture mechanics to the application of the elastic–plastic fracture mechanics, has becom...

The phenomenon of ductile-to-brittle transition (DBT) in ferritic steels, widely used in design of nuclear reactor pressure vessels, has been a pervasive semi-centennial research topic. Due to the extremely pronounced experimental data scatter, the statistical approach to characterization of this problem has become inevitable from the earliest anal...

Additive manufacturing technologies have developed rapidly in recent decades, pushing the limits of known manufacturing processes. The need to study the properties of the different materials used for these processes comprehensively and in detail has become a primary goal in order to get the best out of the manufacturing itself. The widely used ther...

Polypropylene (PP) is a relatively new material in fused deposition modeling (FDM) technology. The main feature of this material is its ability to significantly elongate under applied load, unlike any other thermoplastic material used in FDM technology. Not much research has been conducted on this FDM material so far, hence, the subject of this pap...

Selective laser sintering (SLS) is one of the additive manufacturing technologies dedicated to the production of high-quality parts with complex geometries. Here, polyamide 12 (PA12) is a commonly used material, for manufacturing parts with sufficient mechanical and thermal properties. In SLS, many manufacturing parameters have an effect on the mec...

A selection of suitable materials is critical for the safety of any hydrogen application. Most engineers know that hydrogen embrittlement and other hydrogen-specific damaging mechanisms of various metallic materials represent serious threats. The deleterious hydrogen effects and provoked degradation of mechanical properties of steel are expressed i...

3D printing, also known as additive manufacturing, significantly advances production processes compared to conventional manufacturing. Computer-aided (CAD) modelling provides detailed customization capabilities followed by freedom in manufacturing, resulting in lower production costs and easier repeatability of finished parts. Apart from its numero...

This paper presents the development of numerical models which were used to simulate the behaviour of welded joints containing different combinations of multiple defects under tensile loads. Four representative combinations of defects were selected (including undercuts, incomplete root penetration, misalignments...), based on practical experience. I...

Using austenitic steel in welding structures requires both destructive and non-destructive testing (NDT) to approve the use of intended welding specification, but also testing of material properties, even if they are guaranteed by manufacturer. In this particular case, X2CrNiMo17-12-2 (commercial trademark AISI 316L) is the material that has to be...

The Second International Symposium on Risk Analysis and Safety of Complex Structures and Components (IRAS 2023) took place between 2-4 April 2023 at the Faculty of Mechanical Engineering of the University of Belgrade. The guest editors of the IRAS 2023 deeply acknowledge all members of the International Scientific Committee, Thematic Sessions Organ...

Bucket-wheel excavators are continuously working machines for removal of waste and useful materials in open-pit mines, mainly used for mining of lignite. The purpose of a tooth gear ring is to rotate the excavator using two reducers. Due to this, the structural integrity of such elements is of great importance for the safe and reliable operation of...

The large scatter of the experimental fracture toughness data, characteristic of all ferritic steels in the ductile-to-brittle transition temperature region, imposed the need to include statistical methods for data processing. Due to the inherent stochasticity, the application of fracture mechanics concepts in the characterization of the DTB transi...

Crack size and undermatching effects on fracture behavior of undermatched welded joints are presented and analyzed. Experimental and numerical analysis of the fracture behavior of high-strength low-alloyed (HSLA) steel welded joints with so-called small and large crack in undermatched weld metal and the base metal was performed, as a part of more e...

The effect of the shielding gas arc welding process on the cavitation resistance of the three-component aluminum alloy AlMg4.5Mn and its welded joints was investigated. Welding was performed using the GTAW and GMAW processes in a shielded atmosphere of pure argon. After the welding, metallographic tests were performed, and the hardness distribution...

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 propert...

The mismatching constraint effect on crack propagation through the heat‐affected zone (HAZ) in a welded joint is presented in this paper. It is shown that due to this effect, the fracture behavior of an overmatched welded joint depends on the mechanical properties and the size of the region of the crack tip location, as well as on the properties an...

This paper deals with the damage growth in High-Pressure Turbine (HPT) cooling holes of the case assembly made of Inconel 718. Several marks (cuts) were made on cooling holes into parent material during the service due to the non-skilled use of Electrical Discharge Machining (EDM) in the workshop. After a certain time, the case assembly returned to...

The Second International Symposium on Risk Analysis and Safety of Complex Structures and Components (IRAS 20233) is organised by ESIS TC12 (with support from local institutions, such as the Faculty of Mechanical Engineering and its Innovation Center). It will take place in the Faculty of Mechanical Engineering of the University of Belgrade, in the...

This paper deals with a three-component aluminum alloy AlMg4.5Mn that was welded using a GTAW process in the shielded atmosphere of Ar+70%He+0.015%N2. The weld-metal toughness was evaluated at three different temperatures using instrumental Charpy pendulum impact testing to measure not only the total energy, but also the crack initiation energy and...

This paper presents a review of different approaches through history concerning DTB transition phenomenon of ferritic steels and their characterization using FM concept, from the earliest studies based on LEFM to the application of the EPFM concept. The large scattering of the experimental fracture toughness data, characteristic of all ferritic ste...

This paper presents development of numerical models for simulation of the behaviour of titanium alloy hip implants under static and dynamic loads, which is a part of extensive research involving the structural integrity of such implants under various loading conditions, as well as under exposure to aggressive environments. Numerical models were cre...

This paper describes the formation of an analytical model of heat generation and transfer during friction stir welding. By solving differential equations of heat transfer, adapted for friction stir welding, the foundations for the formation of an analytical model were laid. In order to vary the technological parameters of welding that affect the ge...

The research represents the ongoing investigation of the welded joints behavior made of low-carbon low-alloyed steel in the presence of different multiple defects. Following the initial experimental and numerical analyses performed on low-grade steel, a set of experiments were performed with specimens made of steel EN 1.0044 (commercial designation...

PLA polymer is probably the most used thermoplastic material in FDM technology nowadays. Besides prototyping purposes, FDM materials are also considered for functional application use, thanks to the fast fabrication of components, relatively simple workflow, and the absence of material waste that this technology offers. Except for static material p...

Plane-strain fracture toughness is one of the main parameters in linear elastic fracture mechanics and its purpose is to show the material capability to withstand load while having a defect. Main validity aspect for such an assessment is to provide a wide enough crack front to enable plane-strain condition. Nonetheless, in FDM (Fused Deposition Mod...

The paper involves experimental testing of titanium alloy Ti-6Al-4V specimens, based on which numerical models are made to provide the basis for further investigation. Due to the exploitation conditions these implants are subjected to, experimental tensile tests are performed on three types of specimens: regular type, and specimens previously subje...

The reparation of vessel 970 is shown, since the risk is very high (close to the worst case of both probability and consequence, being the highest). Since the defect location was not suitable for digging out and repair welding, it was decided to make a circumferential stiffener, to reduce the stress acting on the welded joint, so that both the stre...

Data on the strain and stress status of the pipe in the circumferential direction are required for various pipe manufacturing procedures (e.g., in the oil business, the process of manufacturing seamless pipes with a conical shaft). The aim of this study is to develop a procedure to determine the strain and stress behavior of Pipe Ring Tensile Speci...

In the friction stir welding (FSW) model there is more than twenty parameters. Most certain are the parameters of the model geometry, and the velocity and the rotational speed at which the tool should move. Other parameters, as density, mechanical and thermal properties of materials, coefficients of interactions, are mostly uncertain. Apart from su...

Fatigue crack growth in different panels, made of AA6156 T6, was investigated experimentally and numerically. Three different types of panels were used, simple one, so-called base metal (BM), panel with 4 welded stringers and panel with 4 welded stringers and 3 welded clips. Experimental investigation indicated benefits of stringers, especially in...

Causes of damage occurrence in vital components of welded structures of the bucket-wheel excavator boom (DU1) at the coal landfill of the thermal power plant 'Nikola Tesla A' in Obrenovac (Serbia) are investigated. Bucket-wheel excavator was produced by French company 'Ameco' and it moves along the circular track. Taking into account lack of techni...

The majority of manufacturers of polymer filaments for FDM technology rely their datasheets only on tensile tests, so their documentation usually lacks any data concerning fracture mechanics parameters. Having in mind the importance of fracture mechanics parameters in material design and application e.g., plane-strain fracture toughness, and the fa...

Successful application of Cr-Mo steel depends crucially on behaviour of all zones in welded joints, i.e. base metal (BM), heat-affected-zone (HAZ) and weld metal (WM), both at room and working temperature. Different amplitude loadings were applied for testing of specimens without a crack, made of welded joint as a whole and of BM, in order to obtai...

Fatigue crack growth in a panel with 4 stringers and 3-clips, made of AA6156 T6, was modelled numerically using xFEM. The central crack of the length a=17 mm was propagated in the total of 91 steps (in each step crack length increased by 2 mm) and after 14 steps the first clip began to deform. At the same time, crack continued to grow through the b...

This study is aimed to explain the behaviour of different orthopedic plate designs, under uniaxial bending, with cracks initiated in the stress concentration areas. Extended finite element method (XFEM) in ANSYS software was used for simulating the fatigue crack growth in 5 orthopedic plates with different geometries. Results for crack length vs, p...

Component failures due to the hydrogen embrittlement (HE) were observed in different industrial systems, including high-pressure hydrogen storage tanks, aircraft components, high-strength alloy components, and high-strength steel fasteners [1,2]. The contemporary approach in studying the effects of hydrogen on the mechanical properties of steels at...

This paper presents the analysis of the behavior of welded joints made of 9–12% Cr-Mo steel SA-387 Gr. 91. The successful application of this steel depends not only on the base metal’s (BM) properties but even more on heat-affected-zone (HAZ) and weld metal (WM), both at room and at operating temperature. Impact testing of specimens with a notch in...

This study is aimed to analyse fatigue life of orthopedic plates due to cracks initiated in the stress concentration areas. Material used for this analysis was typical orthopedic alloy, Ti-6Al-4V, strong but not very ductile, meaning also sensivite to cracking, as indicated by its mechanical properties, such as tensile strength, impact toughness an...

The aircraft industry is a leading industry in terms of the implementation of new materials and technologies. In the development of a light aircraft several different materials were considered for the engine cover design and the final decision was to select a composite material. Part of the research performed on the cover design is presented in thi...

Results of extensive experiments involving the fatigue behaviour of welded structures which are a part of the “Gazela” bridge in Belgrade, Serbia, are presented in this paper. After non-destructive testing of these structures, crack-like defects were detected, and welded plates containing them were taken out for the purpose of destructive testing....

During recent revitalization of Kaplan turbine aggregate made of structural steel St 3 (GOST standard), experimental investigation was performed. Base metal and welded joints were tested by non-destructive methods (NDT), and by testing of mechanical properties, including fracture mechanics parameters. Ultrasound testing (UT) indicated lack of penet...

Fatigue crack growth in orthopaedic locking compression plates (LCP), under four-point bending, has been simulated by the extended finite element method (xFEM) to assess LCP optimal geometry in respect to remaining life. Loads corresponded to those occurring in human tibia during gait cycle for different body weights (60, 90 and 120 kg). Experiment...

Stress corrosion crack growth in mild steel was investigated by using the finite element simulation method. A model simulating crack growth considered an edge crack located on the metal surface, under tensile remote stress acting on a sample. Numerical analysis was performed using the Code _Aster software to simulate crack growth. Three related var...

The aim of this paper was to improve the technological procedure, operations and construction of the vibro-motor coupling of the crusher bucket from steel grade C45. The work defines important materials, approaches and methods of welding and plasma cutting. Problems with time-consume and additional finances which are appearing in manufacturing proc...

Relevant local characteristics of fatigue loading are the largest stress amplitudes in the related mean stress values. They should be determined for the whole components. The relevant material properties are then compared with the stresses to assess integrity and life of a panel, made of Al allow, with welded stringers. To determine the maximum str...

This paper involves the numerical analysis of fatigue behaviour of welded joints made of steel SA-387 Gr. 91, with special attention devoted to its regions, which have very different mechanical and fatigue properties. Extensive experimental research, which was performed in order to obtain the coefficients necessary for the analysis of fatigue life...

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 loadin...

This paper deals with analysis and comparison of the equivalent plastic strain and temperature fields in the aluminium alloy 2024 T3 welded joint, with macro/microstructure appearance and hardness profile. In the alloys hardened by heat treatment, grain size and particle size of the precipitate are functions of equivalent plastic strain, strain rat...

Joining process play a significant role in producing lightweight constructions. Specifically, the use of Aluminum alloys for structural components or body airplane panels is one of the major challenges for joining because AA6xxx are very susceptible to hot cracks forming during fusion welding. As laser beam welding is increasingly used for welding...

The effect of proof over-pressure on pressure vessels structural integrity is analysed. Risk based approach is applied using Failure Analysis Diagramme to assess likelihood of failure. Special attention is paid to crack-like defects detected by NDT regular testing which are unacceptable by standards, but difficult to be repaired. It was show, using...

In order to assess the integrity of welded pressure vessel containing a crack, the behavior of three-point bending specimens made of HSLA steel welded joint are tested at -40°C, and their fracture behaviour analyzed, as a conservative measure of crack resistance. Specimens were made of low-alloyed steel NIONIKRAL 70, welded by SAW process. Surface...

The review of non-destructive testing of pressure vessel for compressed air is given, as well as the assessment and analysis of defects on the integrity of the vessel itself. The focus here is on welded joints, as the most critical areas in pressure vessels, especially if thickness is large, like in the case considered here (50 mm), cylindrical air...

Risk based assessment of structural integrity of corroded oil drilling pipe is presented and applied on prototype (welded pressure vessel made of pipe) with artificial defects, which was previously investigated under service (10 MPa) and testing (22 MPa) pressure. The new concept based on application of structural integrity estimation to assess ris...

In order to define a procedure for integrity assessment of pipelines and determining the fracture mechanics parameters, a new type of specimen with a sharp notch, Pipe Ring Notched Tension (PRNT) specimen, is tested. The aim of the study is to determine the influence of the specimen geometry (cylindrical shape, as well as number and length of stres...

Abstract The paper describes non-destructive testing and the repair welding technology for eliminating defects in the pressure equipment of RHE BB (Bajina Bašta) (located in Serbia). The obtained results had justified the proposed technology.