Search

This paper deals with the tool plunge stage of friction stir welding which precedes the formation of the T-joint. A threedimensional 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 thermomechanical conditions in the welding zones has been analysed, as well as the conditions for eliminating the joining line in the weld root. The tool rotation speed and shoulder plunge depth are varied. Two tools are used for analysis with different tool pin lengths: 2.6 mm and 3 mm. Increase in tool rotation speed raises the temperature in the welding zone and creates conditions for eliminating the joining line in the weld root. In addition, the increased tool pin length is also beneficial. It is obtained that the tool rotation speed exceeding 500 min–1 is necessary for this joint and tool geometries., U ovom radu je analizirana faza uranjanja alata pri formiranju T spoja primenom postupka zavarivanja trenjem sa mešanjem. Za termomehaničku analizu je korišćen trodimenzionalni numerički model, razvijen u softverskom paketu Abaqus®. Radne ploče su od legure aluminijuma visoke čvrstoće 2024-T3, debljine 3 mm. Praćena je promena termomehaničkih uslova u zoni zavarivanja tokom uranjanja alata, kao i uslovi potrebni za eliminisanje linije spajanja u korenom delu zavara. Menjana je brzina rotacije alata i dubina uranjanja čela alata. Za analizu su korišćeni alati sa dužinom trna 2.6 mm i 3 mm. Povećanjem brzine rotacije alata, povećava se temperatura u zoni zavarivanja i stvaraju se uslovi za eliminisanje linije spajanja u korenu zavara. Povećanje dužine trna alata utiče na eliminisanje linije spajanja. Prema dobijenim rezultatima, brzina rotacije iznad 500 min–1 je potrebna za razmatrane geometrije spoja i alata.

Velike posledice organizovanog kriminala i zahtevi društva za efikasnijom zaštitom uslovili su potrebu za preduzimanjem proaktivnih aktivnosti. Za jasno definisane proaktivne aktivnosti neophodna je objektivna procena i prognoza. U radu je predstavljen metodološki okvir za procenu pretnje od teškog i organizovanog kriminala i postupak izbora prioriteta u okviru ciklusa politike Evropske unije za suprotstavljanje teškom i organizovanom kriminalu. Drugi deo rada posvećen je strateškim aktima donetim u Republici Srbiji, Strateškoj proceni javne bezbednosti i Proceni pretnje od teškog i organizovanog kriminala sa najvažnijim činjenicama o organizovanim kriminalnim grupama i oblastima kriminala koje su bile predmet navedenih dokumenata. U zaključku su iznete preporuke za unapređenje metoda za prikupljanje i razmenu podataka, odnosno za unapređenje analitičkih kapaciteta neophodnih za objektivnu izradu svih strateških dokumenata., The consequences of organinized crime and society’s demands for more effective protection have caused the need to undertake proactive activities. An objective assessment and forecast is necessary for clearly defined proactive activities. The paper presents a methodological framework for assessing the threat of serious and organized crime and procedure for choosing priorities within the Europian Union’s policy cycle for combating serious and organized crime. The second part of the paper is dedicated to the strategic acts adopted in the Republic of Serbia, the Strategic Public Security Assesment and the Serious and Organized Crime Threat Assesment with the most important facts about organized criminal groups and areas of crime that were the subject of the aforementioned documents. In the conclusion, recommendations for the improvementof methods for data collection and exchange. i.e. for the improvement of analytical capacities necessary for the objective preparation of all strategic documents, are presented.

Cilj ovog istraživanja je da se primenom naučno-istraživačkih metoda identifikuju, naučno opišu, klasifikuju i delimično objasne sličnosti i razlike između Policijsko-obaveštajnog modela (eng. Intelligence-LedPolicing) sa sličnim modelima i konceptima proaktivnog rada policije. Primenom Policijsko-obaveštajnog modela policijski poslovi se nadograđuju nedostajućlm elementima, kao što su: prikupljanje, obrada i analiza podataka, izrada kriminalističko-obaveštajnih informacija, donošenje odluka i planova i njihovo sprovođenje koje uključuje koordinaciju, kontrolu i upravljanje kvalitetom. Prema tome, policijski poslovi se usmeravaju na: strateški pristup čiji je cilj sprečavanje i suzbijanje kriminaliteta, koordinaciju rada svih policijskih službenika (uniformisanih i kriminalističke policije), uspostavljanje ravnoteže, naročito u reaktivnom i proaktivnom postupanju, planiranje operativnih akcija usmerenih na višestruke izvršioce najtežih krivičnih dela koja izazivaju uznemiravanje javnosti i inkorporiranje proaktivnog rada kao sastavnog dela strategije za kontrolu kriminaliteta. Standardizacija rada primenom ovakvog modela doprinosi boljoj koordinaciji, transparentnosti, a pre svega kvalitativnom i profesionalnom nivou. Istraživanje je sprovedeno kao teorijsko, gde su u njegovoj realizaciji kombinovano korišćene metode teorijskih istraživanja odnosno: opštenaučne i logičke metode. U daljem radu predstavljene su sličnosti i razlike izmedu Policijsko-obaveštajnog modela i: koncepta rada policije u sistemu društvene samozaštite, rada policije u zajednici (Community Oriented Policing- COP), problemski orjentisanog rada policije (Problem Oriented Policing - POP) i rada policije usmerenog na kriminalna žarišta (Hotspotspolicing - HSP)., The goal of this research is to identify, scientifically describe, classify and partly explain the similarities and differences between the Intelligence-Led Policing and similar models and concepts of proactive police work by applying scientific research methods.By applying the Intelligence-Led Policing, police work is upgraded with missing elements, such as: collection, processing and analysis of data, preparation of criminal-intelligence information, decision-making and plans and their implementation, which includes coordination, control and quality management. Therefore, police affairs are focused on: a strategic approach aimed at preventing and suppressing crime, coordinating the work of all police officers (uniformed and criminal police), establishing a balance, especially in reactive and proactive actions, planning operational actions aimed at multiple perpetrators of the most serious crimes acts that cause public disturbance and incorporating proactive work as an integral part of the crime control strategy. Standardization of work using this model contributes to better coordination, transparency, and above all to a qualitative and professional level. The research was conducted as a theoretical one, where theoretical research methods were used in its realization, that is: general scientific and logical methods. In the following work, the similarities and differences between the Intelligence-Led Policing and: Of the concept of police work in the system of social self-protection,Community Oriented Policing - COP, Problem Oriented Policing - POP and Hot spots policing - HSP.

The cementless Corail stem is one of the most frequently implanted stems and has undergone several design changes. Currently in use is the third generation, named Corail AMT. Until now, only one third-generation Corail stem neck fracture has been described in 2020. In our paper, we present an almost identical complication with an additional analysis of the fracture using a scanning electron microscope. The revision surgery consisted of changing the broken implant with a Corail revision stem, along with replacing the polyethylene liner and the femoral head with new one, after which the patient achieved a full recovery. According to the available literature, this is the second case of this extremely rare complication.

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 rate and temperature. By analyzing the equivalent plastic strain fields and temperature fields it is possible, to some extent, to capture the effect of welding parameters and thermo-mechanical conditions on grain structure, and therefore hardness and strength in the welded joint. A coupled thermo-mechanical model is applied to study the material behaviour during the linear welding stage of friction stir welding (FSW). Three-dimensional finite element (FE) model has been created in ABAQUS/Explicit software using the Johnson-Cook material law. The values of thermo-mechanical quantities during the welding stage are obtained from the numerical model and shown as distributions across the joint. The obtained values of these quantities are related to the microstructure of the joint zones and hardness distribution, and this relation is discussed.

The influence of friction stir welding parameters on thermo-mechanical behavior of the material during welding is analyzed. An aluminum alloy is considered (Al 2024 T351), and different rotating and welding speeds are applied. The finite element model consists of the working plate (Al alloy), backing plate and welding tool. The influence of the welding conditions on material behavior is taken into account the application of the Johnson-Cook material model. The rotation speed of the tool affects the results. If increased, it contributes to an increase of friction-generated heat intensity. The other component of the generated heat, which stems from the plastic deformation of the material, is negligibly changed. When the welding speed, i.e. tool translation speed, is increased, the intensity of friction-generated heat decreases, while the heat generation due to plastic deforming is becoming more pronounced. Summed, this leads to rather small change of the total generation. The changes of the heat generation influence both the temperature field and reaction force. Also, the inadequate selection of welding parameters resulted in occurrence of the defects (pores) in the model.

The aim of this work was to establish a temperature of finish rolling stage of Nb/Ti microalloyed steel containing 0.06 wt.% C, 0.77 wt.% Mn, 0.039 wt.% Nb and 0.015 wt.% Ti, using physical simulation. Samples were subjected to laboratory simulation at a twist plastometer at high temperatures, i.e. between 825 and 950 degrees C. Five pass deformation and interpass times were selected in accordance with a processing parameters at five stand finishing hot strip mill. Restoration (recovery and/or recrystallization) behavior was evaluated by calculation of Fraction Softening (FS) and Area Softening Parameter (ASP) values. At 950 degrees C all individual pass stress-strain curves, FS and ASP show full recrystallization in all interpass intervals. On the other hand, with a decrease in temperature to the interval of 875-825 degrees C, the extent of restoration is decreasing, leading to recovery as a sole softening mechanism at 825 degrees C, which was confirmed by the stress-strain curve shape, and values of FS and ASP. It is assumed that, due to high supersaturation, strain-induced precipitation promoted pinning of grain and subgrain boundaries and suppressed recrystallization. Therefore, the critical temperature for finish rolling was estimated to be 825 degrees C.

Cleavage fracture of the V and Ti-V microalloyed forging steels was investigated by the four-point bending testing of the notched specimens of Griffith-Owen's type at -196 degrees C, in conjunction with the finite element analysis and the fractographic examination by scanning electron microscopy. To assess the mixed microstructure consisting mostly of the acicular ferrite, alongside proeutectoid ferrite grains and pearlite, the samples were held at 1250 degrees C for 30 min and subsequently cooled instill air. Cleavage fracture was initiated in the matrix under the high plastic strains near the notch root of the four-point bending specimens without the participation of the second phase particles in the process. Estimated values of the effective surface energy for the V and the Ti-V microalloyed steel of 37 Jm(-2) and 74 Jm(-2), respectively, and the related increase of local critical fracture stress were attributed to the increased content of the acicular ferrite. It was concluded that the observed increase of the local stress for cleavage crack propagation through the matrix was due to the increased number of the high angle boundaries, but also that the acicular ferrite affects the cleavage fracture mechanism by its characteristic stress-strain response with relatively low yield strength and considerable ductility at -196 degrees C.

The paper presents the concept and characteristics of nuclear security, the elements of the nu- clear safety strategy, the legislative framework and the most important solutions from the Law on Radiation and Nuclear Safety and Security. At the international level, the most important entity in this field is the International Atomic Energy Agency, while at the national level, most important is the Directorate for Radiation and Nuclear Safety and Security of Serbia. An important role is played by the Vinča Institute of Nuclear Sciences as the most referential scientific institution in this field, as well as the operational bodies - Nuclear Facilities of Serbia, the Ministry of Internal Affairs, Ministry of Defence, and the Serbian Armed Forces. Engagement of these bodies is carried out in regular peacetime circumstances, emergency situations and wartime. The most important challenges, risks and threats to nuclear security of Serbia were pointed out as well as the need to harmonize norms, procedures and processes in purpose of the strengthening institutional mechanisms in the field of nuclear security.

The subject of this paper is the structural design of a safety steel device that is located between the standard wagon buffer and the collision energy absorber. The safety steel device is a sacrifical part able to withstand normal operating loads from the buffer across the absorber to the vehicle bearing structure without any permanent deformation, but experiences fully controlled fracture when the load exceeds the defined threshold. Following fracture, the load path is through the energy absorber. The sacrificial part is a ring made from quenched and tempered low alloyed steel with precisely defined heat treatment and material properties. Experimental investigations of scaled samples were performed to get mechanical characteristics of the material and geometry. A full-scale prototype of the safety device was produced, and final quasi-static and dynamic experiments were conducted. The results validate the anaytical predictions, and thus validate the design method used here for dimensioning the safety steel device.

The influence of friction stir welding parameters on thermo-mechanical behavior of the material during welding is analyzed. An aluminum alloy is considered (Al 2024 T351), and different rotating and welding speeds are applied. The finite element model consists of the working plate (Al alloy), backing plate and welding tool. The influence of the welding conditions on material behavior is taken into account the application of the Johnson-Cook material model. The rotation speed of the tool affects the results. If increased, it contributes to an increase of friction-generated heat intensity. The other component of the generated heat, which stems from the plastic deformation of the material, is negligibly changed. When the welding speed, i.e. tool translation speed, is increased, the intensity of friction-generated heat decreases, while the heat generation due to plastic deforming is becoming more pronounced. Summed, this leads to rather small change of the total generation. The changes of the heat generation influence both the temperature field and reaction force. Also, the inadequate selection of welding parameters resulted in occurrence of the defects (pores) in the model.

U cilju poboljšanja bezbednosti i efikasnosti železničkog saobraćaja u eksploataciji, potrebno je redukovati učestanost raskinuća vozova, kao jedne od vrsta nesreća i nezgoda koje se mogu javiti u železničkom saobraćaju. Istraživanju uzroka raskinuća se često daje mali značaj, što ima za posledicu ponavljanje pojava raskinuća i dovodi do povećanja neplaniranih troškova u eksploataciji, koji bi inače mogli biti izbegnuti. Kako u stručnoj literaturi, pored analize pojedinačnih slučajeva raskinuća, ne postoji sveobuhvatna i sistematska analiza uzroka raskinuća, ovo istraživanje je aktuelno u domaćim uslovima eksploatacije, gde je prosečan broj raskinuća teretnih vozova u prethodnih 15 godina oko 40 slučajeva godišnje. Primenom metode konačnih elemenata (MKE) modela izabranih elemenata vučnih uređaja i opterećenja koja se mogu očekivati u eksploataciji verifikovano je stanje elemenata utvrđeno ispitivanjem. Utvrđivanjem glavnih uzroka raskinuća voza predložene su odgovarajuće preventivne mere radi smanjenja ove štetne pojave, čime se direktno utiče na povećanje bezbednosti i sigurnosti u železničkom saobraćaju, i na smanjenje troškova u slučaju raskinuća u eksploataciji. Ovo istraživanje predstavlja značajan doprinos nauci s obzirom da ne postoji sistematsko istraživanje u ovoj oblasti. Naučni doprinos ovog istraživanja se ogleda u kvantifikaciji parametara koji utiču na pojavu raskinuća i procenu nastanka raskinuća pri poznatim uslovima eksploatacije i stanja vučnih uređaja. Praktični značaj ove disertacije ogleda se u mogućnosti da se u određenoj meri unaprede postojeći postupci dijagnostike i opravke vučnih uređaja, na osnovu saznanja dobijenih analizom otkaza, čime bi se unapredilo održavanje i smanjili otkazi vučnih uređaja., In order to improve the safety and efficiency of railway traffic in operation, it is necessary to reduce the frequency of train breaking, as one of the types of accidents and incidents that can occur in railway traffic. Research the causes of breaking is often of little importance, resulting in recurrences of breaking and leading to an increase of unplanned operating costs, which could otherwise have been avoided. In the railway literature, despite the analysis of individual cases of breaking of train, there is no comprehensive and systematic analysis of the causes of breaking, this research is authentic in domestic operating conditions, where the average number of breaking of freight trains in the previous 15 years is about 40 cases per year. By applying Finite Element Method (FEM) on coupling system and loads that can be expected in operation, the condition of the elements determined by testing was verified. By determining the main causes of breaking of train, appropriate preventive measures have been proposed in order to reduce this occurrence, which directly affects the safety and security in railway traffic, and the can lead to reduction of costs in case of breaking of train in operation. This research represents a significant contribution to science as there is no systematic research in this area. The scientific contribution of this research is in the quantification of parameters that affect the breaking of train and the assessment of the breaking under known operating conditions and the condition of coupling system. The practical significance of this dissertation is in the possibility to improve, to some extent, the existing procedures for diagnostics and repair of coupling systems, based on the findings of failure analysis, that would improve the maintenance and reduce failures of coupling system.

Isothermal transformation characteristics of a medium carbon Ti-V microalloyed steel were investigated using light microscopy, scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), and by uniaxial compressive testing. Samples austenitized on 1100 degrees C were isothermally treated in the range from 350 to 600 degrees C and subsequently water quenched. The final microstructure of the samples held at 350 degrees C consisted of bainitic sheaves and had compressive yield strength, approximately from 1000 MPa, which is attributed to high dislocation density of low bainite. At 400 and 450 degrees C, acicular ferrite became prevalent in the microstructure. It was also formed by a displacive mechanism, but the dislocation density was lower, leading to a decrease of compressive yield strength to approximately 700 MPa. The microstructure after the heat treatment at 500 degrees C consisted of coarse non-polygonal ferrite grains separated by pearlite colonies, principally dislocation free grains, so that the compressive YS reached a minimum value of about 700 MPa. The microstructure of the samples heat-treated at 550 and 600 degrees C consisted of pearlite and both grain boundary and intragranular ferrite, alongside with some martensite. After 600 s, austenite became stable and transformed to martensite after water quenching. Therefore, the presence of martensite increased the compressive YS to approx. 800 MPa.

Two modes of failure are analysed for coupling links, the mechanical connections that transmit traction forces between vehicles along the length of a train. Coupling links are designed to withstand the dynamic loads in normal operation but may break if applied loads exceed safe operating limits. Fractography of two failed links revealed that one had failed through brittle fracture, and one through ductile fracture. Metallography indicated that one sample was hardened and tempered with typical tempered martensite microstructure and the other was normalized with a ferrite-pearlite microstructure. A numerical model of a coupling link is developed and validated against experimental data. Results indicate that the failed links experienced loads above the permitted limit.

Predmet ove disertacije je odreĎivanje nastajanja i razvoja oštećenja vatrostalnih materijala na bazi bazalta pod dejstvom kavitacije. Kao osnovni materijal za izradu uzoraka za ispitivanje: rovni, liveni i sinterovani uzorci, korišćen je olivin–piroksenski bazalt iz leţišta Vrelo–Kopaonik..., The subject of this dissertation is the determination of the formation and development of damage to refractory materials based on basalt under the effect of cavitation. As the basic material for the preparation of samples for testing: raw, cast and sintered samples, it was use olivine-pyrroxene basalt from the Vrelo– Kopaonik deposit...

Copper-based alloys and composites, owing to their convenient properties, are being considered essential materials in various industries. Since copper possesses an ability to develop high corrosion resistance, putting it in the domain of a desirable material in the manufacturing of valves, pipes, and also systems that carry industrial gases and aqueous fluids. Its usage is also invaluable for cables and electrical wires. This review paper describes diversity in copper alloy processing techniques (powder and ingot metallurgy) which are alongside the phase transformation kinetics interpreted and explained in detail. Furthermore, the focus is put on the copper alloys, as well as the kinetics present in these systems, with the application being highlighted. Correlation between physical properties and phase transformation kinetics in copper alloys is made. It is shown that if certain alloying elements are to be added, different properties could be improved. The effect of phase precipitation on phase transformation kinetics of copper alloys is shown by studying the Cu-15Ni-8Sn alloy.

Imajući u vidu heterogenost svojstava zavarenog spoja, a naročito uske zone pod uticajem toplote, u ovoj disertaciji je eksperimentalno ispitivano i analizirano ponašanje niskolegiranog čelika povišene čvrstoće (HSLA) u uslovima niskocikličnog zamora, na glatkim okruglim epruvetama iz osnovnog metala i epruvetama dobijenim termičkom simulacijom zone pod uticajem toplote. Takođe je ispitivano ponašanje osnovnog metala i simulirane zone pod uticajem toplote u uslovima dejstva kavitacije. Čelik, Nionikral 70 (NN-70), odabran u ovoj disertaciji za istraživanje ponašanja pri zamornom opterećenju i dejstvu kavitacije, spada u grupu niskolegiranih čelika povišene čvrstoće koji se, između ostalog, primenjuju u brodogradnji kao i za izradu posuda pod pritiskom. Ciljevi istraživanja su da se, u odsustvu pouzdanijih teorija o zamaranju i kavitaciji, pogodnom metodom ispitivanja, tj. simuliranjem strukture materijala i dejstva opterećenja odnosno deformacija, u laboratorijskim uslovima na odgovarajućim uzorcima - epruvetama, dođe do rezultata koji su posredno ili neposredno primenljivi u proračunima i da se dobijeni rezultati eventualno iskoriste i za fundamentalna proučavanja tokova procesa zamaranja i kavitacije kako osnovnog metala, tako i zone uticaja toplote zavarenih spojeva., In this dissertation the experimentally investigated and analyzed behavior of a low-alloyed high strength steel exposed to the low cycle fatigue is done. Taking into account the welded joint properties heterogeneity, especially its narrow heat-affected zone, experiments were performed on two kinds of specimens: smooth round specimens made of parent material (PM) and specimens obtained by thermal simulation of the heat-affected zone (SHAZ). The behavior of PM and SHAZ affected by cavitation were also investigated. Steel designated as Nionicral 70 (NN-70), selected in this dissertation to investigate the behavior of fatigue and cavitations’ loads, belongs to a group of lowalloy steels of high strength, which are, among other things, applied in shipbuilding as well as for the production of pressure vessels. The research aims are that, in the absence of more reliable theories of fatigue and cavitation, a suitable test method, i.e. simulating the structure of the material and the load and/or deformation in laboratory conditions on the appropriate specimens, results are obtained which are directly or indirectly applicable in the calculations, and that the obtained results are possibly used for the fundamental study of the fatigue and cavitation processes of the parent material, as well as its heat-affected zone in welded joints.

The aim of this work was to evaluate the influence of welding speed on microstructure, mechanical properties, as well as Intergranular corrosion (IGC) susceptibility of EN AW-5083 alloy welded using FSW. FSW was performed using constant rotation speed of 750 Rev/min, while welding speed was varied from 73 mm/min, 150 mm/min to 190 mm/min. Results show that increase of welding speed lead to decrease of the size of the nugget. This behavior is attributed to decrease of heat input during welding. Accordingly, lower grain size provides increase of the strength. All tested welds are resistant to IGC, evaluating by mass loss according to NAMLT test, and resistivity slightly decrease with increasing welding speed.

Some aspects of deformation, precipitation, and recrystallization behavior in medium carbon V-microalloyed and low carbon Nb/Ti-microalloyed steels are presented in the paper. Changes in microstructure are explained together with methods of quantification. The temperature of No-recrystallization (Tnr) is defined as a milestone to show the onset of retardation of recrystallization while the apparent activation energy for hot working shows the extent of this retardation. In the case of high cooling rates, this method is not sufficiently sensitive and Trl (recrystallization limit temperature) and Trs (recrystallization stop temperature) must be evaluated from softening data. Paper presented the possibility to estimate Tnr temperature on six stands finishing train at Hot Strip Mill in HBIS Iron and Steel Serbia, Smederevo as well as the activation energy for static recrystallization, QSRX, derived from Tnr temperatures.

Stress and strain distribution at the onset of cleavage fracture during fourpoint bending testing at liquid nitrogen temperature of two commercial mediumcarbon V and TiV microalloyed forging steels, with predominantly acicular ferrite structure, was examined using finite element analysis. The finite element models were based on notched four-point bending Griffiths-Owens’s type specimens, while the material mechanical properties data input was based on stress-strain curves obtained by tensile testing at liquid nitrogen temperature. Results of the modeling showed that there were no distinct differences in strain distribution along the distance from the notch tip between the two steel samples, aside from strain magnitude which stems from the differences in stress-strain curves. Based on the recorded load at fracture, the corresponding displacement calculated by finite element analysis was somewhat larger for the V steel. While the TiV steel breaks at crosshead displacement between 0.3 and 0.5 mm, the V steel breaks between 0.6 and 0.9 mm. Plastic strain at the cleavage initiation site for the TiV steel ranges from 0.0595 to 0.1612, while for the V steel these values range from 0.3694 to 0.6338. Observed differences in plastic deformations near the notch root, where cleavage initiation sites were detected, seem to reflect differences in deformation behavior at liquid nitrogen temperature. Moreover, such difference could be ascribed to the observed differences in structure, primarily in the volume fraction of acicular ferrite. It was concluded that deformations are more uniformly distributed when acicular ferrite is predominant in the structure of the steel. It could be ascribed to the effect of “gradual yielding” related to the high dislocation density in acicular ferrite, somewhat lower yield stress and higher ductility of the TiV steel with predominantly acicular ferrite structure.

Tehnički problem koji se rešava ovim pronalaskom je automatsko odbravljivanje i zabravljivanje klizne grede poluprikolice, čime se omogućava operateru-vozaču vučenog vozila da tovarnu površinu u svakom trenutku, prema potrebi, može povećati (produžiti) ili smanjiti (skratiti) daljinskom komandom.

Imajući u vidu heterogenost svojstava zavarenog spoja, a naročito uske zone pod uticajem toplote, u ovoj disertaciji je eksperimentalno ispitivano i analizirano ponašanje niskolegiranog čelika povišene čvrstoće (HSLA) u uslovima niskocikličnog zamora, na glatkim okruglim epruvetama iz osnovnog metala i epruvetama dobijenim termičkom simulacijom zone pod uticajem toplote. Takođe je ispitivano ponašanje osnovnog metala i simulirane zone pod uticajem toplote u uslovima dejstva kavitacije. Čelik, Nionikral 70 (NN-70), odabran u ovoj disertaciji za istraživanje ponašanja pri zamornom opterećenju i dejstvu kavitacije, spada u grupu niskolegiranih čelika povišene čvrstoće koji se, između ostalog, primenjuju u brodogradnji kao i za izradu posuda pod pritiskom. Ciljevi istraživanja su da se, u odsustvu pouzdanijih teorija o zamaranju i kavitaciji, pogodnom metodom ispitivanja, tj. simuliranjem strukture materijala i dejstva opterećenja odnosno deformacija, u laboratorijskim uslovima na odgovarajućim uzorcima - epruvetama, dođe do rezultata koji su posredno ili neposredno primenljivi u proračunima i da se dobijeni rezultati eventualno iskoriste i za fundamentalna proučavanja tokova procesa zamaranja i kavitacije kako osnovnog metala, tako i zone uticaja toplote zavarenih spojeva., In this dissertation the experimentally investigated and analyzed behavior of a low-alloyed high strength steel exposed to the low cycle fatigue is done. Taking into account the welded joint properties heterogeneity, especially its narrow heat-affected zone, experiments were performed on two kinds of specimens: smooth round specimens made of parent material (PM) and specimens obtained by thermal simulation of the heat-affected zone (SHAZ). The behavior of PM and SHAZ affected by cavitation were also investigated. Steel designated as Nionicral 70 (NN-70), selected in this dissertation to investigate the behavior of fatigue and cavitations’ loads, belongs to a group of lowalloy steels of high strength, which are, among other things, applied in shipbuilding as well as for the production of pressure vessels. The research aims are that, in the absence of more reliable theories of fatigue and cavitation, a suitable test method, i.e. simulating the structure of the material and the load and/or deformation in laboratory conditions on the appropriate specimens, results are obtained which are directly or indirectly applicable in the calculations, and that the obtained results are possibly used for the fundamental study of the fatigue and cavitation processes of the parent material, as well as its heat-affected zone in welded joints.