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The paper presents a functionality investigation of the key dam elements based on finite element analysis. A detailed analysis of filtration processes, dam strength, and the surrounding rock mass was conducted. Dam elements whose potential damage could jeopardize the normal functioning of the embankment dam have been identified. A particular emphasis was placed on the analysis of dam elements that have been identified as weak points. A numerical analysis of the impact of individual grout curtain zone failure on leakage under the dam body, a strength analysis of the overflow section, as well as the analysis of the slope stability that can compromise the functioning of the spillway have been performed. To analyze the partial stability of individual structural elements, a new measure of local stability was introduced as the remaining load-bearing capacity. As a case study, the Zavoj dam, which is a part of the Pirot reservoir system in the Republic of Serbia, was used. Investigation revealed that local damage to the grout curtain will not significantly increase leakage under the dam body, the overflow section is one of the most robust elements of the dam, but the slope above the spillway can compromise the functioning of the overflow and thus the safety of the entire dam. Based on the analysis of the results of the remaining load-bearing capacity, the dependence of the spillway capacity on earthquake intensity has been defined. The established relationship represents a surrogate model for further assessment of dynamic resilience of the complex multipurpose reservoir system, within the scope of the advanced reservoir system management.

Rezime: Uspešno projektovanje čeličnih konstrukcija u velikoj meri zavisi od poznavanja mehaničkih karakteristika materijala koji se koriste. Kod konstrukcija koje su izložene udarnim opterećenjima, neophodno je raspolagati sa dinamičkim karakteristikama materijala, koje se kod pojedinih materijala mogu značajno razlikovati u odnosu na kvazi-statičke karakteristike određene standardnim metodama. Uspešno određivanje dinamičkih karakteristika materijala, podrazumeva razvoj i usavršavanje novih eksperimentalnih metoda, u zavisnosti od željenih primena. Razvoj složenih čeličnih konstrukcija, koje podrazumevaju upotrebu procesa spajanja delova postupkom zavarivanja, dodatno je uslovljen poznavanjem ponašanja zavarenih spojeva i njihovog uticaja na ostatak konstrukcije. Složenost određivanja dinamičkih karakteristika utiče na manju dostupnost podataka u literaturi, ujedno povećavajući sumnju u njihovu verodostojnost. S tim u vezi, razvoj uređaja za ispitivanje materijala i metodologije za određivanje specifičnih parametara koji opisuju dinamičko ponašanje materijala, predstavlja opravdanu težnju svih laboratorija. Istraživanjem razvoja i analizom savremenih rešenja uređaja za dinamičko ispitivanje materijala, u okviru Centra za inženjerski softver i dinamička ispitivanja Fakulteta inženjerskih nauka Univerziteta u Kragujevcu, dizajniran je i napravljen zatezni Hopkinsonov štap. Njegovom upotrebom, u kombinaciji sa servohidrauličkom kidalicom, stekli su se potrebni uslovi za određivanje parametara materijalnih modela koji u obzir uzimaju promenljivu brzinu deformacije. Ovom doktorskom disertacijom obuhvaćena je metodologija eksperimentalnog određivanja parametara Johnson-Cook-ovog materijalnog modela. Određivanje parametara je podrazumevalo sprovođenje serije eksperimenata na sobnoj i povišenim temperaturama, pri različitim brzinama deformacije. Upotrebom savremenih optičkih mernih sistema, dobijeni rezultati predstavljaju osnovu za precizno određivanje parametara koji opi, Successful design of steel structures depends to a great extent on the knowledge of the mechanical characteristics of the used materials. For structures that are exposed to impact loads, it is necessary to have dynamic properties, which can differ significantly in certain materials in relation to quasi-static characteristics determined by standard methods. Successful determination of dynamic characteristics implies the development and testing of new experimental methods, depending on the desired applications. The development of complex steel structures, which involves the use of the process of connecting parts by the welding process, is further conditioned by knowledge of the behaviour of welded joints and their influence on the rest of the construction. The complexity of determining dynamic characteristics influences the availability of data in the literature, at the same time increasing doubt in their trustiness. About that, the development of a testing device for materials and a methodology for determining specific parameters describing the dynamic behaviour of materials represents a justified aspiration of all laboratories. Research of the developments and analysis of modern solutions for dynamic material testing, within the Center for Engineering Software and Dynamic Testing of the Faculty of Engineering Sciences in Kragujevac, a built-in tensile Hopkins bar was also designed. With its use, together with the servo-hydraulic device, the necessary conditions have been obtained for determining the parameters of the material models which take into account the variable strain rates. This doctoral dissertation includes the methodology of experimentally determining the parameters of Johnson-Cook's material model. The determination of the parameters involved the implementation of a series of experiments at room and elevated temperatures at different strain rates. Using modern optical measurement systems, the obtained results are the basis for precise determin

U disertaciji je razvijen modul za proračun turbulentnog strujanja koji se primenjuje za proučavanje medicinskih fenomena koji se javljaju u arterijskim bifurkacijama sa stenozama. Razvoj turbulentnog modula za proračun strujanja fluida u ovom radu zasniva se na metodu konačnih elemenata (MKE). Razvijeni turbulentni modeli k − i LES su primenom metoda konačnih elemenata dodati u program PAK-F. Dobijeni rezultati su verifikovani na osnovu eksperimentalnih rezultata na više različitih problema. Simulacija laminarnog i turbulentnog strujanja je izvedena na realnim modelima arterijskih bifurkacija. Može se zaključiti da je prikazana metodologija koristan alat koji pruža značajne informacije kardiolozima o zdravlju pacijenta i da li ima potrebe za intervencijom., In the dissertation, a turbulent flow calculation module was developed that is used to study medical phenomena occurring in arterial bifurcations with stenoses. The development of a turbulent fluid flow calculation module in this paper is based on the Finite Element Method (FEM). Developed turbulent models k − and LES are added to the PAK-F program using finite element method. The obtained results were verified on the basis of experimental results on several different problems. The simulation of laminar and turbulent flows is performed on real models of arterial bifurcations. It can be concluded that the methodology presented is a useful tool that provides significant information to cardiologists about the patient's health and whether there is a need for intervention.

Large amounts of information are nowadays easily obtainable using the Internet, and using implicit feedback whether a reader finds a text interesting is desirable. Eye-tracking technology could be used for such a feedback, and a combination of eye-movement features and a textual complexity measure can be used to predict the user's interest. In this paper we give an overview of a platform developed to evaluate and visualize implicit feedback of a person who reads a text. Based on the eye-movement samples provided, a model is trained that could be used to predict comprehensibility of a user reading a text. This prediction is combined with objective complexity evaluation of the text using data mining methods, and the outcome is used to select a text (from a repository) that a user may find more valuable (interesting). We briefly discuss the requirements, architecture and implementation of this platform.

Pouzdanost analiza geotehničkih problema numeričkih metoda kao što su metoda konačnih elemenata..., Accuracy and reliability of geotechical analysis by numerical methods such ....

REZIME Funkcionalno gradijentno raspoređeni materijali (FGM), kao grupa savremenih materijala u porodici inženjerskih kompozita dobijaju sve širu primenu u raznim granama industrije sa ciljem da se, odgovarajućim kombinovanjem potencijala dostupnih materijala, njihove osobine iskoriste na najbolji mogući način. Otkaz ili delaminacija, izazvana visokim lokalnim interlaminarnim naponima, je najveći i najčešće proučavani problem kod konvencionalnih kompozitnih laminata. U cilju prevazilaženja pomenutih problema, u okviru ove disertacije proučavane su i implementirane teorijske osnove, kao i analitičke i numeričke procedure kojima se može obezbediti predviđanje ponašanja ploča od funkcionalno gradijentno raspoređenih materijala izloženih različitim vrstama opterećenja. Prikazane su osnovne karakteristike FGM i ukazano je na njihove prednosti u odnosu na konvencionalne kompozitne laminate. Izvršena je njihova klasifikacija u odnosu na različite kriterijume i opisan je širok spektar oblasti u kojima se primenjuju. Posebna pažnja je posvećena definisanju matematičkih funkcija, koje na adekvatan način mogu da opišu njihovu gradijentnu strukturu. Te funkcije su poslužile kao osnova za dobijanje matematičkog modela FGM za naponsko-deformacionu analizu ploča koja je urađena u okviru ove disertacije Izvršena je sistematizacija teorija ploča koje se koriste u analizi konvencionalnih kompozitnih lamina. Data je analiza prednosti i nedostataka klasične teorije ploča i smicajnih deformacionih teorija prvog i višeg reda. Smicajna deformaciona teorija višeg reda zasnovana na 13 različitih funkcija oblika, koje su prvenstveno razvijene od strane različitih autora za analizu kompozitnih laminata, u ovoj disertaciji je prilagođena i implementirana u teorijske postavke za analizu ploča od FGM. Kako se veliki broj inženjerskih problema matematički opisuje modelom ploče na elastičnoj podlozi, proučene su i teorijske postavke ploče od FGM na elastičnoj podlozi. Primenjen je Vinkler-Pasterna, Functionally graded materials (FGM), as a group of modern materials in the family of engineering composite materials, are being increasingly used in various branches of industry, striving to make the best use of their characteristics by combining adequately the potentials of available materials. Failure or delamination, caused by high local interlaminar stresses, is the biggest and the most commonly studied problem with conventional composite laminates. With the aim of overcoming those problems, this thesis provides a study and implementation of theoretical basis, as well as analytical and numerical procedures which can predict the behaviour of plates of functionally graded materials exposed to different kinds of loading. The basic characteristics of FGM are presented and it is pointed to their advantages over conventional composite laminates. They have been classified according to various criteria and a wide range of areas of their use has been presented. Special attention has been given to defining mathematical functions which can adequately describe their graded structure. Those functions were used as a basis for getting a mathematical model of FGM for stress-strain analysis of plates which has been done within this thesis. A systematization of plate theories which are used in the analysis of conventional composite laminates has been done. The thesis also gives an analysis of advantages and disadvantages of the classical plate theory as well as of the first order and high order shear deformation theories. High order shear deformation theory based on 13 different shape functions, which were previously developed by various authors for the analysis of conventional composite laminates, has been adjusted and implemented into theoretical postulates for the analysis of FGM plates. Since a big number of engineering problems are mathematically described by a model of plate on an elastic foundation, the thesis studies theoretical postulates for FGM plates on an el

Granularne materijale čini skup vema velikog broja sitnih solida (zrna, granula, čestica) čije ponašanje zavisi od energije koju solidi poseduju i predstavljaju nakon vode drugu najmanipulisaniju materiju u inženjerstvu. Za numeričku analizu uređaja za transport, skladištenje i obradu granularnih materijala, neophodno je tačno modeliranje opterećenja kojima granularni materijal deluje na pomenute uređaje. U okviru ove disertacije data je teorijska analiza ponašanja granularnih materijala od mikro nivoa gde je analiziran kontakt između dva zrna, do makro nivoa u kome se analizira ponašanje celokupnog materijala. Metoda diskretnih elemenata je korišćena za modeliranje troosnog testa, eksperimenta koji se najčešće koristi za određivanje materijalnih karakteristika, kao i traka smicanja i vrtolga koji se pri tom javljaju u granularnom materijalu. Opterećenja u granularnom materijalu nisu ravnomerno raspoređena, već najopterećenija zrna formiraju lance sila dok ostala zrna igraju potpornu ulogu. Deformacije granularnog materijala izazivaju kidanje starih i formiranje novih lalnaca sila, a promene opterećenja su analizirane za izabrana zrna. Glatka čestična hidrodinamika je numerička metoda zasnovana na mehanici kontinuuma, a njen bezmrežni karakter omogućava analizu velikih deformacija u realnim problemima, pa je generalisani materijalni model sa kapom ugrađen u program i korišćen za modeliranje granularnih materijala. Metoda konačnih elementata je najčešće korišćena numerička metoda u inženjerstvu, a da bi se koristila za analizu uređaja za transport, skladištenje i obradu granularnih materijala povezana je sa glatkom čestičnom hidrodinamikom po principima fluid-solid interakcije, a kontaktni algoritam između ove dve metode je proširen tretmanom trenja na osnovu Kulonovog zakona. Metodologija analize podrazumeva korišćenje dva programa za pre-procesiranje i jednog za post-procesiranje koji su povezani sa solverima pomoću programa prevodioca. Materijalni model, sprezanje, The granular materials consists of large number of small solids (grains, granules, particles) whose behavior depends on the energy they have and represent the second most manipulated matter in engineering (water is the first). For numerical analysis of devices for transport, storage and processing of granular materials, it is necessary to accurately model load which granular materials exert on the aforementioned devices. As a part of this dissertation the theoretical analysis of granular materials behavior is presented, both at the micro levels where the contact between two grains is analyzed, and a macro level in which the behavior of the whole material is analyzed. Discrete element method was used for modeling of triaxial tests, experiments that are commonly used to determine material characteristics, as well as shear bands and vortexes which occur in the granular material during these tests. Loads in the granular material are not evenly distributed, with most loaded grains forming force chains, while other grains play only a supporting role. Deformation of granular materials causes breaking of old and the formation of new force chains and load changes are analyzed in selected grains. Smoothed particle hydrodynamics is a numerical method based on continuum mechanics, and its meshless character allows analysis of large deformation in real problems, so generalized material model with cap was coded into the program and used to model granular materials. Finite element analysis is the most widely used numerical methods in engineering, but in order to be used for the evaluation of construction for transportation, storage and processing of granular materials it needed to be connected with smoothed particle hydrodynamics using the principles of fluid-solid interactions, and contact algorithm between these two methods is expanded by friction treatment on the basis of Coulomb's law. The methodology of analysis involves the use of two programs for pre-processing and one for

Iz inženjerske prakse je poznato da su vagonske čelične konstrukcije tokom eksploatacije izložene složenim kombinovanim opterećenjima. Modernizacijom pruga, povećavanjem brzine kretanja, optimizacijom vagonskih konstrukcija, korišćenjem novih materijala, stvoreni su veliki izazovi u oblasti vagonske industrije. Paralelno sa povećanjem izazova, zahtevi u pogledu pouzdanosti i bezbednosti vagonskih konstrukcija postajali su sve veći. Predmet proučavanja i cilj rada na ovoj disertaciji je razvoj pouzdane metodologije za eksperimentalnu i numeričku procenu integriteta vagonskih konstrukcija izloženih promenljivim dinamičkim opterećenjima. Za potrebe procene integriteta delova vagonskih konstrukcija eksperimentalno su određivane karakteristike konstrukcionih čelika i čelika koji su već bili u fazi eksploatacije. Cilj ovih eksperimentalnih istraživanja je dobijanje dovoljnog broja podataka o materijalima i geometriji kritičnih zona vagonskih konstrukcija. Sistematizacijom dobijenih rezultata i onih koji su već dostupni u raznim oblicima literature napravljena je osnova za tumačenje rezultata dobijenih numeričkim proračunima. Kao plod razvijene metodologije, na realnim primerima iz prakse, prikazan je postupak procene integriteta nosećih delova rekonstruisane vagonske konstrukcije, koja je izložena promenljivim zamornim opterećenjima. Na osnovu eksperimentalnih i numeričkih rezultata izvršena je analiza postavljenog problema u skladu sa standardima u oblasti vagonskih konstrukcija. Drugi primer predstavlja procenu preostalog radnog veka, određivanje broja ciklusa do otkaza kritičnih zona nosećih delova vagonske konstrukcije na osnovu eksperimentalno dobijenih podataka i numeričkih rezultata proračuna. Korišćenje razvijene metodologije na konkretnim primerima i njena verifikacija u praksi, dovodi do znatne uštede pri veoma skupim ispitivanjima različitih prototipova vagona. Praktična primena razvijene metodologije u budućnosti bi mogla ostvariti pozitivan uticaj u oblasti v, It is well known from the engineering experience that, during exploitation, steel structures of wagons are exposed to the complex combined loads. Modernization of rails by increasing the velocity, optimization of the wagon structures, using new materials, created great challenges in the field of wagon industry. Together with increasing challenges, the requirements in terms of reliability and safety of the wagon structure have increased as well. The subject of studying and purpose of this thesis is to develop a reliable methodology for the experimental and numerical evaluation of the integrity of the wagon structures exposed to the alternating dynamic loads. For the purpose of integrity estimation of the wagon parts, the characteristics of structural steel and steel in the phase of exploitation have been experimentally determined. The aim of this experimental research is to obtain sufficient data on materials and geometry relating to the critical zones of the wagon structures. Systematization of the obtained results and those that are already available in various forms of literature enabled forming the basis for the interpretation of the results of the numerical calculations. As a result of the developed methodology, the procedure of assessment of the integrity of loadbearing parts of the reconstructed wagon structure exposed to fatigue loads, is presented on the real examples in practice. The analysis of a problem was performed in accordance with the standards in the field of the wagon industry and based on the experimental and numerical results. Another example presents the remaining service life assessment, determination of the number of cycles to failure of critical load-bearing parts of the wagon structure according to the experimental data and numerical calculation results. Using of the developed methodology on concrete examples and its verification in practice lead to the significant savings in the very expensive tests of different prototypes of the wagon. Pra

U makromehaničkoj linearno-elastičnoj analizi kompozitnih laminata moguće je koristi dva usvojena teorijska pristupa: pristup kontinualnosti napona i princip kontinualnosti deformacija. U ovoj disertaciji primarno je razvijen postupak analize laminata zasnovan na kontinualnosti deformacija. U tu svrhu razrađene su smicajne deformacione teorije višeg reda. Nedostatke klasične teorije ploča i smicajne deformacione teorije prvog reda, koje ne uzimaju u obzir geometrijsku nelinearnost, pri deformisanju, normale na srednju površ laminatne ploče, moguće je otkloniti uvođenjem smicajnih deformacionih teorija višeg reda. U ovoj disertaciji detaljno su opisane deformacione teorije zasnovane na funkcijama oblika, kao i polinomne deformacione teorije drugog i trećeg reda. Na osnovu pretpostavljenih oblika pomeranja izvedene su komponente vektora deformacije i urađena makromehanička analiza laminata uz definisanja matrica koje nastaju kao rezultat slaganja slojeva u laminatu. Prikazane su osnove varijacionog računa koji se koristi za dobijanje statičkih jednačina ravnoteže i dinamičkih jednačina kretanja. Razrađeni su najbitniji varijacioni principi koji se koriste u pomenute svrhe. Razrađene su analitičke metode za proučavanje statičkih problema savijanja i izvijanja slobodno oslonjenih laminatnih ploča uz primenu smicajnih deformacionih teorija višeg reda. Takođe su razrađeni postupci za proučavanje modova slobodnog oscilovanja laminatnih ploča. Implementiran je nov postupak za analizu slobodnih vibracija ukrštenih i umreženih simetričnih i antisimetričnih laminatnih ploča. Uveden je i nov postupak za određivanje slobodnih vibracija umreženih antisimetričnih laminata uz primenu proizvoljne smicajne deformacione teorije trećeg reda. Analizirana je propagacija elastičnih talasa u kompozitnim laminatima. Pažnja je usresređena na Lambove talase. Problemi propagacije su posmatrani sa aspekta 3D elastične teorije, kao i sa aspekta primene deformacionih teorija višeg reda. Prikazan, In macro mechanical linear-elastic analysis of composite laminates‚ it is possible to use two adopted theoretical approaches: stress continuity approach and the principle of strain continuity. This thesis primarily develops the process of strain continuity based laminate analysis. With this aim higher-order shear deformation theories are developed. The disadvantages of the classical plate theory and the first-order shear deformation theory, which do not take into consideration geometric non-linearity of the line normal to the middle plane of a laminate plate upon deformations, can be eliminated by introducing higher-order shear deformation theories. The present thesis presents in details deformation theories based on shape functions as well as second and third order polynomial deformation theories. Based on the assumed displacement fields, components of deformation vector are derived and macro mechanical analysis of laminates is done defining the matrices which occur as a result of stacking of plies in a laminate. Moreover, the basics of variation calculations are presented, which is used for obtaining static equations of equilibrium and dynamic equations of movement. The thesis develops the most important variation principles that are used for these purposes. Analytical methods are developed for examining bending and buckling static problems of simply supported laminate plates using higher-order shear deformation theories. The thesis also elaborates the models of examining the modes of laminate plate free vibrations. A new approach is implemented for analysing free vibrations of cross-ply and angle-ply symmetric and antisymmetric laminate plates. Moreover a new approach is introduced for determining free vibrations of angle-ply anti-symmetric laminates applying any third-order shear deformation theory. The propagation of elastic waves in composite laminates is analysed with the focus on Lamb's waves. Propagation problems are considered from the aspect of 3D elastic

Kardiovaskularni sistem je jedan od najvažnijih sistema u ljudskom organizmu. Istraživanja strujanja krvi su klinički veoma značajna zbog mogućnosti poboljšane dijagnostike bolesti, planiranja odgovarajućih preventivnih mera, analize transporta lekova itd. Ove pojave se teško eksperimentalno ispituju i zbog toga u ovoj oblasti numeričke simulacije mogu da doprinesu dobijanju mnogo novih i korisnih informacija. U okviru ovog rada predstavljen je kompletan numerički model koji uspešno simulira trodimenzionalno strujanje krvi kroz krvne sudove u ljudskom organizmu. Ovo je pokazano na nekoliko primera, gde je modelirano strujanje krvi kroz ljudsku aortu, karotidnu i koronarnu arteriju. Takođe, predstavljen je numerički model koji simulira kretanje crvenih krvnih zrnaca i sfernih čestica kroz kompleksne geometrijske domene, kao što su mali krvni sudovi sa stenozom, bifurkacijom, kao i kroz mikrofluidne čipove za separaciju kancer ćelija, ali i kroz realne domene dobijene eksperimentalnim snimanjem protoka krvi kroz posebnu vrstu ribe, tzv. zebra ribu. S obzirom da jedan ovakav softver za naučne simulacije zahteva mnogo računarskih resursa i da izvršavanje jedne simulacije traje dosta dugo, prilikom implementacije numeričke metode posebna pažnja posvećena je tehnikama paralelizacije. Kompjuterski program je razvijan tako da pored rada na standardnim PC računarima, može da se izvršava i na kompjuterskim klasterima sa velikim brojem procesora, kao što su Tesla superkompjuteri, koje proizvodi svetska kompanija NVIDIA. Postignuta su značajna ubrzanja razvijenog softvera, tako da se numeričke simulacije mogu izvršavati za samo nekoliko minuta, naspram par sati koliko je potrebno za izvršavanje iste simulacije na standardnom PC računaru, što omogućava praktično interaktivno praćenje kretanja deformabilnih tela u realnom vremenu. Zbog numeričke metode koja dosta realno oslikava uslove u ljudskom organizmu, velike tačnosti koja je pokazana kroz poređenje sa eksperimentalnim rezul, Cardiovascular system is one of the most important systems in human organism. Investigation of blood flow is clinically very relevant due to the possibility of improved diagnostic of diseases, planning of appropriate preventive measures, analisys of drug transport etc. Experimental investigation of these phenomena is difficult and therefore numerical simulation can contribute to the acquisition of manu new and useful information. Within this dissertation a complete numerical model is presented, that is capable of simulating three-dimensional blood flow through the blood vessels in human organism. This is demonstrated on several examples, where blood flow through human aorta, carotid and coronary arteries is modelled. Also, numerical model that simulates solid-fluid interaction is presented and this model is used to simulate motion of red blood cells and spherical particles through complex geometric domains, such as small blood vessels with stenosis and bifurcation, as well as microfluidic chips for cancer cell separation and real domains obtained by experimental recording of blood flow through a specific type of fish, so called zebrafish. This type of software for numerical simulation requires a lot of computer resources and the execution of one simulation lasts quite long. Therefore, during the implementation of the numerical method, special attention was dedicated to parallelisation techniques. The software was developed such that beside execution on standarad PC computer, it is possible to execute the program on computer clusters with large number of processors, such as Tesla supercomputers, that are manufactured by the world known company NVIDIA. Significant speed-ups were obtained and numerical simulation can now be executed in several minutes, instead of several hours, which was the case when the same simulation was executed on standard PC computer. This enables interactive tracking of motion of deformable bodies in real time. Due to the numerical method that

U ovoj doktorskoj disertaciji zavarena konstrukcija je posmatrana kao složen sistem elemenata sa kompleksnim interakcijama koji su heterogeni iz aspekta materijala, oblika i dimenzija, mehaničkih karakteristika, kao i eksploatacionih i funkcionalnih uslova. Heterogenost elemenata zavarene konstrukcije uslovljava njihove različite karakteristike i odgovore na opterećenje, dok nehomogenost njihove mikrostrukture uslovljava i dodatno usložnjava naponsko-deformaciono stanje. Specifičnosti projektovanja zavarenih mašinskih konstrukcija sagledane su iz aspekta složenosti oblika, materijala, koncentracije napona i temperature eksploatacije. Eksperimentalno određivanje mehaničkih karakteristika i analiza ponašanja u eksploatacionim uslovima, na sobnoj i povišenim temperaturama, izvedena je na modelima od mikrolegiranog čelika povišene jačine. Ispitivani modeli pored zone zavarenog spoja sadrže i zonu geometrijskog diskontinuiteta kao dodatni izvor koncentracije napona što je čest slučaj kod elemenata zavarenih konstrukcija. Skup faktora koji uslovljavaju projektovanje zavarenih konstrukcija identifikovan je sveobuhvatnom analizom eksperimentalnih rezultata i verifikovan je teorijskim razmatranjem naponsko-deformacionog stanja koje nastaje kod razmatranih modela. Posebna pažnja je posvećena analizi mehaničkih osobina i karakteristika mikrolegiranih čelika povišene jačine za izradu veoma odgovornih zavarenih mašinskih konstrukcija, kao savremenog materijala, čija upotreba omogućava ostvarivanje niza prednosti, ali sa sobom donosi i specifične probleme koji moraju biti adekvatno rešeni tokom procesa projektovanja ovih konstrukcija. Identifikovanjem faktora koji određuju konstrukciono rešenje zavarenih mašinskih konstrukcija i utvrđivanjem njihovog uticaja date su preporuke kojima se utemeljuje racionalno korišćenje materijala i energije, ostvaruje smanjenje ukupnih troškova uz prihvatljive ekološke efekte i istovremeno unapređuje sigurnost i pouzdanost zavarenih mašinskih kons, In this dissertation welded constructions are analyzed as complex systems of elements with complex mechanisms of interactions that are heterogeneous from the aspects of materials, shape and dimensions, mechanical properties, so as exploitation and functional conditions. Heterogeneity of elements of welded constructions cause their different characteristics and their different response to load, while inhomogeneity of their microstructure cause complex stress-strain state so as additional complication of this state. The specific characteristics of welded constructions design are highlighted from the aspect of shape complexity, material, stress concentrations and exploitation temperature. Experimental determination of mechanical properties and analysis of mechanical response to load during exploitation at room and elevated temperatures were done at models made of low alloyed high strength steel. Tested models besides zone of welded joint have zone of geometrical discontinuities as additional source of stress concentration that is common case at elements of welded mechanical constructions. Set of parameters that influent to design of welded constructions is identificated by analysis of experimental results and verified by theoretical considerations of stress-strain state at tested models. Special focus is put on analysis of characteristics and mechanical properties of low alloyed high strength steels for welded mechanical constructions as present material with usage that obtain number of advances, but also bring some specific problems that must be solved during process of design of those constructions. By identification of factors that influent to constructional solution of welded construction and determination of their influence, recommendations are given to establish rational usage of material and energy, obtained reduction of total costs with minimal ecological impact and with simultaneous improve of safety and reliability of welded constructions.

Shape memory alloys (SMA) have wider and more frequent application in cases when it is useful to employ their advantages through specific behavior (pseudoelasticity and shape memory effect) in various conditions. As a side effect due to the high thermosensitivity, strong thermomechanical coupling occurs what increases the need for simulation of complex thermomechanical response in realistic problems. The complex stress states and deformation range impose the requirements for accurate analysis of large strain problems. The presented requirements are solved in several steps: (1) Phenomenological constitutive SMA model (Lagoudas) has been reformulated by derivation of variables to depend on effective values of stress and strain and martensitic volume fraction. Gibbs free energy is reduced to scalar form what provides stress integration in the direction of deviatoric stress for forward transformation or total transformation strain for the reverse transformation. (2) Simulation of SMA thermomechanical behavior is realized using partitioned approach by coupling of programs for structural analysis - PAK-S and heat transfer PAK-T. Dissipative energy of martensitic phase transformation imposes change of the material temperature as an internal heat source. As a communication interface between the PAK-S and PAK-T, Component Template Library (CTL) is used. (3) Extension to the large strain problems is based on multiplicative decomposition of the deformation gradient to decompose deformation on elastic and inelastic part. Using the energy conjugated stress and strain measures, easy extension of the algorithm for small strain is provided to solve complex stress states for large strains. (4) Experimental investigation of TiNi SMA samples under various loading rates is used for verification of thermo-mechanical coupling. Numerical simulation of initiation, development and saturation of the martensitic phase transformation under various loading rates is compared to experimental resu