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Predmet ove doktorske disertacije je istraživanje ponašanja zavarenih konstrukcija sa smanjenim stepenom sigurnosti prema krtom lomu i otpornost na prsline u cilju ocene njenog integriteta i veka. U tom slučaju posebna pažnja se posvećuje mestima koncentracije napona, jer se krti lomovi ovih konstrukcija po pravilu događaju upravo na takvim mestima. Radi detaljnog proučavanja nakstanka i rasta prsline, neophodna je primena principa mehanike loma, jer klasični pristup konstruisanju (projektovanju) preko faktora koncentracije napona i čvrstoće u tom slučaju nije dovoljan. Primenom parametra mehanike loma, kao što je faktor inteziteta napona, čiji opseg definiše brzinu rasta prline, a čija kritična veličina (žilavost loma) određuje kritičnu dužinu prsline. Time se obezbeđuje pouzdana procena integriteta konstrukcije (ako se dokaže da je faktor intenziteta napona manji od žilavosti loma), odnosno procena veka konstrukcije (primenom zakona mehanike loma na izračuvavanje krritičnih parametara za poznatu ili pretpostavljenu početnu dužinu prsline, njenu kritičnu vrednost, kao i izračunati opseg faktora intenzitata napona). Konzervativni pristup u svim koracima ove procedure obezbeđuje pouzdanu eksploataciju konstrukcije sa smanjenim stepenom sigurnosti., The subject of this doctoral dissertation is the research of the behavior of welded structures with a reduced degree of safety on brittle fracture and crack resistance in order to assess its integrity and age. In this case, special attention is paid to the stress concentration points, since the fractures of these structures tend to occur exactly in such places. For the detailed study of the crack and growth of the crack, it is necessary to apply the principle of fracture mechanics, since the classical approach to design (design) through the factor of stress concentration and strength is not sufficient in that case. Using the fracture mechanics parameter, such as the voltage intensity factor, whose range defines the rate of crack growth, and whose critical size (fracture toughness) determines the critical crack length. This ensures a reliable assessment of the integrity of the structure (if it is proven that the stress intensity factor is less than the tensile strength of the fracture), or the assessment of the century of construction (by applying laws of fracture mechanics to calculate critical parameters for known or assumed initial crack length, its critical value, as well as calculate the range voltage intensities factor). A conservative approach in all steps of this procedure ensures reliable exploitation of a structure with a reduced degree of safety

Na deponiji uglja termoelektrane "Nikola Tesla A" u Obrenovcu (Srbija), rade dva rotorna bagera interne oznake DU1 i DU2, koji su proizved francuske fabrike "Ameco" i kreću se po kružnoj stazi (tzv. polarna staza), uz napomenu da u Istočnoj Evropi rade samo tri bagera tog tipa. Treći rotorni bager istog proizvođača radi na deponiji uglja termoelektrane "Nikola Tesla B" u Obrenovcu. U radu je prikazana analiza stanja vitalne čelične konstrukcije kabine rukovaoca rotornog bagera DU 2, izrađene od cevi različitih prečnika i debljina lima, nakon havarije izazvane udarom kamena u poprečni nosač konstrukcije. Kamen se nalazio u otkopanom uglju jedne od kašika rotora bagera. Prilikom udara kamena poprečni nosač konstrukcije kabine rukovaoca se savio i popucali su zavareni spojevi između prirubnica na sredini poprečnog nosača i zavareni spojevi na mestima veze poprečnog nosača sa vertikalnim nosačima konstrukcije. S obzirom da korisnik bagera ne poseduje projektnu i tehničku dokumentaciju sanacija oštećenja sprovedena je pod predpostavkom da je rešetkasta konstrukcija kabine rukovaoca bagera izrađena od konstrukcijskih čelika, koji se uglavnom primenjuju za izradu rotornih bagera. Na osnovu analiza stanja nakon privremene sanacije oštećenja došlo se do zaključka da je za trajno obezbeđenje integriteta noseće čelične konstrukcije kabine rukovaoca rotornog bagera du2 kao celine potrebno izvršiti zamenu oštećenog poprečnog noseća čelične konstrukcije., There are 2 bucket -wheel reclaimers, internally labelled as DU1 and DU2, made by French manufacturer 'Ameco', that operate at the open pit surface mine which belongs to the thermal power plant 'Nikola Tesla A' in Obrenovac. They are moving along the polar path and it should be noted that there are only 3 reclaimers of that kind in Eastern Europe. The third bucketwheel reclaimer, made by the same manufacturer, operates at the open pit surface mine that belongs to the thermal power plant 'Nikola Tesla B' in Obrenovac. In this paper the state analysis of the vital steel structure of the bucket-wheel reclaimer DU2 operators' cabin, made of pipes of various diameters and thicknesses, after the breakdown caused by a rock that hit the horizontal support of the structure is presented. The rock was located in the excavated coal within a bucket of the bucket-wheel reclaimer. The horizontal support of the operators' cabin structure has Bent and welded joints between flanges at the middle of the horizontal support, as well as welded joints at bonds of the horizontal support with vertical supports of the structure, have cracked due to the impact of the rock. Taking into account the fact that the user of the bucket-wheel reclaimer does not own the design and technical documentation, damage repair was carried out under the assumption that the lattice structure of the operators' cabin was made of structural steels, which are mostly being used for the manufacture of bucket-wheel reclaimers. On the basis of state analysis after the temporary repair of damages the conclusion arose that for the permanent provision of integrity of the support steel structure of the bucket-wheel reclaimer DU-2 operators' cabin as a whole it is necessary to replace the damaged horizontal support.

U ovom radu su prikazani inicijacija i rast prsline u T spoju ploče od aluminijumske legure AA2024 –T351, zavarenom mešanjem trenjem (Friction Stir Welding - FSW), primenom mehanike loma. Svi analizirani modeli su napravljeni od legure 2024-A351. Osobine materijala i dimenzije u oblasti FSW spoja su usvojene na osnovu dostupnih eksperimenata..., In this present work, application of fracture mechanics is used to present a fatigue crack initiation and growth of friction stir welded (FSW) T joint plate made of aluminum alloy AA2024 –T351. All analyzed models are made from aluminum alloy 2024-T351.The properties of materials in the areas of joints and geometry measures of FSW joint are adopted from available experiments...

In this present work, application of fracture mechanics is used to present a fatigue crack initiation and growth of friction stir welded (FSW) T joint plate made of aluminum alloy AA2024 –T351. All analyzed models are made from aluminum alloy 2024-T351.The properties of materials in the areas of joints and geometry measures of FSW joint are adopted from available experiments. The effect of crack growth on fatigue life of unstiffened and stiffened structures is considered by using the numerical method based on finite elements - extended Finite Element Method (XFEM). ABAQUS software and Morfeo are used to display the results of the growth of cracks in welded T joint plates of FSW in all regions. Three point – bending load is applied, with stress intensity ratio R = 0. Tension fatigue load is also applied with different stress ratio of R = (0.5, 0, and -1) All analyzed models are made from aluminum alloy 2024-T351. Material properties in joints zones and geometry mesures of FSW joint are adopted from available experiments. Following examples are analyzed: - Example 1 Finite element modelling of butt welded joint under static pure Three - Point Bending Load - Example 2 Finite element modelling of T welded joint under static pure Three - Point Bending Load - Effect of stiffeners on fatigue crack propagation of welded plate - Example 1 Finite element modelling of butt welded joint under static tensile loading - Example 2 Finite element modelling of T welded joint under static tensile loading - Example 3 Finite element modelling of double T welded joint under static tensile loading - Effect of stress ratio on fatigue crack propagation of double T welded joint plate under static tensile loading - Example 1 Stress ratio of 0.5 - Example 2 Stress ratio of 0 - Example 3 Stress ratio of -1 - Experimental Validation of Numerical Results of friction stir welded T-joints Following results are obtain - Numerical computations: - Points coordinates of crack front x, y, z for every pr, U ovom radu su prikazani inicijacija i rast prsline u T spoju ploče od aluminijumske legure AA2024 –T351, zavarenom mešanjem trenjem (Friction Stir Welding - FSW), primenom mehanike loma. Svi analizirani modeli su napravljeni od legure 2024-A351. Osobine materijala i dimenzije u oblasti FSW spoja su usvojene na osnovu dostupnih eksperimenata. Uticaj rasta prsline na zamorni vek neukrućenih i ukrućenih konstrukcija je razmatran primenom numeričkih metoda zasnovanih na analizi konačnim elementima – proširenoj metodi konačnih elemenata (PMKE). Korišćeni su softverski paketi ABAQUS i Morfeo za prikaz rezultata rasta prsline u svim oblastima T spojevia ploča zavarenih mešanjem trenjem. Urađeno je ispitivanje savijanja u tri tačke, sa odnosom napona R = 0. Takođe je zadato i zatezno zamorno opterećenje za različite odnose napona (0.5, 0 i -1). Svi analizirani modeli su napravljeni od legure 2024-A351. Osobine materijala i dimenzije u oblasti FSW spoja su usvojene na osnovu dostupnih eksperimenata. Analizirani su sledeći primeri: - Primer 1 Modeliranje konačnim elementima sučeonog zavarenog spoja pod čistim statičkim savijanjem u tri tačke - Primer 2 Modeliranje konačnim elementima T zavarenog spoja pod čistim statičkkim savijanjem u tri tačke - Uticaji ukrućenja na napredovanje zamorne prsline zavarene ploče - Primer 1 Modeliranje konačnim elementima sučeonog spoja pod statičkim zateznim opterećenjem - Primer 2 Modeliranje konačnim elementima T zavarenog spoja pod statičkim zateznim opterećenjem - Primer 3 Modeliranje konačnim elementima dvostrukog T spoja pod statićkim zateznim opterećenjem - Uticaj odnosa napona na napredovanje zamorne prsline u dvostrukom T zavarenom spoju pod statičkim zateznim opterećenjem - Primer 1 Odnos napona 0.5 - Primer 2 Odnos napona 0 - Primer 3 Odnos napona -1 - Eksperimentalna verifikacija numeričkih rezultata dobijenih za T spojeve zavarene mešanjem trenjem Dobijeni su sledeći rezultati - Numerički proračuni: - Koordinate x, y i z za vrh p

U radu je na primeru loma i oštećenja sučeono zavarenih spojeva na konstrukciji strele (katarke) bagera dreglajna EŠ 5/45 dat metodološki pristup za analizu uzroka otkaza i saniranje oštećenja. Dati pristup se može primeniti za različite tipove bagera kašikara, a njegova primena u preventivnom održavanju bi doprinela produženju radnog veka bagera., The example of break and failures of welded joints of a structure of the arrow at dredger line ES 4/45 and methodological access for analysis faults causes and sanitation failures are presented in this paper. That access may be adapted for other types of spoonful dredger. Application of this methodology in servicing could contribute prolongation of dredger work life.

Iskustvo iz eksploatacije cevovoda hidroelektrana ukazuje na moguće procurivanje posle stabilnog rasta prsline ili raspucavanje u slučaju krtog loma. Uvođenje zavarljivih čelika visoke čvrstoće za izradu cevovoda donosi značajne uštede, ali se zahteva otpornost prema prslinama, naročito prema krtom lomu, osnovnog metala, metala šava i zone uticaja toplote. Za cevovod hidroelektrane "Bajina Bašta" je korišćen zavarljiv čelik visoke čvrstoće (do 700 MPa nazivnog napona tečenja), pa je investitor tražio dokaze o njegovoj otpornosti prema prslinama i krtom lomu. Prikazani su rezultati ispitivanja modela cevovoda i zavarenih spojeva, kojima je dokazana zadovoljavajuća zavarljivost čelika sa metalom šava niže čvrstoće (andermečing) i otpornost prema prslinama i krtom lomu., Experience from service of hydro electrical power plant indicates the possible leakage after stable crack growth or bursting in the case of brittle fracture. Introduction of wield able high strength steels for production of penstock brings important savings, but crack resistance especially to brittle fracture, of parent metal, weld metal and the heat-affected-zone is required. For the penstock of "Bajina Bašta" hydro electrical power plant weld able high strength steel is applied (up to 700 MPa nominal yield strength) and investor requested the proof for its resistance to cracks and brittle fracture. The results of testing of penstock model and welded joints are presented, which confirmed acceptable weld ability of under matched weld metal (under matched effect) and resistance to cracks and brittle fracture.