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Local approach to ductile fracture of low steel welded joints

dc.contributor.advisorRakin, Marko
dc.contributor.otherSedmak, Aleksandar
dc.contributor.otherGubeljak, Nenad
dc.contributor.otherArsić, Miodrag
dc.contributor.otherManeski, Taško
dc.creatorMeđo, Bojan I.
dc.date.accessioned2016-01-05T12:43:04Z
dc.date.available2016-01-05T12:43:04Z
dc.date.available2020-07-03T09:22:29Z
dc.date.issued2012-12-14
dc.identifier.urihttp://eteze.bg.ac.rs/application/showtheses?thesesId=1209
dc.identifier.urihttp://nardus.mpn.gov.rs/handle/123456789/2949
dc.identifier.urihttps://fedorabg.bg.ac.rs/fedora/get/o:8123/bdef:Content/download
dc.identifier.urihttp://vbs.rs/scripts/cobiss?command=DISPLAY&base=70036&RID=45148687
dc.description.abstractPredmet disertacije je analiza nastanka žilavog loma i stabilnog rasta prsline mehanizmom žilavog loma u niskolegiranom čeliku i zavarenim spojevima primenom lokalnog pristupa. Razmatrani su spojevi koji sadrže jedan ili dva metala šava, od kojih jedan ima manju (undermatch - UM), a drugi veću (overmatch - UM) čvrstoću od osnovnog materijala. Ispitivane su epruvete za savijanje u tri tačke (SENB) sa početnom prslinom u metalu šava kod svih spojeva. Početna prslina kod spojeva sa dva metala šava imala je tri različita položaja: samo u overmatch delu, samo u undermatch delu, ili kroz oba metala šava - po celoj debljini spoja. Takođe, analiziran je razvoj oštećenja u šavnim cevima bez početne prsline, sa koncentratorom napona tipa zareza. Ovakva geometrija je aproksimacija cevovoda oštećenih lokalnom korozijom, čiji integritet se u literaturi po pravilu procenjuje u odnosu na plastični kolaps uz zanemarujivanje loma kao mehanizma otkaza. U ovom radu je razmotren nastanak prsline na dnu žleba kao kriterijum gubitka nosivosti oštećenog dela cevi. Proračuni metodom konačnih elemenata (MKE), koji uključuju primenu lokalnog pristupa (kompletnog Gursonovog modela - CGM) u analizi zavarenih spojeva i cevi sa simuliranim korozionim oštećenjima, su urađeni u programskom paketu Abaqus. Analiziran je uticaj heterogenosti materijala, izazvane različitim zateznim osobinama osnovnog materijala i dva metala šava, na ponašanje spojeva pri lomu. Zbog odgovarajućeg opisivanja oštećenja, određene su mikrostrukturni parametri koji utiču na mehanizam žilavog loma čelika i zavarenih spojeva čelika - sadržaj nemetalnih uključaka i srednji slobodni put između njih. Ispitan je uticaj širine spoja i dužine početne prsline na ponašanje pri lomu. Utvrđeno je da kod OM spojeva povećanje širine spoja dovodi do smanjenja, a kod UM spojeva do povećanja otpornosti prema lomu. Takođe, uočeno je da se razlika u rezultatima dobijena ispitivanjem UM spojeva širine 12 i 18 mm jako mala, i pokazano je da za širine preko 12 mm heterogenost materijala nema većeg uticaja na rast prsline. Imajući u vidu lokalni karakter oštećenja mehanizmom žilavog loma, naročita pažnja je posvećena uticaju mreže konačnih elemenata na otpornost prema lomu. Ispitivanjem spojeva sa jednim metalom šava (OM ili UM) zaključeno je da postoji razlika u veličini elementa koja najbolje opisuje početak rasta i rast prsline. Naime, za OM spojeve ova veličina odgovara srednjem slobodnom putu između nemetalnih uključaka, dok je za UM spojeve ona tri puta veća...sr
dc.description.abstractThe subject of this dissertation is analysis of ductile fracture initiation and stable crack growth by ductile fracture mechanism in low alloyed steel and welded joints. The analysis is conducted using local approach to fracture. Welded joints with one or two weld metals are examined; one of them has lower strength (undermatch - UM) while the other has higher strength in comparison with the base metal (overmatch - OM). Precracked three point bending (SENB) specimens are analysed. In the joints with two weld metals, the pre-crack has three different positions: only in overmatch part, only in udermatch part or through both of them - through thickness dirrection. The damage development is also analysed in the seam pipes, without a pre-crack but with a notchtype stress concentrator. This geometry is aproximation of the pipeline damaged by local corosion; in the literature, integrity of such structures is often assessed based on the plastic collapse, neglecting the fracture as failure mechanism. In this work, fracture initiation at the bottom of the notch is applied as the failure criterion for damaged portion of the pipeline. Finite element calculations, which include the application of local approach (complete Gurson model - CGM) in analysis of welded joints and pipes with simulated corrosion damages, are conducted using the software package Abaqus. The inflence of the material heterogeneity, caused by different tensile properties of the base metal and two weld metals, on the fracture behavior of joints is analysed. For appropriate damage description, microstructural parameters affecting the ductile fracture mechanism in steel and its welded joints are determined - volume fraction of non-metallic inclusions and mean free path between them. The influence of joint width and initial crack length on the fracture behavior is assessed. For OM joints, the increase of the joint width decreases the fracture resistance, while fracture resistance of UM joints grows. It is also shown that the difference in results for UM joints with 12 and 18 mm width is rather small, and the increase of width over 12 mm does not have a significant influence on the crack growth. Bearing in mind the local character of the damage by ductile fracture mechanism, special attention is devoted to the influence of the finite element mesh to the fracture resistance. Testing the joints with one weld metal (OM or UM) revealed a difference in element sizes that result in the most adequate description of the crack growth initiation and stable growth. For OM joints, this size approximates the mean free path between the non-metallic inclusions, while in the case of UM joints element size is three times larger...en
dc.formatapplication/pdf
dc.languagesr
dc.publisherУниверзитет у Београду, Технолошко-металуршки факултетsr
dc.relationinfo:eu-repo/grantAgreement/MESTD/Basic Research (BR or ON)/174004/RS//
dc.rightsopenAccessen
dc.sourceУниверзитет у Београдуsr
dc.subjectLokalni pristupsr
dc.subjectLocal approachen
dc.subjectductile fractureen
dc.subjectwelded jointsen
dc.subjectfinite element methoden
dc.subjectmicromechanical modelsen
dc.subjectfracture mechanicsen
dc.subjectmaterial damageen
dc.subjectžilav lomsr
dc.subjectzavareni spojevisr
dc.subjectmetoda konačnih elemenatasr
dc.subjectmikromehanički modelisr
dc.subjectmehanika lomasr
dc.subjectoštećenje materijalasr
dc.titleLokalni pristup žilavom lomu zavarenih spojeva niskolegiranog čelikasr
dc.titleLocal approach to ductile fracture of low steel welded jointsen
dc.typedoctoralThesisen
dc.rights.licenseBY-NC-ND
dcterms.abstractРакин, Марко; Манески, Ташко; Губељак, Ненад; Aрсић, Миодраг; Седмак, Aлександар; Међо, Бојан И.; Локални приступ жилавом лому заварених спојева нисколегираног челика; Локални приступ жилавом лому заварених спојева нисколегираног челика;
dc.identifier.fulltexthttp://nardus.mpn.gov.rs/bitstream/id/17951/Disertacija.pdf


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