Razvoj prsline zavarenih heterogenih spojeva

Abstract

Eksperimentalno analiziranje rasta prsline u pojedinim konstituentima zavarennh spojeva kompleksno legirannh čelika visoke čvrstoće na epruvetama i u realnim konstrukcijama, kao i uticaj rasta prsline na sigurnost zavarenog spoja upravo je cilj ovog rada. Da bi se omoguhilo zavarivanje takvih konstrukcijskih čelika, dodatni materijal za zavarivanje se projektuje tako da metal šava nakon zavarivanja ima nešto manju čvrstoću od osnovnog metala (andermečing efekt). U tako zavarenom spoju do plastičnog tečenja će doći prvo u metalu šava. Tek nakon ojačavanja MŠ do nivoa granice tečenja OM dolazi do ppastičnog deformisanja OM. Cilj ovog rada je da se pokažu numerički modeli, doprinos analizi problema iz referentne oblasti koji se sastoji upravo u mogućnosti da se na brz i relativno jednostavan način razvoja modela koji će na merodavan način predstaviti realno ponašanje epruveta,, u pogledu koncentracije napona i polja deformacijatokom relevantnih opterećenja. Numeričkom analizom moguće je prikazati i širenje prsline, odnosno promena njene dužine u odnosu na inicijalnu vrednost od 2.3 mm. Ovi rezultati se takođe mogu iskoristiti i kao osnova za buduća istraživanja, koja bi mogla da se bave ispitivanjem ponašanja ovakvih epruveta na zamorno opterećenje, s obzirom da su posude pod pritiskom (oblast primene ovakvih materijala) upravo izložene ovakvom opterećenju i najčešće otkazuju usled istog. Dakle, prvo su primenjene metoda konačnih elemenata kao numerička metoda, kao i dve eksperimentalne metode metoda mernih traka i metoda za digitalnu korelaciju slika. Detaljno je sakupljena, proučena i sistematizovana naučna literatura iz oblasti vezana za sve aspekte ove disertacije. Analizirana je razlika u ponašanju zavarenog spoja kao celine i njegovih konstituenata i zatezanjem su ispitane epruvete sa metalom šava manje i veće čvrstoće u odnosu na osnovni metal što je važno i za ocenu otpornosti prema širenju prsline, daje osnovne podatke o ponašanju materijala pri opterećivanju...

The main goal in this research is the experimental crack growth analysis for certain welded joint constituents of complex high strength alloyed steels, concerning both the specimens and real structures, as well as the influence of crack growth on the safety of the welded joint. In order to perform the welding of such structural steels, the welding filler material is designed to obtain a somewhat lower value of the weld metal strength than the strength of the parent metal (PM) (undermatching effect). The onset of plastic flow in this type of welded joint occurs initially in the weld metal (WM). Thus, plastic deformation in the PM does not occur until the deformation hardening of the WM reaches the plasticity limit of the PM. First, the finite element method is applied as a numerical tool, followed by two experimental methods: the strain gauge method, and the digital image correlation method. Literature connected to all the disciplines concerning this research has been collected, studied and systematized in detail. The difference in the welded joint behaviour as a whole and its constituents has been analysed through tension testing of specimens produced with both overmatched and undermatched weld metal, which is important for assessing the crack growth resistance, since it brings major results on the material behaviour of the loaded structure. In the effort to prove this assumption, at first - based on experimental results the numerical simulation is performed by applying ABAQUS software on three-point bending specimen behaviour. The application of the finite element method has proved an acceptable weldability of the undermatched steel weld and the resistance to crack growth and brittle fracture. The possibilities for a fast and relatively simple model development are shown, representing competent realistic specimen behaviour, both concerning stress concentrations and deformation fields in external loading experimental conditions. These models clearly depict the crack propagation. The procedure for experimental analysis is defined, and based on the results obtained, the stresses and plastic deformations have been confirmed to reach the highest levels at locations of acting loads and crack tips, as has been expected...