Compatibility of fracture mechanics parameters and fatigue crack growth parameters in welded joint behaviour evaluation

Problem određivanja žilavosti loma, KIc, na vrhu pukotine lokalizirane u zavarenom spoju postavlja se načelno, zbog toga što mehanika loma pretpostavlja homogen materijal, ne samo u okolini vrha pukotine već i na udaljenosti od njega, kako bi ostale u važnosti teorijske pretpostavke i značenje žilavosti loma kao svojstva izmjerene nekom od metoda mehanike loma. Zavareni spoj predstavlja nehomogenost po mikrostrukturi i mehaničkim svojstvima, često po geometrijskom obliku, a također i po polju naprezanja, na koje utječu razni faktori kao i zaostala naprezanja nakon zavarivanja. Sigurnost zavarenih spojeva pri djelovanju promjenjivog opterećenja je u današnje vrijeme dominantna tema svih ozbiljnijih istraživača u ovom području ispitivanja, tako da je dio istraživanja u okviru ovog rada usmjeren i na analizu utjecaja promjenjivog opterećenja na ponašanje zavarenog spoja u prisustvu greške tipa pukotine, odnosno određivanje parametara rasta zamorne pukotine.Problem of fracture toughness, KIc, determination on a crack tip localized in a welded joint is set in principle, since fracture mechanics presumes homogeneous material, not only in a crack tip surrounding but on a distance from it, in order to maintain valid the theoretical presumptions and the meaning of the fracture toughness as a property measured by some of the fracture mechanics methods. Welded joint represents the non-homogeneity by its microstructure and mechanical properties, often by geometrical form, and by stress field as well, which are affected by different factors as well as residual stress after welding. Safety of a welded joint submitted to a variable load is a dominant topic of all serious researches in this area nowadays, thus a part of research in this paper is aimed at the analysis of variable load influence on a welded joint behaviour in the presence of a crack type defect, or in other words to the determination of the fatigue crack growth parameters