Elastic-plastic behavior of high strength steel welded joint under static and dynamic loading
Elastoplastično ponašanje zavarenog spoja čelika visoke čvrstoće pri delovanju statičkog i dinamičkog opterećenja
Doktorand
Hemer, Abubkr Mohamed Abdulhamid AbdulahMentor
Milović, LjubicaČlanovi komisije
Putić, SlavišaGrbović, Aleksandar
Metapodaci
Prikaz svih podataka o disertacijiSažetak
Welding is one of the most common process in industrial or production engineering practice for
components joining. Its main advantages are high speed in manufacturing combined with low costs
and, usually, a high degree of flexibility, integrity and reliability. Nevertheless, welding is a highly
complex metallurgical process and, therefore, weldments are susceptible to cracking, flaws and
residual stresses which may lead to structural failure and life time reduction.
Welded structures have wide range of applications in many industries. Steel grade DIN
15NiMoCrB4-5, which is a low-carbon microalloyed steel alloyed with Nickel and Molybdenum,
which is used in line pipes for transporting oil and natural gas has been investigated. Its yield stress
is 668 MPa and the UTS are close to 820 MPa. Catastrophic structure failure made of this steel grade
due to fatigue is reported to cause sudden damage and loss to human-lives, as well as property. Hence,
from end application point of view, knowled...ge on fracture toughness is of immense importance.
Several tests were conducted on the welded joints. Fracture mechanics toughness testes using three
point bending specimens were done. Obtained results of the applied force and CMOD were processed
in order to determine the value of KIC, CTOD or J-integral.
The pre-crack was created using fatigue and the crack propagation was measured using the unloading
compliance method. Calculation of critical values ��� are compared with the values obtained by using
FEM. The FEM model was defined on the basis of experimental condition in program Ansys.
The goal of this research was to determine effect of welded joint geometry (different zone sizes) and
crack location on fatigue life. First welded joints were made using the MIG procedure and
investigated in terms of mechanical and fatigue properties. The focus of this study was on
experimental and numerical analysis, with special focus on the heat-affected zone.
Zavarivanje je jedan od najčešćih procesa spajanja komponenata u industrijskoj ili proizvodnoj
praksi. Njegove glavne prednosti su brzina izrade kombinovana sa niskom cenom i obično sa visokim
stepenom fleksibilnosti, integriteta i pouzdanosti. Bez odzira na to, zavarivanje je izuzetno složen
metalurški postupak i prema tome, zavareni spojevi su osetljivi na stvaranje prslina, grešaka i zaostale
napone, što može dovesti do otkaza konstrukcije i skraćenja veka.
Zavarene konstrukcije imaju široku primenu u mnogim granama industrije. U ovom radu je ispitan
čelik 15NiMoCrB4-5 čvrstoće popuštanja 668 MPa i zatezne čvrstoće blizu 820 MPa. Ovaj materijal
je niskougljenični mikrolegirani čelik legiran niklom i molibdenom, koji se koristi za izradu cevovoda
za transport nafte i prirodnog gasa. U takvoj primeni, katastrofalni lom izazvan zamorom uzrokuje
iznenadna oštećenja imovine i pogibiju ljudi. Stoga je, sa stanovišta krajnje primene, poznavanje
žilavosti loma od ogromne važnosti.
Urađena s...u eksperimentalna ispitivanja na zavarenim spojevima. Od ispitivanja mehanike loma
urađeno je ispitivanje žilavosti loma na epruvetama za savijanje u tri tačke. Obrađeni su rezultati
izmerene primenjene sile i CMOD da bi se utvrdila vrednost KIC, CTOD ili J-integrala.
Stvaranje zamorne prsline i propagacija prsline su merene metodom popuštanja. Izračunate kritične
vrednosti, JIC, su upoređene sa vrednostima dobijenim pomoću MKE. Model MKE je definisan na
bazi eksperimentalnih uslova u programu Ansys.
Cilj ovog istraživanja je bio da se utvrdi uticaj geometrije zavarenih spojeva (različite veličine zona)
i položaja prsline na zamorni vek. Najpre su zavareni spojevi napravljeni MIG postupkom i ispitani
su u pogledu mehaničkih osobina i osobina zamora. Fokus izučavanja je bio na eksperimentalnoj i
numeričkoj analizi, sa posebnim osvrtom na zonu pod uticajem toplote.