Study on the effect of weld defects on fatigue life of structures

Abstract

Welding is a type of joining process which is widely used in automobile sectors, power plants, industries, etc. Welded joints in structural elements may contain defects like porosity, lack of penetration, undercut and lack of fusion, which can be treated as a flaw. Cracks may initiate due to high stress concentration from this flaw under cyclic loading conditions and starts growing. Welding standards proposes acceptable level of weld defects as it is practically inevitable to avoid weld defects. This research article focuses on the evaluation of fatigue life of welded structures in the presence of acceptable level of weld defects. The fatigue life of any component depends on many factors which includes the critical crack size that depends on the fracture toughness of the material and stress intensity factor solution. Though several codes are available to predict the fatigue crack growth phenomenon, numerical analysis tools become a comfortable environment in fracture mechanics. Before attempting the evaluation of fatigue life of a pressure vessel, good confidence on the fracture mechanics approach was gained using simple test problem. Then, the numerical analysis of a 3-D pressure vessel with different crack types, cracks in different weld joints, different element sizes is simulated under constant cyclic loading conditions using XFEM in ABAQUS software. The examination gives a basic help to estimate fatigue life of pressurized structures and deciding standard length of the crack which can happen in the pressure vessel, in view of estimations of stress intensity factors (SIF's) assessed in the numerical simulation.