The effect of combined mechanical load/welding residual stress on mixed mode fracture parameters of a thin aluminum cracked cylinder

In this paper, the gas tungsten-arc welding (GTAW) process of a thin cylinder made of Al6061-T6 alloy was simulated using 3-D finite element model in the ABAQUS code and the induced distribution of residual stress was obtained. Temperature dependent thermo-mechanical properties were considered for the aluminum alloy and for simulating the heat source of tungsten arc welding; Goldak's double ellipsoid model was employed. The numerical simulation method employed for the GTAW process of investigated aluminum material was validated experimentally using the hole drilling method as well. High residual stresses were found around the weld line and HAZ area which can increase the risk of crack initiation and propagation in this region of welded aluminum cylinder. Hence in the second part of this research, a longitudinal semi-elliptical crack was considered in the wall of aluminum cylinder subjected to combined internal pressure and torsional loads and its mixed mode I/II fracture parameters (i.e. KI, KII and T) were determined numerically along the crack front and for different crack geometries. Finally the influence of obtained residual stress field on the computed fracture parameters was reanalyzed using the coupled residual stress/mechanical loading applied to the cylinder. The residual stress field had no effect on the mode II fracture component but the most influence of this factor was observed for mode I stress intensity factor (KI) and the deepest point of 3D elliptical crack.