The purpose of this project was to investigate why welded T-joints of different materials from previous projects showed a tendency to fracture in the last welded side in LCF. The investigation consists of experimental, numerical and theoretical analyses of the governing physical effects related to fracture in the T-joints. The experimental analysis includes measurement of local difference in mechanical properties, residual stresses and flaw size from side-to-side. The measurement results are compared with theory and a finite element model, which simulates residual stress formation and cyclic relaxation phenomena.
It has been found that the residual stresses in mild steel specimens generally are about 50-60 [MPa] larger in the last welded side and are relaxed after a few loading cycles in most tests. The hardness is found to be slightly lower in the last welded side of the specimens. Flaws in the last welded side are more frequent and larger. These effects contribute to more material damage in the last welded side, which generally amplifies the crack growth. Therefore it is concluded that the failure side tendency is a combined effect of the governing parameters investigated.