Assessment of stress concentration factors of welded joints based on 2D- and 3D-reverse engineering

Start-stop positions (intermittent welds) are known to cause significant variations in geometry, which can result in high stresses and, consequently, a reduced fatigue life. Based on 3D-Scans intermittent fillet welds specimen were related to different quality levels according to ISO 5817 (B, C and ' D). Experimental fatigue test results showed that no significant differences in fatigue life were determined between specimen with start-stop positions that refer to different quality levels. A reverse engineering approach was used based on the translation of 3D-surface scans (point clouds) into 2D- and 3D-Finite Element Analysis (FEA) for the determination of local stresses. A combination of critical distance and linear elastic fracture mechanic approach was used to cover the effect of surface near variation of weld quality and stress concentrations. In addition, an assessment based on 2D-models and 3D-models was conducted. A local and a global 3D-effect are observed that lead to differences between 2D- and 3D-FEA. The results of 3D-FEA showed that this can be explained by different a/c -ratio during crack propagation and statistical size effects.