Critical distance approach for the fatigue strength assessment of magnesium welded joints in contrast to Neuber's effective stress method

In the present paper, the critical distance method was used to evaluate the fatigue behaviour of magnesium welded joints. The main objective of the study was to determine the applicability of the critical distance method and to compare the findings with Neuber's stress averaging method. To realise this objective, experimental data, determined for three different weld geometries under three different stress ratios, were evaluated. Stress distributions of each specimen geometry, i.e. full penetrated butt weld, incomplete penetrated butt weld and transversal stiffener, were acquired by finite element analyses and were used to calculate effective stresses. The critical distance a is a material constant, which is independent of the used notch radius rref. For its determination, an identification process was used where the scatter of the resulting S-N line of effective stress is minimised. The critical distance a=0.06 mm was determined versus the microstructural length r∗=0.12 mm.