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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 r ref . 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 ρ ∗ = 0.12 mm.

In this study, the microstructural length of magnesium welded joints was determined by using experimental data acquired from three different weld geometries and Neuber's stress averaging method. The aim was to determine microstructural length, which is assumed to be a material constant that is identical for all Mg-materials, so that it can be employed for effective stress and fictitious notch radius rf calculations. By considering the worst case scenario, rreal = 0, this fictitious notch radius can be used as a new reference radius rref for magnesium welded joints. Using the reference radii from two different hypotheses rref = 1 mm and rref = 0.05 mm, calculations were performed for notches and data were employed in the calculations. Also FE-analyses were utilised in order to identify the stress gradients for weld geometries. Effective stresses were calculated using experimental data along with the stress gradients in Neuber's stress averaging method. Finally, S-N lines were derived by correlating effective stresses with fatigue life for the worst case with R = 0.5 to account for possible high tensile residual stresses. The scatters of these S-N lines were calculated and compared for every ?* iteration. The length value that resulted in the minimum scatter corresponded to the microstructural length. The identified microstructural length was ?* = 0.12 mm. Until now, there were no published results for microstructural length of magnesium welded joints and the findings in this paper can be used to replace the current recommendations regarding magnesium welded joints. © 2016 Elsevier Ltd