Influencing factors on fatigue strength of welded thin plates based on structural stress assessment

Abstract

New lightweight structures in shipbuilding aim at plate thicknesses below 5 mm in combination with welding processes characterised by low heat-input, i.e. laser and laser-hybrid welding. In the European research project BESST—“Breakthrough in European Ship and Ship Building Technologies”, an extensive fatigue test programme was carried out for butt- and fillet-welded specimens, which were manufactured by conventional arc, laser and laser-hybrid welding processes. Plate thicknesses down to 3–4 mm were included. The test programme covered also the different production quality including various levels of misalignments. Utilising the extensive fatigue test results, the present paper aims to identify the factors that influence fatigue strength based on the structural stress approach. Secondary bending stresses due to misalignments are directly considered in the structural stress. Different methods of stress determination are applied, such as the through-thickness linearization, surface stress extrapolation, Haibach’s approach and Xiao and Yamada’s approach. Special attention is given to quality aspects such as undercuts. Based on the results, the suitability of the different structural stress approaches to the fatigue assessment of thin-plated joints in particular are discussed with special consideration of the various welding processes and quality aspects.