AbstractThe welding of block joints in shipbuilding often requires much effort as the fabrication without
margins sometimes leads to large gaps between them. The high constraint during the welding
process can lead to unfavourable high residual stresses. For this reason, a project was
undertaken to investigate whether butt joints welded with larger gaps fulfill the requirements. The
objective was to determine the sufficient strength of welds performed with gaps of up to 30 mm.
For this purpose, butt joints of 250 mm-wide and 15 mm-thick plates made of mild and highertensile
steel, welded with different gaps, were investigated with respect to their fracture
toughness and fatigue strength. Welding was performed under definite, elastic restraints
corresponding to the stiffness of the surrounding ship structure. Apart from the width of the gap,
further parameters were varied including the welding method (string-bead, weaving technique).
From the fracture mechanics point of view, no objections exist regarding the large gap of 30 mm
welded by weaving. The specimens welded with the string-bead technique achieved relatively
low, partly uniform critical fracture toughness values. The fatigue tests confirm the results of
FITNET. Despite a small decrease of fatigue strength, the weaving technique agrees with the
existing fatigue class. The string-bead technique results in a fatigue class which is consistent with
the nominal stress approach. However, the local approaches result in non-conservative fatigue
assessments and therefore do not fulfill the requirements. Generally, fatigue as well as fracture
investigations indicated a clear influence of welding technique on the fatigue and fracture strength
of a weld.