ELASTIC-PLASTIC STRAIN DISTRIBUTIONS AT FILLET WELDS

Steel plates 25 mn thick were fillet-welded to 50 mm thick plates acco rding to good offshore welding practice. The thinner plates were incli ned at 90 degrees or 60 degrees to the thicker ones to represent, at f ull size, the crown or saddle positions of a structural tubular T join t. Slices 4 mm or 10 mm thick were cut from these weldments and the el astic, elastic-plastic and residual plastic strains in the surfaces of these sections were measured using photoelastic coatings and moire in terferometry. The slices were loaded by tensile forces on the 25 mm wi de parts, reacted at pin joints near the ends of the 50 mm wide part. The positions and directions of loading were arranged to load the weld s in the same way as in a tubular T joint; loaded in tension. Yielding initiated at the weld toes and could be clearly identified in the moi re fringe patterns. It progressed into the plates, being inhibited by the heat-affected zone. Maximum plastic strains also occurred at the w eld toes. Measurements of residual plastic strains showed that the act ual strain range, which 'drives' fatigue failure, differs from predict ions based on elastic analyses. Post-weld heat treatment is beneficial , but extending the weld along the plate reduces the strain concentrat ions much more.