Fatigue Crack Propagation from Fillet Weld Toes

The fatigue crack propagation behavior of two types of fillet welded specimens is investigated and the application of fracture mechanics for the prediction of fatigue life is discussed. Small scale fillet welded stiffener and gusset specimens were tested under constant amplitude stress cycles. The crack propagation behavior is estimated from dye-markings on the fatigue fracture surface. The dye penetrant technique permits a crack depth of as small as 0.1 to 0.2 mm to be visibly marked. Along the fillet weld toes of the stiffener specimens, single or multiple cracks, 0.47 to 0.6 mm deep, could be dye-marked, after about 30% of the fatigue life. Cracks could be marked even earlier in the gusset specimens due to a higher stress concentration. Applying the method of fracture mechanics, the fatigue behavior of these dye-marked specimens are analysed. Measured crack shapes and fillet weld toe geometries are taken into account. The computer fatigue life is in good agreement with the test results.