FATIGUE BEHAVIOR OF WELDED-JOINTS UNDER C OMBINED IN-OF-PHASE AND OUT-OF-PHASE MULTIAXIAL LOADING

Welded crucifix-type specimens from fine grained steel StE 290 and fla nge-tube as well as tube-tube joints from fine grained steel StE 460 w ith unmachined and machined welds were investigated under biaxial cons tant amplitude loading in the range of 10(3) to 5 . 10(6) cycles to cr ack initiation and break-through, respectively. In order not to interf ere with residual stresses they were relieved by a heat treatment. In- phase loading can be treated fairly well using the conventional hypoth eses (von Mises or Tresca) on basis of nominal, structural or local st rains or stresses. But the influence of out-of-phase loading on fatigu e life is severely overestimated if conventional hypotheses are used. However, the introduced hypothesis of the effective equivalent stress leads to fairly well predictions. Herefore, the knowledge of local str ains or stresses is necessary. They are determined by boundary-element e analyses in dependency of weld geometry. This hypothesis considers t he influence of out-of-phase loading by taking into account the intera ction of local shear stresses acting in different surface planes of th e material. Further, size effects resulting from weld geometry and loa ding mode were included.