The influence of internal defects on the fatigue behaviour of cast and welded steels

Abstract
Very often internal defects in components can not be avoided during production. In this case their influence on the fatigue behaviour has to be taken into account. According to the present state of the art the internal defects are treated as cracks, that are propagating continuously during cyclic loading. From this assumption crack propagation life can be calculated with sufficient accuracy. In order to exclude an unexpected early failure of the critical part, additional security inspections during service have to be foreseen. On the other hand, crack initiation life, which represents a major part of the total service life, is totaly neglected in this case. For that reason a method to assess the influence of internal defects on fatigue life to crack initiation was developed. The accuracy of the new calculation procedure was proved by constant amplitude fatigue tests on several cast and welded steels with ferritic and austentic microstructure containing a various range of internal defec ts.