Investigations in order to characterise the behaviour of defects in castings subjected to creep stress, fatigue stress and creeping fatigue stress

The so far obtained results have shown that, despite of the complicated geometry of the defects, the simple approaches of the fracture mechanics are sufficient to describe the behaviour of the defects (open and partly healed thermal cracks) with respect to the crack initiation subjected to long period stress in a conservative way and in conjunction with the results of the optimised US test technique. A comparison with creeping crack experiments at fracture mechanics specimen revealed, that these results can be used for the evaluation of the defect behaviour. However, the results of the investigations with practice-orientated small tensions and long test period must still be evaluated. Regarding the behaviour of the defects in the 1% CrMoV steel cast subjected to pulsating tensile stresses, especially of open and partly healed thermal cracks the results revealed, that the applied methods of the test technique and the mechanical fracturing description are appropriate to depict the behaviour of cast defects in the fatigue range. Further information is expected from the supporting finite-element calculations of the time-dependent deformation behaviour and from an instability analysis at the idealised geometry of defects. (orig.)