A NUMERICAL-SIMULATION OF FATIGUE GROWTH OF MULTIPLE SURFACE INITIALLY SEMICIRCULAR DEFECTS UNDER TENSION

The shape development of a row of five small initially semicircular su rface defects through the thickness of a plate under tension is numeri cally predicted by the step-by-step finite element simulating techniqu e developed by the present authors. Fatigue growth of these cracks dur ing pre-coalescence, coalescence and post-coalescence periods is exami ned in detail. The fatigue crack growth of a single surface crack with the same initial size is also simulated and compared with that of the multiple crack configuration. The comparison shows that the fatigue g rowth of each individual defect is almost independent prior to coalesc ence and the interaction between them is very limited even as they app roach each other very closely. The fatigue crack growth curve predicte d by the numerical technique is compared with those obtained by the AS ME Pressure Vessel Code and the 'no interaction and immediate transiti on (NIIT)' simplified method. The results show that the two simplified estimations are more conservative than that of the present numerical simulating method.