Asahiko Futamura

Effect of grain and grain boundary strengths on the life of main creep crack initiation in a notched plate specimen.

Effect of grain and grain boundary strengths on the life of main creep crack initiation in a notched plate specimen was investigated, using an austenitic heat resisting steel. In a range of lower grain strength below about HV 300, the life of main crack initiation increases with an increase in grain strength, independent of grain boundary strength. In a range above HV 300, however, it decreases drastically with increasing grain strength when a specimen has a weaker grain boundary strength. On the contrary, if a specimen has a stronger grain boundary strength, it continues to increase with increasing grain strength. Further, a relationship between the main crack initiation life, ti, and the mean notch opening displacement rate, V^^·m, that is, tiV^^·nm=C (n and C are constant), was obtained which was analogous to the Monkman-Grant relationship. Finally, the effect of grain and grain boundary strengths on ti was discussed in terms of the relationship tiV^^·nm=C, considering the effect of both strengths on V^^m and a critical notch opening displacement at the time of main crack initiation.