Effect of Grain and Grain Boundary Strengths on the Life of Main Creep Crack Initiation in a Notched Plate Specimen

• Published in: Transactions of the Japan Society of Mechanical Engineers Series A Vol. 55; no. 518; pp. 2113 - 2118
• Main Authors: YAMAMOTO, Masaru, MIYAGAWA, Ohmi, KOBAYASHI, Mitsuyuki, FUTAMURA, Asahiko
• Format: Journal Article
• Language: English; Japanese
• Published: The Japan Society of Mechanical Engineers 1989
• Subjects: Crack Initiation; Creep; Grain Boundary Strength; Grain Strength; Iron and Steel; Notch; Notched Plate Specimen
• ISSN: 0387-5008; 1884-8338
• DOI: 10.1299/kikaia.55.2113

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.