Affiliations: Department of Nano Mechanics, Graduate School of Engineering, Tohoku University, Aoba 6-6-01, Aramaki, Aoba-ku, Sendai-shi 980-8579, Japan | Department of Materials Research for Power Plants, Hitachi Ltd., Omika-cho 7-1-1, Hitachi-shi 319-1292, Japan | National Institute for Materials Science, Independent Administrative Institution, Sengen 1-2-1, Tsukuba-shi 305-0047, Japan | Metallurgy Department, Research Institute, Ishikawajima-Harima Heavy Industries Co. Ltd., Toyosu 3-1-15, Koto-ku, Tokyo 135-0061, Japan
Abstract: When materials are used as component of a structure, the multi-axial stress field may be caused due to the locality of stress field in component structures such as plastic constraint, which is related to the structural brittleness. Furthermore, it has been observed that cracking is induced by the deterioration of the material microstructure, which is related to the aging effect. From the point of practical use, it is important to consider the characterizations of the creep crack growth rate and its life under these conditions to predict the life of creep crack growth. In the present paper, the effects of multi-axial stress and aging on the law of predicting the life of creep crack growth were investigated. High temperature creep crack growth tests were conducted using mimic time sequential deteriorated CT specimens ranging from 7000 to 10,000 hr by conducting various equivalent heat treatments. These results were compared with those of the effect of multi-axial stress on creep crack growth rate and its life. For the effect of multi-axial stress (Structural brittleness), not only the numerical values of the activation energy and the exponent of stress but also the algebraic form of equation for creep crack growth life were found to be strongly influenced by the effect of multi-axial stress (Structural brittleness). For the effect of aging, on the other hand, the equation of the law of creep crack growth life was found to take the same algebraic form between an aged material and an as-received material.
