Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : September 03, 2017 - September 06, 2017
Creep-fatigue damage in high-temperature components gradually proceeds at stress concentrate portion during start-steady state-stop operation. Clarification of the damage evolution process under creep-fatigue loading is important to develop life assessment methods. In this study, strain control creep-fatigue tests with one hour hold time were conducted by using round notch bar specimens on CrMoV forging steel and damage condition was observed for test interrupted specimens. Failure lives of the round notch bar specimens were much shorter than those of smooth bar specimens under the same conditions. Microstructure observation of creep-fatigue damaged specimens indicated that a grain boundary crack initiated from notch root and grew toward inside of the specimen with increasing the creep-fatigue damage. It was found that cyclic loading superimposed on creep loading causes reduction of rupture time due to acceleration of crack initiation and growth. Finite element analysis results also indicated that an axial stress after hold time remains the highest at the notch root.
