This study seeks to contribute to remaining life assessment of high temperature structures such as turbine rotor which suffers from various loading. Typical loading phase of turbine rotor can be divided into three different phase i.e., cold start, hold at high temperature under steady state condition and shut down.
In case of turbine component, creep damage such as crack and cavity has been a primary concem of rotor design. Under steady state loading operations, crack which initiated from stress concentrated region grows along grain boundary where the cavity caused by creep deformation seriously occurred. So one of the primary damage mechanism is creep deformation.
Fracture toughness in steady state operation phase is enough high that sudden brittle fracture does not occur until the crack length become sufficiently large. But in case of transient operating conditions such as start up and shut down fracture toughness drastically decreases to lower level so that material may cause a sudden brittle fracture. So in this case fracture toughness becomes an important concerns whether the failure occurs.
In this study fracture toughness of material which priory damaged by creep crack growth, was experimentally measured. From these results relations between fracture toughness and loading parameter which controls the creep crack growth rate also studied.