ABSTRACT
Thermal fatigue is by definition a process of nucleation and subsequent, gradual development of damage in elements exposed to cyclically or periodically repeated temperature changes. The resultant failure of the element should be widely under stood as a state of partial or complete dysfunction, including rupture as an extreme case, or for instance the appearance of thermal fatigue cracking on the surface that can easily be reclaimed, or finally, as the excessive creep rate due to metallurgical changes in the fatigued material. Thermal fatigue can be accompanied by (1) stresses introduced by machining or during former service, (2) aggressive environment (e.g., corrosive or erosive media, neutron flux exposure), and (3) ex ternal load: steady or varying.
