Abstract
The materials used in high temperature equipments are often subjected to the cyclic straining at the temperatures where fracture is often controlled by time dependent phenonena. The cyclic fracture at such high temperatures sometimes cannot be evaluated by the conventional creep or creep-fatigue fracture criteria. Therefore, a new fracture criterion utilizing the static and cyclic creep rupture time and static creep rupture ductility is proposed. In the criterion, fracture is considered to occur when the sum of the ductility exhaustion damage (which is proportional to the unidirectionally accumulated strain) and the creep damage (determined by time devided by cyclic creep rupture time) reaches a constant value.
The criterion was successfully applied to the life prediction of the inscale fracture model of a high temperature heat exchanger made of Inconel 617 alloy. Furthermore, the strain rate dependency of cyclic life under various saw tooth waves was proved to be explainable by the same criterion if the local strain behavior was examined.
