3161, stainless steels are mostly used for structures in high temperature nowadays. In fast reactor plant, main components have been and will be made of 316L stainless steels because of their superior high-temperature strength and ductility. Many components operating in high temperature structures, like power generating plant, fast breeder reactor, pressure vessel and so on, are subjected to combined creep-fatigue damage. Unexpected failures which bring severe disasters can occur by this damage. It is very important to predict the fatigue life of materials under creep-fatigue condition because accurate life prediction can make the materials used safely and efficiently.
In order to quantify the effect of tensile hold time on the fatigue life, creep-fatigue tests with a tensile strain-hold wave form were carried out on 3161, stainless steels. In this test method, the creep loading and fatigue loading were repeated alternately. Three levels of tensile hold time were considered.
A New purposed creep-fatigue life prediction model is based on the linear damage summation rule. The linear damage summation rule assumes that when the fatigue damage and the creep damage sum to unity the failure under the creep-fatigue condition can occur. In this new life prediction model, the fatigue damage component is derived from the cycles ratio summation and the creep damage component is formulated as a function of the amount of stress relaxation. According to the verification of the adequacy of this new life prediction model, the predicted life agreed well with the observed life and a new purposed life prediction model is more accurate than original life prediction methods (Time fraction rule, ductility exhaustion rule)