Abstract
In order to determine a damage tolerance limit of a ratchet strain in operational conditions of fast reactors, the authors developed a new experimental method for fatigue strength of 316FR steel, taking an accumulated strain ε_a and a ratchet-expired cycle N_0 into account. An influence of a ratchet deformation to fatigue strength was investigated, and the results were as follows; the influence of the ratchet deformation is small in the tests of strain range Δε=0.5 %, the accumulated strain ε_a=1.4% and the ratchet-expired cycles N_0=20, 500, 1000. The fatigue life decreases in the tests of strain range Δε=0.5%, the accumulated strain ε_a=4.0% and the ratchet-expired cycles N_0=1000. A mean stress σ_m and loading period of the mean stress Nσ_<mean>/N_f could explain the decrease of the fatigue life.
