In order to investigate the notch effect on creep-fatigue interaction of metallic materials at elevated temperatures, three types of tests of static tensile creep, zero to tension low cycle fatigue and fatigue with the hold time under a constant tensile stress were performed. For the tests, three types of notched cylindrical specimens with the stress concentration factors of 2.0, 4.8 and 6.4 were used. Super alloy steel_A286 was used and the tests were performed at 650°C. From the experiments, the following conclusions were derived.
(1) Different notch effects on the rupture time of the material were observed in the three types of tests. In the creep test, the rupture time ratio of the notched specimen to the smooth specimen was greater than unity for all of the elastic stress concentration factor K_t employed and it took the maximum value at K_t of nearly 4. On the other hand, in the fatigue test, the rupture time ratio was smaller than unity for all K_t employed and the decreasing rate became smaller at a larger K_t. In the fatigue test with the hold time, the rupture time ratio was partly greater than unity at K_t of nearly 2 and decreased monotonously to the value of smaller than unity with increasing value of K_t.
(2) From the calculation obtained by applying the cummulative damage rule to the rupture life of materials in the fatigue test with the hold time, the combined damage φ of both creep damage φ_c and fatigue damage φ_f of the material was apparently dependent on the elastic stress concentration factor K_t and the fatigue damage φ_f was predominant in the condition of a larger K_t.