Study on the Effect of Prior Fatigue and Creep-Fatigue Damage on the Fatigue and Creep Characteristics of 316 FR Stainless Steel. 1st Report. The Effect of Prior Fatigue Damage on the Creep Characteristics.

The effect of prior fatigue damage on the creep characteristics of 316FR stainless steel was studied to investigate the applicability of two creep-fatigue life evaluation procedures, Time Fraction Rule and Ductility Exhaustion Method, widely used in the recent high temperature structural design codes. Creep tests were conducted at 550°C by using the specimens exposed to prior fatigue cycles at the same temparature and interrupted at 1/4 Nf, 1/2 Nf and 3/4 Nf cycles. The creep strength of the pre-damaged material showed almost no reduction compared with the virgin material until the fatigue damage of 1/2 Nf cycles, and simple summation of creep damage and fatigue damage by using Time Fraction Rule was not formed. On the other hand, the creep ductility of the predamaged material showed monotonic reduction with the prior fatigue damage from the initial stage of the damage, and the relationship between creep damage and fatigue damage evaluated by the Ductility Exhaustion Method was almost linear. These results show that the application of the stress-based Time Fraction Rule is unsuitable and the application of the strain-based Ductility Exhaustion Method is promising to the exaluation of creep-fatigue interaction damage of the 316FR stainless steel.