抄録
The effect of two-step varying load on the fatigue crack propagation of SNCM 439 was investigated in room air, distiled water and 3.5% NaCl solution. A small number of cycles at higher stress level were applied periodically during a large number of cycles at lower stress level than the fatigue limit. After each cycling, the crack growth was measured and the growth rate was compared with that at each steady stress amplitude.
The conclusions are as follows;
(1) 2 cycles at higher stress only caused the acceleration of crack growth at higher stress side. On the other hand, in all other cases the acceleration was not observed.
(2) In the application of the linear cumulative damage concept, the cumulative damage life extended remarkably compared with the life at steady stress.
(3) The similar tendency above mentioned of crack propagation behavior also appeared in corrosive environments.
(4) It is confirmed that the crack propagation behavior depends on the number of cycles at higher stress in one program unit.
