The influence of environment on the acceleration of crack growth at peak loading and the retardation after peak loading in room air and 1% NaCl solution was discussed and compared with the results of cyclic loading. The load sequence used consisted of fatigue loading at lower load level (K2) subsequent to 2 cycles at peak load (K1) in rotating bending. The material was SNCM 439 tempered at 200°C.
The results obtained are as follows:
(1) At peak loading the crack growth rate was accelerated remarkably. The rate was several tens times as fast as that in fatigue loading at the same load level. While the rate in fatigue loading was several times faster in 1% NaCl solution than that in room air, this accelerated crack growth rate was almost the same in both environments.
(2) The number of retardation cycles (ND) decreased under peak loading compared with that under cyclic loading. ND in 1% NaCl solution was smaller than that in room air under the same loading condition.
(3) The crack growth rate in retardation period was almost equal irrespective of loading conditions. On the other hand, the rate in retardation period was influenced significantly by the test environment. The rate in 1% NaCl solution was about 10 times faster than that in room air.
