Abstract
In this study, strain-controlled low-cycle fatigue tests at 650°C were carried out in an air environment in order to examine the effect of strain waveform on the fatigue fracture mode. Four different strain waveforms producing four basic inelastic strain ranges (i. e., PP, PC, CF and CC types) given in the strain range partitioning method by Manson et al. were sellected in these tests. The surface and internal cracking modes of the failed specimens were observed by means of a scanning electron microscope as well as an optical microscope.
The results obtained in this study were as follows;
(1) The cracking mode under PP and PC strain waveforms was of transgranular type, and striation was observed on both of the fracture surfaces.
(2) The cracking mode under CP and CC strain waveforms was intergranular. A lot of internal grain-boundary cracks were also observed in the CP type fatigue, but few in the CC type fatigue.
(3) The failure life in the PC type fatigue was shorter than in the PP type fatigue at the same inelastic strain range. This difference may be interpreted mainly as a difference in life to crack initiation between the two types.
