COMPARISON OF FATIGUE BEHAVIOR OF SINGLE-CRYSTALS AND POLYCRYSTALS

The available fatigue characteristics of single crystals and polycrystals are compared from the point of view of their convertibility using a simple conversion factor both for the stress and the plastic strain values. The S-N curves for single crystals were found to be in very good agreement with the S-N curves for polycrystals converted by the Taylor factor M = 3.06. The cyclic stress-strain curves for pure iron can also be very well converted using this factor, while the cyclic stress-strain curves for f.c.c. metals can be converted to a first approximation only. The application of the conversion factor to the Coffin-Manson curves of f.c.c. metals does not lead to any satisfactory agreement. The explanation is based on the considerably different volume fraction of zones exhibiting higher cyclic slip activity in single crystals and in polycrystals.