Comparison of fatigue properties of single crystals and polycrystals

Abstract

A comparison is made between fatigue strength properties of single crystals and polycrystais determined by the method of constant stress amplitude. When the S-N curve is expressed as shear stress amplitude versus number of cycles, the results with polycrystais are found to coincide with those on single crystals in both iron and copper. When the shear stress amplitude is normalized by the shear modulus, the resulting S-N curves of iron and copper are of the same order of magnitude. The few existing results suggest for aluminium a corresponding value of about half of that above. This is in accordance with the idea that there is correlation between fatigue and stage III of unidirectional work-hardening.