The influence of cyclic strain amplitude on the fatiguk behaviour and sub-structure of pure iron

Annealed and cold worked polycrystalline iron 8uhjectedto p l.n s Ic s t r a f n rang ’H v a r y Lng b c t wc ’n O.OOJ und 0.048 s howcdhardening and sol L ’!lInK respectively to COIIIII)()n s n t u r a t Lon I:lLrC8Hlevels which were directly related to the strain range. Onsat.uration, .subg r a Lns of a definite size were formed and the sizewas found to be inversely proportional to the saturation stress.The relation between the cell size (L) and the plastic strain range1 -n(6E ) may be expressed by L = 8(6E /2)p . pn the cyclic strain ’hardening exponent.where {’ is a constant andTh~ hardening rates were. ”found to increase with plastic strain range whereas the softeningrates after a prestrain of 25% decreased. The number of cyclesfpr saturation (N ) increased with decreasing plastic strain ranges,for both hardening and softening according to the relation, NsR exp(-m/6E ), where R and m are constants. The hardening andpsoftening curves may be normalized resulting in saturation occurringfat a .coris t an t value of the function [6E + 0.13 Log. NJ where N ispnumber of cycles •