Effects of stress wave form and superposition of vibratory stress on cyclic SCC crack growth behavior in an Al-alloy.

Abstract

Influences of stress wave form and the superposition of vibratory stresses at maximum stress under low frequency varying load on cyclic SCC crack growth behavior have been investigated on a high-strength Al-alloy, and the loading condition dominating over cyclic SCC and the competition of cyclic-and dynamic SCC have been discussed. The threshold stress intensity factor for cyclic SCC Kmax=KFSCC is independent of hold time at maximum stress but increases with a decrease of varying load rate versus time K. At higher ΔKeff, however, da/dN accelerates with a decrease of ΔKeff, i.e., at longer rise time, and it is similar to that of conventional corrosion fatigue. On the other hand, the superposition of vibratory stresses promotes corrosion-products induced wedge effect, with Kop=Kmax. In this case, KFSCC is determined by the threshold stress intensity factor KDSCC for dynamic SCC that is corresponding to secondary loading condition.