Effects of Stress Wave Form and Superposition of Vibratory Stresses on Cyclic SCC Crack Growth Behavior in an Al-Alloy

Abstract

Influences of stress wave forms and superposition of vibratory stresses at the periods of the maximum stress under a low-frequency varying load on cyclic SCC have been investigated with a high-strength aluminum alloy, and the loading condition dominating over cyclic SCC and the competition between cyclic and dynamic SCC have been discussed. The threshold stress intensity factor for cyclic SCC, Kmax = KFSCC, is independent of hold time at the maximum stress, but increases with a decrease in varying load rates per time K^^·. At higher ΔK%lt;eff%gt;, however, da/dN is enhanced with a decrease in ΔK^^·%lt;eff%gt; i.e., at longer rise time; this is similar to those of conventional corrosion fatigue. On the other hand, the superposition of vibratory stresses promotes corrosion products-induced wedge effects with Kop =Kmax. In this case, KFSCC is determined by the threshold stress intensity factor, KDSCC, for dynamic SCC under the secondary vibratory stress condition.