Synergism between corrosion and fatigue of Al2024-T3 alloy

Corrosion and fatigue are two major factors that contribute to the aging of aircrafts. These two factors act synergistically in various ways. The mechanism of synergism is often studied when both factors are present simultaneously. However, in reality they may be present sequentially. For example when an airplane is in flight, factors such as engine vibration and flutter produce extended cyclic load while corrosion is minimal; and when it is on the ground, corrosive environment has its maximum effect while there is little or no cyclic loading. In this paper we present some results of Al 2024-T3 specimens first subjected to various amount of fatigue loading and then immersed in a corrosive solution for a fixed amount of time. Subsequently the specimens are fatigued to failure. The results are compared to those obtained previously for the same material subjected to fatigue alone or first to corrosion and then fatigue. We find that a modest amount of initial fatigue increases the fatigue life of the corroded specimens, compared to the net fatigue lives after corrosion. We also find that the total fatigue life (sum of fatigue lives before and after corrosion) exceeds that of the virgin samples, provided that the initial fatigue cycle has consumed more than half of the fatigue life of the specimen. It is believed that the blunting of microcracks and voids created at initial stage of fatigue is a major reason for this increased fatigue life.