Overload effects on corrosion fatigue crack initiation life and life prediction of aluminum notched elements under variable amplitude loading

Abstract

In this study, corrosion fatigue tests under both constant and variable amplitude loading are carried out to investigate the overload effect on the corrosion fatigue crack initiation (CFCI) life and life prediction model of the notched specimens of LY12CZ aluminum alloy sheets, which has the continuous strain hardening characteristics. Analysis of test results of CFCI life in 3.5% NaCl solution environment shows that overload increases the CFCI threshold but has no appreciable effect on the CFCI resistance coefficient, and thus increases the CFCI life. Further analysis gives the overload effect factor for CFCI life, z, which can be used to characterize the load interaction effect in load spectrum. Furthermore, three load spectra are designed and used for testing and predicting the CFCI lives under variable amplitude loading (VAL). Test results of CFCI life under above mentioned load spectra show that the load pattern has great effect on CFCI life of LY12CZ alloy notched elements even the difference among the load spectra is small. It means that the overload effect should be taken into account in CFCI life prediction under VAL. Finally, the equivalent stress amplitude approach is put forward to predict the CFCI life under VAL by using Miner’s rule and the CFCI life expression considering the overload effect. The predicted CFCI lives of LY12CZ alloy notched elements under VAL agree well with test results. Based on the above test results and analysis, it may be thought that Miner’s rule can be used to predict the CFCI life of notched elements of metals with continuous strain hardening characteristics if the overload effect on CFCI life is taken into account in life prediction under VAL.