ON THE CORROSION-FATIGUE CRACK INITIATION MODEL AND EXPRESSION OF METALLIC NOTCHED ELEMENTS

In the present study, attempts are made to extend the application of t he mechanical model for the fatigue crack initiation (FCI) and the FCI life formula of metallic notched elements in laboratory air to those in the corrosive environment. The test results and analysis of the cor rosion FCI (CFCI) life of aluminum alloys and Ti-6Al-4V show that the expression of the CFCI life obtained by modifying the FCI life formula in laboratory air can give a good fit to the test results of the CFCI life. The salt water (3.5% NaCl) environment has no effects on the CF CI resistant coefficient compared with the FCI resistant coefficient i n laboratory air. However, 3.5% NaCl environment greatly decreases the CFCI threshold of aluminum alloy, but has little effect on the CFCI t hreshold of Ti-6Al-4V. The loading frequency ranging from 1 Hz to 10 H z has no appreciable effect on the CFCI life, and thus, the CFCI thres hold of aluminum alloys investigated. Hence, the expression for the CF CI life of metallic notched elements proposed in this study is a bette r one, which reveals a correlation between the CFCI life and the gover ning parameters, such as, the geometry of the notched elements, the no minal stress range, the stress ratio, the tensile properties and the C FCI threshold. However, this new expression of the CFCI life needs to be verified by more test results. (C) 1997 Elsevier Science Ltd.