DFR method based on Gerber model under corrosion conditions

Abstract

In order to study the influence of the equal-life curve models on DFR, the fitting accuracies of Gerber model and Goodman model for high-cycle fatigue data were compared with six typical aviation materials．The formula of DFR based on Gerber model and the expression of corrosion conversion coefficient CC were derived， pre-corrosion fatigue tests for 0 h, 6 h, 12 h, 24 h, 36 h, and 72 h of 2024-T3 aluminum alloy (surface anodizing) were carried out，and the fatigue fracture of pre-corrosion for 72 hours was analyzed. The results show that Goodman model is suitable for brittle materials while Gerber model is suitable for ductile materials. As the pre-corrosion time increases, the DFR of 2024-T3 aluminum alloy decreases．The DFR based on Gerber model are 84.251 MPa, 84.721 MPa, 79.683 MPa, 80.745 MPa, 77.026 MPa and 74.996 MPa respectively, and the CC is 1.006, 0.946, 0.958, 0.914 and 0.890，the fitting curve of the DFR with the pre-corrosion time is $ DFR=84.251{\left[ {\lg \left( {t + 10} \right)} \right]^{ - 0.15578}}$. It is found that when N95/95 > 105, the DFR method based on Gerber model can give full play to the fatigue performance of ductile materials．Corrosion pits produced by pre-corrosion and inclusions in materials can accelerate the formation and expansion of fatigue cracks, but DFR of the anodized specimens is decreased in a corrosive environment compared with the bare materials.

Keywords

• pre-corrosive fatigue test
• detail fatigue rating (DFR)
• equal-life curve
• fracture analysis