Investigation On Corrosion Fatigue Strength Of2024-T351Alloy In3.5%NaCl Salt Solution

There are variety of environments occurred during service of the aircraft, such as moist air, salt solution and industrial pollution environment. Due to the remarkable effect of the salt solution environment on fatigue life of materials, it is of important practical significance for the lifetime determination of new general aviation structures to study the fatigue mechanical behavior of aluminum alloy under salt solution environment.The corrosion fatigue properties of2024-T351alloy (the smooth and notch specimen) in3.5%NaCl salt solution were carried out in this paper at different stress ratio (R=-1,0.06and0.5).The stress control fatigue experiment was carried out in3.5%NaCl solution. It is showing that the cyclic deformation characteristic of2024-T351alloy in3.5%NaCl salt solution is related to the mean stress and stress amplitude. It is shown that cyclic softening in the first dozens of cycles and then cyclic stabilization phenomenon in the following cycles under the three stress ratios (R=-1,0.06and0.5). The curves of S-N and p-S-N at different stress ratio were obtained through the statistical analysis of the experimental results. In salt solution condition, the Soderberg equation can describe the influence of average stress to corrosion fatigue life well. The curved surface which describes the relationship among average stress, stress amplitude and fatigue life was established and also with the p-Sa-Sm-N curved surface.The notch fatigue effect of the aluminum alloy in the saline environment was investigated and an experimental correlation between the fatigue notch factor, Kf, and fatigue life, N, under different stress ratios was obtained by comparing the fatigue strength of smooth specimens with that of notched specimens. The applicability of the approximate equations for estimating the fatigue notch factor such as Neuber equation, Peterson equation and Heywood equation, was also verified in the corrosion environment and with a mean stress by comparing the estimated Kf with the measured values. The results show that the modified Neuber formula can be used to predict the fatigue notch factor of2024-T351aluminum alloy in3.5%NaCl solution. Therefore, the approximate formula of fatigue notch factor can be recommended for the anti-fatigue design of aircraft structure.