| Ultra high strength structural AF1410 steel is commonly used in critical aircraft structural components in aerospace and marine application, because it possesses high toughness and outstanding mechanical properties. However, there exists a lack of knowledge of its corrosion-fatigue properties and hydrogen embrittlement. This study attempts to undertake an accurate simulation of actual service conditions mimicking a realistic environment and to characterize the hold time-fatigue interaction on aircraft structural members. AF1410 steel was evaluated in marine environment and electrolytic hydrogen charged conditions. A decrease in lifetime of AF1410 was observed as a function of increasing severity of the simulated environment and reducing test frequency. The crack growth rate of hydrogen charged specimens and under simulated marine environment was higher than specimens evaluated without hydrogen (air), when evaluated using sinusoidal and trapezoidal loading forms. Furthermore, hydrogen charged specimens at one and two lateral surfaces exhibited a drastic reduction in the lifetime caused by simultaneous effect of hydrogen and fatigue loading. Our results show that hold time effect under environmental hydrogen embrittlement conditions was detrimental on fatigue lifetime of AF1410 steel which is frequently ignored under environmental temperatures. Additionally, the hydrogen charged specimens underwent a change in the fracture modes from ductile to brittle. Since, hydrogen has not permeated the entire specimens; the experiments provided a more realistic approach to the study of large aircraft components during service. In addition, a phenomenological mathematical model for lifetime prediction was developed to account for the effect of hydrogen on the fatigue crack growth rate for AF1410 steel. Finally, the phenomenological model developed shows an excellent agreement between the experimental and predicted results. |
