13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Performance Deregulation Rule of Aircraft Fatigue Critical Components in Consideration of Calendar Environment Chao Gao1, , Yuting He1*, Haiwei Zhang1, Bo Hou1, Teng Zhang1 1Aeronautics and Astronautics Engineering College, Air Force Engineering University, Xi’an 710038, China * Corresponding author: hyt666@tom.com Abstract The 2A12-T4 aluminum alloy specimens were studied with accelerated environment test to simulate different parking calendar years. Afterwards, these specimens were implemented with fatigue test to fracture. Through analyzing the test data, the relationship between S-N shape parameter and parking calendar years was caculated with dynamic S-N curve method. Then, the performance deregulation rule of aircraft fatigue critical components in consideration of calendar environment was established. In addition, the rule between Detail Fatigue Rating (DFR) and parking time was also set up. Compared with the similar specimens’ life from retired aircraft, the life with S-N curve and DRF method was in good agreement with actual value. The result shows that aircraft fatigue cirtical components’ performance declines with the prolonging parking calendar time. Keywords 2A12-T4 aluminum alloy, fatigue critical component, calendar environment, dynamic S-N curve, Detail Fatigue Rating 1. Introduction Currently, the service life index of aircraft component in China includes fatigue life denoted by flight hours and calendar life denoted by calendar life. The first repair, major repair and total life are controlled according to the principle of first reach of service life index [1]. The calendar life mainly aims at the corrosive critical component and the degree of corrosive damage is the basic premise whether the component is in good working order [2]. The fatigue life mainly aims at the fatigue critical component and the remaining life depends on the degree of fatigue damage and the number of repair. Aimed at the corrosive fatigue critical component, the method of corrosive influence coefficient is usually used for the general engineering purpose to revise the attenuation of fatigue life because of the corrosive effect during service life [1,3,4]. Generally speaking, the corrosive effect of componen is mainly considered for the calendar life, however, the remaining fatigue life of component is that the design target subtracts the consumed fatigue life and don’t take the effect of environment into account. Because the calendar life of aircraft at present are over 20 years [4], the representative aircraft—B-52, the calendar life are over 50 years. The effect of environment for a long time can result in the corrosion of component and reduce the anti- fatigue performance of material [1-10]. The fatigue critical component is exposed to the parking environment for a long time, which can’t result in the obvious corrosion of component but can cause the microscopic damage. However, the instance that the performance is degrading for the fatigue critical component of parking aircraft because of environmental effect is never reported at home and abroad. Aimed at the problem of performance decline for the fatigue critical component in parking environment, the accelerated environment test of different parking calendar time was carried out by using the 2A12-T4 aluminum alloy standard specimen until the specimen fracture, then the relation was calculated between the shape parameters and the parking calendar time, the model for life decline was established about the fatigue critical component under the parking condition. The model for Detail Fatigue Rating (DFR) and accelerated time were calculated and compared with the fatigue life of the same material from the retired aircraft. The result shows that the model is reliable. The result indicates that the parking environment can cause the fatigue performance decline for the fatigue critical component, and more attention should be paid to the usage and life-saving for the
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