Materials Performance

AUG 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Page 56 of 92

54 AUGUST 2018 W W W.MATERIALSPERFORMANCE.COM MATERIALS SELECTION & DESIGN L Based on the Transport Wing Stan- dard (TWIST) load spectrum, the effect of corrosion and fatigue interac- tion on the fatigue life of aviation materials was evaluated. First the TWIST gust load spectrum was simpli- fied, then the alternation process of airborne fatigue plus ground corro- sion was simulated, and finally the fracture surface was observed using a scanning electron microscope. The results showed that the fatigue life of the material decreased as corrosion time increased, while the number and the area of the fatigue crack sources and density of corrosion pits increased. In the microstructure, special forms of corrosion fatigue crack propagation appeared, such as deflection and bifurcation. Life prediction and extension of aircraft structural compon ents have becom e a focus of major industry research. 1-3 During operation, an aircraft is affected by the constant action of various external forces. Furthermore, corrosion can cause damage to all its metal elements if they are exposed to harsh environments for extended peri- ods when the aircraft is on the ground. The alternating processes of airborne fatigue and ground corrosion can become syner- gistic. Fatigue of an aircraft is mainly the result of a complex action of load spectrum when it is flying at an altitude above 3,000 m. While the plane is on the ground, the aircraft is mainly affected by the corrosive Corrosion-Fatigue Effect on the Life of Aluminum Alloy Fusheng Wang, Xuntao Zhang, a ilun Wang, and Yajun Chen, Sino-European Institute of Aviation Engineering, Civil Aviation University of China, Tianjin, China effect of the environment, which is more pronounced in coastal areas and inland tropical areas. Corrosion greatly affects the fatigue life of aircraft structures. 4 In most aircraft metals, corrosion initially takes the form of pits that form on the surface of the material. Many studies have been con- ducted on the corrosion fatigue life of alu- minum alloys. Xu and Wang 5 used the finite element method to determine pit dimen- si o n s a n d d e s c r i b e d t h e p i t - t o - c ra c k transition. This article reports on using a simpli- fied Transport Wing Standard (TWIST) spectrum—a standardized load sequence for flight simulation tests on transport air- craft wing structures—to simulate the pro- cess of airborne fatigue plus ground corro- sion by alternating influences of a corrosive environment and cyclic load on fatigue life. It also includes observations of the micro- structure of a corrosion fatigue fracture and analysis of the failure mechanism. The material used in this study was 2024-T4 aluminum alloy, and its mechani- cal properties were measured in a tensile test. The ultimate tensile stress of this material was 515 MPa, and the tensile yield stress was 365 MPa. All fatigue specimens were prepared according to ASTM E647. 6 Experimental Procedures Simplified Load Spectrum For civil aviation and navigation aircraft, a ground-air-ground load cycle is the typical loading form of a single flight. This cycle is the main factor that causes fatigue damage, shortens the fatigue life of an aircraft's major components, and contributes to

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