Abstract
Based on the small time scale method, the influence of grain boundary on the fatigue crack growth of 7050-T7451 has been investigated. The interaction between fatigue crack and grain boundary was investigated by in situ SEM testing. Results showed that the fatigue crack growth will be retarded by grain boundary when the angle between fatigue crack and grain boundary is greater than 90 degrees. Mechanism analysis showed that the fatigue crack tip would not be able to open until the loading reached the 55% of maximum load, and the fatigue crack had been closed completely before the loading was not reduced to the minimum value, which led to the crack growth retardation. When the 7050-T7451 aluminum alloy suffered from fatigue loading with constant amplitude, a behavior of unstable fatigue crack growth could be observed often, and results indicated that the bridge linked mechanism led to the behavior. The grain boundary was prone to fracture during fatigue loading, and it became the best path for the fatigue crack growth. The fatigue crack tip would be connected with fractured grain boundary eventually, which led to the fast crack growth in different loading stage.
Highlights
7050-T7451 is a kind of high strength aluminum alloy which has been widely used in aerospace fields for its excellent properties, such as high specific strength, good fracture toughness, and stress corrosion resistance [1, 2]
Due to the fact that the aircraft bears complicated loadings in service, including maneuver loading, gust loading, and ground loading, the accumulation of fatigue damage will appear in the structure of 7050-T7451 aluminum alloy, which may lead to the fatigue fracture and cause disastrous accidents
The interaction between grain boundary and fatigue crack growth was researched in the experiment, such as retardation effect on the fatigue crack growth, as well as the behavior of unstable fatigue crack growth within one loading cycle; the result could provide the basis for the optimization and life prediction of 7050-T7451 aluminum alloy
Summary
7050-T7451 is a kind of high strength aluminum alloy which has been widely used in aerospace fields for its excellent properties, such as high specific strength, good fracture toughness, and stress corrosion resistance [1, 2]. The in situ testing is able to observe the whole process of fatigue crack growth in real time; existing methods mainly focused on the research of damage mechanism between hundreds or thousands of loading cycles, and seldom studies focused on the behavior of fatigue crack growth within one loading cycle. Scale used for the analysis of fatigue crack growth [11] has been developed, and it is different with existing cycle-based method for improving the accuracy The advantage of this method [12] is that it could be used for analyzing the crack growth behavior at any time instant during one loading cycle. The influence of grain boundary on fatigue crack growth of 7050-T7451 aluminum alloy has been investigated based on the small time scale method. The interaction between grain boundary and fatigue crack growth was researched in the experiment, such as retardation effect on the fatigue crack growth, as well as the behavior of unstable fatigue crack growth within one loading cycle; the result could provide the basis for the optimization and life prediction of 7050-T7451 aluminum alloy
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