An Investigation Of Failure Character Under Vibration Loading For Areoplane Joint Structure

In this thesis, the fracture properties of LY12 aluminum alloy plate riveted joint structures and TC4 titanium alloy plate welded structures which are all widely used in the airplane structures are studied at cantilevered restraint and the first natural frequency. The fatigue limit of LY12 aluminum alloy riveted joint structures is 72MPa. In LY12 aluminum alloy riveted joint structures, fatigue crack initiates from specimen surface, and propagates along riveted hole. The fatigue limits of TC4 titanium alloy plate welded structures are 155MPa (for I model specimen which weld is in minimum section) and 151MPa (for II model specimen which weld is in maximum stress position), respectively. Weld has no effect on fatigue limit. At low stress level, S-N curve of II model specimen has low slope compare with that of I model specimen, that is, at same stress level, the fatigue life of II model specimen is longer than that of I model specimen, it is because the fatigue crack of II model specimen propagates in the hot effect region of weld, the hot strain due to weld increases crack growth resistance, decreases crack propagation rates, and increases fatigue life. Even in II model specimen, fatigue crack propagates in TC4 plates, indicating that weld has rather high strength. Beach marks are found on the fracture surfaces of two kinds of joint structures, those are typical fatigue failure.