Failure Analysis of Landing Gear Bolt

Aiming at the failure problem of landing gear bolt, material analysis, hardness tests and strength check were used to analyze the quality of materials and design, and methods of microscopic analysis, metallographic testing were used to explore the corrosion reasons. The results show that the material and design meet the requirements, and corrosion products adhere to the fracture. The source area showed shell-shaped morphology and extended area showed fatigue banded and fatigue arc appearance characteristics. The bolt mainly bore radial shear loads, and the additional load of head was due to residual assembly stress concentrated. Therefore, the failing process consised of early micro-crack formation and crack propagation: the chrome protective layer around the corner was worn and pits were formed under the head of the extra load. Then the electrochemical corrosion between exposed steel and remained etching solution happened to form early micro cracks, finally under the effect of alternating long-term radial shear loads, the micro cracks propagated along the arc tangent direction and led to the eventual fatigue failure of the landing gear bolt.