FRACTURE ANALYSIS ON THE RETRACTABLE ACTUATOR OF THE MAIN LANDING GEAR OF A BOEING 747SP AIRPLANE

Fracture analysis on the retractable actuator of the main landing gear of a Boeing 747SP airplane of a foreign airlines has been conducted by means of macroscopical and microcosmic fracture surface analysis and crack metallurgical analysis. The results indicated that the fracture of the actuator was of corrosion fatigue. The corrosion fatigue cracks initiated from the surface cracks that are in net shape in the outer wall of the actuator. These surface net cracks had been formed before plating of the actuator, so these cracks are a kind of machining defect. The net shape and original depth of these surface cracks conform to the character of grinding crack.