Causes of cracks in aircraft steering gear shell

Oil leakage faults occurred many times in the service process of a aircraft steering gear shell. The oil leakage shell was detected and analyzed by means of chemical composition analysis, fluorescent penetrant testing, fracture analysis and metallographic examination. The mechanical properties of different batches of shell materials were tested. The results show that under the action of pulsed oil pressure, the sensor hole wall of the steering gear shell cracked and further expanded, resulting in oil leakage. The failure batch shell material was recrystallized equiaxed crystal structure, and the normal batch shell material was dendritic network grain boundary structure. The difference of microstructure led to the difference of mechanical properties of the material.The transverse mechanical property, fracture toughness and fatigue property of the failure batch shell material were lower than those of the normal batch shell material. The decrease of mechanical property was the main reason of fatigue crack in thin wall of sensor hole.