Failure analysis of cracks in the upper shaft of torque arm

In the periodic inspection of a plane having flown for 300 h, cracks were found in the upper shaft of the torque arm of the landing gear. In addition to visual examination, other experimental investigation techniques were 1) crack morphology and fracture characteristics by scanning electron microscopy, 2) metallographic observation of cracks, 3) chemical constituents and hydrogen-content testing, 4) hardness testing, 5) impact and bending simulation test, and 6) comparison of wear condition for the crack-free upper shafts with other batches. The results were obtained through the analysis of processing and experimental data. Because of higher surface frictional shear stress and tensile stress, the cracks propagated in the form of stress corrosion after the initiation, which was unrelated to the coating, matrix material, and hydrogen content.