Meili Ding

Failure Analysis of Aviation Torsional Springs

Cracks and fractures occur during the assembly process to a type of torsional springs used in the aviation mechanism. Besides visual examination, other experimental techniques used for the investigation are: 1) fracture characteristics, damage morphology and fractography by scanning electron microscopy (SEM), 2) spectrum analysis of covering, 3) metallographic observation of cracks and 4) hydrogen content testing. The results are obtained through the analysis of manufacture process and experimental data. Since no changes of microstructure are found, failures are irrelevant to the material. The cracks and fractures initiate on the inner surface, cracks initiate before the cadmium plating and after the winding. No obvious stress corrosion cracks are found near the crack source region. The opening direction of cracks is consistent with the residual tensile stress of the spring inner surface, and the springs are easy to contact hydrogen media between the spring winding and the cadmium plating. The cracks are caused by hydrogen-induced delayed cracking under the action of the residual tensile stress and hydrogen.

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.

Tensile fracture characteristics of nitrile rubber after aging at different temperatures

In this paper, the morphology characteristic of tensile test fracture of nitrile rubber after aging at different temperatures for 24 hours was observed through scanning electron microscopy. Combined with the performance data of tensile test, the effect of aging temperature on the properties and fracture behavior of nitrile rubber was studied. The results show that the fracture of nitrile rubber includes rough region, mirror surface region and flat region, and the higher the aging temperature is, the more flat the fracture becomes. Aging temperature has large effect on the tensile mechanical properties. With the rise of the temperature, the tensile strength generally presents an upward trend, while the elongation increases at first and then decreases.

Fractured profiles analysis of silicone rubber of different stretch rate

After taking five different stretch rate at the same specifications silicone rubber, and getting 10mm sample with a fracture from the teared fracture respectively, low magnification microscopy and scanning electron microscopy are used to observe the sample. Experiment results show that, with the stretch velocities increase, the tear strength of the five samples get larger. Fracture analysis shows that the tear strength is determined by stretch velocities and the uneven of the materials.