Failure Analysis Of Tooth Fracture Of The Heavy Planetary Gear Box

The planetary gear of the KPBV150 gear box used as crash equipment of some company ruptured in work process gear, and the mean time bring the sun wheel, planetary frame, box body and other parts into distortion, rupture, and at last lead the invalid of the reducer gear box. The planetary gear ruptured from its inner hole, so firstly explored the inner hole to observe whether existed other microcosmic or macrocosmic crack to confirm the main invalid part. And then stress on applying the technologies of macro-examination, micro- examination, chemical analysis etc, to process analysis to the fracture of the rupture gear. Make certain that the invalid mode of the rupture gear is high circle fatigue rupture. The original era of the crack is in the hypo-surface of the gear inner hole and become conscious of hollow defects in this era. These hollow defects directly destroy the continuity of the materials and reduce the mechanical capability of the materials. Enduring the working load, engender stress concentrate around the hollow defects which place a premium on crack initiation, and then with the effect of the fatigue load, the fatigue crack grow till the rupture of the gear. Therefore we determinant the hollow defects of the gear material are the fundamental reason for the gear fatigue rupturing.Process the mechanical capability examination of the material of the gear to achieve the mechanical capability parameters which incarnate the capability of standing against with the failure of the fatigue, and using them as the material parameters to forecast the life of the gear. Through the tensile testing of the material, achieve the mechanical capability parameters such as tensile strength, yield strength, percentage elongation and percentage reduction of area after fracture. Through the fatigue testing of the material, applying the ascend-descend standard to achieve the fatigue limit of the material. Through the fracture mechanics testing, achieve Fracture toughness, fatigue crack propagation threshold, and applying regress analysis the data of fatigue crack propagation to fit expression for fatigue crack propagation.During the practical run, synthetically calculate the magnitude of the moment transferred by the gear and the shrunk-fitting remnants stress, calculate the practical stress by finite element analysis. Finally, apply fracture mechanics based on the theory of damage tolerance design to process the life prediction of the gear. The result indicates that the life of fatigue crack growth is shorter than the practical life of the gear that indicates that the life of crack initiation based on the hollow defects of material is significant composed portion, if we want to calculate the life prediction of the gear more precise, we need do further research on the mechanism and mode of fatigue crack initiation based on the hollow defects of this material.