Failure analysis of a planetary gear carrier of 1200HP transmission

A systematic failure analysis of the defect planetary gear carrier of tracked vehicle transmission was carried out. The analysis was focused on the metallurgical and mechanical points of views. Metallurgical analysis is composed of macroscopic, microscopic, chemical composition and spheroidal graphite rate analysis. We supposed that the blowholes around the hub corner observed by macroscopic analysis had resulted in a fracture due to concentrated and repeated mechanical stress. Fatigue striations which are the typical features of fatigue failures were observed by a scanning electron microscope. The effects of defect blowholes of the gear carrier in terms of stress distribution were evaluated by finite element analysis. The stress distribution of the defect planetary gear carrier is concentrated around blowhole regions and the maximum stress of the gear carrier is increased 26% more than the normal gear carrier. The results of finite element analysis were well matched with the results of metallurgical analysis, thus supporting the hypothesis of the failure causes. We concluded that the failure was caused by blowholes affecting fatigue fractures of the planetary gear carrier.