Fracture Analysis of the Double-Circular-Arc Gear Reducer Shaft

Abstract

A fractured shaft was made of 45 steel. The properties and reasons of the shaft were found by micro and macro observation on fracture surfaces, metallographic examination and hardness testing. The results showed that the fracture mode of the shaft were one-off overload fracture of the central zone and fatigue fracture of the brim. The fatigue source zone was in the subsurface. The fracture was caused by the original defects existed in the shaft central zone. It propagated an about 140 mm crack in operation. The crack source propagated laterally along the big crack edge, which resulted in fracture morphology and fracture forms became complicated. The shaft heart material was made of ferrite-pearlite, inclining widmanstatten structure. According to the YB31-64 standard, it rated column C level 1.Due to uneven grains, mixed crystal phenomenon existed. In addition, because the shaft surface heat treatment process control improperly, the surface hardness was not high to reach the structure standard by quenching and tempering treatment.