Fracture Analysis of Toughness Fracture Failure on Flexspline of Harmonic Reducers During the Service

Abstract

The reasons of the fatigue failure of flexspline are analyzed by observation analysis， observation and hardness determination of fracture morphology of microstructure. The results show that the micro-structure of the flexspline of the failed harmonic reducer are tempered troostite， and there is more severe grade 3 banded structure on the flexspline . Although the 4.42 μm micropores caused by MnS and Al2O3 inclusions exist， they are not the main cause of breakage due to its small size and number . Meanwhile the overall grain size of the sample， especially the grain size at fracture crack， is coarse， and the grain at the fracture crack is thicker and more uneven. the grain size at the fracture crack is 1.4 times that away from the fracture grain. The coarse grain assembly leads to smaller grain boundary area， which not only leads to more uneven plastic deformation， but also more prone to stress concentration， which causes primary cracks， and is difficult to hinder crack expansion， resulting in fracture failure of the sample.Therefore， the primary austenite grain is the main cause for fatigue fracture of flexspline. The grain refinement can be achieved by circulating heat treatment or adding normalizing pretreatment.

Keywords

• harmonic reducer； flexspline； fracture failure