| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 769844 | Engineering Failure Analysis | 2006 | 8 Pages |
This paper presents a failure analysis of two diesel engine rocker arms used in trucks, which failed in service. The fracture occurred at the hole of the rocker arm shaft in two cases. Beach marks and fatigue steps can be observed on the fracture surface. Multiple-origin fatigue is the dominant failure mechanism. A detailed metallurgical investigation was conducted on the failed rocker arms, and compared with a new one. The failed rocker arms present general metallurgical characteristics that the spheroidization of cementite in pearlite appears in all the matrix structure, and a banded structure was observed in the crack origin region. The appearance of the granulated pearlite makes the hardness of the material decrease so as to reduce the fatigue strength of the rocker arms. A normalizing treatment test was performed on the material of the failed and new rocker arms. The formation of a well-distributed lamellar pearlite structure, the increase in hardness, and the disappearance of the banded structure indicate that the unsuitable normalizing technology was responsible for the microstructure defects.
