Cause of fracture in fatigue life test of guiding arm

During the fatigue life test of a certain guiding arm, early fracture occurred. The reasons for the fracture of the guide arm were analyzed using macroscopic observation, chemical composition analysis, metallographic examination, hardness testing, scanning electron microscopy analysis. The results show that the guiding arm experienced low cycle fatigue fracture, with the source region located on the lower surface of the guiding arm, exhibiting multi-source and line source characteristics. No metallurgical defects or processing damage were found in the source region. There was a decarburization layer on the surface of the guide arm, and the low hardness and reduced fatigue resistance of the decarburization layer were the main reasons for the early fatigue fracture of the guide arm. The surface of the guiding arm did not form an effective shot peening layer, resulting in a decrease in its fatigue strength, which promoted the fracture of the guiding arm.