Cause of Fracture of Piston Rod of Steering Cylinder for Loader

Several earring root fracture accidents occured during the service of 45 steel piston rods of steering cylinder for loader treated by quenching and tempering, and the piston rod body bended during the operation of the machine. The causes of fracture on the root of piston rod earring were analyzed by fracture morphology, microstructure observation, and chemical composition analysis and mechanical property test. The service condition of piston rod was simulated by finite element software. The results show that the fracture of piston rod earring was multi-source low cycle fatigue fracture. The over travel groove existed in the earring and rod body, when the piston rod expanded and contracted, there was stress concentration and the stress concentration factor was high reached 7. 68, and the stress level was higher than the fatigue limit of the material, which leading to the initiation and propagation of fatigue cracks, and finally the fracture of the earring root.