Fatigue Fracture of a Truck Diesel Engine Rocker-Bracket
A diesel engine rocker-bracket fractured after trial running for 460 h. Fracture originated from the fillet root of cylinder of rocker-bracket. Fractographic analysis indicates that fatigue is the dominant failure mechanism of the rocker-bracket. Serious wear damage took place in the located region of the contact surfaces between the cylinder of the rocker-bracket and the rocker-arm. Occurrence of a great abnormal alternative bending load on the cylinder of rocker-bracket from the assembled rocker-arm is mainly responsible for the fracture failure of the rocker-bracket. The over-small root fillet radius of cylinder of rocker-bracket (below the specified limit) increases the stress concentration at the fillet to facilitate initiation and propagation of crack, and eventually premature fracture.