Fracture Analysis of Piston Valve Connecting Rod Rocker Arm of Aviation Piston Engine

Although the aviation piston engine has many similarities with the automobile engine, due to the bad working conditions, the reliability design is required to be higher. For example, automotive piston engines rarely operate at high power output, but aviation piston engines often need to operate at full power, which will lead to higher loads on some core stressed components. In this case, an aviation piston engine failed during use. It causes the engine to shake in the air and the power is significantly reduced. After the plane landed, the end cover of the aviation piston engine was opened, and the rocker arm installed on the valve ejector rod was found to be broken. The fracture analysis showed that the bolt, bearing housing and participating parts were all suspected to be caused by instantaneous fracture, and no fatigue damage was found in the relevant parts. Further SEM examination revealed that the motion position of the rocker arm was restricted due to the blockage of the exhaust valve. Under the action of the engine thrust, the bolt of the rocker arm breaks instantaneously, and the bearing bush of the mounting bolt of the rocker arm is squeezed, resulting in instant extrusion fracture.