Comprehensive Root Cause Failure Analysis and Numerical Evaluation of Fractured Piston Head

The uncommon piston failure occurs, and it happens in a short piston lifespan. The paper presents a comprehensive procedure for failure analysis of a piston head. A unique form of failure mechanism has been found. The crack was initiated from the sharp edge zone at the piston skirt, not from the piston crown that was hit by radial impact. The crack was then propagated by a fatigue phenomenon macroscopically characterized by cleavage and combined slip plane, and microscopically characterized by striation and microcleavage. Thus, there was a combination of impact and fatigue that caused piston failure. Validation by numerical method showed that the crack propagation line agrees with the stresses contour map, and the crack initiation and propagation occurred due to compressive stress. The chemical composition analysis showed that the Si content of the piston was less than the standards which caused the piston to be a hypoeutectic alloy, instead of eutectic or hypereutectic alloy. The suggestions to prevent recurring failure are to ensure the alignment of the connecting rods, to improve piston design by reducing the stress concentrator zone, to control the manufacturing process, and to use the proper alloys as per the standards.