Fretting-initiated Fatigue in Large Bore Engines Connecting Rods

Large bore four stroke diesel engines are widely employed in power demanding applications such as large ships and terrestrial power plants. Due to the extremely high number of cycles they are subject to (above 108), components are designed according to the infinite-life approach. Although fatigue cracks are well below the propagation threshold, concurring damage phenomena such as corrosion, wear, fretting, and overloads can trigger them, leading to failure in relatively short times and posing great challenges to an accurate root cause failure analysis.In this paper, the fatigue failure of connecting rods initiated by fretting damage is described. Fracture mechanics and Hertz theory were employed to assess the main parameters controlling the damage and to define thus appropriate corrective actions. Connecting rods which were considered to be susceptible to fatigue crack propagation were subsequently monitored through a tailored ultrasonic testing procedure.