Hydrogen Embrittlement and Fatigue Fracture of a Crankshaft of an Internal Combustion Engine

A trainer military aircraft, equipped with alternative internal combustion engine, experienced an overspeed during preflight operations. In the aftermath, maintenance personnel performed magnetic particles NDT and found two cracks on the crankshaft. These were located at the front support of the part and were both about 46 ÷ 48 mm long. The crankshaft is a critical item for the engine and in order to prevent other similar incidents a technical investigation took place. Therefore, this report shows the results obtained by fractography, metallographic, chemical analysis and numerical simulation: the root cause of the cracks was the embrittlement of material due to an excessive hydrogen content. This made possible a fatigue fracture mechanism under normal operative cyclic loads.