Abstract
The fracture of a shaft belonging to the speed controller of a ship’s engine is presented. An over-speed situation occurred as a result of the fracture of this shaft, which led to severe damage to the engine.
The failure examination concentrated first on the study of the available evidence, which included the analysis of the shaft’s material and fracture surface.
The shaft’s material was studied as concerns chemical composition, mechanical properties and micrographic structure. The fracture surface was studied using scanning electron microscopy. Several different destructive laboratory tests were conducted on the material, in order to obtain fracture surfaces which could be used for comparison purposes, and thus help to identify the cause of the fracture.
The next step of the failure analysis consisted of a stress analysis of the shaft under service conditions.
A probable scenario for the failure was proposed, which helped the interested parties to reach an agreement concerning responsibilities for the failure. It was found that the shaft material presented low notch toughness. The stress levels at the time of the accident imply that it is unlikely that the fracture was due to fatigue. The probable cause of the failure was sudden blockage of the shaft.
