A trunnion bolt that was part of a coupling in a metropolitan railway system failed in service, causing cars to separate. The bolt had been in service for more than ten years prior to failure. Visual examination showed that the failure resulted from complete fracture at the grease port and surface groove located at midspan. Drillings machined from the bolt underwent chemical analysis, which confirmed that the material was AISI 1045 carbon steel, in accordance with specifications. Two sections cut from the bolt were subjected to metallographic examination and hardness testing. The fracture origin was typical of fatigue. The...