Sprocket Locking Device Failure
A failed tapered-ring sprocket locking device consisted of an assembly of four tapered rings that are retained by a series of cap screws. The middle wedge-shaped rings were pulled closer as the screws were tightened forcing the split inner ring to clamp tightly onto the shaft. One of the wedge-shaped middle rings fractured prior to having been fully torqued, preventing the sprocket from being locked to the shaft. “Woody” fracture features, as a result of decohesion between a high volume fractions of manganese sulfide stringers and the matrix, was revealed during examination. The material was revealed by chemical analysis to be resulfurized grade of carbon steel (SAE type 1144, UNS G11440) which has enhanced longitudinal tensile properties but low transverse properties. It was observed that when the fastening screws were torqued, a significant hoop stress was placed on the middle rings and it caused the failure at the large inclusion present at the minimum section thickness zone of the middle ring. It was concluded that since the material contained a high volume fraction of these inclusions, the material choice was not appropriate for this application. A nonresulfurized grade of low-alloy steel was suggested as recommendation.