In-service fatigue cracking of the propeller shafts joined by a spline-pinned construction to the engines of AN-24, AN-26, and IL-18 aircrafts

摘要

The paper delivers a critical review of the research data on the crack initiation and crack growthpatterns characteristic of the components of the spline-bolted joints between the propeller shaft and reducershaft at An-24, An-26, and Il-18 aircrafts. Cracks in the shafts nucleated because of reduced bolt-fasteningforce. Actually, the bolt (bolts) failed first (also by fatigue) and then fatigue cracks nucleated and grew in theshafts, the spline surface fretting zones and/or sharp edges of the attachment (bolt-conducting) holes makingthe crack origin sites. The crack growth history shows itself through the regular Macro-Beach Marks, each marksequentially pointing to the next loading event of the propeller shaft, i.e., to each next flight. The cracks ceasegrowing for some while in the airscrews and their shafts just replaced to another aircraft. For the airscrewshafts, the critically assessed data show the crack growth period Np ranging as five to ten percent of a totalrunning period Nf . We recommend performing nondestructive inspection of the airscrew shafts on every 250-hour running period to ensure the safety flights.