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

Abstract

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

Fretting Wear in Selected Elements of Rail Vehicles

“…Research conducted by the author of [1] demonstrated that the measurable traces of damage at the surface of the examined elements occur as early as at approximately 10 3 load cycles. When the number of cycles becomes greater, wear intensity increases as long as the cycle number reaches over 10 6 .…”

“…The sample wear test parameters were as follows: -revolutions: n = 1360 rpm -load on the sample: Q = 550 N -number of cycles: 7×10 6 .…”

“…Fretting wear also occurs in other fields of technology, where a pair of elements touching each other is subjected to oscillatory tangential displacement. It follows from the review of literature that fretting wear is found in, for example, aviation industry [5][6][7], in medicine [8][9][10] in orthopaedic items connecting fractured limbs and in artificial joints, as well as in the automotive industry [11].…”