Fatigue life scatter of aluminium alloy helicopter lugs

Fatigue tests were performed on lugs in five cases with stress ratio R = 0. 1 and maximum load F-max=44 kN. However, it was found that there was a rema rkable scatter of fatigue lives even in identical tests. Fractography of th e fractured lugs has shown that each crack initiated at one origin, which w as on the hole surface and near one side of the lug. Stress analysis has de monstrated that the crack origins locate in a high stress region and the fa tigue stresses make the lugs fail in range of 10(5)-10(6) cycles. Detailed examination of the microstructure of the lugs has shown that the recrystall ization degrees in the lugs vary. It is the scatter of recrystallization de gree that increases the fatigue lives of lugs. A further analysis has indic ated that the scatter of recrystallization degree may result from the diffe rences of original bar stock sizes and deformations in die forging. (C) 200 0 Elsevier Science Ltd. All rights reserved.