Failure Analysis of Cables of Undercarriage Door Control Mechanism : AN-32 Aircraft

The failed cables are regular lay cables of seven strands and each strand consists of seven wires. The wire failure occured predominantly at locations of abrasive wear between adjacent strands. These wear sites are iden-tifiable by a large reduction in diameter; however, redu-ction in area is not responsible for the location of failure. Fractrography studies revealed fatigue crack initiation sites located opposite the characteristic wear site. The primary failure mechanism of majority of wires within a strand is believed to be a function of contact stress at the wear sites, which in turn produce large alternating tensile stresses on the opposite side of the wire. The mechanism may be termed contact-stress-acce-lerated fatigue. The geometrical arrangement of fatigue zone in wire cross section indicated that the primary failure is due to bending fatigue. This mechanism and the affiliated wear pattern are both consequences of inter-strand contact. The core wire in majority of strand is found to have cup-cone fracture due to tensile overload which is secondary in nature.