Abstract
Broken wires of an old suspension bridge in USA were investigated. Tension strength, elongation, chemical composition of the broken wires are almost the same as those of the recent galvanized high strength wires. However, the torsional strength is low and high residual stress exists due to the bent shape. Observation of fracture surface with electrical microscopes indicates that the crack initiation position is the corrosion notch on the wire surface. The crack gradually progresses from that point and beech-mark like stripes appear. Since the fracture surface is similar to a typical fracture surface of corrosion fatigue failure specimen instead of hydrogen embrittlement specimen, it is estimated that the wire breakage occurs by the mixed effects of corrosion, fatigue and hydrogen.
