Mechanics of environment-assisted cracking in bridge cable wire

Broken wires retrieved from suspension bridge cables display a wide range for the critical crack sizes and corresponding ultimate strength. During tensile tests, most specimens fracture at short crack depths at a strength lower than the yield strength. This paper presents the analysis of environment-assisted short crack growth in bridge wire. It will be shown that the degrading environment in the bridge cable causes the reduction in the fracture toughness of the wire at the short crack location leading to brittle fracture. The paper will present a case study of short cracks observed during laboratory testing of bridge wire samples which failed at tensile loading below the maximum yield strength. The paper confirms the validity of linear elastic fracture mechanics in the analysis of environment-assisted short crack growth in the bridge wire at fracture. It is shown that the effective fracture toughness, (K-C)(M), at a short crack location could be significantly reduced due to environmental degradation. The fracture toughness criterion is utilized to forecast the degraded strength of cracked wire. Crack branching is shown to have no role in the mechanism of crack growth in the high strength steel bridge wire.