Stress corrosion cracking fracture mechanism of cold-drawn high-carbon cable bolts

Abstract

Premature failures of cable bolts due to stress corrosion cracking (SCC) in underground reinforcement systems are universal issues with limited practical countermeasures at present. To determine the SCC fracture mechanism which is an essential step to develop the potential solutions, the environment conditions leading to SCC failures were examined using four-point bend tests. Fractographic features of both serviced-failed and laboratory-failed cable bolts were investigated and compared. It was identified that the fracture surfaces of cable wires were characterised by step-shape fracture mode. The highly-oriented wavy lamellae microstructures of cable wires, produced during cold-drawn manufacturing process, have significant effects on the direction and path of crack propagation. Hydrogen-assisted SCC was suggested as the dominant fracture mechanism in cable bolt failures. SCC only occurred in the environmental conditions that promoted the diffusion of hydrogen diffusion into the cable wires, and crack growth rates were determined by the hydrogen diffusion rates. This study provided fundamental knowledge on fracture mechanism of cable bolts which can be applied to further study in identifying potential countermeasures against the SCC of cold-drawn high-carbon cable bolts.