Failure of copper wires in a railway Motor Operation Contact

Many engineering alloys can fail by environmentally assisted cracking (EAC). The risk of failure is dependent on the specific combination of material, the environment and the stress. Identification of the stresses (applied and residual) can be difficult because of the retrospective nature of failure investigation and the commonly complex character of stresses in real engineering applications. A routine inspection of a Motor operation contact installed aside a railway line in the British countryside found that the copper wire contact had failed. Standard failure investigation techniques combined with fractography were applied to identify an intergranular failure mode. Experimental observations combined with a review of the relevant literature allowed the root cause to be assigned to environmental assisted cracking in the presence of gaseous ammonia in the local environment.