Two clamps that support overhead power lines in an electrified rail system fractured within six months of being installed. The clamps are made of CuNiSi alloy, a type of precipitation-strengthening nickel-silicon bronze. To identify the root cause of failure, the rail operator led an investigation that included fractographic and microstructural analysis, hardness testing, inductively coupled plasma spectroscopy, and finite-element analysis. The fracture was shown to be brittle in nature and covered with oxide flakes, but no other flaws relevant to the failure were observed. The investigation results suggest that the root cause of failure was a forging lap that occurred during manufacturing. Precracks induced by the forging defect and the influence of preload stress (due to bolt torque) caused the premature failure.

An electric transport vehicle, similar to an electric trolley or subway rail car, experienced frequent breakdowns due to in-service fractures of torsion springs that support the weight of an overhead electric pickup assembly. Scanning electron microscopy and metallographic examinations determined that the fractures stemmed from electric arc damage. Intergranular quench cracks in the transformed untempered martensite on the surface of the spring provided crack initiations that propagated during operation causing fatigue fracture.

Wire ropes, pulleys, counterweights, and connecting systems are used for auto tensioning of contact wires of electric railways. A wire rope in one such auto tensioning system suffered premature failure. Failure investigation revealed fatigue cracks initiating at nonmetallic inclusions near the surface of individual wire strands in the rope. The inclusions were identified as Al-Ca-Ti silicates in a large number of stringers, and some oxide and nitride inclusions were also found. The wire used in the rope did not conform to the composition specified for AISI 316 grade steel, nor did it satisfy the minimum tensile strength requirements. Failure of the wire rope was found to be due to fatigue; however, the ultimate fracture of the rope was the result of overload that occurred after fatigue failure had reduced the number of wire strands supporting the load.