Failed portions of a 4140 steel axle from a prototype urban transit vehicle were examined to determine the cause of failure. The testing procedures included visual examination, macrofractography, metallography, chemical analysis, and hardness and tensile testing. The analysis showed that a salvage welding repair had resulted in the formation of martensite that developed cracks, leading to fatigue failure of the axle. It was recommended that no weld buildup or repair be permitted on the axles.
W.B.F. Mackay, Fatigue Failure of an Axle From a Prototype Urban Transit Vehicle, Handbook of Case Histories in Failure Analysis, Vol 1, Edited By Khlefa A. Esaklul, ASM International, 1992, p 92–94, https://doi.org/10.31399/asm.fach.v01.c9001040
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