Abstract: Fracture occurred on a spring of pantograph on the top of a tram during normal vehicle operation. In order to find the cause, the spring was analyzed by means of scanning electron microscope, energy spectrometer, optical microscope and direct reading spectrum analyzer for macroscopic observation, fracture scanning, metallographic examination and chemical composition. The hardness gradient test was also carried out. The results show that the fractured spring is subjected to tensile stress during service and exposed to corrosive medium in the service environment. According to that the stress condition and the medium condition are satisfied simultaneously, the failure mode of the spring is judged to be stress corrosion fracture.

Key words: tram pantograph, spring, stress, medium, stress corrosion fracture