Analysis of the failure of a tramcar pantograph component through combined experimental approaches

Tramcar vehicles collect the required electrical power from the overhead contact line by means of a pantograph that carries a pan head with collector strips in sliding contact with the contact wire. Therefore, any failure of pantograph or of its components has a direct effect on the correct tramcar operation. The paper deals with a case of unexpected failures occurred on a connection element of the articulated frame of the pantograph of tramcars, causing the interruption of the service. No evidence of impact with the overhead line was detected, only it was clear that the immediate cause was the fatigue failure of a pin of the articulated connection between the upper and the lower arms of the frame of the pantograph. To clarify the original cause of the fatigue failure, an approach combining field measurements, laboratory tests and data processing to obtain the stresses acting on the pantograph failed components under service condition was adopted. It was found that the pantograph was subjected to high level of vibrations coming from the vehicle carbody, mainly due to the track irregularity. A comparative failure analysis was carried out and a solution to upgrade the component subjected to failure was proposed and implemented.