Design of an efficient crashworthy lifeguard for current and future electric multiple unit bogies

Abstract

Lifeguards are energy-absorbing devices fitted to the leading edges of train bogies under driving cab ends. Their primary function is to deflect obstacles away from the wheel/rail interface and in the process absorb excessive impact energy through plastic deformation. This paper presents an experimental investigation into the crashworthiness, the deformation mechanisms and failure phenomena of steel lifeguards for the Class 465 electric multiple unit (EMU) train bogies. Their performance, based on tight specification, is evaluated under both quasi-static and impact loading. Under quasi-stactic loading, the lifeguards have been shown to be capable of withstanding, without permanent deformation to the bogie and its attachment to the axlebox, a load of up to 35 kN applied horizontally in the global longitudinal axis of the train towards the adjacent wheel. The deformation history is found to be that of a plastic hinge developing at the neck or narrowest section which proceeds by rotating the tip about the deformed section. Typical loads necessary for triggering the plastic failure are between 40 and 58 kN; this rises to a maximum of 60-67 kN as the tip rotates around the single hinge mechanism. Under impact loading, the lifeguard shows a failure mechanism that is to some extent similar to that observed under quasi-static testing. The difference, however, is in the collapse mechanism hierarchy which begins with a local plastic indentation at the point of load application and is followed by rotation of the neck about the global principal axes resulting in a three-dimensional failure of the tip. Typical dynamic loads are between 3.5 and 3.8 times the quasi-static loads. Based on the mechanism of deformation observed from the experimental results of the developed lifeguard, preliminary theoretical predictions have been carried out using finite element analysis. The computer outputs show good correlation with experimental results.