Novel thermo-mechanical triggers processed by friction stir to enhance the crashworthiness of an automobile crash-box

Abstract

Thin-walled tubular structures, also known as crash-boxes, are found to be efficient in dissipating kinetic energy of external impact. It is observed that the conventional aluminium square crash-boxes are characterised by higher initial peak crushing force and low crush force efficiency. In this work, a novel concept of inducing “Thermo-Mechanical Triggers” (TMTs) at discrete locations in a conventional aluminium square crash-box to enhance its crashworthiness behaviour is studied. TMTs are induced with the help of “Friction Stir Processing” (FSP), which is a localized heat treatment. The material properties of a crash-box are modified wherever TMTs are induced using FSP. The effect of changes in the location and the number of TMTs along the length of an aluminium crash-box is examined. By triggering a conventional square crash-box with TMTs, significant improvement is observed in its crashworthiness performance. The improvements are: (1) a 24% reduction in the initial peak force and (2) a 23% increase in the crush force efficiency. Therefore, TMTed crash-boxes will prove to be effective in enhancing passenger safety, which is a major concern in the automobile industry. The crashworthiness performance of a TMTed crash-box can be improved further by optimizing both the location and the number of TMTs.