Experimental investigation of the energy absorption capability of bonded crash boxes

In the design of vehicle structures for crashworthiness there is a need for rigid subsystems that guarantee an undeformable survival cell for the passengers and deformable subsystems able to efficiently dissipate the kinetic energy. The front rail is the main deformable component dissipating energy in a frontal impact, which is the most dangerous crash situation. In frontal impact these rails have the greatest influence on vehicle crash performance. The design of the front rail, usually consisting of a thin walled prismatic column, requires definition of the geometry, that is, of the shape and dimensions of the cross section, of the thickness of the material, and of the material itself. In this work the analysis of the effect of different cross sections of the front rail and of the joining system is carried out. Furthermore, the collapse during crash is influenced by the loading rate since the loading speed has substantial influence on the mode of collapse and on the material behaviour. In fact, the structural materials used in this application are known to be strain-rate sensitive. Within the work, different types of sections are compared. The ground-breaking joining technology of bonding is examined: three different types of adhesive are compared, an acrylic, a one component epoxy and a two component epoxy. Adhesives can be used as a substitute to the widely used spot-welding to improve the structure performance mainly because of the continuous joint. The effects of the loading speed are taken into account by comparing quasi-static crush tests with dynamic impact tests. Dynamic tests have been performed under a drop tower testing apparatus built within the Vercelli campus of the II Faculty of Engineering of the Politecnico di Torino.