Experimental Investigation of the Energy Absorption Capability of Continuous Joined 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 crash, which is the most dangerous crash situation, and for which the structural behaviour is mostly affecting. 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 dimension 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. Different non-common continuous joining technologies are examined: three different types of adhesive an acrylic, one component epoxy and two components epoxy and laser welding. Adhesives and laser welding can be used as an alternative to the widely used spot-welding to improve the structure performance due to the continuous joint. The effects of the loading speed are taken into account by comparing quasi-static crush tests to dynamic impact tests. Dynamic tests have been performed under a drop tower testing apparatus built within the campus of the II Faculty of Engineering of Politecnico di Torino.