Dynamic characteristics of adhesive bonded high strength steel joints

With an increase in the use of advanced high strength steels in vehicle architectures, materials joining issues have become increasingly important. Among the various joining methods, adhesive bonding is increasingly used in automobile manufacturing. Successful implementation of adhesive bonding to improve structural crashworthiness and reduce vehicle weight requires the knowledge of issues related not only to processing but also to joint performance. In this study, the impact strength of adhesive bonded high strength steel joints is evaluated with the split Hopkinson tension bar (SHTB) technique. The influences of loading speed and thickness of the steels on the shear strength of the joints were examined. Comparative quasi-static lap shear tests were also conducted on a tensile testing machine. Test results showed that strength and energy absorption of bonded steel joints increase with loading speed, and is greatly affected by the thickness of the steels. As the loading rates are increased to 1100 s(-1) (i.e. 20 m s(-1)), bonded 0.75 mm thick DP600 steel shows a 152% increase in strength and an 83% increase in energy absorption when compared to its quasi-static values. Examination of the impact tested specimens showed the failure mode changes from coarse cohesive mode to fine cohesive mode with increasing loading speed. The results from this study will provide the information for a better understanding of impact failure mechanisms of adhesive bonded high strength steels.