Characterisation and modeling of adhesives for steel joints under crash loading situations

The behaviour of adhesive bonds of Betamate 1496V and steel under crash loading situations was investigated with high rate tests at strain rates up to 104 s-1 under tensile and shear loading by Fraunhofer IWM within a common German AiF-project P828 (IGF 338 ZN25) of various institutes, see [1]. High speed video imaging in combination with digital image correlation (DIC) analysis were used to measure the in part very small elongations of only 40 mm up to failure. The results show a significant rate sensitivity of Betamate 1496V with increasing tensile and shear strength by about a factor of two from static to crashsimilar loading rates. The corresponding tensile strains at failure decrease, whereas the shear strains at failure remain practically independent on strain rate. Beyond yielding, the high rate shear curves become less steep, thus approaching the statically measured curves, which is explained by increasing adiabatic heating of the adhesive. This was confirmed by simulations with a material model of IWM resulting in an increase in temperature of about 50 K for high rate shear tests compared to only about 10 K for tensile tests. In addition, this adiabatic heating was verified by measurements with an infrared high speed camera.