High strain rate response of S355 at high temperatures

In this paper the high strain rate behaviour in tension and in a wide range of elevated temperatures of the S355 structural steel is presented. A SplitHopkinson Tensile Bar for themechanical characterisation at high strain rates, equipped with a water-cooled induction heating system is used. These data are collected with the purpose of evaluating the extreme combined effect of dynamic loadings and elevated temperatures (200 degrees C, 400 degrees C, 550 degrees C, 700 degrees C and 900 degrees C), e.g., a fire load followed by an explosion. The reduction factors for the main mechanical properties are reported. The novelty of our data is the addition of the strain rate dependency to the temperature. High strain rate tests at 550 degrees C highlighted the phenomenon known as blue brittleness where an increase of strength and a decrease of ductility were ascribed to the dynamic strain ageing. Focusing the attention on the thermal softening parameter, m, the widely used constitutive law proposed by Johnson and Cook during the eighties is critically reviewed highlighting some weaknesses. The results can be of great interest for the assessment of robustness in structures where a fire induced progressive collapse should be evaluated focusing the attention to the extreme combined effects. (C) 2016 Elsevier Ltd. All rights reserved.