High strain rate response of S355 at high temperatures

Forni, Daniele and Chiaia, Bernardino and Cadoni, Ezio (2016) High strain rate response of S355 at high temperatures. Materials and Design, 94. pp. 467-478. ISSN 0261-3069

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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 Split Hopkinson Tensile Bar for the mechanical 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 °C, 400 °C, 550 °C, 700 °C and 900 °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 °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.

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