Mechanical behaviour of a very-high strength steel (S960QL) under extreme conditions of high strain rates and elevated temperatures

Abstract

The lack of full stress-strain data sets under the coupled effect of high strain rates and elevated temperatures is one of the main concerns in a multi-hazard (blast and fire) approach of very-high strength steel (VHSS) structures. The main research challenge is represented by the assessment of the strain rate behaviour in tension and in a wide range of temperatures of a very-high strength steel (S960QL). For this purpose a split Hopkinson tensile bar equipped with a water-cooled induction heating system is used for the mechanical characterisation at high strain rates (250 s−1, 500 s−1 and 950 s−1) and in a wide range of temperatures (20 ∘C, 400 ∘C, 550 ∘C, 700 ∘C and 900 ∘C). A special focus on the influence of the relative sample position in thickness such as core and peripheral material was examined. A comparison between reduction factors of main mechanical properties, in both dynamic and quasi-static conditions, is presented.In addition, some predictive equations were developed to define the dynamic strength decrease with increasing temperatures. Finally, the constitutive parameters of the Johnson-Cook strength model for both core and peripheral materials were reported.