Plasticity and ductile fracture behaviour of four armour steels

Under ballistic impact or blast loading, the strength and fracture behaviour of armour steels is key to their response, however a comprehensive understanding and modelling of material behaviour for multiple grades of high strength armour steels has not been presented in literature. This experimental and numerical investigation comprehensively characterises the plasticity and ductile fracture behaviour of four high strength armour steels: rolled homogenous armour (RHA); improved rolled homogenous armour (IRHA); high hardness armour (HHA); high strength abrasive resistant steel (ARS) with a TRIP strengthening mechanism. Thirteen specimen types are used to investigate a range of stress states from uniaxial tension to high stress triaxiality plane strain as well as elevated temperatures and strain rates. A modified Johnson-Cook strength model with combined Voce-Ludwik strain hardening and a J3-dependant yield function was calibrated and used. A new calibration approach for the ductile fracture model is presented that incorporates the time-dependence of the stress state taken from inverse numerical modelling of each experiment. The modelling is shown to accurately capture material response up to fracture across all specimens. High strain rate experiments identified dislocation drag effects at 2700s−1, which were captured by the modelling approach. The experimental results provide a characterisation of armour steels to an extent not previously seen in literature, particularly considering comparison of four materials across identical test conditions.