Evaluation of a hydrocode in modelling NATO threats against steel armour

Abstract

Having identified relevant constitutive models and the likely fracture mechanisms, a benchmarking study was undertaken to numerically compute a perforation solution based on the work by Børvik et al [1]. Material strength of ductile metals subjected to high strain phenomena is often described through the Johnson-Cook model [2] or the Zerilli-Armstrong [3] relation; both describe strain rate sensitivity, strain hardening and thermal softening albeit by different means. Phenomenological models like Johnson and Cook’s [2] and the associated fracture criterion by the same authors [4] have been extensively used [1,5-8] across a number of research areas. Whilst useful in capturing the main deformation and failure mechanisms, the author’s note the inherent deficiencies present in these models and resolve to calculating conservative solutions. The study also evaluates the blast response of an elasto-plastic plate using the commercial FEA code LS-DYNA[10]. The peak displacement of each plate is compared to literature [11] through two blast analysis techniques, namely the CONWEP blast code which is embedded in the hydrocode and the computationally expensive, but more accurate, technique of fluid structure coupling via a multi-material ALE formulation. The blast threat is a 6 kg TNT mine modelled using the steel pot test criteria set out by the NATO standard in AEP-55 Vol.2. The ALE formulation is competently described in [12] and we apply it to validate wether it’s applicable for near field blast analysis. We aim to shed some light on the nuances and the problems associated with modelling highly dynamic problems. In the words of Jean Lemaitre and Rodrigue Desmorat [14]: “Very accurate calculations are too often made with a very poor accuracy of the material parameters”