High strain rate and high temperature response of two armour steels: Experimental testing and constitutive modelling

¹ School of Engineering, RMIT University, PO Box 71, Bundoora, Victoria 3083, Australia
² Defence Materials Technology Centre (DMTC), 24 Wakefield St, Hawthorn, Victoria 3122, Australia
³ Defence Science and Technology Group (DST-G), 506 Lorimer St, Fishermans Bend, Victoria 3207, Australia
⁴ School of Engineering and Information Technology, University of New South Wales, Northcott Dr, Campbell, ACT 2612, Australia

^* Corresponding author: s3333246@student.rmit.edu.au

Published online: 7 September 2018

Abstract

Under ballistic impact or blast loading, the high strain rate and high temperature behaviour of armour steels is key to their response to a given threat. This experimental and numerical investigation examines the tensile response of a class 4a improved rolled homogenous armour steel (IRHA) and a high hardness armour steel (HHA). Cylindrical tensile specimens were tested at a range of strain rates from 0.001 s^-1 to 2700 s^-1. Quasi-static, elevated temperature tests were performed from room temperature up to 300^° C. While the HHA is strain rate insensitive, the IRHA displays a significant increase in strength across the range of loading rates reducing the ultimate strength difference between the materials from 19% at 0.001s^-1 to 4.6% at 2700s^-1. An inverse numerical modelling approach for constitutive model calibration is presented, which accurately captured the dynamic material behaviour. The modified Johnson-Cook strength and Cockcroft-Latham (C-L) fracture models were capable of predicting the ballistic limit of each material to within 5% of the experimental result and to within 10% for deformation under blast loading. The blast rupture threshold of both materials was significantly over-estimated by the C-L model suggesting stress state or strain rate effects may be reducing the ductility of armour steel under localised blast loading.