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

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.

Plastic dynamic response of simply supported thick square plates subject to localised blast loading

“…In the case of impulsive loads, the inertia term is identical to Eqn. (37) and the deformation fields are furnished as per Eqn. 's (70) and (71).…”

“…the CEL models), each prescribed a density of 7850kgm -3 , Young modulus of 200GPa and characteristic in-plane lengths of 400×400mm, thicknesses of 60mm (Mild steel) and 10mm (armour steel), with modified Ramberg-Osgood material model which was idealised as elastic-perfectly plastic. The visco-plasticity phenomenon was disregarded as armour steel material are impervious to the strain rate up to 3000 −1 [37]. However, the flow stress was taken as the average of yield stress and ultimate tensile stress to approximate the influence of strain hardening.…”