Experimental and numerical study on fragmentation of steel projectiles

¹ Structural Impact Laboratory (SIMLab), Centre for Research-based Innovation (CRI) and Department of Structural Engineering, Norwegian University of Science and Technology, Rich. Birkelandsvei 1A, 7491 Trondheim, Norway
² Norwegian Defence Estates Agency, Research & Development Department, PB 405, Sentrum, 0103 Oslo, Norway
³ SINTEF Materials and Chemistry, Rich. Birkelandsvei 2B, 7465 Trondheim, Norway

^a e-mail: knut.gaarder.rakvag@ntnu.no

Abstract

A previous experimental study on penetration and perforation of circular Weldox 460E target plates with varying thicknesses struck by blunt-nose projectiles revealed that fragmentation of the projectile occurred if the target thickness or impact velocity exceeded a certain value. Thus, numerical simulations that do not account for fragmentation during impact can underestimate the perforation resistance of protective structures. Previous numerical studies have focused primarily on the target plate behaviour. This study considers the behaviour of the projectile and its possible fragmentation during impact. Hardened steel projectiles were launched at varying velocities in a series of Taylor tests. The impact events were captured using a high-speed camera. Fractography of the fragmented projectiles showed that there are several fracture mechanisms present during the fragmentation process. Tensile tests of the projectile material revealed that the hardened material has considerable variations in yield stress and fracture stress and strain. In the finite element model, the stress-strain behaviour from tensile tests was used to model the projectile material with solid elements and the modified Johnson-Cook constitutive relation. Numerical simulations incorporating the variations in material properties are capable of reproducing the experimental fracture patterns, albeit the predicted fragmentation velocities are too low.