Ballistic performance of multi-layered metallic plates impacted by a 7.62-mm APM2 projectile

Abstract

This paper presents a numerical investigation of the ballistic performance of monolithic, double-and triple-layered metallic plates made of either steel or aluminium or a combination of these materials, impacted by a 7.62-mm APM2 projectile in the velocity range of 775-950 m/s. Numerical models were developed using the explicit finite element code LS-DYNA. It was found that monolithic plates have a better ballistic performance than that of multi-layered plates made of the same material. This effect diminishes with impact velocity. It was also found that doublelayered plates with a thin front plate of aluminium and thick back steel plate exhibit greater resistance than multi-layered steel plates with similar areal density. These predictions indicate multi-layered targets using different metallic materials should be investigated for improved ballistic performance and weight-savings. Keywords INTRODUCTIONIn recent years, the ongoing threat of ammunition and explosively-formed projectiles to civil and military structures has increased the need to optimise protective structures. Armoured shields normally consist of a monolithic high-strength metallic plate; however, multi-layered plate configurations are often used because armour materials are not always manufactured to the required thickness, and multiple layers are necessary to fabricate shields that meet design specifications [1]. Although there are a number of studies dealing with the ballistic behaviour of multi-layered plates, their scope is limited when compared to studies of monolithic plates [2][3][4]. Moreover, the study of multi-layered plates remains an open research topic since conclusive results of its effectiveness have not been obtained to date, as is remarked in recent investigations [3][4].A numerical study conducted by Zukas and Scheffler [1] shows that 31.8 mm thick monolithic steel targets exhibit greater resistance than that of multi-layered targets with equal thickness when impacted by 65-mm long hemi-spherical nosed rods with a diameter of 13 mm and an initial velocity of 1164 m/s. They found that the weakening of the multi-layered configuration is due to the reduction of bending stiffness in the structure. They also found that the reduction of resistance in multi-layered targets becomes more apparent when the number of plates is increased while keeping the total thickness constant [1], which has also been observed experimentally [5][6]. Almohandes et al. [5] reported that monolithic steel plates are more effective than multi-layered plates of the same total thickness when impacted by a 7.62-mm projectile with an initial velocity of 826 m/s.An investigation conducted by Dey et al.[2] on the ballistic resistance of Weldox 700E steel in the sub-ordnance velocity range shows that 12 mm monolithic plate has better ballistic performance against ogival projectiles when compared with double-layered plates with same thickness, while the opposite effect is observed when blunt projectiles are used. Borvik et al. [7] studied experimentally the...

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