Polyurea coated composite aluminium plates subjected to high velocity projectile impact Damith Mohotti a,⇑ , Tuan Ngo a , Priyan Mendis a , Sudharshan N. Raman b a Department of Infrastructure Engineering, The University of Melbourne, Victoria 3010, Australia b Department of Architecture, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia article info Article history: Received 19 March 2013 Accepted 18 May 2013 Available online 30 May 2013 Keywords: High velocity impact Composite plates Polyurea Aluminium alloy Projectiles abstract High velocity projectile penetration through polyurea coated AA5083-H116 aluminium alloy plates has been studied. The effect of different polyurea thickness on the residual velocity of full metal jacket (FMJ) projectiles is examined and presented. Steel-tipped 5.56 calibre (5.56  45 mm) projectiles were fired at coated aluminium plates from a distance of 10.0 m at a fixed velocity of 945 m/s. Seven config- urations of plate arrangements with different total thicknesses were used. Each configuration consisted of combinations of 5 mm and 8 mm base plates (AA5083-H116) with 6 mm and 12 mm polyurea layers. A 5.56 calibre gun was used to shoot at close range, where the targets were placed perpendicular to the fly- ing direction of the projectile. The input and output velocities were measured using two laser velocity screens. The effectiveness of the polyurea coating in terms of reduction of the residual velocity, damage mechanism, kinetic energy absorption of the plates, and the effect of different layer configurations on residual velocity are presented and discussed. By comparing the different thicknesses of polyurea coat- ings, it indicated a good ability in absorbing energy, and subsequently, in a reduction of the residual velocity of the projectiles. Also, the ability of the polyurea coating to act as a protective shield against fly- ing particles and fragments was established. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Over the last few decades, many researchers have investigated the use of polyurea as a protective coating material due to its abil- ity to absorb a considerably high amount of energy compared to most other similar coating materials. In recent years, researchers have drawn their attention towards the application of polyurea to enhance the resistance of structures and systems against ex- treme impulsive loadings. With adequate surface preparation, polyurea bonds well with most structural materials (such as con- crete, steel and aluminium), thereby forming composite behaviour. It can be used either as the outer face of a structure, or as an inter- layer material, by utilising its compressive or tensile properties depending upon the nature of the load transmitted. However, most previous research work on polyurea coated plates has been focussed only on distributed dynamic loadings induced from an event such as a blast. Very limited attention has been paid to inves- tigate its behaviour under localised loadings which can be gener- ated from an event of ballistic impact. Xue et al. [1], Sayed et al. [2] and Roland et al. [3] are a few instances where the polyurea coated materials were investigated under ballistic loadings. These investigations were studied on considerably larger diameter pro- jectiles in comparison to handgun ammunitions where the impact object’s diameter is in the range of 3–10 mm. This study attempts to address this gap in knowledge by examining and quantifying the velocity reduction ability of different thicknesses of coatings and the possibility of using polyurea as a protective coating against bal- listic threat scenarios. Ballistic impacts generally induce localised failure in their tar- gets. The working mechanism of real ammunition starts by creat- ing a ductile crater and enlarging it till the ammunition reaches complete penetration or loses its momentum completely. This whole process depends on the behaviour of materials during the deformation process, as well as the structural dynamics effect in- volved during the impact and penetration process. In order to understand this complex mechanism comprehensively, one must study the real ammunition penetration at the recommended veloc- ities rather than simplifying the process with rigid non-deformable projectiles. As highlighted above, several investigations have been per- formed over the last decade to study the ability of polyurea in reducing the destructive effects from projectile impact. A detailed numerical and experimental program of rigid projectile penetra- tion through polyurea coated DH-36 steel plates was performed by Xue et al. [1]. They observed a positive contribution from the polyurea coating in terms of improving resistance against ballistic 0261-3069/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2013.05.060 ⇑ Corresponding author. Tel.: +61 425531977. E-mail address: pushpajm@unimelb.edu.au (D. Mohotti). Materials and Design 52 (2013) 1–16 Contents lists available at SciVerse ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes