Dynamic behaviour of ceramic armour systems

Protection against high-velocity impact from objects such as projectiles is of major concern for bothmilitary and civilian purposes. Lightweight body armour systems for ballistic protection of personnel can be designed by combining different materials with different properties. These hybrid systems typically have a hard ceramic strike face that blunts, fractures and erodes the projectile, and a soft backing, made from ballistic fibres, that absorbs the residual energy. FFI has for many years been involved in the development of, and research on, body armour for protection of military personnel. In the period from 2004 to 2007, the technology behind an armour plate was developed in cooperation with industry. For future developments, however, it is necessary to have knowledge about the mechanisms that are acting under ballistic impact. Today, this topic is studied in several projects at FFI, and this report was written as a part of that work. The most common ceramics for armour purposes are - in order of improved performance - aluminium oxide, silicon carbide and boron carbide. The ceramics generally have relatively low density and high hardness. These, and other properties, make them useful in armour applications. The mechanisms by which a ceramic armour fails is quite complex, and involve failure mechanisms such as radial cracking, cone cracking and comminution due to micro-cracking. To what extent they appear and the relative timing of these mechanisms, depends on factors such as the impact velocity, the ceramic and projectile properties, and the dimensions of the ceramic and projectile. To improve the ballistic performance of the ceramic armour system, it is desirable to delay the failure of the ceramic for as long as possible. This allows more time for deformation and erosion of the projectile. It has been shown in the literature, and by work conducted at FFI, that the ballistic performance, both in terms of single-hit and multi-hit capacity, can be improved by radially confining the ceramic tile, by covering it with a sheet of another material, and/or by tuning the interfacial strength between the cover and the ceramic. The main aim of this report is to give an overview of the mechanisms that are involved in ballistic, or dynamic, failure of ceramics and ceramic-based hybrid armour. The failure mechanisms, the factors that govern the failure mechanisms, and what can be done to delay the failure of the ceramic, are discussed on the basis of some of the available literature on the topics.