The importance of interlayer optimisation in ceramic armour systems

Abstract

The modern requirement for vehicle armour has been demonstrated by recent conflicts, with armoured vehicles utilised as vital warfighting platforms. The engineering ceramics currently applied in these armour systems are not entirely understood under impact conditions, with little consensus on the critical properties required for optimal performance. The comparatively thin adhesive bonding interlayer between the ceramic (disruptor) and the typically metallic backing material (absorber) is an underresearched component of ceramic armour systems, potentially improving armour performance with minimal increases in mass. The acoustic impedance of this interlayer was believed to be critical, controlling the passage of potentially harmful shock waves within the armour system. Literature was surveyed to identify the design considerations, science, and failure mechanisms of ceramic armour. This formulated several possible interlayer solutions: tungsten-doped epoxy interlayers; metallic brazed interlayers; additively manufactured surface geometries in ceramics; and a thin molybdenum interlayer. Each solution was further assessed through reviewing specific literature prior to qualititative and quantitative characterisation. Varying increases in acoustic impedance were observed, although often at the expense of other important interlayer properties such as shear strength, attenuation, or manufacturability. Through ballistic impacts between 850-1,000 m/s with both scaled long rod penetrators and armour-piercing 7.62 mm rounds, alumina-steel targets with these various interlayers (excluding the additively manufactured ceramics) were investigated. A comprehensive understanding was developed beyond that of the current literature into the multiple inherent challenges of selecting optimum ballistic experimental setups, especially to isolate the effect of the interlayer. These insights potentially limited the conclusions drawn from this experimentation, relying more broadly on qualitative data. Changes in the interlayer / interfacial failure and ceramic failure mechanisms were observed with different interlayers. However, these caused little-to-no difference in the 1-dimensional penetrative resistance of the armours tested, suggesting that thin interlayers do not affect the penetration of kinetic energy projectiles into ceramic armour. However, the interlayers investigated may be critical in multi-hit performance through the control of shock transmission to surrounding ceramic tiles, identifying this as a key area for additional research. This research has provided a unique body of work exploring the importance of interlayers in the context of ceramic armour systems. By filling an identified gap within the literature, not only have experimental techniques been refined, but key insights into potentially optimum interlayers (and their positioning within the armour system) were identified.