Armour Structures for Ballistic Impact

Traditionally, armours of been made of monolithic high hardness steel. Recently, however, there is high demand for lightweight armour for improved mobility in various applications, including personal body armour, vehicular armour, and on aircraft. This has led to the use of non-metallic materials, including ceramics and composites. Ceramics have become widely used due to their low density, high hardness, high rigidity and high strength. However, ceramics also have low strength low fracture toughness in tension. Tensile stress can be introduced due to global bending due to impact, or due to reflection of a compressive stress wave off a free surface (which changes it into a tensile wave). This has led to the development of composite armours where a ceramic faceplate is backed by a ductile material such as metal or polymeric composite to resist the tensile stresses. During ballistic impact, the projectile is first shattered or blunted by the hard ceramic, dissipating the energy over a larger area; and the backing plate bends to absorb the remaining kinetic energy, delaying tensile failure in the ceramic, and allowing more projectile erosion. This is now the accepted design for lightweight armours. However, the performance of multi-layered composite armours in ballistic impact is yet to be fully understood, and so the design of multi-layered configurations is not well founded in physics; and there are open questions around design parameters like layer thickness ratios for stress wave management, and what are favourable material response characteristics, particularly at the interface which bonds layers together.