Armour Structures for Ballistic Impact

传统上，盔甲是由整体高硬度钢制成的。然而，最近对轻型装甲的需求很高，以改善各种应用的机动性，包括个人防弹衣，车辆装甲和飞机。这导致了非金属材料的使用，包括陶瓷和复合材料。陶瓷具有密度小、硬度高、刚度大、强度高等特点，得到了广泛的应用。然而，陶瓷在拉伸中也具有低强度、低断裂韧性的特点。拉应力可以由于冲击引起的整体弯曲而引入，或者由于从自由表面反射压应力波（将其转变为拉应力波）而引入。这导致了复合装甲的发展，其中陶瓷面板由韧性材料（如金属或聚合物复合材料）支撑，以抵抗拉伸应力。在弹道冲击中，抛射物首先被坚硬的陶瓷击碎或变钝，在更大的区域内耗散能量；背板弯曲以吸收剩余动能，延缓陶瓷的拉伸破坏，并允许更多的弹丸侵蚀。这是现在公认的轻型装甲设计。然而，由于对多层复合装甲在弹道冲击中的性能还没有完全了解，因此多层复合装甲的设计还没有很好的物理基础；还有一些悬而未决的问题围绕着设计参数，比如应力波管理的层厚比，以及什么是有利的材料响应特性，特别是在将层粘合在一起的界面上。

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.