Why Aren't Metal Foams/Metal Sponges Used as Direct Ballistic Armor?
When searching for metal foams or metal sponges as a ballistic armor solution, it's often observed that they are predominantly used as impact absorbers. Why isn't this material considered as a direct ballistic armor? While ceramics are often praised for their performance, metal foams are a cost-effective alternative that can provide remarkable impact absorption. This article aims to explore the reasons behind their limited use in direct ballistic armor.
The Role of Metal Foams as Impact Absorbers
Metal foams, due to their honeycomb structure and open-cell architecture, excel at absorbing impact energy. They can significantly reduce the force of impacts without compromising the overall structural integrity of the armor. When used as a stand-alone layer, metal foams are highly effective in mitigating the damage caused by exploding shells and other high-velocity projectiles. This capability makes them a preferred choice for impact absorption applications.
The Limitations of Metal Foams as Direct Ballistic Armor
From a mechanical engineering perspective, metal foams are not ideal for direct ballistic applications. Their open-cell structure can easily perforate under the high-momentum impact of kinetic rounds, making them less effective as a primary armor material. However, when sandwiched between two ballistic plates, metal foams can provide excellent impact absorption. This configuration helps in reducing the overall weight of the armor while maintaining a defined level of protection.
Why Add an Extra Layer?
Integrating metal foams into a multi-layered composite armor system is a common strategy. Caged armor, for example, is an additional layer designed to reduce the effects of HEAT (High-Explosive Anti-Tank) warheads. While metal foams can't effectively mitigate the impact of kinetic energy rounds, they excel in dispersing energy. This dispersion can significantly increase the chances of the other armor materials in the system to successfully deflect or absorb the incoming threat.
Options for Ballistic Protection
For non-exploding shells, the primary goal is to obstruct the path of the projectile with mass. While almost any material can serve this purpose, denser materials are more compact and effective. Metal foams, though lighter, are less dense compared to solid metal plates, making them less effective in this context. Additionally, mechanical absorption can play a critical role, based on the material's strength. Foamed metal can provide some absorption, but it is less compact and can be less effective than solid metal due to its less dense structure.
Neutralizing the Effects of Impact
To ensure true ballistic protection, it is essential to design armor with multiple layers that can effectively absorb and neutralize the impact. A hard, dense surface is crucial for deflecting the initial impact, while the subsequent layers, possibly lighter and softer, can absorb the remaining energy. Even theoretically indestructible armor could be rendered ineffective if the resulting impact causes blunt trauma. The soft backing layer ensures that while the armor is hit, the force is distributed, reducing the likelihood of injury to the target.
In summary, while metal foams are highly effective as impact absorbers, their open-cell structure makes them less practical as direct ballistic armor. Their integration into multi-layered composite systems can significantly enhance the performance of the armor, providing a balance between weight, impact absorption, and overall protection. Ceramic armor remains a strong contender due to its superior performance in ballistic applications, but metal foams offer a viable and cost-effective alternative for impact absorption purposes.