Extremely hard and at the same time incredibly light – these are the properties that protective materials used for military equipment must have. What may sound like a contradiction is in fact a life-saving paradigm for military forces: maximum protection at minimum weight. Ceramics have increasingly been replacing the steel materials previously used for personal and vehicle protection in military applications.
After diamond, boron carbide in crystalline form is the hardest material known to man. At the same time, it has a comparatively low density and is therefore a material that’s particularly suitable for ballistic protection. Because of its properties, boron carbide also performs better than ceramic alternatives such as silicon carbide and aluminum oxide.
Maximum protection at minimum weight: ceramics have increasingly been replacing the steel materials previously used for personal and vehicle protection in military applications.
High-performance ceramics beat armor steel
“Today’s military personnel need protection that’s effective but at the same time light” – this is what you hear from everyone at defense congresses and fairs. They list the potential dangers in the field: ballistic projectiles from small arms, medium and large caliber rounds, artillery and mortar fragments, explosively formed projectiles (EFPs), improvised explosive devices (IEDs) and rocket-propelled grenades (RPGs).
If projectile bodies or fragments hit a plate made of hard ceramic, the kinetic energy is effectively distributed over the plate and then diverted into the composite matrix below. Hard ceramic protective plates can even withstand hollow charges. Unlike ordinary metal armor, which behaves like a liquid when hit by a hollow charge, hard ceramic merely reacts by forming cracks. At the same time, fragments of the ceramic penetrate the metal spike of the hollow charge or penetrator and widen it, which compresses them in front of the spike and inhibits penetration far more effectively than armor steel.
Boron carbide composite systems for ballistic protection only weigh 30 kg/m2, while aluminum oxide-based systems are 42 kg/m2.
Deflecting impacts in the composite
This particularly high level of protection is effective because the ceramic is manufactured as a composite with a special fiber coating. This can be made from Spectra Shield or Dyneema, or even polyamide fibers such as Kevlar and Twaron (also called “backing”). Using high-performance adhesive, the ceramic plates are then glued to a module like a “sandwich”. With such GRP composite armor, the projectile can be reliably destroyed during the penetration process. The projectile’s remaining fragments as well as the residual energy are effectively absorbed by the soft, elastic polymer matrix. Modern designs even have three layers. The most effective of these – also against kinetic energy projectiles – is an intermediate layer made of a particularly hard and dense material such as boron carbide. That’s because this composition also offers good protection against multiple hits. Due to their properties, such ceramic composite armor systems can be used in a wide variety of applications – from clothing for personal protection, to vehicle and marine applications, to helicopters and airplanes. For example, one clever application is hot-pressed boron carbide plates used for pilot seats.
Because the underbody protection against explosions in many combat vehicles has increasingly been reinforced by massive metal plates – as protection against, for example, anti-tank mines – these vehicles have become very heavy. Some of this additional weight can now be compensated and reduced by retrofitting vehicle components with light ceramic composite panels to protect against ballistic fragments or projectiles. These weight savings have a positive effect on the load capacity, fuel consumption and range, as well as the ability to transport the vehicle and its floatability.
Comparison between ballistic protective materials made of ceramic and steel:
|Silicon carbide||Boron carbide|
|Hardness||100 %||250 %||300 %|
|Young’s Modulus||100 %||166 %||192 %|
|Compressive strength||100 %||166 %||208 %|
|Density (weight)||100 %||50 %||40 %|
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