Armor: Foaming It In

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June 26, 2019: Three years after it was realized the CMF (Composite metal foam) could provide superior protection against bullets and be much lighter as well, the theory was put to the test and it worked. This was done by modifying existing composite armor designs by substituting CMF for steel. This resulted in armor that weighed less and had superior stopping power. Composite armor is most widely used for tank armor. This is also called Chobham armor, after the place where it was developed in Britain during the 1960s. Composite armor used layers of metal (steel, depleted uranium and now CMF) separated by layers of ceramics to provide the most effective tank armor ever. Composite armor remains popular because it provides superior stopping power compared to the same weight of just high-quality steel plate armor. CMF takes this one step further by adding another lighter material, this time to replace some of the steel layers.

While the initial CMF composite armor works and is lighter, developers believe that by experimenting with thinner ceramic and aluminum layers between layers of CMF this new armor will be even lighter and more effective. With CMF you can have lighter and thinner armor while still providing the superior projectile stopping power. What makes CMF so effective is that the metal foam compresses when it is hit by a high-speed projectile. The CMF absorbs over 75 percent of the projectile momentum.

CMF that is produced by bubbling gas through molten metal to form a lightweight metal matrix. CMF was first introduced in 2015 as a lightweight solution to blocking various types of radiation, and it still does. CMF alone is very useful for protecting space satellite components from higher radiation levels encountered outside the earth’s atmosphere. Some researchers realized that this metallic foam if braced by layers of a more rigid material, could provide superior projectile stopping capability. Subsequent tests found that CMF could indeed stop high-speed bullets, including the armor piercing type. This would not only solve the problem of heavy body armor but also the weight problems created as armor is added to unarmored vehicles or to enhance the armor protection on existing armored vehicles, just as the original Chobham composite armor did. Some Chobham designs, like the one in the American M-1 tank, used a layer of depleted (non-radioactive) uranium (the densest of dense metals) that turned resulted in armor that could stop all known anti-tank projectiles. Alas, composite armor that thick could only be used in the front-facing portions of the tank. But it worked and forced opponents to try and get a shot at the thinner side, rear or top armor. Even so, the depleted uranium composite armor on the M-1 proved to be a significant battlefield advantage.

The development of new ceramics during the Cold War and their use in composite (Chobham) armor on tanks came about at the same time as ERA (Explosive Reactive Armor). Both of these innovations revolutionized armor protection for tanks. But these innovations were not as useful in a thinner, lightweight version. With CMF there is now the possibility of providing more effective body armor for infantry as well smaller combat vehicles. Ceramic plates are already used in infantry body armor, but only to protect the heart and lungs from larger caliber, high-speed rifle bullets. These ceramic plates are heavy and brittle. That is, they tend to shatter after stopping one high-speed bullet. That is a lifesaver, and the soldier has a large bruise on his chest or back and must get a new ceramic plate to insert into his protective vest. Composite armor is also damaged, but not shattered, from direct hits by high-speed armor-piercing shells and must eventually be replaced.

 


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