Composites are widely used in military applications for numerous reasons, with cost being low on the list of priorities (unlike commercial applications). The need to have the best technology to win a battle is paramount. During the First World War when aerial combat first took place, canvas and dope (shellac) covering for airplane wings and fuselages was used, and that is one of the earliest uses of composite materials, as we know them, today. By the time the war ended, Baekelite (invented in 1907) was in commercial production. When the Second World War started a canvas and phenolic resin composite was being widely used for airplane and marine components.
But what about other composites such as concrete? The material was widely used to construct defences in both World Wars (such as the French Maginot Line and the German Siegfried Line) and river barges. During the Second World War concrete ships were used by the Allies to support invasions. One of the most remarkable uses of concrete was the construction of two Mulberry Harbours in England, which were towed section by section across the English Channel and assembled at the D Day Beaches. Without these the Allied invasion could not have succeeded. Large parts of one survive today, a testament to the designers and the material’s durability.
Research by chemists led to polyester resins and the use of glass reinforced polyester for the construction of small naval craft by the time the Second World War ended, and the material has continued in widespread military use, even being used for small ships – minesweepers – where non-magnetic hulls are important.
Apart from the more obvious aerospace and missile applications where structural weight saving is a major design consideration, carbon and aramid fiber composites are widely used for vehicular, structural and armor applications by the military. The Pentagon has been seeking a replacement for the Humvee for many years, and the shortlist for the Joint Light Tactical Vehicle (‘JLTV’) is now down to three. All utilize high proportions of composites from advanced battery-plate technology to blast resistant tires, besides the more obvious armor. Even the windows are composite.
Composite armor is fitted to the US M1 Abrams and UK Challenger battle tanks. It is technically a composite of ceramic plates, bonding compounds, a metal matrix and other elastic layers but lacks durability as its efficiency is dependent on its brittleness. The precise formulations and structures are still secret - it has never been directly defeated in battle, though it is a far cry from our usual idea of a composite as being a GRP-like material.
The humble soldier’s life expectancy is increased not only by Kevlar vests but by composite helmets, advanced composite goggles, gloves and more effective, lighter weaponry using composites in their construction. The general weight reduction of standard equipment has not lessened his (or her) load though – one just has to carry additional equipment.
However what has changed is that there are many soldiers alive today who would be dead were it not for advanced composite armor and flak jackets.
The key advantages of composites in military applications are:
- Low maintenance
- Corrosion resistance
- Self lubrication (specialized composites)
- Long life (if UV protected)
- Low weight (compared to the alternatives) – especially important for air-transportable equipment (such as the JLTV replacement for the Humvee).
- Tailorability of physical properties to suit specific applications
- Low thermal signature
There are other advantages which are specific to particular composites and especially dependent on the reinforcing fiber used.
Given the advantages of composites, their future for military applications is assured. Even concrete continues to be used and there is no sign of that changing. Volume production of the more exotic raw materials such as carbon and aramid fibers is reducing costs and accelerating use of these materials. Newer materials such as carbon nanotubes will further extend the use of composites in military applications.
And finally, how about the composite soldier? We may be stretching the definition a bit, but fighting suits which offer a human soldier not only protection but augmented strength, built-in weapons and other capabilities – even flight – are under development. The composite soldier is coming soon to a war near you, but his load will still be over 100 lbs.