Military and defense composites play a critical role in making the modern army as safe as it can possibly be. Among their diverse capabilities is a remarkable ability to perform as ballistic armor for both vehicles and personnel.
The best armor is designed with ballistic laminates that combine key scientific principles to keep soldiers safe. These laminates offer superior protection through a sophisticated combination of layered composite materials that absorb, dissipate, and resist energy. It is just what soldiers and military vehicles need to protect against high-velocity projectile penetration.
The underlying principle behind ballistic laminates builds on the basic principles of composites themselves. A composite material, like carbon fiber reinforced plastic, gets its strength from the fibers that reinforce it. By arranging fibers in specific directions, engineers can add strength where it is needed most.
Think of the multiple layers in a laminate as being like the individual fibers in a composite product. Laminates add strength with each layer embedded within. The layers can be aligned in such a way as to enhance penetration resistance.
A favorite for ballistic protection is ultrahigh molecular weight polyethylene (UHMWPE). Another is Kevlar (an aramid fiber). Even carbon fibers embedded in a resin matrix can be used as part of a ballistic laminate. The choice of composites depends on the properties an engineer wants to stress.
As you might imagine, the key to preventing projectile penetration is energy absorption and distribution. When a projectile strikes a piece of armor, it is the first layer of the laminate that takes the impact force. This first layer then undergoes compressive deformation or cracking. This generates shock waves that travel through the remaining layers underneath.
As energy makes it to each layer, tensile deformation and delamination occur. These natural processes spread the kinetic energy of the impact across the entire surface area, allowing the layers to absorb through stretching, pulling, and fracturing. The result is that the projectile’s penetration force is greatly diminished.
Though it sounds counterproductive, we actually want composites to fail in a ballistic laminate scenario. Failures designed into each layer are the key to dispersing energy. So from an engineering standpoint, we look at different mechanisms of failure and what they can bring to the table.
Consider delamination. This occurs when two or more layers in a laminate separate from one another. Delamination helps absorb energy as the layers move. Likewise, matrix cracking and fiber breakage convert kinetic energy into mechanical work, thereby dissipating it.
Of course, failure must be controlled. Uncontrolled failure could be a catastrophic failure. So when engineering ballistic laminates, designs must be continually tested, modified, and improved to create just the right amount and type of failure without being catastrophic.
Designing personnel and vehicle armor with varying mechanisms of failure dictates the use of different materials for each layer. This is where engineering plays its most critical role.
Each layer in a ballistic laminate is chosen for a specific mechanical property. It’s critical to understand these properties and the mechanisms of failure in order to ensure that the layers are stacked in the best possible order. That requires understanding how energy is dissipated with each layer’s failure.
Designing military defense composites is about protection first and foremost. It is about ensuring that soldiers come back alive. Yet it’s hard to deny that the science behind ballistic laminates is fascinating. It is one of the things that motivates us to do the best possible job we can.
