Rose-Hulman Institute of Technology

Jeannette Geisler, Jojay Lee, and Eric Halvorson

 The Science Behind The Armor

          

           It comes as no surprise that the chief goal in designing good body armor for military or police applications is the prevention of bullet wounds.  However, due to constraints such as the load on the wearer, the task is not so simple.  Engineers must solve the difficult problem of providing good protection without harming or restricting the motion of the wearer.  The most common solution is to use a combination of a ceramic and either a ductile metal or a tough polymer.

 

The Ceramic Layer

 

           One likely knows from experience that ceramics are brittle and tend to shatter easily.  While at first this may seem to be counter to the purpose of personnel armors, the property can actually be of some benefit.   (Of course, one would prefer the ceramic not to break, but the result of fracture is not completely detrimental.)

          

Kauffman, in his article Influence of material properties on the ballistic performance of ceramics for personal body armour, put it simply, “The function of the ceramic facing is to destroy the tip of the incoming projectile, distribute the load over a large area of the composite and to decelerate the projectile” [1].  Ceramics with exceptional hardness are sought for the purpose of improving the armor’s ability to shatter the point of the incoming projectile.  One commonly used material is boron carbide for just this reason – and a relatively new process that will be discussed below may allow it to perform even better.

 

           The way in which the ceramic breaks once struck with a projectile aids in the load distribution on the energy-absorbing material.  The fractured material expands in a “conoid” fashion to the backing material, and this enlarged area for force distribution reduces the pressure exerted on the wearer.

 

The Backing

 

           The purpose of the backing is to absorb the impact energy.  Therefore, the material must be ductile and tough rather than brittle like the ceramic facing.  Properly chosen materials will deform near the impact without puncturing.  Aluminum is a popular material for the backing due to its relatively low cost and good ductility.