Protecting our Enforcers

© 2006 FrontLine Security (Vol 1, No 1)

Ensuring the personal protection of enforcement officers is a complex task. Take the need for body armour for example. Canadian soldiers on the streets Kandahar, as they attempt to bring stability to the region and win the hearts and minds of the local populace, or enforcement officers in Canada, as they sprint after armed insurgents, require protection that is lightweight and yet protects against high-energy projectiles. Some might think that light-weight strength requirements are mutually exclusive, but Canada’s scientific community has dedicated years of work to this challenge of improving personal protection options for military and police.

Throughout history, personal protection has evolved to meet increasing threats and differing operational needs. From the crude protection designs using thick layers of animal hides for protection against blunt impacts, to the metal armour of mounted knights protecting them from sharp implements, this evolution continued, until the advent of firearms in the 15th century rendered all previous personal protection ineffective. Although several types of personal body armour were developed and fielded over the next few hundred years, most were only partially effective, intended to protect the wearer from fragments, and incapable of addressing the evolving high velocity pistol and rifle projectiles.

It wasn’t until the 1970’s, with the invention of Kevlar® (an aramid fibre belonging to the nylon family), that true ballistic protection was available in the form of soft or flexible body armour. Not long after, the advent of high hardness and armour piercing projectiles led to the need for improved protection known as hard armour.

Today, protective armour is classified as soft or hard. Soft armour describes the common fabric-based vests worn by police officers, meant typically to protect against lower energy and soft projectiles. Hard armour is commonly used in conjunction with a soft armour vest and is designed to protect against high energy projectiles that may contain hard or piercing-type cores.

Of course, there are several competing factors affecting the design of optimum armour, not the least of which is matching the level of protection to the anticipated threats. These threats can be broadly classified as fragments and projectiles, where fragments take on many shapes and impact velocities.

Projectiles can be classified as soft or ball rounds and as hard or armour piercing, with the kinetic energy (1/2mv2) being a good measure of the aggressiveness of the projectile.

Soft projectiles are lead-filled and deform significantly on impact. Soft or fabric-type protective armour and laminated composite panels can address these projectiles at moderate impact energies. On the other hand, very high-energy soft projectiles, or hard projectiles incorporating hard cores of steel or tungsten carbide, are designed to penetrate such protection. In particular, the high-velocity, large-caliber, and hard-core projectile is considered one of the most aggressive projectiles to challenge personal body armour composition and design.

As the opening examples indicate, personal body armour is designed to protect the human body from ballistic impacts while being as light as possible for comfort and operational mobility. Although it is possible to protect against most projectiles encountered by Peacekeepers and First Responders, mobility requirements focus on lightweight systems and protection of the ­critical areas of head and torso. This trade-off is very important since key ­thorax protection requires hard or plate-type armour, incorporating advanced ballistic materials and different forms of ceramic. This need is becoming greater as larger caliber, armour-piercing projectiles are becoming a more common challenge and thus formed the focus of a multi-year development project aimed at improving armour performance and reducing weight.


Samples of various high energy, piercing-type ­projectiles ­too ­commonly faced by law enforcement officers. For reference, the two projectiles on the left require ‘hard armour’ while the two on the right can be stopped by soft armour.

Let us look at where we are now in this developmental project. Protection from high-energy piercing type projectiles, such as those shown above, requires hard or plate-type armour, which includes a ceramic facing (below) to disrupt the projectile, and a laminated composite backing to stop or catch the debris. This laminated composite backing is made from the same ballistic materials as soft armour, but is laminated with a polymeric matrix material to increase the panel ­stiffness and reduce overall deformation during impact.

The most obvious goal in personal protection is to prevent projectile penetration. The performance of body armour is typically rated using the National Institute of Justice (NIJ) standard, which sets ­limits on the penetration resistance of the armour, and is relative to the measured velocity at which 50% of the projectiles are expected to penetrate the armour. Importantly, even if penetration is prevented, the dynamic deformation of the armour during impact must be maintained at acceptable levels to protect the vital organs in the thorax from trauma.

Significant deformation can lead to blunt thoracic trauma, also known as Behind Armour Blunt Trauma (BABT). Although this is still under investigation in the armour community, past experience of auto crash and blast trauma has shown a significant correlation of trauma levels to deformation rate. For body armour, the dynamic deformation is limited to 44 mm, as measured in a standard clay backing.


Conventional two layer hybrid armour system

Conventional hybrid (hard plate) armour has been used effectively in its current form for many years; however, when addressing high-energy armour piercing projectiles, the weight of conventional armour plate designs is prohibitive.

 
Conventional Hybrid Armour – the ceramic fractures and disrupts the projectile, while the composite backing stops the resulting debris.

This dilemma led to a three-year project to develop personal protection for a 12.7mm amour-piercing projectile (7.75 kJ energy). Testing began at the component level. Several ballistic ceramic materials including alumina, silicon carbide and boron carbide were investigated using depth of penetration testing to evaluate ceramic impact performance. Upon initial impact, a shock wave is created in the ceramic (see DOP testing, above). A fracture front (damage) follows this initial wave, and the pulverized ceramic material is then ejected. A similar process occurs in the armour-piercing projectile, where an appropriate design will completely fracture the projectile core allowing the composite backing material to ‘catch’ the debris.

Parallel studies involving modeling and optimizing composite backings were also undertaken. The composite backing is intended to catch the ceramic and projectile debris while avoiding penetration and minimizing dynamic deformation. This role can vary greatly depending on properties of the particular fiber, matrix and processing conditions as well as the effectiveness of the ceramic. BABT can also be reduced through the addition of special energy-absorbing foam materials, also known as anti-trauma layers.

Although the individual components are important, the components of the armour system must be designed to work together, and in balance, to minimize weight. Using a conventional design, it was found that it was easy to stop the high-energy armour piercing projectile, but very challenging to stop it well. That is, conventional designs could meet the penetration requirements within acceptable weight levels, but unfortunately, dynamic deformations were significant for the high-energy projectile, and thus required a new approach.


Impact of 9 mm on a composite panel, showing the typical mushroom shape of a soft projectile.

An innovative solution using advanced materials and integration concepts led to a significant reduction in armour weight (as much as 40% compared to conventional solutions) while providing protection from these high energy projectiles. The enhanced system performance was developed through extensive modeling, component testing, and armour system testing.

This new system has allowed us to meet our objectives in providing protection against high-energy projectiles while achieving acceptable levels of dynamic deformation. Future efforts are focused on optimizing this system for combat-caliber, lower-energy projectiles.

What might seem, to some, to be a simple and age-old problem, the optimum protection of the soldier and first responder while allowing them to do their work effectively, continues to challenge the ­scientist and the science of today, but it is a task very much worth pursuing, and improvements are on the way.

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Dr. Duane Cronin is an Assistant Professor in the Department of Mechanical Engineering at the University of Waterloo, Ontario. He specializes in Impact Biomechanics with interests in numerical modeling and high rate characterization of materials to understand trauma to the human body and develop Personal Protective Equipment. Dr. Cronin participated in the NATO Task Group on Behind Armour Blunt Trauma and has been investigating improved protective armour through the support of the Ontario Centres of Excellence. More information can be found at his website: www.me.uwaterloo.ca/~dscronin/
© FrontLine Security 2006

 

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