Humans have waged war on one another for centuries. Weapons have evolved from sticks and stones through cutting and bludgeoning implements to today’s smart bombs and missiles. But the evolution of the means to protect oneself from the impact of those weapons has not kept pace. However, a new technology combining two advanced materials – Kevlar and shear-thickening fluid – may hold the promise of light, flexible and effective full body armor.
Today’s body armor is a compromise between protection and agility. Most modern body armor comprises many layers of woven Kevlar, sometimes with ceramic plates to give extra protection. Kevlar is an aramidic fiber, which forms hydrogen bonds between its chains of molecules and thus has a very high tensile strength and high toughness. It is five times stronger than steel on an equal weight basis and it already saves countless lives.
Although Kevlar offers vastly increased protection for the wearer, it does have some drawbacks. For effective protection, up to 30 or 40 layers of Kevlar are needed. This many layers, together with additional ceramic plates, make the armor bulky, stiff and heavy, meaning that the wearer cannot move around as easily. Also, body armor does not offer protection for extremities, such as arms, legs or the neck because the number of layers of Kevlar needed to offer sufficient protection would be too stiff and bulky for use as sleeves, trousers, and so on.
The liquid technology can improve both the performance and the utility of Kevlar fabric. Saturating Kevlar fabric in a shear-thickening fluid causes the fluid molecules that are already bonded with each other to also form weak chemical bonds with the polymer chains of the Kevlar fibers. The weak bonding allows the fabric to remain flexible. When a projectile strikes the fabric, it becomes rigid within two-thousandths of a second, preventing penetration. Furthermore, the reduced flow of the fluids in the liquid armor restricts the motion of the fabric yarns in relation to each other, resulting in an increase in the area over which the impact energy is dispersed. As a result, the material does not distort as much as the standard body armor, which generally extends inwards substantially when a projectile strikes, causing considerable pain and injury. Once the event is over, the fabric returns to its former flexible state.
The mechanical properties of the material are being evaluated using a wide range of tests and test equipment. Drop towers test puncture resistance with knives and icepicks as well as various shapes and sizes of instrumented tups. Load frames are used to test resistance to abrasion, fiber pullout, and tearing. Gas guns are used to fire ballistics such as bullets and shrapnel.
Impregnating Kevlar with a shear-thickening fluid strengthens the fabric to such an extent that improved protection can be achieved with a material that is one-third the thickness of Kevlar alone. Therefore, the body armor can be lighter, more flexible and yet offer greater protection from projectiles, shrapnel and explosive devices – the major causes of injury and death in modern conflicts. Seventy per cent of all non-fatal injuries and sixteen per cent of deaths in a war zone are due to trauma to extremities. Because fewer layers are necessary with the new material, supple armor for arms and legs is now possible. Extremity armor using shear-thickening fluid impregnated Kevlar could significantly reduce the number of injuries in battle as well as saving lives.
Today’s body armor is a compromise between protection and agility. Most modern body armor comprises many layers of woven Kevlar, sometimes with ceramic plates to give extra protection. Kevlar is an aramidic fiber, which forms hydrogen bonds between its chains of molecules and thus has a very high tensile strength and high toughness. It is five times stronger than steel on an equal weight basis and it already saves countless lives.
Although Kevlar offers vastly increased protection for the wearer, it does have some drawbacks. For effective protection, up to 30 or 40 layers of Kevlar are needed. This many layers, together with additional ceramic plates, make the armor bulky, stiff and heavy, meaning that the wearer cannot move around as easily. Also, body armor does not offer protection for extremities, such as arms, legs or the neck because the number of layers of Kevlar needed to offer sufficient protection would be too stiff and bulky for use as sleeves, trousers, and so on.
A great deal of largely US-military-funded research has taken place over the last few years into combining Kevlar fabric with a shear-thickening fluid. Shear-thickening fluid is an example of a "smart material," a class of materials that can sense and respond to changes in the environment, for example through the application of electricity or magnetism, or to changes in temperature. Shear-thickening fluids increase their viscosity in response to changes in pressure. An example of a fluid under research is ethylene glycol containing suspended nano-particles of silica. Under normal conditions, the particles are weakly bonded to each other and can move around with ease. The shock of an impact strengthens those chemical bonds and the particles lock into place. Once the force from the impact dissipates, the bonds weaken again.
The liquid technology can improve both the performance and the utility of Kevlar fabric. Saturating Kevlar fabric in a shear-thickening fluid causes the fluid molecules that are already bonded with each other to also form weak chemical bonds with the polymer chains of the Kevlar fibers. The weak bonding allows the fabric to remain flexible. When a projectile strikes the fabric, it becomes rigid within two-thousandths of a second, preventing penetration. Furthermore, the reduced flow of the fluids in the liquid armor restricts the motion of the fabric yarns in relation to each other, resulting in an increase in the area over which the impact energy is dispersed. As a result, the material does not distort as much as the standard body armor, which generally extends inwards substantially when a projectile strikes, causing considerable pain and injury. Once the event is over, the fabric returns to its former flexible state.
The mechanical properties of the material are being evaluated using a wide range of tests and test equipment. Drop towers test puncture resistance with knives and icepicks as well as various shapes and sizes of instrumented tups. Load frames are used to test resistance to abrasion, fiber pullout, and tearing. Gas guns are used to fire ballistics such as bullets and shrapnel.
Impregnating Kevlar with a shear-thickening fluid strengthens the fabric to such an extent that improved protection can be achieved with a material that is one-third the thickness of Kevlar alone. Therefore, the body armor can be lighter, more flexible and yet offer greater protection from projectiles, shrapnel and explosive devices – the major causes of injury and death in modern conflicts. Seventy per cent of all non-fatal injuries and sixteen per cent of deaths in a war zone are due to trauma to extremities. Because fewer layers are necessary with the new material, supple armor for arms and legs is now possible. Extremity armor using shear-thickening fluid impregnated Kevlar could significantly reduce the number of injuries in battle as well as saving lives.
3 comments:
"When a projectile strikes the fabric, it becomes rigid within two-thousandths of a second, preventing penetration." That is 2000 micro-seconds - which is far too slow to prevent high velocity projectile penetration! May work for slower knife penetration but NOT for Level 3 or 4 ballistic threats.
But for inner layers STF is good enough to reduce the deflection of soft armor and decrease of trauma!
Not only did it say that it was more efficeint, meaning you can use less for more. The .002 seconds part concers me but you can still use the same amount of kevlar and then you couldn't complain. but it also includes shrapnel. If you can get shrapnel proof sleeves, or a knife proof shirt (and kevlar is neither) i'd take it.
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