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One of the liquids used to reinforce a Kevlar armor is the magnetorheological liquid, also known as the MR fluid. In this piece I’m going to chat about the mechanics behind liquid body armors.

Before I continue with the primary discourse I’ll have to talk about first the parts of an MR liquid.

What is a magnetorheological fluid?

Fundamentally, magnetorheological liquids are oils full of particles of iron. The iron particles are kept suspended in the oil by the surfactants that surround them. The MR fluid is usually made up of 20-40% iron and 60-80% oil.

These iron particles are micro miniscule, just around 3 “10 microns. But they have got a terribly strong effect with the general consistency of the fluid.

The way in which the process of toughening occurs

When these particles are exposed to a magnetic field, they line up and then cause the liquid to seriously thicken. The presence of the magnetic field can change both the viscosity and the form of the MR fluid. The term magnetorheology was coined from this effect “rheology is an offshoot of engineering concentrating on how force changes the shape of a particular material.

Generally the hardening of the liquid takes nearly 20 thousandths of a second and this can alter depending on the fluid’s composition and the shape, size and strength of the magnetic field. Example, spherical iron particles can slip past each other even within a magnetic field, so limiting the hardness of the armor.

How MR liquids are inserted into body armors

Since those who are wearing the body armors will not be around a magnetic field all of the time, and since it is unrealistic to carry a big magnet around for the suit to toughen, analysts embedded miniscule circuits all over the armor.

The circuits are managed by a small switch, so flipping the switch off and on will cause the body suit to either soften or toughen.

When these circuits are not turned on, the body armor stays flexible and soft. However , when they are turned on, current flows throughout the circuits, causing a rapid movement of electrons and then creating an induced magnetic field in the act. This magnetic field instantly causes the armor to toughen and stiffen.

Other uses of MR fluids

Magnetorheological fluids are also utilized in bomb blankets, used to cover bystanders from shrapnel caused by explosions.

The jump boots of paratroopers also use these MR fluids. They can toughen when activated or on impact, thus protecting the paratroopers ‘ boots.

A fun experiment with MR fluids

If you want to see an experiment on how an MR fluid works, you can do so by employing iron fillings and then some regular oil. If you don’t have iron fillings, you can just mine iron ore from a regular sandbox. You can find the main points of the experiment clicking here. There are times when magnet causes the fluid to take pretty, artful shapes. Some artists use magnetorheological liquids or other forms of ferrofluids to form work of arts.

For further facts on magnetorheological fluids and associated hardware, go to Magnetorheological Damper Lab. When selecting your damper technology, select magnetorheological!