Liquid armor

{{Short description|Material with potential military applications}}

Liquid armor is a material under research by defense institutions and universities around the world including the United States Army Research Laboratory (ARL).{{Cite web|url=https://www.army.mil/article/104229/Army_explores_futuristic_uniform_for_SOCOM/|title=Army explores futuristic uniform for SOCOM}}{{Cite news|url=https://www.bbc.com/news/10572072|title=How liquid armour 'stops bullets'|work=BBC News|date=9 July 2010}}{{Cite web|url=http://www.popsci.com/poland-develops-bulletproof-liquid-armor|title = Poland Developing Liquid Body Armor|date = 18 March 2019}} Some of the earliest research in this area was performed at Massachusetts Institute of Technology{{Cite web|url=https://patents.google.com/patent/US20040173422A1|title = Fluid-filled cellular solids for controlled}} and University of Delaware{{Cite web|url=https://patents.google.com/patent/US20060234577A1/en|title = Advanced body armor utilizing shear thickening fluids}} in 2003. Liquid armor was initially presented as a way to increase the survivability of soldiers in high risk roles while retaining their mobility, as reported by NPR in an interview with MIT professors and a U.S. admiral.{{Cite web|title=Special Ops Envisions 'Iron Man'-Like Suit To Protect Troops|url=https://www.npr.org/sections/alltechconsidered/2013/08/05/209241687/special-ops-envisions-iron-man-like-suit-to-protect-troops|access-date=2021-06-25|website=NPR.org|language=en}}

Typically, it consists of Kevlar that is soaked in one of two fluids - either a shear thickening fluid or a magnetorheological fluid.{{Cite web|url=http://science.howstuffworks.com/liquid-body-armor.htm|title=How Liquid Body Armor Works|date=26 February 2007}} Both these fluids show the behavior of a non-Newtonian fluid, behaving like a liquid under low or normal pressure and solid under higher pressure or applied fields.

The shear thickening fluid is normally made with polyethylene glycol and the solid part is made of nano-particles of silica. This liquid is soaked into all the layers of a Kevlar vest.{{cite web|last=Johnson|first=Tonya|title=Military.com|url=http://www.military.com/NewsContent/0,13319,usa3_042104.00.html|publisher=Military.com|accessdate=5 March 2015}}

The magnetorheological fluid consists of magnetic (typically iron) particles in a carrier fluid such as oil. They respond to magnetic fields by increasing in viscosity dramatically, almost acting like a solid.{{Cite web|url=https://abcnews.go.com/Technology/talos-body-armor-lets-soldiers-act-iron-man/story?id=20532892|title = Iron Man-Like Body Armor for Soldiers in the Works| website=ABC News }}

BAE Systems has been researching a similar Kevlar vest with a fluid between layers of polymer. BAE acquired the US research company Armor Holdings, who were doing research based on suspensions of silica particles.{{cite news|last=Gill|first=Victoria|title=BBC|work=BBC News|date=9 July 2010|url=https://www.bbc.co.uk/news/10569761|accessdate=5 March 2015}}{{cite magazine|title=The Economist|date = 2 August 2010|url=https://www.economist.com/node/16731563?story_id=16731563|publisher=The Economist|accessdate=5 March 2015}}