Audiences throughout the nation and around the world have been entranced by the high-tech Iron Man body suit and Tony Stark’s eccentric mind. Imagined by Marvel Comics, the Iron Man suit allows Stark to fly through the sky, shoot sonic blasts, and withstand bullets. In addition, the metallic strength of the armor does not detract from the suit’s maneuverability, rendering Tony Stark capable of effortlessly fighting international criminals and alien monsters.
Minus the sonic blasts, flying capabilities, and some other supernatural powers, Iron Man has now become a reality . Shear thickening fluid (STF), a recent innovation in materials science, has sparked the imagination of scientists throughout the nation. Funding from the United States military has stimulated research and development in the field. In the near future, it is likely that the invention will become thoroughly integrated in society due to its flexibility and cost-efficiency. Different industries already take advantage of STF, such as sports equipment production and automotive design, and more are expected to in the future. Most importantly, there is significant potential in using STF in military equipment.
Shear thickening fluid, in combination with other materials, strengthens the durability of a product yet does not detract from its maneuverability like most material support systems do. The army currently uses bulletproof vests made out of Kevlar armor, which tend to be large, bulky, and hard to move around in . Moreover, upon impact with bullets, the material still protrudes inward . While the conventional armor largely prevents death, it does not completely protect the soldier from physical damage, such as bruising, broken bones, and trauma to organs . However, in combination with shear thickening fluid, the Kevlar armor becomes not only stronger but also more flexible . It allows the impact energy of a bullet to be distributed over a larger area and causes the armor to be more resilient and more likely to return to its original shape . In addition, the material can be made 45 percent thinner , and vests with shear thickening fluid could weigh about four pounds less than those without STF .
Termed “bullet proof custard,” STF is a non-Newtonian fluid . These types of fluids seemingly defy scientific norms: non-Newtonian fluids are liquids that harden and become solids upon impact with fast moving objects or when stress (the pressure per unit area on a particle exerted by another) is applied . In other words, above a certain shear rate (the rate at which parallel internal surfaces move past each other), particles within the fluid form molecular masses, or hydroclusters . As the shear stress overwhelms the inherent repulsive intermolecular forces between the liquid’s molecules, the friction between them and thus the viscosity of the fluid significantly increases . Furthermore, like other non-Newtonian fluids, STF is a colloid composed of carrier liquids and suspended particles . Different combinations of substances result in a variety of shear thickening phenomena, and specific variables that affect the thickening process include particle size, shape, and concentration .
Dr. Eric Wetzel, a mechanical engineer from the Weapons and Materials Research Directorate, has been working with Dr. Norman J. Wagner and a team of students from the University of Delaware conducting research on the applications of shear thickening fluid for around three years, with specific emphasis on military usability . Currently, Armor Holdings, a manufacturer of specialized equipment for military, law enforcement, and safety prices STF-infused vests at about $500 to $600 each . Thus, Wetzel, Wagner, and their team of students aim to manufacture a material with STF that is more affordable while remaining light weight .
Wetzel firmly believes that “the sky’s the limit” and that the technology has much undiscovered potential. He states that shear thickening fluid can be infused into material on soldiers’ sleeves, pants, and other areas unprotected by armor . Moreover, he attests that STF can be used in bomb blankets covering explosives and jump boots to support soldiers’ ankles .
In addition, Wetzel claims that law enforcement entities can significantly benefit from products made with shear thickening fluid. Prison guards and police officers, who are often confronted with sharp weapons in close combat, would have reduced risk of injury . Indeed, if security personnel were to wear uniforms made with shear thickening fluid, their occupations would be significantly less dangerous. They would be able to perform previously life-threatening actions with the assurance that their chances of survival were significantly greater than before. Furthermore, with the added safety benefit of shear thickening fluid, law enforcement job opportunities would seem more attractive. This development would significantly increase interest in law enforcement, benefitting society as a whole.
Another example of a shear thickening fluid application rests closer to home for U.S. citizens, particularly athletes. Products cover a wide range, from mouth guards for minimizing teeth damage to helmets for decreasing the risk of concussion . This benefit is of significant importance due to the long term effects of multiple concussions. Indeed, physicians have found that concussions can lead to mild cognitive impairments, chronic traumatic encephalopathy, and post-concussion syndrome . In other words, permanent neurologic damage is a potential harm . Thus, football, water polo, and other contact sports players would benefit from such inventions. Other examples of products with shear thickening fluid include gloves to protect hands from dangerous collisions and shoe designs to protect athletes’ ankles and feet . Soccer players would most likely appreciate these specific examples since goalies would have less risk of injured fingers and their team members would have more supportive footwear to power them up and down the field during a game.
Shear thickening fluid can also be used in modes of transportation. Trains, airplanes, and cars can be built, internally and externally, with shear thickening fluid parts . STF seat cushioning and neck support benefit drivers and passengers normally and in the instance of an accident. During collisions, parts on the outside structure of the vehicle with STF are more capable of resisting change from bending, twisting, elongation, and compression . Indeed, STF-infused materials in vehicles would act like they would in military body armor: They would protect both people and the automobile. The STF would spread the collision impact over a larger area, thus decreasing the impact force and potential likelihood of drastic damage to the vehicle and passenger inside. Thus, damage to both humans and the mode of transportation would be significantly reduced.
Several corporations and non-profit organizations have filed for patents for their inventions that use shear thickening fluid. For instance, in 2011, Extrude Hone Corporation, a manufacturing company that specializes in airplane and automobile parts, received their intellectual property rights over their invention that “provides an energy absorbent and form compliant article for cushioning animate and inanimate objects” . The company listed several possible applications of the product, including sports padding articles, like shin guards and rib protection; hand protection, such as gloves; seat cushioning in vehicles, especially race cars; medical padding, such as for use during X-rays and neck braces; extreme trauma cushioning for protective gear, like military vests; and industrial equipment packaging to reduce shock and vibrations, such as in motor mounts .
Thus, with the increase of companies entering the shear thickening fluid market, more products utilizing the material will emerge. Consumers will benefit from applications of STF such as those of Etrude Hone Corporation, and shear thickening fluid will soon become integrated into daily life. While shear thickening fluid has not yet led to a Tony Stark version of an Iron Man suit, it has resulted in the invention of more durable, flexible, and useful products for all members of society to enjoy.
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Image References: Accessed March 24, 2015. http://upload.wikimedia.org/wikipedia/commons/b/b5/Iron_Man_Mark_4%2C_5%2C_6%2C_7.jpg  Accessed March 24, 2015. http://upload.wikimedia.org/wikipedia/commons/7/7a/Hydroclustering.jpg
Sophia Luo is a rising senior at The Harker School in San Jose, California. She enjoys examining the interdisciplinary connections between various STEM fields and is interested in solutions that target quotidian problems in our society.