An aerospace engineer at Worcester Polytechnic Institute (WPI) is conducting wave motion research to one day create a bulletproof vest that not only will sense the speed, angle of approach, and size of an incoming bullet, but the material inside the vest will instantly change properties to provide greater shock protection at the exact point of impact. These materials could be used in protective gear, and to create protective covers for buildings, satellites, and underwater missile silos. The pioneering work is being funded by a five-year, $500,000 Faculty Early Career Development Program (CAREER) award from the National Science Foundation.
Nikhil Karanjgaokar, assistant professor of aerospace engineering, is using his expertise in wave motion and interruption to explore the mechanical and physical properties of granular materials that can alter their shapes or change their original properties to absorb and redirect the force of an incoming bullet or object. Karanjgaokar hopes to develop shock protection technology that can protect people and objects from being pierced or affected by the shock from projectiles. The technology could be used in personal protective equipment, such as vests and helmets, that can be worn by the military, police, and other professionals, like athletes and construction workers. The technology also could be used as a protective covering for buildings or even to protect NASA’s International Space Station, satellites, and spacecraft from being damaged by space junk and meteorites.
“I want to design materials that can absorb impact,” said Karanjgaokar, whose previous research was focused on understanding wave motion through granular material. “People trying to protect themselves from bullets or shrapnel have used sandbags since before the Second World War to absorb impacts. I’m working from the same basic principle. How can we create a versatile material to create a barrier against any impact?”
Focusing on Interrupting Wave Motion
Karanjgaokar will focus on the effect of interrupting or diverting wave motion. He said to think of the force of a bullet’s impact as surface waves moving across a pond. Impact waves, and the power behind them, move similarly through any collection of unconnected particles that are the same size, shape, and material. But if the particles inside hazard protective gear could change their internal structure in the area of an incoming impact, they could disrupt the direction, speed, and force of the wave away from the person wearing the vest or helmet.
“The idea is that we want the forces from an impact to die down by the time they reach whatever is being protected,” said Karanjgaokar, who explained that a sensor, which is not part of the research project, on the vest or covering would detect an incoming projectile and trigger a change in the materials inside it. “In order to do this, one strategy I’m exploring is introducing obstacles amid the grains in the vest to divert the impact waves so they are stopped or diverted away from what we are trying to protect.”
To make that happen, Karanjgaokar starts with granular materials, which would fill a bulletproof vest or helmet, for example. The materials would start out with the same properties—the same size, shape, and density. He then changes the properties of the granules in a specific location with electric or magnetic fields, causing the materials to respond. For instance, electroactive polymers change their size and shape when stimulated by an electric field. When the field is turned off, the material returns to its original state. He is experimenting with making the materials larger, and stiffer or softer, such as rubber instead of hard plastic. The modified particles act as an obstacle to the wave created by the bullet’s impact, and disperses it so the person being protected doesn’t feel the full impact, providing shock protection.