A better way to stop a bullet? | Science News for Students

A better way to stop a bullet?

Teen’s data suggest the fabric in body armor would work better if it were woven differently
May 19, 2017 — 12:00 pm EST
body armor

Body armor made with a three-directional weave (image) would provide better protection that that provided by the two-directional weave similar to what’s found in a window screen.  

Lynn

LOS ANGELES, Calif. — Body armor is a critical piece of safety equipment for police officers and military troops. It helps keep bullets and other projectiles from getting an opportunity to pierce flesh. But the fabric-based body armor could offer even better protection if it were woven differently, a teen’s new tests suggest.

The most common forms of body armor, including bulletproof vests, are woven from a super-strong plastic fiber sold under the trade name Kevlar. First developed in the 1960s, it is stronger than steel but weighs much less. The fibers in body-armor fabric typically run in two directions and cross at 90-degree angles, notes Lucas Lynn. He’s an 11th-grader at Wetumpka High School in Alabama. Such fabric typically has square holes in its mesh. It looks similar to the material used in a window screen, only it's woven much more tightly. Lucas wanted to see if he could improve body armor’s performance by changing the fabric’s weave.

He purchased Kevlar fiber and used it to create two different weaves. One made the normal, two-fiber square mesh. The other used three threads that intersected at 60-degree angles. The mesh this created had triangular holes. Those holes also tended to be smaller and the weave tighter than in a two-fiber, 90-degree mesh.

Lucas covered each mesh with a mixture of powdered calcium carbonate (the same mineral as chalk) and a particularly viscous form of polyethylene glycol. It’s a common chemical used in both manufacturing and medicine. The resulting goopy mixture works as a shear-thickening liquid, the teen explains. That means it flows rather smoothly under slow and steady pressure, but stiffens greatly when something hits it suddenly — such a bullet.

Lucas tested his goop-covered meshes by shooting BBs at them. BBs are small, round projectiles that are often fired from a gas-powered gun or rifle. BBs typically range between 4.3 and 4.4 millimeters (about 0.17 inch) in diameter. But flying at about 190 meters per second (430 miles per hour), these tiny projectiles can pack a big punch, Lucas notes. So behind each mesh he added two layers of foam rubber. He placed a cardboard box behind that to catch any BBs that penetrated the foam.

The square-grid mesh didn’t stop any of the BBs from reaching the box, Lucas found. But the triangular mesh slowed down or stopped every BB. In only two cases did the BB shot make it to the second layer of foam.

Lucas showcased his research, here, at the Intel International Science and Engineering Fair. Created by Society for Science & the Public and sponsored by Intel, the competition lets students from around the world show off their winning science fair projects. (The Society also publishes Science News for Students.) This week, nearly 1,800 high school students from more than 75 countries competed for big prizes and the ability to display their research findings.

Lucas conducted additional tests by weaving fabrics out of 3.2-millimeter (0.125-inch) Kevlar cord. These fabrics, also coated with the goop, worked even better than those made of Kevlar thread. Again, the square-mesh fabric did not stop any of the BBs, while the triangular-meshed fabric stopped all six BBs fired at it. Two of the BBs even ricocheted, or bounced, off of the fabric. The teen concludes that his three-fiber weave provides better protection that one woven with two fibers.

UPDATE: For this project, Lucas received a $1,500 award at Intel ISEF from the Society for Experimental Mechanics.

Power Words

(for more about Power Words, click here)

angle     The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.

BBs   A type of small pellets, usually made from steel, which are fired by shotguns and air rifles. They can ricochet off of hard surfaces, making their use dangerous in confined spaces.

blog     Short for web log, these Internet posts can take the form of news reports, topical discussions, opinionated rants, diaries or photo galleries.

calcium carbonate     The main chemical compound in limestone, a rock made from the tiny shells of ancient marine organisms. Its formula is CaCO3 (meaning it contains one calcium atom, one carbon atom and three oxygen atoms). It’s also the active ingredient in some antacid medicines (ones used to neutralize stomach acids).

degree     (in geometry) A unit of measurement for angles. Each degree equals one three-hundred-and-sixtieth of the circumference of a circle.

diameter     The length of a straight line that runs through the center of a circle or spherical object, starting at the edge on one side and ending at the edge on the far side.

engineering     The field of research that uses math and science to solve practical problems.

fabric     Any flexible material that is woven, knitted or can be fused into a sheet by heat.

fiber     Something whose shape resembles a thread or filament.

grid     (in mathematics or mapping) A network of lines that cross each other at regular intervals, forming boxes or rectangles, or an orderly field of dots that mark where each pair of lines intersect, or cross one another.

Intel International Science and Engineering Fair     (Intel ISEF) Initially launched in 1950, this competition is one of three created (and still run) by the Society for Science & the Public. Each year, approximately 1,800 high school students from more than 75 countries, regions, and territories are awarded the opportunity to showcase their independent research at Intel ISEF and compete for an average of $4 million in prizes. 

Kevlar     A super-strong plastic fiber developed by DuPont in the 1960s and initially sold in the early 1970s. It’s stronger than steel, but weighs much less, and won’t melt.

mineral     Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns).

plastic     Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

polyethylene glycol    Also known as PEG, this common, viscous chemical has many commercial uses, from medicine to industrial manufacturing.

pressure     Force applied uniformly over a surface, measured as force per unit of area.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible.

shear thickening liquid     A material with unusual properties: It appears to be a liquid until something strikes it or moves it forcibly. Then its behavior switches to become like a solid, essentially hardening in a tiny fraction of a second.

viscous     The property of being thick, sticky and hard to pour. Molasses and maple syrup are two examples of viscous liquids.

NGSS: 

  • MS-PS1-3
  • MS-ETS1-2
  • HS-ETS1-2

Citation

Meeting: L. Lynn. Shear radial strength: Combining web geometry with shear thickening fluids to create a better body armor. Intel International Science and Engineering Fair. May 15, 2017. Los Angeles, Calif.

Further Reading

More about Intel ISEF 2017:

Intel ISEF 2017 begins.” May 15, 2017.

Welcome to Intel ISEF 2017.” May 16, 2017.