Designing Safety Helmets

For many athletes at the 2012 Summer Olympics, safety helmets will be an essential part of their athletic gear. Nikhil Gupta, a mechanical engineer at New York University's Polytechnic Institute, explains how safety helmets are designed, constructed and tested. ʺScience of the Summer Olympicsʺ is a 10-part video series produced in partnership with the National Science Foundation.

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LIAM McHUGH, reporting: As Olympic athletes push themselves to jump higher, pedal faster, and hit harder, one of their most important pieces of equipment is the safety helmet.

QUEEN UNDERWOOD (U.S. Boxing Team): It does get rough in there, you know. Sometimes you have to get wild and get crazy.

McHUGH: Whether it's boxing headgear that absorbs multiple blows - or a cycle or riding helmet that cushions a single impact, safety helmets are designed for peak performance and maximum protection by engineers like Nikhil Gupta.

NIKHIL GUPTA (Polytechnic Institute of New York University): As a designer it's a big challenge to develop a helmet which provides safety and at the same time it provides comfort and also does not compromise the performance of the athlete.

McHUGH: Gupta is a professor of mechanical and aerospace engineering at the Polytechnic Institute of New York University, and is supported by the National Science Foundation. In his lab, he and his team test the strength of materials used in safety helmets to determine how well they protect an athlete's head - and especially brain - from the energy of a sudden impact.

GUPTA: All helmets have a three-part construction. This is the hard outer shell. Then there is a stiff layer of foam inside. And then the innermost part is a flexible foam.

McHUGH: In the equestrian event of show jumping, the helmet worn by three-time Olympic medalist Beezie Madden incorporates the look and feel of the sport's past, with an extra protective outer layer.

GUPTA: This outer shell is made of a thermoplastic composite, most of the time it is fiber reinforced. And it can provide protection against hard falls for an equestrian athlete. It's thin on the backside, and it's very thick on the center part, and thickness again is slightly reduced on the front side. So if a rider is falling down head first, this part is supposed to provide the most protection during those conditions.

McHUGH: One way to determine the strength of a helmet's hard outer layer is by using a drop impact test. Gupta secures a sample to a hard surface and, after raising the loading head to a certain height and adding the necessary weight, releases it.

GUPTA: If you look carefully the damage is a little bit more on the front side compared to the back side here.

McHUGH: In addition to studying the visible damage, Gupta uses ultrasound imaging to reveal damage that can't be seen with the naked eye.

GUPTA: Every test is conducted at least five different times on the same material so that we know the variability and properties, and then we look at the damage and if everything matches well, then we are fine.

McHUGH: Engineers use the results of tests like these to design materials and helmets that are even better at protecting the athletes who wear them. The helmet of track cyclist Sarah Hammer has a sleek, aerodynamic design to help cut down on wind resistance as she whizzes around the velodrome at speeds of more than 40 miles per hour. Its hard protective outer shell is lined with an inner layer of foam.

GUPTA: It's similar to what you have in your Styrofoam cups for hot beverages. It's a very stiff foam. And the inner part, this foam, is flexible to provide you comfort and also a good fit on the head.

McHUGH: To test the strength of inner layer materials, Gupta uses a compression gun that fires a steel rod into the foam, causing an impact with forces similar to what a cyclist would experience in a high speed crash. A special camera records the test at 10,000 frames per second, showing exactly how the material deforms or fractures as it uses up the energy of the impact.

GUPTA: See, this is now crushed under high speed compression.

McHUGH: Once again, Gupta is interested in how the foam has held up at the microscopic level. In this case he uses an electron microscope to study how it handled the impact.

GUPTA: Now you can see everything is completely crushed here. All the walls are now meshing with each other. So in this case, this foam cannot protect anybody any more.

McHUGH: While cycle and equestrian helmets are designed to protect the wearers for just a single impact, other helmets, such as the headgear worn by boxer Queen Underwood, are designed to withstand multiple punches.

GUPTA: They are designed to have a thick layer of foam such that the force of the punch is absorbed as much as possible inside the headgear itself.

McHUGH: Boxing headgear covers the parts of the head and face that are most likely to receive blows, but it's also lightweight enough that the boxer can still bob and weave to avoid contact altogether.

UNDERWOOD: I'm not trying to get hit in my face, you know, or take any unnecessary blows.

McHUGH: Which leads to the final phase of testing that Gupta must undertake - studying how the safety helmet holds up under real world conditions.

GUPTA: Field testing is extremely important because of functionality and also comfort perspective. If the helmet does not fit on the head of an athlete, the performance level is definitely going to be much lower compared to a helmet that fits.

McHUGH: Gupta's tests are helping guide the design and development of better safety helmets, giving athletes the protection they need as they go for the gold in London.