When a car crash occurs, people with osteoporosis and other brittle bone disorders often suffer more serious injuries. To better protect these "fragile" motorists, three Johns Hopkins undergraduate engineering students have devised a harness and vest system that significantly reduced impact forces when tested on a high-tech crash dummy.
The students were responding to a challenge from the Center for Injury Research and Policy in the Bloomberg School of Public Health at Johns Hopkins. "We estimate that as many as 13 million people with osteoporosis, osteogenesis impefecta (brittle bone disorder) and hemophilia need some additional protection from forces applied to the torso during a car crash," said Gary S. Sorock, an associate professor at the center. "The assignment was to design and test a restraint system that would reduce these forces, protecting the ribs and the sternum in particular."
During their two-semester Engineering Design Project course in the Department of Mechanical Engineering, the team of three seniors addressed this problem. The team designed a vest filled with three layers of foam padding, each with a different density, to absorb some of the energy that causes a motorist's chest to compress during a crash. In people with weakened bones, this compression can lead to broken ribs and other serious internal injuries. The students also replaced a conventional three-point shoulder belt with a four-point race car harness, which distributes the crash forces across a wider area of the body and keeps the body in a tighter fit against the seat.
In May, the students brought their system to the Impact Biomechanics Test Facility at The Johns Hopkins University Applied Physics Laboratory. The staff assisted the students in conducting tests on a dummy that simulated a 108-pound woman, belted onto a sled moving at an average speed of 18.5 mph. The dummy was equipped with sensors to gauge the effect on various parts of the body during the equivalent of a 20-mph head-on crash or a 35- to 40-mph crash involving a moving car striking a parked vehicle. A high-speed camera mounted on the crash sled also captured closeup images of the dummy as it was jarred by the impact.
The students tested the dummy with a conventional shoulder belt alone, with a shoulder belt and their prototype foam-filled vest, with the four-point harness alone, and finally with both the harness and vest. When the dummy was outfitted with the vest under the conventional restraint, chest compression was reduced by approximately 8 percent (from 26.9 to 24.9 millimeters). Testing with the harness provided a different loading mechanism to the dummy torso and created much less sternum deflection (3.5 millimeters). Despite the reduced loading, the addition of the vest further decreased the sternal compression by 17 percent to 2.9 millimeters. The students also compared crash impact forces, measured from the seatbelt. This dropped from 644 pounds of force with the standard shoulder belt alone to about 436 pounds with the harness.
The student inventors, all seniors, were Richard Chen, a 21-year-old biomedical engineering major from Lexington, Ky.; Patrick Danaher, a 23-year-old mechanical engineering major from Bedford, Mass.; and Ryan Lavender, a 21-year-old mechanical engineering major from Atco, N.J. They were required to work within a sponsored budget of $8,000 but wound up spending only about $5,500 to produce the crash protection system.
"These students have done a very nice job of tackling a very difficult problem," said Andrew Merkle, an associate researcher at the Applied Physics Laboratory's Biomechanics and Injury Prevention Office. Merkle supervised the students' crash dummy tests.
"We were happy to see the reduction in blunt force upon the dummy using this system," Chen said. "The vest might also have some applications in helping to prevent injuries in sports like football or snowboarding."
Lavender agreed. "I think the vest has the potential to help a much wider audience than I originally thought," he said. "I can see it protecting older people and children from injuries."
Danaher enjoyed putting the knowledge he'd acquired in other engineering classes to use in the type of team project he may face soon in the working world. "The senior design course was incredible," he said. "It gives you the kind of hands-on challenge that many other college students don't get the chance to experience."
The crash protection system was one of nine Johns Hopkins projects completed this year by undergraduates in the engineering design course. The class is taught by Andrew F. Conn, a Johns Hopkins graduate with more than 30 years of experience in public and private research and development. Each team of three or four students, working within budgets of up to $10,000, had to design a device, purchase or fabricate the parts, and assemble the final product. Corporations, government agencies and nonprofit groups provided the assignments and funding. The course is traditionally a well-received, hands-on engineering experience for Johns Hopkins undergraduates.
View an online video about this project here: http://www.jhu.edu/news_info/news/audio-video/mediavest.html
Johns Hopkins Department of Mechanical Engineering: http://www.me.jhu.edu
Johns Hopkins Center for Injury Research and Policy: http://www.jhsph.edu/InjuryCenter/index.html
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