Physics in the Crumple Zone Demonstrate How Less Stiff Materials, Like Plastic, Can Help Prevent Injury and Save Lives
- Crumple zones are structural areas in the front and sometimes rear of a vehicle that are designed to absorb energy upon impact in a predictable way.1
- When a car crashes, the goal is for the structure to crush in a relatively gradual, predictable way that absorbs much of the impact energy, keeping it away from the occupants in what is termed a “controlled crush.” 2
- Crash test results from the National Highway Traffic Safety Administration’s New Car Assessment Program (NCAP) indicate that occupant injury and fatality risk can be reduced by designing vehicles with softer front end structures resulting in larger “maximum crush,” provided there is no intrusion.3
- Newton’s first law states that an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. As a result, if a vehicle is going 50mph, the bodies inside are as well, and if the vehicle hits a solid wall and comes to a stop immediately, the bodies will want to continue going in the same direction at 50mph.1
- Passengers will continue to move forward at the same speed until they come in contact with a part of the automobile or another human being, causing injury. Even after a human body comes to a stop in an accident, its internal organs continue to move, slamming against each other because of the impact, often causing serious injury or death.4
- Newton’s second law of motion, force = mass x acceleration, conveys that as the time it takes for an automobile to come to rest or change direction is increased, the force experienced by the automobile (and its occupants) is decreased. Conversely too, if the time to stop is shorter, the force experienced is greater. Crumple zones add time to the crash by absorbing energy.5
- Crumple zones allow the front of the vehicle to crush like an accordion, absorbing some of the impact of the collision and giving some off in the form of heat and sound. The front of the vehicle effectively acts as a cushion that slows the time it takes for the vehicle to come to a complete stop, applying less force on passengers, which could help save their lives.1
- When used in crumple zones, lightweight plastic components can help absorb energy and save vehicle weight at the same time. Located in the front crumple zone, the plastic fan/shroud reservoir of the 2000 Dodge Dakota and Durango saved 1.1 lbs/vehicle, while the plastic bumper beam of the Saturn VUE saved 2.5 lbs in vehicle weight.6
- Composite driveshafts are made of carbon and polymer fiber that is designed to break into small fiber fragments or “broom” upon failure, posing little danger.7
- “Prior to 1959, people believed the stronger the structure, the safer the car. But in actuality, such construction proved deadly to passengers, because the force from impact went straight inside the vehicle and onto the passenger.” 8
- According to Jason Rowe, chief material engineer for Lotus Engineering, a composite front end will provide the same crash protection in less space than a steel one, which gives developers more room to add pedestrian impact measures.9
- “Crumple zones with rigid cabs are now the standard in every car made throughout the world.” 8
- A 1999 study by the Society of Automotive Engineers found that light trucks with 4 and 5 star ratings (lower risk of severe injury) have more maximum crush, lower maximum deceleration, and longer duration crash pulses than those with 1 and 2 star ratings (higher risk of severe injury).10
- In 1967, the Mercedes Heckflosse was the first production car in the world with “crumple zone” safety features including a safety cage with crumple zones and a trunk that had been made almost 50% bigger.1
1 K-12 school Web pages in Newfoundland and Labrador. “Crumple Zones.” Sourced through the American Institute of Physics. (accessed April 28, 2006).
2 Ashley, Steven. “Composite car structures pass the crash test.” Mechanical Engineering, December 1996. (accessed April 20, 2006).
3 Van Auken, R.M and J.W. Zellner. Supplemental Results on the Independent Effects of Curb Weight, Wheelbase, and Track on Fatality Risk in 1995-1998 Model Year Passenger Cars and 1985-1997 Model Year LTVs. Torrance, CA: Dynamic Research, Inc., May 2005.
4 National Highway Traffic Safety Administration. “Crash Test.” National Highway Traffic Safety Administration. (accessed April 28, 2006).
5 Erickson, Christopher. “Crumple Zones in Automobiles.” Sourced through the American Institute of Physics. (accessed April 28, 2006).
6 American Plastics Council. Automotive Learning Center. Plastics: Your Key to Fuel and Cost Savings. Arlington, VA: American Plastics Council, 2001. A brochure. (accessed April 28, 2005).
7 Advanced Composite Products and Technology, Inc. “Safety Features.” Advanced Composite Products and Technology, Inc. http://www.acpt.com/driveshaft/safety.html (accessed April 24, 2006).
8 PBS: NOVA Online. “Escape Through Time.” Sourced through the American Institute of Physics. http://www.pbs.org/wgbh/nova/escape/timecar.html (accessed April 28, 2006).
9 Diem, William. “Banking on Composites.” Ward’s AutoWorld, June 1, 2005. http://wardsautoworld.com/ar/auto_banking_composites/ (accessed April 20, 2006).
10 Van Auken, R.M and J.W. Zellner. Supplemental Results on the Independent Effects of Curb Weight, Wheelbase, and Track on Fatality Risk in 1995-1998 Model Year Passenger Cars and 1985-1997 Model Year LTVs. Torrance, CA: Dynamic Research, Inc., May 2005.