Car_Rollover_Testing_12_SS

Video credit : Mitchell Powers
Photo credit : Sanjay Suchak

U.Va. Researcher

JASON KERRIGAN
Assistant Professor
Mechanical and Aerospace Engineering

While rollover crashes account for only about 2 percent of all crashes, they constitute roughly one-third of all occupant fatalities – about 7,500 highway deaths each year in the United States. The annual cost of rollover injuries and fatalities is about $50 billion. Yet, there currently are no crash-test dummies specifically designed for rollovers.

Researchers at the Engineering School’s Center for Applied Biomechanics, using a $5 million grant from the National Highway Traffic Safety Administration and $2 million from car manufacturers, have determined that there are no crash-test dummies that accurately reflect how the human body may react to and become injured in this type of crash.

Mechanical engineer Jason Kerrigan used the funds to develop a unique full-scale indoor rollover crash test sled system. It can rotate a sport-utility vehicle – the type of vehicle most susceptible to rollovers – at 400 degrees per second and drop it onto a moving roadbed, simulating a rollover accident.  With the system in place, he studied occupant injury risk and vehicle structure crashworthiness.

The figure compares human (dotted line and grey area are average and +/- 1 SD) and crash dummy (others) torso response in a rollover crash by comparing longitudinal motion of the top of the torso relative to vehicle roll angle. These data indicate that not only is there no dummy that falls within the corridor of human response, crash dummies, in general, move in a direction that is opposite of the direction that humans move. This research was the first to demonstrate the relatively low biofidelity, or similarity to human response, of current crash dummies for use in rollover crash tests.
The figure compares human (dotted line and grey area are average and +/- 1 SD) and crash dummy (others) torso response in a rollover crash by comparing longitudinal motion of the top of the torso relative to vehicle roll angle. These data indicate that not only is there no dummy that falls within the corridor of human response, crash dummies, in general, move in a direction that is opposite of the direction that humans move. This research was the first to demonstrate the relatively low biofidelity, or similarity to human response, of current crash dummies for use in rollover crash tests.

“Rollover crashes can take up to 10 to 15 seconds to complete as a vehicle rotates and makes often repeated strikes on a roadway – a long period of time for a person, or dummy, to be undergoing those kinds of circumstances,” Kerrigan says.

“When you’re in a car that is airborne and rotating, your body is being drawn toward the roof with up to four times the force of gravity. You’re upside down or you’re on your side, or you’re at an angle and when you hit, it’s going to be a severe impact. We’re trying to understand that as well as possible through precise and repeatable tests.”

Data from that testing is helping Kerrigan’s team delve into how to make a better dummy, one that will be humanlike, or “biofidelic” – mimicking as much as possible the size, shape, weight and flexibility of an actual person undergoing the prolonged and unique stresses of a rollover crash.

“Manufacturers design and tailor the crash safety features in their cars – such as airbags, seats and seatbelts – based on how crash test dummies respond in various scenarios, such as rollovers,” says Qi Zhang, a Ph.D. candidate with the biomechanics center who is developing a dummy for his dissertation that is specifically for testing and predicting injury risk in rollover crashes. “One of the things I’m doing is adding more elements and sensors to current dummies to emulate the flexible human spine, and to eventually also create active muscle structures that can respond to stresses in the same way human muscles tense in a crash.”

Zhang is using computational modeling, based on his data, to design the specialized dummy. Interestingly, dummies currently used to study rollovers were designed only for frontal crashes – impacts that happen in hundreds of milliseconds and then are over with – and are ill suited for understanding or predicting injury risk in rollovers. Zhang said rollovers present a particular challenge to dummy design, in that vehicle occupants move into different positions and postures as the vehicle rotates, resulting in damage to the side or top of the head as the vehicle’s side impacts the road, turns and the roof hits the road and compresses.

“One of the most important results we’ve seen is that the human spine extends, straightens and aligns itself with the acceleration vector in a way we have never seen in other types of crashes,” Zhang says. “This puts the human head close to the roof, and closer to injury, at the time the roof gets impacted by the ground when the vehicle rolls over.”

Zhang expects to build, based on his computer model, a rollover dummy prototype sometime next year.

“Our ultimate goal is to learn how to protect people in rollover crashes,” Kerrigan notes. “What we learn in this lab is of great use to automobile manufacturers, researchers at other test facilities, and can be used for vehicle design improvements to eventually substantially reduce death and serious injury from these types of crashes.”

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