When it comes to traffic safety research, Jack Carney is no crash-test dummy. An international expert on impact attenuation devices, Carney holds 10 patents in this area of research.
His interest in impact mechanics began in the 1970s, while he was on the civil engineering faculty at the University of Connecticut. After a couple of state Department of Transportation employees were killed while on the job, transportation officials contacted Carney for help. He designed one of the first truck-mounted attenuators – devices that absorb the impact of a crash. “They’re basically crash cushions that cantilever off the back of a truck,” Carney explains.
One device, developed while he was at Vanderbilt, is constructed from a “smart” material that collapses, dissipates kinetic energy, and then regains its original shape.
From there, Carney developed new devices designed to reduce the impact of traffic accidents on highways. Many of his patented devices can be found lining highways all around the country.
“It’s a high-molecular-weight, high-density polyethelene” that the Tennessee Department of Transportation was using in underground drainage pipe applications. Intrigued with the material’s mechanical characteristics under high strain-rate loading conditions, Carney conducted some experiments to find its material properties under impact loading.
He discovered that the material was highly ductile and did not fracture under loading, even at very low temperatures. More importantly, he discovered that the material could be subjected to large deformations, dissipate energy, and then restore itself to its original shape. Carney realized that he could use the material to design reusable, maintenance-free impact attenuation devices.
“My previous research had employed mild steel cylinders to dissipate kinetic energy,” Carney says. “Such devices, although very effective, were sacrificial in that they had to be replaced after every significant impact.” These days, Carney’s reusable crash cushions line highways in the United States and in many other countries around the world.