New York -- A counter-intuitive finding from scientists at New York University (NYU) and Polytechnic Institute of New York University (NYU-Poly) is that the foam used in helmets and other body armour absorbs damage when compressed slowly but can cause as much injury as a hard object when hit at high speeds.
These findings will help diagnose hidden explosive shock wave and sports injuries, said a press statement from the two institutions, Their findings could also change the methods of diagnosis for soldiers and football players whose injuries are not immediately detectable but whose symptoms evolve over time.
The materials scientists also found that bones themselves fracture differently according to loading -- another factor that will lead manufacturers to select protective materials according to the speed of impact, whether for sports equipment, military armour, car interiors or submarines.
Nikhil Gupta of NYU-Poly's Department of Mechanical Engineering and Paulo Coelho of NYU's Department of Biomaterials and Biomimetics led the team that undertook two recent studies on rabbit femur bones. The team expects similar results on human bones.
Advanced engineering and medical equipment such as CT-scanners, electron microscopes and high-speed camera systems documented how bones and lightweight composite materials deformed and fractured under high loading rates.
In addition to helmets and armour, the lightweight foams are widely used in marine structures such as boats. Describing the importance of the findings on foams, Gupta said, "The foam materials that seem soft when slowly compressed can actually become much stiffer as the loading rate is increased. A foam that would crush when slowly compressed can cause injury if punched hard."
In follow-up studies, the team plans to investigate whether such change in material behaviour at high loading rates can actually increase the risk of injuries.