Newly found metal foam could cut car crash severity by 48% without adding weight
A car's front rails absorb the brunt of a frontal collision, deforming to slow deceleration before that force reaches the people inside. A new study finds that swapping the metal inside those rails for a foam-like composite material could let vehicles survive dramatically faster crashes before hitting critical safety limits.
The research tested whether replacing conventional front rail designs with composite metal foam, or CMF, could improve how much energy a vehicle absorbs.
The team focused specifically on high-speed frontal impacts. Afsaneh Rabiei, professor of mechanical and aerospace engineering at North Carolina State University, is the study's corresponding author. She led the work alongside first author Aman Kaushik, a postdoctoral researcher at NC State.
Hollow spheres, strong foam
CMF consists of hollow metal or alloy spheres, often steel, embedded inside a metallic matrix. That structure makes the material lightweight while remaining highly effective at absorbing compressive and impact forces. Those properties have already drawn interest for aircraft wings, vehicle armor, and body armor.
Rabiei said CMF's unique structure lets it absorb energy more effectively during high-velocity impacts than conventional metals, despite weighing less. That matters directly for vehicle safety, since slowing a car's deceleration rate during a crash reduces the forces transmitted to its occupants.
Testing two designs
Researchers compared CMF front rails , built from an aluminum tube with a steel CMF core, against two front rail designs already used in commercial vehicles. Those included rectangular cross-section steel rails and double-octagonal aluminum rails. Using extensive experimental CMF data alongside publicly available specifications for conventional rails, the team ran detailed computational models simulating high-velocity frontal impacts.
Compared with double-octagon rails , vehicles fitted with CMF front rails could travel roughly 34 percent faster before reaching the critical crash-severity limit. They could also travel about 40 percent faster before reaching the threshold linked to head injury risk. Against rectangular rails, those margins widened further, to about 32 percent and 48 percent respectively.
Gains at highway speed
At a standardized 55 mph impact speed, CMF rails of identical weight and length to their double-octagon counterparts reduced maximum deceleration by about 38 percent. Overall crash severity fell by about 45 percent, and the Head Injury Criterion, a standard measure of serious head injury risk, dropped by roughly the same amount. Against rectangular rails at the same speed, the improvements grew sharper still. Deceleration fell by about 84 percent, crash severity by about 94 percent, and Head Injury Criterion scores by about 83 percent.
Rabiei said CMF outperformed conventional rails across the board, with the performance gap widening further as impact speed increased. Because the CMF rails matched the weight and length of the designs they replaced, the safety gains came without any fuel-economy penalty. Rabiei said the rails could potentially be shortened while still improving safety, which would boost fuel efficiency further still.
Combined with CMF's previously documented resistance to heat and fire, the researchers see potential applications extending into electric vehicles. That includes structures designed to protect high-voltage battery packs from crash damage. Rabiei said her team is open to working with automakers, suppliers, and battery manufacturers to test CMF-based structures directly, including protection systems built specifically for EV battery packs.
The research was published in the Journal of Composites Science .
