A car’s front end is designed to sacrifice itself in a collision. As the structure bends and crushes, it absorbs energy that would otherwise be transferred more directly to the people inside.

New research suggests that composite metal foam, or CMF, could make this protective process considerably more effective without increasing the weight or length of existing crash structures.

Using detailed computer simulations, researchers compared CMF-based front rails with two conventional designs already used in vehicles. The results, published in the Journal of Composites Science, indicate that the metal foam could reduce violent deceleration and lower measures associated with serious head injury during high-speed frontal impacts.

How Metal Foam Absorbs A Crash

Front rails sit behind a vehicle’s bumper and form an important part of the crumple zone. During a frontal collision, energy from the impact is transferred into these structures, which are engineered to deform progressively rather than transmitting the full force towards the passenger compartment.

The new design uses an aluminium tube containing a steel composite-metal-foam core. CMF is made from hollow metal or alloy spheres embedded in a metallic matrix. This unusual internal structure produces a material that is relatively light but capable of absorbing substantial compressive and impact forces.

Researchers compared it with two established front-rail configurations: hollow rectangular steel rails and double-octagonal aluminium rails formed from two stacked octagonal sections.

Afsaneh Rabiei, professor of mechanical and aerospace engineering at North Carolina State University and corresponding author of the study, explained that CMF’s structure allows it to absorb high-impact energy while remaining lighter than many conventional metals. Slowing the rate at which a vehicle decelerates is particularly important because abrupt deceleration can expose occupants to severe forces.

Higher Speeds Before Safety Limits

The study was based on computational modelling rather than full-scale vehicle crash tests. Researchers used extensive experimental information about CMF alongside publicly available data on conventional front-rail materials and designs.

In the simulations, CMF rails allowed the vehicle to reach considerably higher impact speeds before crossing predefined safety thresholds.

Compared with double-octagonal rails, a vehicle equipped with CMF rails could travel around 34% faster before reaching the critical crash-severity threshold and roughly 40% faster before reaching the head-injury threshold. Against rectangular rails, the corresponding increases were about 32% and 48%.

These percentages do not mean that passengers would automatically remain safe at those higher speeds. They describe when particular modelling measures reached critical limits and should not be interpreted as direct predictions of survival or injury in every real crash.

Major Differences At 89 Km/H

The researchers also examined a frontal collision at 55 mph, equivalent to about 89 km/h.

Compared with an equal-length, equal-weight double-octagonal rail, CMF reduced maximum deceleration by approximately 38%. Overall crash severity fell by around 45%, while the Head Injury Criterion, or HIC, also decreased by about 45%. HIC is a standard measure used to estimate the likelihood of serious head trauma during an impact.

The difference was even greater against conventional rectangular rails. At the same impact speed, CMF reduced maximum deceleration by about 84%, crash severity by roughly 94% and HIC by approximately 83%.

Importantly, these improvements did not require a larger or heavier crash structure. The CMF rails used in the comparison had the same weight and length as the conventional alternatives.

Potential For Lighter Cars

The researchers believe this performance could give vehicle designers more flexibility. Rabiei suggested that shorter CMF rails might still provide improved crash protection while reducing overall vehicle weight, potentially supporting better energy efficiency. That possibility remains to be tested in actual vehicle designs.

The material may also have particular value for electric vehicles. Previous research has shown that composite metal foam can resist heat and fire, raising the possibility of using CMF structures around high-voltage battery packs where both impact protection and thermal resistance are important.

Researchers are now interested in working with manufacturers, suppliers and battery companies to test CMF in existing front-rail designs and explore dedicated structures for electric vehicles.

The findings are promising, but the technology has not yet been proven in production cars through full-scale real-world crash testing. The next challenge is therefore turning strong simulation results into physical components and establishing whether the same advantages remain under the complex conditions of actual collisions.