Better Blast Helmets from Fluid Dynamics

Today’s blast helmets do not adequately protect soldiers from high-pressure shockwaves produced when roadside bombs and other improvised explosive devices (IEDs) explode, and this failure has contributed to an epidemic of brain damage in the military.

Now, a team of engineers from North Dakota State University (NDSU) has used engineering modeling software to show how blasts injure the brain despite the helmets—and to provide crucial clues for a much-needed helmet redesign that could protect soldiers from lasting brain damage.

Sixty percent of all traumatic brain injuries in soldiers are caused by blasts, and blasts injure via high-pressure shockwaves. These shockwaves injure the brain via a different mechanism than blunt-impact trauma. Like waves that reverberate around a swimming pool, shockwaves within the confines of a helmet can amplify each other to create powerful waves that move the brain within the confines of the head, said Mariusz Ziejewski, an NDSU professor of mechanical engineering who worked on the research.

The traditional helmets and face shields don’t provide much help. They offer some protection from blasts that originate in front of the head, but for blasts coming from the side and back, they can actually make things worse, Ziejewski said. 

A Protective Helmet

To protect the head from shockwaves, the key is designing a helmet that prevents the wave from entering, Ziejewski said. “This is very different protection than we are used to thinking about when we think about a helmet.”

To design a more protective helmet, Ziejewski and his colleagues first needed to test how today’s helmets protect the brain from shockwaves. He and a team of engineers led by Hesam Sarvghad-Moghadam, a mechanical engineer at Harvey Mudd College, developed a computational model using finite linear analysis, a tool that helps to measure stress and strain on a structure.

In their computer simulation, they detonated a blast of TNT with the force of a car bomb a bit more than half a meter from a soldier’s head. When the simulated blast came from the front of the head, the use of a helmet and face shield together reduced the strain, or deformation forces, on the brain by 15 percent. When the blast came from the side of the head, the combined protective gear reduced the strain by 18 percent.

But for a blast from the back of the head, the protective gear actually increased the strain by 9 percent.

Using a helmet alone was worse: A blast from the side of the head increased strain by 39 percent compared with no helmet.

Using Fluid Dynamics

The team postulates that pressure waves can penetrate the protective gear through the gaps near the back and side of the head. As they do, the waves ricochet off the helmet and face shield and amplify, imposing more forceful pressure pulses on the head.

To better protect the head, Ziejewski thinks adding a shield at the back of the helmet could deflect shock waves away from the head. Alternatively, adding shoulder supports could offer additional protection against blast-induced brain acceleration. “We have to think of this like fluid dynamics and flow,” he said.

Either way, computational models like theirs could point the way toward a redesign that accounts for the current deficiencies in protective gear, Ziejewski said. And helmets designed using fluid-dynamics principles could help slow the epidemic of traumatic brain injury in today’s military. 

Monique Brouillette is a science and technology writer based in Cambridge, Massachusetts.