The Promise of Pads

Research into new materials may change shape, efficiency of combat helmet pads to offer stronger defense against shock waves

By T’Jae Gibson, ARL Public Affairs Office

New Army studies of the padding inside combat helmets are expected to reveal new insights on ways to prevent shock waves from a detonated improvised explosive device, for example, from damaging Soldiers’ brains.

Army scientists say not enough information exists to determine the degree to which shock waves move past combat helmets’ outer shells and padding, and through the human skull. So while research is underway to understand that, ARL is also investigating the relationship between blast waves and traumatic brain injuries.

Dr. Thomas Plaisted, a mechanical engineer at the U.S. Army Research Laboratory is leading research efforts to develop new materials and pad geometries to best use the space within the helmet for optimal protection.

He said the current Army Combat Helmet and its padding are designed to protect against impact velocities up to 10 feet per second.

“Battlefield threats are constantly evolving and the Army is seeking to push the level of protection higher, perhaps even to a level double that of the current impact velocity specifications, but while retaining as much of the current dimensions – like pad thickness – as possible,” Plaisted said.

He said until researchers understand how the brain is injured in blast events and how the padding influences the injury, “it is difficult to confidently engineer an improved pad for blast protection.”

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A jump master with the XVIII Airborne Corps Special Troops Battalion readjusts the pads of a Corps’ Soldier’s Advanced Combat Helmet during manifest call for the Corps’ final pre-deployment jump, Jan. 15, at Fort Bragg, N.C. (Photo by Army Staff Sgt. Jeremy D. Crisp)

The current ACH pads were introduced to replace the sling suspension system used in the Personnel Armor System for Ground Troops, or PASGT helmet, which was first issued in the mid 1980s and was fielded en masse to Warfighters until the mid-2000s.

A 2007 study conducted by the National Center for Biotechnology Information concluded that the most frequently reported problems for the PASGT involved discomfort. Their analysis indicated that there was a strong soldier preference for the ACH over the PASGT, which could enhance its already superior protective qualities.

“When the (current) padding system was introduced, it received favorable feedback from the soldier’s in terms of improved comfort. In addition the padding system protected the soldier to a higher level impact than the sling system,” Plaisted said.

The current helmet pad is approximately three quarters of an inch thick at all locations inside the helmet. Plaisted said the shape of the pads vary by location within the helmet. For example, the crown region of the helmet has a circular pad geometry, and all other locations have a rectangular or trapezoidal geometry that interfaces with the forehead, sides, or back of the head.

The pad material composition consists of two layers of polyurethane foam, each layer approximately 0.375 inch thick. The layer that is closest to the head is a lower density, more compliant foam, with the function of providing a comfortable interface and fit. The layer closest to the helmet shell is a higher density foam with a stiffer response that is more tuned to absorb energy during impact. The foam is encased in an airtight polymer film to keep out moisture and that assembly is in turn encased in a thin fabric with moisture wicking properties,” Plaisted explained.

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As a whole, these pads are known as the suspension system for their role in suspending the helmet above the soldier’s head, while serving additional roles of improving the fit between the soldier’s head, which of course varies from person to person, and the defined curvature of the ACH shell, as well as providing low velocity impact protection. (U.S. Army photo)

He said padding inside the helmet limits the amount of force and “level of acceleration imparted to the skull when a helmet is impacted.”

“Excessive acceleration of the head can lead to concussion and potentially mild traumatic brain injury. Generally, the thicker the padding the lower the head acceleration, however we can only devote so much space to the pads while making the helmet comfortable and minimizing its affect on soldier performance like mobility, visual awareness and aiming weapons,” he said.

ARL researchers are using computer modeling of various impact conditions to determine the optimal properties and go to the lab to engineer those properties into materials and pad geometries.

Plaisted is also leading a research effort to create synthetic cranial bones to capture material and architecture response, specific to the human skull. He said the skull simulant ARL researchers are developing is made of synthetic materials with the goal of creating a uniform response that is representative of the soldier population to use in tests to understand how to best protect the head during exposure to blast waves and blunt impact.

“In the future, when the final skull surrogate is developed, it will be tested with new helmet padding materials in simulated blast and impact conditions to determine how the pads and helmet shell materials protect the head from injury. Right now there is not a direct back and forth between these two programs but that is the intent in the future.”

For information on ARL’s helmet pad research, please visit here.

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Padding Geometries: “The crown region of the helmet has a circular pad geometry, and all other locations have a rectangular or trapezoidal geometry that interfaces with the forehead, sides, or back of the head,” explained Dr. Thomas Plaisted, ARL. (U.S. Army photo)

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