TBIs on the battlefield are mostly caused by ballistic impacts and exposure to shock waves from explosions.
The use of high-explosive materials has recently increased the frequency of blast Traumatic Brain Injuries (bTBI) among military personnel and civilians.
Insights into the mechanisms of TBI and brain damage thresholds is critical for understanding the influence of ballistic helmets and padding systems on the biomechanical responses of the brain under dynamic ballistics and blast loads.
In a ballistic collision, a part of the kinetic energy of the penetrating bullet will be expended during helmet fracture. A Part of the blast waves are reflected as they reach the head, while others penetrate through the skull and into the brain. The massive deformations of the pads will disperse a considerable portion of this impact energy.
As a result of these ballistic impacts, stress waves, pressure, and motion are formed in the helmet, skull, and brain, which can impair brain tissues.
The padding system is a crucial component of any ballistic helmet. Pads in helmets that use energy-absorbing materials can significantly reduce the amount of transmitted load.
Foams are well-known energy-absorbing materials that are frequently used in helmet pads. Foam materials have the ability to undergo significant compressive deformations and absorb large amounts of applied energy. The energy is reduced by bending, buckling, or cracking the cell. Padding efficiency, on the other hand, is highly reliant on the material, form, geometry, and padding system configuration.
Before a helmet system can be certified for military use, it must fulfil a number of requirements. Some of these criteria are specific to the helmet shell or other components and must be tested in accordance with the applicable standards.
The following are critical structural features of the padding system that must be met:
- The pad system must be available in multiple components and should be simple to attach and disengage from the helmet in order for the wearer to customize for comfort.
- Typically, one circular pad, two trapezoidal pads, and four oval pads are being used and are typically designed in two thicknesses: ¾ and 1 inch.
- Pads must fulfill three functions: an inner fabric layer which gets direct interaction with the wearer’s head and wicks moisture, a padded layer that provides comfort and protection, and an outside fabric layer that binds to the helmet.
- Padding systems are intended to provide “standoff, comfort, safety, and stability.”
- Hook discs are adhesively affixed to the interior of the helmet to provide a medium for the outer fabric layer to adhere to.
- A sufficient number of hook discs are required to allow pad movement and personalization of pad location, and at least 1/2 of the interior of the helmet shell will be covered with discs.
- Each padding system must include a permanent label indicating the pad thickness as well as other production details.
The padding system also must meet the following performance requirements.
- The outer fabric layer should be composed of a material that can be attached to the interior of the helmet shell and has a specified peel strength (3.5 lbs/inch of width).
- The Padding material must be capable to be compressed repeatedly without failing and resistant to vibrations.
- The Hook discs must be robust enough to resist removal from the interior of the helmet shell and have a sufficient peel strength (3.5 lbs/inch width).
- While doing a buoyancy test, the pads should not get detached from the helmet.
- The colorfastness of the inner and outer padding layers should achieve the required standards.
- The pads should maintain structural integrity and demonstrate no structural loss at temperatures ranging from -60°F to 130°F, as well as pressures at sea level and 15,000 feet.