Head Impact Modeling to Support a Rotational Combat Helmet Drop Test.

Area of Science:

• Biomechanics
• Neuroscience
• Materials Science

Background:

• The Advanced Combat Helmet (ACH) military specification (mil-spec) uses blunt impact acceleration criteria for warfighter protection.
• Current ACH testing relies on a linear constrained drop test, primarily measuring translational headform response.
• Rotational head movements are known to generate higher brain tissue strains than translations, potentially leading to traumatic brain injury (TBI).

Purpose of the Study:

• To investigate whether the ACH specification's linear drop test underreports the potential for TBI.
• To compare brain tissue strain under the current ACH testing protocol versus a modified protocol incorporating rotational forces.

Main Methods:

• Conducted linear constrained drop tests per ACH specification and verified with simulations.
• Developed and validated a high-fidelity human head digital twin against experimental results.
• Modified the ACH test configuration to include a Hybrid III headform, freefall cradle, and inclined anvil target to induce both translational and rotational responses.

Main Results:

• The modified experimental configuration, which included rotational forces, produced brain strains 4.3 times greater than those from the linear constrained configuration.
• Simulations confirmed agreement between experimental and simulated headform impact responses.

Conclusions:

• The ACH mil-spec's linear drop test may underestimate TBI risk by not accounting for rotational forces.
• Revision of the ACH specification to include rotational components is scientifically motivated to enhance TBI relevance.
• A revised testing protocol could lead to improved TBI protection for warfighters.