Computational Investigation of Shock-Mitigation Efficacy of Polyurea When Used in a Combat Helmet

Polyurea falls into a category of elastomeric co-polymers in which, due to the presence of strong hydrogen bonding, the microstructure is of a heterogeneous nature and consists of a compliant/soft matrix and stiff/hard nanometer size hard domains. Recent investigations have shown that the use of polyurea as an external or internal coating/lining had substantially improved ballistic-penetration resistance of metallic structures. The present work aims to use computational methods and tools in order to assess the shock-mitigation ability of polyurea when used in the construction of different components (suspension-pads, internal lining and external coating) of a combat helmet. Shock-mitigation capability of combat helmets has become an important functional requirement as shock-ingress into the intra-cranial cavity is known to be one of the main causes of traumatic brain injury (TBI). To assess the shock mitigation capability of polyurea, a combined Eulerian/Lagrangian fluid/solid transient non-linear dynamics computational analysis of an air/helmet/head core sample is carried out and the temporal evolution of the axial stress and particle velocities (for different polyurea augmented helmet designs) are monitored. The results obtained show that improvements in the shock-mitigation performance of the helmet are obtained only in the case when polyurea is used as a helmet internal lining and that these improvements are relatively small. In addition, polyurea is found to slightly outperform conventional helmet foam, but only under relatively strong (greater than five atm) blastwave peak overpressures. The present approach studies the effect of internal linings and external coatings on combat helmet blast mitigation performance. Published in Multidiscipline Modeling in Materials and Structures, v8 n9 p297-331, 2012. Prepared in collaboration with the Naval Surface Warfare Center, Carderock Division, West Bethesda, MD and in cooperation with Clemson University, Clemson, SC and Corvid Technologies, Mooresville, NC.