Towards a generalized model for predicting projectile penetration in block stone barriers: A meso-scale discrete element analysis

In contemporary military defensive systems, block stone ballistic shielding layers serve as the primary line of defense for both personnel and critical infrastructure, making the accurate prediction of projectile penetration depth essential. Current empirical and semi-empirical formulas primarily focus on mortared block stone concrete, leaving a systematic understanding of unmortared block stone structures largely unexplored. Such discrete structures pose significant challenges for continuum mechanics-based finite element methods. This study employs a discrete element bound particle model to develop meso-scale models of both mortared block stone concrete and unmortared block stone assemblies. The influence of mortar strength, aggregate strength, and aggregate size on penetration resistance is quantitatively studied. Results indicate that for high aggregate volume fractions, penetration resistance is significantly more sensitive to aggregate strength and size than to mortar strength. Furthermore, when the target thickness is less than ten times the aggregate diameter, the use of mortar or other binding materials is recommended to enhance penetration resistance. Based on a previous dimensionless framework, a new predictive model incorporating mesoscopic factors is developed. This model accurately predicts the penetration depth of rigid projectiles into various block stone ballistic shielding layers, with or without mortar, and shows strong agreement with numerical simulations.