The Ballistic Resistance of Adobe Masonry : An analytical model for impacts on mud bricks and mortar

A significant number of published papers in the field of penetration mechanics devotes attention to the study of targets made of metal and ceramic materials for protective equipment. In recent times, the progression in harshness of urban warfare is leading western governments to investing in research focused on the ballistic response of building materials. Adobe, a traditional form of masonry made of unburnt soil bricks and mud mortar, is spread in areas of the world often involved into military conflicts. Knowledge on the material properties of the components and on the overall dynamic response of these structures is still scarce. Therefore, a ballistic campaign aimed at studying the penetration processes in Adobe was performed by TNO: residual velocity or penetration depth were measured for different small calibre projectiles impacting at different velocity Adobe walls with different composition and strength. The resulting information was collected and organized into a database. It was used as statistical basis to develop an analytical predictive model capable of correctly addressing the terminal ballistic depth, namely penetration length, in case of small calibre impacts on Adobe targets. The proposed phenomenological model, that belongs to a class of models based on Newton’s 2nd law, parametrizes the sources of energy dissipation during penetration through a linear dependent bearing resisting force model. The properties of the targets were experimentally determined during an additional experimental characterization campaign performed on Adobe components in 2016 in the Netherlands. The paper presents the experimental data, the analytical model developed and the calibration of parameters, providing the relation between the experimental and the predicted penetration lengths.

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