This paper discusses the relationship between chest injury and the depth and shape of the body armor’s backface deformation in clay that is associated with the force of impact.
Measuring the imprint of body armor backface deformation in clay is still the most widely-used method to assess BABT. Previous efforts have demonstrated that the current metric using the maximum depth in clay may not predict injuries as well as a metric containing the velocity of the armor backface deformation; however, measuring the velocity requires upgrading facilities with expensive equipment and, even then, backface velocity is difficult to capture. This study investigates the association of thoracic injury with the depth and shape of the backface deformation in clay that is associated with the energy and energy density of the impact. This metric including depth and shape reflects the empirical evidence that deeper deformations are more likely to cause injury; but for similar depths, deformations with larger volumes are more injurious. Reconstructions of several law enforcement survivor cases of behind-armor blunt trauma to the chest were performed to obtain the backface signature in clay for these known injury events. Moulds were made of the backface signatures and then scanned to characterise the diameter, depth, volume, and surface area of the deformations. The relationship between the depth and surface area/volume ratio and the injuries from the survivor cases were determined. The depth and surface area/volume ratio showed good correlation to the injury severities reported in the survivor cases. The analysis also confirmed that even if the surface area to volume ratio between two different backface deformations were maintained, the impact that results in a deeper clay depth has a higher risk of increased injury severity. The dataset for this analysis is currently limited, but the relationship exhibits potential for an improved metric that can be easily implemented into current testing methodologies and facilities. (Published Abstract Provided)