Explosive blast loading experiments for TBI scenarios: Characterization and mitigation

As a result of the growing military conflicts over the past eight years, the focus on traumatic brain injuries sustained from explosive blasts in wartime scenarios has gained tremendous attention in the scientific and medical communities. During previous warfare conflicts in history, military armor was not as technologically advanced as it is today. As a result, the understanding of traumatic brain injuries is limited since previous blast occurrences typically resulted in higher fatalities due to non-primary blast effects. It is, therefore, the intent of this work to advance the knowledge on traumatic brain injuries from explosive blasts. The study focuses on two aspects. The first focus is on surrogate modeling of the human anatomy subjected to blast loading conditions and the resulting behavior that occurs which provides insight into injury mechanisms and needed model validation data. The second focus is on preventive protection against explosive blasts by studying various materials and the effectiveness of each material to attenuate blast profile characteristics. The physical modeling aspect of the study was accomplished by varying surrogate materials, geometric configuration, and blast loading conditions in order to determine the measurable behavior variations. Quantitative results were obtained through pressure, acceleration, strain, and displacement measurements. These results suggested large initial amplification of pressures at anterior locations near the shell/gel interface. Material property effects and geometric features effects were seen by larger responses with the material of lower stiffness and more severe responses with the facial feature shell models over the solid shell models. Extreme accelerations were experienced with oscillatory behavior over the duration of the blast. In addition, significant relative displacement was observed between the shell and the gel material suggesting large strain values. Further quantitative results were obtained through shadowgraph imaging of the blast scenarios. The shadowgraph imaging confirmed the approximation that global movement of the target was minimal during the blast occurred on a different time scale. The complete results then provided a means of comparison to actual measured behavior from surrogate models to injury mechanisms in computational and clinical trials. Furthermore, the data obtained can be used in computational validation. The blast mitigation aspect of the study was accomplished by applying blast loading conditions to various mitigant materials. Composite structures were constructed using various filler materials which varied density, porosity, viscosity, and particle size. Quantitative results were then obtained by measuring transmitted wave profiles behind the respective samples and comparing to free-field loading conditions. Attenuation effectiveness was then determined by the reduction of blast profile characteristics (peak overpressure, pulse duration, and impulse). The results of these experiments showed that lower density, porous materials caused blast profile resembling scaled air blasts. Specifically shorter wave front rise times and negative overpressure values were observed. The higher density materials exhibited the greatest attenuation by lowering the overall peak pressure, lengthening the duration, and slowing the rise to peak amplitude. This resulted in lower overall impulse values. Furthermore, significant frequency distribution was observed surpassing the effectiveness of the solid foam control sample and the lower density materials