Physical mechanisms for near-field blast mitigation with fluid-filled containers
Creators: name: Bornstein, Huon
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401005
subject: Risk engineering
classificationCode: 401099
subject: Engineering practice and education not elsewhere classified
classificationCode: 401706
subject: Numerical modelling and mechanical characterisation

description: Landmines and buried improvised explosive devices (IEDs) have been an increasing threat to occupants within armoured vehicles during recent conflicts. Whilst there a range of blast protection technologies available for armoured vehicles, such as v-shaped hulls and energy attenuating materials and seating systems, a recent study has shown the potential to use water for near-field blast mitigation. Whilst that study identified the potential to use water on-board an armoured vehicle for blast mitigation, there was minimal understanding of the physical mechanisms that govern the mitigation, which makes optimisation of any design using water extremely challenging. As water is already carried on-board armoured vehicles inside containers, its use as part of the protection system is attractive as it would require no added mass. This ensures that enhancements in the survivability of the vehicle only have a minimal impact on other critical functionality such as mobility. This PhD thesis focuses on understanding the physical mechanisms responsible for near-field blast mitigation with water, and then uses that knowledge to optimise the design of water-filled containers.<br><br>The methodology used throughout the investigation was to conduct a series of experiments that examined the mitigation provided to a flat, high-strength steel plate (representing a simplified armoured vehicle belly plate) by a water-filled container subjected to near-field blast loading. Experiments were conducted using an explosion bulge die test setup with a 5.06 kg cylindrical PE4 charge placed at a stand-off distance of 600 mm from the steel plate. The water-filled containers were placed between the steel plate and the explosive charge. Assessments of performance were made in terms of the reduction in deformation of the steel plate. Numerical simulations were then validated against the experimental results and further interrogated to understand the mechanisms responsible for the blast mitigation.<br><br>The first major body of research focused on understanding the influence that container geometry had on the blast mitigation provided by a quadrangular-shaped container. The experimental results showed that taller and narrower water-filled containers provided the best mitigation. The best performing container provided a 65% reduction in peak deformation when compared to the bare plate setup. The numerical simulations were performed using a coupled Euler-Lagrange approach in ANSYS® AUTODYN®. Validated numerical simulations were then used to identify and quantify the roles of each of the key mitigation mechanisms. These were found to be the mass of the water; the shadow region generated by the container deflecting the detonation products; and the radial spreading of the water. The level of blast mitigation provided by the water-filled containers was governed by the trade-off between these mitigation mechanisms and the increase in loading at the container surface due to its closer proximity to the explosive charge. The trade-off between the increased loading and the enhancement of the mitigation mechanisms was found to result in an optimum container width for a given height.<br><br>The second major body of research focused on using the mitigation mechanisms identified to optimise the design of the container geometry. Numerical simulations were used to develop a range of novel container shapes, which were then experimentally assessed to determine their effectiveness. The container shapes evaluated included; 1) cone, 2) inverted cone, 3) diamond, 4) mushroom, and 5) array of water containers described as a kinetic energy defeat device (KEDD). A mushroom-shaped container was found to provide more efficient blast mitigation than the best performing quadrangular containers due to its enhancement of the shadowing and spreading mitigation mechanisms.<br><br>The research also focused on understanding the role of the mitigant within the container. Experiments were conducted to compare the water to; 1) aerated water, 2) sand, 3) expanded polystyrene (EPS), 4) combination of EPS and water, and 5) shear thickening fluid made with corn starch and water. The water was found to provide the best mitigation per unit mass, while the sand, which was the densest mitigant, provided the best mitigation per unit volume. Validated numerical simulations of each of the experiments identified the loading and mitigation mechanisms for each mitigant type. The key mitigation mechanisms were still found to be mass, shadowing and spreading for each of the mitigants, with their performance determined by their ability to exploit each of these mechanisms.<br><br>The research then focused on understanding the integration issues associated with using a water-filled container on an armoured vehicle. The first integration issue addressed was the influence of generating a stand-off between the container and the target. The experiments and numerical simulations showed that there was minimal difference in target deformation for small container stand-off distances. However, the blast mitigation was reduced when the container was placed too close to the explosive. The second integration issue addressed was the influence of multiple containers placed in proximity to one another. Experiments were conducted to assess the influence of gap size between containers for explosive charges placed above a central container as well as above the gap between two containers. Increasing the gap size between containers resulted in less blast mitigation, although in all cases the water-filled containers provided some mitigation. Limitations in this investigation identified that further work was required to assess whether these findings were consistent for multiple container sizes and loading conditions.<br><br>The research outcomes from this PhD thesis have contributed to the body of knowledge in understanding the physical mechanisms associated with using a range of mitigant-filled containers for near-field blast mitigation. This includes identifying a range of methods to isolate each of the loading and mitigation mechanisms, which can be used in other blast protection investigations in the future. The thesis also provides guidance to designers in terms of optimising the container geometry to maximise protection and identifies some of the challenges associated with integrating these designs onto an armoured vehicle.<br>