Browsing by Author "Chung, Kim Yuen Steeve"

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    A study on the response of a target plate to a foreign object placed at various depths in a cylindrical Charge
    (2023) Hoare, Matthew; Chung, Kim Yuen Steeve; Govender Reuben Ashley
    The threat of Improvised Explosive Devices (IEDs) has grown exponentially in the 21st century, as the methods and means of warfare have adapted to modern threats such as terrorism. IEDs are especially damaging and lethal because they are often randomly embedded with a variety of projectiles that consist of readily available items, such as ball bearings, nails or glass. The versatile nature of IEDs makes it very difficult to conduct a generalised study on their impact. One major challenge in IED research is the wide range of potential IED geometries, sizes, explosion types and embedded object configurations. Understanding the behaviour of a simplified IED, consisting of a blast-driven ball bearings embedded in explosive charges, will provide insights into the mechanics of IEDs and its subsequent interactions with a target with a view to developing better protection from IEDs. This dissertation presents the results of a study investigating the damage caused by a simplified IED which consists of a cylindrical explosive charge that was embedded with a single ball bearing. The influence of the placement of a ball bearing along the axis within a rear-detonated cylindrical charge was studied and the placement effects were evaluated in terms of the impact velocity of the ball bearing and its subsequent damage on a Domex 700 steel (also referred to as Strenx in Europe) target plate. Typical deformation of a structure from an IED is a result from of blast loading (pressure wave) and impact loading from the shrapnel/fragment. In this study the combined blast and impact events of a simplified IED were decoupled into separate events to gain a better understanding of the contributions of the different loading conditions. The target plates were exposed to bare charges to quantify the effects on blast loading events. Impact tests were carried out using a two-stage gas gun to relate impact velocity to the deflection of the target plate. Tests were also carried out with explosive charges embedded with a ball bearing at varying depths to analyse the combined event. For all blast tests, the charge diameter was kept constant. Three different charge masses with varying placements of the ball bearing were investigated. Computational simulations, validated using experimental data, were used to elucidate additional details to gain insight about the momentum transfer during the blast event. The results showed similar critical influence of the placement of the ball bearing relative to the charge for the different charge masses used.
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    Stress Wave Propagation In A ‘Simplified Surrogate Tibia’ Subjected To Blast Loading
    (2023) Seenzayi, Davison; Chung, Kim Yuen Steeve
    Landmines are a continuous and serious threat to mankind, resulting in thousands of casualties globally each year. Casualties have risen due to the proliferation of improvised explosive devices (IEDs), cluster munition remnants, and other explosive remnants of war. In these terrible occurrences, both the civilians and military and security personnel suffer great losses. Despite anti-mine awareness programs and the development of new mitigating measures, the number of landmine victims continues to rise. While anti-vehicle and anti-personnel landmines offer major hazards, anti-vehicle landmines create much larger energy transfers than anti-personnel landmines, resulting in more severe and complicated lower limb injuries frequently presenting distinct rehabilitation issues. Understanding the mechanics leading to tibia injuries in anti-vehicle landmine occurrences helps develop and enhance safety and well-being of vehicle occupants exposed to anti-vehicle landmine blast scenario. The study of stress wave propagations in the tibia during an anti-vehicle landmine blast aids in scientific understanding of blast injuries produced by anti-vehicle landmines by refining current ideas, discovering novel phenomena, and filling information gaps. This study aimed to understand the stress wave propagation through the tibia caused by an anti-vehicle landmine explosion. Simplified tibia models were developed and used in an experimental approach for capturing blast-induced stress wave propagations through the tibia. The floor of a vehicle was represented by deformable and nondeformable witness plates. Aluminium tubular structures were used to develop simplified surrogate tibia models with different cross-sections which used to calibrate a Finite Element Model (FEM). Strain gauges were installed on the centre of tubular structure to record the direct stress induced by the blast load. A numerical model, developed using LS-Dyna software, was validated using the experimental blast test stress results on the tubular structures. Once validated, the numerical model was updated by replacing the tubular structures with a 3D CAD tibia. The replacement of tubular structures with tibia model was undertaken to enable the investigation of stress distribution within the tibia with greater precision and accuracy. A parametric study was, thereafter, carried out investigating the effect of geometry on stress propagations and its correlation with associated injuries. The parametric study successfully explored the blast induced stress waves propagations and its distribution within the tibia model during a blast event. The tibia model experienced a compressive load cycle followed by a tensile load cycle as the stress waves got reflected upon encountering boundaries. Analysis of stress-time response graphs revealed the highest strain levels at the interface between the tibia model and the witness plate, indicating greater susceptibility to blast injuries in the lower extremities, particularly at the point of contact. In the numerical simulations aluminium was implemented as the “bone” material for simplification. It should be noted that bone is a complex composite material which is hard to characterise and not considered in the scope of this study. The focus of this study was to gain an understanding how the stress wave resulting from the blast load would propagate in a structure with varying geometries such as a tibia and analysis of the peak stresses. The information gained from these simulations provided valuable insights into injuries caused by blast and their potential effects on the tibia when subjected to anti-vehicle landmine explosions. The severity of the injury depends on the material properties and geometry of the tibia. Additionally, the study explored the effect of deformable and non-deformable witness plate on the load transmitted to the tibia, resulting in different injury mechanisms and patterns.
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    The Response of a Structural Target to an Explosive Charge Incorporating Foreign Objects: A Numerical Study
    (2020) Kang, Gi Ah; Chung, Kim Yuen Steeve
    This dissertation reports on the results of a numerical investigation into the effect of incorporating foreign objects into explosive and its subsequent influence on the response of a target structure. The explosive, the container and the ball bearings were simplified representation of the key components of an improvised explosive device (IED). The numerical study was aimed at studying the ball bearing interaction with blast when incorporated into charge, and was based on previous experiments. In the experiments, 22g of plastic explosive charge (26mm in diameter with a length-to-diameter ratio of 1) was detonated inside a fully confined cylindrical mild steel container of 9.3mm wall thickness and 273mm outer diameter. Different experiments were carried out using charges with varying numbers of ball bearings arranged in different configurations. The ball bearings were either packed around the cylindrical charge in row(s), or were randomly embedded into the charge. In the numerical simulations, i) a quarter symmetry model in the radial plane and ii) a half symmetry model in the axial plane were developed in ANSYS AUTODYN using Euler and Lagrangian meshes, based on the previous experiments. The cylindrical target and the ball bearings were modelled using Lagrangian elements, while the air and the PE4 plastic explosive were modelled using Eulerian elements. Ball bearings of fixed diameter 5mm, were placed at positions relative to the charge corresponding to the experimental conditions. The predicted crater depth created in the cylindrical target by ball bearing impact were compared to the experimental results. A comparative numerical study was then conducted to investigate how different factors influenced the ball bearing behaviour and the target response. The parameters tested included the total number and size of ball bearings incorporated in the explosive charge, the manner in which the ball bearings were distributed inside or outside the charge, and the length-to-diameter ratio of explosive used. The numerical models provided insights into how the ball bearing interacted with the blast when incorporated into charge. 2D numerical simulation techniques were used to simulate the velocity distribution of a cased cylindrical explosive charge. The results of the numerical simulations were verified against previously reported equations for fragments and pre-formed fragments, which are based on experimental data which indicated a non-uniform velocity distribution along the cylinder axis. Overall, there was a good agreement between the 2D model and the experimental measurements, including the distribution of the lower velocity values near the cylinder edges. The ball bearing velocity - crater depth correlation was also compared to the projectile velocity equations from literature. A good correlation was shown in all radial simulations. In the axial plane simulations, a good correlation was observed only when the projection angle of the ball bearing was nearly perpendicular to the charge surface. The effect of the ball bearing presence on the overall pressure observed in the confined space is also studied. The inclusion of ball bearings in the charge resulted in an overall decrease in peak pressure, and the percentage decrease was proportional to the total number of ball bearings. Charge covered in rows of ball bearings acted similar to encased charges, especially to charges with pre-fragmented casings. It was observed that an increase in length-to-diameter ratio of the charge led to an overall increase in blast magnitude.