Browsing by Author "Langdon, Genevieve"

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    A Volume of Fluid (VoF) based all-mach HLLC Solver for Multi-Phase Compressible Flow with Surface-Tension
    (2021) Oomar, Muhammad Yusufali; Malan, Arnaud; Langdon, Genevieve
    This work presents an all-Mach method for two-phase inviscid flow in the presence of surface tension. A modified version of the Hartens, Lax, Leer and Contact (HLLC) approximate Riemann solver based on Garrick et al. [1] is developed and combined with the popular Volume of Fluid (VoF) method: Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM). This novel combination yields a scheme with both HLLC shock capturing as well as accurate liquid-gas interface tracking characteristics. To ensure compatibility with VoF, the Monotone Upstream-centred Scheme for Conservation Laws (MUSCL) [2] is applied to non-conservative (primitive) variables, which yields both robustness and accuracy. Liquid-gas interface curvature is computed via both height functions [3, 4] and the convolution method [5]. This is in the interest of applicability to both cartesian and arbitrary meshes. The author emphasizes the use of VoF in the interest of surface tension modelling accuracy. The method is validated using a range of test-cases available in literature. The results show flow features that are in agreement with experimental and benchmark data. In particular, the use of the HLLC-VoF combination leads to a sharp volume fraction and energy field with improved accuracy (up to secondorder).
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    Dynamic response of aluminium foams
    (2011) Merrett, Richard Peter; Langdon, Genevieve
    This thesis presents the results of an investigation into the response of two types of aluminium foam (ALPORAS and Cymat) to quasi-static, impact, and blast loading. The design of experiments and experimental results are reported.
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    The effect of bend radius on the impulse transfer characteristics of V-hulls
    (2015) Shekhar, Vinay Ramaswami; Langdon, Genevieve
    This work is based primarily on the effects of V-tip bend radii on the impulse transfer to V-plates subjected to localised blast loading. Three rigid V-plates with V-angles of 60°, 90° and 120° were designed and fabricated from steel plates. Blast tests with PE4 charges ranging from 19 g to 58 g at a stand-off distance (SOD) of 34mm were performed. The geometric scaling was based on the dimensions of the TM-57 landmine and the Casspir APC MK II. In the numerical model, the optimum element length for the air mesh was obtained by performing a mesh convergence study on the Arbitrary Lagrangian-Eulerian (ALE) mesh, and validated using the impulse values measured from a 58 g detonation onto a 120° V-plate as it resulted in the highest impulse. Element lengths of 1.5, 2.0 and 3.0mm were investigated. Element lengths of 1.5 and 2.0mm both produced accurate results, though the run-time for an element length of 2.0mm was significantly lower. A validation study compared the numerically predicted impulses with those of the experiments and the results were found to be within an acceptable percentage variation. Hence a 2.0mm element length was chosen for the Arbitrary Lagrangian-Eulerian mesh.
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    The influence of charge geometry on the response of cylinders to internal air blasting
    (2016) Davids, Sean; Langdon, Genevieve
    The effect of charge geometry on the structural response of right circular cylinders, subjected to internal blast loading, was investigated. Thin-walled, seamless 304 stainless steel cylinders were subjected to blast loads from partially confined bare cylindrical PE4 charges with different diameter and aspect ratios(charges length to charge diameter). The diameters of interest were: 25 mm (aspect ratios of 0.5 -3). 30 mm (aspect ratios of 0.5 -1.6). 35 mm (aspect ratios of 0.5 - 1.1). 40 mm (aspect ratios of 0.5 - 0.9). The effect of aspect ratio, for the constant diameter or constant mass cases, on the structural response of the cylinders (that is, diametric deflection, axial impulse, and axial shortening) is reported. Cylindrical charges with an aspect ratio of 1, were compared to spherical charges of equivalent mass. For charges with constant diameter with varying length: The diametric deflection increased with increasing aspect ratio. The axial shortening increased with increasing aspect ratio. The axial impulse increased with increasing aspect ratio. For charges with constant mass with varying diameter and length: The long charges (that is, charges with aspect ratios greater than 1) caused larger diametric deflections than their mass equivalent short (that is, charges with aspect ratios less than 1) charges. This is because the long charges had more side effective charge mass (that is, the mass of the charge that contributes directly to the diametric deflection of a cylinder) than the shorter charges. The short charges transferred more axial impulse to the ballistic pendulum, because they had more axial effective charge mass (that is, the mass of the charge that contributes directly to the axial impulse that is transferred to a ballistic pendulum) than their mass equivalent long charges. It was observed that a lighter charge can diametrically deflect a cylinder more effectively than a heavier charge, if its side effective charge mass is greater than that of the heavier charge. The structural responses of the cylinders obtained from cylindrical charge detonations were greater than those obtained from the mass equivalent spherical charge detonations. The deflections resulting from the cylindrical charges were also more localised compared to the spherical charges.
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    An investigation of the response of different materials to blast loading
    (2012) Lee, Wei-Chi; Langdon, Genevieve
    This dissertation reports on the results of an experimental and numerical investigation into the response of different materials to air-blast loading. Mild steel, armour steel (Armox 370T and 440T), Aluminium alloy 5083-H116, Twintex and Dyneema square plates were blast loaded on a horizontal pendulum at the Blast Impact and Survivability Research Unit (BISRU), University of Cape Town. The blasts were generated by detonating disc-shaped PE4 explosives of various diameters and standoff distances. The chosen plates are of side length 500mm (4mm thick mild steel and armour steel plates) and side length of 400mm (aluminium, Twintex and Dyneema panels). The charge mass was varied between 9g and 60g for two charge diameters, namely: 50mm and 75mm, and stand-off distances of 25mm, 38mm and 50mm. A polystyrene bridge was used to position the charges at the centre of plates, without any polystyrene between the charge and the plate in order to minimise any effects the polystyrene may have had on the plate deformation. The transient response of the 500mm square plates (mild steel and Armox 370T) was measured with the use of Light Interference Equipment (LIE) and numerical simulations performed in ANSYS AUTODYN, with the aim of gaining greater insight into the response of the two different materials. The details of the experimental setup and method used for the LIE as well as the development of the AUTODYN computational model are presented. The air and explosive were modelled as Arbitrary Langrange-Euler (ALE) elements while the test plates were modelled as Langrangian shell elements. Since the geometry of the plates was square, the simulations had to be performed in 3D quarter-symmetry. The transient response, permanent final displacement and maximum transient displacement of the numerical simulations were compared to the corresponding experimental results. The mild steel plates all exhibited good correlation between experimental and simulated results. However, the Armox 370T simulated results showed an under-prediction of the displacement magnitude and impulse compared to the experimental results. Experimentally, both the mild steel and armour steel exhibited a linear increase in deformation with increasing charge mass. Blast tests were also performed on 3mm thick mild steel, aluminium, Twintex and Dyneema square plates of 400mm side length. The aim was to gain a greater understanding and compare of the response of different material types (ferrous, non-ferrous, Glass Fibre Polypropylene and Ultra High Molecular Weight Polyethylene) under blast loading. The aluminium plates performed better than the mild steel, on an equivalent mass basis, in terms of permanent displacements and failure threshold impulse. The aluminium plates were significantly thicker (10.5mm compared to 3mm) than the mild steel plates, which may have contributed to its response under blast. The Twintex panels mostly exhibited failure in the form of fibre fracture and matrix failure whereas the Dyneema panels only exhibit large inelastic deformation, although the Dyneema were clamped differently to the other panels. Dimensionless analysis was performed on all of the materials except for Dyneema. Initially a scaling factor was used to account for the varying stand-off distances but proved to be unnecessary due to the type of confinement used (unconfined free air-blasts versus partially confined tube). Once the scaling factor was removed, the dimensionless impulse values showed relatively good linear correlation with the predicted trend.
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    The response of aluminium and glass fibre FMLS subjected to blast loading
    (2015) Volschenk, Gideon; Langdon, Genevieve; Von Klemperer, C J
    Fibre-Metal Laminates (FMLs) have long been of interest to the aeronautics industry due to their exceptional strength to weight ratio, fatigue and impact resistance. Due to the increasing global risk of subversive activity in this industry, the focus of research in recent years has shifted to the blast resistance of these materials. A particularly interesting material being GLARE, a commercially available Aluminium-GFRP FML. This dissertation presents the results of an experimental study into the effects of glass fibre configuration and epoxy type on the response of glass fibre reinforced, epoxy-based FMLs, subjected to localised and uniform blast loading conditions. Standard tensile specimens and Single-Leg Bend (SLB) specimens were manufactured and tested to determine the properties constitutive materials and interfacial bond strength. Bond strength between the composite and metal interfaces was improved by employing a combination of surface treatments, consisting of both mechanical and chemical as well as the use of a film adhesive. FMLs were manufactured from Al 2024-T3 and e-glass fibre reinforced epoxy composite. Both woven and unidirectional fibre configurations were used as part of either a prepreg or wet layup to construct the composite layers. Tensile and SLB specimens were used to characterise the constitutive materials and interfacial bond strength. SLB tests were used to determine the effect of cure cycle and composite layup technique on interfacial bond strength. These tests and revealed a variety of interfacial failure modes for different cure cycles and epoxy configurations, each resulting in different levels of strength. The modes, in increasing order of strength, included debonding of the film adhesive from either the metal or composite interface or both, and in some cases also included delamination in the composite layer. Tests showed that a single stage layup and cure cycle resulted in the strongest bonds between interfaces, compared to a multi-stage manufacturing processes. It was also shown that the use of prepreg resulted in stronger inter-facial bonds than a wet-layup process. The properties of the constitutive materials were used to construct a numerical model to aid in experimental design. The model was used to determine a suitable range of charge masses for testing.
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    The response of concave singly curved fibre reinforced moulded sandwich and laminated composite panels to blast loading
    (2018) Ghoor, Ismail B; Von Klemperer, Christopher J; Langdon, Genevieve
    Composite materials are increasingly being used in a wide range of structural applications. These applications range from bicycle frames and building facades to hulls of marine ships. Their popularity is due to the high specific strength and stiffness properties, corrosion resistance, and the ability to tailor their properties to a required application. With the increasing use of composites, there is a need to better understand the material and damage behaviour of these structures. In recent years, the increased frequency of wars and terror attacks have prompted investigations into composite failure processes resulting from air-blast. Most of the research has been focused on flat panels, whereas there is relatively little on curved structures. This dissertation reports on the effect of air-blast loading on concave, singly curved fibre reinforced sandwich and composite panels. Sandwich panels and equivalent mass glass fibre laminates were manufactured and tested. Three types of curvature namely a flat panel (with infinite curvature), a curvature of 1000 mm radius and a curvature of 500 mm radius were produced, to determine the influence of curvature on panel response. The laminates were made from 16 layers of 400 g/m² plain weave glass fibre infused with Prime 20 LV epoxy resin. The sandwich panels consisted of a 15 mm thick Airex C70:75 core sandwiched between the 12 layers of 400 g/m² plain weave glass fibre and infused with Prime 20 LV epoxy resin. This arrangement produced a balanced sandwich panel with 6 layers of glass fibre on the front and back respectively. For all panels, vacuum infusion was used to manufacture in a single shot process. Mechanical properties of samples were tested for consistency in manufacturing. It was found that mechanical properties of the samples tested were consistent with low standard deviations on tensile and flexural strength. The panels were tested in the blast chamber flat the University of Cape Town. Blast specimens were clamped onto a pendulum to facilitate impulse measurement. Discs of plastic explosive, with charge masses ranging from 10 g to 25 g, were detonated. After blast testing, a post-mortem analysis of the damaged panels was conducted. Post-mortem analysis revealed that the failure progression was the same irrespective of curvature for both the sandwich panels and the laminates. Sandwich panels exhibited the following failure progression: delamination, matrix failure, core crushing, core shear, core fragmentation, core penetration and fibre fracture. The laminates displayed the following progression: delamination, matrix failure and fibre fracture. Curved panels exhibited failure initiation at lower charge masses than the flat panels. As the curvature increased, the failure modes initiated at lower charge masses. For example, as the charge mass was increased to 12.5 g the front face sheets of the flat and the 1000 mm radius sandwich panels exhibited fibre fracture, but the 500 mm radius sandwich panel exhibited fibre fracture and rupture through the thickness of the front face sheet. The 500 mm radius laminate exhibited front face failure earlier (15 g) than the 1000 mm radius (22.5 g) and flat panel (20 g). Curved laminates exhibited a favoured delamination pattern along the curved edges of the panel for both 1000 mm and 500 mm radii laminates. As the curvature increased, more delamination was evident on the curved edges. The curved panels displayed more severe damage than flat panels at identical charge masses. Curved sandwich panels experienced through thickness rupture at 20 g charge mass whereas the curved laminates did not exhibit rupture at 25 g charge mass. The flat laminates were the most blast resistant, showing no through-thickness penetration at 25 g (the highest charge mass tested) and initiated failure modes at higher charge masses when compared to the other configurations.
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    The response of partially-confined right-circular cylinders to internal blast loading
    (2012) Ozinsky, Adam; Langdon, Genevieve
    This report presents results of an experimental and numerical investigation into the response of partially-confined, thin-walled, stainless steel cylinders subjected to internal blast loading. "Partial-confinement" refers to an enclosure that may retain a significant, quasi-static pressure following an internal explosion, while "thin-walled" implies that the cylinder wall thickness is small relative to other geometric dimensions. The cylinder deformation is used to gauge the level of blast damage. The chosen cylinders are of length l = 300mm, inner radius a = 150mm, and wall thickness h = 2mm, and cut from seamless 304 stainless steel pipe. Partial-confinement is achieved by keeping one end of the cylinders closed in all tests. The experimental tests are conducted on the horizontal ballistic pendulum at the Blast Impact and Survivability Research Unit (BISRU), University of Cape Town. The blasts are generated by detonating radially-centred, spherical PE4 charges inside the cylinders. The charge mass is varied between 20g and 75g at two axial charge positions, specifically 150mm and 225mm, relative to the closed end. These axial positions are denoted 0.5 l and 0.75 l respectively. Polystyrene annuli are used to position the charges within the cylinders, and the influence of this polystyrene on the cylinder deformation is briefly investigated as an additional parameter. Details are presented of the development of an LS-DYNA Release 6.0.0 computational model that simulates the cylinder response to blast loading. Several 1D and 2D preliminary simulations and convergence studies are presented, the results of which inform the mesh sizes in the final model. The air and explosive are modelled using solid Arbitrary- Lagrange-Euler (ALE) elements, and the cylinders are modelled using Lagrange solids. Since the cylinders and explosive are all circular in section, the simulations are performed in 2D axisymmetry to reduce computational expense. The maximum cylinder deflections and selected final profiles, as well as the impulses imparted to the pendulum, are compared to the corresponding experimental results. With the exception of the 0.75 l tests at larger charge masses, the results exhibit generally good experimental-simulation correlation. For the 0.5 l tests, the cylinders exhibit a linear increase in deformation with increasing charge mass, while the relationship is an exponential increase for the 0.75 l axial charge position. For charges below 45g, the deformations from both axial charge positions are similar, however the responses diverge with increasing charge mass, indicating that the confinement effect of the cylinders is a function of the axial position and is influential only beyond a given mass of explosive. This confinement effect is greater when the charge is located nearer the open end of the cylinder. The computational models provide insight into the transient behaviour of the systems which cannot be achieved experimentally. The influence of the charge position is confirmed by comparing the simulated deformation-time histories for the different axial charge positions. Two pressure fronts are evident in the simulations: one moving radially and one axially. The significant structural damage is caused by the radial pressure incident on the cylinder wall, while the laterally moving pressure drives gas out from the open end. In the case of the 0.75 l simulations, the pressure incident on the cylinder wall has longer to act before it is expelled by the laterally moving pressure. For higher charge masses, the high pressure acting during this additional time is the cause of late-time deformation. Two tests are performed using a half-annulus of polystyrene. Relative to the other tests, these two exhibit greater radial disparity, with the deformation biased to the side with polystyrene. This preliminary result suggests that placing polystyrene between the charge and the cylinder increases the structural deformation, and necessitates further investigation.
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    Response of plates subjected to air-blast and buried explosions
    (2017) Curry, Richard; Langdon, Genevieve
    Explosive threats have become more prevalent in both military and terrorist theatres of conflict, showing up largely in the form of Improvised Explosive Devices (IED) which are often buried in soil to conceal them and increase their effectiveness. The response of a structure subjected to a blast load is influenced by many factors, namely stand off distance, mass of explosive, degrees of confinement and medium surrounding the charge. This study focuses on characterizing the transient deformation of test plates which have been exposed to different explosive loading conditions including free air blasts (AIR), backed charge (VBP) and buried charge (SBP) configurations. In the three loading configurations, four charge masses are considered, utilizing 10g, 15g, 20g and 25g masses of PE4 plastic explosive which were moulded into cylindrical charges of a constant 38mm diameter. The transient deformation of the test plates was captured using high speed Digital Image Correlation (DIC), which utilized two high speed cameras to record the experiments. Extensive modifications to the blast pendulum to incorporate the cameras was necessary to adapt this technique in a different method to that used in previous literature. The mounting method proposed allowed the cameras to record the experiment while capturing the impulse imparted on a test plate using a blast pendulum. The experimental plates exhibited only Mode I failure, which is plastic deformation, enabling the effect of different loading configurations on the transient and final plate deformation profiles to be identified. Numerical simulations of the experiments were developed to further the understanding of the load arising from the three configurations and the deformation mechanisms involved. The experimental results are used to validate the numerical models, which allow for a better understanding of the evolution of the deformation and strains across the plate. The transient data for the numerical simulation and the experiments were found to match closely. This work clearly shows the effect that the different loading conditions have on the tests plates, specifically the impulse distributions and transient strain in the plates. It was observed in this study that the impulse imparted on a test plate increases with the addition of sand while keeping other test conditions constant. The impulse recorded was observed to increase by 490-540% and 19-100% when compared to AIR and VBP 50mm SOD tests respectively. The loading profile acting on the test plate as a result of the specific impulse changes significantly with the inclusion of sand. The midpoint deflection increases with a decrease in stand off distance, increase in charge mass, increase in level of confinement or the inclusion of an overburden of sand. The observed increase in midpoint deflection of between 90-160% and 30-40% when compared to AIR and VBP 50mm SOD tests respectively was reported. The transient plate profile does not match the final deformation profile.
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    The response of singly curved fibre reinforced sandwich and laminate composite panels subjected to localised blast loads
    (2014) Sinclair, Gregory Maurice; Langdon, Genevieve; Von Klemperer, C J
    This report presents results from a study on the response of singly curved fibre reinforced polymer (FRP) sandwich and laminate panels subjected to localised blast loads. The aim of the project was to investigate and compare the blast mitigation potential of each panel type and the influence of curvature on the response. Three radii of curvature were examined for both panel types, namely infinite (flat), 1000mm and 500mm. The FRP laminate panels were designed to consist of 1-5 layers of Eglass fibre reinforced epoxy sheets. The FRP sandwich panels consisted of a PVC foam core with 6 layers of FRP sheets on either side. Vacuum infusion, with the aid of three moulds, was used to manufacture the panels. The average thicknesses and areal densities of the FRP sandwich and laminate panels were 18.7mm and 4.9mm; and 862-8g/1m2 and 8458-g/m2 respectively. Three point quasi-static flexural tests were conducted on FRP sandwich and laminate specimens where the localised compression failure beneath the central loading bar was evident on both types of structures. The presence of the core reduced the damage observed on the back face of the FRP sandwich specimens. Blast tests were conducted on a horizontal ballistic pendulum at the Blast Impact and Survivability Research Unit (BISRU), University of Cape Town. Localised blasts were generated by detonating circular cylinder PE4 plastic explosives, placed at a constant standoff distance of 10mm. The charge mass ranged from 10g to 32.5g across all the panels. The failure modes of the blast loaded panels were identified by a post-test inspection. The failure mode initiation charts for the F RP sandwich panels revealed that failure modes were initially observed on the front face sheet and core material with slight appearance of delamination on the back face sheet. Increasing the charge mass resulted in the rupture of the front face sheet and penetration of the core. Additional failure of the back face sheet was also evident as the charge mass increased. The failure mode initiation charts of the FRP laminate panels exhibited less severe failure modes across a greater charge mass range that eventually lead to complete fibre rupture at higher charge masses. Delamination of the front face sheet of the flat FRP sandwich panels was initially observed in the centre of the panel and spread into the exterior region for increasing charge mass. The failure of the core material initially reduced the delaminated area of the back face sheet, however once the rupture of the front face sheet occurred, the delaminated area of the front face sheet reduced and the delaminated area of the back face sheet increased. This was similar for the curved FRP sandwich panels except that the delaminated area was predominately parallel to the axis of curvature prior to rupture and perpendicular to the axis of curvature subsequent to rupture. Delamination in the flat FRP laminate panels was initially observed in the centre of the panel and along the clamped boundary. Increasing charge mass resulted in the delaminated region spreading across the panel. As with the FRP sandwich panels, the delaminated area of the curved FRP laminate panels was initially observed parallel to the axis of curvature prior to rupture. Debonding of the FRP sandwich panels was initially observed at both of the front and back interfaces. For the front interface, the debonded lengths were observed in the centre and in exterior test area of the panel, but only in exterior test area for the back interface. With the rupture of the front face sheet, the debonded length of the front interface decreased and the back interface increased and spread across the entire test area. The blast rupture threshold of the two panel types were compared in terms of largest charge mass resisted. For each radii category, the FRP laminate panels outperformed the FRP sandwich panels, namely by 5g for the flat panels (25g vs 20g) and 9g for the 1000mm curved panels (27.5g vs 18.5g). However, for the 500mm curved panels the FRP laminate and sandwich panels ruptured at identical charge masses of 27.5g.
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    Study of dynamic behaviour of multi-layered structures subjected to blast loading
    (2012) Ahmad, Muhammad Saeed; Nurick, Gerald N; Langdon, Genevieve
    The objective of this research work is to assess the response of multi-layered plates in comparison to single plates to gain physical understanding of different phenomena taking place at micro level during localized blast loading. Since layered plates have been shown to give improved ballistic performance under certain circumstances, it is useful to ascertain and understand the influence of layering on blast performance. This investigation is carried out both experimentally and numerically. A finite element model was developed to design the blast experiments for two different steels of various thicknesses.
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    The effect of blast loading on composites that contain sustainable materials
    (2022) Gabriel, Sherlyn; Langdon, Genevieve; von Klemperer Chris; Kim Yuen, Steeve Chung
    In the pursuit of global environmental sustainability, bio-based resins, and natural fibres as reinforcements in Fibre Reinforced Polymer (FRP) composites offer potential benefits, and some of these can be used in different applications particularly when strength is of secondary importance (such as automotive, architecture, and mass-transportation industries). However, there is a constant possibility of explosive threats, and little is known about the blast response of these materials. This study focusses on the effect of blast loading on composites with sustainable constituent materials. Seven different FRP composites were examined. Two were chosen as control materials, namely glass fibre reinforced epoxy composite and a common medium density fibreboard (MDF). The five sustainable materials were: vacuum infused flax fibre reinforced epoxy using both bio-epoxy and conventional epoxy, vacuum infused jute fibre reinforced epoxy, flax fibre reinforced epoxy made using hand lay-up and glass fibre epoxy manufactured using a bio-epoxy. These composites were subjected to quasi-static and blast loading conditions. Initially, some of the material properties of the seven composite systems were characterised though a series of quasi-static tensile, flexural and interlaminar fracture tests. Blast testing was undertaken on a ballistic pendulum facility, capable of measuring the impulse imparted by the plastic explosive. The glass fibre reinforced composites had better blast resistant properties in comparison to natural fibre composites, following the trends observed during quasi-static testing. Delamination was observed on the glass fibre reinforced composites and the damage tended to increase progressively. Large amounts of inelastic deformation, surface and through-thickness cracking were observed on the natural fibre composites. The jute fibre reinforced composites tended to have a sudden destructive failure whereas the flax fibre reinforced composites and, to some extent, MDF sustained progressive damage. Substituting the epoxy resin for the more sustainable bio-based resin had little effect on the blast resistance for both glass and flax fibre reinforced composites, which is encouraging because this suggests that a sustainable resin can be substituted in those panels without significant degradation in blast protection properties. The manufacturing method played a role for the flax fibre reinforced composites, with hand lay-up specimens exhibiting a lower level of protection and inconsistent properties compared to the vacuumed infused panels. The results also indicated that the addition of more glass fibre plies enhanced the blast resistance considerably. Of the composites tested, the best performing composite that takes sustainability into account was the glass fibre reinforced bio-based epoxy composite. The results of the experimental study presented discusses the blast behaviour of these materials which are relevant to engineers considering alternative sustainable materials in various applications where explosive loading is a threat.
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    The effect of stand-off distance on the failure of thin plates subjected to blast loads
    (2005) Jacob, Neville; Nurick, G. N.; Langdon, Genevieve
    [page 31 missing] This investigation examines the effect of stand-off distance on the response of fully clamped circular plates subjected to blast loads. The experimental procedure consists of creating a blast load using disc shaped plastic explosive mounted onto a tube of required length. The length of the tube is the stand-off distance. Different lengths of tubes are used ranging from 25mm to 300mm. The internal diameter of the tube is 106mm. The dimension of the circular test plate is governed by the internal diameter of the tube. Hence all tests are conducted on 106mm diameter circular plates of thickness 1.9mm. The test plate is clamped between two clamping plates. The tube is screwed onto one of the clamping plates. The plate responses range from large inelastic deformation to complete tearing at the plate boundary. The deformed plate profile is dependent on stand-off distance. For stand-off distances ranging from 13mm to 40mm an inner dome atop a larger global dome is observed. In the case of stand-off distances ranging from 50mm to 300mm the deformed plate profile resembles a large global dome. The results show that mid-point deflection decreases with increasing stand-off distance for a given charge mass. The mid-point deflection drops rapidly from standoff distance of 13mm to 50mm, from stand-off distance of 75mm to 300mm the midpoint deflection asymptotes with similar values measured for a given charge mass. The results show two distinct loading regimes that occur depending on the stand-off distance between the explosive charge and the plate. At stand-off distances less than the plate radius of 53mm (13mm to 40mm}, the blast load is considered to be focused. This type of loading is referred to as localised loading. For stand-off distances greater than the plate radius (100mm to 300mm), the loading is said to be uniformly distributed over the entire plate area. At stand-off distances of 50mm to 75mm, the plate deformations exhibit a transition phase from localised loading to uniform loading. Theoretical and empirical analysis using Jones damage number, Nurick and Martin damage number and strain energy analysis to predict mid-point deflection of the deformed plate is performed. Appropriate modifications are made to above mentioned damages numbers and strain energy analysis to account for the effect of iii stand-off distance on plate deformation. The modified analyses show satisfactory correlation with experimental results.
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    The effect of venting configuration on the blast response of an aircraft unit load device
    (2019) Kriek, Shaun; Langdon, Genevieve; Nurick, Gerald
    The inclusion of venting areas in aircraft unit load devices (ULDs) as a potential blast mitigation technique is investigated in this work. Damage to the ULD, such as large deflections or container rupture, from an internal explosion threatens to tear the aircraft skin and cause fuselage decompression. The loading within a luggage container was expected to be reduced when the explosive products were vented into the adjacent ULDs. Although previous work has investigated the effect of venting on ULD blast loading, this has only considered a single venting side and not multiple venting configurations. To determine if a multiple-venting system would be beneficial in ULDs, experimental blast testing was performed by subjecting a 1:6 scaled ULD box to representative blast loads with different venting configurations. The blast response of the side of the ULD which would be positioned closest to the fuselage was measured. Numerical simulations were established to provide insight into the blast loading effects not measured experimentally. The loading within the ULD box, in terms of the number and magnitude of blast wave reflections, and internal pressure build-up, was reduced when introducing venting areas. Final deformations were reduced by 11% and 22% when using a single- and double-venting configuration, respectively. Further deformation reduction was expected if more venting area was made available: unconfined blasts tests (demonstrating complete absence of ULD confinement) reduced deformations by 44%. The fully-confined (no venting) blast test resulted in rupture failure when blasted with a 20 g explosive, whereas the vented tests exhibited no tearing when blasted with higher charge masses. The double-venting configuration demonstrated better blast mitigation than the single-venting configuration. However, since both reduced the deformations and rupture probability of the container, the implementation of a multiple-venting system within aircraft ULDs would improve the survivability of the ULD container during a blast event.
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    The influence of cylindrical charge geometry on the velocity of blast-driven projectiles in one dimension
    (University of Cape Town, 2020) Qi, Ruixuan; Langdon, Genevieve; Chung Kim Yuen Steeve; Cloete, Trevor
    The impact of improvised explosive devices (IEDs) on the safety of civilians can be devastating, especially when solid objects are inserted into the explosives. These inserts are propelled at high speed and increase the lethality of an IED detonation. Due to the wide range of possible IED configurations, a fundamental understanding of momentum transfer from explosives to the solid inserts is required. This project investigated the influence of charge geometry on the velocity of a 5 mm diameter stainless steel ball bearing. The ball bearing was half-buried and centrally placed on the at face of a cylindrical charge which was detonated centrally on the opposite face. The geometric parameters of interest were the charge diameter and the charge aspect ratio (length/diameter). Investigations were carried out in the project through blast and impact experiments as well as numerical simulations. The impact velocity of the explosively driven ball bearing was inferred using the impact crater depth on a witness plate. The correlation between crater depth and the impact velocity was determined using impact experiments which was performed using a gas gun. The average velocity (between detonation and impact) was captured by tracking the time of detonation and impact. The time of impact was recorded through a Hopkinson Pressure Bar (HPB) behind the witness plate. Additionally, the total axial impulse and the localised impulse, over the face of the HPB, were recorded by a ballistic pendulum and the HPB. Numerical simulations were conducted using a commercial software, Ansys Autodyn 18.0. The blast arrangement was simulated using a two-dimensional, axisymmetric model. The maximum velocity, average velocity, impact velocity, total axial impulse and localised impulse were 'extracted' from the simulations. The simulated velocities agreed well with experimental measurements, showing less than 2% variation. The deformed shape of the blasted ball bearings displayed similar characteristics to the model predictions. There were differences in the simulated impulse, with the numerical model predicting higher magnitudes but a less localised distribution. For a constant charge diameter, the bearing velocity increased in a nearly logarithmic manner with the increase in aspect ratio until a critical aspect ratio of 3/2 was reached. At a constant charge mass, the bearing velocity decreased with the increase in charge diameter. The numerical model suggested that the influence of charge geometry on the bearing velocity was likely caused by the shape of the detonation pressure waves. The detonation pressure profile is sensitive to the charge aspect ratio and the diameter.
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    What is the research experience of young scientists in South Africa?
    (2013) Schutte, Aletta E; Wright, Caradee Y; Langdon, Genevieve; Lochner, Christine; Myers, Bronwyn
    The results of an online survey - the SAYAS Survey of Young Scientists that involved the participation of 1021 postgraduate students and postdoctoral fellows from tertiary institutions in South Africa - were released in a report launched in November 2013. In this commentary we highlight some of the key findings from the report: The Research Experience of Young Scientists in South Africa.1