Browsing by Author "Yuen, Steeve Chung Kim"

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    Analysis of a car door subjected to side impact
    (2016) Long, Christopher Robert; Yuen, Steeve Chung Kim; Nurick, Gerald N
    The study presented in this thesis focuses on the response of a side impact beam located in a car door to impact loading in close conformation to the Federal Motor Vehicle Safety Standard 214 (FMVSS 214) standard. The side impact beam is situated in both the front and rear side doors of a vehicle between the inner and outer shells to minimise intrusion into the passenger compartment whilst absorbing as much impact energy as possible in a collision. While some manufacturers use tubular side impact beams, others use corrugated structures. Different materials are also considered, depending on the class of vehicle, a nd market for which it is intended. In this study, a numerical model of a light -weight passenger car, developed by the National Crash Analysis Center (NCAC ) of The George Washington University under contract with the Federal Highway Administration (FHWA) and National Highway Traffic Safety Administration (NHTSA ) of the United States Department of Transportation (US DOT ), was used to simulate a side impact on the front side door using the LS -DYNA R7.1.1 explicit solver . The resulting deformation of the door from the full vehicle model was used to design an experiment for an impact test on a passenger door, which was used to validate an equivalent numerical simulation. In the experiments, the car door was modified and subjected to a drop mass of 385 kg from a height of 1.27 m. The drop mass and height were chosen such that the maximum deflection in the car door impact test would be of similar magnitude to the deflecti n of the door in full vehicle model when subjected to an impact load in accordance with the FMVSS 214 Standard - which requires that the vehicle be projected into a rigid vertical 10 inch diameter pole at 29 km/h in a direction 75° to the longitudinal axis of the vehicle . The results from the numerical simulation of the struck door test were in good agreement with the experiments in both shape and magnitude of deformation. The behaviour of the side impact beam located in the passenger door was isolated and further studied. Drop test experiments on beams with square and round cross -sections were carried out to validate the equivalent finite element model. The drop mass and height of the striker was varied such that the transient response of the isolated side impact beam matched the response of the beam in the simulation of the equivalent door model and full vehicle model. In the impact test experiments, the tubular structures were subjected to a 200 kg mass dropped from six incrementally varying heights of 250- 500 mm. Both square and round tubes were observed to buckle at approximately 835 mm from the free end with different magnitude s of maximum deformation (depending on the drop height). The results from the numerical simulations showed good correlation with the experiments for shape and magnitude of deformation. A quadratic curve fit to the experimental maximum transverse deflection resulted in an R -squared value of 0.92 and 0.96 for the square and round tubes respectively. A parametric study was carried out on the side impact beam to investigate the effect of: Thickness and material of a singular tube configuration, and: Inner tube length and outer tube thickness of a compound tube structure. The performance of the different configurations were assessed in terms of Crash Force Efficiency (CFE and Specific Energy Absorption (SEA). A parametric study on the effect of the tube thickness showed that thicker tubes of the same material exhibited deformation of lo wer magnitude and had lower SEA. Aluminium tubes absorbed two or more times the energy per unit mass than the equivalent steel tubes. A round aluminium tube with a thickness of 2.175 mm was found to give the best balance between SEA and maximum deflection with values of 1.5 kJ/kg and 350 mm respectively. The compound tube configuration with the inner tube extended beyond the buckling point performed better in terms of SEA and maximum deflection provided the length of the inner tube did not exceed 90% of the length of the outer tube. The optimised compound tube configuration performed better than the single tube configuration in the full vehicle model with a 1mm reduction in the overall intrusion of the rigid pole.
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    Changes in material characteristics of AISI 430 stainless steel plates subjected to repeated blast loading
    (2017) Shangase, Thobani Paul; Yuen, Steeve Chung Kim; George, Sarah L
    Structures deform at high strain rates and temperatures when exposed to impulsive loads. To accommodate the macro change there are microstructural changes that occur, i.e., grain morphology and shear banding. Most studies report on macroscopic response, i.e., large inelastic deformation and tearing of the structure, while limited studies have reported on microscopic changes that develop in the structure. The microstructure is directly related to the mechanical properties and performance of the material. Therefore, understanding the effect of high strain rate loadings on the microstructural evolution and subsequent mechanical properties of metals and alloys is necessary for mechanical design. The main objective of this research was to investigate microstructural changes to characterise the strain distribution and plastic deformation, owing to impulsive loading. Features within the microstructure that could be used to characterise deformation included grain size morphology changes, the presence of shear bands and sub-grain networks. The electron backscatter diffraction (EBSD) technique, which used Kikuchi patterns to characterise the strain distribution in the crystal of the deformed material, was also used as a characterisation tool. The first step in the experimental procedure was to select the appropriate material to investigate these microstructural changes. There was also the systematic investigation into the use of single and double heat treatments. These were used to achieve a large equiaxed grain structure, which was desirable from a microstructural point of view but was not desirable for blast-resistant material selection. The two-step heat treatment was concluded to be the most suitable heat treatment for the annealing and homogenisation of the AISI 430 stainless steel plates. The AISI 430 stainless steel plates used were 244 mm by 244 mm in size and had a circular exposed area of 106 mm. These plates were subjected to repeated explosive blasts, using a plastic explosive (PE4). The charge mass was varied for each test and the stand-off distance was kept constant at 150 mm for uniform loads and 13 mm for localised loads. Two plates were selected to investigate the uniform loading scenario. The first plate, a torn plate, used a charge mass of 30 g and one blast and the second plate, an inelastically-deformed plate, used a charge mass of 10 g and was exposed to three blasts. These two plates offered the same overall charge load with a different strain path. A further two plates were chosen for the investigation into the localised loading scenario. One plate, a petalled plate, used a 6 g charge mass and was exposed to two blasts and the second plate, an inelastically-deformed plate, used a 5 g charge mass and was also exposed to two blasts. The latter two plates offered an investigation into the effect of an increased charge load, where charge load affected the strain rate of the deformation resulting from the blast load. All four plates were sectioned across the midline of the dome and then ground and polished to a mirror finish, using OP-S. The polished samples were analysed, using optical microscopy and EBSD. In addition, Vickers hardness tests were carried out along the midline of the sectional plate profiles, in order to evaluate the extent of strain hardening. All the plates showed either a response of inelastically deforming or of complete or partial tearing failures when subjected to blast loads. For inelastic deformation failures, a global dome was characteristic of the uniform loading condition and an inner dome superimposed by the global dome was characteristic of the localised loading condition. Variation of charge mass and the number of blasts showed an increasing linear relationship between the impulse and midpoint deflection. The macrostructure showed a large variation of failures in the localised condition. The microstructural characterisation results produced micrographs showing regions of long, flat grains with multiple sub-grain networks, indicating deformed microstructures of the blast loaded plates. Parts of the microstructures displayed equiaxed/recrystallised grains characteristic of restoration processes, owing to high temperatures. Vickers hardness tests indicated an increase in material hardness as the number of blasts was increased, with a maximum hardness in the central region of the plates. In the first investigation, into uniform loading, the material characterisation results, combined with the fractography results, indicated brittle failure modes typical of high strain rate failures in strain rate sensitive materials, such as the chosen AISI 430 stainless steel plates. In the second investigation, into localised loading, the material characterisation results, combined with the fractography results, indicated a more ductile failure, owing to a 1 g incremental increase of charge mass, which confirmed the strain rate sensitivity of this material.
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    Deformation and tearing of uniformly blast-loaded quadrangular stiffened plates
    (2000) Yuen, Steeve Chung Kim; Nurick, Gerald N
    An investigation into the deformation and tearing of stiffened quadrangular plates subjected to a uniform blast load is presented. A series of experimental results and numerical modelling using the finite element package; ABAQUS, on built-in quadrangular mild steel plates of different stiffener configurations and sizes subjected to a uniform blast load are reported. The main objectives of this investigation are to determine the dynamic response of stiffened quadrangular plates subjected to uniform blast loads, to assess the effect of the stiffener configuration and size on plate failure and to use a new approach that uses material properties that include temperature dependency to model the plate response. The experimental procedure consists of creating an impulsive load with the use of plastic explosive and measuring the resulting impulse using a ballistic pendulum. Explosive is centrally laid out in two concentric rectangular annuli on quadrangular plates of thickness 1.6mm with stiffeners of sizes; 3x3mm, 3x7mm, 4x3mm and 4x7mm; and configurations; none, single, double, cross and double cross; to provide the impulse required to give deformations up to plate tearing. In all the tests of Mode I category of large inelastic deformation, the plate profiles are characterised by a uniform global dome. The results of mid-point deflection versus impulse for the various stiffener sizes and configurations for Mode I show a generally linear relationship. In all the experiments, thinning mechanisms at the boundary are observed for all plates despite different stiffener sizes and configurations. Thinning, however, is not consistent all around the boundary. Thinning is also observed at the stiffener side closest to the boundary for double and double cross stiffened plates. There is, furthermore, a reduction in the stiffener width where two stiffeners cross each other perpendicularly.
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    The effects of blast induced imperfections on the energy absorption characteristics of square tubes
    (2006) Yuen, Steeve Chung Kim; Nurick, Gerald N
    This investigation examines how blast-induced imperfections at opposite sides of a square tube affect the thin-wall structure and reduce its crush load when compressed in the axial direction i.e. its energy absorption characteristics.
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    The response of circular plates to repeated uniform blast loads an experimental and numerical study
    (2013) Henchie, Travis Foster; Yuen, Steeve Chung Kim; Nurick, Gerald N
    On-going war and terrorist attacks contribute to a variety of impulsive loading of structures that often result in life changing injury or death. Improvised explosive devices (IEDs) and landmines accounted for 1761 deaths in Afghanistan during 2009 [1], with many more casualties as a result from conflict occurring throughout the world.
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    The response of quadrangular plates to buried charges
    (2011) Pickering, Erik Green; Yuen, Steeve Chung Kim; Nurick, Gerald N
    This dissertation reports on the results of an experimental and numerical investigation into the response of quadrangular plate structures to buried charges. The plate structure and PE4 explosive charge were scaled to the APC and the TM-57 Anti-tank mine respectively...
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    Study of a simplified bumper system subjected to offset impact loading
    (2012) Opperman, Christiaan Jan; Yuen, Steeve Chung Kim
    This thesis reports on the behaviour of a simplified bumper system, with regards to energy absorbing characteristics. The simplified bumper system comprises of three components, the crossbeam and two longitudinal members. In the study, several parameters are altered to investigate the change in behaviour of the individual components as well as the bumper system. These parameters of the bumper system include: Wall-thickness of the crossbeam (1.0mm to 4.0mm in increments of 0.5mm), Two profiles of a crossbeam (straight and curved), Two longitudinal member profiles (straight and tapered). Experiments are carried out to study the behaviour of the bumper system subjected a 40% offset impact loading condition.
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    The response of quadrangular plates to buried encased charges
    (2017) Warncke, Dale; Yuen, Steeve Chung Kim
    This dissertation reports on a series of experiments and numerical simulations that were carried out to investigate the response of quadrangular plates to buried encased charges with a view of understanding landmine effects on simple structures. Different loading scenarios were carried out for comparison. In total, four loading scenarios were investigated; namely bare and encased charges detonated in air, and bare and encased charges detonated under sand. A vertical pendulum was used to measure the impulse imparted onto the target plates, and dry construction sand was used to bury the charges. The geometric scaling of the target plates and PE4 explosive charge was based on the Casspir APC and TM-57 Anti-tank mine respectively. The experiments were carried out under varying conditions, such as different standoff distances (50-90 mm) and depths of burial (0-10 mm). In general, the impulse and midpoint deflection decreased with an increase in total distance for all loading scenarios. Burn diameters were observed on plates loaded in air, with dissimilar scorch areas observed on plates subjected to buried charges. Scorched areas on plates subjected to encased charges indicated a focussing effect of the explosive products provided by the charge casing. Plates subjected to encased charges detonated in air typically resulted in ’capping’ in the central area, accompanied by significant shrapnel damage. In general, presence of a charge casing in buried charge tests resulted in more damage to the target plate. Larger impulses and midpoint deflections were measured for charges detonated under sand compared to bare charges detonated in air. Encased charges detonated under sand resulted in decreased impulse imparted onto the target plate, accompanied by an increased plate midpoint deflection when compared to bare charges detonated under sand. The presence of sand in encased charge tests tended to mitigate the shrapnel damage caused by the charge casing. ANSYS AUTODYN was used to perform numerical simulations on three variable standoff distance test series, one with no sand and a bare charge, one with a constant depth of burial and a bare charge, and the last with a constant depth of burial and an encased charge. These simulations mirrored the experimental test series. The simulations consisted of two-dimensional axisymmetric models, with lagrangian meshes representing the target plate and explosive casing, and an eulerian mesh used to model the behaviour of the PE4, sand and air. The blast was simulated in two phases, namely detonation of the explosive and loading of the structure. The casing mesh was only included in the detonation phase. Two separate models were used to simulate the impulse and the plate behaviour. The impulse model used a reflective boundary to represent the plate and pressure histories on the reflective boundary were used to calculate the impulse. The plate loading model included a lagrangian mesh to represent the plate and simulate its deformation. The plate loading model used and additional unloading phase to allow plate oscillations to subside. The numerical model was validated using the impulse, plate midpoint deflection and plate profile measured during the experiments. The numerical model showed good correlation with the results of the experiments in terms of midpoint deflections and impulse trends. The model provided insights into the experiments, such as how the gas products expanded after detonation and their interaction with the target plate.
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    The use of cellular materials to alleviate the damage from blast-induced fragments
    (2014) Ranwaha, Nzudzanyo; Yuen, Steeve Chung Kim
    This study aims to understand how different cellular materials mitigate the damage that is caused by a blast‐induced fragment. In the experimental arrangement, a front plate is subjected to localised blast load to release a “controlled” fragment (cap) to impact a similar plate positioned 190mm apart. A cylindrical charge of Plastic Explosive 4 (PE4) of different diameters (27mm, 36mm and 43mm) and masses ranging from 7g to 11g are used to create fragments of different sizes and masses propelled at different velocities to impact the rear plate. Both front and rear plates are made from 1.6mm thick mild steel sheet with an exposed circular area of 106mm diameter. Tests are carried out with and without energy absorbing materials to investigate the protective performance of the different materials investigated by means of the mode of failure and maximum deflection of the rear plate. The different energy absorbing cellular materials investigated in this study include aluminium foam, aluminium honeycomb, balsa wood, Corecell M‐80 foam, Divinycell H200 PVC foam and rigid polyurethane 200 foam. The 40mm thick energy absorbing materials are 106mm in diameter (same size as the exposed plate area) are placed in front of the rear plate.