Browsing by Author "Nurick, Gerald N"
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- ItemOpen AccessA Precision Experiment for the Deformation and Fracture of Blast Loaded Plates(2022) Cloete, Trevor John; Nurick, Gerald NThe purpose of this thesis is to present a novel laboratory scale precision test [1] apparatus, developed specifically to study of the deformation and fracture of blast loaded plates. A review of published laboratory scale blast testing showed that classical ballistic pendulum techniques satisfy several precision testing criteria. However, specific aspects required improvement. Therefore, an instrumented ballistic pendulum has been developed, incorporating a central support, in the form of a Hopkinson bar, for use with a novel peripherally clamped centrally supported (PCCS) plate specimen, which allows the reaction force history at the inner boundary to be captured. Hence, in addition to the traditional impulse vs deflection data, this approach allows details such as the total deformation duration or the exact timing and magnitude of fracture processes to be captured. Furthermore, when used with a peripherally clamped annular (PCA) plate specimen, this approach allows the blast load pressure history to be captured. A literature review found several classical closed form solutions for the large deflection of impulsively loaded peripherally clamped solid (PCS) circular plates. However, several crucial aspects of the solutions were contradictory and/or incomplete. To address this a generalized energy method for modelling impulsively loaded axisymmetric plates was developed which subsumes previous solutions and facilitated novel analytical solutions that provide a theoretical framework for interpreting the experimental data. Extensive experimental results reported in this thesis provide a rich set of novel data for code validation. While the PCCS and PCA plate configurations require a refined definition of the observed failure modes, the transitions between the modes and the fracture behaviour are studied in great detail. The data is analysed using dimensionless impulse expressions obtained from the analytical solutions in this thesis. In addition to accurate deflection predictions, these solutions also provide improved deflection duration predictions using a novel two phase solutions that can also accommodate finite load duration. It is concluded that the instrumented ballistic pendulum, incorporating a central support in the form of a Hopkinson bar, in conjunction with the novel PCCS and PCA plate configurations and analytical solutions, satisfies all the requirement of a precision test.
- ItemOpen AccessActive control of passive safety in passenger motor vehicles : a feasibility study investigating dynamic denting of members using pyrotechnic devices(1995) Marshall, N S; Nurick, Gerald NThis report describes a feasibility study investigating dynamic denting of members using pyrotechnic devices to engineer favourable energy absorption characteristics into thin walled tubes. A tube of sufficiently low slenderness ratio and wall thickness, when loaded axially to failure, will collapse in the progressive buckling mode. After the ultimate buckling load has been exceeded, and as the tube continues to compress, the load oscillates between loads considerably lower than the ultimate buckling load. The object of introducing an advantageous deformation is to decrease the ultimate buckling load to a magnitude comparable with the subsequent peak loads, but at the same time avoiding a change in the buckling mode which is not advantageous. Testing was limited to thin walled square mild steel tubes. The test procedure began with a process to determine the limitations imposed on the geometric imperfections that could be achieved by the use of explosive. It was found that all the explosively induced deformations were rounded, i.e. the dents were hemi-spherical in shape. It was also found that a smooth edged round hole could be created in the centre of the dent with the use of a round, flat explosive charge. Geometric imperfections that could be induced explosively in the specimens (as well as other deformation shapes, tested for comparative purposes) were mechanically formed in the specimens. The tubes were then quasi - statically crushed to determine the energy absorption characteristics induced by the deformations. When spherical dents were induced, the deformation affected the tube beyond the immediate spherical dent and hence the distance between the plastic hinges was increased and instabilities in the crushing process were introduced. Holes (without any visible denting) decreased the distance between the plastic hinges and thus also induced instabilities. In both cases the tubes tended to skew over to one side and in extreme cases Euler buckling ensued.
- ItemOpen AccessAnalysis of a car door subjected to side impact(2016) Long, Christopher Robert; Yuen, Steeve Chung Kim; Nurick, Gerald NThe 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.
- ItemOpen AccessAnalysis of deformation and tearing of uniformly blast-loaded circular and square plates rectangular beams and T-beams(2001) Muluh, Esau Ticha; Nurick, Gerald NThis investigation examines the failure of circular and square mild steel plates, aluminium rectangular beams and T-beams subjected to impulsive loads. The objective of this investigation is to numerically determine the dynamic response of circular and square plates, rectangular beams and T-beams clamped and built-in (integral) at the boundary subjected to uniform blast loading; use material properties that include and exclude temperature dependency to model the plates and beams response and failure and finally to compare the numerical results with experimental results.
- ItemOpen AccessAssessing the effect of friction on compression split Hopkinson pressure bar tests(2004) Hartley, R S; Nurick, Gerald NAn enhanced understanding of material behaviour during rapid loading allows designers to improve the safety and efficiency of industrial processes and commercial products. These improvements are due, in part, to the use of increasingly powerful and sophisticated numerical simulation codes, which in tum, depend on accurate high strain rate material data. A Split Hopkinson Pressure Bar (SHPB) facility had previously been developed at the University of Cape Town to allow high strain rate testing of materials in compression. However, uncertainties regarding aspects of the test method that can affect the accuracy of the results, such as interface friction and specimen inertia, still required further clarification. This report details a thorough experimental and numerical investigation into the effect of friction on SHPB test data. The objectives are to assess the magnitude of the effect of friction under various conditions and to suggest strategies for reducing friction error in SHPB tests to an acceptable level. The ring compression test was used to obtain experimental friction factors. The effect of surface finish, lubricant, and strain rate on the friction experienced by mild steel, copper and aluminium samples was investigated. Numerical simulation was used to assess an energy-based analytical solution by Avitzur [1], and in particular to establish the effect of neglecting barrelling. Avitzur's analytical solution [l] Was then used to interpret the experimental results. The tested specimen microstructure was examined and used to estimate the stress distribution in the specimen during deformation. Uneven deformation and fold-over diminished at higher strain rates. Optimal surface finish and lubricant conditions were found for which experimentally measured coulomb friction coefficients lay between J.l = 0.04 and 0.08, with copper samples exhibiting marginally higher friction. By Avitzur's analytical solution [1] the error in SHPB tests under these recommended conditions was estimated to lie between 1% and 2%. The results show that roughened compression and specimen surfaces, lubricated with a suitable grease containing molybdenum disulphide, are useful in effectively reducing the error in SHPB tests due to friction effects.
- ItemOpen AccessAn assessment of software packages as applied to particles in a rotating mill(2001) Sonn, Leigh M; Nurick, Gerald NThis thesis evaluates three different software packages to test their potential use i ncomminution. The packages are ELFEN, ABAQUS and Particle Flow Code (PFC²D). The numerical codes differe in the method of inputting data as well as the theoretical models used. ELFEN and ABAQUS are finite element (FEM) packages wheras PFC²D uses the discrete element method (DEM). The packages also differ in the integration and contact schemes, as well as the method used to calculate the critical time step in the analysis.
- ItemOpen AccessBlast loading of sandwich panels with thin-walled tube cores(2007) Theobald, Matthew David; Nurick, Gerald NAn investigation into the response of a novel sandwich panel under blast loading is presented. Thin-walled tubar members have been used extensively as energy absorbers under impact conditions. The progressive folding mechanism induced by axial crushing of the tubes allows for efficient dissipation of kinetic energy. The present study investigates the use of such tubes as a sandwich core material. Several thin-walled tubes are configured in parallel, between mid-steel fase sheets. A programme of experimental, numerical, and analytical investigations are conducted to characterise the energy absorption properties of the sandwich structure under blast loading.
- ItemOpen AccessThe characterisation of magnetic couplings and the development of a thruster module for an ROV(2015) Hope, Timothy Patrick; Nurick, Gerald N; Booysen, TracyThis dissertation focuses on the development of thruster modules and the characterisation of magnetic couplings for a Remotely Operated Underwater Vehicle (ROV). The dissertation begins with an introduction to the Seahog ROV developed at the University of Cape Town's Robotics and Agents Research Laboratory (RARL). The history, relevance and features of commercial ROVs are discussed in chapter two to introduce the reader to this form of underwater robotics. After this the dissertation is divided into two separate sections. The first section, chapters three to eight, detail the mechanical and electrical modifications made to an existing, magnetically coupled, thruster module design. The objective of this section was to improve the thruster module in order to achieve performances that are similar to commercially available thrusters. The modifications included changes to the drivetrain, the design of new electronics and motor drivers and a reduction in weight of the module's housing. A fundamental analysis of the thruster module is presented, no Computational Fluid Dynamics (CFD) is provided as the propeller and kort-nozzle designs remained unchanged. Even though the improvements produced a reliable and efficient thruster module a greater understanding of magnetic couplings was required to produce a design that was as lightweight as commercial modules. Therefore the second section of this dissertation, chapters nine to twelve, implement and validate an analytical model to calculate the torque and slip characteristics of magnetic couplings. The dissertation is concluded in chapter thirteen with recommendations that incorporate the knowledge gained in magnetic coupling design with the modifications made to the thruster module to produce a thruster design that is both efficient and light.
- ItemOpen AccessA concept model for a multi-fingered prosthetic hand(1997) Kotze, Johan; Nurick, Gerald NThe various attempts by individuals to replace the hand has led to some ingenious and practical designs, but if compared to the real hand these designs are still light years behind. Till recently the most functional prostheses developed were body powered because of the simple, light weight designs. The designs for these hands have not changed must in the last few decades indicating that the design has reached its functional limit. This and the latest technology have initiated designers ' renewed interest in externally powered prostheses. Existing externally powered hands only have one degree of freedom which limits the function of hands considerably whereas practical multi-fingered hands would provide a new dimension to the functionality of prosthetic hands. For this project a concept model for a multi-fingered prosthetic hand was developed using Lego as design medium. The objective was to develop and test mechanisms as well as control strategies which can be used in a real prosthetic hand. A proper study of the human hand was done to determine its basic anatomy as well as its functioning. An extensive literature study on prosthetic and robotic hands was also done to evaluate existing designs and determine the level of existing technology. Special emphasis was laid on the anatomical design of the human hand which led to a model with a unique design. The model incorporates a tendon driven finger mechanism instead of the traditional linkage systems. This design provides an adaptable closing finger trajectory providing better grip. The model also provide actuation to all five fingers contrary to the three fingers of existing hands. This is achieved by a simple differential mechanism driving the last three fingers semi-independently with one actuator. The model also provides abduction of all fingers as well as opposition of the thumb improving the hands versatility. The hand is controlled using a personal computer and two interface boxes. Software was developed in Visual Basic to provide the user with a control analogue to that of a real myoelectric prosthesis.
- ItemOpen AccessCrushing characteristics of axially stacked square tubes(2008) Ronchietto, Fabio Federico Piraino; Nurick, Gerald NThe crushing and energy absorption characteristics of thin-walled specimens consisting of single, welded and two axially stacked plate-divided mild steel square tubes were investigated by the performance of numerous quasi-static and dynamic axial crushing tests and FEM (finite element modeling). The simulation was carried out using the finite element package ABAQUS/Explicit 6.7.1. Lengths of the specimens ranged from 300mm to 1700mm encompassing the three main modes of buckling of square tube specimens; namely progressive, global bending and transition between the buckling modes.
- ItemOpen AccessDeformation and tearing of uniformly blast-loaded quadrangular stiffened plates(2000) Yuen, Steeve Chung Kim; Nurick, Gerald NAn 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.
- ItemOpen AccessDesigning and modelling an automated packaging system(1997) Tollner, Martin Ernst; Nurick, Gerald NThis thesis describes the design and modelling of an improved materials handling system for a beverage cap production factory called BevCap, located in Epping, Cape Town. The factory consists of twelve production lines, which produce various types of aluminium and metal screw on caps. Each production line is fully automated except for the filling, packaging, labelling and storing procedures at the end of each production line. The finished product is counted electronically and packed into carton boxes, labelled, sealed and palletised manually. The manual materials handling procedures, at the end of each production line, are causing problems and therefore an improved automated system is required.
- ItemOpen AccessDetermination of material properties of mild steel at different temperatures and strain rates(2007) Vara, Amit Rashiklal; Nurick, Gerald NQuantification of material properties through physical experiments is of significant importance. Test data from such experiments aid in the understanding of the material behaviour when exposed to a variety of loading conditions. Such data also help in the formulation of empirical and constitutive relations that can be applied in numerical simulations. This project dealt with the determination of the variation of the yield stress of mild steel with temperature and strain rate. This was achieved by carrying out high temperature tensile tests at different strain rates on mild steel specimens. These experiments also helped set a methodology for carrying out high temperature tensile tests using a servohydraulic universal tester. Results from the tests indicated that increases in temperature tended to decrease the yield stress, whereas increases in strain rate had the opposite effect. This was found to be consistent with data found in literature. It was also noted that the temperature effect was more dominant than the strain rate effect over quasi-static strain rates.
- ItemOpen AccessDetermination of the power losses on a tyre-mounted ore-grinding mill(1998) Tyabashe, Loyiso; Nurick, Gerald N; Tait, Robert BThe objective of this study was to determine the power losses occurring on a tyre-mounted ore-grinding mill designed by Dorbyl Heavy Engineering for Mintek. In order to understand the type of losses occurring on this mill it was decided that a scaled model be built and tested. Such a model mill was designed through the dimensional analysis and similitude technique. This technique enables the reduction of the number of variables to be tested by grouping them into a set of dimensionless parameters, and also allows the results obtained by means of experimentation with the scaled models to be related to the full-scale prototypes. The model mill was constructed in the Mechanical Engineering Workshop at the University of Cape Town. The overall dimensions of the model are 1400 mm long, 1070 mm wide and 892.5 mm high. Its drive-train comprises an electric motor, the wedge and timing belts with the appropriate pulleys, a differential gear set, the tyres, a shell and a disc brake sub-assembly. The tyres used to drive the shell can either be of the pneumatic or solid rubber types. The model mill was designed such that the tyre parameters required in the theoretical solution for power losses, which utilises the Light Vehicle Dynamics Simulation tyre model, could also be measured.
- ItemOpen AccessDevelopment and proving of a split Hopkinson pressure bar used for high strain rate materials testing(2001) Marais, Stephen Thomas; Tait, Robert B; Nurick, Gerald N; Cloete, T JAs a result of increasing demand to improve analysis of manufacturing techniques and safety in structures, it is necessary to determine material properties at high strain rates. Conventional screw-driven or servo-hydraulic methods of testing materials at high strain rates are not adequate as oscillations and stress waves are set-up within the testing apparatus. These oscillations and stress waves foul the transducer reading, thus making the data obtained unusable. To overcome these limitations the split Hopkinson pressure bar (SHPB) was developed. A SHPB facility was developed at UCT to measure material properties at high strain rates. The development, discussed in this thesis, included the design and manufacturing of a SHPB, strain gauge amplifiers and a data acquisition system. In addition to this a data processing package, including a dispersion correction routine was also developed.
- ItemOpen AccessThe development and validation of a geometrically simplified and an accurate finite element model of the wrist joint(2009) Iyer, Yolande-Leigh; Nurick, Gerald NThe injury to the wrist joint resulting from a fall onto the outstretched hand was simulated using two models. The two validated three-dimensional wrist joint models were created using the general purpose finite element software, ABAQUS. The first model, a Geometrically Simplified half symmetry Model (GSM), was created using an approximation of real bone geometry, with material properties that could be varied.
- ItemOpen AccessThe effect of boundary conditions on the failure of thin plates subjected to impulsive loading(1995) Thomas, B M; Nurick, Gerald NThis report presents the results of an investigation into the effects of edge boundary conditions on the failure of thin plates subjected to impulsive loading. In previous investigations the discrepancy between experimental results and theoretical solutions and effects observed at the edges of deformed plates have brought the method of securing the plate into question. This investigation examines the effect of edge boundary conditions by comparing the results of previous experiments where the plates were secured by clamping - with experiments where the plates are built-in (integral) with their supports.
- ItemOpen AccessThe effects of blast induced imperfections on the energy absorption characteristics of square tubes(2006) Yuen, Steeve Chung Kim; Nurick, Gerald NThis 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.
- ItemOpen AccessThe effects of different degrees of confinement on the deformation of square plates subjected to blast loading(2012) Geretto, Carlo; Nurick, Gerald NThis work relates to the effcts of the degree of confiement for air blasts only. The response of a structure subjected to a blast load is dependent on several factors; for instance stand off distance, geometry and mass of explosive, geometry of the structure, medium (air, water, soil) and degree of confinement. Depending on the location of the explosion relative to the surrounding structures different degrees of confinement are obtained. In addition, depending on the degree of confinement the accumulation of high temperature gas products will exert additional loads on the structure. This thesis reports the results of experimental and numerical investigations into the effct of the different degrees of confinement and target plate thickness on the response of square mild steel target plate.
- ItemOpen AccessThe effects of the slip amplitude and lubricant type on the rate of false brinelling in roller bearings(1995) Jordan, Ivan Keith; Noyes, Roy; Nurick, Gerald NFalse brinelling is a wear phenomenon that occurs in stationary rolling element bearings. Vibrations from adjacent running machinery are transmitted to the stationary bearing via the machinery foundations, and result in relative motion between the rollers and the races. This results in wear scars at the point of contact between the rollers and the race. The wear scars result in premature failure of the bearings. There are a large number of parameters that affect the rate of false brinelling. Most of these parameters are not free to be altered by the user of the bearing. There are two parameters that can be altered, the type of lubricant, and the slip amplitude of the vibration. The slip amplitude can be altered by changing the stiffness of the foundation of the equipment. By varying these two parameters it should be possible to limit the amount of damage to the bearing. In the work reported here, a shaker was used to axially vibrate a flat "outer race" in a lubricant bath, against a cylindrical roller. The relative motion was measured by means of a proximity probe. Two lubricants were tested: SAE 30 oil and LGEP 2/1 grease. Two different wear mechanisms, exhibiting vastly different wear rates, were discovered for the oil tests. At low slip amplitudes, smaller than 25um, the results suggested that elastic deformation of the contacting surfaces was the means of displacement accommodation. At larger slip amplitudes the results suggested relative motion between the two contacting surfaces, which was marked by a bifurcation in the wear rate versus slip amplitude curve. The one branch of the curve, which for ease of explanation is called wear mechanism one, exhibited a low wear rate, which increased in a linear fashion with respect to the slip amplitude. The second branch of the curve, wear mechanism two, approximated a step function, with a very rapid increase in the wear rate with respect to the slip amplitude. This rapid increase is followed by a slow linear increase in the wear rate with respect to the slip amplitude.