Mechanical Engineering

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Aerodynamic modelling and further optimisation of solar powered vehicle.
(2016) Lawrence, Christopher Jon.; Bemont, Clinton Pierre.; Veale, Kirsty Lynn.
Computational fluid dynamics was used to optimise the aerodynamics of a solar powered vehicle via the addition of airflow alteration devices that interact with the boundary layer airflow. These features were designed, manufactured and applied to the vehicle while ensuring that the bulk geometry remained unmodified. The modifications had to be added to the vehicle non-invasively, and had to allow for removal during race conditions. The solar vehicle raced in both the Sasol Solar Challenge (SASC) which took place in September 2014 and the Bridgestone World Solar Challenge (WSC) which took place in September 2015. Aerodynamic drag is the single largest energy loss experienced by a solar vehicle; it is therefore essential that the aerodynamics of these vehicles be highly refined if they are to be competitive. The UKZN solar vehicle placed first in South Africa in the SASC and 13th in the WSC - indisputably outstanding results. The features to be refined were chosen to reduce aerodynamic drag caused by the wheel spokes as well as the canopy due to these being high turbulence zones and having high curvatures respectively. The principles applied were to reduce turbulence caused by the wheel spokes by adding to the wheel geometry, and adding turbulence to the canopy airflow through the use of a technique commonly known as flow tripping. While turbulence caused by the wheels is undesirable, the turbulence added by flow tripping is desirable as it reduces the size of the separated region of airflow behind the canopy, allowing for a net reduction in aerodynamic drag. Wheel geometry alteration was done via the addition of smooth and dimpled covers, so as to mitigate the turbulence caused by the wheel spokes. Many techniques were considered to trip the airflow on the canopy, it was found that vortex generators of specific geometry and dimensions would reduce drag more effectively. Another airflow altering device, a NACA duct, was designed and manufactured. This duct was placed on the canopy to allow airflow into the driver compartment which enabled adherence to race rules and allowed for driver cooling and ventilation. Each wheel cover was manufactured from two layers of carbon fibre to allow a net gain in efficiency with regards to rolling resistance and drag reduction when considering weight added by the wheel covers. The vortex generators and NACA duct were 3-D printed using ABS plastic. The wheel covers and NACA duct were applied to the car for the World Solar Challenge while only the wheel covers were applied for the Sasol Solar Challenge. The vortex generators were not applied due to the efficiency gain from the application being uncertain at the time of the race. A gain in aerodynamic efficiency with the addition of wheel covers to a front wheel was shown through CFD testing. The drag was reduced by approximately 0.5 Newtons (5 %) relating to translational forces and 0.02 Newtons per meter (44 %) percent with regards to rotational forces. The addition of vortex generators resulted in a drag reduction ranging from approximately zero to three percent when considering straight airflow and crosswinds respectively.
Critical tracking and stress analysis of Transnet engineering trailers.
(2017) Dwarika, Yuvraj.; Bemont, Clinton Pierre.
Transnet Engineering (TE) produces specialised trailers that are not commercially available. The design of the trailers is based on experience plus knowledge of original equipment manufacturer (OEM) designed and operational trailers. Since trailers are a new specialised product to TE no design data is available and for safety and reliability the trailer is “over”- designed. The risk of any part failing during operation is however minimised, if the trailer is soundly designed throughout, rather than focusing on critical areas and optimising the structure. Since no trailer analysis has previously been undertaken in Transnet, the design had to be monitored and validated with the aim to reduce material costs and tare weight by approximately 10%. The aim of this project was to undertake and improve a theoretical simulation analysis and implement a practical system to measure and capture critical data on bath-tub and multi-purpose trailers. This would allow a better understanding of the loading characteristics of the trailers in the port environment and validate the existing design with the data acquired from practical field testing. Based on the theoretical simulations and data acquired during field testing, an efficient design is proposed that will save on material and labour thus reducing the net tare weight. A reduction in tare weight will allow for better tractive power from the hauler and improve the life span of the parts such as the brakes, tyres and bearings. Worldwide knowledge regarding this project is limited; OEMs and tertiary institutions have undertaken similar projects but only for highway trailers and related topics. The current open market does not offer a study which meets this project’s needs; by adapting this practice to other aspects of the mechanical design, the product can be optimised for its application.
Design and analysis of a multi-trailer system for the Durban container terminal.
(2018) Govender, Theo.; Brooks, Michael John.; Bemont, Clinton Pierre.
Multi-trailer systems (MTS) allow for the transportation of multiple shipping containers in a single movement as opposed to the conventional trailer systems often used within a port terminal environment. The adoption of MTSs creates an opportunity for container terminal operators to reduce the operational costs associated with container movements between the container vessel and stacking areas during the vessel loading and unloading operations while maintaining, and in certain cases improving, the port’s quayside productivity. A reduction in operational costs can potentially result in lower tariffs levied to container vessel operators, improving the competitiveness of a port. While MTSs have been in existence for many years and have been successfully implemented in many international port container terminals, the influence of this type of trailer on the operational costs of the waterside horizontal-transport system and on the quayside productivity within South African ports has not been investigated or demonstrated to date. This study set out to determine the influence which an indigenously designed MTS has on the abovementioned factors at South Africa’s largest container port, the Durban Container Terminal. Discrete event simulations were used to benchmark the current performance of the container movement operations at Pier One of the Durban Container Terminal using the existing tractor-trailer units (TTUs). The performance of the operations was then analysed for the scenario of replacing the TTUs with MTSs that have twice the container carrying capacity. The results showed that nine MTSs can replace the existing fleet of fifteen TTUs without compromising on the quayside performance for the vessel unloading operations, which leads to a 25% reduction in operational costs. A reduction in labour costs accounts for 88% of the saving. Use of MTSs for the vessel loading operations showed minimal benefit and the performance using the existing TTUs for this operation can be considered equivalent. The results imply that an MTS configuration with the ability to uncouple the individual trailers in the set for use as TTUs was required. This lead to the selection of a semi-trailer lead MTS configuration incorporating the use of a converter dolly for the indigenous design conducted here. The indigenous MTS design consisted of two identical semi-trailers connected using a converter dolly, allowing for interchangeability in the MTS set and for use of the semi-trailers as TTUs. The terminal’s existing semi-trailers could have been used with the converter dolly designed in this study for the MTS, however an improved semi-trailer design with regards to mass, cost and manoeuvrability has been provided. The new semi-trailer design was shown to have a 21.4% lower tare mass and a 14.1% lower product manufacturing cost over the existing design. For the MTS configuration, up to an 11.6% improvement in manoeuvrability is expected when using the newly designed semi-trailer.
Design and analysis of the tooling to manipulate and install complete sectors in the ATLAS new small wheel within narrowly defined stress parameters.
(2015) Singh, Shuvay.; Bemont, Clinton Pierre.; Yacoob, Sahal.
Abstract available in PDF file.
Design and optimisation of the sector transport, storage and assembly tooling and procedures of the New Small Wheel for the Atlas Experiment.
Sinclair, Peter James.; Bemont, Clinton Pierre.; Yacoob, Sahal.; Veale, Kirsty Lynn.
This report describes the design of the transport, storage and assembly tooling for the sectors of the ATLAS Experiment’s New Small Wheel. This tooling is to be used during the 2018 Large Hadron Collider’s shutdown, Long Shutdown 2. Comprehensive design reports following the Eurocode and CERN’s unique design environment and philosophies are presented. The NSW sector transport tool is an adaption of a previously used ATLAS EO muon transport tool, taking new sector masses, geometries and other transport restrictions into account. A safety document is provided for this tool confirming safety with regards to applied stresses in line with the Euro-code. The document also confirms lifting stability during all of the tool’s intended procedures. The assembly tool allows the sTGC components to be assembled to the Micromegas chambers to create NSW sectors for the New Small Wheel. This tool also provides a platform for repairs and adjustments to be made to the NSW sectors before installation. The NSW sector assembly station is also designed in line with the Euro-code. A floor layout allocating space for transport, assembly and storage procedures in Building 191 of the Meyrin, CERN site is provided as specified by the project requirements. An investigation confirming the validity of the finite element analysis techniques and simplifications used on the Micromegas wedges is conducted and presented. This investigation uses the results obtained from experimental thermal tests and analytical calculations of a Micromegas multiplet mock-up called the MMSW and compares them to finite element analysis results modelled to the same testing conditions. The results obtained from this investigation show that the computational results have an error of 7.6 % when compared to the attained experimental results. Consequently, because the finite element model is created in an identical manner to the one used for the Micromegas wedges, an assumption of similar errors can be applied to future simulations conducted on the Micromegas wedges, using this technique.
Development of a comprehensive energy model to simulate the energy efficiency of a battery electric vehicle to allow for prototype design optimisation and validation.
(2017) Woods, Matthew Allan Ray.; Bemont, Clinton Pierre.; Brooks, Michael John.; Pitot de la Beaujardiere, Jean-Francois Philippe.
This dissertation describes the development of an energy model of a battery electric vehicle (BEV) to assist designers in evaluating the impact of overall energy efficiency on vehicle performance. Energy efficiency is a crucial metric for BEVs as it defines the driving range of the vehicle and optimises the limited amount of energy available from the on-board battery pack, typically the most expensive component of the vehicle. Energy modelling also provides other useful information to the designer, such as the range of the vehicle according to legislative drive cycles and the maximum torque required from the motor. An accurate, fast and efficient model is therefore required to simulate BEVs in the early stages of design and for prototype validation. An extensive investigation into BEV modelling and the mechanisms of energy losses within BEVs was conducted. Existing literature was studied to characterise the effect of operating conditions on the efficiency of each mechanism, as well as investigating existing modelling techniques used to simulate each energy loss. A complete vehicle model was built by considering multiple domain modelling methods and the flow of energy between components in both mechanical and electrical domains. Simscape™, a MathWorks MATLAB™ tool, was used to build a physics based, forward facing model comprising a combination of custom coded blocks representing the flow of energy from the battery pack to the wheels. The acceleration and speed response of the vehicle was determined over a selected drive cycle, based on vehicle parameters. The model is applicable to normal driving conditions where the power of the motor does not exceed its continuous rating. The model relies on datasheet or non-proprietary parameters. These parameters can be changed depending on the architecture of the BEV and the exact components used, providing model flexibility. The primary model input is a drive cycle and the primary model output is range as well as the dynamic response of other metrics such as battery voltage and motor torque. The energy loss mechanisms are then assessed qualitatively and quantitatively to allow vehicle designers to determine effective strategies to increase the overall energy efficiency of the vehicle. The Mamba BEV, a small, high-power, commercially viable electric vehicle with a 21 kWh lithium-ion battery was simulated using the developed model. As the author was involved in the design and development of the vehicle, required vehicle parameters were easily obtained from manufacturers. The range of the vehicle was determined using the World-Harmonised Light Duty Vehicles Test Procedure and provided an estimated range of 285.3 km for the standard cycle and 420.8 km for the city cycle.
The development of a paraffin wax/nitrous oxide hybrid rocket slab motor.
(2019) Theba, Raisa.; Veale, Kirsty Lynn.; Bemont, Clinton Pierre.
Slab motors are used to determine and investigate the regression rate characteristics of hybrid rocket propellant combinations. This information is fundamental to the overall design and thus used to determine the payload, altitude and thrust parameters of a rocket. The Phoenix Hybrid Sounding Rocket Programme in the University of KwaZulu-Natal’s (UKZN) Mechanical Engineering Department uses paraffin wax and nitrous oxide in their series of hybrid sounding rockets. The regression rate behaviour of paraffin wax with nitrous oxide has not previously been investigated in slab motors. This study focused on the regression rate behaviour and entrainment mechanism with regards to non-classical fuels including those with metal additives. This was used to gain a greater understanding of the increased regression rates associated with these fuels. The addition of metal additives, such as that of aluminium to fuel grains, was explored since the research suggested that it increases the regression rate of pure paraffin wax by 30%. A hybrid rocket slab motor visualisation test stand was developed to observe and obtain regression rate data. The stand includes a feed system, injector and a combustion chamber. All the components were manufactured using brass and stainless steel materials for their nitrous oxide compatibility, strength, and thermal resistance. Quartz glass windows were incorporated into the combustion chamber design for visualisation purposes. Due to the presence of quartz glass the use of finite element analyses became critical and more complex in order to ensure that the glass could withstand the operating conditions of the slab motor. A side-glass spacer was implemented to minimise the effects of side burning and to observe the influence of regression rate. Tests were conducted at a 130 g/s oxidiser mass flow rate and an atmospheric chamber pressure. A data acquisition system using LabVIEW software was implemented to obtain tank readings for the duration of the burn and to ensure safe motor operation. The regression rate of Sasolwax 0907 fuel was volumetrically determined and observed to be on average 3.74 mm/s. This shows a much higher regression rate than other paraffin wax compositions which have been found to regress at 1.5 mm/s. The characteristics of the entrainment process were validated for the investigated propellants, and the high regression rate mechanism of paraffin wax was observed in the liquid melt layer, droplet entrainment, and roll waves. Tests using aluminised wax fuel grains at atmospheric conditions proved to beunsuccessful with nitrous oxide as the oxidiser. A possible reason for this could be due to the aluminised fuel grains requiring increased heat transfer, therefore not producing sufficient apourisation of the fuel. Moreover, decomposition of the oxidiser appeared to be inhibited by the combination of the oxidiser mass flow rate and the port area which prevented combustion.
Development of a titanium sheet manufacturing process via direct powder rolling and spark plasma sintering.
(2022) Moosa, Fathima.; Bemont, Clinton Pierre.
The intention of this research was the improvement of titanium processing in South African industry. South Africa currently has limited ability to efficiently process its titanium reserves and the results of this research, combined with other work in the associated research consortium, has the potential to lead to significant positive economic impact. A novel method of titanium processing, combining the processes of direct powder rolling (DPR) and spark plasma sintering (SPS), was explored in the course of this research. A rolling mill was designed using modelling and simulation techniques, manufactured based on the resulting design, and the DPR-SPS process parametrically tested on the rolling mill using commercially pure titanium powder. The mechanical aspects of this project included experimental testing on a range of titanium powder samples to determine the properties of the powder, modelling of the rolling mill behaviour using MATLAB, 3D modelling of the proposed and iterated rolling mill frame design and its components using Siemens NX and OnShape, finite element analysis of the rolling mill frame and auxiliary components using Siemens NX, and manufacture and parametric testing of the mill for titanium powder compaction. The electrical aspects of this project included connecting and programming a variable speed drive and AC motor to control the speed of the mill rolls, simulating the behaviour of the integrated SPS-type sintering circuit using Simulink, designing a suitable method for safely and effectively transmitting the large SPS current to the rotating rolls, and building and testing the circuit for titanium compact spark plasma sintering. The manufactured direct powder rolling mill compacts titanium powder into strip through a pair of rolls, measuring 350mm diameter and 50mm width. Each of the rolls is mounted on the same shaft as a worm-driven gear. A 5.5kW three phase AC motor drives the worm shafts, which have opposing threads to ensure the rolls rotate in opposing directions. The worm and gear arrangement serves to both evenly transmit the drive power to both rolls, and to increase the torque from the motor to the rolls. The motor is controlled using a variable speed drive – this allows the roll speed to be adjusted as necessary, to optimise the consolidation process. The bearings used on the roll and worm shafts were designed and manufactured using an insulating bearing material to ensure the current used for sintering is not instead transmitted through the steel rolling mill frame. Flexible couplings with polymeric inserts isolate this current from the motor and between each worm gear. The minimum density of the green compact required for further handling was determined empirically as being greater than 65 % of the theoretical density of titanium. The mill was designed for an optimal density of 81%. The density range achieved by varying the parameters of roll speed, number of passes through the mill, and roll gap, was 55 – 84%. It is expected that the strip density may be greatly increased with implementation of the improvements and parameter changes identified. The spark plasma sintering circuit sinters the titanium either during the direct powder compaction process (simultaneous DPR-SPS), or following it (sequential DPR-SPS) during re-rolling through the same set of rolls used for compaction. A number of electrical circuits with different output types were designed for the SPS process; one of these was built and tested towards proof of concept of the DPR-SPS process. The tested circuit uses a DC source to apply a sintering current through the titanium sample. Application of the SPS current to the titanium resulted in a theoretical density increase of 11 –14% compared to DPR only, depending on whether the processes were performed sequentially orsimultaneously This multidisciplinary project employed a broad range of combined materials, mechanical and electrical design and analysis methods. The resulting mill can be used as is for further parametric testing, improved as will be discussed for the same process, or adapted to a range of different applications.
Independent assessment and benchmarking of no/low cost finite element analysis software for linear and non/linear static structural analysis.
(2016) Rugdeo, Saien Bemont.; Pitot de la Beaujardiere, Jean-Francois Philippe.; Bemont, Clinton Pierre.
The aim of this research was to determine if the development of low-cost (less than 500 USD) or no-cost analysis software, specifically in the area of computational structural mechanics through finite element analysis (FEA), has advanced to the point where it can be used in place of trusted commercial FEA software packages for linear and non-linear static structural analyses using isotropic materials. This was done by conducting an initial market research study and identifying a range of available no-cost/low-cost FEA packages. Eighteen suitable packages were identified and a preliminary analysis was done to identify analysis capabilities, presence of internal modules, extent of available user documentation, and end user support. The packages underwent a process of systematic elimination from the preceding phases of the research if they were unable to meet the minimum imposed criteria. Six packages were deemed suitable and were further investigated. From these, three packages were chosen to be subjected to performance benchmarking, namely: Code_Aster/Salome Meca; Mecway and Z88 Aurora. SimScale, a browser-based analysis package was included as well because it met all the baseline criteria and has the potential to offer a completely cloud-based approach to computer aided engineering, potentially reshaping the way an engineering business views its operational capabilities. Performance benchmarking assessed the ability of a package to generate a model and obtain accurate solutions relative to industry accepted benchmark publications, trusted analytical solutions found in reputable engineering text, as well as experimental results obtained in this work. The benchmarking process was also done on commercial FEA packages so that a comparison can be made between the no-cost/low-cost packages and those considered to be the premium FEA software packages available. It was found that the no-cost/low-cost options were able to perform adequately for most of the test cases. SimScale and Z88 Aurora had difficulties with generating suitable meshes which meant that compromises in model generation approaches needed to be made. Overall, the results yielded by the low-cost/no-cost options showed good correlation with test case target values as well as exhibiting many capabilities and tools found in the high-cost, trusted commercial packages investigated. It is therefore concluded that there are no-cost/low-cost FEA packages that can be used in place of high-cost commercial packages for linear and non-linear static structural analyses of isotropic materials.
Lightweight structural design of UAV wing through the use of coreless composite materials employing novel construction techniques.
(2017) Moore, Neall Neville.; Bemont, Clinton Pierre.
A new structural layout was designed for an existing UAV wing with the aims of lightening the wing by eliminating the use of cored composite construction and reducing the manufacturing time of the wing by making use of waterjet-cut internal frames while satisfying strength and stiffness requirements. Two layouts, a traditional metal wing layout and a tri-directional rib lattice layout, were selected for consideration based on the literature surveyed. In order to present a valid comparison with the previous wing design the same composite materials were used in the design of the new wing layout and material tests were performed according to ASTM testing standards to obtain the mechanical properties of these materials. Load cases for the wing in flight were calculated according to FAR-23 standards and the loads on the wing were found using XFLR5 vortex-lattice methods. An empirical, spreadsheet-based initial sizing tool was developed to obtain initial layups for an iterative FEA-based optimisation process that employed the SolidWorks Simulation Premium software package and made use of the Tsai-Wu composite material failure criterion and empirical buckling equations. The iterative optimisation resulted in the traditional metal wing layout being selected and predicted a weight saving of 14% over the original wing design. A full scale prototype wing was constructed in the CSIR UAS Laboratory using wet layup techniques and laser cut internal frames as it was found that the waterjet cutting of thin composite frames was not practical as a result of the high working pressure of the waterjet cutter. The prototype wing showed an actual weight saving of 14% but took considerably longer to manufacture due to the necessity of constructing specialised jigs to aid in the bonding and alignment of the internal frames. The prototype wing was tested using a custom set-up whiffle tree rig up to its maximum limit load of 4.9 g and showed an average of 4% error between measured and predicted deflections thereby validating the FEA models. It was concluded that a UAV wing can be significantly lightened through a coreless structural design, but at the expense of an increase in construction time. It is hoped that this study will contribute towards a changed design philosophy in an industry where cored construction is the norm. It is recommended that the methods developed during this project be applied to the rest of the aircraft components in order to obtain a lighter overall structure.
Modeling and experimental validation of a loop heat pipe for terrestrial thermal management applications.
(2013) Page, Matthew Christopher.; Brooks, Michael John.; Roberts, Lancian Willett.; Bemont, Clinton Pierre.
The Loop Heat Pipe (LHP) is a passive, two-phase heat transfer device used, most commonly, for thermal management of aerospace and aeronautical electronic equipment. A unique feature is a porous wick which generates the necessary capillary action required to maintain circulation between the heat source and the heat exchanger. What differentiates LHP devices from traditional heat pipes, which also work through the use of a wick structure, is the constrained locality of the wick, placed solely in the evaporator, which leaves the remainder of the piping throughout the device as hollow. This provides the LHP with a number of advantages, such as the ability to transport heat over long distances, operate in adverse gravitational positions and to tolerate numerous bends in the transport lines. It is also self-priming due to the use of a compensation chamber which passively provides the wick with constant liquid access. These advantages make LHPs popular in aerospace and aeronautical applications, but there is growing interest in their deployment for terrestrial thermal management systems. This research had two aims. Firstly, to create and validate a robust mathematical model of the steady-state operation of an LHP for terrestrial high heat flux electronics. Secondly, to construct an experimental LHP, including a sintered porous wick, which could be used to validate the model and demonstrate the aforementioned heat exchange and gravity resistant characteristics. The porous wick was sintered with properties of 60% porosity, 6.77x10-13 m2 permeability and an average pore radius of 1μm. Ammonia was the chosen working fluid and the LHP functioned as expected during horizontal testing, albeit at higher temperatures than anticipated. For safety reasons the experimental LHP could not be operated past 18 bar, which translated into a maximum saturated vapour temperature of 45°C. The heat load range extended to 60 W, 50 W and 110 W for horizontal, gravity-adverse and gravity-assisted operation respectively. Because of certain simplifying assumptions in the model, the experimental results deviated somewhat from predicted values at low heat loads. Model accuracy improved as the heat load increased. The experimental LHP behaved as expected for 5° and 10° gravity-assisted and gravity-adverse conditions, as well as for transport line variation, in which performance was assessed while the total tubing length was increased from 2.5 m to 4 m. Overall, the construction of the LHP, particularly of the porous wick, its operation and the modeling of the constant conductance mode of operation proved to be successful. The variable conductance mode of operation was not accurately modeled, nor was expected behaviour in the elevation testing encountered, although the reasons for these results are suggested.
Optimisation of welding parameters to mitigate the effect of residual stress on the fatigue life of nozzle–shell welded joints in cylindrical pressure vessels.
(2017) Zondi, Mthobisi Clyde.; Adali, Sarp.; Bemont, Clinton Pierre.
The process of welding steel structures inadvertently causes residual stress as a result of thermal cycles that the material is subjected to. These welding-induced residual stresses have been shown to be responsible for a number of catastrophic failures in critical infrastructure installations such as pressure vessels, ship’s hulls, steel roof structures, and others. The present study examines the relationship between welding input parameters and the resultant residual stress, fatigue properties, weld bead geometry and mechanical properties of welded carbon steel pressure vessels. The study focuses on circumferential nozzle-to-shell welds, which have not been studied to this extent until now. A hybrid methodology including experimentation, numerical analysis, and mathematical modelling is employed to map out the relationship between welding input parameters and the output weld characteristics in order to further optimize the input parameters to produce an optimal welded joint whose stress and fatigue characteristics enhance service life of the welded structure. The results of a series of experiments performed show that the mechanical properties such as hardness are significantly affected by the welding process parameters and thereby affect the service life of a welded pressure vessel. The weld geometry is also affected by the input parameters of the welding process such that bead width and bead depth will vary depending on the parametric combination of input variables. The fatigue properties of a welded pressure vessel structure are affected by the residual stress conditions of the structure. The fractional factorial design technique shows that the welding current (I) and voltage (V) are statistically significant controlling parameters in the welding process. The results of the neutron diffraction (ND) tests reveal that there is a high concentration of residual stresses close to the weld centre-line. These stresses subside with increasing distance from the centre-line. The resultant hoop residual stress distribution shows that the hoop stresses are highly tensile close to the weld centre-line, decrease in magnitude as the distance from the weld centre-line increases, then decrease back to zero before changing direction to compressive further away from the weld centre-line. The hoop stress distribution profile on the flange side is similar to that of the pipe side around the circumferential weld, and the residual stress peak values are equal to or higher than the yield strength of the filler material. The weld specimens failed at the weld toe where the hoop stress was generally highly tensile in most of the welded specimens. The multiobjective genetic algorithm is successfully used to produce a set of optimal solutions that are in agreement with values obtained during experiments. The 3D finite element model produced using MSC Marc software is generally comparable to physical experimentation. The results obtained in the present study are in agreement with similar studies reported in the literature.
Structural analysis of a composite monocoque chassis for use in a high performance electric vehicle.
(2018) Witteveen, Nicholas Tjebbe.; Pitot de la Beaujardiere, Jean-Francois Philippe.; Brooks, Michael John.; Bemont, Clinton Pierre.
The adoption of electric vehicle technology is becoming more prevalent, as society strives to reduce the negative impact of greenhouse gas emissions and focuses on a sustainable future. This thesis details the design and structural analysis of a carbon composite monocoque chassis for application in a light-weight, high-performance electric vehicle for a South African market, based on the fundamental principles of automotive vehicle design. Handling characteristics and the design impacts they have on the decisions made in developing a vehicle chassis were explored. The two-dimensional geometry of the chassis structure was developed in the Siemens NX design environment, taking into account the spatial requirements of the mechanical and electrical system components, as well as occupant ergonomics. A zonedbased approach was taken in defining the composite layup for the chassis panels, using material data for locally obtained fabrics and epoxy resin. The chassis’ composite lay-up configuration was developed using several static load cases, simulating operational loading, as well as extreme loading arising in certain accident scenarios. The composite structure was analysed, with the first ply composite failure criterion being used to predict failure in the constituent materials. Design refinement was undertaken until the failure criterion predicted structural survivability for all the extreme loading cases considered.
Structural characterisation and response modelling of paraffin-based hybrid rocket motor fuel grains.
(2020) Veale, Kirsty Lynn.; Adali, Sarp.; Pitot de la Beaujardiere, Jean-Francois Philippe.; Bemont, Clinton Pierre.
Abstract available in PDF.
Trip steels as smart sensor alloys.
(2013) Bemont, Clinton Pierre.; Bright, Glen.; Cornish, Lesley.
Upon deformation, TRIP steels undergo progressive irreversible transformation from paramagnetic austenite to more thermodynamically stable, ferromagnetic αʹ-martensite. The change in magnetic permeability is readily detectable, and since TRIP steels also have excellent mechanical properties, this presents the opportunity for implementing cheap, robust structural health monitoring systems. However, the extent of martensitic transformation in TRIP steels is affected not only by the degree of deformation, but by environmental temperature at the time of deformation and strain rate. This creates inherent inaccuracy when implementing TRIP steels as sensor materials. In this thesis it has been demonstrated that it is possible to design TRIP steels that are less susceptible to these factors, show good deformation induced transformation, and can function simultaneously as sensors and structural elements. As-cast alloys were tested in compression, while annealed, hot-rolled and warm-rolled alloys were tested primarily in tension. There was considerable variation between alloys in rate of transformation with deformation. Martensitic transformation was evaluated magnetically and correlated with optical and scanning electron microscopy and X-ray diffraction results. Changes in magnetisation and magnetic permeability curves with deformation were characterised to ensure optimal electronic monitoring. Equations from literature for determining characteristic transformation temperatures, Ms and Md30 were evaluated experimentally for the alloy range of interest, and the best equations were selected to aid in the design of high alloy TRIP steels exhibiting strong transformation and low temperature sensitivity. Temperature sensitivity between alloys was found to vary as predicted. Temperature sensitivity was also compared in annealed, hot rolled and warm rolled conditions; the annealed condition showed the lowest sensitivity, and this is thought to be related to lower dislocation densities. Mining was targeted as a primary industry for application of these sensor systems because of the pressing need for greater safety and more efficient structural support at low cost. Two distinct devices for monitoring the structural health of mines were designed, built and tested, and a third was developed for the aerospace industry. Better understanding and control of the temperature sensitivity of martensitic transformation in TRIP steels is expected to aid not only structural health monitoring, but also the application of such materials to other areas of technology, such as sheet forming and high impact resistance applications. Although there are limitations on the extent to which TRIP steel transformation characteristics can be controlled, it was shown that they can be manipulated to enable successful implementation of new alloys for smart load or damage sensors. Practical, robust, low cost structural health monitoring sensors based on the smart properties of TRIP steels were shown to be feasible.

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