Theses and Dissertations (Mechanical Engineering)

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Structural performance of KAT-7's ball screw raceway in the elastic region subjected to varying loads
(Vaal University of Technology, 2017-12) Steenekamp, Nicolaas Kruger; Masu, Leonard, Prof.; Alugongo, Alfayo, Prof.
The structural performance of a KAT-7’s ball screw raceway is not known. No performance data has been generated analytically, numerically nor experimentally. For this study, data was generated in the elastic region of the material. This research was undertaken in three different ways namely analytically, numerically and experimentally. A calibrated load cell was used to validate the analytical solutions. Solid Edge, a parametric software package was used to validate analytically the accumulated rain water mass and structural mass. Abaqus, a finite element analysis software package, was used to model and obtain the ball bearing Hertzian contact stresses numerically. The numerical solution was used to validate the laboratory compression test results on a replica KAT-7 ball screw assembly. The weighted percentage errors between the analytical model data and load cell data were found to be higher for load case scenarios with zero m/s and 10 m/s wind speeds respectively. The parabolic reflector rigid body assumption, exclusion of wind induced hysteresis effects and the quasi-static wind loading site measurement conditions contributed to the weighted percentage error variations. The laboratory and numerical model compression force results revealed a gradual percentage error increase beyond a compression force of 261288 N and up to 572526 N. The percentage error increase had minimum and maximum errors ranging between 6.24 percent and 14.69 percent respectively. The percentage error increase in the numerical model was due to the singular representation of a ball bearing instead of a 212 ball bearings set as experimentally conducted in the laboratory compression test on a replica KAT-7 ball screw assembly. The maximum axial force, F0 , result for load case scenario five was -94469 N with a Hertzian contact stress of 3939 MPa on the raceway surface. The static load rating required to Brinell a deep groove ball bearing raceway was found to be a Hertzian contact stress ranging between 4500 MPa and 4800 MPa. It was evident that the contact stresses incurred under the three considered loads of accumulated rain water, wind loading and structural mass were unable to exceed the 4800 MPa Hertzian contact stress. It was found that a replica KAT-7 ball screw raceway Brinelled under an axial force of 408126 N. The numerical ball screw raceway model Brinelled under an axial force of 380457 N. The Hertzian contact stress at the numerical ball screw raceway surface was determined to be 4898 MPa. Therefore, the Replica KAT-7 ball screw raceway material behaves elastically under an approximate load of up to 38 tonnes.
Enhancing wind turbine performance in cold climate through analysis of aerodynamic lift and drag
(Vaal University of Technology, 2022) Odiagbe, Franklin Oyakhilomen; Masu, L. M., Prof.; Alugongo, A. A., Prof.
Wind energy is one of the most economically sustainable energy, and power plays an important role in the diversification of energy security. Renewable energy resources such as wind energy are constantly replenished, and it is inexhaustible. Being one of the most environment-friendly and renewable, wind energy attracts enormous interest globally. However, wind energy production faces severe challenges in harshly cold climates or low-temperature conditions. Cold weather reduces the aerodynamic lift and increases aerodynamic drag, as ice accretes on the wind turbine blades. Some of the best sites for wind farms installation are cold regions, where the air density is favourable because of low-temperature conditions. Super-cooled droplets and precipitation affect the wind turbine operations and change the aerodynamic profile of the blade through ice accretion. This dissertation focuses on enhancing wind turbine performance in cold climate through ice accretion. this dissertation focuses on enhancing wind turbine performance in cold climate through analysis of aerodynamic lift and drags, using Computational Fluid Dynamics (CFD) and electromagnetic radiation principles. This is based on heat and mass transfer mechanisms of operation to prevent ice accretion on the turbine blades. To optimize the large wind turbines operation in ice prone cold regions, it is important to better understand the ice accretion behaviour and its effects on aerodynamic performance and power production losses. Numerical simulations on ice accretion for wind turbine aerodynamic were carried out for glaze and rime ice conditons using ANSYS. A multiphase based Computational Fluid Dynamic ANSYS was used to analyse electromagnetic radiation and the heat and mass transfer on the wind turbine. Results show that icing on a wind turbine can be mitigated using electromagnetic radiation and heat and mass transfer. Conservation of momentum and heat and mass transfer was applied to determine the effect of ice accretion on aerodynamic lift and drag. Ice mainly accretes along the leading edge of blade profile, which changes the aerodynamics profile by increasing surface roughness and heat fluxes during glaze and rime ice accretion. The effect of electromagnetic radiation on icing time and wind turbine rotation speed were analysed using the working principle of the infrared thermography ice sensing technique. Data collected by infrared sensors were used to retrieve features and parameters (temperature, icing time and wind turbine rotation speed) of the observed surface, without physical contact. The performance of electromagnetic radiation on wind turbine blades aerodynamic forces using Computational Fluid Dynamics (CFD) with Navier-Stokes equations and heat and mass transfer has been analysed and recommendations were drawn from the conclusions. The results from this investigation shows that electromagnetic energies are promising techniques for measuring critical parameters such as wind speed, icing time, and temperature of ice accretion. The electromagnetic energy (thermal infrared sensor) also detects the presence, type, location, thickness, and rate of the ice on a blade's surface. The combination of passing temperature gradients of fluid and solid requires heat transfer. The flow rate of passing temperature through the process (heat and mass transfer) has an essential impact on the application of Navier-Stroke equations for fluid around the wind turbine aerodynamic coefficients.
Improving the performance of membrane backwash system for efficient and stable wettability process during oil/water separation
(Vaal University of Technology, 2022-10) Mopeli, Motebang Josias; Alugongo, A. A., Prof.; Sob, P. B., Dr.; Tengen, T. B., Prof.
Membrane technology has enormous potential for oil/water separation applications. However, membrane performance is hampered by the ongoing fouling issue. Membrane fouling does not only affect the water permeability and separation efficiency but it also reduces the membrane lifespan. Numerous studies on backwash optimization have been conducted to reduce the fouling effect. However, it's worth mentioning that none of the studies in membrane backwash on oil/water separation applications has attempted to improve the cleaning procedure by identifying critical operation conditions through numerical model simulation and experimentation. In the past, accurate modelling of the backwash flow to dislodge the foulants found on the membrane pores or surfaces (concentration polarization) in pressure-driven membrane processes was hindered by complex couplings between the flow equations and the variable operating properties. However, the developed backwash model in this study is based on Navier Stokes laws which govern the entire flow field that incorporate the backwash media flow domain, and oil droplet dislodgement on the membrane domain. The varying nature of flow necessitates different modelling methodologies to help predict the behaviour of backwash flow. As such, Navier Stokes's laws governing the fluid flow were the obvious choice, due to their high accuracy and diversity in describing a whole set of flow phenomena:, from laminar to turbulent under Newtonian flow. Additionally, incorporating computational fluid dynamics (CFD) ANSYS Fluent numerical model simulation, as a preliminary evaluation tool to improve the backwash cleaning efficiency for oil/water separation application has shown to be an effective approach. This developed backwash model depends heavily on the backwash critical operating parameters such as temperature, driving back-pressure, and the subsequent backwash flow velocity. The theoretical numerical simulation model and experimental results were in good agreement that oil droplets can be dislodged effectively, only if the critical backwash operating conditions for oil/water separation application are identified and utilized. These critical operating parameters are identified to improve the backwash system, such as the thermal forces applied to lower the oil viscosity (critical temperature 0 65 c) and the critical pressure (190kpa) was subsequently utilized to loosen the interfacial tension force(adhesive forces). Consequently, the oil droplet blockage was easily dislodged by the backwash flowmedia (backwash velocity). Ultimately, this study investigated the dynamic relationship of the proposed critical operating parameters (temperature, pressure, and the subsequent backwash flow velocity) with membrane material capable of withstanding this proposed intense backwash procedure. The evaluation criteria were focused on permeate flux recovery, thermal stability, and the ability of the membrane to withstand harsh operating conditions during the backwash procedure. Consequently, this study developed an improved backwash cleaning procedure in relation to membrane material selection for efficient wettability which has proven to be an effective approach to control fouling during oil/water separation. According to the results obtained, the use of critical backwash pressure resulted in efficient fouling removal. In addition, the thermal stability of ceramic membrane permits the use of high temperature by backwash parameter to lower the oil droplets viscosity, subsequently allowing easy dislodgement of foulants found on the membrane structure. Consequently, this attempt to exploit the research gap in membrane backwash has led to this dissertation contributing to advancing new knowledge of membrane technology for application in oil/water separation. The contributions of the project includes: 1. Establishing the most efficient backwash process, through the identification of critical operating conditions (temperature, pressure, and the subsequent backwash flow velocity) using Navier Stokes laws under fluid flow modelling. 2. Designing a numerically simulated model by utilizing computational fluid dynamics (CFD) ANSYS Fluent software tool, as a preliminary evaluation measure, to validate an improved backwash procedure 3. Establishing an improved backwash cleaning procedure in relation to membrane material design for efficient wettability to mitigate fouling during oil/water separation.
Impact of equal channel angular pressing operational parameters on the mechanical properties of characterized Titanium-Based powders
(Vaal University of Technology, 2020-03) Nhlapo, Mirriam; Machio, C., Dr.; Masu, L., Prof.
The powder metallurgy technique Equal Channel Angular Pressing is a severe plastic deformation method. Where desired microstructure and texture can be developed by applying temperature, changing the orientation of the billet through a number of successive passes. It has been extensively researched as a tool for processing solid metal, where it has been shown to provide components with ultra-fine grains that impart superior mechanical properties. The ECAP of titanium-based powder has the potential to greatly aid the cheaper production of titanium-based components. The main objective of this study was to investigate the fundamental interaction between titanium powder characteristics and ECAP process parameters to establish a one on one relationship between powder characteristics, ECAP process parameters and the mechanical properties of the green compacts. Six different titanium powders were used in this study to determine major powder characteristics such as particle size distribution, morphology, density, flowability and chemical composition. The powder was compacted using ECAP technique to produce billets which are also called green compacts. The green compacts were produced based on selective ECAP parameters which were considered effective. Thereafter the green compacts were analysed to check any improvement on mechanical and physical properties. The particle size distribution test results obtained agreed with the supplier’s particle sizes. Four of the powder’s compositions were found to be cohesive, the other two powders, one was freeflowing, the other one flowability could not be measured, due to large particle size distribution. The test results revealed that the morphology for all the powders was irregular with some powders showing angularity, others were dendritic. The tests revealed that the interstitial elements were within the required limits for all the compositions. After the ECAP process, it was found that particle size distribution alone has some effect on the mechanical properties of components. But the morphology, density, flowability and chemical composition, have major effect on mechanical properties of ECAP samples. The relative density was measured after ECAP process, the free-flowing and cohesive powders yielded a relative density of 90% and above, after ECAP first and second pass. The microhardness of the new ECAP billets was found to match that of steels and wrought iron. It was found that application of temperature, backpressure and great number of passes improved the mechanical and physical properties of the billets.
Identification and analysis of steam temperature maldistribution in superheater tubes via measured and derived parameters
(Vaal University of Technology, 2019-08) Vilakazi, Lethukuthula Nokwazi; Rousseau, Pieter, Prof.; Alugongo, Alfayo, Prof.
Superheater and reheater heat exchangers in power plant boilers can experience temperature excursions and gradients significantly above design values due to cyclic operations. This may result in accelerated life consumption of these components. To understand better the influence of different operating conditions, research is ongoing to develop detailed thermo-fluid process models of the various boiler heat exchangers, and real-plant data are required in the validation of these models. In this study, the final superheater of a 620 MW coal-fired power plant unit was analysed based on real plant measurements taken during steady state operation at 100, 80 and 65 percent of the current boiler capacity. Process parameters routinely measured via the plant distributed control system (DCS), such as the steam temperatures, pressures and mass flow rates, were used as input data to derive other unmeasured parameters using the mass and energy balance (MEB) methodology. Thermocouples were installed previously on the inlet and outlet final superheater stub boxes as well as the outlet manifolds. Thermocouple data were collected from a data logger at the corresponding dates and times of the DCS MEB inputs. Measurement uncertainties were determined by considering instrument and statistical uncertainties, which were then propagated through the MEB calculation to the derived parameters. The MEB methodology was applied to determine the flue gas temperature and flow rates at different operating loads (65, 80 and 100 percent). The good comparison obtained between the values calculated with the MEB and those of the C-schedule for the 100 percent boiler maximum continuous rating (BMCR) provided confidence in the validity of the MEB. The MEB was also compared to real plant data of flue gas temperature. The comparison provided a difference that is less than 26℃. Identification of the measurement uncertainties provided a detailed analysis on each instrument and or measurement and how certain I could be about each measurement. Uncertainties of parameters derived using the MEB methodology were determined. This was achieved by uncertainty propagation through the MEB model. Uncertainty propagation also provided a sensitivity percentage relative to the propagated uncertainties. The extent of temperature maldistribution was determined based on the measured outside tube metal temperatures. The results from the thermocouple measurements on the steam pipes connected to the final super heater inlet and outlet manifold headers show that there is temperature maldistribution between the inlet headers of the four legs. There is also significant maldistribution at the outlet headers resulting in noticeable local temperature gradients. It can also be concluded that the low load of 65 percent resulted in the highest temperature maldistribution compared to the higher loads, of 100 and 80 percent. Super heater tube metal temperatures are exposed to high temperatures at low loads which may lead to tube leaks.
Mechanical and crystallisation properties of polyetheretherketone polymer from dry solid lubricants
(Vaal University of Technology, 2023-06) Ladipo, Taiwo Lolade; Nziu, P. K., Dr.; Masu, L. M., Prof.
Polyetheretherketone (PEEK) polymer suffers high viscosity during fused filament fabrication (FFF). Adding solid lubricants as fillers to PEEK should reduce its viscosity. However, very little research has been conducted on the tribological properties of PEEK printed using FFF. This study dealt with filament-making, tensile properties, crystallinity, and tribological characterisation of FFF-printed PEEK impregnated with dry solid lubricants. PEEK, graphite, and Molybdenum disulphide (MoS2) were sourced, tested, and analysed. Three active functional groups were found in the PEEK: oxy, phenyl, and carbonyl. While the MoS and graphite powder indicated sulfide and Carbon functional groups. The PEEK and both lubricants had an average particle diameter of 100 microns. Three weight ratios of each solid lubricant were mechanically blended into PEEK powder. Seven samples were prepared using a tabletop extruder. Each filament was 3D printed into 35 dog bones and seven discs for ultimate tensile testing, X-ray diffraction analysis (XRD), and disc on-pin testing. The diagrammatic Hermans-Weidinger approach with XRD analysis was used to evaluate the degree of crystallinity. It was established that the MoS2-filled PEEK is better than the graphite-filled PEEK. MoS2-filled PEEK reinforces as the weight content of MoS2 increases up to 104 MPa at 10 wt%. This reinforcement suggests perfect adhesion between PEEK and MoS2. On the other hand, the graphite-filled PEEK decreased in tensile strength to 36 MPa due to agglomeration at 10 wt% filling of graphite. No existing planar peaks were destroyed by introducing MoS2 and graphite, but a new peak was formed per solid lubricants and intensified on the increase of the solid lubricants. Generally, the MoS2-filled PEEK has the best-recorded crystallinity level at about 70% for 5 wt.% while the lowest recorded value was 3 wt.% of graphite valued at 31%. The tribological observation showed that the average response time for pure 3D-printed PEEK is about 950 seconds, indicating that FFF-printed PEEK has a weak capacity to minimise friction independently. Impregnating PEEK with MoS2 and Graphite decreases the response time by about 73%. However, the coefficient of friction of graphite-filled PEEK was initially reduced but started increasing after 5 wt.% due to agglomeration. The MoS2-filled PEEK has a minimum of 30 % decrease in the wear rate, while the graphite-filled PEEK initially decreases to 9% but later spikes to about 6% due to agglomeration. The agglomeration of Graphite in PEEK at a high weight fraction makes graphite a non-perfect choice for FFF compared to MoS2.
Characterisation and flowability of titanium grade 5 alloy powders
(Vaal University of Technology, 2013-09) Nziu, P. K.; Mendonidis, P., Prof.; Labuschagne, D., Dr.; Masu, L. M., Prof.
Flowability is one of the essential physical characteristics considered during the use of any powder in a manufacturing process. However, very little research on flowability of titanium powder has been conducted. To this end, this study dealt with global market survey of titanium powder manufacturers and suppliers. In addition, the effects of various physical parameters such particle size, shape, chemical analysis, density and soundness on flowability of titanium grade 5 alloys powder in additive manufacturing application were investigated. Twelve powder samples of titanium alloy grade 5 (Ti6Al4V) were sourced, tested and analyzed using various methods. The choice of the characterization method used depended on its accuracy, equipment availability and application. Particle size and shape were characterized using laser diffraction and scanning electron microscope techniques, respectively. Quantitative and crystallographic analyses were done to determine the chemical composition as well as alpha and beta phases. Shear cell and dynamic tests were performed to determine bulk density, stability, flow energy and flowability where as particle density was performed by a pcynometer. Research on potential manufacturers was conducted using questionnaires. It was established that high cost of titanium powder is partly driven by titanium powder firms that are not willing to disclose information about the product. It was observed that powder flowability is affected by particle size, shape, chemical composition, density and soundness. The particle density was found to be a function of chemical composition that is the alloying elements and impurities present in the powder. It was noted that bulk density, porosity, cohesion and agglomeration were affected by particle size. Soundness of the powder was also found to improve with sphericity of the particles. Among the physical parameters studied, particle size had the highest effect on powder flowability. The highest flowability was noted at particle size of 41 μm.
An investigation of the damping response and structural strength of a fibreglass and rubber particle composite sleeper
(Vaal University of Technology, 2022-09-12) Mbatha, Abednigo Jabu; Maube, O., Dr.; Nkomo, N. Z., Dr.; Alugongo, Prof.
A railway sleeper is a supporting and dampening beam placed underneath the railway track and can be made of different materials. There are four main types of railroad sleeper materials: timber or wooden, steel, concrete and composite material. The railway structural material often suffers from aggressive loading and vibration in the locomotive industry, and the sleepers' current durability and their vibration properties are not sufficiently resilient to vibration. There is a need for a structural material that can withstand significantly higher static and dynamic loads as trains become heavier and faster. Tyre disposal is a global challenge to the environment, with approximately 1.5 billion tyre waste generated annually. Tyres are non-biodegradable, making their disposal extremely difficult.This study seeks to find a way to recycle the waste tyres in an environmentally friendly manner in accordance with Sustainable Development Goal 11, which focuses on sustainable cities and communities. The study aimed to optimize a hybrid composite sleeper using waste tyres ground into particles, fibreglass reinforcement and polyester resin to enhance the composites' structural strength while increasing the composite sleeper's damping. The specific objectictives were to characterized rubber particles of waste tyres and fabricate a composite railroad sleeper material using waste rubber particles, glass fibre, and polyester resin..Thereafter , evaluate the mechanical properties of the composite sleeper under loading conditions and damped vibration properties .Lastly , determine the optimal composite sleeper . The rubber particles were characterized through sieving, moisture analysis and SEM. Thereafter, the composite was fabricated following the full experimental design. After that composite was fabricated using the hand lay-up method where the rubber volume fraction of 5, 10, 15 and 20% were varied, and fibreglass volume fractions of 5, 6, 7 and 8 % were obtained. The UTM (universal testing machine) was used to carry out mechanical tests, which included tensile strength, compression strength and flexural strength. Then Leeb hardness was carried out, and the damping properties of composites were determined using a shaker table. Minitab software was used for the optimisation of the composite mix The ANOVA test showed the model's accuracy in predicting tensile strength, compression strength, flexural strength, and vibrational damping, as shown by R2 values of 60.69%, 86.60%, 60.05% and 81.41 %, respectively. However, the model was not reliable for hardness which had an R2 value of 37.87%. The optimisation model indicated that rubber particles of size 150 μm with 7.48% volume fraction of rubber particles and fibreglass volume fraction of 8% are optimum. The corresponding mechanical properties responses for the optimum are tensile strength of 13.3851 MPa, the compression strength of 36.0272 MPa, the flexural strength of 36.5865 MPa and Leeb hardness of 647.7510. The damping properties of composite gave a value of 0.1416. Thereafter, optimum results were validated experimentally, and the model was shown to represent the data accurately. The fabricated composite could help to absorb aggressive forces caused by heavily loaded trains. At the same time, maintain the composite's mechanical strength and eliminate pollution caused by tyres in our environment. Further investigation is required into the impact of using a variety of rubber particle sizes 75 m on the vibrational damping and mechanical characteristics of the composite railway sleeper. Studying the impacts of various synthetic and natural rubber kinds on composite characteristics is also necessary.
Formulation of nanocellulosic fibres and particle fillers and their mono and hybrid reinforced polymer composites
(Vaal University of Technology, 2022-03) Webo, Wilson Wachuli; Nziu, P. K., Dr.; Masu, L. M., Prof.
This study aimed to focus on the state of knowledge and practice on natural fibres, extract cellulose, and subsequent formation of nanocellulosic fibres and particles from selected natural fibres. Moreover, both mono and hybrid composites were fabricated and modeled using ABAQUS software. After that, the formulation of the optimal mix ratio of both the fibres and the matrix for different mechanical applications was determined using the Minitab software version 2017. Sisal and rice husk were selected for this purpose due to their ease of availability. An experimental solution was used to extract cellulose, and, subsequently, nanofibres and nanoparticles were formed. These were then used to fabricate composites. The possibility of using new processing technology for modeling both sisal and rice husk nanocomposites in their mono and hybrid forms through the use of Finite Element Analysis (FEA) is a novel idea that has been explored in this study. Finite Element Analysis (FEA) using ABAQUS/CAE software version 2018 was used to develop novel models of mono and hybrid nanocomposites and to determine their mechanical properties of strength and stiffness. The finite element analysis method incorporates the effects of nonlinearities which are very common in composite fabrication. Furthermore, this study sought to formulate the optimal combination mix ratio of fibres and matrix for different mechanical applications using the Minitab software version 2017. A total of 198 finite element part models were created and analyzed. The Finite Element Analysis (FEA) models developed predicted correctly the flexural and tensile properties of the nanocellulosic composites that had been modelled. The experimental method was used to validate the FEA results. Moreover, analysis of variance (ANOVA) was performed for each property of the mono and hybrid composites in this study. The tensile and flexural properties of the mono and hybrid composites were found to gradually increase with an increase in fibre volume fraction up to a certain optimum point, beyond which they gradually began to reduce with more fibre additions. The analysis of variance of properties indicated that, for all the tensile and flexural properties under study, the F statistic > F critical, and the P-value < 0.05, implying that the tests were significant and there was a difference between the means of the groups. In the thermal analyses, the Thermogravimetric Analysis(TGA) graph exhibited three distinct sections: An initial flat section, then a section with a constant slope and finally a flat section. In the Dynamic Scanning Calorimetry (DSC) graphs, all the samples exhibited a glass transition temperature of between 50ºC and 75ºC. Furthermore, all the samples exhibited a melting temperature of between 350ºC and 400ºC. Overall, the hybrid nanocomposites had better tensile, flexural and thermal properties than the mono composites. Regarding the formulation of the optimal combination mix of the fibres and the matrix for use in different mechanical applications, this study established that: a ratio of fibres to a matrix of 4:1 is suitable for mechanical applications where all the flexural and tensile properties of the mono and hybrid composites are maximized. For applications that require the flexural properties of mono and hybrid nanocellulosic composites to be maximized, while the tensile properties of the mono and hybrid nanocellulosic composites are minimized, the ratio was found to be 1:2. A similar ratio was found to be suitable for applications that require the tensile properties of mono and hybrid nanocellulosic composites to be maximized while the flexural properties are minimized. For applications that required a target of 10 MPa for the tensile and flexural strength of mono and hybrid nanocellulosic composites and 10 GPa for the tensile and flexural stiffness of mono and hybrid nanocellulosic composites, this ratio was found to be 2:3.
Optimal geometric configuration of a cross bore in thick compound cylinders
(Vaal University of Technology, 2021-09) Kiplagat, N.; Nziu, P. K., Dr.; Masu, L. M., Prof.
The purpose of this research was to develop optimal numerical solutions that can be employed during the design of cross bored thick-walled compound cylinders. The geometric design parameters of a cross bored compound cylinder that were optimized include shrinkage pressure, cross bore size, shape, location, and obliquity. Finite Element Analysis (FEA) modeling software called Abaqus version 2019 was used to generate numerical solutions. A total of 48 different part models were created and analyzed in this work. The generated FEA results from these models were validated using analytical solutions developed from Lame’s theory. The effects of shrinkage pressure on hoop stresses and Stress Concentration Factor (SCF) were studied to determine the optimal conditions. The optimum shrinkage pressure obtained was henceforth used for further analysis in this work. In addition, using one factor at time optimization technique, an optimization process was carried out to determine the optimal combination of the cross bore configuration geometry that gives minimum SCF. These parameters of cross bore configuration geometry include different sizes of either circular or elliptical-shaped cross bore, positioned at radial, offset, and/or inclined. The analyses of the effects of shrinkage pressure ranging from 4.4733 to 223.662 MPa on 11 different part models, established that the shrinkage pressure of 89.464 MPa generated the minimum SCF magnitude of 3.02. After analyzing 8 different circular cross bore size ratios ranging from 0.1 to 0.8, at the radial position, it was established that the hoop stress increases with an increase in a cross bore size. The smallest cross bore size ratio of 0.1 gave the lowest hoop stress and minimum SCF of 3.02. Whereas the highest stress was developed at the cross-size ratio of 0.8 with an SCF magnitude of 6.75. The minimum magnitude of SCF translates to a reduction of the pressure carrying capacity of the compound cylinder by 67% than a similar plain compound cylinder. Generally, offsetting of the circularly shaped cross bore from the radial position, led to a reduction of the magnitude of SCFs. For instance, from the 8 offset positions analyzed, the minimum SCF occurred at the offset position of 0.006 m with a magnitude of 2.50. This SCF magnitude indicated a reduction of pressure carrying capacity of 60% in comparison to a similar plain compound cylinder. Evaluation of 12 different diameter ratios of elliptical-shaped cross bore ranging from 0.5 to 10, at the radial position, established the lowest SCF magnitude of 1.33 that occurred at a diameter ratio of 5. Henceforth, this optimum diameter ratio was used for further analysis. This aforesaid SCF magnitude translated to a reduction of the pressure carrying capacity of the compound cylinder by 24.81% when compared to a similar plain compound cylinder. Besides, offsetting of elliptically shaped cross bore generally decreased the magnitudes of SCFs. Therefore, for elliptically shaped cross bore, the lowest SCF occurred at radial position with magnitude of 1.33. A general comparison between the effects of circular and elliptical cross bore, established that the elliptical-shaped cross bores generated both lower hoop stresses and SCFs than those of circularly shaped cross bores. On the other hand, oblique elliptical offset cross bores along the Z-axis of the compound cylinder led to an increase in SCFs. As the oblique angle increased from 0 0 to 75 0, the SCFs also increased progressively, however, there was a significant increase in SCF when the inclination angle increased from 60 0 to 75 0. The lowest and highest SCF magnitude was 1.52 and 1.92 at 15 0 and 6.19 at 75 0, respectively. Overall, the optimum geometric configuration of a cross bore in a thick compound cylinder was found to be elliptically shaped, offset at radial position which is an obliquity angle of 0 0 having a diameter ratio a/b of 5.
Quasi-static mechanical properties of treated and untreated sisal fibre reinforced epoxy resin composites
(Vaal University of Technology, 2017-12-15) Webo, Wilson Wachuli; Maringa, Maina, Prof.; Masu, L. M., Prof.
Sisal is a vegetable fibre extracted from the leaves of Agave Sisalana. The fibre is long, bold and creamy white in colour besides being exceptionally strong. It can be used for making agricultural and parcelling twines of various kinds as well as ropes, sacks, carpet and upholstery. The primary purpose of this research was to study and evaluate the use of sisal as a reinforcing fibre in both treated and untreated forms with epoxy resin matrices. The casting process employed during the composite production was the the vacuum infusion. The effects of both the treated sisal fibre-epoxy resin composites and the untreated sisal fibre-epoxy resin composites on the tensile strength and stiffness, flexural strength and stiffness, impact toughness, shear strength, compression strength and hardness were evaluated. Finally, the occurrence of transverse matrix fracture and fibre pull-out were also studied. It was found that the quasi-static mechanical properties of both the treated sisal fibre-epoxy resin composites and the untreated sisal fibre-epoxy resin composites improved with increases in reinforcement weight fractions. Further, fibre surface treatment on the sisal fibres and the attendant increase in the interfacial bond also resulted into improved quasi-static mechanical properties of the treated sisal fibre-epoxy resin composites when compared to untreated sisal fibre-epoxy resin composites.
Controllability and stability of selectively wettable nanostructured membrane for oil/water separation
(Vaal University of Technology, 2019-12) Sob, Peter Baonhe; Alugongo, A. A., Prof.; Tengen, T. B., Prof.
Presently, the current membrane technologies used in oil/water separation are inefficient with poor controllability and stability during oil/water separation. The has led to the current problem of membrane fouling and degradation during oil/water separation. Several approaches have been used to modify or design a better wettable surface with limited success since the current problem of membrane fouling is persisting. It is, therefore, necessary for scientists, engineers, and researchers to come up with a new membrane technology that will be more efficient with stable wettability and controllability during oil/water separation. Membranes are made up of nanoparticles on their surface, which are both random in nature. Furthermore, the collection of membrane particles to form mesh membranes are made of pores with further ransom spatial distribution. Thus, it was necessary to use the tools of stochastic processes to theoretically characterize these parameters. These parameters affect both internal and external factors as well as characteristics of random membrane particle and pores on wettability like surface tension and surface energy were established in the current project. Design and production of the membrane material according to established relationships was by both low and high-pressure spay jet coating in a controlled laboratory environment, and microscopic characterization performed using SEM. TEM, EDS, statistical analysis, and Image J particle analyzer. The spread, orientation, morphology, spatial distribution, inter-separation distances, surface roughness, surface smoothness, contact angles, surface density of the particle, mean size of the coated nanoparticle on the membrane surface after different coating rounds were analyzed so as to establish conditions for optimal wettability. The testing of produced membranes under the application of external and internal factors was done. A centrifugal pump was used to pump contaminated oil and water mixture through the membrane under a steady flow rate of 10 L/s with a gauge pressure of 180 kPa at room temperature conditions. The membrane materials from different coating rounds were tested for their abilities to produce pure collected water or oil particles in the collected water. The separated water was analyzed using oil and grease analysis US EPA method 1664B with the SPE-DEX 1000 oil and grease system. As revealed theoretically and validated experimentally, it was found that the random natures of nanoparticle size, the spatial distribution of membrane channels, and their morphology have impacts on surface energy-driven separability of oil and water mixture. It was also observed that the scattering of nanoparticles on the membrane surface during coating lowered surface energy, which enhanced oil/water separation. It was also revealed that there is an optimal nanoparticle size, scattering, morphology, and spatial distribution of membrane channels that offer better separation of water from oil. From the microscopy analysis, different microstructures were revealed for glass, ceramics, and sediment during LP and HP coating. The microstructure characterization showed different surface densities of nanoparticles, mean particle sizes, surface roughness or smoothness, and nanoparticles inter-separation distances. It was also revealed that the materials, which were more stable and efficient with more controlled wettability were glass, sediment, and ceramic HP 3rd rounds of coating. Clusters were observed on the membrane surface during HP and LP coating rounds with more clusters observed in LP coating when compared with HP coating. These clusters increased surface energy, which negatively affected oil/water separation. It was concluded that to improved the wettability surface. membrane clusters must be minimized during coating rounds. This thesis contributed new knowledge to existing body knowledge of membrane technology used in oil/water separation in a number of ways by: (1) Designing a new membrane surface with a more controlled, efficient, and stable wettability process during oil/water separation. (2) Applying the logic of surface energy-driven separability, which has not been previously used extensively to study membrane wettability. (3) Establishing a model for the optimal membrane pore sizes that offer optimal membrane wettability during oil/water separation. (4) Establishing a model for optimal nanoparticle coating that offers optimal membrane wettability during oil /water separation. (5) A great attempt was made in characterizing nanoparticle surface densities, spread, particle coating, and nanoparticles intensity on a wettable membrane surface.
Optimisation of maintenance strategies employed on the critical electromechanical equipment in Sasol Synfuels Catalyst Preparation unit
(Vaal University of Technology, 2021-11) Maphosa, Pretty Phumla; Nziu, P. K., Dr.; Masu, L. M., Prof.
The subject of maintenance optimisation is not new, and many researchers have explored it. However, it is seen that one optimisation solution cannot be used in all industries. Each industry and equipment thereof are unique as the product streams differ, layouts and operation variables, to name a few. Though Turn-around management is the most used strategy in petrochemical industries. Equipment downtime remains the biggest challenge thus, the purpose of the study was to optimise the maintenance practices used on the critical electromechanical equipment in Sasol Synfuels Catalyst Preparation using both the Analytical Network and Analytical Hierarchy multi-decision approach. Data was collected from the SAP system database, of which the breakdown work orders was obtained from the period of January 2016 to June 2021. The data was collected for each 13 electromechanical equipment identified in the catalyst preparation unit. The applied maintenance strategies employed on the electromechanical equipment in the catalyst preparation unit was also analysed using the Meridium maintenance strategy software tool utilised in Sasol Synfuels. An analysis and identification of the critical equipment within the unit were obtained with the use of two different methods, namely the JADERI, (2019) and AFEFY, (2010) approaches. A theoretical distribution was drawn after that in order to assess the effectiveness of the current maintenance strategy compared to the identified key performance indicators. The theoretical distribution analysis was used to determine the plant utilisation, availability, and maintenance cost. The analytical network and hierarchy process application, and the super decision network model framework, were analysed to obtain the maintenance optimisation solution. Though the ANP and AHP approaches have different problem identification frameworks and cluster dependencies, it is seen that both methods portray more or less similar results. Both methods indicate that in order to achieve an optimised maintenance strategy within the catalyst preparation unit, condition-based maintenance strategy is the most weighed alternative node with 50% for optimal maintenance solution. The least most weighed alternative node is corrective maintenance, weighed at 7%. This is true as corrective maintenance is applied once a breakdown has occurred, of which the aim is to avoid unforeseen breakdowns. Fixed time maintenance is the second most weighed maintenance strategy with 30%, followed then by the operate to failure strategy at 13%. Considering that the operation to failure maintenance strategy is applied based on the consequence of failure and maintenance cost as well as mean time to repair, this is then concluded as practical as RCM priorities predictive and preventative strategies to be employed. It was drawn, for criteria nodes, that the ANP approach resulted in the environmental safety impact as the most important criteria to consider when applying the optimal maintenance strategy in the Sasol Synfuels Catalyst preparation unit. The environmental safety impact was rated at 0.33, followed by availability with a factor of 0.32. The least weighed criteria nodes are then the maintenance cost and MTTR, both with a factor of 0.17. This proves to true considering that the petrochemical industry is considered a high-risk industry as it processes and produces hazardous chemicals The AHP approach structure however, does not consider interdependencies through the criteria and alternative clusters thus the alternative weight could not be defined. The results obtained prove that the ANP approach is the most practical mutli criteria decision making method for maintenance optimisation compared to the AHP approach.
Optimization of a waste polyethylene terephthalate/fly ash hybrid concrete composite in slabs
(Vaal University of Technology, 2022-08) Nkomo, Nkosilathi Zinti; Nziu, P. K., Dr.; Masu, L. M., Prof.
Cracked concrete slabs are a problem due to several factors such as poor maintenance, insufficient reinforcement or steel corrosion leading to crack propagation. There is a need to increase the load-bearing capacity of concrete slabs and increase their life span. The use of waste Polyethylene Terephthalate (PET) fibres and fly ash in a hybrid composite slab dramatically alleviates the problem of crack propagation and failure sustainably. This study aimed to optimize a waste PET fibre/fly ash hybrid cement composite for use in slabs. This study characterized the raw materials used, including fly ash and aggregates. After that, concrete test specimens were fabricated using the PET fibres and fly ash following the full factorial experimental design. The developed specimens were then tested to ascertain their material strength properties. Model development was carried out using Minitab Software Version 14, and subsequent experimental validation was carried out. After that, the PET and fly ash optimisation for maximum favourable response outcome was carried out. The fly ash was found to belong to the Class F category with particle size ranging from 0.31 μm to 800 μm. The fly ash was mainly spherical and consisted of Ca, Al, P, Si, and trace amounts of Ti and Mg. The spherical shape of the fly ash helped improve the concrete's workability. The river sand had a fineness modulus of 3.69, considered coarse sand. The fine aggregate showed uniform particle size distribution with a uniformity coefficient of 4.007. The coarse aggregate characterisation was carried out and revealed that the aggregate particle size was 13 mm in size. The coarse aggregate had a uniformity coefficient of 4.007, which implied the aggregate was well graded. The coarse aggregate had a high flakiness index of 74.82 % and an acceptable elongation index of 46.72 %. Full factorial methodology experimental design was employed to fabricate the test specimens by simultaneously varying the independent factors to develop a model for overall response variation. The slump value was observed to increase with the addition of fly ash. However, the addition of PET fibre decreased the slump value with incremental amounts of fibre. The combined effect of fibre addition and fly ash showed a general decreasing slump value for all quantities of fly ash content. The compressive strength of PET fibre only composite had maximum strength at 0.5% fibre addition, and the composite with fly ash alone had the maximum compressive strength at 15%. The combined optimum compressive strength for fibre and fly ash was at 0.5 % and 15 %, respectively, with a 15.54 N/mm2. The split tensile strength decreased with an increase in fibre content. However, the fibre provided crack retardation. Fly ash increased the split tensile strength significantly to a peak of 2.35 N/mm2 for 20 % fly ash addition. The combined addition of fibre and fly ash had an optimum split tensile strength of 2.79 N/mm2 at 0.5 % fibre and 20 % fly ash. The addition of fibre had an optimum split tensile strength at 0.5% of 1.82 N/mm2. The fly ash increased the flexural strength, with optimum strength at 15 %. The combined addition of fibre and fly ash created optimum flexural strength at 0.5% and 30 %, respectively. The trend observed by the rebound number followed that of the compressive strength. However, the non-destructive rebound hammer method gave significantly lower strength values than the destructive test method. The addition of fly ash had the effect of lowering the cost of producing the slab. However, the addition of fibres marginally increased the cost. The combined effect of fibre and fly ash resulted in a significant cost saving. Numerical optimisation was carried out concerning the fibre reinforced concrete's fresh and hardened mechanical properties. Predictive modified quadratic equations were developed for slump value, compressive, flexural, split tensile strength and total cost. Analysis of variance test carried out for all the responses indicated that the model could predict the slump value and mechanical properties of the fibre reinforced concrete correctly and effectively with a coefficient of determination in the range of 0.4151 to 0.9467. The developed model can predict the required fibre reinforced fresh and hardened properties in order to assist in decision making in construction in slabs. The optimum constituent combination for maximum mechanical strength at the lowest possible cost was found to be 15.7576 % Fly ash and 0.3232 % PET fibre with optimum responses as shown in Table 4-26. These predictions were validated experimentally, and a good correlation was observed between the actual and predicted values based on the observed standard deviations of 0.1335, 0.031, 0.005, 0.676, 0.02 for compressive strength, flexural strength, tensile strength, slump value and cost, respectively. Concrete slabs were optimised for various possible end uses, and the optimum PET fibre % and fly ash % were ascertained as shown in Table 4-27.
Development of a conducting multiphase polymer composite for fuel cell bipolar plate
(Vaal University of Technology, 2020-06) Alo, Oluwaseun Ayotunde; Pienaar, H. C. vZ., Prof.; Alugongo, A., Prof.; Otunniyi, I. O., Prof.
On account of their lightweight, low-cost, corrosion resistance, and good formability, conductive polymer composites (CPCs) are promising for the production bipolar plate (BP) for polymer electrolyte membrane fuel cell (PEMFC). However, a high conductive filler loading is needed to impart the required level of electrical conductivity to the insulating polymer matrix and as a consequence, the toughness of the plate deteriorates considerably. By using immiscible blend of polymers that have complementary hardness and ductility as matrix, with conducting multi-fillers of different morphologies, it is possible to optimize the matrix strength characteristics and favour the formation of conducting network to produce CPC meeting BP performance standards. Of course, a lot will depend on the formulation of the most favourable composition and production variables. In this regard, polypropylene-epoxy and polyethylene-epoxy blends, filled with zero- and two-dimensional carbon forms – graphite, carbon black (CB), and graphene (Gr) – were investigated over an extensive range of compositions and compression moulding pressures, in this study. Several compounding runs (using melt mixing), at different stages, followed by compression molding, were done. The goal is to obtain combination of composite formulation and processing conditions that will produce the most promising combination of properties for BP application. In the first stage of the investigations, by using thermogravimetric analysis, two-stage decomposition behavior of PP-epoxy and PE-epoxy blends was revealed, which confirms the immiscibility of PP and PE with epoxy resin. Scanning electron microscope (SEM) micrographs of the PP-epoxy and PE-epoxy blends revealed a co-continuous structure, which can be attributed to the close-to-symmetric composition of the blend and compatibilizers added. Preferential localization of synthetic graphite (SG), CB, and Gr in the polymer blends was also revealed by the SEM micrographs. This confirms the fact that CPCs based on PP-epoxy and PE-epoxy blends can be explored further. PP-epoxy and PE-epoxy blends filled with only SG, 30 – 80 wt %, were produced and characterized for their electrical conductivity and flexural properties. In-plane electrical conductivity ranged from 12.09 to 68.03 Scm-1 for PP-epoxy/SG and 11.68 to 72.96 Scm-1 for PE-epoxy/SG composites produced. These are higher than values reported for several single matrix polymer composites at similar filler loadings. With reference to the United States Department of Energy performance targets for BPs, PE-epoxy/SG composites performed better in terms of electrical conductivity, while PP-epoxy/SG composites exhibited better flexural properties. Thereafter, using SG and CB double filler, PE-epoxy/SG/CB composites performed better than PP-epoxy/SG/CB composites in terms of electrical conductivity, while PP-epoxy/SG/CB composites exhibited superior flexural properties than the PE-epoxy/SG/CB composites at similar filler loadings. However, with respect to the DOE targets, composites based on PP-epoxy blend exhibited a more promising combination of electrical conductivity and flexural properties than PE-epoxy blend matrix. PP-epoxy filled with SG/CB was studied further, by using graphene (Gr) as second minor filler. In-plane and through plane electrical conductivities as well as thermal conductivity and thermal diffusivity of the PP-epoxy/SG/CB/Gr composites increased as total filler content was increased from 65 to 85 wt%. It implies that more conductive networks between filler particles were formed. Also, flexural strength, flexural modulus, and impact strength decreased as the total filler content increased from 65 to 85 wt%. The reduced flexural properties could be due to increased agglomeration of CB and Gr, and poor filler wetting at higher filler loadings and low matrix material, which leads to the formation of microvoids and a reduction of the load bearing capacity of composites. With respect to the DOE targets, PP-EP/SG/CB/Gr composite with 80 wt% (i.e., PP/EP/73G/6.2CB/0.8Gr) filler has the best combination of properties. Further improvement in properties of the PP-EP/SG/CB/Gr composite with 80 wt% filler was achieved by molding at higher pressures. As molding pressure was increased from 4.35 to 13.05 MPa, in-plane electrical conductivity increased from 116.31 to 144.99 Scm-1, while flexural strength increased from 29.62 to 42.57 MPa, satisfying the performance requirement targets for bipolar plates.
Optimal strength of carbon fibre overwrapped composite high-pressure vessels
(Vaal University of Technology, 2021-12-08) Numbi, M. N.; Nziu, P. K., Dr.; Masu, L. M., Prof.
The purpose of this study was to design a composite overwrapped pressure vessel by combining the best optimal structural options. This study investigated the effects of constituents such as fibre and shell thickness, on the bursting strength. Thereafter, these constituents were combined in order to achieve optimization of strength for an improved sustainable composite pressure vessel. The analytical method was carried out using the Tsai-wu failure theorem. The developed analytical equations were solved with Matlab 2016 software to determine composite fibre and shell thickness. With variation of the vessel’s liner, a total of 56 parts were created on two different profiles with purpose of generating of vessels resistant to bursting failure. Henceforth, the structural integrity of fibre imparted into the design was optimally analyzed at an angle of 55⁰, through the negative and positive directions. The shell thickness overwrapping the liner, being as well an influential factor to this optimization, was, therefore, analyzed on symmetrical and asymmetrical lamination patterns. The optimal fibre and shell thickness range were thereafter determined on a first ply failure and hoop stress threshold approach. Additionally, the identified optimal range of pressure vessel constituents were numerically validated, on Abaqus/CAE software, to have a degree of reassurance on the result generated, using Hashin failure criteria. Optimal design with improved strength and weight factor was therefore achieved by combining the generated optimal vessel constituents yielded from Minitab software version 2016. The generated results of the study revealed no change on the fibre thickness determined with respect to direction. For shell thickness on the other hand, asymmetrical pattern was identified as the desired sequence of lamination. In addition, with two profiles considered in the research, the composite constituents were found for a p value of 0.066, to be optimal on profile 1 at 0.0048 mm of liner, 0.0005 mm of fibre and 0.0027 mm of shell. The profile 2 on the other hand, revealed optimization of liner at 0.0095 mm, fibre at 0.0021 mm and shell at 0.0055 mm. Through combination of these ultimate constituents the response optimizer on Minitab software generated optimal bursting strength with factor of 4% improvement with a weight reduction of 33% compared to the stainless steel vessel. It was, therefore, concluded that profile 1 was the most optimal with hoop strength of 123.43 MPa, Von Mises of 178.56 MPa and Tresca of 179.48 MPa.
Modification of ceramic membrane surface by nanoparticle coating for improved wettability during oil-water separation
(Vaal University of Technology, 2022-03-07) Maome, Tshepo G.; Alugongo, Alfayo A., Prof.; Sob, Peter B., Prof. (Assistant); Tengen, Thomas B., Prof.
The developed oil-water separation membranes used in membrane technology are currently inefficient due to their poor morphological and topographical properties during nanoparticle coating. Researchers have developed different wettable membrane surfaces using jet spray coating. Most of these developed membranes are inadequate due to poor morphological and topographical properties normally observed as clusters, creating a rougher membrane surface that hinders wettability. This has resulted in the existing membrane fouling and degradation during the oil/water separation process and again due to different responses to corrosion and rusting. In the current study, membrane clusters were minimised on the ceramic membranes to create a smoother surface, improving membrane wettability. These clusters were minmised at optimal coating force, optimal coating distance and optimal coating angle. Part one of the study was to model and simulate different parameters that decreased clusters using the jet-spray coating. A theoretical model was derived from the first principles and all the external and internal forces that impact membrane clusters were considered during the model derivation. These forces are the force due to applied pressure from the spray gun, the force of nano-particles, the force of viscosity, the upward force on solid wall due to nanoparticles, the downward force on solid wall due to nanoparticles and the reaction force on the solid wall due to nanoparticles. The tools of stochastic theory and the concept of fluid dynamics were used in the modelling process. The total coating force from the jet spray gun nozzle was increased from 0,2x107 kN to 2,4x107 kN, which gave optimal coating force. The coating distance from the jet spray gun nozzle to the membrane surface was increased from 10 mm to 24 mm, which gave optimal coating distance. The jet spray angle in the spray region was also increased from 1⁰ to 9⁰ with reference from the vertical axis to the membrane surface, which gave optimal coating angle. This lead to optimal spread of nanoparticles on the membrane surface thus resulting to optimal cluster minimisation during the coating process. This decreased cluster sizes during nanoparticle coating, resulting in a smooth membrane surface, thus leading to lowered surface energy on the membrane. Part two of the study was to fabricate the ceramic membrane with fewer clusters on the surface for improved wettability using the jet-spray coating. It was important to produce the ceramic membrane surfaces with minimised membrane clusters by considering the optimal parameters revealed to minimise these membrane clusters during coating. Nanoparticle coating was performed under a controlled laboratory environment, and the optimal parameters that were studied to minimise membrane clusters were revealed. These parameters are coating force, coating distance and coating angle. More coating rounds were applied on ceramic samples and clusters were minimised during these coating rounds. The coated samples were analyzed by a scanning electron microscope and the nanoparticles on the membrane surfaces were characterised for optimal performance during oil-water separation. The scattering, orientation, morphology, spatial distribution, surface roughness, surface smoothness, contact angles, surface density of the particles, pore size network, mean size of the coated nanoparticle on the membrane surface after different coating rounds were characterised and analysed to minimise membrane cluster during nanoparticle coating. It was shown that more clusters were observed in 1st LP, 2nd LP, 3rd LP and 4th LP coating rounds when compared to 1st HP, 2nd HP, 3rd HP and 4th HP coating rounds. It was also shown that material surface roughness increased the formation of clusters in membrane surface as more clusters were observed in rough membrane surface when compared to the smooth membrane surface. The microstructure revealed a smoother membrane surface where membrane clusters were minimised. Part three of the study was to compare the newly designed ceramic membrane with the previously designed ceramic membrane from previous the literature. The correlation was done on the experimental results obtained in this study with the experimental results obtained from the previous literature. Different coating rounds were performed from the current study and the previous literature to design nanostructured ceramic membranes with fewer clusters on the surface. The results in the last coating round in this study, revealed a smooth membrane with a homogeneous substrate with fewer clusters and small sizes compared to other coating rounds.
Topology optimization of a unitary automotive chassis: chassis design through simple structural surfaces and finite element analysis methods
(Vaal University of Technology, 2020-08) Matsimbi, Manuel; Maringa, M., Prof.; Nziu, P. K., Dr.; Masu, L. M., Prof.
The purpose of this study was to develop a design synthesis approach that can be used to reach an optimal design solution (in terms of the strength, stiffness and weight) of automotive body structures during the conceptual stages of the design process. Two conceptual model variants; standard sedan and open-top unitary body structures that were made from the same platform were analysed for their maximum bending moment, stresses, deflections and their maximum load carrying capacity. Topology optimization was also undertaken in order to find a lightweight design of the body structures. The body structures were modelled using three different modelling techniques, namely; the simple beam model, the simple structural surface (SSS) method and the finite element (FE) method. The simple beam model was used to determine the axle reaction forces and the maximum bending moment of a body structure that was subjected to static and dynamic loading conditions. Dynamic load factors and an extra safety factor were used to simulate the dynamic bending loads. The factors were varied from 1.0 to 4.5 with a step of 0.5. It was found that the maximum bending moment under dynamic loading is simply a multiple of the static maximum bending moment and they both occur at a position that is close to the rear part of the front seats. The effects of different geometries on the strength, stiffness and the weight of body structures were studied using the finite element method. The two conceptual models were made into four different plane FE models with each concept having two different FE models. The panels of these models were constructed as simple structural surfaces and were based on the SSS analysis of the standard sedan. The models were subjected to bending and torsion load cases. Each load case was varied similarly for 19 different iterations until the yield point was reached for each FE model. It was also found that the load-displacement graphs were linear for loading within the elastic range, even if there are subassemblies that are missing. However, it was found that this relationship ceases to apply once the body structures are subjected to the torsion loads that are above the yield load. It was also found that the qualitative response to torsion loads was similar for all four body structures. However, the quantitative response was quite observable. It was found that the stiffness can be reduced by at least 37% by omitting subassemblies for the same platform and almost the same mass of the body structure. In addition, the effects of different materials on the strength, stiffness and the weight of body structures were also studied. It was found that lightweight designs can be achieved by using lightweight materials. However, both the bending and torsion stiffness were observed to be reduced or increased in proportion to the Young’s modulus or modulus of elasticity of the material that was used to construct the models. It was also noted that, the stiffness to weight ratio remained almost the same for the same models made from different materials. Topology optimization was undertaken in order to determine alternative load paths of the body structures. The two conceptual models were made into four different solid FE models. It was observed that the load paths remain similar for different volume fraction constraints for similar models under similar loading conditions. It was also noted that at least 20% in weight savings and at least 5% in torsion stiffness improvement can be achieved when topology optimization is used to determine the alternative load paths for a standard sedan model. Besides, the load carrying capacity was found to remain similar. However, the bending stiffness was noted to have reduced due to the reduction in the mass of the structure. In contrast, it was found that for an open-top model, both the bending and torsion stiffnesses were reduced in proportion to the reduction in the mass of the body structure. In addition, it was observed that a further reduction in the mass of the open-top body structure can also significantly reduce its load carrying capacity. Although the stiffness of the optimized open-top model was noted to have reduced due to the reduction in the mass of the structure. The stiffness to weight ratio of the optimized body structure was higher than that of the non-optimal structure.
Optimisation of casting process of sand cast austenitic stainless-steel pump impeller using numerical modelling and additive manufacturing
(Vaal University of Technology, 2018-12) Mugeri, Hudivhamudzimu; Adebiyi, Isaac Damilola, Dr.; Matizamhuka, Wallace R., Dr.
The production of austenitic stainless-steel pump impellers in foundries present a huge challenge mainly due to its thin-walled blades, pouring temperature, presence of junctions and chemical composition. Two different alloys were used namely nodular cast iron and austenitic stainless-steel. Nodular cast iron was used as a comparison alloy due to its excellent flowability whereas austenitic stainless-steel was chosen due to its attractive corrosion and wear resistant properties. Austenitic stainless-steel alloy showed difficulties during casting because of its chemical composition and freezing range. Thin-walled sections are more susceptible to filling defects like misrun and cold-shut. This results in high scrap rate and high processing costs during high production of thin-walled components. High pouring temperature is considered one of the most effective methods to improve filling ability of thin-walled castings. However, there is a major drawback in using this method owing to the high occurrence of shrinkage defects and hot tearing especially at junctions. 1060 aluminium was used as a benchmark to evaluate the effect of wall thickness on the filling and feeding of thin-walled Al components with complex geometry during sand casting. The aim of this dissertation is therefore to optimize casting process of sand cast austenitic stainless-steel pump impeller. Numerical modelling and additive manufacturing were used to optimize the production of this product. The use of casting simulation software combined with three-dimensional (3D) mould printing technology has enabled optimisation of casting parameters to minimise the occurrence of casting defects. Casting parameters of five test samples of complex geometry and varying thicknesses (1.0 mm;1.5 mm;2 mm;2.5 mm and 3.0 mm) were optimised using MAGMAsoft® at a constant pouring temperature of 700 °C and 1060 Aluminium as an alloy. Simulation and casting results showed that complete filling was only possible at a wall thickness of 3 mm. The simulation results showed that as the wall thickness increased from 1 mm to 3 mm the filling ability increased by 67.5 % whereas experimental casting results showed that filling ability increase by 75 %. The combination of MAGMAsoft® simulation and 3D printed moulds proved to be effective tools in predicting filling and feeding of thin-walled aluminium components during sand casting. MAGMAsoft® casting software was used to simulate metal flow and predict the degree of filling at different pouring temperatures. Test samples were cast using 1060 Aluminium alloy at temperatures of 702 °C, 729 °C, 761 °C, 794 °C, 800 °C and 862 °C. Complete mould filling was predicted at 800 °C using the simulation model and 761°C during actual casting. At temperatures above 761°C tearing at the junction was quite pronounced. An optimal of 761°C pouring temperature was found to be appropriate pouring temperature when casting thin-walled aluminum components using sand casting. MAGMAsoft® casting software proved to be an effective tool in optimizing filling and feeding of thin-walled aluminium components during sand casting. Nodular cast iron pump impeller was optimized at 1500 °C using MAGMAsoft® and 3D mould printing technology. Design variables used were feeder radius (17 mm, 18 mm, 19 mm and 20 mm), feeder height (32 mm, 33 mm, 34 mm, 35 mm) and number of feeders of (3, 4 and 5). Simulation and casting results showed a completely-filled casting. The high fluidity of nodular cast iron promotes mould filling ability and prevent any form of misrun defect. Minimum shrinkage was noted at the junctions and top surface of the casting. A new design was proposed to eliminate shrinkage defects at the junctions of the nodular cast iron pump impeller. The design used a tapered circular runner bar with straight ingates. Optimization of nodular cast iron was now done at 1390 °C with the use of MAGMAsoft® and real casting was done 1385 °C. Simulation and casting were in correlation to each other since both showed completely-filled mould cavity with no misrun, cold-shut and shrinkage porosity defect. Simulation proved to be an effective tool in optimizing filling and solidification of nodular cast iron during sand casting. Austenitic stainless-steel pump impeller was optimized at 1500 °C using MAGMAsoft® and 3D mould printing technology. A high quality mould and core print were printed with the use of Voxeljet VX1000 at a minimum period of time. Design variables used were feeder radius (17 mm, 18 mm, 19 mm and 20 mm), feeder height (32 mm, 33 mm, 34 mm, 35 mm) and number of feeders of (3, 4 and 5). An increase in feeder size and the number of feeders greatly reduced hot spot and porosity of the casting but it also reduced the casting yield. The quality of the casting was found to be inversely proportional to the casting yield. Simulation showed a completely-filled casting with actual casting showing only 50 % filling ability. High viscosity of the molten metal and thin walled blades promote quick solidification which caused misrun defects. A new design was proposed to eliminate misrun defects of the first design. MAGMAsoft® was used to optimize this design at 1550 °C. The design used a tapered circular runner bar with tapered ingates. The actual casting showed improved filling ability from 50 % to 80 % while simulation showed completely-filled mould cavity (100 %). Major factors which contributed to low filling ability of austenitic stainless-steel pump impeller were chemistry, runner system and men. Numerical modelling and additive manufacturing did optimize filling and feeding of sand cast austenitic stainless-steel pump impeller.
Rub-impact of coupled vibration of vertical rotor-stator system submerged in incompressible fluid
(Vaal University of Technology, 2020-01-21) Sozinando, Desejo Filipeson; Tchomeni, B. X.; Alugongo, A. A., Pof.
Fault diagnosis of a rotor system operating in a fluid is one of the most difficult aspects of rotating machinery. Fluid in machinery plays a significant role in concealing the allowable rubbing stress limit during the impact generated from the rotor-stator rub which may progressively deteriorate the rotating system. Therefore, a numerical and experimental investigation was performed to analyse the influence of the fluid during the rotor-stator contact of a vertical rotor system partially submerged in an incompressible inviscid fluid with a focus on detecting rubbing fault in the presence of axial load. The theoretical model of lateral-torsional rotor consists of a 3-D rub-impact induced parametric excitation, which was assimilated to operate as elastic vertical rotor system by considering the transient vibration of a flexible axial force and energy of the vertical shaft system. The model was established based on Jeffcott rotor, time-varying stiffness and the rotor-stator fluid interaction. The Lagrangian principle was used to establish the governing equation of motion. The hydrodynamic forces acting on the vertical rotor were established and introduced into the system based on the Laplace form of the linearized Navier–Stokes equations under lateral excitation yielding a highly nonlinear 5-DOF system. To evaluate the dynamic response and ensure the accurate acquisition of rubbing features in a fluid, the classical Fast Fourier Transform (FFT) and the vibration waveform have been discretised and illustrated through the frequency components. Furthermore, for effective extraction of some hidden features of rub, the nonlinear features embedded in the vibration waveform have been discretised and illustrated through to the lateral deformation of the rotor and the orbit patterns of the shaft. Qualitative numerical analysis suitable for highly nonlinear and non-stationary signal Time-Frequency strategies, Wavelet Synchrosqueezed Transform (WSST) and Instantaneous Frequency (IF) technique were employed to successfully extract the frequency of oscillating modes and the periodic frequency response of the faulted rotor system. It is demonstrated that the coupled lateral-torsional vibration of the submerged vertical rotor system has the potential to enhance the much-unwanted hidden frequencies of vibration that leads to significant instability of the rotor system. In particular, the responses revealed the existence of unstable regimes with respect to the lateral-torsional deflection as well as the angular velocity. High harmonic peaks were also identified at the critical speed, which can be considered as a monitoring index to detect the rubbing in rotating shafts in a fluid. It was found that even at relatively slow rotating speed fluid elastic forces induced by the co-rotating flow surrounding the shaft significantly affect the transverse natural modes of vibration of the shaft. Despite the interaction between the fluid and the rotor generates self-excitation of low frequencies, obtained results indicated that the fluid-rotor interaction reduces the dynamic vibration response of the faulted system running below the second critical speed. It has been analytically demonstrated that the time-varying stiffness induced is the principal cause of the frequency-modification feature of the dynamic response of an unbalance-rub rotor system at the contact region. The model investigated in this study has potential application for drill string-borehole shaft system used in the oil industry.

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