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Welcome to the NWU Repository, the open access Institutional Repository of the North-West University (NWU-IR). This is a digital archive that collects, preserves and distributes research material created by members of NWU. The aim of the NWU-IR is to increase the visibility, availability and impact of the research output of the North-West University through Open Access, search engine indexing and harvesting by several initiatives.

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Recent Submissions

Effect of annealing time on residual stress in selective laser melted Co-Cr-Mo components
(North-West University, 2023) Rousseau, Genevieve; Kloppers, CP; Marais, D; Fourie, J
Additive manufacturing (AM) is a three-dimensional (3D) manufacturing technique that allows the user to manufacture designs with complex geometries. Selective Laser Melting (SLM) is an AM technique where a layer-wise process of melting metal powder is used to manufacture 3D objects. A major disadvantage of SLM is the deformation of parts during the print cycle or after the part is removed from the build plate. The thermal inconsistencies inherent in this layer-wise manufacturing process cause residual stress build-up that may exceed the yield stress of the material and lead to print failures. The residual stress in AM parts manufactured with metal powder is similar to the residual stress that builds up in cold-worked metal parts due to the applied stresses stored within the material. The residual stress is stored in the form of dislocations and stress-relief annealing is commonly used to minimize this residual stress. Several studies have investigated the effect of stress-relief annealing on the microstructure, mechanical properties and residual stress in AM components. The research indicates that stress-relief annealing can change the microstructure, improve mechanical properties and reduce residual stress. Limited knowledge is available on the effect stress-relief annealing hold time at maximum temperature has on the residual stress in AM parts. This study aimed to investigate the effect of stress-relief anneal time on the residual stress in Co-Cr-Mo components manufactured with SLM with the use of neutron diffraction techniques and Simufact Additive software. Neutron diffraction is a non-destructive method for determining residual stress in a material. Simufact Additive software is simulation-based software that uses thermo-mechanical simulations to analyse the AM process. Six Co-Cr-Mo samples were manufactured on the ORLAS Creator with SLM and five of the samples were stress-relief annealed using varying time profiles. The annealing times and process parameters were chosen from the literature to provide comparable results. The samples were annealed at 1065oC with annealing times of 15 minutes, 1 hour, 2 hours, and 3 hours. One sample was annealed at 750oC for 1 hour. The results obtained through simulation and neutron diffraction analysis showed good correlation. The samples heat treated to 1065oC showed more residual relief than 750oC indicating that the heat treatment temperature had a significant effect on the degree of residual stress relief. The results related to samples heat treated to 1065oC indicated that shorter annealing times resulted in near- identical residual stress values than longer annealing times. This discovery indicated that residual stress relief occurred in a shorter time frame than anticipated and that heat treatment duration longer than 15 minutes did not result in improved residual stress relief results.
An experimental and modelling approach to develop a winnowing pilot plant for fine dry coal beneficiation
(North-West University, 2023) Morgan, Lee-Roy; Campbell, QP; Le Roux, M
The constant increase in the amount of fine coal being generated through day-to-day mining and processing activities is unavoidable, and thus the technology used to beneficiate fine coal is constantly evolving. Environmental and economic factors such as water shortage, waste management, and processing cost motivate the research in fine coal beneficiation and even more so in dry fine coal beneficiation. One of the more recent developments in dry fine coal beneficiation over the past few years is the use of the winnowing method as a dry beneficiation technique and this method has been proven capable of beneficiating -6 mm coal. The method of winnowing has been successfully implemented in the agricultural and pharmaceutical sectors for many years with several studies showing that the method is a viable option when implemented on the coal sector for dry fine coal beneficiation. Over the past few years several studies have been done on the method, however, there is still very little data available other than lab scale experimental results. Research done on fine coal suggests that winnowing can separate coal particles by size, shape, and density; however, previous studies have shown the system to be size sensitive, and for this reason, a 2-stage separation is needed for the beneficiation of fine coal. The equipment used for the winnowing method has also not been fully developed to suit the needs of the coal mining industry and thus an opportunity exists to design and implement a winnowing machine capable of beneficiating fine coal. This thesis investigates winnowing in general, starting with the method itself and aiming towards designing and ultimately constructing a winnowing plant that can be used to test the method in future studies. The papers presented in this thesis will cover the basics of winnowing but mostly focus on the design of the winnowing equipment which is the aim of this study. Two pieces of equipment were designed with the aid of Computational Fluid Dynamics (CFD) and mathematical models. These prototypes were tested using density tracers and -6 mm coal. The first piece of equipment was a size separation nozzle to aid with the size sensitivity of the method, however initial tests indicated that the nozzle favoured a density separation instead of the intended size separation and further tests are needed to confirmif the nozzle is capable of performing a density separation, or if the nozzle will work as a size separation unit as indicated and by the CFD simulations. The second piece of equipment that was designed was the density separation chamber, capable of separating particles into multiple densities ranging from 1.2 g cm-3 to 2.2 g cm-3. The initial results did indicate that the chamber is size sensitive and that a density separation is possible given the correct size interval. Both units work on negative pressure and initial results show that both machines have the potential to work as a combined 2 stage separation plant. The design of the winnowing plant was successful, and a working pilot plant was constructed. There is still some optimization and testing required to improve the operation of the plant as indicated by the results in the final paper of this thesis, however initial testing looks promising.
Valorization of lignin through selectivedepolymerization to polyols for synthesis of nonisocyanate polyurethane foam
(North-West University, 2023) Mkonto, Reply Dan; Marx, S; Venter, RJ
Plastic products are an integral part of our everyday lives. They are utilised in the form of packaging, building materials, insulation, and for providing comfort. The exclusive dependence on non-renewable fossil fuel resources as feedstock poses a negative impact on the environment. Its high demand by consumers is directly linked to high waste generation, which negatively affects river streams, underground water resources, human and animal health. Polyurethane is one of the fast-growing plastics that is utilized in many forms due to its versatility. The production, however, is fully dependent on toxic isocyanates and petroleum-derived polyols that are non-biodegradable. The transition from using fossil fuels into renewable feedstock such as lignin will reduce the environmental concern, while at the same time adding market value to lignin. The novel non-isocyanate polyurethanes (NIPU) whose production can be derived from the reaction between polycarbonates and polyamines presents an opportunity for this realization. This work presents three green pathways for modifying lignin into a green polycarbonate that can be used to synthesize NIPUs. The first phase involved the conversion of lignin into a hydroxyl and phenolic-rich bio-oil through hydrothermal liquefaction using alkali catalysis. Selective depolymerization was conducted by mixing Lignex (a Sappi waste sodium lignosulfonate that is used as a fuel source in the recovery boilers) and water at a mass ratio of 1:10 and 5% NaOH with respect to the mass of lignin. The liquefaction process was conducted in an autoclave semi-batch reactor at 300°C for a period of 20 minutes before the reaction was quenched with cooling systems. The second phase involved grafting of an epoxy group into the bio-oil through glycidylation. 5 g of bio-oil was dissolved in 13.3 g of epichlorohydrin at molar ratio of 1:15 and mixed with 12 ml of water. 0.2% TBAB with respect to mass of bio-oil was added as a catalyst. The contents were heated to 70°C before 12 ml of 10% NaOH solution was added. The reaction was allowed to proceed for 3 hours at a constant temperature while stirring. A high yield of epoxidized oil was attained after washing. The last phase of the modification method involved the carbonation of epoxidized oil into polycarbonates. The process was conducted in an industrial microwave fitted with gas insertion equipment. Bio-oil was mixed with TBAB at a molar ratio of 5% prior to being pressurized with carbon dioxide to 20 bars. The reaction was conducted at 120°C for a period of 1, 6, and 16 hours, where after each cycle the sample was collected for analysis. The chemical structure of Lignex and the reaction products were characterized using FTIR, H-NMR, GC-MS, and GPC. The presence of lignin was confirmed through FTIR characterization where the skeletal vibration of phenolic hydroxyl groups, the presence of G-unit phenols and the presence of the thiol-sulfur functional groups were identified. The presence of methoxyl, methyl, and methylene groups was confirmed using H-NMR scanning. The vibration of sulfonate and primary hydroxyl groups could not be confirmed due to peak overlapping. The molecular weight and polydispersity index of the Lignex structure was determined using GPC scanning. The selective depolymerisation of Lignex by attacking the β-O-4 and the C-C bonds was confirmed through GC-MS characterisation whereby high phenolic products and hydrocarbons in the bio-oil were obtained. The addition of NaOH proved to supress char formation and favour the production of methyl-branched phenols through weakening of the interunit linkages. FTIR and H-NMR characterisation confirmed the occurrence of demethoxylation, demethylation and hydrodeoxygenation. However, H-NMR characterisation of the bio-oil could not detect the presence of phenolic hydroxyls. Instead, a high intensity peak representing phenolic acetates was confirmed. The use of hydrogen donor solvents such as ethanol and ethyl acetate favoured the production of large molecular weight esters. The second phase of grafting epoxy rings into the structure of bio-oil was first confirmed by the presence of epoxy ring vibration through FTIR scanning. A reduction in the intensity of the phenolic hydroxyl confirmed the occurrence of the glycidylation reaction between the phenolic hydroxyls and epichlorohydrin. H-NMR characterisation revealed the resurface of phenolic hydroxyl, which could be a result of a ring-opening reactions. The obtained spectra also indicated the presence of residual epichlorohydrin in the sample although at different vibrations. Finally, the successful synthesis of cyclic carbonate was confirmed by the appearance of a carbonyl functionality characteristic of a cyclic carbonate. A direct proportionality relationship was also observed between the diminishing epoxy group and the formation of cyclic carbonate. The results were consistent with the H-NMR characterisation where the epoxy peak disappeared with an appearance of peaks characteristic of the cyclic carbonate rings. The detection of high-intensity aliphatic acetates confirmed the occurrence of the ring-opening reaction. In conclusion, the possibility of using high-quality bio-oil from lignin to synthesise a polycarbonate for the synthesis of NIPU was possible, yielding 82% of polycarbonate from 85% conversion of the epoxy group. The study on the effect of epichlorohydrin/bio ratio during epoxidation would prove to be significant in improving the epoxy value, hence offering the possibility of synthesizing high-quality polycarbonate.
Factors influencing the development of identity in late adolescence in South Africa: A rapid review
(North West University, 2021) Pawson, Anri
South African youth is facing an identity crisis. Answering the questions “Who am I” and “Where am I going?” are at the core of each adolescent's identity development. Although identity development is embedded within the lifespan theory of development, it is important to note that it is a process with its onset mainly during adolescence. Many challenges are being faced by these individuals, which makes it difficult for them to establish and maintain an identity. A youth struggling with the development and establishment of a secure and healthy identity has detrimental consequences for the applicable society and country's economic, educational, and psychosocial future. Theorists such as Erikson, Marcia, Crocetti, and Luycks indicated that identity development revolves around a process of exploring options within the main domains of career choices, sexuality, political views, religion, spirituality, as well as life goals and ultimately committing to a certain identity stance within each of these domains. For this study, a rapid review was conducted to answer the research question: What are the factors influencing the identity development of late adolescents in South Africa? After following a rigorous and scientific method to screen and appraise all relevant articles, a final eight articles were analysed and synthesised to identify themes and subthemes that could help answer the formulated research question.After the analyses of the identified articles, it was found that the main factors influencing identity development of late adolescents in South Africa are centred around: (1) Being myself: Factors influencing identity development on an (vii) intrapsychic level, (2) Being myself in relation to others: Factors influencing identity development on an interpersonal level, and (3) Being myself in different contexts: Factors influencing identity development on a contextual level.When integrating these identified themes with other relevant literature on this topic, it was clear that identity development amongst adolescence does not develop in isolation. The depth and richness of identity development are in it’s being a multidimensional, multi-layered dynamic process where the magic lies in the reciprocal interaction between the various factors identified. When dividing the identified factors into constant and fluid factors, a dynamic and interactional process occurs where awareness of the constant factors is combined with the activation of the fluid factors, which could be useful in informing pro-active interventions for the adolescents in South Africa. Schools could raise awareness and implement certain interventions embracing and accepting the constant factors contributing to identity development (gender, culture, psychosocial development) and the activation of the multi-layered fluid factors and systems surrounding these schools such as parents (parenting styles), the community (relationships with peers and neighbours), local government and policies (educational and socio-political resources and support). If these interventions can pro-actively launch the process of thorough, in-depth identity exploration and investigation before premature and foreclosed identity commitments are made, it could add value in guiding the culture of identity development in respective communities and South Africa as a whole.
Implementing monocular-inertial SLAM on the Nvidia Jetson TX2 embedded platform
(North-West University, 2024) Matthee, Jacques; Uren, KR; van Schoor, G; van Daalen, CE
SLAM is a complex computational problem where a robot or vehicle concurrently creates a representation of its environment while determining its position within the environment. State-of-the-art SLAM algorithms can achieve high accuracy at high speeds. However, these algorithms are usually developed, tested, and optimised on high-end desktop computers, which are not used in the design of the robots or vehicles that implement SLAM. These robots or vehicles use embedded platforms with limited processing power, which can cause severe degradation in the execution speed of the SLAM algorithm. Thus, since it is practically more feasible, SLAM algorithms need to be tested on embedded platforms. The study aims to create a prediction model that can estimate the performance that a SLAM algorithm can achieve on an embedded platform. ORB-SLAM3 is a state-of-the-art visual SLAM algorithm that supports multiple camera settings and configurations. ORB-SLAM3 will be implemented on the Nvidia Jetson TX2, Raspberry Pi 3b+, and Raspberry Pi 4B embedded platform, where the performance will be measured. The EuRoC MAV dataset is used as it provides camera and inertial sensor data with accurate ground-truth measurements. ORBSLAM3, built with the default version of OpenCV 3.2.0, was profiled, and it was identified that OpenCVs’ FAST function is the bottleneck when executing on the Nvidia Jetson TX2. Investigating the OpenCV3.2.0 source code showed that the FAST function does not use SIMD instructions on ARM architectures, meaning the hardware resources of the Nvidia Jetson TX2 are not fully utilised. ORB-SLAM3 was containerised and executed on the three embedded platforms, and the average tracking time was measured. PassMark is used to benchmark the embedded platforms to characterise the CPUs of the platforms. Since three embedded platforms are a small sample size, artificial CPUs are generated by varying the CPU frequencies and core counts. The results from the benchmarking and the execution of ORB-SLAM3 were used to create a dataset to train and test prediction models. The prediction model’s target is the average tracking time that ORB-SLAM3 can achieve on embedded platforms. The inputs to the model were selected using cross-correlation and guided by the profiling results of ORB-SLAM3. The inputs used to create the prediction model are the CPU frequency, PassMark Single CPU score, PassMark NEON CPU score and PassMark Integer score. Three modelling techniques are used to create prediction models: A simple linear regression, an Extra Trees Regressor, and a Multi-Layer Perceptron model. Two experiments are investigated for verification and validation. The first experiment, which serves as verification, is to create the models using the entire dataset of 429 unique entries, with a 75:25 ratio for training and testing. The second experiment that serves as validation is when a CPU is removed from the dataset to see how the prediction models react on an unseen CPU. The performance criteria that the models should achieve are an MAE and RMSE % of less than 10 %, and a R2 of more than 0.9.