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Friction stir welding of dissimilar materials – statistical analysis of the weld data

  • Authors: Akinlabi, Esther Titilayo , Akinlabi, Stephen A.
  • Date: 2012
  • Subjects: Friction stir welding
  • Type: Article
  • Identifier: uj:5336 , ISSN 2078-0966 , http://hdl.handle.net/10210/8879
  • Description: This paper reports the results of statistical analysis conducted on the weld data obtained from friction stir welding of aluminium and copper. The welds were produced by varying the process parameters; the rotational speed was varied between 600 to 1200 rpm and the welding speed varied between 50 and 300 mm/min. The Statistica (version 9.0) statistical analysis software package was used to generate the scatter and surface plots relative to the experimental results obtained from the tensile testing and the FSW data. Regression analysis was also done on the weld data. It was found that the downward vertical force has a significant effect on the Ultimate Tensile Strength of the weld and a strong relationship exist between the heat input into the welds and the measured electrical resistivities of the welds.
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Non-destructive testing of dissimilar friction stir welds

  • Authors: Akinlabi, Esther Titilayo , Levy, Adrian C. S. , Akinlabi, Stephen A.
  • Date: 2012
  • Subjects: Friction stir welding , Non-destructive testing , Aluminum alloys , Copper
  • Type: Article
  • Identifier: uj:5333 , ISSN 2078-0966 , http://hdl.handle.net/10210/8876
  • Description: friction stir welds between 5754 aluminium alloy and C11000 copper. The Friction stir welds of 5754 aluminium alloy and C11000 copper were produced at different tool rotational speeds and feed rates. The tool rotational speed was varied between 600 and 1200 rpm while the feed rate was varied between 50 and 300 mm/min. The visual inspection and the x-ray radiographic testing techniques were employed to conduct the tests; these tests were conducted on the welds to ascertain the joint integrity before characterization to have an idea of the quality of the welds. No visual defects were observed on all the welds considered but the x-ray radiography technique revealed the presence of wormhole defects and discontinuities in some of the welds. It was found that the welds produced at 950 rpm with varied feed rates were the best quality welds produced and this was substantiated with the microstructural evaluation of the joint interface. It was found that these welds have good mixing and metallurgical bonding at the interfaces.
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Design of a support system for a re-configured milling machine to achieve friction stir welds

Friction stir welding of aluminium and copper : fracture surface characterizations

  • Authors: Akinlabi, Esther Titilayo , Akinlabi, Stephen A.
  • Date: 2014
  • Subjects: Aluminium , Copper , Fracture surfaces , Friction stir welding
  • Type: Article
  • Identifier: uj:4745 , ISSN 2078-0966 , http://hdl.handle.net/10210/11731
  • Description: Butt welds of aluminium alloy and copper alloy were produced by Friction Stir Welding by varying the feed rate and keeping all other parameters constant. The final weld matrix was composed of welds produced by a constant rotational speed of 600 rpm and the feed rate varied between 50 and 300mm/min. The microstructure and fracture surfaces of the joint interfaces were investigated. The results revealed that the joint interface was characterised with mixed layers of both materials joined. The strongest weld was produced at the highest feed rate employed at 300 mm/min. The fracture surfaces were characterised with thin layers of intermetallic compounds and can be considered fit for practical applications.
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A review of femtocell

  • Authors: Akinlabi, O. A. , Paul, B. S. , Joseph, M.
  • Date: 2014
  • Subjects: Interference management , Femtocells
  • Type: Article
  • Identifier: uj:4785 , ISSN 2078-0966 , http://hdl.handle.net/10210/11968
  • Description: The popularity of wireless networks has attracted the attention of researchers to improve the network system and this motivated the operators to find a new technology called femtocells with the aim of meeting the increased coverage and data demand in the indoor environment. The application of femtocells in both indoors and office environment has provided good quality service and high performance network gains. However, femtocells face challenges of interference management which deteriorate the capacity and quality of network. But to cope with these challenges, many researchers have come up with solutions to solve the problems, some of which include interference cancellation and interference avoidance.
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Experimental investigation of laser beam forming of titanium and statistical analysis of the effects of parameters on curvature

  • Authors: Akinlabi, Stephen A. , Akinlabi, Esther Titilayo
  • Date: 2013
  • Subjects: Laser beam forming , Titanium alloys
  • Type: Article
  • Identifier: uj:4746 , ISSN 2078-0966 , http://hdl.handle.net/10210/11732
  • Description: Laser beam forming, a non-contact manufacturing process has become a viable manufacturing process for shaping metallic components. The capability of laser beam forming and bending demands more experimental studies to identify an optimized parameter setting and the likely parameters influencing the formed curvature. This paper investigates experimental laser beam forming of Ti6Al4V titanium alloy using a 4.4 kW Nd: YAG laser and studied the effects of the process parameters on the formed curvature. It was established that an increase in both the laser beam power and the number of scan tracks reduces the radius of curvature in the formed sheets having a more dome shape. The scan speed on the other hand, achieved the same good curvature at a slower or reduced scan speed to allow enough laser – material interaction. Furthermore, both the ANOVA and the regression analysis confirmed the repeatability of the experimental data. A simple regression model was developed based on the known active parameters to determine approximate curvatures instead of running a series of experiments.
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Synthesis and characterization of new nitrogen donor ligands

Synthesis and characterization of new nitrogen donor ligands

A study of South African natural zeolites properties and applications

  • Authors: Diale, Palesa. P. , Muzenda, Edison , Zimba, Josephat
  • Date: 2011
  • Subjects: Zeolites - South Africa
  • Type: Article
  • Identifier: uj:6067 , ISSN 2078-0966 , http://hdl.handle.net/10210/10669
  • Description: The morphology and chemistry of natural zeolites, whose occurrence is ubiquitous to the South African provinces of Kwa-Zulu Natal (KZN) and Western Cape (WC), were studied using scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray fluorescence (XRF) and the Brunauer-Emmett-Teller (BET) nitrogen adsorptiondesorption technique. The stability of these zeolites in varying pH conditions and their cation exchange capacity (CEC) was also investigated. The main mineral constituent of the natural zeolites was found to be clinoptilolite, with plagioclase, quartz and muscovite being the common impurities. The zeolite footprint was not altered after treatment with a hydrochloric (HCl) acid. The BET surface area ranged from 65.5 to 33.22 m2/g while the pore size ranged from 3 to 10 nm for the natural zeolites. These properties make them good prospective materials for application in biomedicines, environmental preservation and agriculture.
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Sizing of an anaerobic biodigester for the organic fraction of municipal solid waste

  • Authors: Kigozi, R. , Aboyade, A. O. , Muzenda, Edison
  • Date: 2014
  • Subjects: Anaerobic digestion , Biogas digesters , Clean energy , Municipal solid waste management
  • Type: Article
  • Identifier: uj:4982 , ISSN 2078-0966 , http://hdl.handle.net/10210/13114
  • Description: The anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) for biogas production is a potential solution to the growing challenges associated with municipal solid waste (MSW) management while simultaneously providing an alternative clean energy source. Biogas is produced by the anaerobic digestion (AD) of biomass using microorganisms in specifically designed plants called biogas digesters under controlled conditions or naturally in marshes and landfills. It is a rather clean and versatile fuel as opposed to fossil fuels. To design an efficient AD system, a proper understanding of the quality and quantity of available feedstock must be made as well as prevailing operating conditions. This paper represents steps that were taken to come up with an optimal size of biodigester to treat OFMSW produced at the University of Johannesburg’s Doornfontein Campus in downtown Johannesburg. The campus generates 232.2kg of OFMSW per day which required 30m3 of biodigester capacity.
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Characterizing the effect of processing parameters on the porosity of laser deposited titanium alloy powder

  • Authors: Mahamood, Rasheedat M. , Akinlabi, Esther Titilayo , Shukla, Mukul , Pityana, Sisa
  • Date: 2014
  • Subjects: Laser metal deposition , Medical implants , Porosity , Processing parameters , Titanium alloy
  • Type: Article
  • Identifier: uj:4739 , ISSN 2078-0966 , http://hdl.handle.net/10210/11725
  • Description: Laser Metal Deposition (LMD) is an additive manufacturing technique that produces parts layer by layer directly from the Computer Aided Design (CAD) file. Highly customized parts with complex shapes such as medical implants can well be manufactured using the LMD process. LMD has been used to produce a wide range of patient specific (customized) parts. Porous parts are of particular importance as medical implants because they can potentially aid the healing process and proper integration of the implant with the body tissues. In this research porous samples of titanium alloy (Ti6Al4V) were produced using the LMD process. Spherical shaped Ti6Al4V powder of particle size ranging between 150 to 200 μm was used. The effect of laser power and scanning speed on the shape, size and degree of porosity of the deposited tracks was investigated. The results showed that as the laser power was increased and the scanning speed decreased, the degree of porosity was reduced. The size of the porosity was also found to reduce as the laser power was increased.
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Review of silver recovery techniques from radiographic effluent and x-ray film waste

  • Authors: Masebinu, Samson O. , Muzenda, Edison
  • Date: 2014
  • Subjects: Hydrometallurgy , Pyro-metallurgy , Radiographic waste , Silver recovery
  • Type: Article
  • Identifier: uj:5006 , ISSN 2078-0966 , http://hdl.handle.net/10210/13146
  • Description: This paper highlights the techniques for silver recovery from radiographic waste; effluent and X-ray films. The decline in silver natural resource has increased the cost of sourcing for pure silver. The ecological problems caused by the disposal of radiographic waste is a huge motivation for increased recovery, regeneration and recycling process. The negative impact of pure silver on human and the environment is low but its soluble salt and emission from its recovery process pose a great risk to the ecosystem. Pyro-metallurgical processes of silver recovery requires heat >950°C which also destroys the polymer substrate. Hydrometallurgical processes such as electrolysis, metallic replacement, chemical precipitation and adsorption, are often used and provides high purity and efficiency. A proposed research work for silver recovery based on chemical precipitation using oxalic acid has been presented.
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The status of used vegetable oil (UVO) biodiesel production in South Africa

  • Authors: Mbohwa, Charles , Mudiwakure, Alexander
  • Date: 2013
  • Subjects: Oil-derived biodiesel , Biodiesel production technology - South Africa , Biodiesel technology benchmarking
  • Type: Article
  • Identifier: uj:6040 , ISSN 2078-0966 , http://hdl.handle.net/10210/10440
  • Description: This paper discusses the status of used oil derived biodiesel production in South African. It highlights the positives and shortcomings of the technology used and identifies the potential for improvement. All known South African used oil biodiesel producers were targeted. The response rate was 40% out of 200 producers. Technology used was benchmarked with established advanced biodiesel producing countries such as Germany, Brazil and the USA. Production rate, yield, product quality were the key performance indicators assessed. Results show that biodiesel production in South Africa is still in its infancy and production rates are low ranging from 100litres/day to a maximum 8000litres/day. Most plants are locally manufactured. Imports from India, China and Australia make up the remainder. Batch reactors are favoured over continuous reactors because of low acquisition cost, simple design and ease of operation. They allow for phase to phase quality control. This has resulted in low volume production militating against economies of scale. Yields, at up to 94% are acceptable and competitive. The products are contaminated with methanol and free fatty acids. The standards set for biodiesel quality were found to be restrictive and prohibitive but prospects for sustainable production are excellent.
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A fuzzy grouping genetic algorithm for care assignment task

  • Authors: Mutingi, Michael , Mbohwa, Charles
  • Date: 2014
  • Subjects: Care tasks , Task assignment , Fuzzy grouping genetic algorithm , Fuzzy theory
  • Type: Article
  • Identifier: uj:4935 , ISSN 2078-0966 , http://hdl.handle.net/10210/13035
  • Description: The assignment of care tasks to nurses is often done manually in most hospitals. A high quality care task schedule is crucial for efficient and effective execution of nursing care duties. High quality schedules seek to satisfy patient preferences over time window for the care, schedule fairness among nurses, and management goals regarding care activity completion times and labor costs. This paper suggests a grouping genetic approach to care task scheduling in a hospital setting. By taking advantage of the group structure of the problem, the algorithm uses fuzzy evaluation techniques, permuting tasks across candidate nurse schedules and within each nurse schedule. Results of the computational experiments show that the proposed approach is effective.
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Simulated metamorphosis - a novel optimizer

  • Authors: Mutingi, Michael , Mbohwa, Charles
  • Date: 2014
  • Subjects: Metamorphosis , Evolution , Optimization , Algorithm , Metaheuristics , Simulated metamorphosis
  • Type: Article
  • Identifier: uj:4972 , ISSN 2078-0966 , http://hdl.handle.net/10210/13073
  • Description: This paper presents a novel metaheuristic algorithm, simulated metamorphosis (SM), inspired by the biological concepts of metamorphosis evolution. The algorithm is motivated by the need for interactive, multi-objective, and fast optimization approaches to solving problems with fuzzy conflicting goals and constraints. The algorithm mimics the metamorphosis process, going through three phases: initialization, growth, and maturation. Initialization involves random but guided generation of a candidate solution. After initialization, the algorithm successively goes through two loops, that is, growth and maturation. Computational tests performed on benchmark problems in the literature show that, when compared to competing metaheuristic algorithms, SM is more efficient and effective, producing better solutions within reasonable computation times.
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A fuzzy-based particle swarm optimization algorithm for nurse scheduling

  • Authors: Mutingi, Michael , Mbohwa, Charles
  • Date: 2014
  • Subjects: Nurse scheduling , Nurse rostering , Personnel scheduling , Particle swarm optimization
  • Type: Article
  • Identifier: uj:4926 , ISSN 2078-0966 , http://hdl.handle.net/10210/13026
  • Description: The nurse scheduling problem (NSP) has a great impact on the quality and efficiency of health care operations. Healthcare Operations Analysts have to assign daily shifts to nurses over the planning horizon, so that operations costs are minimized, health care quality is improved, and the nursing staff is satisfied. Due to conflicting objectives and a myriad of restrictions imposed by labor laws, company requirements, and other legislative laws, the NSP is a hard problem. In this paper we present a particle swarm optimization-based algorithm that relies on a heuristic mechanism that incorporates hard constraints to improve the computational efficiency of the algorithm. Further, we incorporate soft constraints into objective function evaluation to guide the algorithm. Results from illustrative examples show that the algorithm is effective and efficient, even over large scale problems.
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Volatile organic compounds – biphenyl thermodynamic interactions

  • Authors: Muzenda, Edison
  • Date: 2014
  • Subjects: Absorption , Activity coefficient , Phase equilibrium , Volatile organic compounds , Thermodynamics
  • Type: Article
  • Identifier: uj:4989 , ISSN 2078-0966 , http://hdl.handle.net/10210/13124
  • Description: This work focused on the thermodynamic interactions involving volatile organic compounds (VOCs) and biphenyl. The solubility of 60 VOCs in biphenyl was studied using group contribution methods. The modified UNIFAC Dortmund and Lyngby were used to compute the required phase equilibrium in the form of infinite dilution activity coefficients. Six family groups were studied mainly alkanes, alkenes, alkynes, aldehydes, alcohols, and carboxylic acids. The Modified UNIFAC Dortmund performed better than the Modified UNIFAC Lyngby. Biphenyl showed excellent absorption affinity for all VOCs in particular for alkynes and aldehydes. The solubility decreased with increase in VOC molecular weight.
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Effect of pH on the recovery and grade of base metal sulphides (PGMs) by flotation

  • Authors: Muzenda, Edison , Afolabi, Ayo S. , Abdulkareem, Ambali S. , Ntuli, Freeman
  • Date: 2011
  • Subjects: Platinum Group Metals , Metal sulphides , Flotation
  • Type: Article
  • Identifier: uj:4713 , ISSN 2078-0966 , http://hdl.handle.net/10210/10959
  • Description: This study investigated the effect of pH on the recovery and grade of the Platinum Group Metals (PGMs) and base metal sulphides from the UG2 ore of the Bushveld Complex. This was achieved through running a series of test work in a Denver flotation cell at varying pH 6-11 at constant reagent dosage. The UG-2 reef is characterized by two predominant gangue phases i.e. chromite and silicate, that have significantly different physical and chemical properties. The test work was aimed at evaluating which pH gives best recoveries, and finding the effect of the chrome content in these recoveries. A pH of 9 gave the highest recovery compared to other pH ranges. However, the highest PGM grade was attained at a pH of 6 which is slightly acidic. Ideally this trend could be expected since the collectors (xanthates) are more stable in alkaline medium. The higher PGM recovery was also accompanied by higher chrome content as a result of their similar chemical properties.
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A simple static headspace method for phase equilibrium measurement

Bio-methane generation from organic waste : a review

  • Authors: Muzenda, Edison
  • Date: 2014
  • Subjects: Anaerobic digestion , Biodegradable material , Biogas
  • Type: Article
  • Identifier: uj:4987 , ISSN 2078-0966 , http://hdl.handle.net/10210/13119
  • Description: Anaerobic digestion of organic waste can address both energy recovery and pollution control. A variety of agricultural, industrial and domestic wastes can be anaerobically digested as they contain easily biodegradable material. Biogas contains 50 -70% methane and 30-50% carbon dioxide as well as small a amounts of other gases with calorific value of about 21-24 MJ/m3. This paper reviews the history of biogas, biogas production stages and operating parameters. The anaerobic digestion configuration and potential substrates for biogas production are also considered.
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