Bio

Background

Senior Lecturer and Chairman, Department of Mechanical and Manufacturing Engineering
Office: Engineering Bloack, Room E312 and Room E402
Telephone: +254 (020) 4913527
Email address: tmbuya@uonbi.ac.ke

Academic Background:
- PhD in Engineerng Materials (2012) Engineering Materials Group, Engineering, University of Southampton, UK
- MSc in Mechanical Engineering (Industrial Engineering Option) (2003) - University of Nairobi
- BSc in Mechanical Engineering (1997) – University of Nairobi

Research Interests

Curriculum Vitae

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Publications


2021

Shagwira, H, Mwema FM, Obiko JO, MBUYA TO, Akinlabi ET.  2021.  The Optimization of the Surface Roughness of Milled Polypropylene + 60wt.% Quarry Dust Composite Using the Taguchi Technique. Advances in Material Science and Engineering. Lecture Notes in Mechanical Engineering:169-174. Abstracthttps://link.springer.com/chapter/10.1007/978-981-16-3641-7_20

This study is based on the optimization of the parameters that influence the computer numerical control (CNC) milling operation during the machining of polypropylene+60wt.% quarry dust composite. The input parameters studied are the cutting speed, the feed rate and the depth of cut. These input parameters were optimized using the Taguchi optimization technique with the output response taken into consideration was the surface roughness. An L9 orthogonal array (OA) was selected and formulated in a commercial software Minitab 19 based on three factors and three levels combination. The signal-to-noise (S/N) ratio was analysed to give a combination of values of the input parameters that produced optimum results for surface roughness. The analysis of variance (ANOVA) was then conducted to determine the significance and percentage contribution of each parameter. From the results, the optimum values obtained were cutting speed of 1000 rpm, feeding rate of 120 mm/min and depth of cut of either 0.5 mm or 0.8 mm. The cutting speed had the highest contribution towards the surface roughness at 81.98%, followed by the depth of cut at 7.43% and the feed rate having the least contribution at 3.69%.

Wang’ombe, DN, Mose BR, Maranga SM, MBUYA TM.  2021.  Effects of friction stir welding on microstructure and mechanical properties of extruded secondary aluminum 6061 alloy. Materialwissenschaft und Werkstofftechnik. 52(3):270-278. Abstracthttps://doi.org/10.1002/mawe.202000094

Experiments were carried out to determine the effects of friction stir welding on microstructure and properties of recycled Aluminum 6061 alloy, whose alloy content varied from that of primary alloy. The alloy was processed at tool speed and feed ranges of 530 rev/min–1320 rev/min and 40 mm/min–100 mm/min respectively. Microstructure examination; tensile test and Vickers microhardness evaluation were carried out. Microstructure of the alloy was in four zones including: base metal, heat affected zone, thermo-mechanically affected zone and stirred zone. Average grain size of unprocessed material was 93 μm. Processing the alloy at 530 rev/min and 100 mm/min resulted in grains of average size 93 μm, 183 μm and 7 μm; in base metal, heat affected zone and stirred zone respectively. Tensile failure occurred in heat affected zone; that was exposed to high heat. The alloy hardness decreased to a minimum in heat affected zone, followed by a brief rise in thermo-mechanically affected zone, to another maximum in stirred zone. Processed zone hardness was inversely proportional to tool speed and directly proportional to feed rate. Increase in the speed and decrease in feed, increased heat which deteriorated the properties.

H Shagwira, H, MBUYA TO, Mwema FM, Michael H, Akinlabi ET.  2021.  Taguchi Optimization of Surface Roughness and Material Removal Rate in CNC Milling of Polypropylene + 5wt.% Quarry Dust Composites. IOP Conference Series: Materials Science and Engineering. 1107(1):012040. Abstractdoi:10.1088/1757-899X/1107/1/012040

The Taguchi optimization technique was utilized to determine the optimal milling parameters that can be used in end face CNC milling operation of polypropylene+5wt.% quarry dust using high-speed steel (HSS) tool. Three milling input parameters i.e. the feed rate (f), the cutting speed of the spindle (N) and the depth of cut (dc) were optimized while considering the surface roughness (Ra) of the machined composite material and the material removal rate (MRR) during machining as the responses of the experimental design. From the results, the cutting speed (100 rpm) and the feed rate (120 mm/min) were the most important control parameters which greatly influence the surface roughness at 41.4% and 28.8% contribution respectively. In the case of the material removal rate, the depth of cut (0.8 mm) was the dominating factor at 98% contribution.

Shagwira, H, MBUYA TO, Akinlabi ET, Mwema FM, Tanya B.  2021.  Optimization of material removal rate in the CNC milling of polypropylene + 60 wt% quarry dust composites using the Taguchi technique. Materials Today: Proceedings. 44(1):1130-1132. Abstracthttps://doi.org/10.1016/j.matpr.2020.11.229

This research paper focuses on the optimization of the input parameters used in the computer numerical controlled (CNC) milling of polypropylene + 60 wt% quarry dust composite. The efficiency and profitability of the cutting operation was assessed using the material removal rate (MRR). Finding the optimal and suitable parameters to use in the cutting of polypropylene + 60 wt% quarry dust composite is crucial when it comes to increasing productivity without increasing the cost of production and machining time. Therefore, the Taguchi technique was utilized to optimize the cutting speed, the feed rate and the depth of cut used while focusing on their effects on the material removal rate. The analysis of the input parameters was carried out using the L9 Taguchi orthogonal array, the signal-to-noise (S/N) ratio and the analysis of variance (ANOVA). The finding showed that the optimal milling parameters for efficient productivity were; the cutting speed of 600 rpm, a feed rate of 200 mm/min and depth of cut of 0.8 mm. Additionally, the feed rate is the most contributing factor in affecting the material removal rate, followed by the depth of cut and lastly the cutting speed at 53%, 17 and 10% respectively.

Shagwira, H, Mwema FM, MBUYA TO.  2021.  Advances in animal/plant–plastic composites: preparation, characterization and applications. Plant and Animal Based Composites. , Berlin: De Gruyter Abstract

This book chapter aims at exploring the preparation, characterization and applications of plant/animal fiber-reinforced polymer composites. The book addresses several key research work that have been happening as well as some of the drawbacks that affect the application of these composites in real-life applications. Each chapter begins with an overview of the various forms of plant/animal fiber-reinforced polymer composites, followed by examples of composites made up of plant/animal fibers and their promising future in terms of research and development and application in domestic and engineering products. Today, man has realized that if the environment is not preserved, the over-consumption of naturally existing resources and a drastic reduction in the amount of fresh air generated in the world would endanger him. Forest conservation and the efficient use of agricultural as well as other renewable resources such as solar, wind and tidal energy have already become critical issues globally.With this kind of concern, the utilization of renewable materials such as plant/animal fiber-reinforced polymeric composites is slowly becoming a key design requirement for the design and development of parts for a wide range of industrial products. An extensive research into such composites can, to an extent, lead to an even greener and healthier environment

Shagwira, H, Mwema FM, MBUYA TO.  2021.  Lightweight Polymer–Nanoparticle-Based Composites. Nanomaterials and Nanocomposites. , Boca Raton: CRC Press Abstract

The increasing demand for eco-friendly materials in various fields including the construction industry has led to increased efforts toward the development of more materials to suit such fields. In this work, a specific review of polymer–nanoparticle-based composites is presented with an emphasis on the nano-silica reinforcements. A background on applications, processing methods, and state-of-the-art review of the subject is presented. It is noted that there is limited literature focusing on the recycling of polymers using silica nanoparticle-based reinforcements for the construction industry. Gaps in the literature are identified, and the direction for future research focus is presented.

Barasa, NW, Njoroge KD, MBUYA TO.  2021.  An investigation of the effects of extraction and brushing variables on the properties of hedge sisal fibers using a raspador. Journal of Natural Fibers. :InPress. Abstracthttps://doi.org/10.1080/15440478.2020.1870641

Natural fibers have emerged as an important component in the development of composite materials because of their mechanical properties. The properties are highly influenced by environmental conditions and processing techniques. This variability makes their usability in reinforcement unpredictable. There are satisfactory attempts to quantify the variation of the properties with environmental conditions. However, the quantification of how the properties vary with processing methods is unsatisfactory. This study, therefore, investigated and quantified the effects of processing variables on the properties of sisal fibers using a raspador. The raspador was designed, fabricated, and utilized in processing sisal fibers. Processing variables such as gap size, number of extraction and brushing elements, and drum speed were investigated. The mechanical properties were determined based on ASTM C1557 standard. High correlation coefficients were found between fiber properties and the processing variables. The brushing process, mostly ignored in many cases, improved the properties of the sisal fibers.

Nyiranzeyimana, G, Mutua JM, Mose BR, MBUYA TO.  2021.  Optimization of process parameters in fused deposition modelling of thermoplastics: A review. Materialwissenschaft und Werkstofftechnik. 52(6):682-694. Abstracthttps://doi.org/10.1002/mawe.202000193

Among the several techniques for additive manufacturing (AM), fused deposition modelling (FDM) is widely used. Fused deposition modelling process uses a thermoplastic material, which is melted and then extruded layer by layer through a nozzle, in order to create a three-dimensional object. As a result of the default setting of process parameters provided by the manufacturers, produced parts normally have a poor surface finish, low mechanical properties, low dimensional accuracy, and increased residual stresses compared to the parts produced using conventional manufacturing processes like molding (casting). Qualities of fused deposition modelled (FDMed) parts are generally affected by process parameters including the layer thickness, extrusion temperature, build orientation, printing speed, raster angle, infill density, raster width, nozzle diameter, and air gap. Increasing infill density, printing temperature, and decreasing print speed and layer thickness lead to increase mechanical strength and improve the surface finish of the printed parts. The optimal process parameters are preferred to achieve superior properties of the parts. This paper reviews the optimal fused deposition modelling process parameters on part qualities for making the stability of used deposition modelled parts for use. Various process parameters are identified in order to obtain desirable qualities in the manufactured parts. Areas for future research are proposed.

Polline, M, Mutua JM, MBUYA TO, Kyekyere E.  2021.  Recipe Development and Mechanical Characterization of Carbon Fibre Reinforced Recycled Polypropylene 3D Printing Filament. Open Journal of Composite Materials. 11(3):47-61. Abstracthttps://doi.org/10.4236/ojcm.2021.113005

Recycled polypropylene filaments for fused filament fabrication were investigated with and without 14 wt% short fibre carbon reinforcements. The microstructure and mechanical properties of the filaments and 3D printed specimens were characterized using scanning electron microscopy and standard tensile testing. It was observed that recycled polypropylene filaments with 14 wt% short carbon fibre reinforcement contained pores that were dispersed throughout the microstructure of the filament. A two-stage filament extrusion process was observed to improve the spatial distribution of carbon fibre reinforcement but did not reduce the pores. Recycled polypropylene filaments without reinforcement extruded at high screw speeds above 20 rpm contained a centreline cavity but no spatially distributed pores. However, this cavity is eliminated when extrusion is carried out at screw speeds below 20 rpm. For 3D printed specimens, interlayer cavities were observed larger for specimens printed from 14 wt% carbon fibre reinforced recycled polypropylene than those printed from unreinforced filaments. The values of tensile strength for the filaments were 21.82 MPa and 24.22 MPa, which reduced to 19.72 MPa and 22.70 MPa, respectively, for 3D printed samples using the filaments. Likewise, the young’s modulus of the filaments was 1208.6 MPa and 1412.7 MPa, which reduced to 961.5 MPa and 1352.3 MPa, respectively, for the 3D printed samples. The percentage elongation at failure for the recycled polypropylene filament was 9.83% but reduced to 3.84% for the samples printed with 14 wt% carbon fiber reinforced polypropylene filaments whose elongation to failure was 6.58%. The SEM observations on the fractured tensile test samples showed interlayer gaps between the printed and the adjacent raster layers. These gaps accounted for the reduction in the mechanical properties of the printed parts.

Barasa, NW, Njoroge KD, MBUYA TO.  2021.  Design, Fabrication, and Testing of a Raspador for Simultaneous Extraction and Brushing of Sisal Fibers by Small-scale Sisal Farmers. Journal of Natural Fibers. :InPress. Abstracthttps://doi.org/10.1080/15440478.2021.1975597

Demand for natural fibers is on the rise as awareness of environmental protection keeps abreast. Sisal fibers, for instance, are largely utilized not only in the manufacture of mats, ropes, carpets, and sacks but also in the reinforcement of polymer composites. With the increased demand for sisal fibers, there is a need to equally increase the exploitation of sisal by small-scale farmers. UNIDO, for instance, recommended that appropriate small-scale machines that are accessible to small-scale holders should be developed. This research examines the progress in the development of small-scale machines and designs a raspador for simultaneous extraction and brushing of sisal fibers. This is to ensure that there is value and income addition for the small-scale farmers in East Africa and perhaps the rest of the world.

Shagwira, H, Mwema FM, MBUYA TO.  2021.  Polymer-Silica Based Composites in Sustainable Construction: Theory, Preparation and Characterizations. , Boca Raton: CRC Press Abstracthttps://doi.org/10.1201/9781003231936

This book presents the application of Polymer-Silica Based Composites in the Construction Industry providing the fundamental framework and knowledge needed for the sustainable and efficient use of these composites as building and structural materials. It also includes characterization of prepared materials to ascertain mechanical, chemical, and physical properties and analyses results obtained using similar methods. Topics such as life cycle analysis of plastics, application of plastics in construction and elimination of plastic wastes are also discussed. The book also provides information on the outlook and competitiveness of emerging composites materials.

Covers theory, preparation and characterizations of polymer-silica based composites for green construction.

Discusses technology, reliability, manufacturing cost and environmental impact.

Reviews the classification, application, and processing of polymer-silica composites.

Gives a deeper analysis of the various tests carried out on polymer-silica composites.

Highlights role of such composites in the Industry 4.0 and emerging technologies

The book is aimed at graduate students and researchers in civil engineering, built environment, construction materials, and materials science.

2020

Mwangi, P, Muvengei O, MBUYA TO, Ndeto M.  2020.  Energy Optimisation of a Single Toggle Jaw Crusher using Discrete Element Method. Journal of Sustainable Research in Engineering. 5(4):180-193. Abstracthttps://jsre.jkuat.ac.ke/index.php/jsre/article/view/98

Comminution process has always been associated with very low energy efficiencies. Most of the energy during
comminution is lost through noise, heat and vibrations. Therefore, it is necessary to obtain the optimal operating parameters of a comminution machine. In this research, the efficiency of a jaw crusher has been optimised using Genetic Algorithms (GA) and Discrete Element Method (DEM) techniques. DEM, even though a powerful tool, demands high computational capabilities hence a scaled down jaw crusher was used for simulation purposes. The GA codes were used in determining the critical velocity and also in developing the equation for up-scaling the jaw crusher. Critical parameters which affect the power consumption of a jaw crusher are toggle speed, throw and reduction ratio. These parameters were varied during the simulation as guided by the design of experiment technique. In addition, a Bonded Particle Model (BPM), was used in modelling the rock used in the simulation. A BPM model gives more realistic results than Particle Replacement Model (PRM) and Fast Breakage Model (FBM). To create the BPM of an irregularly shaped rock, custom API factory was coded in C++ and loaded to EDEM software. At the end of this research, the optimal energy efficiency was obtained as 59.7758% at a toggle speed of 157.7965 rpm, a throw of 33.445 mm and a reduction ratio of 4. A mathematical model showing the relationship between energy efficiency and process parameters was also developed.

Shagwira, H, Mwema FM, MBUYA TO, Adediran A.  2020.  Dataset on impact strength, flammability test and water absorption test for innovative polymer-quarry dust composite. Data in Brief. 29( April):105384. Abstracthttps://doi.org/10.1016/j.dib.2020.105384

In this article data on impact strength, flammability and water absorption tests for innovative plastic-quarry dust composite is presented. The composites were prepared through moulding with virgin HDPE and PP plastics and quarry dust. The quarry dust was used at 0%, 5%, 20%, 40%, 60% and 80% weight percentages. The prepared samples were characterised for strength, fire resistance and hydrophobic properties using Charpy impact, flammability and water absorption tests respectively. For impact strength test was conducted according to ISO 179–1:2010 (E). The flammability test was conducted according to ASTMD 2863 while the water absorption test was carried out in accordance to ASTM D 570–98. These data illustrate the potential of the plastic quarry dust composite application in construction industry and model for regeneration of waste plastics for green building technologies.

2019

Wangombe, DN, Mose BR, Maranga SM, Nganga SP, MBUYA TO.  2019.  Recycling of Aluminium scrap in Kenya: A Survey of Foundry Enterprises and Mechanical Properties of Resultant Alloys. Journal of Sustainable Research in Engineering. 5(1):25–33.. Abstracthttps://jsre.jkuat.ac.ke/index.php/jsre/article/view/84

Small and medium scale foundry enterprises occupy an important position in the economic growth and development in our societies. They are the main force behind a large number of innovations and contribute significantly to the nation’s growth through employment creation, investments and exports. Their contribution to poverty reduction and wealth creation is enormous. This study investigated the aluminium scrap recycling practices through a survey of 45 foundry enterprises in Kenya; and evaluated the effectiveness of scrap segregation, melt cleanliness and post cast processing in reducing failures of load bearing products using commonly used cylinder head scrap. Survey data was acquired through a questionnaire, onsite observations and individual interviews with the foundry men. Three alloys were developed from carefully segregated cylinder head scrap; which include BA (base alloy), BA + 0.6%Fe and BA + 0.6%Fe + 0.3%Mn. Analysis of microstructure and mechanical properties was done on as cast and T6 heat treated alloys. The foundries involved in the survey were classified into ‘‘jua kali’’(micro), small, medium and large enterprises based on capital investment, number of employees, volume of castings produced and level of technology. It was found that ‘‘jua kali’’ enterprises were majority at 44%. Their operations were limited by low capital base, low level technology and inadequate skills; forcing them to operate below 40% capacity. Further, the approaches adopted for sorting scrap were found to lead to unpredictable chemical composition and uncertainties in mechanical performance. Use of alloying additives to adjust the alloy chemistry and improve properties of load bearing castings was utilized by 10% of the enterprises. This resulted in production of low quality and unreliable castings. BA had composition similar to that of parent cylinder head alloys. A small increase of Fe by 0.2 % as an inclusion in the as cast alloy, resulted in a drop of strength and ductility by 7 and 20 % respectively. Mn mitigated the harmful effects of Fe by increasing strength and ductility by 5 and 12 % respectively. T6 heat treatment of as cast alloy improved the strength and decreased ductility by 40 and 18 % respectively. It was shown that sorting separately the aluminium scrap component by component, observation of melt cleanliness, use of additives, and post cast processing can yield good mechanical performance of the resulting alloy. International market requirements have set quality standards, which local foundries must fulfill through adoption of scrap segregation, casting and melt control procedures in order to ensure high quality products.

Gaudence, N, Aimable N, MBUYA TO, Mose BR.  2019.  Effect of Fe, Mn and Sr on the Microstructure and Tensile Properties of Secondary Al-Si-Cu-Mg Cast Alloys. Journal of Engineering Research and Technology. 8(5):284-289. Abstracthttp://dx.doi.org/10.17577/IJERTV8IS050281

This paper presents results on the effect of Sr, Fe and combined additions of Fe and Mn on the microstructure and tensile properties of a secondary Al-Si-Cu-Mg alloy. The microstructure features of base alloy consisted mainly of a structure with primary Al-matrix, coarse acicular Si particles and intermetallic phases such as Al2Cu and AlCuNi. When 0.02%Sr was added to the base alloy, coarse acicular Si particles were modified to a fine fibrous form. With addition of 0.38%Fe, results in the formation of large eutectic silicon particles and Fe rich intermetallic. Moreover, when 0.45%Mn was added in combination with 0.9%Fe, the Al2Cu, and -AlFeMnSi with Chinese script morphology were identified. It is noticed that after T6 heat treatment, the Si particles are seen to spheroidize and fragment while the Al2Cu phases dissolve completely. These changes lead to improved mechanical performance of the alloy. The addition of strontium decreases the ultimate Tensile strength and increases percent elongation while addition of low iron and iron with manganese decreases UTS and percent elongation in the as cast condition. T6 heat treatment increases the ultimate tensile strength while ductility decreases due to the fragmentation and spheroidization of eutectic silicon particles.

Mwema, FM, MBUYA TO, Akinlabi ET, Reed PAS, Obiko JO.  2019.  Data on the effect of high-pressure torsion processing on secondary cast Al–10%Si– Cu piston alloy: Methods, microstructure and mechanical characterizations. Data in Brief. 25(August):104160. Abstracthttps://doi.org/10.1016/j.dib.2019.104160

The dataset presented here shows the microstructure and mechanical properties of secondary (recycled) cast aluminum-silicon (Al–Si) piston alloys processed through severe plastic deformation technique, known as high-pressure torsion (HPT). The HPT processing was undertaken for 1/4, 1/2, 1 and 10 turns of the lower anvil (rotating at constant speed of 1rpm) while the upper anvil maintained at a normal pressure of 3.0 GPa. The data on microstructural evolution obtained at the central region and edge of the circular (disk) HPT sample were obtained using optical and scanning electron microscopy and these data are presented here. The data on the analysis of the particle shape, sizes and distribution from the micrographs using ImageJ software are also presented. Data on mechanical properties characterized using Vickers microhardness measurement across the surface of HPT sample are also shown. Pictures depicting the microhardness measurement scheme, high-pressure torsion facility and sample nomenclature are presented.

Mwema, FM, Obiko JO, Leso T, MBUYA TO, Mose BR, Akinlabi ET.  2019.  Wear Characteristics of Recycled Cast Al-6Si-3Cu Alloys. Tribology in Induastry. 41(4):613-621. AbstractDOI: 10.24874/ti.2019.41.04.13

Recycling of Al-Si alloys for high integrity structural components for the automotive industry applications has gained attention in the recent times. In this article, scrap of cylinder heads containing 6.01%Si and 2.62%Cu were recycled by casting into four alloys invariants: base alloy (no alloying elements added), 0.02%Ca, 0.38%Fe and 0.9%Fe+0.45%Mn additions. The structural properties were analysed through optical and SEM/EDS microscopy, X-ray diffraction (XRD). The wear characteristics of the alloys were investigated using a multi-pass ball on the flat reciprocating method under a normal load of 30 N and velocity of 4 mm/s. The results showed delamination and adhesive wear as the predominant wear mechanisms for the recycled Al-Si alloys. The base and 0.02%Ca alloys exhibited the lowest coefficients of friction and rates of wear. A comparison of the wear data to the published data on primary alloys revealed that our secondary alloys have the potential for applications in the automotive industry.

2018

Kimanzi, E, Ikua, MBUYA TO.  2018.  Key Performance Indicators for Manufacturing Safety in Paint Manufacturing: A Case of the Kenyan Industry. International Journal of Engineering Research and Technology. 7(3):43-47. Abstracthttp://dx.doi.org/10.17577/IJERTV7IS030043

Manufacturing safety is a key priority in the success of any business, as it can affect both the present and future competitive position of an organization. Organizations must measure safety in order to find areas of weakness, and then implement actions aimed at raising safety levels. Industrial accidents in the chemical industry indicate a need for both leading and lagging indicators of safety in the workplace.

The purpose of this study was to formulate and validate a set of key performance indicators that can be used in the measurement and reporting of manufacturing safety, and ensure a safe working environment for the workers on a continuous basis. The final results consisted of 21 Key Performance Indicators (KPIs), with fire safety being the most relevant KPI. The information gathered during a manufacturing safety performance measurement exercise can be used to implement activities directed towards reducing the level of worker exposure to health and safety risks within the factory, and thereby recommend application of these KPIs in managing of manufacturing safety in paint manufacturing and allied products industries.

2017

Mose, BR, Kil SD, Mbuya TO.  2017.  Microstructure and mechanical performance of a secondary cast aluminium piston alloy with minor element additions. International Journal of Cast Metals Research. 30(6):348-355. Abstracthttps://doi.org/10.1080/13640461.2017.1323455

The effect of individual and combined minor element additions (Sr, Sb, Mn, Cr and Al-5Ti-1B grain refiner) on microstructure and mechanical performance of a secondary cast aluminium piston alloy, with 1 wt-% Fe was investigated. It was observed that addition of Cr of up to 1% was better than a 0.53%Mn addition in improving tensile strength, impact energy and percent elongation of the alloy. The high mechanical performance recorded with addition of 1%Cr alloy was attributed to the significant reduction in porosity levels compared to all other minor element additions. It also resulted in a microstructure with fine compact intermetallic compounds. Other element additions also resulted in improved mechanical properties with 0.53%Mn performing better than 0.3%Mn + 0.2%Cr. Marginal improvements in mechanical performance were recorded with addition of 0.02%Sr (or 0.05%) and 0.02%Sb individually or in combination with 0.53%Mn. This was attributed to general increase in porosity and volume fraction of intermetallics.

MBUYA, TO, Gu Y, Thomson RC, Reed PAS.  2017.  Effect of intermetallic particles and grain boundaries on short fatigue crack growth behaviour in a cast Al–4Cu–3Ni–0.7Si piston alloy. , Fatigue and Fracture of Engineering Materials and Structures. 40(9):1428–1442.. Abstracthttps://doi.org/10.1111/ffe.12586

The short fatigue crack growth behaviour in a model cast aluminium piston alloy has been investigated. This has been achieved using a combination of fatigue crack replication methods at various intervals during fatigue testing and post-mortem analysis of crack profiles. Crack–microstructure interactions have been clearly delineated using a combination of optical microscopy, scanning electron microscopy and electron backscatter diffraction. Results show that intermetallic particles play a significant role in determining the crack path and growth rate of short fatigue cracks. It is observed that the growth of short cracks is often retarded or even arrested at intermetallic particles and grain boundaries. Crack deflection at intermetallics and grain boundaries is also frequently observed. These results have been compared with the long crack growth behaviour of the alloy.

MBUYA, TO, Sinclair I, Soady KA, Reed PAS.  2017.  Application of X-Ray Microtomography to Evaluate Complex Microstructure and Predict the Lower Bound Fatigue Potential of Cast Al–7(0.7)Si–4Cu–3Ni–Mg Alloys. Advanced Engineering Materials. 19(11):1700218. Abstracthttps://doi.org/10.1002/adem.201700218

The 3D architecture of intermetallics and porosity in two multicomponent cast Al–7(0.7)Si–4Cu–3Ni–Mg alloys is characterized using conventional microscopy and X-ray microtomography. The two alloys are found to contain intermetallic phases such as Al3Ni, Al3(NiCu)2, Al9FeNi, and Al5Cu2Mg8Si6 that have complex networked morphology in 3D. The results also show that HIPping does not significantly affect the volume fraction, size, and shape distribution of the intermetallic phases in both alloys. A novel technique similar to serial sectioning that circumvents quantification difficulties associated with interconnected particles is used to quantify the intermetallics. The largest particle size distribution is then correlated to fatigue performance using extreme value analysis to predict the maximum particle size in a sample of S-N fatigue specimens and subsequently, the lower bound fatigue life. The predictions are found to correlate well with fatigue data. The effect of HIPping on porosity characteristics is also characterized. Large pore clusters with complex morphology are observed in the unHIPped versions of both alloys, but more significant in the low Si (Al–0.7Si–4Cu–3Ni–Mg) alloy. However, these are significantly reduced after HIPping. The differences between 2D and 3D pore morphology and size distribution is discussed in terms of the appropriate pore size parameter for fatigue life prediction.

2016

ODUORI, MF, Musyoka EK, MBUYA TO.  2016.  Material Selection for a Manual Winch Rope Drum. WASET International Journal of Chemical, Molecular, Nuclear, Materials and Metallurgical Engineering. 10(1):129-141. Abstracthttps://doi.org/10.5281/zenodo.1124199

The selection of materials is an essential task in mechanical design processes. This paper sets out to demonstrate the application of analytical decision making during mechanical design and, particularly, in selecting a suitable material for a given application. Equations for the mechanical design of a manual winch rope drum are used to derive quantitative material performance indicators, which are then used in a multiple attribute decision making (MADM) model to rank the candidate materials. Thus, the processing of mechanical design considerations and material properties data into information that is suitable for use in a quantitative materials selection process is demonstrated for the case of a rope drum design. Moreover, Microsoft Excel®, a commonly available computer package, is used in the selection process. The results of the materials selection process are in agreement with current industry practice in rope drum design. The procedure that is demonstrated here should be adaptable to other design situations in which a need arises for the selection of engineering materials, and other engineering entities.

2014

MBUYA, TO, Reed PAS.  2014.  Micromechanisms of short fatigue crack growth in an Al–Si piston alloy. Materials Science and Engineering: A. 612:302-309. Abstracthttps://doi.org/10.1016/j.msea.2014.06.046

The short fatigue crack growth behaviour of a model cast aluminium piston alloy has been investigated. This has been achieved using a combination of fatigue crack replication methods at various intervals during fatigue testing and post-mortem analysis of the crack profiles. Crack-microstructure interactions have been clearly delineated using a combination of optical microscopy and scanning electron microscopy. Results show that intermetallic particles and eutectic Al–Si regions play a significant role in determining the crack path and growth rate of short fatigue cracks. It is observed that the growth of short cracks is often retarded or even arrested at intermetallic particles and Al–Si eutectic regions. Crack deflection at intermetallics and eutectic Si is also frequently observed. These results have been compared with the long crack growth behaviour of the alloy.

2012

ODUORI, MF, MBUYA TO, Sakai J, Inoue E.  2012.  Kinematics of the Tined Combine Harvester Reel. Agric Eng Int: CIGR Journal. 14(3):53-60.. Abstracthttps://cigrjournal.org/index.php/Ejounral/article/view/1577

Although derivation of the kinematic equations of the combine harvester reel is readily achieved, certain inferences thereof suggest possible improvements in its kinematical design. A mathematically computed reference value of the reel index (ratio of the product of the reel radius and rotational velocity to the reel advance velocity) is found to be larger than commonly recommended values. The point, either spatial or temporal, within the cycle of reel motion, at which the tinebar should preferably enter the crop is discussed. The pick-up performance of the tines is qualitatively analyzed and its possible improvement through redesign of reel tine kinematics is suggested.

MBUYA, TO, Sinclair I, Moffat AJ, Reed PAS.  2012.  Micromechanisms of fatigue crack growth in cast aluminium piston alloys. International Journal of Fatigue. 42:227-237. Abstracthttps://doi.org/10.1016/j.ijfatigue.2011.10.015

The fatigue crack growth behaviour in as-cast and hot isostatically pressed (HIP) model cast aluminium piston alloys with hypoeutectic Si compositions of 6.9 wt% and 0.67 wt% has been investigated. The HIP alloys showed slightly improved fatigue crack growth resistance. Analysis of the crack path profiles and fracture surfaces showed that the crack tends to avoid Si and intermetallic particles at low ΔK levels up to a mid-ΔK of ∼7 MPa√m. However, some particles do fail ahead of the crack tip to facilitate crack advance due to the interconnected microstructure of these alloys. At higher levels of ΔK, the crack increasingly seeks out Si and intermetallic particles up to a ΔK of ∼9 MPa√m after which the crack preferentially propagates through intermetallic particles in the 0.67 wt%Si alloy or Si and intermetallics in the 6.9 wt%Si alloys. It was also observed that crack interaction with intermetallics caused crack deflections that led to roughness-induced crack closure and possibly oxide-induced crack closure at low to mid-ΔK. However, crack closure appears unimportant at high ΔK due to the large crack openings and evidenced by the fast crack growth rates observed.

Oduori, MF, Mbuya TO, Sakai J, Inoue E.  2012.  Modeling of crop stem deflection in the context of combine harvester reel design and operation. Agric Eng Int: CIGR Journal. 14(2):21-28. Abstracthttps://cigrjournal.org/index.php/Ejounral/article/view/1575

A model of crop stem deflection by the combine harvester reel is formulated. The equations derived thereof are evaluated on the basis of empirical data that were acquired through deflection of crop stems in a ready-for-harvest Japonica rice in the field. The empirical data are found to be in agreement with the theoretically derived equations. Applications of crop stem deflection to reel design and operation are discussed. The derived crop stem deflection model should be applicable in other situations in which it becomes necessary to study the deflection of crop stems, particularly in the domain of agricultural machinery engineering.

2011

Mbuya, TO, Sinclair I, Moffat AJ, Reed PAS.  2011.  Analysis of fatigue crack initiation and S–N response of model cast aluminium piston alloys. Materials Science and Engineering: A. 528(24):7331-7340. Abstracthttps://doi.org/10.1016/j.msea.2011.06.007

Fatigue crack initiation and S–N fatigue behaviour of hipped model Al7Si–Sr and Al0.7Si piston alloys have been investigated after overaging at 260 °C for 100 h to provide a practical simulation of in-service conditions. The results show that hipping did not affect the S–N behaviour of Al7Si–Sr. This is attributed to the lack of significant change in porosity distribution in this alloy because of its low porosity levels even in the unhipped state. However, hipping profoundly improved the fatigue performance of alloy Al0.7Si due to the significant reduction in porosity. In this investigation, it was observed that porosity was rendered impotent as a fatigue crack initiator in both hipped alloys. Instead, fatigue cracks were observed to originate mainly from intermetallic particles (particularly the Al9FeNi phase) in both alloys and sometimes from oxide particles in Al0.7Si alloy. Fatigue cracking was also frequently observed at intermetallic clusters in hipped Al0.7Si. The observed scatter in fatigue life is discussed in terms of the size of fatigue crack initiating particles and the overall particle size distribution which follows a power law distribution function.

2010

MBUYA, TO, ODERA BO, Ng'ang'a SP, Oduori FM.  2010.  Effective Recycling of Cast Aluminium Alloys for Small Foundries. AbstractWebsite

A method of effective recycling of aluminium castings suitable for small foundries was investigated. Automotive cast aluminium scrap obtained from various scrap vendors was sorted into groups of similar components, namely; pistons, cylinder heads and housings (gearbox and rear-axle housings). This sorting method was adopted with the hypothesis that the resulting alloys could be closely equivalent to the commercial alloys that were originally used to make the components. The remainder of the scrap was grouped as miscellaneous scrap and contained various parts such as alternator covers, exhaust manifolds, oil sumps and other assorted scrap. As hypothesised, the chemistry of the resulting alloys were found to be consistently equivalent to the commercial alloys commonly used to cast the various components that were melted. For example, the alloy chemistry of secondary alloys from piston scrap was consistently equivalent to commercial piston alloys such as AC8B and LM26. Furthermore, alloys from cylinder head scrap were equivalent to commercial alloys such as 319, LM27 and AC2B. On the other hand, the alloy chemistry from unsorted scrap was not found to be consistent nor equivalent to a specific group of commercial alloys except for the 319 and 380.0 workhorse alloys. These results are discussed against the possibility of reusing the alloys in casting components similar to those that they were recycled from, in addition to other possible applications.

2009

Mose, BR, Maranga SM, MBUYA TO.  2009.  Effect of Minor Elements on the Fluidity of Secondary LM25 and LM27-Type Cast Alloys. AbstractWebsite

In this study, the effect of individual and combined additions of Fe, Mn, Cr, Sr and Al-5Ti-1B grain refiner on the fluidity of secondary LM25 and LM27-type cast alloys was investigated. No change in fluidity was observed when the Fe level was increased from 0.14 to 0.4% in LM25, but it increased by 21% when Fe was raised to the critical content of 0.48%. Furthermore, a decrease of 32% resulted when the Fe level was increased to 0.6%. A combination of 0.3%Mn or 0.6%Cr with 0.6%Fe in LM25, resulted in a fluidity increase of 13 and 8%, respectively compared to the base alloy, but a combination of 0.6%Fe, 0.3%Mn and 0.2%Cr decreased the fluidity by 9%. A 34% increase in fluidity was observed when the Fe content in LM27 was raised from 0.41% to the critical level of 0.6%Fe with further increase when Mn was raised to 0.3%Mn. Increasing the Fe content to 1% in LM27 led to a drop in fluidity of 9%. Addition of 0.015%Sr and 0.02%Sr increased the fluidity of LM25 and LM27 by 9% and 21% respectively. Furthermore, a 0.28% Al-5Ti-1B grain refiner addition decreased the fluidity of LM 25 and LM27 by 2% and 19% respectively while a combined addition of 0.02%Sr and 0.28%Al-5Ti-1B decreased the fluidity of LM27 by 8%. Possible reasons for these observations are discussed.

2006

MBUYA, TO, ODUORI MF, Rading GO, WEKESA MS.  2006.  Effect of runner design on mechanical properties of permanent mould aluminium castings. AbstractWebsite

A comparison of the influence of different runner designs on the mechanical properties of aluminium castings has shown that filtered rectangular runners (FRRs) yield aluminium castings with higher and more reliable mechanical properties than the conventional unfiltered rectangular runners. Unfiltered vortex flow runners have also been shown to improve the reliability of the modulus of rupture of cast aluminium alloys over unfiltered rectangular runners. In the present paper, experimental results of a comparative study on the effect of the unfiltered vortex flow and FRR designs on the tensile strength of permanent mould aluminium castings are reported. The results show that an FRR yields castings with higher and more reliable tensile strengths than the unfiltered vortex flow runner. Castings poured into a mould with an FRR had strengths between 269 and 291 MPa and a Weibull modulus of 50·2 while castings poured into the vortex flow runner had strengths between 255 and 280 MPa and a Weibull modulus of 40·3.

OCHUKU, MRMBUYATHOMAS.  2006.  T.O. Mbuya, G. O. Rading, M. F. Oduori, and M. S. Wekesa . KLB. : WFL Publisher
OCHUKU, MRMBUYATHOMAS.  2006.  T.O. Mbuya, B.O. Odera, S.P. Ng. KLB. : WFL Publisher
OCHUKU, MRMBUYATHOMAS.  2006.  M.F. Oduori and T.O. Mbuya, . KLB. : WFL Publisher
OCHUKU, MRMBUYATHOMAS.  2006.  T.O. Mbuya, B.O. Odera, S.P. Ng. KLB. : WFL Publisher
FRANK, DRODUORIMOSES, OCHUKU MRMBUYATHOMAS.  2006.  T.O. Mbuya, . KLB. : WFL Publisher

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