Maina Maringa

Prof. Maina Maringa

Mechanical and Mechatronics Engineering, Central University of Technology, Bloemfontein, Free State, South Africa
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Research Focus & Metrics

Academic Career Length

12Years (2015-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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26 November 2020 in Materials
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Amos MuiruriAmos Muiruri
Amos Muiruri
Maina MaringaMaina Maringa
Maina Maringa
Wilhelm du PreezWilhelm du Preez
Wilhelm du Preez
Dislocations play a central role in determining strength and flow properties of metals and alloys. Diffusionless phase transformation of β→α in Ti6Al4V during the Direct Metal Laser Sintering (DMLS) process produces martensitic microstructures with high dislocation densities. However, heat treatment, such as stress relieving and annealing, can be applied to reduce the volume of these dislocations. In the present study, an analysis of the X-ray diffraction (XRD) profiles of the non-heat-treated and heat-treated microstructures of DMLS Ti6Al4V(ELI) was carried out to determine the level of defects in these microstructures. The modified Williamson–Hall and modified Warren–Averbach methods of analysis were used to evaluate the dislocation densities in these microstructures. The results obtained showed a 73% reduction of dislocation density in DMLS Ti6Al4V(ELI) upon stress relieving heat treatment. The density of dislocations further declined in microstructures that were annealed at elevated temperatures, with the microstructures that were heat-treated just below the β→α recording the lowest dislocation densities.

1 January 2018 in Advances in Materials Science and Engineering
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WWW.ilson Webo
W.ilson Webo
LMLeonard Masu
Leonard Masu
Maina MaringaMaina Maringa
Maina Maringa
The effect of the combined chemical treatment of sisal fibres through the subsequent processes of mercerisation (alkali treatment), then silane treatment and eventually acid hydrolysis, on sisal fibre was investigated. The effect of the treated fibres on the impact toughness and hardness of their composites with epoxy resin was also studied. Scanning electron microscopy of the surfaces of the treated and untreated fibres showed that the chemical treatment processes enhanced the removal of surface impurities and therefore increased the roughness of the surfaces of the fibres. This avails an increased surface area for interlocking with matrix and is, therefore, expected to enhance adhesion of the two. The treated fibre reinforced composites were observed to have higher values of impact toughness and hardness than the untreated fibre reinforced composites. These higher values were attributed to better interfacial bonding due to better mechanical interlocking between the treated fibres and epoxy resin arising from the increased roughness of the treated fibres.

12 August 2020 in Crystals
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Amos MuiruriAmos Muiruri
Amos Muiruri
Maina MaringaMaina Maringa
Maina Maringa
Wilhelm du PreezWilhelm du Preez
Wilhelm du Preez
This paper reports on an investigation of crystallographic texture of as-built and heat-treated Ti6Al4V (ELI) produced by direct metal laser sintering (DMLS). The texture analyses were conducted using electron backscatter diffraction (EBSD). The β-phase texture from the obtained EBSD data was ascertained based on a reconstruction method using the Automatic Reconstruction of Parent Grain for EBSD data (ARPGE) program. A significant improvement of the maximum intensity of the texture from the pole figure was also noted upon heat treatment. The as-built samples and samples heat-treated just below the α→β transformation temperature showed a stronger fibrous texture of the reconstructed β-grains with the ⟨100⟩ directions almost parallel to the build direction. The alignment of the fibrous texture in the build direction disappeared after heat treatment above the α→β-grain transformation temperature.

18 May 2020 in Metals
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Amos MuiruriAmos Muiruri
Amos Muiruri
Maina MaringaMaina Maringa
Maina Maringa
Wilhelm du PreezWilhelm du Preez
Wilhelm du Preez
LMLeonard Masu
Leonard Masu
A study was undertaken on the compressive high strain rate properties and deformation behaviour of Direct Metal Laser-Sintered (DMLS) Ti6Al4V (ELI) parts in two separate forms: as-built (AB) and stress relieved (SR). The high strain rate compression tests were carried out using a Split Hopkinson Pressure Bar test system at ambient temperature. The average plastic strain rates attained by the system were 400 s−1 and 700 s−1. Comparative analyses of the performance (flow stresses and fracture strains) of AB and SR specimens were carried out based on the results obtained at these two plastic strain rates. Microstructural analyses were performed to study the failure mechanisms of the deformed specimens and fracture surfaces. Vickers microhardness test values were obtained before and after high strain rate compression testing. The results obtained in both cases showed the strain rate sensitivity of the stress-relieved samples to be higher in comparison to those of as-built ones, at the same value of true strain.

23 May 2022 in Crystals
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Amos MuiruriAmos Muiruri
Amos Muiruri
Maina MaringaMaina Maringa
Maina Maringa
Wilhelm du PreezWilhelm du Preez
Wilhelm du Preez
This study documents a systematic analysis of the global Schmid factor for different deformation mechanisms in α′/α and β-grains in different forms of direct metal laser sintered (DMLS) Ti6Al4V(ELI) based on EBSD data. A novelty of this study is the use of these data to calculate the values of the Schmid factor and the subsequent determination of their distribution and frequency, which, when compared to the slip systems of crystal structures, helps in determining the favourable slip systems in play. Both retained β-grains and reconstructed prior β-grains were considered in this analysis. The reconstruction of the prior β-grains was executed using the Automatic Reconstruction of Parent Grain for EBSD data (ARPGE) program. The distribution of the global Schmid factor for these Ti6Al4V phases was calculated using the MATLAB-based MTEX toolbox program. This analysis of deformation modes in the α′/α-phase was based on a uniaxial load state acting on the x, y, and z axes, while only the load along the build direction (x-direction) was considered in the analysis of deformation mechanisms in the β-phase of the alloy. The results of this study showed that the DMLS build direction influenced the distribution of the global Schmid factor for the basal slip system of α′/α-grains in as-built specimens and those samples that were heat treated below the α→β transformation temperature.

16 February 2024 in Applied Sciences
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MCMunashe Ignatius Chibinyani
Munashe Ignatius Chibinyani
TDThywill Dzogbewu
Thywill Dzogbewu
Maina MaringaMaina Maringa
Maina Maringa
Amos MuiruriAmos Muiruri
Amos Muiruri
Lattice structures are useful in the aerospace, automotive, infrastructural, and medical fields due to the way they incorporate a lightweight design and good mechanical properties, because of their hollow shapes. This review paper documents work carried out using various analytical models for lattice structures designed with different polygon hollow shapes, for loading in the in-plane and out-of-plane directions, in order to advise their ranking in terms of mechanical behaviour. A primer on lattice structures and polygon hollow shapes is first provided. This is followed by a review of relevant analytical models applied to lattice structures with various polygon hollow shapes that are available in the literature, and then a ranking of the polygon hollow structures in terms of their mechanical properties is performed. Following on from this, a review of the mechanical properties of polygon hollow structures is given. Engineering applications of different polygon hollow structures are then identified. A next-generation structural optimisation and design guide is then highlighted, and some of the primary prospective areas to be focused on when designing lattice parts are pointed out. The last section highlights current challenges, as well as recommendations for extending the use of design for the additive manufacturing of lattice parts.