Ronald Machaka

Bio: Ronald Machaka is an academic researcher from Council for Scientific and Industrial Research. The author has contributed to research in topics: Spark plasma sintering & Alloy. The author has an hindex of 11, co-authored 59 publications receiving 321 citations. Previous affiliations of Ronald Machaka include University of the Witwatersrand & Council of Scientific and Industrial Research.

Nanoindentation studies of the mechanical behaviours of spark plasma sintered multiwall carbon nanotubes reinforced Ti6Al4V nanocomposites

Abstract: In this study, the influence of multiwall carbon nanotubes (MWCNT) additions on the mechanical properties of sintered Ti6Al4V-based nanocomposites was investigated. The nanocomposites were fabricated with varying weight fractions of MWCNT (0.5, 1.0 & 1.5 wt%) using the spark plasma sintering (SPS) technique. Investigations were carried out using nanoindentation of varying indentation loads (50 mN, 75 mN and 100 mN) to assess the nanohardness (H) and reduced elastic modulus (Er) of the alloy and nanocomposites. Further analysis was done to evaluate the elastic recovery index ( W e W t ) , plasticity index ( W p W t ) , elastic strain resistance ( H E r ) and yield pressure ( H 3 E r 2 ) at the maximum load. Microstructural analysis revealed the presence of the MWCNT dispersed across the alpha and beta phases of the Ti6Al4V matrix. The nanoindentation studies showed that the nanohardness, elastic modulus, elastic recovery index, elastic strain resistance and anti-wear properties improved with the MWCNT addition and continually increased with increase in nanotubes content. Also, it was observed that the nanohardness and reduced elastic modulus of the fabricated nanocomposites are in the range of 4677–9276 MPa and 29.3–60.9 GPa respectively which declined with increase in indentation load. The sintered Ti6Al4V displayed the least resistance to plastic deformation.

Modelling and optimization of surface roughness during AISI P20 milling process using Taguchi method

Abstract: Surface roughness Ra is a parameter normally used to indicate the level of surface irregularities during machining operations. This work aims to model the cutting process, correlate and optimise the critical process parameters using the Taguchi method during the milling operation of AISI P20 in order to reduce surface roughness. The Autodesk Fusion 360 (2.0.5357) was employed for modelling the stress, displacement and thermal behaviour of the cutting tool and work piece under different cutting conditions. The experimental plan was based on Taguchi’s technique including L9 orthogonal array with three factors and three levels for each variable and studying the contribution of each factor on surface roughness. The Taguchi method was used to study the effect of process parameters and establish correlation among the cutting speed, feed and depth of cut with respect to the major machinability factor, surface finish. The machining parameters evaluated in this study are the depth of cut (d), spindle speed (N) and cutting feed (fm) while the response factor measured is surface roughness. The physical experiments were conducted on M200 TS material on a DMC 635 V DMG ECOLINE, Deckel Maho Germany, Siemens 810D, 3-Axis, CNC vertical milling machine using carbide inserts and the surface roughness was measured using the Mitutoyo SJ–201, surface roughness Machine. The statistical analysis of both the numerical and physical experiments brought about the development of a mathematical model and optimum solutions for the evaluation of surface roughness during the milling process with high degree of correlation with experimental values thus validating the developed model.

Analysis of the Indentation Size Effect in the Microhardness Measurements in B 6 O

Abstract: The Vickers microhardness measurements of boron suboxide (B6O) ceramics prepared by uniaxial hot-pressing was investigated at indentation test loads in the range from 0.10 to 2.0 kgf. Results from the investigation indicate that the measured microhardness exhibits an indentation load dependence. Based on the results, we present a comprehensive model intercomparison study of indentation size effects (ISEs) in the microhardness measurements of hot-pressed B6O discussed using existing models, that is, the classical Meyer's law, Li and Bradt's proportional specimen resistance model (PSR), the modified proportional specimen resistance model (MPSR), and Carpinteri's multifractal scaling law (MFSL). The best correlation between literature-cited load-independent Vickers microhardness values, the measured values, and applied models was achieved in the case of the MPSR and the MFSL models.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Thin films and nanostructures of niobium pentoxide : fundamental properties, synthesis methods and applications

Abstract: As one of the transition metal oxides, niobium pentoxide (Nb2O5) offers a broad variety of properties that make it a potentially useful and highly applicable material in many different areas. In comparison to many other transition metal oxides, Nb2O5 has received relatively little attention, which presents a significant opportunity for future investigations aimed at fundamentally understanding this material and finding new and interesting applications for it. In this article, a general overview of Nb2O5 is presented which focuses on its fundamental properties, synthesis methods and recent applications, along with a discussion on future research directions relevant to this material.

High-entropy energy materials: challenges and new opportunities

Abstract: The essential demand for functional materials enabling the realization of new energy technologies has triggered tremendous efforts in scientific and industrial research in recent years. Recently, high-entropy materials, with their unique structural characteristics, tailorable chemical composition and correspondingly tunable functional properties, have drawn increasing interest in the fields of environmental science and renewable energy technology. Herein, we provide a comprehensive review of this new class of materials in the energy field. We begin with discussions on the latest reports on the applications of high-entropy materials, including alloys, oxides and other entropy-stabilized compounds and composites, in various energy storage and conversion systems. In addition, we describe effective strategies for rationally designing high-entropy materials from computational techniques and experimental aspects. Based on this overview, we subsequently present the fundamental insights and give a summary of their potential advantages and remaining challenges, which will ideally provide researchers with some general guides and principles for the investigation and development of advanced high-entropy materials.