Journal Articles
http://ir.ttu.ac.ke/xmlui/handle/123456789/4
Contains Journal Articles from Taita Taveta University Community2024-03-28T23:59:03ZRevealing a Transformation‑Induced Plasticity (TRIP) Phenomenon in a Medium‑Entropy Alloy
http://ir.ttu.ac.ke/xmlui/handle/123456789/93
Revealing a Transformation‑Induced Plasticity (TRIP) Phenomenon in a Medium‑Entropy Alloy
Ibrahim Ondicho; Bernard Alunda; Dicken Owino; Luke Otieno; Melody Chepkoech
A transformation-induced plasticity phenomenon in Fe65(CoCrMnNi)35 medium-entropy alloy was investigated. According to the X-ray diffraction patterns, the as-cast specimen contains a single-phase face-centered cubic (fcc), while low-temperature
annealing at 500 °C and 600 °C leads to the introduction of a body-centered cubic (bcc) phase as a secondary phase. Further increment of the annealing temperature to above 700 °C eliminates the bcc phase, and the microstructure was found to contain a single-phase fcc. At 20% true strain, an fcc-to-bcc phase transformation is observed; whereas, at 28% true strain, an fcc-to-hcp phase transformation takes place as an additional deformation mechanism. This strain-induced phase transformation
phenomenon leads to improved tensile properties of this alloy
2020-01-01T00:00:00ZA simple way to higher speed atomic force microscopy by retrofitting with a novel high-speed flexure-guided scanner
http://ir.ttu.ac.ke/xmlui/handle/123456789/92
A simple way to higher speed atomic force microscopy by retrofitting with a novel high-speed flexure-guided scanner
Bernard Ouma Alunda; Yong Joong Lee; Soyeun Park
A typical line-scan rate for a commercial atomic force microscope (AFM) is about 1 Hz. At such a rate, more than four minutes of scanning time is required to obtain an image of 256 ' 256 pixels. Despite control electronics of most commercial AFMs permit faster scan rates, default piezoelectric X–Y scanners limit the overall speed of the system. This is a direct consequence of manufacturers choosing a large scan range over the maximum operating speed for a X–Y scanner. Although some AFM manufacturers offer reduced-scan area scanners as an option, the speed improvement is not significant because such scanners do not have large enough reduction in the scan range and are mainly targeted to reducing the overall cost of the AFM systems. In this article, we present a simple parallel-kinematic substitute scanner for a commercial atomic force microscope to afford a higher scanning speed with no other hardware or software upgrade to the original system. Although the scan area reduction is unavoidable, our modified commercial XE-70 AFM from Park Systems has achieved a line scan rate of over 50 Hz, more than 10 times faster than the original, unmodified system. Our flexure-guided X–Y scanner can be a simple drop-in replacement option for enhancing the speed of various aging atomic force microscopes.
2018-05-08T00:00:00ZExperimental study of bubble behaviors and CHF on printed circuit board (PCB) in saturated pool water at various inclination angles
http://ir.ttu.ac.ke/xmlui/handle/123456789/91
Experimental study of bubble behaviors and CHF on printed circuit board (PCB) in saturated pool water at various inclination angles
Elvira F. Tanjung; Bernard O. Alunda; Yong Joong Lee; Daeseong Jo
Experiments were performed to investigate bubble behaviors and pool boiling Critical Heat Flux (CHF) on a thin flat rectangular copper heater fabricated on Printed Circuit Board (PCB), at various inclinationangles. The surface inclination angles were 0 , 45 , 90 , 135 , and 180 . Results showed the Onset of Nucleate Boiling (ONB) heat flux increased with increasing heater orientation from 0 to 90 , while early ONB occurred when the heater faced downwards (135 and 180 ). The nucleate boiling was observed to be unstable at low heat flux (1e21% of CHF) and changed into typical boiling when the heat flux was above 21% of CHF. The result shows the CHF decreased with increasing heater orientation from 0 to 180 . In addition, the bubble departure diameter at the heater facing upwards (0 , 45 , and 90 ) was more prominent compared to that of the heater facing downward (135 ). The nucleation site density also observed increased with increasing heat flux. Moreover, the departed bubbles with larger size were observed to require a longer time to re-heat and activate new nucleation sites. These results proved that the ONB, CHF, and bubble dynamics were strongly dependent on the heater surface orientation.
2018-01-01T00:00:00ZPrediction of rock fragmentation using the Kuznetsov-Cunningham-Ouchterlony model
http://ir.ttu.ac.ke/xmlui/handle/123456789/90
Prediction of rock fragmentation using the Kuznetsov-Cunningham-Ouchterlony model
E.K. Mutinda; B.O. Alunda; D.K. Maina; R.M. Kasomo
Assessment of blast fragment size distribution is critical in mining operations because it is the initial step towards mineral extraction. Different empirical models and techniques are available for predicting and investigating the consequences of blasting, one of which is the Kuznetsov-Cunningham-Ouchterlony (KCO) model. In this paper we summarize the advances in the empirical models from inception until now, and explore the improvements that have been made so far with particular emphasis is on the most recent KCO model. Utilization of the model and the errors that arise between expected and the actual outcomes are analysed. The results indicate that the KCO model remains useful for predicting the blast fragmentation at limestone mine sites, despite the availability of other advanced prediction models. It is also a valuable instrument for pre-surveying the impact of varying certain parameters of a blast plan.
2021-03-01T00:00:00Z