International Journal of Engineering Research in Africa Vol. 44

Abstract: Hollow fly ash microspheres (FAMs) were successfully coated with copper (Cu) deposits via microwave (MW) irradiation. Ascorbic acid was used to reduce Cu²⁺ ions from copper sulphate pentahydrate solution. Subsequently, metallic Cu wasdeposited on FAMs within 2 to 6 min of MW irradiation. Microstructural examinations revealed that the sizes of the Cu coating on FAMs increased as MW time increased. The average approximate sizes increased from 1.56 μm to 4.04 μm as the MW processing time increased from 2 min to 6 min. Therefore, coating size could be controlled by adjusting MW irradiation time. Furthermore, EDX and XRD results confirmed the presence of Cu coating on FAMs, which agreed with the findings from the microstructural characterization. The results presented here showed that MW irradiation could be used to provide rapid and uniform heating of reactants to deposit Cu on FAMs within a short time. These Cu-coated FAMs have potential use as electrical conducting fillers in composite materials.

Abstract: Persea Americana is well known for its short shelf life while the seed is widely considered a waste material by domestic consumers and industry processors. This paper presents the results of the study carried out to evaluate the possibility of using three parts of the Persea Americana namely: its seed, a combination of the Persea Americana seed and its pulp and the Persea Americana pulp as filtration loss control additives in a non-aqueous drilling fluid while using Sodium Asphalt Sulfonate as a control. The evaluation was conducted under high pressure, high temperature (HPHT) static filtration test conditions (at 250°F and 500 psi) based on American Petroleum Institute Standard. From the study, the result showed that all three samples from the Persea Americana fruit showed good potential to control filtration loss when used to formulate a synthetic oil based mud. The filtration control capacity increased as their concentration in the mud was increased. However, in comparison, the pulp was 2.5 times and 1.5 times more efficient in controlling filtration loss when compared to the seed only and the seed and pulp combination respectively. Also, in terms of filtrate volume and filtered cake thickness, an equal concentration of Sodium Asphalt Sulfonate and the proposed additive gave good results; but the existing filtration loss control additive is slightly better than the proposed one. The low fluid loss volumes recorded with Persea Americana as fluid loss additives at HPHT conditions is an indication of its stability at elevated temperature conditions. The cake thickness was thin, impermeable and 1mm in size for all the samples of the Persea Americana. This meets the API requirement of mud cake thickness of less than 2mm.

Abstract: In addition of binding the patch to the cracked material, adhesives play an important role in bonded composite repair because they make the bridge of transfer of loads between the patch and the cracked material. Indeed, any damage in adhesives will affect the efficiency and the performance of the repaired structure by composite patches.In this paper, two different adhesive shapes were numerically investigated, using finite element method in order to estimate the damage zone area on the adhesive bonded composite repair in 5083 marine grade aluminum alloy and its effect on the efficiency and performance of the repaired structure. The obtained results proved that the circular shape causes less damage than the rectangular one for the three crack lengths chosen. Moreover, both shapes of adhesive maintain their performance repair without disband risk and without reaching the critical value defined by Ban and co-authors (Dr=0.2474). Furthermore, it is concluded that the damage zone increases with the increase of the adhesive thickness and the decrease of the patch thickness and the use of circular shape is more effective than the rectangular one for the configurations and loading conditions studied.

Abstract: The article deals with the development of approach for providing of structural strength of complicated thin-walled machine-building structures, which operate in the conditions of geometric and physical nonlinearities using design solution validation. The developed approach is based on the use of mathematical model for stress-strain state taking into account geometric and physical nonlinearities and methods of approximation for constructing functions describing the evaluated characteristics of the object under study. The various factors behind the search for design solutions (including characteristics of strength, rigidity, technological and economic factors), are being added into this function. The developed algorithm for rational parameters search, which takes into account the peculiarities of the response surface shape observed in solving applied problems, is applied to them. In this case, the solution is sought over the whole range of parameter changes. Thus, in the search process, global trends of changes in design decisions are taken into account, and not local ones, as in other approaches. This allows obtain a rational solution that is stable to changes in parameters, which are possible in course of design work and production conditions. Investigations are illustrated on the freight rail-car, tractor cabin frame, carrier personnel hull.

Abstract: This study presents the results of a new approach for structural reliability analyses using adaptive kriging, confirmation simulation, and the pilot point method. Its main objective is to develop an efficient and accurate global approximation while controlling the computational cost and accuracy of prediction. The main contribution of research is to reduce computation time and successfully analyze complex problems with accurate results while ensuring excellent predictive quality of the approximation. For an excellent predictability of the kriging approximation, pilot point method and confirmation simulation are proposed. Simply, the predictive quality of the initial kriging approximation is improved by adding adaptive information, and the points are referred to as “pilot points” in areas where the kriging variance is maximized. Outcomes are confirmed with numerical simulations. The purpose is to select the minimum number of design experiments to ensure a good relative accuracy of the predictors with respect to the original models. Numerical examples show the efficiency of the proposed method compared to other structural reliability approaches.

Abstract: The consumption of natural resources like sand and stones for concrete production has resulted not only in their scarcity but also in environmental degradation associated with their extraction, and air pollution due to the generated quarry dust as result of the rock crushing. Also, with increase of mining sites in Rwanda, the amount of mine tailings has extremely increased, and their dumping is becoming a big challenge. The purpose of this study was to search for an engineering solution to the above dual problem, analyzing the performance of both mine-tailings and quarry dust as potential replacements for ordinary aggregates in concrete. The methodology consisted of evaluating the properties of the two materials, and then the analysis of strength characteristics for the new concrete manufactured using the two new aggregates. Concrete preparation was done by keeping constant the mine tailings portion as coarse aggregate, while partially replacing river sand by quarry dust at different fractions as 0%, 10%, 30% and 50%. It was established that, comparatively to normal concrete at 28 days, the compressive and tensile strengths of concrete with mine-tailings and river sand increased from 27MPA to 37.5 MPA, and from 1.9 to 3.1 MPA respectively on one hand, and on the other hand the compressive and tensile strengths decreased with partial replacement of river sand by quarry dust from 37.5 to 27.9MPA and from 3.1 to 2.3 MPA at replacements from 0% to 50% respectively. It was concluded that mine tailings and quarry dusty can be used together as concrete new aggregates in replacement of ordinary aggregates, with a due attention to concrete workability and its area of application.

Abstract: This work focuses on the numerical investigation of different modes of heat exchangebetween the habitat and its environment in an extremely hot climate to optimize thermal comfort.Notably, to optimize habitable comfort, it is essential to model the solar flux and the temperatureabsorbed by the habitat walls. In this context, we have developed an analytical model to predict heatexchange for a habitat in the Adrar region. The heat transfer equations have been established in eachwall of the habitat. These equations were discretized by the finite difference method and solvedusing the Gauss algorithm. The models developed were validated with climatic data measured in theresearch unit ''URER'MS'' in Adrar. The results obtained showed that building materials andextreme weather conditions were the decisive parameters of unwanted overheating.

Abstract: In this study atmospheric aerosols distribution over Lagos area of southwestern part of Nigeria was analyzed using backward air mass trajectory model. GPS information of the study region was used to simulate meteorological variables and aerosol data that have been stored by satellite imagery from the National Oceanography and Atmospheric Administration (NOAA) and Air Resource Laboratory (ARL). Hybrid Single-Particle Lagrangian Integrated Trajectories HYSPLIT was used to determine the wind-field information and also to obtain the backward air mass trajectory for atmospheric aerosols transport pattern at heights 0, 1000m and 2000m above ground level. The result showed that aerosols of sea-salt origin evolved from Atlantic ocean and spread over Lagos during the period under consideration. The average wind speed observed within the period ranged between 4 and 7m/s in south westerly direction which is attributed to the influence Atlantic Ocean. The results also showed that aerosol traversing Lagos area are mainly sea salts

Abstract: The Nimba Range and its western extension are located in the Nimba region on the borders of the Republic of Guinea, Liberia and Côte d'Ivoire. It is a mountainous region made up of metavolcanic and metasedimentary rocks. Metavolcanic rocks are gneisses, granites, amphibolites and quartzites, which constitute the lower part of Archean age. The upper part consists of Proterozoic rocks of metasedimentary origin. It contains important deposits of itabirites which occupy the top of the mountains and hills of the region. The petrographic study of the banded iron formations reveals the existence of silicate banded iron formations (SIF) and oxidized banded iron formations (OIF). The results of the scanning electron microscope (SEM) and metallogenic analyzes show the presence of iron minerals (magnetites, hematites, pyrites, goethites, martites and siderites). These analyzes also reveal the presence of the metamorphic index minerals associated with the banded iron formations, hence the existence of several types of ferriferous formations (silicate (SIF) and oxidized (OIF) banded iron formations). Overall, there is an increase in the degree of regional metamorphism from east to west of the Nimba region. The geochemical analysis of the banded iron formations reveals that with the exception of Na₂O, all the major elements have a negative linear correlation although dispersed with Fe₂O₃. This correlation is explained by a decrease in quartz, garnet, micas (muscovite and biotite), amphibole, pyroxene, plagioclase, titanium and phosphorus contents. Conversely, there is an increase in iron ore content: magnetites, pyrites, hematites, goethite. But the alkali content remains constant in these banded iron formations. Then, the lower the Fe₂O₃ content, the higher the FeO content, while those of SiO₂ and Al₂O₃ are constant in all of these formations in the Nimba region except in the chlorite banded iron formation where both are anticorelated. Finally, the ratio SiO₂ / Fe₂O₃ vs MgO + CaO + MnO / Fe₂O₃ of the banded iron formations of the Nimba region compared to the same formations of the whole world allows to give them Proterozoic age. Some itabirites have high levels of magnetite, hematite, and goethite (same feature as itabirites of Lac supérieur and Pic de fon) and only chlorite itabirite has a low to medium Mg-Si-BIF content.

Abstract: Drilling is a chip machining process widely used in manufacturing .The term drilling includes all methods for making cylindrical holes in a work piece with chip cutting tools. There are many applications where drilling is used, such as drilling holes in PCBs. Robotic systems are used today to perform the drilling process. A problem that affects the use of these systems is the drilling sequence, as there are usually a number of points to visit. The determination of the drilling sequence is similar to the problem of synchronization of movement and travel time. The main objective is to optimize the time and trajectory of the three axes robot equipped with an automatic drill that seeks the best performance. In this paper, we have built a genetic optimization and problem solving algorithms to shorten the machining time to drill a given group of holes and reduce machining costs in order to improve the efficiency of the machining process as well robotic machining with three axes without degradation of the precision of the movement. The results of the experiments show that the proposed approach is feasible and practical. It is particularly useful in planning and scheduling systems for real-time manufacturing processes.