International Journal of Engineering Research in Africa Vol. 41

Abstract: This study focuses on the evolution in the microstructure, texture and mechanical properties of medium carbon steel wires obtained by wire drawing at Tréfissoud Company for the manufacturing of the spring mattress. Wire drawing induces elongation of grains in the direction of drawing with the development of the <110> fibre texture parallel to the wire axis. Kinking and bending of cementite lamellae were observed during the drawing process. The work was carried out respectively on three states, wire rod and drawn states for two different amounts (ε %=43,6 and 60 %), using the optical and SEM microscopy, electron backscatter diffraction and X-ray diffraction analysis for examination of the microstructure and texture evolution, the hardness Vickers and tensile test to follow the curing of the studied wires.

Abstract: The aim of this work is to study the plastic instabilities occurring on the stamped sheets during deep drawing process. The analysis of the plastic deformation of the material showed that the deformation occurs in bi-axial extension at the bottom of the punch due to thinning of the sheet, in local necking together at the vertical wall level of the sheet and below the blank holder due to thickening of the sheet. As a first step, an experimental characterization of the material is undertaken, whose experimental tests made it possible to determine the fundamental characteristics of the material. In the second step, a study of the material behaviour during forming process by numerical simulation using Abaqus finite element code is proposed. The various simulations undertaken showed the variation of the two parameters; the blank holder force and the friction effect. The blank holder force and friction, applied respectively to the blank flange region and between the tool-blank surfaces, make it possible to optimize the deformation limits and to repel any instability which may appear on the material in deep drawing. The simulations carried out on Abaqus code allow to visualize the material behaviour during deformation, by locating the thinning and necking zones on the sheet and from there, in order to locate areas at risk of failure. An optimization of the process is proposed by varying the considered parameters in a validated numerical model. Satisfactory results have been obtained which clearly show the failure and the safe zones.

Abstract: The synthesis of Si-based refractory compounds from coconut shells (CS) by carbothermal treatment was investigated. Coconut shells, an agro-waste was utilised in the processing of the Si-based refractory compounds in a single stage carbothermal processing route. The treatment scheduled was carried out in a conventional heat treatment furnace at a temperature window of (900-1900 °C) at 10 °C/min heating rate in a controlled atmosphere. X-ray Diffractometer (XRD) was used to analyzed and quantify the crystalline and amorphous phases in the reaction products. The results from Fourier transform infrared spectroscopy (FTIR) revealed that, the dominant functional groups present after the carbothermal treatment were mainly Si-O-Si and Si-C groups. Also, the XRD results showed that the polytypes are mainly of α-SiC type precipitating as hexagonal symmetry of 6H-SiC and 4H-SiC type. The silica polytypes amount to about 8-14 wt.% of the silica polytypes as observed for different processing temperatures adopted. However, the total yield of SiC-made up between 11 to 40 wt.% of the crystalline phases as identified by XRD from the process. It is evident that the adoption of this processing route is a viable option for the synthesis of coconut shells as potential reinforcement for composites design.

Abstract: The quality loss caused by tolerance of factors can be reduced when the nominal values of design-factors are carefully chosen. Therefore, the parametric optimization method is significant to an optimally define the Quality Loss cost (QLc). In this work, the Design Exploration (DE) and Taguchi Methods along with unforced Rotordynamic analysis have been used to find the optimal levels of factors affecting the QLc. Under definite constraints, the mathematical models are developed for an optimization problem and then utilized to develop Machine Motorized Spindle (MMS). In order to find the optimal levels of the factors, the sensitivities of factors on structural weight and First-Order-Nature-Frequency (FONF) has been analyzed using Response-Surface (RS) method, while the Taguchi method is used to find the QLc. The results found shown that there are significant enhancements in signal-to-noise ratio for structural weight and FONF. The QLc has been saved to about more than half-time by comparing to its initial values. The results also indicated that the proposed optimization approach is feasible and successful in improving dynamic characteristics and QLc saving for the MMS. Keywords: Machine Motorized Spindle, Finite Element Method, Unforced Vibration, Rotordynamic Analyses, Response Surface Method, Taguchi Quality Loss cost.

Abstract: This paper presents a Backstepping controller for five degrees of freedom Spherical Inverted Pendulum. Since the system is nonlinear, unstable, underactuated and MIMO and has a nonsquare form, the classic control design cannot be applied to control it. In order to remedy this problem, we propose in this paper a new method based on hierarchical steps of the Backstepping controller taking into a count the nonlinearities that cannot be neglected. Furthermore, a Linear Quadratic Regulator controller and LQR + PID based on the linearized system model are also designed for performance comparison. Finally, a simulation study is carried out to prove the effectiveness of proposed control scheme and is validated using the virtual reality environment that proves the performance of the Backstepping controller over the linear ones where it brings the pendulum from any initial condition in the upper hemisphere while the base is brought to the origin of the coordinates.

Abstract: This experimental research proposes a contactless silicon-based two-dimensional (2D) Hall sensor capable of simultaneous parallel-and perpendicular-directional magnetic sensing, with a 360° angle measurement. The Hall sensor was of non-symmetrical five-ohmic contact configuration (C1 – C5). In the study, experiments were carried out in three stages. In the first-stage experiment, the current (I) and voltage (V) of the 2D Hall sensor were determined under three schemes: schemes A (C1&C2), B (C2&C5), and C (C3&C4). In the second-stage experiment, the parallel and perpendicular absolute sensitivities of the 2D sensor were examined. Considering the discrepancy between the parallel and perpendicular absolute sensitivities, signal conditioning circuitry was incorporated into the sensor system to compensate, and the rotational angles measured in the final-stage experiment. The results revealed that the I-V curves were dominantly linear, corresponding to Ohm’s law. However, the parallel and perpendicular absolute sensitivities were low and unequal. Thus, signal conditioning circuitry was incorporated into the system to address the discrepancy and improve the performance. Importantly, the 2D Hall sensor exhibited a mere ±3^o discrepancy between the measured and reference rotational angles, given the magnetic flux density of 1000 G, with the hysteresis error of 2.8%. In essence, the proposed contactless silicon-based 2D Hall sensor possesses high potential for high-precision industrial applications.

Abstract: The most challenging issue in the design of wireless sensor networks for the application of localization in the underground environment, mostly for miner’s location, is the sensor nodes’ energy consumption, efficiency and communication. Underground Wireless Sensor Networks are active and promising area of application of Wireless Sensor Networks (WSNs), whereby sensor nodes perform sensing duties in the underground environment. Most of the communication techniques used in the underground environment experience a high path loss and hence, hinders the range needed for transmission. However, the available option to increase information transmission is to increase the transmission power which needs large size of apparatus which is also limited in the underground. To solve the mentioned problems, this paper proposed a Magnetic Induction based Pulse Power. Analytical results of the Magnetic Induction based Pulse Power with an ordinary magnetic induction communication technique show an improvement in Signal-to-Noise Ratio (SNR) and path loss with variation in distance between nodes and frequency of operation. This paper further formulates a nonlinear program to determine the optimal data (events) extraction in a grid based WUSNs.

Abstract: Bridges are commonly used lifelines; they play an important role in the economic activity of a city or a region and their role can be crucial in a case of a seismic event since they allow the arrival of the first aid. Reinforced concrete (RC) bridges are worldwide used type view their durability, flexibility and economical cost. In fact, their behavior under seismic loading was the aim of various studies. In the present study the effect of two structural parameters i.e. the height and the type of piers of reinforced concrete bridges on seismic response is investigated. For that reason, different multi-span continuous girder bridges models with various geometrical parameters are considered. Then, non-linear dynamic analyses are performed based on two types of piers which are: multiple columns bent and wall piers with varying heights. In this approach, a serie of 40 ground motions records varying from weak to strong events selected from Building Research Institute (BRI) strong motion database are used including uncertainty in the soil and seismic characteristics. Modelling results put most emphasis on the modal periods and responses of the top pier displacements, they show the influence of the considered parameters on the behavior of such structures and their impact on the strength of reinforced concrete bridges.

Abstract: The article is devoted to the research into the utilization of large volume industrial wastes to produce mineral-polymer composite construction materials. To produce the composites, polyvinyl chloride wastes have been suggested as binding thermoplastic matrix and ash-and-slag wastes, which are the by-product of coal combustion at TPP of Irkutsk Oblast, as mineral filler. Since the problem of accumulation and storage, such as large volumes of power generation industry wastes is becoming more and more serious, the recycling of these wastes with the production of useful products is the vital task. Plants that manufacture products from PVC also produce plastic wastes in the form of rejected and substandard raw material, which can be recycled. At the same time, the problem of production available construction materials for the Baikal region from the local cheap raw material is solved. The team of Irkutsk National Research Technical University has conducted a number of the industrial trials on the production of mineral-polymer composites by the method of extrusion. As a result, the principal opportunity of co-utilization of PVC wastes and ash-and-slag materials during the production of composite construction materials has been testified. Local construction companies can use the produced materials.

Abstract: Concrete use is fundamental to most infrastructural development plan of humanity today. This underscores the need to understand the strength characteristics of concrete made with crushed glass aggregate as partial replacement for fine aggregate and mixed with magnetic field treated water (MFTW). This study investigates the mechanical properties of concrete mixes prepared and cast into cubes of varying constituents such as concrete mixed with normal water, concrete mixed with MFTW, concrete with varying degree of crushed glass as replacement of fine aggregate from 15 to 45% with or without MFTW. The cubes were thereafter crushed after 7, 14, 28 and 56 days of curing to determine their compressive and tensile strengths. From the results obtained, it was observed that the optimum percentage partial replacement of sand with crushed glass aggregate is 15% to attain a suitable using MFTW in the mixing of the concrete. At this percentage replacement, it was observed that both the compressive and tensile strengths of the concrete mixed with MFTW improved by 25-30% relative to the conventional concrete. The study therefore recommend the use of MFTW in place of normal water in concrete production and use especially when partially replacing fine aggregate with crushed glass aggregate.