International Journal of Engineering Research in Africa Vol. 46

Abstract: The mechanical and electrochemical properties of a low carbon steel alloy were improved with titanium (Ti) nitrides thin films. A nitriding process ensures the adhesion of the deposited thin films and provides the nitrogen source involved in the formation of the desired nitrides. A hybrid reactor was used to permit this duplex surface treatment and to avoid the oxidation of our samples. The X-ray diffraction revealed the formation of nitrided phases (TiN and Ti₂N). The scanning electron microscopy showed an improvement in the adhesion of the deposited thin films with increasing negative bias voltages. The nanohardness of the duplex treated samples was found to be improved. The results obtained after the corrosion tests indicate a reduction of electrochemical activity and therefore an improvement of corrosion resistance.

Abstract: Currently, Zr-alloys are widely used in nuclear power reactors for fuel cladding and structural components. Many types of zr-based alloys were developed to overcome the challenges encountered in the progress of nuclear reactors (high-burnup and high-duty). Oxygen diffused into the cladding, hydrogen absorbed in the cladding (breakaway oxidation and ruptured balloons) and rapid oxidation rate are results of chemical interaction of cladding material with steam at high temperature. Zirconium alloys seem to be the most suitable for use in fuel cladding, if they can overcome the rapid oxidation at temperature higher than 1200 °C. Previous studies on the oxidation behavior for some Zr-alloys nuclear fuel cladding tubes in steam and steam–air atmospheres at high temperatures are reviewed. The oxidation behavior of zirconium-alloys is strongly affected by the chemical composition of alloys and its surface conditions.

Abstract: Aluminum alloys development always exit in the manufacturing process. Al/Mg alloys have been attracted significant attention because of their excellent mechanical properties. The microstructural evolution and deformation mechanisms are still challenging issues, and it is hard to observe directly by experimental methods. Accordingly, in this paper atomic simulations are performed to investigate the uniaxial compressive behavior of Al/Mg phases; with different ratio of Mg ranging from 31% to 56%. The compression is at the same strain rate (3.10¹⁰ s⁻¹), at the same temperature (300K) and pressure, using embedded atom method (EAM) potential to model the interactions and the deformation behavior between Al and Mg.From these simulations, we get the radial distribution function; the stress–strain responses to describe the elastic and plastic behaviors of β-Al₃Mg₂, ε-Al₃₀Mg₂₃, Al₁Mg₁ and γ-Al₁₂Mg₁₇ phases with 31, 41, 50 and 56% of Mg added to pure aluminum, respectively. The mechanical properties, such as Young’s modulus, elasticity limit and rupture pressure, are determined and presented. The engineering equation was used to plot the stress-strain curve for each phase.From the results obtained, the chemical composition has a significant effect on the properties of these phases. The stress-strain behavior comprised elastic, yield, strain softening and strain hardening regions that were qualitatively in agreement with previous simulations and experimental results. These stress-strain diagrams obtained show a rapid increase in stress up to a maximum followed by a gradual drop when the specimen fails by ductile fracture. Under compression, the deformation behavior of β-Al₃Mg₂ and γ-Al₁₂Mg₁₇ phases is slightly similar. From the results, it was found that ε-Al₃₀Mg₂₃ phase are brittle under uniaxial compressive loading and γ-Al₁₂Mg₁₇ phase is very ductile under the same compressive loading.The engineering stress-strain relationship suggests that β-Al₃Mg₂ and γ-Al₁₂Mg₁₇ phases have high elasticity limit, ability to resist deformation and also have the advantage of being highly malleable. From this simulation, we also find that the mechanical properties under compressive load of ε-Al₃₀Mg₂₃ phase are evidently less than other phases, which makes it the weakest phase. The obtained results were compared with the previous experimental studies, and generally, there is a good correlation.The Al-Mg system was built and simulated using molecular dynamics (MD) software LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator).

Abstract: The acceptance and application of functional parts produced via additive manufacturing technologies is faced with challenges of poor surface finish, dimensional accuracy and mechanical properties among other which is mostly dependent on process parameters employed. In this study, the effect of infill density, layer thickness and extrusion temperature on mechanical properties of polylactic acid (PLA) part manufactured using fused deposition modelling process was investigated to obtain optimum process parameters to achieve the best properties. Solid cuboid bars were produced from which tensile, impact and hardness test specimens were obtained. A statistical approach based on Taguchi design of experiment was employed with process parameters varied and grey relational analysis coupled with principal component analysis was employed to obtain the unified optimum parameter. The single optimisation results showed that 50% infill density, 220°C extrusion temperature and 0.4 mm layer thickness resulted in best tensile strength; 30% density, 210°C temperature and 0.2 mm layer thickness is required to achieve the best impact strength, while 50% density, 215°C temperature and 0.3 mm thickness is required for highest hardness. The multi-response optimisation indicated that for the best of all the three properties to be achieved at once in a PLA built part, 50% infill density, 220°C extrusion temperature and 0.3 mm is required which yielded tensile strength of 30.02±2.15 MPa, impact strength 4.20±0.12 J and hardness of 76.80±0.38 BHN.

Abstract: In this paper a numerical modeling was carried out to study the problem of plane elasticity in a medium cracked by the method of the extended finite elements (XFEM) in a thin cracked plate made of aluminum using the software Abaqus 6.13.This method improved the capability of the classical finite element method especially the crack propagation problems. Furthermore, the extended finite elements method has been used to simulate tensile and fracture behavior of the study materials. Based on variation in size and shape of crack, the results obtained will be compared with those obtained experimentally, this comparison shows a good agreement.

Abstract: The rising awareness of the importance of moringa seeds has geared interest in its mass production. A major step in making the seed available for it vast usage is shelling. Most rural farmers of moringa seed use the traditional methods of shelling. These methods are tedious, time consuming with attendance low outputs that produce unhygienic products. The need to develop appropriate machines and equipment for processing of moringa seeds become necessary. This work developed a moringa seed shelling machine using available local materials. The development of the shelling machine was based on engineering mechanics of impact and shearing forces. The machine consists of a hopper, shelling unit, shafts, cleaning unit, sieve, discharge unit, power transmission unit and frame. The machine was evaluated based on variation in speed and feedrate to obtain the shelling efficiency, throughput capacity and percentage seed damage at 14% (d.b) moisture content powered by a 0.75 kW electric motor. The results obtained show that the machine has the highest shelling efficiency of 72.72% at 60 g/min feedrate with a throughput capacity of 8.31 kg/hr and the minimum percentage seed breakage of 2.22%. Machine speed of 250 rpm favoured the smooth operation and performance of the machine. The machine is very useful for rural people, farmers and small scale industries for post-harvest processing of moringa seeds since it cost and operational principle is within their technical know-how and capability.

Abstract: In free space optical (FSO) communication systems limited by atmospheric turbulence, the use of non-adaptive decision thresholds to determine the transmitted bits results in bit error rate (BER) floors at high BER values in all turbulence regimes. Practically implementing an adaptive decision threshold that can properly track the fluctuations due to atmospheric turbulence is challenging, therefore, devising ways of optimising the non-adaptive decision threshold used by FSO designers is necessary. In this paper, the investigation of gain saturated pre-amplified FSO communication systems using non-adaptive decision thresholds in the presence of atmospheric turbulence, pointing errors (PEs), geometric spread (GS) and amplified spontaneous emission noise is carried out by applying analytical methods and Monte Carlo (MC) simulation techniques. System performance is carried out for various turbulence regimes, normalised beam widths, normalised PE standard deviations and small signal gains using fixed gain and gain saturated optical amplifiers (OAs). Results obtained show that in the presence of atmospheric turbulence, PE and GS, optimal BER performances are obtained with OA input powers higher than the internal saturation power of the OA. Also, by using high gain OAs and varying the decision threshold level, acceptable BER performances can be obtained in strong turbulence regimes with a non-adaptive decision threshold.

Abstract: This paper presents a facial expressions recognition system to command both mobile and arm robot. The proposed system mainly consists of two modules: facial expressions recognition and robots command. The first module aims to extract the ROI (Region Of Interest like: mouth, eyes, eyebrow) using Gradient Vector Flow (GVF) snake segmentation and the Euclidian distance calculation (compatible with the MPEG-4 description of the six universal emotions). To preserve the temporal aspect of the processing from FEEDTUM database (video file), Time Delay Neural Network (TDNN) is used as classifier of the universal facial expressions such as happiness, sadness, surprise, anger, fear, disgust and neutral. While the second module, analyzes recognized facial expressions and translates them into a language to communicate with robots by establishing command law.

Abstract: This paper employs a comparative study between three recent versions of particle swarm optimization (PSO) algorithm to find the optimal scheduling of reactive power resources. Scheduling of reactive power resources is formulated as non-linear complex optimal reactive power dispatch (ORPD) problem. The main objective function of ORPD is to minimize the transmission power losses (P_loss). For this target, three modified versions, which present three variations applied on velocity equation of PSO algorithm, are considered. To achieve fair comparative study, the competitive versions are checked through 13 studied cases on IEEE 14-, 30-, 57- and 118-bus test systems. The effectiveness of these variations is proven for the non-linear complex optimization ORPD problem with different decision variables according to the system size. The obtained results confirm that these variations on PSO algorithm can make a noticeable reduction of P_loss at acceptable level in terms of power system operation view point.

Abstract: The present paper discusses the integration as well as contribution of doubly fed induction generator (DFIG) based wind turbines in load frequency control (LFC) of the modern electric power system in order to supply the quality as well as pollution free electric power to the modern customers. In addition the control areas are connected via HVDC tie-line in parallel with EHVAC line with diverse sources i.e. hydro, thermal and gas based power generations in each area. Efforts have been made to propose an optimal LFC design based on the feedback of few state variables which are available for the measurement and contains good information of the complete power system. The LFC design based on few states are implemented and the obtained results are presented to show the LFC enhancement considering DFIG and parallel HVDC/EHVAC lines. Atlast, the beauty and effectiveness of LFC based on few states are compared with LFC design depends on all system states under similar working conditions and the application results are presented.