International Journal of Engineering Research in Africa Vol. 53

Abstract: This study aims to investigate the effects of powder particle size on the densification and microhardness properties of spark plasma sintered superalloy. Three particles size ranges of nickel were used in this study, namely, (3-44, 45-106 and 106-150 μm), and this is the matrix in the IN738LC superalloy composition (powder), used in the study. The effects of the particle size were examined at a specific applied temperature and pressure. The transitioning stages during the sintering process of the green powders to the formation of the sintered alloy were analyzed and given as the particle rearrangement stage, the localized deformation stage and the neck formation/grain growth stage. There was the formation of γ, γ' and a solid solution within the microstructure of the sintered alloys. The effect of particle size was more pronounced on the grain sizes obtained, while the phases formed is the same for the three alloys. The results indicate that the nickel particle size (>60% of the total composition) has a significant influence on the densification, porosity, grain size and hardness properties of the IN738LC sintered alloy. Finer nickel particle size resulted in a sintered product with smaller grain size (9 µm), reduced percentage porosity (3.9%), increased relative density (96.1%) and increased hardness properties (371 Hv).

Abstract: The high entropy alloys have attracted the interest of material scientists due to theirspecial mechanical properties and a very good corrosion behavior. The corrosion resistance is provided by the formation of a passive, thin and compact oxide film that prevents the chemical dissolution of the metallic matrix. The effect of aluminum in AlxCrFeCoNi high entropy alloys (with x = 1; 1.5 and 2) that were obtained by electric arc melting under argon atmosphere has been studied in the paper. In order to understand the processes involved in metal corrosion, the alloys have been tested by polarization resistance method in 3.5% NaCl solution and main corrosion parameters have been analyzed (i.e. corrosion potential; corrosion current density; corrosion rate and polarization resistance). The surfaces of the corroded samples were examined by scanning electron microscopy to estimate the effect of the chemical composition on corrosion resistance. The corrosion tests have shown that the corrosion resistance of the HEA decreases by increasing the aluminum content from about 15 at.% to 32 at. % Al and reducing the chromium content from 28 at. % to 18 at.% Cr.

Abstract: The huge nutritional value and industrial potentials inherent in Moringa oleifera have not been fully tapped and used because of the labour intensive method of shelling and grinding the seeds into fine powder. A Roller Type Shelling Device (RTSD) Moringa oleifera seed sheller was designed, constructed and tested in this study. The hopper, shelling drum, shelling paddle, screen, cleaning fan, frame, seed outlet, chaff delivery chute, and electric motor made up this functional machine. The performance indices evaluated for the developed sheller were based on shelling efficiency, cleaning efficiency, throughput capacity, mechanical damage index and shelling performance index at moisture content levels of 7.64, 9.45, 17.53, 21.73 and 25.52% (w.b). The sheller had maximum shelling efficiency, cleaning efficiency, throughput capacity, mechanical damage index and shelling performance index of 88.14%, 89.41%, 12.48 kg/h, 12.75% and 87.66% respectively at moisture content levels of 7.64% (w.b). With the output of the sheller, full industrial processing of Moringa oleifera seed is feasible with minimal limitation.

Abstract: To improve the pressure-bearing capacity, a novel high-pressure die with cemented carbide as the first layer of supporting ring was designed. The novel high-pressure die increases the ultimate load-bearing capacity of the high-pressure die by increasing the pretension of the tungsten carbide cylinder. As the volume of the cemented carbide increases, the difficulty of manufacturing increases, therefore, to reduce the manufacturing difficulty of the cemented carbide supporting ring and reduce the shear stress of the supporting ring, the cemented carbide supporting ring is splited. And through reasonable derivation calculations, the calculation formula suitable for the optimal interference amount of the high-pressure die is obtained. The numerical analysis results show that: when a pressure of 6.2 GPa is applied on the inner wall of the tungsten carbide cylinder, high-pressure die mold that uses cemented carbide as the first layer of support ring (hereinafter referred to as double-layered cemented carbide novel high-pressure die) is lower than the ordinary high-pressure die in term of circumferential stress by 93.34%. In terms of von Mises stress by 21.4%, and term of maximum shear stress by 21.37%. The three principal stress images of the two molds are drawn, which proved that the double-layered hard alloy novel high-pressure die can fully exert the performance of the material and can withstand greater pressure.

Abstract: As product structure becomes more and more complex, the fault mode presents a diversified trend, and it is more difficult to determine the causes of system failure for a complex product. The main objective of this study is to provide an effective failure analysis method based on the combination of fault trees analysis (FTA) and generalized grey relation analysis (GGRA) for complex product. In this method, the product system failure is defined and the fault tree is constructed by FTA methodology firstly; and then GGRA is employed to identify the correlations between each fault mode and the system failure; finally, the main causes of system failure are identified and the corresponding measures can be made. A case study of a WD615 Steyr engine is conducted throughout the text to verify the validity of this method. The present study would help facilitate the failure and reliability analysis for complex product and benefit designers for the product improvement.

Abstract: Sandcrete block is a vital building material used in the construction of building structures. The sandcrete blocks are produced by different manufacturers using river sand obtained from different locations as aggregate material without recourse to the minimum quality standard for the blocks produced. The study assessed the strength parameters of river sand used as an aggregate material in block production to determine its quality and suitability in relation to the strength of block produced. Three (3) block manufacturing sites in Nigeria were visited and 27 (twenty-seven) blocks of size 450 mm x 225 mm x 225 mm were selected randomly from the sites. The properties of the river sand was analyzed through sieve analyses, bulk density, silt content and water absorption while the compressive strength of the blocks was also tested. The result of sieve analysis of the river sand used in block production for this study all satisfied the particle size requirements of BS EN 933-1:1997 for general construction work including block production. The result of the study also shows that blocks produced with the river sand after 28days have an average compressive strength of 1.23 N/mm2 (SW), 1.54 N/mm2 (SE) and 1.95N/mm2 (NE). The study, therefore, concluded and recommended that regulatory and professional bodies in partnership with relevant associations should organize seminars for producers of sandcrete blocks on the best practices involved in producing quality sandcrete blocks.

Abstract: This study utilized Finite Element Method (FEM) to analyse the structural behaviour and failure modes of Reinforced Self Compacting Concrete (RSCC) deep beams. Eighteen deep beam specimens subjected to four-point loadings were modelled and analyzed using Abaqus modelling tool. Damage plasticity model was used to characterised the nonlinear behaviour of concrete material while linear elastic, linear-plastic-hardening model represented the reinforcing steel material behaviour. The results of the finite model were compared with four different Strut and Tie Models (STMs) using one-way Analysis of Variance (ANOVA). Results of the numerical study revealed that the concrete strength and shear span to depth ratio mostly affect the load-deflection response of the beams. Also, the failure modes of the studied deep beams were influenced by shear span to depth ratio, concrete strength as well as web reinforcement distribution. The ANOVA results also showed that the FEM outperformed the existing STMs.

Abstract: Current cement-based building materials have a huge disadvantage that they are easily broken due to thermal decomposition at high temperature (over 500°C) of structures of hydrated cement. This is easily observed at construction works when burned, the cement-based mortar and concrete materials and plaster are susceptible to collapse causing damage to buildings or structures. More seriously, these accidents easily cause injuries or loss of life for residents and people working there. Therefore, research on fire resistance and structural stability at high temperatures of building materials is always an interested topic of many scientists. This study utilized resources of highly active alumino silicate materials such as coal bottom ash and rice husk ash to produce geopolymer using sodium silicate solution as an alkaline activator. The ash-based geopolymer has good engineering properties responding to requirements of ASTM C55 and C90 for lightweight concrete brick. It is interesting to note that the geopolymer product was tested for thermal properties at 1000°C such as heat resistance, volumetric shrinkage, mass loss. The experimental results show that the ash-based geopolymer material has high thermal stability with increasing significantly of compressive strength after heated at 1000°C. Moreover, the geopolymer was also carried out to characterize microstructure before and after exposed at high temperature using methods of X-ray diffraction (XRD), scanning electron microscope (SEM). Thermal analysis methods such as thermogravimetric (TG), differential thermal analysis (DTA), and dilatometry-thermal expansion (CTE) were used to evaluate microstructural stability of the geopolymer-based materials.

Abstract: Roads are the key infrastructure that is needed to support the smooth transportation to improve the condition of the community economy. Along with the passage of time and the use of the road, the road will suffer damage due to natural factors as well as other technical factors, so it takes serious handling efforts from the local government to maintain excellent road infrastructure for the community. In case of road damage handling in some areas still found problems that need to be resolved immediately, one of them is the problem of availability of budget that is not comparable to the level of damage of the road is quite a lot required a method to know the order of the road priority should be addressed immediately. To determine the prediction and priority order of road handling, the Analytic Hierarchy Process (AHP) algorithm is used with consideration of damage, traffic, and economic factors as criteria decision. The result shows that area of Serang city with the value 0.231 (23.1%) as the most priority road to be repaired.

Abstract: As a first step for image processing operations, detection of corners is a vital procedure where it can be applied for many applications as feature matching, image registration, image mosaicking, image fusion, and change detection. Image registration can be defined as process of getting the misalignment of pixel's position between two or more images. In this paper, a modified corner detector named Synthetic Aperture Radar-Phase Congruency Harris (SAR-PCH) based on a combination between both phase congruency, named later PC, and Harris corner detector is proposed where PC image can supply fundamental and significative features although the complex changes of intensities. Also, the proposed approach overcomes the Harris limitation concerning the noise since the Harris is more sensitive to the noise. The performance was similitude with Shi-Tomasi, FAST, and Harris corner detectors where experiments are conducted first with simulated images and second with real ones. Mean square error (MSE) and peak signal-to-noise ratio (PSNR) are used for the simile. Experimental results, carried out in a standard computer, verify its effectiveness where it utilizes the privileges of image constitutional depicting, allowing extraction of the most powerful key points since it preserves robustness of co-registration process using image frequency properties which are not variant to illumination. Reasonable results compared to the state of art method as Shi-Tomasi, FAST, and Harris algorithms were achieved on the expense of high computational processing time that can be recovered using hardware having high capabilities.