International Journal of Engineering Research in Africa Vol. 45

Abstract: WC-Co cemented carbide is one of the widely hard materials used for cutting in machining industry, due to its microstructural and mechanical stability even at high temperature. However, diffusion wear is the most serious problem that WC-Co suffers from. One of the most applied approaches to improve the WC–Co cemented carbide performances is the addition of transition metal carbides such as: TiC, TaC and NbC which prevents diffusion wear thanks to the gamma phase (Ti,Ta,Nb,W)C which is formed during sintering. Therefore, and in order to understand the thermal metallurgical reactions occurred between WC-Co cemented carbide and (Ti, Ta, Nb)C transition carbides and theirs effects on the microstructural and mechanical properties. The WC–TiC– TaC– NbC–Co cemented carbide was elaborated by conventional powder metallurgy then thermal, microstructural and mechanical investigations were performed on the elaborated carbide. A temperature of sintering was determined to be more than 1347 oC by differential thermal analysis (DTA) and differential scanning calorimetry (DSC). Scanning electronic microscopy (SEM) coupled with energy dispersive spectrometer (EDS) observations showed that the microstructure consists in a mixture of angular WC grains and (W,Ti)C rounded grains embedded in the Co-rich binder. X-ray diffraction analysis confirmed the presence of these three phases with free carbon. The results of EDS analysis highlight the solution-reprecipitation phenomena caused by liquid phase sintering and clearly revealed the presence of small amount of free carbon. The mechanical characterizations showed that the WC–TiC– TaC– NbC–Co cemented carbide exhibits excellent hardness-fracture toughness combination.

Abstract: Fatigue failure due to stress raiser regions on critical rotating components in gas turbine engines, such as the shaft, is a crucial aspect. Methods to reduce these stresses and improve fatigue life are a source of ongoing research. Laser shock peening is a method where compressive residual stresses are imparted on the stress raisers of such components. However, numerical based studies on multiple laser shock peening applied to stress raisers is under-researched. Hence, this study will attempt to predict the fatigue life at fillet radii step induced stress raiser regions on a high-speed gas turbine engine shaft by utilization of laser shock peening. The objective of this study was achieved by developing a more computational efficient finite element model to mimic the laser shock peening process on the fillet radii step induced stress raiser regions of a shaft. A modified laser shock peening simulation method for effective prediction of the residual stress field was introduced. Furthermore, the fatigue life improvement due to laser shock peening was predicted by employing Fe-safe fatigue software. From the results, the modified laser shock peening simulation method provided accurate prediction of the residual stress field with a reduced computational time of over 68% compared to conventional methods. The fatigue life revealed an improvement of 553% due to laser shock peening, which is comparable to similar findings in the literature. Hence, from the findings and results achieved, the developed finite element model can be an appropriate tool to assist in the fatigue life estimation of laser shock peening applied to stress raisers.

Abstract: Surface finish accrued extra-production cost, reduced effective sheet thickness, stir zone galling, undesirable flash-root stress concentration and fatigue cracks are consequences of bulk expulsion of flash during friction stir spot welding of aluminum alloys. This paper attempts to cutback the abovementioned challenges and improves the weld strength (shear failure load) of friction stir spot welded joints of an Al alloy by adopting an integrated Grey relational analysis-entropy measurement method as a multi-objective optimization tool. Shear failure load, and expelled flash properties (pushed out length and thickness) are the three examined quality characteristics of the joint while tool rotational speed (600-1400 rpm), dwell time (3-6 s) and plunge depth (1.5-1.7 mm) are the studied process parameters. The experiment was planned via the use of Taguchi method whereas the entropy measurement method facilitated the identification of the precise weighting values required for the estimation of the unified grey relational grade. The failure load of the joint was maximized while both flash height and pushed-out length were minimized. The optimized shear failure load and flash properties were attained at a parameter setting of 1400 rpm rotational speed, 6 s dwell time and 1.5 mm plunge depth. The tool rotational speed was found to have the most significant effect and percentage contribution on the combined responses with 67.75%, followed by plunge depth (12.88 %) and dwell time (11.94 %) respectively. The validation results confirm the robustness of the entropy measurement-based multi-objective optimization as a tool for improving the quality responses of friction stir spot welds.

Abstract: Effect of glass fines and cement as a composite mixture on the geotechnical properties of a poor lateritic soil obtained from a borrow pit at Aroje, Ogbomoso, Nigeria was investigated as a reuse method of managing wasted glass. Glass fines up to 12% at intervals of 4% by mass of the soil sample were added to the lateritic soil stabilized with cement of 0, 2, 4, and 6% by mass of the soil sample. Sieve analysis, Atterberg limit, British Standard (BS) Compaction, California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) tests were conducted on the stabilized soil specimens. Results showed that Liquid Limit (LL), Plastic Limit (PL) and Plasticity Index (PI) decreased while compaction and UCS of the lateritic soil increased from 0 to 8% addition of glass fines. The CBR of the soil increased continuously from 0 to 12% glass contents. However, addition of cement increased the LL and PI while it decreased the PL between 0 and 4% but increased beyond this range. The compaction, UCS and CBR of the stabilized soil increased significantly with increasing cement content. Hence, the soil can be stabilized with the addition of 8% glass fines and 6% cement content to be used as improved subgrade material for construction of light trafficked pavement.

Abstract: The structures are prone to dynamic loads such as earthquake as they often generate uncomfortable movement into existing structures. In order to reduce extreme vibration generated by dynamic or operational loads passive, active or hybrid controlling devices are used. And the advantages of passive systems are well accepted due to their inexpensiveness and simplicity. This study investigates the performance of a newly developed uniaxial tuned mass damper (TMD). The novelty of the developed device is that the properties of the damper are adjustable based on the structural requirements. And most importantly, another key design criterion is to make a low-cost affordable device. To do this end, a toy two degree of freedom (2-DOF) system is considered and the experiments are conducted. The experimental tests and numerical simulations are carried out on the structure without and with TMD along with extra masses of 25 kg, 30 kg and 35 kg on the floors to observe the effect of floor mass changes. The scaled El Centro 1940 earthquake data is used as input excitation. In order to determine the optimal performance of the damper, it is tuned to modal mass of 0% (i.e., without TMD), 5%, 7.5%, 10%, 12.5%, and 17.5%. The experimental results have shown that the structure without TMD has pronounced vibration (i.e., displacement) as compared to the structure with TMD. As the percentage of modal mass increases, the vibration of the structure decreases. It is observed that up to 12.5% of modal mass for both 20 and 25 sec excitation duration could be the optimum amount that minimizes the vibration of the structure. The overall performance of this device is capable of reducing vibration in a reasonable manner and has the possibility to use it for the real engineering application.

Abstract: Work-related Musculoskeletal Disorders (WMSDs) have been seen as major health problems that have direct impacts on workers’ physical/psychosocial well beings, health, and productivity. Thus, the assessment of Musculoskeletal Disorders (MSDs) in sawmills will lead to a suitable platform for development and execution of proper ergonomic intervention programmes to achieve desirable workplaces. This research focused on determining the prevailing factors associated with MSDs and establishment of exposure’s level of sawmill workers to MSDs, based on risk and postural analyses using Quick Exposure Check (QEC), Rapid Entire Body Assessment (REBA) and Rapid Upper Limb Assessment Method (RULA); and physical strain assessment using relative Cardiovascular Load (% CVL), Cardiovascular Strain (% CVS) and Relative Heart Rate (%RHR) equations. Six hundred and sixty – three (663) male and thirty – three (33) female workers participated in the research survey and the participants were classified into two groups: machine operators’ classification (which included: Band-saw Operators (BOs), Circular-saw Operators (COs) and Planer Operators (POs)) and sawmill workers’ classification (which included: Machine Operators (MOs), Mill Workers (MWs), Dust Parkers (DPs); and Machine Maintenance Personnel (MMPs)). Ninety – six (96) workers each from each machine operators’ classification group (making 288 MOs), 240 MWs, 96 DPs, and 72 MMPs were considered for this study. Two cities were considered in each six Southwestern States of Nigeria, namely: Ekiti, Lagos, Ogun, Ondo, Osun, and Oyo States and a minimum of two sawmills were used in each city. The results of the postural analysis using QEC, REBA, and RULA show that an appreciable number of workers were working above the secured limit. Physical strain assessment results showed that not less than 60% of the workers were operating under high or very high-level discomfort and 61.8% of the workers were subjected to either heavy or very heavy work intensity.

Abstract: This paper presents a study of the monthly variability of wind energy potential at several heights and an investigation of the best fitting commercial wind turbine in the Cotonou coast (Benin Republic). The monthly Weibull parameters are calculated at 10 m and extrapolated at 30 and 50 m heights. The monthly Weibull wind power density and the wind speed carrying maximum energy are calculated at 10, 30 and 50 m. We showed that wind resource in the Cotonou coast is favorable for wind energy production at 30 and 50 m heights. The capacity factor of selected commercial wind turbines is calculated to investigate the best fitting wind turbine in the Cotonou coast. It turns out that Polaris 19-50 is the best fitting wind turbine in the selected turbines with a mean capacity factor of 0.49.

Abstract: In this paper an attempt is made to design the regulator for automatic generation control (AGC) of an interconnected energy delivery system to regulate the frequency and tie-power to original value for sudden change in the energy demand of the customers. The considered energy delivery system is having the power generation via thermal, hydro and gas sources and connected via means of parallel AC/DC tie-lines. Further, most of AGC studies focussed on regulator design using application of control theory such as optimal control to manage the balance between generation and load demand considering all system states. However, inreality it is hard enough to measure all system states and design effective regulator for AGC action. Hence in this paper efforts are made to design regulator for AGC problem using few states which are easily measurable and available in real situation of the system i.e. output vector feedback. The feasibility & stability of proposed AGC is tested for 1% change in power demand and compared with optimal AGC which is based on all system states using obtained system responses, feedback gains of control as well as closed loop eigenvalues.

Abstract: The concept of distributed generation (DG) has been developed as a hopeful solution to meet the demand increase in distribution systems. The optimal DG deployment in the distribution system can improve the technical benefits. This study presents a framework to find the optimum location and size for different types of DG units to enhance the voltage stability index (VSI), improve the voltage regulation and reduce the daily energy losses. The emission effect and cost function (environment and economic benefits) are augmented in the multi-objective function. Combinations of DG types are introduced to obtain the best benefits from each one. The daily load variations and dynamic output of each DG type are considered in the problem formulation. The genetic algorithm (GA) technique is used to find the optimal allocation for different cases. The typical IEEE 33-bus system is utilized to evaluate the proposed framework.

Abstract: This study has been carried out to demonstrate the control of a reactive distillation process in which the production of biodiesel was taken as the case study using an advanced control method, which is known as dynamic matrix control. The control was accomplished by employing the transfer function model of the reactive distillation process developed, using the System Identification Toolbox of MATLAB, from the dynamic data generated when the prototype plant of the process was simulated with the aid of ChemCAD process simulator. The results obtained from the dynamic matrix control were compared with those of a proportional-integral-derivative (PID) control system tuned with Ziegler-Nichols and Cohen-Coon methods, and it was discovered that the dynamic matrix control was able to perform best among the three (dynamic matrix control method, PID tuned with Ziegler-Nichols method and PID tuned with Cohen-Coon method) because it (the dynamic matrix control) was able to make the biodiesel mole fraction response not to exceed the maximum limit value of 1 in addition to having the lowest sum of absolute errors (SAE) and sum of squared errors (SSE) from the control systems that were simulated.