International Journal of Engineering Research in Africa Vol. 33
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摘要: AlMgSi alloys (6XXX series) provide a good strength due to the precipitation of β” and β (Mg2Si) phases. They have also very good formability which is required for different forming process after appropriate heat treatments.This work was carried out to investigate the effect of the addition of copper and the excess of Si on the response of natural and artificial aging of two Al-Mg-Si alloys. The aging parameters on precipitation sequence of two Al-Mg-Si alloys with and without excess Si were studied by DSC, MET and Vickers hardness measurement. The combined effect of Cu, Fe and excess of Si was found to accelerate the precipitation of the hardening phases. The additions of copper to the AlMgSi refine the average of the grain size and have a greater hardening effect compared to the excess silicon addition.
摘要: The objective of the present work is an analysis of vibratory responses due to the impact of projectile in steel against a glass/polyester composite material under hygrothermal conditions with different energy levels. In the first part of this study, by means of a data acquisition system, a signal processing analysis of the contact force and acceleration of the projectile is carried out in order to deduce the oscillations of the responses. These are generated by the vibrations induced by the contact between the plate and the impactor. The analysis of the vibrations by the calculation of the Fast Fourier Transform (FFT) applied to the oscillations of the contact force allows to defining the resonance frequencies of the plate for the different energy levels. The measure of the Frequency Response Functions (FRF) from the obtained responses allows the determination of the damping of the impacted composite material.In the second part of this study highlights quantitatively and puts into evidence the influence of hygrothermal conditions on the mechanical responses such as contact force, acceleration, frequency and damping of aged and non-aged composite plates.
摘要: This study developed the necessary underlying experimental data and models to demonstrate the feasibility of using pre-compression of scrap tire strips as components of laminates within building structures. The approach presents an economical alternative for the reuse of scrap tires, while accounting for the tire material properties that may not be directly suitable for use in building structures. The proposed approach exploits the elasticity of the tire material as the basis for creating adhesion between the strip tire laminates. Pre-compression of the tire laminates creates frictional forces that prevent layer separation, and able to withstand winds up to 140 mph. Both experimental and theoretical approaches are presented to show the approaches potential.
摘要: The bearing capacity of shallow foundation near slope has always been one of the subjects of major interest in geotechnical engineering for researchers and practical engineers. This study focuses on the numerical analysis of the undrained bearing capacity for a strip footing near a slope, and subjected to a centered vertical load, using the explicit finite difference code FLAC (Fast Lagrangian Analysis of Continua). Theoretical and experimental studies confirm that, when a strip footing is near a slope, the bearing capacity must be assessed using reduction coefficients. In this study, several geometrical and mechanical parameters have been considered in order to evaluate the effect of the slope on the undrained bearing capacity. The numerical values have been compared with those available in the literature. The results show the influence on the undrained bearing capacity of the location of the footing with respect to the slope.
摘要: The study evaluated the properties of gravel aggregate sourced within Oyo north senatorial district for concrete production in place of crushed granite crushed at exorbitant cost since characteristic properties show significant reflections on the qualities of gravel aggregate used and also play major role in determining the properties of hardened concrete.Samples of gravel from four commonly used borrow pits: Aroje, Bolanta, Sunsun and Olomi sites were obtained and tested for Aggregate Crushing Value (ACV), Aggregate Impact Value (AIV), Specific Gravity, Water absorption Capacity, Bulk Density, Moisture Content and Particle Size Distribution. On the average the results of the observation for the selected four locations were 22.56 g, 28.17 g, 33.37 g and 40.19 g for Aggregate Crushing Value (ACV), 2.44 g/ml, 2.53 g/ml, 2.57 g/ml and 2.62 g/ml for Bulk density, 0.17 %, 1.43 %, 2.42 %, and 2.48 % for moisture content, 2.02 %, 2.92 %, 2.00 % and 3.15 for water absorption, 2.52, 2.63, 2.60 and 2.55 for specific gravity, 41. 55 %, 45.25 %, 45.59 % and 47.08 % for aggregate Impact respectively.The study revealed that, gravel aggregates from Aroje has superior properties over those of Sunsun, Bolanta and Olomi as compared with coarse aggregate properties in BS 812: 1995 and BS 882: 1992. It is hereby recommended for coarse aggregate in concrete production.
摘要: In this paper, steady state sensible performance analysis on multi pass parallel cross flow exchanger was considered. The inputs to the heat exchanger were described through meaningful physically significant parameters such as number of transfer units, capacity rate ratio and dimensionless input temperature. The inputs to the heat exchager were varied systematically and a parametric study was conducted to determine the thermal performance at each individual pass of the heat exchanger. Heat exchanger’s thermal performance was described through the discharge temperatures that were expressed in a dimensionless form. The results from the study were presented in the form of performance tables. The performance tables employed meaningful and industry recognized dimensionless input parameters and the heat exchanger‘s performance was described through dimensionless discharge temperatures at every pass of the heat exchanger. The developed performance tables shall serve two critical aspects. First, it will help the heat exchanger designers to readily choose an optimum heat exchanger. An undersized heat exchanger shall not deliver the requirements and likewise an oversized heat exchanger shall add unnecessary weight and cost. This aspect was clearly observed in this study as indefinetly increasing the number of transfer units (or surface area) beyond a threshold value didn’t enhance the heat transfer. By employing the performance tables as a guide, the heat exchanger designers can quickly ascertain the performance of the heat exchanger without having to perform simulations and/or lengthy calculations. Second, during operational phase of the heat exchanger, the performance tables can be used to understand the performance variation of the heat exchanger with respect to mass flow rates and/or can help the engineers to choose appropriate mass flow rates for the required heat transfer. The highest heat exchanger performance was observed at the lowest capacity rate ratio and likewise the lowest heat exchanger performance was observed at the highest capacity rate ratio. In-addition, during the operational phase, the performance tables can help to detect an underperforming heat exchanger and can help the engineers to schedule maintenance activity on the heat exchanger equipment.
摘要: In this article, the motion of two-dimensional Casson fluid flows with temperature dependent plastic dynamic viscosity together with double (i.e. thermal and solutal) stratification in the presence of Lorentz force is investigated. The case where the viscosity of the fluid tends to take energy away from the motion (kinetic energy) and transform it into internal energy is considered. The nonlinear governing equations and their associated boundary conditions are transformed and non-dimensionalized using similarity variables which are thereafter solved numerically using the shooting method together with the Runge-Kutta technique. The effects of the magnetic field parameter, temperature dependent viscosity parameter, Casson parameter, Eckert number, velocity power index, pressure gradient parameter and wall thickness parameter on the velocity, temperature, and concentration profiles are showed graphically and discussed. Substantial increase in temperature distribution is certain with an increase in the magnitude of Eckert number. Local skin friction coefficient decreases with an increase in pressure gradient parameter.
摘要: The problem of unsteady non – Newtonian flow past a vertical porous surface in the presence of thermal radiation is investigated. Using the theory of boundary layer analysis, the flow of micropolar fluid in the presence of exothermic and endothermic kind of chemical reaction is considered. It is assumed that the relationship between the flow rate and the pressure drop as the fluid flows over a porous medium is non – linear. Using local similarity transformation, the governing partial differential equations of the physical model are reduced to ordinary differential equations. The corresponding boundary value problem is solved numerically using shooting method along with Runge-Kutta Gill method together with quadratic interpolation. It is found that increase in micro-rotation parameter increases the velocity while the micro- rotation decreases across the flow region. Maximum micro-rotation of tiny particles is guaranteed at higher values of suction parameter. Local heat transfer rate decreases with an increase in exothermic /endothermic parameter.
摘要: In this article, a comparative analysis of free convective Blasius and Sakiadis flows of a viscous fluid over a vertical porous surface is presented. The relationship between the flow rate and pressure drop as the Newtonian fluid flows past a porous medium is linear; hence Darcy model is adopted. Suitable similarity variables are employed to transform the governing non-linear partial differential equations into a set of coupled non-linear ordinary differential equations. An approximate analytical solution of the coupled ordinary differential equation is obtained using Optimal Homotopy Analysis method (OHAM). The computational results for velocity and temperature profiles are shown graphically for various flow parameters and analyzed. The results show that an increase in convective parameter leads to increase in velocity and temperature profiles. Also, increasing buoyancy parameter increases the velocity profile and decreases the temperature profiles for both Sakiadis and Blasius flow. The temperature distribution at the maximum value of Prandtl in Sakiadis case is greater than the temperature distribution at the maximum value of Prandtl even in Blasius case.
摘要: The magneto-hemodynamic laminar flow of a conducting incompressible viscous nanofluid (blood) through a channel of slowly varying width under a transverse magnetic is investigated using perturbation and numerical methods. For this purpose, Buongiorno’s model is employed for the analysis in four different channels namely, convergent, divergent, locally constricted and wavy channels. Oberbeck-Boussinesq approximation is used and the partial differential equations are solved using perturbation series method. For validation, the governing differential equations are also solved numerically. Both perturbation and numerical results are compared and are found in good agreement. The effects of pertinent parameters on the fluid flow, heat and mass transfer in the selected channels are analyzed for special cases. The results show that both thermal and solutal Richardson numbers have opposite behaviour for skin friction, heat and mass transfer in each channel.