Archive for the ‘Faculty of Engineering’ Category

INFLUENCE OF QUENCHING ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF INOCULATED GREY CAST IRON

September 14, 2016

Author: Okoyeh Frank Chukwuemeka
Department: Metallurgical and Materials Engineering
Affiliation: Nnamdi Azikiwe University

This research work highlights the influence of quenching in different media on the microstructure and physical properties of grey cast iron. The physical properties were investigated using two criteria, namely the effect of ferrosilicon and quenching media. The standard heat treated specimens were subjected to various mechanical tests. Their micrographs were equally taken using metallurgical microscope (CETI.0703552). After the experiments, results showed that at the three quenching media the following specimens gave the optimum values:- 0.1% ferrosilicon, quenched in brine (Yield strength 113MPa, 0.431% elongation, 34.28HRC hardness and impact strength of 1.153 J), 0.1% ferrosilicon, quenched in water (Yield strength 96.93MPa, 0.419% elongation, 29.8397 HRC hardness and impact strength of 1.45 J) and 0.2% ferrosilicon quenched in oil which gave a yield strength of 195.597 MPa, 0.27% elongation, 18.5538 HRC and 2.188 J of impact strength. Study of the microstructures showed that as the percentage of graphite increased, the amount of under-cooling required for the formation of cementite increased and this promotes the formation of nodular/mottled during solidification.

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EFFECT OF AGEING TIME AND TEMPERATURE ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALUMINUM BRONZE ALLOY

September 14, 2016

Author: Anene Franklin Amaechi
Department: Metallurgical and Materials Engineering
Affiliation: Nnamdi Azikiwe University Awka

This research studied the feasibility of producing a dual-phase aluminum bronze alloy as a potential replacement for conventional structural materials, particularly steels, by the use of selected heat treatments to improve on the
mechanical properties of the produced alloy. Sand casting was used due to its advantages of low cost, ease of use and flexibility in the production of a dual phase aluminum bronze alloy with 10% aluminum content. The selected heat
treatments were solution heat treatment, quenching and ageing. The cast specimens were solutionized at 900oC for 1hr, quenched in water and then aged at temperatures of 150oC, 250oC, 350oC and 450oC and soaked for 0hr, 1hr, 2hrs and 3hrs respectively at each ageing temperature. The standard heat treated specimens were subjected to various mechanical tests (UTS, yield strength, %E, Vicker’s hardness and impact strength tests). Their micrographs were equally taken using metallurgical microscope. The results showed that the specimen aged at 350oC for 2hrs gave optimum mix of tested mechanical properties with UTS of 610MPa, %Elongation of 17.5%, yield strength of 480 MPa, Vicker’s hardness value of 350Hv and impact energy of 26J. This makes the alloy suitable as alternative material to steel in low/medium strength structural applications. Response Surface Methodology (RSM) was used to determine the optimum operating conditions at which the best mechanical properties are achieved. RSM shows the optimum process conditions (ageing temperature of 337oC and soaking time of 167mins) as the best condition for production of aluminum bronze alloy and the optimum values obtained as UTS of 587.062MPa, yield strength of 491.921MPa, %E of 15.23%, hardness of 363.672Hv and impact strength of 26.498J respectively. The result from the optimization met ASTM requirement for aluminum bronze alloy. Study of the micro structures showed that as ageing temperature and soaking time increased, finer agglomerates of α+γ2 phase were precipitated from the martensitic β’ phase which caused the improved mechanical properties of the heat treated specimens.

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HUMAN IMMUNODEFICIENCY VIRUS (HIV)-BLOOD INTERACTIONS: CONTACT ANGLE APPROACH

September 14, 2016

Author: Ozoihu Ephriam Maduabuchi
Department: Mechanical Engineering
Affiliation: Nnamdi Azikiwe University Awka

Measurement of contact angle and surface tension provides a better understanding of the interaction between the solids and liquids. Such interaction occurs between the HIV and T lymphocytes (CD4+) in liquid serum during infections. In order to study these interactions; the physiochemical properties such as the surface interfacial energies are explained using van der Waals concept of particle interactions as reported in Hamaker’s classical papers on separation of particles suspended in a liquid. The concepts of van der Waals forces are useful in predicting attraction or repulsion between the interacting particles (HIV and T lymphocyte). The surface free energies when determined from contact angle data are used to verify among other physiochemical properties, the negative Hamaker coefficient which confirms the possible repulsion between the virus and lymphocytes. The contact angles are measured on HIV infected bloods and uninfected bloods using the three probe liquids (water, glycerine and diiodomethane).The CD4+ cell counts were also measured using Partec flow Cytometry instrument. It was found that the contact angles measured on infected blood are generally higher than uninfected blood and tends to increase with decrease in CD4+ count for infected blood. From the contact angle data, the change in interfacial free energy of adhesion was found to be – 23.00 mJ/m2 indicating that van der force is attractive. This means that attraction occurs between HIV and lymphocyte during HIV infection. The absolute Hamaker coefficients for infected T4 cell A22,was found to be 0.227×10-16 mJ/m2 also indicating that attraction occurs between HIV and lymphocytes at a low surface energy of about 31.81mJ/m2 .The absolute Hamaker coefficient for uninfected T4 cell A11, were also obtained from the contact angle data and found to be 0.176×10-16 mJ/m2 .The positive value of Hamaker coefficient shows that attraction exist between HIV and T4 cells but lower value of A11 indicated less attraction for uninfected T4 cells and hence suggest a zero or negative concept that made repulsion to be attainable. However, the negative concept of combined Hamaker coefficient A132, was verified using the pair-wise summation of the geometric mean of the absolute Hamaker coefficients for lymphocytes A11, HIV A22 and Serum A33.The result (-0.6637X10-19mJ/m2) indicated that isolation of virus is attainable. In the resent work of Achebe, a negative value (-0.2809X10-25J) was obtained to support the claim that the van der Waal force is repulsive during particle separation. Therefore, finding an agent that will reduce the surface tension of serum (such that A11>A33>A22 or A11<A33<A22) to obtain a negative value of Hamaker coefficient will be the next step in formulating a drug to be recommended to the pharmaceutical industries for eradication of HIV infection and this calls for further research.

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PERFORMANCE EVALUATION OF CASSAVA FLASH DRYING IN A VERTICAL UPWARD PNEUMATIC CONVEYING DRYER

September 14, 2016

Author: Otuu Obinna Otuu
Department: Mechanical Engineering
Affiliation: Nnamdi Azikiwe University Awka

One-dimensional steady-state non-equilibrium two-phase model has been developed to simulate the convective drying of cassava cultivar, TMe 419 in a vertical upward pneumatic conveying dryer. The model takes into account the momentum, heat and mass transfer between the continuous phase and the dispersed phase. The work determined the physical thermal and aerodynamic properties of cassava cultivar TMe 419. The results indicated that particles of grated cassava are irregular and their size distribution is grater-specific. The density of dewatered mash was determined to be 866.82 kg/m3 while the particle hardness was 0.769 kg/mm2, way below the abrasive threshold of 800 kg/mm2. The terminal velocity of TMe 419 particle is correlated to the particle diameter by the expression 􀝒􀯧 = 0.0813􀝀􀯣 􀬷 − 0.6624􀝀􀯣 􀬶 + 2.9718􀝀􀯣 + 0.3967 . The specific heat capacity, thermal conductivity and thermal diffusivity of TMe 419 were determined to be 3.1422 􀝇􀜬/(􀝇􀝃°􀜥), 0.4634 􀜹 􀝉 °􀜥 and 0.1164 (􀯠􀰮􀯦 ) respectively. The drying curve for TMe 419 also showed that the expected moisture content is lower than the critical moisture content. This implies that flash drying is carried out within the constant-rate drying period. These data were inputted into the model which was solved numerically using fourth order Runge-Kutta implemented on ComsolScript platform for the dispersed phase. The data generated from the solution of the gas phase was used to determine the state of the solid phase by simulation on ComsolMultiphysics platform based on finite element method of analysis. The implementation of the ComsolScript allowed the investigation of the effects of different variables on the operating conditions during pneumatic drying and also on each other. Dryer variables like air inlet velocity, temperature and pressure drop is required in the selection of an appropriate blower and heat exchanger rating. Coupling the data from the gas phase to a finite element model of the particle, on ComsolMultiphysics platform predicted the moisture concentration as drying progresses and enables the prediction of optimal flash tube height. Overall the work has provided a tool for gaining insight into the workings of pneumatic conveying drying of TMe 419 but could easily be adapted for other material or operating conditions by simply changing the relevant input data. Here a tool for the design and performance assessment of existing pneumatic conveying dryers has been developed.

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TENSILE AND FATIGUE STRENGTHS OF GLASS FIBRE REINFORCED WITH POLYESTER RESIN IN DIFFERENT ENVIRONMENT

September 14, 2016

Author: Obende Ezekiel Omeiza
Department: Mechanical Engineering
Affiliation: Nnamdi Azikiwe University Awka

The use of conventional Engineering materials like metals, steel, alloys etc. has been for a long time because they provide the required properties needed by the designer, but fibre composite materials which have good qualities as compared with other conventional materials are gradually being accepted by designers and manufacturers in recent time. These composite structures used in this work have considerable strength, light weight, moisture resistance and good corrosion resistance. In this work, laminated composite structure with different fibre arrangement i.e. CWC having thickness of 3.2mm, WCW having thickness of 2.85mm were made locally using materials that are readily available in the open market. After the composites materials have been produced, the materials were cut into the desired sizes (i.e. 160mm x 20mm, 300mm x 30mm and 200mm x 20mm) for Tensile, Flexural and Fatigue tests respectively, for testing with the help of a diamond cutter. Before testing was done, the materials were soaked in
different solutions for some specified time (aging) to determine the effect of environment on the specimens. Characterization of the specimen was done to evaluate various physical and mechanical properties of the specimen according to the America Society for Testing and Materials (ASTM). The numerical analysis was also carried out on the specimen. The results obtained were presented in tables and graphs and were discussion accordingly. The composites material has fatigue strength and tensile strength of about192 × 104N/m2 and 18.125 × 105N/m2 respectively compared to 500 Mpaof Steel /Metals.

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