Browsing by Author "Mohammed, Omar"

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    Attempts Towards the Synthesis and Characterization of some Mixed Ligand Complexes of Ni, Cu and Cd
    (Addis Ababa,University, 1985-09) Mohammed, Omar; Retta, Negussie (PhD)
    Visible sPGctra for solutions of i :bi y , i :bi- ~y :.r ea , Ni :bipy : , , i : hun : , Ni ;phen :urea , Ni :phen : 1111. , Cu :bipy , C.u :b i py :urea anc. CU :b i py : J, were recorded . For the Ni c?mplexes the I ) max di d not hift with increase in pH but the intersity de creased . For the c01)per complexes l' ncrease l' n H SIll' fted the ' to .l:' 1'\ max shorter 'i'lave l ength in the basic medium . The synth sis was c arried out in aci i c medium. 'I'he complex formed between Ni and b i py '. in t he molar r ntio 1 :1 COl1_d not be isolHted , but when the concentration cf bi y increased t wo times ink c ol ored crystals of th~ fu r Qula Ni(biPY)3C12 . 6H20 were isolated . Jm attemp'c to synthesise a nickel mixed ligand complex r.rith bipY :"Q. reG. and bi py :mal onamide was done , but in both cases Ni(bipY)3C12 . 6H20 was isol ated . The binary cc,mplex Ni(phen) C12 06H20 was synthes lsed by the r eacti on of hen Rnd NiC12 . 6H20 . The synthesis of the mixed ligHncl complex with hen :ur ea G.nd phen :malonamide was then tried but in both cases Ni(phen) C12. 6H20 was the product . \•Jhen CuC12 • 2H2O and bipy re cted in the mol ar r tio 1 :1 at pH 4.5 Cu(bipy)C12 vJas is olc~ te but Hhen the H was ad justed t o 7 • 0 a co lex -ith a probale for ula Cu ( bip~ (OH)C l . 3H20 v us isolate" . lin attempt vJaS maue to ynthesise tl e mixed I i and complex of " co per \ ith bi ) :urea an b i py :malonamicle . In both cases Cu (bipY)C12 was formed. The b i nary compl exes of ur ea and malonami e v;'"i th co p er we r e syn"ches i se
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    Fatigue Analysis of Pantograph Head Materials for Better Contact
    (Addis Ababa University, 2017-10) Mohammed, Omar; Daniel, Tilahun (PhD)
    In general, the motorized units of the trainsets are powered through the pantograph-catenary system. Loose of contact between the catenary and pantograph is one of the main problems in the railway industry. This loose in contact is caused by many parameters like corrugation effect on rail, speed of the train, load and deformation on the pantograph head material. From the above stated causes, the damage of pantograph head material due to wear and fatigue damage accounts the greater amount. The purpose of this paper is done to do The Fatigue Analysis of Pantograph Head Materials for Better Contact. For this project, two pantograph head materials copper/carbon (Cu/C) alloy and copper/carbon/rice bran ceramics (Cu/C/RBC) composite are selected for analysis. Copper/carbon (Cu/C) is the current material used by AALRT and copper/carbon/rice bran ceramics (Cu/C/RBC) is a newly developed composite material used for pantograph head. The pantograph head model is done by software called CATIA and finite element model (FEM) analysis is done by ANSYS. For this project a simple pantograph model is used with a static structural fatigue analysis. The thermal and electrical stress is not considered for the analysis. By applying a structural load of 148.4N on the pantograph head, the max vonmises stress, deformation and fatigue damage results such as life, damage and safety factor is evaluated for the two pantograph head materials. From the analysis the following results have been found, max von mises stress, deformation and fatigue life, damage and safety factor are 9.40*10^7Pa, 0.075m, 4.7326*10^5 cycle, 2133 and 0.67135 or 1.0206 respectively for copper/carbon (Cu/C) alloy while 9.34*10^7Pa, 0.073428m, 4.8647*10^5cycle, 2055.6 and 0.68094 or 1.1236 for Cu/C/RBC head material. From the analysis result comparison of the pantograph head materials based on fatigue analysis, it can be concluded that the newly developed composite material (Cu/C/RBC) is the better one with compare to the current material.