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Emt 2102: Material Science Question Paper

Emt 2102: Material Science

Course:Bachelor Of Science In Mechatronic Engineering

Institution: Dedan Kimathi University Of Technology question papers

Exam Year:2012

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KIMATHI UNIVERSITY COLLEGE OF TECHNOLOGY University Examinations 2010/2011 FIRST YEAR SECOND SEMESTER EXAMINATIONS FOR THE DEGREE OF BACHELOR OF SCIENCE IN MECHATRONIC ENGINEERING EMT 2102: MATERIAL SCIENCE DATE: 8TH DECEMMBER 2010 TIME: 2.00PM – 4.00PM Question one
a) What are three main advantages of composites as engineering materials? (3 marks)
b) Define the following terms as applied to materials
i) Endurance limit (2 marks) ii) Resilience (1.5 marks) ii) Creep (1.5 marks) c) Give two main advantages and disadvantages of Brinell hardness test. (4 marks) d) Iron exists as face centered cubic and body centered cubic crystal structure with lattice parameters of 3.591x10-10m and 2.863x10-10m respectively. The atomic mass of Iron is 55.85g/mol and Avagadro Number is 6.02x1023 atoms/mol.
i) Sketch the two unit cells. (2 marks)
ii) Determine the theoretical densities of the two polymorphs.(4 marks)
iii) The actual density of the body centered cubic polymorph is found to be 7870kg/m3. Assuming that the difference between theoretical and
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actual density is due to vacancies, determine the actual number of atoms per unit cell. (1.5 marks)
e) Give three main factors that determine the properties of a composite material and explain the effect of each. (4.5 marks) f) What is thermal emission and how is it used in the measurement of temperature of a material. (3 marks) g) Describe how valency and interstitial inter-metallic compounds are formed. (3 marks) Question Two
a) Derive an expression for Vickers Hardness Number VHN in terms of applied load P and the diagonal of impression made d. (7.5 marks)
b) Vickers hardness test was carried out to determine the hardness of a cutting blade after heat treatment process. The average diagonal of indentation was found to be 0.18mm when a load of 10kg was applied.
i) Determine the Vickers Hardness Number VHN. (1.5 marks) ii) What should be the minimum thickness of the blade for the results to be valid? (1.5 marks)
c) With the aid of sketches, describe the following crystal defects
i) Substitutional atom (2 marks)
ii) Grain boundary (2 marks)
d) Sketch the following Miller Indices i) [122], [?01] (1.5 marks) ii) (020), (101) (3 marks)
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Question Three a) A mild steel specimen is stressed up to fracture in a tensile test experiment. Sketch the expected stress-strain graph and briefly explain the various regions of the graph. (8 marks) b) What effect does temperature have on the properties measured in a tensile test? How is this made use of in metal forming processes. (3 marks) c) Explain the significance of slip in determining the mechanical properties of metals. (3 marks) d) What are the main properties that a material for use as an electric insulator should have and why are they important? (6 marks) Question Four
a) Draw to scale and fully label the equilibrium phase diagram between two metals X and Y given the following information:
Inter-metallic compound formed XY2 Atomic mass of X = 200 Melting point of X = 3300C Atomic mass of Y = 25 Melting point of Y = 7000C Melting point of XY2 = 5500C Eutectic temperature A/ XY2 part = 2500C Eutectic temperature XY2/Y part = 4600C Maximum solubility of X in Y is 25% at 4600C Maximum solubility of Y in X is 1% at 2500C Eutectic composition of X/ XY2 part = 2.5% Y Eutectic composition of XY2/Y part = 30% Y Solubility of X in Y and Y in X is negligible at 00C and both metals are insoluble in XY2.
Use straight lines for all phase boundaries. (12 marks)
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b) For 600g of the above alloy containing 65% Y,
i) Determine the phases present their chemical composition and quantities at 5000C. (6 marks)
ii) Sketch the expected microstructure at 2000C. (2 marks)
Question Five a) Give four main factors that should be considered at the design stage of metal structures/components in order to limit corrosion and for each factor explain why it is important. (8 marks) b) Explain how the volume of oxide layer formed during direct corrosion affects corrosion. (3 marks) c) With the aid of a sketch describe how pitting corrosion takes place. (3.5 marks) d)i) With the aid of a sketch describe how fatigue test of a material is carried out. (3.5 marks) ii) Explain how the results of fatigue test may be used in the design of shafts. (2 marks)
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Emt 2102: Material Science Question Paper

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