ME2151E

NATIONAL UNIVERSITY OF SINGAPORE

EXAMINATION FOR

ME2151E – Principles of Mechanical Engineering Materials

(Semester I: 2009/2010)

Time Allowed: 2 Hours

________________________________________________________________________

INSTRUCTIONS TO CANDIDATES 1. This examination paper contains TEN (10) questions and comprises FIFTEEN (15)

printed pages. 2. This paper consists of TWO Sections – SECTION A and SECTION B. Answer ALL

questions in the space provided against the questions.

3. The questions DO NOT carry equal marks. 4. This is a Closed Book examination.

MATRICULATION NO: _______________________

SECTION A  MAX. MARKS  MARKS OBTAINED 

Question 1  25   

Question 2  25   

SECTION B     

Question 3  5   

Question 4  5   

Question 5  10   

Question 6  10   

Question 7  5   

Question 8  5   

Question 9  5   

Question 10  5   

TOTAL  100   

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SECTION A: Answer ALL questions Question 1 (a) (i) Determine the Miller indices for the planes (A and B) in the cubic unit cell shown in

the figure below.

(Figure for Question 1(a) (i))

(ii) List the coordinates of the first three lattice points (including the point at origin) lying on the [112] direction in the FCC and BCC lattices, respectively.

(15 marks)

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Question 1(b) (i) Draw in unit cubes the crystal planes that have the following Miller indices:

( ) ( ) ( ) ( ) ( ), , , ,111 102 212 312 133

(ii) Draw direction vectors in unit cubes for the following cubic direction:

, , , ,110 113 021 223 101⎡ ⎤ ⎡ ⎤ ⎡ ⎤ ⎡ ⎤ ⎡ ⎤⎣ ⎦ ⎣ ⎦ ⎣ ⎦ ⎣ ⎦ ⎣ ⎦

(10 marks)

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(This is a blank page for you to use for Question 1 (a) and 1 (b))

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Question 2 (a) (i) There are several mistakes in phase diagram shown below. Find the mistakes and

state the reasons, and sketch the correct phase diagram.

(Figure for Question 2(a) (i)).

(10 marks)

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(This is a blank page for you to use for Question 2 (a))

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Question 2 (b) (5 marks) (i) What are lattice, basis and crystal structure? (ii) How many lattice points are there in FCC unit cells? State your calculation. (iii) What are the significances of the Dislocations? (iv) What is Gibbs phase rule? (v) What are hypoeutectic and hypereutectic alloys?

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Question 2 (c)

Refer to the following isothermal transformation diagram for a 1.13 wt% C steel. Assume that the specimen is heated to 900oC for long enough time to achieve complete and homogenous austenitic structure. Sketch and label time-temperature paths to produce the following microstructures:

(i) Approximately 10% proeutectoid cementite and 90% coarse pearlite. (ii) Approximately 50% fine pearlite and 10% martensite. (iii) 100% martensite. (iv) Approximately 25% proeutectoid cementite, 25% fine pearlite, 25% bainite and

25% martensite.

(Figure for Question 2(c))

(10 marks)

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(This is a blank page for you to use for Question 2 (c)) - END OF SECTION A -

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SECTION B: Answer ALL questions Question 3 Differentiate between edge and screw dislocations. Describe briefly, how the dislocations assist in explaining the slip process in metallic materials.

(5 marks)

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Question 4 Pure aluminum is synthesized using conventional casting and rapid solidification processes. Conventionally cast aluminum displayed 100 micron average grain size while rapidly solidified aluminum displayed 5 micron average grain size. Identify whether conventionally cast or rapidly solidified aluminum will exhibit higher strength. Justify your answer.

(5 marks)

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Question 5 Describe the method(s) to determine the elastic modulus of a material exhibiting non-linear elastic behavior. Suggest three methods to enhance elastic modulus of engineering materials.

(10 marks)

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Question 6 Differentiate between the S-N curves of ferrous and non-ferrous materials. Can we realize infinite fatigue life in case of ferrous materials? Justify your answer.

(10 marks)

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Question 7 What is the thermodynamic criterion for oxidation to take place?

(5 marks) Question 8 Is it advisable to couple two materials that are far apart in EMF series? Justify your answer.

(5 marks)

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Question 9 Name the corrosion that you can expect under loose deposits? Briefly describe its mechanism and the most logical way to minimize it.

(5 marks) Question 10 List three ways in which gaseous environment can be changed to minimize corrosion.

(5 marks)

- END OF SECTION B - - END OF PAPER -