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Str - Final Exam (2007).pdf

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ENGR 2220U – Structure and Properties of Materials Final Examination: Fall 2007 Part 2: Duration - 120 Minutes Instructor: Ghaus Rizvi DO NOT OPEN THIS BOOKLET UNTIL TOLD TO DO SO Important: If you have your laptops, do not leave unattended. You can keep them under your desk. Instructions: 1. Fill out your name and ID on the exam booklet 2. The exam is closed book, closed laptops and closed notes. Calculators and one A4 sheet with hand written notes on both sides is allowed 3. Write clearly;
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  ENGR 2220U – Structure and Properties of Materials Final Examination: Fall 2007 Part 2: Duration - 120 Minutes Instructor: Ghaus Rizvi DO NOT OPEN THIS BOOKLET UNTIL TOLD TO DO SO Important : If you have your laptops, do not leave unattended. You can keep them under your desk. Instructions: 1.   Fill out your name and ID on the exam booklet 2.   The exam is closed book, closed laptops and closed notes. Calculators and one A4 sheet with hand written notes on both sides is allowed 3.   Write clearly; you should not expect marks for something that cannot be read 4.   Part 2 will be marked out of 80. There are 8 questions and they carry different marks. Allocate your time accordingly 5.   Brief answers are preferable 6.   Figures in parentheses indicate the marks   2Q1. a. Briefly describe the differences between Metals, Polymers and Ceramics in terms of molecular bonding. (3)  b. Which of the material from the above three would you select for strengthening the floor of an elevated platform on which industrial machinery, which generates impacts and vibrations, is located and why? (3) Q2. a. What is atomic packing factor? (3)  b. Which crystalline structures exhibit the maximum atomic packing factor values? (2) Q3. a. Write down the names of the defects 1 through 5, which are shown in the accompanying figure (3)  b. What is the common feature of all these defects? (1)   3Q4. We want to achieve a concentration of 0.5%wt of carbon at a depth of 0.2 mm  below the surface of the slab of a metal. The initial concentration of carbon in the metal is 0.1wt%. We first do an experiment by applying a concentration of 5%wt of carbon at the surface of a similar slab and maintaining the system at 900 K for an hour. We find that this is just adequate to produce the required concentration at a depth of 0.1 mm. We now take the srcinal slab and apply a concentration of 5wt% of carbon at the surface, at a temperature of 1200 K. The diffusion coefficient of this metal increases by a factor of 2 when the temperature is raised to 1200 K from 900 K. How long must it be maintained at this temperature to achieve the required concentration? (10)  Hint: You do not need the error function tables. Q5. a) What is the difference between Resolved Shear Stress and Critical Resolved Shear Stress? (1)  b) A single metallic crystal is oriented such that the normal to the slip plane and the slip directions are at angles of 50 and 40 degrees respectively, with the tensile axis. If the dislocations in the plane start moving when the resolved shear stress is 6.2 MPa, what is the tensile stress at which yielding occurs? (4) Q6. The iron carbon phase diagram is given below. For a 99 wt% Fe – 1.0 wt% C alloy at a temperature just below the eutectoid temperature, determine the following: (18)  a. The fractions of total ferrite and cementite phases (6)  b. What is the pro-eutectoid material? (2) c. The fractions of the pro-eutectoid material and pearlite (6) d. The amount of ferrite and cementite in the pearlite (4)   4 Q7. The isothermal transformation diagram of an alloy is shown below. (17)  a) Is it a eutectoid alloy, hypo-eutectoid alloy or hyper-eutectoid alloy? (3)  b) What will be the microstructures formed if the following heat treatments are  performed. i) Suddenly cooled to 580ºC and held at that temperature for a very very long time. (4) ii) Suddenly cooled to 600ºC and held at that temperature for 1 second then suddenly cooled down to 300ºC and held there for 1000 seconds and then quenched suddenly to room temperature. (4) c) What heat treatment will you impart if the desired structure is 50% fine pearlite and 50 Martensite (3) d) How will you produce a spheroidite structure in this alloy? (3)
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