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ENB104-T1-S2-2008 - GUT Surname Given Name/s III-I...

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Unformatted text preview: GUT Surname Given Name/s III-I..- Examination Paper SEMESTER: SECOND SEMESTER EXAMINATIONS 2008 UNIT: ENB‘IO4 ENGINEERING MATERIALS — THEORY 1 DURATION OF EXAMINATION: PERUSAL: 10 MINUTES WORKING: 2HOURS EXAMINATION MATERIAL SUPPLIED BY THE UNIVERSITY: EXAMINATION BOOKLETS - THREE (3) PER STUDENT FORMULAE AND CONSTANTS - THREE (3) PAGES ATTACHED CRA - TWO (2) PAGES ATTACHED EXAMINATION MATERIAL SUPPLIED BY THE STUDENT: WRITING IMPLEMENTS - CALCULATORS — ANY TYPE INSTRUCTIONS TO STUDENTS: Students are prohibited from having mobile phones or any other device capable of communicating information (either verbal or written) in their possession during the examination NOTES MAY BE MADE ONLY ON THE EXAMINATION PAPER DURING PERUSAL TIME SECTION A - W - ALL THREE (3) QUESTIONS ARE TO BE ATTEMPTED ALL FOUR (4) QUESTIONS ARE TO BE ATTEMPTED SECTION C - ALL THREE (3) QUESTIONS ARE TO BE ATTEMPTED ATTEMPT EACH SECTION IN A SEPARATE EXAMINATION BOOKLET MARKS FOR EACH SECTION ARE AS INDICATED Queensland University of Technology eur Kelvin Grove 1 All Questions Are to be Attempted All Sections Have Equal Weighting Use a Separate'Answer Book for Each Section SECTION A: KNOWLEDGE AND APPICATIONS QUESTION 1 Selection of materials (a) You have been asked to choose a material for a bicycle helmet. List five factors that are important in the selection of the material? 0)) Briefly explain three of this factors by considering the material properties you will need to look for and other conditions relevant to the selection process. QUESTION 2 Corrosion of metallic materials (a) Briefly indicate with the aid of an appropriate diagram and chemical equations the process of corrosion on a carbon steel pipe carrying salt water and sand. Explain what effect the flow rate has on the corrosion of the pipe. ' (b) List three possible mitigation techniques for the steel pipe situation above and explain how each prevents the corrosion of the steel. QUESTION 3 Polymeric materials (a) Explain melting temperature and glass transition temperature in polymeric materials and how they relate to each other. (13) Discuss briefly three factors that affect both the melting and glass transition temperatures of polymers. QUESTION 4 Ceramic materials (a) Briefly explain the working principle of piezoelectric material. (b) Describe how piezoelectric material is used to measure Young’s Modulus of materials and explain the advantage of using this method as compared to ordinary measurements. END OF SECTION A ENB104T1.082 .../cont 2 SECTION B: INTERPRETATION AND ANALYSES QUESTION 5 Stress-Strain Curve (a) Draw a typical engineering stress-stain curve for metal. (b) Analyse the properties of the metal at the various points of the curve and discuss five important properties. QUESTION 6 Microstructures With the aid of the TTT-curve for eutectoid steel (0.76%C) (Figure 1) answer the following questions: (a) Good combinations of hardness, strength, and toughness can be obtained from a mixture of 50% Bainite and 50% Martensite micro-constituents. Explain how this microstructure can be obtained to achieve the desired materials properties. (b) A hardness of HRC 42 is desired for a shaft. Determine the heat treatment process to achieve this hardness value. son.- arm: 3’30 '14: J: 600? as E? U 1.: ) ‘40 _ g 5w 5;“. 13'3” 4st}. 4-2 g Q . a a "3001- .52 m. .E‘“ ' 200 57 i 100: (as 9n Time-(s) _.._.....; Figure 1. Time-Temperature Transformation (TTT) Diagram for Eutectoid (0.76%C) steel. The scale on the right is the expected hardness of the various types of steel. P=Pearlite, B=Bainite, M: Martensite, yzAustenite. QUESTION 7 Failure of materials An engineer investigating the cause of an automobile accident finds that the right rear wheel has broken off at the axle. The axle is bent. The fracture surface reveals a Chevron pattern pointing toward the surface of the axle. (a) Analyse the information given above and identify the mode (type) of failure. (b) Suggest whether the accident caused the failure of the axle or the axle failure caused the accident. END OF SECTION B ENB104T1.082 .../cont 3 SECTION C: CALCULATIONS QUESTION 8 Design of Lift Car You are asked to design a cable car to be used for lifting people to the top of a building. The lift car weighs 20,000 N. The cable used is made of steel of diameter 1 cm and has a length of 20 m. The elastic modulus and yield strength of the steel cable are 210 GPa and 250 MPa, respectively. Compute, (a) The extension in the cable due to the weight of the car. (b) The total weight (car and people) that can plastically deforms the cable. (c) The number of people that can get in the lift before the cable plastically deforms (assume one person = 70 kg). QUESTION 9 Diffusion A plate of iron is exposed to a carbon-rich atmosphere at a temperature of 727 CC The diffusion coefficient, D, of carbon in iron at this temperature is 10'10 mZ/s. The activation energy for the diffilsion of carbon in iron is 80 kJ/mol. Calculate the diffusion coefficient of carbon in iron at 600 °C. QUESTION 10 Composite Materials A stiff and light weight bicycle is obtained from composite materials. A 67% volume fraction of carbon fibre (Young's Modulus=200 GPa) is used in epoxy (Young's Modulus=5 GPa) when making the composite material. Calculate the Young's modulus of the composite material parallel to the fibres. END OF SECTION C END OF PAPER ENB104T1.082 (i) FORMULA AND C ONS T AN T S SHEET (ENBIM — Engineering Materials) Crystallography 7cm y (cos¢cosfi)m ( ) m4 = 1 ‘0 VCNA ( ) -1 Uy=00+kyd2 ,14 Diffusion %CW = AO'Ad x100 (15) dC A J = ~D — (2) 0 abc a 32 d” — do" = Kt (16) _C = D C; (3) at 8x Failure Mechanisms Cx'Co =1—erf [ X J (4) KC =YO'\/7l'a (17) C5-C0 NE Q 01, = 02} = W (13) D = D “—1 5 0 exp[ RT] ( ) fl = A(AK)m (19) dN Elastic and Plastic Properties AK = K a _ Km (20) 0' 2 Es _ 6 E : 5; = K20" exp [—i) (21) flay (7) 0” RT .9 v = Jix = “—y- (8) 82 gz Ceramics E=ZG(1+V) (9) _ n‘(ZAC+ZAA) P - VENA (22) l. = 1 —1 10 5T “[10] ( ) E=E0(1—1.9P+0.9P2) (23) a} =O'(l+£) (11) ST =1n(1+8) (12) Strengthening Mechanisms ENB104T1.082 CsCl structure Rocksalt structure Geometrical constrains for stable coordination of ions. Coordination number OOON-lh-UJN Polymers fin :inMf fiw=ZWiMi g1 E | 51 E | E=ijmj Composites EC = Eme +EPVP ENB104T1.082 Cation-Anion ratio < 0.155 {1155-0225 0225-0414 0.414—0.732 0.732—1 .0 (24) (25) (26) (27) (23) (29) (ii) EE E=——LL— C ng+gg a=gm+gn E .ag C VmEf + VfEm Corrosion CPR =— Electronic Materials (30) (31) (32) (33) (34) (35) (36) (37) (38) prom! :p(+pi+pd , 1.24 Eg (m eV) = B=floH+floM Values of Selected Constants Avogadro’s number, NA = 6.023x1023 molecules per mole. Boltzmann’s constant, k Min m) (39) (40) (41) (42) (43) (44) (45) Physical : 1.3 8x10'23 J/atom—K. Gas constant, R = 8.31 J/mole-K. Permittivity of Free Space; 80 =8.85x10'12 F/m. Permeability of Free Space; p0 ENB104T1.082 (iii) =41cx10'7 H/m. Faraday’s constant; 8 =96 500 C/mole. Planck’s constant, h: 6.63XIO'34 J-s or 4.41x10'15eV-s. 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