FinalExam_2008 - 4608 Semester 1, 2008 page 1 of 10

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Unformatted text preview: 4608 Semester 1, 2008 page 1 of 10 ________________________________________________________________________________ SEAT NUMBER: ..................................... FULL NAME: ........................................... SID: ……………….................................... Faculty of ENGINEERING School of Civil Engineering CIVL2110: Materials Duration: 3h Reading time: 10 mins INSTRUCTIONS TO CANDIDATES: - Closed-book exam Programmable calculators allowed Do not remove paper from exam room 4608 Semester 1, 2008 page 2 of 10 ________________________________________________________________________________ This exam is composed of three distinct parts that all need to be answered: Part A: Metals (100 marks) Part B: Soils (40 marks) Part C: Concrete (100 marks) On the last page of this exam, you will find the equation sheet previously circulated to all of you. PART A: METALS by Dr. Gwénaëlle Proust This part contains 6 problems. The value of each problem is indicated for your information. Problem 1: (18 marks) a) The following table gives the composition of two steel alloys. Determine and explain which of the two alloys will be easier to weld. Alloys 1010 4130 %C 0.13 0.33 % Si 0.35 0.35 % Mn 0.60 0.70 %P 0.04 0.04 %S 0.04 0.04 % Cr 1.20 % Mo 0.25 b) For the less weldable alloy, give two measures that can be taken to improve its weldability. c) Name regions A, B and C of the weld joint shown in Figure 1. Explain how and why the microstructure has been modified during the welding process in each region of the joint. A B Figure 1: Weld joint. C 4608 Semester 1, 2008 page 3 of 10 ________________________________________________________________________________ Problem 2: (18 marks) a) A cylindrical steel pressure vessel of 7.5 m diameter and 40mm wall thickness is to operate at a working pressure of 5.1 MPa. The design assumes that a surface crack in the inside wall will gradually extend through the wall by fatigue. If the fracture toughness of the steel is 200 MPa m1/2 would you expect the vessel to fail in service by leaking (when the crack penetrates the thickness of the wall) or by fast fracture? Assume Y = 1 for the fast fracture equation. Given: the hoop stress of a cylindrical vessel σ= pr 2t where p is the internal pressure, r the radius of the cylinder and t the wall thickness. b) During service the growth of a flaw by fatigue is given by: da 4 = A(∆K ) dN where A = 2.44 x 10-14 MPa-4m-1 If the initial length of the crack is 5mm, what is the pressure to which the vessel must be subjected for failure to occur after 3000 loading cycles from zero to full load and back? Problem 3: (16 marks) The data shown in the following table were obtained for a carbon steel and an aluminium alloy (the data has also been plotted on Figure 2). a) Show that the yield strengths of this steel and aluminium alloy obey the Hall-Petch relationship. Determine 0 and ky for each material. b) Certain microalloyed steels contain small additions of vanadium or niobium that permit the grain size to be reduced to about 2 m if the processing of the steel is carefully controlled. Likewise, advanced aluminium alloys containing special types of particles can be processed to have a grain size of about 2 m. Suppose we reduce the grain size to steel and aluminium from 150 m to 2 m by such processing. Would a substantial increase in the strengths of these materials result? Comment on your answer Carbon Steel Grain size Yield Strength d ( m) y (MPa) 406 93 106 129 75 145 43 158 30 189 16 233 Aluminium alloy Grain size Yield Strength d ( m) y (MPa) 42 223 16 225 11 225 8.5 226 5.0 231 3.1 238 4608 Semester 1, 2008 page 4 of 10 ________________________________________________________________________________ 250 y (MPa) 200 150 100 50 Steel Aluminium 0 0 0.2 0.4 0.6 d-1/2 ( m-1/2) Figure 2: relation between grain size and yield strength for a carbon steel and an aluminium alloy. Problem 4: (18 marks) Describe why, how and where the corrosion occurs for the three following forms of corrosion. For each of these three forms of corrosion cite two measures that can be taken to prevent and control it. a) Galvanic corrosion b) Pitting c) Stress corrosion Problem 5: (10 marks) An aluminium bar 125mm long and having a square cross section 16.5mm on an edge is pulled in tension with a load of 66,700 N, and experiences an elongation of 0.43 mm. Assuming that the deformation is purely elastic, calculate the elastic modulus of that material. 4608 Semester 1, 2008 page 5 of 10 ________________________________________________________________________________ Problem 6: (20 marks) A cylindrical cantilever beam of radius r and length L is subjected to a force F (see Figure 3). The length L, the maximum displacement and the force F are fixed. Figure 3: Schematic of the cantilever showing its dimensions. a) Write an expression for the mass of that cantilever as a function of the material density . b) The beam end deflection is given by the following expression: FL3 δ= where E is the elastic modulus and I the moment of inertia. 3 EI For a cylindrical beam the moment of inertia is given by: Derive an expression for the radius of the cantilever. I= π r4 4 . c) Using the equations derived in parts a) and b), derive a new expression for the mass of the cantilever and determine the design parameter for a light and stiff cantilever. d) Using the property chart shown on Figure 4 explain how to determine the materials with the best combination of properties to obtain a light and stiff cantilever beam. Which material of steel and aluminium alloys possesses the best design parameter for this particular application? Explain. 4608 Semester 1, 2008 page 6 of 10 ________________________________________________________________________________ Figure 4: Elastic modulus – density material selection chart. 4608 Semester 1, 2008 page 7 of 10 ________________________________________________________________________________ PART B: SOILS by A/Prof David Airey Answer all questions. Your answers should contain sufficient discussion, and sketches if appropriate, to demonstrate an understanding of the issues. a. Explain the physical basis for friction between two hard flat surfaces in contact b. Would you expect the surface roughness to affect the friction coefficient and if so how and why? c. A concrete foundation, shown schematically in Figure 1, is to be designed to resist normal force, X and lateral force, Y. Three different designs have been proposed with contact areas with the soil A1 > A2 > A3. Discuss what factors would affect the choice of footing area. d. Discuss what properties affect the frictional resistance of a sandy soil. e. If the foundation in Figure 1 was constructed on a sandy soil would you expect the coefficient of friction between the sand and the concrete to be greater than, the same, or less than the friction angle of the sand alone? Justify your answer. X Foundation Soil Figure 1 Y 4608 Semester 1, 2008 page 8 of 10 ________________________________________________________________________________ PART C: CONCRETE by Mr. Paul UNO !" # $%&' * + , () - 0 % % * #3 6*7 .# % 687%0# 6%7%.* 6!7 1*2 % & 6*7% 687 % 6%7 % 6!7% %.# %0# %.* // % * #3 * * * * . % %1*2 4 / 5 5 # # # # 3 3 3 0( 9 / 0:,; 0 ,; <> = 6 -: 7 =5 6*70 ,; 6870=,; 6%7.0 ,; 6!7) 1 ' / 6*7 687 6%7 6!7* = 9 3 & ; * 6*7& 687 & 6%7 & 6!7& : 1 * ?; %*% ' * 6*7# 687# 6%7( 6!7( * * 5 4608 Semester 1, 2008 page 9 of 10 ________________________________________________________________________________ # $%&' 8 + () @ & 2 % * * % ) . 5 9 ; 2 # 2 5 < A B 5 - ' / > 5 A 0 A B 5 ; # . B 3C * 3 0> 5 1 ?; * / / .0 ,; ?8 3 = .0 ,; : > ?; /> 0 5 C 9 75 6 : * DE8 @ - / / 0 0 . ) 6 7 9 5 5 & 2 ' 1> $ 3 < 6 75 & 6 7$ 0 & 0 %$ 6 7 4608 Semester 1, 2008 page 10 of 10 ________________________________________________________________________________ Equation Sheet Mechanical Properties of Metals E = 2 G (1 + ν ) Fire Consideration σ y (T ) = 1 When 0°C < T σ y (20 ) UTS (MPa) = 3.45 x HB Dislocation and Strengthening Mechanisms σ y = σ 0 + k y d −1 / 2 % CW = A0 − Ad ×100 A0 215°C σ y (T ) 905 − T = When 215°C < T 905°C σ y (20 ) 690 E (T ) = 1.0 + E (20 ) T 2000 ln T 1100 When 0°C < T Failure σ m = 2σ 0 600°C T 690 1 − E (T ) 1000 = E (20 ) T − 53.5 1/ 2 a ρt 2Eγs σc = πa 1/ 2 When 600°C < T 1000°C K c = Yσ c π a Ramberg-Osgood Equation ∆K c = ∆σ c π a ε= da = A ∆K m dN σ E0 ln Q ε = K 2σ n exp − c RT Larson-Miller Parameter: n= ln T (C + log t r ) + 0.002 0.002 0.0001 σ 0.002 σ 0.0001 Concrete P − B ratio = f 'cm = f 'c + 1.65s CPR = KW ρ At Carbon Equivalent Formula CE (% ) = %C + % Mn % Mo %Cr % Ni %Cu % P + + + + + 6 5 5 15 15 3 n σ 0.002 ln(20) = Corrosion and Degradation of Materials AO ρ M a AM ρ O σ ln σ 0.002 σ 0.0001 ...
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This note was uploaded on 09/01/2011 for the course YEAR 1 taught by Professor Various during the Three '11 term at University of Sydney.

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