x4562 - I - . — — fl ES 021a " ~ ., 3360234....

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Unformatted text preview: I - . — — fl ES 021a " ~ ., 3360234. FIOHL/ Final Exam m If) STUDENT NAME: STUDENT NUMBER: The University of Western Ontario Faculty of Engineering Science ES 021a — Properties of Materials Final Exam December 13, 2004 2:00 pm —— 5:00 pm Time: 3 hours Aids: Programmable calculators 1 Handwritten Crib Sheet 8V2” >< 11”, both sides Format: 60 Multiple choice questions to be answered on the form provided UNIVERSIT OLICY STATESTAT I LSTIC FE THE COMMISSION OF A SCHOLASTIC OFFENSE IS ATTENDED BY ACADEMIC PENALTIES WHICH MIGHT INCLUDE EXPLUSION FROM THE PROGRAM. IE YOU ARE CAUGHT CHEATIN G, THERE WILL BE NO SECOND WARNING. Record your answers to the multiple-choice questions as on the form below: PRINT NAME lNSTRUCTOR SIGNATURE COURSE - - — -- -- Do not put any marks in the answer sheet Enter IMPORTANT Ha PENCIL ONLY! EXAMPLE: (E I II) it (1! ERASE COMPLETELYTO CHANGE If your student number has fewer than 9 digits, add lead-off zeroes. 7 , Exam Code 111 8.9. 1234567 becomes 001234567 1 LS} OU.W.0. “This material has beewa ~- with permission of this Facu‘t‘tlyi; resale or further capyyg of Barrie“: prohibited. _ Page 1 of 19 ES 021a December 13, 2004 Final Exam 1) Which type of atomic bond is best described as “the sharing of valence electrons with immediate neighbours”? a) Ionic Bonding b) Covalent Bonding c) Metallic Bonding d) Van der Waal’s Bonding e) Cooperative Bonding 2) Which of the answers below correctly lists the types of atomic bonds in order of strongest to weakest (generally speaking)? a) Van der Waal’s 9 Metallic 9 Ionic b) Metallic 9 Covalent 9 Van der Waal’s c) Covalent 9 Van der Waal’s 9 Ionic d) Ionic 9 Metallic 9 Van der Waal’s e) Covalent 9 Metallic 9 Ionic 3) In Figure 1, the bond strength is most closely related to: a) the horizontal position of point A b) the horizontal position of point B c) the height of the force curve near point C d) the slope of the energy curve near point A e) the slope of the force curve near point B 4) In Figure 1, the equilibrium spacing of the atoms at O°K is indicated by: a) the horizontal position of point A b) the horizontal position of point B c) the horizontal position of point C d) the slope of the energy curve near point A e) the slope of the force curve near point B 5) If the material modeled by the curves in Figure 1 had a stronger atomic bond, the point labeled C would definitely move: a) Left b) Right c) Up (1) Down 6) Can not be answered without more information. 6) The crystal structure shown in Figure 2 is: a) BCC b) FCC c) HCP d) Metallic e) Ionic , Page 2 of19 ES 021a December 13, 2004 Final Exam 7) The number of independent close-packed planes in the crystal structure shown in Figure 2 is: a) O b)1 c) 2 d)4 e) 8 8) The lattice parameter for any cubic unit cell is: a) the length of the face diagonal b) the length of the edge of the cube c) 1/2 the length of the edge of the cube d) the distance between close packed atoms e) none of the above 9) The crystal structure shown in Figure 3 is: a BCC b) FCC c) HCP (1) Metallic e) Ionic 10) For the unit cell shown in Figure 3, the relationship between lattice parameter, a, and atomic radius, r, is: a) a=4r b) “7% C) “4% d) a=2J§r e) “876 11) Which of the following is a “line” defect? a) A vacancy b) An edge dislocation c) A grain boundary d) a, b, and c are all line defects e) None of the above 12) The atomic weight of copper is 63.54 g/mol. 45 g of copper therefore contains: a) 1.90 X 10 2] atoms b) 4.26 x 1023 atoms c) 7.65 X 10 24 atoms d) 2.71x 10 25 atoms e) 1.72 X 10 27 atoms Page 3 of19 ES O21a December 13, 2004 Final Exam 13)Nickel has an FCC crystal structure, an atomic radius of 0.125 nm and an atomic weight of 58.69 g/mol. The theoretical density of nickel is closest to: (1nm=1><10‘7cm ; Avogadro’s number: 6.023x1023 ) a) 1.93 g/cm3 b) 4.41 g/cm3 c) 8.82 g/cm3 (1) 13.2 g/cm3 e) 16.2 g/cm3 14) At 20°C, a metal has a vacancy ratio (i.e. vacant sites / total sites) of 2.5 ><10'16. The activation energy for vacancy formation in this metal is closest to: Recall: Nv = N exp£— and Boltzmann’s constant = 8.62 ><10’5 eV/atom-K) a) 6.3 ><10_18 eV b) 6.2x10'2ev c) 0.91 eV d) 20.9 eV e) 1.2x10“ eV 15) Using the intercept method, the average grain size of the steel sample shown in Figure 4 is closest to: (check units) a) 1.2 mm b) 54 um c) 430 mm d) 8.1 m e) 26mm 16) The dislocation line of the defect shown in Figure 5: a) is parallel to the x-direction b) is parallel to the y-direction c) is parallel to the z-direction (i.e. in to the page) (1) could be any direction in the x-y plane 6) could be any direction in the x-z plane 17) When subjected to a sufficiently high shear stress, 1:, shown in Figure 5, the dislocation line will move: a) in the positive x-direction b) in the negative x-direction c) in the positive y—direction d) in the negative y—direction e) in the positive z—direction Page 4 of 19 ES 021a December 13, 2004 Final Exam 18) The defining feature of a screw dislocation is: a) The screw dislocation contains an extra half plane of atoms above the slip plane. b) The screw dislocation moves in a direction that is parallel to the Burger’s vector. c) The Burgers vector is parallel to the dislocation line direction. (1) The Burgers vector is perpendicular to the dislocation line direction. e) Both b) and c) are correct. 19) The initial dimensions of the gauge length of a tensile sample before testing are: diameter d0=l .0 cm and length 10=1O.O cm. The specimen is cylindrical. For such a specimen of low alloy steel, the length of the gauge under an applied load of 39,270 N is closest to (Use Table 1): a) 10.00000 cm. b) 10.0240 cm. c) 10.1000 cm. d) 10.24 cm. 6) the length cannot be estimated from the information given. 20) If identical cylindrical tensile specimens were made from each of the materials in Table 1 and loaded elastically to the same tensile strain, the material with the largest diameter under this stress would be material: a)1 b)2 c) 3 d)4 e) 5 21) Samples of the 5 metals shown in Table 1 are tested to failure. The metal that would support the largest tensile stress before failing is: a)1 b)2 c) 3 d)4 e) 5 22) A brittle material has an effective strength of 1700 MPa when internal flaws are 100 pm in diameter. The fracture toughness of the material is therefore in the range: (Assume K ,C = 0.9 O'x/E where the symbols have their usual meaning.) a) 19.2MPaJE b) 171MPaJZ c) 19.2x103MPaJ; d) 19.2x106MPafnZ e) 1.71x109MPaJn? Page 5 of19 ES 021a December 13, 2004 Final Exam 23) A ceramic part (i.e. a brittle material) fails in tension at 50 MPa. Microscopy reveals an internal flaw 190nm long) in the failed part that caused the failure. It is known that samples with no flaws fail at 550 MPa. Calculate the radius of curvature of the flaw. Recall em = ZGOJ-a: r a) 1X10'6m b) 2.1X10'6m c) 3.14X10'6m d) 0.95X10'6m e) 6mm 24) A shaft is to be used to transmit an alternating normal stress of +/- 600 MPa. Data for the material is given in the diagram shown in Figure 6. The expected fatigue life of the shaft is approximately: a) < 10,000 cycles b) 40,000 cycles c) 50,000 cycles (1) >100,000 cycles e) the shaft should never fail by fatigue 25) The Charpy test involves: a) slow tensile loading to the yield point b) slow tensile loading to fracture c) impact loading of a tensile bar (1) impact loading of an unnotched bar in bending e) impact loading of a notched bar in bending 26) A tensile test is performed on a single crystal (i.e. one grain) of (f.c.c.) copper. The crystal is oriented such that the normal to a close-packed plane is at an angle of 60° to the tensile axis. It is known that the critical resolved shear stress 16 MPa. It is found that the yield strength of the grain is 37 MPa. The angle between the slip direction and the tensile axis must be: Recall: r = acosgocosl a) 086° b) 30° c) 60° d) 64° 6) 78° Page 6 of 19 ES 021a December 13, 2004 Final Exam 27) It is required to reduce the thickness of an annealed plate of steel by cold working in order to attain the desired mechanical properties. If you wish to reach 60% cold work and the initial thickness of the plate is 12.5mm, what will be the final thickness of the plate? a) 5.0mm b) 7.5mm c) 8.0mm d) 9.7mm e) 11.9mm 28) The yield strength, cry, of a material is found to depend on the grain size, d, according to the following form of the Hall—Fetch equation; oy = 7 + 1.53d‘“2 where try is in MPa and d is in meters. To increase 0y from 160 MPa to 200 MPa it is required to: a) Increase the grain size by 62.8%. b) Increase the grain size by 37.2%. 0) Reduce the grain size by 25%. d) Reduce the grain size by 37.2%. e) Reduce the grain size by 62.8%. 29) An application requires a metal alloy with a yield strength of at least 300 MPa, and a ductility of greater than 30%. They can be cold worked if necessary. Of the three alloys in Figure 7, which ones can be used? ‘ a) 1040 steel only b) brass only 0) copper only d) 1040 steel and brass e) brass and copper 30) It is necessary to produce a sheet of brass by cold rolling. The final thickness must be 3 mm and the yield strength must be 400 MPa. Using Figure 7 and assuming that your starting material is fully annealed, the required initial thickness of the sheet is closest to: a) 1.2mm b) 4.7mm c) 7.5mm (1) 10mm 6) 12m Page 7 of 19 ES 021a ' December 13, 2004 Final Exam 31) The steady state creep rate for a metal follows the functional form (the student is expected to know the definitions of each term: R is the gas constant): . 1 Q £=K0' ex — C s 2 pi RT Experimentally, the steady state creep strain rate is measured for a number of temperatures at a constant stress. The activation energy for creep can be obtained most easily by plotting the variables on an XY graph and calculating from the slope as follows: X-axis Y—axis- Slope a) In as 1/R QC b) In as l/T — Q /R c) as In K 20'" — Q /R d) l/T 1n 8', -— Q /R e) K 20'” In 6', - QF 32) A creep test involves the measurement of which two parameters? a) stress and time b) stress and strain c) strain and time d) strain and ductility 6) stress and Poisson‘s ratio 33) A stress of 17 MPa is applied to a polymer serving as a fastener in a complex assembly. At a constant strain, the stress drops to 16.5 MPa after 100 hours. If the stress on the part must remain above 14.5 MPa in order for the part to function properly, the total life of the assembly is approximately: a) 119 hrs b) 254 hrs c) 487 hrs d) 532 hrs e) 962 hrs 34) As the temperature decreases between the melting temperature and the glass transition temperature, the stiffness (modulus) of a thermoplastic polymer a) Increases b) Decreases c) Remains approximately constant (1) Increases, then decreases as you approach Tg e) Decreases, then increases as you approach Tg Page 8 of 19 ES 021a December 13, 2004 Final Exam 35) A single polymer chain is comprised of atoms that are bonded by: a) Metallic .bonds b) Ionic bonds c) Covalent bonds (1) Van der Waal’s bonds e) Hydrogen bonds 36) The homologous temperature is: a) 0°K (-273°C) b) The temperature at which any material is homogeneous (all one phase) 0) The temperature at which an amorphous material crystallizes d) The absolute temperature divided by the absolute melting temperature of a material C) The temperature (measured in °C) divided by the temperature measured in °K. 37) Choose the correct statement from the list below. When conducting creep experiments, assuming the temperature is held constant, as the temperature is increased: a) Instantaneous deformation will increase and rupture life will decrease b) Steady-state creep rate will increase and rupture life will increase. c) Steady-state creep rate will decrease and rupture life will increase. d) Instantaneous deformation will decrease and rupture life will decrease e) Steady-state creep rate will increase and total creep strain will increase 38) A cylindrical component is fabricated from a low carbonnickel alloy with a diameter of 20.0mm. The maximum load that may be applied for it to survive 10000 hours at 538°C is closest to (see Figure 8): a) SON b) 100N c) 15,7OON d) 31,400N e) 35,000N 39) The microstructure of a traditional ceramic such as china is best described as: a) a pure glass b) a mixture of glass and grains of inorganic crystals 0) a mixture of glass, grains of inorganic crystals and pores d) grains of inorganic crystals fused together 6) grains of inorganic crystals fused together with some porosity 40) The viscosity of a material is: a) the temperature of the “glass transition” point in a ceramic or polymer. b) the coefficient relating the tensile strength of a material to its surface energy. 0) the coefficient that relates the applied shear stress to the resulting shear strain rate. d) the coefficient that relates the applied tensile stress to the resulting tensile strain. 6) the coefficient that relates the amount of amorphous to crystalline phases in the microstructure. Page 9 of 19 ES 021a December 13, 2004 Final Exam 41) In order for a glass—blower to bend a tube of Pyrex (borosilicate glass, Figure 10), the tube should be heated to approximately: a) <500°C b) 700—800°C c) 900—1100°C d) 1200—1500°c e) >1500°C 42) The diagram in Figure 9 contrasts the volume — temperature relationship for a glass and for a crystalline material. When the material is between the points 2 and 3, it is best described as: a) a glass b) a supercooled liquid 0) a liquid (1) an elastomer e) a crystalline solid 43) Which of the following conditions is the most suitable for promoting the crystallization of a thermoplastic polymer? a) The molecule must have large side groups and be rigid b) The molecule must have a regular architecture and be flexible c) The molecule must be cross linked and the network flexible d) The molecule must be branched and the side groups small 6) The molecule must be a copolymer and the branches are small. 44) The repeat unit for polyvinyl chloride is shown in Figure 11. The atomic weights of hydrogen, carbon and chlorine are 1, 12, and 35.5 respectively. If a single chain of PVC has a molecular weight of 17,200 g/mol, its degree of polymerization is closest to: a) 172 b) 275 c) 355 d) 550 e) 717 45) From the data provided in Table 2, the number average molecular weight of the polymer is closest to (g/mol): a) 32,000 b) 33,040 0) 36,240 (1) 66,080 e) 72,080 Page 10 of 19 ES 021a December 13, 2004 Final Exam 46) Vulcanizing an elastomeric polymer: a) removes_covalent cross-links b) increases its stiffness c) decreases its strength d) reduces its flammability e) decreases its stiffness. 47) A weight is supported by a polymer rod that creeps. As the temperature increases, the length: a) increases more rapidly b) increases more slowly c) decreases more rapidly d) decreases more slowly e) does not change 48) A continuous, aligned fiber composite is tested in tension parallel to the fiber direction. The modulus of the composite is measured to be 36 GPa. If the modulus of the fibers and the matrix are 69 GPa and 3 GPa respectively, the volume fraction of fibres in the composite is closest to: a) 20% b) 30% c) 40% d) 50% e) 60% 49) An aligned fibre composite is fabricated from the materials described above. If the volume fraction of fibres is 70%, the modulus of the composite tested perpendicular to the fiber direction is closest to: a) 4.2 GPa b) 9.0 GPa c) 16 GPa d) 23 GPa e) 49 GPa 50) When a continuous, aligned fiber composite is loaded parallel to the fibers, the strain is assumed to be: a) always highest in the matrix b) always highest in the fibres c) always highest in the component with the lowest Young’s modulus d) always highest in the component with the highest Young’s modulus e) equal in the fibres and matrix Page 11 ofl9 ES 021a December 13, 2004 Final Exam 51) A discontinuous, aligned fiber composite consists of glass fibers in a polymer matrix. The tensile strength of the glass is 3.45 GPa and the modulus is 72.5 GPa. The critical fiber length-fiber diameter ratio is 50. The shear strength of the fiber—matrix bond is closest to: ofd (1C 216) a) 25.1 b) 34.5 c) 50.0 d) 69.0 e) 94.5 52) The mobility of electrons in a metal is equal to: a) (the maximum velocity of electrons)/(electric field applied) b) (the minimum velocity of electrons)/(electric field applied) 0) (the drift velocity of the electrons)/(electric field applied) (1) (the drift velocity of the electrons)/(voltage applied) e) (the drift velocity of the electrons)/(current applied) 53) The resistance of two wires: one a metal and the other an intrinsic semiconductor is measured at different temperatures near room temperature. The expected behaviour for the resistance is: as the temperature increases, the resistance: Metal Semiconductor a) increases increases b) increases decreases 0) decreases decreases d) decreases increases e) remains unchanged for both materials 54) Devices made from extrinsic semiconductors are typically used in the exhaustion range because: a) The electrical conductivity is at its minimum b) The electrical conductivity is at its maximum 0) The electrical conductivity is approximately independent of temperature (1) No more electrons can be promoted to the conduction band 6) All valence electrons have been promoted to the conduction band 55) An n—type semiconductor has a band structure Which a) is similar to that of an insulator b) is similar to that of a metallic conductor c) is similar to that of a single atom d) has a donor level in the band gap e) has an acceptor level in the band gap Page 12 ofl9 ES 021a December 13, 2004 Final Exam 56) A schematic of a bipolar junction transistor shown in Figure 13. If an input voltage of 0.5V creates an emitter current of lOmA, the power amplification (111% j for an output voltage of 10V is approximately: (assume that the base current is 0A) a) 1 b) 5 c) 10 d) 20 e) 50 Questions 57) — 60) refer to a bar of intrinsic germanium measuring 2 X 2 X 20 cm long which, at 25°C, has the following properties: Conductivity = 2 9'1-m", ue=0.38 mz-V'l-s'l, [LP=O.l8 mz-V'l-s'], q=1.6x10'19 c 57) The resistance along the length of the bar is: a) 4x10'5 9 b) 1.6x10‘4 9 c) 2509 d) 1.0x103 9 e) 2.5x10“ 9 58) The power lost when 0.4A flows along the length of the bar is: a) 6.4x10'5 W b) 40W c) 100W (1) 160W e) 1.0x103W 59) The number of electrons carrying the current would be: a) equal to the number of positive holes b) greater than the number of positive holes by the ratio 0.38 / 0.18 c) less than the number of positive holes by the ratio 0.38 / 0.18 d) very much greater than the number of holes 6) very much less than the number of holes 60) The total number of charge carriers would be approximately: a) 4.5x10‘20m'3 b) 9x10’2°m_3 c) 1.1x10‘9m'3 d) 2.2)(1019m_3 e) 3.3x10‘9m'3 Page 13 ofl9 ES 021a December 13, 2004 Final Exam Fi ures and Tables att b) Force rep Figure 1. a) Potential energy and b) Force as a function of separation for two atoms ina solid. Fi ure 2 Page 14 of 19 ES 021a December 13, 2004 Final Exam Fi ure 4. Micro a h of steel 800 w 700 Applied Stress [MPa] 01 o O V 400 300 200_T__L_L_x_L_11_LI ;L_1L_J|l_l_l_ l__llt__|1_J._t_1 __1_ 1.E+04 1.E+O5 1.E+06 1.E+O7 1.E+08 Number of Cycles Figure 6. Fatigue data for a selected material Page 15 of19 ES 021a December 13, 2004 Final Exam 1040 Steel 1040 Steel 120 700 - E 600 a E 700 (100 g .80 5 E E .C .5 fi 500 E» ‘50 600 E’ 5 e s g a E 2 8° 3 'D 60 —- r: = - 400 w m 5": 5—. g 500 E 300 '60 200 . 40 100 o 10 20 30 4o 50 60 70 200o 10 20 30 4o 50 60 70 Percent cold work Percent cold work (a) , (b) 70 60 d 40 as E . ‘3 30 D O 10 20 30 40 50 60 70 Percent cold work Figure 7. Selected data for cold working of 1040 steel, brass, and copper. Page 16 0f19 ES 021a December 13, 2004 Final Exam \427vc (800°F) ' ‘ 20 100 so 60 4O — 30 20 538°C (1000“F) Stress (M Pa) 0 Stress (103 psi) 649°C (1200°F) ' mwbmmw 102 1o3 104 105 Rupture lifetime (h) 200 100 80 60 427°C (800°F) 4O 30 Stress (MPa) Stress (103 psi) 538°C (1000° F) 20 10 649°C (1200"F) 10-2 10'1 1.0 Steady-state creep rate (%/1000 h) Temperature (“Fl 400 800 l200 1600 2000 2400 2800 3200 10‘6 ~» Borosihcate _ glass 96% silica Fused 10‘6 \ lass silica 10” r— g Strain point 10” 10‘2 t 1012 10 A? 10 g _ 1010 c. a 8 “ 10 ‘3 ___________ __Sg't_eglr1s_v_°i2t____ 10“ g > 10° Melting point Soda-Irma glass , l I 200 400 600 800 1000 1200 1400 1600 1800 ,— 1 Emma" Temperature [°C) Figure 9. The volume — temperature Figure 10. The Viscosity of various glasses relationship for a glass and a crystalline material as a function of tem€erature Page 17 of19 ES 021a December 13, 2004 Final Exam voltage voltage Figure 13. Page 18 0f19 ES 021a December 13, 2004 Final Exam Brass Zirconium an” Alloy (6061 -T4) (304 (Naval, sand annealed) 0350 (Reactor Grade) (3) (4) - ' Poisson‘s ratio ltimate tensile 235 MPa 1150 MPa 620 MPa 310 MPa 550 MPa strenth 70 GPa 208 GPa 200 GPa 95 GPa 100 GPa Table 1. Mechanical property data for five different metals Number fraction fraction Molecular Weight Range (g/mol) woo-16,000 16900-24900 24900-32900 32900-40900 40900-48900 M 48,000-56,000 0.11 Table 2. Molecular Weight Data for a batch of polyvinyl chloride Page 19 of 19 ...
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This note was uploaded on 06/20/2008 for the course ENG 021a taught by Professor Jones during the Winter '07 term at UWO.

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x4562 - I - . — — fl ES 021a &amp;quot; ~ ., 3360234....

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