Engineering Materials
Busha
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Test 4—Version D
■ Put away your books, notes, and mobile phone. ■ You may use an ordinary engineering calculator (not your phone).
■ Print your name and student ID number at the top of each page.
■ Clearly mark your answers on the test. ■ Show your calculations on this test. ■ You have 120 minutes to complete the test.
The first six questions refer to the following figure, showing a 1.02-kg box on a flat plane. A horizon- tal string is attached to the box. For the box on the plane, µs = 0.8 and µk = 0.4.
1.02 kg FT
Round your calculations to the nearest newton, and choose from the following answers:
A. 0 N
B. 1 N
C. 2 N
D. 4 N
E. 6 N
F. 8 N
G. 10 N
H. None of these
1. What is the magnitude of the normal force F⊥ acting on the box?
2. If FT = 0 N, what is the magnitude of the fric- tional force on the box?
3. Suppose the horizontal tension is 1 newton (FT = 1 N). What is the magnitude of the fric- tional force?
4. What is FT when the box is just about to start sliding?
5. What FT is required to keep the box moving at a constant speed of 0.8 m/s?
6. What FT is required to keep the box moving at a constant speed of 1.0 m/s?
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7. What is boundary lubrication?
A. Lubrication by electromagnetic suspension
B. Lubrication by a magnetohydrodynamic flow
C. Lubrication between two surfaces by ad- sorbed active molecules
D. Lubrication by a full viscous film between two surfaces
E. None of these
8. What is case-hardening?
A. Method used to toughen ceramic ball bear- ings
B. Hardening of the interior of a steel compo- nent
C. Method for improving the embeddability of a steel component
D. Hardening method developed by the Case Lock Company of New Haven
E. None of these
9. What is meant by the conformability of a bear- ing?
A. High load-bearing ability
B. Ability to flow to adjust to minor misalign- ments
C. Flexibility of the steel backing strip
D. Use of an easily replaceable split shell
E. None of these
10. What property of rubber explains why the work of compression is not completely recovered when the rubber relaxes to its original length?
A. Anelasticity
B. Elasticity
C. Creep
D. Ductility
E. None of these
11. Why is “high-hysteresis” rubber used in tire treads?
A. High-hysteresis rubber resists flexing.
B. High-hysteresis rubber reduces fuel con- sumption.
C. High-hysteresis rubber “grips” the road to prevent skidding.
D. High-hysteresis rubber minimizes frictional heating.
E. None of these
For the next four questions, choose from the fol- lowing answers:
A. Stiffness
B. Ductility
C. Yield strength
D. Fracture toughness
E. None of these
12. Young’s modulus E is a measure of which prop- erty?
13. The shear modulus G is a measure of which property?
14. The critical stress intensity Kc is a measure of which property?
15. The strain at fracture ϵf is a measure of which property?
16. The hardness H is related to which property of a metal?
17. Which property determines the formability of a material?
18. What is the effect of substitutional solutes on the strength of a metal?
A. Substitutional solutes decrease strength.
B. Substitutional solutes have no effect on strength.
C. Substitutional solutes increase strength.
D. It is impossible to generalize.
19. What are valence electrons?
A. Electrons in outermost occupied shell
B. Electrons in a 2s orbital
C. Paired electrons
D. Core electrons
20. Which of the following contributes to good elec- trical conductivity?
A. Dipoles interact.
B. Valence electrons are delocalized.
C. Valence electrons are strongly held by the anion.
D. Valence electrons are localized in bonding orbitals.
21. How do defects affect charge carriers?
A. Defects scatter charge carriers.
B. Defects increase the number of charge carri- ers.
C. Defects increase the charge on the charge carriers.
D. Defects increase the mobility of the charge carriers.
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22. What is the effect of substitutional solutes on the conductivity of a metal?
A. Substitutional solutes decrease conductivity.
B. Substitutional solutes have no effect on con- ductivity.
C. Substitutional solutes increase conductivity.
D. It is impossible to generalize.
23. What is the effect of temperature on the yield strength of a metal?
A. Strength is increased at high temperature.
B. Strength does not change with temperature.
C. Strength is decreased at high temperature.
D. It is impossible to generalize.
24. What is the effect of temperature on the con- ductivity of a metal?
A. Conductivity is increased at high tempera- ture.
B. Conductivity does not change with temper- ature.
C. Conductivity is decreased at high tempera- ture.
D. It is impossible to generalize.
For the next six questions, choose from the fol- lowing answers:
A. Piezoelectrics
B. Ferroelectrics
C. Dielectrics
D. Semiconductors
E. Conductors
F. Superconductors
Note that the same answer may be used more than once.
25. Which materials become polarized in an ex- ternal electric field, but lose their polarization when the field is removed?
26. Which materials may retain polarization in the absence of an external electric field?
27. Which materials become polarized when strained?
28. Which materials change shape appreciably when polarized?
29. Which materials have little or no electrical re- sistance at very low temperatures?
30. Which materials are typically used to insulate electrical wires and cables?
Conductivity can be represented by
κ = |e|Ceµe + |e|Chµh (1)
31. Which quantity in Equation (1) is a measure of how easily electrons can jump from one empty valence location to another?
A. |e| B. Ce
C. µe
D. Ch
E. µh
32. Which item in Equation (1) cannot be changed?
A. |e| B. Ce
C. µe
D. Ch
E. µh
33. If the temperature of an undoped semiconduc- tor is increased, what is the effect on µe?
A. µe increases.
B. µe is unchanged.
C. µe decreases.
D. It is impossible to generalize.
34. If the temperature of an undoped semiconduc- tor is increased, what is the effect on Ce?
A. Ce increases.
B. Ce is unaffected.
C. Ce decreases.
D. It is impossible to generalize.
35. In which type of material is Ce = Ch?
A. dielectric
B. intrinsic semiconductor
C. n-type semiconductor
D. p-type semiconductor
E. None of these
36. In which type of material is Ce < Ch?
A. dielectric
B. intrinsic semiconductor
C. n-type semiconductor
D. p-type semiconductor
E. None of these
37. If the temperature of an intrinsic semiconductor is increased, what is the effect on κ?
A. κ increases.
B. κ is unchanged.
C. κ decreases.
D. It is impossible to generalize.
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38. If the temperature of a metal is increased, what is the effect on κ?
A. κ increases.
B. κ is unchanged.
C. κ decreases.
D. It is impossible to generalize.
E. None of these
39. Which term is used for a fictitious positively- charged “particle”?
A. electron
B. hole
C. ion
D. positron
E. None of these
The next seven questions refer to the following binary phase diagram for a system consisting of components A and B:
0 10 20 30 40 50 60 70 80 90 100
Composition (wt % A)
α
α + β
α + L
β + L β
L
j
k l
n
o
m
p
Use the following answers:
A. Pure solid A
B. Pure solid B
C. Single solid phase composed of A and B
D. Mixture of two solid phases
E. Pure liquid A
F. Pure liquid B
G. Single liquid phase composed of A and B
H. Liquid and solid mixture
I. Eutectic point
40. What does Point 1 represent?
41. What does Point 2 represent?
42. What does Point 3 represent?
43. What does Point 4 represent?
44. What does Point 5 represent?
45. What does Point 6 represent?
46. What does Point 7 represent?
The next four questions refer to the following binary phase diagram for a system consisting of components A and B:
0
200
100
300
400
500
600
700
800
10 20 30 40 50 60 70 80 90 100
Composition (wt % A)
Te m
p e
ra tu
re (
°C )
α
α + β
α + L β + L
β
L
Choose from the following answers:
A. 10%
B. 20%
C. 30%
D. 40%
E. 50%
F. 60%
G. 70%
H. 80%
I. 90%
47. What is the overall composition (in wt% A) of the system indicated by the arrow?
48. What is the composition (in wt% A) of phase α of the system indicated by the arrow?
49. What is the composition (in wt% A) of phase β of the system indicated by the arrow?
50. What is the eutectic composition?
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